The magnetic particle testing method may be applied to detect cracks and other discontinuities on or near the surfaces of ferromagnetic and electrically conductive materials. Magnetic particle examination techniques thus allow the detection of surface breaking cracks in steel objects of complex geometry, which typically is a challenge for RT methods. The sensitivity is greatest for surface discontinuities and diminishes rapidly with increasing depth of subsurface discontinuities below the surface. Typical types of discontinuities that can be detected by this method are cracks, seams, laps and cold shuts.

Direct current (DC) and alternating current (AC) are both suitable for magnetizing parts for MT. The primary difference between the two currents is, the fields generated by DC penetrate the cross section of the part, and the fields generated by the AC are confined to the metal at or near the surface of the part. Therefore, AC should not be used for subsurface discontinuities.

Before commencing each magnetic particle test, the surface that is going to be examined and all adjacent areas within at least 1 in. (25 mm) shall be made dry and free of all dirt, grease, lint, scale, welding flux, weld spatter, paint, oil, and other extraneous matter that could obscure and obstruct surface openings or otherwise interfere with the examination.

Magnetic particle testing is easy to understand and the training needed to complete this inspection method is straightforward. This is a good method for detecting surface cracks of all sizes in weld and other areas and although easier to use than radiographic testing it is limited to use with ferromagnetic materials. Ahead of any magnetic particle test the surface area does need to be well prepared and any paint and coatings must be removed which can be time consuming.

Either dry or wet magnetic powders may be used for magnetic particle testing. Dexon is not only a provider for magnetic particle testing services but also the distributor for Bycotest magnetic particle products in Thailand and Asia.