Fire and Gas, Instrument , Mecheniacal Questions & Answers

Allen-Bradley PLC 5/40

2010-11-14T06:31:00.000-08:00

PLC 5/40 Details

The front face showing Status LEDs, Communication Ports, Keyswitch, Battery and EEPROM installation
The LEDs are for (from the top) Battery status, Processor status, Force status and Channel 0 communication status
Apart from that, Each port (1A,2A,1B,2B) having their own status LEDs
The steady green shows healthy, Red for fault
1A and 2A Channels are used for Serial data transfer to DCS on DH+ Network
2B used for Panelview/MMI on PC/Redundant I/Os
1B used for RIO communication
Channel 0 is for RS 232/ RS 422 Communication with the PC
Lithium battery is for retaining the program in Processor when it is Powered OFF.
EEPROM is to provide memory backup when processor memory corrupted

PLC In Refinery

Mainly Allen-Bradley make
PLC 5 and SLC family
PLC 5/40 Having CPU Level Redundancy
PLC 5/40L, 5/60 And SLC Installation
Controls Operation of the Compressors, Heaters, Filters, F&G, Analyzer Safe Guarding and Other package units

Processor Architecture

PLC System Architecture

Input means Signals from Proximity switch, pressure switch, pressure transmitters etc.
Output means I/P converter, relay etc.
This Inputs and Outputs are connected to the Digital Input cards, The digital output cards, Digital Output cards, Analog Input cards, Analog Output cards installed in the Remote I/O Chassis
The PLC having local Chassis and Remote I/O Chassis
The Remote I/O chassis is connected with PLC thru Belden 9463 (blue Color)
Why Remote Chassis are required?
Remote I/O adaptor Card is required for the Communication with the Processor. It always remains in the first slot of the Chassis
The Power Supply card in the Chassis is required to supply power to the complete chassis
The 110Vac power supply is required for Power Supply card
There are two Local chassis containing Processor.
One processor is in primary mode and the other is in secondary mode
The processor is having node address which can set by switch settings on the card
The primary processor is connected on the DH+ network
The connection is made in the Station connector normally mounted near to the chassis
The primary processor appears as node no “n” in the DH+ network and the secondary processor appears as “n+1” in the network
The KF2 module is connected on the network
KF2 Module Converts DH+ data into RS-232 Signals which is compatible with AB Integrator in DCS architecture
The KF2 and AB Module are act as link between PLC and DCS
The Panel view is used for monitoring the data of the process as well as controlling the operation
It is connected to the 2B channel of the processor
The baud rate used for communication is 57.6 K
Programming Terminal for Viewing, Modifying and Configuring the PLC Programming

Signal Flow In PLC

The Field Signals are connected with I/O cards in RIO chassis
Processor taking data from RIO chassis thru Remote I/O link and stores in I/P image tables / memory
The data is being updated on every scan of the PLC
The data is processed in Processor according to the program written
The result is transferred to the output cards in RIO Chassis.
The Output will be in the terms of 4-20mA or Contacts.
The Processor updates the data on every scan, The scan time is in terms of milliseconds (averagely 40 mS)
The scan of the processor means processor doing input scan, then program scan, then output scan, service communication and housekeeping. The time taken for completing this activities once is call scan time

System Redundancy

Redundant DH+ Network for communication with the DCS (A and B network for DCS)
The BEM cards are installed for increasing the no. of communication channels available for networking.
Redundant 1770-KF2 modules for communications with DCS
Both the PLC executes Application program
Primary processor controls the I/O, but Secondary can monitor only
The Switch over between processor is doing by BCM and BEM card

Software

The program can written in Ladder Logic, Sequence function charts or Structured text format
We have used Ladder Logic
The Programming package is RsLogix5 (Windows based) and 6200 series Software (DOS based)
The Software package can load into PC / Laptop
The PC requires KT card and the Laptop requires PCMK card
If KT/PCMK not available, then Processor can communicate on COM port of PC/laptop Serially thru CH0 on processor
The RsLinx software is also required for the Communication over the network and serially
The PLC program is protected with 4 different level access passwords
In our complex, there is no password for the Reading the program online

Diagnostics

There are status LEDs on the processor face
The first LED is battery status indicator, if it glows RED, then Either the battery is low or missing
If the Second LED is steady green, processor is healthy
If it is flashing red, the program downloading is under progress or major fault, for steady red, hardware fault
The force glows steady amber when any I/P or O/P are forced in the program
If Comm LED flashing green, the Channel 0 communication is working
Any of the channel status LED glowing steady green, then that channel is healthy
If it glows flashing Green, bad communication
When it is red, adaptor fault

Hand Protection - Handle with Care

2010-11-09T09:54:00.001-08:00

Next to our eyes, our hands are probably the most important part of our body when it comes to doing our work. They’re involved in almost every thing we do. Yet many of the things we do with our hands are done without any deliberate thought. Your hands have no fear. They’ll go anyplace they’re sent and they only act as wisely as the person they belong to; so before you use your hands think of their safekeeping.
Here are the most common types of hand injuries and what you can do to prevent them:
Traumatic injuries often occur from careless use of machinery or tools. Hands and fingers get caught, pinched or crushed in chains, wheels, rollers, or gears. They are punctured, torn or cut by spiked or jagged tools and edges that shear or chop. Safety precautions should include using shields, guards, gloves, or safety locks; handling knives or tools with care; and keeping hands, jewelry and clothing away from moving parts.
Contact injuries result from contact with solvents, acids, cleaning solutions, flammable liquids and other substances that can cause burns or injure tissue. To protect against these injuries, read the product labels, use the right glove or barrier cream, and wash hands frequently. result from contact with solvents, acids, cleaning solutions, flammable liquids and other substances that can cause burns or injure tissue. To protect against these injuries, read the product labels, use the right glove or barrier cream, and wash hands frequently.
Repetitive motion injuries happen when tasks require repeated, rapid hand movements for long periods of time. Manufacturing, assembling, or computer work may lead to these injuries. Change your grip, hand position, or motion. If possible, rotate tasks to give your hands a rest.
You can protect yourself from hand injuries by remembering the following basic safety rules:

Recognize hazards.
Think through each job before you begin.
Follow safety rules.
Avoid shortcuts.
If an accident happens, seek prompt treatment.
Report injuries to your supervisor.

Healthy hands are built to last a lifetime. Injuries can last a lifetime, too. Be aware of your hand placement and take precautions to guard them.

Fire Safety - In Case Of Fire

2010-11-09T09:50:00.001-08:00

You are responsible for fire prevention at work for your safety and that of your co-workers. The best way to prevent workplace fires is to be aware of and on the lookout for potential fire hazards. Report hazardous situations to the supervisor. Know the location of fire extinguishers and other emergency equipment that is available to you. During an actual emergency, protect yourself. Do not get involved if it is not safe.
If you ever discover a fire, keep your cool but think fast and act with caution. Size it up fast; knowing when to attempt extinguishing the fire yourself and when to call for help is essential.
In case of fire, follow your company’s fire response procedures. The important thing is to know what to do and do it fast. The exact order to do the things depends on the established company procedures.
Sound the alarm and evacuate the area. Call the emergency numbers you’ve been given, and give the details about the fire (location, how it started etc.). Never hesitate to call the fire department, even if the fire seems minor and you manage to put it out before firefighters arrive. The quicker the alarm is sounded, the sooner firefighters can attempt to get it under control. Have someone meet the firefighters to tell where the fire is. They can lose valuable minutes if they have to find it themselves.
You are responsible for preventing fires, but not to put out major fires. Fight the fire only if you can do it safely with proper extinguishing materials. In general, never battle the blaze unless the firefighters request your help.
Warn anyone in the area so they can get to safety. This is especially important with indoor fires. Most people die from smoke, poisonous gases and panic (usually the result of not knowing what to do). If there is an escape plan, adapt it to the emergency.
Most fires start small, but they can rage out of control in a few minutes. It is important to know where the fire extinguishers are located and how to operate them properly. Distinguish before you extinguish. Choose the correct extinguisher for the type of fire (paper/wood, grease/gas/flammable liquids, electrical). If you are not trained or authorized to use an extinguisher, don’t try. The time you waste in figuring out how to operate an extinguisher could mean the difference between minor damage and a major disaster.
Review your company’s fire safety procedures often so you’ll now what to do. Act with caution. Sound the alarm. Warn others in the area. Evacuate and stay back unless you’re asked to help. In case of fire, being informed and prepared can keep you and your co-workers safe from injury.

Detention Facility Worker

2010-11-09T09:03:00.000-08:00

Personnel in detention and prison facilities should be continuously aware and constantly prepared for the risks they face on the job. Work in these facilities can be extremely stressful both physically and mentally for guards, custodians, or medical personnel. Workers also run the risk of exposure to physical attack or infection from bodily fluids.
Security personnel perform facility inspections to ensure inmate safety and custody. When walking the grounds and perimeter, watch for uneven ground that can cause trips and falls. When you inspect roof vantage points, stay at least 6 feet from the edge if it does not have a guard rail.
Everyone should inspect the workplace for hazards and correct or report them. Maintain good housekeeping. No items should be stored or even temporarily piled in walkways or exits. Ensure that lights, locks, and flooring are in good repair. Equipment such as carts and communication devices must be in working order. Evaluate chemical storage and use at your facility; prevent inmate access to concentrated chemicals that could be used as a weapon. Maintain strict control of knives and other sharps that could be used as weapons.
You know how dangerous violence in your workplace can be. Inmates may fight each other or attack workers. Stay in top physical condition and remain alert when you work in the facility. Get training such as managing aggressive behavior and verbal judo to help control behavioral crises. Have an emergency code and response plan for these incidents. Practice and drill the response frequently and in different scenarios.
Bloodborne pathogen exposure from splashes or contact with blood is a serious hazard when violence erupts. The most common exposure is a splash of blood or other bodily fluids to a mucous membrane (eye, nose, mouth) or a puncture from a bite, scratch, or other wound. If you are required to respond to these emergency incidents, wear body armor, long sleeves, and pants to protect your body. Gloves and safety glasses or goggles protect you from accidental splashes. Evaluate different equipment to ensure that it does not hamper your response while protecting you.
Avoid situations where an inmate can use blood, urine, or feces as a potential weapon by controlling access to cups and containers and wearing the appropriate protective gear. Use proper techniques to enter inmate cells. Know what to do if you have an exposure, including who to report it to and how to follow-up with medical attention. Vaccination for Hepatitis B, one of the most easily transmittable blood borne diseases, protects your health.
Tuberculosis (TB), a respiratory disease, is a concern in detention facilities. If you suspect an inmate has TB, isolate and transport them for medical attention. Use respiratory protection such as an N95 respirator when entering isolation rooms or working with potentially infectious inmates. TB vaccination is not common in the United States, so get a yearly TB test to ensure you have not been exposed.
Your work environment can be indoors, outdoors, and physically challenging. Wear comfortable layers of clothing and sturdy, comfortable footwear. Get plenty of rest and eat healthfully to maintain your awareness on the job and help your body cope with demanding shift work. Maintain your fitness so that you can respond to any type of emergency on the job.
The level of required alertness and the unpredictable nature of the inmates in your workplace cause stress. Good fitness and overall health help you better manage job stress. Get the training you need to feel prepared and in control at work. Talk about your job tasks and stresses with your supervisor to get guidance on controlling stress. After emergency incidents, get debriefing counseling individually or as a group to help you cope with the emotions and stress.

Common Sense Safety

2010-11-09T05:33:00.000-08:00

There are a number of safety problems common to most workplaces and job sites that can be solved with a little common sense. Planning and thinking ahead can help eliminate most of these hazards. Take a close look at your workplace with these suggestions in mind.

Eliminate junk piles. Organize a cleanup program to remove trash, broken parts, and scrap from work areas, walkways, storerooms, and neglected corners. Look for materials that have been stacked improperly. An unstable stack is a real danger to anyone who may be near if the material suddenly falls. Check such things as wood pallets, dock freight, storeroom boxes, construction materials and even office files to see that materials are stacked properly.

Examine all the operations of your workplace to determine if personal protective clothing is needed, then make it readily available. Ear protection, eye protection, hard hats, gloves, safety shoes or other protective clothing and equipment must be worn according to the hazard exposure.

Make sure all electric power tools are grounded. Protect yourself from electric shock by using tools with three-prong plugs, a ground-fault system or double insulation. Never cut off the ground plug on a three-prong plug. Check electrical cords and wires for any damage. Guard power tools and moving machine parts. Tools and equipment should never be operated with the guards or shields removed.

Inspect portable ladders to make sure they are secure and don’t shake or wiggle. Nonslip feet are a must. If a ladder seems weak, get rid of it – don’t let others use a defective ladder. Mark it defective and throw it away.

Fire extinguishers are a must and should be mounted properly, readily accessible, and in working order. Check fire regulations to make sure they are properly placed and the right type for your work area. When was the last time your fire extinguishers were tested? Extinguisher inspections should be made regularly then tagged to show when and who performed the tests.

Exits should be clearly marked with easy to read signs place above the doors. Signs with arrows should also be used to guide people to the exit if the layout of the workplace is confusing to those unfamiliar with your facility. Illuminated signs should be kept in working order at all times. Don’t block exits or signs with vehicles or material. Another good idea is to mark doors that are not exits with “This is Not An Exit,” “Restroom,” “Storeroom” or “Closet.” Put rails on all stairways. The stairs themselves should be in good shape with nonskid treads. Repair those that are damaged or chipped.

Safety meetings are one of the most important parts of a good safety program, so hold them regularly. Impress upon every worker that it’s important that they take every precaution to keep the workplace safe. Both employee and employer attitudes toward safety provide a key to a successful safety program. Posters, handouts, and training programs can all be part of your safety communication.

Back Injury Prevention

2010-11-09T01:08:00.000-08:00

Extent of the problem

Back injuries are cited as the most common reason for absenteeism in the general workforce after the common cold. About 80 percent of adults are estimated to experience a back injury in their lifetime, and about 10 percent will suffer a re-injury.

Organizations are taking steps to reduce back injury in the health-care workplace, most prominently the U.S. Occupational Health and Safety Administration (OSHA). For example, OSHA released final ergonomic guidelines for nursing homes, offering guidance to workers when it comes to lifting home residents or other large objects. Additionally, OSHA entered into its first strategic alliance with a medical association - the American Academy of Orthopaedic Surgeons (AAOS). Both organizations plan to use their collective expertise to reduce and prevent ergonomic injuries in the workplace

National health-care statistics: In the United States, back disorders account for over 24 percent of all occupational injuries and illnesses involving days away from work, according to the National Institute of Occupational Safety and Health's (NIOSH) Worker Health Chartbook, 2004. In healthcare, back injuries, frequently caused by overexertion, occur at a very high rate. Healthcare industry workers sustain 4.5 times more overexertion injuries than any other type of worker. (See the U.S. Department of Labor, Bureau of Labor Statistics, 2000.) According to national statistics, six of the top 10 professions at greatest risk for back injury are: nurse's aides, licensed practical nurses, registered nurses, health aides, radiology technicians, and physical therapists. Greater than one third of back injuries among nurses are attributed to handling patients and the frequency with which they are required to manually move patients. From a worldwide perspective, back injuries to nurses have point prevalence of approximately 17 percent, an annual prevalence of 40-50 percent and a lifetime prevalence of 35-80 percent. (See A Business Case for Patient Care Ergonomic Interventions, 2005). As staggering as these statistics are, they still do not tell the whole story. According to Bernice Owen, RN, Ph.D., former professor at the University of Wisconsin-Madison School of Nursing, as many as one-third of nurses who sustain work-related back injuries do not even report them. (See Caring for Ourselves, by Bernice Owen.)

Personal impact: About 80 percent of back injuries are short in duration, and workers are able get back to normal health. In the short-term, they may experience pain and reduced functioning. For some, the pain and suffering is long-term. And for a small percentage of people, it is lifelong. For employees with long-term, disabling musculoskeletal injuries, lifetime earnings may drop significantly. These employees may also suffer a loss of independence and a diminished quality of life.

National impact: With a critical nursing shortage, back injuries among nursing personnel can seriously diminish the nation's ability to provide quality care. The following recent resources describe the crisis:

Nursing workforce, General Accounting Office report,
Hospital nurse staffing and patient mortality and
A white paper from the Joint Commission on Accreditation of Healthcare Organizations.

Causes of back injuries

Organizational causes: Many factors affect back injuries among healthcare personnel: an aging workforce, sicker patients, staffing shortages, obesity in both patients and employees, gender, and stress due to organizational change.

Individual causes: Back pain and other work-related musculoskeletal injuries may be caused by:

A single traumatic event, such as a slip and fall or a car accident.
Other factors, such as genetics; age (older populations experience an increase in arthritis and disc degeneration); being out of shape or overweight; having poor posture; bending, standing, sitting, or lifting improperly; tension, emotional problems or personal stress; pregnancy; tobacco smoking; poor physical condition; and sports or hobbies.
Cumulative trauma to the spine and related structures.

Equipment and prevention

Equipment solutions: Preventing serious back injuries must include the use of patient lifting and transfer equipment for most patients, but especially for obese (bariatric) patients. A Patient Lift and Transfer Resources List may be helpful in identifying companies, examples of equipment (including bariatric patient needs), and contact information. In addition, an organizational assessment will reveal the various types and numbers of equipment needed, which depends on the patient population and the type of care provided. A proposed Injury Prevention Program is described below in this module.

Special concerns - the bariatric patient: Lifting and transferring of bariatric patients has become a concern for many organizations and healthcare personnel. It is estimated that about five to 10 percent of the general population is obese. Due to their weight and size, special considerations can reduce the potential lifting hazard for caregivers. To determine obesity, one may refer to the chart conversion.

When the BMI is greater than 38, there is a possible need for special bariatric equipment. If the BMI is greater than 39, the patient is considered morbidly obese. For example: a 5'8" tall, 255-pound person has a BMI of 39.

Special considerations are not only needed to meet quality of care standards for these high-risk patients, but to also prevent potential lift and transfer injuries to caregivers. Often, the lifting assistance available on site is not rated for use with bariatric patients.

A process for identifying equipment needs and a list of types of equipment to consider may be found in "Bariatric Equipment Considerations," included in the sample procedures and tools section of this module.

A plan of action

Identify potential solutions: Based on the data gathered, solutions to correct the problem may be formed. The plan should:

Define the criteria to determine when assistance is needed.
Determine the need for lifting equipment.
Review affected policies and procedures to incorporate changes.
Review training needs for both supervisory and patient care personnel.

Criteria: The final program combines work practices, equipment use, and body mechanics. How each is incorporated depends on the goals set by the organization. In OSHA's guideline, the goal is to "minimize manual lifting of [patients] in all cases and eliminate it when possible," (See Ergonomics for the Prevention of Musculoskeletal Disorders: Guidelines for Nursing Homes).

Determine need for lifting equipment: Organizations must first determine the need for patient transfer equipment, both for the majority of patients and for the obese. This will vary depending on the type of care provided and the patient population served. Algorithms describing what assistance to provide in various lifting situations may be helpful. Then, organizations must decide what types of equipment are needed. An equipment criteria worksheet and the previously mentioned patient lift and transfer resources may provide some direction at this stage. Finally, organizations must be clear on how frequently the equipment will be used.

Policies and procedures: Policies and protocols should be unique to each organization. In developing policies, organizations need to ensure consistency with their injury reporting process and return-to-work programs as related to back injuries. When lifting assistance is considered a critical part of the program, caregivers need clear direction on making decisions on assistance. Only then can they be held accountable for following the lifting requirements. A sample policy from the Veteran's Administration may suggest further ideas for consideration.

Training: Training needs should be identified and provided for all levels of personnel. This includes:

Caregiver management, so they will support the use of safe lifting practices and equipment.
Caregivers, so they understand the benefits and are comfortable using the equipment.
Maintenance personnel, so they can complete preventative maintenance tasks.

Gain top management support: Perhaps the biggest initial hurdle program promoters face is getting management approval for implementing a program that, by its complex nature, necessitates a great deal of organizational commitment and resources to be successful.

Strategies to gain support: How do program promoters get upper management buy-in to program change? Most organizations have basic back injury prevention programs. However, most are either incomplete or not comprehensive as evidenced by statistics indicating injuries from lifting and transferring patients continue to occur and in fact, are increasing. Senior management may not see the need to add additional resources to support a more complete program.

Suggestions to enlist leadership support for program change include:

Change the focus: Many decision-makers grapple with the fact that money has been spent on back injury prevention programs before, yet back injuries continue to occur. Management may be even more reluctant to invest in another potentially unsuccessful program. To help overcome this hurdle, one group decided to change the focus of the program. Rather than preventing back injuries in patient care personnel, they promoted improving patient care. Even the program title was changed to reflect this approach: "Preventing Back Injuries in Nursing Care" became "Patient Handling and Movement." Regardless of the term chosen, if the focus includes patient care, decision-makers may be more receptive to providing the extensive backing - and monies - required by a truly successful program.

Review the current legislative environment: The Occupational Safety and Health Administration (OSHA) has listed ergonomics, especially in health care, as a top priority. (See news release "OSHA Announces Comprehensive Plan to Reduce Ergonomic Injuries, April 5, 2002.) Additionally, OSHA's citable general duty clause states that a workplace should be "free from recognized hazards." Overexertion injuries from lifting people have been formally recognized as workplace hazards, ever since OSHA ruled that overexertion injuries resulted from lifting and transferring of residents. (See news release Nursing Home Company Settles Case-Beverly Adopts Ergonomic Measures to Reduce Back Injuries, January 15, 2002).

JCAHO surveyors have also taken a greater interest in employee and patient safety issues related to lifting and transferring. For example, organizations report that surveyors have asked to see their OSHA 300 logs. The surveyors then asked about preventative measures taken for the most frequent and/or costly types of injury, many of which are musculoskeletal disorders.

Demonstrate success: Data are critical to demonstrating proven injury-prevention systems. Facilities implementing ergonomics-based injury prevention programs with effective engineering and work practice controls have achieved considerable success in reducing worker-related injuries and workers' compensation costs. Some institutions have experienced additional benefits, including reduced staff turnover and associated training and administrative costs, reduced absenteeism, increased productivity improved morale, reduced resident injury and increased resident comfort. Many examples exist of effective ergonomics program in nursing homes. The following examples highlight some aspects of successful programs:

Citizens Memorial Health Care Facility in Bolivar, Missouri: In the four-year period following implementation of a program that combined the use of assistive devices and staff education OSHA-recordable lifting-related injuries were reduced by 45 percent annually with a direct savings of $150,000 in worker's compensation costs.
Kennebec Health system, August, Maine: Following the implementation of an ergonomic management program that included the use of lifting devices, the system reduced lost workdays from 1,097 to 48, and lowered its insurance premium from $1.6 million to $770,293.
Surrey Memorial Hospital, British Columbia: After implementing an ergonomics-based program with a "no lift policy," the hospital reduced injuries by 95 percent.
Veterans Health Administration (VHA), Florida: A financial evaluation conducted two years after the implementation of a project aimed at reducing the number of injuries to nurses and nursing associates with direct patient handling, showed an annualized savings of greater than $200,000 per year including medical care and associated employee costs. An 18 per cent decrease in missed work days due to work-related injuries was also demonstrated

Direct costs include workers' compensation, medical treatment, and vocational rehabilitation. Estimates of the total cost of low back pain to society in 1990 were between $50 billion and $100 billion per year, with a significant share (about $11 billion) borne by the workers' compensation system. (National Occupational Research Agenda (NORA) Priority Research Areas: Low Back Disorders. April, 1996) The observed average costs per healthcare staff-related musculoskeletal injuries per 100,000 work hours are greater than $160,000. (A Business Case for Patient Care Ergonomic Interventions, 2005) Nationally, the estimated average cost per claim is $24,000. If surgery is involved, the cost for claims increases significantly to $40,000 per injury or higher. One example of a back injury involving surgery totaled $240,000.

The Wyandotte County Nursing Home in Upper Sandusky, Ohio, reported that staff had suffered back injuries, including a single injury that resulted in worker's compensation costs of $240,000. The facility acquired 18 ceiling lifts, as well as portable total lifts, a sit-to-stand lift, a lift walker, and 58 electrically adjustable beds at a cost of approximately $150,000. Since Wyandotte implemented a policy of performing all assisted resident transfers with mechanical lifts or gait belts, back injuries from resident lifting have been eliminated. Increased efficiency has allowed staff members to spend more time with residents and caregiver's attitudes and energy levels have reportedly improved. In addition, residents no longer complain of shoulder pain and bruises that had previously been associated with manual resident handling. (Source: OSHA draft guideline)

Indirect costs: Indirect costs, while much harder to quantify, have a significant impact on quality patient care. Many experts estimate that indirect costs are four to seven times higher than direct costs and may cause: decreased employee morale, continual employee hiring and training, use of replacement workers, overtime, medical management, incident reporting and other paperwork, the increased costs of workers' compensation insurance, and the increased costs of employee healthcare.

Many of the organizational costs of back and other musculoskeletal injuries can be quantified through use of a cost benefit analysis adapted from the VA guide.

The cost to the patient: Inadequate solutions for patient lifting and transferring also result in costs to the patient, both physical and psychological. For example, the manual lifting of patients can result in skin tears from being dragged across surfaces. Skin injury can also be caused from using pants instead of a gait belt for a handhold.

Another frequently used but dangerous manual lifting technique involves lifting a patient under the arm, in the sensitive axilla area, and then transferring them. Using this technique, often called "hook and toss," patients are "hooked" under the arm and "tossed" to a new location. This transfer, used because of simplicity and speed of execution, is often painful for the patient. It may also result in subluxation (shoulder joint separation) or other shoulder and upper arm injuries.

There may be psychological distress to the patient as well. For example, when manual techniques are used for lifting, larger people often feel badly that a caregiver will have to lift their weight. As a result, some may not let their caregiver know that they have to use the restroom. Chronic delays in using the restroom can lead to bowel and urinary problems, such as constipation and urinary tract infection.

Many of the costs to the patient can also be measured and documented through use of the Cost Benefit Analysis.

Implement the solutions: Organizations should establish the program's infrastructure before implementing any educational component. This includes acquiring the lifting and transferring equipment and a clear plan about when to use it. Implementation should be unique to each organization, as it depends on supplementing components already in place. Perhaps additional lifting equipment is required, policies and procedures need to be updated, or subsequent training and education need to be supplied.

Regardless of the improvements made, organizations are encouraged to include employee representation from all levels of the program to endure their needs are met and to gain valuable insight and buy-in.

Follow-through: The same measures gathered in the initial program goal development phase, should be used to determine the success of the program. It requires ongoing monitoring and evaluation and incorporation of findings into new prevention strategies. If measures are not producing the results identified in the goals according to the projected timeline, the program should be re-evaluated to determine appropriate corrective measures.

Conclusion

Few people would disagree that back injuries and other musculoskeletal disorders are a common and serious occurrence in patient care personnel. However, many also believe it is not possible to prevent such injuries and that the cost of prevention is greater than the cost of the injuries. However, with the advent of new technology, our current regulatory landscape, the increasing cost of workers' compensation, and the nursing shortage, this mindset is beginning to change. Someday soon, it is hoped that caregivers will be taking care of other people with back injuries, and will no longer need to worry about their own.

Eye Protection Safety Topic

2010-11-08T03:49:00.000-08:00

In just the blink of an eye, an incident can injure or even blind a worker who is not wearing proper protective eye wear. The type of eye protection-safety glasses, goggles, face shields, or helmets must meet the requirements of the Occupational Safety and Health Administration (OSHA) and the American National Standards Institute (ANSI). In hazardous workplaces, street wear eyeglasses should only be worn in conjunction with ANSI-approved additional cover protection.
Eye safety requirement signs should be posted for anyone entering a work area that requires industrial-quality eye protection. Warning signs should be placed near machines, equipment, or process areas that require specific eye protection.
Eye injuries can be reduced when workers are trained to recognize the eye hazard they may encounter and to use and care for eye protection equipment properly. Workers in hazardous areas should also know what to do in case of an eye injury. In all eye injury cases, professional medical attention should be sought as soon as possible after taking initial first-aid measures. There are several causes for eye injury:

Foreign particles such as dust, dirt, metal, wood chips, even an eyelash can cause eye damage. These get into the eye from the wind or activities like chipping, grinding, sawing, brushing, hammering, or from power tools, equipment, and machinery. Flush the object out with water. Never rub or try to remove objects embedded in the eye. This can cause further damage. Loosely bandage eyes to stop movement then seek professional care.
Chemical splashes from solvents, paints, hot liquids, or other hazardous solutions can cause great damage. Go immediately to the nearest emergency shower or water source. Look directly into the stream of water. With fingers hold eyes open and flush eyes for at least 15 minutes.
Light burns can be caused from exposure to welding, lasers, or other radiant light. Their effect may not be felt until hours later when the eyes begin to feel gritty and become sensitive to light, then redness or swelling may occur. Keep eyes closed while awaiting medical attention.
Bumps and blows to the eyes can be helped if a cold compress is applied for 15 minutes to reduce pain and swelling.
Cuts in or around the eyes should be loosely bandaged to stop any eye movement until professionally attended. Don’t rub, press, or wash the cut; this can cause further damage.

Eye safety is no accident. Nothing can replace the loss of an eye. Protect your eyesight from workplace hazards by wearing and caring for appropriate, approved protective eye wear. You’ll see the difference.

GC Process & Type of Detector

2010-11-05T02:36:00.000-07:00

Gas Chromatography(GC)

This method depends upon the solubility and boiling points of organic liquids in order to separate them from a mixture. It is both a qualitative (identity) and quantitative (how much of each) tool.
All chromatographic systems (paper, column, thin layer, gas, etc.) have two phases: a stationary phase and a moving phase. As the terms imply, the stationary phase is some kind of surface on which the sample is placed. The moving phase, true to its name, moves or flows over the stationary phase carrying some compounds with it and leaving some compounds behind. If the components of a mixture have varying tendencies to stick to the stationary phase or flow with the moving phase, they can be separated by chromatography, analyzed for identity and quantity, and even collected for further use since the process of separation has purified the original mixture into its components.

In the type of chromatography which we will use, gas chromatography (GC), the stationary phase is inside of a long piece of hollow metal tubing. The moving phase is helium gas.
A schematic diagram of the GC is shown below. Metal or glass tubing is filled with small, solid, insoluble particles coated with a high boiling liquid. This is the chromatographic column and is the stationary phase. The column is coiled and placed in an oven so that it can be maintained at temperatures above those of ambient conditions.
An inert gas such as helium is passed through the column as a carrier gas and is the moving phase. A sample is injected into a port which is much hotter than the column and is vaporized. The gaseous sample mixes with the helium gas and begins to travel with the carrier gas through the column. As the different compounds in the sample have varying solubility in the column liquid
and as these compounds cool a bit, they are deposited on the column support. However, the column is still hot enough to vaporize the compounds and they will do so but at different rates since they have different boiling points. The process is repeated many, many times along the column. Eventually the components of the injected sample are separated and come off of the column at different times (called "retention times").
There is a detector at the end of the column which signals the change in the nature of the gas flowing out of the column. Recall that helium is the carrier gas and will have a specific thermal conductivity, for example. Other compounds have their own thermal conductivities. The elution of a compound other than helium will cause a change in conductivity and that change is converted to an electrical signal. The detector, in turn, sends a signal to a strip chart recorder or to a computer. Detectors come in several varieties, for example, thermal detectors, flame-ionization and electron capture detectors.

The readout shows the order of elution (order of components coming off the column), the time of elution (retention time), and the relative amounts of the components in the mixture. The order of elution is related to the boiling points and polarities of the substances in the mixture. In general, they elute in order of increasing boiling point but occasionally the relative polarity of a compound will cause it to elute "out of order". This is why it is important to run a standard before using your sample.

Compound	Boiling Point (0C)
pentane	36
hexane	69
cyclohexane	80
isooctane (2,2,4-trimethylpentane)	99
toluene	110
4-methyl-2-pentanone	117
octane	126

The observed elution pattern appears below. Notice the reversed elution of toluene and 4-methyl-2-pentanone.

Gas Chromatography (GC)

Introduction

Gas chromatography is a chromatographic technique that can be used to separate volatile organic compounds. A gas chromatograph consists of a flowing mobile phase, an injection port, a separation column containing the stationary phase, and a detector. The organic compounds are separated due to differences in their partitioning behavior between the mobile gas phase and the stationary phase in the column.

Instrumentation

Mobile phases are generally inert gases such as helium, argon, or nitrogen.

The injection port consists of a rubber septum through which a syringe needle is inserted to inject the sample. The injection port is maintained at a higher temperature than the boiling point of the least volatile component in the sample mixture. Since the partitioning behavior is dependant on temperature, the separation column is usually contained in a thermostat-controlled oven. Separating components with a wide range of boiling points is accomplished by starting at a low oven temperature and increasing the temperature over time to elute the high-boiling point components. Most columns contain a liquid stationary phase on a solid support. Separation of low-molecular weight gases is accomplished with solid adsorbents. Separate documents describe some specific GC Columns and GC Detectors.

Schematic of a gas chromatograph

Type of GC Detectors:

Thermal Conductivity Detector (TCD)

Introduction

A TCD detector consists of an electrically-heated wire or thermistor. The temperature of the sensing element depends on the thermal conductivity of the gas flowing around it. Changes in thermal conductivity, such as when organic molecules displace some of the carrier gas, cause a temperature rise in the element which is sensed as a change in resistance. The TCD is not as sensitive as other detectors but it is non-specific and non-destructive.

Instrumentation

Two pairs of TCDs are used in gas chromatographs. One pair is placed in the column effluent to detect the separated components as they leave the column, and another pair is placed before the injector or in a separate reference column. The resistances of the two sets of pairs are then arranged in a bridge circuit.
Schematic of a bridge circuit for TCD detection

The bridge circuit allows amplification of resistance changes due to analytes passing over the sample thermo conductors and does not amplify changes in resistance that both sets of detectors produce due to flow rate fluctuations, etc.

Flame-Ionization Detector (FID)

Introduction

An FID consists of a hydrogen/air flame and a collector plate. The effluent from the GC column passes through the flame, which breaks down organic molecules and produces ions. The ions are collected on a biased electrode and produce an electrical signal. The FID is extremely sensitive with a large dynamic range; its only disadvantage is that it destroys the sample.
Schematic of FID

Electron Capture Detector (ECD)

Introduction

The ECD uses a radioactive Beta emitter (electrons) to ionize some of the carrier gas and produce a current between a biased pair of electrodes. When organic molecules that contain electronegative functional groups, such as halogens, phosphorous, and nitro groups pass by the detector, they capture some of the electrons and reduce the current measured between the electrodes. The ECD is as sensitive as the FID but has a limited dynamic range and finds its greatest application in analysis of halogenated compounds.
Schematic of an ECD

Moisture In Gases In Liquid

2010-11-05T02:01:00.000-07:00

Process Analyzers

Some of the industrial process analyzers are of the probe type (capacitance, fiber-optic infrared probes), others can through the process stream in the pipe (microwave); while the majority requires some form of a sampling system.

Sampling Systems

There are some sampling system features peculiar to moisture analyzers, and these are covered below. The function of any sampling system is to deliver a clean, representative sample to the measuring element at the required pressure, temperature, and flow rate. Measurement of moisture, although simple in principle, is complicated by the fact that all materials adsorb and desorb moisture. At moisture levels in the percent range, moisture absorption is not a serious problem; however, at moisture levels in the low parts per million (ppm) ranges, sampling system materials must be selected so as to minimize their effect on the moisture level in the sample. Materials which are least likely to contribute to the moisture in the sample are stainless steels, Teflon, Viton, Kel-F, nickel and nickel-plated materials, and cadmium and cadmium-plated materials. Materials that should be avoided are copper and its alloys, rubber, neoprene, and elastomers.
It is important to apply the material considerations to all parts of the sampling system, including the internals of valves and filters.

Electrolytic Hygrometer

The principle of measurement utilized involves the electrolysis of water into oxygen and hydrogen. Since two electrons are required for electrolysis of each water molecule, the electrolysis current is a measure of the water present in the sample. If the volumetric flow rate of the sample gas into the electrolysis cell is controlled at a fixed value, then the electrolysis current is a function of water concentration in the sample.

Capacitance Hygrometer

The principle of measurement utilized is the change of capacitance associated with a change of the sample dielectric constant between capacitor plates. The value of capacitance is a function of plate area, plate spacing, and the dielectric constant of the material between the plates. The dielectric constant of a material has a unique value for each substance and is related to the polar characteristics of the molecules. This property can, therefore, be used to detect the presence of a specific substance in a pipeline stream.
The measuring cell of the hygrometer consists of two electrically insulated concentric metal cylinders to form the measuring capacitor plates. The annulus between the cylinders is filled with alumina desiccant. Two porous metal discs support the cylinders and retain the desiccant in the annulus. The sample is allowed to flow through the annulus and process water is absorbed or desorbed by the desiccant, which remains in equilibrium with the sample in terms of percent saturation. The moisture content of the sample is thus amplified by the desiccant because the saturation level of the desiccant is very much higher than that of the sample. The measuring capacitor is part of an electrical circuit, which includes a reference capacitor. This circuit is powered by a 15-kilocycle, fixed-amplitude sine wave. The measuring and reference capacitors are switched alternately into the circuit, in such a way that its output voltage is a function of connected capacitance. The output signal is a 15-kilocycle sine wave whose amplitude varies with the measuring and reference capacitors as they are switched into the circuit. This difference in amplitude is related to the measured capacitance, which in turn is a function of the moisture content of the sample.

Thin-film Capacitance Probes

These units are suitable for explosion-proof area classifications and can be used in measuring the moisture content of liquid hydrocarbons. The probe units are suitable for installation in high-pressure processes and are provided with microprocessor-based electronics capable of self-diagnostics and of multiple measurements or unit conversions.

Impedance Hygrometer

This instrument measures the water content of a sample by means of a probe whose electrical impedance is a function of the vapor pressure of moisture in the fluid. Impedance is the apparent opposition to the flow of alternating current. The probe consists of an aluminum strip, which is anodized to form a porous layer of aluminum oxide. A thin coat of gold is applied over the aluminum oxide. Leads from the gold and aluminum electrodes of the probe connect the sensing element to the measuring circuitry.
Water vapor penetrates the gold layer and equilibrates on the aluminum oxide. The number of molecules adsorbed to the aluminum oxide is a function of the water vapor pressure in the sample. Each water molecule adsorbed contributes a distinct increment to the total conductivity of the aluminum oxide. The total probe impedance, the reciprocal of probe conductivity, is thus a measure of water vapor pressure in the sample. Water vapor pressure of a gas sample uniquely determines the dew-point temperature and moisture content of the sample. The output is normally calibrated to these units since they are more convenient to use than vapor pressure.

Piezoelectric Hygrometer

Piezoelectric quartz crystals have a number of uses: in communications, to control frequencies and, in industry, to measure temperature and thickness of metal films, and to generate ultrasonic waves. In moisture measurement, advantage is taken of the oscillating crystal's sensitivity to deposits of foreign material on its surface. Commercially available crystals will show a frequency change of 2000 cycles per second (cps) per microgram of material deposited. For moisture measurement, the quartz crystals are coated with a hygroscopic material and exposed to the sample; water from the sample is absorbed by the crystal coating, thus increasing the total mass and decreasing the oscillating frequency of the crystal. In order to measure changes of decreasing moisture concentration and to simplify the frequency measurement, two crystals are used. One crystal is exposed to wet sample and the other to a dry reference gas for a short period. Then sample and reference gas flows are switched so that moisture is absorbed by one while being desorbed by the other crystal. Sample switching is controlled by a cycle timer in the instrument. The frequency difference between the two crystals is in proportion to their mass difference and the moisture content of the gas.

Heat Adsorption Hygrometer

The process of adsorption and desorption involves an exchange of energy. During adsorption, energy is released to and during desorption energy is removed from the environment. When wet gas is passed through a column of adsorbent, which selectively adsorbs moisture, the temperature rise due to heat liberation is in proportion to the amount of moisture adsorbed. Other factors which affect the heat of adsorption, such as the nature of the adsorbent and operating temperature, are selected to maximize the heat of adsorption.

Infrared Absorption Hygrometer

Water absorbs electromagnetic radiation in the infrared (IR) region of the spectrum. Specifically, infrared radiation of 1.4 and 1.93 micron wavelength is absorbed strongly by water. By measuring the attenuation (decrease of light intensity) of a beam of this wavelength as it passes through a sample, the moisture content of the sample can be determined. However, other factors such as reflection and dispersion of the radiant energy will contribute to the attenuation. Therefore, it is necessary to either calibrate these factors out of the measurement, or to use a reference wavelength which is not absorbed by moisture but is affected by all other factors to the same extent as the measuring wavelength. The difference in attenuation of the measurement and reference wavelength is then a function of moisture content only.
The sensing element consists of three groups of components: an IR radiation source, sample cell, and radiation pickup. The radiation source consists of a lamp, filters to pass the measuring and reference wavelengths, and optics to direct the beam through the glass sample cell. The radiation pickup consists of optics to collect the transmitted radiation and a photocell to convert the electromagnetic energy to an electric current. The measuring and reference wavelengths are allowed to impinge alternately on the photocell, so that two sets of current pulses are produced. These pulses are converted into two direct current (DC) signal levels whose ratio represents the moisture content of the sample

Microwave Absorption Hygrometer

In the microwave frequency band of 20 to 22 0Hz (K band), the wavelength is about 13 to 15 mm. In this frequency band moisture (free water) is most specific, as it is only the water molecule that produces molecular resonance. The microwave radiation can be guided by waveguides or be transmitted through the process stream from source to receiver.
The principle of operation of this instrument is the same as that of the infrared absorption hygrometer; namely, selective absorption of electromagnetic energy by moisture in the sample. However, in this case, radiant energy in the microwave length is used. A transmitter provides a microwave beam, which can either be transmitted through or reflected by the sample material. The receiving unit senses wave attenuation and phase shift and provides a readout. The unit senses the mass of moisture in the beam path so that the readout is normally in terms of the mass of moisture per unit volume. However, with calibration, readout in weight percent can be achieved.
Several probe configurations are possible depending on the application. On type has the transmitting and receiving probes welded into a section of pipe. Internally, Teflon contacts the sample. This type of arrangement can be used to advantage on slurries and pastes since there are no obstructions to flow. The units described above measure the attenuation by moisture of a microwave beam in the sample. The reflectance-type unit contains the source and detector in one housing. Rather than detecting the transmitted microwave energy, this design measures the amount of energy reflected by the sample. The probe of the reflectance unit does, however, require contact with the process material.

Yokogawa Centum CS Field Control Station

2010-07-04T06:56:00.000-07:00

Field Control Station

· High Reliability

Pair and Spare redundancy

· Input and Computation of Floating-Point Data

· Reduced wiring costs through Remote I/O

· Standard Function Blocks (PID, Seq. Table, Logic Charts, SFC, etc.)

· High capacity due to RISC Processor

· Direct Connection of Subsystems

Application Size of FCS

FCS Optional Software Package

Pair and Spare Redundancy

§ Error detection improvement

§ Bumpless Transfer ( Control Computation is always proceeding on standby side )

§ Memory + ECC

Installation Control Cabinets

Control Signals

· Single Loop Integrity

· Free arrangement of Inputs and Outputs

· Reduction of spare parts

· No signal conditioners required

· Modules configurable from engineering platform

I/O Level Redundancy

· Analog Input: Dedicated Function Block

· Analog Output: Additional Output Card

I/O Modules (1)

· Current/Voltage Input

· mV, Thermocouple, RTD Input

· Pulse Input

· Current/Voltage Out

· Field bus (future)

· Voltage Input

· mV Input

· RTD Input

· 2-wire transmitter input

· 4-20 mA Output

I/O Module (2)

· 16 -pt. Input (isolated)

· 16 -pt Output (isolated)

· 32 -pt. Input

· 32 -pt. Output

· 16 -pt. Input

· 16 -pt. Output

I/O Module (3)

· 16 -pt. Input (isolated)

· 16 -pt Output (isolated)

· 32 -pt. Input

· 32 -pt. Output

· RS-232C

· RS-422

· RS-485

Engineering

Off line engineering without Target Hardware

Choice of Engineering Environments

Configuration Testing

Control Area, Control Block

· P&ID Compatibility

· Control Block (Max. 4096/FCS)

· Control Drawing (MAx. 255/FCS)

· Control Area (Max.8/FCS)

Control Area’s

· Control function loading, builder operation and test operation can be done on each control area.

Control Drawing

· Function blocks of regulatory control and sequence control can be on the same drawing

· Free to exchange signal between drawings

· Loop configuration and function blocks can be registered as a module.

· The control drawing can be displayed on the operator station dynamically

Faceplate Block

· Providing a faceplate per compound block control for operators

Internal Data (1)

Ø Feature

· Processed as engineering unit data in system

Ø Purposes

· to process data in standard format (Floating-point format as specified by IEEE754)

· to improve arithmetic precision

· to eliminate normalized numbers

Ø Data flow

· Process Input : Engineering unit conversion data at input module

· Between function block : Engineering unit data transmission and receiving

· Calculation in function block : Engineering unit data

· Process Output : 0-100% data

Internal Data (2)

Function Blocks

Control Block Library

Regulatory Control Block

· Input Processing

· Square root extraction

· Pulse train input

· Digital filter

· Totalizer

· PV overshoot function

· Calibration

· Alarm Processing

Control Block - PID

· Control calculation processing

· Control algorithm (PID)

· Nonlinear gain

· Control output action (velocity type, positional type)

· Direction of control action (positive or negative action switching)

· Reset limiter

· Dead band

· Control Period

· I/O compensation

· Input tracking

· Set point limiter

· Set point pushback

· Bumpless switching

· Initialization manual

· Control hold

· MAN fallback

· AUT fallback

· Computer backup

· Mode conversion interlock

· PRD mode action

Regulatory Control Block - MLD Manual Loader Block

· Output processing

· Output signal conversion

· Output limiter

· Output velocity limiter

· Output tracking

· Output range tracking

· Manipulated output index

· Pulse width output

Regulatory Control Block - Batch Set Block

Analyzer Basic

2010-06-23T09:06:00.000-07:00

Photometry

Photometry Measurement Non-Dispersive Gas Analysis

Molecules convert Absorbed Energy into Oscillatory or Rotational Energy
Absorbing Capability Requires a Dipole Moment
Each Component Absorbs at specific Wavelengths
Preconditions for IR active Components
Move of Electrons inside the Atoms to higher Levels
Requires higher Energy in Visible or Ultraviolet Range
Selectivity via Detector, Filters or Narrow-band Beams

Absorption of Radiation

Advantage of NDIR / UV / VIS Technology

Several Components absorb in NDIR Region
Some Components Show Cross Interference's due to overlap in Absorption of Radiation
Especially Hydrocarbons, H₂O and CO₂ may cause cross Interference's
NDUV or NDVIS is an Alternative Method to NDIR
SO₂, NO₂and Cl₂ Show less or no Interference's in NDUV / VIS Region

Lambert-Beer Principle - Non-Linear Curve

Paramagnetic – PMD

Paramagnetic Technology

Magnetic Susceptibility

All gases exhibit some form of magnetic susceptibility. This susceptibility causes the gas to be attracted or repelled by a magnetic field. Oxygen exhibits a very strong paramagnetic susceptibility with respect to most other gases, and therefore is drawn to a magnetic field. Most other gases are weakly diamagnetic (repelled from a magnetic field).

Based on this fact, the paramagnetic detector consists of a test body filled with N₂ and suspended in a non-uniform strong magnetic field. A mirror is attached to the center of the test body and a light source/photocell combination is used to measure the movement of the test body. The final part of the detector is a current loop used to pull the test body back to its “null” position.

When sample is introduced to the device, the oxygen present in the sample is drawn to the magnetic field. The buoyancy of the test body causes it to be displaced out of its null position in the field.
The light focuses a beam on the mirror of the test body and is reflected to the photocells. When the test body moves, the photocells register an imbalance and drive a restoring current to pull the test body back to its null position.
The intensity of this restoring current is directly proportional to the concentration of oxygen present. By measuring this current, we can accurately derive the oxygen concentration of the sample.

Paramagnetic Detector

Thermal Conductivity Detection – TCD

Thermal conductivity detector

One of the most important detectors.
The detector consists of a metal block with four cells. The sample will flow through two of them and the other two will be the reference.
Platen- or Wolfram-filaments in a Wheatstone bridge circuit.
Electrical power will go through each filament and will heat up the filament.
The resistance is depending on the thermal conductivity of the gas, which will flow through the cells.
Changes of the gas composition will cause changes in the temperature and resistance of the filaments of the cell.
The equilibrium of Whetstone bridge circuit will be disturbed.
The temperature of the sample cells will be stabilized on a higher temperature level if the gas has less thermal conductivity than the reference gas. The temperature of the reference filaments will not change. This temperature difference causes an voltage discrepancy. The voltage discrepancy will be amplified and can be measured with an instrument (PC, printer etc.)
The resulting signal is proportional to the concentration of the component.
With the TCD one can measure all species of organic and inorganic % to high ppm levels
Hydrogen, Helium, Argon or Nitrogen as carrier

Flame Ionization Detection - FID

How does the FID detector work?

A hydrogen flame is generated in a burner
Sample gas with hydrocarbons is introduced into the hydrogen flame
Hydrocarbon molecules are ionized in the hydrogen flame
Ions formed produce an electrical current
Current is proportional to the carbon count in the hydrocarbon molecules

FID Burners

Flow Diagram - 400A

Chemiluminescence Detection – CLD

Chemiluminescence - Theory of operation

Nitrogen oxide (no) reacts with ozone (o₃) to form nitrogen dioxide (no₂) in an excited state.
No₂ immediately reverts to ground state by emitting a photon of light ==> chemiluminescence.
Light intensity is proportional to the concentration of no/nox in the sample gas.
The silicon photo diode detector measures light intensity and generates an output signal.

CLD Detector Technology

Theory of Operation (CLD)

Nitrogen oxide (no) is measurable in a gas stream by its chemiluminescence
Reaction properties:

NO + O₃ = NO₂* + O₂ (1)

NO₂* = NO₂ + hV (Photon) (2)

Emission of photon = chemiluminescence

PLC Basic

2010-05-31T12:23:00.000-07:00

HISTORY
Introduced in late 1960's Bedford associates proposed something called a modular digital controller (modicon) to a US car manufacturer.
The MODICON 084 brought the world's first PLC into Commercial production.
Disadvantages of Relay based logic
o Relays are electromechanical devices and so have a limited life.
o Requires strict adhesion to maintenance schedules.
o The size of a complicated relay based system could be mind boggling.
o Complicated internal wiring of so many individual devices.
o No diagnostics and fault finding very difficult.
o Changes in the logic very cumbersome to implement.

Standards

IEC 1131-3: Merging of PLC programming languages under one international standard.
What's inside the box?
The PLC mainly consists of CPU, memory area, and appropriate circuits to receive input/output data. We can consider it to be a box full of hundreds or thousands of separate relays, counters, timers and data storage.

What does each part do?

Internal Relays:

These are connected to the outside world. They physically exist and receive signals from switches, sensors etc. Typically they are not relays but rather they are solid state transistors.
Counters:
These again do not physically exist. They are simulated counters and they can be programmed to count pulses. Typically these counters can count up, down or both up and down.

Timers:

They also do not physically exist. They come in many varieties and increments. The most common types are on-delay and off- delay. Increments vary from 1ms to 1 second.
Output Relays:
These are connected to the outside world. They physically exist and send on-off signals to solenoids, lights etc. They can be transistors, triacs, or relays depending upon the model chosen.
Data Storage:
Typically there are registers assigned to simply store data. They are usually used as temporary storage for math or data manipulation. They can also be used to store data when power is removed from the PLC.

How does a PLC work?

A PLC works by continually scanning a program. We can think of this scan cycle as consisting of three important steps.

Step 1 - Check Input Status First the PLC checks at each input to determine whether it is on or off. It records this data into its memory to be used during the next step.
Step 2 - Execute Program Next the PLC executes the program one instruction at a time. May be the program said that if the first input was on then it should turn off the first output. Since it already knows which inputs are on-off from the previous step it will be able to decide whether the first output should be turned on based on the state of the first input. It will store the execution results for use later during the next step.
Step 3 - Update Output Status Finally the PLC updates the status of the outputs. It updates the outputs based on which inputs were on during the first step and the results of program execution during the second step.
After the third step the PLC goes back to step one and repeats the steps continuously. One scan time is defined as the time it takes to execute the three steps listed above.
The total response time is defined as:
Total Response Time = I/P response Time + Program execution Time + O/P Response Time
Case Study (Level application)
Purpose: Control of lubricating oil being dispensed from the tank. Instrumentation: 2 sensors (One near the bottom & one near the top), PLC Sensor not immersed in liquid they will be ON. When they are immersed they will be OFF.
Logic: Fill motor to pump lubricating oil into the tank until the high level sensor turns on. At that point we want to turn off the motor. It should start only after level falls below the low level
Sensor: We need three I/O's (Inputs & Outputs), 2 are inputs (the sensors) and 1 is an output (the fill motor). Both the inputs will be normally close (NC). We will give each input and output device an address.

Initially the tank is empty so both the sensors for high and low level are not immersed. So they are ON (True). So input 0000 is true and input 0001 is also true. Gradually the tank fills because fill motor (500) is on. After 100 scans the oil level rises above the low level sensor and it becomes open (False).
Notice that even the low level sensor is false there is still a path of true logic from left to right. This is why we used an internal relay. Relay 1000 is latching the output (500) on. It will stay this way until there is no true logic path from left to right. (ie when 0001 becomes false).
After 1000 scans the oil level rises above the high level sensor as it becomes open (ie false). Since there is no more true logic path, output 500 is no longer energized (true) and therefore the motor turns off. After 1050 scans the oil level falls below the high level sensor and it will become true again.
Notice that even though the high level sensor became true there still is NO continuous true logic path and therefore coil 1000 remains false.
After 2000 scans the oil level falls below the low level sensor and it will also become true again.
Specifications

Specifications for Discrete Modules ( General I/O )

Operating Temperature: 0 0 C to 60 0 C
Storage Temperature: -40 0 C to 85 0 C
Operating Humidity: 5% to 95% (non condensing)
Noise Immunity: NEMA standard ICS 2-230
Vibration (Operating): Displacement: 0.015 in peak at 5 to 57 Hz
Acceleration: 2.5 Gs at 57 to 2000 Hz
Shock (Operating): 30Gs (all modules except relay contact)
Isolation: 1500 V
Agency Certification: UL listed
CSA certified
CE compliant
Hazardous Area Classification: Class I, Division 2 Hazardous Environment

Specifications for Input Modules

Voltage Category 24 V ac/dc or 125 V dc
Number of Inputs 16
Points per Common 16 / individually isolated
Operating Voltage Ac 10 to 30 V ac
Dc: 10 to 30 V dc
Backplane Current Consumption 0.085 A
Signal Delay (max) on = 9 ms, off = 9 ms
Off State Voltage (max) 20.0 V dc
Off State Current (max) 0.8 mA
Nominal Input Current Ac: 8 mA at 24 V ac
Dc: 8 mA at 24 V dc
Inrush Current (max) 0.02 A

Typical wiring Schematics for Analog Input Devices

2 Wire Transmitters

3 Wire Transmitters

4 Wire Transmitters

Start-up Procedures

This, of course, assumes that you have already debugged the program to be certain it is working as you intended it to. If not, it is probably a good time to do so by using a simulator/emulator or perhaps by breaking the program into blocks for piece checking.

Verify power is off to the PLC.
Open all E-stops so the machine will not run until we want it to.
Disconnect output wiring terminals from output modules to
Disable the outputs until we are ready for them.
Generally you should check and re-check equipment installation to make sure all is well. Are the sensors adjusted? Are all bolts properly torque? Belts are tight? etc.
Check to verify that all PLC modules have been inserted into the Base properly.
Check that all wires are fully inserted into their proper Connection points.
Check to make sure all communication cables are connected. If the PLC requires dip-switches to be set for communications, verify that this has been done.
Verify that the proper power is connected to the PLC. Does it require 110VAC or 24VDC or... whatever it is; make sure the connections are proper.
Verify the PLC will NOT be powered up in run mode.
Power-on PLC.
Check CPU LEDs. Are any on? Any error lights on? Power down and correct the fault if necessary and then repeat from the beginning.
Check input module LEDs. Are any on? Should any be?

If all is well, let's power down and move on to checking the inputs!

Input Checking Procedures

Verify power is off to the PLC.
Open all E-stops so the machine will not run until we want it to.
Make sure all outputs are disconnected from the PLC.
Verify all body parts are out of the way and don't test the inputs with ANY body parts. Use a safe device (like a test rod) to test them.
Power-on PLC.
Activate input devices one-by-one and verify the appropriate LED on the input module turns on. If it doesn't, check the devices wiring.
If the wiring is ok, verify the device is working and when in doubt, try another input point on that module. If it still doesn't work, try connecting it to another module. If it works now, probably there is a fault with the original module, so replace it and begin again.
Continue on until all input devices and module input points have passed the tests. If all is well, let's power down and move on to checking the outputs!

Output Checking Procedures

Verify all body parts are out of the way
Verify power is off to the PLC.
Open all E-stops so the machine will not run until we want it to.
Use a simple debug program to test your outputs. Generally we won't use the original program. Create a simple debug rung like this:

Input output
-| |---( )--
Let 'input' be a simple toggle switch connected to an unused input or use an internal relay when available. Output will be the address of actual output we are testing.
If you're really lucky, your PLC will have a force function available for your debugging use. In that case, we can manually force each output on in succession to test them.
o Regardless of which method we're using, energize each output via the PLC program one at a time. Each time, ensure the safety of the surrounding people and the machine itself.
o If the output device does not turn on, verify that the appropriate output LED does indeed turn on. If the LED is on, check the wiring to the output device. If the wiring is ok, check the device itself to verify it is working as we believe it should. If the LED does not turn on, verify that the address is correct within your program.

Final Verification Procedures

Verify all body parts are out of the way
Verify power is off to the PLC.
Open all E-stops so the machine will not run until we want it to.
Reconnect everything that needs to be connected.
Clear the PLC memory. Generally, we can do this via our PLC programming software.
Download the final working version of our PLC program.
Verify once again that everything is connected and safe. Then, run the program.
Troubleshoot the machine when and as necessary to ensure all is working as needed.
When you are happy with the performance, make a last backup copy of the program and store it in a safe place. It will be needed again when you least expect it. Yes, you will need it and someday you'll be extremely happy to have that backup. And don't forget to create backup copies of the documentation...

Chemical Hazard Labels

2010-05-30T11:06:00.000-07:00

A chemical hazard label is a pictogram applied to containers of dangerous chemical compounds to indicate the specific risk, and thus the required precautions.
There are several systems of labels.
The U.S. based NFPA has a standard NFPA 704 using

A diamond
With four colored sections
Each with a number indicating Severity 0 - 4
0 (zero) for NO hazard,
4 indicate a severe hazard.
The RED section denotes flammability.
The BLUE section denotes health risks.
Yellow represents reactivity (tendency to explode).
The WHITE section denotes special hazard information.

o This label is used primarily in the USA.

NFPA Labeling System

White – Special
W: reacts with Water in an unusual or dangerous manner (e.g., cesium, sodium)
OX or OXY: Oxidizer (e.g., potassium per chlorate, ammonium nitrate)
COR: Corrosive; strong acid or base (e.g. sulfuric acid, potassium hydroxide)
ACID and ALK to be more specific.
BIO: Biological hazard (e.g., smallpox virus)
POI: Poisonous (e.g. Spider Venom),
The Radioactive trefoil { } is radioactive (e.g., plutonium, uranium)
CRY or CRYO: Cryogenic (e.g. Liquid Nitrogen)
Only W and OX/OXY are officially part of the NFPA 704 standard,
But other self-explanatory symbols are occasionally used in an unofficial manner.
The use of non-standard symbols or text may be permitted, required or disallowed by the authority having jurisdiction

UN Classifications

o Class 1 Explosives

o Class 2 Gases

o Class 3 Flammable Liquids

o Class 4 Solids

o Class 5 Oxidizing Substances

o Class 6 Toxic and Infectious Substances

o Class 7 Radioactive Substances

o Class 8 Corrosives

o Class 9 Miscellaneous Substances

Explosives – Label

Compressed Gases

Flammable liquids -

Flammable solids

Oxidizing substances

Toxic substances

Radioactive substances

Class label – Corrosives

o White Over Black background

o Test tube over hand / metal symbol on top.

o Number 8 on bottom

o “CORROSIVE” wording

Hazard Communication

2010-05-29T11:27:00.001-07:00

OBJECTIVE

Requirements of the standard.
To know how and where to find specific hazard information.
Inform employees about Hazards of chemicals.
Precautions and protective measures when using, handling and contacting chemicals.

HAZARD COMMUNICATION

Also known as HAZCOM.
Everyone working with Hazardous materials has the “RIGHT TO KNOW” about Hazardous materials used or produced in their work area.

DEFINITIONS

Hazard is defined as a physical or chemical characteristic of chemicals that has the potential for causing harm to people, the environment or property.

Chemicals: - Any element, chemical compound, or mixture of elements and /or compound.

Hazardous substance: - Any chemical / product / catalyst or waste classified as such by applicable national / local legislation and chemical/substance/material identified by organization as harmful to people, property and the environment.

Hazardous chemical - means any chemical which is a physical hazard or a health hazard.

Physical hazard - means a chemical for which there is scientifically valid evidence that it is a combustible liquid, a compressed gas, explosive, an organic peroxide, an oxidizer, pyrophoric, unstable (reactive) or water-reactive.

Health Hazard – The term health hazard includes chemicals which are carcinogens, toxic or highly toxic agents, irritants, reproductive toxins, corrosives, sensitizes which acts on hematopoietic (blood forming) system and agents which damage lung, skin, eye or mucous membranes.

Hazard Warning – Any word, picture, symbol or combination thereof appearing on the label or other appropriate form of warning which convey the hazards of the chemical of the container.

Container- Any bag, barrel, bottle, vessel. Storage tank or the like that contains hazardous chemical.

Develop and implement management system that accomplishes the requirement of this sub element.

Responsibility to ensure compliance of this Sub-element in accordance with SHEM-00.01: Management Commitment, Accountability and Responsibilities.

Roles, Responsibilities of all other positions that are responsible for implementation of this programme shall be clearly identified, documented and communicated.

Each department will keep and provide the ISD with an accurate list of all hazardous chemicals used, produced, and / or stored at each process or operation.

Written Hazard Communication Program

Each department will Develop, Implement, and Maintain at each workplace, a written hazard communication program which at least includes

List of chemicals,
Labels and other forms of warning methodology,
Material safety data sheets, and
Employee information and training.

Multi-employer workplaces: Where Contractor Employees may be exposed, The Hazard Communication Program shall ensure

Method to provide information to onsite Contractors –

On each hazardous chemical the contractor employee might exposed.
Precautionary Measures
Labeling system used in the work place.

The written Hazard Communication programme shall be made available to all the Employees, Contractors and Auditors upon request.

Hazard communication for Manufacturer / Importer – Label

Any chemical containers that leave Company must be labeled, which convey the hazard information of the substance they contain.

The label must identify the following:

The contents of the container,
The name and address of the chemical manufacturer or importer, as well as the emergency telephone number.
The physical and health hazards associated with the chemical.

Exception - Signs, placards, process sheets, batch tickets, operating procedures, or other such written materials may be used in lieu of labeling of containers, provided:

The containers can be readily identified
The alternative warnings must contain the information required for labels and be readily accessible to employees at all times.

An employee who transfers a quantity of a hazardous chemical from a labeled container into a portable container for his immediate use shall not be required to label the portable container.
Existing labels on incoming containers of hazardous chemicals shall not be removed, covered up, or defaced unless the container is immediately marked with the required labeling information.
Labels or other forms of warning shall be legible, and prominently displayed on the container, or readily available in the work area throughout each work shift.
The department receiving a shipment shall inspect incoming containers to ensure adequate and appropriate labeling of hazardous chemicals / materials.
Each operating organization shall ensure appropriate and adequate labeling of hazardous chemical storage containers under their jurisdiction.

Hazard communication for Employer- MSDS

Company shall obtain or develop Material Safety Data Sheets (MSDS) for all hazardous chemicals used in the workplace.
Industrial Hygienist shall maintain a master copy of all MSDS(s) prepared or received for hazardous chemicals produced or used by Yansab.
MSDS shall have minimum information as given in definition under SHEM 12.3 (American National Standards Institute (ANSI) has proposed a 16 section format MSDS presented in ANSI Z400.1 – 2004)

Employee Information & Training

Training on all Hazardous Chemicals –

Upon initial assignment of employee exposed to the hazardous chemicals, and
Whenever any new hazardous chemicals are introduced into the work area.

Employee shall be informed of

The requirements of the Hazard Communication Standard.
Operations in the work area where hazardous chemicals are present.
The location and availability of the written hazard communication program, The list of hazardous chemicals in the work area and the MSDS(s) or hazardous chemicals in the work area

Employees shall be trained on:

The methods and observation that may be used to detect the presence or release of a hazardous chemical in the work area.
The physical health hazards of the chemicals at the work area.
The measures employees can take to protect themselves from these hazards. (Appropriate work practices, engineering and administrative controls, Existing labeling system and personal protective equipment).
Details of the Hazcom Program, including An explanation of the labeling system, MSDS and how employee can obtained and use this information.
The hazards of non-routine tasks and unlabeled piping systems.
That the employee and the employee's physician has a right to receive information regarding hazardous chemicals to which the employee may potentially be exposed.

Records – All training records shall be maintained for entire employment period of the employee.

Verification –The position(s) that are assigned the responsibility to ensure compliance to this Sub-element shall conduct Self-Assessment in accordance with SHEM-00.06: Compliance Audit & Evaluation.

Heat Detector

2010-05-28T05:56:00.001-07:00

Heat Detectors are used mainly in kitchens and turbine compartments. Those used in turbine compartments are color coded for various temperatures (at which the detector gives alarm/trip signal)

These are Bi-Metallic Switches and function based on temperature rise in the surrounding. They are preferred to smoke detectors in Kitchen as Kitchens produce smoke during cooking and used in Turbine compartments since the ambient temperature in Turbine compartments are very high and smoke detectors cannot function at theses high temperatures.

The Heat Detectors used in Kitchen are usually Rate of Rise detectors and operate at about 85 deg. C (my figure may not be accurate). The Heat Detectors used in the kitchen very similar to conventional smoke detectors except that there is no opening for the passage for smoke (as it functions based on heat and not on smoke).

The Heat Detectors employed in Turbine enclosures carry a color code, to specify the temperature at which the detectors change state (change of state of switch). Currently I do not have the information on the color code corresponding to the temperature at which the detector changes state. The Heat detector for each area in the turbine is selected based on the ambient temperature in which the detector is to be installed. As for example close to the Burner compartment the heat detector selected may be as high as one to operate at 350 deg C (as for example) and the near auxiliary compartment may operate at 120 deg C (as for example).

While replacing the detector, if the color is not clear in the detector refer to the drawing to find out the temperature class of the detector to be mounted.

The Heat Detector is tested using a Hot Air Blower which can generate sufficient heat for the detector to change state.

The number of Heat Detectors may also be connected to each zone just like smoke detectors and all the precautions and explanations provided above regarding the zone modules apply for heat detectors as well.

The power to the field devices is usually provided from the zone module. So, whenever a field device is to be replaced, if we pull out the zone module the power to the field will be last. However before pulling out the module check the cause & effect sheet.

Mechanical Questions And Answer

2010-05-27T08:21:00.000-07:00

1. Name parts of the centrifugal pump?

Rotary parts;

· Shaft

· Impeller

· Coupling

· Mechanical seal

· Oil rings

Stationary parts;

· Casing

· Stuffing box

· Bearing housing

2. Explain overhauling steps for a back pullout pump?

Remove coupling guards after getting clearance of safety aspects like electrical isolation, process lines drainage etc.
Remove coupling spacer and loose the casing bolts connects the stuffing box frame after removing and draining oil level glass and lube oil from bearing housing.
Pullouts back the pump from casing with care of casing gasket.
Dismantle all parts from the pump unit as impeller, mechanical seal assembly, shaft sleeve, coupling, and bearings respectively with high care.
The following factors should be checked and recorded for future to estimate the performance condition of the pump, are wear ring clearance, seal compression, shaft deflection, thrust, trueness etc while or after dismantle.
Proper tracing of parts need to any vision able damage like crack, score, break etc.
Best is changing new one comparing reconditioning of parts.
Assemble is the reversing procedure of dismantle as before seen.
Before coupled alignment should be checked or corrected

3. What is impeller back clearance?

The clearance between the backside of the impeller (shroud) and the stuffing box or crown

(Wear) plate.

Actually this clearance standardize the stuffing box pressure and should be strictly followed incase of depressurizing vanes on impeller and semi open impellers.

4. How do you check impeller back clearance?

By the use of feeler gauge and with dial indicator as possible.

5. How do you adjust impeller back clearance?

· Add or remove shims behind the stuffing box.

· Changing the position of the rotor depends clearance if possible.

· Machining of impeller hub if there is no another way.

6. What is impeller front clearance?

The clearance between the front side of the impeller (crown) and the casing or wear plate.

This clearance should be strictly followed incase of semi open impellers.

7. How do you check impeller front clearance?

By the use of feeler gauge and with dial indicator as possible

8. How do you adjust impeller front clearance?

Add or remove casing gasket thickness

9. What is fixed bearing?

The bearing fixed with out any allowable axial clearance to permit thermal expansion.

This bearings bears the thrust load and only has thrust allowance as 0.001 – 0.003 inches

10. Where is fixed bearing located?

· In back pullout pumps, fans – inboard

· Double suction single discharge pump – outboard

· Mixers (agitators) – top bearing

11. What is floating bearing?

The bearing fixed with allowable clearance to permit thermal expansion. And takes radial load normally.

12. Where is floating bearing located?

· In back pullout pumps, fans – outboard

· Double suction single discharge pump – inboard

· Mixers (agitators) – bottom bearing

13. What is necessity of floating bearing?

· Elongation due to thermal expansion of shaft

· Axial fluctuation effects by load

14. Why bearing back-to-back arrangement is provided?

The back-to-back arrangement can support combined axial and radial loads and will keep the pump shaft end movement within acceptable limits. A bearing pair will support an axial load equally in either axial direction. It should preferably have a slight clearance (0 to 0.002 inches) with the bearing housing end cover.

16 .In which series bearing back-to-back arrangement is available?

· Single row angular contact ball bearing

· Taper roller bearing.

17. How do you check plain journal bearing clearance?

· By taking measurement difference between shaft outer and bearing inner diameters.

· By the use of plastic gauge or lead wire.

18. Is there any thumb rule for journal bearing clearance?

Bearing clearance necessary depends upon oil viscosity, speed and load.0.001per 1 inch of journal diameter plus 0.0015 inches up to 9000 feet per minute journal velocity. Above this speed 0.002 inches per 1 inch of journal diameter for shaft larger than 2.5 inches.

19. Have you seen tilting pad journal bearing?

Yes.

20. What are the various ways to check tilting pad journal bearing clearance?

keeping dial indicator on shaft vertically besides bearing and lift the shaft to find out clearance of bearing through indicator reading.
By the use of mandrel as same diameter of shaft and moving bearing.
By manual measurement = diameter of pivot – (2 x thickness of individual pad) – diameter of the shaft.

21. What is the advantage of tilting pad journal bearing over plain journal bearing?

Suitable for higher speeds and loads and has greater stability. It avoids the possibility of oil whirl and allows self-aligning.

22. How do you adjust tilting pad journal bearing clearance?

By add or remove shims behind the shoes of tilting pads.

23. Give the ‘go’, ‘no go’ gauge dimensions for a 100 mm journal diameter with a minimum bearing clearance of 0.16 mm and maximum bearing clearance of 0.25 mm?

Go gauge dimension - 100.16 mm

No go gauge dimension- 100.26 mm.

24. Why plastic gauge are preferred rather than lead wire?

· Lead wire expands after removal from cap

· It can be become embedded in the Babbitt; especially in soft, high lead Babbitt bearing.

· Plastic gauge doesn’t need skill more and it is easy to identify just comparing the compressed width of plastic with the gauge paper.

25. How do you polish journal bearing?

With the use of special polish oil and 4/0 fine emery sheet or sponge pad. A special tool named as bearing scrapper used to clear deep able scratches.

26. What is spherical seated journal bearing?

The spherical seated journal bearing in which the shell of bearing in the form of spherical by which it allows self-accommodation on housing depends shaft aligns.

28. What is bearing crush?

Actually it defines the compression fit of the split type journal bearings diametrically and will not exceed more than maximum of 0.003 inches.

29. How do you check bearing crush?

Keeping 0.004 to 0.010 inches of shim according the plastic gauge series on the face of half split bearing housing and measuring the clearance between the bearing shell and cap (top cover) of bearing housing with the use of plastic gauge after tightening cover.

Now the bearing crush = shim thickness – plastic gauge reading.

30. How do you adjust bearing crush?

By providing shim piece in-between bearing shell and top cover of the bearing housing.

31. How do you check thrust-bearing clearance?

Keep the dial indicator horizontally on rotor in any accessible point. Move the rotor shaft longitudinally to find out the thrust clearance of the bearing after fixation of radial and thrust bearings.

32. How do you adjust thrust-bearing clearance?

Add or remove shims on the thrust-bearing collar if provision given otherwise Machining carried on in case of no other way.

33. How do you identify bearing pads based on their pivot?

Left hand and right hand pads.

34. How do you identify RH & LH pivoted pads?

If the loading point of pad on the right side called RH pads when seeing in front of the pad face. If the loading point of pad on the left side called LH pads when seeing in front of the pad face.

35. If the DOR of a rotor CW looking from C/E, where will you locate RH & LH pads?

Right hand pads on opposite side of coupling.

Left hand pads on the coupling side.

36. What is adaptor sleeve & withdrawal sleeve?

These sleeves used to fix and remove bearings easily on that and to be fixed any accessible place on the rotor. In adaptor sleeve, bearing is fastened while the adaptor sleeve nut tightened. In withdrawal sleeve nut is used to withdraw bearing from its position from the withdrawal sleeve.

37. How do you specify a bearing lock nut & lock washer?

N for bearing locknut

W for bearing lock washer

38. What is rotor free float?

It defines the total axial movement of rotor without thrust bearing.

39. Explain rotor centering?

It is the process of keeping rotor half of the free-float through the position of thrust bearing in the bearing housing fixation.

40. How do you adjust rotor centering without affecting axial float?

Increase or reduce the thickness of centering spacer fixed behind the thrust bearing on shaft. Add or remove gasket on the end covers of bearing housing. It allows only slight adjustment otherwise machining carried out on end cover in case of no other way.

41. What is radial centering?

Aligning the rotor axis in the same line with centerline of casing confined recess provided for the fixation of wear ring, neck bush, etc. radially. This centering keeps and helps to maintain constant gap between wear ring, neck bush, etc.

42. How do you adjust radial centering?

By the use of adjusting screws provided on the bearing housing carrier.

43. Explain the overhauling sequence for a multi stage centrifugal pump?

44. What do you mean by wear rings?

Wear rings are removable rings fixed on either impeller eye and casing or both of them.

45. What is the purpose of wear rings?

To avoid the change of impeller and casing due to pitting corrosion.

46. What are the different types of wear rings?

· Serrated wear rings

· Stepped wear rings,

· Reverse thread wear rings,

· Thrust balancing wears rings,

· Flat wear ring,

· L shaped wear ring,

· Impeller wear ring,

· Casing wear ring,

· Double ring with labyrinth leakage joint wear ring.

47. How do you check wear ring clearance?

Means of measuring the outer diameter of impeller wear ring or impeller eye and the inner diameter of the casing wear ring inner diameter by the use of micrometer or vernier caliper and with the use of feeler gauge if possible.

48. How do you adjust wear ring clearance?

By machining wear rings or change as new one if the clearance more.

49. How do you fix eyewear ring & casing wear ring?

Interference fit with Allen screw lock, pin with spot weld, direct bead weld, threading etc.

50. What the different types of shaft sleeve?

Threaded sleeve, sleeve with locknut, sleeve with Allen lock, straight sleeve, stepped sleeve, throttle sleeve, throat sleeve, etc.

51. Where are throttle sleeve & throat sleeve located in a rotor?

Throat sleeves located on throat bush area to control the flow of pumping liquid in to stuffing box area. Throttle sleeves are used in slurry service to avoid the flow of slurry liquid into seal area with the use of throttle packing which allows only the flushing liquid into pumping liquid area instead of reversing that’s why flushing fluid pressure is kept 15 psi more than suction pressure. ENSIVAL pump design has the provision of both throttle and throat bush arrangement.

53. Why balanced opposed rotor arrangement is preferred?

This arrangement minimizes axial thrust load of rotor by keeping the low pressures (suction pressure) on both side by the arrangement of impellers.

The balancing drum is located, behind the last stage of impeller.

55. What is the purpose of balance drum?

Used to take 90% of thrust load by liquid and the residual thrust is supported by the thrust bearing.

56. What is the applicable API standard for centrifugal pumps?

API 610.

57. What do you mean by oil wedge?

Under normal operating condition, the shaft of the machine will rise slightly up the side of the bearing. The amount of rise depends on shaft RPM, rotor weight and oil pressure. The shaft, thus operating in an eccentric position relative to the bearing center, draws oil to produce a pressurized load-carrying film called as ‘oil wedge’.

58. What do you mean by oil whirl and oil whip?

The eccentricity of oil wedge is momentarily increased from its equilibrium position, perhaps due to a sudden surge, an external shock load or other transient condition, additional oil is immediately pumped into the space vacated by the shaft. The result is an increase in the pressure of the load-carrying film. The additional force developed by the oil-film can drive the shaft into a whirling path around the bearing. If the damping within this system is sufficiently high, the shaft returns to its normal position in the bearing; otherwise the shaft continues in a whirling path called ‘oil whirl’

Lack of lubrication or improper lubrication causes excessive friction between the stationary bearing and rotating shaft, and the friction excites vibration in the bearing and other related parts similar wiping a moisture finger over a dry plane of glass called ‘oil whip’.

59. What is hydrostatic lubrication?

The pressurized lubrication oil given on oil wedge for lubricating and creating oil film in-between the moving parts. This type of lubrication called hydrostatic lubrication.

60. What is hydrodynamic lubrication?

The moving parts make the lubricating film in between contact area while running itself. This type of lubrication named as hydrodynamic lubrication.

61. What is forced feed lubrication?

Actually it is a pressurized lubrication, oil wedge formed by the pressure induced from separate lube oil pump, which driven by either separate drive or with drive from running rotor.

62. What is oil thrower ring?

The ring provided on the shaft in bearing housing to make efficient lubrication.

63. What is the purpose of oil thrower ring?

It is used to lubricate the bearing effectively by splashing out lube oil quenched and rotates the contact motion of shaft while running.

64. What is oil scoop?

It is a small bucket shaped part fixed on rotate able crankshaft

65. What is the purpose of oil scoop?

Used to splash lube oil intermediately for effective lubrication.

66. What is oil control ring?

A ring made of aluminium, brass or bronze fixed in the end covers of bearing housing.

67. What is the purpose of oil control ring?

The labyrinth grooved ring (oil control ring) used to avoid the leakage of lube oil to atmosphere and entry of moisture in to the bearing housing.

68. Why auxiliary lube oil pump is used?

Normally it’s a motor driven pumps used,

1. To maintain the lube oil pressure when starting and running time.

2. Auto start, incase of main lube oil pump failure.

3. To give lube oil circulation when the rotor is in ideal.

70. What is torque wrench?

It’s a mechanical tool used for tightening the bolts of equipments with proper torques by the help of the torque indicator attached with it.

71. What is rotor run out?

Rotor run out defines the accuracy of trueness of the rotor. This should not exceed more than 0.002 inches.

72. How do you check rotor run out?

After keeping the rotor on the bearings or lathe center, with the use of dial indicator.

73. What are the various ways of impeller fixing arrangements?

1. Threaded

2. Sliding fit with key and lock nut

3. Snug fit with sleeve lock nut.

4. With use of collets

74. What is the general value of rotor run out at various locations?

· Impeller- 0.0025”

· Sleeve – 0.0015”

· Bearing – 0.001”

· Coupling – 0.0025”

75. What is NPSH?

Net positive section head= static head + velocity head of liquid – vapor pressure at ambient temperature

76. What are NPSH required and NPSH available?

NPSH required establish the pump capability of working in minimum of positive suction head.

NPSH available establish the original working condition of pump in process with positive suction head.

NPSH available should be more than that of NPSH required.

77. What is cavitation?

Cavitation is the process of air or vapor lock in a pump. Reason for cavitation

1. Wrong NPSH

2. Pin hole or any air leak on suction line

3. Starvation of pump

4. Low velocity of liquid in the suction eye.

78. What is inducer?

A small low head, axial flow impeller that attaches to the conventional impeller is called as inducer.

79. Why inducer is used?

Inducer is used to increase the pump’s suction head (pressure), and prevent cavitation problems. The inducer will reduce the net positive suction head required of the pump or permit the pump to run at a higher speed.

Not all pump manufacturers have this feature available.

80. What is different between discharge head and discharge pressure?

Discharge head expressed in feet of the liquid being pumped from the discharge port.

The head varies depends on its discharge pressure.

Example: 1 Psi liquid raises 2.32 feet of height of liquid with the specific gravity of 1.

Discharge pressure expressed as Psi.

81. What is minimum flow check valve?

Minimum flow check valve is a non-return valve with a regulating by-pass port in the application of high temperature (near saturation temperature on the discharge) liquid services. Example- boiler feed water pump

82. Why minimum flow check valve is used?

To avoid the backing of vapor lock in the application of near saturation temperature liquid service by giving circulation of liquid while pump in ideal.

When the pump in ideal condition the by-pass port opens and allows the circulation of liquid and when the pump starts, the by-pass port closes by the action of main check valve opening.

83. What is vertical in line pump?

The pump fixed in the line of flow of liquid itself in vertical axis called vertical in line pump. Actually it is a booster pump for giving extra energy to liquid while flowing.

84. How do you center the rotor and position the coupling of a vertical in line pump?

Normally this pump have rigid muff split coupling attached with help of Allen screws, the shaft and coupling steps and grooves matched with together while fixing.

Add or remove the metal shims in-between the pump and motor frame for centering the rotor.

85. Explain the procedure for mechanical seal renewal of vertical in line pump?

· To get proper work and safety aspect from operations

· Remove coupling and before ensure the compression of seal unit by removing gland bolts.

· Remove coupling and take out gland plate outside

· Pull out compression unit (retainer) by special puller, care seal parts

· Check the packing area of sleeve for fretting corrosion and confirm any other defects in sleeve

· If the sleeve condition is good assembly of seal can start otherwise sleeve should be replaced by the pump overhauling

· Assemble is the same reverse procedure of the dismantle procedure before seen

· While assembling the following aspects should be checked, retainer seating on sleeve slot with lock pin perfectly, seal setting compression, bearing condition of the motor and alignment.

86. What is vertical sump pump?

The vertical pump designed and fixed on a sump called vertical sump pump

87. What is steady bearing?

Steady bearings are fixed in the vertical pump intermediately between the drop columns. It is actually bush bearing fixed in steady rest housing.

89. What do you mean by balancing line in multi stage centrifugal pump?

The line connects intermediate labyrinth of balancing drum (discharge side) with the suction port for thrust balancing of rotor named as balancing line in multistage centrifugal pump.

90. What is the purpose of balancing line?

Used for thrust balancing by connects suction port and balancing drum.

91. Why mechanical seals are used?

Used for hazardous and toxic liquids

· Zero leak proof

· Reliable

· Less friction loss comparing packing

· High efficiency

92. How do you specify a mechanical seal?

As per API –682

X₁ X₂ X₃ X₄ X₅

X_{1 –}Balanced (B) and unbalanced (U)

X₂– single (S), double (D), tandem (T)

X₃– Type of seal gland (T- throttle bush, A- auxiliary sealing device)

X₄– gasket material (R- Graf oil)

X₅– face material (M – means tungsten carbide Vs carbon)

93. Name few seal manufactures?

John crane, Pacific, Borg Warner, Dresser rand, Dura metallic

94. What is 15WRS seal?

It is a seal made of john crane as per API – 610

95. What is applicable standard for mechanical seal?

API – 682 (shaft sealing systems for centrifugal pump as well as rotary pumps)

96. What is the average life expected out of a seal as per API –682?

2 Years in normal working condition

97. Name few types of mechanical seal?

1. Single coil mechanical seal

2. Multi coil mechanical seal

3. Balanced mechanical seal

4. Unbalanced mechanical seal

5. Pusher/ non pusher mechanical seal

6. Single/ double mechanical seal

99. Explain the complete dismantling and assembly procedure for a mechanical seal?

1. Remove the gland from stuffing box to access mechanical seal with care after checking the seal setting compression.

2. Take out sleeve with retainer set and check any vision able effects like carbon crack, struck, wear on facing area both carbon and seat

3. Remove the seat from gland and justify the condition of secondary packing of seat.

4. Remove retainer set by loosing Allen screws before make conform the retainer houses on the shoulder of sleeve other wise take measurement of retainer position.

5. Full view of inspection to be done on each and every mechanical seal parts like springs, thrust plate, drive lugs, snap ring, seat seating area on gland, sleeve surface due to fretting corrosion, seal matting face of both seat and seal ring.

6. Changing new parts is better than reconditioning (lapping)

7. Assembling is the reverse procedure of dismantling on time the following aspects should be check:

· Square ness and rectangularity of seat after fixation on the gland plate.

· Trueness of the shaft and sleeve.

· Correct fit of wedge packing/ “O” ring with backup ring on the sleeve.

· The recess confined with gland plate and stuffing box.

· Seal setting compression as per drawings or as same before.

100. What is seal setting compression?

The seal setting compression given by the retainer in to matting faces as per designed by the suppliers

101. What is cartridge type of mechanical seal?

The seal is mounted on a sleeve that can be secured to the shaft from outside the seal chamber. It’s an advance-designed seal supplying by the seal manufacturers to make the installation easier. There is no need measurement while fixing and just changing as new set of cartridge seal instead of reconditioning.

102. Can you change the seal settings compression of a cartridge type mechanical seal?

No.

103. Explain the assembly procedure of a cartridge type mechanical seal?

Is a simple and easy assemble procedure comparing a normal mechanical seal

Just fix the cartridge seal set on the shaft and tight the gland plate with stuffing box. Tight the Allen screws on sleeve to lock with shaft then remove the seal setting lock plate provided on gland plate by loosening the sets screw.

104. How do you identify a balanced / unbalanced mechanical seal?

Identification of balanced seal:

1. Stepped sleeve on seal ring area.

2. Reduced contact area of seal ring by the provision of step.

105. What is pusher/ non-pusher type mechanical seal?

When the secondary packing of seal ring is affected due to the thermal expansion in ambient condition and the axial end movement of rotor called as pusher seal. Otherwise called as non-pusher seal.

Normally pusher seals are single & multi coil mechanical seals

And non- pusher seals are bellow seals.

106. What is all the pre check to be made on a pump before starting positioning a mechanical seal?

· Shaft true ness

· Stuffing box bore square ness

· Shaft deflection

· Thrust movement of rotor

· Dust free condition

107. What is stuffing box square ness?

It’s a process of checking the concentricity of stuffing box bore with shaft rotation by the use of dial indicator. The maximum allowable square ness is 0.0025”

109. What type of mechanical seal prefer for hot oil? Why?

Non-pusher seal (bellow seals) to avoid fretting corrosion

110. What type of mechanical seal prefers sulphur duty?

Single coil mechanical seal with seal ring made-up of carbon and matting ring made – up tungsten carbide to with stand high temperature distortion and slurry service.

111. What is seal flushing fluid? Name few seal plans?

Seal flushing fluids used in the mechanical seal system for cooling, cooling and lubricating the mating seal faces.

112. What is seal quenching fluid? What is its purpose? Name few seal plans?

Seal quenching fluid used behind the mechanical seal system in the gland plate design provision to avoid the hazardous or toxic liquid with atmosphere if the seal leaks in the form of liquid or gas state.

113. What is stuffing box cooling water jacket? Why it is used?

The integral or removable jacket provided in the pump for circulating the cooling water to maintain the stuffing box temperature into desirable limit for attaining the mechanical seal life reliable.

114. Why seal coolers are used?

To reduce the temperature of flushing fluid while entering into the mechanical seal system to maintain stuffing box temperature and better lubrication in the seal mating faces in running condition.

115. Name few MOC of seal faces?

Carbon, tungsten carbide, silicon carbide, stellite, peramic, ceramic, bronze, etc.

116. What is seat ring and mating ring?

The ring has the provision (springs or bellows) to give seal setting compression called as seat ring.

The ring mates with seat ring for sealing called as mating ring.

117. How many elastomers are used in a mechanical seal assembly?

1. Between seat ring and sleeve or shaft

2. Between mating ring and gland plate

3. Between shaft and sleeve

4. Between gland and stuffing box.

118. Name few MOC of elastomers?

Neoprene, viton, glass/ asbestos filled Teflon, Graf oil, Buna-N, buna-S, etc.

119. What is snap ring in a mechanical seals?

Snap ring is a cut off circular ring used to hold seal ring with advance compression. Snap ring rests on the groove made on retainer.

120. What are the usual problems faced with mechanical seals?

1. Sleeve fretting corrosion

2. Retainer springs struck

3. Seat or mating ring crack

4. Lack of reliable of secondary packing

5. Excessive wear of mating faces, etc.

121. Does the axial float have something to do with mechanical seal?

Yes. Seal setting compression will change.

122. What is double mechanical seal? Why it is used?

It is the two sets of simple mechanical seal. It is used in the application of;

1. High hazardous of pumping liquid

2. Usage of separate flushing fluid

3. A seal leak could cause a pollution problem

4. The product is very costly

123. Name two types of mechanical seal? Where is it used?

1. Back to back. The worst possible choice if used in the rotating seal version. Stationary versions are acceptable because the sealing fluid is located at the outside diameter of the seal faces where we can take advantage of centrifugal force

2. Tandem. One seal behind the other requiring a low pressure buffer fluid between the seals. This arrangement cannot be used if a higher-pressure barrier fluid is required or desirable.

124. What do you mean by barrier fluid? Name few barrier fluid?

Any time you use two seals in an application you will need a fluid between them. If the fluid between the seals is higher than stuffing box pressure we call it barrier fluid

Water is a good barrier and buffer fluid.

125. What do you mean by buffer fluid? Name few buffer fluids?

If the fluid between the seals is lower than stuffing box pressure we call it buffer fluid.

126. What is the difference between barrier fluid and buffer fluid?

Any time you use two seals in an application you will need a fluid between them. If the fluid between the seals is higher than stuffing box pressure we call it barrier fluid. If it is lower than stuffing box pressure we call it buffer fluid. The liquid can be circulated either by forced circulation, a pumping ring or convection. The method that you will use will be dictated by the pressure, pump speed and shaft size. Water is one of the best barrier or buffer fluids because of its high specific heat and good conductivity. Petroleum oil is probably one of the worse because of its low specific heat and poor conductivity

127. Where do we use cyclone separator in a mechanical seal?

In the application of the stuffing box pressure is more than the suction pressure of the pump to separate the foreign materials if anything in flushing fluid from the discharge of the pump by the action of centrifugal force.

128. What is pumping ring in a mechanical seal? What is its purpose?

The thermodynamic grooves feature made on the ring or the circumference of the retainer of the seal system is named as pumping ring. This has two types of radial and axial pumping ring. Used to give circulation and pressure to flushing fluid

129. What is the difference between inside mounted seal & outside mounted seal?

The inside mounted seal. All components are in the pumping fluid.

· Advantage. The elastomer can move to a clean surface as the seal face wears. Centrifugal force throws solids away from the seal components allowing the lapped seal faces to stay in co

· Disadvantage. All the metal components must be corrosion resistant to the pumping fluid.

· If the product solidifies or crystallizes when the pump is stopped, the seal can become inoperable.

The outside mounted seal. None of the metal components are in contact with the pumping fluid. Most designs clamp to the shaft rather than using setscrews that damage ceramic or glass coated shafts.

· Advantage. This is the most common solution to non-metallic pump sealing.

· Disadvantage. Centrifugal force throws solids into the lapped seal faces and can prevent the sliding components from moving freely. Higher pressure applications can cause the retaining clamp to slide on the shaft

130. What is seal balance ratio?

It is the ratio between the effective area of fluid pressure acting and the loading area of mating seal faces. It is actually defines the balancing of hydraulic forces.

131. What is the seal balance ratio for balanced/ unbalanced seal?

For balanced seal- 0.75

For unbalanced seal- 1.25 to 1.35

132. Differenciate centrifugal pump and reciprocating pump?

Centrifugal pump:

1. Working in the principle of centrifugal force

2. The main part is impeller

3. In the application of high capacity

4. Constant pressure with variable capacity

5. High efficiency

Reciprocating pump:

1. Working in the principle of reciprocating compression

2. The main part is piston/ plunger

3. In the application of high pressure

4. Constant capacity with variable pressure

5. Low efficiency

133. How do you measure Valve lift in a reciprocating pump?

In feather plate valve type the valve lift is equal to the thickness of the spacer used in-between seat plate and spring (cushion) plate; valve lift – 0.8 to1.5 mm. For the wing disc valve type it is the gap between disc top faces with the valve cover; valve lift- 3 to 6mm.

134. What is the necessity of pulsation dampener?

To minimize the fluctuation of flow of liquid in the reciprocating pump (+ve displacement).

135. Name few types of pulsation dampener?

1. Bladder

2. Diaphragm

3. Mechanical

4. Bellow

136. How do you fill up gas in an accumulator?

Gas is filled in an accumulator by the use of flow regulator valve into the desired pressure, which is normally 40 to 70% of the working pressure of the line to be damp.

138. What is web deflection? How do you measure web deflection?

Any movement of crank webs from their ideal position during the 360-degree rotation of the crankshaft is web deflection.

It is measured with the deflection meter or electronic web deflection system.

139. How to check big end bearing & small end bush clearance?

Big end bearing clearance:

Keeping dial indicator on connecting rod and lift it by a jack

Small end bearing:

By measuring outer diameter of gudgeon pin with inner diameter of bush in the small end or with the use of dial indicator or feeler gauge or plastic gauge which is adaptable.

140. What do you mean by stroke length?

The traveling length of piston/ plunger from BDC to TDC. It is the equal to the distance between crank pin center to crank shaft center.

141. What is gudgeon pin?

The pin, which connects the small end bush of connecting rod with the piston or cross head. The pin is well hardened to with stand tensile and compression load acting on the piston/ plunger.

142. What is crosshead slide/ shoe?

It is the two Babbitt lined adjustable shoes fixed to guide the reciprocal motion of the crosshead with an allowable clearance.

143. Name few ways of locking arrangement of piston/ plunger?

· Threaded with locknut

· Flanged bolted

· Locked by pin

· With split threaded coupling

144. How to ensure in-line concentricity of crankshaft to cylinder bore?

Keeping the two-dial indicators on the piston/ plunger rod with 90 degree of position and checking the deflection run out of the longitudinal movement of the rod on both sides when rotating crankshaft. The maximum deflection should be less than that of neck bush clearance otherwise the position of cylinder bore with crankcase is adjusted to attain the reading with in limit.

145. What are dosing pumps?

These are all the tiny low capacity reciprocating plunger pumps.

146. Name few types of dosing pumps?

1. Simplex

2. Duplex

3. Multiplex

4. Single acting

5. Double acting

6. Horizontal

7. Vertical

147. Why dosing pumps are used?

Dosing pumps are used to pump a low capacity liquid injected into a high-pressure process operation.

148. What are the probable reasons for cylinder knocking in a reciprocating pump?

1. Valve seat or parts damaged

2. High temperature of pumping fluid

3. Foreign materials in suction area

4. Valve holder looseness

5. Plunger looseness

6. Air / gas mixed on liquid

7. Flow restriction, etc.

149. What are the probable reasons for valve knocking in a reciprocating pump?

1. Worn out seating area

2. Springs broken

3. Valve holder looseness

4. Improper valve lift

5. Valve loose by improper tightening

6. Reusing worn parts

7. Foreign matters in valves, etc.

150. What are the probable reasons for vibration in a reciprocating pump?

1. Foundation looseness

2. Cylinder or valve knocking

3. Misalignment

4. Worn parts

5. Failure of vibration dampener

6. Wrong installation and assembly, etc.

151. Where do we use screw pumps & gear pumps?

In the application of moderate pressure and capacity & constant capacity with variable pressure requirement.

152. What do you mean by flute?

Flute is a helical wave formed on the screws of the screw pump. In between the flutes pumping fluid passes.

153. What is idler screw?

The screw on the screw pump driven by the engagement of the flutes of the main screw coupled with prime mover.

154. How drive is transmitted to idler screw?

Through the engagement of the flutes of main screw of the screw pump.

155. How do you measure radial clearance & axial clearance between flutes?

Radial clearance: With the use of feeler gauge

Axial clearance: Keeping the dial indicator on the main screw shaft end and moving it longitudinally.

156. How do you measure gear backlash?

With the use of feeler gauge or dial indicator measurement reference with pitch diameter of the gear.

157. What is the usual gear hardness value?

Gears made of alloy- steel; maximum hardness value – 38 HRC & pinion 2 HRC more than gear.

Gears made of hardened alloy steel; surface hardness up to 60 HRC.

158. Name few parts of a centrifugal compressor?

1. rotor

2. casing

3. diaphragm

4. diffuser

5. labyrinth

6. seal

7. Bearings, etc.

159. What is the applicable standard for centrifugal compressor?

API- 617

160. How do you specify a centrifugal/ horizontally split compressor?

MCL- horizontal split type centrifugal compressor, simply specify as ‘M’.As per the design of BHEL.

162. How do you center a compressor rotor?

Measure the total float, which is the axial displacement of the rotor with out thrust bearing and with journal bearings on both sides to avoid the rest of rotor on the labyrinth edges.

Now the centering of rotor is the half of the total float while the thrust plate loaded on the active side of the thrust bearing and is achieved through:

1. Increase/reduce the width of centering spacer fixed behind the thrust plate

2. Machining on the active thrust bearing collar and adding spacer behind the in active thrust bearing

3. Add/ remove the shims on the thrust bearing if the adjustable requirement is less.

163. How do you check labyrinth clearance for a barrel type centrifugal compressor?

Securing the half split labyrinth with together by a hose clip firmly and checking the measurement difference with use vernier or micrometers.

164. What is the compound used in the split half of the casing?

Copalite, key-paste, permatex.

165. How do you leak check a barrel type compressor?

The compressor pressurized to operating pressure by an inert gas like N₂. the shaft turn slowly with seal oil delta pressure 0.5 Kg/ CM², and leakage seal across HP seals is measured with this, it is possible to judge the fitness of the seals.

167. Name the different types of labyrinths?

1. Conventional labyrinth seal

2. Straight type labyrinth

3. Stepped labyrinth

4. Knife edge labyrinth

5. J type labyrinth

6. Turbine type labyrinth

7. Honey comb labyrinth

168. How do you measure labyrinth clearance in barrel type compressor?

Securing the half split labyrinth with together by a hose clip firmly and checking the measurement difference with use vernier or micrometers.

169. How do you measure labyrinth clearance in horizontally split type compressor?

1. With the use of feeler gauge

2. Securing the half split labyrinth with together by a hose clip firmly and checking the measurement difference with use vernier or micrometers.

170. What is diaphragm?

It constitutes the dynamic profile of the stator parts of the compressor. Then are divided into three types viz. suction, intermediate and delivery. Suction diaphragm guides the gas to the first impeller. Intermediate diaphragms have the function of transforming the kinetic energy into pressure, return to channel serves to guide the gas to the next impeller with shock less entry. It has contoured passage leading from the diffuser of one stage to the impeller of the next stage. Some diaphragms are constructed with baffled passages for the flow of coolant. Delivery diaphragm forms the diffuser for the last impeller and delivery spiral.

172. What is balance piston?

The balance piston or drum fixed behind the last stage of impeller to take 90% of thrust load by gas and the thrust bearing supports the residual thrust.

In balancing piston the area in suction pressure side through balancing line is more comparing discharge side of last stage of impeller. Labyrinths on the balancing drum effects to reduce leak off between the both sides of pressure acting.

174. What is bridge over arrangement?

Bridge-overs are provided to reduce the number of compression stages and the omission of an impeller in the rotor assembly is

1. To provide an internal for a large side stream in connection

2. To make the critical speed of rotor out of normal operating range

3. To avoid interrupt of adjacent nozzle flanges each other.

176. What is lube oil run down tank?

It is an overhead tank for lube oil to supply for bearing lubrication in case of emergency purpose when the both lube oil pump failured, designed still the rotor stops and coming into atmosphere temperature.

177. What is the normal filtration size of LO & SO filter?

Lube oil filtration size- 20 to 40 microns

Seal oil filtration size- 10 to 20 microns

179. What is the purpose of PCV?

The pressure control valve is used to maintain the pressure of the seal oil in the header line.

180. What is the purpose of LCV in the seal oil circuit?

The temperature control valve is used to maintain the level of seal oil in the overhead tank.

181. What will happen if PCV opens more?

1. The pressure of the seal oil header increases

2. The level in the over head tank increases

3. LCV tends to open more to lower the level of over head tank

182. What is flow through valve?

The recycle gas compressors are applied 3 rings seal configuration because of high sealing pressure. However at start up operation handling gas pressure for regeneration is so low that insufficient seal oil quantity makes over heat of seal rings if seal system is used as is so, this is considered to solve such problem at start up operation by apply by-pass flow (flow-through) system with the use of a control valve called as flow- through valve.

183. Why buffer gas is used in the seal oil circuit?

The buffer gas is an inert or non- hazardous gas used in the seal oil circuit to avoid the contact of process gas with the seal parts and seal oil, if the process gas has hazardous or toxic or corrosive. The buffer gas pressure is normally 7 psi more than that of process gas.

184. Is there any other source for isolating the seal oil from process gas?

Yes. Dry gas seal.

185. What is dry gas seal?

It is a non- contacting gas lubricated seal compressor seal with controlled buffer or flushing gas. They have a rotating seat with a broad face and V grooves. When the seat rotates, the V grooves force gas between the sliding faces. The resulting rise in pressure causes the sliding faces to lift off and run with out making contact.

187. What is polytropic head & polytropic efficiency?

Polytropic head (H);

The work usually required to compress unit gas flow along the polytropic compression curve is called polytropic head. i.e. actual head developed by the compressor.

Polytropic efficiency;

It is the ratio between the power required to develop polytropic head in to the power actually supplied.

188. What is surging?

Surge can be defined as the capacity below 55 to 70%, which the centrifugal compressor performance becomes unstable. When surging occurs, the high-pressure gas at the discharge of the machine flows back through the compressor in a complete reversal of the normal direction of flow causing the collapse of pressure producing ability will repeat and cycle through the same sequence. Surging controlled by;

1. Increase the flow from process to compressor suction

2. By-pass some discharge through coolers, back to suction of the unit

3. Decrease the pressure ratio.

189. What is stone wall effect?

Chocking or stone wall effect is in the large flow region, if the flow velocity reaches sound velocity anywhere in the compressor. The compressor can’t generate the head and all input energy are spend to over come the friction.

190. What is stalling?

Is a performance of vortex gas flow generated in the impeller internal or diffuser area as a symptom of surging when gas flow is decreased. To accompany this phenomenon, resonance of impeller and vibration sound (humming sound) will be generated. For corrective measure increase compressor flow

Simply stalling means fluctuation in flow rate.

192. What is contact type & non- contact type seal?

The sliding faces of seal mating together when running called as contact type seal.

The sliding faces of seal with out mating contact with together when running called as non-contact type seal.

193. Is the seal rings stationary, rotating or floating?

Floating.

194. How do you measure seal ring clearance?

With the use of vernier caliper or micrometers.

195. Does the seal ring have clearance with housing? Why?

Yes. Because of floating on its position.

196. What is the general value of seal ring clearance?

Inner seal ring (gas side) – 0.002 to 0.004 inches

Outer seal ring (oil side) – 0.005 to 0.006 inches

198. What is honeycomb labyrinth?

The use of honeycomb labyrinths offers even better control of leakage rates (up to 60% reduction compared to straight pass type). It operates at approximately half of the radial clearance of conventional labyrinth seals. It consists of S.S. foil about 10 mills thick. Hexagonal shaped cell make are enforced structure that provides a larger number of effective throttling points. In addition S.S. honeycomb retains its strength at high temperature and pressure levels, which would cause weakening of an aluminum labyrinth.

199. What is head?

Head used to close either side of the barrel and house the bearing end gas seals and oil seals made of solid forging. Depending gas medium either carbon steel or stainless steel are selected.

200. What is head puller?

It is arrangement of mechanical tool used to pull up head from the barrel of compressor on its position.

201. What is bellyband?

It is a large steel clamp fabricated to hold the full assembly of rotor with diffuser and diaphragm housings with together for lifting and transporting the assembly safely.

202. Differentiate bundle ‘o’ring & head ‘o’ ring?

Bundle ‘o’ ring avoids the leakage between suction and discharge side of gas flow.

Head ‘o’ring avoids the leakage of discharged pressure gas into atmosphere. This ‘o’ring should be used with a back up Teflon ring to neglect extrusion due to high-pressure ratio.

203. What is hydraulic fit coupling?

The coupling can be fixed or removed in the shaft easily with hydraulic pressure by a separate hydraulic pump. This coupling has interference fit with shaft.

205. What is pusher pump & expander pump?

The pump connected in the jack to pull or push the coupling into shaft named as pusher pump.

The pump used to induce high hydraulic pressure between the contacting face of coupling and the shaft to make work easy named as expander pump.

206.Is hydraulic fit couplings with ‘o’ rings or with out ‘o’ rings?

With ‘o’ rings.

207. How do you ensure fit of taper coupling?

By the projection of the coupling face with the shaft end face. It is between 1/16 to 1/8 inches.

208. What is diaphragm coupling?

It is one of the flexible coupling used between compressor and steam turbine. All parts of this coupling are solidly bolted together, no moving or no wearing parts, therefore no lubrication is necessary.

209. What is active shim & store shim?

The shims connected on coupling with drive or driven hubs to transmit load with flexible named as active shims.

The extra shims bolted steady with coupling and these have not take the load of transmission named as store shims. It should be fixed for the consideration of dynamic balancing of the rotor and add or remove the shims in between the coupling depends span length.

210. What is shear plate coupling?

This coupling has the several of round plates with holes for bolting coupling spacer with hub intermediately and it has be sheared & failured in case of high torsion force of drive exceeds ultimate limit. It is simply known as metal flex coupling.

211. Name different types of coupling?

Rigid coupling

1. Flanged coupling

2. Muff coupling

3. Threaded sleeve coupling

4. Four piece coupling (in Gould’s sump pump)

Flexible coupling

1. Metal flex coupling

2. Diaphragm coupling

3. Gear coupling

4. Grid coupling

212. What is the allowable vibration level as per API standard?

As per API 670

Vibration amplitude = root of (12,000 / RPM) mills per second.

213. Name few parts of a reciprocating compressor?

1. Cylinder

2. Piston

3. Valves

4. Cross head

5. Connecting rod

6. Crank shaft

7. Crank case

214. What is the applicable standard for reciprocating compressor?

API 618

216. What is top dead center? How do you measure it?

The end of transverse movement of the piston towards cylinder head is the top dead center of the reciprocating compressor.

It is measured by keeping lead wire in the cylinder towards head end and rotating the compressor till the piston come back after compressing the lead wire. Now the top dead clearance is equal to the thickness of the lead wire.

217. Is there any means to increase TDC? How to do it?

TDC can be increased through;

1. Increase or decrease the thickness of the cylinder head gasket

2. Loose or tightening the piston rod in the cross head if threaded with piston rod locknut

218. What is bottom dead center? How do you measure it?

The end transverse movement of piston towards crankshaft end is the bottom dead center.

It is measured by keeping lead wire in the cylinder towards crank end and rotating the compressor till the piston come back after compressing the lead wire. Now the bottom dead clearance is equal to the thickness of the lead wire.

219. Why TDC is more than BDC?

For the consideration of thermal elongation of crank, connecting rod, piston rod towards the cylinder head side at working temperature.

220. What is rod deflection? How do you measure it? When will it increase?

It is the deflection of the piston rod from its trueness position while running.

Measuring: keeping two dial indicators on the piston rod with 90 degrees each of the recess in the distance piece of reciprocating compressor and measure the reading of indicator while rotating compressor. Deflection will increase due to

1. Accelerated wear and scuffing – piston to liner, piston rings, piston rod packings.

2. Broken rod

3. Damaged cross heads

4. Damaged pin bushings

5. Frame failure

6. Misaligned concentricity of cylinder bore with crank shaft.

221. What are the various clearances measured during overhauling of reciprocating compressor?

1. piston end clearance

2. piston ring side clearance

3. piston ring end clearance

4. diametrical clearance between piston with cylinder/ liner

5. rider ring diametric clearance

6. web deflection

7. piston rod run out

8. connecting rod big & small end bearings clearance

9. crank shaft main bearing clearance

10. crank shaft thrust allowance

11. cross head with cross slide clearance

12. gas & oil wiper packings clearance

222. What is cylinder to piston clearance? How do you measure it?

It is the diametrical clearance of piston outer with cylinder or liner bore.

It can be measured by feeler gauge or micrometers.

223. How do you check piston ring end clearance?

By inserting the piston ring in to the cylinder bore and checking the clearance of the piston ring ends with the use of feeler gauge.

224. What is difference between piston ring & bearer ring?

Piston ring, which used to avoid leakage from the piston end compressed gas to outwards through piston circumference.

Rider or bearer ring used to guide the piston movement and neglect the scuffing of piston with cylinder liner when the piston rings are damaged. It has less clearance with the cylinder bore.

225. What is the MOC of piston ring & bearer ring?

1. Cast iron

2. Carbon

3. Bronze

4. Teflon

5. Phenolic

226. How much the normal clearance between piston ring to piston groove?

It simply specified as piston ring side clearance

For MOC of cast iron, bronze, carbon – 0.001 inches

For MOC of Teflon – 0.012 inches

227. Name different types of gas packing rings?

1. pressure breaker ring

2. radial cut ring

3. tangential cut ring

4. anti extrusion ring

228. What is pressure breaker ring? Where it is located? Which one is pressure breaker ring?

This is the simplest form of packing ring acts to break or slow down gas passage only with out actually sealing it completely. This prevents damage to packing rings and garter springs due to the shock effect of the differential pressure involved.

It has a limited clearance at the cut only and should not exceed more than 0.010 inches per inch of bore diameter. Obviously this ring should not be allowed to operate with out end clearance because its life would be very short. This ring located in prior towards gas side.

229. What is sealing ring? Where is it located? Which one is sealing ring?

The true sealing ring made up of a pair of rings, the first of which is radially cut with considerable clearance at each end. The second ring is tangentially cut forming an overlapping seal joint that prevents gas passage from the outside periphery toward the rod bore. The inner radial cuts of this tangent ring are arranged so that they occur approx. between the radial cuts of the first ring in the pair. In this manner, gas passage along the rod is blocked so that there is no through escape.

This type of ring is single acting or directional in that it seals pressure from one side only.

232. Is there any clearance between cup to packing? Why that clearance is given?

Yes. This clearance given for

1. space for oil film lubrication

2. shock effect of the differential pressure involved

233. What is the MOC of gas packing rings?

1. Tetra fluro ethylene

2. Carbon

3. Bronze

4. Teflon

5. Babbitt material

6. Cast iron

234. What are various methods of capacity control?

1. speed regulation

2. suction throttling

3. holding inlet valve open

4. clearance volume variation

235. What is clearance pocket?

Clearance pocket made up of a cylinder with a piston to regulate the capacity in high-power compressor by varying the clearance volume. It can be operated manually or by automatic means and divided into two types of

1. constant clearance pocket

2. Variable clearance pocket.

When this pocket in operation the compressor neither draws in nor delivers any gas: both valves are closed and a constant amount of gas is expanded and compressed in the cylinder.

236. What is suction unloader?

It is a pneumatically operated piston-type device overcomes the tension of a spring and moves down the rod of the piston like element terminates in fork, the prongs of which will keep the inlet valve plate off the seat. As a result no gas will be compressed and delivered because the inlet valve will be open, and the will be pushed out of the cylinder into the intake line until the air pressure relived in the piston of unloader. Thus the compressor capacity is reduced by skipping the discharge strokes.

239. How do you recondition the valves of a reciprocating compressor?

The main work of reconditioning the valve is to make the seating area of plates in perfect appropriate level by lapping. Out of this well vision able inspection of valve plate, seat plate, lock screw and the condition of springs should be adapted.

240. How do you leak check a valves of a reciprocating compressor?

1. liquid filled observe for 1.5 minutes and slots of seat must still be half full

2. Leak check by connecting to metered air supply system.

241. Second stage discharge pressure is high? What is the problem? How will you identify?

Causes

1. inter cooler between second and third stage or after cooler has not effective cooling – feeling cooling water circulation

2. unloader not working – check the unloader spindle position any marked

3. second stage discharge valve not opened properly – feel temperature of valve

4. improper piston end clearance

5. third stage suction valve not opened – checking with stethoscope

242. There is a capacity reduction in the compressor? What is the problem?

1. suction valve damage/passing

2. discharge valve damage/passing

3. clearance pocket may be in open condition

4. unloader loaded

5. damage piston rings or packing rings

6. excessive piston end clearance

7. speed less

243. There is a reduction in the discharge pressure of the compressor? What is the problem?

1. Suction valve damage/passing

2. Discharge valve damage/passing

3. Clearance pocket may be in open condition

4. Unloader loaded

5. Damage piston rings or packing rings

6. Excessive piston end clearance

7. Speed less

244. What is the normal pressure ratio of discharge to suction?

14: 1

245. Why intercoolers are used?

a. Remove heat of gas taken by compression

b. Reduce the volume of gas consistence to other stage

c. Save in power

d. Increase efficiency

246. What is distance piece?

This piece with inspection doors fixed in between compressor cylinder and the cross slide house. It accomplishes space for gas packings gland and wiper rings through inspection door. Drain line attached bottoms of it for identification incase of gas or oil leakage if any.

This can be aligned with cylinder or crankcase with measurement of rod deflection.

247. What is oil wiper packing?

Wiper packings fixed on the piston rod in the side of cross slide to avoid the leakage of oil outside and avoid the entry of gas into crosshead area incase of gas packing rings leakage. These packings are same like gas packing seal rings.

249. What is cylinder jacket?

The jacket made with cylinder integrally or passage sealed with cylinder liner ‘o’ rings for removing heat from gas by compression and friction heat of piston rings.

250. What is stuffing box jacket?

Cooling water circulated jacket provided in gas packing stuffing box for removing heat generated through the friction of packing rings with piston rod.

251. How the cooling water is prevented from entering the gas side?

With the use of ‘o’ rings on cups of stuffing box.

252. What is volumetric efficiency?

It is the ratio of the actual capacity of the compressor to displacement (swept volume) and is expressed as a percentage.

253. What is need for cylinder liner? What is its MOC?

Cylinder liner is used to avoid the change of cylinder or major recondition incase of high scuffing due to friction with damage or broken piston rings.

Liners are normally made of cast iron.

255. What is cylinder liner lubrication?

A force feed lubrication given to cylinder liner to minimize the friction with piston rings is called cylinder liner lubrication.

More lubrication causes the discharge valve plates to stick.

256. How do you lubricate the cylinder liner?

Force-feed lubrication by lubricator pumps given into the center of stroke length in the cylinder port provided.

257. what is single acting, double acting and balanced opposed?

Single acting:

Compression of gas takes place in one side of the piston only.

Double acting:

Compression of gas takes place on both sides of the piston.

Balanced opposed:

Two set of piston and cylinder arrangement made in the single crank shaft horizontally 180 degree oppose for dynamic balancing and admit of rotative speeds higher than other types.

Instrumentation Overview

2010-05-21T05:00:00.001-07:00

Instrumentation Overview

What is Instrumentation?

Instrumentation is art and science of measurement and control.
It makes available the necessary process information [indication / trending / status] at a predetermined destination in a predetermined form.
It also controls the parameter within a specified limit / at specified value.
Instrumentation provides a means to the plant operator to operate the plant safely, continuously, and consistently with optimum productivity.
It minimizes the human element in the plant operation
Instrumentation provides handle for monitoring:
Health of the process,
Health and performance of Equipments
Draws attention to the exceptional conditions

In fact instrumentation acts as eyes and ears for engineers of all the disciplines in general and chemical engineers in particular.

Parameters Measured

The parameters encountered in a process industry are:

· Pressure

· Level

· Flow

· Temperature

· Quality of intermediate and finished products

o Physical

o Chemical

· Speed/vibration/displacements for rotary machines

Every possible law of physics and chemistry has been exploited to achieve accurate measurement of the above parameters
All the field instruments/devices adhere to Ingress Protection (IPnn) & Area Classification norms

Evolution of Instrument Engg Field

Instrumentation and Automation” was recognized as a separate branch of engineering in between the two world wars as the concept of mass production came into vogue due to war efforts.

Changing Technologies

1. Indication local

2. Indication remote

- Pneumatic

- Analog electronics

- Digital electronics

- Microprocessors (Configurable)

- DCS & PLC (Programmable)

3. Recording

- Paper-pen

- Thermal charts

- Trending

4. Exception reporting/Alarms

- Local

- Remote audiovisual – annuciators

- Alarm logs

5. Control

- Local instruments

- Local panels

- Plant wise control room

- Centralized control room for number of plants

Transmission media

- Pneumatic air pressure 0.2 to 1.0 kg/cm2 through tubes

- Electrical 4 to 20 ma through copper conductor

- Digital signals through twisted / shielded pairs

- Light signals through Fiber optic cables

- Air waves – wireless

Connectivity

- One to one

- Multiplexing

- Multidrop – bus topology

- Networks

Logics

- Switches

- Relay

- PLC

- ESD

· Hardware Base

· Configuration Base

· Software Base

CPUs have shifted approach from individual instruments to systems.

Networking capabilities have shifted approach towards large integrated systems.

System Components

- Power supply ®

- Central Processing Unit ®

- Memory

- Input Modules

- Output Modules

- Communication Modules ®

- Bus/network ®

- Programming terminal

- Human Machine Interface

System Features

Redundancy

Fall back – primary/main – secondary/standby

Sharing – 50/50 – 100/0

Cold standby: If primary system fails, the changeover to secondary is manual. Interruption in operation. Moderate cost. Almost obsolete.

Hot standby: Both primary and secondary are running continuously & processing I/Os in parallel. Only the primary has control on outputs. If primary fails, secondary immediately takes charge bump-lessly. Widely used. Moderate cost.

Ø Easy troubleshooting

Ø Easy expandability

Ø High availability – redundancy

Ø High reliability – fail safe design

Ø Self-diagnostic capability

Ø Alarm handling & Sequence Of Events (SOE)

Ø System security from unauthorised changes.

Ø Hierarchical Presentation like Complex, Plant, Unit, Tag.

Ø Historisation & data logging for ease of maintenance.

Each system has the capability to communicate with another system in general and DCS in particular

Objectives of Control Systems

- Operating personnel and Plant safety.

- Simplified and Efficient Plant operation.

- Automated stepwise start – loading – unloading – S/D

- High Plant availability.

- Easy and guided maintenance/diagnostics.

- User friendliness for Engineering, Operation and Monitoring functions.

- Fast and accurate analysis.

Instrumentation Systems

- DCS

- PLC

- ESD

- F&G

- MCMS

- ATG

- CTM

- BMS

- AMS – lab / online analyzers

- CCTV & Security Automation

Distributed Control System

The distribution can be

o Functional (most commonly used)

o Functional + Physical

Operator window for interface with plant
Integrated in to a single site wide system.
Single window to operations makes plant more manageable by reducing operator training by supporting information from all the other control systems.
Used for monitoring & control of regulatory level, advance control & Optimisation.
Self documenting features like loop diagrams.
Redundancy is provided in all control processors & communications.
Two to three operator console monitors are provided per operator.
Provides detail History of plant with Alarm summary, Trend displays, detail displays etc.

PLC System

PLCs are used for control & monitoring of packaged equipment like compressors, fired heaters, water treatment plants, back wash filters, etc.
Stand alone control system & also having considerable facilities for centralized configuration & data monitoring.
Systems are redundant in processors, power supplies & communications.
Each PLC system has serial interface with DCS for centralized data & status monitoring by control room operators.
Both CPUs run the application programmer. Primary CPU only controls the I/O & secondary CPU monitors the I/O.
Windows based HMI software packages can be used for standalone control of the PLC.

Emergency Shutdown System

Monitors & controls start-up & shutdown of entire plant.
These systems are fault tolerant, Triple Modular Redundant (TMR) with a high availability, self test & self diagnostic facilities. Three CPUs solve logic parallel and output is based on 2oo3 voting.
Sequence of events recording facility.
All ESD systems are connected to plant wide DCS.
Fail safe philosophy is adopted.
2oo3 logic is utilized in critical areas.
ESD devices are separate from process instruments & will be used only for the the purpose of shutdown.
Start ups are automated as far as possible.
Soft/Key lock bypass switches with status indication.
All bypasses are serially interfaced with DCS for monitoring.

Scan Time comparison for DCS, ESD & PLC

- DCS - 500 msecs

- PLC - 20 TO 50 msecs

- ESD - 1 msec

Hazards in Refinery

- Fire

- Leakage of Toxic Gases

- Leakage of Combustible Gases

- Rise in Temperature

Fire and Gas Monitoring System

- Detection of LEL, Toxic gas, Fire, Smoke, Heat.

- Also displays wind speed & Direction.

- Universal viewing at all strategic points like Fire stations, Security offices, Plant Control Rooms, Site in-charge’s offices etc.

F&G Indicators

- Stand alone indicator

- Addressable LCD display

- Dedicated F&G Work Station

- Integrated DCS F&G Work Station

F&G Devices

Machine Condition Monitoring System

The system is used for monitoring health and protection of the rotary machines.The following machine parameters is normally measured:

- the vibration levels of the casing and / or the shaft

- the shaft RPM

- axial shift of the shaft

- temperature of the thrust bearing pads / bearing housing

- Measure "Rider band” wear and tear (Rod drop measurement) in case of Reciprocating Compressor.

Following sensors are used in general to take vibration and temperature data of the rotary machines:

- Displacement probes

- Velomitors

- Accelerometers

- RTDs

ATG types of tanks

- Cone Roof Tank (With or W/O N2 purging)

- Open Floating Roof Tank

- Internal Floating Roof Tank. (With N2 Purging)

- Dome Roof Tank

- Sphere

- Horizontal ( Bullet )

ATG Objective

Raw parameter measurements in tank

- Level

- Temperature – multi spot / single spot

- Hydrostatic Pressure

- Static Pressure

- Water bottom

Calculated Tank Inventory

- Gross volume @ amb.

- Net Volume @ amb.

- Net standard volume @ 15 deg C.

- Mass

- Ullage

The above values are either calculated in TIS/DCS

Types of Tank gauging

- Servo

- Hydrostatic

- Radar

Custody Transfer Metering System

- Used For Custody transfer of raw materials & finished products

- N+1 meter run configuration for providing standby & master meter.

- Individual meter runs are corrected for pressure, temp. & density in the flow computers.

- Provers are provided for calibration of flow meters.

- Accuracy of the system should be 0.25% or better and repeatability should be 0.02% or better.

- Integrated with DCS.

- Used For Custody transfer of raw materials & finished products

- N+1 meter run configuration for providing standby & master meter.

- Individual meter runs are corrected for pressure, temp. & density in the flow computers.

- Provers are provided for calibration of flow meters.

- Accuracy of the system should be 0.25% or better and repeatability should be 0.02% or better.

- Integrated with DCS.

Burner Management System

BMS is required for controlling the Fired Heaters light up sequence and also to monitor the safe operation of the furnaces.
Relays/PLCs are used for the implementation of the BMS logic.
A local panel is provided near fuel skid for operator interface during heater start up operation.
For the detection of individual flames, ionization rods are provided for the pilot flame & IR scanners are provided for the main flame.
Automatic shut off valves in double block & bleed arrangement are provided for fuel lines in fuel skid.
Start up sequence can be typically divided in to leak test, purging, pilot firing & main fuel firing.
Hard wired interface with ESD system for shutdown.
Serial interface with DCS for monitoring by control room operator.

Heater trip logic is in general based on following philosophy:

Event Pilot Fuel Trip Main Fuel trip

Loss of pilot pressure/flame Y Y

Loss of fuel pressure/flame N Y

Rise in furnace pressure N Y

Analyzer Management System

Various types of Analysers include:

Steam & water quality analyzer – pH, Conductivity, silica, oil in water
Gas Analyzers – CO, O2, H2S, SOX/NOX, SO2, H2
Physical property analyzers - Flash point, Pour Point, Distillation, Moisture, density, Smoke/Opacity, Viscosity
Gas Cinematography – It can analyze multiple components based on retention & evolution in/from an adsorption media.

Sampling: It is the extraction of the process fluid and its delivery to the analyzer.

Sample conditioning: It consists of assembly of components which remove moisture, particulate and regulates sample pressure, temperature & flow at acceptable limits to the analyzer

Sampling Delay: It is the time taken by the sample in reaching the analyzer from the process.

Fast Loop: Part of the sample is recycled to the process to avoid dead volume in the sampling system.

Cycle Time: It is the total analysis time taken by the analyzer for analyzing desired components in the

Process stream.

Analyzer Houses are located at strategic locations to collect various samples required for analysis & reduce the length of sample lines.
All analyzers are connected to analyzer management system for collection of data.
The system

o monitors the healthiness of sampling system

o monitors the healthiness of analyser electronics

o trends the parameters

CCTV & Security Automation

CCTV system

Is used for monitoring of flare stacks, General surveillance (loading /unloading, major equipment's monitoring), fire prone areas etc.
Time lapse video recording is provided for reviewing history.

Security system

- Used for access control

- Automatic movement of gates

Controllers

One of the basic functions executed by instrumentation system in process industry is ‘controlling the process parameter’. There may be two types of controls:

- Open Control Loop

- Close Control Loop (Automatic Feedback Control)

PID/Regulatory Control

- Proportional Action

o Output = K1 * e

- Proportional + Integral Action

o Output = K1 * e + K2òedt

- Proportional + Integral + Derivative Action

o Output = K1 * e + K2òedt + K3 de/dt

Where

e = error (difference between set point and measured variable)

K1 = Gain

K2, K3 = constants

Instrumentation Controls

- Application specific

o Compressors – Anti-surge, performance, speed control

o Furnace/Boiler – Lead-Lag control

o Boiler – 3-Term Control

- On-off / PID controls

- Complex loops / traditional advanced control

o Ratio, feed forward, cascade, adaptive

Introduction to Vibration

2010-05-21T00:39:00.000-07:00

What is Vibration?

Mechanical vibration is the dynamic motion of machine components.

Vibration measurement is the measurement of this mechanical vibration relative to a known reference.

How does Vibration Start?

Energy must be put into the system through an applied force, either internal or external.

The force may be instantaneous, an impulse, or continuous. In machines this energy is diverted from the process. This reduces the machine’s efficiency and may also result in damage to the machine’s components.

What Characteristics are measured?

Amplitude
Frequency
Phase Angle

Absolute Phase Angle
Relative Phase Angle

What Affects These Characteristics?

Mass
Spring Stiffness
Damping

AMPLITUDE

Peak-to-peak refers to the total amount of vibration.

Zero-to-peak refers to the total amount of vibration from the maximum height of either the positive or negative peak to the zero voltage axes.

Root mean square (RMS) is a function of the signal conditioning performed in the monitor or diagnostic instrument and not the output of the transducer.

Frequency

Frequency is defined as the repetition rate of a periodic vibration within a unit of time.
The frequency of vibration (cycles per minute) is most often expressed in multiples of rotative speed of the machine.
Basic frequency measurements can be performed with an oscilloscope and Keyphasor signal.

Phase

PHASE ANGLE

The phase angle is defined as the number of degrees from the Keyphasor pulse to the first positive peak of vibration.

Form

Vibration form is the raw waveform displayed on an oscilloscope and can be separated into two categories:

Time base presentation
Orbit presentation

VIBRATION FORM

ORBIT- is the output of two transducers at 90° angles to one another (XY plane) in the X-Y mode of the oscilloscope. The orbit is the representation of the shaft centerline movement.

Measurement References

The three basic frames of reference for vibration measurements on rotating machines are:

Rotor motion relative to the bearing (Shaft relative Vibration).

Casing motion relative to a fixed reference (Casing Absolute Vibration).

Rotor motion relative to a fixed reference (Shaft Absolute Vibration).

Position Measurements

Axial Position

Thrust Position
Rotor Position

Radial Position

Differential Expansion

Case Expansion

Eccentricity

AXIAL POSITION

Thrust Position

Measurement of the position of the thrust collar in the thrust bearing assembly and how much bearing material may be used up.
The probes are mounted on the thrust bearing observing the movement of the rotor position within the thrust bearing.

Thrust Position Normal/Counter

Normal - direction the rotor would normally be forced to move due to the designed operation of the machine.

Steam turbine typically Away from high pressure (HP) inlet towards the LP inlet.

Counter - direction of thrust opposite the direction the rotor is normally designed to move.

Indicates the machine is experiencing an abnormal operation

RADIAL POSITION

Proximity Probes are used in the X-Y configuration to measure radial vibration, the dc signal from

the transducer can be used to indicate the radial position of the rotor within the bearing

DIFFERENTIAL EXPANSION

CASE EXPANSION

ECCENTRICITY

Smoke Detectors

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Smoke Detectors
Smoke detectors/alarms are important safety devices, because of their obvious potential to save lives and property. There are two types of smoke detector commonly available in many countries.

There are two types of smoke alarm:

· Ionization Type

· Optical Type

Ionization Type

Referring to the adjacent diagram Electrode A is treated with a Very level of Radiation material and a potential is applied between Electrodes A and B. On account of Radiation the air between the Electrodes A and B is ionized and ionization current flows between the Electrodes. In the presence of smoke between the electrodes the ionization current varies (due to the smoke particles) and thus the smoke is sensed. The Output from the electrodes is fed to an Electronics amplifier and a schmmit Trigger which will give an ON / OFF output for the Presence / Absence of smoke.

The smoke Detector is tested periodically (once in 6 months or as the case may be depending on the policy of the organization) by an Aerosol spray from a smoke canister. (NOT BY CREATING A SMOKE)

The Optical Type

The Optical type is based on the principle that when smoke passes through a source of Light (LED) and a photodiode / photocell the current through the Photocell / Photodiode varies. The arrangement is a source of light (says LED) is mounted in front of a Photodiode or a Photocell or may be a photo-resistor, under “No Smoke” condition the light falls on the photocell and a quiescent current flows in the circuit. When smoke passes through (between) the Light and the photocell the current in the circuit varies sensing the smoke. The signal is further processed (amplified and fed to a schimmt trigger) and a switch action is generated for the presence or absence of smoke.

The smoke Detector is tested periodically (once in 6 months or as the case may be depending on the policy of the organization) by an Aerosol spray from a smoke canister.

(NOT BY CREATING A SMOKE)

Usually one smoke detector will be located for each 3 Square meters of area. There is a NFPA (National Fire Protection Agency / Association, USA) regulation for the number of detectors for a given area.

Normally a number of smoke detectors will be associated with one zone. Due to atmospheric humidity many times smoke detectors may give rise to false alarms. As a result whenever there is a trip connected with smoke detectors it will never be based on one smoke detector sensing the smoke. Normally a given area will be divided into two zones and when one smoke detector from each zone in the same area simultaneously sense smoke then only the control action will be initiated. Consequently while testing the smoke detectors ensure that the smoke detector under test is (alarm acknowledged) reset before testing another smoke detector in the same area (look at the cause & Effect Sheet).

Each F & G system has a “Zone Module” to which the field devices are connected. Each Zone module gives an output depending on the alarm generated by the field devices. Each zone module has the following indications:

1. Power On Indication

2. smoke / Fire Alarm indication

3. Card / Device Inhibit indication

Each zone module has the following controls:

1. Alarm Accept / Acknowledge

2. Alarm Reset

3. Output Action Inhibit

Normally there will be a facilities module in the Panel (may be in each row) to which all the

Alarms and control actions are wired in the row.

HSSD / VESDA

High Sensitivity Smoke Detection system / Very Early Smoke Detection Apparatus works similar to Optical smoke detector except that a high sensitive detection system (LASER) is used for detection. Further an Aspirator / pump is installed in the detection system that sucks the air sample and the same is passed through the detection system. This arrangement combined with the high sensitive detection system gives a high sensitive detection / Very Early Detection of smoke.

The principle difference between a normal smoke detector and High Sensitivity Smoke Detection system / Very Early Smoke Detection Apparatus is that in the latter the smoke is detected very early even when the smoke is in incipient stage (beginning to from) so that corrective action can be taken at a very early stage of smoke.

There is no fire without smoke. So the objective is to tackle the situation before it can get out control! The smoke is detected very early before it is too late.

There is a special test for testing the Very Early Smoke Detection Apparatus. A wire provided by the manufacturer is connected to a transformer (provided by the manufacturer) and the transformer is powered. The wire is located where the air will be sucked by the pump, this will be sensed by the VESDA and alarm is generated in the device.

Cantrol Valves

2010-05-07T09:30:00.000-07:00

CONTROL VALVE

INTRODUCTION:

A control valve is a device capable of modulating flow at varying degrees between minimal flow and full capacity in response to a signal from an external control device. The control valve often referred to as “the final control element,” is a critical part of any control loop, as it performs the physical work and is the element that directly affects the process.

A control valve is comprised of an actuator mounted to a valve. The valve modulates flow through movement of a valve plug in relation to the port(s) located within the valve body. The valve plug is attached to a valve stem, which, in turn, is connected to the actuator. The actuator can be pneumatically, electrically or hydraulically operated.

Control valve parts:

Body - That part of an automatic control valve in which the flowing medium is contained. The body provides the pipe connecting ends, the fluid flow passageway and may support the seating surfaces.

Actuator - That part of an automatic control valve, which causes the valve stem to move

Bonnet: those portions of the valve pressure-retaining boundary, which may guide the stem and contains the packing box and stem seal. It may also provide the principal opening to the body cavity for assembly of internal part of the valve body. It may also provide for the attachment of the actuator to the valve body. The bonnet can be bolted, threaded or welded to or integral with the body. Types of bonnets are Bolted, flange bonnet, Extension bonnet, Finned bonnet and bellows

Bonnet Gasket: A deformable sealing element between the mating surfaces of the body and bonnet.

Yoke: A structure by which the diaphragm case assembly is supported rigidly on the bonnet assembly

Packing: A sealing system consisting of deformable material of one or more mating and deformable elements in a packing box which may have an adjustable compression means to obtain or maintain an effective pressure seal. Common materials used are Teflon; Teflon impregnated asbestos and Graphite asbestos

Packing Box: The chamber in the bonnet, surrounding the stem and containing packing and other stem sealing parts.

Packing follower: A part, which transfers mechanical load to the packing from the packing flange or nut

Lantern ring: A rigid spacer assembled in the packing box with packing normally above and below it and designed to allow lubrication of the packing or access to a leak-off connection.

Plug: The moveable part of the valve that makes contact with the valve seat when the valve is closed, and which varies the area controlling the flow. The three most common types of control valve plugs are contoured, V-port, and quick opening. A contoured plug controls flow by a shaped end and is usually end-guided at the top or bottom (or both) of the valve body. A V-port plug has a cylinder (called a skirt), which rides up and down in the scat ring. The skirt guides the plug, and by virtue of shaped openings in the skirt, varies the flow area. Quick-opening plugs are machined to provide maximum flow quickly when the plug lifts from its seat. These plugs can be either end-guided or guided by wings riding in the seat ring.

Seat Ring: A part that is assembled in the valve body and may provide part of the flow control. The seat ring may have special material properties and may provide the contact surface for the closure member.

Cage: A part in a globe valve surrounding the closure member to provide alignment and facilitate assembly of other parts of the valve trims. The cage may also provide flow characterization and or a seating surface for globe valves and flow characterization for some plug valves.

Guide: That part of the valve plug that keeps the plug aligned with the valve seat. Top or bottom guides on a valve plug are usually located so they do not influence flow but merely accomplish the centering function. Valve guides often have the added function of determining the valve flow characteristic. These are known as skirt guides and usually have notches or Vs cut into them to characterize flow.

Port: This term refers to the flow-controlling opening between the seat and the disc when the valve is wide open. It does not refer to body size or end connection size. Standard valve ports are the sizes normally used in the valves. Valves with reduced ports have flow equal to a smaller valve with a standard port.

Trim: Trim consists of all parts of a valve that are in contact with the flowing medium but are not part of the valve shell or casting. Thus, plugs, seats, discs, stems, packing rings, etc. are all trim components. The term "trim" is usually used in connection with trim materials.

Important control valve terminology

Capacity: The rate of flow through a valve under stated test conditions
Flow coefficient: It is a constant related to the geometry of a valve. The quantity of water in gal/min at 60 F (16 C) that flows through a given wide-open valve with a pressure drop of 1 lb/in2. The symbol for capacity index or flow coefficient is Cv. Once the Cv of the valve has been determined, the flow of any fluid through the same valve can be calculated provided the characteristics of the fluid and the pressure drop through the valve are known.
Flow characteristic: The relationship between the flow rate through a valve and travel of the closure member as the closure member is moved from the closed position to rated travel with a constant pressure drop across the valve, is called the inherent flow characteristic. The same relationship, when the pressure drop across the valve varies as influenced by the system is called installed characteristic. The important flow characteristics are:

Equal percentage: An equal increment of stem travel produces equal percentage in existing flow. The change is always proportional to the quantity flowing before the change. They are mostly used a pressure application. A combination of linear and equal percentage is known as modified parabolic characteristic and a combination of linear and quick opening termed as modified linear are other two types of characteristic available.

Quick-Opening Characteristic: This characteristic provides larger flow variation at low stem travel while maintaining a linear relationship through most of the stem travel. In figure 90 percent flow rate obtained at 30% valve opening and a straight-line relationship to that point. They are used primarily in on-off service.

Linear Characteristic: A valve, which produces flow directly proportional to the valve lift. These are specified for level control and application, which requires constant gain.

Inherent Flow Characteristics For Common Valve Trim Designs

Leakage: The quantity of fluid passing through a valve when the valve is in fully closed position under stated closure forces, with the pressure differential and temperature as specified. Leakage is usually specified as a percentage of the valve capacity at full rated travel.
Travel Coefficient: The ratio between the flow at a given valve stem position and the flow through the valve at its wide-open position, usually expressed as a decimal fraction.

Rangeability: The ratio of the maximum controllable flow to the minimum controllable flow. For instance, a valve with a rangeability of 50 to 1 and having a total flow capacity of 100 gal/min, fully open, will control flow accurately down as low as 2 gal/min. The valve may or may not have tight shutoff. However, for this particular valve you could not depend upon getting steady flow of, for instance, 1.5 gal/min if this were necessary to maintain stable load conditions. Generally, rangeabilities in the range of 50 to 1 or 40 to 1 are considered excellent for extreme precision of control. Valves with high rangeability are very expensive to manufacture since very close tolerances are involved between the disc and the seat. Competitively priced control valves ordinarily have rangeability of less than 30 to 1. In many cases wide rangeability compensates automatically for deviations from anticipated conditions without loss of control.

Turndown: The ratio between maximum usable flow and the minimum controllable flow; usually less than the rangeability. For instance, as stated above, after the 100-gal/min valve has been applied at a job, it might turn out that the most flow you would ever need through the valve is 68 gal/min. Since the minimum controllable flow is 2 gal/min, the turndown for this valve is 34 to 1. In comparing rangeability and turndown, we may say that rangeability is a measure of the predicted stability of the control valve, and turndown is a measure of the actual stability of the valve

Shut –Off: The shut -off rating of a valve is the maximum allowable pressure drop to which the valve may be subjected while fully closed. This rating is usually a function of the power available from the valve actuator for holding the valve closed against pressure drop, but structural parts such as the stem sometimes are the limiting factor. The shut -off rating is independent of the actual valve body rating.

Direct / Reverse acting valve: A control valve that travels to the closed position when the signal to the actuator increases is called direct acting and the valve that travels to the open position when the signal increases is called reverse acting.

Seat Leakage

Control valves are designed to throttle. However, this is not a perfect world, and control valves are also usually expected to provide some type of shut-off capability. A control valve's ability to shut off has to do with many factors. The type of valves for instance. A double-seated control valve will usually have very poor shut-off capability. The guiding, seat material, actuator thrust, pressure drop, and the type of fluid can all play a part in how well a particular control valve shuts off

There are actually six different seat leakage classifications as defined by ANSI/FCI 70-2-1976. But for the most part you will be concerned with just two of them: CLASS IV and CLASS VI. CLASS IV is also known as METAL TO METAL. It is the kind of leakage rate you can expect from a valve with a metal plug and metal seat. CLASS VI is known as a SOFT SEAT classification. SOFT SEAT VALVES are those where either the plug or seat or both are made from some kind of composition material such as Teflon

Valve Leakage Classifications:

Class I. Identical to Class II, III, and IV in construction and design intent, but no actual shop test is made.

Class II. Intended for double-port or balanced singe-port valves with a metal piston ring seal and metal-to-metal seats. Air or water at 45 to 60 psig is the test fluid. Allowable leakage is 0.5% of the rated full open capacity.

Class III. Intended for the same types of valves as in Class II. Allowable leakage is limited to 0.1% of rated valve capacity.

Class IV. Intended for single-port and balanced single-port valves with extra-tight piston seals and metal-to-metal seats. Leakage rate is limited to 0.01% of rated valve capacity.

Class V. Intended for the same types of valves as Class IV. The test fluid is water at 100 psig or operating pressure. Leakage allowed is limited to 5 X 10 ml per minute per inch of orifice diameter per psi differential.

Class VI. Intended for resilient-seating valves. The test fluid is air or nitrogen. Pressure is the lesser of 50 psig or operating pressure. The leakage limit depends on valve size and ranges from 0.15 to 6.75 ml per minute for valve sizes 1 through 8 inches.

Nominal Port Diameter                   Allowable Leakage
       (Inches)    (ml Per Minute) (*Bubbles Per Minute)
            1    0.15                        1
            1.5                               0.30    2
            2                                  0.45                        3
            2.5                               0.60    4
            3                                  0.90    6
            4                                  1.70                       11
            6                                  4.00     27
            8                                  6.75                       45
           10                                 9.00                       63
           12                                 11.5                       81

Bubbles per minute as tabulated are a suggested alternative based on a suitable calibrated measuring device, in this case a 0.25-inch O.D. X 0.032-inch wall tube submerged in water to a depth of from 1/8 to 1/4 inch. The tube end shall be cut square and smooth with no chamfers or burrs. The tube axis shall be perpendicular to the surface of the water. Other measuring devices may be constructed and the number of bubbles per minute may differ from those shown as long as they correctly indicate the flow in milliliters per minute.

Type of valves

There are basic two types of control valves as per the motion of the closure member. They are rotary and linear. Linear-motion control valves commonly have globe, gate, diaphragm or pinch type closures. Rotary-motion valves have ball, butterfly or plug closures. Each type of valve has its special generic features, which may, in a given application, be either an advantage or a disadvantage.

a) Linear Valve Features

• TORTUOUS FLOW PATH
• LOW RECOVERY
• CAN THROTTLE SMALL FLOW RATES
• OFFERS VARIETY OF SPECIAL TRIM DESIGNS
• SUITED TO HIGH-PRESSURE APPLICATIONS
• USUALLY FLANGED OR THREADED
• SEPARABLE BONNET

b) Rotary Valve Features

• STREAMLINED FLOW PATH
• HIGH RECOVERY
• MORE CAPACITY
• LESS PACKING WEAR
• CAN HANDLE SLURRY AND ABRASIVES
• FLANGELESS
• INTEGRAL BONNET
• HIGH RANGEABILITY

Control Valve Classification

a) Single ported Globe Valve

• Simple in construction
• Used in sizes 2” and below
• Can get tight shut off

The balancing in this valve is achieved by porting through the body or plug so that the same pressure acts on both sides of the valve plug.

b) Double ported valves

High flow capacities
Smaller stem force required when compared to single seated valve
Should not be used where tight shut off is needed.

C) Three-way valves
It is used to mix or divert flowing steam. In blending (mixing) service there are two inlets and one outlet in diverting service two outlets and one inlet in mixing, it is modified double port body.

d) Angle Valves

 Used where space is at a premium.
 In services where the pressure drop is high.
 Where the effect or turbulence, contention percent problems.

e) Butterfly valve

• It has a shaft supported vane or disc rotating with in a cylindrical body.
• Used in high-pressure drop, high static pressure and tight off services.
• Economical in larger size ranges due to their simple design.

f) Diaphragm valves (Saunder’s valve)-

• Well suited for slurries and viscous Fluid.
• Very high capacity.
• Low cost.
• Very poor control characteristic and Low turn down ratio.

Actuators

Actuators must overcome the unbalance force caused by the pressure drop across the valve, friction in between and weight of the moving parts and stem unbalance. There are pneumatic, hydraulic or manual actuators available. Most of the control valves are pneumatically actuated. There are two types of pneumatic actuators: (a) Spring /diaphragm types and (b) piston type.

In spring type depending on whether air to open or air to close vent is required, direct acting or reverse acting actuator can be used.

The main advantage of a piston actuator is its capacity for longer travels and large possible effective areas. It also generally tolerates higher actuating pressure. As with the diaphragm style, the piston can be spring opposed, air to extend or air to retract. Piston actuators can also be used in double acting mode with pressure on either side of the piston by using a double acting positioner.

Accessories

Manual override or Hand wheel, Limit switches, Position transmitter, solenoid valves, air regulator, volume booster, positioner.

The I to P converter receives current signal (4-20 mA signal) from the controller (control room) and convert it to a proportional pneumatic signal (3-15 psi) and feeds the positioner. A control valve positioner is basically a relay that senses both instrument signal and control valve position. The primary function is to have the valve stem position proportional to the input signal.

Advantages:

• To minimize friction in the movement of the stem.
• To overcome hystresis
• As pressure boosters in a split range valves
• A control valve signal can be reversed using a positioner.

Site specific information:

In the refinery a large number of control valves are used as the final control element for flow, level, pressure and temperature. They belong to different type, size and manufacturer.

Instrumentation Ltd, MIL / Dresser Masonielan & Fisher are the common manufacturers. For certain applications few valves of the following make is also available like Motoyama, Kitamura, Neles Jamesburry, Copus Vulcan, Blakeborough, Fouress, Gulde, Continental, Mazda, Dempla, RK engineering, Dezurick, Valtek, Virgo, Brooks, Microfinish, Sereg Schlumberger etc.

Generally air to close valves are painted green and air to open valve are painted red.

Critical valves are generally serviced during shutdown using in house expertise or outside agencies. Routine problems encountered are listed below:

• Problems associated with the fault of electrical signal from control room, air pressure, faulty I to P, faulty air regulators and positioner.
• Gland leak and bonnet leak can generally be attended on line but in certain cases may require opening of the valve.
• Body leak can be attended by welding or body replacement.
• Valve put on high temperature services after servicing may develop bonnet leak and may require hot bolting.
• Calibration of valve may also be required to be done in certain cases.
• Actuator casing damage due to corrosion, spring and diaphragm damage,
• Bending of stem
• Damage of internals like plug & seat due to erosion. Corrosion and cavitation.
• Damage of diaphragm in case of diaphragm valves (mainly in DM plant)

Whenever valves are attended for maintenance jobs on line, it has to be ensured that valve isolation and trapped quantity draining is done.

For shutdown valves positioner are not used since they do not have any intermediate position other than full open or full close. Solenoid valves are used to on / off air supply to the valves.

In the truck-loading gantry, Brooks digital valves are used where the fluid pressure itself is used to operate a spring opposed piston. The pressure on the piston is varied by operating a NO and NC solenoid each for varying times, which either admits fluid from valve upstream into the valve actuator or drains fluid from the actuator to valve downstream and thus controls the valve opening.

Temperature Measurement

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Temperature

The following types of instruments are used for temperature measurement.

Thermocouple
Resistance temperature detector
Non contact type
Temperature gages
Temperature calibrators

Thermocouple

Thermocouples are the most common type of temperature measuring instrument used in the refinery. Its principle is as follows:

Any two wires of different materials can be used as a thermocouple if connected together as in Figure 1. The AB connection is called the "junction". When the junction temperature, T_Jct, is different from the reference temperature, T_Ref, a low-level DC voltage, E, will be available at the +/- terminals. The value of E depends on the materials A and B, on the reference temperature, and on the junction temperature.

Different types of thermocouples are used. A comprehensive list of the different types of thermocouples is shown below. Since there can be a large distance between the sensor and the connected electronics (for cold junction compensation and further processing for displaying in engineering units), instead of the thermocouple cable, compensating cables are used.

Thermo well are used along with thermocouple as thermocouples are seldom placed in process stream line. The use of thermo wells make replacement of thermocouple easier without affecting the process. Generally flanged SS thermo wells are used but there are threaded ones also. Sheathed thermocouples are available as grounded and ungrounded. Grounded thermocouple provide faster response but they are not electrically isolated form the sheath. Since all the temperature loops are connected to DCS through isolating barriers, grounded thermocouple are mainly used in the refinery. The thermocouple is physically insulated from the sheath by MgO powder (soft).

In case of process where the velocity of the fluid is very high that may erode the well and so satellite coating may be done as in FCCU reactor- regenerator and orifice chamber.

In certain tank gauging systems MTT s are used to get the average temperature for the products. The use thermocouples for their function.

Currently temperature transmitters are being used rather then, connecting the thermocouple to the electronics at the control room through compensating cable. This eliminates the requirement of compensating cable. Since the transmitter output is standard 4- 20mA, no special cards in the control room is required and it can be treated just like any other transmitter signal. Moreover, these temperature transmitters can be used for any type of temperature sensors like thermocouple & RTD.

Resistance temperature detector:

A basic physical property of a metal is that its electrical resistivity changes with temperature. All RTD's are based on this principle. The heart of the RTD is the resistance element.

Some metals have a very predictable change of resistance for a given change of temperature; these are the metals that are most commonly chosen for fabricating an RTD. A precision resistor is made from one of these metals to a nominal ohmic value at a specified temperature. By measuring its resistance at some unknown temperature and comparing this value to the resistor's nominal value, the change in resistance is determined. Because the temperature vs. resistance characteristics are also known, the change in temperature from the point initially specified can be calculated. We now have a practical temperature sensor, which in its bare form (the resistor) is commonly referred to as a resistance element.

Through years of experience, the characteristics of various metals and their alloys have been learned, and their temperature vs. resistance relationships is available in look-up tables. For some types of RTD's, there are also equations that give you the temperature from a given resistance. This information has made it possible for instrument manufacturers to provide standard readout and control devices that are compatible with some of the more widely accepted types of RTD's.

Most RTD elements consist of a length of fine coiled wire wrapped around a ceramic or glass core. The element is usually quite fragile, so it is often placed inside a sheathed probe to protect it.

Common Resistance Materials for RTDs:

· Platinum (most popular and accurate)

· Nickel

· Copper

· Balco (rare)

· Tungsten (rare)

The RTD is a more linear device than the thermocouple, but it still requires curve fitting. The Callendar-Van Dusen equation has been used for years to approximate the RTD curve: ⁹

Where:

R_T = Resistance at Temperature T

R₀ = Resistance at T = O⁰C

a = Temperature Coefficient at T = O⁰C

(Typically +0.00392W/W/⁰C)

d = 1.49(typically value for .00392 platinum)

b = 0 T>0

0.11(typical) T<0

The exact values of coefficients a, b, and d are determined by testing the RTD at four temperatures and solving the resultant equations. This familiar equation was replaced in 1968 by a 20^th order polynomial in order to provide a more accurate curve fit.

The plot of this equation shows the RTD to be a more linear device than the thermocouple.

An RTD is inherently a 2-wire device, but lead wire resistance can drastically reduce the accuracy of the measurement by adding additional, uncompensated resistance into the system. Most applications therefore add a third wire to help the circuit compensate for lead wire resistance, and thus provide a truer indication of the measured temperature.

Four-wire RTD's provide slightly better compensation, but are generally found only in laboratory equipment and other areas where high accuracy is required. When used in conjunction with a 3-wire instrument, a 4-wire RTD will not provide any better accuracy. If the fourth wire is not connected, the device is only as good as the 3-wire RTD, if the fourth wire is connected, new errors will be introduced. Connecting a 3-wire RTD to a 4-wire instrument can cause serious errors or simply not work at all, depending on the instrument circuitry. A 2-wire RTD can be used with either a 3 or a 4 -wire instrument by jumping the appropriate terminals, although this defeats the purpose and reintroduces the uncompensated resistance of the leads.

When wires A &B are perfectly matched in length, their impedance effect will cancel because each is an opposite length of the bridge. The third wire C acts as a sense lead and carries no current.

Generally in the refinery RTD’s are used in temperature probes for the conditioning monitoring of compressors. They are also used in certain process applications also where the temperature encountered is comparatively low as in the case of truck loading and PIBU unit. In certain tank gauging systems MRT s are used to get the average temperature for the products. The use RTDs for their function

Non-contact type:

The Pulsar 11 model 7000SR from E2 Technology Corporation is used in SRU unit for reactor temperature measurement. The basic principle is described below. Similar type of principle is used for DHDS flare monitoring also.

All objects above absolute zero emit infrared energy. The amount of energy emitted is proportional to the body temperature. The PULSAR II collects this energy by means of a focusing optical system concentrating the energy from a body onto a sensitive infrared detector. Specialized amplification circuitry converts the signal generated by the detector into linear output signals corresponding to 1mV/^O and 4 -20mA.

The efficiency of energy emission from different objects varies significantly. A perfect energy emitter is known as a blackbody radiator and is assigned an emissivity value of one. Any object that emits with less than perfect efficiency is assigned an emissivity value between zero and one, and a perfect reflector is assigned an emissivity value of zero.

The PULSAR II calibrated against nearly perfect blackbody radiators in the laboratory. However, the emissivity of objects and processes which you are measuring with typically fall somewhere between zero and one. This results in the need for an adjustment of the PULSAR II’s emissivity setting to obtain a match against a known reference temperature. Once the emissivity setting has been adjusted for a particular installation, the PULSAR II will accurately track temperatures as they rise and fall.

Temperature gauges:

Temperature gauges are of different types namely Mercury in steel, Gas filled and Bimetallic type. All these type of gages are available in different ranges, dial size, stem length and connections

Mercury-In-Steel Thermometers deploy Mercury as an expansion liquid filled into a closed system comprising of a bulb (of Steel or Chrome – Moly Steel), a microbore capillary (of Steel or Stainless Steel) and a spiral or ‘C’ shaped Bourdon Tube (of MS or SS). This system when heated at bulb end the mercury in the bulb expands and a pressure is generated within which moves the spiral / ‘C’ Shaped bourden as it is the only the elastic element. This movement is transmitted to a rack and pinion movement, which drives a pointer thus showing temperature on a calibrated dial. Rigid stem (horizontal, vertical and any angle) and capillary type are available. They have an inherent time delay in transmission.

Gas Filled Thermometers deploy Nitrogen Gas at high pressure as an expansion gas filled into a closed system comprising of a bulb (of Steel or Chrome – Moly Steel), a microbore capillary (of Steel or Stainless Steel) and a spiral or ‘C’ shaped Bourdon Tube (of MS or SS). This system when heated at bulb end the Gas in the bulb expands and a pressure is generated within which moves the spiral / ‘C’ Shaped bourden as it is the only the elastic element. This movement is transmitted to a rack and pinion movement, which drives a pointer thus showing temperature on a calibrated dial.

Bimetal thermometers are the most common type used in refinery. Strips of two different metals, one with high coefficient of expansion and the other with lower coefficient of expansion are welded together by a special process to form bimetallic strip. Such strips are coiled to form a helix, which is fastened at one end, and the other end is free. Such coils when heated tend to decoil resulting into a rotational movement of the free end. This free end is attached to a shaft connected a pointer which rotates pointer on a calibrated dial indicating the temperature. They are not available in capillary tube. The most commonly used material is an invar-nickel-crome alloy.

Temperature Calibrators:

For actual temperature simulation and checking, temperature bath can be used. They can be set at the desired temperature, and the reading of the instrument to be calibrated can be compared to the bath reading. One of the temperature bath available is of the dry type, which can be used directly without pouring any oil into the well.

For field checking of thermocouples, portable temperature calibrators can be used which when connected to the thermocouple senses the mill volt generated and display in terms of the temperature. The type of the thermocouple has to be selected in the calibrator. RTD calibrators are also there which can be used to measure the temperature form an RTD source wherein they provide the bridge circuit and other necessary electronics for RTD measurement. Many of these calibrators have the facility to simulate Thermocouple and RTD sensors so that the complete field wire and connected electronics (DCS or other devices) excluding the sensor can be checked.

Pressure Measurement

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PRESSURE

The entire pressure measurement instruments in the refinery can be very broadly classified into following categories.

• Pressure Transmitters
• Pressure gauges
• Pressure switches
• Pressure calibrators

Pressure Transmitters

The pressure transmitters are used to measure the pressure and transmit the reading in electrical / electronic signals for remote indication. They can be classified into three categories namely Absolute, Gage and Differential transmitters.

The absolute instruments measure the pressure with respect to absolute zero (perfect vacuum) and are generally used in vacuum column pressure measurement.

The gage pressure is the pressure with respect to the local atmospheric pressure and they are mainly used for all pressure measurement.

The differential pressure transmitters measure the pressure difference between two points and are the most widely used instrument in the refinery, when compared to any other type of process instrument. Almost all the restriction type of flow sensors uses the differential pressure transmitter to convert the generated differential pressure to an electronic signal. A large number of level measurement instruments using the hydrostatic principle also used the differential pressure transmitter. They are also used for purge type level measurement.

The common make of these transmitters are Rosemount, Yokogawa, Honeywell, Fuji, Siemens, ABB, Yamatake etc. Different vendors use different sensing technologies as per the type, range & accuracy required and the common technologies used are variable capacitive, variable reluctance, piezo electric, semiconductor etc. The transmitter output earlier were analog but recently digital transmitters (SMART) are also used (mainly using HART protocol). In case of smart transmitters, the communication to the control rooms are still done using analog signal (4-20 mA) but with the help of hand held communicators and PCs loaded with suitable communication software digital communication to the transmitter is also utilized. This digital communication enables easy re ranging and easy problem diagnostics. Moreover smart transmitters give very wide range ability.

In case of liquids, which may get concealed in pipes (impulse) due to temperature, it is better to provide stream tracing (1/4” OD Copper tube) wound round the impulse piping (coiled) up to the instrument. After tracing it, cover the exposed tubing with asbestos rope and apply “thermo cement” which will help to retain the temperature to avoid plugging. The effectiveness of the steam tracing depends on the way it is wound and also the proper working of the steam traps.

Pressure gauges

Pressure gages are used to measure and locally indicate the pressure. They are very cheap when compared to pressure transmitters but are less accurate and only local dial indication is possible.

A pressure gage consists of socket, sensing element, tip movement, case, die and pointer, lens, bezel, optional feature and accessories. The figure shows the basic items:

The socket connects the pressure source to the sensing element and also it supports the other components. Connection sixe is generally ½ “ NPTM. Other connections like ¼”, 1/8 “ and BSP threads are also used. Socket is made of brass, stainless steel and are made from bar stocks.

The sensing elements used are mainly Bourdon, bellows and diaphragm type. The tip of the pressure gauge acts as a seal and also to provide attachment to the pointer. The movement consists of geared section and pinion. Heleical, magnetic and gear less. The case encloses all the internal parts. The mainly used accessories are pulsation damper, chemical seals and siphons.

Sensing elements:

a) Bourdon tube

Bourdon tube is the most commonly used pressure sensor and are known as deformation elements. There are three types of bourdon available namely C – Bourdon, spiral and helical.

Advantages

1. Low cost
2. Simple construction
3. High pressure application

Limitations

1. Precision measurement only below 60 psi
2. Susceptible to shock and vibration
3. Subjected to hysteresis

The bourdon tube is secured at one end in a fixed socket where the sensing pressure is applied and the other end is sealed. With the pressure applied, the tubes straighten. This movement is balanced against the spring of the tube. The movement of the tube is non linear but linearity is obtained through a geared pinion and sector movement.

Spiral bourdon tube is used where the free end of C type is not enough to provide the requisite motion. Since greater movement of the free end is attained with the spiral element, better accuracy is obtained.

Helical type bourdon is similar to spiral except it is wound in the form of helical. The number of coils depends on the range of the instrument. These gauges provide more power than spiral elements and have over range capabilities.

The common materials used are phosphor bronze (low pressures and non corrosive services), Beryllium copper and SS 316 (high pressure and corrosive).

b) Bellows:

Bellows are usually formed from a thin seamless tube. In order to get better accuracy and long life, its movement is supported by spring so that only a part of the maximum stroke is used. This system is termed as spring-loaded bellows. They are used to measure absolute gauge and differential pressure. While measuring absolute pressures, two bellows are to be used. The evacuated bellow is used for atmospheric pressure compensation. The greatest use of bellows elements probably is that of receiver elements, for receivers and controllers for pneumatic instrument, also in low range pressure switches. Usually they are made of brass, phosphor bronze, beryllium copper, SS or monel. It is widely used in low pressure measurement.

c) Diaphragm:

The operating principle is similar to that of the bellows. Pressure is applied to the element, causing it to expand in direct proportion to the pressure applied. The movement of the diaphragm depends on the thickness and diameter of the material used. Diaphragm element is either a flat disc or a corrugated surface. In some cases two diaphragms are bonded together at their circumstances and are termed as capsule. When measuring absolute pressure, the capsule has to be evacuated. Materials of construction available are: Beryllium copper, Ni-Span C, Inconel, Monel, Hastalley & Nickel. Used mainly in low ranges.

Accessories:

The mainly used are:

(a) Pulsation dampness
(b) Chemical sears
(c) Pigtail siphons

a) Pulsation damper:

Pulsation dampers or snubbers are needed when pressure cycling is periodic enough to damage the measuring sensors. A damper is a restriction device, which produces a sufficient resistance to flow that pressure at the element changes slowly enough for the element to respond.

b) Chemical seals:

When the process liquid is corrosive, to prevent the bourdon from damage, a seal is used. It can also be used where the process liquid may clog the leads. A seal is constructed of thin flexible diaphragm as a separating member between the process fluid and the pressure element. The space above the diaphragm and all connections to the element are filled with a selected temperature stable liquid. The movement of the diaphragm is transmitted through this liquid system. This type of instrument operates satisfactorily in all applications. But the limitation is the volumetric capacity of the seal. This is kept to a minimum but sufficient enough to move the pointer to its full scale.

c) Pigtail siphons:

They are used in (i) to form a liquid seal in condensate vapour services (ii) to isolate hot vapours from reaching the sensing element. It is widely used in steam services.

Pressure switches

Pressure switches are widely used in a variety of process applications to give a contact output (open or close i.e., NO or NC) when the sensing pressure reaches a particular value called the set value. They can be high or low switch. A high switch, switches the contact on the rising pressure and low switch generates the contact on the lowering pressure. These contacts will be suitably wired to other control systems for necessary actions (indication or control).
The pressure to be sensed is applied to a sensor (manometric, tube, bellows, bulb). Whenever there is a change of pressure, the sensor is distorted and acts on a force balance connected to a microswitch.
Opposite this sensitive element, an adjustable spring enables the working point to be adjusted: whenever the pressure on the sensor is sufficient to counter the spring pressure, the force balance changes position.
Adding a second adjustable spring permits greater or lesser increase of the hysteresis (dead-band) or to act on dislocation between the two contacts if the instrument is thus equipped.
Sensors:
a) Bellows: The most conventional sensitive element used in our pressure and temperature switches is a metallic bellows (bronze or stainless steel) made up of a corrugated tube fitted with two airtight rigid ends. Flexible by nature, it compresses or elongates axially under the effect of pressure and provides excellent transmission.

b) Diaphragm: For low pressure, bellows, which are too rigid, are replaced by an elastomer diaphragm, which is hold in place, by two metal plates. "Diaphragm" technology is also used in cases of excessively high pressure and pulsating phenomena.
c) Manometric tube: For very high pressures, the sensor used is a stainless steel tube curved into a C shape which is closed at one end and which changes position under the effect of pressure.
Differential pressure switch
A differential pressure switch is fitted with two connections: one of them (HP) is connected to the highest pressure, the other (BP) to the lowest pressure which means, in the majority of cases, that it has to be fitted the right way round. These two connections correspond either to two sets of bellows fitted opposite one another or to the two sides of the diaphragm. The resultant of the two different pressures acts on the internal mechanism, which then functions like a standard instrument.
Absolute pressure switch
The pressure switch is fitted with a differential measuring element with bellows, one of which is vacuum-sealed so as not to be affected by atmospheric pressure.

Pressure Calibrators

Pressure calibrators are used to calibrate the pressure measuring instruments. They are kept in the instrument lab.

Portable pressure calibrators:

Common among them are portable pressure calibrators, which can be taken to field and calibrate the instruments. These portable calibrators have a hand pump and accurate pressure indicating instrument (digital or analog) for comparing the reading. These calibrators are available in different ranges. The common make are Scandura, Druck, Nagman, Ametek, Beamex etc.

Apart from these portable devices manometers and dead weight testers are also used for calibration.

Manometers:

Manometers are used for calibrating low range instruments in lab. Their advantage is that they are very simple to construct, high accuracy and good repeatability. Sometimes they are also used as measuring instruments in the field also for low-pressure purpose. They are classified as gravity balance pressure device. They measure unknown pressures by balancing against the gravitational force of liquid heads. A wide variety of liquids are used as manometer fluid. Their specific gravity varies from 1 to 13.6. The main criteria for the fluid are non-corrosive, stable, non-toxic and compatible with the measured fluid in contact with the manometer liquid. The advantages of manometers are simple and time proven construction

Different types of manometers are
a) U-type
b) Well type
c) Inclined manometer

a) U-type

This is widely used as a differential pressure-measuring device. With one end open to atmospheric, it can be used to measure pressure.

b) Well type

This is similar to U type except for a reservoir on the high-pressure side.

c) Inclined manometers

It provides a greater accuracy in low range of measurements. A small change in vertical height provides an amplified liquid movement along with slopes. Available ranges are 0 - 0.5 inches of H2O and 0 – 4 inches of H2O.

Dead weight Tester

This is used as a primary standard to calibrate other pressure elements. When used with the controlled pressure source, it is termed as “Dead Weight Piston Gauge”. In principle, a piston of known area is inserted into a close fitting cylinder. Weights loaded on one side or the piston are balanced by fluid pressure applied at the other end. The piston areas are precision built and the weights are certified.

The tester available in our shop is provided with two pistons, one for lower ranges and the other for higher ranges. All calibration of pressure gauges and pressure transmitters are done using this weight tester in the shop.

Level Measurement

2010-05-07T07:40:00.000-07:00

The various types of level measurement used are:

· Float & tape type

· Displacer type

· Differential head type

· Purge type

· Radar type

· Servo type

· Ultrasonic type

· Level switches

Float & tape type

This is the simple and oldest method available for indication, generally used in storage tanks. Even though they are very simple, only a very few are used now. In certain cases, the liquid level of the tank raises or lowers the float, which moves the indicating cable. Cable movement drives the indicator up and down the gauge board on the side of the tank.

The liquid level in inches, feet, meters or decimeters is shown by the indicator position on the gauge board. These types are used in quarries for water level measurement.

Float & tape type ATG (Automatic tank gauging) are used in Benzene & PIBU tanks, Where the level measurement is displayed using a dial and counter built into the gauge head. The gauge head is installed at the tank side. When coupled with suitable electronic transmitter, a signal 4-20 MA can be transmitted to a remote point. In these types of gauges, the stainless steel float is attached to a stainless steel perforated tape to detect the liquid level. The float follows the liquid level as it rises and falls due to the constant pullback tension provided by a powerful negator spring. The precisely perforated tape engages a pin on a sprocket wheel that it turns drives the counter assembly.

Displacer type

Displacer type level measurement instruments are widely used in the refinery. This works on the Archimedes principle. When a body is submerged in a liquid, it suffers a loss of weight proportional to the weight of the liquid displaced by it. The body is termed as displacer. The torque tube is the best-known method of using displacers for level measurements. The torque tube twists a specific amount for each increment of buoyancy change. The displacer rod is designed to absorb the side ways forces and minimize friction by a knife-edge bearing. They are calibrating for a particular specific density and any variation from the calibrated density induces error in the reading.

Calibration of level transmitter

A. Externally mounted displacer and chamber

Let us assume displacer length is 800mm and the specific gravity of the liquid is 0.8. For calibration, using water, proceed follows:

The total height to which water is to be filled in the chamber is determined by multiplying displacer length and specific gravity of the liquid, i.e. 800 X 0.8 = 640 mm

From the center marked on the float chamber, measure length equal to 400mm downwards, and mark that point as 0%.

From zero mark measure 640mm and mark that point as 100%.

Similarly from bottom calculate 25%, 50% and 75%, by dividing the total length equally.

Connect a white transparent tube to the bottom of the chamber with draining facility. Set the density dial at 1.0

Add water from the top of the chamber and check the output of the transmitter at zero mark, it should be4 mA. Adjust zero.

Take level to the 100% mark and check whether the output is 20mA. If not adjust the PB dial to have 20mA.

Repeat step (f) and (g) till you get satisfactory result.

Now check the reading up scale from 0 to 100% in steps of 25% and down scale and note down the readings. Change the specific gravity to 0.8. The instrument is now ready for installation.

B. Internally mounted chamber add float

As the float and the chamber are mounted inside, the procedure described in (A) cannot be followed. From the data provided by the manufacture, the weight of the float can be calculated. Let it be W1. Calculate he loss of weight when it is fully submerged in a liquid of specific gravity. Let it be W2.

To the torque tube, which the displacer is connected, attach a pan to carry weights.

Add weight W1 in the pan and check the output. It should be 4mA. Otherwise adjust zero of the instrument.

Remove weights W1 and add weight equal to (W1-W2) check the output. It should be 20mA. Otherwise adjust p.g. dial to have 20mA.

Repeat steps (c) and (d) till the reading match.

Add weights equal to W1 – W2 , W1 – W2 , ¾

4 2

(W1 – W2) and check the outputs. It should be 8, 12 and 16 mA.

Instrument is now ready for installation.

C. Calibration procedure for inter-face level measurement

Let us take an example to illustrate this. Consider two liquids of specific gravity 1.0 and 0.9 and the interface level is to be measured. Let the float length be 800mm. Since we are using water as the calibration liquid, the level up to which the chamber is to be filled with water in case of specific gravity of liquid 0.8 is the rate of the specific gravities multiplied by the float length.

i.e. 0.8 X 800 = 640

The second liquid is water itself. The level of water to be taken on to the chamber should be equal to the length of the float. When the chamber is filled with the second liquid of specific gravity 1.0, there will be no trace of liquid of specific gravity 0.8, as it will float over water. This corresponds to 100% level for calibration. Similarly, when the chamber is full of liquid (specific gravity 0.8), the second liquid will be below the first liquid. This corresponds to zero level.

When there is a mixture of two liquids inside, the loss of weight is the addition of loss of weight in liquid I up to which the float is immersed and loss of weight in liquid II up to which the float is immersed.

Note the Center of the float and from center mark 400mm downwards to identify the bottom of the float.

From this mark measure 640mm, upwards and this will be 0% point.

From the bottom mark measure 800mm and mark this position as 100%.

Take water in to the chamber and when the level raises up to 0 mark, note down the output of the transmitter. It should be4 mA.

Increase water level up to 100% mark and note down the transmitter output. It should be 20mA.

Note down the output of the transmitter at 25%, 50% and 75% of the level. It should be 8, 12 and 16 mA respectively.

The transmitter is ready for installation.

For pneumatic transmitters (still some are used in CDU1 & FCCU) instead of 4, 8,12,16 & 20 mA, 0.2, 0.4, 0.6, 0.8 & 1.0 Kg/cm2 respectively has to be set.

Differential head type level measurement

The application of displacer type level measurement is limited by length of the chamber in which the displacer if fixed.

One of the primary principles underlying industrial level measurement is that different materials and different phases of the same material have different densities. This basic law of nature can be utilized to measure level via differential pressure, that at the bottom of the tank relative to that in the vapor space or to atmospheric pressure

Level measurement based on pressure measurement is also referred to as hydrostatic tank gauging (HTG). It works on the principle that the difference between the two pressures (d/p) equal to the height of the liquid (h, in inches) multiplied by the specific gravity (SG) of the fluid

By definition, specific gravity is the liquid's density divided by the density of pure water at 68° F at atmospheric pressure. A pressure gage or d/p cell can provide an indication of level (accurate to better than 1%) over wide ranges, as long as the density of the liquid is constant. When a d/p cell is used, it will cancel out the effects of barometric pressure variations because both the liquid in the tank and the low-pressure side of the d/p cell are exposed to the pressure of the atmosphere. Therefore, the d/p cell reading will represent the tank level.

When measuring the level in pressurized tanks, the same d/p cell designs are used as on open tanks. It is assumed that the weight of the vapor column above the liquid is negligible. On the other hand, the pressure in the vapor space cannot be neglected, but must be relayed to the low-pressure side of the d/p cell. Such a connection to the vapor space is called a dry leg, used when process vapors are non-corrosive, non-plugging, and when their condensation rates, at normal operating temperatures, are very low (Figure 7-1C). A dry leg enables the d/p cell to compensate for the pressure pushing down on the liquid's surface, in the same way as the effect of barometric pressure is canceled out in open tanks.

It is important to keep this reference leg dry because accumulation of condensate or other liquids would cause error in the level measurement. When the process vapors condense at normal ambient temperatures or are corrosive, this reference leg can be filled to form a wet leg. If the process condensate is corrosive, unstable, or undesirable to use to fill the wet leg, this reference leg can be filled with an inert liquid.

These fill fluid generally used is Glycerin. In certain cases water, and sometimes the process fluid itself may be used as fill fluid. Generally a seal pot is also used when seal fluids are used so as to have not much variation in fluid head due to small leakage of fill fluid, reduction in temp and hence condensation in case of steam and easiness of filling.

The exact value of suppression or elevation is calculated as per the HP (high pressure) & LP (low pressure) impulse tubing length, range required and density of the fill liquid. Modern transmitters do not require any setting of zero suppression or zero elevation as such, but only assigning of LRV (low range value) and URV (upper range value).

The working and other details of differential pressure transmitter is explained in the section “pressure transmitters”.

When the process fluid is sludge, a viscous polymer or is otherwise hard to handle, the goal is to isolate the dirty process from the d/p cell. A flat diaphragm can be bolted to a block valve on the tank nozzle so that the d/p cell can be removed for cleaning or replacement without taking the tank out of service. If it is acceptable to take the tank out of service when d/p cell removal is needed, an extended diaphragm design can be considered. In this case, the diaphragm extension fills the tank nozzle so that the diaphragm is flush with the inside surface of the tank. This eliminates dead ends or pockets where solids can accumulate and affect the performance of the cell.

Diaphragm pressure seals are available with various fill liquids such as glycol and various oils. These seals are used when plugging or corrosion can occur on both sides of the cell. A broad range of corrosion-resistant diaphragm and lining materials is available. Teflon® lining is often used to minimize material build-up and coating. Level measurement accuracy does suffer when these seals are used. Capillary tube lengths should be as short as possible and the tubes should be shielded from the sun. In addition, either low thermal expansion filling fluids should be used or ambient temperature compensation should be provided, as discussed in connection with wet legs. If the seals leak, maintenance of these systems is usually done at the supplier's factory due to the complex evacuation and backfilling procedures involved.

When the process fluid is liquid nitrogen or some other cryogenic material (as in HPN plant), the tank is usually surrounded by a thermally insulated and evacuated cold box. Here, the low pressure (LP) side of a direct acting d/p cell is connected to the vapor space above the cryogenic liquid. As the liquid nitrogen approaches the HP side of the d/p cell (which is at ambient temperature outside the cold box), its temperature rises. When the temperature reaches the boiling point of nitrogen, it will boil and, from that point on, the connecting line will be filled with nitrogen vapor. This can cause noise in the level measurement. To protect against this, the liquid filled portion of the connecting line should be sloped back towards the tank. The cross-section of the line should be large (about 1 inch in diameter) to minimize the turbulence caused by the simultaneous boiling and re-condensing occurring at the liquid-vapor interface.

Purge type:

Purge type (Bubbler tubes) provide a simple and inexpensive but less accurate (±1-2%) level measurement system for corrosive or slurry-type applications. Bubblers use air (sometimes water or flushing oil) introduced through a dip pipe. Gas flow is regulated at a constant rate (usually at about 500 cc/min). Generally a restriction orifice maintains constant flow, while the tank level determines the backpressure. As the level drops, the backpressure is proportionally reduced and is read on a calibrated transmitter. The dip pipe should have a relatively large diameter (about 2 in.) so that the pressure drop is negligible. The bottom end of the dip pipe should be located far enough above the tank bottom so that sediment or sludge will not plug it. Also, its tip should be notched with a slot or "V" to ensure the formation of a uniform and continuous flow of small bubbles.

In pressurized tanks, two sets of dip pipes are needed to measure the level). The two backpressures on the two dip pipes can be connected to the two sides of DP transmitter. The purge gas supply should be clean, dry, and available at a pressure at least 10 psi greater than the expected maximum total pressure required (when the tank is full and the vapor pressure is at its maximum).

These type of level measuring instruments are generally used in services where there are chances of fluid blocking the impulse tubing like in regenerator level, molten sulphur level, slurry services and also open vessels like water sumps.

Radar type:

Radar type gages are used in automatic tank gages (ATG). The different types of gages and their details are mentioned in section 3.6.

Servo type:

Servo type gages are used in automatic tank gages (ATG). The different types of gages and their details are mentioned in section 3.6.

Ultrasonic type:

API sump level at Wagon Loading is measured by VEGA Ultrasonic Level Indicator - VEGASON 51K

The continuous level measurement with Ultrasonic sensors is based on the running time measurement of ultrasonic pulses. Piezoceramic high-performance transducers emit focused ultrasonic pulses, which are reflected from the surface of solids and liquids. The meas. signal prepares a precise picture of the meas. Environment out of the running time and signal shape of

the reflected ultrasonic pulses.

Due to the physical sound velocity and the detected actual running time of the emitted sound impulses, the meas. Electronics calculates precisely the distance between transducer and product. The distance is converted into a level proportional meas. Signal according to the sensor parameter adjustment as exact scaled level.

The instruments operate with emitting frequencies from 16KHz to 70 KHz. to be prepared for the different distances and requirements.

As the sound velocity is subjected to a temperature influence, the transducer detects continuously the ambient temperature so that the level is provided precisely even with varying ambient temperature.

The indicating instrument at wagon Loading Control Room is VEGADIS 371EX, which connects to the VEGASON in a two-wired loop. VEGADIS is a digital indicating instrument with integral level switches and current output.

The instrument configuration parameters can be set /modified either by

By MINICOM module, which is a detachable 6 key module with, display, which has to be plugged into the ultrasonic sensor or VEGADIS? OR

By HART Handheld Configuration.

Level switches:

Level switches are widely used in a variety of process applications to give a contact output (open or close i.e., NO or NC) when the level reaches a particular level. They can be high or low switch. A high switch, switches the contact on the rising level and low switch generates the contact on the lowering level. These contacts will be suitably wired to other control systems for necessary actions (indication or control).

The buoyant force available to operate a float level switch (that is, its net buoyancy) is the difference between the weight of the displaced fluid (gross buoyancy) and the weight of the float. Floats are available in spherical, cylindrical, and a variety of other shapes. They can be made out of stainless steel, Teflon®, Hastelloy, Monel, and various plastic materials. Typical temperature and pressure ratings are -40 to 80°C (-40 to 180° F) and up to 150 psig for rubber or plastic floats, and -40 to 260°C (-40 to 500°F) and up to 750 psig for stainless steel floats. Standard float sizes are available from 1 to 5 inches in diameter. The float of a side-mounted switch is horizontal; a permanent magnet actuates the reed switch in it.

Floats should always be lighter than the minimum expected specific gravity (SG) of the process fluid. For clean liquids a 0.1 SG difference might suffice, while for viscous or dirty applications, a difference of at least 0.3 SG is recommended. This provides additional force to overcome the resistance due to friction and material build-up. In dirty applications, floats should also be accessible for cleaning.

The switch itself can be mercury (Figures 7-6A and 7-6C), dry contact (snap-action or reed type, shown in Figure 7-6B), hermetically sealed, or pneumatic.

Displacer Switches

Whereas a float usually follows the liquid level, a displacer remains partially or completely submerged. The apparent weight of the displacer is reduced as it becomes covered by more liquid. When the weight drops below the spring tension, the switch is actuated. Displacer switches are more reliable than regular floats on turbulent, surging, frothy, or foamy applications. Changing their settings is easy because displacers can be moved anywhere along the suspension cable (up to 50 ft). These switches are interchangeable between tanks because differences in process density can be accommodated by changing the tension of the support spring.

Flow Measurements

2010-05-07T05:11:00.000-07:00

FLOW

Many types of flow meters are used in the refinery for flow measurement. They are as follows

· Restriction type

· Coriollis Mass flow meters

· Thermal Mass flow meters

· Electromagnetic flow meters

· Rotameters

· Vortex flow meters

· Ultrasonic flow meters

Restriction type:

Consider a fluid travailing in a pipe cross-section area at a steady rate of flow. If on inserting a restriction in that pipe, since the flow is steady, the same number of molecules should flow through any section of the pipe per unit time. Therefore, the molecules pass through cross-section at a faster rate than the unrestricted pipe-cross-section .In order to bring about this increase in velocity the fluid must decrease its energy content of another form termed as static pressure. Therefore, there exist difference in static pressure between these two points. This is the principal behind flow meter, i.e. a restriction is used to develop a differential pressure. The point at which the minimum fluid area coincides with the minimum pipe diameter is called vena-contracta.

The various devices used in the refinery to create a differential pressure are:

a)Orifice plate

b)Venturimeter

c)Wedge flow meter

d)Pilot tube

a) Orifice Plate

The most widely used primary device is orifice plate and they form the majority of the flow meters. There are different types of orifice plates like concentric orifice plate (a circular disc having a concentric circular base with a sharp 90^ocorner at the inlet face), eccentric orifice plate (a circular disc having an eccentric circular bore with a sharp 90^o corner at the inlet face) and segmental orifice plate (circular disc with a bore which is a segment of the concentric circle and has a sharp 90^ocorner at the inlet face).

The material of construction of these plates is stainless steels. The concentric orifice is widely used in services. In services where the following medium is sticky or slurry, segmental orifice is preferred. The pressure recovery at the downstream of the orifice plate is about 75 to 80 percent.

b) Venturimeter

Venturimeter is a volume flow-measuring instrument consisting of a convergent – divergent pipe. A standard venturimeter has a 30 degree included angle in the convergent section and 7 degree angle in the divergent section. The diameter ratio “d throat” to “d pipe” is equal to 2. This is used mostly in slurry services. The divergent section allows smooth expansion of the flow back to the flow rate and therefore the pressure recovery is about 87% and so it is best suited in services where the pressures are low.

When compared to orifice meter, this is bulky and costly but the pressure loss is less and also susceptible to less wear and tear.

In the refinery there are only very less number of venturimeters. They are generally used in compressor inlet flow measurement as in the FCCU unit WGC & MAB air inlet flow, acid gas flow in DHDS SRU unit etc.

c) Wedge Flow meter

A wedge-shaped segment is inserted perpendicularly into one side of the pipe while the other side remains unrestricted. The change in cross section area of the flow path creates pressure drops used to calculate flow velocities.

Since the bottom part is unrestricted, this is used in slurry services. In refinery very few of these types are used like in CDU 2 total Crude flow measurement and FCCU (FV12 SLURRY RECYCLE FLOW

d) Pitot Tube

The pitot tube measures the fluid velocity by converting the kinetic energy of the flow to the potential energy. This indication of velocity combined with the cross-sectional area of the pipe provides an indication of flow rate.

Averaging pitot tube (Annubar) is similar to pitot tube but uses multiple openings as shown in the figure for averaging the pressure.

The main disadvantage is that foreign matter materials can clog the pitot. This is used in large pipelines with averaged out by drilling pre-determined holes along the length of the pipe.

In the refinery annubar is commonly used in very large pipelines for cooling water and raw water services. They are also used in large air ducts used for combustion air to heaters.

CORIOLLIS MASS FLOWMETER

There are several types of flow meters that respond to the mass of the flowing fluid rather than volume, area, or velocity. Examples of mass flow meters are thermal mass meters, gyroscopic mass meters, angular momentum mass meters, and Coriollis mass meters.

Coriollis mass meters can measure the density of the fluid in addition to the mass flow. Since volume flow equals mass flow divided by density, the associated electronics can be programmed to output in volume. So these mass flow meters can also be used to measure the volume flow but the accuracy of the volume flow depends both on the accuracy of the mass flow and density.

Principle of operation:

When a particle moves across the surface of a rotating body, it is caused to accelerate by a force called Coriollis force, which acts normally, to both the direction in which the particle moves and the axis of rotation of the body. The magnitude of the coriollis force is directly proportional to the product of the mass of the particle and coriollis acceleration.

Instead of rotating the body about a fixed point, Coriollis force can be generated by vibrating the tube. The smallest amount of energy to vibrate the tube is at the natural frequency of the tube. Ina typical commercial meter, a U tube is supported at free end while the two pipe sections are anchored

Between the inlet anchor (A) and the point of vibration (B), the fluid particles experience increasing acceleration at right angles to their motion and hence an increasing coriollis force. Between point B and the point outlet anchor (C) coriollis force decrease since the amplitude of vibration goes from a maximum at B to zero at C. These forces are equal and opposite in direction and set up a mechanical couple and cause the U tube to twist. . The maximum amount of twist q is proportional to the mass flow within the tube and is sensed by transducers located at the points of maximum deflection. The tube is vibrated at its natural frequency using electromagnetic devices. Coriollis manufacturers use various proprietary standards to measure the magnitude of the distortion and process the measured signals and convert them to useful information. In practice, for larger line sizes, two U tubes in parallel or in series are vibrated in opposition to each other to neutralize the vibration induced into the piping system.

A typical construction is shown below:

In addition to measuring the Coriollis force, most meters are capable of utilizing the frequency of vibration of the tube(s) to measure density. Density is related to frequency, though not linearly.

In order to compensate for the effect of pressure and temperature on the sensor, pressure and temperature compensations are provided in certain sensors by using an inbuilt RTD and external pressure transmitter.

The design and construction of the individual mass flow sensor determine the accuracy, sensitivity and repeatability of the meter. These meters are generally factory calibrated against traceable standards and each sensor will have its own calibration factors.

Typical measurement accuracy is between 0.15 % and 0.25% of rate plus a zero shift, which is also termed zero stability. The zero shift error is due to small varying offsets in both the sensor and electronics. Due to zero error, accuracy is degraded as the flow approaches zero. To obtain the best possible low-end performance, coriollis flow meters offer the ability to check and adjust zero at actual line operating conditions.

These meters can be checked / verified using master meters or other volumetric / gravimetric methods and the reading can be adjusted by adjusting a particular factor generally called the meter factor.

In most of the cases a separate transmitter is connected to the sensor, which powers the sensor and also converts the sensor data to useful digital or analog outputs. The calibration constants, meter factors and other factors, which determine the type of output, are configured in this transmitter.

Advantages & Disadvantages:

Advantages

§ A clear tube provides a fundamental means of measuring mass flow.

§ No moving components and requires less maintenance.

§ Available in a range of corrosion – resistant materials.

§ Calibration independent of viscosity and flow profile.

Disadvantages

§ Accuracy degraded at low flow rates due to zero shifts.

§ Performance is affected by the presence of air or gas pockets.

§ Signal will be corrupted due to slug flow conditions caused by the presence of large void fractions and hence not suitable for two phase flow.

§ Sensitive to vibration

§ High-pressure drop at full in some designs.

§ They are bulky in some designs.

§ Maximum size is only 150mm

§ Extremely expensive.

In the refinery there are a large number of mass flow meters of different make (Micro motion, Rheonik, Bopp & Reuther, Krohne Marshall) are used in various units because of its specific advantage over other conventional volume meters. A large number of them are used in Truck loading area for custody transfer (sales) of products, fuel oil meters to heaters and very few in process units (DHDS).

Thermal Mass Flow Meters:

Earlier few thermal mass flow meters were used in the flare flow measurement purpose, which are now replaced with ultrasonic type instruments. The thermal mass flow measurement principle are now limited to few flow switches used in combustion air to heaters. They are of M/s. Fluid Components Inc. (FCI) make using thermal dispersion principle.

Thermal Dispersion technology uses the principal of measuring the heat loss, or cooling effect, of a fluid flowing across a heated cylinder. A typical flow element configuration uses two RTDs, sheathed in thermowells, separated by a gap. Heat is applied internally to one RTD relative to the other, creating a differential temperature between the two. This differential temperature is greatest at no flow conditions and decreases as flow increases, cooling the heated RTD.

Changes in flow velocity or immersion of the flow element into a liquid directly affect the extent to which heat is dissipated and, in turn the magnitude of the temperature differential between the RTDs. This differential is electronically converted into an electrical signal that can be used to trip a relay.

Since the relationship between flow rate and cooling effect is directly related to mass in gas applications, Thermal Dispersion technology, combined with advanced signal linearizing circuitry, is used to provide a highly repeatable and accurate measurement of gas or air mass flow rates.

Electromagnetic Flow Meter

Electromagnetic flow meters measure the volume flow of electrically conductive liquids and slurries. An electric conductor, in this case the electrically conductive medium, passes through a magnetic field.

The voltage U induced in this medium is directly proportional to the mean flow velocity v.

The induced voltage signal is picked up either by two measuring electrodes in conductive contact with the medium or indirectly by capacitive coupling.

A signal converter amplifies the signal and converts it into a standard analog signal (e.g. 4 to 20 mA) and a frequency signal (e.g. 1 pulse for every US gallon or cubic meter of medium flowing through the measuring tube).

To ensure that the voltage is not short-circuited by the pipe wall, the measuring tube is made of an electrically insulating material or fitted with an insulating liner.

Measurement is largely independent of the flow profile and other properties of the medium, such as pressure, temperature, viscosity, density, consistency, electrical conductivity, and electrode contamination.

The electromagnetic flowmeter consists of a primary head that is installed in the pipeline, and a signal converter. The compact design has the signal converter mounted directly on the primary head.

Only few instruments of these types is used in the refinery. In LOCAT SRU unit M/s. Krohne make electromagnetic flow meter is used.

Rotameter

Rotameters are the most widely used type of variable-area (VA) flowmeter. In these devices, the falling and rising action of a float in a tapered tube provides a measure of flow rate (see Figure). Rotameters are known as gravity-type flowmeters because they are based on the opposition between the downward force of gravity and the upward force of the flowing fluid. When the flow is constant, the float stays in one position that can be related to the volumetric flow rate. That position is indicated on a graduated scale. Note that to keep the full force of gravity in effect, this dynamic balancing act requires a vertical measuring tube.

Figure: - The rotameter's operating principle is based on a float of given density's establishing an equilibrium position where, with a given flow rate, the upward force of the flowing fluid equals the downward force of gravity. It does this, for example, by rising in the tapered tube with an increase in flow until the increased annular area around it creates a new equilibrium position. By design, the rotameter operates in accordance with formula for all variable-area meters, directly relating flow rate to area for flow.

The term rotameter derives from early versions of the floats, which had slots to help stabilize and center them and which caused them to rotate. Today’s floats take a variety of shapes, including a spherical configuration used primarily in purge meters. The materials of construction include stainless steel, glass, metal, and plastic.

The tapered tube’s gradually increasing diameter provides a related increase in the annular area around the float, and is designed in accordance with the basic equation for volumetric flow rate:

Where:

Q	= volumetric flow rate, e.g., gallons per minute
k	= a constant
A	= annular area between the float and the tube wall
g	= force of gravity
h	= pressure drop (head) across the float

With h being constant in a VA meter, we have A as a direct function of flow rate Q. Thus, the rotameter designer can determine the tube taper so that the height of the float in the tube is a measure of flow rate.

These types of meters are generally used in low size and low flow application and where local indication alone is required (In certain cases using magnetic coupling and suitable electronics, 4-20 mA output for remote indication is also taken).

Vortex Flow meter:

The vortex flowmeter is used for measuring the flow velocity of gases and liquids in pipelines flowing full. The measuring principle is based on the development of a Karman vortex shedding street in the wake of a body built into the pipeline where Re > 20,000.

The periodic shedding of eddies occurs first from one side and then from the other side of a bluff body (vortex-shedding body) installed perpendicular to the pipe axis. Vortex shedding generates a so-called “Karman vortex street” with alternating pressure conditions whose frequency is proportional to the flow velocity. The non-dimensional Strouhal number S (primary head constant) describes the relationship between vortex shedding frequency F, width b of the body, and mean flow velocity v. These alternating pressures are measured using piezoelectric sensors, which gives the current signal to the signal convertor.

F = S * v / b

These type of meters are installed in air compressor discharge (M/s. Krohe make) line and are capable of indicating the Free Air Discharge (FAD) since they also measure temperature (using RTD) and pressure (strain gauge).

Ultrasonic Flow meters:

a) Milltronics OCM 111 Flow meter:

The Milltronics OCM 111 open channel flow meter is an ultrasonic instrument to measure flow in Outlet C. As a system it is used in conjunction with a remote ultrasonic transducer and a temperature sensor. The OCM 111 transmits a pulse signal to the transducer, which is then emitted as ultrasonic pulses. The pulses echo off the water surface, which are then sensed by the transducer. The time for a pulse to echo back from the water surface is temperature compensated and converted into a measurement of head. The OCM 111 converts the head measurement into flow rate. The flow rate is totalized and stored in a data log to provide flow analysis. An infrared programmer is used to communicate with the OCM 111 transducer.

b) Panametrics Mass Flowmeter for Flare lines

Flow rate in flare systems are characterised by unsteady flow, pulsating pressure, varying composition, varying temperature at wide flow ranges and sometimes bi-directional

The Digital Flow GF868 Mass Flowmeters have been installed in Flare gas lines which measures mass flow rate by using a patented algorithm to determine the instantaneous average molecular weight of the gas being flared and the flare gas flow rate is measured using patented Correlation Transit-Time technique.

Principle of measurement

It uses two ultrasonic transducers located in the gas flow, each of which is capable of both sending and receiving ultrasonic pulses. The electronic circuits measure the time it takes for an ultrasonic pulse to travel from one transducer to the other. A pulse traveling in the direction of the flow arrives at the opposite transducer in a shorter period of time than a pulse traveling against the flow. From the time difference, The GF868 calculates the flow velocity of gas at the transducer installation point in the flare system. Once the sound speed of the gas has been determined by the GF868, its on-board computer uses temperature and pressure inputs in conjunction with the sound speed to calculate instantaneous average molecular weight and mass flow rate of the gas. Hence a Pressure transmitter and Temperature transmitter also is provided on the line, near the transducer location and their outputs are connected to the GF868 system.

Groups of time measurements are repeated rapidly. Measurements are averaged to give a steady meter reading and smooth output.

The configuration data like Pipe parameters such as Transducer path length, Pipe dia, etc and details of analog I/O Pressure transmitter and temperature ranges are entered from the instrument keypad.

The wide range ability of this instrument allows measurement of flow rate from 0.03 up to 85 meters/second.

These meters have dual channel option, which gives it the ability to measure two paths in one pipe for maximum accuracy, or two flow rates in separate pipes with one installation.

Each analog input card in the GF868 has two analog channels to which the Pressure and temperature transmitters are connected in 2 - Wire mode. Each analog out put card has 4 analog channels, which is used to indicate Mass Flow, Sp. Gravity etc in DCS.

In KRL, we have 4 Nos. GF868 Dual channel flowmeters, and 1 No. Single channel Flowmeter at the following locations.

Tag No.	Location	Remarks
YFE -334 YFE - 335	FCCU LEFPU	Dual Channel
YFE -336 YFE - 337	PRI H2 PRI HC	Dual Channel
YFE –1604 YFE - 1605	ARU CDU2	Dual Channel
YFE -1606 YFE - 1607	SRU1 SRU2	Dual Channel
YFE - 338	CPP	Single Channel

How to read P&ID

2010-05-06T06:32:00.000-07:00

Instrumentation detail varies with the degree of design complexity. For example, simplified or conceptual designs, often called process flow diagrams, provide less detail than fully developed piping and instrumentation diagrams (P&IDs). Being able to understand instrumentation symbols appearing on diagrams means understanding ANSI/ISA’s S5.1-1984 (R 1992) Instrumentation symbols and identification standard. S5.1 that defines how each symbol is constructed using graphical elements, alpha and numeric identification codes, abbreviations, function blocks, and connecting lines.
Deciphering symbols
ISA S5.1 defines four graphical elements—discrete instruments, shared control/display, computer function, and programmable logic controller—and groups them into three location categories (primary location, auxiliary location, and field mounted).
Discrete instruments are indicated by circular elements. Shared control/display elements are circles surrounded by a square. Computer functions are indicted by a hexagon and programmable logic controller (PLC) functions are shown as a triangle inside a square.
Adding a single horizontal bar across any of the four graphical elements indicates the function resides in the primary location category. A double line indicates an auxiliary location, and no line places the device or function in the field. Devices located behind a panel-board in some other inaccessible location are shown with a dashed horizontal line
Letter and number combinations appear inside each graphical element and letter combinations are defined by the ISA standard. Numbers are user assigned and schemes vary with some companies use of sequential numbering, others tie the instrument number to the process line number, and still others adopt unique and sometimes unusual numbering systems.
The first letter defines the measured or initiating variables such as Analysis (A), Flow (F), Temperature (T), etc. with succeeding letters defining readout, passive, or output functions such as Indicator (I), Record (R), Transmit (T), and so forth.
Example shows the story
Referring to the Example P&ID diagram, FT 101 represents a field-mounted flow transmitter connected via electrical signals (dotted line) to flow indicating controller FIC 101 located in a shared control/display device. A square root extraction of the input signal is applied as part of FIC 101’s functionality. The output of FIC 101 is an electrical signal to TY 101 located in an inaccessible or behind-the-panel-board location. The output signal from TY 101 is a pneumatic signal (line with double forward slash marks) making TY 101 an I/P (current to pneumatic transducer). TT 101 and TIC 101 are similar to FT 101 and FIC 101 but are measuring, indicating, and controlling temperature. TIC 101’s output is connected via an internal software or data link (line with bubbles) to the setpoint (SP) of FIC 101 to form a cascade control strategy.
Often P&ID’s include a cover page where common and typical terms, symbols, numbering systems, etc., are defined. On the example, Typical YIC would likely appear on the cover page and the simplified form of YIC would appear throughout the P&IDs.
Typical YIC indicates an on/off valve is controlled by a solenoid valve and is fitted with limit switches to indicate open (ZSH) and closed (ZSL) positions. All inputs and outputs are wired to a PLC that’s accessible to the operator (diamond in a square with a solid horizontal line). The letter 'Y' indicates an event, state, or presence. The letter 'I' depicts indication is provided, and the letter 'C' means control takes place in this device.
Adherence to ISA’s S5.1 Instrumentation Symbols and Identification standard ensures a consistent, system independent means of communicating instrumentation, control, and automation intent is developed for everyone to understand.

Fire and Gas, Instrument , Mecheniacal Questions & Answers

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Common Sense Safety

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Eye Protection Safety Topic

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Instrumentation

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Level Measurement

Calibration of level transmitter

API sump level at Wagon Loading is measured by VEGA Ultrasonic Level Indicator - VEGASON 51K

the reflected ultrasonic pulses.

Flow Measurements

c) Wedge Flow meter

Rotameter

b) Panametrics Mass Flowmeter for Flare lines

Principle of measurement

Location

Remarks

Dual Channel

CDU2

How to read P&ID