Failure analysis of SCC and SRB induced cracking of a transmission oil products pipeline

In April 2004, a transmission oil products API 5L X52 pipeline in northern part of Iran cracked, which led to oil leakage. Causes of Corrosion were studied and simultaneous effects of SCC and SRB induced cracking were demonstrated. The results of the investigation indicated that the applied polyethylene tape coating on the external surface of the pipeline became loose and overlapped, i.e., opened and disbanded in the corroded area, consequently, the surface of the buried pipeline was exposed to the surrounding wet soil environment. As a result of the chemical interactions and the formation of carbonate–bicarbonate solution, and the existence of underweight arising bending stress, SCC induced cracking was introduced. In addition to SCC, sulfate reducing bacteria (SRB) activities have intensified corrosion and related cracking process. The mechanisms and morphologies of SCC and SRB induced cracking propagation into the pipeline microstructure were studied and investigated.