Pipeline Inspection Gauge
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 tool used in pigging.
A 'pig' is typically a soft, bullet shaped polyurethane plug that is forced through pipelines to clean them, separate products to reduce mixing, and inspect the pipeline. There are several types of pigs; some have tungsten studs or abrasive wire mesh on the outside to cut rust or calcium deposits off the inside of the pipe, others are plain plastic covered polyurethane.
Inline inspection pigs use various methods for inspecting the condition of a pipeline. A gauging plate is simply a notched round piece of metal which bend when it encounters a bore restriction. More complicated systems exist for inspecting various aspects of the pipeline. Smart pigs incorporate a computer or electronics which provide more information. These pigs use technologies such as magnetic flux leakage and ultrasonics. Some of these inspection pigs use have fingers that measure the inside diameter of the pipeline.