Research on focused array magnetised pulsed eddy current sensor for localised corrosion detection in cladded pipelines

Pulsed eddy current (PEC) testing is effective for detecting uniform wall thinning in cladded pipelines; however, reliable localised corrosion remains challenging. Under large lift-off, the excitation field reaching pipeline substrate is strongly attenuated, and the high relative permeability of ferromagnetic pipelines further limits penetration, resulting in weak defect signals with low sensitivity and signal-to-noise ratio (SNR). To overcome these limitations, this work proposes a dual enhancement strategy that combines array focusing with DC bias magnetisation. Based on this concept, a focused array magnetised PEC (FAM-PEC) sensor is developed, integrating multiple synchronised excitation coils with differential receiving coils and an external magnetising module. A finite-element model is established to elucidate the mechanisms and guide optimisation of the focusing geometry and magnetisation design. Experiments compare four configurations: a traditional single-excitation sensor, an array-only sensor, a magnetisation-only sensor, and the proposed integrated sensor. Results show that the proposed sensor the strongest defect responses and the highest SNR. For a cladded pipeline with a 100 mm lift-off, the sensor successfully detects Φ10.0 mm × 6.4 mm flat-bottom hole defects on both the outer and inner walls. Compared with the traditional sensor, the outer-wall detection SNR is improved by 13.9 dB, and reliable detection of inner-wall defects is achieved with an SNR of 15.9 dB. These findings provide a practical and experimentally validated sensing solution for high-sensitivity localised corrosion inspection in thickly cladded ferromagnetic pipelines.