Corrosion inspection in oil and gas pipeline
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Corrosion inspection in oil and gas pipeline Corrosion inspection in oil and gas pipeline Document Transcript

  • 1. Introduction1.1 AimThe aim of this report is to investigate the main causes of corrosion of pipelines inAustralia. This report has been prepared for Australian Oil and Gas Companies inorder to reduce the hazards and costs of the pipelines accidents caused by corrosion.1.2 BackgroundIt is common knowledge that, Corrosion is the progressive demolition of metal due toits reaction with the surroundings, resulting to deterioration that can lead tomalfunction. It is an electrochemical procedure and requires the attendance of wateror salt water to growth, which, even little amounts, can lead to a serious corrosionassault of oil and gas pipelines( champion technologies 2012,p.1). Corrosion metalsaffected of society infrastructure, Industrial facilities, services and accessories, andindustrial sectors, including refineries, factories, public utilities, bridges, shipping,pipelines and storage(. It is estimated that the annual cost resulting from corrosion inthe world than a trillion dollars US1.8,It is estimated that a 3 to 4% of gross domestic product (GDP) in industrializedcountries (Schmitt 2009, p.5). The pipelines are widely used around the world fortransmission of water, gases, oils and hazard fluids. There are more than 33,000km ofhigh-pressure steel pipelines in Australia, of which more than 25,000 kilometres areused for natural gas transmission (Australian pipeline industry 2011).In addition, 663km 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 asacting of fluid pressure and containment (Ahammed & Melchers 1997, p. 988). Asresult to the location of most Australian cities on the coast is a major problem tocontributing to the presence of corrosion frequently . This phenomenon may reachedan impact on human lives and marine animals and the Economiy. Material losses andbuilding damage resulting from the corrosion is too high and incurred to Australiabillions of dollars annually and the cost associated is that of the environment andhealth from the use of corrosion inhibitors, such as chromate (csiro 2011,p.). Inaddition, as a consequence of corrosion many dangerous accidents are occurred. 1
  • Therefore, it is necessary to analyse the causes of this issue and identify feasiblemethods to reduce and control the corrosion of pipelines.1.3 ScopeCauses and effect of corrosion on pipelines in the Australia will be investigated froma 1988 to 2012.1.4 MethodologyThis report will examine studies from different scientific papers, which discuss thecauses and effect of corrosion on pipelines. Data and information are gathered fromreliable sources such as scientific books, professional journals, academics research,databases and relevant internet sites.1.5 PlanInitially, a detailed investigation of the perceived major causes of the problem ofcorrosion of pipelines will be undertaken. Following this, the effects of this problemdiscussed, and then recommendations provided to Oil and Gas Companies inAustralia. Moreover, illustrated data and tables will be introduced to explain theextent of the corrosion problem.2. Findings and Discussion2.1 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 2
  • 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 CausesCorrosion in the distribution networks is a very complex situation which is influencedby many water characteristics, by the metals used, and by any stray electrical current.Although there are many interconnected and complex causes of corrosion of thepipeline problems, this report will focus on three perceived major causes; StressCorrosion Cracking, Pitting corrosion and Galvanic Corrosion. 3
  • 2.2.1 Pitting corrosion“Pitting corrosion is a concentration of corrosion in one particular area whereby themetal 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 ironpipes” (Angel Fire, n.d.).Figure (2) illustrates the morphology of pitting corrosion. It is started by assistance ofcorrosive environment at the external surface. Then, pits subsurface and attack thegrains 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 corrosiveenvironment and attacks pipes causes pitting corrosion.Furthermore, “The susceptibility of spun pipe to external corrosion can be increasedby damage to the annealing oxide scale, which inevitably occurs during normalhandling and installation” (Angel Fire, n.d.). The damage of annealing scale with apresence of corrosive environment, they localize attack take place in external surface.The degree of aggressive pitting corrosion depends on soil resistivity. Lowest soilresistivity has more corrosion rate than the highest soil resistivity, as shown in table(1). Table (1): Rough Indications of Soil Corrosivity vs. Resistivity 4
  • 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 soilhas the low resistivity. On the other hand, pitting rate decreases with increase soilresistivity (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 CrackingStress corrosion cracking, scientifically defined is a cracking produced bycombination actions of stress and an environment on susceptible metal or alloy. Figure (4): Stress Corrosion Cracking Susceptibility Diagram 5
  • Source: (Jayaraman & Prevey 2005, p. 2)Figure (4) illustrated that stress corrosion cracking in pipes takes place in presence oftensile stress and corrosive environment (Jayaraman & Prevey 2005, p. 2).The mechanism of stress corrosion cracking as shown in figure (5) which starts bynucleated at a particular pitting damage area on the pipe wall surface. It is developingunder the presence of stress action like fluid pressure and corrosive media like a soilor 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 CorrosionGalvanic corrosion is a type of localizing corrosion is occur when two dissimilarmetal connect together or connection of similar new and old metal in the presence ofan 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 conditionsare must be available for galvanic corrosion take place as shown in figure (6): 6
  • a) Two dissimilar metal or similar new and old metal, which one becomes anodeand 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 ofelectrolyte solution. The galvanic corrosion will take place by flow of electrons fromthe iron pipe, Anod, to copper pipe, Cathode, (Gedeon, n.d., p. 24). Figure (7): Galvanic Corrosion at Iron-Copper Pipe Junction 7
  • Source: (Gedeon, n.d, p. 24.)The major factor has a great effect on acceleration of galvanic corrosion is corrosionpotential difference between two metals as shown in table (2). The greater separationbetween metals tends to the more galvanic corrosion activity due to greater potentialdifferences. On the other hand slow galvanic corrosion generation occurrs when twometals 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 8
  • When the corrosion takes place in the three forms are pitting corrosion, stresscorrosion cracking and galvanic corrosion, the thickness of wall pipe start degradationand loses their mechanical properties was designed to meet the requirement for thepurpose to use. Moreover, failure of pipes during transmission of gases and oils due tothese types of corrosion may cause the injury or fatal incidence to the operator.Furthermore, cost of maintenance and repair damage pipes is concerning.3. ConclusionDespite the efforts of the Gas and Oil Companies’ to minimize and control thedamage of pipelines due to the corrosion problem, it is incurred the state treasurybillions of dollars annually.It is concluded that there are three major causes for corrosion of pipelines. Firstly, theprimary mode of degradation of iron pipes is pitting corrosion. It attacks the pipes inparticular area from outer to inner surface, due to the corrosive environment aroundthe pipe. Secondly, the most dangerous type of pipelines failure is stress corrosioncracking. It is unexpected failure time due to, fast crack propagation. Finally, thegalvanic corrosion is takes place when two dissimilar pipes in potential series arejoints together in electrolyte corrosive environment.As a result of this, the following recommendations are proposed for Oil and GasCompanies in Australia to minimize and control corrosion of pipelines. 9
  • 4. RecommendationsAll recommendations in this section are addressed to the Oil and Gas Companies inAustralia.4.1 Environmental modification and material selectionThe environment and pipe type are important roles of pitting corrosion progress.Therefore, it is necessary that the modification of corrosive environment is needed tominimize corrosion reaction. Corrosion inhibitors are added to the corrosive soil toimprove its resistivity which in turn improves corrosion resistance. Furthermore, theselection of proper material is essentially to reduce the attack of pitting corrosion. Thealloying elements like molybdenum and chromium are add to the alloy material toprevent the pitting corrosion (Roberge 1999, pp. 364-365).4.2 Mechanical, Metallurgical and Environmental manipulationAccording to Parkins (2000, pp. 200-203) and as mentioned in the Finding andDiscussion section, there are three contributing factors to stress corrosion crackingtakes place; tensile stress, susceptible metal and corrosive environment. Therefore, itis 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 10
  • 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 junctionA galvanic current flow through two dissimilar metals from one to the other whenexposed to the electrolyte environment causes a galvanic corrosion. Therefore, it isrecommended that to reduce the effect of galvanic corrosion, the junction materialsare closed together galvanic potential current are used to avoid the flow of highcurrent through it. Moreover, non-conducting materials like a composite or highstrength are used to stop current flow. Also, when the dissimilar junctions cannot beavoided, the applying of coating film on anodic material is used to inhibit theacceleration of galvanic corrosion (Roberge 1999, pp. 363-364). 11
  • GlossaryCorrosion: The chemical deterioration of a material, usually a metal,because of a reaction with its environment.Stress Corrosion Cracking: Cracking producing by the combinedactions of stress and an environment on a susceptible alloy.Pitting Corrosion: Localized corrosion of a metal surface is occurs atpoints or small areas.Galvanic Corrosion: Corrosion associated with the current of a galvaniccell consisting of two dissimilar conductors in an electrolyte or twosimilar conductors in dissimilar electrolytes. Where the two dissimilarmetals are in contact, the resulting reaction is referred to as couple action.Morphology: The characteristic shape, form, or surface texture orcontours of the crystals, grains, or particles of (or in) a material, generallyon a microscopic scale.Grain: An individual crystal in a polycrystalline material; it may or maynot contain twinned regions and subgrains. 12
  • Grain boundary: A narrow zone in a metal or ceramic corresponding tothe transition from one crystallographic orientation to another, thusseparating one grain from another; the atoms in each grain are arranged inan orderly pattern.Ductile iron: A cast iron that has been treated while molten with anelement such as magnesium or cerium to induce the formation of freegraphite as nodules or spherulites, which imparts a measurable degree ofductility to the cast metal. Also known as nodular cast iron, spheruliticgraphite cast iron, and spheroidal graphite (SG) iron.Annealing: A generic term is denoting a treatment consisting of heatingto and holding at a suitable temperature followed by cooling at a suitablerate, used primarily to soften metallic materials. When applied only forthe 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 agiven soil, the less electric current passes through.Tensile Stress: A stress that causes two parts of an elastic body, on eitherside 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 atthe electrode that corrosion occurs and metal ions enter solution. Contrastwith cathode.Cathode: The negative electrode of an electrolytic cell at whichreduction is the principal reaction. (Electrons flow toward the cathode inthe external circuit.) Typical cathodic processes are cations taking up 13
  • electrons and being discharged, oxygen being reduced, and the reductionof 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, containingions 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 metalthat changes structure and properties.Residual Stress: The stress existing in a body at rest, in equilibrium, atuniform temperature, and not subjected to external forces.Ductility: The ability of a material to deform plastically withoutfracturing.Yield Stress: The stress level of highly ductile materials at which largestrains 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 appliedby 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 withambient natural factors or those of a particular, artificially createdatmosphere, without degradation or change in properties.Galvanic Series: A list of metals and alloys arranged according to theirrelative corrosion potentials in a given environment. Compare withelectromotive force series.Galvanic Current: The electric current that flows between metals orconductive non-metals in a galvanic couple. 14
  • pH: A measure of the acidity or alkalinity of a solution, numericallyequal to 7 for neutral solutions, increasing with increasing alkalinity anddecreasing with increasing acidity. The pH scale commonly in use rangesfrom 0 to 14 ReferencesAhammed, M and Melchers, RE 1997, ‘Probabilistic analysis of undergroundpipelines subject to combined stresses and corrosion’, Engineering Structures, vol. 19,no. 12, p. 988, 27 March 2011, ScienceDirect.Angel Fire, n.d., External Corrosion and Protection of Ductile Iron Pipe, Angel Fire,retrieved 24 March 2011, < http://www.angelfire.com/pop/myfile/EXTDIPhtml.htm>.Cathodic Protection of Pipeline 2009, Forms of corrosion, Science of Metallurgy &Materials, retrieved 29 March 2011, < http://metallurgy.eg.vg/2009/04/forms-of-corrosion-2/>.CC Technologies 2006, Funds Cost of Corrosion Study, CC Technologies, retrieved27 March 2011, < http://www.corrosioncost.com/piechart.htm>.Corrosion Doctors 2005, Pipeline Failure Causes, Corrosion Doctors, retrieved 22March 2011, <http://corrosion-doctors.org/Pipeline/Pipeline-failures.htm>.Gedeon, n.d., Corrosion Overview, Continuing Education and Development, retrieved4 April 2011, < http://www.cedengineering.com/upload/Corrosion.pdf>.Jayaraman, N and Prevey, PS 2005, An overview of the use of engineeredcompressive residual stresses to mitigate SCC and Corrosion Fatigue, Lambda 15
  • Research, retrieved 1 April 2011,<http://www.lambdatechs.com/html/resources/264.pdf>.Koch, GH, Brongers, M. P. H., Thompson, NG, Virmani, YP and Payer, JH 2002,Corrosion Costs and Preventive Strategies in the United States: Cost of CorrosionStudy Unveiled, NACE International, retrieved 27 March 2011,<http://events.nace.org/publicaffairs/images_cocorr/ccsupp.pdf>.Parkins, RN 2000, ‘Stress Corrosion Cracking’, in R. Winston (ed.) CorrosionHandbook, 2nd ed., John Wiley & Sons, New York, 2000, retrieved Knovel.Roberge, PR 1999, Handbook of corrosion engineering, McGraw-Hill, New York.Swathi 2006, Metallic Corrosion: Intergranular Attack, Steel Alloys information steelparts, retrieved 11 April 2011, < http://steelalloys.blogspot.com/2006/11/metallic-corrosion-intergranular.html>.Thacker, BH, Light, GM, Dante, JF, Trillo, E, Fengmei, S, Popelar, CF, Coulter, KEand Page, RA 2010, ‘Corrosion Control In Oil And Gas Pipelines’, Pipeline & GasJournal, vol. 237, no. 3, p. 62, EBSCOhost.The Stainless Steel Information Center, n.d., Galvanic Corrosion, SSINA KnowledgeBase, retrieved 11 April 2011, < http://www.ssina.com/corrosion/galvanic.html>.Thompson, NG 2006, Gas & Liquid Transmission Pipelines, CC Technologies, 27March 2011, <http://www.corrosioncost.com/infrastructure/gasliquid/index.htm>.Zhang, XG 2000, ‘Galvanic Corrosion’, in R. Winston (ed.) Corrosion Handbook,2nd ed., John Wiley & Sons, New York, 2000, retrieved Knovel. 16