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Corrosion of metals and polymers: A vital concern

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Corrosion costs nearly $4 Trillion worldwide each year. April 24, 2012 has been dedicated to raising awareness about what can be done to prevent the impact of corrosion on people, infrastructure, and the environment. Though Codes and standards on corrosion exist on the basis of physical parameters, there is little focus on performance criteria. .The US is losing more than $276 billion and India Rs 1 Lakh crore per annum on account of corrosion. The annual loss due to corrosion can be compared with that of other natural calamities like fire, floods, hurricanes, tornadoes, earthquakes and cyclones; only its impact is indirect. Corrosion destroys the objects made up of metals and their alloys but the modern world can not afford without the use of these materials. Around 80 per cent of the unscheduled shutdowns and breakdowns in industries are due to corrosion. Corrosion causes plant shut downs, waste of valuable resources, loss or contamination of products, reduction in efficiency and costly maintenance. Corrosion solutions are highly customized as standards must be created on the basis of prevailing local conditions as India is a tropical country and environment and climatic conditions differ from region to region. If this corrosion cannot be eliminated completely, industries can ensure the prevention at the design stage. Improved technology and awareness can only come through consistent research and development activities. While this has become a reality in some industries such as nuclear power, refineries, space, railways, shipping and defense, most medium and small-scale industries do not take up corrosion issues seriously or are simply not aware of them. Additionally, corrosion may lead to loss of metals and their strength which in turn can cause serious accidents, loss of manpower and human lives. Out of the total loss due to corrosion, 25 per cent of loss can be easily saved with pro-active approach and protecting the system by applying protective coatings. Creating awareness and propagating knowledge about corrosion is therefore very important. Corrosion needs to be addressed by all industries. The protection of assets and environment from effects of corrosion is a must.
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Paper from Proceeding of the National Conference “Science in Media 2012” Organized by YMCA University
of Science and Technology, Faridabad, Haryana (India) December 3 rd -4th 2012 Published by
IJMRS's International Journa l of Engineering Sciences, ISSN (Online): 2277 -9698
www.ijmrs.com
IJMRS
www.ijmrs.com
4
Corrosion of metals and polymers: A vital
concern
Aditi Sharma,UICET, Panjab University, Chandigarh, India
Anuradha Sharma,YMCA University of Science and Technology, Faridabad, India
Mamta Sharma, PEC University of Technology, Chandigarh, India
Abstract— Corrosion costs nearly $4 Trillion worldwide
each year. April 24, 2012 has been dedicated to raising
awareness about what can be done to prevent the
impact of corrosion on people, infrastructure, and the
environment. Though Codes and standards on
corrosion exist on the basis of physical parameters,
there is little focus on performance criteria. .The US is
losing more than $276 billion and India Rs 1 Lakh crore
per annum on account of corrosion. The annual loss due
to corrosion can be compared with that of other natural
calamities like fire, floods, hurricanes, tornadoes,
earthquakes and cyclones; only its impact is indirect.
Corrosion destroys the objects made up of metals and
their alloys but the modern world can not afford
without the use of these materials. Around 80 per cent
of the unscheduled shutdowns and breakdowns in
industries are due to corrosion. Corrosion causes plant
shut downs, waste of valuable resources, loss or
contamination of products, reduction in efficiency and
costly maintenance. Corrosion solutions are highly
customized as standards must be created on the basis of
prevailing local conditions as India is a tropical country
and environment and climatic conditions differ from
region to region. If this corrosion cannot be eliminated
completely, industries can ensure the prevention at the
design stage. Improved technology and awareness can
only come through consistent research and development
activities. While this has become a reality in some
industries such as nuclear power, refineries, space,
railways, shipping and defense, most medium and
small-scale industries do not take up corrosion issues
seriously or are simply not aware of them. Additionally,
corrosion may lead to loss of metals and their strength
which in turn can cause serious accidents, loss of
manpower and human lives. Out of the total loss due to
corrosion, 25 per cent of loss can be easily saved with
pro-active approach and protecting the system by
applying protective coatings. Creating awareness and
propagating knowledge about corrosion is therefore
very important. Corrosion needs to be addressed by all
industries. The protection of assets and environment
from effects of corrosion is a must.
I. INTRODUCTION
Corrosion costs nearly $4 Trillion worldwide each
year. April 24, 2012 has been dedicated to raising
awareness about what can be done to prevent the
impact of corrosion on people, infrastructure, and the
environment. Though Codes and standards on
corrosion exist on the basis of physical parameters,
there is little focus on performance criteria. .The US
is losing more than $276 billion and India Rs 1 Lakh
crore per annum on account of corrosion. The annual
loss due to corrosion can be compared with that of
other natural calamities like fire, floods, hurricanes,
tornadoes, earthquakes and cyclones; only its impact
is indirect. In any case, corrosion represents a
tremendous economic loss and much can be done to
reduce it.(Fig 1,2) [1,5].
Fig-1: Rusting in a drainage water pipeline
2. DEFINITION
Corrosion is defined as the destruction or
deterioration of a material because of reaction with
its environment. These materials include metals like
iron, copper etc and non metals like ceramics,
plastics, rubber etc. Corrosion can be fast or slow.
Where on one hand, sensitized steel is badly attacked
in hours by polythionic acid while on the other hand
Railroad tracks usually show slight rusting over many
years. The Famous Iron pillar in Delhi was made
Paper from Proceeding of the National Conference “Science in Media 2012” Organized by YMCA University
of Science and Technology, Faridabad, Haryana (India) December 3 rd -4th 2012 Published by
IJMRS's International Journa l of Engineering Sciences, ISSN (Online): 2277 -9698
www.ijmrs.com
IJMRS
www.ijmrs.com
5
almost 2000 years ago and is almost as good as new.
(Fig 3a, 3b)
Fig-2 Corrosion of Railings
Fig-3 (a), (b) Iron pillar in Delhi
Corrosion destroys the objects made up of metals and
their alloys but the modern world can not afford
without the use of these materials.Around 80 per cent
of the unscheduled shutdowns and breakdowns in
industries are due to corrosion. Corrosion causes
plant shut downs, waste of valuable resources, loss or
contamination of products, reduction in efficiency
and costly maintenance.
3.ELECTROCHEMISTRY OF CORROSION
The same metallic surface exposed to
an aqueous electrolyte usually possesses sites for
an oxidation (or anodic chemical reaction) that
produces electrons in the metal, and
a reduction (or cathodic reaction) that consumes
the electrons produced by the anodic reaction.
These "sites" together make up a "corrosion cell".
The anodic reaction is the dissolution of the
metal to form either soluble ionic products or an
insoluble compound of the metal, usually an
oxide. Several cathodic reactions are possible
depending on what reducible species are present
in the solution. Typical reactions are
the reduction of dissolved oxygen gas, or the
reduction of the solvent (water) to produce
hydrogen gas. Because these anodic and cathodic
reactions occur simultaneously on a metal
surface, they create an electrochemical cell [2,4].
The sites where the anodic and cathodic
reactions take place, the anodes and the cathodes
of the corrosion cell, are determined by many
factors: (i) they are not necessarily fixed in
location; (ii) they can be adjacent or widely
separated so that, for example, if two metals are
in contact, one metal can be the anode and the
other the cathode, leading to galvanic
corrosion of the more anodic metal; (iii) there
can exist variations those sites exposed to the
environment containing the lower oxygen
content – differential aeration corrosion; (iv) or
similarly, variations in the concentration of metal
ions or other species in the environment, arising
because of the spatial orientation of the
corroding metal and gravity; or finally, (v)
variations in the homogeneity of the metal
surface, due to the presence of inclusions,
different phases, grain boundaries, disturbed
metal, and other causes, can lead to the
establishment of anodic and cathodic sites. The
flow of electrons between the corroding anodes
and the non-corroding cathodes forms the
corrosion current, the value of which is
determined by the rate of production of electrons
by the anodic reaction and their consumption by
the cathodic reaction. A driving force is
necessary for electrons to flow between
the anodes and the cathodes. Thisdriving force is
the difference in potential between the anodic
Paper from Proceeding of the National Conference “Science in Media 2012” Organized by YMCA University
of Science and Technology, Faridabad, Haryana (India) December 3 rd -4th 2012 Published by
IJMRS's International Journa l of Engineering Sciences, ISSN (Online): 2277 -9698
www.ijmrs.com
IJMRS
www.ijmrs.com
6
and cathodic sites which exists because
each oxidation or reduction reaction has
associated with it a potential determined by the
tendency for the reaction to take place
spontaneously [3].
3. RUSTING
Corrosion occurs in the presence of moisture. For
example when iron is exposed to moist air, it reacts
with oxygen to form rust. (Fig 4)
Fig-4 Rusting of Iron
The amount of water complexed with the iron (III)
oxide (ferric oxide) varies as indicated by the letter
"X". The amount of water present also determines the
color of rust, which may vary from black to yellow to
orange brown. The formation of rust is a very
complex process which is thought to begin with the
oxidation of iron to ferrous (iron "+2") ions.
Fe ----> Fe+2 + 2 e-
Both water and oxygen are required for the next
sequence of reactions. The iron (+2) ions are further
oxidized to form ferric ions (iron "+3") ions.
Fe+2 ------> Fe+3 + e-
The electrons provided from both oxidation steps are
used to reduce oxygen as shown.
O2+ 2H2O + 4e---->4 OH-
The ferric ions then combine with oxygen to form
ferric oxide [iron (III) oxide] which is then hydrated
with varying amounts of water. The overall equation
for the rust formation may be written as :
The formation of rust can occur at some distance
away from the actual pitting or erosion of iron as
illustrated below. This is possible because the
electrons produced via the initial oxidation of iron
can be conducted through the metal and the iron ions
can diffuse through the water layer to another point
on the metal surface where oxygen is available. This
process results in an electrochemical cell in which
iron serves as the anode, oxygen gas as the cathode,
and the aqueous solution of ions serving as a "salt
bridge" as shown below (Fig 5).
Fig-5 Mechanism of Rusting
The involvement of water accounts for the fact that
rusting occurs much more rapidly in moist conditions
as compared to a dry environment such as a desert.
Many other factors affect the rate of corrosion. For
example the presence of salt greatly enhances the
rusting of metals. This is due to the fact that the
dissolved salt increases the conductivity of the
aqueous solution formed at the surface of the metal
and enhances the rate of electrochemical corrosion.
This is one reason why iron or steel tend to corrode
much more quickly when exposed to salt (such as
that used to melt snow or ice on roads) or moist salty
air near the ocean [1-5].
4. FORMS OF CORROSION
The Table 1 below gives a detailed account of the
example, corrosion testing and prevention techniques
of the various forms of corrosion [1 -5].
But there is another side of corrosion too. Our
economy would drastically change if there was no
corrosion. For example automobiles, ships,
Paper from Proceeding of the National Conference “Science in Media 2012” Organized by YMCA University
of Science and Technology, Faridabad, Haryana (India) December 3 rd -4th 2012 Published by
IJMRS's International Journa l of Engineering Sciences, ISSN (Online): 2277 -9698
www.ijmrs.com
IJMRS
www.ijmrs.com
7
underground pipelines and home appliances would
not require coatings. The stainless steel industry
would essentially disappear and copper would be
used only for electrical purposes. Most metallic parts,
as well as consumer products, would be made of cast
iron or steel.
Although corrosion is inevitable, its cost can be
considerably reduced. Keeping this in consideration
Corrosion Engineering was introduced which is the
application of science and art to prevent or control
corrosion damage economically and safely [1-5].
TABLE 1- TESTING & PREVENTION OF CORROSION
S
.
N
Forms of
Corrosion
Example
Corrosion Testing
Prevention
1
Galvanic
Corrosion
The rusting of corrugated iron sheet, which
becomes widespread when the
protective zinc coating is broken and the
underlying steel is attacked.
It consists of a large
brass sheet with a steel
nut bolted to the center
of the sheet
Keep small anodes from contacting
large cathodes,application of
sacrificial coating,paint coatings,
applying plastic, or other non-
metallic barriers.
2
Pitting
Corrosion
Pitting corrosion is common in passive
metals above pitting potential (Ep) like
Steel buried in the soil corrodes with the
formation of pits.
Expose a large piece
of specimen in a
corrosive liquid for a
fairly long period of
time.
Reduce Cl- content in the
electrolyte, Lower acidity of
solution, lower O2, Shot peen the
surface. Avoid stagnant solutions in
tanks, tubes, pipes & Redesign to
ensure proper drainage
3
Uniform
Corrosion
A piece of steel or zinc immersed in dilute
sulfuric acid will normally dissolve at a
uniform rate over its entire surface
A piece of steel or zinc
dipped in sulphuric
acid
Use thicker material for corrosion
allowance, use paints or metallic
coatings, cathodic& anodic
protection
4
Erosion
Corrosion
Characterized in appearance by grooves,
gullies, waves, rounded holes, and valleys
and usually exhibits a directional pattern
Spinning Disk test
Streamline the piping to reduce
turbulence, control fluid velocity,
using corrosion inhibitors or
cathodic protection, using more
resistant materials
5
Selective
Leaching
Selective removal of zinc in brass alloys
(dezincification)
Uniform
dezincification of
Brass pipe
Removing oxygen from the solution,
Cathodic protection &
appropriate selection of alloy
6
Stress
Corrosion
Cracking
Aluminum alloys crack in the presence
of chlorides, mild steel cracks in the
presence of alkali (boiler cracking)
and nitrates, copper alloys crack
in ammoniacal solutions (season cracking)
Bend Tests, Slow
strain rate test
SCC is the result of a combination
of three factors a susceptible
material, exposure to a corrosive
environment, and tensile stresses
above a threshold. Elimination any
one of these factors SCC initiation
becomes impossible.
7
Inter
Granular
Corrosion
Small amounts of iron in aluminum,
wherein the solubility of iron is low, have
been shown to segregate in the grain
boundaries and cause intergranular
corrosion
For stainless steels-
Nitric acid test, Huey
Test, Streicher Test &
Warren Test
Use post weld heat treatment, use of
low carbon grade of stainless steel.
8
Crevice
Corrosion
Small volumes of stagnant solution caused
by holes, gasket surfaces, lap joints, surface
deposits, and crevices under bolt
Material’s resistance
to crevice corrosion is
tested by wrapping the
specimen with string,
chord or rubber bands
Reduce crevices in design ,Use
welding if possible instead of
bolting two surfaces in contact
Avoid electrolyte stagnation ,Use
none-absorbent gaskets such as
Teflon instead of absorbent gaskets
such as fiber and wood gaskets &
Cleaning to reduce local conc. of
acids
... Corrosion occurs at various rates, and a large variety of materials from metals like iron and copper, and non-metals like ceramics and rubber. It is a thermodynamic and electrochemical process that occurs for example; when a metallic surface is exposed to an aqueous electrolyte, this forms an anodic site (oxidation process) that produces electrons in the metal and a cathodic site (reduction process), that make up the corrosion cell [2]. Corrosion is widely studied as there is so much to gain from its prevention, various methods of coating and techniques of substrate inhibition have been invented and innovated into practical applications for various fields, such as in the oil and gas sector in off-shore areas which possess various solutes in the sea water, and the field of transportation where various parts of mechanical devices are lubricated with oils and liquids to enable better movement of parts and reduce wear, still have detrimental effects to the materials themselves are they are subjected to the forces that dissolve and degrade them in these solutions. ...
... Hydrogen molecules are formed from reduced hydrogen ions at the cathode and these molecules bubble out as hydrogen gas [3]. x Stress corrosion cracking: Stress corrosion cracking occurs due to the stresses or fatigue which weakens already weak sections of a metal undergoing forces, which undergo corrosion, thereby undergo cracking in specific solutions, as aluminum alloys crack in the presence of chlorine and mild steel cracks in the presence of various alkali solutions [2]. x Intergranular corrosion: The segregation of iron in grain boundaries, when small amounts of iron are available in aluminum as an example, wherein the solubility of iron is low, causing intergranular corrosion [2]. ...
... x Stress corrosion cracking: Stress corrosion cracking occurs due to the stresses or fatigue which weakens already weak sections of a metal undergoing forces, which undergo corrosion, thereby undergo cracking in specific solutions, as aluminum alloys crack in the presence of chlorine and mild steel cracks in the presence of various alkali solutions [2]. x Intergranular corrosion: The segregation of iron in grain boundaries, when small amounts of iron are available in aluminum as an example, wherein the solubility of iron is low, causing intergranular corrosion [2]. Intergranular attack is hastened by the potential difference between grains and various grain boundaries, this means that the attack is based on the accessibility of the anodic sites at grain boundaries [5]. ...
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Abstract. The present study is to evaluate the performance of steel reinforcement under NaCl concentration chloride exposure. The loss of weight, yield stress and ultimate stress were tested to evaluate the performance of steel reinforcement before and after exposure. The exposure was also repeated under a variable temperature of (50, 60 and 70 C0). The steel was treated to improve its properties by using hardening in the oxy-acetylene torch, epoxy coating and aluminium spread coating. Results showed that the reduction in reinforcement properties was reduced significantly by using the hardening method and the maximum reduction in the performance of steel reinforcement was in the higher temperature chloride exposure. The increasing of concentration (0.1, 0.2, 0.3 and 0.4 NaCl %) was due to high corrosion in steel wire. The results showed that the treatment of reinforcement was significantly improved.
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