Page 232 - Corrosion Engineering Principles and Practice

CHAPTER 7

Corrosion Failures,

Factors, and Cells

7.1 Introduction
As described in the Chapter 6, corrosion damage may take various
forms triggered themselves by apparently different compounding
factors. The initiation and progression of corrosion processes indeed
depend on the complex interaction of a multitude of factors such as

• Nature of the metal or alloy
• Presence of inclusions or other foreign matter at the surface
• Homogeneity of the metallic structure
• Nature of the corrosive environment
• Incidental environmental factors such as variations in
the presence of dissolved oxygen, of temperature, and in the
velocity of movement either of the environment or of the
system itself
• Other factors such as stress (residual or applied, steady
or cyclic)
• Oxide scales (continuous or broken)
• Presence of deposits on surfaces
• Fayed surfaces and the possibility of corrosion crevices
• Galvanic effects between dissimilar metals
• Occasional presence of stray electrical currents from external
sources

The nature of the driving forces behind these factors has been the
subject of scientific studies by many scientists in the early part of the
twentieth century. In a landmark paper, Mears and Brown have
summarized 18 mechanisms, listed in Table 7.1, by which differences
in potential may develop on metal surfaces [1].

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