Magnetic particle testing is used to inspect the defects on
surface or very near to the surface of ferromagnetic materials. The principle
of this type testing explains that when a magnetic flux is applied to a
material, the surface imperfections promote the formation of ‘Leakage Fields’.
These leakage fields tends to attract magnetic particles towards themselves
thus making an investigation of surface imperfections. By using special
pigments, a contrast is formed among substrate and magnetic particles. The
procedure is only applied to ferromagnetic materials over a wide range of
temperature.
What is MPE?
MPE stands for Magnetic Particle Examination, new name for
magnetic particle testing. It is defined as the investigation of surface or
near surface imperfections by using basic magnetic principles. Simple magnetism
and magnetic field phenomenon is applied that are not only easy to operate but
also helps in certain ways. Following are the key points that make magnetic
particle testing an exceptional technique.
1. Ferromagnetic Materials
Type of non-destructive testing that is used in
inspection of surface defects only in ferromagnetic materials.
2. Easy to operate
Less level of skills are expected from the operator and easy
in manipulation. A personal need less duration of time for training. There are
many institutes in worldwide that offer training programs for MPE.
3. Cost effectiveness
The testing equipment and apparatus are cost effective and
produce highly optimal results for a very low expenditure as compared to other
non-destructive inspection techniques.
4. Swift Inspection
Time saving Inspection technique that provides expeditious
results. Investigation of surface imperfections can be made swiftly but in
efficient manner. Cracks are appeared directly on surface by background
contrast.
5. Sensitivity
The technique shows strong sensitivity towards minor defects
of surface and quickly detects them. This behavior is only observed in
ferromagnetic materials. Also the cracks which are close to surface (within
3mm) can be detected by MPI.
6. Less Surface Preparation
No hard conditions are required for surface preparation before
magnetic particle inspection. Normally less level of surface preparation is
required because surface pollutants may not hinder the inspection as happen in
other inspection techniques. Also the post cleaning is normally not required
after inspection.
7. Portable
Magnetic Particle Inspection can easily be carried out
during manufacturing and repair works of pressure equipment and structural
constructions. Portable equipments are also available in market for the
examination of small sections and components.
8. Safety
Magnetic particle examination is a safe process because
materials and equipment are non-hazardous. Less level of risk is expected for
injuries and accidents. No poisonous and combustible materials are used during
examination.
9. Direct Visibility
Surface imperfections are made directly visible on surface
by using pigmented materials. Magnetic particles which are used for
investigation are available either in wet (suspension in liquid) or in dried
form. A contrast is made between the imperfection and background. Sometimes
magnetic particles are made visible and sometimes background is made white by
coating.
Last comments
Cheap Non-destructive Examination Technique with safe
materials, used for examination of surface discontinuities in ferromagnetic
materials only. Although nothing is without limitations. Same with MPI, there
are some disadvantages that hinder its use in certain applications.