Corrosion behavior of ni base alloys and 316 stainless steel in less oxidizing or reducing SCW containing HCL

The objectives of this study are to evaluate the corrosion behavior of candidate corrosion-resistant alloys in less oxidizing or reducing supercritical water (SCW) environment containing hydrogen chloride and to understand the corrosion mechanism for determining the corrosion resistance of these alloys in the upgrading of low-quality hydrocarbon resources process. Four kinds of Ni base alloys, UNS N06625(Alloy 625), UNS N10276(Alloy C-276), Ni-45Cr-lMo (MC alloy) and Ni-19Cr-19Mo (MAT 21) and a 316 stainless steel were used in this study. Test temperature was changed from 350 to 550°C. Test pressure was fixed at 25MPa. Parametric study was carried out to investigate the influences of environmental variables such as temperature, anion, pH and the hydrogen partial pressure, on the effect of corrosion rate and corrosion morphology of the alloys. A static autoclave was used in this study. In reducing SCW, corrosion rate of 316 stainless steel was always higher than that of other Ni base alloys. While weight changes of 316 stainless steel and MC alloy was small in deionized water, weight losses were significantly increased with increasing hydrogen partial pressure. In less oxidizing SCW containing HC1, the weight loss of 316 stainless steel increased with increasing HC1 concentration. In reducing SCW containing HC1, Ni base alloys containing both Cr and Mo, such as Alloy C-276 and MAT21, were found to be more resistant to corrosion than NrCr binary alloys.