Pigging is a routine maintenance procedure that plays a critical role in oil and gas pipelines for mitigating and monitoring internal corrosion, and for preserving safety and integrity.
The process involves inserting devices known as “pigs” into a crude or natural gas line via a launcher. The pig travels through the line without interrupting flow, and depending on its design, can perform any number of tasks such as cleaning, liquid removal or inline inspection.
Pigging can be performed one of two ways: manually or automatically. Manual pigging is a labor-intensive process that can be cost-prohibitive, particularly in liquid-rich shale plays where excessive fluid accumulation requires multiple pigs to be launched daily.
In recent years, as pipeline operators have sought to improve flow efficiencies and reduce O&M costs, the extensive time and manpower requirements associated with manual pigging systems have become problematic. To address this, many companies are turning to automation.
Manual vs. Automated Pigging Systems
For decades, manual pigging systems have been used to launch and receive pipeline pigs without stopping product flow. A system consists of a launcher unit upstream and a receiver unit downstream of the section of pipeline to be pigged. The units are isolated from the pipeline with valves, which allow pressure to be released and product drained or vented so pipeline pigs can be inserted and extracted safely. The systems are designed to load, launch and retrieve a single pig at a time.
Automated pigging systems, on the other hand, allow for multiple pigs to be loaded simultaneously, which eliminates the need to blow down the pig barrel and vent pipeline contents every time a pig is released. Labor costs are reduced, safety is improved, and the need to open and close valves and closure doors when launching is minimized. Automated systems can be operated remotely or set on a timer, which allows operators to initiate launches from anywhere, thereby minimizing the risk of mishaps due to unexpected complications that can arise in the field.
Benefits of Automated Systems
The ability of automated pigging systems to reduce labor costs has been the primary driver for growth in recent years. In pipeline systems where unpredictable fluid accumulation and high paraffin build-up and corrosion are a concern (that is, liquid-rich shale plays), multiple pigs may need to be launched daily. This includes disc pigs used for cleaning and spherical pigs used for liquid removal. In such cases, the cost associated with having dedicated field personnel working around the clock to manually launch pigs can be up to $5,000 per day.
The installation of an automated pigging system with the capability to load multiple pigs simultaneously reduces overall labor costs in proportion to the pigging frequency required by the pipeline. In other words, as the number of pigs needing to be launched increases, so do the cost savings and return on investment of an automated system. Those savings are often magnified in remote regions where field personnel must to travel large distances to launch and receive pigs.
In addition to the extensive cost and labor requirements of manual pigging systems, there are also mechanical wear considerations that make the use of automated systems advantageous. As mentioned previously, manual pigging requires opening and closing of a number of valves. Over time, as this operation is repeated, the risk of valve seat failure increases. Frequent cycling of launcher and receiver barrels can also lead to cyclic fatigue and excessive release of hazardous hydrogen sulfide gas often present in raw product.
Worker and environmental safety is a concern with manual pigging systems as well. During pigging operations on natural gas pipelines, traditional launcher and receiver systems must be depressurized every time a pig is launched or received, which results in the release of methane emissions. Because they allow for multiple pigs to be loaded simultaneously, the use of an automated pigging system reduces the frequency of depressurization.
The volume of emissions reduction is based on the total number of pigs staged and launched (the more pigs the launcher can hold, the fewer emissions). This is not always the case, as automated pigging systems utilizing supply gas pneumatic launch systems may be a potential source of fugitive emissions.
Automated Pigging System Type and Design
Multiple automated pigging system design exist on the market today. In general, these systems fall into one of the three following categories:
Vertical launch barrel design – In vertical launch barrel designs, pigs are loaded and gravity-fed into the downstream pigging valve. The system is actuated with a pneumatic gas supply, and can be controlled manually or set using a timer to achieve the desired pigging frequency.
Angled launch barrel design – In these systems, multiple pigs are gravity-fed to a downstream launch mechanism. The launch mechanism will typically consist of two insertion pins retracted hydraulically or pneumatically to allow the pipeline pig type to be launched. Angled barrel gravity-fed systems are used predominantly for liquid removal with spherical pigs.
Horizontally oriented design – Horizontal automated pigging systems are one of the more recent advancements on the pigging market. Unlike many vertical, gravity-fed systems—horizontal systems allow for a wide range of pig types and lengths to be loaded into a launch barrel.
Horizontal automated pigging systems offer a number of advantages and can be used for a variety of pigging functions. Based in Houston, WeldFit Energy Group is a pioneer in the development of horizontal pigging systems. The company’s SureLaunch automated pigging system features a horizontally oriented barrel, which allows up to 10 pigs to be loaded at one time.
The system can be incorporated into bidirectional pipelines and combines all four pigging functions (liquid removal, cleaning, batching and inspection). In pipeline systems where multiple pigs are launched daily, the savings from employing such as system can be substantial.
In the Woodford Shale Play, for instance, the use of a horizontal automated pigging system on a natural gas pipeline is helping an operator save $4.5 million over a five-year period.
In the coming years, the pipeline pigging market will continue to expand. Its growth will be driven by several factors – most notably the combination of increased production from U.S. shale plays and a greater need to manage corrosion in aging pipeline infrastructure. The increased trend of exploration and production companies moving into the midstream market and electing to dehydrate (for example, remove liquid) raw natural gas in a centralized location away from the wellhead will also necessitate the need for more aggressive internal corrosion mitigation measures.
Automated pigging systems have proven to be effective in addressing these issues, and will continue to play an important role in maintaining the world’s pipeline infrastructure.