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THE
EFFECT OF ENVIRONMENT ON CORROSION
ABSTRACT
In this research
project, the various nail were subjected to six environments so as to check the
effect of the environments on corrosion of the nails.
Two sets of nails was
used; normal nail and concrete nail. Six of each type while the other not
coated.
The research was
carried out in the physical chemical laboratory of the institute of management
and technology.
The environments used
are acidic solution, alkaline solution, salt solution, boiled water, air medium
and lubricating oil medium, which served as a control medium.
It was observed from
the graphs of the weight of metal against time, that acidic environment gave
rise to corrosion at a faster rate that other environment. It was also
observed that normal nails gave rise to corrosion at a faster rate than
concrete nail.
Coating of metals was
also concluded to be a method of preventing the rate of corrosion of metals
even though it does not stop corrosion.
CHAPETR
ONE
INTRODUCTION
In its broadest sense
the term corrosion applied to the destructive alteration of a metal or alloy by
chemical reaction with any substance, solid, liquid, or gas. The pattern of
attack will be governed largely by the combined influence of several factors
relating to the metal or alloy, to the conditions of service, and to the
chemical nature of the environment.
1.
The metal may corrode uniformly over
its entire surface, as in the resting of iron in the atmosphere.
2.
It may suffer only a superficial attack
that does not seriously affect the strength of the metal or alloy but does
discolour the surface, as in the tarnishing of silver in the atmosphere.
3.
Corrosion may develop at local areas on
an otherwise unattached surface, leading to pitting that may in some instances
result in early failure by perforation.
4.
An alloy may be attacked in such
a way as to remove one or more of its constituents, leaving a weakened residue
of unattached element with poor metallic properties, as in the dezincification
of yellow brass or in the graphitization of cast iron.
5.
Excessive corrosion may occur in local
area where poor design features tend to aggravate the corrosion conditions, as
crevices under rivets, bolts and faying surface.
6.
Use of dissimilar metals sometimes can
lead to severe attack of the more active metal where they are joined together.
7.
High tensile stresses plus specific
corrosive conditions may result in cracking of a metal because of a corrosion
reaction along critical paths in the metal.
In order to provide a
quantitative basis for reporting corrosion rates and intensity of attack, the
average weight loss of metal per unit area per unit time or the loss in
thickness per unit time is usually recorded. Loss in thinckness per unit
time is more useful in those instances where the engineer is concerned with
life of equipment or structure. Average loss is reported in mils per year (MPY)
or inches penetration per year (ipy). Where product contamination is
vital, the average corrosion rate is expressed in milligrams of metal corroded
per square decimeter per day (mdd).
Corrosion process
usually occurs because the metal has a tendency to return to its native state,
the form in which it is found in nature. This require that the metal
atoms relinquish their valence electrons to the environment and because ions in
the process. The newly formed ions may then combine with other ions to
from compounds. This, when iron corrodes in water, the iron atoms are
converted to ferrous ion upon the loss of two electrons.
Fe
Fe2++2e-
The ferrous can then
combine with hydroxyl ions to from insoluble ferrous hydroxide.
Fe
Fe2++20H
Fe(0H)
This compound
eventually becomes oxidized through content with oxygen the familiar red iron
rust, ferric hydroxide. In the electrons from the iron are accepted by
oxygen gas molecules and iron oxides are formed.
1.1
OBJECTIVED OF THE STUDY
The objective of this
study in based on the fault that corrosion which has been a major problem in
our modern industries has to be prevented and curbed to the barest minimum by
putting it environment into consideration in selecting material a structure or
piece equipment.
1.2
SCOPE OF THE STUDY
The main metallic
material that is being used in this work is nail (iron). This material
will be subjected to different medium (environment) viz air medium salt
solution medium, distilled water medium acid solution medium, alkaline solution
medium and a lubricating oil medium. The observable change brought about
by the environment reaction to the material under survey was studied.
Iron of varied coatings will also be used.
1.3 SIGNIFICANCE OF THE RESEARCH
A complete
understanding of corrosion phenomena in all fact requires intensive and
prolonged study. However, a general knowledge of the subject can be
gained by the engineer through a review or survey of the various ways in which
corrosion manifest itself, the factors that govern corrosion process, and the
means available to the engineer for controlling or preventing corrosion.
This work will
provide a survey that will serve to guide the material engineer his
consideration of corrosion behaviour of metals and alloys virus, it will enable
those in the oil and gas sector to install pipelines in an environment that
will be favourable.
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