Technical basis for hydrogen-water chemistry: Laboratory studies of water chemistry effects on SCC [stress-corrosion-cracking]

The influence of different impurities, viz., oxyacids and several chloride salts, on the stress-corrosion-cracking (SCC) of sensitized Type 304 stainless steel (SS) was investigated in constant-extension-rate-tensile (CERT) tests in 2890C water at a low dissolved-oxygen concentration (<5 ppB). Cyclic loading experiments on fatigue precracked fracture-mechanics-type specimens of this material and Type 316NG were also performed at 2890C in low-oxygen environments with and without sulfate at low concentrations. In these experiments, the crack growth behavior of the materials was correlated with the type and concentration of the impurities and the electrochemical potentials of Type 304 SS and platinum electrodes in the simulated hydrogen-water chemistry environments. The information suggests that better characterization of water quality, through measurement of the concentrations of individual species (SO42-, NO3-, Cu2+, etc.) coupled with measurements of the corrosion and redox potentials at high temperatures will provide a viable means to monitor and ultimately improve the performance of BWR system materials