Fatigue crack growth behavior of surface crack in low-carbon stainless steel, SUSF316 (NG) in simulated BWR water environment

摘要

It is important to evaluate the fatigue crack growth rate in light water reactor (LWR) condition, because the crack growth rate in high temperature water is accelerated by environmentally assisted cracking (EAC). To understand the fatigue crack growth behavior of surface cracks in low-carbon stainless steel in simulated Boiling Water Reactor (BWR) water environments, the fatigue crack growth tests were conducted using SUSF316(NG) CT specimens and flat plate specimens with surface crack. For low-carbon stainless steel, the crack growth rates of the deepest and surface points of surface cracks are nearly equal to the rates for CT specimens. Crack growth rates obtained experimentally were compared with reference curves proposed for stainless steel in LWR water environments. One of the reference curves was proposed in NUREG/CR-6176 by W.J. Shack, et al., and the other was proposed in the Japanese Society of Mechanical Engineers (JSME) Standard, rules of fitness-for-service for nuclear power plant components. The crack growth rates in this study are higher than those for the reference curve proposed in NUREG/CR-6176. On the other hand, the reference curve in the JSME Standard, based on experimental data for sensitized and non-sensitized stainless steel, SUS304 is located at the upper bound of the experimental data for SUSF316(NG). This confirms that the reference curve for stainless steels in the JSME Standard can be applied as a reference curve for low-carbon stainless steel SUSF316(NG) in BWR environments.