Plastic Strain Correction in Fatigue Analysis of Nuclear Power Plant Equipment

The nuclear power plant equipment is subjected to in-service cyclic loading, and the stress variation amplitude usually exceeds twice the yield strength of the material. In the case of elastic analysis, strain is underestimated. A simplified elastoplastic fatigue analysis is included in NPP design codes. It is based on the design fatigue curve using the plastic strain correction factor (K-e) to refine stresses by elastic analysis, followed by the fatigue one. Different stress origins determine mechanical and thermal plastic strain correction factors to be used for the stresses induced by mechanical and thermal loadings, respectively. Fatigue analysis was performed with different plastic strain correction factors. The total stress calculations give correct results by employing the mechanical plastic strain correction factor, especially in the case of thermal stress predominance, the analysis result is too conservative. In engineering practice, the correction factors can be used for refining stresses induced by mechanical and thermal loadings.