The Behavior of Resistive Layers in the Localized Corrosion of Stainless Steel

The dissolution of austenitic stainless steels in artificial crevices has been studied as a function of potential and chloride ion activity. Impedance measurements have shown the presence of a resistive layer on the steel which limited the rate of the electrode reaction in the localized corrosion of stainless steels. The potential across the layer, equal to the product of the direct current and layer resistance, varied linearly with the electrode potential indicating ohmic ionic conduction across the layer. The growth of the layer was limited by its solubility and the diffusion of metal cations in the aqueous phase in the cavity. The layer had the properties of a metal chloride with a given solubility product. Increased chloride activity decreased the saturation concentration of the metal cation, its concentration gradient, and gave decreased dissolution rates or currents.