Axial magnetized patch for efficient transduction of longitudinal guided wave and defect identification in concrete-covered pipe risers

Pipe risers partially covered by a wall are difficult to test because the concrete causes large attenuation and mode conversion. Both reasons make it difficult to analyze the signal. This paper reports the design of an axial magnetized magnetostrictive patch transducer (AM-MPT) for efficient  transduction of longitudinal guided wave, which can be used to detect defects in concrete-covered pipe risers. First, the paper started with a theoretical background about influence of length to width ratio of the magnetized rectangular patch on the demagnetizing factors and the magnetic field intensity of the patch. Second, the simulation and experimental results proved that the length to width ratio of the magnetized iron cobalt patch has a great influence on its magnetic field intensity and signal amplitude of the AM-MPT. Comparison experiments proved that the static magnetic field of AM-MPT provided by an iron cobalt patch led to larger signal amplitudes than those provided by magnets. Third, the attenuation of L(0,2) in concrete-covered pipe riser were studied using the AM-MPT experimentally, which were according with Disperse simulation results basically. And the experimental results proved that AM-MPT was more suitable to be applied in concrete-covered pipe risers testing than original MPT. Finally, the AM-MPT was applied in a defect identification of concrete-covered pipe riser sample. The experimental results for the AM-MPT and the piezoelectric transducer (PZT) showed that the AM-MPT can potentially be applied in pipe riser defect identification.