Single-boss crevice former for studying crevice corrosion of UNS S32003 in chloride-containing solution at high temperature

Abstract

We studied crevice corrosion of UNS S32003 using a single-boss crevice former. This crevice assembly with a single boss at the center is a modification of the commonly used multiple-crevice assembly (MCA). This design effectively prevents unwanted crevice corrosion outside the crevice of interest. Our single-boss crevice assembly produces comparable repassivation potentials obtained using cyclic potentiodynamic polarization (CPP), Tsujikawa–Hisamatsu Electrochemical (THE), potentiodynamic–galvanostatic–potentiodynamic (PD–GS–PD), and potentiostatic (PS) techniques. Considering the degree of attack, we found that the THE technique is the most powerful for forming a deep, wide, and continuous crevice corrosion site, while the PS technique is the least powerful technique at potentials slightly above the repassivation potential. A galvanostatic hold in step 2 of the THE and PD–GS–PD techniques successfully grows a deep localized corrosion site, as indicated by a deep crevice corrosion attack found in samples tested with these techniques. The PS step (step 3) in the THE technique allows the grown localized corrosion site formed by a previous step (a galvanostatic hold) to propagate inward and along the crevice mouth, creating a wide and continuous crevice corrosion attack along the crevice mouth. Metastable pits play a role in crevice corrosion of UNS S32003 alloy in this study, as indicated by a large number of metastable pits in the crevice region. The ferrite phase is preferentially attacked by metastable pits.