Pipeline Pigging / How Pipeline Pig Work

What is pig?
 Pig is a device which is inserted into, and travel throughout the length of a pipeline, driven by the product flow. Pig can be divided into two categories: ‘utility’ pigs - which perform a function such as cleaning, separating or dewatering the pipeline, and in-line inspection, or more simply, ‘ILI tools’ (sometimes referred to as ‘intelligent pigs’ or ‘smart pigs’) - which provide information on the condition of the line as well as the extent and location of any problems.

Source : http://www.polyeurope.com/site/images/home_slider/pig_animation.gif

Why is it called pig ?
One story goes that two pipeliners were told to go out to the pipeline and listen for the pipe cleaner to go by. This pipe cleaner consisted of a steel pipe or mandrel body with flanges welded on both ends. Discs made of leather sheets were stacked together to provide thickness, and attached to the flanges. As the pipe cleaner travelled down the line pushing out debris, it made a squealing, scraping, noise. As the cleaner went by, one pipeliner made a comment to the other about “hearing that pig squeal”. These stories are generally accepted as possibly being true.

Whether they are true or not, they at least indicate that pigs have been around for a long time. For more than half of a century pigs consisted of steel bodies and rubber, leather, or urethane cups or discs. They were equipped with wire brushes, scrapers, knife blades, and other devices for ploughing.

Types of Pipeline Pig
Utility pig
Utility pigs are used to clean the pipeline of debris or seal the line. Debris can accumulate during construction, and the pipeline is pigged before production commences. Also, debris can build up on the pipeline, and the utility pig is used to scrape it away. Additionally, sealing pigs are used to remove liquids from the pipeline, as well as serve as an interface between two different products within a pipeline. Types of utility pigs include mandrel pigs, foam pigs, solid cast pigs and spherical pigs.

Debris after pigging
Source: www.ppsa-online.com

Inspection pigs
Inspection pigs also referred to as in-line inspection pigs or smart pigs, gather information about the pipeline from within. The type of information gathered by smart pigs includes the pipeline diameter, curvature, bends, temperature and pressure, as well as corrosion or metal loss. Inspection pigs utilize two methods to gather information about the interior condition of the pipeline: magnetic flux leakage (MFL) and ultrasonics (UT). MFL inspects the pipeline by sending magnetic flux into the walls of the pipe, detecting leakage, corrosion, or flaws in the pipeline. Ultrasonic inspection directly measures the thickness of the pipe wall by using ultrasonic sounds to measure the amount of time it takes an echo to return to the sensor.

Source: www.ppsa-online.com

Specialty pigs
Specialty pigs such as plugs, are used to isolate a section of the pipeline for maintenance work to be performed. The pig plug keeps the pipeline pressure in the line by stopping up the pipeline on either side of where the remedial work is being done.

Source: www.ppsa-online.com

Gel pigs
A combination of gelled liquids, gel pigs can be used in conjunction with conventional pigs orby themselves. Pumped through the pipeline, there are a number of uses for gel pigs, including product separation, debris removal, hydrotesting, dewatering and condensate removal, as well as removing a stuck pig.

Source: www.ppsa-online.com

Pig Deployment
Smart pigs are deployed through devices aptly named, Pig Launchers. Essentially, there is a pipe that holds the launcher branched off from the main pipeline. The launcher barrel is drained and then sealed off. The pig is then loaded through a hatch at the end of the pipe and closed. Through some fancy control settings they unseal the pipe and the flow of oil and pressure helps carry the smart pig to the next station where it is captured by a piece of pipe very similar to the launcher pipe. As you can imagine, this pipe works similar to the pig launcher, but is where the smart pig is unloaded. This section is called the pig trap.


Source : http://smartpigs.net/media/Pig_Launcher1.jpg 

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