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 | 6-12. General Surface Corrosion
9/27/01
SECTION 2. TYPES OF CORROSION
AC 43.13-1B CHG 1
6-11. GENERAL. All corrosive attacks be
gin on the surface of the metal making the
classification of corrosion by physical appear
ance a convenient means of identification.
(See figure 6-3.)
6-13. PITTING CORROSION. Pitting
corrosion is one of the most destructive and
intense forms of corrosion. It can occur in any
metal but is most common on metals that form
protective oxide films, such as aluminum and
magnesium alloys. It is first noticeable as a
white or gray powdery deposit, similar to dust,
which blotches the surface. When the deposit
is cleaned away, tiny holes or pits can be seen
in the surface. (See figures 6-5(a) and 6-5(b).)
These small surface openings may penetrate
deeply into structural members and cause
damage completely out of proportion to its sur
face appearance.
FIGURE 6-3. Corrosion attack.
6-12. GENERAL SURFACE CORRO-
SION. General surface corrosion (also re
ferred to as Uniform Etch or Uniform Attack
Corrosion) is the most common form of corro
sion and results from a direct chemical attack
on a metal surface and involves only the metal
surface. (See figure 6-4.) General surface cor
rosion usually occurs over a wide area and is
more or less equal in dispersion. On a pol
ished surface, this type of corrosion is first
seen as a general dulling of the surface, and if
allowed to continue, the surface becomes
rough and possibly frosted in appearance. The
discoloration or general dulling of metal cre
ated by exposure to elevated temperatures is
not to be considered general surface corrosion.
FIGURE 6-5(a). Pitting corrosion (external view).
FIGURE 6-5(b). Pitting corrosion (magnified cross sec
tion).
FIGURE 6-4. General surface corrosion.
Par 6-11
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