Role of alloyed molybdenum on corrosion resistance of austenitic Ni-Cr-Mo-Fe alloys in H2S-Cl- environments

Corrosion test and surface analysis were conducted in the H2S-Cl- environments to elucidate the role of alloyed molybdenum on the corrosion resistance of Ni-Cr-Mo-Fe alloys. The alloyed molybdenum improves the localized corrosion resistance. The surface film is of double layers which comprise sulfide including molybdenum and chromium oxide. However, the Ni-Mo-Fe alloy also shows good corrosion resistance in the H2S-Cl- environment. This good corrosion resistance is considered to be due to the cation selectivity of molybdenum sulfide, which can form in such environments. The role of alloyed molybdenum on the corrosion resistance of Ni-Cr-Mo-Fe alloys in H2S-Cl- environments is proposed.