Abstract
Traditional ultrasonic imaging methods have a low accuracy in the localization of defects in austenitic welds because the anisotropy and inhomogeneity of the welds cause distortion of the ultrasonic wave propagation paths in anisotropic media. The distribution of the grain orientation in the welds influences the ultrasonic wave velocity and ultrasonic wave propagation paths. To overcome this issue, a finite element analysis (FEA)-based ultrasonic imaging methodology for austenitic welds is proposed in this study. The proposed ultrasonic imaging method uses a wave propagation database to synthetically focus the inter-element signal recorded with a phased array system using a delay-and-sum strategy. The wave propagation database was constructed using FEA considering the grain orientation distribution and the anisotropic elastic constants in the welds. The grain orientation was extracted from a macrograph obtained from a dissimilar metal weld specimen, after which the elastic constants were optimized using FEA with grain orientation information. FEA was performed to calculate a full matrix of time-domain signals for all combinations of the transmitting and receiving elements in the phased array system. The proposed approach was assessed for an FEA-based simulated model embedded in a defect. The simulation results proved that the newly proposed ultrasonic imaging method can be used for defect localization in austenitic welds.
Highlights
Dissimilar metal welds (DMWs) of ferritic steel and austenitic stainless steel are widely used in nuclear power plants [1], where primary water stress corrosion cracks have been found in DMW areas between the pressure vessels and piping [2]
The grain orientation was extracted from a macrograph obtained from a dissimilar metal weld specimen, and the anisotropic elastic constant was iteratively optimized by minimizing the ultrasonic wave propagation velocity difference between the test and simulation results
finite element analysis (FEA)-based ultrasonic imaging methodology austenitic welds is proposed matrix in the phased array system was calculated through a series of finite element analyses in this paper
Summary
Dissimilar metal welds (DMWs) of ferritic steel and austenitic stainless steel are widely used in nuclear power plants [1], where primary water stress corrosion cracks have been found in DMW areas between the pressure vessels and piping [2]. The coarse grain size causes signal scattering and energy attenuation, and the anisotropic material properties of columnar grains result in a change in grain orientation in the welds, distorting the ultrasonic wave propagation paths [4]. For practical applications of phased array systems in welds, information on grain orientation distribution, anisotropic material properties, and precise simulation of ultrasonic wave propagation behavior are required. The proposed ultrasonic imaging method uses the total focusing method (TFM) and a wave propagation database, which was constructed using FEA that considered the grain orientation and anisotropic material properties of the welds. The grain orientation was extracted from a macrograph obtained from a dissimilar metal weld specimen, and the anisotropic elastic constant was iteratively optimized by minimizing the ultrasonic wave propagation velocity difference between the test and simulation results. The TFM was applied to build a defect image in the finite element (FE) model
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