Magnetic particle testing (MT)
Magnetic particle testing is used for the testing of materials which can be easily
magnetized. This method is capable of detecting open to surface and just below the surface flaws.
In this method the test specimen is first magnetized either by using a permanent or an
electromagnet or by passing electric current through or around the specimen. The magnetic field
thus introduced into the specimen is composed of magnetic lines of force. Whenever there is a
flaw which interrupts the flow of magnetic lines of force, some of these lines must exit and reenter
the specimen. These points of exit and re-entry form opposite magnetic poles. Whenever
minute magnetic particles are sprinkled onto the surface of such a specimen, these particles are
attracted by these magnetic poles to create a visual indication approximating the size and shape of
the flaw. Figure 1.3 illustrates the basic principles of this method.