Guided Wave-Based Inspection for Pipe Bends in Marine Seawater Pipelines

Marine seawater pipelines function in harsh environments prone to defects, particularly at pipe bends, which represent key inspection targets. Although ultrasonic guided waves can effectively inspect pipelines, the complex geometry of pipe bends poses distinct challenges to their propagation. This study rigorously examined guided-wave testing methods for pipe bends in marine pipelines. The semi-analytical finite element method was initially used to compute the dispersion curves and mode structures of the guided waves for a typical marine pipeline. Mode structure analysis at the pipe bends identified the torsional T(0,1) mode, focusing on the extrados. Finite element simulations then characterized the T(0,1) mode scattering at the pipe bends. Using the trigonometric circumferential distribution of guided wave modes, signals for specific circumferential orders were extracted from the simulated data to elucidate the modal composition and propagation paths of the primary T(0,1) scattered signals. This establishes a theoretical framework for interpreting guided wave signals in pipe-bend inspections. Experiments confirmed the heightened sensitivity of the T(0,1) mode to extrados defects, validating theoretical mode structure analyses.