Measurement of Stress at the Crack of Long-Distance Oil and Gas Pipelines Based on Dual-Magnetic Field Detection Method

The safe functioning of pipelines is severely jeopardized by the lack of effective internal detection techniques for pipeline crack stresses. Dual-magnetic field detection technology (DMFDT) is an effective method to solve this issue. The article sets the magnetomechanical model of the magnetic signal of a crack with external magnetic field (EMF), analyzes the distribution features and changing rule of crack magnetic signal when the stress and EMF change, and identifies the relation between the magnetic potential matrix and the stress and dimension of cracks with dual-magnetic field. The findings indicate that the magnetic signal of the crack increases with the increase in stress and the EMF, and the dual-magnetic field detection signal thereby completes the detection of crack stress and enhances the stress detection signal under the EMF. Furthermore, the dual-magnetic field detection signals in cracks are the superposition of crack dimensions and stress effects. The magnetic potential matrix of cracks under the effect of dual-magnetic fields does not vary with crack dimensions but decreases with increasing stress, for which it can be efficiently applied to extract stress signals from pipeline cracks. In the proposed detection method, both the peak point of the axial component signal and the over-zero point of the radial component signal are located at the center of the crack and do not fluctuate with changes in the EMF and stress.