damp and unattended or left for prolonged periods in a
damp shelter. Canvas is a heavy, coarse, and closely
woven fabric of cotton, kemp, or flax. Tarp or tarpaulin
Almost all rusting is a form of stress corrosion
is coarse linen. Both of these fabrics are organic materi-
because man-made iron or steel is a stressed by-product
als and, as such, keeping them clean and allowing them
of natural ores. Stress corrosion is most often associated
to air out will prevent the formation of mildew.
with metals or rubbers under even greater stress due to
the design application. Steel forced by loads into a bend
is an example. If such steel is exposed further to rusting,
it becomes structurally weaker. The result is a raising of
2-17. Acid Rain.
the level of stress placed on the metal; the greater the
stress, the more the corrosion acts upon the metal. In
a. Acid rain is commonly understood as the
heavy metals such as steel, the effects of stress
bombardment of the earth by chemical wastes from
corrosion are one of the causes of metal fatigue. In
industry. It is viewed as a major problem in heavily
other applications, stress corrosion will cause cracking
populated and industrial areas. Wherever there are oil
along with an increase of stress and accelerated
burning furnaces or chemical mills in use, there will be
emissions which are felt to be the cause of acid rain.
Acid rain is chiefly composed of dimethyl sulfide and
hydrogen sulfide. The chemicals attack painted metal
2-15. Fretting Corrosion.
surfaces causing pitting and cracks. This is not a major
corrosion factor, however, since scheduled cleaning of
This is a form of stress corrosion. It is caused by
the affected vehicle will nullify the effects of the
friction of the metal against other surfaces during
transportation and handling, especially if the metal
product is not well secured, thereby causing shifting
b. Acid rain is also caused by marshy areas such as
during movement. The resultant friction may wear away
swamps or bogs which naturally produce dimethyl
at the metal's protective film. In the presence of
sulfide and hydrogen sulfide through the decaying of
moisture, it will also accelerate the corrosion process.
matter. Again, the solution is to keep vehicles as clean
The result will be pitting or stress corrosion induced
as possible at all times.
2-18. Corrosion Caused by Oils, Chemicals,
Although mildew is not strictly corrosion, it does
Corrosion can occur when metal comes in contact
contribute to corrosion in metals and is very destructive
with various substances. This contact may occur during
to other Army products. Mildew is a gradual deteriora-
the repair, testing, or shipment of a vehicle. Tables 2-2
tion of organic material such as canvas or tarpaulin
and 2-3 list corrosive solvents and their effect on
caused by the growth of fungus on or in the material.
This growth occurs if the canvas or tarpaulin is left
Table 2-2. The Corrosive Effects of Fuel Oil, Coolants, and Other Fluids.