Cleaning pigs can be used to remove dirt or general construction debris that may have been left inside the pipe during construction; during the hydrostatic testing process they can be propelled through the pipeline with the test water as a tool to expel air from the line. Following this, a cleaning pig is used to dewater and dry the pipeline before commissioning. During operation, cleaning pigs are used to remove debris, millscale, paraffin wax and other deposits for a more efficient flow of product, and to control corrosion.

Pig manufacturing company Rosen says that there are three considerations that interact when choosing the right cleaning pig for the job: the duty of the pig, the geometry of the pipeline, and the operating conditions of the pipeline.

Girard Industries agrees, saying that it is important to consider “pipeline characteristics which include bends, valves, diameter changes, intersections and intrusive devices.”

BJB Services and Enduro Pipeline Services point to other characteristics such as the type of launch and receive facilities present on the pipeline, and whether the pipeline has an internal coating.

Types of cleaning pig

Because of the differences inherent in each pipeline, and the product’s varied uses, cleaning pigs are available in a number of different designs.

Foam and polyurethane pigs

Foam and polyurethane pigs are available in various densities and shapes. They can be bullet shaped, have concave ends or flat ends, be coated, or have a silicone carbine coating for more-aggressive cleaning. In addition, some foam pigs can have a crisscross pattern with silicone carbine implanted in the pig, providing extra abrasion resistance in medium-length pipe runs.

The shape of the pig dictates how fast it travels while in the pipe. The travel speed in turn determines the force of the pig’s cleaning edge, with higher-speed pigs being able to remove tougher debris.

According to Enduro “Foam pigs are good to clean a dry pipeline once the bulk of the water or liquids have been removed. They are also good to use when starting a cleaning programme, when there may be a large amount of debris present in the system, causing partial blockage. For this, you would start with undersized pigs and work your way up to running metal-bodied pigs in different configurations, or running all-urethane pigs.”

BJB explains “Medium and high-density foam pigs are often used as the first pigs in a cleaning operation because they are able to push significant quantities of loose debris in the line, and are flexible enough to pass through many restrictions.”

Light-density foam pigs are often used to soak-up liquids as their open-cell foam aids drying the pipeline after hydrostatic testing.

Solid polyurethane pigs are also used as a first or second pig for a cleaning operation, and can be designed to be used in batching or displacement of fluids in petroleum, chemical or process industry pipelines. Batching refers to when a pig is used between batches of product, such as between petrol and various other types of fuel. A displacement pig displaces one fluid with another and is used in the commissioning process.

BJB says “Solid urethane pigs have a longer wear life than foam pigs but have less flexibility.”

Polyurethane pigs are often used on internally-coated pipelines, as they are not equipped with cleaning devices that could damage or remove the coating. If a gas pipeline is free of internal coating, a cleaning pig with brushes can be used.

Mandrel pigs, cups and discs

Mandrel pigs have a metal body with seals, scraper cups or discs on the exterior. The pigs can be used to clean the line, for an ovality check or for gauging the internal diameter of the pipe, as a sealing pig, as a combination clean/sealing pig, or for batching, dewatering and drying after testing.

According to Inline Services “The majority of highly efficient cleaning pigs are mandrel pigs, using drive or cleaning cups and discs, or aggressive brushes that are matched for the application and conditions.”

Rosen agrees, stating that guiding and sealing discs for mandrel pigs are provided with a selected hardness for improved performance and can be refurbished for use on different pipeline projects.

Extra discs, brushes or cups can be provided to attach to mandrel pigs to scrape extra debris: for example, crude oil lines can get a heavy wax build-up and sometimes require extra discs on the pig to clean the line.

Cups are also used to push debris out of a pipeline. BJB explains that it provides cups of different shapes that vary in cleaning strength. “A conical cup is our least aggressive cup profile and is generally used when the condition of the line is not well known or significant quantities of debris are expected. The scraper cup has a similar profile, but has a built-in scraper edge providing a more aggressive clean.”

Inline Services says that discs are used to either seal or scrape the pipe wall. “Sealing discs are usually softer, while scraping or guide discs are sized close to the pipe’s internal diameter and made from harder materials.”

Girard Industries adds “A disc pig is generally considered more efficient at removing liquids than a cup pig.”

In addition, both metallic and non-metallic brushes can be attached to mandrel pigs. Generally brushes are used when more aggressive cleaning is required to remove tough debris. Liquids’ pipelines are best cleaned with a pig equipped with cleaning devices attached, such as brushes, which can remove fine solids that may have settled in the pipeline.

Enduro states “Brushes can be manufactured from a number of different materials: round wire bristles, flat coarse bristles, pencil brushes and nylon bristles.”

Rosen also says that it supplies a large variety of accessories for cleaning pigs such as spring-loaded brushes, standard accessory flanges for installation of transmitters and data loggers, and the additional Roplast Easy Clean range for pre-commissioning and routine pigging operations in most pipelines.

Market developments

BJB Services says that pig designs are becoming increasingly diversified to allow for greater flexibility when cleaning a line, with pig-tracking equipment becoming much more sensitive, and wireless applications beginning to appear on the scene.

“In the United States, we are seeing that the majority of the cups we have sold over the past year are being run in lines that have never been pigged, or that have not had a pig run through them in over ten years. We have also seen an increase in the number of launcher and receiver installations over the past year. Hopefully, this is a sign that industry awareness of pigging is improving,” the company says.

Enduro states that it is working toward improving its pig designs for dual-diameter and multiple-diameter pipelines. “We are working on custom-designing pigs for pipelines that have in the past been deemed non-piggable due to diameter changes or other ‘non-piggable’ features.”

Inline Services has also observed a number of market developments. “With the current demand for inspecting pipelines with in-line inspection tools, cleaning prior to inspection has increased dramatically. Although inspection tools are very robust, they require a clean pipeline to ensure that the environment they are operating in allows for collection of usable data.

“In addition to the use of pencil brushes to clean corrosion pits, there are several new innovative concepts being used. One is the use of cutter discs which incorporate a serrated outer edge that helps to scrape debris from the pipe wall. This is especially effective in wax, sludge, and black powder applications.”