corr prot prog for high temp sub pipe

8/10/2019 Corr Prot Prog for High Temp Sub Pipe

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C O R R O S I O N P R O T E C T I O N P R O G R M F O R H I G H T E M P E R T U R E S U B S E P I P E L IN E

M ike Surke in and S teve Leb lancE x x o n M o b i l U p st re a m D e v e lo p m e n t C o m p a n y

Pos t Off ice Box 4876H o u s t o n Te x a s 7 7 2 1 0

S h a n n o n R i c h a rd sE x x o n M o b i l P r od u c ti o n C o m p a n y

1555 Poy dras StreetN e w O r l e an s L o u i s i a n a 7 7 0 11 2

John P. La Fon ta ine

Deep wate r Cor ros ion Serv ices Inc .6830 N. E ldr idge Parkw aySui te 211

Hou s ton Texas 77041

A B S T R A C T

A subsea p ipe l ine has been ins ta l l ed wi th a nove l cor ros ion p ro tec t ion scheme. The p ipe l ineand assoc ia ted comp onen ts have been p ro tec ted f rom cor ros ion wi th a com bina t ion o f a h ightempera tu re p ipe l ine fus ion bonded epoxy coa t ing a the rmal sp ray a luminu m coa t ing and sac r i fi c iaca thod ic p ro tec t ion anodes . Due to the h igh opera ting t empera tu re o f the p ipe l ine anode b race le t

ins ta l la t ion on the p ipe l ine was no t des i rab le . A ca thod ic p ro tec t ion a tt enua t ion mo de l w as used todes ign the anodes fo r the p ipe l ine . The mo de l ind ica ted tha t the sac r i f i c ia l anodes cou ld be ins ta l l ede i the r end o f the two-m i le p ipe l ine . To assure adequa te cor ros ion con t ro l was ach ieved by the ca thopro tec t ion sys tem a soph is t i ca ted in - s itu moni to r ing sys tem was ins ta l led . Also a d ive r inspec t ion wconduc ted to measure ca thod ic p ro tec t ion pe rfo rmance . Th i s paper p resen t s the cor ros ion con t ro ldes ign approach used fo r each o f the major com ponen ts inc lud ing the r ise r s p ipe l ine and bur iedexpans ion boxes . The des ign bas i s wi l l be comp ared to the resu l ts o f the in - si tu and d ive r ga the redm oni to r ing da ta .

Copyright 2001 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole must be in writing to NACEInternational, Publications Division, 1440 South Creek Drive, Houston, Texas 77084-4906. The material presented and the views expressed in this paper aresolely those of the author(s) and not necessarily endorsed by the Association. Printed in U.S.A.

01500CORROSION 2001Paper No.


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I N T R O D U C T I O N

A typ ica l one-w el l deve lopm ent fo r a h ightempera tu re we l l in sha l low w ate r inc ludes a th reefour-pi le pla t form , we l lhead coolers , and ut i l i ties . The se faci l i t ies are required to protect the f lowfrom the inc reased cor ros ion rates and m echan ica l d i ff i cu l ti e s tha t i t wi l l exper ience a t fu l l we l l s t r

t empera tu res . For the deve lopm ent be ing d iscussed , we l lhead t empera tu res range f rom 265 F 129to 315 F 157 C) . The cha l l enge o f th i s des ign was to min im ize the we l lhead fac i li ty by e l iminathe coo le r and i t s a s soc ia ted u t i l it i e s, whi le add ress ing the cor ros ion and m echan ica l d i ff i cu l ti e s .

The mechan ica l des ign concerns fo r h ightempera tu re , bur ied f lowl ines a re the rmal expans ion upheava l buck l ing . Therm al expans ion wi l l occur when the f lowl ine opera ting temp era tu re is h igthan i ts a s - ins ta ll ed tempera tu re . In bur ied env i ronm ents , na tu ra l f lowl ine expans ion i s cons t ra inedthe ax ia l and l a te ra l loads o f the so i l on the f lowl ine . W here the re a re imper fec t ions in the f lowprof i le , the l ine wi l l t end to exper ience l a te ra l o r upheava l mo vem ent .

To o v e r c o m e t h e t h e r m a l e x p a n s i o n c h a l l e n g e s ; t h e f l o w l i n e w a s d e s i g n e d w i t h e x p a n s idog legs . The dog legs were housed in expans ion boxes F igure 1). The expans ion boxes a llowla te ra l g rowth o f the f lowl ine

Cor ros ion concerns a t e l eva ted tempera tu res inc lude h igh ca thod ic p ro tec t ion consum pt ion coa t ings degrada t ion . Ano dic cur ren t dens i ty inc reases and i ts capac i ty decreases wi th inc reastempera tu res . Bo th o f these cond i t ions wo rk aga ins t a s tandard sys tem of b race le t anodes ins tad i rec t ly on to the f lowl ine . The cha l l enge in se lec t ing a su i tab le coa t ing is to f ind a sys tem tha t s t aup to h igh t em pera tu res and res i st s ca thod ic d i sbondm ent .

T E M P E R AT U R E E F F E C T S O N C AT H O D I C P R O T E C T I O N

In genera l co r ros ion is a r rested whe n the cur ren t dens i ty on the ca thode exceeds the oxyg enrep len i shme nt ra te , accord ing to the equ a t ion :

0 2 + 4 e - + 2 H a O .-> 4 O H ) - 1)

This reac t ion ra i ses the pH a t the boundary, and i f ca lc ium carbona te co ncen t ra t ion in the e lec t ro ly tnear the so lubi l i ty l imi t , i t wi l l precipi ta te out on the cathod e, res t r ic t ing oxy gen diffus io n to thecathode, and cu rrent densi ty decreases .

Ca thod ic p ro tec t ion anode co nsum pt ion inc reases d ras ti ca l ly a t the d es ign t empera tu res o f th isf lowl ine . The cur ren t dens i ty requ i red to p ro tec t bur ied ba re s t ee l a t 77 F i s 2 m A/f t2 1). Astempera tu re inc reases , the cur ren t dens i ty requ i reme nt inc reases a t a r a te o f 0 . lm A /f t2 per 1 .8Fincrease above 77F 0 .1 mA /m2 as t empera tu re inc reases above 25 C) . Con verse ly, the anode cur ren

capac i ty decreases as the t empera tu re inc reases as shown in F igure 2 2 ). S ince no indus t ry da ta wafound a t the des ign t empera tu res fo r th i s f lowl ine , the anod e p roper t i e s were ex t rapo la ted .

O R R O S I O N O N T R O L F O R T H E P I PE L I N Eoa t ings

Corros ion con t ro l o f m ar ine p ipe l ines is usua l ly ach ieved th rough the use o f p ro tec t ive coa t ingsand supp lem enta l ca thod ic p ro tec t ion . W hen se lec t ing a coa t ing sys tem for a p ipe l ine o r s t ruc tu reseveral cons ide ra t ions mus t be mad e inc lud ing :


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1 . Effec t o f ca thod ic p ro tec t ion2 . Tempera tu re3 . L i fe4 . Cos t

M ar ine coa t ings m us t be su i t ab le fo r se rv ice wi th ca thod ic p ro tec t ion . S pec i f i ca l ly, they mus t beres i s t an t to ca thod ic d i sbondmen t . Ca thod ic d i sbond men t i s the des t ruc t ion o f the adhes ion be tweecoa t ing and the su r face due to ca thod ic p ro tec tion . The coa t ing sys tem m us t be su i t ab le fo r the se rt empera tu re o f the p ipe l ine , in th i s case up to 150 C 300 F) . The c oa t ing chosen fo r th i s app l i ca t iow a s a d u a l c o a t s y s t e m o f f u s i o n - b o n d e d e p o x y a n d c h e m i c a l l y m o d i f i e d p o l y p r o p y l e n e F B E / C M

a thodic P ro tec tionSevera l bas ic des igns were c ons ide re d fo r p rov id ing ca thod ic p ro tec t ion to th i s l ine :

1 . S tandard b race le t anode m ounted d i rec t ly on the p ipe l ine2 . Impressed cur ren t3 . Rem ote A 1-Zn-In anode s l eds mounted on the p la t fo rms a t e i the r end o f the f lowl ine

The redu c t ion in anode e ff i c i ency due to e l eva ted t empera tu re e l im ina tes the f ir s t s t r a tegy. Imprescur ren t ca thod ic p ro tec t ion was feas ib le , however such a sys tem would requ i re pe r iod ic ma in tenanth rough the se rv ice l i f e o f the p ipe l ine . At the an t i c ipa ted h igh t empera tu res, s t r a t egy 3 was mos tappropr ia t e . Us in g ga lvan ic anodes f rom a remote loca t ion a l lows the anodes to opera te in amb ientempera tu res where the y a re mos t e ff i c i en t . I t a l so becom es log i s t i ca l ly eas ie r than p lac ing anodest h e p i p e li n e i ts e lf . A l u m i n u m a n o d e s a l l o y e d w i th z i n c a n d i n d i u m a re c o m m o n l y u s e d f o r m a r i n eapp l i ca t ions due to the i r r e l i ab i l ity and h igh e ff i c i enc y and po ten t i a l .

DesignTo co ns ide r p lac ing the ano des a t e i the r end o f the f lowl ine , i t was e ssen t i a l to conduc t a

ca thod ic p ro tec t ion a t t enua t ion mode l o f the f lowl ine . The ca thod ic p ro tec t ion po ten t i a la t t enua t ion p ro f i l e o f the p ipe l ine , and to ta l cu r ren t ou tpu t r equ i red f rom the CP sys tem w ereca lcu la ted based o n the fo l lowing re la t ionsh ips .

V = K i ( 2)

V = C h a n g e i n p i p e l i n e p o t e n i a l f r o m n a t i v e s t a te

i = A p p l i e d c u r r e n t d e n s i t y

K = C o n s t a n t f o r a n y t e m p e r a t u r e

oI = To ta l c u rr e n t p ic k e d u p b y t h e l in e b e t w e e n m i d p o i n t a n d s e g m e n t n

n

V n+O - V n = C h a n g e i n p o t e n t i a l a l o n g a s h o r t i n c r e m e n t a l l e n g t h o f p i p e l i n e

R = L i n e a r R e s i s t a n c e o f i n c r e m e n t a l l e n g t h o f p i p e l i n e


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es ign ProcedureFrom the attenuation model the total current required was calculated. Assumin g (-) 1.00 Volt

vs. Ag/AgC1 (silver / silver chloride) polarization potential at the end points of the pip eline (drainpoints for the anode sleds), and (-) 0.800 V at the mid point, a successive iteration solution to thismod el is valid for a 5 bare surface area. This bare surface or coatin g breakd own value is cons ider ed

conservative for a new pipeline. The required current predicted by this model was used to size theanode sleds. Provision was made for the installation of one mixed metal oxide impressed currentanode on each sled in case additional current is required. A standard weight/curren t solution designcan be perf ormed to determine anode number and wei ght for anode sleds at each end o f the pipeline.

Anod e current output is determined by oh m' s law:

I = E / R 4 )

I = c u r r e n t o u t p u t

E = d r i v i n g p o t e n t i a l

R = c i r c u i t r e s i s t a n c e

Anode-to-el ectrolyte resistance was calculated according to Dwig ht' s equati on for long slenderstandoffs:

R a = p 1 2 1 r L ) I n 4 L/ r ) - 1 ) 5 )

p = S e a w a t e r r e s i s t i v i t y o h m - c m )

L = A n o d e l e n g t h

r = E q u i v a l e n t r a d i u s

A mutual interference factor was used to account for the redu ced current output caused by anodesarranged in parallel at close distances:

C . F. = 1 + I n [ C o t 8 2 / 2 ) C o t t Y 3 /2 ) . . . .C o t 8 n /2 ) ] / [ I n 4 L / r ) ] - 1 6 )

e n = A r c C o t L / n s )

L = L e n g t h o f a n o d e

s = S p a c i n g b e t w e e n a n o d e s

n = n u m b e r o f a n o d e s i n p a r a l l e l

r = r a d i u s

Anodes must have adequate weight to satisfy the equation:w / c > IL 7)

w = a n o d e w e i g h t

C = a n o d e c o n s u m p t i o n r a te I b s / A m p X Ye a r )

I = a n o d e c u r r e n t o u t p u t i n a m p s

L = d e s i r e d d e s i g n l if e i n y e a r s

The anodes were arranged in a sled frame. One frame was mou nted on the well caisson and the otherwas moun ted on the production platform (Figure 3.). The sleds were electrically isolated from thestructures by placing neoprene underneath the clamps. Continuity with the pipeline was establishedthrough a cable jumper.


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C O R R O S I O N C O N T R O L F O R T H E P I PE L I N E I N S ID E T H E E X P N S I O N B O X E S

C o a t i n g sThe coa t ing s ys tem on the p ipe l ine ins ide the expan s ion boxes m us t m ee t the same c r i t e r i a

t h e re s t o f th e l i ne . H e n c e , t h e F B E / C M P P s y s t e m u s e d o n t h e r e st o f t he p i p e l i n e w a s t h e c o a ti n gchoice .

C a t h o d i c P r o t e c t i o nThe exp ans ion boxe s sh ie ld the p ipe l ine ins ide f rom rece iv ing ca thod ic p ro tec t ion f rom the

anode s l eds . There fo re in the CP des ign o f the p ipe l ine , these segm ents were as sum ed to be i so la tef rom the res t o f the l ine . To p ro tec t th i s por t ion o f the p ipe l ine an independ en t C P sy s tem wasnecessa ry. L im i ted access ib i l i ty to these loca t ions made ga lvan ic sac r i f i c i a l anodes the mos tappropr ia te opt ion.

D e s i g nThe meta l l i c r e s i s t ance in the p ipe l ine ins ide the boxes i s r e l a t ive ly ins ign i f i can t . As a r e su l

po ten t i a l a t t enua t ion i s no t a concern . T he use o f t ru ly remote anodes to avo id the e ffec t o f e l eva tetempera tu re was n o t v iab le due to the phys ica l r e s tr i c t ion o f the box . The bes t op t ion w as to use acom pos i t e b race le t anode des ign (F igure 4 ). In th i s approach , the anode segm ents a re ac tua l ly smas tandoff anodes a r ranged rad ia l ly 4 (10 cm) o ff the p ipe . Off se t t ing the anodes f rom the p ipe a l lothe anodes to opera te in a r educed t emp era tu re env i ronm ent .

In th i s e l eva ted t empera tu re en v i ronm ent the cu r ren t capac i ty o f the anodes i s deva lued suchtha t anode w e igh t i s the l imi t ing des ign pa ramete r ( a s opposed to cu r ren t ) , hence th i s des ign was awe igh t -based so lu t ion . A coa t ing e ff i c i ency o f 0 .9 was used was used fo r the chosen coa t ing sys teTh i s va lue m ay be cons ide red conse rva t ive bu t had l imi ted impac t on the f ina l sys tem layou t .

C O R R O S I O N C O N T R O L F O R T H E E X P N S I O N B O X E SC o a t i n g s

T h e r m a l s p r a y a lu m i n u m ( T S A ) w a s c h o s e n a s th e c o a ti n g s y s t e m f o r t h e b ox e s . T S A d i f fef rom organ ic coa t ings in severa l a reas :

1 . I t i s condu ct ive2 . Hig her impac t r e s i s tance3 . Hig her se rv ice t empera tu re r ange

C a t h o d i c P r o t e c t io n

The l a rge su r face a rea o f the boxes , and the fac t tha t they a re e l ec t r i ca l ly i so la ted f rom thep ipe l ine make i t impor tan t to ins ta l l a sepa rate CP sys tem fo r the boxes . F lush mo unted an odes wese lec ted because the i r low prof i l e dec reased the chance o f damage dur ing ins ta l l a t ion .

D e s i g nThe ca thod ic p ro tec t ion requ i reme nts fo r the ins ide and ou t side su r face were ca lcu la ted

independ en t ly. Th i s approach was necessa ry because each su r face i s in a d i ffe ren t env i ronm ent (mand seawater ) , and geomet r i c sh ie ld ing res t ri c t s e l ec t rochemica l comm unica t ion . A we igh t -basedso lu t ion ca lcu la t ion was pe r fo rmed to ca lcu la te the quan t i ty o f anodes requ i red . A s w i th the p ipe l in


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t he des ign cur ren t dens i ty and cur ren t capac i ty was ad jus ted fo r t empera tu re e ffec ts . The coa t ingeff i c i en cy fac to r used fo r the TS A coa t ing sys tem was 0 .9. Th i s num ber i s conse rva t ive , a s f i e ld don TS A i s l imi ted .

M O N I T O R I N G

In o rde r to ve r i fy the pe r fo rmance o f the ca thod ic p ro tec t ion sy s tem, an on l ine f ixed moni tosys tem was des igne d and ins ta l l ed on the p ipe l ine and boxes .

Poten t ia lFor ca thod ic p ro tec t ion to be ach ieved , the e l ec t rochem ica l po ten t i a l o f s t eel vs . Ag/AgC1

e lec t rode mus t be more nega t ive than - ) 0 .800 vo l t s . The op t im um pro tec t ive po ten t i a l r ange i sbe twee n approx im ate ly - ) 0 .900 to - ) 1 .050 Vol t s . Refe rence e lec t rodes are r equ i red at seve ra lloca t ions to ve r i fy p ro tec t ive l eve l s . The loca t ion o f r e fe rence e lec t rodes a t the fo l low ing po in t s weselected:

On the r i se r jus t above the mud l ine Aw ay f rom the r i se r in the sand d i s t ance based on the rmal g rad ien t s ) Ins ide the boxes On the cu r ren t dens i ty sensors Outs ide su r face o f the boxes

Cur ren t Dens i tyCurren t dens i ty mon i to r s coa ted /uncoa ted) were ins ta l l ed on the p ipe a t the fo l lowing

locat ions:

On the r i se rs above the mud l ine On the p ipe l ine jus t be low the mud l ine On the p ipe l ine ins ide the boxes

These moni to r s p rov ide a dd i t iona l da ta tha t wi l l be va luab le in fu tu re des igns , i . e . t he po la r i za t ionbehav io r o f ba re and coa ted s t ee l a t e l eva ted t empera tu res . Each ins t rument com bines , cu r ren t denspo ten t i a l, and t empera tu re me asur ing capab i l i t i e s F igure 5 ). The CD p la tes inc luded ba re s t ee l , t heFB E/C M PP, and TS A coa ted su r faces . For each se t o f CD p la tes the re was an Ag/AgC1 re fe rence and t empera tu re p robe .

nodesThe rem ote anode s l eds a s we l l a s the ind iv idua l b race le t s on the l ine ins ide the boxes w ere

mon i to red fo r cu rren t ou tpu t us ing shun ted sensors. In add i t ion to tops ide da ta acqu i s i t ion , d ive r /Raccess ib le cu r ren t measur ing bo xes w ere ins ta l l ed on the s leds F igure 6 . ). These dev ices can be rem a n u a l l y u s in g a D i v e r / R O V p r o b e F i g u re 7 ).

Te m p e r a t u r eIn add i tion to the comb ina t ion sensors , independen t t empera tu re p robes w ere ins ta l l ed on th

r i ser s , and ins ide the boxes . These sensors a re in teg ra ted c i r cu i t t empera tu re t r ansducers tha t p roduan ou tpu t cu rren t p ropor t iona l to abso lu te t empera tu re . The da ta acqu i s i t ion un i t supp l ie s power, a


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ou tpu t cu r ren t is passed th ro ugh a r e si s to r. The vo l t age d rop i s measu red ac ross the r e s i s to r andrecorded b y the da ta acq u i s i t ion un it .

Data cquis i t ionA remote m oni to r ing s ys tem was used to r ecord the s igna l ou tpu t . The sy s tem i s a mod ula r

des ign based on 2 , 19 rack mounted ch ass i s tha t a re da i sy cha ined toge the r (F igure 8 .) . A l l channare fu ll d i ff e ren t i a l wi th r anges o f + / - 4000 mV DC fo r the r e fe rence ce l l s , and 80+/ - mV DC fo r ao the r s. The sys tem recorded s to red s igna l s a t p rogram med in te rva l s . The PL C sys te m on theproduc t ion fac i l i ty in te r faced wi th the sys tem an d recorded s igna l s d i rec tly.

R E S U LT SPipel ine Polar izat ion

The r isers polar ize d to ( -) 1 .050 V vs . Ag/Ag C1 severa l days af ter f i rs t o i l (Figure 9) . Pr ior f i r st o i l, t he po ten t i a l s were m ore nega t ive than ( - ) 1 .100 V. The p ipe l ine po ten t i a l s c lose to theproduc t ion p la t fo rm a re more nega t ive than the we l l ca i s son s ide o f the p ipe l ine . These resu l t s a rel ike ly due to t empera tu re e ffec ts . The h igh er tempera tu re on the we l l s ide inc reases cu r ren t dens i tyrequ i rements . The po ten t i a l s f rom bo th the r i se r s and the 1st jo in t in the mu d show the l ine to be fupolar ized. The des ign potent ia l for these locat ions is ( - ) 1 .00 V.

A su rvey was pe r fo rm ed on 24-June-1999 to ve r i fy the en t i r e leng th o f the p ipe l ine hadproper ly po la r ized . The po ten t i a l o f the p ipe l ine was meas ured us ing a d ive r he ld , dua l Ag/A gCIcon tac t probe . The su rvey da ta a long wi th the des ign mod e l a re show n in F igure 10. To ve r i fy theaccuracy o f the a tt enua t ion des ign mode l approach , the mode l w as reca lcu la ted us ing the ac tua l enpo in t su rvey po ten t ia l s . The o r ig ina l des ign mode l w as ca lcu la ted wi th end po in t po ten t i a l s o f ( -) 1V vs . Ag/AgC1 and 5% bare s tee l . The actual end potent ia ls used for the recalcula t ion were ( - ) 1 .02and ( - ) . 1050 V vs . Ag/AgC1. In compar i son w i th the su rvey da ta , the o r ig ina l des ign assumpt ionshave p roven to be conse rva t ive .

n ode C ur r en t Ou tpu tBefore s t a rtup , the cu r ren t ou tpu t o f the we l l ca i s son mou nted anode s l ed w as =0 .3 amps .

Imm edia te ly a f t e r s ta r tup (mid-M ay) cu r ren t ou tpu t inc reased to 1 .8 amps then dec reased s t ead i ly be low 0 .8 am ps (F igure 11) . The p rod uc t ion p la t fo rm s led ou tpu t fo l low ed a s imi la r pa t t ern . Th i sphen om enon i s l ike ly due to the inc rease in t empera tu re f rom am bien t to 290 F. To da te the cu r renou tpu t o f the s l eds has been fa r be low the des ign cur ren t o f 6 amps f rom each s l ed . The cur ren t ouby the anode b race le t in the enc losure nea r the we l l ca i s son d ec reased f rom 0 .035 amp s to 0 .015 amover th i s pe r iod (F igure 12) . In compar i son , the des ign cur ren t o f 0 .178 amp s has sho wn to beconse rva t ive .

Curren t Dens i tyThe cur ren t dens i t i e s o f the moni to r s on the r i se r s and the depar t ing p roduc t t emp era tu re a re

show n in F igure 13. Dur ing s t a rtup in mid-M ay, the unco a ted s t ee l su r face b r i e f ly r eached 10.7 m A(115.0 m A i m 2 .F r o m M a y t h r o u g h m i d A u g u s t t h e c u r r e n t d e n s i t y s t e a d i ly d e c re a s e d t o b e t w e e n 4and 3 .7 m A ] f t (43 .0 an d 3 9 . 8 mA/m2) . Th i s dec rease in r equ i red cur ren t dens i ty i s due to po la ri za t ioPo la r i za t ion o f the s t eel r e su l ts in p roduc t ion o f hydro xy l ions . Th i s r a i ses the pH a t the boundary, i f ca lc ium ca rbona te concen t ra t ion in the e l ec t ro ly te i s nea r the so lub i l i ty l imi t , it w i l l p rec ip i t a t e oon the ca thode , r e s t r ic t ing oxyg en d i ffus ion to the ca thode , and cur ren t dens i ty dec reases .


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The TS A sur face recorded nega t ive cu r ren t dens i t ie s f rom s ta r tup un t i l mid-Ju ly. Th i s r e su lind ica tes tha t the TSA sur face was ac t ing as an anode dur ing th i s pe r iod . The F BE /CM PP coa tedsur faces d rew cu r ren t dens i t i e s o f be tw een 0 .05 and 0 .15 mA /f t 2 (0 .54 and 1 .6 mA/m2) . Us ing da taf rom 1-Ju ly to 11 -Aug , the pe rcen tages o f uncoa ted s t ee l on the FBE /CM PP and TS A on the r i se r w2.75 an d 4 .84 m A/f t 2 (29.6 an d 52.1 m A/m2), resp ect ively .

The cur ren t dens i ty da ta fo r the p ipe l ine ins ide the L-shap ed exp ans ion box i s shown in F ig14. The cur ren t dens i t i e s on the coa ted su r faces were h igh er than on the r i se r. Cur ren t den s i ty on tTS A was 2 -4 mA/f t 2 ( 21 .5 - 43 .0 mA/m2) , wh ich equa tes 51.45 ba re s t ee l f rom 1-Ju ly to 11-AugThe cur ren t dens i ty on the FB E/C M PP sur face was ranged f rom 0 .4 to 0 .8 m A/f t 2 (4 .3 to 8 .6 mA/mThe pe rcen t ba re st ee l on the FB E/C M PP sur face was 12 .66 . I t i s l ike ly tha t t empera tu re e ffec t s the r i se r su r face a re no t a s p ronounced as in the box as these su r faces a re expo sed to the bu lk seaw

Expans ion oxesT h e b o x e s b o t h p o l a r i z e d i m m e d i a t e l y to p r o t ec t e d p o t e n ti a l s. B o t h e x p a n s i o n b o x e s p o l a r i

to va lues more neg a t ive than ( -) 1 .030 V vs . Ag/AgC I and (+) 0 .020 V vs . Z inc .

C O N C L U S I O N S

1. The ca thod ic p ro tec t ion sys te m i s pe r fo rm ing we l l . The p ipe l ine has ach ieved fu l l po la r i za t ion ai s we l l p ro tected . The da ta r ev iew ed to da te shows the cu r ren t r equ i red to r each p ro tec ted l eve l s tolowe r than o r ig ina l ly ca lcu la ted . Th i s i s new tec hno lo gy however, an d shou ld be moni to red in to thfu tu re to a s su re long- te rm per fo rmance .

2 . The C P sys tem i s work ing w e l l ins ide the boxes . The cur ren t ou tpu t i s le s s than the des ignparamete r s . How ever, da ta f rom th i s a rea shou ld con t inue to be ana ly zed , a s cu r ren t dens i t i e s a re hon the m oni to red su r faces .

3 . The b oxes have po la r i zed to des ign p o ten t i a l s and a re we l l p ro tec ted .

4 . The low cur ren t dens i ty on the FBE/CMPP coa ted su r faces ind ica tes tha t th i s coa t ing sys tepe r fo rm ing op t ima l ly. TSA co a ted su rfaces in some cases r ecorded nega t ive cu rren t densind ica t ing anod ic p roper t ie s even wh en used w i th ca thod ic p ro tec tion .


9/15

R E F E R E N C E S

1 . D e t N o r s k e Ve ri ta s , R e c o m m e n d e d P r a c t ic e B 4 0 1 C a t h o d ic P r o t e ct io n D e s i g n ,199 3 .

2 . S c h r e ib e r , C . F. a n d R . W . M u r r a y, E f f e c t o f H o s t i l e M a r i n e E n v i r o n m e n t s o n t h e A 1 -Z n - I n - S i S a c r if ic i a l A n o d e , p a p e r n o . 3 2 P r e s e n te d a t C O R R O S I O N / 9 7 , M a r c h 1 9 8 8 , S t .L o u i s , M i s s o u r i .

Remotew e ll } ~ . ~ ~caisson

~ Expans ion og legboxes

7 plaflorm [FIG UR E 1 Simp lified diagram of the high temperature f lowline

F I G U R E- E f f e c t o f t e m p e r a t u r e o n t h e c u r r e n t c a p a c i t y o f A 1 - Z n - I n a n o d e s i ns e a w a te r.

1

= r 1 i i

E 700


10/15

' : , ] u r a l

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i

. f~ri t~ . . . . .. . . .. . . . .. . . . .. . . . .. . . . .. . . . . ~ I l

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: i ii i ~

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F I G U R E 3 - P i p e l i n e a n o d e sl e d .

" " - , ' " ' - " .' S - . . / i, ~ " ~ : ~ ' ~ , . . ; . ~ 7 - j T - ' ". ~ . ' i . , ., .- ' t ~ p : ; ~ ;~ i . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .. i

. J ' . * . > ; J ,~ ' - . 7 ~ " ~ - - .. ~j J y . . .. .. . . . . . /. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . . 7 ; . . . . . . . . . . . . . . . . . . . . . . . . . . . . > . . - ~, ' . ' ~ . > . . . . . . 7 +( ' 7 - . % .... : . . .

X j' * ': ~-. /. -.

i ...... :I C u r r e n t D e n s i t y

M o n i t o r I

F I G U R E 4 - S c h e m a t i c o f a n o d e b r a ce l e t o n t h e p i p e l i n e in s i d e th e e x p a n s i o n b o x e s .


11/15

i ~ , C C ' i ~ .O X , , ,

/ ' ~ \ , , / \~ \. . . . . .l t W . . . , + . i . . . . . .. . . ~ . i ~ . . . . ~ l ~ . . z . ~ - i t . ~ . ~ ' ~ . . . . . . . : ~. ~i t. , ' ,. ~ . _ . . ~ ] . , , . ~ . . . . . . . . . . . . . . ~ \ t ~ - . . ~ . . . . . . . .. .. .. .. .. . . . . . . . . . . . . . . . . . . . \

. ~ , _ ~ , .. ~. ~ ~ - . . . ~ . , , ~ . . - , . ~ . ~ -~ , ~ . ~ , , . .~ , , ~ . . . . . . . . . ~ , , . '. . . . . . . . . . .. . . . . . . . . . . . .. . . . . ~ . - - : ~ : - ' _ ) , ~ . . . . . . . . . . . . . . . . . . . . . ~ t ~ , - : ~ . . . . . . . . . . . . . . . . . . . . . . ~ . ~ : ~ - . . . . . . . . . . . . . . . . . ~ . . , ~ . . ~ , . . . . . . . . . . . . . . . . . . . . . . . . . . .~(-. . . . . . . . . . . . . . . . . . . . . . . .

~ ~ ........... ~ , ......... ~ ...............w ~ - " ~ . . . . . , ~ " ~ ' ~ " e . .. .. .. .. .. .. .. ..t . . . . .

F I G U R E 5 S c h e m a t i c o f t h e c u rr e nt d e n s i t y m o n i t o r .

F I G U R E 6 D i v e r / R O V a c c e s si b le cu r re nt m e a s u r i n g b o x e s .


12/15

F I G U R E 7 S e l f C o n t a i n e d D i v e r / R O V c a t h o d i c p r o te c t io n p r ob e .

F I G U R E 8 R e m o t e m o n i t o r i n g d a ta a c q u is it io n s y st e m .


13/15

>

o

800 300

850

9O0

950

1000

Departing Temperature

A I -

. - - - - - - - i

Well Caisson Riser P otential

Boarding Temperature

x

250

2OO

@t -C

150

O O ~E

50

1 0 5 0 ~ 0

1~ Host Platform RiserP o t e n -

- 1 1 0 0 , 501 0 M a y 20 M a y 3 0 M a y 9 J u n 1 9 J u n 2 9 J u n 9 J u l 1 9 J u l 2 9 J u l 8 A u g 1 8 A u g

T i m e

F I G U R E 9 R i s e r p o t e n ti a ls a n d t em p e r a tu r e d u r in g s p r i n g s u m m e r 1 9 9 9 .

1 100mModeledResets iCPSURVEY ~ Design i

1.050 /

~ 1 . 0 0 0 ~ / ~

~ .

/ /~ o . a o o - - v - - . ~ : '

0.7500 2000 4000 6000 8000 10000

D i s t a n c e ( F e e t )

F I G U R E 1 0 Potent ia l a t tenuat ion mod els . The grap h shows the or iginal design, datafrom the f ie ld survey, and the model based on the actual end point Riser) potent ia ls .


14/15

F I G U R E 11 - W e l l c a i s s o n - m o u n t e d a n o d e sl e d c u r r en t o u t p u t s p r i n g - s u m m e r 1 9 9 9 .

2

1.8

1 . 6 ~ - - ,

1 . 4 -

1.2

|0 . 8 ~

a 6

[ -= ,~Anode S ledCurrent Output ]

0.4

0 . 2 -

0

1 0 -M a y 2 0 -M a y 3 0 - M a y 9 - J u n 1 9 - J u n29 Jun 9 - J u l 1 9 - J u l 2 9 - J u l B - A u g 1 B -A u gT i m e

0.1

0.09

0.08 - -

0.07

0.06

~ 0.05

~ = A n o d e B r a c e l e t C u r r e n t O u t p u t

0.04

o.o3 ~

0.02 I

0.01h

0

10-May 20-May 30-May 9 -J un 19- Ju n 29-Jun 9-Ju l 19 -J u l 29-Jul 8 -Aug 18-Au gT i m e

F I G U R E 1 2 - A n o d e b r a c e le t c u r r en t o u t p u t s p r i n g - s u m m e r 1 9 9 9 .


15/15

2 i Tem pe a ture , l l m l ~ l ~ m ~ ] 300

. . . . . 250

20O

E150 ~

1 O

5O

0

l O -M a y 2 0 -M a y 3 0 -M a y 9 - J u n 1 9 - J u n 2 9 -J u n 9 - J u l 1 9 - J u l 2 9 - J u l 8 - A u g

Ti m e

-5018-Aug

F I G U R E 1 3 C u r r e n t d e n s i t i e s o n v a r i o u s s u r f a c e s o n t h e w e l l c a i s s o n r is er .

12 300

10

6E

-- | ~,J I , ~ ==~ ~- = : I1 ~ ~-: -= - ' J- __ 250

2 0 0

o o

FBE/CMPP Plates _~ ~ 0

(~ - 5 01 0 - M a y 2 0 -M a y 3 0 -M a y 9 - J u n 1 9 - J u n 2 9 -J u n 9 - J u l 1 9 - J u l 2 9 - , J u l 8 -A u g 1 8 - A u g

Time

F I G U R E 1 4 C u r r en t d e n s it i e s o n t h e p i p e l in e i n si d e t h e e x p a n s i o n b o x .

corr prot prog for high temp sub pipe

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