Gauging

A gauging pig is an important inspection tool run during the pipeline’s construction. Its function is to ensure that the minimum diameter is maintained during the construction as oval sections are created at the field bends. It will also identify any other internal obstruction such as a poor weld protrusion.

The diameter of the gauging plate varies is between 90% and 95% of the pipe's normal inside diameter. Most modern gauging plates are made of soft aluminium cut into segments to help identify the shape and orientation of any restriction.

The gauging plate records only in contact with the pipe wall so other multiple smaller restrictions and the locations are often missed. An alternate is the instrument pig designed to not only measure the inside diameter of the pipeline but also identify the location of any restriction. These are known as 'geometry' or 'caliper' pigs and are best run in a liquid controlled environment.