Pigs are devices utilized when carrying out various pipeline operations during its lifetime. The most serious threat for each pigging operation is stoppage in the pig movement. "Pig Rescue" operations refer to the activities for making the pig continue its path and move along the pipeline. Normally when the pig gets stuck, the first task is to estimate the location of pig in the pipeline. Situation is even more disastrous for the case of offshore pipelines since locating the position of the pig would be a hard and costly task.
Most reputable pipeline service contractors and operators have gradually built their own knowledge base when dealing with different scenarios of pig rescue operations. However, choosing a cost-effective engineering solution in a reasonable time period is always a major challenge.
This article describes the lessons learned from pig rescue activities done during precommissioning operations of a 290 km offshore pipeline from Siri Island to Asaluyeh Port in the Persian Gulf. The 32-inch natural gas pipeline is considered the longest offshore pipeline in the region. As a series of valuable experiences achieved from the project, this paper presents different procedures for moving the stuck pig based on the pipeline conditions and the type of pig itself. Some of the procedures include pressurizing the pipeline with gas or liquid, performing sudden fluid discharge, inserting other pigs inside the pipelines, etc. Furthermore, necessary engineering and safety considerations when following up the pig rescue procedures are discussed that would be absolutely useful for practitioners in the oil and gas industry.
