Types of Pigs

There are many types of PIGs available for pigging operations. Based on pigging purpose PIGs are classified in various types as shown below:

Batching Pig

Also known as a swabbing pig, the batching pig is designed to act as a simple barrier between dissimilar fluids or to provide a sweep of a line.

Gauging Pig

The inclusion of a simple gauge plate, made of a soft metal (generally aluminium), on batching pigs provides the function of confirming the integrity of the flow area of the pipe. Any major intrusions into the line will cause damage to the gauge plate, highlighting there is a problem, though not highlighting where.

Cleaning Pig

Pigs can be configured with various tools to aid cleaning. Circular brushes, spring-mounted brushes, scrapers, or plough blades for waxes and sludges or more aggressive tools such as carbide "pins" for removal of scales.

Magnetic Pig

Inclusion of powerful rare earth magnets on the circumference of the pig mandrel allows the pig not only to lift ferrous debris from the line, but can also provide the secondary function of activating pig signallers. Foam pigs also allow the addition of gauge plates, brushes, abrasives etc., although these are either fitted into the pig using bolts, or by direct casting into the polyurethane coating.

Intelligent Pigs

Research and development into inline inspection tools began in the late 1960’s. Advances in technology have led to pigs that can carry out complex tasks and data logging as they traverse the line. Mapping, geometry measurement, crack detection, measurement of metal loss, and many other tasks can be carried out. Intelligent pigging is now an industry within an industry. [6]

Gel Pigs

For certain tasks and in certain conditions, a viable alternative to running mechanical pigs is the use of gel pigs. Rather than use a solid barrier between fluids, a gelled substance can perform the same task. Various mediums can be gelled, including water (fresh and salt), glycol, methanol, solvents, diesel, and crude. The gels can be designed specifically to a required viscosity or cast as solid with chemical components designed to break down the gel after a given time or when a set temperature or pH has been reached. Gels have their limitations and are not generally suitable for long runs, in dry pipelines, or where the propelling medium is gas because they tend to suffer from "gas cutting" or excess bypass.

Intelligent PIG performs following actions:

• Measures and records information used to assess pipeline.
• Performs non-destructive assessment of pipeline defects.
• Performs an internal assessment of the pip.