Ultrasonic Guided Wave-Based 3D Localization and Failure Mode Recognition for Shield Can Cracks in Nuclear Main Pumps

To address the challenge of early failure detection for cracks in the shield can of nuclear main pump motors, this study proposes a non-invasive inspection method based on ultrasonic guided waves. By deriving the dispersion equation of the shield can, the non-dispersive <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{T}(\mathbf{0, 1})$</tex> mode <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\mathbf{9 0 ~ k H z})$</tex> was selected as the detection waveform. A 3D multi-physics model incorporating cracks, bulges, and corrosion defects was constructed using COMSOL, with ultrasonic signals generated and received via an annular ultrasonic transducer array. Simulation results demonstrate that three-dimensional crack localization (relative error <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\leqslant 5 \%)$</tex> can be achieved by analyzing phase differences and time delays in ultrasonic echoes. Crack size quantification (relative error 2.2%) was realized through amplitude attenuation ratios, while bulge and multi-point corrosion failure modes were distinguished based on wave group phase distribution characteristics. This method provides theoretical and engineering foundations for online diagnosis of early-stage shield can failures in complex electromagnetic environments.