SCC Behavior of Low-Alloy Steels in Simulated PWR Secondary Water Environment

Abstract Low alloy steels have been used as the pressure boundary component materials of LWR coolant systems. So it is important to clarify stress corrosion cracking behavior of the alloys. Slow strain rate tensile (SSRT) tests were carried out on two heats of low alloy steels in a simulated PWR secondary water environment under various combinations of temperatures and dissolved oxygen concentration (DO) concentrations. The results obtained are as follows; a high sulfur steel had SCC susceptibility at the temperatures ≧ 453 K in 0.1 ppm DO. While, a marginal susceptibility was observed in a low sulfur steel at the temperatures between 453 K, and 493 K in 0.1 ppm DO. Both of the steels were almost immune to SCC in DO < 0.005 ppm except in the high sulfur steel at 453 K. Impurity ions of Cl- and SO42- increased SCC susceptibility of the low sulfur steel very much, with no remarkable effect of these ions observed in high sulfur steel. No large difference was observed in SCC behavior in simulated PWR secondary and BWR water environments. Critical DO concentrations as a function of sulfur content were derived form the SSRT results in simulated BWR and PWR secondary water environments.