Corrosion and Stress Corrosion Cracking of Alloy 22 in Lead-Containing Solutions

The susceptibility of Alloy 22 to localized corrosion and stress corrosion cracking was evaluated in lead-containing solutions. Speciation calculations indicate that aqueous dissolution of PbCl2 resulted in the formation of Pb2+ and Pb-Cl complexes. PbCl2 was selected among several lead compounds for its high solubility and dissociation rate. The total dissolved lead species concentration was measured by inductively coupled plasma-atomic emission spectrometry. Comparative anodic polarization tests were conducted in a range of deaerated, acidified PbCl2 solutions. The presence of lead species in a super-saturated PbCl2 solution with apH of 0.5 promotes the occurrence of apronounced anodic peak and significantly increases the passive current density. Enhanced dissolution of Alloy 22 resulted, as characterized by the presence of randomly distributed etch pits. At an applied potential of -100 mVSCE, which is the potential corresponding to the anodic peak, Alloy 22 was found to be resistant to stress corrosion cracking when tested in super-saturated PbCl2 solutions (pH 0.5) at 95 °C [203 °F]. Moreover, no deleterious effect of lead species on localized corrosion was observed in crevice specimens over a wide range of lead concentrations with the exception of acidified, super-saturated PbCl2 solutions. Provided that these high lead concentrations are not attainable in the anticipated repository environments, Alloy 22 is unlikely to be susceptible to stress corrosion cracking or localized corrosion.