Research on a New Electromagnetic Ultrasonic Pipeline Unidirectional Wave Defect Imaging Method

Pipeline inspection has long been a major research topic in non-destructive testing (NDT). Conventional electromagnetic acoustic transducers (EMATs) generally generate bidirectional ultrasonic waves, which exhibit several inherent limitations in defect detection, including low signal amplitude, limited directivity, and incompatibility with pulse-echo inspection configurations. The use of unidirectional guided waves generated by EMATs offers a potential means of addressing these limitations in pipeline inspection. In this study, a method for pipeline defect imaging using electromagnetic ultrasonic unidirectional waves is investigated. First, the generation mechanism of unidirectional waves is theoretically analyzed based on the principle of wave superposition. Subsequently, finite element simulations are performed to investigate the effects of key transducer parameters on the amplitude of the generated unidirectional waves, and an optimal combination of excitation parameters is determined. Finally, defect imaging experiments are conducted on pipelines containing different types of defects. The simulation and experimental results show that the signal amplitude of the electromagnetic ultrasonic unidirectional waves increases by approximately 57.3% after optimization using an orthogonal experimental design. Experimental B-scan results show that the proposed bidirectional B-scan synthesis method provides a qualitative visualization and profile assessment of the defects.