FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 6. Corrosion, Inspection, and Protection | 10. Ferrous Metals | 6-166. Special Treatment of Stainless Steel
9/8/98
SECTION 10. FERROUS METALS
AC 43.13-1B
6-164. GENERAL. One of the most famil
iar kinds of corrosion is red iron rust. Red iron
rust results from atmospheric oxidation of steel
surfaces. Some metal oxides protect the un
derlying base metal, but red rust is not a pro
tective coating. Its presence actually promotes
additional attack by attracting moisture from
the air and acts as a catalyst to promote addi
tional corrosion.
a. Red rust first shows on bolt heads,
hold down nuts, and other unprotected aircraft
hardware. Red rust will often occur under
nameplates that are secured to steel parts. Its
presence in these areas is generally not dan
gerous. It has no immediate effect on the
structural strength of any major components.
However, it shows a general lack of mainte
nance and may indicate attack in more critical
areas.
b. When paint failures occur or me
chanical damage exposes highly-stressed steel
surfaces to the atmosphere, even the smallest
amount of rusting is potentially dangerous and
should be removed immediately.
6-165. SPECIAL TREATMENT OF
HIGH-STRENGTH STEEL. (High-strength
steels heat treated above Rockwell C40,
180,000 psi tensile strength). Any corrosion
on the surface of a highly-stressed steel part is
potentially dangerous, and the careful removal
of corrosion products is mandatory. Surface
scratches or change in surface structure from
overheating can cause sudden failure of these
parts. The removal of corrosion products is
required and will be performed carefully and
completely.
a. Acceptable methods include careful
use of mild abrasive mats, cloths, and papers,
such as fine grit aluminum oxide, metallic
wool, or fine buffing compounds.
b. Undesirable methods include the use
of any power tool because the danger of local
overheating and the formation of notches that
could lead to failure. The use of chemical cor
rosion removers is prohibited, without engi
neering authorization, because high-strength
steel parts are subject to hydrogen embrittle
ment.
6-166. SPECIAL TREATMENT OF
STAINLESS STEEL. Stainless steels are of
two general types: magnetic and nonmagnetic.
a. Magnetic steels are of the ferritic or
martensitic types and are identified by num
bers in the 400-series. Corrosion often occurs
on 400-series stainless steels and treatment is
the same as specified in high-strength steels.
(See paragraph 6-165.)
b. Non-magnetic stainless steels are of
the austenitic type and are identified by num
bers in the 300-series. They are much more
corrosion resistant than the 400-series steels,
particularly in a marine environment.
(1) Austenitic steels develop corrosion
resistance by an oxide film, which should not
be removed even though the surface is discol
ored. The original oxide film is normally
formed at time of fabrication by passivation. If
this film is broken accidentally or by abrasion,
it may not restore itself without repassivation.
(2) If any deterioration or corrosion
does occur on austenitic steels, and the struc
tural integrity or serviceability of the part is af
fected, it will be necessary to remove the part.
Par 6-164
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