Gauging Pig is one of the most important inspection tools available as it provides a fast, cost effective way to determine whether there is an obstruction in the pipeline. The gauging pig is used during the pre-commissioning and maintenance, operations and repair activities and is designed to suit dual diameter pipelines.
Pigging with a gauging pig during the construction process can be one of the most important inspection tools available to verify the pipeline is laid as specified. Since a pipeline is designed to deliver a certain throughput based on a minimum diameter, it is therefore necessary to be sure that the minimum diameter is not lost during the laying process.
The oldest means of gauging this minimum diameter is by installing a plate on a pig. The diameter of the plate varies somewhat between pipeline companies but usually is between 90% and 95% of the pipe's normal inside diameter.
In the early days of pigging, gauge plates were made from steel. Today’s gauge plates are made from aluminum to avoid causing damage to the pipe walls. The plate is sized proportionately to the minimum internal diameter of the pipeline, then added the appropriate style of pig, such as Steel Mandrel or MULTI-CAST™ depending on the application. The addition of the gauge plate then classifies the pig as a Gauging Pig. Guide discs, seal discs and cups can be added to a gauging pig, as well as transmitters and magnets for pig tracking purposes.
While traversing the pipeline, if the Gauging Pig passes through any obstructions or restrictions, the plate will show wear. Examining the wear on the plate and tracking the pigs location allows for isolating problem areas in the line. Once problem areas are identified in the line, the appropriate next steps can be taken to correct the issue, such as implementing a more aggressive pigging program to remove the debris, or making pipeline repairs to correct line damage causing the restriction.