The significance of the local electrode potential within pits, crevices and cracks

Abstract A reveiw of the experimental measurements of the electrode potential within pits, crevices and cracks shows a significant number of similar findings for several commercially important alloy systems. Recent results for crevicing in iron give further insight into the relationship of the important parameters within the cavity: IR drop, Flade or passivation potential and solution composition. The key relationship for stable crevice corrosion is that the electrode potential in the crevice is less oxidizing than the Flade potential of the crevice solution. The consequences of this finding are discussed for pitting corrosion, stress corrosion and corrosion fatigue. Some expected consequences regarding the initiation of localized corrosion are presented. In this mechanism, the modified solution compositions that are found inside occluded cells promote local cell action through their influence on the potential shift, e.g. acidification facilitates local cell action by shifting the Flade potential in the noble direction.