Application of a model for predicting corrosion fatigue crack growth in reactor pressure vessel steels in lwr environments

The mechanisms of corrosion fatigue crack growth in low-alloy steels have been studied extensively in several laboratories, so that the long-term behavior of postulated flaws in LWR pressure vessels can be more confidently predicted from short-term laboratory measurements of crack growth rates. The physically-based models which are emerging from this research take explicit account of the effects of crack-tip deformation rate on the crack growth rate. Application of one such model to crack growth data for A533B-1 and A508-2 steels shows that the dependence of corrosion fatigue crack growth on stress intensity and cyclic frequency can be interpreted by a simple data correlation in the time domain. The result suggests that current ASME Code methods for flaw assessment are highly conservative in some regimes of stress and frequency, but there is a possibility of growth rates well above the ASME XI, Appendix A curves in a very low-frequency, high stress regime. An upper bound to the time rate of corrosion-assisted crack growth in low-alloy steel is well supported by the data. The threshold conditions for the onset of this high rate are less well-defined and require further investigation