Research Article Microbial Corrosion of API 5L X-70 Carbon...

Research ArticleMicrobial Corrosion of API 5L X-70 Carbon Steel byATCC 7757 and Consortium of Sulfate-Reducing Bacteria

Arman Abdullah12 Nordin Yahaya1 Norhazilan Md Noor1 and Rosilawati Mohd Rasol1

1 Reliability Engineering and Safety Assessment Research Group (RESA) Faculty of Civil EngineeringUniversiti Teknologi Malaysia (UTM) 81310 Skudai Johor Malaysia

2 Faculty of Chemical Engineering and Natural Resources Universiti Malaysia Pahang (UMP) Lebuhraya Tun Razak26300 Kuantan Pahang Malaysia

Correspondence should be addressed to Arman Abdullah armanabdullahumpedumy

Received 26 May 2014 Revised 8 July 2014 Accepted 8 July 2014 Published 13 August 2014

Academic Editor Tingyue Gu

Copyright copy 2014 Arman Abdullah et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Various cases of accidents involving microbiology influenced corrosion (MIC) were reported by the oil and gas industry Sulfatereducing bacteria (SRB) have always been linked to MIC mechanisms as one of the major causes of localized corrosion problemsIn this study SRB colonies were isolated from the soil in suspected areas near the natural gas transmission pipeline inMalaysiaTheeffects of ATCC 7757 and consortium of isolated SRB upon corrosion on API 5L X-70 carbon steel coupon were investigated usinga weight loss method an open circuit potential method (OCP) and a potentiodynamic polarization curves method in anaerobicconditions Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were then used to determinethe corrosion morphology in verifying the SRB activity and corrosion products formation Results from the study show that thecorrosion rate (CR) of weight loss method for the isolated SRB is recorded as 02017mmyr compared to 02530mmyr for ATCC7757The Tafel plot recorded the corrosion rate of 03290mmyr for Sg Ular SRB and 02500mmyr forDesulfovibrio vulgaris Theresults showed that the consortia of isolated SRB were of comparable effects and features with the single ATCC 7757 strain

1 Introduction

Deterioration of metal by corrosion processes directly orindirectly involving microorganisms has gained enormousattention recently A few terms have been used by engineersand the scientific community to highlight this type of corro-sion such as microbiologically influenced corrosion (MIC)biodeterioration and biocorrosion [1] Various accidentshave been reported involving MIC in soil fresh water andseawater environments in almost all industries such as theoil and gas power generation marine and nuclear industries[2ndash4]Themost highlighted accidents likely involvingMIC asthe culprit are the Carlsbad NewMexico natural gas pipelineexplosion [5] and the 2006 Alaska pipeline leak [6] Con-sequently these devastated accidents have caused turmoilin the global oil market [6] According to the investigationsulfate-reducing bacteria (SRB) were the prime suspect forthe accident in Alaska proving how severe the corrosion

can progress under microbial activity influence There aremany types of bacteria that can lead to corrosion initiationor the increase of corrosion rate such as SRB acid producingbacteria (APB) and nitrate reducing bacteria (NRB) [7] SRBis regarded as one of the most troublesome groups of bacteriainfluencing the MIC mechanism SRB is usually attributedto the chemical corrosiveness of H

2S facilitated abiotic H+-

reduction at deposited FeS and biological consumption ofchemically formed (ldquocathodicrdquo) H

2 However recent studies

by Venzlaff et al [8] and Enning et al [9] have shown thatcorrosive SRB indicated direct consumption of iron-derivedelectrons rather than H

2as a crucial mechanism

Bacteria need four elements to grow namely a carbonsource water an electron donor and an electron acceptor[10] A recent theory put forward to explain the MIC mech-anism is by Gu et al namely Biocatalytic Cathodic SulfateReduction (BCSR) [11] Xu and Gu found that SRB starvedof organic carbon are more aggressive in terms of corrosion

Hindawi Publishing CorporationJournal of ChemistryVolume 2014 Article ID 130345 7 pageshttpdxdoiorg1011552014130345

2 Journal of Chemistry

of carbon steel compared to well-fed SRB [12 13] Underpoor nutritional conditions SRB cell can possibly scavengeorganic carbons from dead cells [14] and also maintain theirenergy by turning to iron (Fe) as an electron donor due toa similar reduction potential value of lactate (Fe2+ minus447mVand lactate minus430mV) Xu et al [15] explained their BCSRtheories by showing the combined redox reaction to have apositive potential of +230mV This positive value of redoxpotential means the reaction is thermodynamically favorableConsider

Anodic 4Fe 997888rarr 4Fe2+ + 8eminus (Iron dissolution)

119864

o1015840= minus447mV

(1)

Cathodic SO4

2minus+ 9H+ + 8eminus 997888rarr HSminus + 4H

2O (BCSR)

119864


(2)

Petroleum products and natural gas are commonly trans-ported by buried pipelines under the soil for mechanicalprotection from third-party damage to provide thermalinsulation [16] Failure mechanisms associated with pipelinescan be classified into three categories third-party damagematerial defects and corrosion Corrosion is recognised asone of the most dominant forms of the deterioration processand has been identified as one of the major causes of lossof containment in steel pipelines [17] Corrosion may attackthe pipelines either internally or externally or both Externalcorrosion is amajor factor contributing to the deterioration ofburied pipelines by weakening the pipe wall which increasesthe risk of failure [18] Even though buried pipelines areprotectedwith coatings and cathodic protection the pipelinesare still vulnerable to various types of corrosion mechanisms[19] MIC is one of the possible threats to buried pipelinesbecause SRB grow well in soil sediment [20]

In order to understand the intrinsic mechanisms of MICit is necessary to study if the consortium of SRB bacteriaspecies may diversify the influence on corrosion mechanismIn this paper the corrosion behavior of ATCC 7757 SRB iscompared to consortia of SRB isolated from Malaysian soilThe corrosion of carbon steel grade API 5L X-70 subject tomicrobial activity is monitored and measured under labora-tory conditions The findings may reveal the discrepanciesbetween a single strain of SRB and the consortium of SRBisolated from underground in terms of bacteria metabolismand corrosion initiation This topic is also relevant for initialrecognition of bacterial species

2 Materials and Methods

21 Sulfate-Reducing Bacteria Two types of SRB were usedin this study obtained from different sources The firstbacteria strain was sourced from the American Type Cul-ture Collection with reference number ATCC 7757 whilethe second SRB strain was obtained by a simple isolationtechnique from soilmud near the natural gas pipeline in

Peninsular Malaysia during pipe maintenance work The sitewas selected based on the pipeline operator maintenancerecord (severe external corrosion from pigging record) TheSRB strain was named SRB Sg Ular for easy identificationof the site location The simple isolation was conducted byinoculating the black stainbiofilm from the pipeline undera disbonded coating in 500mL nutrient-rich Baarrsquos mediumunder anaerobic conditions at 37∘C The composition ofthe medium consisted of sodium lactate 60 gL sodiumsulfate 45 gL ammonium chloride 10 gL yeast extract10 gL potassium phosphate 05 gL sodium citrate 03 gLcalcium chloride 006 gL magnesium sulfate 006 gL andiron sulfate 0004 gL The pH of the medium was adjustedto 70 before being autoclavedThemediumwas sparged withoxygen-free nitrogen after being autoclaved SRB were thendetected by regrowth of the SRB with Starkeyrsquos medium asthe selective growth medium The bacteria strains obtainedfrom the above exercise were then tested using a SRB kit aniron reduction bacteria (IRB) kit (LAB-BART Kit DroyconBioconcepts Inc Canada) and a Sani SRB test kit from Sani-Check product number 100 (Sani Check Biosan Lab IncUSA)

22 Materials The corrosion specimens were machinedfrom an actual segment of API 5L X-70 pipe obtained froma local gas operator The composition of the carbon steelis as follows 97093 Fe 0078 C 167 Mn 015 Ni0012 P 03 Si 0023 Cu 0275 Cr 011 Ti and0002 S [21] Prior to use the metal coupons were polishedwith a SiC grit paper graded 200 400 and 600 followedby cleaning with acetone and coated with Teflon leavingonly the flat surface exposed to the medium in an anaerobicbottle experimentThe corrosion specimen used as a workingelectrode was mounted in an epoxy resin with copper wireconnected to an exposed flat surface approximately 1 cm2in areas Figure 1 shows the microstructure of the API5L X-70 carbon steel under the microscope The couponsconsisted of ferrite and eutectoid pearlite based on thelight and gray constituent color from the microstructureimage

23 Method

231 Experiment The experiment was performed in a125mL sealed anaerobic vial and in a 1-liter electrochemicalglass cell All devices involved in this experiment weresterilized in an autoclave at 121∘C Necessary care wastaken at all times to avoid bacterial contamination andthe experiments were conducted under simulated anaerobicconditions Nitrogen for the medium was purged by usingfiltered oxygen-free nitrogenThe deoxygenation process wasconducted for approximately 1 hour for 1 liter of medium Anopen circuit potential (OCP)measurement was conducted byusing a saturated calomel electrode (SCE) as the referenceelectrode and carbon steel as the working electrode in astandard electrochemical glass cell with the SRB medium aselectrolyte A multimeter (Kyoritsu KEW1051) was utilized toread the OCP value Potential dynamic polarization curves

Journal of Chemistry 3

Figure 1 Microstructure of carbon steel API 5L X-70 undermicroscope

were conducted in an ASTM standard cell [18] with athree-electrode system a carbon steel coupon as a workingelectrode a platinum electrode as a counterelectrode anda saturated calomel electrode as a reference electrode AnAutolab PGSTAT 30 with General Purpose ElectrochemicalSystem (GPES) software was used to monitor the corrosionrate of the experiments

232 Cell Counts Planktonic SRB cell enumeration was per-formed to monitor bacteria growth A sterile syringe wasused to withdraw the medium from the vials before themediumwas precisely diluted in distilled water Enumerationof bacteria was counted in the Petroff-Hausser chamberunder an optical microscope at 400x (three times for eachsample) The SRB test kit from Bio Sani-Check productnumber 100 (Sani Check Biosan Lab Inc USA)was also usedto validate the result

233 Weight Loss and SEM Observations The corrosion ratewas calculated based on the weight loss method calculatedfrom the following equation [17]

CR =(119898

1minus 119898

2)

119878 times 119905

(3)

where1198981is the mass of the specimen before corrosion (mg)

119898

2is the mass of the specimen after corrosion (mg) 119878 is the

total exposed area of the specimen (cm2) 119905 is the exposuretime (h) andCR is corrosion rate (mg cmminus2 hminus1)Thebiofilmson the coupon surface were observed using FESEM (modelSupra 35VP) Sessile cells in the biofilm were first fixed in4 (wt) glutaraldehyde for 4 hours and then rinsed witha series of ethanol solutions (25 50 75 and 100purities) to dehydrate the biofilm They were subsequentlydried bymeans of critical point dried (CPD) equipment usingsupercritical CO

2and coated with gold (Au) prior to the

biofilm being examined under FESEM Pits observation onthe coupon surface was obtained by removing the biofilmusing Clarkersquos solution (ASTM G1-03) and washing withdistilled water before being observed under FESEM

3 Results and Discussions

31 Isolated SRB Growth The presence of SRB was detectedbased on visual observation after an incubation period of 7days in Baarrsquos liquid medium The medium turned to blackafter an incubation period of 3 to 4 days at 37∘C After allselective mix-cultures were isolated only 2 samples showedthe presence of SRB (from the SRB kit) while no sampleindicated the presence of iron reducing bacteria (from theIRB kit) Both Sg Ular SRB samples showed rapid growth ina liquid medium The samples also showed positive resultswith the Sani SRB test kit from Bio Sani-Check productnumber 100 (Sani Check Biosan Lab Inc USA) The blackprecipitate was indicative of iron sulfide (FeS) as a reductionof sulfate (SO

4

2minus) to sulfide (S2) The Sg Ular SRB was

grown in solid agar under anaerobic conditions Some ofthe surfaces of the agar have turned black and it was astraightforward task to visualize the SRB colonies (Figure 2)A strong smell of rotten eggs was detected indicating theproduction of H

2S as a result of sulphite-reducing activity

by the SRB Microorganisms were frequently found as amixed culture in their natural habitat Most cells survived byadhering to a surface after they were covered with a layer ofpolysaccharide normally known as biofilms In the biofilmsthe microorganisms developed their own microenvironmentin which their own species could resist harsh conditions[22] The morphologies of the isolated Sg Ular SRB revealedtheir features as related to the Desulfovibrio species basedon the above results Nevertheless in this study no geneticsequence was conducted to identify the type of Desulfovibriosp However it will be undertaken as future work for thisresearch

Figure 3 illustrates the SRB growth curve in the 100mLanaerobic vials incubated at 37∘C for 240 hours The SRBgrowth curve was attained by counting the bacteria cellsunder a microscope at 400x magnification and using a hae-mocytometer method for ATCC 7757 and Sg Ular strainIt is noticeable that the cell number of Sg Ular SRB startedto decrease after 96 hours and the trend continues until theend of experiment The SRB growth curve for both SRBstrain results can be divided into three phases The firstwas an exponential phase that started from the first hourup to 96 hours The number of SRB increased quickly andthe SRB can potentially achieve their maximum number Inthe second phase which was from 96 hours to 168 hoursthere was a steady state where the number of SRB wassteadily maintained for ATCC 7757 SRB only The deadphase was the third phase where the SRB started to dieDuring this phase the number of SRB started to decreaseand the active SRB almost disappearedThe experiments wereconducted in batch units and the bacteria growth decreasedafter a certain period due to the increase in the toxicityof sulfates (FeS or H

2S) towards SRB metabolism Both

SRB strains showed similar behaviour for 240 hours dueto the limited carbon source in the medium This growthcurve also reveals that the Sg Ular SRB showed comparablebehaviour towards a prepared medium and carbon source(lactate)


Figure 2 Colony of Sg Ular SRB grown on agar after 7 days ofincubation at 37∘C anaerobiclly

0 20 40 60 80 100

120

140

160

180

200

220

240

260

Cel

l num

bers

(cel

lmL)

Time (hours)

000E + 00

200E + 07

400E + 07

600E + 07

800E + 07

100E + 08

120E + 08

140E + 08

ATCC7757SRB Sg Ular

Figure 3 SRB growth curves for ATCC and Sg Ular SRB strain for240 hours at 37∘C

32 Corrosion by SRB The corrosion rates of the couponsinoculatedwith andwithout SRBwere calculated as describedin the weight loss procedure [21] and are shown in Table 1Coupons exposed in ATCC 7757 bacteria show higher cor-rosion growth rate (CR) compared to coupons in SRB SgUlar after a 30-day incubation period The values of CR forboth inoculated mediums show similar trends with a higherCR observed compared to a sterile medium proof of theinfluence of SRB activity in the inoculation medium HigherCR values were observed in both inoculated vials certainlydue to S2minus produced by SRB activity Iron sulfide precipitatedon the surface of the coupons to form a passive filmThe EDSanalysis detected the iron sulfide in corrosion products at thecouponsrsquo surface for both types of SRB

The EDS revealed the presence of the corrosion productscell spores and EPS fibres distributed over the coupon TheEDS analyses of the corrosion products for SRB Sg Ularand ATCC 7757 are illustrated in Figures 4(a) and 4(b)respectively Analysis of the corrosion products on thecoupon surface revealed extensively large sulphur (S) andiron (Fe) peaks Gold (Au) peak was observed in Figure 4(b)

CS

FeFe

Fe

O

N

1 2 3 4 5 6 7 8 9 10

(keV)

Full scale 2182 cts cursor 2969 (58 cts)

Spectrum 1

(a)

CS

FeFe

Fe

Fe

ON Au

AuAu

CaCa

070 140 210 280 350 420 490 560 630 700

(keV)

(b)

Figure 4 EDS analysis of biofilms for isolated SRB bacteria andATCC inoculated at 37∘C for 30 days

due to the gold coated procedure conducted for ATCC 7757sample Oxygen peak was also revealed by the analysis due tothe exposure to oxygen during the handling processThe ironsulfide layer was formed on themetal surface by Fe2+ reactingwith the hydrogen sulfide produced by SRBmetabolism [23]

Figure 5 shows the results of open circuit corrosionpotential where (119864corr) was measured again using a standardsaturated calomel electrode in culture solution The 119864corras function of time data showed that the SRB growthsubstantially shifted the 119864corr to a more positive value Thisshift in 119864corr value is known as ennoblement The potentialshift clearly supported the activity and growth of SRB inthe culture medium by enhancing the redox quality of themedium and accelerating the iron dissolution The SRBattached on the coupon surface to develop biofilms and theactive metabolism altered the electrochemical process in thecoupon surface The positive shift of the 119864corr as a functionof time can be observed in Figure 5 for both bacteria Theennoblement can be attributed to the bacteria colonizationand biofilms formation which resulted in organometalliccatalysis and acidification of the electrode surface The enno-blement also promoted localized corrosion such as pittingcorrosion due to the transpassive dissolution of the passivefilm [24]

Figure 6 illustrates the polarization curves (PC) for bothSRB strains inoculated in Baarrsquos medium for incubationperiods of 7 days and 21 days From the extrapolation of theTafel slope corrosion current density (119868corr) corrosion ratesand anodic (120573a) and cathodic (120573c) for SRB in Baarrsquos mediumwere computed as shown in Table 2 At the initial stage ofPC testing on day 7 the surface of the carbon steel couponmight not yet have been fully covered with thick biofilm andcorrosion products This could have contributed to the lowCR recorded (SRB activity still did no influenced the CR)


Table 1 Comparison of corrosion rate for ATCC 7757 and isolated SRB (Sg Ular) inoculated at 37∘C for 30 days

ATCC 7757 SRBrsquos bacteria Corrosion rate (mmyr) Sg Ular SRBrsquos bacteria Corrosion rate (mmyr)Sterile (without bacteria) 00507 plusmn 0013 Sterile (without bacteria) 00346 plusmn 0010Inoculated 02530 plusmn 0040 Inoculated 02017 plusmn 0032

Table 2 Corrosion parameters obtained from Tafel plots for ATCC 7757 and Sg Ular strain for 7 and 21 days of exposure

DaysSRB 119868corr (Acmminus2) Corrosion rate (mmpy) 119861a (Vdec) 119861c (Vdec)

7 ATCC7757 1036119864 minus 5 01204 0280 0060Sg Ular 9385119864 minus 6 01090 0949 0095


OCP

(mV

SCE

)

0 1 2 3 4 7 8 9 10 11 14 15Time (day)

minus750

minus700

minus650

minus600

minus550

minus500

minus450

minus400

ATCC 7757Sg Ular SRB

Figure 5 Plots of open circuit potential for carbon steel with SRBATCC 7757 and Sg Ular SRB

Sg U-A

Sg U-B ATCC-AATCC-B

minus0250

minus0350

minus0450

minus0550

minus0650

minus0750

minus0850

minus0950

minus1050

1000times10minus8

1000times10minus7

1000times10minus6

1000times10minus5

1000times10minus4

1000times10minus3

1000times10minus2

1000times10minus1

Tafel plots-corrosion analysis

E(V

)

i (A)

Figure 6 Tafel plot for ATCC 7757 and Sg Ular Sg U-A is for SgUlar for a 21-day incubation period while Sg U-B is for Sg Ularfor a 7-day incubation period ATCC-A is ATCC 7757 SRB bacteriaincubated for 21 days and ATCC-B is ATCC 7757 for 7 days

Figure 7 SEM micrograph of the morphology of the corrosion forSg Ular SRB strain after 30 days

Higher CR was recorded on day 21 for both SRB strains Thiscould be attributed to the fact that the SRB activity producedhydrogen sulfide (H

2S) as a secondarymetaboliteH

2S which

can easily be diluted in the medium to corrode carbon steelThis is evidence to suggest that the electrochemical corrosionbehaviour of carbon steel is influenced mainly by the redoxquality on the biofilm and the redox quality mainly dependson the SRB metabolism activity The corrosion rate is barelyrelated to SRB itself but the biology activity of SRB is the keyfactor in influencing the corrosion

33 Microscopic Observation Figures 8 and 9 show the SEMimages of corrosion products and biofilms developed oncarbon steel coupons exposed to the Sg Ular strain andATCC 7757 for 30 days Figures 8 and 9 represent the SgUlar SRB strain and the ATCC 7757 SRB strain respectivelyAccording to the images as shown in Figure 8 typicalDesulfovibrio sp SRB cells were observed with rod shapeswith approximately 15minus20 120583m sizes After the carbon steelsamples were cleaned the surface analysis was done again toobserve the morphology of the coupon Figure 7 show someof the morphology of the carbon steel coupon exposed tothe SRB Sg Ular Pitting corrosion was observed with thesize approximated 20 120583m The morphology of the corrosionprocess is identified as localised to form pitting defect


Figure 8 SEM images of the biofilms incubated at 37∘C for 30 daysfor isolated Sg Ular strain

Figure 9 SEM images of the biofilms incubated at 37∘C for 30 daysfor ATCC 7757 strain

4 Conclusion

The consortium of bacteria suspected to be the SRB strainwas successfully screened from the mudsoil sample takenfrom Sg Ular site Even though no genetic sequence wasconducted according to the results from SRB kits morphol-ogy images corrosion studies and other methods of testingshowed comparable effects and features with the ATCC 7757strain The growth of SRB in the limited containing culturemedium showed three stages of SRB growth namely theexponential phase the steady phase and the dead phaseThe ennoblement mechanism was observed from both of

the Sg Ular SRB and ATCC 7757 strains by shifting thecorrosion potential to a more positive value The corrosionrate of the carbon steel coupon was mainly affected by theSRB metabolisms activity by producing H

2S and changing

the redox potential Surface analysis showed pitting corrosionmorphologies on the carbon steel coupon inoculated withisolated SRB The EDS analysis supported the finding withhigh peak of Fe and S due to the presence of iron sulfideThe modelling of potential metal loss of steel pipeline in SgUlar area can be carried out using the laboratory ATCC 7757strain since the growth behaviour and the impact on metalloss by this manufactured strain are comparable to Sg UlarSRB strain hence minimising the isolation of bacteria strainfrom the site

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors wish to acknowledge the financial support fromMinistry of Education of Malaysia through RAGS Votenumber RDU131414 Universiti Malaysia Pahang (UMP) andUniversiti Teknologi Malaysia (UTM)

References

[1] C G Peng and J K Park ldquoPrincipal factors affecting microbi-ologically influenced corrosion of carbon steelrdquo Corrosion vol50 no 9 pp 669ndash675 1994

[2] R Jeffrey and R E Melchers ldquoBacteriological influence in thedevelopment of iron sulphide species in marine immersionenvironmentsrdquo Corrosion Science vol 45 no 4 pp 693ndash7142003

[3] R Javaherdashti ldquoA review of some characteristics of MICcaused by sulfate-reducing bacteria past present and futurerdquoAnti-Corrosion Methods and Materials vol 46 no 3 pp 173ndash180 1999

[4] R Zuo D Ornek B C Syrett et al ldquoInhibiting mild steelcorrosion from sulfate-reducing bacteria using antimicrobial-producing biofilms inThree-Mile-Island processwaterrdquoAppliedMicrobiology and Biotechnology vol 64 no 2 pp 275ndash2832004

[5] R Sooknah S Papavinasam and R W Revie ldquoValidation ofa predictive model for microbiologically influenced corrosionrdquoin Proceedings of the Corrosion Conference and Expo (CORRO-SION rsquo08) NACE International Houston Tex USA 2008

[6] G A Jacobson ldquoCorrosion at Prudhoe Baymdasha lesson on thelinerdquoMaterials Performance vol 46 no 8 pp 26ndash34 2007

[7] D Xu Y Li F Song and T Gu ldquoLaboratory investigation ofmicrobiologically influenced corrosion of C1018 carbon steelby nitrate reducing bacteriumBacillus licheniformisrdquoCorrosionScience vol 77 pp 385ndash390 2013

[8] H Venzlaff D Enning J Srinivasan et al ldquoAccelerated cathodicreaction in microbial corrosion of iron due to direct electronuptake by sulfate-reducing bacteriardquo Corrosion Science vol 66pp 88ndash96 2013


[9] D Enning H Venzlaff J Garrelfs et al ldquoMarine sulfate-reducing bacteria cause serious corrosion of iron under elec-troconductive biogenic mineral crustrdquo Environmental Microbi-ology vol 14 no 7 pp 1772ndash1787 2012

[10] M Madigan Brock Biology of Microorganisms Pearson Ben-jaminCummings San Francisco Calif USA 12th edition 2009

[11] T Gu K Zhao and S Nesic ldquoA practical mechanistic modelfor MIC based on Biocatalytic Cathodic Sulphate Reduction(BCSR) theoryrdquo in Proceeding of the CORROSION ConferenceNACE International Atlanta Ga USA 2009

[12] D Xu and T Gu ldquoCarbon source starvation triggered moreaggressive corrosion against carbon steel by the Desulfovibriovulgaris biofilmrdquo International Biodeterioration amp Biodegrada-tion vol 91 pp 74ndash81 2014

[13] D Xu and T Gu ldquoBioenergetics explains when and why moresevere MIC pitting by SRB can occurrdquo in Proceedings of theCORROSION Houston Tex USA 2011

[14] J W Costerton The Biofilm Primer Springer New York NYUSA 1st edition 2007

[15] D XuWHuang G Ruschau J Hornemann JWen and T GuldquoLaboratory investigation of MIC threat due to hydrotest usinguntreated seawater and subsequent exposure to pipeline fluidswith and without SRB spikingrdquo Engineering Failure Analysisvol 28 pp 149ndash159 2013

[16] C Y Cheuk W A Take M D Bolton and J R M S OliveiraldquoSoil restraint on buckling oil and gas pipelines buried in lumpyclay fillrdquo Engineering Structures vol 29 no 6 pp 973ndash982 2007

[17] M Ahammed ldquoProbabilistic estimation of remaining life of apipeline in the presence of active corrosion defectsrdquo Interna-tional Journal of Pressure Vessels and Piping vol 75 no 4 pp321ndash329 1998

[18] M Ahammed and R E Melchers ldquoProbabilistic analysis ofunderground pipelines subject to combined stresses and corro-sionrdquo Engineering Structures vol 19 no 12 pp 988ndash994 1997

[19] J Xu K Wang C Sun et al ldquoThe effects of sulfate reducingbacteria on corrosion of carbon steel Q235 under simulateddisbonded coating by using electrochemical impedance spec-troscopyrdquo Corrosion Science vol 53 no 4 pp 1554ndash1562 2011

[20] D Cetin andM L Aksu ldquoCorrosion behavior of low-alloy steelin the presence ofDesulfotomaculum sprdquoCorrosion Science vol51 no 8 pp 1584ndash1588 2009

[21] N M Noor N Yahaya A Abdullah M M Tahir and L KSing ldquoMicrobiologically influenced corrosion of X-70 carbonsteel by Desulfovibrio vulgarisrdquo Advanced Science Letters vol13 pp 312ndash316 2012

[22] WAHamilton andWGCharacklis ldquoRelative activities of cellsin suspension and in biofilms in Charaklisrdquo in Structure andFunction of Biofilms W G Charaklis and P A Wilderer EdsJohn Wiley amp Sons New York NY USA 1989

[23] F K Sahrani M Aziz Z Ibrahim and A Yahya ldquoOpen circuitpotential study of stainless steel in environment containingmarine sulphate-reducing bacteriardquo Sains Malaysiana vol 37no 4 pp 359ndash364 2008

[24] I T E Fonseca M J Feio A R Lino M A Reis and V LRainha ldquoThe influence of the media on the corrosion of mildsteel by Desulfovibrio desulfuricans bacteria An electrochemi-cal studyrdquo Electrochimica Acta vol 43 no 1-2 pp 213ndash222 1998

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of carbon steel compared to well-fed SRB [12 13] Underpoor nutritional conditions SRB cell can possibly scavengeorganic carbons from dead cells [14] and also maintain theirenergy by turning to iron (Fe) as an electron donor due toa similar reduction potential value of lactate (Fe2+ minus447mVand lactate minus430mV) Xu et al [15] explained their BCSRtheories by showing the combined redox reaction to have apositive potential of +230mV This positive value of redoxpotential means the reaction is thermodynamically favorableConsider

Anodic 4Fe 997888rarr 4Fe2+ + 8eminus (Iron dissolution)

119864


(1)

Cathodic SO4

2minus+ 9H+ + 8eminus 997888rarr HSminus + 4H

2O (BCSR)

119864


(2)

Petroleum products and natural gas are commonly trans-ported by buried pipelines under the soil for mechanicalprotection from third-party damage to provide thermalinsulation [16] Failure mechanisms associated with pipelinescan be classified into three categories third-party damagematerial defects and corrosion Corrosion is recognised asone of the most dominant forms of the deterioration processand has been identified as one of the major causes of lossof containment in steel pipelines [17] Corrosion may attackthe pipelines either internally or externally or both Externalcorrosion is amajor factor contributing to the deterioration ofburied pipelines by weakening the pipe wall which increasesthe risk of failure [18] Even though buried pipelines areprotectedwith coatings and cathodic protection the pipelinesare still vulnerable to various types of corrosion mechanisms[19] MIC is one of the possible threats to buried pipelinesbecause SRB grow well in soil sediment [20]

In order to understand the intrinsic mechanisms of MICit is necessary to study if the consortium of SRB bacteriaspecies may diversify the influence on corrosion mechanismIn this paper the corrosion behavior of ATCC 7757 SRB iscompared to consortia of SRB isolated from Malaysian soilThe corrosion of carbon steel grade API 5L X-70 subject tomicrobial activity is monitored and measured under labora-tory conditions The findings may reveal the discrepanciesbetween a single strain of SRB and the consortium of SRBisolated from underground in terms of bacteria metabolismand corrosion initiation This topic is also relevant for initialrecognition of bacterial species

2 Materials and Methods

21 Sulfate-Reducing Bacteria Two types of SRB were usedin this study obtained from different sources The firstbacteria strain was sourced from the American Type Cul-ture Collection with reference number ATCC 7757 whilethe second SRB strain was obtained by a simple isolationtechnique from soilmud near the natural gas pipeline in

Peninsular Malaysia during pipe maintenance work The sitewas selected based on the pipeline operator maintenancerecord (severe external corrosion from pigging record) TheSRB strain was named SRB Sg Ular for easy identificationof the site location The simple isolation was conducted byinoculating the black stainbiofilm from the pipeline undera disbonded coating in 500mL nutrient-rich Baarrsquos mediumunder anaerobic conditions at 37∘C The composition ofthe medium consisted of sodium lactate 60 gL sodiumsulfate 45 gL ammonium chloride 10 gL yeast extract10 gL potassium phosphate 05 gL sodium citrate 03 gLcalcium chloride 006 gL magnesium sulfate 006 gL andiron sulfate 0004 gL The pH of the medium was adjustedto 70 before being autoclavedThemediumwas sparged withoxygen-free nitrogen after being autoclaved SRB were thendetected by regrowth of the SRB with Starkeyrsquos medium asthe selective growth medium The bacteria strains obtainedfrom the above exercise were then tested using a SRB kit aniron reduction bacteria (IRB) kit (LAB-BART Kit DroyconBioconcepts Inc Canada) and a Sani SRB test kit from Sani-Check product number 100 (Sani Check Biosan Lab IncUSA)

22 Materials The corrosion specimens were machinedfrom an actual segment of API 5L X-70 pipe obtained froma local gas operator The composition of the carbon steelis as follows 97093 Fe 0078 C 167 Mn 015 Ni0012 P 03 Si 0023 Cu 0275 Cr 011 Ti and0002 S [21] Prior to use the metal coupons were polishedwith a SiC grit paper graded 200 400 and 600 followedby cleaning with acetone and coated with Teflon leavingonly the flat surface exposed to the medium in an anaerobicbottle experimentThe corrosion specimen used as a workingelectrode was mounted in an epoxy resin with copper wireconnected to an exposed flat surface approximately 1 cm2in areas Figure 1 shows the microstructure of the API5L X-70 carbon steel under the microscope The couponsconsisted of ferrite and eutectoid pearlite based on thelight and gray constituent color from the microstructureimage

23 Method

231 Experiment The experiment was performed in a125mL sealed anaerobic vial and in a 1-liter electrochemicalglass cell All devices involved in this experiment weresterilized in an autoclave at 121∘C Necessary care wastaken at all times to avoid bacterial contamination andthe experiments were conducted under simulated anaerobicconditions Nitrogen for the medium was purged by usingfiltered oxygen-free nitrogenThe deoxygenation process wasconducted for approximately 1 hour for 1 liter of medium Anopen circuit potential (OCP)measurement was conducted byusing a saturated calomel electrode (SCE) as the referenceelectrode and carbon steel as the working electrode in astandard electrochemical glass cell with the SRB medium aselectrolyte A multimeter (Kyoritsu KEW1051) was utilized toread the OCP value Potential dynamic polarization curves






CR =(119898

1minus 119898

2)

119878 times 119905

(3)


119898







4










0 20 40 60 80 100

120

140

160

180

200

220

240

260

Cel

l num

bers

(cel

lmL)

Time (hours)

000E + 00

200E + 07

400E + 07

600E + 07

800E + 07

100E + 08

120E + 08

140E + 08

ATCC7757SRB Sg Ular




CS

FeFe

Fe

O

N

1 2 3 4 5 6 7 8 9 10

(keV)


Spectrum 1

(a)

CS

FeFe

Fe

Fe

ON Au

AuAu

CaCa

070 140 210 280 350 420 490 560 630 700

(keV)

(b)












OCP

(mV

SCE

)

0 1 2 3 4 7 8 9 10 11 14 15Time (day)

minus750

minus700

minus650

minus600

minus550

minus500

minus450

minus400



Sg U-A

Sg U-B ATCC-AATCC-B

minus0250

minus0350

minus0450

minus0550

minus0650

minus0750

minus0850

minus0950

minus1050

1000times10minus8

1000times10minus7

1000times10minus6

1000times10minus5

1000times10minus4

1000times10minus3

1000times10minus2

1000times10minus1


E(V

)

i (A)





2S which






4 Conclusion



2S and changing




Acknowledgments


References



































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of






CR =(119898

1minus 119898

2)

119878 times 119905

(3)


119898







4










0 20 40 60 80 100

120

140

160

180

200

220

240

260

Cel

l num

bers

(cel

lmL)

Time (hours)

000E + 00

200E + 07

400E + 07

600E + 07

800E + 07

100E + 08

120E + 08

140E + 08

ATCC7757SRB Sg Ular




CS

FeFe

Fe

O

N

1 2 3 4 5 6 7 8 9 10

(keV)


Spectrum 1

(a)

CS

FeFe

Fe

Fe

ON Au

AuAu

CaCa

070 140 210 280 350 420 490 560 630 700

(keV)

(b)












OCP

(mV

SCE

)

0 1 2 3 4 7 8 9 10 11 14 15Time (day)

minus750

minus700

minus650

minus600

minus550

minus500

minus450

minus400



Sg U-A

Sg U-B ATCC-AATCC-B

minus0250

minus0350

minus0450

minus0550

minus0650

minus0750

minus0850

minus0950

minus1050

1000times10minus8

1000times10minus7

1000times10minus6

1000times10minus5

1000times10minus4

1000times10minus3

1000times10minus2

1000times10minus1


E(V

)

i (A)





2S which






4 Conclusion



2S and changing




Acknowledgments


References



































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



0 20 40 60 80 100

120

140

160

180

200

220

240

260

Cel

l num

bers

(cel

lmL)

Time (hours)

000E + 00

200E + 07

400E + 07

600E + 07

800E + 07

100E + 08

120E + 08

140E + 08

ATCC7757SRB Sg Ular




CS

FeFe

Fe

O

N

1 2 3 4 5 6 7 8 9 10

(keV)


Spectrum 1

(a)

CS

FeFe

Fe

Fe

ON Au

AuAu

CaCa

070 140 210 280 350 420 490 560 630 700

(keV)

(b)












OCP

(mV

SCE

)

0 1 2 3 4 7 8 9 10 11 14 15Time (day)

minus750

minus700

minus650

minus600

minus550

minus500

minus450

minus400



Sg U-A

Sg U-B ATCC-AATCC-B

minus0250

minus0350

minus0450

minus0550

minus0650

minus0750

minus0850

minus0950

minus1050

1000times10minus8

1000times10minus7

1000times10minus6

1000times10minus5

1000times10minus4

1000times10minus3

1000times10minus2

1000times10minus1


E(V

)

i (A)





2S which






4 Conclusion



2S and changing




Acknowledgments


References



































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of








OCP

(mV

SCE

)

0 1 2 3 4 7 8 9 10 11 14 15Time (day)

minus750

minus700

minus650

minus600

minus550

minus500

minus450

minus400



Sg U-A

Sg U-B ATCC-AATCC-B

minus0250

minus0350

minus0450

minus0550

minus0650

minus0750

minus0850

minus0950

minus1050

1000times10minus8

1000times10minus7

1000times10minus6

1000times10minus5

1000times10minus4

1000times10minus3

1000times10minus2

1000times10minus1


E(V

)

i (A)





2S which






4 Conclusion



2S and changing




Acknowledgments


References



































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




4 Conclusion



2S and changing




Acknowledgments


References



































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

Research Article Microbial Corrosion of API 5L X-70 Carbon...

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