MAGNETIC PARTICLE TESTING MT | NON DESTRUCTIVE TESTING

 

MT MAGNETIC PARTICLE TESTING

MAGNETIC PARTICLE TESTING MT:

MT  is based on the principle of magnetisation of materials.

STEPS INVOLVED IN MAGNETIC PARTICLE TESTING MT:

  • Pre clean the surface.
  • Demagnetize the object.
  • Clean the surface.
  • Inspect visually for any gross irregularity.
  • Magnetise the object.
  • Apply the magnetic particles.
  • Observe for indications and mark them..
  • Record the observations.
  • Clean and de-magnetize the object.
  • Apply protective coating.

CLEAN THE SURFACE:

MT

 

 MAGNETIZM:

MT

Random Orientation Of Molecules

in an Un-magnetized Specimen

MT

Magnetically Aligned Molecules

in a Magnetized Specimen

MT

Cut-and-Fused Bar Magnet Illustrating Opposite Polarity

DOMAIN:

A saturated macroscopic structure in ferromagnetic materials where the elementary particles (electron spins) are aligned in one direction by inter atomic forces. A domain would be a saturated permanent magnet.

RETENTIVITY:

  • The capacity of a substance to retain magnetism after the magnetizing force is reduced to zero.

COERCIVE FORCE:

  • The magnetizing field strength required to bring the magnetic flux density of a magnetized material to zero.

LONGITUDINAL MAGNETIZATION:

  • Magnetization in which the flux lines traverse the component in a direction essentially parallel to its longitudinal axis.

CIRCULAR MAGNETIZATION:

  • The magnetization in an object resulting from current passed longitudinally through the object itself or through an inserted central conductor.

CURRENT FOR MAGNETIZATION:

  • AC.
  • DC.
  • HWDC.

APPLICATION OF MAGNETIC PARTICLE TESTING MT:

  • Can be applied for detection of both surface and sub-surface discontinuities.
  • Cost of testing MT  is comparatively lower than other methods.
  • Required level of operator skill is not high .
  • Portable and Stationery equipments are available.
  • MT have permanent records of the indications.
  • Interpretation of indications is not difficult .

LIMITATIONS OF MAGNETIC PARTICLE TESTING MT:

  • Volumetric discontinuities cannot be detected. Depth of detection is up to 6mm only.
  • Can be applied only on ferromagnetic materials
  • Possibility of local overheating and burning exist.