Effect of lithium hydroxide on primary water stress corrosion cracking of Alloy 600 tubing

Primary water stress corrosion cracking (PWSCC) studies were performed on Alloy 600 in simulated PWR high lithium primary water. Tests were conducted at 330 degree C with Li concentrations ranging from 0.7 to 3.5 ppM in solutions containing boric acid and dissolved hydrogen. Highly stressed, Alloy 600 reverse U-bend specimens (RUBs) were predominantly used for tests. Both mill-annealed (MA) and thermally treated (TT) Alloy 600 were tested. The large number of specimens tested allowed the use of rigorous statistical techniques to interpret the variability of PWSCC performance. Results of tests of MA 600 RUBs at 2 stress levels show no effect of chemistry on the time to initiate PWSCC cracks over the range from 0.7 to 3.5 ppM Li. However, results for TT 600 RUBs and in MA 600 RUBs at a third stress level show the tendency for a shorter time to initiate PWSCC cracks at a Li concentration of 3.5 ppM. Analysis suggests that certain Alloy 600 components may experience an increase in PWSCC by using the higher LI content primary water due to a subtle influence of chemistry on PWSCC. 5 refs. 8 figs., 3 tabs