4) The glass beads quickly remove corrosion (about 36 linear inches a
minute) but almost none of the cladding on the aluminum surface.

F. Corrosion Removal -Chemical. The chemical corrosion removal procedure can
be used on the airplane where chemical flow can be controlled and the area
can be fully washed with water. Because the chemicals used for corrosion
removal can also cause corrosion, you must not let the chemicals become
caught in such locations as lap joints, faying surfaces, or splices. on
parts removed from the airplane, the chemical removal procedure could be
better. The chemical agents used in corrosion removal are of the acid type.
Because the chemicals are different for each metal details of the procedures
are given in the applicable paragraphs that follow.

G. Special Corrosion Removal Procedures. Special procedures are applicable
when corrosion damage was caused by other than usual airline service.
Spilled mercury will cause corrosion very quickly. Refer to 20-41-00 for
details. A fire in the airplane can cause corrosion because of ashes and
fire extinguisher chemicals. Refer to 20-42-00 for details. Also, spilled

alkaline or acid agents cause corrosion. Refer to 20-43-00 and 20-44-01 for
details. Livestock and fish as cargo can cause much corrosion of the air-plane structure and make necessary special procedures. Refer to 20-61-00 and
20-62-00 for more data.

8. Corrosion Removal Procedures for Aluminum and Aluminum Alloys

WARNING: OBEY THE SAFETY PRECAUTIONS AND PROCEDURES OF PAR. 2. ABOVE.

A. General. Aluminum and its alloys are the most frequently used materials in
commercial airplanes. The metal is not toxic, not magnetic and because it
can absorb large amounts of energy, it will not spark when hit by other met-als. Although aluminum is high in the electrochemical series, it makes a
tightly bonded anodic oxide film on the surface that gives more resistance
to mild corrosive conditions. One sign of corrosion is a whitish deposit of
corrosion products. General etching, pitting or roughness of the surface
gives an indication of the start of corrosion damage.

B. Corrosion Removal -Mechanical

(1)Make sure the metal is aluminum.

(2)Give adjacent areas protection to prevent more damage from corrosion
products removed during mechanical removal.

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20-40-00
Page 9 OCT 01/01
(3)If you find grease or dirt, clean the area per par. 5.

(4)Remove paint per par. 6, if applicable.

(5)Measure the amount of damage per par. 3.

(6)Remove corrosion by one of the following:

CAUTION: DO NOT USE A CARBON STEEL BRUSH OR STEEL WOOL ON ALUMINUM SURFACES,
OR THE STEEL PARTICLES WILL BE RUBBED INTO THE ALUMINUM AND CAUSE
MORE CORROSION DAMAGE. STEEL FASTENERS MUST BE REMOVED BEFORE COR-ROSION REMOVAL TO MAKE SURE THAT CORROSION IS COMPLETELY REMOVED
　
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