An Introduction to Pipeline Pigging
Pipeline pigging is the act of using a device that goes through a pipeline to aid inspection, cleaning, or dimensioning, according to Girard Industries. The devices that move through the pipelines are generally called "pigs." There are more than 500 types of pigs in use today, according to Girard Industries. Pigging is an important maintenance procedure for keeping pipelines from corroding or cracking and to detect any problems present on the inside of a pipeline.
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Reasons for Pigging
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Pigging a pipeline is important as soon as construction has been completed. A pig is first used to remove debris left over after construction. Lunch boxes, tools, dead animals, and many other items may be stuck in a pipe. A pig can also verify that a pipeline is shaped correctly.
Types
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Cleaning and sealing pigs are the most common, according to Girard Industries. Cleaning pigs remove water, debris, and paraffin from pipelines. They are often used in conjunction with chemical cleaning agents. Sealing pigs are used to water and de-water a pipeline while they check for dents. They are also used as part of hydrostatic testing.
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Pig Traps
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Pig traps are a critical part of the pigging system, according to the PPSA. These "traps" launch pigs into a pipeline and receive them when they return. They are able to remove pigs from a pipeline without stopping the flow of liquid in a pipe. Most traps are custom-built to meet the pipeline owner's needs. Pig traps all have a safety lock, which prevents them from being opened while a trap is pressurized.
Multiple Products
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Pipelines that transport multiple products, such as different grades of heating oils, jet fuels, or gasoline, often use pigs to separate the different products. Pipeline owners cycle through the transport of different grades of oil, according to the American Petroleum Institute (API). Pigs are used to separate each "batch" of oil. Each batch consists of one grade of product. These separations allow many different products (in some pipelines, as many as 50) to be transported without mixing them, which would degrade the products and cause confusion.
Consideration
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Running pigs in dual diameter lines can pose a challenge, according to Girard Industries. Many pigs have a tendency to get stuck when the diameter of a pipeline decreases, according to PPSA. Butterfly pigs, designed to collapse to fit smaller diameters, create a high degree of friction and are harder to design than most pigs. Wheel pigs, although very efficient in dual diameter pipelines, are up to eight times as expensive as normal pigs, according to PPSA.
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