What is magnetic particle testing?
Magnetic particle testing is a non-destructive testing method that is commonly used on ferromagnetic metals to detect discontinuities and defects on the surface (or slight subsurface) of the
material. Ferromagnetic metals are ones which can be magnetized or are strongly attracted to a magnetic field. Some common ferromagnetic metals include iron, steel, nickel, and cobalt. In magnetic particle testing the piece being inspected is magnetized either by having an electric current passed through it, or having a magnetic field applied to it. When the material has been magnetized, iron particles are applied to the surface. If there are any deficiencies on the surface of the piece, the particles will gather there due to the magnetic poles that are created by a crack. From these indications you can tell the size and shape of the discontinuities. The cracks however can only be detected if they are generally perpendicular to the direction of the magnetic field, and therefore the object must be inspected twice, switching the direction of the magnetic field the second time (90 degrees), so that all defects can be detected.
Magnetic particle testing is relatively cheap, is portable, and requires minimal training to do. When the process is finished and the deficiencies have been identified, the part must be demagnetized. To do this a current or magnetic field of greater magnitude must be used than what was applied originally to magnetize the material. The current or magnetic field is then slowly lowered until it reaches zero, and the object is no longer magnetized.
Common uses for this method are in the automotive, aerospace, and power generation industries. Some specific examples of applications would be the testing of engine gears, pressure vessels, connecting rods, crank shafts, and weld repairs.
We look forward to helping you with any NDT testing requirements you may have.
Until Next week,
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Magnetic Particle Testing