Rust Staining Resistance of Stainless Steels in a Marine Environment and its Estimation Method

A new electrochemical evaluation method was presented to estimate the rating number of rust staining of stainless steels in a marine environment. In this accelerated test, rust staining resistance of stainless steels was evaluated from the time to pitting under the thin electrolyte layer that was generated by the capillary phenomenon through a cotton cloth. The incubation time to passive film breakdown under this thin electrolyte layer corresponds to initial atmospheric corrosion resistance. From the results of ten years exposure test, most of stainless steels experienced severe rust staining within the first two years exposure. All the types of stainless steel have the same tendency wherein rating number changes with the square of the inverse time. The rating number of stainless steels in the marine environment can be evaluated from this time dependence and the degree of initial rust staining. The latter can be estimated by newly developed test method.