Study Of CCASS Weld Modeling And Ultrasonic Testing Numerical Simulation

The coolant pipelines of primary circuit in pressurized water reactor (PWR) nuclear power plant are made of centrifugal casting austenitic stainless steel, and they are often connected by the method of welding. For welds, ultrasonic testing is a frequently-used inspection method. But Centrifugal Casting Austenitic Stainless Steel (CCASS) welds show a heterogeneous and anisotropic structure that causes the phenomena of diffusion, attenuation and deviation of the ultrasonic beam which makes the interpretation of test results difficult. So the study for ultrasonic testing of CCASS weld is particularly important. Computer numerical modeling technology is the bridge between experimental techniques and theoretical analysis. And it has an important role in promoting the research of ultrasonic testing for CCASS welds. And an accurate physical model is necessary for simulating the ultrasonic testing of CCASS weld well. In this paper, ultrasonic testing of CCASS welds was investigated by the technology of numerical modeling. The specific work is as follows:(1) Based on the metallographic photo of CCASS weld, the weld is approximately divided into several homogeneous anisotropic areas. Then the elastic constants of every homogeneous area are computed by the method of coordinate transformation of elastic constants. After that, the physical model of CCASS weld was built, and further optimized for better simulating result. The established model can describe the heterogeneity and elastic anisotropy of the microstructure for CCASS welds. The modeling results of ultrasonic scattering in different areas of weld have good agreement with actual situation. However, the description for the scattering of coarse grains still has a certain gap with the experimental results, which indicates that the model still needs to improve.(2) The acoustic performance parameters of CCASS weld are calculated, and come to the following conclusions:The speeds of sound in CCASS weld are closely related with the acoustic wave propagation direction. With the angle between the wave propagation direction and the grain direction increasing, the longitudinal wave velocity CL firstly increase and then decrease, and with a maximum value at angle 45°. While the shear wave firstly decrease an then increase, and with a minimum value at angle 45°. Longitudinal wave attenuation coefficient also firstly decreases and then increases with the angular variation, and with a minimum value at angle 45°. (3) The ultrasonic propagation in CCASS weld with different frequencies and probe diameters are calculated, and come to the following conclusions:When modeling ultrasonic propagation in CCASS weld by normal incidence, the greater the probe frequency (1-5 MHz) is, the larger the attenuation coefficient is. Meanwhile, the larger the diameter of the probe is, the higher the sound wave amplitude is.The simulation results have a good agreement with the experimental results given by the existing literature. It shows that the CCASS model and the simulation method are feasible. In addition, computer numerical modeling technology has the visualization capabilities and is convenient to change the parameters of modeling, which is difficult to realize by experiment. The study of this paper shows great superiority and can provide related technical guidance for actual inspection of CCASS weld.