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WHAT IS
CORROSION ?
Corrosion is the deterioration of materials by
chemical interaction with their environment. The
term corrosion is sometimes also applied to the
degradation of plastics, concrete and wood, but
generally refers to metals. The most widely used
metal is iron (usually as steel) and the following
discussion is mainly related to its corrosion.
THE
CONSEQUENCES OF CORROSION
The consequences of corrosion are many and varied
and the effects of these on the safe, reliable and
efficient operation of equipment or structures are
often more serious than the simple loss of a mass of
metal. Failures of various kinds and the need for
expensive replacements may occur even though the
amount of metal destroyed is quite small. Some of
the major harmful effects of corrosion can be
summarized as follows:
1. Reduction of metal thickness leading to loss of
mechanical strength and
structural failure or breakdown. When the metal is lost in
localized zones
so as to give a crack like structure, very considerable
weakening may
result from quite a small amount of metal loss.
2. Hazards or injuries to people arising from
structural failure or breakdown
(e.g. bridges, cars, aircraft).
3. Loss of time in availability of profile-making
industrial equipment.
4. Reduced value of goods due to deterioration of
appearance.
5. Contamination of fluids in vessels and pipes
(e.g. beer goes cloudy when
small quantities of heavy metals are released by corrosion).
6. Perforation of vessels and pipes allowing escape
of their contents and
possible harm to the surroundings. For example a leaky
domestic radiator
can cause expensive damage to carpets and decorations, while
corrosive
sea water may enter the boilers of a power station if the
condenser tubes
perforate.
7. Loss of technically important surface properties
of a metallic component.
These could include frictional and bearing properties, ease
of fluid flow
over a pipe surface, electrical conductivity of contacts,
surface reflectivity
or heat transfer across a surface.
8.
Mechanical damage to valves, pumps, etc, or blockage
of pipes by solid
corrosion products.
9. Added complexity and expense of equipment which
needs to be designed
to withstand a certain amount of corrosion, and to allow
corroded
components to be conveniently replaced.
NACE International : A recently
released two-year breakthrough study estimates the annual direct cost of
corrosion in the United States to be $276 billions.
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