A general model has been developed for predicting the occurrence of localized corrosion in multicomponent electrolyte solutions. The model is based on calculating the repassivation and corrosion potentials as functions of solution composition and temperature. For the corrosion potential, a previously developed mixed-potential model is used. For the repassivation potential, a new model has been developed on the basis of nonequilibrium thermodynamics of metal dissolution within a pit or crevice. The model assumes that the status of localized corrosion is determined by competitive processes at the metal - salt film - solution interfaces leading to either metal salt or oxide formation. To calibrate and verify the model, an extensive database of repassivation potentials has been established for eleven alloys (UNS N06022, N10276, N06625, N08825, N06600, N06690, N08800, N08367, S31254, S31603 and S41425). The model successfully predicts the observed effects of aggressive species, such as chloride and bromide, inhibiting species, such as nitrate, and non-aggressive species, such as acetate, on the repassivation potential. A generalized correlation has been established to relate the repassivation potential to alloy composition. Further, the model has been validated by predicting the critical crevice temperature in FeCl3 solutions.

Subject
Pits, Ions, Repassivation, Repassivation potentials, Halides, Chloride solutions, Experimental data, Corrosion modeling, Metals, Localized corrosion, Alloys, Chlorides, Corrosion potential
Keywords:
Localized corrosion, stainless steels, nickel-base alloys, repassivation potential, corrosion potential
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2004
Association for Materials Protection and Performance (AMPP)
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