A High-Purity Guided Wave Mode Excitation Method for Defect Detection in Liquid-Filled Immersed Cylindrical Waveguides

The development of effective defect detection methods for underwater pipelines plays an important role in energy transportation safety. Although high-frequency guided waves provide exceptional sensitivity, their performance is limited by multi-mode interference effects in underwater pipelines. To overcome this limitation, this article presents a hybrid method for analyzing high-purity guided wave mode excitation and defect detection in liquid-filled immersed pipes. The proposed method innovatively integrates the semi-analytical finite element, perfectly matched layer, and generalized modal expansion in the guided wave analysis of liquid-filled immersed pipes. The framework is employed to analyze the guided wave propagation characteristics in liquid-filled immersed pipelines, enabling the identification of optimal guided wave modes for defect detection. Transducer parameters are designed for the optimal mode to generate a high-purity guided wave mode using generalized modal expansion analysis based on the accurate solutions of high-frequency guided waves. Then direct defect detection through pulse-echo signal acquisition and time of flight analysis. Simulation results demonstrate that the designed transducer can effectively excite the high-purity target modes at high frequencies for defect detection. Experimental validation was performed through high-purity mode excitation and defect detection tests using high-frequency guided waves in a water-filled copper pipe. The experimental results demonstrate excellent consistency with the theoretical predictions, thereby validating the effectiveness of the proposed method. The results demonstrate that the proposed method effectively selects the optimal guided wave mode for liquid-filled immersed pipe inspection and enables high-purity guided wave mode excitation at high frequencies for defect detection.