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 />
Figure 1-3. Open Cell Foam and Resulting Corrosion<br />
1.6.6.5 <strong>Air</strong>borne industrial pollutants also contribute to the<br />
deterioration of nonmetallic materials and severe corrosion of<br />
metals. The most aggressive are: carbon (from internal combustion<br />
engine exhaust), nitrates (from agricultural fertilizers),<br />
ozone (from electrical motors and welding operations), sulfur<br />
dioxide (from engine exhaust and industrial and ship smoke<br />
stacks), and sulfates (from automobile exhaust).<br />
1.6.6.6 Sand, dust, and volcanic ash are present in many<br />
areas, but particularly in industrial areas where they often contain<br />
a number of tar products, ashes, and soot. Dust is also<br />
found in tropical zones with plentiful rainfall and arid zones<br />
where there is little or no rainfall. Sand and dust are extreme<br />
problems in deserts because the wind carries dry, powdery<br />
sand and dust. During sandstorms, sand and dust can penetrate<br />
sealed equipment and many internal areas of SE. Sand, dust,<br />
and volcanic ash are hygroscopic and can absorb and hold<br />
moisture when present on internal or external surfaces of SE<br />
or electronic parts. Dust from volcanic areas contains chlorides<br />
and sulfates, dust from desert areas may contain chlorides,<br />
carbonates, and sulfates. These materials are extremely<br />
corrosive in the presence of moisture. Although small amounts<br />
of sand or dust may be unnoticed by operating personnel, they<br />
may be sufficient to initiate and accelerate corrosion.<br />
1.6.7 Microbial Induced/Influenced Corrosion. Although<br />
rarely seen on SE, microbial induced/influenced corrosion, as<br />
the term is used in this manual, includes the aggressive action<br />
of bacteria, fungi, or molds that can be found on SE. Microorganisms<br />
are nearly everywhere and outnumber all other types<br />
of living organisms. Those organisms causing the greatest corrosion<br />
problems are bacteria and fungi. Damage resulting from<br />
microbial growth can result from: (1) the tendency of the<br />
growth to hold moisture which then causes corrosion; (2)<br />
digestion of the substrate as food for the microorganism; or (3)<br />
corrosion of the surface beneath the growth by secreted corrosive<br />
fluids of the action of bacteria, fungi, or molds on a metal<br />
surface, see Figure 1-4.<br />
1.6.7.1 Bacteria may be either aerobic or anaerobic. Aerobic<br />
bacteria require oxygen to live. They can accelerate corrosion<br />
by oxidizing sulfur to produce sulfuric acid or by oxidizing<br />
ammonia to produce nitric acid. Bacteria living adjacent to<br />
metals may promote corrosion by depleting the oxygen supply<br />
or by releasing metabolic products. Anaerobic bacteria, on the<br />
other hand, can survive only when free oxygen is not present.<br />
The metabolism of these bacteria requires them to obtain food<br />
sources by oxidizing inorganic compounds such as iron, sulfur,<br />
hydrogen, and carbon monoxide. The resultant chemical<br />
reactions cause corrosion.<br />
1.6.7.2 Microbial attack can be prevented by frequent and<br />
thorough cleaning of the affected areas and applying moistureproofing<br />
coatings to nutrient materials or by drying the interiors<br />
of compartments with desiccants. However, some moisture-proofing<br />
coatings are attacked by microorganisms,<br />
especially if they are used on contaminated surfaces.<br />
Figure 1-4. View of the Results of Microbial Induced<br />
Corrosion<br />
1-6