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Port-said University
Faculty of science
Chemistry department
An introduction in Bio-Corrosion
and its prevention methods
(Microbial-induced corrosion)
Under supervision:
Dr: Samir Abd-Elhady
Prepared by:
Amany Shalaby Abdo Shalaby
Student in 4th year
Biochemistry department
2015-2016
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Acknowledgment In the name of Allah,,,,
Firstly, all thanks to Allah almighty for his generosity in
completing this project.
I wish to express my deepest gratitude to my parents, my
sister and my brothers for their endless love, prayers and
encouragement.
I would like to express my special thanks and sincere gratitude
to Dr/ Samir Abd-Elhady
For his encouragement, valuable advice and for his
constructive guidance that he kindly offered throughout the
development of this research.
And thanks to Dr/Ibrahim Mohiee, Head of Department of
Chemistry.
Finally, all my thanks to my friends for their encouragement
and being beside me all the times.
With my best wishes
Amany Shalaby Abdo
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Table of content
Contents
Introduction ....................................................................................................... 5
The importance of corrosion studies.............................................................................................................. 7
Definitions of corrosion ........................................................................................................................................... 13
Mechanism of corrosion: ......................................................................... 18
Corrosion of metals by non-electrolytes: ........................................................ 19
Corrosion of metals in the presence of electrolytes: ....................................... 19
Potential–pH Diagrams: .................................................................................. 26
Forms of Corrosion: .................................................................................... 31
General (Uniform) corrosion ........................................................................... 32
Galvanic corrosion........................................................................................... 32
Crevice corrosion ............................................................................................ 32
Pitting corrosion .............................................................................................. 33
Erosion corrosion ............................................................................................ 34
Stress corrosion cracking................................................................................. 34
selective leaching ............................................................................................ 34
Liquid metal attack .......................................................................................... 35
Filiform corrosion ............................................................................................ 35
Biological Corrosion: ................................................................................... 36
Mechanism of biological corrosion ................................................................. 42
Sulfate Reducing Bacteria (SRB) ...................................................................... 44
Iron Reducing Bacteria (IRB) ........................................................................... 50
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Prevention of biological corrosion: ..................................................... 51
Selection and Modification of Environment .................................................... 51
Microbial Inhibitors ......................................................................................... 52
Protective Coating: .......................................................................................... 52
Cathodic Protection: ....................................................................................... 53
Protective films ............................................................................................... 53
Use of biocides ................................................................................................ 53
Material change or modification and mechanical methods ............................ 54
Corrosion Science and Corrosion Technology ................................ 55
Reference……………………………………………………………………………………………….………56
5
Introduction
Materials technology is a very vital part of modern technology. Technological
development is often limited by the properties of materials and knowledge about
them. Some properties, such as those determining corrosion behavior, are most
difficult to map and to control.
Corrosion is a disease to materials just like a disease to human beings. Some forms
of corrosion can be prevented through good practices in materials selection and
design, while others can be cured or controlled if diagnosed early.
Corrosion diagnosis involves a number of destructive and non-destructive
inspection and examination techniques such as visual inspection, chemical,
electrochemical, mechanical, metallurgical, and microstructural tests and analyses.
In a modern business environment, successful enterprises cannot tolerate major
corrosion failures, especially those involving personal injuries, fatalities,
unscheduled shutdowns and environmental contamination. For this reason
considerable efforts are generally expended in corrosion control at the design stage
and in the operational phase.
This research discusses fundamentals of corrosion, Mechanism, and forms focuses
on microbial-induced corrosion (MIC) of metallic materials as an introduction
to the recognition, management, and prevention of microbiological corrosion.
Ever since man began recovering metals from their ores and placing them in soil
or aqueous environments, organisms have undoubtedly played a role in
accelerating their corrosion.
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In 1891, the possibility that microorganisms might exert an influence on the
corrosion of metals was mentioned by Garrett [1]. He postulated that the increase
in the corrosive action of lead could be due to the ammonia, nitrites, and nitrates
produced by bacterial action.
Gaines, in 1910, [2] suggested that the corrosion of iron in the soil and aqueous
environments might be caused by sulfate-reducing, sulfur-oxidizing, and "iron"
bacteria. The formation of deposits in water pipes by iron bacteria was reported by
Ellis [3] and Harder [4] in 1919.
Although corrosion was generally associated with the presence of oxygen, the
process of anaerobic corrosion was encountered several times before 1934.
Convincing evidence that corrosion took place in oxygen-free environments and
that bacteria were responsible for it was provided in 1934 by von Wolzogen Ktihr
and van der Vlugt [5]. They had observed severe corrosion of cast iron water pipes
and mains in communities north of Amsterdam, requiring pipes to be replaced
every 2-3 years. The highly anaerobic soil in which these pipes had been placed
was primarily polder land, land which had been reclaimed from the sea.
7
The importance of corrosion studies: [6, 7]
1-Safety:
Premature failure of bridges structures or Failure of operating equipment due to
corrosion can result in human injury or even loss of life. Sudden failure can cause
fire, explosion, release of toxic product, and construction collapse.
2-Conservation:
Applied primarily to raw material metallic resources, the world’s supply of which
is limited, and the wastage of which includes corresponding losses of energy and
water resources accompanying the production and fabrication of metal structures.
Additional human energy and resources are also consumed in the replacement and
redesign of corroded equipment and components.
3-Economic:
Corrosion is not only dangerous, but also costly, with annual damages in the billions of
dollars including the reduction of material losses resulting from the wasting away
or sudden failure of piping, tanks, metal components of machines, ships, hulls,
marine, structures…etc. Economic losses can be divided into direct and indirect
losses.
3.1 Direct losses are those losses associated with the direct replacement of
corroded equipment, components, and structures. Also included are those costs,
both of Labor and material, to maintain equipment and structures to prevent
corrosion from taking place or to control the rate of corrosion.
Falling into this category are such items as painting, application of protective
coatings or linings, operating costs for cathodically protected pipelines and
structures, and routine inspections or testing of equipment by online corrosion
monitoring instruments.
8
Other examples of direct losses include the additional costs incurred by the use of
corrosion-resistant metals or alloys instead of less-expensive carbon steel (when
carbon steel has adequate mechanical properties but insufficient corrosion
resistance), by the application of corrosion-resistant coatings to carbon steel, or by
the addition of corrosion inhibitors to water.
3.2 Indirect Losses although the causes of indirect losses can be listed, it would
be extremely difficult to place an actual cost on these losses. However, it would be
safe to assume that these costs would be some multiple of the direct losses. Typical
of these indirect losses are the following examples:
3.2.1 Shutdown:
Unplanned shutdowns because of the failure of equipment resulting from corrosion
lead to loss of production and consequently loss of profit. Although the actual cost
of maintenance work may be minimal, the value of the lost production can be
considerable. If this type of occurrence is frequent, the cost is usually added to the
cost of the product.
3.2.2 Loss of Product:
Many times, corrosion is so severe that leakage will develop that permits loss of
product. If this leakage occurs in a pipeline, it may go undetected for an extended
period, during which time there is a continuous loss of product. For example, from
a container that has corroded through. If the leaking material itself is a corrosive
material, it will attack its surroundings, thus causing additional loss. There have
also been cases where leakage from underground tanks, such as gasoline, has
contaminated the soil and even in some cases made the water in wells unsuitable
for use.
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3.2.3 Contamination:
During the corrosion of a metal, the fluid being transported, stored, processed, or
packaged in a metallic component can pick up metallic salts. This metallic pick-
up can be detrimental to the product; with soap products a shortened shelf life, with
dyes a color alteration, and in some cases of intermediate products the inability to
carry out succeeding process steps. For many years, lead pipes were used to
transport water until it was determined that the lead pick-up in the water caused
lead poisoning in humans.
3.2.4 Environmental Damage:
Corrosion of equipment used to control atmospheric pollution resulting from
processing operations can result in a decrease in efficiency. Such a decrease
permits pollutants from the manufacturing operation to enter the atmosphere.
3.2.5 Loss of Efficiency:
Corrosion in a piping system can result in the buildup of a scale. This scale can
cause a reduction in heat transfer as well as an increase in the power required to
pump the fluid through the system. The efficient operation of other mechanical
equipment can also be reduced by corrosion. This reduction in efficiency can cause
an increase in operating costs as well as result in increased fuel consumption,
lubricant loss, and reduced work output.
3.2.6 Overdesign:
In many instances when the corrosive effect of the system is known, additional
thicknesses of vessel shells will be provided for in the design. This is known as
corrosion allowance. Because this thickness is in addition to that required for the
design conditions, an extra cost is involved. In some instances, the actual corrosive
effect is not known and consequently, for safety reasons, a much thicker shell
results.
10
Still other consequences are social. These can involve the following issues:
*Health:
For example, pollution due to escaping product from corroded equipment or due to a
corrosion product itself.
*Depletion of natural resources:
Including metals and the fuels used to manufacture them.
*Appearance:
As when corroded material is unpleasing to the eye.
Of course, all the preceding social items have economic aspects also. Clearly, there are
many reasons for wanting to avoid corrosion.
11
GDP: Gross Domestic Product
Cost of corrosion Estimate for 2013 by G2MT Labs
12
Premature failure of bridges or structures due to corrosion can result in human
injury or even loss of life.
Corrosion can result in loss of products.
13
Definitions of corrosion:
Corrosion can be defined in many ways[8]. Some definitions are very narrow and
deal with a specific form of corrosion, while others are quite broad and cover many
forms of deterioration. The word corrode is derived from the Latin corrodere,
which means “to gnaw to pieces.” The general definition of corrode is to eat into
or wear away gradually, as if by gnawing. For purposes here, corrosion can be
defined as a chemical or electrochemical reaction between a material, usually a
metal, and its environment that produces a deterioration of the material and its
properties.
Corrosion is the deterioration or destruction of metals and alloys in the presence
of an environment by chemical or electrochemical means.
In simple terminology, corrosion processes involve reaction of metals with
environmental species.
As per IUPAC, “Corrosion is an irreversible interfacial react ion of a material
(metal, ceramic, polymer) with its environment which results in its consumption
or dissolution into the material of a component of the environment. Often, but not
necessarily, corrosion results in effects detrimental to the usage of the material
considered. Exclusively physical or mechanical processes such as melting and
evaporation, abrasion or mechanical fracture are not included in the term
"corrosion".With the knowledge of the role of various microorganisms present in
soil and water bodies, the definition for corrosion need be further widened to
include microbially influenced factors.
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Corrosion is a natural process. Just like water flows to the lowest level, all natural
processes tend toward the lowest possible energy states. Thus, for example, iron and
steel have a natural tendency to combine with other chemical elements to return to their
lowest energy states. In order to return to lower energy states, iron and steel frequently
combine with oxygen and water, both of which are present in most natural environments,
to form hydrated iron oxides (rust), similar in chemical composition to the original iron
ore. The following Figure illustrates the corrosion life cycle of a steel product.
All metallic materials consist of atoms having valiancy electrons which can be donated
or shared. In a corrosive environment the components of the metallic material get ionized
and the movement of the electrons sets up a galvanic or electrochemical cell which
causes oxidation, reduction, dissolution or simple diffusion of elements.
The metallurgical approach of corrosion of metals is in terms of the nature of the alloying
characteristics, the phases existing and their inter-diffusion under different
environmental conditions.
15
In fact, the process of corrosion is a complex phenomenon and it is difficult to predict
the exclusive effect or the individual role involved by any one of the above mentioned
processes.
Based on the above processes, corrosion can be classified in many ways such as:
Chemical and electrochemical.
High temperature and low temperature.
Wet corrosion and dry corrosion.
Chemical corrosion in which the metal is converted into its oxide when the metal is
exposed to a reactive gas or non-conducting liquids.
Electrochemical corrosion the formation of hydrous oxide film occurs when the metal
is immersed in a conducting liquid containing dissolved reactive substance. The
reaction is considered to take place at the metal solution interface, due to the
heterogeneity on the metal surface, which creates local anodic and cathodic sites on
the metal.
Environmental effects such as those of presence of oxygen and other oxidizers,
changes in flow rates (velocity), temperature, reactant concentrations and pH
would influence rates of anodic and cathodic reactions.
Dry corrosion occurs in the absence of aqueous environment, usually in the
presence of gases and vapours, mainly at high temperatures.
Electrochemical nature of corrosion can be understood by examining zinc
dissolution in dilute hydrochloric acid.
Zn + 2HCl = ZnCl2+ H2
Anodic reaction is Zn = Zn+++ 2e with the reduction of 2H++ 2e = H2 at
cathodic areas on the surface of zinc metal. There are two half reactions
constituting the net cell reaction.
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Basic Causes of Corrosion
Conditions necessary for corrosion [9]:
For the purpose of this manual, electrochemical corrosion is the most important
classification of corrosion. Four conditions must exist before electrochemical
corrosion can proceed:
1- There must be something that corrodes (the metal anode).
2- There must be a cathode.
3- There must be continuous conductive liquid path (electrolyte, usually
Condensate and salt or other contaminations).
4- There must be a conductor to carry the flow of electrons from the anode to the
cathode. This conductor is usually in the form of metal-to-metal Contact such
as in bolted or riveted joints.
The elimination of any one of the four conditions will stop corrosion.
Effect of material selection
One of the fundamental factors in corrosion is the nature of the material.
Materials are usually selected primarily for structural efficiency, and corrosion
resistance is often a secondary consideration in design.
Water intrusion
Water intrusion is the principal cause of corrosion problems encountered in the
field use of equipment. Water can enter an enclosure by free entry, capillary action,
or condensation. With these three modes of water entry acting and with the
subsequent confinement of water, it is almost certain that any enclosure will be
susceptible to water intrusion.
17
Environmental factors
The environment consists of the entire surrounding in contact with the material.
The primary factors to describe the environment are the following:
(a) Physical state—gas, liquid, or solid.
(b) Chemical composition—constituents and concentrations.
(c) Temperature.
At normal atmospheric temperatures the moisture in the air is enough to start
corrosive action. Oxygen is essential for corrosion to occur in water at ambient
temperatures. Other factors that affect the tendency of a metal to corrode are:
1- Acidity or alkalinity of the conductive medium (pH factor).
2- Stability of the corrosion products.
3- Biological organisms (particularly anaerobic bacteria).
4- Variation in composition of the corrosive medium.
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Mechanism of corrosion:
Particularly under the broad definition of corrosion as the deterioration of
materials by reaction with the environment, the number of mechanisms whereby
deterioration occurs is large.
What do we mean by “mechanism of corrosion reaction” [10]?
We mean the behavior of a metal, or the way a metal reacts with an environment.
This behavior may be simple and consist of one stage, for example, corrosion of
iron in the oxygen atmosphere at high temperature.
The corrosion reaction may be more complicated and consist of two and more
stages, for example, when iron comes into contact with water or with hydrochloric
acid. If two dissimilar metals, iron and zinc, contact together in salt water or metal
are under stress in some environment, the corrosion reaction may be more
complicated.
In corrosion, of course, this rate should be as slow as possible. Because these
processes cannot be observed directly on an atomic scale, it is necessary to infer
possible mechanisms from indirect measurements and observations.
In general, a mechanism of corrosion is the actual atomic, molecular, or ionic
transport process that takes place at the interface of a material. These processes
usually involve more than one definable step, and the major interest is directed
toward the slowest step that essentially controls the rate of the overall reaction.
All corrosion reactions are described by two mechanisms:
1. Non-Electrolytes (without the formation of electric current).
2. Electrolytes (with the formation of electric current and potential).
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*Corrosion of metals by non-electrolytes: Non-electrolytes exist in gaseous (O2, Cl2), liquid (Br2) and solid (sugar) states. If
metals come into contact with any dry gas or liquid non-electrolyte, corrosion
(chemical reaction) occurs in one stage. Metals give their outer electrons to non-
metals (O2, Cl2, Br2 or S8) and are oxidized in one reaction:
2Fe (s) + 3Cl2 (g) 2FeCl3 (s)
2Fe (s) + 3Br2 (l) 2FeBr3 (s)
8Fe(s) + S8 (l) 8FeS (s)
Metals contacting with non-electrolytes do not have electric potential at their
surfaces. Usually, such corrosion reactions occur under dry conditions:
without water or, more precisely, without electrolyte. Characteristic feature
of this corrosion mechanism is the absence of electric current and electric
potential on the metal surface during corrosion.
*Corrosion of metals in the presence of electrolytes: Electrochemical corrosion is a process occurring between a metal and the
electrolyte environment not in one electrochemical reaction, and the
corrosion rate depends on the electric potential on the metal surface.
1-Anodic Reactions:
The loss of metal occurs as an anodic reaction. Examples are:
Where the notations (s), (aq), and (l) refer to the solid, aqueous, and liquid phases,
respectively.
20
Each of the above reactions in equations. (1), (2), and (3) is an anodic reaction
because of the following:
(1) A given species undergoes oxidation, i.e., there is an increase in its
oxidation number.
(2) There is a loss of electrons at the anodic site (electrons are produced by
the reaction).
The following reaction is also an anodic reaction:
The oxidation number of the Fe species on the left, i.e., in the ferrocyanate
ion, is +2, and the oxidation number of Fe in the ferricyanate ion on the right
is +3. Thus, there is an increase in oxidation number. In addition, electrons
are produced in the electrochemical half-cell reaction, so Eq. (4) is an anodic
reaction.
By the same reasoning the following is also an anodic reaction:
Although Eqs. (4) and (5) are anodic reactions, they are not corrosion
reactions. There is a charge transfer in each of the last two equations, but not
a loss of metal. Thus, not all anodic reactions are corrosion reactions. This
observation allows the following scientific definition of corrosion:
“Corrosion is the simultaneous transfer of mass and charge across a
metal/solution interface.”
21
2- Cathodic Reactions:
An example of a cathodic reaction is the reduction of two hydrogen ions at a
surface to form one molecule of hydrogen gas:
This is an anodic reaction because of the following:
(1) A given species undergoes reduction, i.e., there is a decrease in its
oxidation number.
(2) There is a gain of electrons at the cathodic site (electrons are consumed
by the reaction).
------------------------------------------------------------------------------
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3- Coupled Electrochemical Reactions:
On a corroding metal surface, anodic and cathodic reactions occur in a
coupled manner at different places on the metal surface. The behavior for an
iron surface immersed in an acidic aqueous environment. At certain sites on
the iron surface, iron atoms pass into solution as Fe2+ ions. The two electrons
produced by this anodic half-cell reaction are consumed elsewhere on the
surface to reduce two hydrogen ions to one H2 molecule.
The reason that two different electrochemical half-cell reactions can occur on
the same metal surface lies in the heterogeneous nature of a metal surface.
Polycrystalline metal surfaces contain an array of site energies due to the
existence of various crystal faces (i.e., grains) and grain boundaries. In
addition, there can be other defects such as edges, steps, kink sites, screw
dislocations, and point defects.
23
Moreover, there can be surface contaminants due to the presence of impurity
metal atoms or to the adsorption of ions from solution so as to change the
surface energy of the underlying metal atoms around the adsorbate.
"Figure illustrates the coupled electrochemical reactions for an iron surface immersed in a neutral or a
basic aqueous solution.”
Metal atoms at the highest energy sites are most likely to pass into solution.
These high-energy sites include atoms located at the edges and corners of
crystal planes, for example. Stressed surfaces also contain atoms that are
reactive because they have a less stable crystalline environment.
When a metal is cold worked or shaped, the metal lattice becomes strained,
and atoms located in the strained regions tend to go into solution more readily
than do atoms in unstrained regions. Once the process of metal dissolution
process begins, a new energy distribution of sites is established. Then, the
positions of anodic and cathodic surface sites change randomly with time so
that the overall effect is uniform corrosion of the metal.
24
The overall chemical reaction is thus the sum of the two half-cell reactions:
At the local anodes Fe (s) → Fe2+ (aq) + 2e−
At the local cathodes 2H+ (aq) + 2e− → H2 (g)
The overall reaction is the sum of these two half-cell reactions:
Fe (s) + 2H+ (aq) → Fe2+
(aq) + H2 (g)
An electrolyte is a solution which contains dissolved ions capable of
conducting a current. The most common electrolyte is an aqueous solution,
i.e., water containing dissolved ions; but other liquids, such as liquid
ammonia, can function as electrolytes.
Electrochemical Polarization:
Electrochemical polarization (usually referred to simply as “polarization”) is
the change in electrode potential due to the flow of a current. There are three
types of polarization [11]:
(1) Activation polarization is polarization caused by a slow electrode
reaction.
(2) Concentration polarization is polarization caused by concentration
changes in reactants or products near an electrode surface.
(3) Ohmic (resistance) polarization is polarization caused by IR drops in
solution or across surface films, such as oxides (or salts).
The degree of polarization is defined as the over voltage (or over potential) η
given by the following equation:
Where E is the electrode potential for some condition of current flow and Eo
is the electrode potential for zero current flow.
25
Anodic and Cathodic Polarization:
Either an anode or a cathode can be polarized:
Anodic polarization is the displacement of the electrode potential in the
positive direction so that the electrode acts more anodic.
Cathodic polarization is the displacement of the electrode potential in the
negative direction so that the electrode acts more cathodic.
26
Potential–pH Diagrams:
Potential–pH diagrams, also known as Pourbaix diagrams [12], are graphical
representations of the stability of a metal and its corrosion products as a
function of the potential and pH (acidity or alkalinity) of the aqueous solution.
PH is an important variable of aqueous solutions, and it affects the
equilibrium potentials of a majority of the possible reactions that can occur.
On this basis, Marcel Pourbaix derived and presented his pH potential
diagrams, also called “equilibrium diagrams” because these diagrams apply
to conditions where the metal is in equilibrium with its environment. These
diagrams have become an important tool for the illustration of the
possibilities of corrosion. Pourbaix diagrams are available for over 70
different metals.
These diagrams indicate certain regions of potential and pH where the metal
undergoes corrosion and other regions of potential and pH where the metal is
protected from corrosion.
*In a Pourbaix diagram, there are three possible types of straight lines:
1-Horizontal lines, which are for reactions involving only the electrode
potential E (but not the pH).
2-Vertical lines, which are for reactions involving only the pH (but not the
electrode potential E).
3-Slanted lines, which related to reactions involving both the electrode
potential E and the PH. Pourbaix diagrams also contain regions or fields
between the various lines where specific chemical compounds or species are
thermodynamically stable.
27
*Pourbaix diagram regions:
1-When the stable species is a dissolved ion, the region on the Pourbaix
diagram is labeled as a region of “corrosion.”
2-When the stable species is either a solid oxide or a solid hydroxide, the
region on the Pourbaix diagram is labeled as a region of “passivity,” in which
the metal is protected by a surface film of an oxide or a hydroxide.
3-When the stable species is the unreacted metal species itself, the region is
labeled as a region of “immunity”.
“Pourbaix diagrams for various metals and metalloids arranged after their nobleness”
28
Example: Potential–pH (Pourbaix) diagram for Fe–H2O system.
“Figure: Pourbaix diagram for Iron”
In the diagram, the horizontal lines represent pure electron transfer reactions
dependent solely on potential, but independent of pH:
1) Fe =Fe2+ + 2e−
2) Fe2+ =Fe3+ + e−
These lines extend across the diagram until the pH is sufficiently high to
facilitate the formation of hydroxides, represented by vertical lines ,thereby
reducing the concentration Fe2+ and Fe3+ ions.
29
The boundary is often set arbitrarily at the concentration of these ions at 10−6
g-ions/liter ,which is indicative of a negligible dissolution or corrosion of the
metal in the medium.
The vertical lines in the Figure correspond to the reactions:
There is no electron transfer involved and the reactions are solely dependent on
pH.
The sloping lines in Figure 2.3 represent equilibria involving both electron
transfer and pH; for example:
The hydrogen and oxygen are also shown in the diagram by the dotted lines.
The hydrogen line represents the equilibria:
2H++ 2e– = H “in acid solutions”
Or
2H2O+2e– = H2+ 2OH– “in neutral or alkaline solutions"
These two reactions are equivalent and their pH dependence of single
electrode potential is represented by:
At pH = 0; that is, for [H+] = 1, EO H+/H2 = 0 and the slope is −0.059V.
Similarly ,for oxygen equilibrium with water the corresponding reactions at
lower and higher pH are:
and
30
The pH dependence of single electrode potential is represented by:
At pH = 0, EO O2 /H2O =1.226 V
and at pH = 1, (i.e., for [OH−] = 1), EO O2 /H2O = 0.401 V.
Here again, the slope of the line is −0.059V. Water is stable in the area
designated by these two lines. Below the hydrogen line it is reduced to
hydrogen gas, and above the oxygen line it is oxidized to oxygen.
The potential–pH diagram shows three clear-cut zones:
1. Immunity zone: Under these conditions of potential and pH, iron remains
in metallic form.
2.Corrosion zone: Under these conditions of potential and pH, iron corrodes ,
forming Fe2+ or Fe3+ or HFeO2−.
3. Passive zone: Under these conditions of potential and pH, protective layers
of Fe(OH)3 form on iron and further corrosion of iron does not take place.
*Uses of Pourbaix diagram
1. Predicting the spontaneous direction of reactions
2. Estimating the stability and composition of corrosion products.
3. Predicting environmental changes that will prevent or reduce Corrosion.
31
Forms of Corrosion:
Corrosion occurs in several widely differing forms [13]. Classification is
usually based on one of three factors:
*Nature of the corrodent: Corrosion can be classified as “wet” or “dry.”
A liquid or moisture is necessary for the former, and dry corrosion usually
involves reaction with high-temperature gases.
*Mechanism of corrosion: This involves either electrochemical or direct
chemical reactions.
*Appearance of the corroded metal: Corrosion is either uniform and the metal
corrodes at the same rate over the entire surface, or it is localized, in which
case only small areas are affected.
Classification by appearance, which is particularly useful in failure analysis,
is based on identifying forms of corrosion by visual observation with either
the naked eye or magnification. The morphology of attack is the basis for
classification.
Forms of wet (or aqueous) corrosion can be identified based on appearance
of the corroded metal. These are:
General (uniform) corrosion
Galvanic (bi-metallic) corrosion
Crevice corrosion
Pitting corrosion
Erosion corrosion
Stress corrosion cracking
Biological corrosion Selective leaching
Liquid metal attack
Filiform corrosion
32
General (Uniform) corrosion:
It is a very common form found in ferrous metals and alloys that are not
protected by surface coating or inhibitors. A uniform layer of ‟rust‟ on the
surface is formed when exposed to corrosive environments Atmospheric
corrosion is a typical example of this type.
Galvanic corrosion:
Galvanic corrosion is a chemical or an electrochemical corrosion. It is due to
a potential difference between two different metals connected through a
circuit for current flow to occur from more active metal (more negative
potential) to the more noble metal (more positive potential), where the active
one corrodes.
Eg: - Copper containing precipitates in aluminium alloys.
Impurities such as iron and copper in metallic zinc.
Crevice corrosion:
It is a localized attack on a metal adjacent to the crevice between two joining
surfaces (two metals or metal-nonmetal crevices). The corrosion is generally
confined to one localized area to one metal. This type of corrosion can be
initiated by concentration gradients (due to ions or oxygen). Accumulation
of chlorides inside crevice will aggravate damage.
33
Pitting corrosion:
It is a localized phenomenon confined to smaller areas. Formation of micro-
pits can be very damaging.
In pitting corrosion the surface of the metal is attacked in small-localized
areas. Organisms in water or breaks in a passive film can initiate corrosion.
In pitting corrosion very little metal is removed from the surface but the effect
is marked.
Pitting corrosion is characterized by the following features:
1. The attack is spread over small discrete areas. Pits are sometimes isolated
and sometimes close together, giving the area of attack a rough appearance.
2. Pits usually initiate on the upper surface of the horizontally placed parts
and grow in the direction of gravity.
3. Pitting usually requires an extended initiation period before visible pits
appear.
4. Conditions prevailing inside the pit make it self-propagating without any
external stimulus. Once initiated, the pit grows at an ever-increasing rate.
5. Stagnant solution conditions lead to pitting.
6. Stainless steels, aluminum, and their alloys are particularly susceptible to
pitting. Carbon steels are more resistant to pitting than stainless steels.
34
Erosion corrosion:
The term “erosion” applies to deterioration due to mechanical force.
Erosion is the removal of metal by the movement of fluids against the surface.
Depending on the rate of this movement, abrasion takes place. The
combination of erosion and corrosion can provide a severe rate of corrosion.
This type of corrosion is characterized by grooves and surface patterns having
directionality. Typical examples are: Stainless alloy pump impeller,
Condenser tube walls.
Stress corrosion cracking:
Structural parts subjected to a combination of a tensile stress and a corrosive
environment may prematurely fail at a stress below the yield strength. This
phenomenon is known as environmentally induced cracking (EIC).
selective leaching: The removal of one of the components of an alloy by corrosion is termed
“selective leaching.” Dezincification is the term used to describe the leaching
of zinc from brass, which is the most common example of selective leaching.
The less noble component of an alloy is usually the element that is removed,
such as zinc in brass.
35
Liquid metal attack: Metallic components may come in contact with liquid metal during
operations such as brazing, soldering, or galvanizing and in some applications
such as the use of molten sodium as a coolant in fast-breeding nuclear
reactors.
Liquid metal may corrode the solid metal component or there may be
diffusion-controlled intergranular penetration of liquid metal in the solid
metal.
Filiform corrosion:
It is a special type of crevice corrosion. Metals with semipermeable coatings
or films may undergo a type of corrosion resulting in numerous meandering
threadlike filaments of corrosion beneath the coatings or films.
36
Biological Corrosion:
Biologically influenced corrosion or Microbial-induced corrosion (MIC)
refer to [14] the degradation of metals caused by the activity of living
organisms. Contributing to the corrosion are both micro- and macro-
organisms in a variety of environments, including domestic and industrial
fresh waters, soils, groundwater, seawater, natural petroleum products, and
oil-emulsion cutting fluids.
Macroorganisms: [15] A wide variety (about 2000 species) of larger
organisms, primarily marine plants and animals, have been associated with
the fouling of metals in sea water. The principal fouling animals include:
barnacles, tubeworms, bryozoa (polyzoa), hydroids, mussels, and tunicates
(sea squirts). The principal plants are algae. A series of well-illustrated
catalogues of these organisms is being published under the auspices of the
Organization for Economic Cooperation and Development [16].
Macrobiological organisms are also capable of causing corrosion as well as
fouling. In most cases, fouling presents more of a problem than corrosion.
Because these organisms remain attached to the metal surface, their
accumulation on the bottom of a ship’s hull increases the drag and power
requirement. Such accumulations in heat exchangers impair heat transfer and
fluid flow, while in pipelines they may clog the pipeline as well as impair
fluid flow. The metabolic by-products of these organisms are often acidic and
therefore corrosive. In addition, the anaerobic conditions underneath the
macroorganisms can favor the growth of anaerobic bacteria, which in turn
accelerates the corrosion of the metal.
37
Microorganisms[17] are usually considered to be organisms so small that
they can be seen only with the aid of a light or electron microscope. The term
“microorganism” covers a wide variety of life forms, including bacteria, blue-
green cyanobacteria, algae, lichens, fungi, and protozoa.
All microorganisms may be involved in the bio-deterioration of metals.
They vary greatly in their nutritional requirements and tolerances to heat,
light, pH, oxygen, moisture, etc.
Most of the microorganisms involved in MIC are chemolithotrophs and can
be aerobic – anaerobic, mesophilic – thermophilic, autotrophs -heterotrophs,
acidophilic- neutrophilic and many are slime formers.
Chemotrophs get energy from chemical sources unlike photosynthetic
organisms.
Microorganisms associated with MIC are generally characterized by a
number of features such as: [18]
Small size (few micrometers)
Ubiquitous and omnipotent
Sessile or motile (active or sedentary)
Ability to attach to substrates and grow colonies.
Extremophiles (tolerant to wide range of metal concentrations, acidity,
temperature, pressure, oxygen and lack of oxygen)
Rapid reproduction.
Generate organic and inorganic acids, alkalis, and extracellular
polymeric substances such as proteins and polysaccharides.
Can oxidize or reduce metals and ions.
38
Bacteria are small, unicellular organisms which reproduce by fission.
The cells exist in anyone of three basic shapes: rods, curved or spiral rods,
and spheres. Bacterial cells possess a cell wall, a cytoplasmic membrane,
nuclear material, and various types of inclusion bodies. Surrounding the cell
wall may be a slime layer and often a capsule. Motile bacteria have
appendages known as flagella which usually serve as a means of propulsion
for the cell. In addition, some bacterial cells (primarily certain rod forms)
form an endospore (spore with a cell).There is wide diversity with regard to
their metabolisms. An important feature of microbial life is the ability to
degrade any naturally occurring compound.
They are classified as to their source of metabolic energy as follows:
39
In addition to energy and carbon sources, nitrogen, phosphorus, and trace
elements are needed by microorganisms[19] .
Nitrogen compounds may be inorganic ammonium nitrate as well as
organically bound nitrogen (e.g., amino acids, nucleotides).
With the help of an enzyme called nitrogenase, bacteria are able to fix
nitrogen from atmospheric nitrogen, producing ammonia that is incorporated
into cell constituents.
Phosphorus is taken in as inorganic phosphate or as organically bound
phosphoroxylated compounds such as phosphorus-containing sugars and
liquids. Phosphorus, in the form of adenosine triphosphate (ATP), is the main
energy-storing compound. For many of the metabolic purposes, trace
elements are needed.
Cobalt aids in the transfer of methyl groups from/to organic or inorganic
molecules. Vitamin B12, cobalamin, is involved in the methylation of heavy
metals such as mercury. Iron, as Fe+2or Fe+3 is required for the electron
transport system, where it acts as an oxidizable/reducible central atom in
cytochrome of non hemo-iron-sulfur proteins.
Those organisms living with the amount of oxygen contained in the air are
called aerobes, whereas those that perform their metabolism without any trace
of oxygen are called anaerobes. The latter are able to use bound oxygen
(sulfate, carbon dioxide) or to ferment oxygen compounds.
40
The methods by which microorganisms increase the rate of corrosion of
metals and/or their susceptibility to localized corrosion in an aqueous
environment are:
1. Production of metabolites. Bacteria may produce organic acids, inorganic
acids, sulfides, and ammonia, all of which may be corrosive to metallic
materials.
2. Destruction of protective layers. Organic coatings may be attacked by
various microorganisms, leading to the corrosion of the underlying metal.
3. Hydrogen embrittlement. By acting as a source of hydrogen and/or
through the production of hydrogen sulfide, microorganisms may influence
hydrogen embrittlement of metals.
4. Formation of concentration cells at the metal surface and, in particular,
oxygen concentration cells. A concentration cell may be formed when a
biofilm or bacterial growth develops heterogeneously on the metal surface.
Some bacteria may tend to trap heavy metals such as copper and cadmium
within the extracellular polymeric substance, causing the formation of ionic
concentration cells. These lead to localized corrosion.
5. Modification of corrosion inhibitors. Certain bacteria may convert nitrite
corrosion inhibitors used to protect aluminum and aluminum alloys from
nitrate and ammonia.
6. Stimulation of electrochemical reactors. An example of this type is the
evolution of cathodic hydrogen from microbially produced hydrogen sulfide.
41
Microbial-induced corrosion (MIC) can result from:
1. Production of sulfuric acid by bacteria of the genus Thiobacillus through
the oxidation of various inorganic sulfur compounds; the concentration of
sulfuric acid may be as high as 10 to 12%.
2. Production of hydrogen sulfide by sulfate-reducing bacteria.
3. Production of organic acids.
4. Production of nitric acid.
5. Production of ammonia.
Biologically influenced corrosion does not represent a special form of
corrosion but rather the aggravation of corrosion under environmental
conditions in which corrosion rates are expected to be low.
Corrosive conditions can be developed by living microorganisms as a result
of their influence on anodic and cathodic reactions.
The metabolic activity can directly or indirectly cause deterioration of a metal
by the corrosion process; this activity can:
1. Produce a corrosive environment.
2. Create electrolytic cells on the metal surface.
3. Alter the resistance of surface films.
4. Have an influence on the rate of anodic or cathodic reactions.
5. Alter the environmental composition.
42
Mechanism of biological corrosion: [20]
Microbial corrosion can occur and advance through two main mechanisms.
The first method of microbially enhanced corrosion occurs from
microorganisms producing acidic metabolic by-products or from
microorganisms participating directly in the electrochemical corrosion of the
pipe.
When it is suspected that a material failure was caused by microbial
corrosion, it is reasonable to ask:
“How do we know that the corrosion process was influenced by
microorganisms?”
To address this question, many research groups have attempted to find a
fingerprint of microbially influenced corrosion (MIC).
Despite significant research effort, no such fingerprint characteristic of MIC
has yet been found, and there are good reasons to believe that a universal
mechanism of microbially stimulated corrosion does not exist.
Instead of a universal mechanism, several mechanisms by which
microorganisms affect the rates of corrosion have been described, and the
diversity of these mechanisms is such that it is difficult to expect that a single
unified concept can be conceived to bring them all together.
From what we now understand, and what has been demonstrated by numerous
researchers, accelerated corrosion of metals in the presence of
microorganisms stems from microbial modifications to the chemical
environment near metal surfaces.
43
An important aspect of quantifying mechanisms of microbially influenced
corrosion is to demonstrate how the microbial reactions interfere with the
corrosion processes and, based on this, identify products of these reactions on
the surfaces of corroding metals using appropriate analytical techniques.
The existence of these products, associated with the increasing corrosion rate,
is used as evidence that the specific mechanism of microbially influenced
corrosion is active. There is no universal mechanism of MIC.
Instead, many mechanisms exist and some of them have been described and
quantified better than other. Therefore, it does not seem reasonable to search
for universal mechanisms, but it does seem reasonable to search for evidence
of specific, well-defined microbial involvement in corrosion of metals.
Microorganisms involved in MIC can be generally classified as:
a) Sulfate-reducing bacteria (SRB).
b) Iron-reducing bacteria (IRB).
Because microbial induced corrosion (MIC) gives the appearance of pitting,
it is first necessary to diagnose the presence of bacteria.
44
Sulfate Reducing Bacteria (SRB):
Sulfate-reducing bacteria (SRB) [21] are a group of the most frequent causes
for bio-corrosion. Common SRB include Desulfovibrio, Desulfobacter and
Desulfotomaculum. SRBs can grow in soil, fresh water and seawater
environments and also in stagnant areas. Tolerate pH ranges 5-9.5 .
Oil, gas and shipping industries are seriously affected by SRB activities
(soil and water) due to H2S generation.
They oxidize organic substances to organic acids or CO2, by reduction of
sulfate to hydrogen sulfide which reacts with metals to produce metal
sulfides as corrosion products through anaerobic respiration.
Oxygen depletion at the surface also provides a condition for anaerobic
organisms like sulfate-reducing bacteria to grow. Aerobic bacteria near the
outer surface of the biofilm consume oxygen and create a suitable habitat
for the sulfate reducing bacteria at the metal surface.
Symptoms of SRB-influenced corrosion are hydrogen sulfide (rotten egg)
odor, blackening of waters, and black deposits. The black deposit is
primarily iron sulfide.
One way to limit SRB activity is to reduce the concentration of their
essential nutrients: phosphorus, nitrogen, and sulfate.
“Sulfate reducing bacteria under microscope”
45
Role of SRB in metallic corrosion can be understood by [22]:
a) H2S generation
b) Creation of oxygen concentration cells
c) Formation of insoluble metal sulfides
d) Cathodic depolarization
Characteristics of some sulfate reducing bacteria relevant to MIC are given
in the following Table:
46
Microscopic images from three sulfate-reducing bacteria obtained from sediments of IODP Site U1301.
(A,B) Desulfovibrio aespoeensis strain; (C,D) Desulfovibrio indonesiensis strain; (E,F) Desulfotignum
47
*Corrosion Mechanism Involving sulfate-reducing bacteria (SRB):
Perhaps the best-known mechanism of MIC involves corrosion cells
generated and sustained on steel surfaces by the action of anaerobic SRB.
These organisms reduce sulfate to sulfide in their metabolism and are
commonly found in mixed microbial communities present in soils and natural
waters.
Kuhr and Vluglt [23] proposed the classical theory of cathodic depolarization
of SRB corrosion , it is the main mechanism of SRB corrosion, it is believed
that under hypoxic conditions, SRB cathodic depolarization effect to remove
the hydrogen atoms from the metal surface, so that the corrosion process
continue. Reaction is as follows:
4Fe →4Fe2+ +8e （Anodic reaction)
8H2O→8H+ +8OH-
8H+ + 8e →8H （Cathode reaction）
SO42- + 8H→S2-+ 4H2O （SRB cathodic depolarization）
Fe2+ + S2- → FeS （Corrosion products）
3Fe2+ + 6OH- → 3Fe(OH)2 （Corrosion products）
The total equation is: 4Fe2+ + SO42- + 4H2O→FeS + 3Fe(OH)2 + 2OH-
48
In industrial systems, [24] biodegradable materials, such as some of the
hydrocarbons found in oil and gas operations or susceptible components of
coating materials, can provide a source of nutrients for microbial growth.
Cathodic hydrogen formed on a metal surface by active corrosion or by
cathodic protection (CP) can specifically promote growth of organisms,
including SRB that are able to use hydrogen in their metabolism.
Severe corrosion cells develop as sulfide, produced by the microbial
reduction of sulfate, combines with ferrous ions, released by the corrosion
process, to produce insoluble black iron sulfides:
Consistent with the importance of this corrosion process in industrial
facilities, commercial test kits have been developed for enumerating or
assessing the activity of SRB in operating systems.
“Customers complain relating to offensive odors at isolated points in a distribution system are often
attributable to sulfate-reducing bacteria”
49
This figure illustrates a plausible mechanism base on a galvanic couple
formed between iron and iron sulfide sustained and extended by the active
involvement of SRB. The way in which electrons are transferred from iron
sulfide to the SRB, for example, is not well resolved. It may occur directly or
via formation of cathodic hydrogen, as shown in the previous figure, or by
another reaction involving reduction of H2S.
Typical rates of metal loss for unprotected line pipe steel in an SRB/FeS
corrosion scenario are 0.2 mm/year for general corrosion and 0.7 mm/year
for pitting corrosion, but the corrosion rate observed depends on the
concentration of FeS.
50
Iron Reducing Bacteria (IRB) :
The iron reducing bacteria (IRB) or Fe-reducing bacteria (FeRB) [25] can grow
either in cold temperatures or in mesophilic and thermophilic conditions.
The iron reducers prefer neutral PH, present in water, with oxygen.
In natural systems, Fe+3 minerals can be microbiologically reduced by strictly
aerobic iron-reducing bacteria (IRB) using a wide range of organic
compounds as electron donors or by using H2.
The role of iron reducing bacteria in MIC is so inseparable from the role of
oxygen. iron bacteria has the capable of oxidation of Fe2+ to Fe3+ ions and use
energy to grow, eventually form Fe(OH)3 precipitation.
Studies suggest that[26], iron bacteria mainly take part in the corrosion in the
form of corrosion scale and in a short time to produce a large number of iron
oxide deposition. The corrosion of iron bacteria occurs through the crevice
corrosion mechanism.
2Fe → 2Fe2+ + 4e （Anodic reaction）
O2+ 2H2O + 4e → 4OH– （Cathode reaction）
2Fe2+ + 4OH– → 2Fe(OH)2 （Corrosion products）
4Fe(OH)2 + O2 + 2H2O → 4Fe(OH)3 （Corrosion products）
The total equation is: 4Fe+ 3O2 + 6H2O→2Fe(OH)3
51
Prevention of biological corrosion:
There are many approaches that can be used to prevent or to minimize MIC.
Before any remedial action can be taken, it is necessary to identify the type
of bacteria involved in the corrosion.
Among the choices are:
1. Selection and Modification of Environment: [27]
As natural environments vary so widely in their corrosive properties,
selection or modification of the environment so as to render it less corrosive
should be the first consideration in corrosion prevention, where possible.
Obviously, utilization of this principle affords greater promise of avoiding
severe corrosion when metal structures are to be placed in the soil rather than
in an aqueous environment. The environment may be changed in the
following ways in order to reduce corrosion rates: Decreasing or increasing
the temperature, the flow velocity, and the content of oxygen.
Mitigation of biological corrosion has been affected by changing the
environment to a less corrosive one in a number of cases.
When placing of metal structures in localized areas of anaerobic soil cannot
be avoided, it may be possible to provide aerobic conditions (air is the
cheapest inhibitor for sulfate-reducers) by surrounding the structure with
gravel, providing there is adequate drainage.
Aeration of water in a closed recirculating system reduces the activity of
anaerobic bacteria
52
2. Microbial Inhibitors
In certain closed systems (oil storage tanks, aircraft wing tanks, oil wells, heat
exchangers, hot-water systems, cooling towers, etc.), inhibitors have been
used with varying degrees of success in controlling corrosion.
Chromates have been widely used as corrosion inhibitors. Part of their
effectiveness is probably due to their strong inhibitory effects on sulfate
reducing bacteria. [28] Other inhibitors, such as chlorophenols, quaternary
ammonium detergents, polyamines, acridine dyes, dichlorodiphenyl
methane have also been found effective inhibitors of sulfate-reducing
bacteria.Ethylene glycol monomethyl ether (EGME) and organoboron
compounds have been demonstrated to be effective in controlling fuel
contamination and resulting corrosion in aircraft fuel systems.
3. Protective Coating:
Insulating the metal surface from its environment by means of a coating is
one of the most practical and effective preventative measures, especially in
nonclosed systems where the environment cannot be controlled or where use
of inhibitors would be too costly and ineffective. Coatings resistant to
microbial attack are most desirable. Coal tar and asphaltic coatings have been
quite successful in protecting underground steel structures and
Pipes. Coating a buried structure with tar, paint, plastic, or the like is often an
effective means to preclude bacteria from the metal surface. [29]
Ships and piers are coated with specially formulated paints containing
compounds toxic to the organisms. Copper compounds are often used
because their released copper ions poison the growth of barnacles and other
marine organisms.
53
4. Cathodic Protection:
The use of cathodic protection in combination with coated metallic structures
is probably the most effective method of preventing or decreasing corrosion
in soil and aqueous environments.
For the protection of ferrous metal, an additional (to -0.85 V) negative
potential (-O.IO V) has been found by Booth to confer cathodic protection on
steel in the presence of bacterial cells.
5. Protective films
The corrosion of metals in natural environments is greatly inhibited to
varying degrees by the formation of protective films of corrosion products.
In the case of aluminum, the oxide film offers considerable protection, while
in the case of iron, much less protection is provided by the oxide films.
Although little studied, it seems reasonable to assume that a mass of
microorganisms on the metal surface may prevent natural oxide film
formation from taking place or removing these films once they have
formed.[30]
6. Use of biocides
Chlorination and treatment with biocides help control populations of some
bacteria, although they are not effective in all cases. Also, the bacteriocides
fail to reach the areas underneath deposits where the bacteria thrive. In closed
systems, fouling can be mitigate by chlorination and periodic injection of
suitable biocides, including copper compounds.
54
7. Material change or modification and mechanical methods
In most affected soils, steel pipes may be replaced by plastic pipes to avoid
microbiological corrosion.
During storage or after hydro-testing, water should not be allowed to stand
for a long period of time.
Complete drainage and drying is advised. Inhibitors may be used in
stagnating water and cutting-oil fluids.
Periodic cleaning of the surfaces of structures and the inside of pipelines helps
reduce the growth of crevice sites. [31]
55
Corrosion Science and Corrosion Technology [32]
It has been said that the aim of science is “knowing why”, while technology
deals with “knowing how”.
One of the famous corrosion scientists, T.P. Hoar, considered the
technologist as a person who utilizes his scientific knowledge to solve
practical problems. This can stand as a wise and useful definition.
However, it is the situation and the technological problem that one is facing
that decides the extent to which the practical solution can be based on
scientific knowledge.
In corrosion technology many problems are solved more or less by pure
experience because the conditions are too complex to be described and
explained theoretically.
On the other hand, it is evident that great progress in corrosion technology
can be obtained by the application of corrosion theory to practical problems
to a much higher extent than what has been done traditionally.
This can be done i) in order to explain corrosion cases, to find the reasons and
prevent new attacks, ii) in corrosion testing with the aim of materials
selection, materials development etc., and in monitoring by electrochemical
methods, iii) for the prediction of corrosion rates and localization, and iv) to
improve methods for corrosion prevention in general, and to select and apply
the methods more properly in specific situations.
56
References
[1] J. H. Garrett, The Action of Water on Lead, H. K. Lewis, London (1891).
[2] R. H. Gaines, Bacterial Activity as a Corrosion Influence in the Soil, J. Eng. Ind.
, Chem. 2, 128-130 (1910).
[3] D. Ellis, Iron Bacteria, Methuen, London (1919).
[4] E. C. Harder, Iron Depositing Bacteria and Their Geologic Relations, U. S.
Government Printing Office. Washington, D. C. (1919).
[5] C. A. H. von Wolzogen Kiihr, Graphitization of Cast Iron As an Electrobiochemical
Process in Anaerobic Soils, U.S. Dept. of Commerce, Springfield, Virginia.
[6] Einar Bardal, Corrosion and Protection–(Engineering materials and processes), chapter
1, July 2003
[7] Philip A. Schweitzer, Fundamentals of corrosion Mechanisms, Causes, and
Preventative Methods, chapter 1, 2010
[8] (National Programme on Technology Enhanced Learning) NPTEL Web Course,
Lecture 1: Corrosion: Introduction – Definitions and Types, Course Title: Advances in
Corrosion Engineering, Prof. K. A. Natarajan, IISc Bangalore
[9] Joseph R. Davis, Corrosion: Understanding the Basics, chapter 1, ASM International,
USA, 2000
[10] ASM International, chapter 1, Fundamentals of Electrochemical Corrosion, 2000
[11] Philip A. Schweitzer, Fundamentals of CORROSION Mechanisms, Causes, and
Preventative Methods, chapter 2, 2010
57
[12] Einar Bardal, Corrosion and Protection–(Engineering materials and processes),
chapter3, July 2003
[13] (National Programme on Technology Enhanced Learning) NPTEL Web Course,
Lecture 1: Corrosion: Introduction – Definitions and Types, Course Title: Advances in
Corrosion Engineering, Prof. K. A. Natarajan, IISc Bangalore
[14] Philip A. Schweitzer, Fundamentals of corrosion Mechanisms, Causes, and
Preventative Methods, 2010, chapter 3, Page50
[15] Warren P. Iverson, BIOLOGICAL CORROSION, Corrosion Section, National
Bureau of Standards, Washington. D.C.
[16] Catalogue of Main Marine-Fouling Organisms, Vol. 1, Barnacles (1963); Vol.2,
Poiyzoa (1965); Vol. 3, Serpulidea (1967); Organisation for Economic Cooperation and
Development, Paris.
[17] G. Fontana, Roger W. Staehle,and w. P. Iverson, ADVANCES IN CORROSION
SCIENCE AND TECHNOLOGY, volume 2,Chapter 1, Biological Corrosion
[18] Prof. K. A. Natarajan, IISc Bangalore, NPTEL Web Course, Course Title:Advances
in Corrosion Engineering, Lecture 27:MIC – Role of Aerobic and Anaerobic
Microorganisms
[19] Philip A. Schweitzer, Fundamentals of corrosion Mechanisms, Causes, and
Preventative Methods, 2010, chapter 3, Page51-54
[20]Hans-Curt Flemming, P. Sriyutha Murthy, R. Venkatesan, Keith Cooksey, Marine and
Industrial Biofouling,Volume 4, Part I Microbial Biofouling and Microbially Influenced
Corrosion, Pages 35:60
58
[21] N. Muthukumar. et al. (2013, Sept). Microbiologically Influenced corrosion in
petroleum product pipelines - A review. Indian Journal of Experimental Biology
[Online]. 41. 1012-1022.
[22] Prof. K. A. Natarajan and IISc Bangalore, NPTEL Web Course , Course Title:
Advances in Corrosion Engineering, Lecture 28: Mechanisms and Models for SRB
Corrosion
[23] R.D. Monds. G.A. O'Toole. (2009, Feb). The developmental model of microbial
biofilms, Trends in Microbiology, 17(2), 73-87
[24] ASM Handbook, Volume 11: Failure Analysis and Prevention, 2002 ASM
International
[25] J. Wright. Inhibiting Rust and Corrosion to Prevent Machine Failures. [Online].
]26] T.S. Rao., Microbial fouling and corrosion: fundamentals and mechanisms, (Nov. ,
2011).
]27]Warren P. Iverson, BIOLOGICAL CORROSION, Corrosion Section, National
Bureau of Standards, page 35
[28] J. P. M. Drummond and J. R. Postgate, A Note on the Enumeration of
SulfateReducing Bacteria in Polluted Water and on Their Inhibition by Chromate,
J.Appl. Bacteriol. 18, 307 (1955).
[29] M. Romanoff, Underground Corrosion, National Bureau of Standards Circular
579(April 1957), pp. 155-160.
59
[30] J. S. Muraoka, Materials for Marine Environments. Effects of Marine Organisms,
Machine Design 40(2), 184--187 (1968).
[31] Philip A. Schweitzer, Fundamentals of corrosion Mechanisms, Causes, and
Preventative Methods, 2010, chapter 3, (54,55)
[32] Einar Bardal, Corrosion and Protection–(Engineering materials and processes),
chapter3, page 3, July 2003
*Some online links used for knowledge about Fundamentals, Mechanism, forms, and
Preventative Method of corrosion:
http://www.corrosionclinic.com/index.html
http://corrosion.org/Organization.html
www.asminternational.org
http://www.corrosionpedia.com/definition/231/cathodic-polarization
