Influence of strain range on fatigue life reduction of stainless steel in PWR primary water

The environmental effect in the pressurized water reactor (PWR) water was investigated for various applied strain range using a type316 stainless steel. The tests were conducted using cylindrical hollow specimens at 325 degrees C. It was shown that the ratio of the fatigue life in the PWR water environment to that in air was about 0.3 to 0.4 regardless of the strain range when the applied strain ranges were 0.8% or more. Crack growth rates identified from spacing of striations observed on fractured surfaces were used to demonstrate that the fatigue life reduction in the PWR water environment could be attributed to the crack growth acceleration. The fractured surface observations revealed that crack initiation was enhanced by the PWR water environment. On the other hand, the reduction in the fatigue life was not significant when the strain ranges were 0.5% and 0.44%, and the specimens did not fail when the strain ranges were 0.38% or less. It was deduced that the crack initiation was not enhanced for the relatively small strain range, and the crack growth was not accelerated. Since the fatigue limit of the test material was 0.4% in the strain range in air, it was concluded that the fatigue limit was not reduced in the PWR water environment.