1

SEMINAR REPORT

ON

“CORROSION ENGINEERING”

Submitted in the partial fulfilment of the requirements for the award of the degree

Of

BACHELOR OF ENGINEERING

(CHEMICAL ENGINEERING)

BY

CHANPREET KAUR GULATI

4804

BE CHEMICAL

Under the guidance of

Prof. M.R.Gaonkar

DEPARTMENT OF CHEMICAL ENGINEERING

JAWAHARLAL NEHRU ENGINEERING COLLEGE

AURANGABAD (2010-2011)

DR. BABASAHEB AMBEDKAR MARATHWADA UNIVERSITY,

AURANGABAD

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CERTIFICATETHIS IS TO CERTIFY THAT THE SEMINAR REPORT

ENTITLED

“Corrosion Engineering”SUBMITTED BY –

CHANPREET KAUR GULATI (4804)

HAS COMPLETED AS PER THE REQUIREMENTS OF

DR. BABASAHEB AMBEDKAR MARATHWADA UNIVERSITY

IN PARTIAL FULFILLMENT OF THE DEGREE OF

B. E. (CHEMICAL)

JAWAHARLAL NEHRU ENGINEERING COLLEGE

FOR THE ACADEMIC YEAR 2010 – 2011

Prof. M. R. Gaonkar Dr. S. V. Dharwadkar Dr. S. D. Deshmukh

Guide HOD Principal

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ACKNOWLEDGMENT

It is a great privilege and pleasure in presenting this seminar report to my college. I express my sincere gratitude towards Prof. M.R.GAONKAR the guide for my seminar report for her guidance. I also thank our HOD Dr.S.V.Dharwadkar

I would also like to thank our staff members, friends who have helped me directly or indirectly.

CHANPREET GULATI

BE CHEMICAL

JNEC AURANGABAD

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INDEX

Sr. No. Topic Page no.

1. Introduction 5

2. Cause of corrosion 7

3. Forms of corrosion 9

4. Corrosion Testing 14

5. Corrosion Prevention 16

6. Cost and future of Corrosion

20

7. Conclusion 24

8. References 25

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Introduction

Corrosion engineering is the application of science and the art to prevent or control corrosion

damage economically and effectively.

Corrosion is defined as the destruction or deterioration of a material because of reaction with

its environment. Some insist that the definition should be restricted to metals, but often

corrosion engineers must consider both metals and non-metals for a solution to the given

problem. For example, deterioration of paint and rubber by sunlight or chemicals, fluxing of

the lining of a furnace, and attack of a solid metal by another molten liquid are all considered

as corrosion.

The serious consequences of the corrosion process have become a problem of worldwide

significance. In addition to our everyday encounters with this form of degradation, corrosion

causes plant shutdowns, waste of valuable resources, loss or contamination of product,

Reduction in efficiency, costly maintenance, and expensive overdesign; it also jeopardizes

safety and inhibits technological progress. The multidisciplinary aspect of corrosion problems

combined with the distributed responsibilities associated with such problems only increase

the complexity of the subject. Corrosion control is achieved by recognizing and

understanding corrosion mechanisms, by using corrosion-resistant materials and designs, and

by using protective systems, devices, and treatments. Major corporations, industries, and

government agencies have established groups and committees to look after corrosion-related

issues, but in many cases the responsibilities are spread between the manufacturers or

producers of systems and their users. Such a situation can easily breed negligence and be

quite costly in terms of dollars and human lives.

Practically in life all environments are corrosive in nature to some degree. Some examples

are air and moisture; fresh, distilled, salt and mine waters; rural, urban and industrial

atmospheres; steam and other gases such as HCL, SO2 and fuel gases; mineral acids such as

hydrochloric, sulphuric and nitric; organic acids such as acetic and formic; alkalies; soils;

solvents; vegetable and petroleum oils; and a variety of food products. In general the

inorganic materials are more corrosive than the organics. For example, corrosion in the

petroleum industry is more due to NaCl, sulphur, hydrochloric and sulphuric acids and water

than to oil, naphtha and gasoline.

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However corrosion is useful in some cases. For example, chemical machining or chemical

milling is widely used in aircraft and other applications. Unmasked areas are exposed to acid

and excess metal is dissolved. This process is adopted when it is more economical or when

the parts are hard and difficult to machine by more conventional methods. Anodizing of

aluminium is another beneficial corrosion process used to obtain better and more uniform

appearance in addition to a protective corrosion product on the surface.

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Causes of corrosion

Practically all environments are corrosive to some degree. In general as we saw that the

inorganic materials are more corrosive than the organic materials. Higher temperature and

pressure usually involve more severe corrosion conditions. Some important causes are

following:

Effect of oxygen and oxidizers

Effect of velocity

Effect of temperature

Effect of corrosive concentration

Effect of galvanic coupling

Effect of oxygen and oxidizers: The effect of oxidizer additions or the presence of

oxygen on corrosion rate depends on both the medium and the metals involved. The

corrosion rate may be increased by the addition of oxidizers. If an active passive

metal is initially passive in a corrosive medium the addition of further oxidizing

agents has only a negligible effect on corrosion rate. This condition frequently occurs

when an active passive metal is immersed in an oxidizing medium such as nitric acid

or ferric chloride

Effect of Velocity: The effects of velocity on corrosion rate are complex and depend

on the characteristics of the metal and the environment to which it is exposed. Typical

observation when agitation or solution velocity is increased. For corrosion processes

that are controlled by activation polarization, agitation and velocity have no effect on

the corrosion rate. When materials such as these are exposed to extremely high

corrosive velocities, mechanical damage or removal of these films can occur,

resulting in accelerated attack. Easily passivated material such as SS and titanium

frequently are more corrosion resistant when the velocity of the corrosion medium is

high. The effect of velocity is virtually negligible.

Effect of temperature: Temperature increases the rate of almost all chemical

reactions. Very rapid or exponential rise in corrosion rate increases with temperature.

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Effects of corrosion concentration: Many materials that exhibit passivity effects are

only negligibly effected by the wide changes in corrosive concentration. As acid

concentration is increased further, corrosion rate reaches a maximum and then it

decreases.

Effect of Galvanic coupling: In complex processes, streams and piping arrangement,

different metals and alloys are frequently in contact with each other and the corrosive

medium. It increases the rate of cathodic reaction and consequently increases the

corrosion rate. Galvanic coupling does not always increase the corrosion rate of a

given metal; in some cases it decreases the corrosion rate.

Factors associated mainly with metals:

Effective electrode potential of a metal in solution

Overvoltage of hydrogen on metal

Chemical and physical homogeneity of metal surface

Inherent ability to form an insoluble protective film

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Forms of corrosion

It is convenient to classify corrosion forms in which it manifests itself; the basis of this

classification lies in the appearance of the corroded metal.

Corrosion has eight forms, which are unique, but all of them are more or less interrelated.

The eight forms are:

1. Uniform or general attack

2. Galvanic or two metal corrosion

3. Crevice corrosion

4. Pitting

5. Intergranular corrosion

6. Selective leaching or parting

7. Erosion corrosion

8. Selective corrosion

Uniform attack:

Uniform attack is the most common form of corrosion. It is normally characterized by a

chemical or electrochemical reaction that proceeds uniformly over the entire exposed surface

or over a large area. The metal becomes thinner and eventually fails. For example, a piece of

steel or zinc immersed in dilute surface will normally dissolve at a uniform rate over its entire

surface.

Uniform attack or in general overall corrosion represents the greatest destruction of metal on

a tonnage basis. This form of corrosion however, is not of too great importance from the

technical point, because the life of the equipment can be accurately estimated by simple tests.

Merely immersing specimens in the fluid involved is often sufficient. Uniform attack can be

prevented or reduced by 1. Inhibitors, 2. Proper materials, 3. Cathodic protection.

Galvanic or two metal protection: A potential usually exists between two dissimilar metals

when they are immersed in a corrosive or conductive solution. If these metals are placed in

contact, this potential difference produces electron floe between them. Corrosion of the less

corrosion resistant metal is usually increased and the attack of the more resistant material is

decreased, as compared with the behaviour of these metals when they are not in contact. The

less resistant metal becomes anodic and the more resistant metal becomes cathodic. Usually

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the cathode corrodes very little or not at all in this type of couple. Because of the electric

currents and dissimilar metals involved, this form of corrosion is called galvanic or two metal

corrosion. Its prevention includes 1. Select combinations of metals, 2. Insulating dissimilar

metals, 3.coatings and 4.inhibitors.

Crevice corrosion: Intensive localized corrosion frequently occurs within crevices and other

shielded areas on metal surfaces exposed to corrosives. This type of attack is usually

associated with small volumes of stagnant solution caused by holes, gasket surfaces, lap

joints, surface deposits and crevices under bolt and rivet heads. As a result, this form of

corrosion is called as crevice corrosion or sometimes, as, deposit or gasket corrosion.

Examples of deposits that may produce crevice corrosion are sand, dirt, corrosion products

and other solids. The deposit acts as a shield and then creates a stagnant condition. The

deposit could also be a permeable corrosion product.

Combating methods of this type include: 1.using welded butt joints, 2.closing crevices in

existing lap joints, 3.designing vessels for complete drainage, 4.inspecting regularly, and

5.welding.

Pitting: This is a form of extremely localized attack that results in holes in the metal. These

holes may be small or large in diameter, but in most cases they are relatively small. Pits are

sometimes isolated pr so close together that they look like a rough surface. Generally a pit

may be described as a cavity or hole with the surface diameter about the same as or less than

a depth.

It is one of the most destructive and insidious forms of corrosion. It causes equipment to fail

because of perforation with only a small percent weight loss of the entire structure. It is often

difficult to detect pits because of their small size and also they are covered with corrosion

products. Pitting is also difficult to predict using lab tests. Sometimes it takes several months

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or a year for a pit to show up. Pitting is actually vicious and intense form of corrosion, and

failures often occur with extreme suddenness.

The methods suggested for crevice corrosion generally also apply to pitting. Materials that

show pitting or tendencies to pit, during the corrosion tests should not be used to build the

plant or equipment. The best procedure is to use the materials that are not known to pit.

Adding inhibitors is sometimes helpful, but this may be dangerous unless the attack is

stopped completely. If not, then the intensity of the pitting may be increased.

Intergranular corrosion: Localized attack at and adjacent to grain boundaries, with

relatively little corrosion of the grains, is Intergranular corrosion. Grain boundary effects are

of little or no consequence in most applications or uses of metal. If a metal corrodes, uniform

attack results since grain boundaries are usually only slightly more reactive. However under

certain conditions, grain interferences are very reactive and Intergranular corrosion results.

It can be caused by impurities at the grain boundaries, enrichment of one of the alloying

elements, or depletion of one of these elements in the grain boundary areas. Small amounts of

iron in aluminium, wherein solubility is low, have shown to segregate in the grain boundaries

and cause Intergranular corrosion.

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Selective Leaching: Selective leaching is the removal of one element from a solid alloy by

corrosion processes. The most common example is the selective removal of zinc in brass

alloys. Similar processes occur in other alloy systems in which aluminium, iron, cobalt,

chromium and other elements are removed. Selective leaching is the general term that

describes these processes, and its use precludes the creation of terms such as

dealuminification, decobatification etc. Parting is a metallurgical term that is sometimes

applied, but selective leaching is preferred.

Erosion corrosion: erosion corrosion is the acceleration or increase in the rate of

deterioration or attack on a metal because of relative movement between corrosive fluid and

metal surface. Generally this movement is quite rapid and mechanical wear effects or

abrasions are involved. Metal is removed from the surface as dissolved ions or it forms solid

corrosive products that are mechanically swept from metal surface. Sometimes movement of

the environment decreases corrosion, particularly when localized attack occurs under

stagnant conditions, but this is not erosion corrosion.

Erosion corrosion is characterized by grooves, gullies, waves, rounded holes and valleys and

usually exhibits a directional pattern.

In many cases, failures because of this occur in a relatively short time, and they are

unexpected because evaluation corrosion tests were under static conditions or because the

erosion effects were not considered.

The methods to combat the corrosion are: 1.materials with better resistance, 2.design,

3.alternation of environment, 4.coatings, and 5.cathodic protection.

Stress corrosion: stress corrosion cracking refers to cracking caused by the simultaneous

presence of tensile stress and a specific corrosive medium. Many investigators have classified

all cracking failures occurring in corrosive mediums as stress corrosion cracking, including

cracking due to hydrogen embrittlement. However, these two types of cracking failures

respond differently to the environment.

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During stress corrosion cracking, metal or alloy is virtually unattacked over most of its

surface, while fine cracks progress through it. The two classic cases of stress corrosion are

season cracking of brass and caustic embrittlement of steel. Both of these obsolete terms

describe the environmental conditions present that led to stress corrosion.

The important variables affecting stress corrosion are temperature, solution composition,

metal composition, stress and metal structure.

The various methods to combat with this type of corrosion are:

1. Lowering the stress below the threshold value if one exists

2. Eliminating critical environmental species

3. Changing the alloy

4. Cathodic protection

5. Inhibitors

6. Coatings

7. Shot-peening.

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Corrosion testing

Thousands of corrosion tests are made every year. The value and reliability of the data

obtained depend on the details involved. Unfortunately, many tests are not conducted or

reported properly, and the information obtained is misleading. Most tests are made with a

certain goal in mind. This may vary from tests designed to teach a student the procedures

involved to the loading of an airplane wing for studying susceptibility of stress corrosion.

Precise results or merely qualitative comparisons may be required. In any case, the reliability

of the test is no better than the thinking and the planning involved. Well planned and

executed tests usually result in reproducibility and reliability. These are the two of the most

important factors in corrosion testing. Corrosion tests, and applications of the results, are

considered to be most important aspect of corrosion engineering.

Many corrosion tests are made to select materials of construction for equipment in process

industries. It is very important for the tests to duplicate the actual plant service conditions as

closely as possible. The greater the deviation from plant conditions the less reliable is the test.

Classification: Corrosion testing is classified into 4 types: 1. Laboratory tests, including

acceptance or qualifying tests, 2. Pilot plant or semi-works tests, 3.plant or actual service

tests, 4. Field tests. The last two could be combined but to avoid confusion in terminology the

following distinction is made: the third involves tests in a particular service or a given plant,

whereas, the fourth involves field tests designed to obtain more general information.

Examples of field tests are atmospheric exposure of a large number of specimens in racks at

one or more geographical locations and similar tests in soils and seawater.

Lab tests are characterized by small specimens and small volumes of solution, and actual

conditions are stimulated as possible. The best that can be done in this regard is the use of

actual plant solutions or atmosphere. Lab tests serve a most useful function as screening tests

to determine which materials warrant further investigations. Sometimes plants are primarily

built on lab tests, but results could be catastrophic and sometimes are.

Pilot-plant tests are usually the best and most desirable. Here the tests are made in a small

scale plant that duplicates the large scale operation. Actual raw materials, concentrations,

temperatures, velocities and volume of liquor to area of metal exposed are involved. Pilot

plants usually run long enough to ensure good results. Specimens can be exposed in the pilot

plants, and the equipment itself is studied from corrosion viewpoint. One possible

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disadvantage is that conditions of operation may be widely varied in attempting to determine

optimum operation. This means careful logging and keeping of thorough records.

Purposes: Perhaps the main justifications for corrosion testing are:

1. Evaluation and selection of materials for a specific environment or a given definite

application. This could be new or modified plant or process where previous operating

history is not available.

It could involve an old plant process that is to be replaced or expanded with more

economical materials that would exhibit less contamination of product, improved

safety, more convenient design and fabrication or substitution of less strategic

materials.

2. Evaluation of new or old metals or alloys to determine the environments in which

they are suitable. Much of this type of work is done by producers and vendors of

materials. The information obtained aids in the selection of material to be tested for a

specific application. Inclusion of tests on others which are known to be of commercial

use in these environments permits helpful comparisons. In the case of new metals and

alloys, the data obtained provides information concerning possible applications. This

category could also include the effects of changes in environment such as additions of

inhibitors or deaereation on the corrosion of metals and alloys.

3. Control of corrosion resistance of the material or corrosiveness of the environment.

These are usually routine tests to check the quality of the material. The Huey test

(boiling 65% nitric acid) is used to check the test treatment of SS. Another example is

, the salt-spray test, where specimens are exposed in a box or cabinet containing a

spray or a fog of seawater or salt water. This type of test is often used for checking or

evaluating paints or electroplated parts. These tests may not be directly related to the

intended services but are sometimes incorporated in specifications in acceptance tests.

In some cases periodic testing is required to determine the changes in the

aggressiveness of the environment because of the operating changes such as

temperature, process raw materials, changes in concentrations of solutions or other

changes that are often regarded as insignificant from corrosion standpoint by

operating personnel.

4. Study of the mechanisms of corrosion or other research and development purposes.

These tests involve specialized techniques, precise measurements, and very close

control.

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Corrosion prevention

Five different main principles can be used to prevent corrosion:

1. Appropriate materials selection

2. Change of environment

3. Suitable design

4. Electrochemical, i.e. cathodic and anodic protection

5. Application of coatings

Material Selection: The most common method of preventing corrosion is the selection of the

proper metal or alloy. Since this is the most important method of preventing and reducing

corrosion. In alloy selection there are several natural metal-corrosive combinations. These

combinations of metal and corrosive usually represent the maximum amount of corrosion

resistance for the least amount of money. Some of these natural combinations are:

1. SS - nitric acid

2. Ni and nickel alloys – caustic

3. Monel – hydrofluoric acid

4. Lead – dilute sulphuric acid

5. Tin – distilled water

6. Steel – conc. Sulphuric acid

In many instances, cheaper materials or more resistant materials are available. For

example, Tin or tin coatings are almost always chosen as a container or piping material

for distilled water.

In terms of metal purification, the corrosion resistance of a pure metal is usually better

than one with impurities. However, pure metals are expensive and are soft and weak. In

general this category is used only for special cases. For example, Al is not that expensive

and can be used in a pure state- 99.5% and is commercially used for handling hydrogen

peroxide.

In non-metallic category, these involve integral or solid non-metallic construction and

also sheet linings or covering. The five general classes here are: 1.rubbers, natural and

synthetic, 2. Plastics, 3.ceramics, 4.carbon and graphite, 5.wood.

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Alteration of environment: Altering the environment provides a versatile means for

reducing corrosion. Typical changes in the medium that are often employed are:

1.lowering temperature, 2.decreasing velocity, 3.removing oxygen or oxydizers,

4.changing concentrations. In many cases, these changes can significantly reduce

corrosion, but they must be done with care.

Inhibitor: An inhibitor is a substance that, when added in small concentrations to an

environment, decreases the corrosion rate. In a sense, it can also be called as retarding

catalyst. There are numerous types of inhibitors and compositions. Most of them have

been developed through experimentation, and many have a proprietary nature and thus

their composition is not disclosed.

The adsorption type inhibitors represent the largest class of inhibiting substances. In

general, these are organic compounds which adsorb on the metal surface and suppress the

metal dissolution and reduce reactions. In most cases, it appears that adsorption inhibitors

affect both the anodic and cathodic processes although in many cases the effect is

enequal. Typical of this class are the organic amines.

The hydrogen evolution poisons are substances such as arsenic and antimony ions,

specifically retarding the hydrogen evolution reaction. But are ineffective in where other

reduction processes such as oxygen reduction are the controlling cathodic reactions.

Scavengers are the substances which act by removing corrosive reagents from solution.

Eg, sodium sulphate and hydrazine. Oxidizers such as chromate nitrate and ferric salts are

primary used to inhibit the corrosion of metals and alloys that demonstrate active-passive

transitions, such as iron and its alloys.

Design: The design of the structure is frequently as important as the choice of materials.

Design should consider mechanical and strength requirements together for an allowance

for corrosion. Some of the design rules that should be followed are:

1. Welding rather than riveting

2. Designing tanks and other containers for easy drainage and cleaning

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3. Avoiding electrical contact between dissimilar metal

4. Avoiding sharp bends in piping systems when high velocities and suspension is

involved.

5. Make sure that the materials are properly selected

6. Be sure that all the codes and standards are met.

7. Properly design against excessive vibration

8. Avoiding hot spots

9. Design to exclude air

10. The most basic rule: avoid heterogeneity

Cathodic protection: Cathodic protection was employed before the science of

electrochemistry had been developed. Humphrey Davy used cathodic protection on British

ships in 1824. The principles of cathodic protection may be explained by considering the

corrosion of a typical metal M in an acid environment. Electrochemical reactions occurring

are the dissolution of the metal and the evolution of hydrogen gas,; for Eg,

M → Mn+ + ne

2H + 2e → H2

Cathodic protection is achieved by supplying electrons to the metal structure to be protected.

Examination of the above eqs. Indicates that the addition to the structure will tend to suppress

metal dissolution and increase the rate of hydrogen evolution. If current is considered to flow

from + to -, as in conventional electrical theory, then a structure is protected if the current

enters the electrolyte.

Conversely, accelerated corrosion occurs if current passes from metal to the electrolyte. This

current convention has been adopted in cathodic protection technology and is used with

consistency. There are two ways to cathodically protect a structure: 1.by external power

supply, 2. by galvanic coupling.

Anodic Protection: In contrast to cathodic protection, anodic is relatively new. It was first

suggested by Edeleaun in 1954. This technique was developed using electrode kinetics

principles and is somewhat difficult to describe without introducing the advanced concepts of

electrochemical theory. Simply it’s based on the formation of protective films on metals by

externally applied anodic currents. Anodic protection can decrease corrosion rate

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substantially. The primary advantage of this is its applicability in extremely corrosive

environments and its low current requirements.

Coatings: Protective coatings are probably the most widely used products

for corrosion control. They are used to provide long-term protection under

a broad range of corrosive conditions, extending from atmospheric

exposure to the most demanding chemical processing conditions.

Protective coatings in themselves provide little or no structural strength,

yet they protect other materials to preserve their strength and integrity.

The main function of a protective coating is to isolate structural reactive

elements from environmental corrosives. The fact that protective coatings

occupy only a very small fraction of the total volume of a system is quite

telling of the heavy requirements imposed on these materials. A coating

must provide a continuous barrier to a substrate, and any imperfection

can become the focal point for degradation and corrosion of the substrate.

Metal finishing comprises a wide range of processes that are practiced by

most industries engaged in manufacturing operations using metal parts.

Typically, metal finishing is performed on manufactured parts after they

have been shaped, formed, forged, drilled, turned, wrought, cast, and so

forth. A finish can be defined as any final operation applied to the surface

of a metal article to alter its surface properties and achieve various goals.

The quality of a coating depends on many factors besides the nature of

the materials involved. Metal finishing operations are intended to increase

corrosion or abrasion resistance, alter appearance, serve as an improved

base for the adhesion of other materials, enhance frictional

characteristics, add hardness, improve solder ability, add specific

electrical properties, or improve the utility of the product in some other

way.

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Cost and future of corrosion

In a recent study by Houston based NACE international, it is found that the cost of corrosion

in India is about 36,000 cr.

An estimate of the annual cost of corrosion in US varies between 8 – 126 billion. It is

believed that 30 billion is the most realistic figure. In any of these cases, corrosion represents

a tremendous economic loss and much can also be done to reduce it. These larger figures in

money are not surprising when we consider that corrosion occurs, with varying degrees of

severity, wherever metals and other materials are used.

According to the Wall Street Journal cost to oil and gas producers is nearly 2 billion. Also

costs are increasing due to deeper wells and more hostile environments—higher temperatures

and corrosive sulphur gases.

Corrosion of bridges is also a major problem as they age and require replacement, which

costs billions. The petroleum industry spends millions everyday to protect underground

pipelines. The paper industry estimates corrosion, as increases the cost of paper by 6 to 7

dollar per ton. Corrosion costs of automobiles-fuel systems, radiators-are in billions.

Approximately 3 million home heaters are changed every year. Corrosion touches all – inside

and outside home, on the road, on the sea, in the plant and in aerospace vehicles.

Although corrosion is inevitable, its cost can be considerably reduced. For example, an

inexpensive magnesium anode could double the life of a domestic hot water tank. Washing a

car to remove road deicing salts is helpful. Proper selection of materials and good design

reduces the costs of corrosion. A good maintenance painting programs pays for itself many

times. Here is where the corrosion engineer enters the picture and is effective- his or her

primary function is to combat corrosion.

Examples of Catastrophic Corrosion Damage:

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Sewer explosion, Mexico

An example of corrosion damages with shared responsibilities was the sewer explosion that

killed over 200 people in Guadalajara, Mexico, in April 1992.6 Besides the fatalities, the

series of blasts damaged 1600 buildings and injured 1500 people. Damage costs were

estimated at 75 million U.S. dollars. The sewer explosion was traced to the installation

of a water pipe by a contractor several years before the explosion that leaked water on a

gasoline line laying underneath. The subsequent corrosion of the gasoline pipeline, in turn,

caused leakage of gasoline into the sewers. The Mexican attorney general sought negligent

homicide charges against four officials of Pemex, the government-owned oil

company. Also cited were three representatives of the regional sewer

system and the city’s mayor.

The Aloha aircraft incident

The structural failure on April 28, 1988, of a 19-year-old Boeing 737, operated by Aloha

airlines, was a defining event in creating awareness of aging aircraft in both the public

domain and in the aviation community. This aircraft lost a major portion of the upper

fuselage near the front of the plane in full flight at 24,000 ft.8 miraculously, the pilot

managed to land the plane on the island of Maui, Hawaii. One flight attendant was swept to

her death. Multiple fatigue cracks were detected in the remaining aircraft structure, in the

holes of the upper row of rivets in several fuselage skin lap joints. Lap joints join large panels

of skin together and run longitudinally along the fuselage. Fatigue cracking was not

anticipated to be a problem, provided the overlapping panels remained strongly bonded

together. Inspection of other similar aircraft revealed disbonding, corrosion, and cracking

problems in the lap joints. Corrosion processes and the subsequent buildup of voluminous

corrosion products inside the lap joints, lead to “pillowing,” whereby the faying surfaces are

separated. Special instrumentation has been developed to detect this dangerous condition.

The aging aircraft problem will not go away, even if airlines were to order unprecedented

numbers of new aircraft. Older planes are seldom scrapped, and the older planes that are

replaced by some operators will probably end up in service with another operator. Therefore,

safety issues regarding aging aircraft need to be well understood, and safety programs need to

be applied on a consistent and rigorous basis.

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The MV KIRKI

Another example of major losses to corrosion that could have been prevented and that was

brought to public attention on numerous occasions since the 1960s is related to the design,

construction, and operating practices of bulk carriers. In 1991 over 44 large bulk carriers

were either lost or critically damaged and over 120 seamen lost their lives.9 A highly visible

case was the MV KIRKI, built in Spain in 1969 to Danish designs. In 1990, while operating

off the coast of Australia, the complete bow section became detached from the vessel.

Miraculously, no lives were lost, there was little pollution, and the vessel was salvaged.

Throughout this period it seems to have been common practice to use neither coatings nor

cathodic protection inside ballast tanks. Not surprisingly therefore, evidence was produced

that serious corrosion had greatly reduced the thickness of the plate and that this, combined

with poor design to fatigue loading, were the primary cause of the failure. The case led to an

Australian Government report called “Ships of Shame.” MV KIRKI is not an isolated case.

There have been many others involving large catastrophic failures, although in many cases

there is little or no hard evidence when the ships go to the bottom.

Future:

The future will place greater and greater demands on corrosion engineers. They must meet

the challenge with their expertise and must exercise ingenuity to solve new problems. Energy

considerations, Material shortages, and political aspects are the relatively new complicating

factors. The abnormal conditions of today will be normal tomorrow. In the past, there has

been an emphasis on the development of bigger and better alloys and other materials, in the

future, acceptable substitutes may be emphasized. For example, a Fe-6Cr-6Al alloy might be

used instead of 18Cr-8Ni where the full corrosion resistance of the latter is not essential. New

research tools are now available and better ones will be available later to aid in the study and

understanding of corrosion and its prevention. Closer collaboration between corrosion

engineers and corrosion scientists is a must.

Closer collaboration between corrosion engineers and design engineers is also must. The

corrosion engineer must be part of the team from the beginning of the project. He or she

should sign off drawings and specifications. The corrosion and design engineers must

understand fracture mechanics and also inspection techniques.

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A large number of plants using corrosive processes will be built in the future. These include

coal conservation power, refineries, synthetic fuel plants, oil and gas wells, thousands of

miles of pipelines, and many other process plants. The number of environmental control

systems will mushroom at great cost. In many cases, corrosion problems may increase.

Now-a-days, there is a great clamour for universities and colleges to provide training in the

field of corrosion. The best way to combat corrosion and to reduce its costs is to have more

practicing corrosion engineers. The prospects are interesting and rewarding career holds for a

corrosion engineer.

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Conclusion

During the preparation of this Seminar Report, I got to know a lot about corrosion then I did

before. The knowledge about its forms, testing and prevention has proved to be very useful to

me.

Corrosion may be destructive but I feel, given the right awareness and producing more

Corrosion Engineers, corrosion can be curbed, or atleast reduced in such a way which would

benefit mankind strategically and economically.

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References

Mars Guy Fontana(2005), corrosion engineering, 3rd edition, New York, Tata

McGraw Hill Companies, ISBN-13: 978-0-07-060744-6

Pierre Roberge(2000), Handbook of Corrosion Engineering, New York, Tata McGraw

Hill Companies, ISBN : 0-07-076516-2

The financial express website, article on cost of corrosion in India