Page 23 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

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INTRODUCTION AND FORMS
OF CORROSION

Corrosion is basically a combination of technical and economic problems. To under-
stand the economics of corrosion, it is necessary that one is proficient in both the
science of corrosion and the fundamental principles of economics. There are many
forms of corrosion, which can be deleterious in a variety of ways. It is logical to
discuss the various forms of corrosion of metallic structures occurring in different
corrosive environments.

1.1 GENERAL OR UNIFORM OR QUASI-UNIFORM CORROSION

General corrosion is the most common form of corrosion. This can be uniform (even),
quasi-uniform, or uneven. General corrosion accounts for the greatest loss of metal or
material. Electrochemical general corrosion in aqueous media can include galvanic or
bimetallic corrosion, atmospheric corrosion, stray current dissolution, and biological
corrosion (Table 1.1).
Dissolution of steel or zinc in sulfuric or hydrochloric acid is a typical example
of uniform electrochemical attack. Uniform corrosion often results from exposure
to polluted industrial environments, exposure to fresh, brackish, and salt waters, or
exposure to soils and chemicals. Some examples of uniform or general corrosion
are the rusting of steel, the green patina on copper, tarnishing silver, and white rust
on zinc on atmospheric exposure. Tarnishing of silver in air, oxidation of aluminum
in air, attack of lead in sulfate-containing environments results in the formation of
thin protective films and the metal surface remains smooth. Oxidation, sulfidation,

Challenges in Corrosion: Costs, Causes, Consequences, and Control, First Edition. V. S. Sastri.
© 2015 John Wiley & Sons, Inc. Published 2015 by John Wiley & Sons, Inc.
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