Microstructural Evaluation of Cumulative Fatigue Damage Steels Used for Pressure Vessels of Light Water Reactors

摘要

Fatigue damage developed in actual use and induced in the laboratory by cyclic deformation near or below the fatigue limit was evaluated microstructurally. Small samples removed from the PWR feedwater nozzle were examined by selected area diffraction(SAD). The damage measured by the SAD well agreed with the microscopic evidence. Cyclic stresses near the fatigue limit were applied to samples of a SA508 steel plate, and these samples were evaluated by the SAD method. The microstructural method is effective to evaluate damage accumulation in real plant components, and the current design curve is adequate in terms of microstructural conditioning.