Consideration of repassivation process based on the measurement pH in crevice and metal dissolution rate of SUS304 stainless steel in artificial seawater

The crevice corrosion test by two-step potentiostatic polarization and the pH in crevice (pHc) with a semiconductor chemical sensor were simultaneously measured, and the repassivation mechanism for SUS304 stainless steel were investigated. The total metal dissolution current density (imetal) of crevice corrosion is shown as the sum of the current density detected externally (iout) and inner crevice corrosion caused by hydrogen generation reaction (4,). When crevice corrosion has progressed sufficiently, there is nice correlation between ioutand pHc. If there is a lot of iin, the consumption of H+will increase and it will be easier to repassivate. The repassivation pH was 2.5 to 3.0 in both ASW and 1/10ASW. Current density threshold (10-5A·cm-2) and relationship between pHcand potential the immobilization potential (ER) obtained from was was 80 mV(SHE) in ASW and 120 mV(SHE) in 1/10ASW, the lower Cl-concentration in the external environment, ERbecame noble. This is because the ratio of iinin imentalis high, the consumption of H+increases, and the effect of diffusion and dilution of anolyte makes it easy to repassivation. © 2021 Japan Society of Corrosion Engineering. All rights reserved.