The Assessment of Pit Chemistry Parameters of 316 Stainless Steel and 304 Stainless Steel by Adding a Molybdate Inhibitor in a Chloride Aggressive Media

Abstract

In this study, the efficacy of Mo as an alloying element and inhibitor on the pit chemistry parameters of 316 stainless steel (316SS) (2 wt% Mo) and 304 stainless steel (304SS) (0.2 wt% Mo) in chloride and molybdate-bearing solution is investigated. To evaluate pit chemistry parameters, three-step polarization and four-step polarization tests using a pencil electrode were conducted. The results suggested that the presence of molybdate ions increased the pit transition potential and repassivation potential. Moreover, molybdate increases the critical, saturation, and supersaturation concentrations at an equal pit depth. Therefore, the concentration of necessary cations increased to precipitate the salt. A comparison of the pit chemistry characteristics between 316SS and 304SS showed that molybdenum increased the potential necessary for salt removal and facilitated the repassivation process of the individual pit.