Page 182 - Corrosion Engineering Principles and Practice

156 C h a p t e r 6 R e c o g n i z i n g t h e F o r m s o f C o r r o s i o n 157

FIGURE 6.10 Corrosion products forming nodules or tubercles over pit
cavities. (Courtesy of Drinking Water Services, City of Ottawa)
• Water chemistry factors that can cause breakdown of a passive
film such as acidity, low dissolved oxygen concentrations
which tend to render a protective oxide film less stable and
high chloride concentrations
• Localized damage to or poor application of a protective coating
• The presence of nonuniformities in the metal structure of the
component, for example, nonmetallic inclusions.

Shallow, wide
Narrow, deep

Elliptical

Subsurface Undercutting

Vertical grain attack
Horizontal grain attack
FIGURE 6.11 Typical cross-sectional shapes of corrosion pits.