AC flux leakage testing
Alternating field or AC flux leakage testing uses two encircling magnetization yokes through which an alternating current flows. These yokes magnetize the test material contactlessly in the transverse direction. The magnetic flux is concentrated on the material surface and is thus particularly sensitive for the detection of µm-sized surface defects from approx. 100 µm in depth. The distance between the yoke and the test material is a few millimeters. Between the yoke legs there are test shoes with protected probes that scan the surface with contact. <br/>The intermittently operating probe only detects a very small part of the entire surface at any one moment. A very minor material defect thus produces a large disturbance in proportional terms. In the case of defect-free material, the magnetic flux produces a closed circuit in the material. <br/>The actual leakage flux results at exposed defects. The higher the frequency of the yoke is set, the closer to the surface the magnetization current flows (skin effect). At defects in the material, the magnetic flux emerges from the material surface above the defect. This is referred to as leakage flux and can eventually be seen as a signal on the user interface.