Localised corrosion of heat treated alloys Part 1 – repassivation potential of alloy 600 as function of solution chemistry and thermal aging

The crevice repassivation potential Ercrev of alloy 600 was measured as a function of chloride concentration, inhibitor concentration, temperature and degree of sensitisation (DOS) due to thermal aging. Electrochemical potentiokinetic reactivation tests were performed on thermally aged alloy 600 to correlate the DOS with Ercrev results. The electrochemical potentiokinetic reactivation results agreed well with the literature, and differed in the apparent sensitisation kinetics from Ercrev. The crevice repassivation potential was found to be inversely related to test temperature, chloride concentration, and DOS due to thermally aging the material. Additions of nitrate were found to significantly elevate the repassivation potential of both annealed and sensitised material. The results form the basis for establishing a model to predict the occurrence of localised corrosion for in service, real world materials used in the processing industry.