Quantitative Prediction of Stress Corrosion Crack Propagation Rate of Small Crack in Alloy 600 for Nuclear Pressure Vessels

Stress corrosion crack (SCC) of small crack has an important effect on the whole-life attenuation process of critical structures in nuclear power plants (NPPs). By combining the film slip-dissolution/oxidation model with the elastic-plastic finite element method (EPFEM), the SCC propagation rate for small crack in reactor pressure vessels (RPVs) of NPPs was quantitatively predicted. According to the crack tip mechanical field analysis, the crack tip strain rate was determined to control the initiation and propagation of small cracks, and it was approximately calculated by the variation of plastic strain (d epsilon(p)/da) at a characteristic distance r(0) to the growing small crack tip. Two methods of dynamic crack propagation and quasi-static crack propagation based on EPFEM were proposed to calculate the variation of plastic strain (d epsilon(p)/da). The contrast of the two calculation methods and the sensitivity analysis of variation of plastic strain with the crack length were carried out. The results show that there is a slight difference between the two methods, and the plastic strain variation is more sensitive to the crack propagation of small crack than to the long crack. The SCC propagation rate of small cracks is larger than that of long cracks, and it is significantly influenced by the characteristic distance r(0). As it is difficult to determine the value of characteristic distance r(0) finally, it is suggested to be determined by combining experimental SCC data with finite element simulation of the single-edge crack panel specimens under the same environmental and material conditions.