TO 1-1-700 - Robins Air Force Base

TO 1-1-700
Although packaging equipment in accordance with MIL-STD-
2073-1 will protect the equipment from corrosive environments,
packaging may be damaged during handling and thus
become ineffective.
3.9.18 Industrial and Ship Emitted Air Pollutants. Smog,
smoke, soot, and other airborne contaminants are extremely
corrosive to exposed C-E-M equipment. Many of the fumes
and vapors emitted by ships and from factories can greatly
accelerate metal corrosion. Industrial atmospheres may exist
over large areas, since wind may carry these corrosive gases
many miles from their source. Generally, air pollutants, when
combined with water, create electrolytic solutions and accelerate
corrosion.
3.9.19 Animal Damage. Damage to C-E-M and associated
equipment may be caused by insects, birds, and various small
animals, especially in tropical environments. Equipment in
storage is most susceptible to this type of attack, since animals
may enter through vent holes or tears in packaging and sometimes
build nests. Moisture absorbed by nests plus excretions
from animals may cause corrosion and deterioration that goes
unnoticed until equipment is put into use and fails. Another
type of damage may occur when organic materials, such as
upholstery, are shredded for nests or consumed as food.
3.9.20 Microorganisms. Microbial attack includes the
action of bacteria, fungi, or molds. Microorganisms are nearly
everywhere and outnumber all other types of living organisms.
Organisms that cause 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; and (3) corrosion of the surface
beneath the growth by secreted corrosive fluids.
3.9.21 Bacteria. 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
ammonia to produce nitric acid. Bacteria living on or adjacent
to metals may promote corrosion either 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.
3.9.22 Microbial Growth Requirements. Fungi make up
one class of microorganisms that feed on organic matter. Low
humidity levels inhibit the growth of most species of fungi and
bacteria. Ideal growth conditions for most fungi and bacteria
are temperatures of +68 °F to +104 °F (+20 °C to +40 °C) and
relative humidity of 85% to 100% RH. It was formerly
believed that microbial attack could be prevented by applying
moisture-proof coatings to nutrient materials or by drying the
interiors of compartments with desiccants. However, even
some moisture-proof coatings are attacked by microorganisms,
especially if the surface to which they are applied is contaminated.
Some microorganisms can survive in spore form for
long periods while dry, and can become active when moisture
is available. When desiccants become saturated, they form
what is known as a “desiccant pump” which pumps their
absorbed moisture into the affected area by evaporation and
allows microorganisms to begin to grow. Dirt, dust, and other
airborne contaminants are the least recognized contributors to
microbial attack. Unnoticed, small amounts of airborne debris
may be sufficient to promote fungal growth by absorbing
moisture.
3.9.23 Microbial Nutrients. Since fungi, bacteria, and other
microorganisms are classified as living, it was previously
thought that only materials derived from living organisms
could provide them with food. Thus wool, cotton, feathers,
leather, etc., were known to be microbial nutrients. To a large
extent this rule of thumb is still valid, but the increasing complexity
of synthetic materials makes it difficult, if not impossible,
to determine from the name alone whether a material will
support growth of microorganisms. Many otherwise resistant
synthetic materials are rendered susceptible to microbial attack
by the addition of chemicals, which change the properties of
the material. In addition, different species of microorganisms
have different growth requirements. The service life, size,
shape, surface smoothness, cleanliness, environment, and species
of microorganism involved all determine the degree of
microbial attack on the affected item.
3.10 DEGRADATION OF NON-METALS.
Non-metallic materials (plastics, elastomers, paints, and adhesives)
are not subject to electrochemical corrosion, since ions
are not easily formed from non-metallic materials and their
electrical conductivity is extremely low. The degradation of
non-metals depends on the chemical makeup of the material
and the nature of the environment. In general, non-metallic
materials on C-E-M and related equipment are selected for
their obvious performance properties (flexibility, transparency,
strength, electrical resistance, etc.) as well as their resistance
to heat, impact, abrasion, ultraviolet radiation, moisture, ozone
and other detrimental gases, and operational fluids such as
hydraulic fluid, lube oil, cleaners, deicing fluids, etc. However,
the use of unauthorized maintenance chemicals and procedures
can accelerate degradation and ultimately lead to
material failure resulting in leakage, corrosion, electrical
shorts, crazing, and/or mechanical failure.
3-19