Magnetic Testing / Particle Testing
Magnetic Particle Testing uses one or more magnetic fields to locate surface and near-surface discontinuities in ferromagnetic materials. The magnetic field can be applied with a permanent magnet or an electromagnet. When using an electromagnet, the field is present only when the current is being applied. When the magnetic field encounters a discontinuity transverse to the direction of the magnetic field, the flux lines produce a magnetic flux leakage field of their own. Because magnetic flux lines don't travel well in air, when very fine colored ferromagnetic particles (magnetic particles) are applied to the surface of the part the particles will be drawn into the discontinuity, reducing the air gap and produce a visible indication on the surface of the part. The magnetic particles may be a dry powder or suspended in a liquid solution, and they may be colored with a visible dye or a fluorescent dye that fluoresces under an ultraviolet (black) light. Many different types of MT inspection methods are available such as the Yoke, Prods, Head Shots, Coil and Central Conductor testing just to name a few.
Liquid Penetrant Testing is that when a very low viscosity (highly fluid) liquid (the penetrant) is applied to the surface of a part, it will penetrate into fissures and voids open to the surface.Once the excess penetrant is removed, the penetrant trapped in those voids will flow back out, creating an indication (crack, porosity, inclusion, etc.) Penetrant Testing can be performed on magnetic and non-magnetic materials, but does not work well on porous materials. Penetrants may be "visible", meaning they can be seen in ambient light, or fluorescent, requiring the use of a black light. When performing a PT inspection, it is imperative that the surface being tested is clean and free of any foreign materials or liquids that might block the penetrant from entering voids or fissures open to the surface of the part.