CHAPTER ONE
1.0 INTRODUCTION
Corrosion is a serious problem in this modern age of technological advancement. This accounts
for a lot of economic losses and irreversible structural damage. The cost of corrosion failures
annually for any nation is difficult to estimate per annum, but it has been stated that the wastage
of material resources by corrosion ranks third after war and disease (Olugbenga et al.2011).
Efforts have been made to restrain the destructive effects of corrosion using several preventive
measures (Loto et al. 1989, Popoola et al.2011 and Davis et al. 2001). The effects of corrosion in
our daily lives can be direct by affecting the useful service lives of our possessions, and indirect,
in that producers and suppliers of goods and services incur corrosion costs, which they pass on to
consumers. At home, corrosion is readily recognized on automobile body panels, charcoal grills,
outdoor furniture, and metal tools (Denny et al. 1996). The corrosion of steel reinforcing bars in
concrete usually proceeds out of sight and suddenly results in failure of a section of bridges or
buildings.
Virtually all metals will corrode to some extent; the fossil–fuel boilers and fossil-fuel fired power
generators equipment experience corrosion problems in such component as steam generator and
water walls surrounding the furnace (Natarajanf & Sivan, 2003). Perhaps most dangerous of all
is corrosion that occurs in major industrial plants, such as electrical power plants or chemical
However, the consequences of corrosion are economic and could lead to:
? Replacement of corroded equipment.
? Overdesign to allow for corrosion.
? Preventive maintenance, for example, painting.
? Shutdown of equipment due to corrosion failure.
? Contamination of a product.
? Loss of efficiency—such as when overdesign and corrosion products decrease the heattransfer
rate in heat exchangers.
? Loss of valuable product, for example, from a container that has corroded through.
? Inability to use otherwise desirable materials.
? Damage of equipment adjacent to that in which corrosion failure occurs.
Corrosion affects most of the industrial sector and may cost billions of dollars each year for
prevention and replacement maintenance. Thus, the modern world has made investigations to
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overcome this problem by conducting enrichment studies of corrosion inhibitors. Corrosion
inhibitors will reduce the rate of either anodic oxidation or cathodic reduction or both. This will
give us anodic, cathodic or a mixed type of inhibition. In an attempt to find corrosion inhibitors
that are environmentally safe and readily available, there has been a growing trend in the use of
biological substrate such as leaves or plant extracts as corrosion inhibitors for metals in acid
cleaning processes.
As a result of increasing awareness on environmentally friendly practices for sustainable
development, the demand for non-toxic inhibitors to replace toxic ones has increased
tremendously. Thus, in recent years, several plant extracts have been investigated for the
inhibition of acid corrosion of metals. This is because plants contain naturally synthesized
chemical compounds that are biodegradable, environmentally acceptable, inexpensive, readily
available and renewable source of materials.
Corrosion is not only dangerous, but also costly, with annual damages in the billions of dollars!
If this is difficult to believe, consider some of the direct and indirect effects of corrosion which
contribute to these costs:
Not only that the economic costs are frightening, there is also potential loss of life and damage to
the environment problems, which can have widespread effects upon modern industrial
businesses. It is essential, therefore, for operators of industrial process plants to have a program
for controlling corrosion.
1.1 Literature Review
Corrosion may be defined as a destructive phenomenon, chemical or electrochemical, which can
attack any metal or alloy through reaction by the surrounding environment and in extreme cases
may cause structural failure. The corrosion occurs because of the natural tendency for most
metals to return to their natural state (reverse of metallurgy); e.g., iron in the presence of moist
air will revert to its natural state, iron oxide.
Corrosion could be basically carried by water intrusion and some environmental factors.
Water intrusion is the principal cause of corrosion problems encountered in the field use of
equipment. Water can enter an enclosure by free entry, capillary action, or condensation. With
these three modes of water entry acting and with the subsequent confinement of water, it is
almost certain that any enclosure will be susceptible to water intrusion. At normal atmospheric
temperatures the moisture in the air is enough to start corrosive action. Oxygen is essential for
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corrosion to occur in water at ambient temperatures. Other factors that affect the tendency of a
metal to corrode are acidity or alkalinity of the conductive medium (pH factor), stability of the
corrosion products, biological organisms (particularly anaerobic bacteria), Variation in
composition of the corrosive medium and temperature.
1.2 Mechanism of Corrosion
In nature, metals are not found in Free State due to their reactivity. Metals are generally in high
energy state because some energy is added during their manufacturing process from the ores.
Low energy - state ores are more stable than the high energy – state metals. As a result of this
uphill thermodynamic struggle, the metals have a strong driving force to release energy and go
back to their original form. Hence the metals revert to their parent state or ore under a suitable
corrosive environment. The electrochemical process involved in corrosion by nature is opposite
to the extractive metallurgy involved in manufacturing of the metals. Therefore, corrosion is
sometimes considered as the reverse process of extractive metallurgy as can be seen below: