Modeling the Effect of Chloride Content on Hydrogen Sulfide Corrosion of Pure Iron by Coupling of Phase and Polarization Behavior

Abstract Localized corrosion of higher alloyed steels has frequently been shown to produce locally aggressive solutions with low pH levels in crevices and pits. It also has been established that such solutions can serve to initiate and propagate stress corrosion cracking. The present model aims at a basic understanding of the time-dependent local acidification process and, in a first approach, uses pure iron as a model metal. The model couples the anodic polarization resistances to the precipitated equilibrium masses of iron disulfide (FeS2), which in a “closed loop” time stepwise procedure are calculated from the solute concentrations in a diffusion boundary layer. With the cathodic process controlled by hydrogen ion reduction, the precipitation of FeS2 enforces local pH reductions at the anodic site depending on the total concentrations of HS−, Fe++, and H+ in the assumed diffusion layer. In the present work, the effects of chlorides on ion migration, sulfide solubility, anodic polarization resistances,...