Page 193 - Corrosion Engineering Principles and Practice

168 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 169

• Crevice corrosion of iron in various electrolyte solutions
• Crevice corrosion of iron in sulfuric acid

Comparison of modeled and experimental data for these systems
gave agreement ranging from approximate to very good.
Real-World Crevices
There are many examples of crevice chemistries at work in all sorts of
designs and applications. The following section describes a few of
these. Other examples can be found throughout the text and
particularly in Chap. 7, where pack rust of steel components and
pillowing of aluminum fayed structures are described.
Crevice and Poultice Corrosion in Cars. The average life of a car was
about 10 to 12 years in 1990, with a rather large scatter between
manufacturers. Generally speaking, the areas which corrode within a
car are those relatively small areas which are badly designed with
regards to corrosion (Fig. 6.23). These areas could be considerable
improved by better design, and greater attention to detail, and
therefore would represent a minimal cost to the first and subsequent
owners. Some examples of these areas are [12]

• Interweld gaps and narrow capillaries which are, by design,
hardly accessible to electrocoat paint;
• Any protruding member at right angle to the direction of
motion will generate spray
• Ledges and vertical panels which are out of the direct wheel
trajectory can suffer from aggravated poultice corrosion
• Raw edged on the formed steel sheets can only be covered by
a thin layer of protective coating

Poultice corrosion is a special form of crevice corrosion which
forms when absorptive debris such as paper, wood, asbestos, sacking,
cloth, and so forth., are in contact with a metal surface that becomes
wetted periodically. No action occurs while the entire assembly is

x

x x x x
x x x x x x x
x x x
x x x
x x x x
x x x x x x

FIGURE 6.23 Diagrammatic view of corrosion prone areas in cars
(adapted from [12]).