Research on pipeline damage detection technology based on mixing-frequency nonlinear L(0,2) mode ultrasonic guided waves

During long-term operation, oil and gas pipelines suffer complicated ambient conditions and cyclic loads from pressure and temperature swings, which generate fatigue-induced microdefects. Such tiny flaws gradually grow into macro damage under sustained stress and trigger pipeline breakdown, making accurate microdefect inspection essential for safe operation. This work proposes a mixed-frequency nonlinear L(0,2) ultrasonic guided wave approach to identify pipeline microcracks and quantify damage degree. Finite element simulations characterize guided wave propagation and its nonlinear interaction with microcracks based on contact acoustic nonlinearity, followed by collinear wave-mixing experiments on specimens with diverse microdefects to verify numerical findings. Results indicate that microcracks cause transmission and reflection of L(0,2) mixed-frequency waves and periodic crack breathing deformation. The sum-frequency nonlinear parameter rises with crack radial depth, varies non-monotonically along the axial direction, and grows when the circumferential distance between sensor and defect shrinks. Numerical and experimental results verify the capability of this technique in microcrack detection and quantitative evaluation; experimental tests cover crack depth and width, whereas length, number and circumferential location will be verified experimentally in follow-up research.