Nondestructive Testing of Harmonic Magnetic Fields in Steel Pipelines Based on Probe Size Adapted Five-Order Response Model

There are difficulties in selecting and designing probe sizes for nondestructive testing of steel pipelines using harmonic magnetic field detection technology under different operating conditions. This study utilized methods such as objective function optimization, the partial derivative of magnetic coupling energy, defect thinning rate, rate of defect extension change in different directions of the pipe, and their integral elements to deeply analyze the influencing factors of the magnetic field excited by the excitation coil vertically placed outside the pipeline. A five-order mathematical response model for pipe diameter, coil diameter, pipe-to-coil distance, defect expansion direction, and its size change was progressively obtained, namely [(d-R-h)–I] to [(d-R-h)–V]. Through these models, the optimal excitation coil size selection scheme for detection probes under different operating conditions was derived. Finally, the effectiveness of the model was verified through experiments with different defect sizes, pipe specifications, and probe lift distances. In addition, a separable pipeline harmonic magnetic field detector was developed, whose coil probe size can be easily replaced to adapt to different detection requirements.