Page 267 - Corrosion Engineering Principles and Practice

240 C h a p t e r 7 C o r r o s i o n F a i l u r e s , F a c t o r s , a n d C e l l s 241

that of the metal that is corroded. Such stresses can cause cracks to
initiate and grow. Stresses from expanding corrosion products can
readily cause adjacent metals to flow plastically, as occurs in nuclear
steam generators in a process called denting. Denting results from the
corrosion of the carbon steel support plates and the buildup of
corrosion product in the crevices between tubes and the tube support
plates. This process is called denting since, when seen from the inside
of the tubes, these deformations seem to produce dents at the
tubesheet locations.
Pack rust* is another example of the tremendous forces created by
expanding steel corrosion products where forces as high as 70 MPa
have been reported [18]. Figure 7.32 illustrates the effect of pack rust
that has developed on steel bridge under repair. The force of expansion
in this particular example was sufficient to break three of the bridge
rivets shown in Fig. 7.32. Such corrosion damage may be a serious
derating factor when the load-bearing capacity of a bridge or of any
other infrastructure component is evaluated during inspection.

FIGURE 7.32
The effect of
pack rust that has
developed on an
important steel
bridge under
repair. (Courtesy
Wayne Senick,
Termarust
Technologies www
.termarust.com).

* The expression “pack rust” is often used in the context of bridge inspection to
describe built-up members of steel bridges that are showing signs of rust packing
between steel plates.