Pigging

Pigging in the context of pipelines refers to the practice of using devices known as "pigs" to perform various maintenance operations. This is done without stopping the flow of the product in the pipeline.

These operations include but are not limited to cleaning and inspecting the pipeline. This is accomplished by inserting the pig into a "pig launcher" (or "launching station") — an oversized section in the pipeline, reducing to the normal diameter. The launching station is then closed and the pressure-driven flow of the product in the pipeline is used to push the pig along down the pipe until it reaches the receiving trap — the "pig catcher" (or "receiving station").

Pigging has been used for many years to clean large diameter pipelines in the oil industry. Today, however, the use of smaller diameter pigging systems is now increasing in many continuous and batch process plants as plant operators search for increased efficiencies and reduced costs.

Pigging can be used for almost any section of the transfer process between, for example, blending, storage or filling systems. Pigging systems are already installed in industries handling products as diverse as lubricating oils, paints, chemicals, toiletries, cosmetics and foodstuffs.

Pigs are used in lube oil or paint blending to clean the pipes to avoid cross-contamination, and to empty the pipes into the product tanks (or sometimes to send a component back to its tank). Usually pigging is done at the beginning and at the end of each batch, but sometimes it is done in the midst of a batch, such as when producing a premix that will be used as an intermediate component.

Pigs are also used in oil and gas pipelines to clean the pipes. There are also "smart pigs" used to inspect pipelines for the purpose of preventing leaks, which can be explosive and dangerous to the environment. They usually do not interrupt production, though some product can be lost when the pig is extracted. They can also be used to separate different products in a multiproduct pipeline.

If the pipeline contains butterfly valves, or reduced port ball valves, the pipeline cannot be pigged. Full port (or full bore) ball valves cause no problems because the inside diameter of the ball opening is the same as that of the pipe.

The original pigs were made from straw wrapped in wire and used for cleaning. They made a squealing noise while traveling through the pipe, sounding to some like a pig squealing, which gave pigs their name. "PIG" is sometimes claimed as an acronym or backronym derived from the initial letters of the term "Pipeline Inspection Gauge" or "Pipeline Intervention Gadget".

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Wikipedia