Detection of fatigue-induced micro-cracks in a pipe by using time-reversed nonlinear guided waves: A three-dimensional model study

Localization of fatigue-related micro-cracks in pipelines is of increasing importance in industrial applications. A three-dimensional (3D) fatigue-crack imaging technique combining nonlinear guided waves with time reversal is proposed in this paper for potential applications in pipeline inspections. By using this method, the non-classical nonlinear guided waves generated from micro-cracks with hysteretic behavior are recorded, and the third harmonic waves are used to reconstruct the fatigue-crack images in a pipe by using a time reversal (TR) process. The feasibility of this method is examined by the imaging simulations for a steel pipe with varied defect areas. A finite-difference time-domain (FDTD) code is programmed to solve the wave equations under cylindrical coordinates, and simulate the experimental process of wave propagation. The results show that: (1) the proposed technique has excellent spatial retrofocusing capability; (2) the accuracy of defect localization and sizing depends on the crack orientation and the adopted guided wave mode; and (3) different displacement/stress components have varied sensitivities to the crack orientation.

► We combined the 3rd order nonlinear guided waves with time reversal.
► Wave propagation in a circular pipe is simulated with FDTD method.
► The technique discriminates fatigue-related micro-cracks with good quality.
► Different guided modes have different sensitivity with regard to a given crack.
► Accuracy of localization also depends on the crack orientation.