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:

 MAGNETIZM:

Random Orientation Of Molecules

in an Un-magnetized Specimen

Magnetically Aligned Molecules

in a Magnetized Specimen

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.