Page 484 - Corrosion Engineering Principles and Practice

450 C h a p t e r 1 1 M a t e r i a l s S e l e c t i o n , Te s t i n g , a n d D e s i g n C o n s i d e r a t i o n s 451

11.4.5 Select Corrosion Prevention and Control Methods
Perhaps even more daunting than selecting the actual materials for a
particular corrosion conscious design is choosing the corrosion
prevention and control technologies that may be needed to protect
the system or its components. Some materials require a minimum of
corrosion control since they possess surface characteristics that make
them resistant to corrosion. Stainless steels are a good example of
such corrosion performance. However, most metals (and some other
materials) need some form of additional protection from the
corrosivity of their operating environment.
Several strategies can be employed to protect a metallic material
from corrosion if and when necessary. One such strategy is to construct
a barrier to prevent the corrosive environment from contacting the
surface. Effective barriers (see Chap. 14) include coatings, surface
treatments, and the use of corrosion preventive compounds (CPCs).
Another strategy is to modify the environment itself. Now obviously
this won’t work when a structure is exposed to the elements
themselves, but corrosion can also happen inside a structure or
system, especially if it is totally enclosed. A good example is a heating
plant where steam is circulated from a boiler to heat exchangers. The
operational environment within this type of enclosed system contains
water, which certainly will be laden with minerals and other
contaminants that can initiate corrosion reactions. In such situations
a chemical substance known as a corrosion inhibitor can be mixed
with the fluid to reduce the corrosivity of the environment (Chap. 8).
Another approach for reducing corrosion is to employ mecha-
nisms that can modify the electrochemical processes that consume
materials. Cathodic protection, either through the use of sacrificial
anodes or an impressed current system, can convert a material that
normally will corrode quite readily into a material that resists corro-
sion. This approach, which is the topic of Chap. 13, works very well
for protecting fixed assets in contact with potentially corrosive envi-
ronments such as soils, seawater, or any other electrolytically con-
ducting medium.

11.5 Design Considerations
Engineered structures should be designed to provide the desired
functional qualities for the required period of service. This implies
that a structure should neither be underdesigned (too risky) nor
overdesigned (too costly). Thoughtful design requires more than the
provision of adequate strength. The part must also last for a given
period of time. However, no single text or academic course can give
an engineer or technologist the answers to all corrosion problems. A
checklist of some potential problems facing them when designing a
new installation is provided in Table 11.3.