Precipitation-Hardened, Nickel-Base Alloys for Sour Gas Environments Available to Purchase

Stress corrosion cracking (SCC) in sour gas environments of γ′ [gamma prime: Ni₃(Ti and/or Al)] and γ″ (gamma double prime: Ni₃Nb) precipitation-hardened, nickel-base alloys has been studied using the slow strain rate tensile (SSRT) test, anodic polarization measurement, and transmission electron microscopy (TEM). The γ′-type alloy containing Ti was more susceptible to SCC in the SSRT tests up to 350 F (450 K) than the γ″-type alloy containing Nb. The susceptibility to SCC was related to their deformation structures in terms of stress localization and sensitivity to pitting corrosion in H₂S solutions. TEM observation showed that the γ′-type alloy deformed by superlattice dislocation pairs in coplanar structures. This mode of deformation induced stress localization at some boundaries, such as grain boundaries and as a result, the susceptibility to SCC of the γ′-type alloy was increased. On the other hand, the γ″-type alloy deformed by single dislocations, not in coplanar structures, so that it was less susceptible to SCC in terms of stress localization. The anodic polarization measurements suggested that the γ′-type alloy was more susceptible to pitting corrosion compared to the γ″-type alloy.