Dry Powders

Dry powders consist of finely divided ferromagnetic particles available in a variety of colours e.g. black, grey, red, orange or yellow, some dry powders may also be fluorescent.

Dry powders are usually applied to a surface by means of a puffer device (insufflator), they should be gently applied to the surface, not blasted, onto the area under test.

Dry powders should ideally be used with A.C. or half-wave rectified current (HWRC) because of the extra mobility that these current types impart onto the powder.

Dry powders must be used when MT is being carried out on hot surfaces, (a maximum of 315°C (600°F), however, at these temperatures convection currents from the test piece make application difficult), a situation where inks would obviously not be suitable. Dry powders are also encountered for use on rough surfaces (e.g. sand castings) and for better indications for slight sub-surface discontinuities.