Effects of Test Methods on Crevice Corrosion Repassivation Potential Measurements of Alloy 22

Alloy 22 (UNS N06022) may be used as the waste package outer container material for disposal of high-level waste at the potential repository at Yucca Mountain, Nevada. Crevice corrosion is one of the corrosion processes that may affect the performance of the waste package outer container. The relative susceptibility of Alloy 22 to crevice corrosion is evaluated through the measurement of crevice corrosion repassivation potential (E_rcrev) using electrochemical test methods. The main purpose of the work described in this paper is to verify some E_rcrev values reported in the literature and investigate the effects of different electrochemical test methods on the measurement of E_rcrev. This work also provides risk insights and reduces the measurement uncertainties associated with evaluating the effects of the fabrication process on crevice corrosion susceptibility. In this work, E_rcrev was measured in various chloride solutions at 90°C (194°F) using three methods: ASTM G61-86, the potentiodynamic polarization plus intermediate potentiostatic hold method, and the Tsujikawa-Hisamatsu Electrochemical (THE) method. The results indicate that at lower chloride concentrations (1 M [molar] sodium chloride [NaCl] and 1.25 M calcium chloride [CaCl₂]), the E_rcrev values using ASTM G61-86 were higher compared to the data in the literature. In addition, for these chloride concentrations, the E_rcrev values measured by using the potentiodynamic polarization plus intermediate potentiostatic hold method were higher than those using ASTM G61-86, whereas the E_rcrev values measured using ASTM G61-86 were slightly higher than those measured using the THE method. At a high chloride concentration (5 M CaCl₂), the E_rcrev values reported in the literature are reproducible and those measured by ASTM G61 and potentiodynamic polarization plus intermediate potentiostatic hold methods were found to be similar. In this chloride concentration, the values measured by using the THE method were about 40 mV higher than those measured by the other two methods.