There are several methods for removing corrosion; chemical treatment; hand sanding with abrasive paper or
metal wool; and, mechanical sanding or buffing with abrasive materials or grinding wheels. The method selected
depends on the type and extent of the corrosion.
Depressions resulting from rework must be faired into the surrounding surface.
The depth of materials removed should not exceed the safe limits.
Reprotecting the surface after corrosion removal is very important. It should be done as soon as the repair
work is finished. The surface should be protected in the same manner as the original surface was protected unless
the manufacturer recommends some other procedure or protective coating.
TABLE II-IIC. TYPES OF METAL CORROSION
Type of Material
Type of Corrosion
Steel
Complete removal of corrosion
by mechanical means.
Aluminum
White to grey powdery material.
Mechanical polishing or
brushing with material
softer than aluminum.
Magnesium (highly susceptible
White powdery snow-like
to corrosion)
mounds and white spots.
Cadmium (plating)
White to brown to black mottling
Mechanical removal of
of surface (plating is still pro-
corrosion should be limited
tecting until iron appears).
to metal surfaces from which
the cadmium has been depleted.
Chromium (plating)
May pit in chloride
Promotes rusting of steel where
environment.
pits occur in the coating.
* Red rust generally shown on bolt heads, hold-down nuts and other aircraft hardware. Its presence in these
areas is generally not dangerous. However, it is indicative of a need for maintenance and also of the
possibility of corrosive attack in more critical areas.
Any corrosion on the surface of a highly stressed steel part is potentially dangerous. A careful removal of
corrosion product using mild abrasives (rouge or fine grit aluminum oxide paper) is necessary, using care not
to overheat the metal when removing the corrosion.
** For abrasion, do not use dissimilar materials (ex. steel on aluminum). Remove only the material required
to clean up the affected area.
PIPER AIRCRAFT
PA-28-161 CADET
AIRPLANE MAINTENANCE MANUAL
Issued: FEBRUARY 28, 1989
HANDLING AND SERV I C I N G
1C13
