Failure Reason of Girth Welds in a Shale Gas Pipeline in Sichuan

Multiple weld cracks were found at the T-joint of a shale gas gathering pipeline in service in Sichuan. A systematic analysis of failed pipe sections was conducted using methods such as macroscopy morphology, microstructure, mechanical properties, and fracture analysis. The possibilities of sulfide stress cracking, hydrogen induced delayed cracking, and stress corrosion cracking were discussed, and the stress corrosion sensitivity of welds in the environment with biocide and corrosion inhibitor was verified using slow strain rate testing. The results show that due to varying degrees of welding defects such as excessive welding height, weld nodules, and uneven thickness welding, the cracking of the pipeline circumferential weld was mainly caused by stress corrosion due to the influence of corrosive media. At the same time, some welds exhibited hydrogen induced delayed cracking.