1. 1. Introduction
1.1 Aim
The aim of this report is to investigate the main causes of corrosion of pipelines in
Australia. This report has been prepared for Australian Oil and Gas Companies in
order to reduce the hazards and costs of the pipelines accidents caused by corrosion.
1.2 Background
It is common knowledge that, Corrosion is the progressive demolition of metal due to
its reaction with the surroundings, resulting to deterioration that can lead to
malfunction. It is an electrochemical procedure and requires the attendance of water
or salt water to growth, which, even little amounts, can lead to a serious corrosion
assault of oil and gas pipelines( champion technologies 2012,p.1). Corrosion metals
affected of society infrastructure, Industrial facilities, services and accessories, and
industrial sectors, including refineries, factories, public utilities, bridges, shipping,
pipelines and storage(. It is estimated that the annual cost resulting from corrosion in
the world than a trillion dollars US1.8,
It is estimated that a 3 to 4% of gross domestic product (GDP) in industrialized
countries (Schmitt 2009, p.5). The pipelines are widely used around the world for
transmission of water, gases, oils and hazard fluids. There are more than 33,000km of
high-pressure steel pipelines in Australia, of which more than 25,000 kilometres are
used for natural gas transmission (Australian pipeline industry 2011).In addition, 663
km of pipelines used for oil transmission and 157 km of pipelines to refined products
(Chartsbin,2010).Usually pipelines are placed underground, whether under railways,
sea , roadways and runways. It is subject to the influence of soil and traffic as well as
acting of fluid pressure and containment (Ahammed & Melchers 1997, p. 988). As
result to the location of most Australian cities on the coast is a major problem to
contributing to the presence of corrosion frequently . This phenomenon may reached
an impact on human lives and marine animals and the Economiy. Material losses and
building damage resulting from the corrosion is too high and incurred to Australia
billions of dollars annually and the cost associated is that of the environment and
health from the use of corrosion inhibitors, such as chromate (csiro 2011,p.). In
addition, as a consequence of corrosion many dangerous accidents are occurred.
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2. Therefore, it is necessary to analyse the causes of this issue and identify feasible
methods to reduce and control the corrosion of pipelines.
1.3 Scope
Causes and effect of corrosion on pipelines in the Australia will be investigated from
a 1988 to 2012.
1.4 Methodology
This report will examine studies from different scientific papers, which discuss the
causes and effect of corrosion on pipelines. Data and information are gathered from
reliable sources such as scientific books, professional journals, academics research,
databases and relevant internet sites.
1.5 Plan
Initially, a detailed investigation of the perceived major causes of the problem of
corrosion of pipelines will be undertaken. Following this, the effects of this problem
discussed, and then recommendations provided to Oil and Gas Companies in
Australia. Moreover, illustrated data and tables will be introduced to explain the
extent of the corrosion problem.
2. Findings and Discussion
2.1 Overview
The direct cost of corrosion incurred by the state treasury of the Australia is
$13 Billion per year result to corrosion, due to most large cities at Coast
(Deacon 2011,p.1 ). In addition to unexpected losses during the failure occurs
due to pipelines corrosion. According to Sydney Morning Herald news on 3
June 2008, a pipeline rupture due to corrosion on Varanus Island caused an
explosion which severed gas supplies to Western Australia. The whole of
Western Australia was affected, particularly those dependant on gas supplies
for their mining and infrastructure projects. As the principal source of energy
for Western Australia, the State lost the benefit of approximately 350TJ of gas
per day, roughly about 30% of its total gas usage,that effect on certain mining
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3. companies and other large users of gas was particularly apparent ( Sydney
Morning Herald 2008). Moreover ,Geographical location is an important
factor for the occurrence of this phenomenon.” For example, than cold marine
climates, because usage temperature has a substantial impact on corrosion
rate.An example of the dependence of corrosion rate on atmospheric salinity is
provided in Figure 1.The figure shows the rate of corrosion in grams per
square decimeter per month (y-axis) is directly dependent on the deposition
rate of salt on the steel in units of mg of salt per square meter per day (x-axis)”
(Benjamin 2006,p.126). In general, corrosion is the result of water with a low
pH.
Figure 1 Corrosion of Steel as a Function of Atmospheric Salinity
Source: (Corrosion prenention and control 2006)
2.2 Causes
Corrosion in the distribution networks is a very complex situation which is influenced
by many water characteristics, by the metals used, and by any stray electrical current.
Although there are many interconnected and complex causes of corrosion of the
pipeline problems, this report will focus on three perceived major causes; Stress
Corrosion Cracking, Pitting corrosion and Galvanic Corrosion.
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4. 2.2.1 Pitting corrosion
“Pitting corrosion is a concentration of corrosion in one particular area whereby the
metal goes into solution preferentially at that spot, rather than at other adjacent areas.
Pitting corrosion has been reported to be the primary mode of failure for ductile iron
pipes” (Angel Fire, n.d.).
Figure (2) illustrates the morphology of pitting corrosion. It is started by assistance of
corrosive environment at the external surface. Then, pits subsurface and attack the
grains in the direction to the inner surface leading to pipe failure.
Figure (2): Morphology of pitting Corrosion
Source: (Cathodic Protection of Pipeline 2009)
Most of the pipelines made from ductile iron are used to transmission gases and oils.
It is normally buried in the soil. For this reason, the soil plays as a corrosive
environment and attacks pipes causes pitting corrosion.
Furthermore, “The susceptibility of spun pipe to external corrosion can be increased
by damage to the annealing oxide scale, which inevitably occurs during normal
handling and installation” (Angel Fire, n.d.). The damage of annealing scale with a
presence of corrosive environment, they localize attack take place in external surface.
The degree of aggressive pitting corrosion depends on soil resistivity. Lowest soil
resistivity has more corrosion rate than the highest soil resistivity, as shown in table
(1).
Table (1): Rough Indications of Soil Corrosivity vs. Resistivity
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5. Resistivity (Ohm-cm) Soil Corrosivity Description
Below 500 Very corrosive
500 – 1,000 Corrosive
1,000 – 2,000 Moderately corrosive
2,000 – 10,000 Mildly corrosive
Above 10,000 Progressively less corrosive
Source: (Angel Fire, n.d.)
As it can be seen, from figure (3) the pitting rate of ductile iron increases when soil
has the low resistivity. On the other hand, pitting rate decreases with increase soil
resistivity (Angel Fire, n.d).
Figure (3): Maximum Pitting Rate of Ductile Iron Pipes vs. Lower Soil Resistivity
Source: (Angel Fire, n.d.)
2.2.2 Stress Corrosion Cracking
Stress corrosion cracking, scientifically defined is a cracking produced by
combination actions of stress and an environment on susceptible metal or alloy.
Figure (4): Stress Corrosion Cracking Susceptibility Diagram
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6. Source: (Jayaraman & Prevey 2005, p. 2)
Figure (4) illustrated that stress corrosion cracking in pipes takes place in presence of
tensile stress and corrosive environment (Jayaraman & Prevey 2005, p. 2).
The mechanism of stress corrosion cracking as shown in figure (5) which starts by
nucleated at a particular pitting damage area on the pipe wall surface. It is developing
under the presence of stress action like fluid pressure and corrosive media like a soil
or chemical solution. Fine cracks branch and propagate are causing pipe to failure
(Swathi 2006).
Figure (5): Schematic view of Stress Corrosion Cracking
Source: (Swathi 2006)
2.2.3 Galvanic Corrosion
Galvanic corrosion is a type of localizing corrosion is occur when two dissimilar
metal connect together or connection of similar new and old metal in the presence of
an electrolyte media allow to pass ions from one to another (Zhang 2000, p. 137).
According to the Stainless Steel Information Center (n.d.) there are three conditions
are must be available for galvanic corrosion take place as shown in figure (6):
6

7. a) Two dissimilar metal or similar new and old metal, which one becomes anode
and the other as cathode.
b) The metal must be contacted to allow electron flow.
c) Electrolyte in which two metals are immersed in.
If one of these conditions is absent, the galvanic corrosion cannot occur.
Figure (6): The conditions of galvanic corrosion
Source: (the Stainless Steel Information Center, n.d.)
Figure (7) illustrate when two dissimilar metals contact with other in the presence of
electrolyte solution. The galvanic corrosion will take place by flow of electrons from
the iron pipe, Anod, to copper pipe, Cathode, (Gedeon, n.d., p. 24).
Figure (7): Galvanic Corrosion at Iron-Copper Pipe Junction
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8. Source: (Gedeon, n.d, p. 24.)
The major factor has a great effect on acceleration of galvanic corrosion is corrosion
potential difference between two metals as shown in table (2). The greater separation
between metals tends to the more galvanic corrosion activity due to greater potential
differences. On the other hand slow galvanic corrosion generation occurrs when two
metals closely to potential series are connected (Stainless Steel Information Center,
n.d.)
Table (2): Potential series of common metals
List of common metal Activity Series
Magnesium
Anodic (active)
Zinc
Galvanized Steel
Aluminium
Mild Steel
Low Alloy Steel
Cast Iron
Lead
Tin
Muntz Metal
Yellow Brass
Aluminium Bronze
Red Brass
Copper
Alloy 400
Stainless Steel (430)
Stainless Steel (304)
Stainless Steel (316)
Silver
Cathodic (noble)
Gold
Stainless Steel Information Center, n.d.)
Source: (Stainless Steel Information Center, n.d.)
2.3 Effect
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9. When the corrosion takes place in the three forms are pitting corrosion, stress
corrosion cracking and galvanic corrosion, the thickness of wall pipe start degradation
and loses their mechanical properties was designed to meet the requirement for the
purpose to use. Moreover, failure of pipes during transmission of gases and oils due to
these types of corrosion may cause the injury or fatal incidence to the operator.
Furthermore, cost of maintenance and repair damage pipes is concerning.
3. Conclusion
Despite the efforts of the Gas and Oil Companies’ to minimize and control the
damage of pipelines due to the corrosion problem, it is incurred the state treasury
billions of dollars annually.
It is concluded that there are three major causes for corrosion of pipelines. Firstly, the
primary mode of degradation of iron pipes is pitting corrosion. It attacks the pipes in
particular area from outer to inner surface, due to the corrosive environment around
the pipe. Secondly, the most dangerous type of pipelines failure is stress corrosion
cracking. It is unexpected failure time due to, fast crack propagation. Finally, the
galvanic corrosion is takes place when two dissimilar pipes in potential series are
joints together in electrolyte corrosive environment.
As a result of this, the following recommendations are proposed for Oil and Gas
Companies in Australia to minimize and control corrosion of pipelines.
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10. 4. Recommendations
All recommendations in this section are addressed to the Oil and Gas Companies in
Australia.
4.1 Environmental modification and material selection
The environment and pipe type are important roles of pitting corrosion progress.
Therefore, it is necessary that the modification of corrosive environment is needed to
minimize corrosion reaction. Corrosion inhibitors are added to the corrosive soil to
improve its resistivity which in turn improves corrosion resistance. Furthermore, the
selection of proper material is essentially to reduce the attack of pitting corrosion. The
alloying elements like molybdenum and chromium are add to the alloy material to
prevent the pitting corrosion (Roberge 1999, pp. 364-365).
4.2 Mechanical, Metallurgical and Environmental manipulation
According to Parkins (2000, pp. 200-203) and as mentioned in the Finding and
Discussion section, there are three contributing factors to stress corrosion cracking
takes place; tensile stress, susceptible metal and corrosive environment. Therefore, it
is recommended that the following:
4.2.1 Stress control
The residual stress is the main cause of stress corrosion cracking due to
fabrication and operating processes. Therefore, the proper heat treatment is
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11. applied to relieve the residual stress. It carries out in a suitable furnace to a
certain temperature and depends on the chemical composition of the pipe,
followed by fast water quenching to room temperature.
4.2.2 Metallurgical approaches
The carbon content and alloying are significant elements in the steel and iron
alloys. Consequently, the control of carbon content tends to minimize stress
corrosion cracking by restricting intergranular cracking through grain
boundaries. Furthermore, the structure of the alloy has effect on strength and
ductility. The additional alloying element should be determined to achieve
proper grain size; because the larger grain size tends to decrease yield stress
and intergranular cracking propagate easily through the grains. As a result,
low carbon content and proper alloying elements are necessaries to obtain
higher strength and small grain size.
4.2.3 Environmental approaches
Control of the environment factors are important to restricted stress corrosion
cracking. The presence of some chemical species should be removed or
inhibited. The chloride is most dangerous species caused iron pipes.
Therefore, the cathodic protection is the effective method to inhibit chloride
activity, due to control of the potential current between iron and chloride.
4.3 Apply coating and selection of similar corrosion potential junction
A galvanic current flow through two dissimilar metals from one to the other when
exposed to the electrolyte environment causes a galvanic corrosion. Therefore, it is
recommended that to reduce the effect of galvanic corrosion, the junction materials
are closed together galvanic potential current are used to avoid the flow of high
current through it. Moreover, non-conducting materials like a composite or high
strength are used to stop current flow. Also, when the dissimilar junctions cannot be
avoided, the applying of coating film on anodic material is used to inhibit the
acceleration of galvanic corrosion (Roberge 1999, pp. 363-364).
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12. Glossary
Corrosion: The chemical deterioration of a material, usually a metal,
because of a reaction with its environment.
Stress Corrosion Cracking: Cracking producing by the combined
actions of stress and an environment on a susceptible alloy.
Pitting Corrosion: Localized corrosion of a metal surface is occurs at
points or small areas.
Galvanic Corrosion: Corrosion associated with the current of a galvanic
cell consisting of two dissimilar conductors in an electrolyte or two
similar conductors in dissimilar electrolytes. Where the two dissimilar
metals are in contact, the resulting reaction is referred to as couple action.
Morphology: The characteristic shape, form, or surface texture or
contours of the crystals, grains, or particles of (or in) a material, generally
on a microscopic scale.
Grain: An individual crystal in a polycrystalline material; it may or may
not contain twinned regions and subgrains.
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13. Grain boundary: A narrow zone in a metal or ceramic corresponding to
the transition from one crystallographic orientation to another, thus
separating one grain from another; the atoms in each grain are arranged in
an orderly pattern.
Ductile iron: A cast iron that has been treated while molten with an
element such as magnesium or cerium to induce the formation of free
graphite as nodules or spherulites, which imparts a measurable degree of
ductility to the cast metal. Also known as nodular cast iron, spherulitic
graphite cast iron, and spheroidal graphite (SG) iron.
Annealing: A generic term is denoting a treatment consisting of heating
to and holding at a suitable temperature followed by cooling at a suitable
rate, used primarily to soften metallic materials. When applied only for
the relief of stress, the process is properly called stress relieving or stress-
relief annealing.
Soil Resistivity: It is a measure of how well a soil passes electric current.
Soil passes electric current in varying levels; the higher the resistivity of a
given soil, the less electric current passes through.
Tensile Stress: A stress that causes two parts of an elastic body, on either
side of a typical stress plane, to pull apart.
Anode: The electrode of an electrolyte cell at which oxidation occurs.
Electrons flow away from the anode in the external circuit. It is usually at
the electrode that corrosion occurs and metal ions enter solution. Contrast
with cathode.
Cathode: The negative electrode of an electrolytic cell at which
reduction is the principal reaction. (Electrons flow toward the cathode in
the external circuit.) Typical cathodic processes are cations taking up
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14. electrons and being discharged, oxygen being reduced, and the reduction
of an element or group of elements from a higher to a lower valence state.
Contrast with anode.
Electrolyte: A chemical substance or mixture, usually liquid, containing
ions that migrate in an electric field.
Inhibitor: A substance that retards some specific chemical reaction, e.g.,
corrosion.
Alloying Element: It is an element added to and remaining in a metal
that changes structure and properties.
Residual Stress: The stress existing in a body at rest, in equilibrium, at
uniform temperature, and not subjected to external forces.
Ductility: The ability of a material to deform plastically without
fracturing.
Yield Stress: The stress level of highly ductile materials at which large
strains take place without further increase in stress.
Chemical Species: Atoms, molecules, molecular fragments, ions, etc.,
being subjected to a chemical process or to a measurement.
Coating: A relatively thin layer (<1 mm, or 0.04 in.) of material applied
by surfacing for the purpose of corrosion prevention, resistance to high-
temperature scaling, wear resistance, lubrication, or other purposes.
Corrosion Resistance: The ability of a material to withstand contact with
ambient natural factors or those of a particular, artificially created
atmosphere, without degradation or change in properties.
Galvanic Series: A list of metals and alloys arranged according to their
relative corrosion potentials in a given environment. Compare with
electromotive force series.
Galvanic Current: The electric current that flows between metals or
conductive non-metals in a galvanic couple.
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15. pH: A measure of the acidity or alkalinity of a solution, numerically
equal to 7 for neutral solutions, increasing with increasing alkalinity and
decreasing with increasing acidity. The pH scale commonly in use ranges
from 0 to 14
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