Sour resistant X65 UOE line pipe for low-temperature service

With the aim of developing sour-resistant API X65 UOE line pipe with good low-temperature toughness, the effects of the aluminum content on the simulated HAZ toughness and the formation of the M-A (martensite-austenite) constituent were examined. It was found that HAZ toughness improves remarkably when the aluminum content is below 0.01 mass %. Reduction in the aluminum content is considered to suppress the formation of the M-A constituent harmful to lowtemperature toughness by facilitating the precipitation of Fe3C from untransformed austenite on cooling after welding. Based on the experimental results, API X65 UOE pipe for sour service was commercially manufactured and its properties were examined. The newly developed API X65 UOE pipe exhibited excellent HIC and SSC resistance, as well as excellent low-temperature toughness at −46 C.