Simulation of Solution Chemistry in Crevice Corrosion for Stainless Steel

摘要

The calculation model to simulate solution chemistry in crevice corrosion for stainless steel immersed in NaCl solution was studied by using mass transfer model and considering formation of complex ions. The calculation was conducted in consideration of metal ions complex ions, Cl~-, Na~+(i=5) and potential, φ. Distributions of concentrations of ions and electrode potential were obtained for Type 316 stainless steels in 3% NaCl solution at 80℃. It was confirmed that only the distribution of Cl~- ion depended on the ratio of t - t_1=[FeCl~+]/([Fe~(2+)]+[FeCl~+]), t_2=[CrCl~(2+)]/([Cr~(3+)]+[CrCl~(2+)]) - because the diffusion coefficient of Cl~-, D_4(Cl~-)=2×10~(-5)cm~2/s, is 4 times larger than those of metal and complex ions, for example D_1(Fe~(2+))=5×10~(-6)cm~2/s. For Cl~- ion, maximum value decreases down to 6.9mol/L from 10.2mol/L by considering complex ions. And almost all Fe and Cr form complex ions of FeCl~+and CrCl~(2+).