On the Evaluation Methods of Ni-Base Corrosion Resistant Alloy for Sour-Gas Exploration and Production

The effect of Cr, Ni, and Mo contents of Ni-base alloy on the corrosion behavior in H2S–CO2–Cl− environment with elemental sulfur at elevated temperature was investigated. The environmental with elemental sulfur was more corrosive than that without elemental sulfur. The stress corrosion cracking (SSC) resistance of Ni-base alloys increases with increasing Ni and especially Mo contents. The main effect of the elemental sulfur is considered that the generation of H2S due to the cathodic reaction of elemental sulfur at a location underneath sulfur deposition, which is related to the viscosity of elemental sulfur. Recommendable chemical composition of Ni-base alloys in H2S–CO2–Cl−-S environment was proposed from the view points of phase stability, stress corrosion cracking, and hydrogen embrittlement (HE). Suitable high-Ni alloys had more than 12%Mo and 15%Cr and the phase stability parameter (Md) value below 0.911.