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ISO 9001 CERTIFIED
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MAGNAFLUX
3624 W. Lake Ave.
Glenview, Il 60026
Phone:
847 657-5300
Domestic Fax Number:
800-421-1569
International Fax Number:
847-657-4720
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magnetic particle inspection faq
NDT History | Definitions
| Liquid Penetrant FAQ's |
Magnetic Particle FAQ's
What is Magnetic Particle Inspection?
A nondestructive test method which provides for the detection of linear,
surface and near surface discontinuities in ferromagnetic (material that
can be magnetized) test materials.
What is a linear indication?
Any indication having a length dimension at least 3-times greater than
its width (L=3 x > W)
What are the advantages of magnetic particle
inspection?
- Test method process is quick and simple in principle and application
- Highly sensitive to the detection of surface and slightly subsurface
linear indications
- Indications appear on the actual test part
- Test method process may often work through contaminant layers and
coating thickness
- The method lends itself to automation and high volume production inspection
- Less expensive than other more sophisticated methods of quality assurance
What are the limitations of magnetic particle
inspection?
- Test material must be ferrous
- Provides limited and variable potential for detection of subsurface
indications
- Care is required to avoid burning and arcing of test part surface
at points of electrical contact
- The magnetic field direction must intercept the major dimension of
the discontinuity
- Complex test part geometry may sometimes pose problems with proper
amperage determination and magnetic field intensity
- Demagnetization of test part following the inspection is often necessary
Are there different types of magnetic particles?
Yes, the different types are:
- Dry method non-fluorescent
- Wet method fluorescent
- Wet method non-fluorescent
What are the properties of dry powder and wet
suspension magnetic particles?
They are Iron Oxide particles, finely divided in sizes varying between
.125 and 60 microns with a high permeability (easily magnetized) and low
retentivity (ability to stay magnetized). Dry particles are chemically
dyed to provide contrast against the background of the test surface. Stock
colors are gray, red, black and yellow. Application is either with a squeeze
bulb or spray gun. Wet suspension particles are suspended in an oil based
or water based liquid vehicle or carrier. With water you must add conditioners
in addition to a wetting agent and corrosion inhibitors.
What is the sensitivity comparison between wet
vs. dry methods?
Wet method provides improved sensitivity for the detection of very fine
surface flaws. Dry method provides improved sensitivity for the detection
of subsurface flaws.
What is the maximum depth that magnetic particles
can detect a discontinuity?
1/4 inch, however .050 to .100 inch is a more realistic depth.
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