Cleaning pig uses
Cleaning pigs have a variety of uses including the removal of debris, paraffin and millscale, the verification of the ovality of the pipe, corrosion control and dewatering during hydrostatic testing. During construction pigs are used to remove dirt or general construction debris that may be inside the pipe as it is being assembled. Pigs are used in the hydrostatic testing process, pumped through the pipeline with 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 extremely important because they are able to remove substances that may obstruct flow within the pipeline, or damage the pipeline itself, while still allowing continuous operation of the pipeline. In addition, through the removal of debris, cleaning pigs ensure that a pipeline maintains its maximum efficiency.
Because of the pigs’ varied uses and the differences inherent in each pipeline, cleaning pigs are available in a number of different designs. The pigs can be of a light or heavy density, depending on the function of the pig. A pig of heavy density may be put through a pipeline first, then lighter density pigs to follow on.Article continues below…
Foam and polyurethane pigs
Foam or polyurethane pigs are available in various densities and shapes. They can be bullet shaped, have concave ends or flat ends, be jelly coated on the outside or sometimes have a silicone carbine coating. In addition, some foam pigs can have a crisscross pattern with silicone carbine implanted in the pig.
Coated foam pigs are used for general cleaning, whereas the more abrasive coating of silicone carbine is used for cleaning lines with build-up. The crisscross pattern is also used for medium-length runs in pipe where extra abrasion resistance is required.
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.
Foam pigs are flexible, enabling them to compress and expand so that they can travel through multi-diameter pipelines and navigate bends in the pipeline.
Light-density foam pigs are used to pass through the pipeline first because their open-cell foam aids the drying of pipelines after hydrostatic testing. Medium-to-heavy density foam pigs are used during pipe construction, start-up, during operations, for maintenance and emergencies.
Solid polyurethane pigs are 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 petrols and various other types of fuel. A displacement pig displaces one fluid with another and is used in the commissioning process.
Mandrel pigs have a metal body with seals, scraper cups or discs on their exterior. The pigs can be used for an ovalarity check or for gauging the internal diameter of the pipe, to clean the line, as a sealing pig, as a combination cleaning/sealing pig, for batching, dewatering and drying after testing.
Extra discs can be provided to attach to mandrel pigs to scrape extra debris. For example, crude lines can get a heavy wax build-up and sometimes require extra discs on the pig to clean the line. Additional cups and brushes can also be acquired.
A brush pig uses both metallic and non-metallic brushes. 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.
Pigs for different pipes
Different pigs are recommended for water, natural gas, oil and liquids pipelines.
The type of cleaning pig used on a natural gas pipeline is often determined by the internal coating of the pipe. If the pipeline is internally coated, the cleaning pig to be used won’t be equipped with cleaning devices that could damage or remove the coating. For example, a polyurethane pig won’t damage the coating. If the natural gas pipeline is free of internal coating, a cleaning pig with brushes can be used.
Plastic-bristle foam pigs can also be used with internally coated pipelines or plastic lines such as PVC, fibreglass and high-density polyethylene. The bristles are forceful enough to remove most build-up but not harmful to the coatings.
Oil pipelines may need pigging to remove wax accumulations on the inside of the pipe wall or an accumulation of water in the pipe. A polyurethane pig is suitable for removing wax from an oil pipeline.
It is important that the right cleaning pig is chosen for an operator’s pigging needs. There are a number of suppliers in Australia providing different pigging products, all willing to help with the right pigging solution. Dawson River case study – pigging raw water line
The 150 mm diameter pipeline is ten kilometres in length, pumping raw water from the Dawson River to the treatment plant to service parts the Duaringa Shire, Queensland.
To remove the internal debris and weed growth built up in the pipeline over a period of ten years.
Due to the location of the site and the urgency of the program, Clearflow Australia worked purely on telephone communication and faxed documents in order to fabricate a pig launcher to suit the conditions onsite. After some difficulties it was made to fit and is now a permanent fixture of the pipe at the river end.
Managing Director David Elderfield said “On inspection of the pipeline at the river and pumping end we adapted the existing fittings, removed a flanged section of the existing pipe and made our pig launcher fit.
“The best location for the discharge was at the water plant. A section of pipe was exposed and removed with the excavation of pit leaving the open end of the pipe discharging into the settling pit.”
There was no confident local knowledge of the pipeline and the only map available was a longitudinal section map, said Mr Elderfield. “It is difficult to know what to expect when launching a pig that is required to travel ten kilometres and at the same time achieve the desired results.”
Most of the pipeline is located in bush terrain with difficult access, with a number breaks in certain sections and unknown debris in the pipe.
As the pipeline had no offshoot sections or designed breaks it was necessary for the pig to travel the entire ten kilometres and achieve the desired result. If the wrong type of pig is used and too much debris is dislodged too early the pig could jam up in the pipe. On the other hand, if the pig is too soft it may break up during the run. Or if the pig travels too quickly we may not get a true idea on the condition of the pipe or the type and amount of debris that is in the pipe to be removed.
At the time of fitting the launcher the pipeline showed signs of encrustation with a large amount of weed slime and sludge – the aftermath of pumping raw water.
Clearflow’s normal procedure on the first run is to try and determine the condition of the pipe. The first run took approximately four hours to travel the pipe, removing large amounts of sludge and slime.
This initial run was not without complications. The pig did jam up with the amount of debris in the pipe and it was decided to release the pressure in the pipe. In doing so; Clearflow drained some of the pipe to get another run with the pig and to try and dislodge the debris.
Under normal conditions the first-run pigs or proving pigs will float, however, in this case, when they were finally discharged from the pipe they were so full of sludge and slime that they just settled on the bottom of the discharge pond. They were stuck in the sludge and at the bottom of the pit.
It is necessary when refurbishing pipelines to try and control the speed of the pigs through the pipeline. After two proving runs the company was confident the pipeline was reasonably true and launched the working pig; a harder compound, poly-foam pig.
This purpose of running this pig was to remove all of the debris of weed sludge and slime as well as any harder encrustation. The results achieved were very good. Clearflow not only removed large amounts of raw water slime sludge and weed growth, but also the heavy scale evident in the bottom of the discharge pit. There were also signs of manganese mixed up with the weed growth. The final analysis
Improved water quality delivery with increased flow rate to the dam of 60 per cent. This alone decreased the operating costs of pumping water.