Page 26 - Corrosion Engineering Principles and Practice

10 C h a p t e r 1 T h e S t u d y o f C o r r o s i o n 11

In order to choose the proper material and overcome a corrosion
problem the corrosion engineer is expected to know what materials
are available and what are their corrosion resistant advantages and
limitations. The environmental degradation of materials is often a
critical and limiting factor in the development of virtually every
advanced technology area, such as power generation, energy
conversion, waste treatment, and communications and transportation.
As new materials enter the marketplace and new engineering systems
evolve to take advantage of their properties, it is of paramount
importance for the corrosion engineer to understand the chemical
limits of these materials and to develop corrosion control approaches
that can be integrated into the design and operation of the systems.
The evolution of traditional and advanced engineering systems
requires engineering materials capable of performing under
increasingly hostile service environments. Unless these materials are
chemically stable in such environments, their otherwise useful
properties (strength, toughness, electrical and thermal conductivity,
magnetic and optical characteristics, etc.) may be compromised. In our
modern, high-technology society, this applies to all materials, including
metals, ceramics, polymers, semiconductors, and glasses. It is therefore
necessary to know a good deal about the corrosive characteristics of
the chemical or chemicals involved and how these are affected by such
factors as concentration, temperature, velocity, aeration, or the presence
of oxidizing or reducing substances or special contaminants.
Regardless of how attractive a material may be from any other
point of view, it is of no use for a particular purpose if it cannot be
secured in the required form. Filter cloth cannot be woven from an
alloy available only as castings. Several materials may possess the
corrosion resistant and mechanical properties required for a job, but
many of them may be too expensive to be considered. For example,
silver might be somewhat better than nickel for tubes in an evaporator
to concentrate caustic soda to 50 percent, but it would not be enough
to justify the extra cost involved, and steel might be a better choice
economically overall for handling dilute caustic under less stringent
conditions [4].
For simple economical reasons, it is much more efficient to prevent
corrosion than to explain why it occurred, suggest what should have
been done to avoid it, or even prescribe how the damage might be
repaired. However, corrosion engineers are often forced to work in
these less than optimal scenarios.
Civil engineers are more concerned with designing and building
bridges that do not collapse than with rebuilding them after failure. If
given the opportunity at the proper time, a good corrosion engineer
should be able to guide, design, specify materials, and know how
they should be fabricated so that costly corrosion failures might
become as rare as catastrophic failures in structural engineering.
In addition, periodic inspection of existing equipment should be
undertaken so that any corrosion may be detected in time to initiate