T.O. 33B-1-1
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softer though still somewhat abrasive. On highly polished surfaces, residual powder from the bath can contribute to
rapid corrosion.
3.2.5.1.2
Vehicle.
The wet method inspection process will normally leave the carrier liquid or vehicle on the test surface. If the vehicle is
oil, it can be removed by vapor degreasing or solvent cleaning. If the vehicle is water, the residue will consist of
wetting agents and water soluble corrosion inhibitors, which may be removed with a plain water rinse or spray.
Regardless of the type of vehicle used, the part should be cleaned as soon as possible after inspection and
demagnetization.
3.2.5.2
Methods.
CAUTION
Post-cleaning methods that use water can cause corrosion of the test surfaces if the
water is not promptly removed. Thoroughly dry off the surfaces by wiping, heating
or blowing off with properly regulated compressed air.
Regardless of whether the wet or dry visible or fluorescent magnetic particle inspection process is used, once the carrier
liquid or vehicle is removed, the requirement for removal of the magnetic particles is the same. Thoroughly
demagnetize the part, and then remove the magnetic particles by wiping or scrubbing. Cleaners or detergents cannot
break the magnetic attraction. The particles cannot be dissolved from the surface, as they are a ferrous oxide.
Mechanical scrubbing or detergent washing may be necessary. Solvents may be used to remove the residue, and in
some cases the use of ultrasonic cleaning has been successful.
3.2.5.3
Requirements Following Post Inspection Cleaning.
After inspection by the wet method using a petroleum distillate as the bath liquid, the surfaces of parts are left
vulnerable to corrosion. The bath vehicle is, by specification, free of any residual non-volatile material, and when it
dries it leaves no protective film. Every effort shall be taken to clean a part and apply a protective finish as soon as
possible after the inspection. When water is the vehicle of the bath, the dried film on the surface of a part consists of
the various conditioners that have been used in the bath formulation in addition to the residual magnetic particles. One
of the conditioners is a corrosion inhibitor, so that some corrosion protection is afforded by this inhibitor after testing.
However, this is by no means permanent and a protective finish should be applied as soon as possible.
3.2.5.3.1
In the event a functional material, such as oil, grease or anti-seize compound, is removed from the part to facilitate
inspection, the same material shall be reapplied after the part has been inspected.
3.2.6
Disassembly Requirements.
3.2.6.1
Requirements.
It is usually preferable to disassemble parts before inspection for the following reasons:
a. Disassembly makes all surfaces and areas accessible.
b. Boundaries between two magnetic pieces, or between a magnetic and a non-magnetic piece, will create
a leakage field that may confuse inspection.
c. It is usually easier to handle disassembled parts.
