Investigation of the Pitting Resistance of SS304 and SS316L in Neat Chemical Products Using EIS

摘要

Corrosion behavior of austenitic stainless steel UNS S30400 (SS304) and austenitic stainless steel UNS S31603 (SS316L) in the presence of neat chemical products was investigated. It was corroborated in previous work that the criteria used to determine the chemical compatibility for SS316L from cyclic polarization could be also implemented to evaluate the compatibility with SS304. The purposes of this study is to confirm, for the same chemicals and metallurgies, that electrochemical impedance spectroscopy (EIS) could be used as a quick and effective tool to investigate the compatibility of neat chemical with stainless steels (as alternative and complementary tests beside cyclic polarization and critical pitting temperature). The second goal is to investigate the effect of molybdenum on the corrosion resistance of the two different stainless steels. It was found that a polarization resistance (R_p) higher than 10000 n.cm~2 determined from the impedance diagram (polarized at 200 mV vs. open circuit potential (OCP)), suggested a high resistance of the passive film. Flags about the presence of pits were suggested by a R_p value lower than 10000 Q.cm~2 (polarized at 200 mV vs. OCP). The R_p for several chemical products was higher for SS316L when compared with SS304, suggesting that the Mo content in the alloy is providing higher resistance of the film.