Failure Investigation of a Natural Gas Transmission Pipeline

PT Transportasi Gas Indonesia (TGI) own and operate a 536 km long natural gas pipeline in South Sumatra, Indonesia which transports natural gas from ConocoPhillips’s gas field in Grissik, South Sumatra to Chevron Pacific Indonesia’s station facilities in Duri. On 29th September 2010, an event occurred that resulted in a release of gas from the pipeline. In response to the emergency, the affected section of the pipeline was isolated by closing block valves upstream and downstream of the leak. The incident was brought under control by TGI on the same day and there were no reported injuries or fatalities. Failure was located in a girth weld on a 28 inch diameter pipe section, which had spread into the adjacent pipe material. Subsequently a failure investigation was requested by TGI. The investigation included a fracture examination and materials testing of the failed girth weld and parent pipe; a geotechnical investigation; and an engineering critical analysis (ECA) of the failure. This paper describes the multidisciplinary works undertaken to investigate the cause of the incident. The primary observation of this failure investigation is that no single factor contributed to the failure that occurred. The pipeline at the rupture location had been subjected to high bending stresses when the pipeline was laid and the stresses were exacerbated following consolidation and creep settlement of the underlying swamp material. The field joint coating had been compromised, leading to the formation of near neutral stress corrosion cracking (SCC). Initial cracking from the SCC had then extended to the point where the remaining ligament then failed by plastic collapse. It was judged that the settlement may also have been enhanced by a recent earthquake.