A simple way to understand this method of inspection is to remember what happens when you have a small bar magnet when approaching small ferromagnetic pieces, stick to the bar that is magnetic. However, if we break the bar magnet in half, then we have two magnets and they have two poles, that if we try to approach each other, some will be repelled and if we reverse one of them will be strongly attracted to the other. Likewise, when a weld or a magnetized ferromagnetic material, in parts where there is a crack, you break the magnetic flux and there are two poles that are attracted to them, so if you sprinkle fine iron particles, ferromagnetic powder, will focus on the zone of discontinuity and thus we see a concentration on those parties that submit inspection, also if these fine particles, the colors of a bright color that contrast strongly against the surface inspection, we can evaluate the area inspected.

Then we have an inspection method has the advantage of being very fast but with the disadvantage of requiring a power source, to energize a yoke magnet capable of magnetizing the area, with the disadvantage that can be done on magnetic materials only. Very suitable for the welding of a structure or a metal part under high stress, which can generate fatigue cracks. This method may be by magnetic particles are visible in normal light or can be fluorescent, so it must use an ultraviolet light. Also, the particles can be suspended in a solution that helps them travel to the area of discontinuities or particles can be applied in dry form, through a blower, leaving a thin layer over the inspection area.

So are most helpful in evaluating the surfaces, and this method is sub-surface and depending on the type of current that magnetize the area, discontinuities can be detected fairly deep and not open to the surface. However, an important aid in evaluating a fault zone, are replicas can be obtained, by passing an adhesive tape over the area of the guidance.

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