LABORATORIUM

The magnetic particle method consists in magnetizing the tested element. The magnetic particle method consists in magnetizing the tested element and detecting the magnetic scattering field appearing in the place of discontinuity occurrence. Typical disconti-nuities include: fatigue cracks, forging, grinding, hardening, sticking, rolling tears, laps, non-metallic inclusions (blisters). This method is applicable only to ferromagnetic, plastic-wrought, welded, thermally processed objects (e.g. pipelines, constructions, shafts, axles, pivots, gears, etc.). In magnetic particle testing it is possible to detect surface open and subsurface discontinuities to the depth of approximately 3-4 mm.

For smooth and sandblasted surfaces the black and white technique is best suited, whereas for machined areas where sensitivity is important the MT test under UV light is best. In the mag-netic method, depending on the thickness and type of workpiece to be tested, we can use one of the two ways of magnetizing with alternating or direct current. The direct current will be used when we have to deal with a large thickness and size of a workpiece, so that we can ob-tain the appropriate intensity of the magnetic field in the whole area examined, especially in the places of shape change. In the case of alternating current we have the effect of skin-effect (flow of current by the shortest route) therefore this method is dedicated to workpieces with uniform shape and con-stant thickness.