The Basic Magnetic Flux Leakage Principle

MFL testing relies on the fact that when a ferromagnetic material is magnetized, magnetic leakage field will be formed on the surface of the test piece due to the defects on or near the surface. Magnetic flux leakage testing is a very important non-destructive testing method, which is widely used. Combined with other methods, it can provide an efficient and cost-effective evaluation for ferromagnetic materials.

With the development of technology, people pay more attention to the automation of detection process. This can not only reduce the labor intensity of the detection work, but also improve the reliability of the test results and reduce the influence of human factors. The following mainly introduces the magnetic flux leakage principle:

After magnetization, if the interior of the tested ferromagnetic material is continuous and uniform, the magnetic induction line will be constrained in the material and the magnetic flux will be parallel to the surface of the material, so there will be almost no magnetic field on the surface of the tested material; if the magnetized material is defective, its permeability will be very small and the reluctance will be so strong that the magnetic flux in the circuit will be distorted, and its induction line will change. Some of the magnetic flux will pass directly through or round the interior defects, while the rest will leak into the air on the surface of the material and form a magnetic leakage field at the defects on the material surface. Magnetic flux leakage signals can be obtained by a magnetic field sensor, and sent into the computer for processing. The analysis of flux density component of leakage magnetic field can help us further understand the corresponding defect characteristics such as width and depth.