The effect of pH on the spontaneous-passivation characteristics of AISI Types 304, 430 and 410 stainless steels has been studied by means of anodic-polarization and potential-time techniques. An inverse linear relationship between the logarithm of the critical current density for passivity and pH was found to hold true for all three steels in both acid sulfate and acid chloride environments.
Critical pH values (below which active corrosion occurs and above which the steels exhibit passivity) determined from electrochemical polarization measurements were found to agree well with those obtained under long-term natural corrosion conditions.
The results show the validity of a critical pH value in ranking stainless steels as to their resistance to acid corrosion.
