fac multiphase ned

Nuclear Engineering and Design 267 (2014) 34 43

Contents lists available at ScienceDirect

Nuclear Engineering and Design

j ourna l h om epa ge: www.elsev ier .com/

Experim cotwo-ph

Wael H. AbdelsalDepartment of ox #87

h i g h l i g h t s

Effect of two-phase ow on ow accelerated corrosion has been investigated experimentally. Experiments were performed for different orice to pipe diameter ratios. The effect The maxim The curren

a r t i c l

Article history:Received 15 MReceived in reAccepted 2 No

1. Introdu

Flow accsteel pipingindustries idesalinationeffect on vasevere FAC

CorresponE-mail add

wael.ahmed@

0029-5493/$ http://dx.doi.oof ow patterns and mass quality on wear patterns is investigated.um FAC wear was found at approximately 25 pipe diameters downstream of the orice.t study will help FAC engineers to prepare reliable plant inspection scope.

e i n f o

ay 2013vised form 30 October 2013vember 2013

a b s t r a c t

The main objective of this paper is to experimentally study the effect of two-phase ow on ow-accelerated corrosion (FAC) downstream an orice. FAC is a major safety and reliability issue affectingcarbon-steel piping in nuclear and fossil power plants. This is because of its pipe wall wearing and thin-ning effects that could lead to sudden and sometimes catastrophic failures, as well as a huge economicloss. In the present study, FAC wear of carbon-steel piping was simulated experimentally by circulatingairwater mixtures through hydrocal (CaSO41/2H2O) test sections at liquid supercial Reynolds num-ber, Re = 20,000, and different air mass ow rates. Experiments were performed for a test section withdifferent orice to pipe diameter ratios (do/D = 0.25, 0.5 and 0.74). The observed ow patterns were com-pared with the available ow pattern maps. Surface wear patterns downstream the orices were alsoanalyzed. The maximum FAC wear was found to occur at approximately 25 pipe diameters downstreamof the orice. The obtained results were found to be consistent with those from a single-phase ow studyreported earlier. Moreover, FAC was found to depend on the relative values of the mixture mass qualityand the volumetric void fraction. Lower values of FAC wear rate were obtained for higher values of massquality. A modied correlation is developed in order to predict FAC wear rate downstream of the pipe-restricting orice with an average RMS accuracy of 10%. However, the location of maximum wear rateis well predicted. The current study is considered as an integrated effort to develop guidelines to FACengineers in power plants in order to prepare more reliable plant inspection scope.

2013 Elsevier B.V. All rights reserved.

ction

elerated corrosion (FAC) material degradation in carbon systems represents one of the major problems in manyncluding nuclear power plants, oil and gas industries,

plants, and many others because of its detrimentalrious piping components. It is widely known that thedamage normally occurs in tees, elbows, downstream

ding author. Tel.: +966 3 860 7507; fax: +966 3 860 2949.resses: [email protected],gmail.com (W.H. Ahmed).

of control valves, ow elements, reducers or orices. The wall thin-ning caused by FAC in piping systems may lead to catastrophicfailures of system components and may also result in serious fatal-ities as reported by Ahmed et al. (2012). Accurate prediction of FACrate in a specic application is one of the very complicated prob-lems since it requires detailed investigation of both the soluble ironproduction (Fe2+) at the oxide/water interface and transfer of thecorrosion products to the bulk ow across the diffusion bound-ary layer. Consequently, the pipe wall thinning rate due to FACdepends on a complex interaction of several parameters such asmaterial composition, water chemistry, and hydrodynamic. Ahmedet al. (2012) indicated that a signicant research has been con-ducted on investigating the effect of uid chemical properties on

see front matter 2013 Elsevier B.V. All rights reserved.rg/10.1016/j.nucengdes.2013.11.073ental investigation of ow acceleratedase ow conditions

Ahmed , Mufatiu M. Bello, Meamer El Nakla,am Al Sarkhi, Hassan M. Badr

Mechanical Engineering, King Fahd University of Petroleum & Minerals, KFUPM, P.O. Blocate /nucengdes

rrosion under

4, Dhahran 31261, Saudi Arabia

W.H. Ahmed et al. / Nuclear Engineering and Design 267 (2014) 34 43 35

Nomenclature

A pipe cross-sectional area, m2

C DeffD J MTC Q Re Sc Sh Shfdx z

Subscriptb eff w

FAC in nuclof two-phas

Materialboth singlewater owspiping/ttinphase watequality (Okaow-inducehigh steampletely diffeIn the later in the matedamage is mment velocby a mecha(2011) wholess than 10rosion prod

The hydows are ephase owsand the com(Kim et al.,phases has sequently thpattern) wicontrolling or gas bubbenergy closThis has bewho showeshear forcethe protecti

Poulson parametersvelocity, sufer coefciemost impoicantly inu

performed by Poulson (1987) for both single-phase and high massquality two-phase ows over a wide range of supercial gas andliquid velocities highlighted two main important conclusions. First,

deling using heat transfer analogy in annular two-phase owo unr at ositithe oped bd thariginplieucinhouline tactaneciesinetnergt ap

et al intoted bded

streo imdelinattery an

orrelds nt the

repocour

LdHL

the l

Q

AL

)

voidistribmass concentrationeffective diffusivity, m2/spipe diameter, mvolumetric ux, m/smass transfer coefcient, m/svolume ow rate, m3/sReynolds number, Re = UD/vSchmidts number, Sc = v/DSherwood number, Sh = MTCD/DeffSherwood number for fully developed owmass qualityaxial coordinate, mvolumetric void fractionkinematic viscosity, m2/sdensity, kg/m3

sbulk uid valueeffective valuewall

ear power plants. However, the hydrodynamic effectse ows on FAC have not been thoroughly investigated.s degradation due to FAC has been observed under-phase and two-phase ow conditions. In single-phase, FAC occurs in carbon steel or low carbon-alloy steelg at a temperature greater than 95 C, while in the two-r-vapor ows, FAC also depends on the value of steamda, 2011). Moreover, when the steam quality is low, thed corrosion process is referred to as FAC. However, for

quality, the degradation mechanism found to be com-rent and referred to as liquid impingement corrosion.case, the value of ow velocity plays an important rolerials damage. For a ow velocity less than 100 m/s, theainly due to chemical process, while for an impinge-

ity greater than 200 m/s, the degradation is controllednical process. This classication is presented by Okada

concluded that liquid droplet impingement velocities0 m/s found to be incapable of removing the solid cor-

the motends ttransfesight p

On develoshoweof its oThis imfor red

It sdetermsion reand spusing klence eefcienNesic dividedsuggessuspenvapour(iv) twent moow p

Remow cReynolaccounknownBoucha

ReL = V

where

VL =(

Theow ducts.rodynamics parameters controlling FAC in two-phasexpected to be more complex than in the case single-. This is mainly due to the effect of phase redistributionplex interactions between the gas and the liquid phases

2007). In this case, the interaction between the twoa major role in the mass transfer mechanism and con-e FAC process. Also, the two-phase ow structure (owthin the piping component plays an important role inthe FAC process in this component. For example, vaporles can have a signicant effect on the turbulent kinetice to the wall and subsequently the mass transfer rate.en supported by the study performed by Jepson (1989)d that high velocity slugs can cause high turbulence ands at the pipe wall and thus enhance the destruction ofve lm which increases FAC rate.(1983) experimentally identied four hydrodynamic

directly affect FAC rate. These parameters are the owrface shear stress, turbulence intensity, and mass trans-nt. He concluded that mass transfer coefcient is thertant parameter among other parameters that signif-ences FAC rate. Furthermore, the experimental work

= jgCOj

where j anthe phase dow patter

Anotherphase ow to predict exhaust steexhaust stesured data under two cal approacmodels to idamage. Ththe previoumulti-dimeAlthough thFAC wear rmodeling aempirical-bdue to its siderestimate the rate of mass transfer. Second, the massthe bend is at a maximum value at the elbow line ofon where the high velocity droplets hitting the bend.ther hand, Chexal et al. (1996) reported a correlationased on experimental FAC data for wet steam ow andt the FAC wear rate is signicantly reduced to about 33%al value when the steam quality is increased by only 10%.s that increasing steam dryness is a very effective wayg FAC damage in two-phase ows.d be noted that modeling FAC requires an ability tohe ow eld and local wall mass transfer rates of corro-ts and products. Therefore, the continuity, momentum

mass transport equations are required to be solvedic energy of turbulence-dissipation along with turbu-y model closures. This has been found to be the mostproach for many industrial applications as reported by. (1993). In the case of two-phase ow, modeling is

four classes based on the void fraction distributions asy Tong and Tang (1997). These classes are: (i) bubblesin the liquid stream; (ii) liquid droplets suspended in theam; (iii) vapor and liquid existing intermittently; andmiscible liquids coexisting in a ow. Therefore, differ-g techniques are applied depending on the two-phase

ns.d Bouchacourt (1992) suggested that the single-phaseations could be used for two-phase ow by adjustingumber with the actual water velocity and taking into

void fraction between the steam and water. The well-rt by Chexal et al. (1996) utilized the idea of Remy andt (1992) and used Reynolds number dened as:

(1)

iquid velocity is expressed as:

.(

1 x1

)(2)

fraction can be expressed as a function of the two-phaseution parameters as:

+ Vgj

(3)

d jg are the mixture and vapor volumetric uxes, CO isistribution coefcient which depends on the two-phasen, and Vgj is the vaporgas drift velocity.

extensive work carried out on modeling FAC in twois developed by Kuo-Tong et al. (1998), who attemptedFAC damage locations on high pressure (HP) turbineam line. The choice of high pressure (HP) turbineam line as a case study was based on the plant mea-of pipe thickness which indicates serious FAC problemphase ow conditions. They proposed a mathemati-h to predict FAC using two-phase ow hydrodynamicnvestigate the impact of the local parameters on FACey reported an improvement of the new approach overs methods used because of the involvement of thensional ow characteristics responsible for FAC wear.e method presented provides more accurate value ofate in two-phase ow, however, it requires intensivend not reasonable for practical calculation. That is whyased correlations continue to receive a great attentionmplicity and suitability for use in practical applications.

36 W.H. Ahmed et al. / Nuclear Engineering and Design 267 (2014) 34 43

In a similar fashion, Yuh et al. (2008) developed FAC modelfor two-phase ow using a case study of extraction piping systemconnecting the low-pressure turbine and feed-water heater at boil-ing water reactors (BWR). They developed a model similar to thatreported byin which spby Ferng etTheir FAC rbutions of fractions, tuthat in two-sidered an imodel was

Extensivseveral comthat a uniqufer coefcie1990) that parameter wear rate aexpected. Fdepends on

In summpipe ttingvalves, teesboth fossil above litera(2012). Thisas well as tstream of ttransfer ratows is stroof these tt

Based onoccurring inhas not recein such locaof FAC couporice. In thtwo-phase to-pipe diaparametersnumber of ration of plfailures duefactor.

1.1. Correla

FAC rateand can be c(MTC) in thas a functioof ferrous iotion of ferro

FAC rate = MAs sugge

mass transfReynolds an

Sh = a Reb

where a, b agiven ow a, is geometusually betw

Poulson (1999) reported that the actual mass transfer proledownstream orices had been examined in details by Coney (1980),who obtained the non-dimensional mass transfer coefcient utiliz-ing the heat transfer data of Krall and Sparrow (1966) and the mass

r dat expr

1 +

Shz eaccal c1979treame (1

0.01

erim

erim1, wtriesWatedriverom ntrocy ofiableoweter

meaw loot tuboxim

ensut secctionhe pgateo/D oed,

o visoric

sectice,

in ated bal delk onentss tras tha

the to tipingtionoxidvelopps oorderer, tssolvecortura Kuo-Tong et al. (1998) coupled with a corrosion modelecial treatment of near-wall uid velocity as suggested

al. (1999a,b, 2000) to express FAC wear distributions.esults were presented as a function of the local distri-uid parameters such as two-phase ow velocities, voidrbulent properties, and local pressure. They concludedphase ow condition, the droplet kinetic energy is con-mportant parameter that dominates FAC damage. Theirqualitatively in good agreement with actual plant data.e work was performed by Poulson (1999) who reviewedplexities in predicting FAC wear rate and he concludede relationship between FAC wear rate and mass trans-nt exists. He also added to his earlier ndings (Poulson,the mass transfer coefcient is the most importantgoverning FAC wear and the relation between the FACnd mass transfer coefcient is not linear as one wouldurthermore, he concluded that FAC wear rate critically

material, environmental and hydrodynamic factors.ary, the piping components located downstream of

s such as sudden expansion or contractions, orices, and elbows are most susceptible to FAC damage inand nuclear power plants systems as explained in theture and in details by Ahmed (2010) and Ahmed et al.

is mainly due to the severe changes in ow directionhe development of secondary ow instabilities down-hese disturbing components, which enhance the masse and consequently FAC. Moreover, FAC in two-phasengly affected by the phase redistributions downstreamings.

the above review, it is clear that the problem of FAC two-phase ows downstream of a restricting oriceived enough attention despite the aggressive corrosiontion. The problem also represents an interesting caseled with two-phase redistribution downstream of theis study, the main objective is to evaluate the effect ofow on FAC downstream of an orice at different orice-

meter ratio. The effect of local ow and mass transfer on FAC wear rate is also evaluated at liquid Reynolds20,000. This will help plant engineer during the prepa-ant inspection scope to avoid sudden and catastrophic

to FAC and consequently improve the plant capacity

ting the mass transfer coefcient

is a direct function of the mass ux of ferrous ionsalculated from the convective mass transfer coefciente owing water phase. Therefore, FAC rate is expressedn of MTC and the difference between the concentrationns at the oxide/water interface (Cw) and the concentra-us in the bulk of water phase (Cb) as:

TC(Cw Cb) (4)sted by Poulson (1999), FAC is well correlated with theer coefcient and can expressed in terms of Sherwood,d Schmidt numbers as follows:

ScC (5)nd c are related to mass transfer which occurs under acondition and the component geometry. The constant,ry-dependent and can be obtained experimentally; b iseen 0.3 and 1, and c is typically between 0.33 and 0.4.

transfecan be

ShZShfd

=

wherestreamempiriet al. (downsand Hu

Shfd =

2. Exp

Expin Fig. geometions. pump plied fby a coaccuraby varwater ow mture isthe ostraighof apprtion tostraightest se

In tinvestiwith dperformtions tof the of testthe oripatternand tesmaterithe bucompothe masame aplants,similarsteel pdissoluof the the descallo

In in watand diwere rfully saa of Tagg et al. (1979). The correlation of Coney (1980)essed as:

AZ

[1 + BZ

(Re0.66O

0.0165Re0.86 21

)](6)

is the local Sherwood number at a distance (z) down-h orice, ReO is the orice Reynolds number, A, B areonstants obtained by Krall and Sparrow (1966) and Tagg), and Shfd is the fully developed Sherwood number far

the orice i.e. in a straight pipe and reported by Berger977) in the form:

65Re0.86Sc0.33 (7)

ental facility and test procedure

ents are conducted in a ow loop schematically shownhich is designed to accommodate different test section

under both single or airwater two-phase ow condi-r is supplied from a 100 L tank through a centrifugaln by a variable speed electric motor. The air is sup-the main lab compressor and the ow rate is adjustedl valve and measured using an air rotameter with an

2% full scale. The water mass ow rate is controlled speed pump in addition to a gate valve located on the

line. The water ow rate is measured using a turbine with an accuracy of 2% full scale, and the tempera-sured using thermocouples at various locations alongp. Experiments were performed using a 1-in. diametering at a Reynolds number of 20,000. A straight sectionately 75 diameters is installed upstream of the test sec-re fully developed inlet ow conditions. An additionaltion of 100 diameters is installed downstream of the.resent study, two types of test sections were used to

the effect of two-phase ow on FAC for three oricesf 0.25, 0.5 and 0.74. The rst set of experiments was

with no mass transfer involved, using acrylic test sec-ualize the two-phase ow redistribution downstreame at different mass qualities (Fig. 2). The second typeon is made of hydrocal (CaSO41/2H2O) downstream ofas shown in Fig. 3, in order to simulate the FAC wear

reasonable test time. This technique has been appliedefore by Poulson (1990) and the dissolution of the wallpends on the mass transfer of hydrocal from wall intow and used to simulate FAC wear in carbon steel pipings. Although the changes to the surface occurring fromnsfer of the hydrocal to the ow may not be exactly thet would occur in carbon steel piping systems in powerwear pattern developed is expected to be reasonablyhat generated over a longer period of time in carbon

component as explained by Wilkin et al. (1983). The of the hydrocal is considered to depict the dissolutione layer in carbon steel pipe. This dissolution leads toment of a rough surface that sometimes referred to asr pours.

to determine the saturation limit of the hydrocalests were performed using ne particles of hydrocaled in the water reservoir and the water conductivityded as explained by El-Gammal et al. (2012). Runningted solution through the hydrocal test section showed


imen

no-wear. Thwere entiretions are noprepared bvacuum forof the nal hall tests afte

The overdeterminedlating watean accuracyexplained ical dissolutFig. 1. Schematic diagram of the experis indicates that the measured wear in the present testsly due to mass transfer and that the hydrocal test sec-t susceptible to mechanical wear. The test section is

y mixing plaster of pairs with deionized water under 2 min to avoid air bubbles and to decrease the porosityydrocal section. The water to plaster ratio was used forr several trials to obtain reliable test sections.all mass transfer over the entire hydrocal test section is

by measuring the electrical conductivity of the circu-r within the ow loop using EU Tech-PC300 meter with

of 1%. The operating principle of this technique wasn detail by Ahmed et al. (2012). The amount of hydro-ion in the water is obtained through a calibration curve

relating thecal. In the pon volume reached andsurements conductivitments are rdetermine t

The locaCMM withof Class 2Mdifference CAD model

Plas ter of Pair s

Pressu re Taps Note:

Plas ter of tubing fo roric

Oric

P1 P2 P3

1

Fig. 2. Test section for two-phase ow exptal facility. water conductivity to the amount of dissolved hydro-resent experiments, a maximum concentration of 4%

basis is found to represent the limit where saturation is the conductivity remains constant. Temperature mea-were used to compensate for the changes in the watery with temperature. The water conductivity measure-ecorded every 2 min during each experimental run tohe overall wear rate within the test section.l wear measurements were obtained using FARO-Axis

Laser Scanner D100 attached to laser power source. The measured wear is calculated by measuring thebetween the actual corroded scanned surface and a

representing the new pipe without corrosion. Wear

Acrylic Tubing

Pa irs Sec on is repl aced by ac rylic ow visuali za on do wnst ream of the

2

eriments.


Fig. 3. Hydrocal test section arrangement.

measurements were obtained by scanning the cut test sections witha measurement accuracy of 037 mm. KUBE software was used tolaser measurement capturing and GEOMAGIC studio software wasused for data processing for each test section. After the cut-test sec-tion was scthe data noThen, the dstretched wmodicatiomaintain ththe GEOMAproles aresurements sample of s

In ordermicroscopysection. Thesection founshown in Fiwas carrieddifferent mtest sectiongrinded wh

F

EM of macropores present in the hydrocal test section before testing.anned, the point cloud data was optimized by reducingise, over lapping triangular mesh and overhanging data.ata was merged into polygons and converted into oneater-polygon structure. It should be noted that no datan or smoothing operation were carried out in order toe original data trend. A CAD geometry was created intoGIC studio to represent the new pipe. Then, the wear

identied by the difference between the surface mea-after wear takes place and the original pipe surface. Acanned proles is shown in Fig. 4.

to characterize the pipe surface, scanning electron (SEM) analyses were carried out for the casted test

mean diameter of macropores for the prepared testd to be within the standard hydrocal (142152 m) asg. 5 and suggested by Villien et al. (2005). The analysis

out on various regions downstream of the orice forass qualities. Specimens were cut from the degradeds, their base and edges were carefully machined andile preserving the inner surface for analysis. All sections

Fig. 5. Sig. 4. Surface wear proles using GEOMAGIC studio. Fig. 6. Inlet ow patterns on Taitel and Duckler map for 1 in. horizontal pipeline.


0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

40 30 20 10 0

Hy

dro

cal

Co

nce

ntr

ati

on

, %

by

vo

lum

e, (

C -

Ci)

Time, t, (m inut es)

Single phase , water (x = 0)

Air-wate r two phas e (x =0.0011 )



d/D = 0.5Re1ph = 20,000

(a)

0.14

Single ph ase wate r (x=0 )

Air-wat er two ph ase (x = 0. 0011)

d/D = 0.7 4 Re1ph = 20,00 0

(b)

Fig. 7. Hydrocratio of 0.74.

were coatedduring SEMtion range the effect o

0

0.002

0.004

0.006

0.008

0.01

0.012

0

Wear rate,%by

volume/min

Fig. 8. Variatiquality for all olu

me,

(C

- C

i)

0.1

0.12Air-wat er two ph ase (x = 0. 0021 )

air-water two phase (x = 0.00 32)

Air-wat er two ph ase (x = 0. 0032 ) Hy

dro

cal

Co

nce

ntr

ati

on

, %

by

v

0

0.02

0.04

0.06

0.08

40 30 20 10 0

Time, t, (minute s)

al concentration variation with time under both single and two phase ow experiments

with gold by ion sputtering to allow better resolution analysis. SEM analysis was carried out at a magnica-(10150) to investigate the surface morphology andf two-phase ow on the shape of wear pattern.

0.001 0.002 0.003 0.004 0.005Mas s qual ity , x

d/D = 0. 25

d/D = 0. 5

d/D=0.74

on of hydrocal wear rate downstream the orice with inlet massgeometries under both single and two phase ow experiments.

3. Results

For a givrate is chancial velocitwo-phase the Taitel aThe ow papresent tesmittent owqualities ofsure and te(1967) equconrmed of the oric

As explabehavior thit approachforming larfor the redstream up tthe ow strdue to the 70 60 50 70 60 50

: (a) orice to pipe diameter ratio of 0.5, (b) orice to pipe diameter

and discussion

en inlet water volume ow rate of 0.4 L/s, the air owged from 0.335 to 0.99 L/s. The corresponding super-ties of both water and air are calculated and the inletow pattern upstream of the orice is identied usingnd Dukler (1976) ow patterns map shown in Fig. 6.ttern is conrmed with the ow visualization. In the

t, it was found that all the experiments represent inter- pattern at the orice inlet. The void fraction and mass

the current test were obtained with the help the pres-mperature measurements and by using the Chisholmation. At the same time, the void fraction results wereusing multiple capacitance sensors at the inlet sectione.ined in detail by Ahmed et al. (2012), a typical owrough orice is characterized by ow acceleration ases the orice then separates at the orice sharp edgege vortices downstream. These vortices are responsibleuction in the ow cross-sectional area further down-o the minimum value at the vena contracta. Although,ucture in two-phase ow experiences more disturbancegas deformation, however, the main liquid ow tends


enstea

to decelerasingle-phasdownstreamdownstreamwithin the c

For the measured a0.0032 and0.377652 astream of thtwo-phase

Fig. 10. Wear(do/D = 0.5).

crease inualitrease to is apilar eions Fig. 9. Two-phase ow redistribution do

te toward the ow reattachment point similar to thee case. Moreover, the velocity at the central core just

of the orice decreases further as the ow develops. Overall, the maximum centreline velocity increasesirculation zone as the orice diameter decreases.orice to pipe diameter ratio of 0.5, wear rates weret different mass quality values ranging from 0.0011 to

the corresponding inlet void fraction varies between

rate dedecreamass qthe decce duphase

Simconditnd 0.438281. The resulting average wear rates down-e orice are shown in Fig. 7 for both single-phase and

ows. It can be seen that the gradients of the dissolution

pattern downstream of the orice at different mass qualities

general, it wdecrease asrates downincreases fobe explainehas a parallthe mass trgaseous ph

Fig. 11. FAC wm of orifces.

se as the mass quality increases. The gure indicates a the dissolution rate by approximately 42% when they increases from 0 to 0.0032. This can be attributed toe in the hydrocal dissolution rate downstream of the ori-the presence of air where mass transfer in the gaseousproximately zero.xperiments were performed at the same operating owusing orice to pipe diameter ratios of 0.25 and 0.74. In

as found that the slope of dissolution rate gradient lines

the mass quality increases. The corresponding wearstream the orice found to decrease as the mass qualityr all of the three do/D ratios as shown in Fig. 8. This cand on the basis that an increase in the inlet mass qualityel increase in the void fraction that results in reducingansfer based on the fact that the mass transfer in thease is insignicant.

ear rate prole in the hydrocal test section downstream the orice.


Fig. 12. Variation of overall wear rate downstream the orice with inlet volumetricvoid fraction for all geometries under both single and two-phase ow experiments.

As observed by Fossa et al. (2006), the increase in the void frac-tion causes a signicant decrease in the liquid level (in comparisonwith fully developed inlet ow conditions) just downstream theorice. This consequently led to a reduction in the overall FAC wearrates in the region downstream the orice. In spite of the increasein the liquid turbulence downstream of the orice, the mass trans-fer decreases dramatically because of the increase of the gas phasecontact area with the pipe wall. This has been conrmed using theow visualization experiments as shown in Fig. 9. It is clear fromthe gure that liquid contact area with the pipe wall becomes lessas the mass quality increases.

For the same mass quality, the liquid ow downstream smallerorice diameter is subjected to higher deceleration compared tolarger orice diameter, however, the pipe downstream remain to

0

5

10

15

20

25

0 2 4 6 8 10 12

FA

C

rate

(m

m/d

ay

)

Z/D

Sing le ph ase water (x = 0)

Air-water two ph ase (x = 0.001)



Con ey (19 80) Corr elati on

"Modified Corr elation (x=0.001 )"



Fig. 13. Comparison between the experimental data and the correlations for FACwear rate downstream the orice (do/D = 0.5).

experience higher wear rate due to the higher liquid turbulenceand consequently higher mass transfer as shown in the cut-testsections of hydrocal (Fig. 10). The gure shows qualitatively thatthe maximum wear occurs in the region Z/D 05 downstreamthe orice. Moreover, the wear rate decreases as the mass quality,x, increases.

The FAC wear rate distributions along the pipe surface down-stream the orice plate for ReL = 20,000 are shown in Fig. 11 forboth cases of single-phase and two-phase ow conditions. The g-ure indicates that the measured FAC wear rate increases steeplydownstream of the orice and reaches a maximum value withinthe ow recirculation region (Z/D 05). The rate then decreasesas the ow develops downstream. Moreover, the peak FAC valueFig. 14. Surface morphology at the location of maximum wear downstream of the orice (do/D = 0.5) at different mass qualities.


decrease as the mass quality increases due to the low mass trans-fer in the gaseous phase. For single phase ow, the peak valueslightly decreases by about 6% and 42% for x = 0.002 and x = 0.003,respectively. The location of the maximum FAC wear rate remainsunchanged

The incrnicantly asingle-phasstudy, the eorice outwReynolds ndecreases athe orice iwith the colocation of of higher tu

The dataof two-phacoefcient prelation of ethe mass tr

ShZShfd

=[1 +

where f (x) ing regresssame diameshould be nis valid for is used to cmass coefalong with

f (x) = (1

The valu0.275 g/100ties tables)beyond thedetails by Ato correlateage Root Memaximum wThis is consis to identiorice for in

Also, it susing SME phase owsthe pipe waof maximuqualities. Inmainly fromThese pits wtransfer ratphase liquiand the surpours also d

4. Conclus

The effestream orisections. Diat supercia

single phase and two-phase ow experiments, the following can beconcluded:

In general, FAC wear rate downstream the orice was foundcreae-phlocateters.massm th

wled

authchnoe Tecport

Fahcknosts, at sect

nces

W.H., als of W.H.,nstreaneerinF.P., Helectr1185al, M

acteri3533, D.,

-phaseB., Homanntric Po., 198

.M., M enge.M., Mion/co342.

.M., Mistrib., Gugce conicatio.P., 1

Journark, J.ee elb. NuclM., Speat Trg, M.Al ow lear Te, Adamnt oures. C., 201ystemmics itions, B., 1504.

, B., 19nce 23, B., 19ioncood

, B., 19746..ease in local liquid velocity has been reported to sig-ffect FAC wear rate downstream the orice undere ow condition (Chexal et al., 1996). In the presentffect of increasing the void fraction downstream theeighs the corresponding effect of increasing the localumber of the liquid phase and the overall wear rates shown in Fig. 12. Hence, the FAC wear rate downstreams reduced for the case of two-phase ow in comparisonrresponding single-phase ow condition. However, thethe maximum wear remains the same due to the effectrbulence in this region.

presented in Fig. 12 are used to correlate the effectse mass quality on the non-dimensional mass transferreviously correlated by Coney (1980). A modied cor-xisting Coney (1980) correlation is proposed to predictansfer coefcient in the form:

AZ

[1 + BZ

(Re0.66O

0.0165Re0.86 21

)]] f (x) (8)

is a function of mass quality and obtained by perform-ion analysis of the data presented in Fig. 10 for theter ratio (do/D) with a correlation coefcient R = 0.87. Itoted that the mass quality multiplier expressed in Eq. (9)0 < x < 0.1. As shown in Fig. 13, the modied correlationalculate the FAC wear rate from the non-dimensionalcient downstream of the orice as expressed in Eq. (8)the mass quality multiplier expressed as:

x0.05) (9)

e of species concentration cw along the wall (equal to g as specied in the hydrocal manufacturers proper-, and the species concentration in the bulk liquid ow

diffusive boundary layer, cb is calculated as explained inhmed et al. (2012). The modied correlation was found

the local FAC wear rate within 10% based on the aver-an Square (RMS) accuracy. Furthermore, the location ofear rate is well predicated by the modied correlation.

idered an acceptable accuracy since the main objectivefy the location of maximum wear downstream of thespection and mentoring purposes.hould be noted that the surface morphology obtainedfor the degraded surface under both single- and two-

helps in explaining the mechanism of mass transfer atll. Fig. 14 shows the surface morphology at the locationm wear downstream of the orice for different mass

can be clearly seen that the surface has pits initiated air bubbles exist in the test section hydrocal material.ere reduced in the case of two-phase ow where mass

e is reduced. As the mass quality decreases to the single-d case (Fig. 14a), the pours evolve and increase in sizeface roughness dramatically increased. The size of theseecreases as the mass quality increases.

ion

ct of two-phase ow on wall mass transfer rate down-ces was investigated experimentally using hydrocal testfferent orice to pipe diameter ratios were consideredl water Reynolds number of Re = 20,000. Comparing the

to desingl

The diamow

The strea

Ackno

Theand TeSciencthe supat Kingfully aSME tecal tes

Refere

Ahmed, Ann

Ahmed, dowEngi

Berger, the 20, p

El-Gammchar(6),

Chisholmtwo

Chexal, NordElec

Coney, MFerng, Y

sitesFerng, Y

eros332

Ferng, Ying d

Fossa, Morimun

Jepson, Wdian

Kim, S., Pdegrow

Krall, K.of H

Kuo-TonlocaNuc

Nesic, S.buleclos

Okada, Hing sdynacond

Poulson497

PoulsonScie

PoulsonErosHorw

Poulson743se under two-phase ow conditions compared to thease ow at the same inlet liquid Reynolds number.ion of maximum wear was found to remain within 5s downstream the orice for both single and two-phase

transfer and consequently the FAC wear rate down-e orice decreases as the inlet mass quality of increases.

gements

ors would like to thank King Abdulaziz City for Sciencelogy (KACST) for funding this work under the Nationalhnology Plan (NSTIP) grant no. 11-ADV1619-04. Also,

provided by the Deanship of Scientic Research (DSR)d University of Petroleum & Minerals (KFUPM) is grate-wledged. The authors thank Mr. Malik for performingnd to Mr. Ahmed Abdel Rehim for fabricating the hydro-ions.

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Experimental investigation of flow accelerated corrosion under two-phase flow conditions1 Introduction1.1 Correlating the mass transfer coefficient

2 Experimental facility and test procedure3 Results and discussion4 ConclusionAcknowledgementsReferences

fac multiphase ned

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