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

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2011,p.). In addition, as a consequence of corrosion many

dangerous accidents are occurred. 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

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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

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.

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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.

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).

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Table (1): Rough Indications of Soil Corrosivity vs. Resistivity

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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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):

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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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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

MagnesiumZinc

Galvanized SteelAluminiumMild Steel

Low Alloy SteelCast Iron

LeadTin

Muntz MetalYellow Brass

Aluminium BronzeRed Brass

CopperAlloy 400

Stainless Steel (430)Stainless Steel (304)Stainless Steel (316)

SilverGold

Anodic (active)

Cathodic (noble)

Stainless Steel Information Center, n.d.)

Source: (Stainless Steel Information Center, n.d.)

2.3 Effect

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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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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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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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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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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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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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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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