Magnetic Particles

The non-destructive magnetic particle method (MT) is a testing method that detects surface and near-surface discontinuities in ferromagnetic materials. This method uses small ferromagnetic particles, colored or fluorescent, and a source of magnetic field that, when established in a material and encountering discontinuities, generates leakage fields with the ability to trap the magnetic particles and group them around it, supporting even the gentle removal of those that are not magnetized, when they are dry particles.

The test object is magnetized using a permanent magnet or electromagnet, or by passing electric current through or around the test object. The magnetic field introduced into the object is composed of magnetic lines of force. Whenever there is a discontinuity that interrupts the flow of the magnetic lines of force, a magnetic field leak will be generated in the area of the discontinuity. In magnetic field leakage the lines leave and re-enter the object. These exit and re-entry points form opposite secondary magnetic poles. If tiny magnetizable particles are scattered over the surface of such an object, these particles will be attracted to these secondary magnetic poles to create a visual indication that approximates the size and shape of the defect.