A review of fluid-driven pipeline pigs and their applications

Pigs are devices that, propelled by fluid flow, travel through pipelines in order to remove deposits, displace product, and inspect or maintain the line. Although first developed for use in the hydrocarbon industries, pigs have been adopted by many fluid handling and process industries. The growing desire for shorter batch runs and increased flexibility of plant as well as demands for greater efficiency and reduced waste have renewed interest in pigging systems within these industries. This paper provides some background to pigs and explains why pigging systems are used as well as why they are not. A review is made of the different types of pigs, their functions, and features. The most common types of pigs are considered as well as some of the specialist pigs that have been designed for specific tasks. Also, the more recent development of non-solid pigs is covered; these include gel pigs for use in the hydrocarbon industries and ice pigs for use in the fluid products and process industries.