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How 'pigging' the pipeline stops problems in their tracks

By Sara Klein | Dix Communications Published: June 8, 2016 9:25 AM
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What squeals like a pig and travels through oil and gas pipelines?

The answer isn’t a science fiction beast: it's an industry standard called a Pipeline Inspection Gauge.

The device, called a “PIG” as an acronym and for the sound it is said to produce while in operation, is an inspection tool that travels through pipelines on a search for gouges, dents, corrosion and more as part of the pipeline maintenance process.

When oil and gas operators “pig the pipeline,” they use the pipeline inspection gauge to collect data about the health of the pipe, including its thickness, pressure and temperature, as well as whether cracks, fissures, erosion or other forms of pipeline deterioration exist.

The idea is to identify and address potential problems before they take a toll on the company’s bottom line by stopping the flow of oil and gas or cause environmental disasters like leaks or explosions.

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Special sensors on an inspection PIG identify not only what the problems are but where in the pipeline they are located, which helps maintenance teams address repairs quickly and efficiently.

PIGs can use magnetic flux leakage, or MFL, which sends magnetic flux into the walls of the pipe, to detect leaks, corrosion or flaws in the pipeline. A second method called “ultrasonic inspection,” or UT, uses ultrasonic sounds to measure how long it takes for an echo to return to the PIG’s sensor. In this way, operators can directly measure the thickness of the pipe wall.

Prior to 2011, some PIGs often weighed up to two tons and relied on the pressure of oil and gas products in the pipeline to power their motion. Conventional inspection devices used magents to determine whether pipe walls had become corroded, but the magnetic field impeded the speed of the PIG.

Today, oil and gas companies are likely to use robotic “smart PIGs” based on a design pioneered by Carnegie Mellon University roboticist Hagen Schempf and his team of researchers.

Called the Explorer-II, Schempf’s pipeline inspection gauge is equipped with a compact electromagnetic coil that can detect corrosion without slowing down the inspection device’s movement.

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Weighing in at fewer than 70 pounds, the robotic PIG’s segmented body is designed to follow the twists and turns of a pipeline, and its drivetrain allows operators to determine precisely where the robot begins and ends its work within the pipeline.

But PIGs are not only for inspecting pipelines. The tools are used for many different aspects of pipeline maintenance.

For example, utility PIGs scour debris from pipelines, which can build up during construction or operation.

These devices are also used to seal the line by removing liquids. Mandrel PIGs, foam PIGs, solid cast PIGs and spherical PIGs are all forms of utility PIGs.

Specialty PIGs, such as plugs, keep the pipeline pressure in the line by stopping up the pipeline on either side of where the remedial work is being done. This operation is undertaken before maintenance work is performed on that section of line.

Gel PIGs, which contain a variety of gel liquids, can be used along with conventional PIGs or by themselves to assist with product separation, debris removal, hydrotesting, dewatering and condensate removal as well as with removing a PIG that can’t move through the line, which gives “stuck PIG” a brand new, high-tech meaning.


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