Magnetic particle testing is one of the non-destructive testing methods to detect surface or near-surface discontinuities in ferromagnetic materials. In some documents, other names of this method, MPI and MPT, are also used

This method is the result of applying the law according to which a part of the material being tested becomes magnetized and the existing discontinuities cause field leakage in the direction of the magnetic field and this field leakage is formed on the surface. The presence of this field leakage means the presence of discontinuity which is It appears from the fine metal particles applied to the surface. so that some particles are collected and accumulated by field leakage. This accumulated set of particles form a pattern that shows the location, size, shape and extent of the discontinuity. Magnetic particles are applied dry or wet on the surface.

Ferromagnetic materials include most alloys of iron, nickel and cobalt. These materials lose their magnetic property above the characteristic temperature or Curie temperature.

This temperature is about 760 degrees Celsius for most ferromagnetic materials.

applications:

The main industrial application of magnetic particle testing is in the final test, during the process, quality control, repair and maintenance of machines and in industries, sites and inspection of large parts.

Limitations:

Paint or other non-magnetic layers have an adverse effect on inspection sensitivity. Other restrictions are as follows:

The magnetic particle inspection method is only applicable to ferromagnetic materials.
For a better conclusion, the magnetic field should be placed in a direction that may interrupt the discontinuity. In most cases, two or more consecutive inspections are required, which is different from the magnetization method.
Sometimes it is necessary to demagnetize and clean the surface of the part from the remaining test material
A very high current is required to test very large parts
In using some methods, it is necessary to take care of local heating of electrical connections
Although observing particles is simple, sometimes it requires skill and experience to interpret and categorize defects.