TO 35-1-3 - Robins Air Force Base

TO 35-1-3
Figure 1-3. Open Cell Foam and Resulting Corrosion
1.6.6.5 Airborne industrial pollutants also contribute to the
deterioration of nonmetallic materials and severe corrosion of
metals. The most aggressive are: carbon (from internal combustion
engine exhaust), nitrates (from agricultural fertilizers),
ozone (from electrical motors and welding operations), sulfur
dioxide (from engine exhaust and industrial and ship smoke
stacks), and sulfates (from automobile exhaust).
1.6.6.6 Sand, dust, and volcanic ash are present in many
areas, but particularly in industrial areas where they often contain
a number of tar products, ashes, and soot. Dust is also
found in tropical zones with plentiful rainfall and arid zones
where there is little or no rainfall. Sand and dust are extreme
problems in deserts because the wind carries dry, powdery
sand and dust. During sandstorms, sand and dust can penetrate
sealed equipment and many internal areas of SE. Sand, dust,
and volcanic ash are hygroscopic and can absorb and hold
moisture when present on internal or external surfaces of SE
or electronic parts. Dust from volcanic areas contains chlorides
and sulfates, dust from desert areas may contain chlorides,
carbonates, and sulfates. These materials are extremely
corrosive in the presence of moisture. Although small amounts
of sand or dust may be unnoticed by operating personnel, they
may be sufficient to initiate and accelerate corrosion.
1.6.7 Microbial Induced/Influenced Corrosion. Although
rarely seen on SE, microbial induced/influenced corrosion, as
the term is used in this manual, includes the aggressive action
of bacteria, fungi, or molds that can be found on SE. Microorganisms
are nearly everywhere and outnumber all other types
of living organisms. Those organisms causing the greatest corrosion
problems are bacteria and fungi. Damage resulting from
microbial growth can result from: (1) the tendency of the
growth to hold moisture which then causes corrosion; (2)
digestion of the substrate as food for the microorganism; or (3)
corrosion of the surface beneath the growth by secreted corrosive
fluids of the action of bacteria, fungi, or molds on a metal
surface, see Figure 1-4.
1.6.7.1 Bacteria may be either aerobic or anaerobic. Aerobic
bacteria require oxygen to live. They can accelerate corrosion
by oxidizing sulfur to produce sulfuric acid or by oxidizing
ammonia to produce nitric acid. Bacteria living adjacent to
metals may promote corrosion by depleting the oxygen supply
or by releasing metabolic products. Anaerobic bacteria, on the
other hand, can survive only when free oxygen is not present.
The metabolism of these bacteria requires them to obtain food
sources by oxidizing inorganic compounds such as iron, sulfur,
hydrogen, and carbon monoxide. The resultant chemical
reactions cause corrosion.
1.6.7.2 Microbial attack can be prevented by frequent and
thorough cleaning of the affected areas and applying moistureproofing
coatings to nutrient materials or by drying the interiors
of compartments with desiccants. However, some moisture-proofing
coatings are attacked by microorganisms,
especially if they are used on contaminated surfaces.
Figure 1-4. View of the Results of Microbial Induced
Corrosion
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