FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 6. Corrosion, Inspection, and Protection | 2. Types of Corrosion | 6-20. Stress Corrosion Cracking
AC 43.13-1B
9/8/98
FIGURE 6-9. Inter-granular Corrosion of 7075-T6 aluminum adjacent to steel fastener.
with a damaging chemical environment. The
stress may be caused by internal or external
loading.
FIGURE 6-10. Exfoliation corrosion.
6-19. GALVANIC CORROSION. Gal
vanic corrosion occurs when two dissimilar
metals make contact in the presence of an
electrolyte. (See figure 6-11.) It is usually
recognizable by the presence of a build-up of
corrosion at the joint between the metals.
6-20. STRESS CORROSION CRACKING.
This form of corrosion involves a constant or
cyclic stress, acting in conjunction
a. Internal stress may be trapped in a
part of structure during manufacturing proc
esses such as cold working or by unequal
cooling from high temperatures. Most manu
facturers follow up these processes with a
stress relief operation. Even so, sometimes
stress remains trapped. The stress may be ex
ternally introduced in part structure by rivet
ing, welding, bolting, clamping, press fit, etc.
If a slight mismatch occurs, or a fastener is
over-torque, internal stress will be present.
b. Internal stress is more important than
design stress, because stress corrosion is diffi
cult to recognize before it has overcome the
design safety factor. The level of stress varies
from point to point within the metal. Stresses
near the yield strength are generally necessary
to promote stress corrosion cracking. (See fig
ure 6-12.) However, failures may occur at
lower stresses. Specific environments have
been identified which cause stress corrosion
cracking of certain alloys.
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