The stress corrosion cracking (SCC) behavior of three different nuclear grade reactor pressure vessel (RPV) steels (SA 533 B Cl.1, SA 508 Cl.2, 20 MnMoNi 5 5) and of a RPV weld filler material was characterized under simulated boiling water reactor (BWR)/normal water chemistry (NWC) conditions by constant and ripple load tests with pre-cracked fracture mechanics specimens. The experiments were performed in oxygenated high- temperature water at temperatures of either 288, 250, 200 or 150 °C. Modern high-temperature water loops, on- line crack growth monitoring (DCPD) and fractographical analysis by SEM were used to quantify the cracking response. It was concluded that there is no susceptibility to sustained SCC crack growth under purely static loading in oxygenated high-temperature water (ECP = 150 mV SHE ) at 288 °C for stress intensity factors K I = 60 MPa•m 1/2 if the water chemistry is maintained within current BWR/NWC operational practice (EPRI water chemistry guidelines). However, sustained, fast SCC cannot be excluded for faulted water chemistry conditions and/or for highly stressed specimens, either loaded near to K IJ or with a high degree of plasticity in the remaining ligament. The conservative character of the ?BWR VIP 60 SCC disposition lines 1 and 2? for SCC crack growth in low- alloy steels (LAS) has been confirmed by this study for 288 °C and RPV base and weld filler material. Preliminary results indicate that these disposition lines may be significantly exceeded in the case of small load fluctuations at high load ratios (ripple loading) or at intermediate temperatures (200 ? 250 °C) in RPV materials, which show a distinct susceptibility to dynamic strain aging (DSA). The concentration of free interstitial nitrogen/carbon might therefore be just as relevant for SCC susceptibility as the steel sulfur content or the morphology, size and distribution of the MnS-inclusions, at least under conditions where DSA is typically observed.
Keywords: Stress corrosion cracking (SCC), low-alloy steel (LAS), BWR/NWC conditions, environmentally- assisted cracking (EAC), RPV weld, dynamic strain aging (DSA)