Development of Magnetization-based Eddy Current Sensors for In-Line Inspection of X65 Pipelines

Traditional in-line inspection (ILI) methods, such as magnetic flux leakage testing (MFLT) and eddy current testing (ECT), have inherent limitations. MFLT suffers from high magnetic attraction forces, which result in excessive friction and instability in low-pressure, low-flow (LP-LF) pipelines. Conversely, conventional ECT is limited in its ability to detect buried defects due to shallow penetration depth. To address these issues, magnetization-based eddy current testing (MB-ECT) has emerged as a promising alternative. It requires lower magnetization than MFLT while effectively detecting both surface and buried defects. Effective implementation of MB-ECT requires optimization of design parameters tailored to the characteristics of the targeted defects and inspection conditions. In this study, an MB-ECT system was developed and optimized. The correlation between defect signals and key parameters—probe configuration, driving frequency, and magnetization level—was investigated through finite element analysis (FEA) and lab-scale experiments. Based on parametric analysis, two MB-ECT probe models were developed: a detection-priority model and a low-force-priority model. Both models demonstrated sufficient detectability under lab-scale noise conditions, with the minimum defect signals achieving SNRs of 11.4 dB and 9.25 dB, respectively. Although the low-force-priority model showed a 15.8% reduction in sensitivity to outer defects compared to the detection-priority model, it offered notable design benefits: an 18.8% reduction in magnetic attraction forces and a 23.7% decrease in magnetizer volume. The low-force model minimizes performance degradation and supports effective use under LP-LF pipeline conditions. These findings offer practical design guidelines for implementing MB-ECT–based ILI tools tailored to pipeline operating environments.