TO 35-1-3 - Robins Air Force Base
TO 35-1-3 - Robins Air Force Base
TO 35-1-3 - Robins Air Force Base
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<strong>TO</strong> <strong>35</strong>-1-3<br />
sion. Improper dilution of cleaning chemicals, combining<br />
cleaning compounds together, or the use of unauthorized<br />
cleaning material can cause the cleaning solution to become an<br />
electrolyte.<br />
1.6.6.1 Moisture is present in air as a gas (water vapor) or as<br />
finely divided droplets of liquid (mist or fog) and often contains<br />
contaminants (such as chlorides, sulfates, and nitrates)<br />
that increase its corrosive effects. Moisture will enter all areas<br />
of SE that air can enter. All enclosed areas, that are not hermetically<br />
sealed, will allow air to enter and leave as the difference<br />
in pressure between the inside and outside the equipment<br />
changes. These pressure differences occur when atmospheric<br />
pressure changes and when the air temperature inside an<br />
enclosed area changes. As the surrounding surfaces are heated,<br />
moisture-laden air is drawn into the enclosed area or absorbed<br />
in open cell foam. As the air around the equipment cool, moisture<br />
will condense in the enclosed areas and settle in the lowest<br />
area of the part. The enclosed areas are often hidden and/or<br />
inaccessible. Moisture is difficult to remove and the subsequent<br />
corrosion may be difficult to identify in the early stages.<br />
1.6.6.2 Salt laden atmospheres pose a continual problem in<br />
locations operating near coastal environments. When dissolved<br />
in water, salt solutions form very effective electrolytes.<br />
The ocean, which is 3.5% to 3.9% salt, is the world's primary<br />
source of salt. Normal sea winds carry from 10 to 100 lbs of<br />
sea salt per cubic mile of air. <strong>Base</strong>s located close to marine<br />
environments are continually exposed to the salt laden atmosphere.<br />
Because dissolved salts are strong electrolytes, it is<br />
easy to understand why coastal environments are listed in the<br />
moderate to severe corrosion prone categories and require frequent<br />
rinsing and cleaning to remove the salt deposits.<br />
1.6.6.3 Condensed moisture will usually evaporate as the<br />
surrounding air warms but will leave behind its contaminants<br />
(residues), including salts. This can result in the build-up of<br />
soils and salt contamination. Salt-laden condensation may collect<br />
at the lowest surface of the equipment. The lowest surfaces<br />
are usually the last to dry. As the condensation continues<br />
to collect at the lowest surfaces the contaminates/ electrolytes<br />
become more concentrated. Condensed moisture and its contaminants<br />
can also be trapped in close fitting, wettable joints,<br />
such as faying surfaces. Some gasket and packing materials<br />
will absorb several times their weight in water and, when<br />
heated, can transmit this retained moisture into the sealed area.<br />
Moisture can accumulate in such areas through successive<br />
cycles of warming and cooling and cause corrosion on the<br />
interior of the part resulting in premature structural failure as<br />
shown in Figure 1-2.<br />
1.6.6.4 Open cell foam, see Figure 1-3, is a sponge-like<br />
material used mainly for sound suppression and insulation.<br />
Humidity, condensation, rainfall, etc., is absorbed into the<br />
foam and ultimately migrates to the mating metal surface to<br />
which it is attached. The absorbed moisture is very slow in<br />
drying out and provides the moisture/electrolyte against the<br />
metal surfaces. When possible, open cell foam should not be<br />
used. Closed cell types of foam may be suitable substitutes for<br />
this material and will not absorb moisture. If open cell foam is<br />
the only material suitable for your needs, prior to installation<br />
in the SE, seal all open cell surfaces and sides of any perforations<br />
in the foam with a polysulfide type sealant such as MIL-<br />
PRF-81733. Sealing any tears in the foam or any unsealed<br />
sides and edges of the foam will preclude any fluid absorption<br />
by the foam.<br />
Figure 1-2. Corrosion Accelerated by Condensed Moisture<br />
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