June 6, 2019

Stressed Out: What Causes Pipelines to Degrade

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Shale gas production over the past several years has caused a flurry of activity and generated a significant amount of physical development in the Commonwealth. Today, Pennsylvania is home to thousands of natural gas wells and hundreds of miles of new as well as previously existing pipelines that gather and transport natural gas. These pipelines, though typically made of steel because of its strength, can significantly degrade over time. A recent study analyzed the stresses that pipelines endure and how these stressors may cause the steel used to make the pipes and their fittings fail.

There are three types of pipelines used in the process of transporting natural gas in its gaseous or liquid state. The first type, which is used to transport gas from the point of extraction, is the gathering line. Gathering lines are relatively small pipes that are used to move natural gas from the well pad to storage facilities. Transmission lines are large diameter pipes that move natural gas from well sites to either natural gas plants for industrial or energy generation use or storage to be used later in homes or businesses. If the natural gas is intended for consumer use, then it will be shipped to homes and businesses via distribution lines. The size, type (gathering, transmission, or distribution), and configuration of the pipeline can affect how it degrades over time. Because of the size of the lines, the volumes they carry, the distances they traverse, and the risks associated with a malfunction, the industry experts are particularly concerned with the endurance of transmission lines over time.

Stressors

A recent study reveals that despite high levels of reliability, the greatest threat to the health and functionality of transmission lines is corrosion. Because many of the lines are underground, they can be subjected to environmental corrosion. This corrosion is considered a, “form of cancer of metallic pipelines”. Transmission lines can also suffer from chemical corrosion caused by soil and/or atmospheric conditions. The presence of certain chemicals or acidity levels in soil can cause the steel pipes to corrode more rapidly. Natural gas itself can also cause the metallic pipe to corrode because some of the chemicals carried with the natural gas has corrosive properties.

In addition to corrosion, transmission (and other natural gas pipelines) can face shifting land from landslides and other natural phenomenon or vibrations from road traffic. As pipelines are typically placed underground, they are subject to the variations in the earth around them. Though extensive testing is conducted to find the best routes to direct pipelines, any sort of movement of the earth can lead to stress on joints, fittings and the pipe itself.

Electrical pollution from nearby industry also may impact pipeline integrity. Electrical currents that pass through the ground as a result of nearby industry and natural occurrences can damage pipes. Research shows that these currents can cause stress in the pipeline and its components, which can lead to failure.

All of these stresses can degrade integral components of the pipeline. Failure of any of these components could cause leaks, which could lead to catastrophic events such as fires and explosions.

Prevention and Treatment

Pipelines are outfitted and treated to lessen the effect of these stressors. Pipes and fittings are routinely lubricated to ensure proper operation, and are painted with an epoxy coating which prevents corrosion and rust. Additionally, many components other than the pipeline itself have had vulnerable metal pieces replaced with corrosion-resistant, but weaker plastics. Steel, however, is the only viable choice for the pipes themselves due to its strength and low cost.

New technology is constantly being researched and developed to improve pipeline safety by identifying corrosion and leaks. Equipment such as “smart pigs” use ultrasound and MRI technology to identify weak spots on pipelines to stop leaks before they happen. Infrared cameras are also being used for leak detection allowing inspectors to see escaping gas that would be otherwise difficult or impossible to see with the naked eye.

As technology develops in the natural gas industry, there is endless potential for new materials and diagnostic tools to be used to make pipelines safer.

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