rivets, bolts, and attaching structures must be inspected for
possible damage.
Make a thorough inspection for rivets that have
partially failed and for holes that have been distorted.
Damage
assessment includes looking for weathering or corrosion.
Damage to
aluminum by corrosion is detected by a white crystalline deposit that
can be seen around loose rivets, scratches, bad dents, or some
portion of the structure where moisture can collect.
If a visual
inspection
of
inside
skin
surfaces
cannot
be
made
without
disassembly, rap your knuckles on the outside skin at various places.
Severe corrosion exists if the light rapping causes dents or a white
dust to appear.
INSPECTING FOR CRACKS
The existence or full extent of cracks in major structural members
cannot be accurately determined by a visual inspection; therefore,
several methods other than visual are used.
They are ultrasonic
waves, X rays, Zy-glo, and a penetrating dye. When using ultrasonic
waves, only one side of the inspected metal need be accessible. With
X-ray equipment both sides of the metal must be accessible. The Zy-
glo method requires blacklight equipment.
Penetrating dye requires
no complex or expensive equipment, and it can be easily used in the
field.
The materials to make a dye-penetrant inspection consist of
the penetrating dye, dye remover, and dye developer, all contained in
an inspection kit. Individual items for the kit can be requisitioned
to replace those which have been used.
The paragraphs that follow
describe how the kit is used.
Preparation. All coats of paint and surface dirt must be removed
before the dye penetrant is applied.
A thoroughly clean surface is
required to ensure an accurate portrayal of the structural member's
condition.
Application. The surface to be inspected is given a final cleaning
by applying dye remover and wiping the surface with clean cloths.
Then a coat of dye penetrant is applied by brushing or swabbing and
allowed to penetrate for 3 to 15 minutes.
Removal. The dye penetrant on the surface is removed by wiping the
excess off, first with a dry cloth and then with a cloth moistened
with dye remover. If a water rinse is used, the inspected part must
be thoroughly dried before applying the dye developer.
Development. A light, even coating of dye developer is
applied with a brush or by spraying. Whichever method is used,
be sure that the coating is free of runs or laps.
The developer
dries and forms a smooth, white coating. Cracks show up as
red lines, and the extent is indicated by the length of the red
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