What is pigging?

A pig is a device that travels through a pipeline, pushed by the product or by a gas or liquid behind it. Pigging is the act of sending one. It is how a pipeline is cleaned, cleared of water after a hydrotest, kept separated between products, and, with the right pig, inspected from the inside without shutting anything down.

Kinds of pig

• Utility pigs clean, scrape, and displace. Foam pigs, cup pigs, and disc pigs are the everyday tools; brush and magnet pigs pull scale and debris.
• Batching pigs separate one product from the next in a line that carries several.
• Gauging pigs carry a soft aluminium plate that deforms on any dent or restriction, proving the bore is clear before anything else is run.
• Inline inspection tools, often called smart pigs, carry sensors that measure wall thickness, find corrosion, and record the geometry of the pipe along its whole length.

Launchers and receivers

Pigs go in through a launcher and come out at a receiver: a section of larger-diameter pipe with a closure door, isolation valves, and a kicker line that introduces the driving flow behind the pig. The design of the traps, the closure, the bypass, and the way the pig is tracked between them are where most of the practical skill lives.

What makes a good pigging job

Knowing the line: its bends, its valves, any change in diameter, and what is in it. Choosing a pig that will pass everything in that line and still do the work. Controlling the speed, because a pig that runs too fast cleans poorly and a pig that stalls has to be found. And tracking it from launch to receipt so that no one opens a trap with a pig still in the line.

Related terms: hydrostatic testing, dewatering and drying.