Pipeline Defect Detection Based on Ultrasonic Guided Wave Technique Using Fiber Bragg Gratings

Ultrasonic guided wave (UGW) is very attractive for the quick inspection of pipeline structures because it can propagate a long distance along the pipe and through-out the whole thickness of the wall. In the conventional UGW-based techniques, piezoelectric transducers (PZTs) are often used as launchers and detectors simultaneously, which, however, makes the processing of actuator-sensor decoupling complicated. As an alternative, a new scheme using fiber Bragg grating (FBGs) to replace PZTs as sensors can be followed. This paper mainly concentrates on the preliminary work concerning the applicability of FBGs to UGW-based pipeline inspection. Based on the formulation of character equations and the analysis of dispersion curves, L(0,2) mode is selected as the testing mode. The response of FBGs to longitudinal ultrasonic waves is then investigated to put forward a hybrid PZT-FBG system for pipeline defect monitoring. A pipe, which is artificially introduced by circumferential and axial cracks with various severities, is numerically modeled based on finite element method (FEM). The results verify the feasibility and effectiveness of the proposed PZT-FBG scheme for pipeline inspection.