Critical Potentials for Pitting and Crevice Corrosion of Type 304 Stainless Steel in NaCl Solution at 423K

Abstract

Critical potentials for pitting (E_pit) and crevicice corrosion (E_crev) for type 304 stainless steel have been determined from long-term steady polarization tests in deaerated NaCl solutions as a function of NaCl concentration at 423K. E_pit and E_crev were expressed by the conventional form: E=A-B log[Cl^-], where A and B in volt vs. SHE were -0.19 and 0.15 for E_pit and -0.20 and 0.10 for E_crev, respectively. The comparison of E_pit with pitting potential (E′_pit) and repassivation potential (E_{R, pit}), which were repeatedly determined from stepwise cyclic polarization tests, showed that E_{R, pit} distributed less nobly than E_pit especially at lower NaCl concentrations and that E_pit could be described as a lower limit of Weibull's distribution function for E′_pit. The similar analysis for crevice corrosion showed that the noblest value of E_{R, crev} for its dependency on corrosion extent corresponded to E_crev but the distribution in E′_crev at different concentrations of NaCl could not be described by the Weibull's function with an identical shape parameter.