Experimental evaluation of crevice corrosion depth for stainless steels in sea water environments

Growth rates of crevice corrosion for various stainless steels in sea water environments were evaluated under potentiostatic condition. And perforation time for the stainless steel plate was estimated by time dependence of the maximum crevice corrosion depth. Crevice corrosion resistance of stainless steels deteriorated with increase of chloride ion concentration. Crevice corrosion initiated and grew for all the stainless steels tested in this study in the solutions with more than 100 ppm chloride ion. Dmax maximum crevice corrosion depth, was approximated as power low function as D max=A•tm. Term A, Dmax at 1 hour, was increased with chloride ion concentration. On the other hand, term m showed from 0.3 to 0.5 independent with chloride concentration. It seems that values of m should be explained by dissolved morphology at corrosion crevice and assuming rate determining step for metal dissolution. For example, perforation time of crevice corrosion for the 1 mm thick SUS 304 stainless steel in 19 ppm chloride ion solution at 50°C was estimated about 4 years, 21 years for SUS316L stainless steel and 66 years for SUS329J4L stainless steel. And perforation times for SUS304 stainless steel were almost same under potentiostatic condition between 300 mV (vs. SSE) and 440 mV (vs.SSE).