Modeling of fatigue crack growth rate for ferritic steels in light water reactor environments Original Research Article

This paper presents the methodology and results of an effort to analyze and model a large set of fatigue crack propagation data on A508 Class 2 and Class 3 and A533B pressure vessel steel in light water reactor (LWR) environments. The data were from a variety of laboratories worldwide, in most cases contributed to the EPRI Database on Environmentally Assisted Cracking (EDEAC). The data were analyzed in a consistent manner using the computer code FATDAC, which minimizes the scatter arising from numerical differentiation during fatigue data reduction. The models were developed in the time domain, then converted to the more conventional da/dN versus ΔK form. Two modes of corrosion fatigue crack growth behavior were identified and modeled, one about a factor of two faster than the rates in air and independent of loading rate and the other up to two orders of magnitude faster and strongly dependent on loading rate. Variables such as material sulfur content, sulfide inclusion morphology, water chemistry, R-ratio, load rise time, stress intensity range, temperature, electrochemical potential, and flow velocity affect both the probability of observing the highly enhanced crack growth rates and the rates themselves. Representative crack propagation models are developed and presented in this paper together with supporting data.