Quantitative Study of Sensor-Pipe Distance in Noncontact Magnetic Detection of Ferromagnetic Pipelines

Noncontact magnetic detection technology has great application potential in buried oil and gas pipelines due to the noncontact online detection of pipeline damage. However, the noncontact magnetic detecting signal is affected by the distance between the magnetometer and the ferromagnetic pipeline, leading to missed detection of pipe defects. It is essential to calibrate the detection height for the noncontact magnetic detecting signal. In this article, the spatial analytical model of noncontact magnetic signals above ferromagnetic pipelines is established. Then, a quantitative variation law of noncontact magnetic detecting signals is obtained under different pipe diameters and internal pressures. Next, a signal calculation model based on the detection height ${h}$ is established. A detection height correction method is proposed to eliminate the influence of detection heights on the magnetic detecting signal. An experimental investigation is carried out to validate the accuracy of the numerical calculation results and the correction method. The results indicate that the magnetic detecting signal has a second-order exponential relationship with the detection height ${h}$ within 0.1–2 m. The average error of the signal correction model is 6.37%. The modified magnetic detecting signal via the signal correction method can reflect the damage status of ferromagnetic pipelines.