What Is the Impact of Theft, Accidents, and Natural Losses From Pipelines?

What Is the Impact of Theft, Accidents, and Natural Losses From Pipelines?

This guest blog post is part of a series written by Edward J. Farmer, PE, author of the new ISA book Detecting Leaks in Pipelines. To download a free excerpt from Detecting Leaks in Pipelines, click here. If you would like more information on how to purchase the book, click this link.

 

Last month’s blog produced uncommon interest, some from old friends and some from persons newly engaged in struggling to preserve assets. One had experience with military operations in Iraq. They understood that theft is not just benign self-interest but may be conducted with the intent of deliberate harm.

Sometimes such operations disclose information about operator capabilities and requirements. Some deliberately embarrass the entities dedicated to preventing such incursions. Perhaps the message is that petroleum is valuable in many contexts and worthy of active care. In some locations and situations our confidence that the pipe we buried last year is still doing just what we intended may be unrealistically naïve.

Possibly the world leader in organized anti-theft effort is Pemex. Monitoring has been in-place on some of its systems for well over a decade and the results have been amazing. Initially some systems were looked at more as free distribution points where “the people’s petroleum” was delivered. Of course, that was never quite the intent, and there are many stories. This year, some estimates put Pemex losses to theft at over USD$1.5 billion. Applying its highly successful aggressive monitoring and interdiction program could, based on actual experience, eliminate most or even all of those losses.

 

If you would like more information on how to purchase Detecting Leaks in Pipelines, click this link. To download a free excerpt from the book, click here.

 

The earliest anti-theft efforts began on lines known to be heavily attacked. Monitoring could detect a tap and its location within minutes. Special pre-positioned response units would be notified and would deploy into tactical positions. Usually the theft operation’s people and equipment could be apprehended. After a few such interdictions word got out. Theft from targeted areas declined to zero. Unfortunately, theft continued unabated in unmonitored areas. The prospect of getting caught diminished enthusiasm, but actual interdiction seemed necessary to completely discourage these operations.In some countries, enabled and exacerbated by corruption or government dysfunction, theft seems to have become normal. It can be hard to curtail these situations once they are firmly started. The spread of corruption seems systemic and the impact severe, not just from damages to the facilities and theft of the product of the producers, but also to the people and businesses that rely on normal access to these products. The fact the petroleum is stolen does not make it free to users – in fact the incursions can produce scarcity, increasing user-level cost.

In these matters, automation helps. Theft can, with appropriate effort, be curtailed or limited. Rational economic outcomes restore some sense of markets and order which tends to normalize and enhance business in the surrounding communities. The power and wealth associated with these activities can be limited or eliminated by fast and decisive action. Even sophisticated theft mechanisms can be identified by appropriate monitoring methods and equipment. Technology moves the endeavor from a conflict of wills to the effective use of resources.

In one country, a pipeline that had been a substantial theft target was estimated to have perhaps 16 active theft taps at any given moment. Losses were in the many thousands of dollars per hour. A monitoring system was deployed, resulting in more than 20 apprehensions over the first few days. Theft attempts continued, but there were far fewer of them. Over a couple of months, theft on the entire pipeline was brought to, and maintained at, zero. Essentially, getting caught stealing oil involved sufficient consequences to concern these thieves, and the chance of getting caught was perceived to be very high. Together, these issues made theft an unattractively expensive activity.

So, technology, along with a determined and ethical attitude, can control these things. It isn’t even all that hard once it is productively organized and initiated. Safety is enhanced. Profitability is enhanced, security along the pipeline is enhanced, and business strength in the region improves – all good things for a successful and organized society.

In this situation, as is often the case, the pipeline crossed a substantial distance covered by a double-canopy forest. People living in the region had long ago discovered the value of the product in the pipeline both for their own use and as a product that could be sold or traded to others. Even with air surveillance it was difficult for the operator to observe the alignment. Roads in and out of the pipeline alignment were available and well known. The monitoring program amounted to detecting the occurrence and location of a leak, transmitting the data to a rapid response force, and then monitoring the progress of the withdrawal until the response team arrived. If the withdrawal terminated early, the response team and their equipment could be re-routed to an exit-way. The results of the project, before and after the onset of monitoring, are shown in the graphic below.

 

Uncontrolled losses from pipelines – be it from accidents, equipment failures, or theft – is not a benign irritation. It can dramatically affect profitable operations and the sustained interest of investors. It can damage livestock and crops. It can initiate unimaginably intense fires and explosions that destroy lives, homes, and businesses along the pipeline. Surrounding businesses, such as fishing and agriculture, can be profoundly affected. Sometimes the damage is truly accidental, sometimes it is the result of poor design or changing operating conditions. Sometimes it results from inadequate maintenance practices such as corrosion control. In any case, the operator’s future may be improved or enhanced by responsible operation and aggressive mitigation. The public may be willing to excuse accidents but will often want to punish whatever they perceive as negligence.

Did you miss the other blogs in this series? Click these links to read the posts:

How to Optimize Pipeline Leak Detection: Focus on Design, Equipment and Insightful Operating Practices
What You Can Learn About Pipeline Leaks From Government Statistics
Is Theft the New Frontier for Process Control Equipment?

About the Author

Edward Farmer has more than 40 years of experience in the “high tech” part of the oil industry. He originally graduated with a bachelor of science degree in electrical engineering from California State University, Chico, where he also completed the master’s program in physical science. Over the years, Edward has designed SCADA hardware and software, practiced and written extensively about process control technology, and has worked extensively in pipeline leak detection. He is the inventor of the Pressure Point Analysis® leak detection system as well as the Locator® high-accuracy, low-bandwidth leak location system. He is a Registered Professional Engineer in five states and has worked on a broad scope of projects worldwide. His work has produced three books, numerous articles, and four patents. Edward has also worked extensively in military communications where he has authored many papers for military publications and participated in the development and evaluation of two radio antennas currently in U.S. inventory. He is a graduate of the U.S. Marine Corps Command and Staff College. He is the owner and president of EFA Technologies, Inc., manufacturer of the LeakNet family of pipeline leak detection products.

If you would like more information on how to purchase Detecting Leaks in Pipelines, click this link. To download a free excerpt from the book, click here.

Connect with Ed:
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Is Theft the New Frontier for Process Control Equipment?

Is Theft the New Frontier for Process Control Equipment?

This guest blog post, the third in a series, was written by Edward J. Farmer, PE, author of the new ISA book Detecting Leaks in Pipelines. If you would like more information on how to purchase the book, click this link. To download a free excerpt from Detecting Leaks in Pipelines, click here. Did you miss the first two blogs in this series? Read them here and here.

 

In the mid-1980s, I demonstrated an early-stage leak detection product to a Latin American company before extensive field testing had been completed. The test section ran from a refinery over some hills, into a storage and distribution point, 80 kilometers or so.

Monitoring was set up at the refinery and leaks were simulated near the center and at the far end of the line. Simulation involved opening a valve into some storage: a vacuum truck in the center and a storage tank at the end. Detection was reliable, but events not associated with known tests were also alarmed. An impression was being created that the system was not differentiating between leak conditions and noise. A somewhat animated discussion developed among the official observers and monitoring was curtailed for the day.

The next day, one of our proponents announced that the line had just been flown and an area discovered in which a road had been cut into the hillside adequate for large tanker trucks to reach the pipeline. A queue of tanker trucks was seen waiting to fill at an ad hoc and unmetered service point.

This was not just theft, it was planned, organized, and even timed to get the desired product into the appropriate truck, all without detection. This operation had apparently been routine for years and was well-known to the nearby diesel-consuming businesses.

Theft is rarely undertaken with the same care and process as company standards prescribe for normal operation. A crew, such as this one, may excavate to gain access to a pipeline and then perform a hot-tap in the usual way. Connections to the tap are seldom made in accordance with any known piping standards which, of course, eliminates the safety practices.

Most taps are not maintained. Care is not taken to prevent environmental damage which often appears as unusual degradation in the area around the taps. That used to be the primary clue that a theft operation has been under way. Automatic monitoring, of course, enables a team to respond directly to the theft site while the theft is taking place.

One can only wonder how such an egregious difference in produced vs. received diesel could have gone undetected under these circumstances for so long. In fact, many aspects of the operation were hard to understand. It was made clear to me that the details were none of my business, but after a few months of operator-internal issues our equipment was purchased to monitor the pipeline.

If you would like more information on how to purchase Detecting Leaks in Pipelines, click this link. To download a free excerpt from the book, click here.

Anti-theft solution benefits

Reduced theft would pay for the system that was deployed in perhaps a few hours, a day or two at the most. As it turned out, though, anti-theft equipment, regardless of payout, was not a simple sale. There were often “other issues” that had to be settled.

Years later, on a project in Southeast Asia, startup of a system monitoring an investor-funded and operated pipeline detected and located leaks at the same site over and over again. Apparently the builder was intimidated into “not noticing” line losses, and communication channels were “unreliable” with a location necessary to produce complete flow balance reports.  One could write a much longer story about life inside and outside of security fences, trusting people, damage that can result from inept line penetration, and all sorts of stuff like that.

Some taps are small, simple, and frighteningly fragile. An accidental footstep can initiate leakage that could go on for hours or days.

All of this is easily detected with modern leak detection and was detectable by properly operated equipment of the day. Loss of a fraction of a percent of line flow rate can be detected and located within meters in very short periods of time.

In a contemporary anti-theft operation for a motivated operator, 44 leakage events were detected over a week-long period – resulting in the arrest of most of the perpetrators. This effort, according to the operator, reduced the worst theft environment in their system to being theft-free.  Again, a pittance cost was amortized in minutes or, at the most, hours.

Top pipeline theft countries

One can wonder: Does this sort of thing really happen? It depends on where you are. Arranged by theft volume the top five theft countries are Nigeria, Mexico, Iraq, Russia, and Indonesia. Theft in these areas is generally thought to be increasing. One study concluded that theft was increasing at about 30 percent per year.

When the size of the operations in these areas is considered it is likely that more oil is being lost to theft than all forms of leakage or accidents. In at least one country it has been estimated that the value of oil stolen from the system actually exceeds that of oil sold. I don’t know that any study has produced a careful and detailed audit of this situation over time but even short-term, operations-focused investigations generally show a huge, preventable, and extremely expensive problem that discourages investment.

Sometimes substantial effort goes into establishing and operating invasive and hazardous taps. The excavation and piping facilitates extraction and use of the fluid but generally at the expense of people and industry along the pipeline. There are stories going back decades of massive damage caused by such clandestine operations.

Thieves have become much smarter over the years. In the past, a thief would hot-tap a line and use conventional, often exposed, piping to fill tanker trucks which would then take the product to market. Now, the business end of theft seems to have become far more subtle, and the technical aspects far more complex.

Compromised process control equipment

For example, there are now instances of process control equipment being used to inject water into a pipeline downstream of the extraction point so that operation appears normal during the theft withdrawal. All of this, of course, can be detected and located with appropriate monitoring.

It has been suggested that proper monitoring has sometimes been limited in order to facilitate theft, and sometimes implemented to control it, or at least modify the business operations involved. I really don’t know; most of the information about such things is anecdotal.

Nonetheless, if pipeline accident rates were increasing 30 percent per year there would be motivation and action. Theft operations can certainly be safety issues, but considering the amount and growth rate of product loss it is also becoming a factor in successful and profitable operation. It is thus worthy of concern as a significant operating issue.

Did you miss the first two blogs in this series? Read them here and here.

About the Author
Edward Farmer has more than 40 years of experience in the “high tech” part of the oil industry. He originally graduated with a bachelor of science degree in electrical engineering from California State University, Chico, where he also completed the master’s program in physical science. Over the years, Edward has designed SCADA hardware and software, practiced and written extensively about process control technology, and has worked extensively in pipeline leak detection. He is the inventor of the Pressure Point Analysis® leak detection system as well as the Locator® high-accuracy, low-bandwidth leak location system. He is a Registered Professional Engineer in five states and has worked on a broad scope of projects worldwide. His work has produced three books, numerous articles, and four patents. Edward has also worked extensively in military communications where he has authored many papers for military publications and participated in the development and evaluation of two radio antennas currently in U.S. inventory. He is a graduate of the U.S. Marine Corps Command and Staff College. He is the owner and president of EFA Technologies, Inc., manufacturer of the LeakNet family of pipeline leak detection products.

If you would like more information on how to purchase Detecting Leaks in Pipelines, click this link. To download a free excerpt from the book, click here.

Connect with Ed:
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What You Can Learn About Pipeline Leaks From Government Statistics

What You Can Learn About Pipeline Leaks From Government Statistics

This guest blog post, the second in a series, was written by Edward J. Farmer, PE, author of the new ISA book Detecting Leaks in Pipelines. If you would like more information on how to purchase the book, click this link. To download a free excerpt from Detecting Leaks in Pipelines, click here. Did you miss the first post in this blog series? Click this link to read it.

 

When designing safety and protection systems, it is always useful to understand the nature of the threat. To that end, the U.S. Department of Transportation (DOT) has accumulated data and statistics regarding leaks on regulated pipelines. Some years ago, my company, EFA Technologies, used DOT data to explore the causes of pipeline leaks over a 10-year period. The results of that work were published and are included in Detecting Leaks in Pipelines as Appendix I.

The DOT categorized reported leaks into six specific categories plus one labeled “Other.” Over the 10-year study period there were 1,901 leaks that required reporting for one reason or another. This chart shows the causes distributed across the classification categories:

The “Other” category includes just over a quarter of the accidents, indicated to be the result of vandalism, gasket failure, “bullet hit the pipe” and a diversity of even more obscure issues which serve to remind us that it is hard to foresee and plan for everything. Appendix I in the book includes a lot more detail than we can explore here. The inescapable conclusion is that while many leaks can be prevented by planning, design, construction, maintenance, and management there are many that cannot.  Damage by others, for example, was the cause of nearly three-fourths of the “Outside Force” accidents.  In a subsequent paper (also in Detecting Leaks in Pipelines), I explored the higher accident frequency at “crossings,” places where a pipeline crosses some other right-of-way such as a railroad, highway, or utility easement.

If you would like more information on how to purchase Detecting Leaks in Pipelines, click this link. To download a free excerpt from the book, click here. Did you miss the first post in this blog series? Click this link to read it.
Clearly, some of the categories can be mitigated by the operator companies. A lot of thought, for example, goes into specifying the metallurgy of line pipe and the anti-corrosion measures that are appropriate on both the inside and the outside. Pipelines, though, often move past their initial purpose and past their design life.  Changing the use of a pipeline, or the fluid in it, or the rate-of-flow, or even features of the installation environment, may suggest different design criteria than what were originally appropriate, perhaps even optimal.

Cost of leaks

The accident statistics investigation also explored the cost of leaks. As one would expect, nearly any leak results in costs in the tens of millions of dollars, and seems to be increasing over time. About a third of the documented costs involve property damage and cleanup.  The rest go to fines, legal costs, and other legally mandated assessments. During this period the president of a major pipeline operator observed that while the costs associated with any accident are significant, the loss of good will by those who will not forget what happened is beyond calculation. Another industry icon, Constantine Nicandros, then president of CONOCO Inc, observed, “Every company in this business may be judged by the performance of the worst among us.” He went on to say that, “We can be sure that if we do not police ourselves, others will be more than happy to take up the task. I believe that in the days ahead our industry will thrive if we do a better job of listening to the public and earning their trust.”

These observations by these industry leaders help answer the question, how important is pipeline safety? They also suggest an analysis of what is required by mandate or regulation may be a subset of what is truly necessary or desirable.

These are old data but were stable during the study period and a couple of decades around them. Only the accident cost showed an upward trend. Appendix I shows a lot more detail.

Theft remains a concern

When this study was done, theft was involved in only a small number of operations. In the U.S., that’s probably still true. In many parts of the world, though, theft is a significant safety and financial hazard. If one were to revisit this study it would be very interesting to assess the impact, if any, of the increase in theft that we see in some parts of the world.

This study is a good place to start evaluation of the risks confronted by any pipeline operation. It provides a good list of threat causes and an assessment of the significance of each of them. While things change over time, and while they vary in each situation, these are factors that should be considered, but as time moves along, perhaps not all the factors that could be involved. Fortunately, there are processes for analyzing risk and some features of those will be discussed in a future blog post.

Did you miss the first post in this blog series? Click this link to read it.

About the Author
Edward Farmer has more than 40 years of experience in the “high tech” part of the oil industry. He originally graduated with a bachelor of science degree in electrical engineering from California State University, Chico, where he also completed the master’s program in physical science. Over the years, Edward has designed SCADA hardware and software, practiced and written extensively about process control technology, and has worked extensively in pipeline leak detection. He is the inventor of the Pressure Point Analysis® leak detection system as well as the Locator® high-accuracy, low-bandwidth leak location system. He is a Registered Professional Engineer in five states and has worked on a broad scope of projects worldwide. His work has produced three books, numerous articles, and four patents. Edward has also worked extensively in military communications where he has authored many papers for military publications and participated in the development and evaluation of two radio antennas currently in U.S. inventory. He is a graduate of the U.S. Marine Corps Command and Staff College. He is the owner and president of EFA Technologies, Inc., manufacturer of the LeakNet family of pipeline leak detection products.

If you would like more information on how to purchase Detecting Leaks in Pipelines, click this link. To download a free excerpt from the book, click here.

Connect with Ed:
48x48-linkedinEmail

 

How to Optimize Pipeline Leak Detection: Focus on Design, Equipment and Insightful Operating Practices

How to Optimize Pipeline Leak Detection: Focus on Design, Equipment and Insightful Operating Practices

This guest blog post, the first in a series, was written by Edward J. Farmer, PE, author of the new ISA book Detecting Leaks in Pipelines. If you would like more information on how to purchase the book, click this link. To download a free excerpt from Detecting Leaks in Pipelines, click here.

 

My new ISA book, Detecting Leaks in Pipelines, has generated quite a bit of interest and so I thought it would be useful to share some of the thoughts and feedback from other professionals. In this first in a series of blog posts, I plan to pass along the substance of various discussions and I’d like to invite your thoughts and input on what might be useful and relevant to your work.

In most petroleum and chemical processing units leaks generate a lot of urgent attention. Years ago, while sitting in a desk on the third floor of the engineering building in a large refinery we were all shocked with the rattling of our windows and the rising smoke from what we all knew as the lube oil unit. There was no doubt something untoward had begun and was continuing, and each of us did our jobs and followed directions. The damage was contained in a fairly small area and there were no injuries. Were we lucky?  Maybe, but this was a large and extremely responsible company with a good sense of organization and safe practice.  Sure, it was an emergency, but just as certainly it was handled according to plan.

While there were some bad moments during, and a few months of disruption after, life went on, and the company’s position in the community remained intact. The company was viewed as competent, responsible, and in-control. That was a long time ago, but I have long remembered the importance of those lessons.  The public will tolerate a refinery in its “backyard” when the refinery demonstrates community responsibility, good and safe working practices, and, above all, control of its operations.

Discovering an event such as this one is pretty easy in a refinery. Something like 3,000 people worked there and the process unit was near a major access road through its center. The fire was visible for miles in daylight. There was a plethora of indications this situation was of significant and urgent attention, and that attention minimized the damage and the social impact.

If you would like more information on how to purchase Detecting Leaks in Pipelines, click this link. To download a free excerpt from the book, click here.
Many processing and transportation facilities, pipelines and lease equipment, for example, are automatically operated at locations rarely visited without specific purpose.  Remote monitoring of such locations can minimize event impact, and can demonstrate a competent and “in-control” industry with the safety of its workers, the public, and the environment clearly in its thoughts.

Additionally, demonstration of responsible operation can forestall the acceleration of regulation.  If, when needs are recognized, an operator implements appropriate and effective mitigation and containment procedures it is more likely safety practices will proceed in a rational and industry-relevant way.  Everyone is familiar with the impact of best intentions implemented under dire circumstances spawning unintended consequences.

Leak detection rarely prevents accidents. Good design, good equipment, and insightful operating practices do that.  Leak detection can, however, advise of conditions approaching hazard limits, and can quickly communicate the occurrence, location, and size of a leak.  This can initiate a timely and appropriate response to the right place, and assist in organizing the support logistics involved in mitigation and containment.

There are also other motivations. Theft is a growing problem is some areas.  It creates safety problems by incompetent or inappropriate taps into the pipeline which easily go wrong, producing explosions, fire, property damage, and injuries. These thefts also involve product loss, substantial amounts in some places. As the money to be made from stealing oil produced by other people increases, thieves become ever cleverer about avoiding timely discovery. Tricks, such as injecting water to replace the stolen oil, challenge all but well-designed leak detection systems. In one area, the operator caught several thieves. Word got out and quickly, the prospect of being caught during a theft operation discouraged the thieves who apparently moved onto less surveilled territory. The operator was asked about the payout time on the leak detection project and equipment and he replied, “Oh, perhaps a few minutes.”  Oil theft at that level is a lucrative business, but only when you don’t get caught!

Sometimes an interest in enhanced safety comes from changes in operation. Some pipelines change purpose over their lifetimes which can also change the anticipated risk. In one installation line velocity decreased due to low production rates which resulted in the accumulation of corrosive sludge and solids at low points. This increased the corrosion rate of already aging pipe, which ultimately required some rethinking of the maintenance program as well as the focus of the leak detection effort.

Think over the condition, use, and exposure of your facilities, and consider the value of being in control of an accident instead of just wishing you were. Consider your safety-oriented practices and tools and evaluate the benefits.

About the Author
Edward Farmer has more than 40 years of experience in the “high tech” part of the oil industry. He originally graduated with a bachelor of science degree in electrical engineering from California State University, Chico, where he also completed the master’s program in physical science. Over the years, Edward has designed SCADA hardware and software, practiced and written extensively about process control technology, and has worked extensively in pipeline leak detection. He is the inventor of the Pressure Point Analysis® leak detection system as well as the Locator® high-accuracy, low-bandwidth leak location system. He is a Registered Professional Engineer in five states and has worked on a broad scope of projects worldwide. His work has produced three books, numerous articles, and four patents. Edward has also worked extensively in military communications where he has authored many papers for military publications and participated in the development and evaluation of two radio antennas currently in U.S. inventory. He is a graduate of the U.S. Marine Corps Command and Staff College. He is the owner and president of EFA Technologies, Inc., manufacturer of the LeakNet family of pipeline leak detection products.

If you would like more information on how to purchase Detecting Leaks in Pipelines, click this link. To download a free excerpt from the book, click here.

Connect with Ed:
48x48-linkedinEmail

 

How to Use Plant-Wide Feedforward for More Flexible and Efficient Production

The following tip is from the ISA book by Greg McMillan and Hunter Vegas titled 101 Tips for a Successful Automation Career, inspired by the ISA Mentor Program. This is Tip #101.

The pressure to reduce inventories, coupled with changing market demands and fluctuations in raw material and energy prices, requires a process plant to be able to respond quickly to maintain optimum operation. To most efficiently support changes in production rate or product grade, flows must change in unison throughout the plant. Feedback loops cannot do this. Feedback loops will eventually arrive at the right flows but time will be lost and product quality may suffer in the interim. Feedforward control allows the plant automation system to respond immediately in unison to changes in production rate or product grade. During normal production, feedforward control can also compensate for composition, pressure, and temperature upsets before they have a significant impact on production rates or product quality.

industrial laser with sparks flying around

Plant-wide feedforward can preemptively move a plant to match the flows and conditions (e.g., temperature and composition) of all important process streams on a process flow diagram (PFD) for a given product and production rate, thereby maintaining material, component, charge, and energy balances. Plant-wide feedforward flow control provides the fastest and least disruptive transition to new operating conditions.

Traditionally, feedforward has been implemented on just the most important loops in the most critical unit operations. The benefit is localized and the other loops are left to fend for themselves. The result is that the plant does not fully reach the new production rate or product grade until the changes in process conditions propagate from one end of the plant to the other. The plant does not settle out until each of the unit operations settles out. For feedback control, the settling time of a loop is at least four deadtimes, based on tuning practices. The total settling time can be roughly estimated as the sum of the settling times of the loops in series. In contrast, plant-wide feedforward control can reduce the plant settling time to the deadtime and settling time of the slowest loop for perfect and imperfect feedforward, respectively. Perfect feedforward requires no feedback correction.

Feedforward control has the ability to provide the preemptive correction of any disturbance that can be measured. The disturbance can be due to maintenance, abnormal conditions, operator actions or sequences, or to changes in load (feed), raw materials, recycle streams, utilities, and/or environmental conditions. The source of sequences can be the batch manager, sequential function charts, and safety instrumentation systems. In feedforward control, a disturbance is measured, filtered, multiplied by a feedforward gain, passed through deadtime and lead-lag blocks for dynamic compensation, and used as the PID output with the proper direction (reverse or direct).

To get the maximum benefit from feedforward, the correction must arrive at the same point in the process and at the same time as the disturbance, and with an effect equal but opposite to the disturbance. If the feedforward signal arrives too soon, the initial process response will be in the opposite direction of the final response to the disturbance. The result will be an inverse response. Feedback action will try to compensate for the feedforward correction, resulting in a second peak. If the feedforward arrives too late, a second disturbance will be created by feedforward action. In either case, an oscillation will develop and the error from the disturbance will be increased.

Concept: Feedforward is the most productive of the advanced PID process control techniques. Feedforward control becomes more important when production rates or grades are frequently varied to meet changing market demands or to take advantage of changes in energy costs.

Details: To avoid inflicting disturbances on a loop and other loops, filter the feedforward signal so that noise does not cause the PID output fluctuations to be larger than the control valve or variable frequency drive deadband. Set the feedforward gain to ensure that the magnitude of the feedforward signal is correct. The feedforward gain must provide a corrective change in PID output equivalent to the effect of the disturbance. Pay attention to engineering units and scales when computing the feedforward gain. To prevent a disturbance from arriving early, set a deadtime in a deadtime block that is the deadtime in the disturbance path minus the deadtime in the correction path. Note that the paths must be to the same point in the process. If the disturbance arrives before the corrective signal due to excessive deadtime in the correction path, nothing can be done via dynamic compensation to make the feedforward signal arrive sooner.

industrial automation, careers, process automation, process industries, manufacturing, instrumentation, process control, control engineering, manufacturing automation

There is no function for undoing deadtime. If the lag in the feedforward path is smaller than the lag in the disturbance path, add a lag to the feedforward dynamic compensation. If the lag in the feedforward path is larger than the lag in the disturbance path, add a lead time to the feedforward dynamic compensation. Use a feedforward summer and provide a visible and adjustable ratio for flow feedforward (Tip #93). If it can be done while meeting production goals, ramp production rates down as quickly as possible when energy costs are high (e.g., the cost of electricity and cooling water during the heat of the day).

Maximize production rates when utility costs are low. For parallel trains of unit operations such as crystallizers and heat exchangers, maximize the feed to the more efficient units as decided online by inferential measurements of overall heat transfer coefficients (UA). For continuous crystallizers, use an inferential measurement of UA to determine when a crystallizer should be defrosted and the flow divided among the remaining crystallizers. Use a similar strategy for catalyst or ionic bed regeneration. When units are started up, bring units to operating conditions based on feedforward ratio control before switching to feedback control.

Watch-outs: When the feedforward signal goes to a valve, the feedforward gain is inversely proportional to the slope of the nonlinear installed valve characteristic; that is, the valve gain. Signal characterization in the DCS can be used to compensate for the nonlinearity (Tip #84) but the installed characteristic is often not known exactly and varies with pressure and frictional losses.

Exceptions: If the feedforward deadtime is larger than the loop deadtime, feedforward will do more harm than good and should not be used until changes in the final control element or secondary process can be made to decrease the feedforward correction path deadtime or increase the disturbance path deadtime. The disturbance often originates from another loop (such as level) or from an operator-initiated change. A deadtime in the operator initiated setpoint change can be inserted to delay the entry of the disturbance into the process. The disadvantage of the delayed action of a level loop or operator change is often less important than the disadvantage of a feedforward arriving too late.

Insight: The use of plant-wide feedforward control can move a plant quickly and smoothly for more flexible and efficient manufacturing.

What are the Benefits of Identifying Deadtime and Ramp Rate

The following tip is from the ISA book by Greg McMillan and Hunter Vegas titled 101 Tips for a Successful Automation Career, inspired by the ISA Mentor Program. This is Tip #89.

In Tip #70, we learned that deadtime was the key to loop performance. The Control Talk blog The ABCs of Controller Tuning describes how tuning settings can be reduced to a simple function of deadtime. The InTech article PID Tuning Rules Factory control roomand the article’s online appendices describe the fundamental relationships between deadtime, performance, and tuning.

Fortunately, deadtime is the easiest aspect of process dynamics to identify. The deadtime is the delay between a change in control output and the beginning of the resulting change in the process variable. To ensure that it is a process response and not noise or coincident unmeasured disturbances, you must ensure that the response is in the right direction and is sustained.

Once measured and confirmed, the deadtime is used by a deadtime block to create an old PV from a new PV at the block input. The ΔPV added to the current PV is a predicted PV on deadtime in the future, which opens up all sorts of opportunities (Tip #90). Convert the ΔPV to a percent of measurement scale. If you divide the Δ%PV by the deadtime (θo), you have a continuous train of ramp rates (Δ%PVt) that are updated with every execution of the block. The ramp rate can be used for a smarter integral mode and feedforward action (Tip #92). If you divide this ramp rate by the change in controller output, you have the integrating process gain (Ki) (Equation 1) that can be used for controller tuning, rapid modeling, and adapting dynamic models online (Tip #98). If you divide a steady-state open loop gain (Ko) by the integrating process gain, you have the open loop time constant (τo) for a self-regulating process (Equation 2). The open loop gain (Ko) can be approximated as the ratio of percent process variable (%PV) to the (%CO) controller output at the setpoint. If you have knowledge of another operating point (%PVo, %COo) or know the %PVo when the controller output is zero (%COo=0), you can subtract these other operating point values from the values at the setpoint to create deviation variables that give a more accurate open loop gain (Equation 3).

Tip89-Equations

The ramp rate for level can be used to create a rate of change of vessel level or weight for an inferential measurement of flow. The deadtime block must use a deadtime much larger than the process deadtime so that the ΔPV, and consequently the ramp rate, is much larger than noise.

Concept: The identification of deadtime and ramp rate opens up a wide spectrum of opportunities. The use of a deadtime block creates a continuous train of ramp rates as fast as the block executes.

101 Tips for a Successful Automation CareerDetails: Use auto-tuner software, adaptive tuner software, or the rapid modeler composite template library block to identify the deadtime, ramp rate, and the integrating process gain or open loop gain, and open loop time constant for any large change in controller output or feedforward signal. Use a noise band to screen out insignificant changes. Make sure the identifier is looking for a change in the right direction. Use a time interval much larger than the deadtime to increase the signal-to-noise ratio when computing the ramp rate for the rate of change of level and weight for an inferential flow measurement. Also increase the time interval when computing the slope of batch processes for batch end point and cycle time optimization (Tip #96). For inverse response, the deadtime will be increased automatically and the ramp rate measured will be based on the response in the right direction. The method can be used to identify the dynamics between any process input and process output. Use the simple relationship between a true integrating or near-integrating process and a self-regulating process to convert between an integrating process gain and steady-state dynamics; that is, open loop gain and open loop time constant. A deadtime block in the identification of the ramp rate and the subsequent integrating process gain is essential to improve the signal-to-noise ratio and provide a continuous train of values. Use the identified dynamics to adapt tieback models (Tip #98). Use deviation variables to get a more accurate open loop gain. For an integrating process or runaway process models, subtract a load equal to normal controller output from the current controller output. This load stops the ramp or divergence when the current controller output balances out the load.

Watch-Outs: The deadtime and ramp rate should only be identified for setpoint changes and output changes in manual, remote output, and output tracking mode that are large enough to make noise and unmeasured disturbances negligible. The deadtime cannot be identified in automatic, cascade, or remote cascade mode if there are no setpoint changes or no injection of a known change in controller output.

Exceptions: Dynamics cannot be identified accurately for processes with a deadtime approaching the execution time of the deadtime block or the identification module.

Insight: The identification of deadtime and ramp rate can provide tuning, rapid modeling, and future values for smart reset, feedforward, and setpoint responses.

Rule of Thumb:
Use a deadtime block to create a continuous train of old PV that when subtracted from the current PV and divided by the deadtime creates a continuous train of ramp rate updates as fast as the deadtime block execution time.

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