Electrochemical noise during exposure of alloy 600 to borated and lithiated high temperature water

The susceptibility of alloy 600 to intergranular stress corrosion cracking (IGSCC) has been tested in pressurized water reactor (PWR) simulated primary water chemistry at 3400 C by slow strain rate testing (SSRT). The electrochemical noise (EN) in current and potential was monitored during these tests. SSRT was also done in solutions in which the specific conductivity was increased by an order of magnitude by increasing the content of boric acid and lithium hydroxide, in order to increase the efficiency of monitoring of EN signals. The presence of 100 ppb each of chloride and sulphate ions in the high conductivity solution caused extensive pitting damage on the sample. Distinct EN signals were monitored before, during and after SSRT and were due to the pitting damage. The characteristics of these signals are reported in this paper. No EN signals were monitored due to the IG crack initiation events. The results are analyzed to deliberate on the mechanism of IGSCC in this environment.