THE CORROSION BEHAVIOR OF NI-AL ALLOYS AND NI-NB-AL ALLOYS IN A H2/H2O/H2S GAS-MIXTURE

The corrosion behavior of two Ni-Al alloys and four Ni-Nb-Al alloys was studied over the temperature range of 600-degrees-C to 1000-degrees-C in a mixed-gas of H-2/H2O/H2S. The parabolic law was generally followed, although linear kinetics were also observed. Multiple-stage kinetics were observed for the Ni-Al alloys. Generally, the scales formed on Ni-13.5Al and Ni-Nb-Al alloys were multilayered, with an outer layer of nickel sulfide with or without pure Ni particles and a complex inner scale. The outer scale became porous and discontinuous with increasing temperature. Very thin scales formed on Ni-31Al. The reduction in corrosion rate with increasing Al content is ascribed to the formation of Al2O3 and Al2S3 in the scale. Platinum markers were found at the interface between the outer and inner scales.