Fire-Side Corrosion: A Case Study of Failed Tubes of …downloads.hindawi.com/journals/ijc/2017/7367046.pdf6 InternationalJournalofCorrosion + − − Anode Anode Solid deposit Liquid

Research ArticleFire-Side Corrosion A Case Study of Failed Tubes ofa Fossil Fuel Boiler

Majid Asnavandi12 Mohaddeseh Kahram12 Milad Rezaei23 and Davar Rezakhani2

1School of Chemistry The University of New South Wales Sydney NSW Australia2Chemistry and Materials Research Centre Niroo Research Institute (NRI) Tehran Iran3Department of Mining and Metallurgical Engineering Amirkabir University of Technology Tehran Iran

Correspondence should be addressed to Majid Asnavandi masnavandiunsweduau

Received 31 August 2016 Accepted 7 December 2016 Published 15 January 2017

Academic Editor Yu Zuo

Copyright copy 2017 Majid Asnavandi 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

The failures of superheater and reheater boiler tubes operating in a power plant utilizing natural gas or mazut as a fuel have beenanalysed and the fire-side corrosion has been suggested as the main reason for the failure in boiler tubes The tubes have beenprovided by a fossil fuel power plant in Iran and optical and electron microscopy investigations have been performed on the tubesas well as the corrosion products on their surfaces The results showed that the thickness of the failed tubes is not uniform whichsuggests that fire-side corrosion has happened on the tubes Fire-side corrosion is caused by the reaction of combustion productswith oxide layers on the tube surface resulting inmetal loss and consequently tubes fractureHowever the tubes corrosion behaviourdid not follow the conventional models of the fire-side corrosion Given that using the corrosion monitoring techniques for theseboiler tubes seems essential As a result the thickness of the boiler tubes in different parts of the boiler has been recorded andcritical points are selected accordingly Such critical points are selected for installation of corrosion monitoring probes

1 Introduction

Fossil fuels are still one of the major sources of energy in oursociety because of their capacity to generate huge amounts ofelectricity However unforeseen failures in boilers cause themto shut down and stop electricity generation Main failures inboilers stem from severe damage in boiler tubes which canbe affected by the tube material boiler service temperatureand chemical composition of the fossil fuel [1] Moreovertube position temperature and pressure can also promotethe boiler collapse Understanding the failure mechanism ofboiler tubes and determining critical points which are under-going themost damage are appropriate approaches to preventboilers shut-downs [2]

The corrosion of boiler tubes is one of the remainingchallenges in fossil fuel power plants Tubes failure leadingto the plant shut-down and tubes repair and replacement andwelding and required welding inspections cause tremendouscosts On the other hand due to depletion of high-grade fuelsand also for economic reasons residual fuel oil along with

coal is extensively used in the energy generation systemswhich contains sodium vanadium and sulphur as impuritiesThese impurities can encourage some sorts of corrosion inboiler tubes For instance high-temperature corrosion in coalfired boilers is mainly caused as a result of the presence ofimpurities like sulphur alkali metals and chlorine in thecoal During boilers operation low melting point depositssuch as Na

2OsdotV2O4sdot11V2O5(Tm = 535∘C) are formed on the

surface of superheater and reheater tubes On the fire sideof a tube the metal protective oxide layer will be dissolvedin these molten deposits and accelerates the corrosion Thisphenomenon is known as fire-side corrosion which can hap-pen either uniformly or in a localized manner and its rate isbetween 50 and 300 nanometers per hour However under asevere condition it can be even faster which decreases thelifetime of tubes to less than two years

In the combustion system sodium sulphate and oxide areformed from the reaction of Na O and S Vanadium reactswith oxygen to form V

2O5and other complex vanadates

These compounds commonly known as ash deposit on the

HindawiInternational Journal of CorrosionVolume 2017 Article ID 7367046 8 pageshttpsdoiorg10115520177367046

2 International Journal of Corrosion

Table 1 Chemical composition of low-alloy steel ASTM A213 T12 and A213 T22

Wt Carbon Manganese Phosphorus Sulphur Silicon Chromium MolybdenumA213 T12 005ndash015 030ndash061 0025 0025 050 08ndash125 044ndash065A213 T22 005ndash015 030ndash060 0025 0025 050 190ndash260 087ndash113

(a) (b)

Figure 1 (a) Cross section of a boiler tube with deposits on the surface and (b) surface of a boiler tube after two years in the service condition

surface of materials and induce corrosion During combus-tion these elements combine to formvarious types of vapoursand condensed phases [3] The chemistry of reactions takingplace during combustion is complex and highly variableDegradation of materials occurs when these molten com-pounds destroy the natural protective oxide layer of themate-rials surface during boiler operation [4] The complex envi-ronment (thermal chemical and mechanical) on the boilerservice conditionmakes it extremely difficult for amaterial toendure all the tough situations imposed on it [1]Therefore toprevent catastrophic failures it is important to understandand predict corrosion behaviour on the tubes surfaces inadvance It should also be noted that temperature and internalpressure are different in different parts of a boilerThus thick-ness measurements of the boiler tubes and determination ofcritical points are appropriate approaches

In this work the in situ thickness measurement of tubesat different parts of a fossil fuel power plant in Iran has beenperformed and the damaged tubes were collected for moreroot cause analysis Optical microscopy (OM) scanning elec-tron microscopy (SEM) with Energy-Dispersive X-ray Spec-troscopy (EDS) and X-ray diffraction (XRD) have been usedto study morphology chemical composition and structureof failed tubes and corrosion products on top of the tubesThickness measurement data has been used to determine thecritical points in the boiler

2 Experimental

Failed tubes of the boiler were transferred directly fromboilerunit to the laboratory After visual inspection the tubes havebeen cut for cross section studies The samples were groundusing successive finer grades of SiC papers up to 2000and then polished to a mirror finish by 03 and 005 120583malumina slurry OM SEM EDS and XRD have been utilizedto characterize the samples and corrosion products In situ

thickness measurement was performed by ultrasonic testing(UT) in the power plant siteThe thickness values reported inthis paper are the average value of at least 3 measurementswith six-month intervals Superheater and reheater tubeswere made of a low-alloy steel ASTM A213 T22 and A213T12 respectively with a chemical composition presented inTable 1 [5]

3 Results

Figure 1 depicts a superheater tube with the corrosion pro-ducts and deposits on its surface The surface of the tubewhichwas exposed to fire is covered by a layer of thick coarseand adhesive deposit Its yellow colour suggests the presenceof sulphur in the layer

The thickness measurements indicate that thickness infailed tubes is dramatically decreased to values lower thanthe critical value for boiler tubes According to Figure 2 thisphenomenon is more apparent in the fire side of tubes

Figures 3ndash6 demonstrate the microstructures of boilerfailed superheater and reheater tubes Based on Figure 3the structure of superheater in the surface vicinity is slightlydifferent from the bulk material with more spherical carbidein grain boundaries compared to the ferritic microstructureof the bulk material Such difference in microstructure haspreviously been reported in the literature [6] In Figure 4 aporous and nonuniform deposit layer on the tube is shown

The microstructure of reheater tube is the same as thesuperheater however the deposit layers on the reheaters areuniform suggesting a general corrosion on the reheater tubesurfaces (see Figures 5 and 6)

The morphology of deposit layers on the external surfaceof the reheater and superheater has further been studied bySEM and the images are shown in Figure 7

Such difference in corrosion products and oxide layers onthe superheater and reheater tubes stems from the position of

International Journal of Corrosion 3

Figure 2 Cross section of a failed boiler tube Metal loss in fire sideof the tube is clear

Figure 3 Optical microscopy image of superheater microstructure

Table 2 XRD results of deposits on the reheater and superheatertube surfaces

Main components Minor componentsNa2SO4

NaV6O15

CrFe(VO4)2

Fe2O3

superheater tubes which are exposed to higher temperaturesand also more fuel impurities particularly alkali metal chlo-rides The chemical composition and structure of corrosionproducts were investigated with XRD (Figure 8) and theresults were summarized in Table 2 in which Na

2SO4and

CrFe(VO4)2are the major components These results are

consistent with Energy-Dispersive X-ray Spectroscopy (EDS)data which showed Fe Cr V Na O and S in corrosionproducts

To understand the source of Na S and V the chemicalcomposition of the fuel that is being used in the boiler hasalso been explored and shown in Table 3

Figure 4 Optical microscopy image of corrosion products on thesurfaces of superheater tubes

Figure 5 Optical microscopy image of reheater microstructure

Table 3 Ca K and Na content in fuel of the power plant

Component Calcium Potassium SodiumAmount (120583gm3) 2877 058 091

4 Discussion

It is well known in fire-side corrosion that some corrosivespecies such as S V Na and K in fossil fuels lead to depositsformation on the tube surfaces and consequently severecorrosion Corrosion mechanism does strongly depend onthe fuel chemical composition boiler working temperatureamount of excess air and the tube materials Fuels impuritiesform low melting point deposits which are ionic conductiveand are able to transfer the electrons Vanadium has differentoxidation states and can be easily oxidized to VO VO

2 and

V2O5 Sulphur also is oxidized to SO

2and SO

3depending on

the temperature and amount of oxygen content in the boilerand according to (1) reacts with fuel impurities

NaOH + SO3997888rarr Na

2SO4+H2O (1)


Figure 6 Optical microscopy image of corrosion products on thesurfaces of reheater tubes

where Na2SO4was detected by XRD (Table 2) In the boiler

condition in initial stages an oxide film forms on the tubesurface Sodium sulphate then deposits on the oxide layerAfterward the outer surface of Na

2SO4layer begins to

become sticky and absorb fly ash particles which results indissolving the oxide layer of metal and increasing the depositthickness By increasing the deposit thickness and tempera-ture gradient in it the deposits and oxide layers start movingand to be washed away from the surface and hence furtheroxidation of the metal will happen [7] Although NaCl doesnot have any direct effect on the corrosion it causes the oxidelayers of metals to peel off and exposes the bare metal to thecorrosive condition In this situation chromium diffusesfrom the bulk material to the surface to form a new pas-sive layer and in consequence Cr depletion has occurred(Table 1) In other words in the presence of NaCl (Figure 9)Cr is lost from the surface as volatile chromic chloride and theoxidation rate to replace the normal chromic oxide film willincrease [8] Nonetheless the seriousmetal loss does not stemfrom gas-phase oxidation if themetal is not exposed to temp-eratures above its intended working range (610∘C for A213T22 eg) High rate corrosions happen in the presence ofliquid phase on the surface of metals There are two mainreasons for high rate of liquid corrosion first chemical reac-tions in liquids are generally faster than solid-solid reactionsand also a liquid phase can act as an electrolyte for electronstransfer [7]

Our studies revealed that NaV6O15

and CrFe(VO4)2are

also formed according to following

Na2SO4+ 5V2O5+ 2VO

2997888rarr SO

3+ 2NaV

6O15 (2)

Cr2O3+ Fe2O3+ 2V2O5997888rarr 2CrFe (VO

4)2

(3)

These compounds melt at low temperature about 625∘Cand destroy the oxide layer Ability to form protective oxidescales has a significant effect on corrosion resistance at hightemperatures In chlorine-containing environments chlorinedisturbs the formation of protective oxides and poorly pro-tective metal oxides may form In the present study detailedmicroscopy images showed that chlorine broke the protectiveoxide layers in superheater tubes surfaces

Alloying with sufficient amount of chromium to forma chromium-rich oxide may thus increase the resistance tochlorination [9] However corrosion under deposits is highlycomplex with a number of competing reactions taking placeand the stability of metal oxides contra metal chlorides is notsufficient to accurately predict alloy performance

Vanadium salts also attack the metal surface in variousways they can act as an oxygen carrier or distort ametal oxidelayer Moreover such salts are able to dissolve the protectiveoxide layers

The areas on the tube surfaces which are covered bymolten sulphates are generally anode We expect to see suchbehaviour on the side of tubes which are exposed to fireTherefore as Figure 8 illustrates the areas with thick depositsare locally cathode while the areas with thinner and moltendeposit layers are locally anodes and expose highest corrosionrate by molten salts In other words there are 4 sites in a tubecross section a safe area on the opposite side of the fire acathodic area with thick deposits and two anodic sites withmolten corrosion products as shown in Figures 10 and 11From the electrochemistry points of view (4) occurs at anodicpart leading to metal loss

Fe 997888rarr Fe3+ + 3eminus (4)

At the cathodic sites a variety of reactions can take place anduse the generated electrons Two most probable reactions are[7]

O2+ 4eminus 997888rarr 2O2minus (5)

SO4

2minus + 8eminus 997888rarr S2minus + 4O2minus (6)

However Figure 2 shows a different behaviour from the afore-mentionedmodel and the most material loss was observed inthe fire-side part It means that the area is experiencing thehighest level of corrosion and cannot be a cathode Sometubes in this study were not following the normal fire-side corrosion mechanism and behave differently It can bebecause of the low thickness of deposit layer and locallyhigh temperature (800∘C) of the material surface which isleading to uniformly melting the whole deposits on the fireside of tubes As there is no comprehensive corrosion modelto predict high-temperature corrosion of all tubes thicknessmeasurements and corrosionmonitoring of boiler tubes seemnecessary since the proposed mechanisms are not able topredict the metals corrosion in harsh condition The presentcorrosion models are taking the temperature of system met-allurgical parameters and to some extent the compositionof fuel to the account while system aerodynamic parametersand the temperature of metal surfaces are not considered

In this part thickness measurement results are discussedThemeasurement has been carried out in platen superheaterfinal superheatermedium reheater andfinal reheater tubes ofthe boiler where they are prone to the high rate of damage andfailure according to the power plant engineers and technicalpersonnel All measurements have been done three timesat three different positions of the tube Figure 12 shows thedrawing of platen superheater The nominal thickness oftubes in this part of the boiler is 4mm and as can be seen in


(a) (b)

Figure 7 SEM images of corrosion products and deposit on the surface of (a) reheater and (b) superheater tubes

70605040302010

0

100

Cou

nts

400

Position 2 (∘)

(a)

0

25Cou

nts

100

70605040302010

Position 2 (∘)

(b)

Figure 8 XRD patterns of corrosion products and deposits on the surface of (a) reheater and (b) superheater tubes

Base metal

Cl2 Cr2O3 CrCl2

Flue Gas

Figure 9 Schematic of the fire-side corrosion in the presence of chlorine


+

minus minus

Anode Anode

Soliddeposit

LiquidLiquid

Flue gas

(due to high heat

transfer rate)

e eCathode

Figure 10 Schematic of corrosion under deposits on the tubes [7]

Figure 11 Cross section image of a boiler tube [10] anodic zoneswith high metal loss rate are indicated

Figure 13 the tube thickness of the fire side in some areas(position 2) is less than critical thickness value Criticalthickness is aminimum required thickness of tubes to servicewith no damage and failure risk in the boiler temperature andpressure These areas are shown with red points in Figure 12

Similarly some areas with a thickness lower than the crit-ical thickness in final superheater with a nominal thicknessof 53mm were determined (Figure 14)

The nominal thickness in medium and final reheatertubes was 35 and 34mm respectivelyThe reheaters schema-tics with the critical points are indicated in Figure 15

5 Conclusion

In conclusion we found that different anodic and cathodicregions are formed under deposits on tube surfaces Thus

A B C DE

Inlet HDR

Outlet HDR

Figure 12 Schematic of the platen superheater with determinedcritical points

Wal

lThic

knes

s Mea

sure

men

t (m

m)

Tube number373533312927252321191715131197531

320

340

360

380

420

400

440

460

Position 1 Position 3Position 2 Critical point = 358mm

Figure 13 Thickness measurements of the platen superheater atzone A

materials corrosion behaviour in harsh condition cannot beanticipated by available corrosion models since the fuelscontain impurities and the tubes work in high pressure andtemperature service condition To estimate the corrosion rateand prevent unforeseen failures frequent inspections arerequested yet the inspections are offline Online corrosionmonitoring is an appropriate approach to monitor tubes cor-rosion in serviceThus monitoring probe should be placed incritical points with the highest corrosion rates In this workcritical points in the fossil fuel boiler have been determinedbyUT thicknessmeasurementsThemost damage corrosionand metal loss were diagnosed in final superheater tubes


Wal

lThic

knes

s Mea

sure

men

t (m

m)

Tube number373533312927252321191715131197531 4745434139 5755535149 6765636159 75737169

Position 1Position 2

Position 3

400

420

440

460

480

500

520

540

560

580

600

620

640

660

AB C D

H G FE

Inlet HDR

Outlet HDR

Critical point = 427mm

Figure 14 Schematic of the final superheater with determined critical points and thickness values of the tubes in zone E

Inlet HDR

Outlet HDR

A

B

C

D

E

(a)Outlet HDR

F G H I

ED C B A

(b)

Figure 15 Schematic of (a) medium reheater and (b) final reheater with determined critical points


Competing Interests

The authors declare that they have no competing interests

Acknowledgments

The authors would like to thank the personnel of the PowerPlant for providing failed tubes and their help in thicknessmeasurements process

References

[1] N S Harding and D C OrsquoConnor ldquoAsh deposition impacts inthe power industryrdquo Fuel Processing Technology vol 88 no 11-12 pp 1082ndash1093 2007

[2] S Srikanth B Ravikumar S K Das K Gopalakrishna K Nan-dakumar and P Vijayan ldquoAnalysis of failures in boiler tubes dueto fireside corrosion in awaste heat recovery boilerrdquoEngineeringFailure Analysis vol 10 no 1 pp 59ndash66 2003

[3] S S Chatha H S Sidhu and B S Sidhu ldquoHigh temperature hotcorrosion behaviour of NiCr and Cr3C2-NiCr coatings on T91boiler steel in an aggressive environment at 750∘Crdquo Surface andCoatings Technology vol 206 no 19-20 pp 3839ndash3850 2012

[4] E Labuda K J Shields and D A Cline ldquoFireside corrosionin coal- and oil-fired units failure mechanisms and methods ofpreventionrdquo Corrosion Paper 00031 2000

[5] ldquoASTM A 213 Standard Specification for Seamless Ferritic andAustenitic Alloy-Steel Boiler Superheater and Heat-ExchangerTubesrdquo 2006

[6] X Tao L Han and J Gu ldquo120574 grain memory in X12CrMoWV-NbN10-1-1 steelrdquo Steel Research International vol 87 no 5 pp571ndash580 2016

[7] W T Reid External Corrosion and Deposits Boilers and GasTurbines Elsevier New York NY USA 1971

[8] C P OrsquoHagan R A Barrett S B Leen and R F D MonaghanldquoEffect of high-temperature corrosion on the service life ofP91 piping in biomass co-firingrdquo Journal of Pressure VesselTechnology Transactions of the ASME vol 138 no 2 Article ID021407 2016

[9] J Soltis ldquoPassivity breakdown pit initiation and propagation ofpits inmetallic materialsndashreviewrdquoCorrosion Science vol 90 pp5ndash22 2015

[10] D N French Understanding Fireside Corrosion View 2015

Submit your manuscripts athttpswwwhindawicom

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CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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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


Nano

materials


Journal ofNanomaterials


Table 1 Chemical composition of low-alloy steel ASTM A213 T12 and A213 T22

Wt Carbon Manganese Phosphorus Sulphur Silicon Chromium MolybdenumA213 T12 005ndash015 030ndash061 0025 0025 050 08ndash125 044ndash065A213 T22 005ndash015 030ndash060 0025 0025 050 190ndash260 087ndash113

(a) (b)

Figure 1 (a) Cross section of a boiler tube with deposits on the surface and (b) surface of a boiler tube after two years in the service condition

surface of materials and induce corrosion During combus-tion these elements combine to formvarious types of vapoursand condensed phases [3] The chemistry of reactions takingplace during combustion is complex and highly variableDegradation of materials occurs when these molten com-pounds destroy the natural protective oxide layer of themate-rials surface during boiler operation [4] The complex envi-ronment (thermal chemical and mechanical) on the boilerservice conditionmakes it extremely difficult for amaterial toendure all the tough situations imposed on it [1]Therefore toprevent catastrophic failures it is important to understandand predict corrosion behaviour on the tubes surfaces inadvance It should also be noted that temperature and internalpressure are different in different parts of a boilerThus thick-ness measurements of the boiler tubes and determination ofcritical points are appropriate approaches

In this work the in situ thickness measurement of tubesat different parts of a fossil fuel power plant in Iran has beenperformed and the damaged tubes were collected for moreroot cause analysis Optical microscopy (OM) scanning elec-tron microscopy (SEM) with Energy-Dispersive X-ray Spec-troscopy (EDS) and X-ray diffraction (XRD) have been usedto study morphology chemical composition and structureof failed tubes and corrosion products on top of the tubesThickness measurement data has been used to determine thecritical points in the boiler

2 Experimental

Failed tubes of the boiler were transferred directly fromboilerunit to the laboratory After visual inspection the tubes havebeen cut for cross section studies The samples were groundusing successive finer grades of SiC papers up to 2000and then polished to a mirror finish by 03 and 005 120583malumina slurry OM SEM EDS and XRD have been utilizedto characterize the samples and corrosion products In situ

thickness measurement was performed by ultrasonic testing(UT) in the power plant siteThe thickness values reported inthis paper are the average value of at least 3 measurementswith six-month intervals Superheater and reheater tubeswere made of a low-alloy steel ASTM A213 T22 and A213T12 respectively with a chemical composition presented inTable 1 [5]

3 Results

Figure 1 depicts a superheater tube with the corrosion pro-ducts and deposits on its surface The surface of the tubewhichwas exposed to fire is covered by a layer of thick coarseand adhesive deposit Its yellow colour suggests the presenceof sulphur in the layer

The thickness measurements indicate that thickness infailed tubes is dramatically decreased to values lower thanthe critical value for boiler tubes According to Figure 2 thisphenomenon is more apparent in the fire side of tubes

Figures 3ndash6 demonstrate the microstructures of boilerfailed superheater and reheater tubes Based on Figure 3the structure of superheater in the surface vicinity is slightlydifferent from the bulk material with more spherical carbidein grain boundaries compared to the ferritic microstructureof the bulk material Such difference in microstructure haspreviously been reported in the literature [6] In Figure 4 aporous and nonuniform deposit layer on the tube is shown

The microstructure of reheater tube is the same as thesuperheater however the deposit layers on the reheaters areuniform suggesting a general corrosion on the reheater tubesurfaces (see Figures 5 and 6)

The morphology of deposit layers on the external surfaceof the reheater and superheater has further been studied bySEM and the images are shown in Figure 7

Such difference in corrosion products and oxide layers onthe superheater and reheater tubes stems from the position of






NaV6O15

CrFe(VO4)2

Fe2O3


2SO4and








4 Discussion


2 and


2and SO

3depending on



2SO4+H2O (1)





2SO4layer begins to



and CrFe(VO4)2are


Na2SO4+ 5V2O5+ 2VO

2997888rarr SO

3+ 2NaV

6O15 (2)


4)2

(3)








SO4





(a) (b)


70605040302010

0

100

Cou

nts

400

Position 2 (∘)

(a)

0

25Cou

nts

100

70605040302010

Position 2 (∘)

(b)


Base metal

Cl2 Cr2O3 CrCl2

Flue Gas



+

minus minus

Anode Anode

Soliddeposit

LiquidLiquid

Flue gas

(due to high heat

transfer rate)

e eCathode






5 Conclusion


A B C DE

Inlet HDR

Outlet HDR


Wal

lThic

knes

s Mea

sure

men

t (m

m)

Tube number373533312927252321191715131197531

320

340

360

380

420

400

440

460





Wal

lThic

knes

s Mea

sure

men

t (m

m)

Tube number373533312927252321191715131197531 4745434139 5755535149 6765636159 75737169


Position 3

400

420

440

460

480

500

520

540

560

580

600

620

640

660

AB C D

H G FE

Inlet HDR

Outlet HDR



Inlet HDR

Outlet HDR

A

B

C

D

E

(a)Outlet HDR

F G H I

ED C B A

(b)



Competing Interests


Acknowledgments


References


















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials








NaV6O15

CrFe(VO4)2

Fe2O3


2SO4and








4 Discussion


2 and


2and SO

3depending on



2SO4+H2O (1)





2SO4layer begins to



and CrFe(VO4)2are


Na2SO4+ 5V2O5+ 2VO

2997888rarr SO

3+ 2NaV

6O15 (2)


4)2

(3)








SO4





(a) (b)


70605040302010

0

100

Cou

nts

400

Position 2 (∘)

(a)

0

25Cou

nts

100

70605040302010

Position 2 (∘)

(b)


Base metal

Cl2 Cr2O3 CrCl2

Flue Gas



+

minus minus

Anode Anode

Soliddeposit

LiquidLiquid

Flue gas

(due to high heat

transfer rate)

e eCathode






5 Conclusion


A B C DE

Inlet HDR

Outlet HDR


Wal

lThic

knes

s Mea

sure

men

t (m

m)

Tube number373533312927252321191715131197531

320

340

360

380

420

400

440

460





Wal

lThic

knes

s Mea

sure

men

t (m

m)

Tube number373533312927252321191715131197531 4745434139 5755535149 6765636159 75737169


Position 3

400

420

440

460

480

500

520

540

560

580

600

620

640

660

AB C D

H G FE

Inlet HDR

Outlet HDR



Inlet HDR

Outlet HDR

A

B

C

D

E

(a)Outlet HDR

F G H I

ED C B A

(b)



Competing Interests


Acknowledgments


References


















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials







2SO4layer begins to



and CrFe(VO4)2are


Na2SO4+ 5V2O5+ 2VO

2997888rarr SO

3+ 2NaV

6O15 (2)


4)2

(3)








SO4





(a) (b)


70605040302010

0

100

Cou

nts

400

Position 2 (∘)

(a)

0

25Cou

nts

100

70605040302010

Position 2 (∘)

(b)


Base metal

Cl2 Cr2O3 CrCl2

Flue Gas



+

minus minus

Anode Anode

Soliddeposit

LiquidLiquid

Flue gas

(due to high heat

transfer rate)

e eCathode






5 Conclusion


A B C DE

Inlet HDR

Outlet HDR


Wal

lThic

knes

s Mea

sure

men

t (m

m)

Tube number373533312927252321191715131197531

320

340

360

380

420

400

440

460





Wal

lThic

knes

s Mea

sure

men

t (m

m)

Tube number373533312927252321191715131197531 4745434139 5755535149 6765636159 75737169


Position 3

400

420

440

460

480

500

520

540

560

580

600

620

640

660

AB C D

H G FE

Inlet HDR

Outlet HDR



Inlet HDR

Outlet HDR

A

B

C

D

E

(a)Outlet HDR

F G H I

ED C B A

(b)



Competing Interests


Acknowledgments


References


















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)


70605040302010

0

100

Cou

nts

400

Position 2 (∘)

(a)

0

25Cou

nts

100

70605040302010

Position 2 (∘)

(b)


Base metal

Cl2 Cr2O3 CrCl2

Flue Gas



+

minus minus

Anode Anode

Soliddeposit

LiquidLiquid

Flue gas

(due to high heat

transfer rate)

e eCathode






5 Conclusion


A B C DE

Inlet HDR

Outlet HDR


Wal

lThic

knes

s Mea

sure

men

t (m

m)

Tube number373533312927252321191715131197531

320

340

360

380

420

400

440

460





Wal

lThic

knes

s Mea

sure

men

t (m

m)

Tube number373533312927252321191715131197531 4745434139 5755535149 6765636159 75737169


Position 3

400

420

440

460

480

500

520

540

560

580

600

620

640

660

AB C D

H G FE

Inlet HDR

Outlet HDR



Inlet HDR

Outlet HDR

A

B

C

D

E

(a)Outlet HDR

F G H I

ED C B A

(b)



Competing Interests


Acknowledgments


References


















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




+

minus minus

Anode Anode

Soliddeposit

LiquidLiquid

Flue gas

(due to high heat

transfer rate)

e eCathode






5 Conclusion


A B C DE

Inlet HDR

Outlet HDR


Wal

lThic

knes

s Mea

sure

men

t (m

m)

Tube number373533312927252321191715131197531

320

340

360

380

420

400

440

460





Wal

lThic

knes

s Mea

sure

men

t (m

m)

Tube number373533312927252321191715131197531 4745434139 5755535149 6765636159 75737169


Position 3

400

420

440

460

480

500

520

540

560

580

600

620

640

660

AB C D

H G FE

Inlet HDR

Outlet HDR



Inlet HDR

Outlet HDR

A

B

C

D

E

(a)Outlet HDR

F G H I

ED C B A

(b)



Competing Interests


Acknowledgments


References


















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Wal

lThic

knes

s Mea

sure

men

t (m

m)

Tube number373533312927252321191715131197531 4745434139 5755535149 6765636159 75737169


Position 3

400

420

440

460

480

500

520

540

560

580

600

620

640

660

AB C D

H G FE

Inlet HDR

Outlet HDR



Inlet HDR

Outlet HDR

A

B

C

D

E

(a)Outlet HDR

F G H I

ED C B A

(b)



Competing Interests


Acknowledgments


References


















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Competing Interests


Acknowledgments


References


















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



Documents

Fire-Side Corrosion: A Case Study of Failed Tubes of …downloads.hindawi.com/journals/ijc/2017/7367046.pdf6 InternationalJournalofCorrosion + − − Anode Anode Solid deposit Liquid