Pipeline pigs are devices that are inserted into and travel throughout the length of a pipeline driven by a product flow. They were originally developed to remove deposits which could obstruct or retard flow through a pipeline. Today pigs are used during all phases in the life of a pipeline for many different reasons.

Although each pipeline has its own set of characteristics which affect how and why pigging is used, there are basically three reasons to pig a pipeline:

• To batch or separate dissimilar product.
• For displacement purposes.
• For internal inspection.

The pigs which are used to accomplish these tasks can be divided into three categories:

• Utility Pigs – which are used to perform functions such as cleaning, separating, or dewatering.
• In Line Inspection Tools – which provide information on the condition of the line, as well as the extent and location of any problems.
• Gel Pigs – which are used in conjunction with conventional pigs to optimize pipeline dewatering, cleaning, and drying tasks.