Effects of Surface Chromium Depletion on Localized Corrosion of Alloy 825 as a High-Level Nuclear Waste Container Material

Abstract

Abstract Effects of the chromium-depleted, mill-finished surface on the localized corrosion resistance of alloy 825 (UNS N08825) were investigated. Tests were conducted in solutions based on the ground water at Yucca Mountain, Nevada, but with a higher concentration of chloride (Cl−). Results indicated that breakdown (Ep) and repassivation (Erp) potentials for mill-finished surfaces were more active than those for polished surfaces. Potentiodynamic polarization tests indicated pits could be initiated on the chromium-depleted surface at potentials of 220 mVSCE in a solution containing 1,000 ppm Cl− at 95°C. Potentiostatic tests identified a similar pit initiation potential for the mill-finished surface. However, under long-term potentiostatic tests, a higher potential of 300 mVSCE was needed to sustain stable pit growth beyond the chromium-depleted layer. An increase in surface roughness also was observed to decrease localized corrosion resistance of the material.