FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 6. Corrosion, Inspection, and Protection | 8. Aluminum and Aluminum Alloys | 6-136. Examples of Removing Corrosion From Aluminum and Aluminum Alloys
AC 43.13-1B
9/8/98
(b) When mechanically removing
corrosion from aluminum, especially aircraft
skin thinner than 0.0625 inch, extreme care
must be used. Vigorous, heavy, continuous
abrasive grinding can generate enough heat to
cause metallurgical change. If heat damage is
suspected, hardness tests or conductivity tests
must be accomplished to verify condition of
the metal. The use of powered rotary files
should be limited to heavy corrosion and
should not be used on skin thinner than
0.0625 inch.
f. Inspect the area for remaining corro
sion. Repeat procedure if any corrosion re
mains.
NOTE: If corrosion remains after the
second attempt, use a stronger
method, e.g., chemical to mechanical.
g. Using a blend ratio of 20:1 (length to
depth) blend and finish the corrosion rework
area with progressively finer abrasive paper
until 400-grit paper is used.
(2) Blasting.
(a) Abrasive blasting may be used on
aluminum alloys using glass beads (Spec.
MIL-G-9954) sizes 10 to 13, or grain abrasive
(Spec. MIL-G-5634) types I and III may be
used as an alternate method of removing cor
rosion from clad and non-clad aluminum al
loys. Abrasive blasting should not be used to
remove heavy corrosion products. Direct pres
sure machines should have the nozzle pressure
set at 30 to 40 psi for clad aluminum alloys
and 40 to 45 psi for non-clad aluminum alloys.
Engineering approval should be obtained prior
to abrasive blasting metal thinner than
0.0625 inch.
(b) When using abrasive blasting on
aluminum alloys, do not allow the blast stream
to dwell on the same spot longer than
15 seconds. Longer dwell times will cause ex
cessive metal removal. Intergranular exfolia
tion corrosion is not to be removed by abrasive
blasting; however, blasting may be used with
powered corrosion removal to determine
whether all exfoliation corrosion has been re
moved.
h. Clean reworked area using dry cleaning
solvent. Do not use kerosene or any other pe
troleum base fuel as a cleaning solvent.
i. Determine depth of faired depressions
to ensure that rework limits have not been ex
ceeded.
j. Apply chemical conversion coating,
MIL-C-81706, immediately after reworking. If
48 hours or more have elapsed since the con
version coating was first applied and the
primer or final paint system has not yet been
applied, then reapply the conversion coating
before continuing.
NOTE: These solutions should not be
allowed to come in contact with mag-
nesium or high-strength steels
(180,000 psi). Do not permit solutions
or materials to contact paint thinner,
acetone or other combustible material:
FIRE MAY RESULT.
k. Apply paint finish to area.
6-137.6-147. [RESERVED.]
Page 6-28
Par 6-136