01 March 2005
NAVAIR 01-1A-509-1
TM 1-1500-344-23-1
TO 1-1-689-1
Most fungus growth is inhibited by temperatures above
unnoticed by operating personnel, they may be
104F (40C). Low temperatures pose no real threat of
sufficient to initiate or promote corrosion.
corrosion except that as temperature drops relative
3-13.8. CLIMATE. Warm, moist air, normally found in
humidity rises. The greatest problem in extremely low
tropical climates, tends to accelerate corrosion. Cold,
temperatures, as in polar regions, is the shrinkage of
dry air, normally found in arctic climates, tends to
seals and gaskets. This results in leakage and
reduce corrosion rates. Corrosion does not occur in
embrittlement of organic materials. If temperatures
very dry conditions. For this reason, desiccants are
vary sufficiently, moisture may condense to form liquid
used in shipping containers to produce very dry local
water in the equipment. Similarly, the introduction of
environments. The operational climate extremes have
always been considered in aircraft design. However,
intrusion occurs, subsequent freezing can cause the
certain areas within an aircraft, such as the cockpit and
entrapped moisture to expand, resulting in structural
air conditioned equipment bays, may be subjected to
damage.
climatic conditions very different from external areas of
the aircraft. Relatively warm, dry air that has been
3-13.6. PRESSURE. Most military equipment is
cooled by air conditioners, thus reducing its ability to
intended for service in low pressure (high altitude)
hold moisture, and ducted into interior areas of the
environments. These environments create the familiar
aircraft, can release sufficient moisture to accelerate
corona, arcing, and poor cooling problems in avionic
corrosion. It is imperative, therefore, to consider not
equipment. Another problem is that of cyclic low and
only the operational environment but also the
high pressures. These varying pressures create leaky
environments in which the equipment will be fabricated,
seals and cause breathing. Breathing promotes
transported, reworked, or repaired.
Low pressure also causes outgassing (loss of volatile
3-13.8.1. Desert. The hot, wind-swept desert creates a
components, such as plasticizers) of plastics and other
organic materials. Very low pressure causes changes
severe maintenance problem because powdery dust
to the physical and chemical properties of some
can penetrate even supposedly sealed components.
materials.
High daytime temperatures, high humidities (in areas
such as the Persian Gulf), ultraviolet radiation, and fine
3-13.7. SAND, DUST, AND VOLCANIC ASH. Some of
dust are the four most serious, destructive elements of
the least recognized contributors to corrosion are sand,
the desert climate. Nonmetallic materials suffer the
dust, and volcanic ash. They often contain a number of
most damage from the hot desert climates, where air
tar products, ashes, and soot. Sand, dust and volcanic
temperatures during the day may reach 124F (50C).
ash are hygroscopic and, when present on internal or
Temperatures inside closed containers may be 100F
(38C) higher than external air temperatures.
external surfaces of aircraft or electronic parts, can
absorb and hold moisture. This provides an electrolyte
3-13.8.2. T e m p e r a t e Z o n e s . T h e t e m p e r a t e o r
for corrosion and the growth of fungus. The presence of
intermediate climate zone encompasses most of the
sand, dust or volcanic ash may also affect the operation
North American and European continents. These areas
of electrical contacts, prevent proper action of rotating
at various times of the year may approximate the
motor-drive devices, and cause malfunctions of
extremes of polar, desert, or tropical temperatures and
indicating instruments. Sand and dust are extreme
humidity. The temperate zone temperatures range from
problems in the deserts, since dry, powdery sand and
-25 to 59F (-32 to 15C) in the winter and from 59 to
dust are easily carried by wind. During sandstorms,
125F (15 to 52C) in summer. The relative humidity
they can penetrate sealed equipment as well as internal
also fluctuates between five and 100%. The most critical
areas of airframes. In arid regions such as deserts,
areas are coastal locations: during the warm periods of
small sand particles are often blown as high as 10,000
the year the relative humidity approaches 100% at
feet by the siroccos (hot, dust laden winds). Sand and
night and the air has high concentrations of salt.
dust on surfaces can cause an abrasive action when the
Moisture from this salt-laden air can condense on
surfaces are moved or vibrated. This removes the
equipment during early evening and morning hours,
protective oxide coatings and leaves the metal exposed.
thereby causing serious corrosion. Because of its
Volcanic ash contains chlorides and sulfates, which
relatively mild temperatures, the temperate zone is
are extremely corrosive in the presence of moisture.
also the most heavily populated. Consequently, the
Although small amounts of sand, dust, or ash may be
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