effect of microstructure on hydrogen diffusion in weld and...

Research ArticleEffect of Microstructure on Hydrogen Diffusion in Weld andAPI X52 Pipeline Steel Base Metals under Cathodic Protection

R C Souza1 L R Pereira1 L M Starling1 J N Pereira1 T A Simotildees12

J A C P Gomes3 and A H S Bueno1

1Mechanical Engineering Department Universidade Federal de Sao Joao Del Rei (UFSJ) 170 Praca Frei Orlando36307-352 Sao Joao Del Rei MG Brazil2Postgraduate Program in Materials Science and Engineering Universidade Federal da Paraıba (UFPB) Joao Pessoa PB Brazil3Metallurgical and Materials Engineering Department Universidade Federal do Rio de Janeiro (UFRJ) Ilha do FundaoBloco F Rio de Janeiro RJ Brazil

Correspondence should be addressed to A H S Bueno alyssonbuenoufsjedubr

Received 28 June 2017 Accepted 7 September 2017 Published 12 October 2017

Academic Editor Ramazan Solmaz

Copyright copy 2017 R C Souza et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

The aim of this research was to evaluate the influence of microstructure on hydrogen permeation of weld and API X52 base metalunder cathodic protectionThemicrostructures analyzed were of the API X52 as received quenched and annealed and the weldedzoneThe test was performed in basemetal (BM) quenched basemetal (QBM) annealed basemetal (ABM) andweldmetal (WM)Hydrogen permeation flows were evaluated using electrochemical tests in a Devanathan cell The potentiodynamic polarizationcurves were carried out to evaluate the corrosion resistance of each microstructure All tests were carried out in synthetic soilsolutions NS4 and NS4 + sodium thiosulfate at 25∘CThe sodium thiosulfate was used to simulate sulfate reduction bacteria (SRB)Through polarization assays established that the microstructure does not influence the corrosion resistance The permeation testsshowed that weld metal had lower hydrogen flow than base metal as received quenched and annealed

1 Introduction

The great challenge for increasing oil and gas productionshas been the need for more detailed studies related to steelfor pipelines applications Therefore the knowledge aboutmechanical behavior and microstructure of steels [1 2] formanufacturing these pipelines is important to assure integrityand safety conditions of operation which is extremely impor-tant for oil and gas industry [3 4]

It requires a continual improvement of steels grade APIX52 [5] in order to prevent failure Han et al [6] showedthat the welding procedure involved in the manufacture ofpipes might modify the microstructure of the base metalin the region of heat-affected zone (HAZ) Therefore themechanical properties in this region are changed

Metal fractures related to ldquoenvironmentally inducedcrackingrdquo are often associated with stress corrosion cracking(SCC) or hydrogen embrittlement (HE) mechanisms [7ndash9]Some researchers believe that the process of external cracking

of pipelines in contact with soil pH near neutral is associatedwith HE instead of SCC [2 4 10]

The initial process in HE is associated with the diffusionof hydrogen through the material Hydrogen permeationstarts when there is atomic hydrogen on the metal surfacetherefore the hydrogen can diffuse into the metal A largeamount of atomic hydrogen can recombine inside the metalforming H

2 which is retained in the form of gas bubble

under high pressure inside the metal Furthermore it is wellknown that initiation and propagation of cracks occur fromthese points of hydrogen concentration [11] Therefore itis important to evaluate if the hydrogen diffusion occursdifferently through different microstructure such as basemetal and weld metal

In pipelines the external HE is associated with theexcessive cathodic potential imposed and soils contaminatedwith sulfate-reducing bacteria (SRB) [12] Contreras et al[13] pointed out that minimal amounts of H

2S are enough

to cause HE Then external cracking caused by hydrogen

HindawiInternational Journal of CorrosionVolume 2017 Article ID 4927210 14 pageshttpsdoiorg10115520174927210

2 International Journal of Corrosion

Table 1 Chemical analysis of the base metal (BM) and the weld metal (WM) API X52 carbon steel

Material Components (wt)C Si Mn P S Cr Ni Mo V Cu

BM 028 033 111 003 002 005 002 001 0001 002WM 016 020 047 003 003 003 002 015 0002 002

embrittlement could be associated with SRB These bacteriause sulfate as an oxidizing agent reducing to sulfide (H

2S)

Plus they can also utilize oxidized sulfur compounds suchas thiosulfate and sulfite or even elemental sulfur In thepresence of H

2S produced by these bacteria the reaction of

atomic hydrogen recombination to molecular hydrogen isretarded thereby permitting the diffusion of atomic hydrogenthrough the metal [10]

Microbiologically influenced corrosion (MIC) is a majorproblem inmany industries such as oil and gas According toXu et al [14] many attacks of anaerobic MIC can be classifiedby two types based on the two anaerobic metabolisms res-piration and fermentation Therefore the mechanism of SRBinvolvesmicroorganisms that perform an aerobic respirationFor example SRB respiration typically uses sulfate as theterminal electron acceptor Venzlaff et al [15] reported thatSRB gain biochemical energy for growth by reducing sulfate(SO4) to sulfide (H

2S HSminus) with natural organic compounds

as electron donors which are oxidized to CO2(also referred

to as sulfate respiration) However if the SRB have contactwith carbon steel the Fe acts as an electron donor for itsrespiration [16] Then the reaction involved in anaerobicrespiration using Fe0 is Fe minus Fe2+ + 2eminus In the absence ofoxygen electrons must be accepted by a nonoxygen oxidant[13] thus SRB use SO

4as an oxidizing agent SO

4is reduced

to H2S and HSminus through the reaction SOminus4 + 9H+ + 8eminus =

HSminus + H2O

Horowitz [17] showed an increase in the amount ofhydrogen during permeation tests with the use of sodiumthiosulfate solution The sodium thiosulfate solution allowsthe generation and stabilization of H

2S on the metallic

surfaceThese tests were carried out applying cathodic poten-tials According to Pourbaix diagram for H

2S when cathodic

potential is imposed the steel is located into H2S domain

[18]Therefore the sodium thiosulfate is reduced to H2SThe

reaction depends on the potential applied and the pH of thesolution

Another problem related to HE is because the steelsused in the manufacture of pipelines for transporting oiland derivatives are exposed to excessive cathodic protectionTherefore cathodic potentials imposed on the external partof pipelines promote hydrogen reduction which becomesthermodynamically spontaneous on the metal surface [19]Bueno et al [4 12] report that API X46 carbon steel exhibiteda decreasing ductility as long as cathodic potentials wereimposed This effect was more evident in soil solutionsthan in NS4 standard solution The deterioration mecha-nism is related to the influence of hydrogen Transgranularcracking occurred even under cathodic conditions wherethe anodic dissolution of the steel can be considered asnegligible

Recent studies gave emphasis to the influence of themetal structure in hydrogen permeation [1 2 20] and discussthe effective diffusion coefficient Lan et al [1] studied thehydrogen permeation behavior in relation to microstructuralevolution of low carbon bainitic steel weldments Theyhave shown that the effective diffusion coefficient in thewelded joint is highly affected by the heat input This ismainly due to coarsening grain and inclusion sizes Parket al [2] tested the hydrogen trapping efficiency of APIX65 and showed an increase in order of ferritedegeneratedpearlite ferritebainite and ferriteacicular ferrite Haq et al[20] showed that due to hydrogen trapping X70 mediumstrip exhibits lower hydrogen diffusivity than the standardMn strip This is mainly due to finer ferrite grains and ahigher density of carbonitride precipitates Fischer et al [21]indicated that under specific circumstances the diffusionof hydrogen cannot be described well by a constant effec-tive diffusion coefficient due to the presence of hydrogentraps and the magnitude of the concentration gradient ofhydrogen

The aim of this paper was to evaluate the influence ofmicrostructure and some inclusions on the susceptibilityof hydrogen permeation of API X52 carbon steel (basemetal and weld metal) submitted to the cathodic protectionsystem Different types of microstructures were obtained byheat treatments such as quenching and annealing underdifferent temperatures The hydrogen permeation tests inthese microstructures were compared and evaluated in thepresence of a synthetic modified soil solution NS4 + sodiumthiosulfate concentration of 10minus2M

2 Methods and Materials

Thematerial usedwas anAPI X52 pipeline carbon steel underdifferent conditions base metal as received welded metalbase metal after quenching heat treatment base metal afterannealed heat treatmentThe evaluation of the chemical com-position was carried out by Optical Emission Spectroscopy(OES) Table 1 shows the results in weight percent (wt) ofthe chemical elements present in the base metal (BM) andthe weld metal (WM)

The microstructures of the samples were produced bydifferent heat treatment Basemetals were heated at 900∘C fortwo hours Then the samples were submitted to a quenchingprocess performed in a solution of water ice and salt Theannealed samples were left in the oven until it reaches at roomtemperature All the tests were performed in triplicate Thespecimens and conditions of heat treatment are described inTable 2

The metallographic analysis and microstructure char-acterization were performed according to Bott et al [24]

International Journal of Corrosion 3

Table 2 Terminology and heat treatment conditions of API X52 carbon steel the samples

Terminology Heat treatment conditionsBase metal (BM) As received of the industryAnnealed base metal (ABM) Heated at 900∘C cold in the ovenQuenching base metal (QBM) Heated at 900∘C cold in water ice and saltWeld metal (WM) Removed from the welded joint of the pipeline as received

in order to reveal the microstructures obtained after theheat treatments described in Table 2 The metallographicanalyses were carried out by optical microscopy (OM Leicamodel DM 2500P) and scanning electron microscopy (SEMHitachi model TM 3000) The samples were embedded inBakelite ground with SiC paper up to 1200 grit polished withdiamond paste up to 025 120583m and polished with 004120583msilica suspension Etching of themetal surface was done usingNital 2 for five seconds The samples used for inclusionsanalysis were evaluated without chemical attack

The presence of austenite-martensite phases was detectedby SEM after double electrolytic attack The following stepswere used to the attack initially 5 g EDTA 05 g of NaF and100ml of distilled water at 5 V for 15 seconds were usedsecondly 5 g of picric acid and 25 g NaOH were used finally100ml of distilled water at 100V for 5 seconds was used

The hardness tests were conducted to supplement thematerials characterization These were performed on Rock-well B scale using sphere 11610158401015840 with a load of 100 kg andRockwell C using diamond cone with a load of 150 kg

The electrochemical test performedwas potentiodynamicpolarization curves The potentiostat used in polarizationtests was AUTOLAB models 120583Autolab type IIIFRA 2 andPGSTAT 128N coupled to computers NOVA 110 softwareThe scan rate adopted was 10mVsdotsminus1 and the appliedpotential range covered a value of minus15 V to 05 V Themeasurements were performed at room temperature (25∘C plusmn3∘C) The cell used was a conventional three-electrode cellbeing platinum as counter electrode saturated calomel (SCE)as reference electrode and the working electrode (samples ofAPI X52 carbon steel)The specimens for the electrochemicaltests were cut embedded in cold resin and ground withSiC paper up to 600 grit The exposed area of the samplesfor permeation tests at Devanathan cell was 075 cm2 Forpolarization experiments the exposed area was 1 cm2

Synthetic soil solution also called NS4 solution wasused during the test to simulate a synthetic soil with pHaround 84 The solution was made according to Parkins etal [25] The composition was (in gl) KCl 0122 NaHCO

3

0483 CaCl2 0093 and MgSO

4 0131 Plus the synthetic

solutionNS4+ sodium thiosulfatewas used to study the effectcaused by sulfate-reducing bacteria It was prepared with aconcentration of 10minus2Mof sodium thiosulfate in the standardNS4 solution Some studies [26] adjust the pH to 65ndash7 inorder to evaluate soils with this characteristic by bubbling amixture of CO

2and N

2

The hydrogen permeation tests were carried out withthe most aggressive solution NS4 + sodium thiosulfate Thepotentiostat used in hydrogen permeation tests was AUTO-LAB models 120583Autolab type IIIFRA 2 and PGSTAT 128 N

coupled to computers NOVA 110 software The Devanathancell was utilized in the test using specimenswith a thickness of2mm Both sides of the steel specimen were in contact withdifferent solutions controlled by independent potentiostatsThe anodic side of the cell was filled with 1M of NaOHsolution and the cathodic side was filled with NS4 + sodiumthiosulfate solution The counter electrode of the anodicside cell was attached to a computer to measure the anodiccurrent Hydrogen permeation tests were carried out in thefollowing steps

(1) Assemble the hydrogen permeation Devanathan cellcontaining the steel specimen

(2) 1MNaOH solution was introduced in the anodic sideand the system was stabilized at the open circuit potential(OCP)

(3) Application of anodic potential 100mV above thefree corrosion potential was done at the anodic side untilthe anodic passive current density became stable and below1Acm2

(4) Introduction of NS4 solutions was done in thecathodic side which remained at the open circuit potentialduring 20 h

(5) Application of cathodic potential of minus15 V (ECS) wasdone for 24 h The test piece used was a flat plate of APIX52 steel polished with diamond paste on both sides withthickness and permeation section area constantThe cathodicpotential applied of minus15 V below OCP was carried out inorder to simulate cathodic protection system [27] once ISO15589-1 indicates that from values lower than minus12 V the steelis already suffering effects of hydrogen embrittlement

The diffusion coefficient (119863) in transient state can bemeasured through various different methods as found in theliterature In this research the three most common methodswere used Time Lag Breakthrough and Fourier calculatedaccording to literature [20 28 29]

3 Results and Discussions

31 Chemical Analysis The API 5L standard [5] classifiescarbon steel for the manufacture of pipes used in pipelinestransportation system in the petroleum and natural gasindustriesThe requirements used in the standard are dividedinto two levels for seamless and welded pipelines PSL1 andPSL2 The PSL1 requirement is a loose standard quality forline pipe whereas PSL2 contains additional testing require-ment and stricter chemical physicals along with differentceiling limits of mechanical properties and requires Charpyimpact testing conditions According to Table 3 base metalreaches the chemical requirement of PSL1 however the sameis nonconformity with PSL2 due to the carbon content limits


Table 3 Chemical composition specification of API 5L PSL1 andPSL2 (wt)

API 5L Pipelines C Mn P S

PSL1-X52 Seamless 0280 1400 0030 0030Welded 0260 1400 0030 0030

PSL2-X52N Seamless 0240 1400 0025 0015Welded 0220 1400 0025 0015

Table 4 Measures hardness of the samples studied

Test condition HardnessAPI X52-BM 84HRBAPI X52-WM 80HRBAPI X52-ABM 67HRBAPI X52-QBM 24HRB

(Table 1) Weld metal is in accordance with the requiredspecifications of PSL2 chemical composition

32 Metallographic Features The metallographic character-ization of the samples was conducted on all heat treatmentconditions specified on Table 2 base metal (BM) weld metal(WM) annealed basemetal (ABM) and quenched basemetal(QBM) The hardness tests were performed to complementthe materials characterization as shown in Table 4 Figure 1shows optical microscopy image of the positions where themetallographic analyses were performed

Figure 2 presents the interface between WM and HAZshowing the difference between the microstructures HAZpresents mainly pearlite grains shown to be affected by theheat produced during the welding process According toVargas-Arista et al [30] SEM analysis HAZ generated bythe welding thermal cycle showed a complex recrystallizedmicrostructure located near to the fusion line formed bycoarse-grained ferrite acicular ferrite small discontinuouspearlite colonies and few bainite grains

Base metal (Figure 3) presented heterogeneous distribu-tion of ferrite and fine pearlite grains with grain bound-aries well-definedThis microstructure arrangement presentsan intermediary value for hardness in Table 4 The samemicrostructure for the API X52 steel was found in severalother literatures [31 32] owning a ferritic-pearlitic combina-tion

The weld metal in region 4 (Figure 4) showed a mi-crostructure formed by low recrystallization where it ispossible to observe pearlitic microstructure and a decreasein grain size with degenerated pearlite regions This fact wasdiscussed by Park et al [2] and can be explained because thedegenerated pearlite structure without the banding patternwas different from pearlite evolved by normalizing and slowcooling treatment The cooling rate in the weld metal washigher thannecessary to form typical pearlite thus the carbondiffusion was not enough to create lamellar structure ofcementite

Figure 5 shows the heat-affected zone (HAZ) where thereis a great similarity with the microstructure of the BM the

1 2

34 5

Figure 1 Optical microscopy image (lowmagnification) of the weldzone in API X52 carbon steel and regions analyzed

little difference is due to the thermal effect caused by thedeposition of the weld bead which provides an increase grainboundary density in the microstructure of HAZ

Scanning electron microscopy (SEM) was performedat 3 different positions at the welded joint as shown inoptical image on Figure 6 The BM (Figure 7(a)) presentspredominate phases of ferrite and pearlite The HAZ andWM (Figures 7(b) and 7(c)) present phases of ferrite andpearlite with constituents of martensiteaustenite (MA) thisconstituent cannot be observed by optical analysis (OM)called constituent MA or micro phase MA regions ofmicroscopic dimensions presented in C-Mn steels and lowalloy that consists of cells stabilized austenite Chatzidouros etal [31] emphasize that most pipeline steels are manufacturedusing thermomechanical processes that involve multipleheating and rolling stages which favor the formation of MAconstituents in low carbon steels This micro constituentdirectly affects the tenacity of material due to high hardnessand fragility where the high density of discordances inthe submicrostructure contributes to this formation TheMA sites are mostly present in the grain boundaries offerrite and bainite grains shown in Figure 7(c) howeverthey occasionally could also be observed within the phase ofpearlite between the cementite lamellar

Observations of the materials without chemical attackrevealed the presence of a significant amount of inclusionsas shown in Figure 8

EDS technique was used to evaluate the composition ofthe inclusions Figure 9 shows the WM inclusions analysesTherefore the inclusions presented in API X52 carbon steelshowed besides aluminum and calcium significant concen-trations of S andMn Haq et al [20] have concluded thatMnSinclusions are considered strong irreversible trapping sitesfor hydrogen working as follows during the solidification ofsteel Mn can combine with S giving rise to MnS inclusionsThe behavior of inclusionsmatrix metal interface is reportedby literature as strong trapping sites for hydrogen conse-quently decreasing the hydrogen flux through the material

After heat treatments SEM analyses show that the ABM(Figure 10(a)) and BM (Figure 7(a)) present the samemicrostructure however the BM grain size is slightly lowerThis is evidenced by the greater hardness submitted by BMThe quenched base metal specimens presented martensiticstructure but due to the low carbon they have noted someferrite sites as proved in Figure 10(b) The heat treatmentchanges can also be noted in hardness values (Table 4) where


WM

HAZ

(a)

WM

HAZ

(b)

Figure 2 Optical microscopy image of the interface between weld metal and the heat-affected zone (a) at position 1 (b) at position 2 (bothwith magnification of 200x)

(a) (b)

Figure 3 Optical microscopy image of base metal at position 3 under different magnifications (a) 200x and (b) 500x

(a) (b)

Figure 4 Optical microscopy image of weld metal at position 5 under different magnifications (a) 200x and (b) 500x


Table 5 OCP current density at 50mV and 100mV above the OCP

Testcondition Solution pH OCP

(ECS)

E50mV

above OCP(mV)

i50mV above OCP

(120583Acm2)

E100mV above OCP

(mV)

i100mV above OCP

(120583Acm2)

BM NS4 84 minus0716 minus0666 2597119864 minus 5 minus0616 6796119864 minus 5

NS4 + thiosulfate 86 minus0766 minus0716 8847119864 minus 5 minus0667 2175119864 minus 4

WM NS4 81 minus0695 minus0645 6247119864 minus 5 minus0595 1185119864 minus 4


QBM NS4 + thiosulfate 79 minus0743 minus0692 1125119864 minus 4 minus0642 3231119864 minus 4

ABM NS4 + thiosulfate 83 minus0766 minus0717 8401119864 minus 5 minus0667 2568119864 minus 4

(a) (b)

Figure 5 Optical microscopy image of heat-affected zone at position 5 under different magnifications (a) 200x and (b) 500x

1 2 3

Figure 6 Optical image of the weld zone in API X52 carbon steeland regions analyzed by SEM secondary electron image with highmagnification

there is a significant difference in hardness betweenQBMandABM

33 Polarization The cathodic and anodic polarizationcurves were carried out in order to evaluate if themicrostruc-ture could affect the corrosion resistance of the API X52carbon steel Curves were obtained in the solutions NS4 andNS4 + sodium thiosulfate shown in Figure 11 related toBM and WM The anodic current density was highest forNS4 + sodium thiosulfate solution and it may be attributedto reduction reaction of sodium thiosulfate that convertedinto H

2S This makes it more aggressive than the NS4

standard solution Thus the electrochemical tests for thespecimens ABM and QBM were performed only in thissolution (Figure 12 and Table 5) Table 5 shows the opencircuit potential (OCP) in each test condition as well as thevalues of current density at 50mV and 100mV (SCE) aboveopen circuit potential (OCP)

All the samples showed active dissolution in all testedconditions Therefore any domain of passivation in a rangeof 700mV of anodic polarization was not observed Thecathodic currents density observed in all tests can beattributed to the reduction reactions of hydrogen and oxygen

It is possible to note a significant variation of the densitycurrent occurred when the sodium thiosulfate was addedshowed on Table 5 The addition of thiosulfate accentuatedthe corrosion process anodic density current increase withrespect to the solution without sodium thiosulfate It provesthat the solutions with sodium thiosulfate presented a corro-sion potentialmore anodic becomingmore aggressive whichevidence the results obtained in the polarization curves

The open circuit potential (OCP) of Figures 11 and 12 andTable 5 was analyzed according to the Pourbaix electrochem-ical equilibrium diagram for the system FeH

2O at 25∘C [18]

All the specimens in both solutions presented OCP withinthe domain of corrosion and below the equilibrium lineHH+ In this case the reactions of FeFe2+ anodic dissolution


UFSJ NL D51 times60 k 10 um

(a)

Inclusions

Constituent AM


(b)

Bainite

ConstituentAM


(c)

Figure 7 SEM secondary electron image of (a) basemetal at zone 1 (b) weldmetal at zone 2 showing the constituentMA and the inclusions(c) HAZ at zone 3 showing the constituent MA and regions formed by bainite

10 m

(a)

(a)

10 m

(b)

(b)

Figure 8 Optical image of (a) base metal and (b) weld metal both without chemical attack

and reduction of hydrogen are thermodynamically sponta-neousThus all of samples showed effect of active dissolutionbeing within the domain of corrosion with solubility of Fe2+ion as well as the reaction of hydrogen reduction on themetal surface In addition it is possible to note that the anodiccurrent densities increase in relation to the applied potentialabove 50mV and 100mV of the OCP proving that all samplespresented active dissolution The anodic current densitiesmeasured at 50 and 100mV above OCP in all specimenstested with NS4 + thiosulfate solution presented similarvalues (Table 5) In other words it is possible to conclude thatdifferent microstructures have no significant effects aboutcorrosion resistance

34 Hydrogen Permeation Figure 13 presents the permeationtest of all specimens They were performed by hydrogenpermeation using an aggressive solution namely NS4 +sodium thiosulfate already evidenced in polarization testand by some authors [33ndash35] as a solution of soil syntheticcontaminated with SRB The permeation tests with cathodicpotential applied of minus15 V below OCP were carried out inorder to simulate cathodic protection system

The solution NS4 + sodium thiosulfate was able to induceabsorption and permeation of hydrogen in allmaterials testedand it was used to simulate the effect of H

2S in synthetic

soil solution The effect of H2S can be compared to the

effect of SRB in the same environment preventing H0from

turning into H2 Due to the addition of sodium thiosulfate

the potential of the cathode side in contact with the API X52carbon steel was located within the domain of stability of H

2S

(Figure 14) Therefore there is an increase in the activity ofions and reduction hydrogen on the steel surface

As found in the literature there are different factors thatinvolve the hydrogen flow through the material During theinitial stage the permeation process resembles a stationarypermeation behavior but in a second stage a progressiveincrease of current starts as the time goes by However thisrise of current occurs differently in the carbon steel Thusthis difference in the current flow is probably due to themicrostructural characteristics like the carbide form andsize of grains differentiated among the studied conditions[1 28]

Hydrogen diffusion coefficient in steel matrix generally isvery small at low temperatures Therefore most of hydrogenis retained not in the unit cells interstices but in differentsites commonly called traps These traps have been relatedto microstructural features such as dislocations interfacesvacancies impurity atoms micro voids or any other latticedefect [19 36] The trap densities are inversely proportionalto the diffusion coefficients [20]


klm-1-H

4 6 8 102

(keV)

0

500

1000

1500

2000

10 m

Fe

Fe

CaS

C

OMn Al

SiMn

(a)

MnFe

Fe

Fe

klm-6-C

0

500

1000

1500

2000

4 6 8 102

(keV)

20 m

(b)

Figure 9 SEM secondary electron image and EDS spectra of (a) inclusions presented in the API X52 carbon steel and (b) an area withoutinclusions


(a)

Martensite

Ferrite


(b)

Figure 10 SEM secondary electron image of base metal after two different heat treatments (a) annealed and (b) quenched

Base metal

NS4NS4 + thiosulfate

minus16minus14minus12minus10minus08minus06minus04minus02

00020406

Pote

ntia

l (V

) ver

sus S

CE

1E minus 6 1E minus 5 1E minus 4 1E minus 31E minus 7 001lＩＡ(i) (AcＧ2)


Weld metal


00020406

Pote

ntia

l (V

) ver

sus S

CE

1E minus 6 1E minus 5 1E minus 4 1E minus 3 0011E minus 7

lＩＡ(i) (AcＧ2)

Figure 11 Anodic and cathodic polarization curves of the base metal (BM) and weld metal (WM) of the API X52 carbon steel immersed inthe NS4 synthetic soil solution and NS4 + sodium thiosulfate 10minus2Mmodified solution


Base metal

QuenchedAnnealed


00020406

Pote

ntia

l (V

) ver

sus S

CE


Figure 12 Anodic and cathodic polarization curves of the annealedbase metal (ABM) and quenched base metal (QBM) of the APIX52 carbon steel immersed in the NS4 + sodium thiosulfate 10minus2Mmodified solution

BMWM

QBMABM

5000 10000 15000 20000 250000Time (s)

0005101520253035404550556065

Curr

ent d

ensit

y (

AcＧ

2)

Figure 13 Hydrogen permeation base metal (BM) weld metal(WM) annealed base metal (ABM) and quenched base metal(QBM) of API X52 carbon steel

Literature [37 38] reports that when the carbon steelis submitted to a heat treatment it changes the structuralarrangement of the carbides (Fe

3C) which assume different

forms for each one These different forms promote signifi-cantly modifications on permeability properties in relation tothe diffusion constant and the solubility of hydrogen in thecarbon steel The typical pearlite formed by both cementite(carbide) and ferrite in lamellar shape is a weak hydrogentrap due to its continuous interphase which acts as a freewayto the hydrogen easing the diffusivity This feature is presentin the BM and ABM and it is one of the reasons that theydisplay high diffusion compared to the other two (Figure 13)

３232minus

H３23minus

H３minus（2S(aq)

S 8

5

4

3

1

minus10

minus05

0

05

10

Pote

ntia

l (V

) ver

sus S

HE

104 6 820

pH

Figure 14 E versus pH for sodium thiosulfate and H2S thermody-

namic equilibrium in aqueous solutions [18]

Table 6 Values of permeation in different microstructures of APIX52 carbon steel

Sample Highest current density (120583Acm2)ABM 59101BM 41086QBM 36555WM 27130

On the other hand the presence of an irregular thin cementitewhich holds hydrogen inside the metal acting as a trapcontributes to the lower diffusivity as is shown by WMSimilar results were obtained by Ramunni et al [38]

There are reports in the literature that affirm that MnS and other inclusions as shown in Figure 9 are some ofthe reasons that contribute to variance of ease with whichthe hydrogen is solubilized or diffused on metallic materialssolid at room temperature [20 39] In other words MnSinclusions are considered strong irreversible trapping sitesfor hydrogen being reported by literature as strong trappingsites for hydrogen consequently decreasing the hydrogen fluxthrough the material However this research had not beenable to perform the hydrogen permeation tests directly on theinclusion to be sure that only they would affect the hydrogenpermeation flux

The data of the permeation tests are listed in Table 6showing the highest density current and the time needed toreach that for each microstructure of the API X52 carbonsteel

These values are in accordance with other authors [238 39] These authors report that so many parameters caninfluence the hydrogen diffusion into themicrostructureThehydrogen permeation cannot be considered constant insidethe metal during the Devanathan cell test because of thehydrogen trapping process Thus only an apparent diffusioncoefficient can be evaluated Moreover the microstructureinclusions dislocations grain boundaries grains shapes


tLtB

1000 2000 3000 4000 50000Time (s)

00

05

10

15

20

25

30

35Cu

rren

t den

sity

(A

cＧ

2)

(a)

F(x)

Trend line

1000 2000 3000 4000 5000 6000 7000 80000Time (s)

minus35

minus30

minus25

minus20

minus15

minus10

minus05

00

ＦＨ(1

minusI t

I oI)

(b)

Figure 15 Effective diffusion coefficient of hydrogen in API X52 steel using different methods (a) Time Lag tL and Breakthrough tB (b)Fourier

Table 7 Data obtained from analysis of the hydrogen permeability plot for all samples of API X52 steel

Sample 119868infin(120583A) Timelowast (s)

Effective diffusion coefficient (119863eff ) (times10minus4mm2sdotsminus1)Time Lag Breakthrough Fourier

tL (s) 119863eff tB (s) 119863app 119863app

BM 2983 12300 2610 2554 590 4460 4902WM 2045 16850 3900 1709 810 3249 3010ABM 4456 4680 1020 6536 310 8489 15040QBM 2751 11160 3180 2096 545 4829 4025lowastTime required for permeation current stabilization (119868infin)

vacancies interfaces with nonmetallic inclusions precipi-tated particles and void can act as traps and affect hydrogenmovement through the materialThen hydrogen diffusibilityis associated with the diffusion process controlled by Fickrsquoslaws and physic-chemical reaction of hydrogen with trapsinside the bulk

The effective diffusion coefficient (119863eff ) is an importantparameter used in studies of chemical elements diffusion onsolid and liquid matrices In the present work the coefficientwas studied for all four different samples submitted to 3different methods to calculate The methods known as TimeLag and Breakthrough are employed to estimate the 119863effvalues using specific points of the permeation curves Fouriermethod is more complex once it uses all the data points fromthe transient part of the permeation curve to determine119863eff however the method is considered more accurate Figure 15shows the hydrogen permeation results for BM samples usingall three methods Permeation times used to calculate 119863effare represented by tL (Time Lag) and tB (Breakthrough) inFigure 15(a) Fourier method was used to estimate 119863eff fromthe graphic in Figure 15(b) [28]

Table 7 summarizes all the data collected from electro-chemical permeation tests for all the conditions Samples

that presented higher stationary permeation currents (119868infin)

also showed higher values of effective diffusion coefficient(119863eff ) WM obtained the lowest effective diffusion coefficientfollowed by ABM BM and QBM respectively

The values obtained for 119863eff are in accordance with theliterature in Table 8 Comparing Tables 7 and 8 Time Lagmethod presented the lowest values of 119863eff while Break-through and Fourier methods showed similar values exceptfor QBM In contrast literature data showed less variationand Fourier method produced low values for API X52 steelThe distinct results obtained could be associated with differ-ent parameters used for the tests Also the different steelsused can imply higher quantities of alloy elements present inthe composition increasing the amount of precipitates whichcontributes to the reduction of the hydrogen diffusion

341 Annealed Base Metal (ABM) The highest hydrogenflux occurred in the ABM samples as evidenced in Figure 13and Table 6 Annealed samples showed in the micrographs(Figure 7) considerable grain growth for ferrite and thepresence of pearlite formation at the edges with the decreaseof hardness Consequently the microstructure with largegrains size favored the increase on the hydrogen flow through


Table 8119863eff values of hydrogen for different steels obtained by literature

Authors Samples(steel)

Effective diffusion coefficient (119863eff )(times10minus4mm2sdotsminus1)

Time Lag Breakthrough Fourier

Haq et al 2013 [20] API X70 (inner)API X70 (edge)

22501970

30202290

21402000

Cheng 2007 [22] API X65 0924 1060 0864Turnbull and Carroll 1990[23] AISI 410 0076 0042 0190

the metal The annealed microstructure (Figure 7) had lowerdiscordances density than other samples Therefore accord-ing to Haq et al [20] ferrite grains often show the highestdiffusivity At the grain boundaries the pearlite does not actas a blocking to the flux The lamellar interface of cementiteand ferrite within pearlite creates an easy path for hydrogenpass through In addition Svoboda et al [39] confirmedthat annealing thermal treatment was enough to recoverthe majority of defects decreasing the discordance densitywith only a small amount of them remaining Thereby thehydrogen atom could easily pass through the metal the factthat was also confirmed by Han et al [6]

The diffusivity of hydrogen in pure 120572-iron (ferrite) isaround 10minus3mm2sdotsminus1 The value obtained for ABM samples(Table 6) (228 times 10minus4mm2sdotsminus1) is lower due to the presenceof pearlite and inclusions In addition it is close to thosefound by Park et al [2] (927 times 10minus4mm2sdotsminus1) that usedsimilar composition The slight difference of values can beexplained by the difference between the parameters used inboth researches the sample thickness and the current densityapplied on the cathodic side were different

342 Base Metal (BM) Base metal was tested as receivedshowing micrographs with similar microstructure to ABMbeing mainly ferrite grains with pearlite formation at theedges However there is a grain size difference Thereforeit is not possible to affirm what heat treatment the BM wassubmitted to during its production however BM presentedsmaller grain size than ABM which was submitted to a heattreatment at the laboratory

The smaller grain size in relation to ABM causes anincrease in the number of discordances and defects raisingthe hydrogen trapping density and decreasing the diffusioncoefficient (Table 6) It was also observed by Haq et al [20]

BM had the second highest hydrogen diffusion belowonly the ABM and above the other samples These resultsare in accordance with Luu and Wu [40] where the authorscompared the diffusion coefficient of different microstruc-tures and concluded that regular ferrite shows the highestvalues Han et al [6] found similar results and concludedthat equiaxed ferrite grains and pearlite as presented in BMfavor the diffusivity of hydrogen due to the low trap densitycompared with other microstructures

Comparing Figures 3 and 10(a) BMpresented small grainsizes than ABM According to Haq et al [20] ferrite grainsizes smaller than 45 120583m can reduce the mobility of hydrogen

by trapping at nodes and triple junctions Then finer grainscould increase the trapping of hydrogen and thereby give riseto a lower diffusion coefficient

343 Quenched Base Metal (QBM) The tests conducted onthe QBM (Figure 13 and Table 6) showed lower current flowand enhancement of the time to reach a stationary valueto hydrogen permeation than the ABM and BM Similarresults were obtained by Nagu et al [37] where the quenchedmaterial had martensitic interlath interfaces with a body-centered tetragonal (BCT)matrix small grains a large exten-sion of grains boundaries high density of dislocations andcarbidematrix interfaces Therefore all these characteristicsacted as hydrogen traps The grain boundaries reduce themobility of hydrogen acting as reversible hydrogen trappingsites at nodes and junction points [20]

The traps of QBM samples were effective in delaying thehydrogen transport compared with the ABM and BM sam-ples The fastest cooling rate during heat treatment processpromoted the phase transformation to martensite at lowertemperature with an increase in dislocations density arisingfrom the transformation volume change (Figures 10(a) and10(b)) Then this behavior is probably due to the differencein grain size caused by thermal treatments performed andgenerated several changes in the structure of the material

Considering the dislocations acting as traps for hydrogenthe combined effect of a lower grain size and higher dislo-cation density could result in the strong trapping hydrogenIt is known that the quenched samples have martensiticmicrostructure which owns an atomic arrangement in body-centered tetragonal (BCT) matrix Thereby stable phases atroom temperature (ferrite and cementite) cannot be formeddue to the fast cooling differently from the annealed samples(ABM) and the base metal (BM) that present a mixtureof ferritecementite (pearlite) and grains of ferrite body-centered cubic system (BCC) [20]

The results are in accordance with literature whereLuu and Wu [40] also showed that lower permeation anddiffusivity of hydrogen occur in martensitic microstructuredue to high density of defects and discontinuities imposedby fast cooling Plus there is the fact that the matrix issaturated with carbon that does not completely diffuseTherefore these combinations of factors act as strong trapsand significantly decrease the hydrogen flow The diffusioncoefficient of martensite reported by Olden et al [41] for APIsteel X70 is 126 times 10minus5mm2sdotsminus1 and it is lower than those


found to ferriteperlite 760 times 10minus5mm2sdotsminus1 These values arein accordance with this present project however it showsone order of magnitude lower It could be explained by thehigher level of micro-allowing elements than those presenton API X52 steel which might form precipitations that actas strong traps Luppo and Ovejero-Garcia [42] also reportedsimilar results affirming that the hydrogen diffusivity attainsa minimum value in a fresh martensite because of the highdensity of lattice imperfections introduced by martensiticstructure Thus it is confirmed that the martensitic transfor-mation acts as traps for diffusing hydrogen atoms and con-sequently a decrease in diffusivity and hydrogen permeationflux

Svoboda et al [39] reported that the main factor affectinghydrogen permeation is the hardness if compared withmicrostructure or chemical composition There is a generaltrend of decreasing the diffusion coefficient with the increas-ing of strength However it is important to note that heattreatment does not change the distribution and chemicalcomposition of the inclusions inside the bulkThen the grainboundaries dislocations and inclusions can act not only ashydrogen traps but also as obstacles to physical diffusionthrough the metal [43]

344 Weld Metal (WM) The WM samples showed thelowest permeation rate of all analyzed samples (see Table 6and Figure 13) Due to melting and the solidification processduring theweldingWMmicrostructure was changedThere-fore the recrystallization and uncontrolled grain growth atthe heat-affected zone (HAZ) caused by thermal cyclesincrease the density of discordance In addition these pro-cesses contribute for any factors such as large changes inthe microstructure due to the spot heat incidence phaseadditions phase changes precipitation residual stressesdiscontinuities in the matrix and many others according toHan et al [6] According to Fallahmohammadi et al [43]hydrogen diffusion decreases when the grains size decreasesAnalyzing Figures 2 and 13 WM had small size of grainscompared to the othermicrostructures causing less hydrogenpermeation rate In addition during the welding processthe weld metal microstructure is charged because of meltingand solidification The process of recrystallization and graingrowth occur differently at the heat-affected zone (HAZ)Then the welded joints can be affected by different weldingheat input and hence to change the hydrogen permeationbehavior through the weld metal

The results imply that an increase seen in the number ofdiscordances was one of the main factors for decay of thediffusion coefficient (Table 6) as seen by [20 34] Moreoverthe presence of inclusions had an important role to holdthe hydrogen Variations of microstructure and a significantpresence of inclusions are showed in the metallographicanalysis of WM in HAZ Figure 9 Haq et al [20] reportedthat a high level of S and Mn on the metal may formMnS precipitates which is a strong reversible trap Theyalso considered that trapping sites increased with S contentTable 3 shows S content inWM as higher than in BM hencethe number of trapping sites is higher as well It is associatedwith the low diffusion coefficient presented by WM

The pearlitic phase is the dominant trap site of diffusedhydrogen [2] These are located at the interface betweenferrite and cementite in lamellar pearlite or the pearliteboundaryThus the large number of interfaces of fine cemen-tite in a bainitic structure as the grains shown in Figure 7(c)acts as a strong inhibitor for hydrogen diffusion The MAconstituents are expected to be a reversible trap howeverthe retained austenite does not trap hydrogen significantlyalone Park et al [2] attribute the great capacity to decreasethe diffusion to the interfaces between retained austenite andmartensitic layer within MA

4 Conclusions

After the experiments current density was not affected by thechanges in microstructure provided by thermal treatmentsThis could imply that thermal treatments possibly do notaffect the corrosion resistance The low permeation anddiffusivity of hydrogen occurred in martensitic microstruc-ture and were related to the high density of defects anddiscontinuities imposed by rapid cooling In addition thereis the fact that the matrix is saturated with carbon thatdoes not completely diffuseTherefore these combinations offactors act as traps and significantly decrease the hydrogenflow Plus the quenched material had martensitic interlathinterfaces high density of dislocations and carbidendashmatrixinterfaces all of these act as hydrogen traps WM samplesshowed the lowest permeation rate of all analyzed samplesas can be seen on the diffusion coefficient calculation Itprobably occurred because of melting and solidificationprocess during welding the weld metal microstructure waschanged Therefore the recrystallization and uncontrolledgrain growth in weld metal and in the heat-affected zone(HAZ) caused by thermal cycles increase the density ofdiscordanceThe lowest rate permeation occurred because ofa huge number of discordances and inclusions that works toretard the hydrogen diffusion

Conflicts of Interest

The authors declare that they have no conflicts of interest

Acknowledgments

This research was financially supported by CNPq CAPESFaperj and Fapemig

References

[1] L Lan X Kong Z Hu C Qiu D Zhao and L Du ldquoHydrogenpermeation behavior in relation tomicrostructural evolution oflow carbon bainitic steel weldmentsrdquoCorrosion Science vol 112pp 180ndash193 2016

[2] G T Park S U Koh H G Jung and K Y Kim ldquoEffectof microstructure on the hydrogen trapping efficiency andhydrogen induced cracking of linepipe steelrdquo Corrosion Sciencevol 50 no 7 pp 1865ndash1871 2008

[3] A H S Bueno B B Castro and J A C Ponciano ldquoAssess-ment of stress corrosion cracking and hydrogen embrittlement


susceptibility of buried pipeline steelsrdquo in Environment-InducedCracking of Materials vol 2 pp 313ndash322 Elsevier 2008

[4] A Bueno E Moreira and J Gomes ldquoEvaluation of stresscorrosion cracking and hydrogen embrittlement in an APIgrade steelrdquo Engineering Failure Analysis vol 36 pp 423ndash4312014

[5] AP Institute ldquoAPI 5L Specification for line piperdquo Api Spec 5LForty Four 2007

[6] Y Han H Jing and L Xu ldquoWelding heat input effect on thehydrogen permeation in the X80 steel welded jointsrdquoMaterialsChemistry and Physics vol 132 no 1 pp 216ndash222 2012

[7] Y Murakam T Nomoto and T Ueda ldquoFactors influencing themechanism of superlong fatigue failure in steelsrdquo Fatigue ampFracture of Engineering Materials amp Structures vol 22 no 7 pp581ndash590 1999

[8] D Eliezer D G Chakrapani C J Altstetter and E NPugh ldquoThe influence of austenite stability on the hydrogenembrittlement and stresscorrosion cracking of stainless steelrdquoMetallurgical Transactions A vol 10 no 7 pp 935ndash941 1979

[9] R J Asaro andWA Tiller ldquoInterfacemorphology developmentduring stress corrosion cracking Part I Via surface diffusionrdquoMetallurgical Transactions vol 3 no 7 pp 1789ndash1796 1972

[10] A H S Bueno and J A C Ponciano ldquoPlano de gerenciamentode integridade de dutos contra corros120587ordquo Corros120587o E Prote120591120587ovol 223 pp 23ndash38 2008

[11] R P Gangloff and B P Somerday Gaseous Hydrogen Embrittle-ment of Materials in Energy Technologies Elsevier 2012

[12] A Bueno E Moreira P Siqueira and J Gomes ldquoEffect ofcathodic potential on hydrogen permeation of API grade steelsin modified NS4 solutionrdquo Materials Science and EngineeringA vol 597 pp 117ndash121 2014

[13] A Contreras A Albiter M Salazar and R Perez ldquoSlow strainrate corrosion and fracture characteristics of X-52 and X-70pipeline steelsrdquo Materials Science and Engineering A vol 407no 1-2 pp 45ndash52 2005

[14] 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

[15] 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

[16] D Xu and T Gu ldquoBioenergetics ExplainsWhen andWhyMoreSevere MIC Pitting by SRB Can Occur inrdquo in Proceedings of theCorros NACE International p 21 Houston Tex USA 2011

[17] H H Horowitz ldquoChemical studies of polythionic acid stress-corrosion crackingrdquo Corrosion Science vol 23 no 4 pp 353ndash362 1983

[18] M Pourbaix and J Burbank ldquoAtlas D-equilibres electrochim-iquesrdquo Journal of The Electrochemical Society vol 111 no 1article 14C 1964

[19] D Hardie E Charles and A Lopez ldquoHydrogen embrittlementof high strength pipeline steelsrdquo Corrosion Science vol 48 no12 pp 4378ndash4385 2006

[20] A J Haq K Muzaka D Dunne A Calka and E PerelomaldquoEffect of microstructure and composition on hydrogen perme-ation in X70 pipeline steelsrdquo International Journal of HydrogenEnergy vol 38 no 5 pp 2544ndash2556 2013

[21] F Fischer G Mori and J Svoboda ldquoModelling the influence oftrapping on hydrogen permeation inmetalsrdquoCorrosion Sciencevol 76 pp 382ndash389 2013

[22] Y Cheng ldquoAnalysis of electrochemical hydrogen permeationthrough X-65 pipeline steel and its implications on pipelinestress corrosion crackingrdquo International Journal of HydrogenEnergy vol 32 no 9 pp 1269ndash1276 2007

[23] A Turnbull and M Carroll ldquoThe effect of temperature andH2S concentration on hydrogen diffusion and trapping in a13 chromium martensitic stainless steel in acidified NaClrdquoCorrosion Science vol 30 no 6-7 pp 667ndash679 1990

[24] I D Bott A F Ballesteros and J A Ponciano ldquoSusceptibilidadede juntas soldadas circunferenciais de aco api 5l x80 a corrosaosob tensao e a fragilizacao por hidrogeniordquo Tecnologia emMetalurgia e Materiais vol 6 no 3 pp 147ndash152 2010

[25] R N Parkins W K Blanchard and B S Delanty ldquoTrans-granular stress corrosion cracking of high-pressure pipelines incontact with solutions of near neutral pHrdquo Corrosion vol 50no 5 pp 394ndash408 1994

[26] J Capelle J Gilgert I Dmytrakh and G Pluvinage ldquoThe effectof hydrogen concentration on fracture of pipeline steels inpresence of a notchrdquo Engineering Fracture Mechanics vol 78no 2 pp 364ndash373 2011

[27] T Gu ldquoNew understandings of biocorrosion mechanismsand their classificationsrdquo Journal of Microbial amp BiochemicalTechnology vol 4 no 4 2012

[28] F Huang J Liu Z Deng J Cheng Z Lu and X Li ldquoEffect ofmicrostructure and inclusions on hydrogen induced crackingsusceptibility and hydrogen trapping efficiency of X120 pipelinesteelrdquoMaterials Science and Engineering A vol 527 no 26 pp6997ndash7001 2010

[29] A Turnbull ldquoHydrogen diffusion and trapping in metalsrdquoin Gaseous Hydrogen Embrittlement of Materials in EnergyTechnologies pp 89ndash128 Elsevier 2012

[30] B Vargas-Arista J Hallen and A Albiter ldquoEffect of artificialaging on the microstructure of weldment on API 5L X-52 steelpiperdquo Materials Characterization vol 58 no 8-9 pp 721ndash7292007

[31] E Chatzidouros V Papazoglou and D Pantelis ldquoHydrogeneffect on a low carbon ferritic-bainitic pipeline steelrdquo Interna-tional Journal of Hydrogen Energy vol 39 no 32 pp 18498ndash18505 2014

[32] N Nanninga Y Levy E Drexler R Condon A Stevensonand A Slifka ldquoComparison of hydrogen embrittlement in threepipeline steels in high pressure gaseous hydrogen environ-mentsrdquo Corrosion Science vol 59 pp 1ndash9 2012

[33] A H S Bueno Avaliacao integrada de mecanismos de falha porcorrosao emdutos Universidade Federal doRio de Janeiro 2007

[34] A H Bueno and J A Gomes ldquoEnvironmentally inducedcracking of API grade steel in near-neutral pH soilrdquo Journal ofthe Brazilian Society ofMechanical Sciences and Engineering vol31 no 2 pp 97ndash104 2009

[35] A B Forero J A Ponciano and I S Bott ldquoSusceptibility ofpipeline girth welds to hydrogen embrittlement and sulphidestress crackingrdquoMaterials and Corrosion vol 65 no 5 pp 531ndash541 2014

[36] M M Hall ldquoEffect of inelastic strain on hydrogen-assistedfracture of metalsrdquo in Gaseous Hydrogen Embrittlement ofMaterials in Energy Technologies pp 378ndash429 2012

[37] G A Nagu Amarnath and T K Namboodhiri ldquoEffect of heattreatments on the hydrogen embrittlement susceptibility of APIX-65 grade line-pipe steelrdquo Bulletin of Materials Science vol 26no 4 pp 435ndash439 2003


[38] V Ramunni T D Coelho and P de Miranda ldquoInteractionof hydrogen with the microstructure of low-carbon steelrdquoMaterials Science and Engineering A vol 435-436 pp 504ndash5142006

[39] J Svoboda G Mori A Prethaler and F Fischer ldquoDeter-mination of trapping parameters and the chemical diffusioncoefficient from hydrogen permeation experimentsrdquo CorrosionScience vol 82 pp 93ndash100 2014

[40] W Luu and J Wu ldquoThe influence of microstructure on hydro-gen transport in carbon steelsrdquo Corrosion Science vol 38 no 2pp 239ndash245 1996

[41] V Olden A Alvaro and O M Akselsen ldquoHydrogen diffusionand hydrogen influenced critical stress intensity in an API X70pipeline steel welded joint ndash Experiments and FE simulationsrdquoInternational Journal of Hydrogen Energy vol 37 no 15 pp11474ndash11486 2012

[42] M Luppo and J Ovejero-Garcia ldquoThe influence of microstruc-ture on the trapping and diffusion of hydrogen in a low carbonsteelrdquo Corrosion Science vol 32 no 10 pp 1125ndash1136 1991

[43] E Fallahmohammadi F Bolzoni G Fumagalli G Re GBenassi and L Lazzari ldquoHydrogen diffusion into three met-allurgical microstructures of a CndashMn X65 and low alloy F22sour service steel pipelinesrdquo International Journal of HydrogenEnergy vol 39 no 25 pp 13300ndash13313 2014

Submit your manuscripts athttpswwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of



Table 1 Chemical analysis of the base metal (BM) and the weld metal (WM) API X52 carbon steel

Material Components (wt)C Si Mn P S Cr Ni Mo V Cu

BM 028 033 111 003 002 005 002 001 0001 002WM 016 020 047 003 003 003 002 015 0002 002

embrittlement could be associated with SRB These bacteriause sulfate as an oxidizing agent reducing to sulfide (H

2S)

Plus they can also utilize oxidized sulfur compounds suchas thiosulfate and sulfite or even elemental sulfur In thepresence of H

2S produced by these bacteria the reaction of

atomic hydrogen recombination to molecular hydrogen isretarded thereby permitting the diffusion of atomic hydrogenthrough the metal [10]

Microbiologically influenced corrosion (MIC) is a majorproblem inmany industries such as oil and gas According toXu et al [14] many attacks of anaerobic MIC can be classifiedby two types based on the two anaerobic metabolisms res-piration and fermentation Therefore the mechanism of SRBinvolvesmicroorganisms that perform an aerobic respirationFor example SRB respiration typically uses sulfate as theterminal electron acceptor Venzlaff et al [15] reported thatSRB gain biochemical energy for growth by reducing sulfate(SO4) to sulfide (H

2S HSminus) with natural organic compounds

as electron donors which are oxidized to CO2(also referred

to as sulfate respiration) However if the SRB have contactwith carbon steel the Fe acts as an electron donor for itsrespiration [16] Then the reaction involved in anaerobicrespiration using Fe0 is Fe minus Fe2+ + 2eminus In the absence ofoxygen electrons must be accepted by a nonoxygen oxidant[13] thus SRB use SO

4as an oxidizing agent SO

4is reduced

to H2S and HSminus through the reaction SOminus4 + 9H+ + 8eminus =

HSminus + H2O

Horowitz [17] showed an increase in the amount ofhydrogen during permeation tests with the use of sodiumthiosulfate solution The sodium thiosulfate solution allowsthe generation and stabilization of H

2S on the metallic

surfaceThese tests were carried out applying cathodic poten-tials According to Pourbaix diagram for H

2S when cathodic

potential is imposed the steel is located into H2S domain

[18]Therefore the sodium thiosulfate is reduced to H2SThe

reaction depends on the potential applied and the pH of thesolution

Another problem related to HE is because the steelsused in the manufacture of pipelines for transporting oiland derivatives are exposed to excessive cathodic protectionTherefore cathodic potentials imposed on the external partof pipelines promote hydrogen reduction which becomesthermodynamically spontaneous on the metal surface [19]Bueno et al [4 12] report that API X46 carbon steel exhibiteda decreasing ductility as long as cathodic potentials wereimposed This effect was more evident in soil solutionsthan in NS4 standard solution The deterioration mecha-nism is related to the influence of hydrogen Transgranularcracking occurred even under cathodic conditions wherethe anodic dissolution of the steel can be considered asnegligible

Recent studies gave emphasis to the influence of themetal structure in hydrogen permeation [1 2 20] and discussthe effective diffusion coefficient Lan et al [1] studied thehydrogen permeation behavior in relation to microstructuralevolution of low carbon bainitic steel weldments Theyhave shown that the effective diffusion coefficient in thewelded joint is highly affected by the heat input This ismainly due to coarsening grain and inclusion sizes Parket al [2] tested the hydrogen trapping efficiency of APIX65 and showed an increase in order of ferritedegeneratedpearlite ferritebainite and ferriteacicular ferrite Haq et al[20] showed that due to hydrogen trapping X70 mediumstrip exhibits lower hydrogen diffusivity than the standardMn strip This is mainly due to finer ferrite grains and ahigher density of carbonitride precipitates Fischer et al [21]indicated that under specific circumstances the diffusionof hydrogen cannot be described well by a constant effec-tive diffusion coefficient due to the presence of hydrogentraps and the magnitude of the concentration gradient ofhydrogen

The aim of this paper was to evaluate the influence ofmicrostructure and some inclusions on the susceptibilityof hydrogen permeation of API X52 carbon steel (basemetal and weld metal) submitted to the cathodic protectionsystem Different types of microstructures were obtained byheat treatments such as quenching and annealing underdifferent temperatures The hydrogen permeation tests inthese microstructures were compared and evaluated in thepresence of a synthetic modified soil solution NS4 + sodiumthiosulfate concentration of 10minus2M

2 Methods and Materials

Thematerial usedwas anAPI X52 pipeline carbon steel underdifferent conditions base metal as received welded metalbase metal after quenching heat treatment base metal afterannealed heat treatmentThe evaluation of the chemical com-position was carried out by Optical Emission Spectroscopy(OES) Table 1 shows the results in weight percent (wt) ofthe chemical elements present in the base metal (BM) andthe weld metal (WM)

The microstructures of the samples were produced bydifferent heat treatment Basemetals were heated at 900∘C fortwo hours Then the samples were submitted to a quenchingprocess performed in a solution of water ice and salt Theannealed samples were left in the oven until it reaches at roomtemperature All the tests were performed in triplicate Thespecimens and conditions of heat treatment are described inTable 2

The metallographic analysis and microstructure char-acterization were performed according to Bott et al [24]









3




2and N

2
























1 2

34 5








WM

HAZ

(a)

WM

HAZ

(b)


(a) (b)


(a) (b)





(ECS)

E50mV

above OCP(mV)

i50mV above OCP

(120583Acm2)

E100mV above OCP

(mV)

i100mV above OCP

(120583Acm2)







(a) (b)


1 2 3









2O at 25∘C [18]




(a)

Inclusions

Constituent AM


(b)

Bainite

ConstituentAM


(c)


10 m

(a)

(a)

10 m

(b)

(b)





2S in synthetic





2S





klm-1-H

4 6 8 102

(keV)

0

500

1000

1500

2000

10 m

Fe

Fe

CaS

C

OMn Al

SiMn

(a)

MnFe

Fe

Fe

klm-6-C

0

500

1000

1500

2000

4 6 8 102

(keV)

20 m

(b)



(a)

Martensite

Ferrite


(b)


Base metal



00020406

Pote

ntia

l (V

) ver

sus S

CE



Weld metal


00020406

Pote

ntia

l (V

) ver

sus S

CE


lＩＡ(i) (AcＧ2)



Base metal

QuenchedAnnealed


00020406

Pote

ntia

l (V

) ver

sus S

CE



BMWM

QBMABM

5000 10000 15000 20000 250000Time (s)

0005101520253035404550556065

Curr

ent d

ensit

y (

AcＧ

2)





３232minus

H３23minus

H３minus（2S(aq)

S 8

5

4

3

1

minus10

minus05

0

05

10

Pote

ntia

l (V

) ver

sus S

HE

104 6 820

pH










tLtB

1000 2000 3000 4000 50000Time (s)

00

05

10

15

20

25

30

35Cu

rren

t den

sity

(A

cＧ

2)

(a)

F(x)

Trend line

1000 2000 3000 4000 5000 6000 7000 80000Time (s)

minus35

minus30

minus25

minus20

minus15

minus10

minus05

00

ＦＨ(1

minusI t

I oI)

(b)




















22501970

30202290

21402000



















4 Conclusions




Acknowledgments


References






















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of










3




2and N

2
























1 2

34 5








WM

HAZ

(a)

WM

HAZ

(b)


(a) (b)


(a) (b)





(ECS)

E50mV

above OCP(mV)

i50mV above OCP

(120583Acm2)

E100mV above OCP

(mV)

i100mV above OCP

(120583Acm2)







(a) (b)


1 2 3









2O at 25∘C [18]




(a)

Inclusions

Constituent AM


(b)

Bainite

ConstituentAM


(c)


10 m

(a)

(a)

10 m

(b)

(b)





2S in synthetic





2S





klm-1-H

4 6 8 102

(keV)

0

500

1000

1500

2000

10 m

Fe

Fe

CaS

C

OMn Al

SiMn

(a)

MnFe

Fe

Fe

klm-6-C

0

500

1000

1500

2000

4 6 8 102

(keV)

20 m

(b)



(a)

Martensite

Ferrite


(b)


Base metal



00020406

Pote

ntia

l (V

) ver

sus S

CE



Weld metal


00020406

Pote

ntia

l (V

) ver

sus S

CE


lＩＡ(i) (AcＧ2)



Base metal

QuenchedAnnealed


00020406

Pote

ntia

l (V

) ver

sus S

CE



BMWM

QBMABM

5000 10000 15000 20000 250000Time (s)

0005101520253035404550556065

Curr

ent d

ensit

y (

AcＧ

2)





３232minus

H３23minus

H３minus（2S(aq)

S 8

5

4

3

1

minus10

minus05

0

05

10

Pote

ntia

l (V

) ver

sus S

HE

104 6 820

pH










tLtB

1000 2000 3000 4000 50000Time (s)

00

05

10

15

20

25

30

35Cu

rren

t den

sity

(A

cＧ

2)

(a)

F(x)

Trend line

1000 2000 3000 4000 5000 6000 7000 80000Time (s)

minus35

minus30

minus25

minus20

minus15

minus10

minus05

00

ＦＨ(1

minusI t

I oI)

(b)




















22501970

30202290

21402000



















4 Conclusions




Acknowledgments


References






















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of















1 2

34 5








WM

HAZ

(a)

WM

HAZ

(b)


(a) (b)


(a) (b)





(ECS)

E50mV

above OCP(mV)

i50mV above OCP

(120583Acm2)

E100mV above OCP

(mV)

i100mV above OCP

(120583Acm2)







(a) (b)


1 2 3









2O at 25∘C [18]




(a)

Inclusions

Constituent AM


(b)

Bainite

ConstituentAM


(c)


10 m

(a)

(a)

10 m

(b)

(b)





2S in synthetic





2S





klm-1-H

4 6 8 102

(keV)

0

500

1000

1500

2000

10 m

Fe

Fe

CaS

C

OMn Al

SiMn

(a)

MnFe

Fe

Fe

klm-6-C

0

500

1000

1500

2000

4 6 8 102

(keV)

20 m

(b)



(a)

Martensite

Ferrite


(b)


Base metal



00020406

Pote

ntia

l (V

) ver

sus S

CE



Weld metal


00020406

Pote

ntia

l (V

) ver

sus S

CE


lＩＡ(i) (AcＧ2)



Base metal

QuenchedAnnealed


00020406

Pote

ntia

l (V

) ver

sus S

CE



BMWM

QBMABM

5000 10000 15000 20000 250000Time (s)

0005101520253035404550556065

Curr

ent d

ensit

y (

AcＧ

2)





３232minus

H３23minus

H３minus（2S(aq)

S 8

5

4

3

1

minus10

minus05

0

05

10

Pote

ntia

l (V

) ver

sus S

HE

104 6 820

pH










tLtB

1000 2000 3000 4000 50000Time (s)

00

05

10

15

20

25

30

35Cu

rren

t den

sity

(A

cＧ

2)

(a)

F(x)

Trend line

1000 2000 3000 4000 5000 6000 7000 80000Time (s)

minus35

minus30

minus25

minus20

minus15

minus10

minus05

00

ＦＨ(1

minusI t

I oI)

(b)




















22501970

30202290

21402000



















4 Conclusions




Acknowledgments


References






















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of



WM

HAZ

(a)

WM

HAZ

(b)


(a) (b)


(a) (b)





(ECS)

E50mV

above OCP(mV)

i50mV above OCP

(120583Acm2)

E100mV above OCP

(mV)

i100mV above OCP

(120583Acm2)







(a) (b)


1 2 3









2O at 25∘C [18]




(a)

Inclusions

Constituent AM


(b)

Bainite

ConstituentAM


(c)


10 m

(a)

(a)

10 m

(b)

(b)





2S in synthetic





2S





klm-1-H

4 6 8 102

(keV)

0

500

1000

1500

2000

10 m

Fe

Fe

CaS

C

OMn Al

SiMn

(a)

MnFe

Fe

Fe

klm-6-C

0

500

1000

1500

2000

4 6 8 102

(keV)

20 m

(b)



(a)

Martensite

Ferrite


(b)


Base metal



00020406

Pote

ntia

l (V

) ver

sus S

CE



Weld metal


00020406

Pote

ntia

l (V

) ver

sus S

CE


lＩＡ(i) (AcＧ2)



Base metal

QuenchedAnnealed


00020406

Pote

ntia

l (V

) ver

sus S

CE



BMWM

QBMABM

5000 10000 15000 20000 250000Time (s)

0005101520253035404550556065

Curr

ent d

ensit

y (

AcＧ

2)





３232minus

H３23minus

H３minus（2S(aq)

S 8

5

4

3

1

minus10

minus05

0

05

10

Pote

ntia

l (V

) ver

sus S

HE

104 6 820

pH










tLtB

1000 2000 3000 4000 50000Time (s)

00

05

10

15

20

25

30

35Cu

rren

t den

sity

(A

cＧ

2)

(a)

F(x)

Trend line

1000 2000 3000 4000 5000 6000 7000 80000Time (s)

minus35

minus30

minus25

minus20

minus15

minus10

minus05

00

ＦＨ(1

minusI t

I oI)

(b)




















22501970

30202290

21402000



















4 Conclusions




Acknowledgments


References






















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of





(ECS)

E50mV

above OCP(mV)

i50mV above OCP

(120583Acm2)

E100mV above OCP

(mV)

i100mV above OCP

(120583Acm2)







(a) (b)


1 2 3









2O at 25∘C [18]




(a)

Inclusions

Constituent AM


(b)

Bainite

ConstituentAM


(c)


10 m

(a)

(a)

10 m

(b)

(b)





2S in synthetic





2S





klm-1-H

4 6 8 102

(keV)

0

500

1000

1500

2000

10 m

Fe

Fe

CaS

C

OMn Al

SiMn

(a)

MnFe

Fe

Fe

klm-6-C

0

500

1000

1500

2000

4 6 8 102

(keV)

20 m

(b)



(a)

Martensite

Ferrite


(b)


Base metal



00020406

Pote

ntia

l (V

) ver

sus S

CE



Weld metal


00020406

Pote

ntia

l (V

) ver

sus S

CE


lＩＡ(i) (AcＧ2)



Base metal

QuenchedAnnealed


00020406

Pote

ntia

l (V

) ver

sus S

CE



BMWM

QBMABM

5000 10000 15000 20000 250000Time (s)

0005101520253035404550556065

Curr

ent d

ensit

y (

AcＧ

2)





３232minus

H３23minus

H３minus（2S(aq)

S 8

5

4

3

1

minus10

minus05

0

05

10

Pote

ntia

l (V

) ver

sus S

HE

104 6 820

pH










tLtB

1000 2000 3000 4000 50000Time (s)

00

05

10

15

20

25

30

35Cu

rren

t den

sity

(A

cＧ

2)

(a)

F(x)

Trend line

1000 2000 3000 4000 5000 6000 7000 80000Time (s)

minus35

minus30

minus25

minus20

minus15

minus10

minus05

00

ＦＨ(1

minusI t

I oI)

(b)




















22501970

30202290

21402000



















4 Conclusions




Acknowledgments


References






















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of




(a)

Inclusions

Constituent AM


(b)

Bainite

ConstituentAM


(c)


10 m

(a)

(a)

10 m

(b)

(b)





2S in synthetic





2S





klm-1-H

4 6 8 102

(keV)

0

500

1000

1500

2000

10 m

Fe

Fe

CaS

C

OMn Al

SiMn

(a)

MnFe

Fe

Fe

klm-6-C

0

500

1000

1500

2000

4 6 8 102

(keV)

20 m

(b)



(a)

Martensite

Ferrite


(b)


Base metal



00020406

Pote

ntia

l (V

) ver

sus S

CE



Weld metal


00020406

Pote

ntia

l (V

) ver

sus S

CE


lＩＡ(i) (AcＧ2)



Base metal

QuenchedAnnealed


00020406

Pote

ntia

l (V

) ver

sus S

CE



BMWM

QBMABM

5000 10000 15000 20000 250000Time (s)

0005101520253035404550556065

Curr

ent d

ensit

y (

AcＧ

2)





３232minus

H３23minus

H３minus（2S(aq)

S 8

5

4

3

1

minus10

minus05

0

05

10

Pote

ntia

l (V

) ver

sus S

HE

104 6 820

pH










tLtB

1000 2000 3000 4000 50000Time (s)

00

05

10

15

20

25

30

35Cu

rren

t den

sity

(A

cＧ

2)

(a)

F(x)

Trend line

1000 2000 3000 4000 5000 6000 7000 80000Time (s)

minus35

minus30

minus25

minus20

minus15

minus10

minus05

00

ＦＨ(1

minusI t

I oI)

(b)




















22501970

30202290

21402000



















4 Conclusions




Acknowledgments


References






















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of



klm-1-H

4 6 8 102

(keV)

0

500

1000

1500

2000

10 m

Fe

Fe

CaS

C

OMn Al

SiMn

(a)

MnFe

Fe

Fe

klm-6-C

0

500

1000

1500

2000

4 6 8 102

(keV)

20 m

(b)



(a)

Martensite

Ferrite


(b)


Base metal



00020406

Pote

ntia

l (V

) ver

sus S

CE



Weld metal


00020406

Pote

ntia

l (V

) ver

sus S

CE


lＩＡ(i) (AcＧ2)



Base metal

QuenchedAnnealed


00020406

Pote

ntia

l (V

) ver

sus S

CE



BMWM

QBMABM

5000 10000 15000 20000 250000Time (s)

0005101520253035404550556065

Curr

ent d

ensit

y (

AcＧ

2)





３232minus

H３23minus

H３minus（2S(aq)

S 8

5

4

3

1

minus10

minus05

0

05

10

Pote

ntia

l (V

) ver

sus S

HE

104 6 820

pH










tLtB

1000 2000 3000 4000 50000Time (s)

00

05

10

15

20

25

30

35Cu

rren

t den

sity

(A

cＧ

2)

(a)

F(x)

Trend line

1000 2000 3000 4000 5000 6000 7000 80000Time (s)

minus35

minus30

minus25

minus20

minus15

minus10

minus05

00

ＦＨ(1

minusI t

I oI)

(b)




















22501970

30202290

21402000



















4 Conclusions




Acknowledgments


References






















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of



Base metal

QuenchedAnnealed


00020406

Pote

ntia

l (V

) ver

sus S

CE



BMWM

QBMABM

5000 10000 15000 20000 250000Time (s)

0005101520253035404550556065

Curr

ent d

ensit

y (

AcＧ

2)





３232minus

H３23minus

H３minus（2S(aq)

S 8

5

4

3

1

minus10

minus05

0

05

10

Pote

ntia

l (V

) ver

sus S

HE

104 6 820

pH










tLtB

1000 2000 3000 4000 50000Time (s)

00

05

10

15

20

25

30

35Cu

rren

t den

sity

(A

cＧ

2)

(a)

F(x)

Trend line

1000 2000 3000 4000 5000 6000 7000 80000Time (s)

minus35

minus30

minus25

minus20

minus15

minus10

minus05

00

ＦＨ(1

minusI t

I oI)

(b)




















22501970

30202290

21402000



















4 Conclusions




Acknowledgments


References






















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of



tLtB

1000 2000 3000 4000 50000Time (s)

00

05

10

15

20

25

30

35Cu

rren

t den

sity

(A

cＧ

2)

(a)

F(x)

Trend line

1000 2000 3000 4000 5000 6000 7000 80000Time (s)

minus35

minus30

minus25

minus20

minus15

minus10

minus05

00

ＦＨ(1

minusI t

I oI)

(b)




















22501970

30202290

21402000



















4 Conclusions




Acknowledgments


References






















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of








22501970

30202290

21402000



















4 Conclusions




Acknowledgments


References






















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of








4 Conclusions




Acknowledgments


References






















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of




















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


effect of microstructure on hydrogen diffusion in weld and...

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