MODELING THE COMBINED EFFECT OF CHLORIDES AND OXYANIONS ON LOCALIZED CORROSION

摘要

Repassivation potentials of stainless steels and nickel-base alloys have been investigated in aqueous environments containing chloride ions as aggressive species and selected oxyanions as inhibitive species. An extensive database of repassivation potentials has been established for six alloys (UNS N06600, N06690, S31254, S32205, UNS S41425, and S31603) in contact with solutions that combine chlorides with hydroxides, molybdates, vanadates, sulfates, and nitrates at various concentrations and temperatures. This database has been used to validate and calibrate a previously developed mechanistic model for predicting the repassivation potential in complex chemical environments. The model accounts for the effect of solution chemistry and temperature on the repassivation of localized corrosion by considering competitive dissolution, adsorption, and oxide formation processes at the metal - occluded site solution interface. The model accurately reproduces the inhibiting effect of oxyanions and correctly identifies the relative concentrations of chlorides and oxyanions at which a transition from localized corrosion to inhibition is observed. Using parameters determined using a limited experimental data set, the model can predict localized corrosion in complex, multicomponent environments.