MIL-HDBK-1138
e
e
e
e
e
e
H2
e
m+
e
m+
Anode
Cathode
ELECTROLYTE
Figure 7
Electrochemical Corrosion Cell
If one or more of the four elements is eliminated, then
corrosion cannot occur. As discussed below, this fact plays an
important role in controlling corrosion. For example, if a
pipeline is buried in the soil, many areas of anodes and cathodes
will be present on the surface of the pipeline. These areas are
developed during the process of producing the pipe and cannot be
eliminated. The connection between the anodes and cathodes
cannot be broken, since the pipe wall serves this purpose.
However, if the outside of the pipe is coated with a protective
coating or wrapped with pipeline tape, the pipe surface will be
isolated or separated from contact with the soil (electrolyte).
Isolating the pipe from the electrolyte eliminates one of the
elements necessary for corrosion. Therefore corrosion cannot
occur, even though the anodes, cathodes and connections still
exist on the pipe. Methods of handling coating defects are
discussed below.
Eight Forms of Corrosion. It is possible to
8.1.2
classify several forms of corrosion, based on the general
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