FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 6. Corrosion, Inspection, and Protection | 11. Other Metals and Alloys | 6-181. Titanium and Titanium Alloys
9/8/98
SECTION 11. OTHER METALS AND ALLOYS
AC 43.13-1B
6-179. NOBLE METAL COATINGS -
CLEANUP AND RESTORATION. Silver,
platinum, and gold finishes are used in aircraft
assemblies because of their resistance to ordi
nary surface attack and their improved electri
cal or heat conductivity. Silver-plated elec
trodes can be cleaned of brown or black sulfide
tarnish, by placing them in contact with a piece
of magnesium sheet stock while immersed in a
warm water solution of common table salt
mixed with baking soda or by using a fine
grade abrasive mat or pencil eraser followed
by solvent cleaning. If assemblies are in
volved, careful drying and complete displace
ment of water is necessary. In general, clean
ing of gold or platinum coatings is not recom
mended in the field.
6-180. COPPER AND COPPER ALLOYS
are relatively corrosion resistant, and attack on
such components will usually be limited to
staining and tarnish. Such change in surface
condition is not dangerous and should ordinar
ily have no effect on the function of the part.
However, if it is necessary to remove such
staining, a chromic acid solution of 8 to 24
ounces per gallon of water containing a small
amount of battery electrolyte (not to exceed
50 drops per gallon) is an effective brightening
bath. Staining may also be removed using a
fine grade abrasive mat or pencil eraser fol
lowed by solvent cleaning.
a. Immerse the stained part in the cold
solution. Surfaces can also be treated in place
by applying the solution to the stained surface
with a small brush.
b. Avoid any entrapment of the solution
after treatment. Clean the part thoroughly
following treatment with all residual solution
removed.
c. Serious copper corrosion is evident by
the accumulation of green-to-blue copper salts
on the corroded part. Remove these products
mechanically using a stiff bristle brush, brass
wire brush, 400-grit abrasive paper or bead
blast with glass beads, (specification
MIL-G-9954, size 13). Air pressure when
blasting should be 20 to 30 psi for direct pres
sure machines. Do not bead blast braided cop
per flexible lines. Reapply a surface coating
over the reworked area. Chromic acid treat
ment will tend to remove the residual corro
sion products.
WARNING: Brushing, sanding, and
abrasive blasting of copper and cop-
per alloys can be dangerous due to the
creation of toxic airborne particles.
Take necessary precautions to ensure
safety.
6-181. TITANIUM AND TITANIUM AL-
LOYS are highly corrosion resistant because
an oxide film forms on their surfaces upon
contact with air.
a. When titanium is heated, different
oxides having different colors form on the sur
face. A blue oxide coating will form at 700 to
800 °F; a purple oxide at 800 to 950 °F; and a
gray or black oxide at 1000 °F or higher.
These coatings are protective discolorations
and should not be removed.
b. Corrosive attack on titanium surfaces
is difficult to detect. It may show deterioration
from the presence of salt deposits and metal
impurities at elevated temperatures so periodic
removal of surface deposits is required. How
ever, if corrosion develops on titanium, it usu
ally occurs as pitting. Acceptable methods for
corrosion removal are:
Par 6-179
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