Veriforce TG CCT 711OP. Training Guide

Transcription

1 Training Guide Directions: This training guide is to be used by a Veriforce Authorized Evaluator/Trainer and Trainee during on-thejob training (OJT) or prior to an evaluation as a resource. (S) Indicates a demonstration or skill task; (K) indicates a knowledge task. OJT Reminder: OJT is an active hands-on process. Practice should be as similar to the actual job task as possible. However, if the training is being provided on an actual job site while a covered task is actually being performed, the Evaluator either needs to be qualified on that covered task or be assisted by someone who is qualified on the covered task. The Evaluator should closely monitor the Trainee's practices to ensure safe and correct task performance. At no time should a non-qualified individual perform, or train for, a covered task unless directed and observed by a qualified individual. However, if the span of control for that particular covered task is 1:0 (requiring only qualified individuals to perform the covered task), the training must be simulated. Training is simulated by "walking through" the task and simulating all actual manipulations (valves, switches, tools, etc.) an individual would use during the performance of a covered task. Simulating includes the use of safety and administrative requirements as if the task were being performed live. Refer to the Veriforce Evaluator Training Program for more on how to conduct formal OJT. Disclaimer: This training resource is offered in good faith. Anyone choosing to utilize or rely on this training resource is doing so at their own discretion, risk and choice. Although every attempt has been made by Veriforce, LLC (the Company ) to ensure the correctness and suitability of this document and to correct any errors brought to the attention of the Company, the Company makes no representation or warranty regarding correctness or suitability (either directly or indirectly) of information referenced or implied within this training resource. In no event shall the Company be liable for any damages (including, but not limited to, special, incidental or consequential damages) whatsoever (including, but not limited to, death, personal injury, damage to person or property, loss of use, and/or loss of revenues), whether in an action of contract, negligence, or other action, arising out of or in any way associated with the use or misuse of this document. All critical information should be independently verified by the user and the user shall not rely on the contents provided herein without such independent verification. The subject matter included in this training has been compiled from a variety of sources and is subject to change without notice. The Company reserves the right to add, remove and alter information contained in this document without notice. The Company may provide links to other sites for your convenience; however, the Company takes no responsibility and makes no representation or warranty regarding the accuracy or currency of information contained within such sites. The Company does not endorse any information, goods, or services referred to within such sites, and the provision of links by the Company shall not be interpreted to be an endorsement of such information, goods or services. The content of this training resource is provided for personal use only, and all other use, copying or reproduction of this training or website or any part of it is prohibited. CCT: 711OP - Inspect, Test, and Maintain Control Systems Page 1 of 20 Copyright 2016 Veriforce, LLC. All rights reserved. 09/12/2016

2 Recommended Student Training or Resources: Recommended Student Training or Resources: DOT 49 CFR (c) DOT 49 CFR (b)(1) Control Systems Transporting and refining oil and gas from the well to the customer requires a lot of processing. This processing could take the form of distillation into gasoline or diesel, or it could be as simple as compressing the gas or pumping the oil downstream. In any case, when there s a process, there will be control systems to monitor the process. Control systems are everywhere, from the compressor station we already mentioned to food processing plants. Oil refineries to office buildings, even traffic control lights, may use control systems to coordinate turning lanes that only turn green when cars are waiting to turn. Can you think of places you ve seen control systems? How would you know if you were looking at one right now? No matter what they look like, control systems pretty much work the same way. But before you read about how control systems function, take a minute to read about what is meant by the word process. A process is a series of actions or steps taken to achieve a result. So to use a compressor station for an example, its process is made up of all the things that need to happen to compress natural gas for pipeline transmission. Keep in mind, though, that a process may be made up of many more processes. A single reciprocating compressor unit has many steps to compressing the gas, but it is just one step in the station s overall process of compression. Sticking with the example of gas compressor stations, the process is to deliver gas to the compressor unit and propel it further downstream. So if you think about natural gas compression, once the gas is in the unit itself, you may notice that there are many steps going on inside the reciprocating compression engine. The right amount of fuel gas must be injected into the cylinder, then a spark plug must ignite the gas at a specific time, causing the engine piston to turn a crankshaft that pushes and pulls a compression piston, thus compressing the gas. The control system monitors and controls all the little steps going on inside that compressor engine. It does this by monitoring conditions from inputs and comparing them to its programming. If any conditions or process variables are out of set-point, or the value they should be at, the control system uses outputs to change conditions to match the set-points in its programming. Basically, it s a computer that keeps process variables at specific values or within a specific range of values. Additionally, if any of these process variables exceed or fall below set-point values the control system can alarm or shutdown the device that it is controlling. An example of controlling process variables would be if a reciprocating compressor unit s oil temperature setpoints were between 135 degrees and 160 degrees and the temp started to exceed 160 degrees. In this scenario, the control system would increase the flow of the coolant to cool the engine oil temperature down. It would do this by first sensing the temperature through a temperature detector, an input device, comparing the real time data to what it should be according to its programming. When the control system sees the real temperature is above the set-point, it would send a signal to an output device, such as a pneumatic control valve, to open and increase the flow of coolant. If the engine became too cool, it would decrease the flow until Page 2 of 20 Copyright 2016 Veriforce, LLC. All rights reserved. 09/12/2016

3 the temperature stayed between the set-points in its programming. Module 1: End Devices Knowledge Identify types of end devices and their purpose. The phrase end device is a catchall term used to describe the many input and output devices at the ends of terminals connected to the control system. These devices act as the control system s eyes and hands, where input devices sense and see the process and output devices move and activate controls to keep the process variables safe and within set-points. There are many makes and models of end devices, each with their own design and purpose, but when we talk about the type of end devices, we are referring to signal type. There are mainly 2 signal types that end devices will come in, and that s digital or analog. Digital Digital end devices provide or accept a discreet (or on/off ) signal. This can also be considered yes/no or present/not present or any variation of a single pair of values. Examples of digital input devices may include pushbuttons, limit switches, selector switches, pressure switches, and flame sensors. Some examples of digital output devices are lights, solenoids, motor starters, and alarms. If the digital device is a switch, it may be configured as normally open (NO) or normally closed (NC). Normally open devices are used for automatic pumps or any device that you want to turn on when the set-point is met. Normally closed switches are usually used when you want something to shut off when the set-point is met. Analog Analog devices work by sending or receiving a continuous and varying signal. The signal is continuous in that it is constantly being sent and varying in that the intensity of the signal dictates the condition. To have a better understanding of analog devices, let's use a pressure transducer as an example. Let's say that the pressure transducer is set to read pressure from 100 PSI to 260 PSI and sends a corresponding signal of 4-20 ma. So if the pressure is at 200 PSI, the transducer will send a steady signal of 14 ma. If the pressure rises 20 PSI to 220 PSI, the transducer would then send a continuous signal of 16 ma. Analog input devices could be a pressure transmitter/transducer, thermocouples, thermometers, and flow and level transmitters. Variable speed drives and control valves are some examples of analog output devices. In any case, either type of signal may be arranged as a normally open or normally closed contact in the control system s programming. We will have a more in-depth discussion on programming in the next module, but for now, know that end devices can be either normally open or normally closed. Pressure Switches Let s now learn about the operating principles behind a pressure switch to get a better understanding of how an end device works as the eyes of a control system. Pressure switches are a form of switch that closes or opens an electrical contact when a certain pressure, called the set-point, has been reached on its input. The switch may be designed to make or break contact either on pressure rise or on pressure fall. Pressure switches vary by design and purpose, but they consist of 2 major components: the pressure element and the switch. The pressure element is typically a bourdon tube, diaphragm, or bellows. The switch itself is Page 3 of 20 Copyright 2016 Veriforce, LLC. All rights reserved. 09/12/2016

4 like any other switch. Consider a standard wall light switch that is operated manually. When you turn your light switch on with your hand you close the contact, thus completing the circuit and directing power to the light. Instead of your hand operating the switch to open or close the contact, pressure will operate a pressure switch. Pressure switches can be normally open (NO) and set to close on either rising or falling pressure. A pressure switch set to close on rising pressure will have an open circuit below the set-point pressure. As the sensing pressure rises to the set-point, the switch will close, completing the circuit, and remain closed above the setpoint pressure. On the other hand, if it s set to close on falling pressure, the action will take place when the pressure falls below the set-point. Some switches can be normally closed (NC) and set to open on falling or rising pressure. If it is set to open on rising pressure, the switch will be closed until the set-point is reached. Once sensed pressure rises to the setpoint, the switch will open, breaking the circuit. If set to open on falling pressure, the switch will open when the pressure falls below set-point. Some switches can even be set to close at one pressure level and open back up at another. In this case, the switch would have a deadband. The deadband is the difference between the first set-point that causes one action and the second set-point that cancels or resets the switch s action. For example, if you have a pressure switch that is set to close at 50 PSI and open back up at 75 PSI, the switch would have a dead-band of 25 PSI. As the monitored pressure meets the switch s set-point and triggers the switch, a signal is sent to the control system. The condition is examined by the control system and adjustments may be made to regulate the monitored process. The control system essentially uses the pressure switch to see when a change in a monitored condition occurs. Knowledge/ Skill Describe maintenance of end devices. End Device Maintenance Just like everything else on a pipeline, end devices require maintenance and calibration. As every control system is different, you will read about 3 examples of commonly found end devices: recorders, pressure transmitters, and I/P (current to pneumatic) transducers. But before you move on, take a look at the terms below. Range refers to the specific range of pressure, temperature, or other measurable condition that a device is designed to work over. The range will be fixed and, if exceeded, will result in permanent damage or destruction of the device. It is common for an end device to be limited over a fixed range so they can provide a predictable performance. Zero is the start point of the range. So if the range is PSI, 100 PSI would be zero. An end device s zero is not to be confused with the number zero as the range could have negative numbers, such as a thermometer with a range of -150 to 200, where -150 would be the device s zero. Span is the highest input value that can be applied to the device. In other words, it is the highest value in the range of an input device. Full scale output is the highest output value that can be applied by a device. Basically, it is the highest value in the range of an output device. Page 4 of 20 Copyright 2016 Veriforce, LLC. All rights reserved. 09/12/2016

5 As we go over these examples of commonly found end devices, remember that there are many makes and models of them, so always refer to the manufacturer s recommendations for your particular piece of equipment for proper inspection, maintenance, and calibration guidelines. Recorders Pressure recorders, also known as block chart recorders, are used to keep a record of measurement changes over a period of time and may use paper strips or polar charts. They are considered output devices as they receive signals from the control system on conditions such as tank level, temperature, and pressure. Perform a visual inspection of the recorder as you approach the equipment. Check for cracks in the housing and loose connections. You must verify that the recorder is calibrated and functioning properly. To verify calibration and function of the recorder, you will need to connect a test medium and apply pressure to the recorder while observing it record. Following model-specific guidelines, introduce a test pressure for the recorder s zero and full scale. If the recorder correctly records the test pressures, it is calibrated. If the recorder is off, then adjust the recorder until the readings are correct. Observe the movement of the recorder and note any malfunction. If the marker pen does not move freely and smoothly, lubricate the recorder per manufacturer s specifications. Document any faults found and any adjustments made to the recorder along with which test equipment you used to perform the maintenance. Pressure Transmitters Pressure transmitters are types of pressure sensors that generate a signal as a function of the pressure imposed. In other words, they interpret the force or pressure from their input into an electrical signal, usually 4 20 ma current or loop that can be read by other devices. Pressure transmitters often function as an input device in a control system. When performing maintenance on a pressure transmitter, you will want to check the transmitter s body for cracks and the connections for looseness or any signs of leaks, such as dirt buildup or discoloration. Next you will want to calibrate the device to make sure that it is working in the proper range. To calibrate a pressure transmitter, you will need to introduce pressure into the transmitter and see if it sends out the correct signal. Follow the device s manufacturer s instructions to determine the proper test method and equipment. Connect a device that will provide pressure in the proper test medium to the input side of the transmitter. If you are calibrating an analog transmitter, connect a suitable test meter either across the test points or in series with the output. If you are working on a digital transmitter, connect the appropriate calibrator to the output of the transmitter. Once the test equipment is connected, adjust the test pressure to the zero and span of the transmitter s input range and observe the signal s corresponding strength on the multimeter. Here s an example of what is meant by corresponding signal. If you have a pressure transmitter with an input range of PSI and an output range of 4 20 ma and you induce a pressure of 100 PSI, the transmitter should send out a 4 ma signal. If you induce 180 PSI, the corresponding output signal would be 12 ma. And if you go to the span and induce 260 PSI, you will get a 20 ma signal. If the induced pressure does not give you the correct signal, then make any necessary adjustments according to the device s manufacturer s guidelines. Document the test s readings as found and left, and record what test equipment was Page 5 of 20 Copyright 2016 Veriforce, LLC. All rights reserved. 09/12/2016

6 used to perform the calibration. I/P Transducer Current to pneumatic, or I/P, transducers are output devices that take an electrical current or loop from the control system and let out air pressure to affect a process. For example, the control system may increase the current to increase the instrument air, further opening a control valve. In order to perform maintenance on an I/P transducer, check the body for cracks and the connections for looseness and any signs of leaks, such as loss of air pressure or the sound of leaking air. Next you will want to calibrate the device to make sure that it is working in the proper range. To calibrate an I/P transducer, connect an adjustable current source that matches the range of the transducer, such as 4 20 ma, to the input side of the transducer. You could also force a value in the PLC programming to produce a current for the transducer. Connect a test gauge that is capable of accurately indicating pressure to the output of the transducer. Adjust the input current to the zero and span of the transducer's range and observe the output pressure. For example, if you have an I/P transducer with an input range of 4 20 ma and an output range of 3 15 PSI and you induce a current of 4 ma, the transducer should push out a pressure of 3 PSI. If you induce a current of 12 ma, the corresponding output pressure would be 9 PSI. And if you go to the span and induce 20 ma, you will get a pressure of 15 PSI. If the results are out of calibration, make adjustments according to the manufacturer s instructions to obtain the desired calibration. Document the found and left readings of the transducer, along with what test equipment was used to perform the calibration ma Considerations There are a few things that you need to know about when working with a 4 20 ma loop, or a loop that uses any size current for that matter. The first thing to keep in mind is the need for proper shielding or insulation of the loop from the potential of a stray current being introduced into the circuit. Stray currents can come from many sources, such as static electricity or switching spikes in the area of the loop. If these sources are not shielded from the loop, false readings may occur, causing potential damage to the control system and the monitored process. Proper grounding is the second consideration to keep in mind as it can not only reduce the risk of stray currents from interfering with the current loop, but it can also aid in the grounding of the control system itself. Typically, wires of a current loop are grounded at the source end of the loop. And finally you will want to keep load balancing in mind. This reduces the potential of the circuit not being able to drive the devices within the loop. If the loop becomes unbalanced, the source may not be able to develop the full current range, 4 20 ma. This could cause inaccuracy in the control system, which may damage the control system and/or the process. Module 2: PLC Programming Page 6 of 20 Copyright 2016 Veriforce, LLC. All rights reserved. 09/12/2016

7 Knowledge Describe PLC hardware and structure. You ve already read about the fact that control systems are pretty much everywhere and how control systems use end devices to monitor and control a process. Now let s talk about how it makes decisions. The control system makes decisions according to its programming, which is housed in a programmable logic controller, or PLC. The PLC essentially acts as the brains for the control system. But before diving into PLC programming, let s learn what hardware is necessary for a PLC to properly function in a control system and how it all comes together to build a control system. PLC Hardware PLC hardware consists of all the physical pieces required for the process to be monitored and controlled. Some examples may include: Field Terminals The field terminal is the location where end devices are connected to the PLC. They will usually look like a strip of wiring connections, where one side may be input end devices and the other side may be output end devices. I/O Modules Input/output modules, or I/O modules, are the circuit boards that a PLC uses to read the data from its input devices and push changes to its output devices. Processors/Co-Processors Processors are the main control unit, or the brains of the PLC. If present, the co-processor can run subroutines or separate programs and report to the processor. Basically, this is where the PLC makes decisions based upon input data compared to its programming. Communications Hub The communications hub, sometimes called a communications card or commo module, acts like a housing or hub that provides multiple connections and even multiple protocols, or languages, for communicating with other devices. This is what allows the PLC to connect to Supervisory Control and Data Acquisition (SCADA) systems, handheld devices, laptops, or host computers for information display, control, or programming. Power Supply Power supply and distribution is the part of the PLC that provides the PLC and attached components with required electricity. Remember that these are examples of hardware found on PLCs only, not hardware for the whole control system. The system itself will have more hardware to support its end devices. Now, let s see how a control system with a PLC is structured. PLC Structure A control system with a PLC is structured much like a triangle. The PLC will sit at the top collecting data on the process conditions and pushing signals out to control the process and keep it within set-points. The outputs affect the inputs, and the PLC balances between monitoring and controlling the process in between. So the PLC acts as the brains while the end devices act like the eyes and hands. Knowledge Describe the basics of PLC programming. Your brain has programming that controls the basic functions of your body. This natural programming tells your body how to breathe, how to interpret signals from your eyes into images, and how fast your heart needs to pump according to your body s needs. A PLC also has programming or software that tells it how to interpret Page 7 of 20 Copyright 2016 Veriforce, LLC. All rights reserved. 09/12/2016

8 signals from input devices and how to use output devices to control a process according to its set-points. Basically, this programming consists of the set-points for operating conditions in a process and the instructions on how to keep those conditions there. The Basics of PLC Programming The programming language, called ladder logic, is modeled after wiring diagrams, and each line of the ladder logic is called a rung. Although PLC software is modeled after wiring diagrams, PLC software and wiring diagrams differ in function. Where wiring diagrams use a contact to complete a circuit and energize a coil, PLCs use logic, arranged on rungs instead of circuits. And this logic is looking for information such as true or false, on or off, and if/then. The difference is how they work. The wiring would use actual electricity like turning on a light. You flip the switch on the wall, closing the contact and allowing electricity to flow to the light. PLCs look at true or false and on or off in the inputs, so it would examine to see if the light switch was on or off and check its logic to see that it should energize the bulb. PLCs work this way because they use bits of information instead of contacts closing a circuit. So instead of the light bulb directly receiving electricity from the circuit, it receives it from the PLC s command to an output device. This system of relaying information on conditions allows for the use of many types of end devices, and as we already saw, those end devices work by sending and receiving either a digital or analog signal. Take a look at what that ladder logic and symbols may look like when displayed. Remember that these are just examples; your symbols and logic formation may look different. 1. Here you can see the polar ends of the programming called power rails. They represent the ends to a string of logic as opposed to the completion of a circuit as in a wiring diagram. 2. Input end devices appear as a contact but are really tied to a bit of information received from an input device. 3. The lines that the logic sits on are called rungs. 4. Output end devices are usually all the way to the right of the rung and may be end devices or relays. Input Symbols A normally open (NO) input will energize the rung if the bit is on (contact closed). This is also sometimes called examine if closed (XIC). Page 8 of 20 Copyright 2016 Veriforce, LLC. All rights reserved. 09/12/2016

9 A normally closed (NC) input will energize the rung if the bit is off (contact open). This is sometimes called examine if open (XIO). Inputs may be signals from an input end device or a relay bit from another line of logic in the programming. Relay bits are outputs that act as an input on another rung. They are often used to stack logic in a rung that requires conditions that are themselves a process. For example, during the startup of a compressor, the compressor engine will need to be warmed up and running and the oil pressure, engine speed, and coolant temperatures must reach a certain point prior to the compressor actually compressing gas. Bit relays would be used for all those permissive conditions on the logic rung that controls the compression speed. Output Symbols An output or coil will energize if all left-to-right conditions are met on the rung. This one is sometimes called OTE - Output Energize. Outputs may consist of an output end device or bit relay (which may act as an input on another rung). Function Blocks A function block represents a specific set of instructions to the rung. Examples could include: Timer on delay A timer on delay is a function block that delays energizing the output until the specified time has passed. So the output will not energize for the length of the timer. Timer off delay A timer off delay is the opposite of a timer on delay; the timer will not begin until the rung is de-energized. This basically leaves the output on for the length of the timer. Counter - A counter is a function block that will not energize the output until a specific number of counts of a condition have been reached. The condition could be number of revolutions of an engine, number of passes of a conveyor belt, etc. Basically, some process or condition has to occur a specified number of times until the output will be energized. Counters can count up or count down. Page 9 of 20 Copyright 2016 Veriforce, LLC. All rights reserved. 09/12/2016

10 Latch A latch is a formation of logic that stays either on or off when initialized. Think of a push button that momentarily energizes a rung, but when the button pops back up, the rung would no longer be energized. A latch function keeps the rung energized by placing another input that is actually the output or relay bit of some other condition. While that relay bit or condition is energized, the rung with the latch will stay energized. So basically, when you push the button to start the motor, the motor being energized will latch the rung and keep it energized. The output that latches the rung may be on a different line of logic; it does not have to be on the same rung as the latch. Knowledge/ Skill Explain how to use ladder drawings to identify shutdown limits. Shutdown Limits Shutdown limits are set-points that, if reached, will begin a shutdown of the process. While not a unique symbol in the programming, the contact will be tied to an input condition. Shutdowns can also be written as formation blocks that compare a condition to a set-point. These formation blocks may be greater than, less than, or differential. Look at some examples of these logic formations. For all of these examples, assume that the output relay is connected to another line of logic that will begin a shutdown. In the first example, we can see that the shutdown relay will energize if the exhaust gas temperature exceeds 1040ºF. In the second example, the shutdown will energize if lube oil pressure drops below 15 PSI. Page 10 of 20 Copyright 2016 Veriforce, LLC. All rights reserved. 09/12/2016

11 In this example, the shutdown will energize if the difference in pressure between lube oil pressure 1 and lube oil pressure 2 is greater than 10. The subtract function is used to determine the difference in pressure between lube oil pressures 1 & 2. The absolute function is used to get the absolute or true value of the difference between the two pressures. This is in case the subtract function results in a negative number. So if the subtract function results in a -9, the absolute function will re-compute that as a 9. Then the greater than function will use that absolute or true value to determine if the relay will be energized. Knowledge Describe starting/shutdown strings using different shutdown contacts. Starting/shutdown strings are a series of logic, which may continue on multiple rungs, that start up a process. These strings of logic may have shutdown contacts or permissive contacts. Shutdown Contacts Shutdown contacts are conditions that, if satisfied, will cause a shutdown to happen. Shutdown contact can take the form of alarms, like an H 2S or fire alarm, or they can take the form of a condition that, if reached, will begin a shutdown, such as low lube oil pressure or high exhaust gas temperature. Take a look at an example rung by rung. In the first rung, you see a push-button latch which consists of 2 normally open (NO) contacts, the push button itself (an end device), and the motor auxiliary, which allows the rung to stay energized when the motor in rung 3 is running. After the latch, we see 2 normally closed (NC) contacts; one is a push-button stop, and the other is the timer off delay. In the 2nd rung, you can see 3 normally closed (NC) contacts, in this case, alarms. These alarms are considered shutdown contact because they will begin a shutdown if they go off. Along with these alarms is a timer reset bypass push button, which will allow the rung to stay energized by manual means if an alarm is tripped. And at the end of the rung, we find the timer off delay (TOF), which will begin a timer to open its destination contact in the first rung if this rung is de-energized by an alarm. The 3rd rung has the relay input from the first rung, and the motor output. Page 11 of 20 Copyright 2016 Veriforce, LLC. All rights reserved. 09/12/2016

12 Pressing the start button will close the start button contact and energize relay 1, which will close the relay contact and run the motor. Pressing the stop button will open the stop button contact and de-energize relay 1, which will stop the motor. Assume that the 1st rung is energized and the motor is running; if one of these alarms goes off, they will open their contact in the programming and cause the timer to begin. Remember that timer off delays begin to time when they are de-energized. Once the timer is done, the contact in the first rung will open and de-energize the relay that energizes the motor in the third rung. Permissive Contacts Permissive contacts represent conditions that must be met in order for startup to continue. The permissive contacts could also take the form of a no alarm condition. In other words, the condition is that there is no alarm. If the permissive condition is not met, the process will begin a shutdown. Many times the string of logic will include a timer on delay that will buy time for a condition to be reached, such as lube oil pressure. Again, take a look at an example line by line. In the first rung, we can see a normally open (NO) start push button with a latch, which is a normally open (NO) permissive contact, and a normally closed (NC) stop push button. After the on and off buttons, we have 3 normally closed (NC) contacts, the no alarm permissive conditions. After the no alarm contacts, you ll see a normally closed (NC) timer on delay relay and a normally open (NO) lube pressure permissive condition. Let s say that this contact is tied to a pressure switch and will close when lube pressure reaches 15 PSI. And finally on this rung, we see an output relay. For this rung to energize you would have to press the start button and have no alarms and either have the timer delay on timing or the lube PSI contact closed, which means that the lube pressure is at least 15 PSI. The second rung has a relay input and a timer on delay, which will be energized until the time has come to an end. The third rung has a relay input and the output motor. Page 12 of 20 Copyright 2016 Veriforce, LLC. All rights reserved. 09/12/2016

13 When the start button is pushed, the rung will energize, and as long as the normally closed (NC) contacts stay closed, the rung will stay energized and turn on the output relay. The output relay will then close the relay input contacts tied to it, thus energizing the 2 nd and 3 rd rungs. Once the 2 nd rung is energized, the timer will start. Note the normally closed (NC) timer input starts off closed and will stay closed until the timer is done timing. This basically buys time in the PLC programming for the lube oil pressure to build up. If it reaches the set-point (in this case 15 PSI), then the contact on the timer bypass on the first rung will close and keep the rung energized. If lube oil pressure does not reach 15 PSI by the time the timer is done (30 seconds in this case), then the normally closed (NC) timer on delay input in the first rung will open and de-energize the rung. If the rung is deenergized, the startup will cease and the engine will shut down. In other words, when the timer is done it will open the contact and if the lube oil PSI is not satisfied and the contact closed then the startup will fail. Module 3: Precautionary Features Knowledge Describe the different alarm indicators and their advantages and disadvantages. A control system s programming and design will be unique to the process it monitors, but in many cases, they will have alarms to warn process operators when conditions may becoming dangerous. Alarms can be set in control system programming to alert operators when a process condition changes to the specified alarm value. Although alarms don t necessarily prevent a process condition from going out of control, they do alert the operator to the problem so that they may take the proper reaction to control the condition. Alarm indicators can be horns, beacons or lights, or any device that can alert personnel of an abnormal condition, such as a control system s display screens. Printers and loggers can be used to record alarm conditions as they happen. As with any type of feature, the different types of alarm indicators each have their Page 13 of 20 Copyright 2016 Veriforce, LLC. All rights reserved. 09/12/2016

14 own advantages and disadvantages. Horns The main advantages of horns are that they are relatively inexpensive and can incorporate different sounds or tones to convey different meanings. They also don't have to be seen to be noticed. Horns do have a few disadvantages, though, as they can be turned off or fail. They also rely on personnel being able to hear them to notice the alarm. Beacons Beacons or lights have many of the same advantages as horns in that they are also inexpensive and can incorporate different colors in order to convey different alarms. Unlike horns, they don t have to be heard; they only have to be seen to notice the alarm. Just like horns, beacons can be turned off, and they can also fail. Beacons and lights have the additional disadvantage of sight in that they must be seen for personnel to notice the alarm status. Other Alarm Devices Display screens and data loggers can show the alarm even if the condition returns to normal, which is great to keep track of potential problems. They can also display more in-depth information as to which condition or device was or is in alarm. Much like beacons or lights, the disadvantage of display screens or loggers is that someone usually must access an error log or be in a certain location to see the alarm status. They are also usually more expensive to install and maintain. Knowledge Explain examples of ISA shutdowns and shutdown safeguards. Shutdowns are automatic subroutines in the PLC programming or end devices that a control system may have in place in order to prevent a process condition from reaching dangerous levels. The Instrument Society of America (ISA), which is now called the International Society of Automation (ISA), identifies 3 classes of shutdowns. They are class A, B, and C. Class A Class A shutdowns are active at all times; they cannot be bypassed during startup. Examples could include an over speed shutdown or facility combustible gas detector. Class B Class B shutdowns are bypassed for a predetermined length of time during startup. They will become active after their bypass time has expired. For example, a low oil pressure shutdown could be set up as a class B shutdown where it will not react to low oil during start up, but once normal operations have begun, it will start a shutdown if oil pressure falls below the set-point. Depending upon the system, these devices can be bypassed by a timer that will not allow the input contact in the programming to be active in the shutdown string until the timer has expired. They can also be bypassed during startup by a pneumatic device, which prevents the shutdown outputs from being pressurized and able to move until the timer expires. Class C Class C shutdowns do not become active, essentially bypassed, until a set-point has been reached. An example of a Class C shutdown would be a low suction pressure shutdown on a gas compressor. The unit could start up with low suction pressure, but upon loading of the unit, the suction pressure would rise above the shutdown set-point. And if the suction pressure would fall below the shutdown set-point, the system s Page 14 of 20 Copyright 2016 Veriforce, LLC. All rights reserved. 09/12/2016

15 shutdowns would activate. Device Safeguards Veriforce TG CCT 711OP Regardless of the class of shutdown, they can be set up with safeguards to protect against faulty or damaged devices. These safeguards can take the form of a voted shutdown configuration, redundancy in devices, and/or fail-safes. A control system can employ either, all, or none of these safeguards, so always be sure to check the pipeline operator s specification for the individual control system you are inspecting. Voted Some control systems can be configured with voted shutdowns. This means that two or more shutdown devices must sense the same condition to allow a shutdown to be activated. All the devices have to agree or vote to shut down; one alone cannot activate a shutdown. For example, flame detectors could be installed in a voted configuration, where two flame detectors must sense a flame to initiate shutdown; one alone would not cause a shutdown. This configuration is a way to protect a process from shutdown in case of a faulty input. Redundancy Redundancy shutdowns employ two or more devices sensing the same condition. Usually, these devices are in series or in line with each other. If either device detects an abnormal condition, either device can provide the shutdown signal. An example of redundancy would be having 2 oil pressure transmitters reading the same engine s oil pressure. Redundancies are installed to allow a shutdown to take place even if there is a failure in an input device. Output devices can also be set up with redundancies where the actions to begin or complete a shutdown will occur even if one of the required output devices fail. Fail-Safes Fail-safes are the final type of shutdown safeguard that we will discuss. These are devices that will cause a shutdown or alarm if they are disconnected or damaged or if they fail during normal operations. A fail-safe is incorporated into the design of an input or output device that is vital to the control system s process. Fail-safes can also be built into PLC programming, where if the input signal is lost or a condition is not met, an alarm or shutdown will initiate. Devices that do not have this feature are considered to be a non-fail-safe device. Knowledge Describe shutdown procedures requirements. You will need to know your company s procedures and the pipeline operator s procedures regarding training, testing, and recordkeeping as they apply to shutdown systems. This will all be dependent on many variables, so look over the examples below. Think of the following example as a template of what you will need to know to perform this task. Training Training will provide individuals with a basic understanding of, and the necessary skills to carry out, the testing and maintaining of shutdown systems they are expected to maintain. The training can be in the form of on-thejob or classroom methods. It can utilize training aids or publications from manufacturers and gas industry associations. Testing Testing is used to determine and document the effectiveness of training. This may take the form of written tests, oral tests, field audits, performance reviews, simulation exercises, follow-up critiques, or other means. Testing also extends to the testing of devices. Devices may require annual testing or semi-annual training. You must know which shutdown devices in your control system must be tested and the required frequency of the testing. Page 15 of 20 Copyright 2016 Veriforce, LLC. All rights reserved. 09/12/2016

16 Recordkeeping Training and testing do not mean anything if there is not a record of them. You must know how your company or pipeline operator keeps records and which forms are used. Remember, there may be different test record forms for each device based upon the required test frequency and device type. Knowledge Explain process condition alarm and/or shutdown examples. Having read about end devices, PLC programming, and alarms/shutdowns, look at a couple of process condition alarm and/or shutdown examples that you may find in a natural gas compression station. These examples will include the type of end device, its set-point, and the action resulting from the alarm or shutdown. Remember, these are only examples. You will need to know your specific control system s end devices, setpoints, wiring connections, purpose or safeguard, and shutdown steps. 1. End devices 2. Set-points 3. Wiring connections 4. Purpose or safeguard 5. Shutdown steps Engine Fluid Pressures In the first example, take a look at an engine s fluid pressures for a reciprocating natural gas compression engine. The fluid can refer to the lube oil, lube oil coolant, engine coolant, or any other fluid that the engine might need to operate. So in reality, this alarm and shutdown example can be applied to many engine fluid conditions. No matter which fluid we are focusing on, the fluid s operating pressure is vital to fulfilling its purpose in the engine. If the pressure is too high or too low, the engine and some of its components could get damaged. For this example, focus on lube oil, which is the engine s lubricating oil. This oil lubricates and cleans a reciprocating compressor engine s moving parts, such as its cylinders, crankshaft, and bearings. But in order to do this, the oil system has to operate in between the proper setpoints. If the pressure gets too low, it can damage the engine, so an alarm and/or a shutdown has been set into the control system to protect the engine. The alarm or shutdown can be initiated by a pressure switch or by a pressure transmitter that changes an input condition in the PLC programming. Some control systems may have both a switch and a transmitter monitoring the condition. If the oil pressure drops below an alarm set-point of 18 PSI, the pressure switch would trigger and send the signal along its wires through the I/O module and into the PLC programming. The PLC will then sound an alarm to alert operators that the lube oil pressure is low and give them a chance to correct the condition. If oil pressure drops below its shutdown set-point of 10 PSI, the control system will initiate a shutdown of the engine by cutting off fuel and intake air. The control system may also shut off the natural gas that is being compressed. The purpose of the low oil pressure shutdown is to shut the unit down prior to damaging bearings, crankshafts, or other lubricated rotating equipment. Page 16 of 20 Copyright 2016 Veriforce, LLC. All rights reserved. 09/12/2016

17 Combustion/Fire Alarms In the second example, you will take a look at the combustion/fire alarms built into compression stations. These are sensors inside of the compression building that are on the lookout for any flash or sign of flame. Some may also be detecting combustible gases. If one of these end devices senses a fire or combustible gas, they will initiate a shutdown of the compressors. They will cut off the flow of natural gas and begin a shutdown of the compressors. In this case, there is no real set-point in relation to level or pressure; the so called setpoint is whether there is the presence of combustible gas or not. Alarm Annunciation Now that you know you will have to trace a shutdown from condition to reaction, you can learn about alarm annunciations, or where the alarm announces at. You will need to know where alarms in your system announce from and how to respond. We will revisit the fluid pressure example and point out where the alarms will annunciate from. If a low oil pressure alarm sounds or shutdown is initiated, it will annunciate, or sound off, at a few places. Any horns or light beacons that are tied to this condition alarm or shutdown will begin to sound or light up. Additionally the compressor engine s control panel, or Human/Machine Interface (HMI), will show the alarm or shutdown status. These are all local annunciations, as they will only alert operators in the area that can either hear the horns or see the beacons and HMI. If the control system is tied into a Supervisory Control and Data Acquisition (SCADA) system, then the alarm or shutdown will show on any screens that are monitoring the process. This would be a remote alarm or shutdown annunciation, as the controllers would not have to be at the location of the alarm or shutdown to see it. Abnormal Operating Conditions (AOCs) Candidates are required to possess the ability to RECOGNIZE and REACT to the listed AOCs for each task. Be prepared to answer questions concerning additional AOCs that may be relevant. Evaluators may ask questions about AOCs throughout the evaluation. An AOC is defined in 49 CFR and as: A condition identified by the pipeline operator that may indicate a malfunction of a component or deviation from normal operations that may: AOC Indicate a condition exceeding design limits; or Result in a hazard(s) to persons, property, or the environment. Recognize: Unintentional releases, vapors, or hazardous atmosphere could be signs that an abnormal operating condition has occurred. Examples could include, but are not limited to: Blowing gas Puddles Dead vegetation Page 17 of 20 Copyright 2016 Veriforce, LLC. All rights reserved. 09/12/2016

18 React/Respond: Veriforce TG CCT 711OP Proper reactions and/or responses to take in the event of an unintentional release, vapors, or hazardous atmosphere include the following: Eliminate potential ignition sources. Move to safe location. Notify emergency response personnel, as appropriate. Limit access to location, as necessary. Follow appropriate procedures for notification, documentation, and remedial action. Recognize: Material defects, anomalies, or physical damage of pipe or a component that have impaired or are likely to impair the serviceability of the pipeline are abnormal operating conditions. Examples include, but are not limited to: AOC Mechanical damage Evidence of corrosion React/Respond: Proper reactions/responses to take in the event of material defects, anomalies, or physical damage of pipe or a component that have impaired or are likely to impair the serviceability of the pipeline include the following: Determine extent, cause, and potential hazard(s) of defect, anomaly, and/or damage. Mark the location so it may be easily located, as appropriate. Follow appropriate procedures for notification, documentation, and remedial action. AOC Recognize: Failure or malfunction of pipeline component(s) is an abnormal operating condition. Examples could include, but are not limited to: Unintended valve operation Unintended facility shutdown React/Respond: Proper reactions/responses to take in the event of a failure or malfunction of pipeline component(s) include the following: Determine extent, cause, and potential hazard(s) of failure and/or malfunction. Follow appropriate procedures for notification, documentation, and remedial action. AOC Recognize: Loss of communication is an abnormal operating condition. Examples could include, but are not limited to: Power failure SCADA/control systems malfunction during test React/Respond: Page 18 of 20 Copyright 2016 Veriforce, LLC. All rights reserved. 09/12/2016