Crevice corrosion testing methods for measuring repassivation potential of alloy 22

Alloy 22 (UNS N06022) belongs to the Ni–Cr–Mo family and is known for its high resistance to both general and localized corrosion; however, it is susceptible to crevice corrosion under aggressive environmental conditions. The objective of this study is to compare various electrochemical methods for determining the repassivation potential of alloy 22, including cyclic potentiodynamic polarization, Tsujikawa–Hisamatsu electrochemical, and several other techniques. Among these, the potentiodynamic–galvanostatic–potentiodynamic technique emerged as the most conservative, providing the lowest repassivation potential in a relatively short testing duration. Furthermore, crevices formed using polytetrafluoroethylene (PTFE)-wrapped ceramic exhibited more severe corrosion compared to those formed with solid PTFE, resulting in higher repassivation potentials. It was also found that higher torque values, exceeding 2 N m, were essential for achieving reliable repassivation potentials. Additionally, surface roughness did not significantly influence the repassivation potential, highlighting the importance of the testing conditions over material surface characteristics. This research contributes to the understanding of crevice corrosion mechanisms in alloy 22 and provides recommendations for evaluating its susceptibility in practical applications.