A SIMPLIFIED MODEL FOR SCC INITIATION SUSCEPTIBILITY IN ALLOY 600, WITH THE INFLUENCE OF COLD WORK LAYER AND STRENGTH CHARACTERISTICS

The effect of cold work on stress corrosion cracking (SCC) susceptibility has been well documented for many alloys. The related and often confounding effect of higher yield strength has also been reported by many, especially in describing the stress dependence of time to initiate SCC. In this paper we propose a quantitative model for indexing the SCC initiation susceptibility for Alloy 600 in pressurized water reactor (PWR) primary water. The model is based on the original concepts of strain-rate damage incorporated in a simplified model described at the 7th International Symposium on Environmental Degradation of Materials. This model is further developed to show a useful correlation between model parameters and material properties data. The proposed model and correlation are shown to be in good agreement with test data on Alloy 600 in PWR and high purity water; the data were obtained from various sources covering a wide range of mechanical properties, cold work levels, and material conditions. The data requirements are noted for further verification of the model. Its application is illustrated for the case of control rod drive mechanism (CRDM) nozzle cracking assessment. The significance of depth of cold work layer—as opposed to the peak surface residual stress—is demonstrated on the basis of application of this simplified model by incorporating a crack growth rate law and the expected gradients in the stress and material properties across the component thickness.