fjc research paper

8/12/2019 FJC Research Paper

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DV NCES IN FIELD JOINT CO TING FOR UNDER GROUN D PIPELINES

Al l N Moosav i , Ph.D.Abu Dhabi Com pany for Onshore Oil Operat ions ADC O)P .O . B ox 270 , A bu Dhab i , Un i ted A r ab E mi r a tesE - ma i l : amoos av i @adc o .c o .ae

B S T R C TThe inc rease in use o f h igh qua l i t y and expens ive p ipe l i ne coat ings has he ightened the need for f i e ldjo in t coat ing sys tems to match the qua l i t y o f the fac tory coat ing . Recent deve lopments i n f i e ld j o in tc oa t ing t ec hno l ogy hav e gon e a l ong way t o add r es s t h is need .Th i s pape r des c r i bes one ma j o r M i dd l e E as te r n o i l and gas c ompany ' s ex pe r i enc e w i t h a number o ff i e ld j o in t coat ing sys tems for th ree layer po l ye thy lene and po lypropy lene coated p ipes . Th isexpe r ience inc ludes coa t ing we l l over a 10 0,000 f ie ld j o in ts in som e o f the toug he s t cond i t i ons(ex t reme he at and hum id ity , coup led w i th sand s torms) ex i s ti ng in any o il gas fi e ld .A com par i son is made betw een the d i f fe rent fi e ld j o in t coat ing sys tem s in te rms o f techn ica lcharac ter i s t ics , co s t and e ase o f app l i ca ti on i n the fi e ld . T he re la t ive sca rc i ty o f i n ternat iona l s tandards ,and he nce the impor tance o f p re-qua l i f ica t i on t ri a ls produ c t ion tes t i ng in the fi e ld i s a l so h igh li gh ted.Keyw ords : coat ing , p ipe l ine , und ergrou nd, f ie ld j o in t , po l ye thy len e, po l ypropy lene, po l yure than e, FBE,heat shr ink s leeve, tape wrap, f l ame spray

Copyright2000 by NACE nternational.Requests or permission o pub lish his manuscript n any orm, in part or in whole must be in writing o NACEInternational,ConferencesDivision, P.O. Box 218340, Houston,Texas77218-8340.The material presentedand the views expressed n th ispaper are solely hose of the author(s)and are not necessarilyendorsedby the Association. Printed n U.S.A.

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I N T R O D U T I O NU nder g r ound s t ee l p i pe l i nes i n t he M i dd l e Eas t , c a r r y i ng o i l and gas , hav e t r ad i t i ona l l y been c oa t eda n d o f te n s u p p l e m e n t e d b y c a t h o d i c p ro t e c ti o n . O n e o f th e m o s t c o m m o n t y p e s o f co a t in g f o r th e s ep i pe l i nes has been c oa l t a r epox y . Env i r onm en t a l c onc e r ns w i t h c oa l t a r hav e l ed t o l i m i t i ng , and i nm o s t Eu r opean and N o r t h Am er i c an c oun t r i es , t o ta l bann i ng o f t he us e o f c oa l t a r bas ed c oa t ings . Ana t t r ac t i v e a l t e r na t i v e appea r ed t o be c o l d w r apped t apes . T hes e o f f e r t he adv an t age o f eas y f i e l dapp l i c a t i on and nega t e t he r equ i r em en t f o r s pec i a l i t y f i e l d j o i n t c oa t i ngs . T he ex pe r i enc e w i t h t hes ec oa t i ngs has , a t bes t , been m i x ed in the G u l f des e r t e nv i r on m e n t 1. A m a j o r r eas on f o r th i s i s t heex i s t enc e o f Sab k ha a r eas in t he A r ab i an des e r t s . T he s e a r e h i gh l y s a l ine m ar s h y s o i ls w h i c h a r e bo t hh i gh l y c o r r os i v e and s ub j ec t t o m uc h m ov em en t . T he c oa t i ngs i n t hes e a r eas a r e t he r e f o r e s ub j ec t edt o s a li ne w a t e r , s t r es s and h i gh t em pe r a t u r es . C o l d w r ap ped t apes 1, and e v en in s om e i ns t anc es f us i onbond ed epo x y ( F B E) 2, hav e been f ound t o und e r go r ap id de t e r i o r a t i on i n t hes e Sab k ha a r eas . T h i s c anc aus e a c c e l e r a t ed c o r r os i on o f t he p i pe l ine l ead ing t o leak s . N o r m a l l y it s hou l d be pos s i b l e t o av o idleaks , a t l eas t in t he shor t t e rm , by ad jus t ing the leve l o f ca th od ic p ro tec t ion . Ho we ver , i f t he coat ingdeter io ra t ion i s on a la rge sca le , o r i f t he CP leve ls a re no t con t inuo us ly m on i to re d , leaks can s t i llo c c u r . T hes e f ac t o r s , and t he need f o r c oa t i ngs w i t h h i ghe r t em per a t u r e r es i s t anc e , has l ed t o t hei nc r eas i ng us e o f t h r ee l ay e r po l y e thy l ene ( PE) and th r ee l ay e r po l y p r opy l en e ( PP) c oa t i ng s y s t em s i nt h e G u l f c o u n t ri e s. In A b u D h a b i C o m p a n y f o r O n s h o r e O i l O p e r a t i o n s ( A D C O ) t h e m a j o r it y o f n e ws t ee l unde r g r ound p i pe l i nes a r e c oa t ed w i t h t hes e t h r ee l ay e r c oa t i ngs .C oa t i ngs c an deg r ade due t o a num ber o f r eas ons . T hes e i nc l ude : P i pe m ov e m en t and s o i l s t r es s H i g h t e m p e r a t u r e s U l t ra V io le t rad ia t ion Bac ter ia l a t t ack Sa l ine m ois tu re in t he so i l C h e m i c a l sT he dam age c an a l s o be done be f o r e p i pe l i ne i ns t a l l a t i on du r i ng t r ans po r t a t i on f r om f ac t o r y t o s i t e .Pe r haps t he g r ea t es t c on t r i bu t o r t o c oa t i ng f a i l u r es i s poo r c oa t i ng app l i c a t i on .T he m a i n f ac t o r s t ha t de t e r m i ne t he s e l ec t i on o f a s u i t ab l e p i pe l i ne c oa t i ng s y s t em a r e : Soi l res is t iv i ty De s ign l ife P i pe l ine des i gn t em p er a t u r e C os t C l i m a t i c c ond i t i ons Eas e o f app l i c a t ion r epa i r P i pe l ine l ay ing m e t hod Ava i lab i l i ty o f sk i l led ap p l i ca tors E q u i p m e n t r e q u i r e m e n t s Co at ing o f f ie ld Jo in t s T r ac k r ec o r d H ea l t h , s a f e t y env i r on m e n t a l r egu l a t i onsIn so i l s w i th very h igh res is t i v i t y i t may be poss ib le to bury a p ipe l ine w i thout any coat ing , par t i cu la r l y i fi t i s be ing ca thod ica l l y p ro tec ted . However , i n low res is t i v i t y so i l , such as the Sabkha areas , cor ros iv i t yl ev e l s a r e h i gh and a good , i m pe r m eab l e c oa t i ng i s r equ i r ed i n add i t i on t o c a t hod i c p r o t ec t i on . Suc h a

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c oa t ing no t on l y s hou ld hav e good r es i s tanc e t o c o r r os ion and wa te r pe r mea t ion bu t a l s o be ab le t ow i t hs tand ex tens i v e s o i l mov emen t and h igh ex te r na l t emper a tu r es .T em per a tu r e is a m a jo r f ac to r in se lec t ing a c oa t i ng . F o r ex am p le , t he c ho ic e be twe en t he t h r ee l ay e rpo ly e thy lene and t h r ee l ay e r po l y p r opy lene c oa t i ng s y s tems i s us ua l l y bas ed on t he max imumo p e r a t in g t e m p e r a t u re . T a b l e 1 p ro v id e s a g e n e r a l g u i d e li n e fo r m a x i m u m o p e r a t in g t e m p e r a t u r e o f anu m ber o f d i f fe rent coat ing s 3.The welded jo in t is the weakes t s t ruc tura l a rea in a p ipe l ine . Un less i t has been s t ress re l ieved, i t canhav e a muc h h ighe r s t r es s c onc en t r a t i on t han t he s u r r ound ing me ta l and t hus be mor e s us c ep t ib le t oc rack ing. I t s cor ros ion res is tance, measurab le by i t s c r i t i ca l p i t t ing temperature (CPT) , is a lso usua l lyless than the pa rent me ta l . I t there fore requ i res exce l len t p ro tec t ion . For th is reason , the qu a l i t y o f thef ie ld j o in t c oa t ing s hou ld be a t l eas t as good as t he r es t o f the p ipe l i ne s f ac to r y c oa t i ng . O the r w is e t hec om b ina t i on o f t he we ld and i n fe ri o r f ie ld jo in t c oa t i ng c an p r es en t a do ub le w ea k s po t in t he p ipe l ine .T he de s e r t env i r onme n t , w i th h igh t emp er a tu r es , hum id i t y and f requ en t s and s to r ms ma k e s uc c es s fu lf ie ld coa t ing ap p l ica t ion very d i f fi cu l t. I t i s a un iversa l b e l ie f tha t sur fac e prep ara t ion is c r i ti ca l to thes uc c es s o f any c oa t i ng , p a r t ic u la r ly in s ev e r e env i r onm en ts 4 5 . T he pe r fo r m anc e o f f i e ld j o in t c oa t i ngshas been d i rec t ly re la ted to sur face c lean l iness 6.T he t h r ee l ay e r c oa t i ng s y s tems hav e bec ome inc r eas ing l y popu la r f o r c oa t i ng o f o i l and gas p ipe l i nes ,bo th i n t he M idd le E as t and t he Nor th S ea . T hes e c oa t i ngs c ons i s t o f a F B E p r imer , a mod i f i edadhes iv e l ay e r and a t op l ay e r o f e i t he r po l y p r opy lene o r po l y e thy lene . T hey a r e app l i ed i n t he f ac to r yin an au toma ted , as s emb ly l i ne manner . P o ly e thy lene and po ly p r opy lene hav e no adhe r enc e t o s tee land t he r e fo r e mus t hav e a p r imer ( us ua l l y F B E ) . P r io r t o c oa t i ng t he p ipe l i ne s u r f ac e i s b las t c leaned ,hea ted , s p r ay was hed ( s om et imes w i t h phos pho r i c acid ), s p r ay r i ns ed w i t h ho t wa te r and d r ied . I fr equ i red , i t c an a l s o be c hem ic a l l y t r ea ted w i t h c h r om ate s o lu t i on .O nc e t he c and ida te c oa t i ng s y s tems pas s t he p r oc edu r e qua l i f i c a t i on t es t s , t he f i na l c ho ic e i s o f t enmade by t he c on t r ac to r s . Cos t , eas e and s peed o f app l i c a t i on and equ ipmen t r equ i r emen ts a r e t henl i k e l y t o bec ome the ma jo r s e lec t i on c r i t e r i a . T ab le 2 g i v es s ome ind i c a t i ons o f r e la t i v e c os t s o f a f ewc oa t ings 3 7 and T ab le 3 o f f e r s a c os t c om par i s on be twe en f ie ld jo in t c oa t i ng s y s tem s fo r po l y p r opy lene .F ie ld j o in t c oa t ing s y s tem s fo r p ipe l ines c oa ted w i t h F B E and 3 l ay e r P E /P P s y s tem s a r e des c r ibed .

F U S IO N B O N D E D E P O X Y F B E ) F IE L D J O I N T C O A T I N GFBE is a very popu lar coat ing fo r p ipe l ines in Europe and Nor th Amer ica . I t i s a lso used f requent ly inthe Midd le Eas t . One o f i t s g reat advantages is tha t i t can be app l ied to the ent i re l ine . I t permi ts thefo r ma t ion o f a p r o tec t iv e m agne t i te l ay e r and d oes no t s u f f e r adv e r s e l y f r om c a thod ic p r o tec ti on 4.Ho we v er ,A DC O s ex pe r ienc e has s how n tha t in t he v e r y agg r es s i v e S ab k ha s o il and unde r t heex t r eme hea t and hu mid i t y o f t he des e r t, t he c om b ina t i on o f h igh s o il s tr es s es , c oup led w i th c on t i nuouswe t t i ng and d r y ing , c an c aus e em br i t tl em en t and d i s bond ing o f F B E c oa t ing 2. T h i s c an happen qu ic k e rthan ex pec ted i f t he c oa t i ng app l i c a t ion has been less t han i dea l . F B E i s a l s o mo r e p r one t omec han ic a l damage du r ing t r ans po r t t han t he t h r ee l ay e r c oa t i ngs .A s m en t ioned abov e , t he c oa t i ng f o r t he fi e ld jo in t s o f F B E c oa ted p ipe l ine i s a l s o F B E . T he f ie ld j o in tsa r e ab r as iv e l y b las ted and induc t i on hea ted up to 240C . F lu id i s ed epo x y po wd er is t hen app l ied t othe p r e - hea ted s u r f ac e by a s emi - au toma ted e lec t r os ta t i c s p r ay mac h ine . T h i s i s no t a c omp lex p iec eo f equ ipm en t and c an eas i l y be t r ans po r ted f r om one loc a t ion t o t he o the r i n the f ie ld .

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I f F B E w as s e l ec t ed f o r f i e l d j o i n t c oa t i ng , t hen i t m ay be s ens i b l e t o c ons i de r dua l F B E c oa t i ng due t oi ts i m p rov ed m e c han i c a l p rope r t i es ov e r s t anda rd F B E c oa t i ng a.

F IE L D J O IN T C O A T I N G S F O R 3 L A Y E R P O L Y E T H Y L E N E C O A T E D P I P EF or t he th ree l ay e r po l y e t hy l ene c oa t i ngs t he m os t c om m o n f i e ld jo i n t c oa t i ng s y s t em s a re hea t s h r i nks l eev es and po l y u re t hane . We us e hea t s h r i nk s l eev es f o r t he f i e l d j o i n t s and po l y u re t hane f o r bendsand f i t t i ngs . F l am e s p ray ed po l y e t hy l ene has a l s o r ec en t l y been us ed on s om e p ro j ec t s i n t he G u l f .

a H e a t S h r i n k S l e e v e sT h i s i s t y p i c a l l y a c ros s l i nk ed po l y e t hy l ene s hee t , c oa t ed on one s i de w i t h a ho t m e l t adhes i v e .S om e t i m es , as an added p ro t ec t i on m eas u re , an ex t r a F B E p r i m e r i s app l i ed t o t he s t ee l j o i n t a reapr io r t o s leeve app l i ca t ion .T he s l eev es a re gene ra l l y app rov ed f o r us e f o r des i gn t em pera t u res up t o 100C . T he f i e l d j o i n t i saga i n b l as t c leaned and p re -hea t ed , t o a t em p era t u re up to 100C f o r F B E p r i m e r app l ic a t ion . I n t hedes e r t env i r onm en t , w i nd s h i e l d s c reens a re o f t en s e t up t o p rev en t s and be i ng b l ow n on t o t he c oa t i ng(F i gu re 1 ) . T he p i pe i s t hen re -he a t ed t o abou t 90C , w h i l s t ens u r i ng t ha t t he epo x y i s s ubs t an t i a l l yc u red a nd d r ied . T he s l eev e i s t hen c a re f u l l y w rap ped a round t he fi e ld j o i n t and hea t ed by a f lam etorch un t i l f u ll adh es ion to the p ipe l ine ha s been a ch ieve d (F igure 2) . Th is wh o le pro ces s i s re la t i ve lyfas t. The m ain d i f fi cu l t ies w i th th is sys te m a re ensur ing an even s up p ly o f heat ing to al l par t s o f t hes l eev e and p rev en t i on o f ov e rhea t i ng a t any po i n t . S om e t i m es , i n o rde r t o ac h i ev e a m ore ev end i s t ri bu t ion o f hea t, o r due t o s pac e c ons t ra i n t s , a m agn e t i c i nduc t i on hea t i ng un i t is us ed (F i gu re 3 ) .We hav e us ed t h i s s y s t em on ou r l a t es t m a i n o i l p i pe l i ne and i n t he t h ree y ea rs s i nc e i ns t a l l a t i on nos i gn i fi c an t p rob l em s hav e been enc o un t e red . R a ndo m ex c av a t i ons o f t he c oa t ed p i pe l ine hav e v e r i fi edth is po in t . I t i s one o f t he eas ie r f i e ld jo in t coat ings to app ly on s i t e and the t ra in ing o f i t s app l i ca tors i sfa i r ly s im p le .b Polyurethane Coat ingT he po l y u re t hane s y s t em o f f e r s t he adv an t ages o f be i ng a one l ay e r c oa t i ng , equa l l y app l i c ab l e t o f i e l dj o i n ts , ben ds and f it ti ngs . It is no rm a l l y app l ied by s p ray . A l thou gh ex pe ns i v e , i t o f fe r s t he ad v an t ag eso f s i m p l e c oa t i ng p roc edu re , du rab i li ty , s t r eng t h and c o r ros i on r es i s t anc e . H ow ev e r , due t o l ac k o ff ac t o r y app l i c a t i on , i t s us e on p i pe l i nes i n t he G u l f has been m a i n l y l i m i t ed t o bends , t ees and s om ef i e l d j o i n t s . A s t udy on pe r f o rm anc e o f v a r i ous c oa t i ng s y s t em s i n t he G u l f s how ed t ha t po l y u re t haneex h i b i ted a life ex pe c t anc y o f 3 -4 y ea rs u nde r s ev e re c o nd i t ions . T he s a m e s t udy s how ed t ha t ac oa t i ng s y s t em c om pr i s i ng o f an i no rgan i c z i nc s i l i c a t e p r i m e r , epox y s ec ond c oa t and po l y u re t hanet op c oa t had a life ex pec t a nc y o f 10 -12 y e a rs unde r s ev e re c ond i t i ons 9.c F lame Sprayed PolyethyleneT h i s s y s t em i s v e r y s i m i l a r t o f l am e s p ray ed po l y p ropy l en e ( s ee be l ow ) and us e s a s pec i a l gun t o s p rayt he po l y e t hy l ene and i t s adhes i v e on an F B E p r i m e r . We hav e no t us ed t h i s s y s t em y e t bu t a re aw areof i ts recen t use on f ie ld jo in t s , ben ds and tees on an o il gas p ipe l ine pro jec t in t he UAE. I tsadvantages are i t s ease o f use , compat ib i l i t y o f f i e ld jo in t coat ing w i th the p ipe l ine coat ing and i t sapp l i c ab i l it y t o w e l d j o in t s , b ends and t ees .

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F IE L D J O I N T C O A T I N G S F O R 3 L A Y E R P O L Y P R O P Y L E N E C O A T E D P IP ECur r en t ly , t he r e a r e f i v e m a in s y s tem s fo r c oa t i ng t he f ie ld jo in t s o f p ipe l i nes c oa ted w i t h t he t h r ee l ay e rpo ly p r opy lene . T hes e a r e :a ) T w o L a y e r F u s io n B o n d e d E p o x y ( F B E ) / S i n te r e d P o l y p r o p y le n e C o a t i n gb ) T h r ee Lay e r F B E / A dh es iv e / Co - ex t r uded P o ly p r opy lene S h ee t Coa t ingc ) T w o L a y e r F B E / C o m b i n e d A d h e s i v e a n d P o l y p ro p y l e n e A p p li e d b y F la m e S p r a y G u nd) P o ly u r e thane Coa t inge ) Hea t s h r ink s leev esa) Two Layer Fus ion B ond ed Epoxy FB E) / S i n tered Po l yprop y l ene C oat i ngT h is s y s tem i s c ompos ed o f an F B E p r imer p lus a po l y p r opy lene t opc oa t . A f t e r b las t c lean ing ands u r fac e p r epa r a t i on , t he p ipe i s i nduc t ion hea ted up to 230C . T hen t he j o in t is c oa ted w i t h F B E us ing as emiau toma t i c f l oc k s p r ay equ ipmen t . F ina l l y , t he po l y p r opy lene t opc oa t i s app l i ed , aga in us ing a f l oc ks p r ay equ ipmen t . S inc e t he adhes ion o f t he po l y p r opy lene t o t he F B E i s dependen t on t he p ipetemp er a tu r e , t he t o ta l th i c k nes s o f the p o l y p r opy lene l ay e r is l im i t ed b y t he p ipe s u r f ac e t empe r a tu r e . I tis no t us ua l ly pos s ib le t o ac h iev e m or e t han 1 .5 m m c oa t ing t h i c k nes s .A p r ob lem, c ommon to s y s tems ( a ) , ( b ) and ( c ) abov e , i s t he po ten t i a l damage c aus ed by t he h igh p r e -hea t t empe r a tu r es t o t he bond be twe en f ac to r y and f ie ld app l i ed p o l y p r opy lene c oa t i ngs 3.W hen d i r ec t me thods o f hea t i ng t he c oa t i ng , s uc h as f l ame to r c h guns , a r e us ed t he r e w i l l be s omec onc e r n abou t pos s ib le l os s in s om e o f t he c oa t ing p r ope r t ies . F o r th i s r eas on , s in te r ed c oa t ings a r eno t as h igh l y r ec om m end ed as f l ame s p r ay ed o r c o - ex t ruded s hee t c oa t i ng s y s tems . I f us ed , c a r e fu lprocedure qua l i f i ca t ion t r ia ls and produc t ion tes t ing shou ld be car r ied out .b) Three Lay er FB E / A d hes i ve / C o-ext ruded Po l ypropy l ene She et C oat i ngT h is f i e ld j o in t c oa t i ng was dev e loped du r ing an ea r l i e r p r o jec t f o r t h r ee l ay e r po l y p r opy lene c oa tedp ipe l ines be ing r ou ted un de r g r ound t h r ough S ab k ha a r eas in t he A bu Dhab i d es e r t env i r on me n t 2.Ear l ie r , FBE had fa i led as a coat ing sys tem on these p ipe l ines .T he 3 .5 m m th i c k s m ar t s hee t o r c o - ex t ruded s hee t s y s tem us ed c ons i s ts o f a F B E p r ime r ( - 30 0#m) , a c hemic a l l y mod i f i ed po l y p r opy lene adhes iv e ( - 200 #m) and a c o - ex t r uded po ly p r opy lene s hee t( - 3000 p .m) .Th e in i tia l s tages o f th is coat ing , i .e . , sur face prepa ra t ion , indu c t ion hea t ing and ap p l ica t ion o f FBE bye lec t ros ta t ic f lock spray ing, a re ident ica l to those o f the s in tered jo in t . A f te r the F BE ap p l ica t ion , amod i f i ed po l y p r opy lene adhes iv e l ay e r i s a l s o app l i ed by t he f l oc k s p r ay equ ipmen t . T h i s adhes iv elay e r f o r ms an i n t ima te c r os s l i nk w i t h t he F B E lay e r. F ina l ly , a p r e - f ab r i c a ted po l y p r opy lene s hee t i sc lamped on a r ound t he f i e ld j o in t and , a f t e r t he s hee t has f u l l y c u r ed , i t i s we lded manua l l yl ong i t ud ina l l y and c i r c umfe r en t i a l l y us ing we ld guns and a s emi - au toma t i c r o ta t i ng we ld ing mac h ine .T y p ic a l ly , i t wo u ld t ak e 45 m inu tes t o c omp le te one s uc h f i e ld j o in t . H owev e r , t he c o a t i ng c an bes ign i fi c an t ly s peed ed up us ing mu l ti p le c r ews as f o l lows :CR E W 1 : S u r fac e p r epa r a t ion and i nduc t i on hea t i ng o f the f ie ld j o in t ( 2 m inu tes ) , F B E a nd adhe s iv eapp l i c a t ion ( 3 m inu tes ) , f o l lowe d by c lam p ing and c u r ing t he c o - ex t r uded s hee t ( 25 m inu tes ) .CR E W 2 : Long i t ud ina l and c i rc um fe r en t i a l we ld ing o f t he c o - ex t ruded s hee t a f t e r c u ring ( 15 m inu tes ) .

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T he g r ea t adv an tage o f t h i s c oa t i ng i s t he f ac t t ha t t he c o - ex t r uded P o ly p r opy lene s hee t i s p r e -f ab r i c a ted i n t he f ac to r y and one t he r e fo r e ob ta ins a un i f o r m i t y i n t he qua l i t y and p r ope r t i es o f t hec oa t ing . T he c hanc es o f de te r io r a t i on in c oa t i ng p r ope r t i es as a r es u l t o f poo r c oa t i ng app l i c a t ion in t hef i e ld and i ns u f f i c i en t qua l i t y c on t r o l i s t he r e fo r e c ons ide r ab ly r educ ed . T he ma in d i s adv an tage o f t h i ss y s tem is tha t i t c an n o t be app l ied t o ben ds and t ees , t hus nec es s i t a t ing t he us e o f ano the r c oa t i ngsys tem for these app l ica t ions . A lso i t i s a re la t ive ly s low process , par t icu lar ly i f car r ied out by a s ing lec rew, and requ i res a degree o f sk i l l in i t s app l ica tors .W e hav e had a r ound 50 ,000 p ipe l ine jo in t s i n t he des e r t c oa ted w i t h t h is s y s tem and i t t he 5 y ea r ss inc e t he j ob c om p le t i on hav e no t enc oun te r ed any s ign i fi c an t p r ob lems . L im i t ed ex c av a t ions hav e no ts hown any th ing t o i nd i c a te o the r w is e .c T w o L a y e r F B E / C o m b i n e d A d h e s i v e a n d P o l y p r o p y le n e A p p l i e d b y F l a m e S p r a y G u nT h is i s one o f t he mos t r ec en t l y dev e loped s y s tems fo r c oa t i ng o f t he f i e ld j o in t s . T he s u r f ac ep r epa r a t ion f o r th i s c oa t i ng i s i den t ic a l t o the o the r two f i e ld j o in t c oa t i ng s y s tem s des c r ibed abov e . T hejo in t sur face is b las t c leaned to ach ieve the requ i red s tandard (F igure 4) . Dur ing the induc t ion heat ing( up t o 230C) , t he f ac to r y app l i ed po l y p r opy lene c oa t i ng a r ound t he f i e ld j o in t i s i s o la ted f r om the hea tby t em por a r y a lum in ium o r f ib r eg las s s h ie lds . F B E and c he mic a l l y mod i f ied po l y p r opy lene powd er s a r ethen app l i ed by f l oc k s p r ay ing ( F igu r e 5 ) . A f t e r t h i s s tage ano the r l ay e r o f c hemic a l l y mod i f i edpo ly p r opy lene i s app l i ed by a f l ame s p r ay gun on t o t he j o in t un t i l t he r equ i r ed t h i c k nes s i s ac h iev ed( F igu r e 6 ) . T he po l y p r opy lene i s t r ans po r ted t h r ough a m ix tu r e o f gas es ( p r opane , n i t r ogen and ox y genor p r opane n i t rogen on ly ) and me l t s i n t he gun efore r eac h ing t he p ipe s u r f ac e . T h e t h i c k nes s o f thef in i s hed jo in t c oa t ing m ay be e qua l o r l es s t han t ha t o f the f ac to r y app l i ed c oa t i ng .W hen us ing a s ing le c r ew , f l ame s p r ay c oa t i ng wou ld r equ i r e a s ho r te r t ime t o r eac h a c oa t i ngth i c k nes s equa l t o t he c o - ex t r uded s hee t . T h i s adv an tage is pa r t ic u la r ly im por tan t f o r o f fs ho r e p ipe l ineswh er e t ime s pen t on s i t e by t he c oa t i ng c r ew c an be v e ry c os t ly . A no the r ad v an tage is tha t th i s s y s temcan be a lso app l ied to bends and tees . I t s equ ipment is re la t ive ly easy to mobi l i se in the f ie ld and i t sapp l ica t ion requ i res a lesser degree o f sk i l l than the co-ex t ruded sheet .

W e h av e us ed t h i s c oa t ing s y s tem on s om e 40 ,000 f i e ld j o in t s r ec en t l y a f t e r ex tens i v e p r oc edu r equa l i fi ca t ion tes t ing . I t i s there fore ear ly days to judg e i t s success in the c l ima t ic cond i t ions ex is t ing inthe G u lf . A s c an be s een in T ab le 4 , mec h an ic a l and o the r as s oc ia ted p r ope r t i es o f f l ame s p r ay ed f i e ldjo in t c oa t i ngs a r e i n fe r i o r t o t hos e o f t he c o - ex t ruded s hee t c oa t i ngs . How ev e r , due t o it s eas ie rapp l i c a t i on and i t s app l i c ab i l i t y t o t he bends , t ees and we lded jo in t s , f l ame s p r ay ed po ly p r opy leneappea r s t o be f av ou r ed by c oa t i ng c on t r ac to r s .d P o l y u r e t h a n e C o a t i n gMos t o f t he t r ac k r ec o r d w i t h po l y u r e thane f i e ld j o in t c oa t i ngs i s w i t h po l y e thy lene c oa ted p ipes . T he r ehav e r ec en t l y been s om e app l ic a t i ons o f th i s c oa t ing t o po l y p r opy lene c oa ted p ipes i n t he Nor th S ea .O ur p r oc edu r e qua l i f i c a t i on t es t i ng has s hown tha t po l y u r e thane ' s weak po in t s a r e i t s adhes ion t o t hefac to r y app l ied po l y p r opy lene and it s res i s tanc e t o h igh t emp er a tu r es .e H e a t s h r i n k s l e e v e sHea t s h r ink s leev es hav e been t r i ed f o r f i e ld j o in t c oa t i ng o f po l y p r opy lene c oa ted p ipe l i nes . I t hasb e e n f o u n d t h a t a t t e m p e r a t u r e s a b o v e 4 0 C t h e y s h o w e d v e r y l o w r e s i s t a n c e t o m e c h a n i c a l d a m a g eand s o i l s t r es s ing and a l s o poo r adhes ion t o bo th t he s tee l s ubs t r a te and t he po l y p r opy lene a t t heov e r lap 3. Howe v e r , i nd i c a t ions f r om the c oa t i ng i ndus t r y a r e t ha t t he n ew gene r a t i on o f hea t s h r inks leev es f o r po l y p r opy lene c oa ted p ipe l i nes w i l l o f f e r s ign i f i c an t impr ov emen ts i n a l l t he abov ew e a k n e s s a r e a s.

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C O L D W R A P P E D T A P E C O A T IN GAnother coating system that, l ike FBE, can be used for coating the entire l ine is cold wrapped tapes.Th is feature, toge ther with their relative low cost and ea se of installation, has ma de the m fair ly popular.Ou r exper ience with tapes has not been very sat is factory. We have obse rved a num ber of failures,especial ly in Sabkha areas, where the tape has disbonded and sal ty water has caused rapid corros ionof the pipel ine. A noth er oi l and ga s com pan y in the UAE has reported a large n um ber of fai lures of coldwrap ped tape co atings 1. The reaso ns for the failures included: Low res is tance to soi l s tress and pipe mo vem ent Insuffic ient and non -uniform tension during application Thermal degradat ion Poor adhe sion to metal surfaceAnother s tudy has reported very poor adhesion of tapes to polypropylene coated pipel ines andextreme ly low res is tance to soi l s tress ing at high tem perature s -1 05 C ) 3. A com par ison of tapes withother f ield joint coating systems, including FBE and heat shrink sleeves, has found them to be muchinf er ior to the rest 1.

P R E Q U A L I F IC A T I O N T R I A L S A N D P R O D U C T I O N T E S T I N GField join t coating selection and qualification is handicapped by the relative scarc ity of internationals tandards on this subject . For example, the s tandards for polypropylene coat ings have been wr i t ten forextruded coatings and ma ny of their qualif ication tests can not be applied to sintered or f lame sprayedpolypropylene coatings. The Shell Design and Engineering Prac tice DE P) on polyethylene andpolypropylene coating fo r l ine pipe 11 doe s not cove r the f ield joints. T he main stan da rds used by us forthe proce dure qualif ication and production testing o f f ield joint coating s of pipelines are the Ge rma nD IN ) 12-14 an d Fre nch N F A) 15 coa ting stan da rds.Like mo st oi l and gas com panies, We have our own coat ing specif ications. The se include stand alonespecif ications for f ield joint coatings. M an y of the tests included in ou r spe cif ications have bee ndeveloped by tr ial and error or improvisation on standard tests.Extensive pro ced ure qualification tr ials PQ T) and production tests should be carried ou t on anyproposed f ield joints. Tab le 4 show s some of the tests u sed in PQT . Fo r hosti le f ield environ me nts,such as the Arabian deserts, the PQT should not be confined to the coating yards but include theactual desert env ironment. Often procedures that look easy in the yard may prove di f f icul t , and evensom etim es impractical in the f ield. Even if the PQ T is confined to the yards, o ne should alwa ys try toimagine the p roce dure taking place in the field and then try to jud ge its eas e of application andpracticality. M ag ne tic induction heating and coating of a f ield join t under dese rt con dit ions are shown inFigure 7 and Figure 8 respectively. The h eat, hum idity and sand sto rm s ma ke f ield join t coating a veryarduou s venture in the desert. When consider ing a num ber of di fferent fie ld joint coat ing system s for ahosti le environment, the ease of application should be given a high priority in the selection criteria. Asmentioned earl ier, m ost coating failures are due to poor application. It is mu ch h arde r to attain idealapplication proc ed ures in tough f ield condit ions e.g., in the dese rt) than in the yard.

C O N C L U S I O N SThree layer polypropylene and three layer Polyethylene are advanced, env iron me ntal ly f riendly coatingsystems for pipelines buried in hosti le environments, such as wet and saline soil, subject to soil

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mov emen t and ope r a t i ng a t e lev a ted ( 65C - 110C) t emper a tu r es . T hey a r e l es s p r one t o mec han ic a ldam age than F B E . M any d i f f e r en t t y pes o f f ie ld j o in t c oa t i ngs ex i s t fo r t he t h r ee l ay e r coa t ings . T hep r e fe r r ed s y s tems fo r c oa t i ng t h r ee l ay e r po l y e thy lene c oa ted p ipes a r e s p r ay ed po ly u r e thane andpo ly e thy lene hea t s h r ink s leev e . T he mos t mec han ic a l l y s ound s y s tem fo r f i e ld j o in t c oa t i ng o f t h r eelay e r po l y p r opy lene c oa ted p ipes is t he c o - ex tr uded po ly p r op y lene s hee t . F lame s p r ay edpo lypropy lene, however , is o f ten pre fer red fo r i t s g reater f lex ib i l i t y and eas ier app l icab i l i t y . An overa l lr ank ing o f the c oa t i ng s y s tem s us ed f o r po l y p r opy lene c oa ted p ipe fi e ld j o in ts i s p r es en ted i n T ab le 5 .T h is i nd i c a tes t ha t , s hou ld po l y u r e thane s y s tem manu fac tu r e r s s uc c eed in impr ov ing i t s t ec hn ic a lc ha r ac te ri s ti c s , i t c ou ld be c om e m uc h m or e po pu la r fo r po l y p r opy lene f ie ld j o in t c oa t ings . A n o the rs e r ious c on ten de r i s po l y p r opy lene h ea t s h r ink s leev es . T h i s has no t as y e t , a t l eas t in t he G u l f reg ion ,bec ome popu la r f o r po l y p r opy lene f i e ld j o in t c oa t i ng . Co ld t ape w r ap has been f ound t o be l es s t hanidea l f o r c l ima tes s uc h as t hos e i n t he we t , s a l i ne and ho t s o i l s f ound in s ome pa r t s o f t he A r ab iandeser ts .T he r e a r e , as y e t , no i n te r na t i ona l s t anda r ds ded ic a ted t o f i e ld j o in t c oa t i ngs f o r po l y e thy lene o rpo ly p r opy lene c oa ted l i ne p ipes . T he r e i s a r ea l need f o r s uc h s tanda r ds t o eas e t he p r oc es s o fs e lec ti on , t es ti ng and i ns pec t ion o f f ie ld j o in t c oa ti ngs . M eanw h i le , i t is r ec om m end ed t ha t tho r oughprocedure qua l i f i ca t ion t r ia ls bo th a t the coat ing yards and in the f ie ld be car r ied out be fore the f ina lse lec t ion is made.

R E F E R E N E S1. A . Dos Santos , In-Serv ice Fai lure of Pipel ine W rapping Tap es, G A S CO in te r na l pub l i c a t i onp r es en ted a t t he S ec ond A DCO Cor r os ion Con fe r enc e , A bu Dhab i , 1998 .2 . K .M. Mo rs i A . E l Key , Corros ion p rompts rep lacem ent o fA bu Dh ab i gas-gather ing sys tem., OilG as J ou r na l , O c tobe r 1993 , p76 - 79 .3. D. Fa irhurs t D. W i l l is , Polypropylene Coat ing Systems for Pipel ines Op erat ing at ElevatedTemperatures, J ou r na l o f P r o tec ti v e Coa t ings L in ings , Mar c h 1997 , p .64 - 82 .4. D. Neal , Two coat ing sys tems contend fo r p remium spot in the market , Pipe L ine Ga s Indus t ry ,March 1998, p43-48.5. C. Steely , Weld Seams: A Weak L ink in the Cha in o f a Co at ing Sys tem ?, Mat . Per . , 33 ,11, 1994.6 . A . And renac c i , D . W ong J . Mo rdarsk i , New Deve lopm ents in Jo in t Coat ing and Fie ld Re pa i rTechnology, Mat. Per . , 38, 2, 1999.7 . M. Nass ivera , TO TAL s exper ience wi th ex terna l p ipe coat ing and f ie ld o in ts , T O T A L in te r na lpub l i c a t ion p r es en ted a t t he S ec ond A DC O Cor r os ion Con fe r enc e , A b u D hab i , 1998 .8 . V . Ro dr iguez , E . Pero zo E . A lvarez , Coat ing App l ica t ion a nd Eva lua t ion fo r Heavy Wal lThickness, T emp erature, and Pressure Pipeline, Mat. Per . , 37,2, 1998.9. J . Carew, at a l , Per formance o f Coat ing Sys tems in Industr ia l Atm ospheres on the Arab ian Gu l f,Mat. Per . , 33, 12, 1994.10. D. Neal , Com par ison o f Per fo rmance o f F ie ld Ap p l ied Girth W eld Coatings , Mat . Per . , 36 ,1 , p20-24.11. Exte rnal Polyethylene and Polypropylene Co at ing for L ine Pipe. S he l l Des ign and E ng inee r ing

P r ac t i c e 31 .40 .30 .31 , Dec ember 1994 .12 . D IN 30 670 , Polyethylene coat ings fo r s teel p ipes a nd f i tt ings, 1991.13 . D IN 30672 , Coat ings o f cor ros ion pro tec tion tapes and heat shr inkab le m ater ia l fo r p ipe l ines(opera t ing cont inuous ly a t tempera tures above 50 ~) , 1991 .14. DIN 30678, Polypropylene coat ings for s teel p ipes, 1991.15 . NF A 49711 , App l icat ion of three laye r extrud ed polyprop ylene co at ings to steel tubes, A F N O R ,1992.

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T A B L E 1P R O J E C T E D M A X I M U M O P E R A T I N G T E M P E R A T U R E S ~'TCo a t in g

Coa l Ta r Ename lCoa l Ta r Enam e l + Conc re teTh ree Laye r Po l ye thy l eneFus ion Bonded EpoxyTh ree Laye r Po l yp ropy lene

T emp era t u re C ( F )7 0 ( 1 5 8 )90 (194)8 5 1 8 5 )90 (194)140 (284)

T A B L E 2C O S T C O M P A R I S O N B E T W E E N D I F F E R E N T C O A T I N G S Y S T E M S 3'7Co a t in g Sys t em O r d e r o f C o s t Co st as of to ta lp ipe l ine cost( o n sh o re )

8oat Ta r Enam el 1FBE 1 .42.0 11 152 .0 -2 .33 layer po lye thy lene3 layer po lyp ropy lene 11

Co st as of to ta lp ip e l in e co s t(o f fshore)11

15

T A B L E 3C O S T C O M P A R I S O N B E T W E E N F IE L D J O IN T C O A T I N G S Y S T E M S F O RP O L Y P R O P Y L E N E C O A T E D P IP E L IN E S *Co at in 9 Sys t emCo-ex t ruded shee tF l ame sp rayedPo l yu re t hane

Ord er o f Co s t ( i n c lu d es ma t e r ia l & in s ta l la t io n )10.90.4*Data ob ta ined f rom o ne p ipe line coa t ing c on t rac to r i n the UA E.


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T A B L E 4C O M P A R I S O N O F P R O C E D U R E Q U A L I F IC A T I O N TE S T S D A T A B E T W E E N F IE L DJ O IN T C O A T IN G S Y S T E M S F O R P O L Y P R O P Y L E N E C O A T E D P IP E L IN E S 7T e s t C o - e x t ru d e d s h e e t F l a m e s p r a y

Bend ing Tes t resu l t No c rack No c rack0 .06 mm 0 .03 mmenet ra tion a t amb ien t temp0 .1 3 mm 0.9 mmenetra t ion a t 110CImpac t res is tance 23 J /mm 16 J /mm

Pee l adhes ion a t am b ien t 1550 N 510 NPee l adhes ion a t 110C 510 N 400 N

0 m m 0 m ma th o d ic D i s b o n d me n t @ 6 5 C /4 8 h o u rsCa th o d i c D i s b o n d me n t @ 1 1 0 C /4 8 h o u rsCa th o d i c D i s b o n d me n t @ 2 0 C /2 8 d a y sImpac t s t reng thOxyg en induc t ion t ime

0 m m1.0 mm

> 16 Mpa50-75 m inu tes

45 minu tes app ly inga 3 .4 mm shee t )

Typica l time for f ie ld jo in t coat ing 3m mthick)

0 m m1.0 mm

> 15 Mpa15-20 minutes18-20 minutes

T A B L E 5R A N K I N G O F T H R E E S Y S T E M S F O R F I E L D J O IN T C O A T I N G O F P O L Y P R O P Y L E N EC O A T E D P I P E L I N E S IN D E S C E N D I N G O R D E R , 1 B E I N G T H E B E S T )Co a t in g Sys t em T ech n ica lCh arac t e r i s t i cs

Co-ex t ruded Shee t 12la me Sp ra y e d

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Ease of F ie ldAp p l i ca t io n3

E q u i p m e n t R e q u i re d f o rF ie ld Jo in t Co a t in g3

2 21 1

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11/16

FIG U RE 1 . Ap p l i ca t i on o f epoxy p r im e r on a p ipe li ne f ie l d jo i n t i n t he de se r t p r i o r t o i ns ta l la t iono f a po l ye thy lene hea t sh r i nk s leeve pho to cou r tes y o f Sh aw Indu s t r ies ) .

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12/16

F IG UR E 2 . I ns ta ll a ti on o f a po lye thy lene hea t sh r ink s leeve on a p ipe l ine f ie ld j o in t byapp l i ca t ion o f gas to rch fl am e hea t ing pho to cou r tesy o f Sh aw Indus t r ies ) .


13/16


14/16

FIGU RE 5 App l ica t ion o f FBE pr imer and mod i fied po lypropy lene ad hes ive by f lock spray ing

FIG UR E 6 App l ica t ion o f po lypropy lene coat ing to a p ipe l ine jo in t by f lame spra y gun

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FIG UR E 7 App l ication of m agne tic induction heat to a pipel ine join t in the desert


16/16

F I G U R E 8 A p p l ic a t io n o f p o l y p r o p y l e n e c o a t in g b y t h e s in t e r in g m e t h o d in t h e d e s e rt

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