Materials Engineering, Evaluation, and Inspection

Magnetic Particle Testing

Spectrum uses Magnetic Particle Testing (MT) to discover surface and subsurface discontinuities, such as cracks and seams, in ferromagnetic materials. MT is used to assess the position, size, shape and scope of imperfections. However, because the sensitivity of MT decreases significantly a short depth under the surface being examined, it used principally to catalogue surface discontinuities. A magnetic field is induced into the examined component and iron particles are applied to the surface as a dry powder or in medium such as water, solvent or light oil. We use a variety of particle colours to best contrast with the material being examined. Discrepancies are highlighted as the particles collect and form around the magnetic flux leakage that surrounds such defects. Welds, castings, forgings, valves, machined parts, pressure vessels, and structural steel are typical candidates for MT inspection.


  • Ferromagnetic materials
  • Surface and slightly subsurface flaws can be detected
  • Can be applied to welds, tubing, bars, castings, billets, forgings, extrusions, engine components, shafts and gears


  • Detection of flaws limited by field strength and direction
  • Needs clean and relatively smooth surface
  • Some holding fixtures required for some magnetizing techniques
  • Test piece may need demagnetization which can be difficult for some shapes and magnetizations
  • Depth of flaw not indicated