Corrosion of similar and dissimilar metal crevices in the engineered barrier system of a potential nuclear waste repository

摘要

Crevice corrosion is considered possible if the corrosion potential (E{sub}(corr)) exceeds the repassivation potential for crevice corrosion (E{sub}(rcrev)). In this study, potentiodynamic polarization and potentiostatic hold were used to determine the E{sub}(rcrev) of similar and dissimilar metal crevices in the engineered barrier system of the potential Yucca Mountain repository in 0.5 M NaCl, 4 M NaCl, and 4 M MgCl{sub}2 solutions at 95 ℃. The results were compared with data previously obtained using crevices formed between Alloy 22 and polytetrafluoroethylene. It was observed that, except for Type 316L stainless steel, all other metal-to-metal crevices were less susceptible to crevice corrosion than the corresponding metal-to-poly tetrafiuoroethylene crevices. Measurements of galvanic coupling were used to evaluate the crevice corrosion propagation behavior in 5 M NaCl solution at 95 ℃. The crevice specimens were coupled to either an Alloy 22 or a Titanium Grade 7 plate using metal or polytetrafluoroethylene crevice washers. Crevice corrosion of Type 316L stainless steel propagated without repassivation. For all the tests using a polytetrafluoroethylene crevice washer, crevice corrosion of Alloy 22 was initiated at open circuit potential by the addition of CuCl{sub}2 as an oxidant, whereas no crevice corrosion of Alloy 22 was initiated for all the tests using Alloy 22 or Titanium Grade 7 metals as crevice washer. However, crevice corrosion propagation was found to be very limited under such test conditions.