Mechanisms of Inhibition of the Chloride-Induced Crevice Corrosion of Alloy 22

Chloride-induced crevice corrosion occurs due to the formation of hydrochloric acid solution in the creviced region. Inhibitors avoid the development of this solution or hamper its deleterious action. Anodic inhibitors are able to produce an increase of E_R,CREV and / or avoid the occurrence of crevice corrosion at R ≥ R_CRIT. This review focuses on the mechanisms of crevice corrosion inhibition of Alloy 22. The localized acidification model is used to explain the different effects of anodic inhibitors on E_R,CREV. Papers on this topic published over the last decade are reviewed. Hydroxyl, nitrate and phosphate are strong inhibitors; carbonate, chromate, molybdate and sulfate are moderate good inhibitors; while fluoride and organic acids are weak inhibitors of the chloride-induced crevice corrosion of Alloy 22. E_R,CREV is the sum of three contributions (E_CORR* + η + ΔΦ). Inhibitors produce an increase of one or more of these contributions by different mechanisms (proton consumption, pH buffering, blocking of preferential dissolution sites, supporting electrolyte effect, ohmic blocking action, etc.). There is a need of a quantitative assessment of the considered mechanisms to account for the observed effectiveness of the inhibitors.