Evaluation of external cracks in small-diameter metallic tubes via bobbin-typedguided-wave electromagnetic acoustic transduction

The bobbin-typed guided-wave electromagnetic acoustic transduction (GW-EMAT) is intensively investigated for detection and assessment of external cracks in small-diameter metallic tubes (SMTs). Based on 3D finite element analysis, the central frequency and waveform of the GW-EMAT excitation are sought. Series of simulations regarding GW-EMAT inspection of SMT have been conducted. The characteristics and relation of the signal response to the external crack are obtained and analyzed by changing the circumferential length and radial depth of the crack. Meanwhile, a GW-EMAT testing system is built up. The experimental signals of cracks in different sizes are acquired and scrutinized. From the investigation results, it can be found that the area of the crack echo increases as the crack depth rises, indicating the feasibility of bobbin-typed GW-EMAT for detecting and evaluating the external cracks in SMTs.