Influence of the surface state on the initiation of crevice corrosion on stainless steels

Results from sea-water and laboratory exposure tests with multiple crevice assemblies are presented. The results from tests on austenitic and ferritic-austenitic stainless steel samples subjected to various surface treatments demonstrate that an acid treatment greatly improves the crevice corrosion resistance of previously ground surfaces. Pickling in dilute sulphuric acid and passivation in nitric acid has thereby virtually the same beneficial effect as the common nitric + hydrofluoric pickling acid. The beneficial effect of pickling and passivation is related to the removal from the surface of sulphide inclusions, being potential nucleation sites for the initiation of discrete pitting attacks preceding the onset of crevice corrosion. Potentiodynamically determined pitting potentials and results from testing in 10% FeCl3 x 6H2O according to ASTM G 48-76 show poor correlation with results from sea-water exposures. (orig.)