In January 2010, stress corrosion cracking was occurred in a high-pressure gas pipeline steel in northern regions of Iran, after almost 40 years since its installation. In this study, failure mechanisms were determined based on available documents and metallographic studies conducted on this pipeline. The results showed that the applied polyethylene tape coating on the external surface of the pipeline became opened and disbonded in the corroded area causing external surface of buried pipeline to be exposed to wet soil around it. As a result of the chemical interactions and formation of carbonate/bicarbonate solution and with the presence of tensile stresses, stress corrosion cracking occurred in the longitudinal direction and at the outer surface of the pipe. In addition, mechanisms and morphology of cracks propagation due to stress corrosion cracking to internal side of the pipe wall were studied.
Keywords: API 5L X60; Stress corrosion cracking; Pipeline; Intergranular