In this work, the hydrogen stress cracking (HSC) resistance of Ni-Cr-Mo-Nb age hardening nickel-based alloys with a Specified Minimum Yield Strength of 120 ksi (827 MPa) will be discussed. The outcome of recent failure investigations on the main age hardened nickel alloy families used in oil and gas production—namely, UNS N07718, N07725, and N07716—will be presented alongside various experimental and characterization techniques. Likewise, the correlation between HSC resistance and alloy microstructure and mechanical properties will be debated.
Results showed that the HSC resistance of age-hardened nickel alloys was strongly influenced not only by microstructure but also by fabrication parameters. Specifically, alloy UNS N07725 exhibited a significant disparity in HSC resistance, with reductions of fracture load in a hydrogen containing environment up to as much as 49%. UNS N07718 gave the best HSC performance with the lowest reduction in fracture load. UNS N07716 had an HSC response in between that of N07725 and N07718. The implications of these findings will be addressed.