Crack Growth Behavior of Ferritic Pressure Vessel Steels in Oxygenated High Temperature Water Under Transient Loadings

The assessment of the influence of the LWR coolant environment and postulated chloride transients on the crack growth is of importance for ageing management with regard to safety and reliability. Aim of the investigations was to determine cyclic crack growth rates at LWR conditions and to study possible size effects and the impact of chlorides on environmentally assisted cracking.Crack growth experiments were performed with fracture mechanics specimens of different size in simulated BWR water of high purity and under the effect of chloride transients with RPV steel 22NiMoCr3-7.Subsequent to a phase of cyclic loading, the specimens were exposed to static load, interrupted by partial unloadings.All cyclic crack growth rates da/dN vs. ΔK in high purity water were in good agreement with ASME XI water curves.No significant influence of specimen size on the crack growth behavior and with regard to SCC could be detected in high purity water environment. Cyclic induced crack propagation immediately stopped when turning to static load. Under static load the chloride transients did not cause crack initiation by SCC.Load transients in chloride containing environment initiated significant SCC-induced crack growth. A “chloride memory effect” with regard to a preceding chloride transient at static load, leading to SCC-induced crack propagation during subsequent load transients in high purity water environment did not arise.Copyright © 2013 by ASME