Pipeline Pigs

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 products;
• 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.

The type of pig to be used and its optimum configuration for a particular task in a particular pipeline should be determined based upon several criteria, which include:

The purpose

• Type, location, and volume of the substance to be removed or displaced in conventional pigging applications,
• Type of information to be gathered from an intelligent pig run,
• Objectives and goals for the pig run.

The line contents

• The contents of the line while pigging,
• Available vs. required driving pressure,
• Velocity of the pig.

Characteristic of the pipeline

• The minimum and maximum internal line sizes,
• Maximum distance pig must travel,
• Minimum bend radius, and bend angles,
• Additional features such as valve types, branch connections, and the elevation profile.