Absrract
The high strength and corrosion resistance of nickel-chromium-iron alloys, such as UNS N07718 (Alloy 718), UNS N09945 (Alloy 945) and UNS N09946 (Alloy 945X) make them particularly good candidates for use in demanding environments in the upstream oil and gas industry. These materials generally perform well where resistance to sulphide stress cracking and chloride stress corrosion cracking is required. However, whilst these alloys are considered ‘NACE compliant' environmentally-assisted failures can still occur. It is generally accepted that for hydrogen cracks to initiate, there must be a critical combination of stress, susceptible microstructure and hydrogen concentration. In this project, the effect of microstructure is explored by heat treating Alloys 718, 945 and 945X to standard and nonstandard conditions. Tensile specimens were slow-strain-rate-tested in air and under cathodic protection (CP) to explore sensitivity to hydrogen embrittlement. Finally, the effect of a severe stress concentration, in the form of a sharp notch, was used to determine whether there is an increased susceptibility to hydrogen embrittlement due to the presence of local stress raisers. The results are compared with tests undertaken by other authors under various hydrogen-charging conditions.
