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

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.