Magnetic powder inspection steps and advantages and disadvantages

 

MAGNETIC PARTICLE INSPECTION IS PERFORMED IN FOUR STEPS:

  1. Induce a magnetic field in the specimen
  2. Apply magnetic particles to the specimen's surface
  3. View the surface, looking for particle groupings that are caused by defects
  4. Demagnetize and clean the specimen

ADVANTAGES OF MAGNETIC PARTICLE INSPECTION

  • Can find both surface and near sub-surface defects
  • Some inspection formats are extremely portable and low cost
  • Rapid inspection with immediate results
  • Indications are visible to the inspector directly on the specimen surface
  • Can detect defects that have been smeared over
  • Can inspect parts with irregular shapes (external splines, crankshafts, connecting rods, etc.)

LIMITATIONS OF MAGNETIC PARTICLE INSPECTION

  • The specimen must be ferromagnetic (e.g. steel, cast iron)
  • Paint thicker than about 0.005" must be removed before inspection
  • Post cleaning and post demagnetization is often necessary
  • Maximum depth sensitivity is typically quoted as 0.100" (deeper under perfect conditions)
  • Alignment between magnetic flux and defect is important
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