Analysis of Failure Caused by In-service Welding in anX52 Gas Pipeline

In the research presented in this paper, a failure analysis were carried out to identify causes of an incident, which had taken place after an operation to repair a leak in an interstate natural gas pipeline. In this operation, a partial encirclement reinforcement (patch) was welded to the carrier pipe according to an available hot taping procedure, while gas was flowing in the pipeline. The failure analysis commenced with preliminary steps of gathering of background data regarding the repair operation and then several samples were extracted for macroscopic and microscopic metallurgical examinations. In addition to fractographic analyses of fracture surfaces, pipe material was examined because the pipeline had been in service for prolonged period and there was not any official material information available. The analyses disclosed that hydrogen-assisted cracking, wrong design of branch connection, paint coating and pipeline operating conditions were major factors contributing to the failure.