Sour service fluids from wells place significant demands on pipeline material, particularly in deeper water. This can present major technical and financial challenges for pipeline operators as the fluids can cause fractures and cracks which affect pipeline performance and reliability. DNV GL has now launched a Joint Industry project to develop a methodology to evaluate fractures and cracks using a Single Edge Notched Tensile (SENT) test designed specifically for sour service environments. Eight participants are on board and the JIP is still open for new participants.
A pipe material and weld that performs well in air will be significantly less tough and resistant in a sour environment. A SENT test is designed to simulate loading conditions and crack depths similar to those experienced by pipelines operating under normal conditions. Research conducted in DNV GL’s laboratories shows that in a sour environment, where fluids such as H2S, H2O and CO2 may be present, results can be highly variable depending on numerous environmental and test parameters. Fracture toughness, for example, tends to decrease with increased H2S concentration (partial pressure of H2S) and decreased loading or strain rate. Current guidance under DNV-OS-F101 and DNV-RP-F108 does not reflect this.