The document discusses corrosion from multiple perspectives. It defines corrosion as the deterioration of metals through chemical or electrochemical reactions with the environment. It notes that understanding chemistry, electrochemistry, and metallurgy is important for understanding corrosion. Corrosion can damage infrastructure and equipment by reducing strength, changing dimensions, and contaminating products. The costs of corrosion are high, with estimates of billions of dollars spent annually to address corrosion in areas like pipelines, structures, and water systems. Proper application of corrosion prevention and control techniques can help reduce these costs.

1.  Corrosion may be defined in a number of
ways:
 Deterioration of metals and alloys by
chemical or electrochemical reactions with its
environment
 Eating away of construction materials
 Deterioration of construction materials by
means other than straight mechanical
 Undesirable interaction of material with its
environment

2.  Physico-chemical interaction between a
metal and its environment which results in
changes in the properties of the metal and
which may often lead to impairment of the
function of the metal, the environment, or
the technical system of which these form a
part. (according to ISO)

3.  Since corrosion involves chemical change, the
student must be familiar with principles of
chemistry in order to understand corrosion
reactions. Because corrosion processes are
mostly electrochemical, an understanding of
electrochemistry is also important.
Furthermore, since structure and composition
of a metal often determine corrosion
behavior, the student should be familiar with
the fundamentals of physical metallurgy as
well.

4.  The corrosion scientist studies corrosion
mechanisms to improve
(a) the understanding of the causes of
corrosion and (b) the ways to prevent or at
least minimize damage caused by
corrosion.
 The corrosion engineer , on the other
hand,applies scientific knowledge to control
corrosion. For example, the corrosion
engineer uses cathodic protection on a
large scale to prevent corrosion of buried
pipelines, tests and develops new and
better paints, prescribes proper dosage of
corrosion inhibitors, or recommends the
correct coating g.

5.  Change in any part of the corrosion system
caused by corrosion.
 Corrosion Damage
 Corrosion effect which is considered
detrimental to the function of the metal, the
environment or the technical system of which
these form a part.

6.  Corrosion has been classified in many
different ways. One method divides corrosion
into low-temperature and high temperature
corrosion. Another method separates
corrosion into direct combination (or
oxidation) and electrochemical corrosion.
NACE International (National Association of
Corrosion Engineers) has identified as many
as eighty forms of corrosion, which can be
grouped into eight forms as proposed by
Fontana.

7.  The preferred classification is
 Wet corrosion or aqueous corrosion, and
 Dry corrosion i.e. oxidation in the absence of
water e.g. reaction between metal and any
oxidizing gas such as carbon dioxide,
oxygen, oxides of sulphur etc. at elevated
temperatures

8.  Wet corrosion occurs when a liquid is present.
This usually involves aqueous solutions or
electrolytes and accounts for the greatest amount
of corrosion by far. A common example is
corrosion of steel by water and oxygen (air).
 Dry corrosion occurs in the absence of liquid
phase or above the dew point of the
environment. Vapours and gases are usually the
corrodents. Dry corrosion is often associated
with high temperatures. An example is attack of
steel by furnace gases

9.  Most corrosion processes are electrochemical
in nature. Corrosion principles are discussed
for understanding the science of corrosion.
Corrosion engineering is the application of
science and art to control corrosion damage
economically and efficiently. In addition to
the knowledge of corrosion science, the
corrosion engineer must have sufficient
knowledge of chemical, metallurgical,
physical and mechanical properties of
materials.

10.  The National Bureau of Standards (NBS) has estimated
that cost of corrosion in the United States of America
in 1975 was $70 billion plus or minus 30% with about
10-45% of the total ($70 billion) as avoidable. The
NBS, result follows the extrapolation from earlier
percentage values since 1947 and works out to about
4% of US GNP in 1975. The %age seems to be some
kind of constant for all economies. The Battele
Columbus Laboratories (BCL) have determined the
total cost of corrosion to the United States $70 billion
or about 4% of the GNP in 1978 and $10 billion of
this cost could be avoided by the use of presently
available corrosion control technology (See Fig 1.4).

12.  Direct economic losses constitute the costs of
replacements of corroded structures and machinery
or their components e.g. condenser tubes, mufflers,
pipelines, metal roofing, repainting of structures
against rusting, cathodic protection and its upkeep
for underground pipe systems. Direct losses also
include the extra cost of using (i) corrosion resistant
materials in place of carbon steel or other cheaper
materials with adequate mechanical properties but
not sufficient corrosion resistance, (ii) adding
inhibitors to enclosed systems, (iii) protective
systems for metal structures etc

13.  The indirect economic losses constitute the
financial losses described under various
heads as follow:
a. Loss of Product
 Considerable losses of oil, gas or water may
occur through a corroded pipe system until
repairs are made. Similarly leaks in industry
for different solvents and other liquids result
in loss of significant value.

14. b. Loss of Production
 For the repair or replacement of a corroded piece
of equipment with a relatively small value, the
whole plant may be shutdown for a day or more.
Under these circumstances shutdown time must
be kept to minimum. Thus the higher cost of
corrosion resistant metals/alloys is justified in
return for longer productive cycle and
maintenance-free periods.

15.  The deposition of corrosion products can
decrease the efficiency of operating a plant.
Examples include the loss of pumping
capacity due to partial clogging of the interior
of water pipes due to accumulation of
corrosion product, reduction in heat transfer
through corrosion deposits in heat
exchangers, loss of critical dimensions in
internal combustion engines through
corrosion.

16.  Fine chemicals, dye-stuffs, food processing
and drug industries cannot tolerate the pick
up of even small traces of metal ions in their
product due to corrosion. Thus to avoid this
contamination, these plants have to
incorporate lined pipeline, reaction vessels,
storage tanks and in some cases the whole
plants are constructed of suitable grade of
stainless steel, thereby raising the capital
cost.

17.  The less corrosion conscious organizations
may suffer heavy commercial losses due to
this type of contamination. Contamination by
the corrosion products in fuel storage tanks
of aircrafts and automobiles may cause
serious quality problems.

18.  The principle of overdesign is applied to allow for
ravages of corrosion and consequently much
thicker sections are used than would normally be
required for mechanical strength. In case of
water treatment and oil industries, corrosion
allowances ranging between 50 to 100% are
made in corrosion susceptible areas of plant,
which means higher capital costs for extra
consumption of materials and are against the
concept of conservation of resources.

19.  Therefore, in terms of overall economic
balance, the concept of overdesign is less
preferable than alternate use of protective
measures for the prevention of corrosion
unless the latter are exceedingly expensive
and economically prohibitive.

20.  To avoid unnecessary delays in scheduled or
unscheduled shutdowns in large factories,
replacement sections of plants and standby
units have to be maintained in readiness to
take over when corrosion failures occur.
Similarly heavy inventories of replacement
items have to be maintained in case of
urgency during normal shutdowns. This also
leads to a considerable increase in capital
investments.

21.  It is quite obvious that indirect losses form a
substantial part of the economic loss suffered
through corrosion, but it is quite difficult to
arrive at a reasonable estimate of total economic
burden within one industry. There are instances
where loss of health or life through fire or
explosion, unpredictable failure of chemical
equipment, resulting in release of toxic vapors,
rupture of vessels containing corrosive liquids
through sudden failure of critical parts, have
occurred.

22.  The cost of human life and material losses
alone including invisibles and overheads may
amount to a staggering figure in large
chemical concerns over the productive life of
the plant.

23. Corrosion
Cost
Applied
Current
Technology
More Hostile
Environments
Environmental
Regulations
Research &
Development
Extentions of
Useful Life
Technology
Transfer
Increased
Performance
Requirments
Deferred
Maintenance
Factors which increase or decrease the
costs of corrosion

24.  Corrosion cannot be defined without a
reference to environment. All environments
are corrosive to some degree. Following is the
list of typical corrosive environments:
(1) Air and humidity.
(2) Fresh, distilled, salt and marine water.
(3) Natural, urban, marine and industrial
atmospheres.

25. (4) Steam and gases, like chlorine.
(5) Ammonia.
(6) Hydrogen sulfide.
(7) Sulfur dioxide and oxides of nitrogen.
(8) Fuel gases.
(9) Acids.
(10) Alkalies.
(11) Soils.

26.  Corrosion may severely affect the following
functions of metals, plant and equipment:
(1) Impermeability: Environmental constituents
must not be allowed to enter pipes , process
equipment, food containers, tanks , etc. to
minimize the possibility of corrosion.

27. 2. Mechanical strength:
Corrosion should not affect the capability to
withstand specified loads, and its strength
should not be undermined by corrosion.
3. Dimensional integrity:
Maintaining dimensions is critical to
engineering designs and they should not be
affected by corrosion.

28. 4. Physical properties:
For efficient operation , the physical
properties of plants, equipment and
materials, such as thermal conductivity and
electrical properties, should not be allowed to
be adversely affected by corrosion.
5. Contamination:
Corrosion, if allowed to build up, can
contaminate processing equipment,

29. food products, drugs and pharmaceutical
products and endanger health and
environmental safety.
6. Damage to equipment:
Equipment adjacent to one which has
suffered corrosion failure , may be damaged.

30. 1. Materials are precious resources of a
country. Our material resources of iron,
aluminum, copper, chromium, manganese,
titanium, etc. are dwindling fast. Some day
there will be an acute shortage of these
materials. An impending metal crisis does not
seem anywhere to be a remote possibility but
a
reality. There is bound to be a metal crisis

31. and we are getting the signals. To preserve
these valuable resources, we need to
understand how these resources are
destroyed by corrosion and how they must be
preserved by applying corrosion protection
technology.
2. Engineering knowledge is incomplete
without an understanding of corrosion.

32. Aeroplanes, ships, automobiles and other
transport carriers cannot be designed without
any recourse to the corrosion behavior of
materials used in these structures.
(3) Several engineering disasters, such as
crashing of civil and military aircraft, naval
and
passenger ships, explosion of oil pipelines
and oil storage tanks, collapse of bridges and
decks and failure of drilling platforms and
tanker trucks have been witnessed in recent

33. years. Corrosion has been a very important
factor in these disasters. Applying the
knowledge of corrosion protection can
minimize such disasters. In USA, two million
miles of pipe need to be corrosion-protected
for safety.
(4) The designing of artificial implants for the
human body requires a complete
understanding of the corrosion science and
engineering. Surgical implants must be very
corrosion-resistant because of corrosive
nature of human blood.

34. (5) Corrosion is a threat to the environment. For
instance, water can become contaminated
by corrosion products and unsuitable for
consumption. Corrosion prevention is integral
to stop contamination of air, water and
soil. The American Water Works Association
needs US$ 325 billion in the next twenty years
to upgrade the water distribution system.