A novel quantum sensing-based in-line inspection technique for micro-crack detection in ferromagnetic pipelines under residual magnetization

Long-distance oil and gas pipelines serve as critical hubs in energy supply chains, and their structural integrity is essential to ensuring secure and stable energy delivery.Micro-scale cracks are difficult to detect using existing magnetic flux leakage technologies. This is primarily because the leakage magnetic fields induced by such cracks are extremely weak and can be readily masked by strong background magnetic fields. In response to this issue, a novel pipeline quantum in-line inspection (PQII) method based on a Spin-Exchange Relaxation-Free atomic magnetometer is proposed for the first time. A new detection system is developed by integrating a miniaturized atomic magnetometer probe with active magnetic compensation and differential sensing units, enabling precise capture of extremely remanent magnetic flux leakage induced by micro-defects in the pipe wall and thereby achieving high-sensitivity and high-accuracy defect detection. Laboratory specimen tests show that the proposed system can detect near-side flat-plate crack defects with widths as small as 0.1 mm. Furthermore, traction experiments demonstrate that the proposed system can reliably identify outer-wall pitting corrosion defects with diameters of 2 mm, as well as outer-wall girth weld cracks with widths of 1 mm. For crack defects, detectable depths exceeding 7.9 mm were achieved under the present experimental conditions. Compared with conventional remanent magnetic flux leakage techniques, the proposed method not only significantly improves defect detection sensitivity but also enables defect localization. Moreover, the lightweight and compact system design has the potential to transform traditional in-line inspection modes and expand application scenarios. The proposed method PQII provides a significant technical pathway for the precise detection of micro-defects in long-distance oil and gas pipelines, and offers substantial engineering value and theoretical guidance for ensuring energy supply security.