Electromagnetic ultrasonic helical guided wave evaluation of cracks inpipes based on the inner-inspection EMAT with S configuration

In order to mitigate the pitfall regarding low sensitivity of traditional axial guided waves to oblique cracks in pipes, based on the mechanism of electromagnetic helical guided ultrasonic wave evaluation, an inner-inspection Electromagnetic Acoustic Transducer (EMAT) in S configuration was proposed. In regard to the proposed transducer, a finite element model was established to explore the propagation process and echo signal characteristics of helical guided waves with different helical angles on the pipes, and its response to cracks in different orientations. In parallel, an electromagnetic ultrasonic helical guided wave testing system was built up. The proposed EMAT was fabricated and adopted for detection of oblique-angled cracks. Results from simulations and experiments indicated that the proposed inner-inspection EMAT in S configuration had higher evaluation sensitivity to oblique cracks, implying the significance for high-resolution evaluation of cracks in metallic pipes.