Laboratory tests on austenitic stainless steel in simulated light water reactor (LWR) coolant environments have been shown to give rise to significant environmental enhancements of fatigue crack growth, especially at low cycling frequencies. The impact of LWR environments on fatigue crack growth has recently been codified in ASME code Case N-809 in terms of parameters such as rise time, stress intensity factor and load ratio. However, plant performance suggests that the application of these predicted environmental effects using current assessment procedures may be unduly pessimistic. This has led to significant number of studies of waveform shape (specifically hold periods) on the corrosion fatigue crack propagation in austenitic stainless steels in LWR environments. The main emphasis of this work addresses the ability of hold periods to cause retardation of environmental crack growth rates.
There has been substantial variability in results of these studies with some authors reporting significant retardation whilst others have failed to observe retardation, or even reported additional environmental enhancement of crack growth rates for nominally similar loading waveforms. Although some of the variability may be accounted for in terms of material composition, there remains a considerable uncertainty both on the impact of holds, especially at different positions in the waveform, and the manner in which hold periods should be taken into account in plant assessments (e.g. in assessment procedures such as N-809). The current paper provides a critical review of published data on the effect of hold periods on corrosion fatigue in LWR environments as well as presenting new targeted data generation and analysis in order to rationalise the reported observations.
Crack growth rates and fracture toughness of irradiated austenitic stainless steels in BWR environments.
