Effects of pH on lead-induced passivity degradation of nuclear steam generator tubing alloy in high temperature crevice chemistries
By Lu, B.T.; Luo, J.L. & Lu, Y.C.
Published in Electrochimica Acta
2013
Abstract
A Cr-depleted anodic film forms at 300 °C on UNS N066900 alloy exposed to an alkaline crevice chemistry and a Cr-enriched one forms if the solution is an acidic one. The presence of lead contamination reduces the pH effect on anodic film composition but increases defects in film structure. Lead impurity hinders dehydration and formation of spinel oxides, and thus Cr in the anodic films exists mainly in hydroxides that are less protective. This effect is enhanced with increasing pH. Depending on pH, lead contamination can promote entry of other dissolved species, such as hydrogen and calcium, which may also affect the passivity.