by one or more of the following causes:
a) Electrochemical (galvanic) -- Two dissimilar metals or portions
of a metallic substance immersed in an electrolyte or ionized medium (such as
water, soil, or chemical solution) will cause an electric current with a
stream of electrons flowing from a relatively positively-charged metal (anode)
to the relatively negatively-charged metal (cathode). As a result, metal ions
will go into solution. Refer to MIL HDBK 1004/10, Cathodic Protection, for
b) Differential Environments -- Metals will corrode when immersed
in substances having different concentrations or ions (such as different
c) Stray Currents -- Small electric currents may stray from
sources of direct current and cause corrosion of metals in their paths.
d) Chemical Attack -- The basic action is electrochemical, but the
attack on metals is uniform rather than localized.
of metals as a result of metabolic activities of micro-organisms.
f) Atmospheric -- Corrosion of metals exposed to high humidity
(over 70 percent) and high concentrations of sulfur dioxide, carbon dioxide,
and salt in air.
g) Stress, Distortion, and Fatigue -- Such attributes or
conditions do not start corrosion but will accelerate it. Highly strained
areas tend to become anodic to remainder of system. Proper design and
selection of suitable materials is the solution.
Use one of the following methods for corrosion
Inorganic Materials. In corrosive environments and transporting
corrosive solutions consider non-metal conduits or:
Reinforced concrete pipe.
Polyvinyl chloride pipe.