Both Magnetic Particle and Dye Penetrant are widely using
non-destructive testing techniques which are applied for the examination of
surface related discontinuities. Although used for the same job but there are
some key features that differentiate them for certain areas of application. Also
there are some features which are common in both techniques. Described below is
a brief comparison between magnetic particle and dye penetrant examination.
1. Cost
Magnetic particle testing offers lower cost equipment and
materials.
Dye Penetrant also offers lower cost for materials and
equipment.
2. Time
MPE is fast inspection technique.
DPE is relatively slower process.
3. Materials
MPE can only be applied in examination of ferromagnetic
materials because they are highly responsive to magnetic principles. It cannot
be applied on all metals and non-magnetic alloys.
Dye penetrant provides optimal results in all metals and
alloys.
4. Discontinuities
Dye penetrant testing only detects discontinuities which are
on surface while magnetic particle testing detects not only surface cracks but
also those imperfections that are very near to surface.
5. Surface conditions
Strict pre-cleaning is required before dye penetrant
inspection to start. The test surface must be clean adequately, providing
smooth and precise inspection. While in case of magnetic particle inspection no
such pre-cleaning and post-cleaning processes are necessary because the surface
pollutants don’t have any adverse effect on inspection results.
6. Temperature
Dye Penetrant Examination is limited to temperature
conditions normally (5-60 degree Celsius). Outside this range DPE is not
applicable because at high temperature the used penetrant becomes dry while at
low temperature the penetrant liquid becomes highly viscous, thus impeding the
penetration phenomenon and reducing the efficiency of testing.
On the other hand Magnetic Particle Inspection is applicable
at extreme temperatures and can be carried out over a considerable range of
temperature (normally below Curie temperature). Curie temperature is a point at
which, change of magnetic properties occurs in materials and this point is
different for different for different materials.
7. Equipment
In MPE fluorescently or (colored) visibly pigmented magnetic
particles are employed which when apply on the test section, indicate the
presence of surface flaws/ imperfections. While in Dye penetrant fluorescent or
visible penetrants are employed along with developer, for examination.
8. Safety
Equipment and materials which are employed in both magnetic
and dye penetrant examination are safe to use. Less level of risk for any loss
or injury to operator.
9. Working Principle
Both non-destructive techniques are used for the same
examination purpose but with different working principle. In Dye penetrant
technique, liquid penetrants penetrate the surface breakings/ flaws. After that
a developer is applied that allows the penetrant to come out from breakings
again, making an indication.
In MPE, the test material is magnetized by using equipment.
The magnetic flux at surface flaws/cracks tends to form ‘Leakage Fields’.
Magnetic particles when employ, gets attracted by these leakage fields over the
cracks, providing an instant examination.
10. Manipulation
Both techniques are easy to operate when compare to other
non-destructive examination techniques. Least amount of training is required
and an operator gets full command after making few practices and exercise. Many
institutes for non-destructive examination courses, are working on training
programs for interested candidates.
Dye Penetrant
|
Magnetic Particle
|
|
Cost
|
Low
|
Low
|
Equipment
|
Fluorescent/visible penetrants.
Developers
|
Fluorescent/visible magnetic particles. Magnetizing systems.
|
Time
|
Comparatively slower than MPE
|
Fast inspection Technique
|
Safety
|
Minimum Risk of loss or injury
|
Non-hazardous
|
Application
|
On all metals and alloys
|
Only on ferromagnetic materials
|
Training
|
Minimum required
|
Minimum
|