Magnetic particle testing is a relatively simple test method that can be applied to ferromagnetic materials including finished articles, billets, hot rolled bars, castings and forgings. Magnetic particle testing requires magnetising the piece to be examined, applying the inspection medium or particles, and interpreting the patterns formed by the particles when they are attracted to the magnetic leakage field created by discontinuities in the part. Magnetic particle testing is performed using visible or fluorescent mediums; the particles can be wet (suspended in a fluid) or in the form of a dry powder.
Visible wet particles are typically black and can be used with white contrast paint to improve visibility. Visible dry particles are available in red, black, yellow, and grey. They may be used with contrast paint to improve visibility.
Fluorescent magnetic particle testing is more sensitive than the visible method. It is only available as a wet method. Contrast paint is not normally used. It requires the use of a UV-A lamp and a darkened area for viewing and interpreting indications.
There are a variety of methods used to provide the magnetic field:
yoke method (indirect), prod/clamp method (direct) and bench method – head shot (direct), coil (indirect).
Typically, magnetic particle testing will require access to a power source to create the magnetic field and for the UV-A lamp necessary for the fluorescent medium.