THE CORROSION BEHAVIOR OF NI-NB ALLOYS IN A MIXED GAS OF H2-H2O-H2S

The corrosion behavior of Ni-Nb alloys containing up to 40 wt.% Nb was studied over the temperature range of 550-800-degrees-C in a mixed H2/H2O/H2S gas. The scales formed on all alloys were multilayered The outer scale was single-phase Ni3S2, while the structure and constitution of the inner scale depended on alloy composition and reaction conditions. Internal oxidation has been found in Ni-20Nb and Ni-30Nb, external oxidation has been observed on Ni-34Nb. Platinum markers were located at the interface between the outer scale and inner scale. The decrease in corrosion rate with increasing Nb content may be attributed to the presence of increasing amounts of Ni-Nb double sulfides as well as to the presence of Nb2O5 in the inner region of the scale.