Magnetic particle inspection is a nondestructive means for detecting discontinuities in ferromagnetic materials.  It consists of there basic operations:

1. Establishing a suitable magnetic field in the test object.
2. Applying magnetic particles to the surface of the test objects.
3. Examining the test object surface for accumulations of the particles and evaluating the serviceability of the test obje

The method can detect all discontinuities at the surface, and under certain conditions, those which lie completely under the surface.  It depends upon the magnetic properties of the test objects and is suitable only for metallic materials which can be intensely magnetized.  Non ferro magnetic materials, which cannot be strongly magnetized, cannot be inspected by this method.  Such materials include aluminum, magnesium, brass, copper, bronze, lead, titanium, and austenitic stainless steels.  With suitable ferro magnetic materials, magnetic particle inspection is highly sensitive and produces readily discernible indications on the surface of the test parts.  A trained inspector can, by examining the nature location, and extent of the indications, interpret their causes and evaluate the discontinuities causing the indications.