A novel fully plastic caliper pig for low-risk pipeline inspection - Design, characterization and field test

Pipe in-line inspection by "intelligent" pigs is a fundamental oil and gas industry practice but still considered as an exceptional operation. In fact, the instrumented pigs addressing such a purpose are expensive and delicate tools with non-negligible operating risks, thus making their deployment rather infrequent (typically, once every several years). In eni we have started a number of R&D initiatives targeted to making pipeline inspection easier and more frequent by significantly reducing the operating risk faced when deploying inspection pigs. In this context, we present a new, low-cost and low-risk plastic pig with inspection capabilities analogous to those of a multichannel caliper pig (i.e. able to detect, locate and size inner diameter changes and deformations) together with additional features allowing to detect internal roughness changes (e.g. due to corrosion) and perform some pH/salinity determinations, also useful for corrosion assessment purposes. One implementation of the new tool makes use of a foam pig "body", providing the required push with a good capability to negotiate restrictions, equipped with specialized sensors and modules for acquisition and storage. Another implementation, targeted to gas lines and called "skeleton caliper pig", deploys the light plastic system without any foam pig carrier, pushed by the gas velocity alone, and is suitable to prevent the massive displacement of condensates from gas lines. The paper describes the design, construction and field testing of this new low-risk caliper pig, together with some comparisons with the information gathered adopting a conventional tool.