9bc803ab3fc1c4a516f3d3zxczczxc30d7640c22(1)

7/28/2019 9bc803ab3fc1c4a516f3d3zxczczxc30d7640c22(1)

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C H A P T E R 9P i p e l i n e In s u l a t i o n9 , 1 I n t r oduc t i onOilf ie ld pipel ines are insula ted mainly to conserve heat . The need to keep the product inthe p ipe l ine a t a t emp era ture h igher than the am bient could ex i st fo r the fo llowing reasonsincluding:9 P revent ing format ion of gas hydra tes9 P revent ing format ion of wax or a spha lt enes9 E nha n c i ng p r oduc t f l ow p r ope rt ie s9 Inc reas ing cool -down t ime a f t e r shu t t ing down9 Mee t ing o the r opera t iona l /process equipment requi rements

In l iquefied gas pipel ines , such as LNG, insula t ion is required to mainta in the coldtemp era ture o f the gas to keep i t in a l iqu id s ta te . Thi s chapte r desc ribes com m on ly usedinsula t ion mater ia ls , insula t ion f inish on pipes , and general requirements for insula t ion ofof fshore and deepw ate r p ipe line .

9 . 2 I n s u l a t i o n M a t e r i a lsPolypropylene, polyethylene, and polyurethane are three base mater ia ls widely used in theindus t ry for pipel ine insula t ion. Their thermal conduct ivi t ies are given in Table 9.1(Car te r e t a L , 20055).Depending on appl icat ions , these base mater ia ls are used in di fferent forms resul t ingin di fferent overal l conduct ivi t ies . A 3-layer polypropylene appl ied to pipe surface has acondu c t iv i ty of 0 .13 BT U/hr - f t -~ whi le a 4- l ayer po lypropy lene has a condu c t iv i tyof 0 .10 BT U /hr - f t -~ Sol id po lypropylene has h igher condu c t iv i ty than polypropylenefoam. Polymer syntac t ic po lyure thane has a cond uc t iv i ty o f 0 .07 BT U/hr - f t -~whi le g las s syntac ti c po lyure than e has a condu c t iv i ty of 0 .09 BT U/hr - f t -~ Thesemater ia ls have lower conduct ivi t ies in dry condi t ions such as that in pipe- in-pipeappl icat ions .

Because of i ts low the rmal conduc t iv i ty , m ore a nd m ore p o lyure thane foams a re used indeep wa ter appl icat ions . Phys ical prop ert ies of po lyure thane foam s include dens i ty, com -press ive s t rength, therm al co nduct ivi ty, c losed cel l con tent , leachable halides , f lamm abi l ity ,tens ile s t rength, tens i le m od ulus , and w ater absorpt ion . T he values of these propert ies vary

107


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1 0 8 O ffshore P ipelinesTABLE 9.1 Th erm al Con du ctivit ies of M aterials Use d i n P i p e l i n eInsulationMaterial Name Therm al Conductivity

(BTU/hr - f t -~ W/m-KPolypropylene 0.13 0.22Polyethylene 0.20 0.35Polyurethane 0.07 0.12

d e p e n d i n g o n d e n s i ty o f t h e f o am . T a b l e 9 . 2 s u m m a r iz e s t h e p r o p e rt i es o f C A P EM O D E R N h i gh - d en s it y p o l yu r et h an e f oa m s.

9.3 Pipe- in-Pipe Insulat ionUnder ce r t a in cond i t ions , p ipe - in -p ipe sys tems may be cons ide red ove r conven t iona ls ing le -p ipe sys tems . P ipe - in -p ipe insu la t ion may be requ i red to p roduce f lu ids f romhigh -p re s su re /h igh - t em pera tu re (above 150~ re se rvo ir s in deepw a te r (Ca rm ichae l et al . ,1 9 9 9 ) . T he annu lus be tween p ipes can be f il led wi th d i f fe ren t types o f in su la t ion ma te r i a l ssuch a s foam, g ranu la r , ge l , and ine r t ga s o r vacuum.

A p ipe l ine bu nd le d sys tem, a specia l conf igura t ion o f p ipe - in -p ip e insu la t ion , can beused to g roup ind iv idua l f lowl ines toge the r to fo rm a bund le (McKe lv ie , 2000) . Hea t -upl ines can be inc luded in the bund le i f necessary. T he com ple te bun d le m ay be t ranspor tedto s i t e and ins t a l l ed wi th a cons ide rab le cos t s av ing re l a t ive to o the r me thods . The ex t ras tee l r equ i red fo r the ca r r i er p ipe and space rs can be som e t imes jus t if i ed by a com bina t ionof the fo l lowing cos t advan tages (Bai , 2001) :9 A ca r r i e r p ipe can con ta in mul t ip le l ine s inc lud ing f lowl ine , con t ro l l i ne s , hydrau l i c

hoses, power cables , glycol l ines, etc .9 Insu la t ion o f the bu nd le w i th foam , ge l, o r ine r t ga s is u sua l ly cheape r than ind iv idua l

f lowl ine insu la t ion .9.4 Ge neral Req ui rem entsThe requ i remen t s fo r p ipe l ine insu la t ion va ry f rom f i e ld to f i e ld . F low as su rance ana lysesn e e d t o b e p e r f o r m e d t o d e t e rm i n e t h e m i n i m u m i n s u la t io n r e q u i r e m e n t s f o r a g i ve n fi el d.These ana lyses inc lude:9 F la sh ana lys is o f the p rod uc t ion f lu id to de te rm ine the hydra te fo rmin g t emp era tu re s in

the range o f ope ra t ing p re s su re .9 G loba l the rma l hydrau l i c s ana lys i s to de te rmine the requ i red ove ra l l hea t t r ans fe r

coeff ic ient a t each loca t ion in the p ipe l ine .9 Loca l hea t t r ans fe r ana lys is to de te rm ine the type and th icknes s o f in su la t ion to be used

a t the loca t ion .


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TABLE 9.2 Properties of CAPE MO DERN High-Density Polyurethane FoamsF o a m P r o p e r t y N o m i n a l D e n s i t y k g / m 3 T e s t M e t h o d

C o m p r e s s i v e S t r e n g th a t 2 0 ~ M P aC o m p r e s s i v e S t r e n g th a t - 1 9 6 ~ M P aT h e r m a l C o n d u c t iv i ty a t 2 0 ~ W / m KT h e r m a l C o n d u c t iv i ty a t - 1 60 ~ W / m KC l o s e d C e l l C o n t e n t , %Le a c h a b l e Ha l i d e s , p p mF l a m m a b i l i t y , / 1 0 S . ET e n s il e S t r e n g th a t 2 2 ~ M P aTe n s i l e S t r e n g t h a t - 1 9 6~ M P aT e n s il e M o d u l u s , M P aW a t e r Ab s o rp t i o n , % Vo l .

1 60 2 2 42 . 0 3 5 4 . 5 631 . 9 9 9 3 . 81 93 . 3 0 0 7 . 4 853 . 4 9 4 7 . 5 4 00 . 0 2 9 2 0 . 0 3 4 50 . 0 2 5 3 0 . 0 3 1 6

95 95< 2 0 < 2 0

10 102 . 4 1 2 3 . 5 1 73 . 2 0 4 4 . 85 4

11.8 19.40 . 1 7 0 . 1 5

3 2 08 . 1 4 49 . 1 4 4

1 5 . 82 91 7 . 1 0 7

O.0407O.O346

9 5< 2 0

106 . 64 98.3O5

2 4 . 00 . 1 2

5OO2 2 . 9 9 82 1 . 2 1 74 8 . 3 9 44 7 . 4 0 8

O.O425O. 0 3 9 0

9 6< 2 0

101 2 . 5 821 5 . 0 5 52 9 . 5

0 . 1 0

A S T M D 1 6 22A S T M D 1 6 2 1 , p er p e n d i c u l arAS TM D 1 62 1 , p a ral l e lA S T M D 16 2 1 , p er p e n d i c u l arAS TM D 1 62 1 , p a ral l e lA S T M C 5 1 8A S T M C 1 77A S T M D 2 8 5 6A S T M D 8 7 1A S T M D 1 6 92A S T M D 1 6 23A S T M D 1 6 23A S T M D 16 24A S T M D 2 8 4 2


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1 1 0 O f f s h o r e P i p e l i n e s9 Local t rans ient hea t t ransfer ana lys is a t spec ia l loca t ions a long the p ipe l ine to develop

c o o l d o w n c u r v e s a n d t i m e s t o t h e c r i t i c a l m i n i m u m a l l o w a b l e t e m p e r a t u r e a t e a c hloca t ion .A n u m b e r o f c o m p u t e r p a c k ag e s ar e av ai la bl e i n t h e i n d u s t r y f o r p e r f o r m i n g t h e s e

analyses efficiently.In s t eady s ta t e f low cond i t ions in an insu la ted p ipe l ine , the hea t f low , Q , th rou gh the

pipe wal l i s g iven byQr = UoArA T

w h e r eQr = H ea t t r ans fe r ra t eUo = Overa l l hea t t r ans fe r coe f f i c i en t (OHTC) a t the re fe rence rad iusAr = Area o f the p ipe l ine a t the re fe rence rad iusA T = D i f f e re n c e i n t e m p e r a t u r e b e t w e e n t h e p ip e l i n e p r o d u c t a n d t h e a m b i e n t t e m p e r a -

tu re ou t s ideT h e O H T C , Uo, fo r a system i s the su m of the the rm a l res is tances and is g iven by

( H o l m a n , 1 9 8 1 ) :1Uo = (9 .1)

( ~ i h ~ s 1 )Ar + +m--I 27rLkm ~ohow h e r ehi = f i lm coe f f ic i en t o f p ipe l ine inn e r su r faceho = f i lm coe f f ic i en t o f p ipe l ine ou te r su r faceAi = a rea o f p ipe l ine inne r su r faceAo = a rea o f p ipe l ine ou te r su rfacerm - - r ad iuskm = t h e r m a l c o n d u c t i v i ty

S imi la r equa t ions ex i s t fo r t r ans ien t hea t f low g iv ing ins t an taneous ra t e fo r hea t f low.Typ ica l ly requ i red insu la t ion pe r fo rm ances in t e rms o f ove ra ll hea t t r ans fe r coe f f ic i en t

(U-va lue ) o f s tee l p ipe l ines o f d i f fe ren t conf igura t ions a re sum m ar ized in Tab le 9 .3 .

9.4 .1 Dry InsulationsP i p e l i n e i n s u l a t i o n c o m e s i n t w o m a i n t y p e s - - d r y i n s u l a t i o n a n d w e t i n s u l a t i o n . T h e d r yinsu la t ions requ i re an ou te r ba r r i e r to p reven t wa te r ing re s s (p ipe - in -p ipe ) . The mos tc o m m o n t y p e s o f t h is a re :9 C l o s e d ce l l p o l y u r e th a n e f o am ( C C P U F )9 O p e n c e ll p o l y ur e th a n e fo a m ( O C P U F )9 P o l y - i so c y a n u r a t e f o a m ( P I F )


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Pipe l ine Insulat ion 111TABLE 9.3 Typ ical Pe rforma nce of Insulated Pipes

,

Insulation Ty pe U-Value W ater D epth (fi)(BTU/hr -f t2 -~ W /m2 -K F ie ld Proven Po ten ti a l

Solid PolypropylenePolypropylene FoamSyntactic PolyurethaneSyntactic Polyurethane FoamPipe-in-Pipe S yntactic Polyurethane Fo amCompositePipe-in-Pipe High EfficiencyGlass Syn tactic Polyurethane

0.50 2.84 5000 13,0000.28 1.59 2100 63000.32 1.81 3600 11,0000.30 1.70 6200 11,0000.17 0.96 9500 13,0000.12 0.68 3200 90000.05 0.28 5300 90000.03 0.17 7000 9000

9 E x t r u d e d P o ly s ty r e n e9 Fiberglass9 M i n e r a l W o o l9 Vacuum Insu la t ion Pane l s (VIP)

For deepwater p ipe l ines , the outer barr ie r i s a s tee l l ine p ipe ca l led the cas ing pipe .These p ipe l ines a re ca l l ed P ipe - in -P ipe (PIP) sys tems . Mos t deepwa te r in su la ted p ipe l inestha t a re insula ted fa l l in to th is ca tegory .

Th e m anufa c tu re o f P IP sys tems cons is ts o f p lac ing the ca r r i e r p ipe co ncen t r i ca l ly in thecas ing p ipe us ing space rs and foaming the annu lus . La rge coa t ing compan ie s in the USs u c h a s B a y o u C o m p a n i e s a n d B r e d e r o - S h a w p r o d u c e t h e s e P i P s y s t e m s i n a n a s s e m b l yl ine and a re the re fo re ab le to p roduce l a rge quan t i t i e s in a shor t t ime fo r o f f shore deep-water use .

For in s t a l l a t ion by ree l me thod o r bo t tom tow, the insu la t ion can be p laced on theca r r i e r p ipe and then pu l l ed in to the ca s ing p ipe by us ing low f r i c t ion space rs o r ro l l e r sa t t ached to the ca r r i e r p ipe . Th i s i s pe r fo rmed manua l ly and the re fo re use s p re fo rmedinsu la t ion pane l s .

In the bo t tom tow me thod fo r deepwa te r p ipe l ines , t he ca s ing i s p re s su r i zed wi thdry n i t rogen to enab le the re duc t ion in the ca s ing wa l l th i cknes s. In such ca ses , t heinsula t ion needs to be open-ce l l PUF, f iberglass , or syntac t ic foam. The open ce l l a l lowsthe p re s su r i zed n i t rogen to pe rm ea te the ce ll s and p reven t an y co ll apse o f the ce l l s. C losedcel ls w ou ld co l lapse und e r the p re s su re . Syn tac t i c foam is des igned to w i ths tand h ighpressures.

In a p re s su r ized gas /n i t rogen env i ro nm ent , t he k -va lue o f the insu la t ion inc reases due toconv ect ion. I f the p ipe l in e is ly ing on a s lope , the "ch im ney effec t" causes con vect ioncurrents to d iss ipa te the hea t and lower increases the e ffec t ive k-va lue . To prevent th is , anHDPE laye r o r p ipe i s p l aced concen t r i ca l ly a round the ca r r i e r p ipe and the annu lus i sf o a m e d . H o l e s a r e p l a c ed i n t h e b o t t o m p o s i ti o n o f t h e H D P E l a ye r t o a ll o w th e n i t r o g e nto pe rm ea te in to the op en ce ll s . Tes ts on such a conf igura t ion o f in su la ted P IP have showni t to work we l l even in a p re s su r i zed n i t rogen env i ronment . F ibe rg la s s in su la t ion can beused ins t ead o f open-ce l l foam fo r s imi la r conf igura t ion . Tab le 9 .4 shows p rope r t i e s o fsome d ry insu la t ions .


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112 O ffshore Pipel inesTABLE 9.4 Prope rties of D ry Insu lations

k-factor @ 75 ~Insulation (B tu-in /hr-ft 2-~Mater ia l Aged D e nsity C o m p r e s s i v e S e r v ic e(lbs/ft3) S t r e n g th p s i ) Temp erature (~C C P U FO C P U FPIF 0.190Polystyrene 0.259Fiberglass 0.24M ineral W ool 0.25VIP 0 .036-0 .055Insulation M aterial k- fa ct or

(Btu/hr-ft2-~Polyurethane 0.035

(PU)-SolidPolypropylene 0.039

(PP)-SolidSyntact ic PU 0 .021-0 .026Syntact ic PP 0.023 -0.039Syntact ic Phenolic 0 .014S y nta cti c E p o x y 0 . 01 7 - 0. 0 24

3 to 6 10 to 652 t o 41.8 to 2 19 to 24 - 2 9 7 to 3006 2 0 -2 9 7 to 1 653.5 to 5.5 0 to 8508.7 12923 .7-9 .0 320Densi ty W ater De pth Serv ice

(Ibs/ft3) (feet) Te m pera ture (~72 24056 9000 2903 8-5 3 3 0 0 -9 0 0 0 1 3 1 -2 4 03 7 -5 0 2 4 031 3923 7 -4 5 60 0 0 -9 0 0 0 1 60 -2 1 2

9.4.2 W et Insu la t ionsWet p ip e l in e i n su l a t i o n s a re t h o se mate r i a l s t h a t d o n o t n eed an ex t e r io r s t ee l b a r r i e r t op rev en t wa te r i n g ress o r t h e wa te r i n g ress i s n eg l ig ib l e an d d o es n o t d eg rad e t h e i n su l a t i o np r o p e r t ie s . T h e m o s t c o m m o n t y p e s o f t h is ar e:9 P o l y u r e t h a n e9 P o l y p r o p y l e n e9 S y n t a c t i c P o l y u r e t h a n e9 S y n t a c t ic P o l y p r o p y l e n e9 M u l t i - l a y e r e d9 O t h e r

T h e m a i n m a t e r i a l s t h a t h a v e b e e n u s e d f o r d e e p w a t e r i n s u l a t i o n s h a v e b e e n p o l y -u re th an e an d p o ly p ro p y len e b ased . Sy n tac t i c v e r s io n s u se p l as t ic o r g lass m at r ix t o imp ro v ei n s u l a t i o n a n d g r e a te r d e p t h c a p a b il it ie s . I n s u l a t io n c o a t in g s w i t h c o m b i n a t i o n s o f t h e t w om ate r i a l s h av e a l so b een u sed . Tab le 9 .5 g iv es t h e p ro p e r t i e s o f t h ese w e t i n su l a t i o n s .

A s c a n b e s e e n f r o m t h e t a b l e , t h e i n s u l a t i o n i s b u o y a n t a n d m u s t b e c o m p e n s a t e d b yth e s t ee l p ip e we ig h t t o o b t a in l a t e ra l s t ab i l i t y o f t h e d eep wate r p ip e l in e o n th e seab ed .

9.5 Heat Transfer An alysis Exam pleIn o rd e r t o su g g es t i n su l a t i o n m ate r i a l s an d th i ck n ess fo r t h e n e tw o rk o f p ip e l in es , t h e h ea tt r a n sf e r g o i n g t h r o u g h t h e p i pe s m u s t b e c a l c u l a te d f o r ea c h p ip e . T h e m a i n a s p e c t o f h e a t


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TABLE 9.5 Prop erties of W et InsulationsPipel ine Insulat ion 113

Insula t ion k-fac tor Dens i ty W a te rDep th Se rv iceM aterial (Btu/hr-ft2-~ (lbs/ft 3) (feet) Tem perature (~Polyurethane (PU)-Solid 0.035 72 240Polypropylene (PP)-Solid 0.039 56 9000 290Syntac tic PU 0.021-0 .026 38-53 300 -9000 131-24 0Syntac tic PP 0 .023-0 .039 37-5 0 240Syntactic Phenolic 0.014 31 392Syntac tic Epoxy 0 .017-0 .024 37-4 5 6000-9 000 160-212

t r an s f e r t h r o u g h t h e p i p e o c c u rs t h r o u g h c o n d u c t i o n o f th e i n s u l a t i o n m a t e r ia l . T h e b a s ice q u a t i o n f o r ra d ia l h e a t t r an s f e r c a n b e f o u n d i n t e x t b o o k s ( H o l m a n , 1 9 8 1 ) . N o r m a l l y i t isa s sumed tha t convec t ive hea t t r ans fe r and conduc t ive hea t t r ans fe r th rough the p ipema te r i a l a re neg l ig ib le . Whi le hea t t r ans fe r ca lcu la t ions fo r p ipe l ines unde r s t eady f lowcond i t ions a re s t ra igh t fo rward , numer ica l compute r s imula to rs a re requ i red and ava i l ab lefo r p ipe l ines unde r t r ans ien t f low cond i t ions . Guo e t a l . (2004) re sen ted ana ly t i ca lso lu t ions tha t can be ea s i ly used to ca r ry ou t the requ i red s t eady s t a t e and t rans ien t hea tt rans fe r ana lyses fo r s ing le p ipes. T hese so lu t ion s a re inc luded in App end ix B o f th i s book .An app l i ca t ion example wi th the ana ly t i ca l so lu t ions i s p re sen ted in th i s s ec t ion .

Suppose a s e t o f da ta in Tab le 9 . 6 i s appl icable to a des ign pipe l ine . Sens i t iv i ty ana lysescan be pe r fo rmed wi th the ana ly t i ca l t empera tu re mode l s to inves t iga te the e f fec t s o fthe rma l conduc t iv i ty , t ime , and f lu id f low ra te on the t empera tu re p ro f i l e in a p ipe .

F igure 9 .1 i l lu s t ra t e s s t eady t empera tu re p ro f i l e s ca lcu la ted us ing d i f fe ren t va lues o fthe rm a l co ndu c t iv i ty o f the insu la t ion . In th i s s itua t ion , i t appea rs tha t a th in l aye r( 1 . 2 7 c m ) o f i n s u l a ti o n w i t h t h e r m a l c o n d u c t i v i t y o f l e s s t h a n 1 W / m - ~ w i ll a l lo w at o t a l t e m p e r a t u r e d r o p o f l e ss t h a n 1 ~ o v e r t h e 1 0 0 0 m p i p e li n e .

F igure 9 .2 p re sen t s the ca lcu la ted t rans ien t t em pera tu re p ro f i le s fo r a s t a r t -up p rocess . I tshows tha t the t rans ien t t empera tu re p ro f i l e approaches the s t eady t empera tu re p ro f i l ea f t e r one ha l f ho ur o f f lu id f low a t a cons tan t ra te . F igure 9 .3 d em ons t ra t e s the ca lcu la ted

TABLE 9.6 Base Data U sed in the He at Tran sfer Ana lyse sTherm al conductivity of insulationOuter radius of p ipeInner radius of pipeTherm al g radien t outside the insulationTherm al g radient angle from pip e axisSpecific he at o f fluidFluid den sityInsulation thicknessFluid f low ra teExternal temperature at flu id entry po intFluid temperature at fluid entry po intPipe length

1 .0 W/m-~0.100 m0.095 m0.005 ~0 degree41,800 J/kg~1000 kg /m 30.0127 m0.0005 m3/s100 ~100 ~1 0 0 0 m


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114 O f f s h o r e P i p e l i n e s101

100

99Ov 98(3 .E 97I-

96

95

94

Thermal Conductivity~ ,, "' ,.w ..~ '~ .'=..-~."4. ,..- ~, ~ . . . . . . . . (W/m-K):

x 10

Flow rate = 0.005 m3/s

ExternalTemperature, , , , , ,

200 400 600 800 1000 1200Length (m)

FIGURE 9.1 Calculated temperature profiles under steady fluid flow conditions.101

100

990v

98L_(3 .E 97(DI-

96

95

94

~ , , - - " :~ - "- ,~, - ~ , ~ Time (hour):~ " , ", " . , " ' . . ~ >o.5~ ' , , " ,, \ , , " ,, \~ , , , , \ \ ', o . a 5\ , \ ' ,~ ' \ \ \ ' \ \ ' ' " 0 2 5~ ' \ \ \ \ , ,

k = l W /m - K ~ . ' \ ' \ \~ \ \ ' \ O . 1 5-~~ ' \ ' " 0 1 0 .Flow rate = 0.005 m3/s ~ \ \ ,

External ~ 0 . 0 5Temperature

0 2 6 0 4 6 0 6 6 0 8 ~ 0 1 0 '0 0 1 2 '0 0Length (m)FIGURE 9.2 Calculated temperature profiles during a fluid flow start-up process.


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P i p e l i n e I n s u l a t i o n101

100

99

0vm 9 81 , . .(Dr lE 97r! -

96

95

94

k = 10 W/m-K

i

Flow rate increased from 0.005m3 /s to O .05m3/s

Time (hour):>0.050.0200.010

%9 0 .005

ExternalTemperature

0 200 400 600 800 1000 1200Length (m)

FIGURE 9.3 Ca lcu la ted tem pe rature pro f i les a f te r a f low ra te increase.

1 1 5

t ransient tem pera tu re prof iles a f te r an increase in f lu id f low ra te from 0.00 5 m 3/s to0.05 m 3/s . A l thou gh a 10- t imes h igher va lue of therm al con duct iv i ty i s u t i lized, i t s ti llshows tha t the t ransient tempera ture prof i le approaches the s teady tempera ture prof i leaf te r one ha l f ho ur of f low a t the new rate. Figure 9 .4 show s the ca lcula ted t ransienttempera ture prof i les dur ing a p ipe l ine shutdown process . I t indica tes tha t a f te r a reduct ionin f lu id f low rate f rom 0.1 m 3/s to 0 .01 m 3/s , the t ransient tem pera tu re p rof i le ap-proaches the s teady temp era ture prof ile a f te r one h a l f ho ur of flow a t the n ew ra te .

Paraffin (w ax) depo si t ion is a serious pro blem in the o i l indus t ry because i t causesplugg ing of the wel lbore , prod uct ion faci li ties , and t ran spo r ta t ion pipe lines . This pro blemis descr ibed in Par t I II of th is book. O i l com posi t ion, pressure , and tem pera tu re a re fac torsaffec t ing paraff in deposi t ion . For a g iven oi l composi t ion, paraff in deposi t ion i s a s t rongfunc t ion o f t empera tu re and weak func t ion o f p re ssu re excep t in t he nea r -c r it ic a l -po in tregion w here i t is also sensit ive to pressure. I t is vi tal ly im po rta nt to pr edict the locat ionswhere paraff in deposi t ion occurs in p ipe l ines . The predic t ion can be used for f lowassurance management i n t he o i l p roduc t ion and t r anspor t a t i on ope ra t ions .

Paraff in deposi t ion i s usua l ly eva lua ted in labora tor ies using Wax Appearance Tempera-tu re (W AT) a t d if f e ren t p re ssu re s. Th e W AT curve d raws a bou nda ry be tween w ax- reg ionand wax-free region in the pressure- tem pera ture (P-T) d iagram . I f the in-s i tu cond i t ion( tem pera ture and pressure) o f p ipe l ine fa l l s in the wax region, paraff in dep osi t ion isexpected to occur a t the point . Figure 9 .5 shows an example P-T diagram genera ted


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Pipe l ine Insulat ion 117w i t h t h e a n a ly t ic a l s o l u ti o n a n d a h y d r au l ic s m o d e l u s in g t h e d a ta b y A h m e d H a m m a m iet al . ( 1 9 9 9 ) . T h i s p l o t s h o w s t h a t t h e P - T p r o fi le f a l ls i n t h e t w o r e g io n s ( w a x a n d w a x -f re e ) ac r os s th e W A T c u r v e . T h e c r o s s - p o i n t is a t l e n g t h o f a b o u t 6 0 0 m . T h i s m e a n s t h a tp a r a ff i n d e p o s i t i o n c o u l d o c c u r i n t h e u p p e r ( lo w t e m p e r a t u r e a n d p r e ss u re ) s e c t i o n o f t h ep ip e l in e ab o v e 60 0 m. A b e t t e r i n su l a t i o n i s r eq u i red t o p rev en t t h e p a ra f f in d ep o s i t i o n .

R e f e r e n c e sB ai, Y.: Pipel ines and Risers , Elsevier Ocean Engineering B oo k Series, Vol. 3 , Am sterdam (2001).Carm ichael , R., Fan g, J . , and T am , C.: "Pipe-in-pipe Systems for De epw ater Developm ents," Proc.

of D eepwater P ipel ine Technology Conference, New Orleans (1999).Carter , R. , G ray, C. , and C ai , J .: "2002 Survey of O ffshore N on-chem ical F low Assurance Solu-t ions," O ffshore M agazine, Ho uston (2003).

Guo, B. , Duan , S., and Ghalam bor, A.: 'Tk Sim ple M odel for Predict ing H eat Loss and T emp eratureProfi les in T herm al Injection Lines and W ellbores W ith Insulations," pa per SPE 86983 presentedat the SPE Internat ional Therm al Operat ions and H eav y Oil Sym posium and We stern RegionalM eeting held in Bakersfield, Ca lifornia, 16-18 March 2004.

H am m am i, A. and Raines, M .A.: "Paraffin Dep osition from C rude O ils: Com parison of LaboratoryResults w ith Field Da ta," paper SPE 540 21 pre sented at the SPE Annual Technical Conferenceand E xhibition held in San Antonio, T exas (5-8 October 1999).Hansen, A .B. , Ry din, C. : "D evelopment and Qualif icat ion of Novel The rm al Insulation System s forDeepw ater Flowlines and Risers based on Po lypropylene," O TC Pap er (2002).

Holm an, J .P . : Hea t T ransfer , M cGraw-Hi l l B ook Com pany, New York (1981) .M cKelvie, M .: "Bund les--D esign and Construct ion," Integrated Graduate Developm ent Scheme,Heriot-Watt Universi ty (2000).Tough, G., Denniel, S., Al Sharif, M., and Hutchison, J.: "Nile-Design & Qualification of Reeled

PIP p ipel ine in Deepwater , O TC Pape r 14153 (2002) .W ang, W., Hershey, E. : "Syntact ic Foa m Insulation for U ltradeep High Tem perature Applicat ions,"OM AE (Ju n e 2 0 0 2) .W ang, X. , Chen, Y .D., Perera, R.M ., and P rescott, C.N .: "C onvection H eat Losses through G apsbetween Pipe and Insulat ion and between Insulat ion Half-Shells," OTC Paper 12033 (2000).W atkins, L. and H ershey, E. : "Syntact ic Foam Insulation for Ultra D eepw ater O il & Gas Pipel ines,"O TC Pap er 1 3 1 3 4 (20 0 1 ).

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