Using Valves to Support Pipeline Integrity

Pipelines are the backbone of many modern industries, providing one of the safest, most environmentally friendly, and economical modes of material transportation. While durable, pipelines are not invulnerable and require proper maintenance and cleaning to operate efficiently and safely. A lack of appropriate maintenance programs can cause blockages, cracks, leaks, and many other problems that compromise a pipeline’s integrity.

By Nicolaas Ainsworth

The Importance of Pipeline Maintenance

Natural gas lines and other wet gas lines, for example, are susceptible to a phenomenon known as liquid loading.¹ Liquid loading is when gases in the pipeline slow down and liquefy, settling in the pipeline.¹ The gas pool collected from the liquidation will begin to erode the pipeline, causing cracks and leaks.¹ These pools can also block gas from running through the line, leading to lost production and blockages.¹

Crude pipelines are vulnerable to wax build-up. Wax build-up is when the crude liquid crystallizes on the sides of the pipe.^2,3 The solidification of the product on the pipelines reduces the flow passage, lowering transportation capacity.³ This build-up can get so significant that it can block the entirety of the pipeline.³ Blockages can create millions of dollars in damages from operation shutdowns and remediation treatments.³

Maintaining Lines Through Pipeline Pigging

What kind of maintenance programs can ensure these situations do not occur? How does an operator clean, maintain, and inspect a deep underground pipeline running across various terrains for hundreds of miles? The answer is pigging. Pigging is one of petroleum’s oldest and most common methods for pipeline maintenance and cleaning.¹ Pigging is when pipeline operators send specialized tools, or Pigs, through a pipeline to purge debris and inspect the line’s condition. Using the pressure of the pipeline, these Pigs squeeze through the line, pushing and purging harmful debris that, if left unchecked, can lead to the previously mentioned issues.^1,2,3 These tools can be manufactured with various features tailored to the type of debris. They can also be outfitted with various electronic and physical inspection hardware to measure the pipeline’s conditions. Figure 1 shows an example of an Apache-manufactured foam bullet-style maintenance PIG (left) and Mandrel PIG (right) that may be used in a pipeline cleaning application.

Traditional Launching and Receiving of Pigs

 Understanding the importance of Pigs and Pigging, one may now ask how to introduce and subsequently remove the Pig into a flowing, pressurized pipeline without shutting down line operation. Pipeline operators must install Pig launcher and receiver stations into a given pipeline segment. These stations are specifically designed to allow the introduction and removal of Pigs into a pipeline while it continues to operate. The conventional design of Pig launchers and receiver stations, often called Pig Barrel Traps or Pig Barrel Stations, are horizontal barrels that operate using a complex system of isolation valves, drain, and kicker valves.

To launch a Pig, the operator will place a Pig in the barrel and close the main line valve, filling the barrel with fluid.⁴ The fluid flow will then push the Pig into the mainline.⁴ Once the Pig is inside the pipeline, the operator will fully open the mainline valve and close the isolation and kicker valves.⁴ The operator pressurizes the receiving line and opens a bypass valve to receive a Pig.⁴ Once the Pig is received, the operator drains and depresses the barrel and removes the Pig. This description is a straightforward overview of the process, as site – and media-specific modifications will inevitably occur. Overall, these stations are complex, and operating them can be equally complex.

Pitfalls Using Conventional Pig Barrel Traps

Conventional Barrel Trap Pig Stations allow operators to maintain pipelines through pigging. However, there are many limitations and risks. In addition to the noted complexity, Barrel Traps pose a significant risk to operator safety. The horizontal alignment places the operator in a potentially precarious position. If there is a mistake in the operation and the barrel is not depressurized correctly, the Pig can become a projectile, flying out of the barrel, potentially striking the operator.^5,6 The speed and force of the Pig in this situation can lead to severe injury and death. There are several documented events of such occuring.7 The complexity of the operation, in combination with the severity of the consequences of an error, makes pigging with a Barrel Trap very hazardous.

From an operations standpoint, the station’s footprint and emissions can also limit its viability in certain situations. The space the infrastructure requires can make it difficult or impossible to introduce onto specific lines. The costly infrastructure can also make it impractical from a financial perspective. Venting and flaring of the relatively large volumes of media necessary to operate these stations also pose an environmental problem as they are high emitters of GHG emissions. The combination of size, heavy emission releases, and safety concerns may lead operators to consider an otherwise “piggable” pipeline “unpiggable.”

A Different Way to Pig

 Pipeline operators can find themselves in a bit of a catch-22 with pigging. If they do not maintain their lines, they risk failures that can compromise the integrity of their infrastructure, leading to profit loss, safety risks, environmental damages, and much more.1,2,3 However, the conventional barrel trap system has limitations. It can pose safety concerns for operators, release significant emissions, and be impractical, if not impossible, to implement due to size and other constraints. Fortunately, there is a solution in the form of Pig launching or receiving ball valve technology, also known as Pig Valves.

The Pig Valve is a trunnion-mounted, quarter-turn ball valve with an added closure that can be used to send and receive Pigs.⁸ These Pig Valve stations allow operators to maintain their lines while overcoming many obstacles of conventional stations. For example, the design of the Argus Pig Valve uses a top-entry mechanism to introduce and remove Pigs.⁸ The entry point eliminates the safety risks of the traditional Barrel Trap by no longer putting operators in a position where they risk being struck by a pressurized projectile.⁸ Furthermore, any pressurization will have already been released when the valve opens and the Pig is exposed.

A station utilizing a Pig Valve’s size is also very compact, negating the large footprint associated with a barrel trap. An Argus Pig Valve also results in a substantially smaller volume of vented media, allowing operators to reduce their pigging emissions dramatically. A substantial reduction in emissions can help companies reach their emissions targets and meet regulatory requirements. Based on findings from an investigation into unauthorized or excessive emissions, the United States Environmental Protection Agency (EPA) has even recommended Pig Valves or multiple pig launchers as potential engineered solutions, shown in Figure 2, to reduce emissions associated with pigging.⁹

Conclusion

 Pipelines require proper maintenance to ensure their integrity and longevity. Without appropriate programs, pipelines are susceptible to liquid loading, wax build-up, excessive corrosion, and many other issues.^1,2,3 These issues can cause blockages, leaks, and a complete shutdown of operations, causing astronomical environmental, safety, and economic harm.^1,3 Operators can avoid these situations by implementing pipeline-pigging programs.

Unfortunately, conventional Pig Launcher/Receiver Stations (known as Pig Barrel Traps) have many limitations, which can cause operators to reconsider introducing pigging to maintain their pipelines. By using a valve design instead of a barrel, operators can cut down on infrastructure size, reduce emissions by up to 91%, and eliminate the projectile safety risks of barrels.⁸ It is just one more way valve technology supports continuous innovations for better operations.