Page 173 - Corrosion Engineering Principles and Practice

148 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 149

Group I: Identifiable by visual inspection

More Less
Noble Noble
Uniform corrosion Pitting Crevice corrosion Galvanic corrosion

Group II: Identifiable with special inspection tools
Load
Flow Movement

Erosion Cavitation Fretting Intergranular
Layer Plug

Exfoliation De-alloying
Group III: Identifiable by microscopic examination
Cracking High temperature attack
Scale

Stress corrosion Corrosion fatigue Scaling Internal attack
cracking

FIGURE 6.1 Main forms of corrosion attack regrouped by ease of identification.

his coauthors have grouped the eight forms of corrosion depicted
graphically in Fig. 6.1 in the following three categories [2]:

Group I: Corrosion problems readily identifiable by visual
examination.

1. Uniform corrosion is characterized by an even, regular loss of
metal from the corroding surface.
2. Localized corrosion during which all or most of the metal loss
occurs at discrete areas. In this scheme crevice corrosion is
said to be a particular form of pitting usually due to localized
differences in the environment (pitting, crevice).
3. Galvanic corrosion occasioned by electrical contact between
dissimilar conductors in an electrolyte.
Group II: Corrosion damage that may require supplementary
means of examination for identification.