Ultrasonic high frequency guided waves for testing of dissimilar metal welds

Abstract Ultrasonic testing of nickel-based dissimilar metal welds (DMWs) in nuclear power plants is always challenging due to its internal structures. Indeed, ultrasonic bulk waves can be severely scattered and attenuated because of coarse grains in DMWs and consequent difficulties such as splitting and skewing can be observed due to the anisotropic and inhomogeneous structure of the weld pool. Ultrasonic high frequency guided waves (HFGW) has the potential to reduce and overcome these issues and can offer a good compromise between the volume coverage and defect sensitivity for testing of DMWs. This work presents defect detection in DMW joints made by 12 mm thickness P91 and alloy 800 plates using HFGW. The generation and propagation characteristics of HFGW on both P91 and alloy 800 have been extensively studied by using 2D plane strain finite element modelling (FEM). For both experimental measurements and FEM, the input parameters such as the excitation frequency, incident angle and scan distance have been optimized with the help of Dispersion curves. It has been observed that the amplitude response of HFGW is more than two times on the P91 plate when compared to the alloy 800 plate. The interaction of HFGW with artificial defects made on the DMW and at the weld interfaces have been tested. It has been noticed that the HFGW can able to detect defect size down to ~ 10% of 12 mm wall thickness and 2 mm diameter side-drilled holes reliably from both sides of P91 and alloy 800.