FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 6. Corrosion, Inspection, and Protection | 1. General | 6-2. Factors Influencing Corrosion
9/27/01
AC 43.13-1B CHG 1
CHAPTER 6. CORROSION, INSPECTION & PROTECTION
SECTION 1. GENERAL
6-1. GENERAL. The purpose of this chap
ter is to provide information that will help
maintenance personnel prevent, control, iden
tify, and treat various types of corrosion. (Re
fer to AC 43-4A, Corrosion Control For Air
craft for a more in-depth study on the detection
and treatment of corrosion.)
6-2. FACTORS INFLUENCING COR-
ROSION.
a. Some factors which influence metal
corrosion and the rate of corrosion are:
(1) Type of metal;
a. Corrosion is a natural occurrence that
attacks metal by chemical or electrochemical
action and converts it back to a metallic com
pound.
b. Four conditions must exist before
electrochemical corrosion can occur. (See fig
ure 6-1.) They are:
(1) A metal subject to corrosion (An
ode);
(2) A dissimilar conductive material
(Cathode), which has less tendency to corrode;
(3) Presence of a continuous, conduc
tive liquid path (Electrolyte); and
(4) Electrical contact between the anode
and the cathode (usually in the form of metal
to-metal contact such as rivets, bolts, and cor
rosion).
c. Elimination of any one of these condi
tions will stop electrochemical corrosion. (See
figure 6-2.)
NOTE: Paint can mask the initial
stages of corrosion. Since corrosion
products occupy more volume than
the original metal, painted surfaces
should be inspected often for irregu-
larities such as blisters, flakes, chips,
and lumps.
(2) Heat treatment and grain direction;
(3) Presence of a dissimilar, less corro
dible metal;
(4) Anodic and cathodic surface areas
(in galvanic corrosion);
(5) Temperature;
(6) Presence of electrolytes (hard water,
salt water, battery fluids, etc.);
(7) Availability of oxygen;
(8) Presence of biological organisms;
(9) Mechanical stress on the corroding
metal; and,
(10) Time of exposure to a corrosive
environment.
(11) Lead/graphite pencil marks on air
craft surface metals.
b. Most pure metals are not suitable for
aircraft construction and are used only in com
bination with other metals to form alloys.
Most alloys are made up entirely of small
crystalline regions, called grains. Corrosion
can occur on surfaces of those regions which
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