Corrosion in civil engineering structure

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EFFECT OF CORROSION IN STRUCTURES

A PROJECT REPORT

Submitted in partial fulfillment of requirements to

ACHARYA NAGARJUNA UNIVERSITY

For the award of the degree

B.Tech in CE

By

A Srikanth Vihari(y7ce805)

T Naga Teja(y7ce872)

Jasawnth Konatham(y7ce829)

G V Siva Reddy(y7ce825)

P Kiran Kumar(y7ce836)

March 2011

R.V.R & J.C.COLLEGE OF ENGINEERING

(Approved by A.I.C.T.E)

(Affiliated to Acharya Nagarjuna University)

Chandramoulipuram: Chowdavaram

GUNTUR - 1

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R.V.R & J.C COLLEGE OF ENGINEERING

DEPARTMENT OF CIVIL ENGINEERING

BONAFIDE CERTIFICATE

This is to certify that the term paper entitled EFFECT OF

CORROSION IN STRUCTURES is the Bonafide work ofA SrikanthVihari(y7ce805), who carried out work under my under my

supervision, and submitted in partial fulfillment of therequirements for the award of B.Tech fourth year final project in Civil

Engineering, R.V.R&J.C college of engineering, Chowdavaram, Guntur

during the academic year 2010-2011.

(Dr. P. Sanjeeva Rao ) (Dr.K.Sai Ram)

Prof. Dept. of CE Prof. & Head, Dept. of CE

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ACKNOWLEDGEMENT

From the idea to the act, from the conception to reality, from the

emotion to the response, from the desire to the spasm, we led by those about

whom to write all words seem meek.

We are very much thankful to Dr. A. Sudhakar, Principal of

R.V.R. & J.C College of Engineering, Guntur, for providing support and

stimulating environment.

We express our sincere thanks to Dr. K.Sai Ram , Head of the

Department of Civil Engineering, and Lecturer-in-charge,

Dr. P. Sanjeeva Rao , Professor in Mechanical Engineering for their

encouragement and support to carry out this project successfully.

We are very glad to express our special thanks to all teaching and

non teaching staff who has inspired us to select this project and for his valuable

advices to work on this project.

A SrikanthVihari

(y7ce805)

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ABSTRACT

Many metals are chemically active elements and get easily affected

by substances like moisture, air, acids, etc. One must have observed

iron articles that are shiny when new, get coated with reddish brown

powder when left for some time. This process is commonly known as

rusting of iron. The problem with iron (as well as many other metals)

is that oxidation takes place and the oxide formed does not firmly

adhere to the surface of the metal causing it to flake off easily. This

eventually causes structural weakness and disintegration of the metal.

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CHAPTER I

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INTRODUCTION

When a metal is attacked by substances around it, it is said to corrode and this

process is called corrosion. Corrosion causes deterioration of essential properties

in a material.

Billions of rupees are lost each year because

corrosion and a huge amount of money is spent in prevention of corrosion and

tarnishing of metals. Corrosion causes damage to car bodies, buildings, bridges,

iron railing, underground water and sewage pipes, ships and all objects made of

metals. Much of this is loss due to the corrosion of iron and steel, although may

other metals may corrode as well.

Much effort has been expended in the past few decades in the attempt to link

degradation of materials exposed to the atmosphere to the causative agents

responsible for the degradation. The utility is doing so is primarily to understand

the cause and effect relationships involved in the atmospheric corrosion process.

Corrosion involves the reaction of a metallic material with its environment and is

a natural process in the sense that the metal is attempting to revert to the

chemically combined state in which it is almost invariably found in the earths

crust. Whilst it is, therefore, a process that may be expected to occur, it should not

be regarded as inevitable and its control or prevention is possible through a

variety of means. The latter have their origins in electrochemistry, since the

reactions involved in causing corrosion are electrochemical in nature, but

corrosion control is as much in the hands of the engineering designer as it is the

province of the corrosion prevention specialist. To the engineer, corrosion may be

regarded as resulting in a variety of changes in the geometry of structures or

components that invariably lead, eventually, to a loss of engineering function e.g.

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general wastage leading to decrease in section, pitting leading to perforation,

cracking leading to fracture.

The rusting of ordinary steel is the most common form of corrosion and overall

adds up to a high proportion of the total cost attributed to corrosion. General

corrosion, in which the whole of the exposed metal surface is attacked, may lead

to failure in the engineering sense, but this is usually avoided by the application of

suitable control measures. All corrosion, however, is not of the general type and

localized effects may pose more complex problems, especially in the engineering

context. It is important to realize that corrosion characteristics are not inherent

properties of alloys, as are yield strength, electrical conductivity and the like,

since they relate to a combination of alloy and environment. Consequently, an

alloy may be very resistant to corrosion in a particular environment, yet perform

poorly in another, and even in a given environment factors like temperature, rate

of flow and geometrical aspects may be critical. In any event, the significance of

corrosion to the engineer is that it leads to loss of engineering function and the

following examples have been chosen to illustrate this in a variety of the branches

of engineering. They also serve to define some of the commoner forms of

aqueous corrosion and their various consequences.

Concrete is a complex material of construction that enables the high compressive

strength of natural stone to be used in any configuration. In tension, however,

concrete can be no stronger than the bond between the cured cement and the

surfaces of the aggregate. This is generally much lower than the compressive

strength of the concrete. Concrete is therefore frequently reinforced, usually with

steel. When a system of steel bars or a steel mesh is incorporated in the concrete

structure in such a way that the steel can support most of the tensile stresses and

leave the immediately surrounding concrete comparatively free of tensile stress,

then the complex is known as reinforced concrete.

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CHAPTER II

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CORROSION IN STEEL REINFORCED CONCRETES

Corrosion-induced deterioration of reinforced concrete can be

modeled in terms of three component steps:

(1) Time for corrosion initiation, Ti;

(2) Time, subsequent to corrosion initiation, for appearance of a crack on the

external concrete surface (crack propagation), Tp; and

(3) Time for surface cracks to progress into further damage and develop intospalls, Td, to the point where the functional service life, Tf, is reached. Figure

illustrates these schematically as a plot of cumulative damage versus time.

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CHAPTER III

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CORROSION REACTIONS:

Some of the anodicand cathodic reactions that occur simultaneously on a metal

surface in a "corrosion cell" are as follows.

A typical anodic oxidation that produces dissolved ionicproduct, for example for

iron metal is:

[1] Fe ==> Fe2+ + 2e-

Examples of cathodicreductionsinvolved in corrosion process are:

[2] O2 + 2H2O + 4e-

==> 4OH-

[3] O2 + 4H+ + 4e- ==> 2H2O

[4] 2H+ + 2e- ==> H2

The cathodic reaction represented by Equation [2] exemplifies corrosion in

natural environments where corrosion occurs at nearly neutral pH values.

Equations [3] and [4] represent corrosion processes taking place in the acidic

environments encountered in industrial processes or for the confined volumes

(pits, crevices) where the pH can reach acidic values because of hydrolysis

reactions such as:

[5] Fe2+ + 2H2O ==> Fe (OH)2 + 2H+

This reaction produces H+ ions, the concentration of which can, under certain

conditions, become large if the H+ ions cannot readily move out from a confined

volume. The overall corrosion reaction is, of course, the sum of the cathodic and

anodic partial reactions. For example, for a reaction producing dissolved ions

(sum of reactions [1] and [4]):

[6] Fe + 2H+ ==> Fe2+ + H2

[7] 2Fe + O2 + 2H2O ==> 2Fe(OH)2

Tafel Equation

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The Tafel equation is an early (1905) empirical relation between the over

potentialof theelectrode and the current density passing through the electrode:

"a" and "b" are characteristic constants of the electrode system. A plot of

electrode potentialagainst the logarithm of the current density is called the "Tafel

plot" and the resulting straight line the "Tafel line". "b" is the "Tafel slope" that

provides information about the mechanismof the reaction, and "a" the intercept,

provides information about the rate constant (and theexchange current density) of

the reaction.

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CHAPTER IV

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FACTORS INFLUENCING CORROSION REACTIONS

In any discussion of the mechanism of a chemical reaction it is advisable to

separate the factors which determine the tendencyor driving force of the reaction

to proceed from those which influence the rate of the reaction made possible by

the existence of this tendency. This tendency is an expression of the fact that the

system is not in a state of equilibrium (or inherent stability); it is measured by the

difference in energy between the initial and final state of the system for any

particular case. In most cases the observed rate is determined not by the absolute

magnitude of this tendency but by other factors, which depend primarily upon the

environment.

In considering the group of three typical reactions involved in corrosion, we shall

denote as primary factors those which determine the tendency of the metal to

corrode and thus influence its initial rate of solution and as secondary factors

those which influence the rate of the subsequent reactions. This term in no wise

implies that these secondary factors are of lesser importance; in fact, by

influencing the nature and distribution of the final corrosion products, they

usually determine the ultimate rate of corrosion, and the useful life of the metal,

in each environment.

In the general case, some one or two of the many factors involved exert

outstanding influence upon the ultimate rate of corrosion; these we term

controlling or dominant factors. In general, the primary factors have to do with

the metal (or alloy) itself; the secondary factors more with the specific

environment. It is convenient to divide them in this way, although no sharp

distinction can be made.

Accordingly on this basis we list below some of the more important factors,

discussing their general significance with respect to the mechanism of corrosion,

and postponing until later chapters the detailed discussion of others.

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Factors Associated Mainly with the Metal

Effective electrode potential of a metal in a solution

Over voltage of hydrogen on the metal

Chemical and physical homogeneity of the metal surface

Inherent ability to form an insoluble protective film

Factors Which Vary Mainly with the Environment

Hydrogen-ion concentration (pH) in the solution

Influence of oxygen in solution adjacent to the metal

Specific nature and concentration of other ions in solution

Rate of flow of the solution in contact with the metal

Ability of environment to form a protective deposit on the metal

Temperature

Cyclic stress (corrosion fatigue)

Contact between dissimilar metals or other materials as affecting localized

corrosion.

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CHAPTER V

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TYPES OF CORROSION

1) Uniform Corrosion

2) Pitting Corrosion

3) Galvanic Corrosion

4) Crevice Corrosion

5) Concentration Cell Corrosion

6) Graphitic Corrosion

1) Uniform Corrosion:

The metal loss is uniform from the surface. Often combined with high-velocity

fluid erosion, with or without abrasives. Generally noticed with industrial and

hydraulic structures.

2) Pitting Corrosion:

The metal loss is randomly located on the metal surface. Often combined with

stagnant fluid or in areas with low fluid velocity, such as water tanks.

Theories of passivity fall into two general categories, one based on adsorption and

the other on presence of a thin oxide film. Pitting in the former case arises as

detrimental or activator species, such as Cl-, compete with O2 or OH- at specific

surface sites. By the oxide film theory, detrimental species become incorporated

into the passive film, leading to its local dissolution or to development of

conductive paths. Once initiated, pits propagate auto-catalytically according to the

generalized reaction,

M+n + nH2O + nCl- M (OH) n + nHCl, resulting in acidification of the active

regionand corrosion at an accelerated rate (M+n and M are the ionic and metallic

forms of the corroding metal).

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3) Galvanic Corrosion:

Occurs when two metals with different electrode potential is connected in a

corrosive electrolytic environment. The anodic metal develops deep pits and

groves in the surface. This type is noticed on other than reinforcement in

structures where different metal fixtures / fittings are used.

4) Crevice Corrosion:

Occurs at places with gaskets, bolts and lap joints where crevice exists. Crevice

corrosion creates pits similar to pitting corrosion. It is noticed in industrial

structures steel structures and hybrid structures.

Crevice corrosion is a localized form of corrosion usually associated with a

stagnant solution on the micro-environmental level. Such stagnant

microenvironments tend to occur in crevices (shielded areas). Oxygen in the

liquid which is deep in the crevice is consumed by reaction with the metal.

Oxygen content of liquid at the mouth of the crevice which is exposed to the air is

greater, so a local cell develops in which the anode, or area being attacked, is the

surface in contact with the oxygen-depleted liquid.

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5) Concentration Cell Corrosion:

Occurs where the surface is exposed to an electrolytic environment where the

concentration of the corrosive fluid or the dissolved oxygen varies. Often

combined with stagnant fluid or in areas with low fluid velocity. Dampness

periodic water retention with Rcc and steel structures are prone to this type of

corrosion.

6) Graphitic Corrosion

Cast iron loosing iron in salt water or acids. Leaves the graphite in place, resulting

in a soft weak metal. As waste water pipes and fixtures are liable for this type of

corrosion.

CHAPTER VI

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REASONS OF CORROSION

The two most common causes of reinforcement corrosion are (i) localized

breakdown of the passive film on the steel by chloride ions and (ii) general

breakdown of passivity by neutralization of the concrete, predominantly by

reaction with atmospheric carbon dioxide. Sound concrete is an ideal environment

for steel but the increased use of deicing salts and the increased concentration of

carbon dioxide in modern environments principally due to industrial pollution,

has resulted in corrosion of the rebar becoming the primary cause of failure of this

material. The scale of this problem has reached alarming proportions in various

parts of the world.

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Following are the contributing factors leading to corrosion:

1) Loss of Alkanity due to Carbonation

It is well known that if bright steel is left unprotected in the atmosphere a brown

oxide rust quicklyforms and will continue to grow until a scale flakes from the

surface. This corrosion process will continue unless some external means is

provided to prevent it. One method is to surround the steel with an alkaline

environment having a pH value within the range 9.5 to 13. At this pH value apassive filmforms on the steel that reduces the rate of corrosion to a very low and

harmless value. Thus, concrete cover provides chemical as well as physical

protection to the steel. However, alkalinity can be lost as a result of

(a) Reaction with acidic gases (such as carbon dioxide) in the atmosphere.

(b) Leaching by water from the surface.

Concrete is permeable and allows the slow ingress of the atmosphere; the acidicgases react with the alkalis (usually calcium, sodium and potassium hydroxides),

neutralizing them by forming carbonates and sulphates, and at the same time

reducing the pH value. If the carbonated front penetrates sufficiently deeply into

the concrete to intersect with the concrete reinforcement interface, protection is

lost and, since both oxygen and moisture are available, the steel is likely to

corrode. The extent of the advance of the carbonation front depends, to a

considerable extent, on the porosity and permeability of the concrete and on the

conditions of the exposure.

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In the case of carbonation, atmospheric carbon dioxide (CO 2) reacts with pore

water alkali according to the generalized reaction,

Ca (OH)2 + CO2 CaCO3 + H2O

It consumes alkalinity and reduces pore water pH to the 89 range, where steel is

no longer passive.

2) Loss of Alkanity due to Chlorides

The passivity provided by the alkaline conditions can also be destroyed by the

presence of chloride ions, even though a high level of alkalinity remains in the

concrete. The chloride ion can locally de-passivity the metal and promote active

metal dissolution. Chlorides react with the calcium aluminate and calcium

aluminoferrite in the concrete to form insoluble calcium chloroaluminates and

calcium chloroferrites in which the chloride is bound in non-active form;

however, the reaction is never complete and some active soluble chloride always

remains in equilibrium in the aqueous phase in the concrete. It is this chloride insolution that is free to promote corrosion of the steel. At low levels of chloride in

the aqueous phase, the rate of corrosion is very small, but higher concentration

increases the risks of corrosion.

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3) Cracks due to Mechanical Loading

Cracks in concrete formed as a result of tensile loading, shrinkage or other factors

can also allow the ingress of the atmosphere and provide a zone from which the

carbonation front can develop. If the crack penetrates to the steel, protection can

be lost. This is especially so under tensile loading, for deboning of steel and

concrete occurs to

some extent on each side of the crack, thus removing the alkaline environment

and so destroying the protection in the vicinity of the deboning.

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4) Stray Currents

Stray currents, arising for instance from railways, cathodic protection systems, or

high voltage power lines, are known to induce corrosion on buried metal

structures, leading to severe localized attack. They may find a low resistance path

by flowing through metallic structures buried in the soil (pipelines, tanks,

industrial and marine structures). a cathodic reaction (e.g., oxygen reduction or

hydrogen evolution) takes place where the current enters the buried structure,

while an anodic reaction (e.g., metal dissolution) occurs where the current returns

to the original path, through the soil. Metal loss results at the anodic points, where

the current leaves the structure; usually, the attack is extremely localised and can

have dramatic consequences especially on pipelines.

Example of stray current from a DC railway line picked up by steel reinforcement in

concrete

5) Corrosion of steel reinforcement due to atmospheric pollution

Most of the times steel reinforcement is exposed to the atmosphere during

transportation and storage in the building sites for a long period before their

installation in the concrete structures. At any of those stages, steel rebars can be

contaminated by chloride ions from sea spray or windblown salt. This fact leads

to the formation of corrosion products on their surface.

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Fiber optical microscope images after three months at open atmosphere

conditions.

6) Moisture Pathwa

If the surface of the concrete is subject to long-term wetting, the water will

eventually reach the level of the reinforcement, either through diffusion through

the porous structure of the concrete, or by traveling along cracks in the concrete.

Concrete roof decks, by their nature, are meant to be protected from moisture.However, the presence of moisture on roofing systems may result from failure of

the roofing membrane, poor detailing of drainage facilities, or lack of

maintenance of drainage facilities.

Overwatered leading to shrinkage cracking

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7) Water-Cement Ratio

Concrete placed with a high water-cement ratio, as seen under Freeze-thaw

cycles, is more porous due to the presence of excess water in the plastic concrete.

The porosity increases the rte of diffusion of water and electrolytes through the

concrete and makes the concrete more susceptible to cracking.

8) Low Concrete Tensile Strength

Concrete with low tensile strength facilitates corrosion damage in two ways. First,

the concrete develops tension or shrinkage cracks more easily, admitting moisture

and oxygen, and in some cases chlorides, to the level of the reinforcement.

Second, the concrete is more susceptible to developing cracks at the point that the

reinforcement begins to corrode.

9) Electrical Contact with dissimilar metals

Dissimilar metals in contact initiate a flow of electrons that promotes the

corrosion of one or the other, by a process known as galvanic corrosion. When

two dissimilar metals are in contact with each other the more active metal (lower

on the list) will induce corrosion on the less active. Such corrosion may induce

cracking and damage in the concrete.

10) Corrosion due to difference in environments

Corrosion occurs when two different metals, or metals in different environments,

are electrically connected in a moist or damp concrete

This will occur when:

1. Steel reinforcement is in contact with an aluminium conduit.

2. Concrete pore water composition varies between adjacent or along reinforcing

bars.

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3. Where there is a variation in alloy composition between or along reinforcing

bars.

4. Where there is a variation in residual/applied stress along or between

reinforcing bars.

11) STRESS INDUCED CORROSION:

Stress corrosion cracking (SCC) is the unexpected sudden failure of normally

ductilemetals subjected to a tensile stress in a corrosive environment, especially

at elevated temperature in the case of metals. SCC is highly chemically specific in

that certain alloys are likely to undergo SCC only when exposed to a small

number of chemical environments. The chemical environment that causes SCC

for a given alloy is often one which is only mildly corrosive to the metal

otherwise. Hence, metal parts with severe SCC can appear bright and shiny, while

being filled with microscopic cracks. This factor makes it common for SCC to go

undetected prior to failure. SCC often progresses rapidly, and is more common

among alloys than pure metals. The specific environment is of crucial importance,

and only very small concentrations of certain highly active chemicals are neededto produce catastrophic cracking, often leading to devastating and unexpected

failure.

The stresses can be the result of the crevice loads due to stress concentration, or

can be caused by the type of assembly or residual stressesfrom fabrication (e.g.

cold working); the residual stresses can be relieved by annealing

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CHAPTER VII

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EXAMPLES OF CORROSION:

1) Bhopal Accident

Bhopal is probably the site of the greatest industrial disaster in history. Between

1977 and 1984, Union Carbide India Limited (UCIL), located within a crowded

working class neighborhood in Bhopal, was licensed by the Madhya Pradesh

Government to manufacture phosgene, monomethylamine (MMA),

methylisocyanate (MIC) and the pesticide carbaryl, also known as Sevin.

On the night of the 2-3 December 1984 water inadvertently entered the MIC

storage tank, where over 40 metric tons of MIC were being stored. The addition

of water to the tank caused a runaway chemical reaction, resulting in a rapid rise

in pressure and temperature. The heat generated by the reaction, the presence of

higher than normal concentrations of chloroform, and the presence of an iron

catalyst, produced by the corrosion of the stainless steel tank wall, resulted in a

reaction of such momentum, that gases formed could not be contained by safety

systems.

As a result, MIC and other reaction products, in liquid and vapor form, escaped

from the plant into the surrounding areas. There was no warning for people

surrounding the plant as the emergency sirens had been switched off. The effect

on the people living in the shanty settlements just over the fence was immediate

and devastating. Many died in their beds, others staggered from their homes,

blinded and choking, to die in the street.

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Many more died later after reaching hospitals and emergency aid centers. The

early acute effects were vomiting and burning sensations in the eyes, nose and

throat, and most deaths have been attributed to respiratory failure. For some, the

toxic gas caused such massive internal secretions that their lungs became clogged

with fluids, while for others, spasmodic constriction of the bronchial tubes led to

suffocation. It is been estimated that at least 3000 people died as a result of this

accident, while figures for the number of people injured currently range from

200,000 to 600,000, with an estimated 500,000 typically quoted. The factory was

closed down after the accident.

The Bhopal disaster was the result of a combination of legal, technological,

organizational, and human errors. The immediate cause of the chemical reaction

was the seepage of water (500 liters) into the MIC storage tank. The results of this

reaction were exacerbated by the failure of containment and safety measures and

by a complete absence of community information and emergency procedures.

The long term effects were made worse by the absence of systems to care for and

compensate the victims. Furthermore, safety standards and maintenance

procedures at the plant had been deteriorating and ignored for months. A listing of

the defects of the MIC unit runs as follows:

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Gauges measuring temperature and pressure in the various parts of the

unit, including the crucial MIC storage tanks, were so notoriously

unreliable that workers ignored early signs of trouble.

The refrigeration unit for keeping MIC at low temperatures (and therefore

less likely to undergo overheating and expansion should a contaminant

enter the tank) had been shut off for some time.

The gas scrubber, designed to neutralize any escaping MIC, had been shut

off for maintenance. Even had it been operative, post-disaster inquiries

revealed, the maximum pressure it could handle was only one-quarter that

which was actually reached in the accident.

The flare tower, designed to burn off MIC escaping from the scrubber,

was also turned off, waiting for replacement of a corroded piece of pipe.

The tower, however, was inadequately designed for its task, as it was

capable of handling only a quarter of the volume of gas released.

The water curtain, designed to neutralize any remaining gas, was too short

to reach the top of the flare tower, from where the MIC was billowing

The lack of effective warning systems; the alarm on the storage tank

failed to signal the increase in temperature on the night of the disaster

MIC storage tank number 610 was filled beyond recommended capacity;

and -a storage tank which was supposed to be held in reserve for excess

MIC already contained the MIC.

2) collapsed Silver Bridge

The collapsed Silver Bridge, as seen from the Ohio side

SCC caused the catastrophic collapse of the Silver Bridge in December 1967,

when an eyebar suspension bridge across the Ohio river at Point Pleasant, West

Virginia, suddenly failed. The main chain joint failed and the whole structure fellinto the river, killing 46 people in vehicles on the bridge at the time. Rust in the

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eyebar joint had caused a stress corrosion crack, which went critical as a result of

high bridge loading and low temperature. The failure was exacerbated by a high

level of residual stress in the eyebar. The disaster led to a nationwide reappraisal

of bridges.

Suspended ceilings in indoor swimming pools are safety-relevant components. As

was demonstrated by the collapses of the ceiling of the Uster (Switzerland) indoor

swimming pool (1985) and again at Steenwijk (Netherlands, 2001), attention must

be paid to selecting suitable materials and inspecting the state of such

components. The reason for the failures was stress corrosion cracking of metal

fastening components made of stainless steel[3] . The active chemical was chlorine

added to the water as a disinfectant.

A classic example of SCC is season cracking of brass cartridge cases, a problem

experienced by the British army in India in the early 19th century. It was initiated

by ammonia from dung and horse manure decomposing at the higher

temperatures of the spring and summer. There was substantial residual stress in

the cartridge shells as a result of cold forming. The problem was solved by

annealing the shells to ameliorate the stress.

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CHAPTER VIII

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PREVENTION METHODS

1) Keep concrete always dry, so that there is no H2O to form rust. Also

aggressive agents cannot easily diffuse into dry concrete. If concrete is always

wet, then there is no oxygen to form rust.

2) A polymeric coating is applied to the concrete member to keep out aggressive

agents. A polymeric coating is applied to the reinforcing bars to protect themfrom moisture and aggressive agents. The embedded epoxy-coating on steel bars

provide a certain degree of protection to the steel bars and, thereby, delay the

initiation of corrosion. These coatings permit movement of moisture to the steel

surface but restrict oxygen penetration such that a necessary reactant at cathodic

sites is excluded.

3) Stainless steel or cladded stainless steel is used in lieu of conventional black

bars.

4) FLY ASH : Using a Fly Ash concrete with very low permeability, which will

delay the arrival of carbonation and chlorides at the level of the steel

reinforcement. Fly Ash is a finely divided silica rich powder that, in itself, gives

no benefit when added to a concrete mixture, unless it can react with the calcium

hydroxide formed in the first few days of hydration. Together they form a calcium

silica hydrate (CSH) compound that over time effectively reduces concrete

diffusivity to oxygen, carbon dioxide, water and chloride ions.

5) A portion of the chloride ions diffusing through the concrete can be

sequestered in the concrete by combining them with the tricalcium aluminate to

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form a calcium chloro-aluminate (Friedels salt). It can have a significant effect in

reducing the amount of available chlorides thereby reducing corrosion.

6) Electrochemical injection of the organic base corrosion inhibitors,

ethanolamine and guanidine, into carbonated concrete.

7) The rougher the steel surface, the better it adheres to concrete. oxidation

treatment (by water immersion and ozone exposure) of rebar increases the bond

strength between steel and cement paste to a value higher than that attained by

clean rebars. In addition, surface deformations on the rebar (such as ribs) enhance

the bond due to mechanical interlocking between rebar and concrete.

8) As the cement content of the concrete increases (for a fixed amount of chloride

in the concrete), more chloride reacts to form solid phases, so reducing the

amount in solution (and the risk of corrosion), and as the physical properties

improve, the extent of carbonation declines, so preventing further liberation of

chloride from the solid phase.

9) Electrochemical Chloride Extraction (ECE) is a relatively new technology

for which long-term service data are limited. This method employs a temporary

anode that is operated at current density 7 orders of magnitude higher than for

cathodic protection, such that anions, including chlorides, electromigrate away

from the embedded steel cathode. Repassivation can then occur, similar to what

was discussed above in conjunction with cathodic protection, although this occurs

in a shorter period of time (12 weeks to several months). Not all chlorides are

removed, but sufficient amounts are displaced from the steel-concrete interface.

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10) Installation of physical barrier systems such as coatings, sealers, membranes,

and overlays toforestall subsequent Clingress

11) A relatively thin zinc surface layer is applied by either hot dipping or electro-

deposition. This methodology relies on a relatively low corrosion rate for zinc and

its potential for being active to the substrate steel, thereby providing galvanic

cathodic protection at defects and penetrations.

12) Cathodic prevention is, in effect, identical to cathodic protection, except that

it is applied to new, Cl- free structures for which current demand is less than for

Cl contaminated ones. In addition, the objective here is not to reduce corrosion

rate itself (because the reinforcement is passive), but instead to establish a

potential gradient that opposes the inward diffusional migration of anions,

specifically chlorides. In this regard, the approach functions similarly to ECE,

except that, instead of removing chlorides, it retards their entry.

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13) Concrete mix design modifications involve such factors as reduced w/c,

including use of waterreducing admixtures or superplastizers; type of cement;

permeability reducing admixtures such as fly ash, silica fume, and blast furnace

slag; and corrosion inhibiting admixtures.

14) Structural design aspects of corrosion control involve factors such as

configurational (geometrical) considerations that minimize or, if possible,

eliminate exposure to corrosives.

15) Remedies for corrosion-damaged concrete include removal of all delaminated

concrete, cleaning of the reinforcement by abrasive blast cleaning, high pressure

water, or needle scaling, and use of a concrete patching material. Rigorous

solutions to corrosion problems are not always available, even

where the circumstances that cause them can be defined and

there is information or experience availableto indicate the likely

outcome. Codes of practice, specifications and the experience of

manufacturers are available for tackling many corrosion

problems and the designer should be aware of these and use

them appropriately. There are particular problems in finding data

for corrosion rates of metals in hitherto unexperienced

environments, especially in relation tochemical processes, and it

is thus necessary to obtain, usually short term, laboratory data

before proceeding with a design. Where the corrosion rates areregarded as not excessive and

the corrosion is spread reasonably uniformly over the exposed

surfaces, even involving some degree of pitting, it should be

possible to make an allowance for the reduction in metal

thickness over the expected lifetime of the structure, so that it

will remain safe throughout this period. The allowance made is

commonly that which would give twice the desired life.

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CHAPTER IX

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CASE-STUDY

As the part of our project we had done a case-study in Dr.Kolli

Sarada Market, Guntur. This market buildings has been failed

due severe corrosion.

Here are following pictures of market building showing corroded

regions:-

In this image it sis clearly shown that the beam and slab ofthe market building are clearly damaged due to the effect of

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corrosion. The beam was failed due to the non provision ofsufficient clear cover.

This image is the perfect example for column

failure due to the effect of corrosion.

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In this it is clearly shown that cracks are formed due to the corrosion and

even small plants are been grown. Due to the plant growth the cracks expand

more thus resulting more damage to walls.

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CHAPTER X

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Conclusion

Where uncertainty or the lack of a technical means of

controlling corrosion render a problem insoluble it may be

necessary to live with it whilst monitoring the corrosion

rate as the plant operates, so that appropriate action may

be taken if the rate reaches unacceptably high levels.

There are a number of ways of assessing on-line corrosion,involving electro chemical measurements or more direct

assessments of effective section, but ins pection visual or

otherwise, for all systems that may corrode has

ramifications for the designer in ensuring that it is

possible.

In some installations this may involve the incorporation of

probes, coupons or test specimens exposed to the same

environment as the plant and therefore simulating the

corrosion of the latter, but in a form which allows easier

assessment of the extent of corrosion.

In other cases inspection holes may be necessary to allow

access to those parts of the structure judged to be most

vulnerable to corrosion.

Where the latter is likely to reach unacceptable limits

before the working life of the plant is reached and

components need replacing the design should facilitate

this, pumps and valves being components most likely to

need replacement.

The implications for the designer of the various points that

have been made in earlier pages can be summarised in

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the suggestion that the aims of design from a corrosion

control viewpoint should be uniformity.

In particular uniformity of contour to avoid sharp changes

in section with their implications for fluid flow, (including

the draining of containers) stress concentration, solution

concentration, temperature distribution and the problems

that they create in relation to the application of surface

coatings for corrosion control.

The effects of fabrication methods also should be

considered in this context, welded, brazed or soldered

joints, where applicable and providing any dissimilar metal

contact problems are taken into account, usually providing

less risk of crevices than mechanical fastening methods,

although whatever method of joining is employed only

careful attention to detail can ensure satisfactory

performance.

Finally, but as an integral part of the total design and not

as an afterthought, the means of corrosion control, by

material modification or by chemical or electrochemical

treatment, should be considered with as much care as is

put into any other aspect of the design process.

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CHAPTER XI

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BIBLIOGRAPHY

1) Luca Bertolini , Maddalena Carsana, Pietro Pedeferri, Corrosion behaviour ofsteel in concretein the presence of stray current, Corrosion Science 49 (2007) 105610682) S. Sawada 1, J. Kubo, C.L. Page *, M.M. Page, Electrochemical injection oforganic corrosioninhibitors into carbonated cementitious Materials, Corrosion Science 49 (2007)118612043) Shihai Cui, Jianmin Han, Yongping Du, Weijing Li, Corrosion resistance and

wear resistance ofplasma electrolytic oxidation coatings on metal matrix composites, Surface &CoatingsTechnology 201 (2007) 530653094) G. Batis, E. Rakanta, Corrosion of steel reinforcement due to atmosphericpollution, Cement &Concrete Composites 27 (2005) 2692755) A. Ali Gurten, Kadriye Kayakrlmaz, Mehmet Erbil, The effect ofthiosemicarbazide oncorrosion resistance of steel reinforcement in concrete, Construction andBuilding Materials 21

(2007) 669676

Corrosion in civil engineering structure

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