2018 年 84 巻 867 号 p. 18-00192
Cast stainless steel (CASS) is widely used in primary coolant piping of nuclear power plants because of its high corrosion resistance and high strength. An in-service inspection based on ultrasonic testing (UT) has to be conducted for such weld joints on the basis of JSME Rules on Fitness-for-Service for Nuclear Power Plants. However, it is difficult to detect and estimate flaws in CASS components with high accuracy because ultrasonic waves are scattered and attenuated due to coarse grains, and anisotropic properties by grain orientations lead to ultrasonic beam distortion. In order to better understand the wave propagation behavior in the CASS, numerical simulations become useful and reasonable manners. To achieve this, it is effective to incorporate three-dimensional (3D) grain microstructures into the simulation model. If the microstructures in CASS can be made from a casting simulation, we can predict wave propagation for a more realistic situation. In this study, the cellular automaton using finite element model is introduced to imitate the grain microstructures in the CASS. Then, the constructed structure is fed into the explicit finite element analysis for 3D wave simulation. Consequently, the wave propagation using the numerical simulation show good agreement with measured wave propagation obtained by contact-scanning on the surface of CASS specimens.
