Effect of Applied Potential and Inhibitors on PbSCC of Alloy 690TT

Abstract

Alloy 690TT has been shown to be susceptible to lead stress corrosion cracking (PbSCC) at pH_T values of 9.1 and above and with no cracks occurring at lower pH_T values like 8.5. Previous work on PbSCC has been completed at the open circuit potential (OCP). A test program has been completed at applied electrochemical potentials for Alloy 690TT at pH_T values of 8.5 and 9.5. Testing has shown sporadic PbSCC occurrence at pH_T 8.5 which previously showed no cracking although an exact causal factor was not identified. At pH_T 9.5, applying a potential did not stop PbSCC from occurring, although at +75 mV applied potential there was the inclusion of an apparent incubation time where none had previously been observed. To minimize to PbSCC, scoping testing was completed on four candidate inhibitors at pH_T 9.5. Three of the four inhibitors tested (TiO₂, H₃BO₃, and CeB₆) showed reductions in maximum crack depths compared to testing without an inhibitor. Although promising, inhibitors still require additional testing before widespread use can be recommended.