An Analytical Modeling Method for Calculating the Current Delivery Capacity of a Thin-Film Cathode and the Stability of Localized Corrosion under Atmospheric Environments

Corrosion resistant materials under atmospheric conditions can suffer from localized corrosion. The stability of such a localized corrosion site requires that the site (anode) must dissolve at a sufficient high rate to maintain the critical chemistry and a wetted surrounding area (cathode) provides matching cathodic current. An analytical method for evaluating the stability of localized corrosion of corrosion-resistant alloys under thin-layer (or atmospheric) conditions is presented. The maximum cathode current available depends on the cathode geometry, temperature, relative humidity, deposition density of salt (i.e., mass of salt per unit area of cathode), and interfacial electrochemical kinetics. The anode demand depends on the crevice geometry, the position of attack within the crevice, and the localized corrosion stability product. By coupling these two approaches, the stability of a crevice can be determined for a given environmental scenario. The method has been applied to the atmospheric localized corrosion of Type 316L stainless steel.