Magnetic leakage inspection refers to: after the ferromagnetic material is magnetized, a magnetic leakage field is formed on the surface of the test piece due to defects on the surface or near surface. One can find defects by detecting changes in the leakage magnetic field. The leakage magnetic field is that when the material has a defect of cutting the magnetic field line, the defect on the surface of the material or the change of the tissue state will cause the permeability to change. Because the magnetic permeability of the defect is small and the magnetic resistance is large, the magnetic flux in the magnetic circuit is distorted, and the flow direction of the magnetic induction line will change. In addition to part of the magnetic flux directly bypassing the defect through the defect or inside the material, there is also part of the magnetic flux that leaks over the surface of the material, bypassing the defect through the air and then entering the material, thus forming a leakage magnetic field on the surface of the material.
Magnetic flux leakage inspection is a very important nondestructive testing method, which is widely used. When magnetic flux leakage inspection is used in combination with other methods, it can provide quick and cheap evaluation of ferromagnetic materials. With the advancement of technology, people pay more and more attention to the automation of the detection process. Magnetic flux leakage inspection can not only reduce the labor intensity of the inspection work, but also improve the reliability of the inspection results and reduce the impact of human factors.