Pipeline inspection gauge
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A pipeline inspection gauge or pig in the pipeline industry is a tool that is sent down a pipeline and propelled by the pressure of the product in the pipeline itself. It is the chief device used in pigging.
There are four main uses for pigs:
- physical separation between different liquids being transported in pipelines;
- internal cleaning of pipelines;
- inspection of the condition of pipeline walls (also known as an Inline Inspection (ILI) tool);
- capturing and recording geometric information relating to pipelines (e.g. size, position).
The original pigs were made from straw wrapped in wire used for cleaning. They made a squealing noise while traveling through the pipe, sounding to some like a pig squealing. The term "pipeline inspection gauge" was later created as a backronym.
One kind pig is a soft, bullet shaped polyurethane foam plug that is forced through pipelines to separate products to reduce mixing. There are several types of pigs for cleaning. Some have tungsten studs or abrasive wire mesh on the outside to cut rust, scale, or paraffin deposits off the inside of the pipe. Others are plain plastic covered polyurethane. Pigs cannot be used in pipelines that have butterfly valves.
Inline inspection pigs use various methods for inspecting a pipeline. A sizing pig uses one (or more) notched round metal plates that are used as gauges. The notches allow different parts of the plate to bend when a bore restriction is encountered. More complex systems exist for inspecting various aspects of the pipeline. Intelligent pigs, also called smart pigs, are used to inspect the pipeline with sensors and record the data for later analysis. These pigs use technologies such as Magnetic flux leakage (MFL) and ultrasonics to inspect the pipeline. Intelligent pigs may also use calipers to measure the inside geometry of the pipeline.
In 1961, the first intelligent pig was run by Shell Development. It demonstrated that a self contained electronic instrument could traverse a pipe line while measuring and recording wall thickness. The instrument used electromagnetic fields to sense wall integrity. In 1964 Tuboscope ran the first commercial instrument. It used MFL technology to inspect the bottom portion of the pipeline. The system used a black box similar to those used on aircraft to record the information.
A pig has been used as a plot device in three James Bond films: Diamonds Are Forever, where Bond disabled a pig to escape a pipeline, The Living Daylights, where a pig was modified to secretly transport a person through the Iron Curtain, and The World Is Not Enough, where a pig was used to move a nuclear weapon through a pipeline.
A pig was also used as a plot device in the Tony Hillerman book The Sinister Pig where an abandoned pipeline from Mexico to the United States was to use a pig to transport illegal drugs.
