ABSTRACT
Chloride-pitting in stainless steels proceeds at noble potentials in the polishing mode of metal dissolution, provided that the pit solution is enriched with chlorides beyond a critical concentration. It ceases to progress by pit repassivation if the pit is small, but it transforms into the active mode of pitting if the pit grows greater than a critical size. The boundary potential between the polishing mode and the active mode of pitting corresponds to the passivation-depassivation potential in the pit solution of the critical chloride concentration. Crevice corrosion is characterised by the crevice protection potential, at which the occluded crevice solution maintains the passivation-depassivation pH of the crevice metal. The crevice corrodes in the active mode at potentials more noble than the protection potential, where the crevice solution is more acidic than the pH. The stability of localised corrosion is represented in a diagram comprising the electrode potential and the size of the localised corrosion.
