Table 3-5. Requirements for Magnetic Particle Wet Method Oil Vehicle (DOD-F-87395)
Flash Point, C(F)
ASTM D 93
ASTM D 1500
Less than the standard
ASTM D 445
Particulate Matter, mg/L
ASTM D 2276
Total Acid Number, mg KOH/L
ASTM D 3242
b. Magnetic particles SHALL comply with ASTM E 1444 and the specific aerospace material specification
(AMS). (see Table 3-6)
Table 3-6. Procurement Data for Magnetic Particles per ASTM E 1444
Type of Particles (Specification Title)
Magnetic Particle Inspection Material, Dry Method
Magnetic Particles, Wet Method, Oil Vehicle
Magnetic Particles, Wet Method, Dry Powder
Magnetic Particles, Wet Method, Oil Vehicle Aerosol Canned
Magnetic Particles, Fluorescent, Wet Method, Dry Powder
Magnetic Particles, Fluorescent, Wet Method, Oil Vehicle
Magnetic Particles, Fluorescent, Wet Method, Oil Vehicle, Aerosol Canned
Current / Particle Application Techniques.
The part may be magnetized first and particles applied after the magnetizing force has been turned off (the residual
method); or the part may be covered with particles while the magnetizing force is still present (the continuous method).
With parts having high retentivity, a combination of these methods is sometimes used. The choice between the residual
and the continuous method is a relatively easy one.
Description and Use.
In the residual method, parts are magnetized and the magnetic particles are then applied. This method can be used
only on parts having sufficient retentivity. The magnetic field they retain must be sufficiently strong to produce
leakage fields at discontinuities, which in turn will produce readable indications. The method in general is reliable
only for the detection of surface discontinuities. Since hard materials which have high retentivity are usually low in
permeability, higher than usual magnetizing currents may be necessary to obtain a sufficiently high level of residual
magnetism. The difference in the behavior between hard steels and soft steels is usually not very serious, if only surface
discontinuities are sought.
Dry Versus Wet.
Either the dry or the wet method for particle application can be used in the residual method. With the wet method, the
magnetized parts may be immersed in an agitated bath of suspended magnetic particles, or they may be flooded with
bath by a spray. In these circumstances a favorable factor occurs that affects the strength of indications. This factor is
the time of immersion of the part in the bath. By leaving the magnetized part in the bath or under the spray for a
considerable time, the leakage fields have time to attract and hold a maximum number of particles even at fine