Environmental Factors Affecting the Critical Potential for Pitting in 18–8 Stainless Steel

Abstract

The concept of a critical potential below which pitting of 18–8 and other passive alloys does not occur in aqueous Cl− media is affirmed. Increasing Cl− concentration shifts the critical potential to more active values. The potential is shifted to more noble values by presence of other anions, e.g., ClO4− , SO4−− , NO3− , OH− , sufficient concentrations of which act as pitting inhibitors. Lowering of temperature similarly enobles the critical potential. The shift at 0°C exceeds the oxidation‐reduction potential for Fe++→Fe++++e accounting for resistance of 18–8 to pitting in FeCl3 solutions at ice temperature but not at room temperature. The critical potential is not affected appreciably in the acid pH range; it moves markedly in the noble direction in the alkaline range corresponding to observed resistance to pitting in alkaline Cl− media. These results are interpreted in terms of competitive adsorption of Cl− and other anions for sites on the alloy surface. Only at a sufficiently high surface concentration of Cl− is oxygen, making up the passive film, displaced locally, and passivity thereby destroyed resulting in a pit. The special behavior of NO3− inhibition and factors affecting reproducibility of measurements are discussed.

The Kinetics of Anodic Dissolution and Repassivation on 316L Stainless Steel in Borate Buffer Solution Studied by Abrading Electrode Technique

“…The passive film formed on stainless steel in aqueous is predominantly a Cr(III) rich oxide film, which have been reported by some investigators [21][22][23] , z = 3, M = 152 g·mol -1 and ρ = 5.2 g·cm -3…”

Effect of chloride and sulfate ions in simulated boiler water on pitting corrosion behavior of 13Cr steel

“…Recently, Tang et al [14] reported that a good linear relationship exists between the metastable pitting potential and the pitting potential, which is similar to that observed in the present work. has the effect of suppressing the pitting corrosion of stainless steels [11].…”

“…On the other hand, it has long been known that SO4 2-has an inhibitory effect on the pitting corrosion of stainless steels [11]. However, there are still many unknown factors regarding the relationship between the initiation and growth mechanisms of pitting corrosion on stainless steels and these impurity ions.…”

Chloride-induced corrosion on reinforcing steel: from the fundamentals to the monitoring techniques

“…The first model was initially proposed by Leckie and Uhlig [17,18] and Kolotorkyn [19] and suggests that breakdown involves adsorption of Cl À with simultaneous displacement of O 2À from the passive layer, leading to initiation of film destruction.…”