Crevice Corrosion Behavior of Various Stainless Steels under Marine Environments

Exposure tests of various stainless steels have been conducted for 10 years with actual sea water. Corrosion resistance of each stainless steel under marine environments was evaluated by two types of tests which were atmospheric corrosion test and seawater spray test. The test results showed that spraying sea water enhanced the proceeding of corrosion. It has been proved that the super austenitic stainless steels defined by Pitting Resistance Equivalent (PRE=%Cr+3.3x%Mo+16x%N) over 40 have excellent corrosion resistance. The corrosion mechanism in this environment was basically estimated as crevice corrosion between the specimen surface and condensed substance originated from adhered chloride ions. In addition, microbes contained in sea water were considered to enhance the corrosion progress. Repassivation potential for crevice corrosion measurements were further carried out for Cl- ion to understand the corrosion mechanism assuming the critical potential of 500mV accounting for the existence of microbes. The obtained curves well support the exposure test results; the steel grades with PRE values over 40 were proved not to corrode under the present test conditions including temperature and Cl- ion concentrations. As a conclusion, the corrosion behavior of stainless steels can be explained by repassivaition potential for crevice corrosion considering microbes.