Table 2-3. Mechanical Working Processes.
Effects Of Mechanical Working.
If a conflict arises pertaining to the proper inspection method to use following
mechanical working, the appropriate engineering activity SHALL be contacted for
Mechanical working removes soils and contaminates by physical action. This physical action may also remove or
deform the part surface. Deformation is in the form of metal flow or displacement on the part surface. The amount of
deformation depends on the type and severity of the working plus the ductility of the part. Even a small amount of
deformation, such as that caused by fine sanding or vapor blasting, may reduce the surface opening of small
discontinuities. This deformation can reduce the effectiveness of the penetrant inspection process. Chemical etching
(see paragraph 18.104.22.168) may be necessary when penetrant inspection is performed after a less severe mechanical
working process. Severe mechanical working processes, such as metal removal, shot peening, or grit blasting, can seal
or close the surface openings of large discontinuities which prevents the formation of penetrant indications. Penetrant
inspection SHALL be accomplished prior to mechanical work processes, such as machining, shot peening, grit blasting,
plastic media bead blasting, or coarse sanding, that severely displace surface metal. If it is not feasible to perform
penetrant inspection prior to these processes, then another inspection method should be considered. An exception to
this requirement is when penetrant inspection is performed to detect discontinuities formed by mechanical working,
such as machining tears or grinding cracks.
Solvent Cleaning With Aerosol Spray Cans.
Isopropyl alcohol and most Class 2 solvent removers are flammable.