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Detecting Pipeline Leaks OPEN ACCESS

Accidents Happen. Discovering them Quickly Can Reduce Their Impact.

[+] Author Notes

Vicki Niesen is head of the hydraulic and flow assurance consulting section for DNV GL, while Melissa Gould is a senior engineer for DNV GL. They both work out of Katy, Texas.

Mechanical Engineering 139(11), 34-39 (Nov 01, 2017) (6 pages) Paper No: ME-17-NOV2; doi: 10.1115/1.2017-Nov-2

This article explores technological advancements for detecting pipeline leaks. An ideal leak detection system should not only quickly detect both small and large leaks, but also do so reliably and not trigger false alarms. Operations in gas pipelines can differ quite a bit from those for liquids, so the experience gained in one type of line may not be entirely applicable when changing jobs. Fortunately, computer simulators are increasingly sophisticated, enabling operators to become comfortable handling a variety of situations. In December 2015, the American Petroleum Institute released a set of guidelines (RP 1175), written by a representative group of hazardous liquid pipeline operators, that established a framework for leak detection management. The focus of the guidelines is getting pipeline operators to use a risk-based approach in their leak detection program, with the goal of uncovering leaks quickly and with certainty. The best-case scenario is for leaks to not occur at all, and the industry is making great strides to keep them from happening. The combination of improved technology and risk-based management should enable operators to keep leaks small and contained, and reduce the impact on the environment as much as possible.

THE REPORT from the National Transportation Safety Board made for sobering reading: On a summer Sunday afternoon, a section of a 30-inch pipeline running through a wetland area in southern Michigan ruptured. At first, when operators of the pipeline heard the alarm set off by the drop in pipeline pressure, they thought it was related to the planned shutdown of the line, which they had almost completed. By the time the leak was stopped, some 19,500 barrels of diluted bitumen had flowed into the wetlands and, eventually, a large river.

More than 480 companies operate roughly 209,000 miles of hazardous liquid pipelines in the U.S.

Image: Getty Images

Grahic Jump LocationMore than 480 companies operate roughly 209,000 miles of hazardous liquid pipelines in the U.S.Image: Getty Images

Although the volume of the that oil spill in 2010 was dwarfed by that of such disasters as the Deepwater Horizon oil spill in the Gulf of Mexico a few months before, locally it was a major accident. The final cleanup costs exceeded $750 million.

More than 480 companies operate roughly 209,000 miles of hazardous liquid pipelines in the U.S., with those lines divided among those carrying crude oil, refined petroleum, and highly volatile liquids. Pipelines are the least expensive and safest method of transporting liquid volumes over distances, and the industry can boast that some 99.999 percent of crude oil and petroleum products reach their destination without incident.

Even that enviable safety record means that incidents still occur. Most leaks are quite small— two-thirds of incidents released less than five barrels—but significant leaks happen in spite of the best efforts of operators and engineers. The causes are many. For example, in 2016, about half were due to material, weld, or equipment failure, while another 20 percent were caused by corrosion in the pipeline. And 14 percent were the result of operator error.

Accidents are costly to operators for multiple reasons, from the loss of the goods transported to the cost of repair and remediation and the ill will engendered by the spill among people living along the pipeline. Over the past 20 years, operators have worked to develop technologies to better inspect pipelines to discover leaks as quickly as possible. Some of those solutions work inside the pipeline, others involve external inspection.

More important, however, has been the improved training of pipeline operators, and their empowerment to halt pipeline operations when they suspect a leak. Operators managing a system holistically via a leak detection program should be able to act quickly enough to contain even a large rupture.

Pipelines are an increasingly critical part of the U.S. energy infrastructure. According to the American Petroleum Institute and the Association of Oil Pipe Lines, 16.2 billion barrels of crude oil and petroleum products were delivered via pipelines in 2014 (the most recent year the groups have reported). That is a 20 percent increase in volume from 2010.

Most spills are tiny, and since 2010, 71 percent of onshore pipeline leaks were contained on the operator's property.

In contrast, rail shipments of crude oil have grown precipitously over a similar period, growing by a factor of 16 between 2010 and 2014 before declining since then. But the volumes transported by rail are a small fraction of pipeline transportation—only 382 million barrels in 2014.

Rail transportation of oil is more expensive than pipelines, often by a factor of three or more. And the safety record of oil tankers is punctuated by spectacular and often deadly accidents. Indeed, pipelines are the safest and least expensive means to transport liquid cargo.

But accidents happen. Since 2010, there have been more than 2,800 reported pipeline leaks, and in total they have released some 622,000 barrels. Yet, that total is dominated by the largest leaks—24 incidents, account for half the volume. The largest spill since 2010 released more than 30,000 barrels of ethane into a wooded area in West Virginia; while the accident touched off an explosion and fire, there were no injuries reported, the spill did not reach any waterways, and the pipeline was repaired and returned to service within three weeks.

Of the 24 largest leaks, six were material or weld-related and four were due to equipment failure. But corrosion, operator error, even lightning strikes could cause a major rupture.

From the other end, more than half the reported leaks released 2 barrels or less and accounted for less than 0.16 percent of the total.

In fact, not only are the vast majority of spills relatively tiny, but since 2010, 71 percent of onshore pipeline leaks were contained on the operator's property. Such leaks are the easiest to control and remediate. Another 23 percent were located on the pipeline right-of-way, while 6 percent started on the operator's property but migrated off the property. Leaks located on the pipeline ROW or leaks that migrated off the operator property have the greatest impact on the public and environment.

Pipeline operators have reduced the number and magnitude of leaks in the past 20 years. Since 1999, for instance, pipeline incidents caused by corrosion are down 68 percent, and the number of leaks along the pipeline right-of-way is down 52 percent. Proactive management systems are being implemented beginning at the construction phase and continuing throughout the life of the pipeline, while public awareness of the need to check for possible underground dangers before excavation work has reduced the number of incidents caused by digging by 78 percent since 1999.

Even with those improvements, more work needs to be done. The Pipeline and Hazardous Material Safety Administration, a branch of the U.S. Department of Transportation, has identified material, weld, and construction quality as a major source of leaks during pre-commissioning hydrostatic pressure tests, the first years of operations, and later in the life of a pipeline. PHMSA's findings indicate a need for better quality assurance in the pipeline construction industry.

A proven method for improving quality is through the implementation of a quality management system. The international standard, ISO 9001, is a widely accepted QMS across industries, and there are several QMS standards specific to the oil and gas industry. Pipeline construction is sufficiently unique to require a tailored QMS, with the objective of promoting consistency, safety, and long-term integrity of the pipeline materials and components, as well as the construction, fabrication, and installation processes. A scalable, risk-based, and processbased approach was adopted to allow a QMS to be used to manage the individual quality concerns for each pipeline construction project and reduce the potential for leaks. PHMSA and DNV GL, the Norwegian-based technical institution where we work, co-funded the development of a QMS system for pipeline construction in 2013, with the final report delivered in 2015.

The QMS framework was designed for a wide range of pipeline construction projects, including liquid and gas transmission pipelines and gas distribution lines. Guidance information was created in the form of tables to help users develop individual quality plans for each construction and pre-commissioning activity. The framework and guidance documents can be used as a stand-alone management system or as the quality component in a company's corporate management system. This report was used as input for the American Petroleum Institute recommended practice (RP 1177) for steel pipeline construction QMS, which will be published shortly.

Drones can fly closer to pipelines than manned planes, and can test for emissions of volatile chemicals.

Photo: Eniday

Grahic Jump LocationDrones can fly closer to pipelines than manned planes, and can test for emissions of volatile chemicals.Photo: Eniday

Even with all these measures in place, leak detection systems are critically important, since discovering a leak quickly keeps it small and contained.

An ideal leak detection system should not only quickly detect both small and large leaks, but also do so reliably and not trigger false alarms. It should accurately calculate leak flow and locations, and operate in a variety of non-ideal circumstances, including transient operations and steady state conditions.

Leak detection is often a human issue—there is usually a human who makes the decision to shut off the pipeline.

There are many different leak detection technologies. Typically, pipeline operators employ multiple leak detection methods to improve the effectiveness of their leak detection programs. Some systems provide continuous monitoring while others provide periodic inspection. And they may be designed to work best under certain operating conditions or for detecting a specific type of incident. The most significant differentiator in leak detection systems, however, is whether they operate outside the pipeline or inside it.

External systems include methods for discovering leaks via detecting vapors rising from the spilled liquids through sensors or cameras, or looking for changes in temperature or strain in the pipeline itself via fiber optic cables running alongside the pipe. Tracer chemicals can be injected into the pipe to uncover very small, hard-to-find seeps.

Human inspectors also play a big part. Ground-based surveillance along the right-of-way, either on foot or in a vehicle, is a vital part of nearly all pipeline monitoring systems, and it has the added advantage of identifying neighborhood changes that could affect the consequences of a leak. And aerial surveillance via airplane or helicopter has been a critically important tool for decades.

Now much of this work can be conducted via unmanned drones. Drones allow highresolution repeat visits to the same location to detect existing leaks or evidence of changes in the right of way, which could help identify future leak sites before the leak occurs. Because they can fly closer to the ground than manned aircraft, drones may also be able to conduct not just visual reconnaissance but also testing for volatile chemicals associated with the leaks.

Other systems rely on information from field sensors measuring internal pipeline conditions. The measurements may include pressure, temperature, flow rate, density, viscosity, product interface location, and product sonic velocity. These measurements can be used to detect leaks through such methods as shut-in pressure testing, hydraulic calculations, or monitoring via supervisory control and data acquisition systems.

The American Petroleum Institute published a set of recommended practices (RP 1130) for internal computational pipeline monitoring leak detection methods, which continuously analyze field sensor data. For instance, operators can take field sensor data to calculate a volume or mass balance for the pipeline system or from meter to meter. If there is a shortage in the line balance—that is, there's more fluid entering the pipeline on one end than is exiting on the other—operators will know there is a leak. Similarly, the pressure or flow can be monitored and an algorithm can be applied to the sensor readings to determine if there is an anomaly. Operators can deploy acoustic sensors to listen for the pressure wave that occurs when the pipe wall is compromised and the product escapes through a hole in the pipe.

Readings from several different kinds of sensors can be fed into a real-time transient model. The model then compares the actual pipeline operation reported by the field sensors to a hydraulic model of the pipeline system, and deviations between the continuous hydraulic simulation and field data are used to identify leaks and leak locations. This methodology is more amenable to detecting leaks during transient pipeline operations than some of the other types of computational pipeline monitoring methods.

Even the best technology is not enough when it comes to detecting leaks. The alarms may sound as they should, but operators can misinterpret those warnings if they figure from experience that they are false alarms.

In the end, then, leak detection is often a human issue—there is usually a human who has to make a decision to shut off the pipeline and investigate.

Training is one important factor. Operations in gas pipelines can differ quite a bit from those for liquids, so the experience gained in one type of line may not be entirely applicable when changing jobs. Fortunately, computer simulators are increasingly sophisticated, enabling operators to become comfortable handling a variety of situations.

More broadly, though, pipeline leak detection needs to be managed holistically by companies. In December 2015, the American Petroleum Institute released a set of guidelines (RP 1175), written by a representative group of hazardous liquid pipeline operators, that establish a framework for leak detection management. The focus of the guidelines is getting pipeline operators to use a risk-based approach in their leak detection program, with the goal of uncovering leaks quickly and with certainty. That certainty will facilitate quicker shutdowns of the pipeline, and therefore, minimize negative consequences from the escaping liquids.

Perhaps the most important part of a holistic management program is creating a culture where operators are empowered to act when they feel certain that a leak is occurring.

Clearly, the best-case scenario is for leaks to not occur at all, and the industry is making great strides to keep them from happening. But nothing is perfect. The combination of improved technology and risk-based management should enable operators to keep leaks small, keep them contained, and reduce the impact on the environment as much as possible.

Copyright © 2017 by ASME
Topics: Pipelines , Leakage
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