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Preliminary Evaluation of the Influence of Hydrogen on the Fracture Toughness of an X65 Gas-Transmission Pipeline Steel

Abstract:

Previous research has indicated that hydrogen decreases the fracture toughness of gas-transmission pipeline steels. This study produced two values of fracture toughness for the X65 steel in the Dampier Bunbury natural gas-transmission pipeline in air (J<inf>Q</inf> of 590 and 778 kJ m<sup>−2</sup>; equivalent to K<inf>Q</inf> of 369 and 487 MPa (Formula presented.)) and two essentially American Society for Testing of Materials–valid values of fracture toughness of K<inf>J1C</inf> of 150 and 189 MPa (Formula presented.) for X65 subjected to in situ hydrogen charging thought to be equivalent to a hydrogen gas pressure of 200 bar. The fracture toughness for hydrogen-charged specimens was lower than in air. The large spread of the fracture toughness in air was attributable to the fact that these J<inf>Q</inf> values were dependent on testing details. The spread of fracture toughness values in hydrogen was attributed to the variability of fracture toughness in hydrogen under these hydrogen-charging conditions. There was considerable stable crack growth. The energy for stable crack growth increased with crack length. The fractography in the presence of hydrogen showed significant ductility, consistent with hydrogen-assisted plastic fracture. The values of fracture toughness in air and with hydrogen were consistent with literature values.