Causes of Pipeline Failure Fracture

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Figure 2-19. Earthquakes In and Near Alaska-Th rough 1974 (Barnes & Hopkins, 1978)


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15000 148.00 146.00 144.00 442.OO 140.0072.00

70.00

68.00 .

66.00

I I I I

200 M

lsobath (M)

t Thrust Fault

-& Anticline

-Syncline4 ---

*-

R

\

c--

+-+e- Structural TectonicTerrace

Boundary

/c--c--,

. 72.00

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I

70.00

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66.00

t48.00 46.00 144.00 f 42 OO 140.0050.00

Epicenters (t) located by the localseismographic network having rm sof travel- t ime residuals Sl . 5 s e c

plot ted on an overlay of the struc-tur al tr ac es in northeast Alaska.Epicenters shown north of 7 N.

latitude are f rom Canadian catalog.

Figure 2-20. Northeast Alaska Earthquakes--1976-1977 Biswas, 1977)

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e p i c e n t e r s a n d o t h e r t e c t o n i c f e a t u r e s i n n o r t he a s t e r n Alaska.

The a v a i l a b l e e a r t hq u a ke d a t a r e p r e s e n t too s h o r t a t i m e

i n t e r v a l t o d e t er m i n e r e c u r r e n c e r a t e s f o r seismic e v e n t s

greater than magni tude 5 . 0 i n t h e area . However, t h e data

are i n d i c a t i v e of t h e need t o d e si g n s t r u c t u r e s able t o w i t h-

s t a n d g ro un d v i b r a t i o n s f rom a s h a l l o w e a r t h q u a k e of magni tude

a t l e a s t 6 . 0 (Barnes and Hopkins , 1978). A r e c e n t s t u d y pre-

pa red f o r t h e Alaska S u b a r c t i c O f f s h o r e Committee by Woodward-

C l y d e C o n s u l t a n t s (1978) examined po ten t i a l g round mot ion

c h a ra c t e r i s t i c s t h a t might be a s s o c i a t e d w i t h e a r t h q u a k e s i n

t h e Beaufor t Bas in a rea . I n t h i s s t u d y , a random earthquake

s o u r c e w a s assumed, and ground motion parameters w e r e computed

on t h e b a s i s of a h y p o t h e t i c a l seismic e v e n t w i t h a magni tudeof 6 . 5 and a r e c u r r e n c e i n t e r v a l of 100 y e a r s . I t w a s found

t h a t such an ea r thqu ake would p roduce g round acc e l e r a t io ns on

t h e order of 0.05 g w i t h assoc ia ted maximum velocit ies of 3 . 1

cm/sec

( 1 . 2 i n / s e c ) . However, t h e au thors warn t h a t t h e ana ly-

sis is v e r y s e n s i t i v e t o t h e s e i s m i c i t y l e v e l an d, s h o ul d

l a r g e r m a g n i t u d e e v e n t s o c c u r , t h e a c c e l e r a t i o n s and v e l o c i t i e s

c o u l d be a l t e r e d ap p rec i ab ly .

T he l i m i t e d da t a a v a i l a b l e c o n c er n in g t h e r e g i o n ' s seis-m i c i t y appear t o i n d i c a t e t h a t t h e seismic h a z a rd t o p i p e l i n e s

is probabl y s l i g h t a n d c o n f i n e d t o a r a t he r s m a l l area of t h e

B e au f o r t S h e l f . However, a d d i t i o n a l d a t a a re r e q u i r e d f o r

p rec ise d e l i n e a t i o n of t h e o f f s h o r e t e c t o n i c s t r u c t u r e and t o

compute r e l i a b l e r e c u r r e n c e r a t e s f o r l a rger seismic e v e n t s .

I t s h o u l d a l so be n ot ed t h a t e p i s o d i c mot ions of smal l magni-

t u d e s e v e n t u a l l y may add up t o s i g n i f i c a n t gr ou nd d i s p la c e me n t s

o v e r a l e n g t h y p e r i o d of t i m e . L i n e a r s t r u c t u r e s , s u c h as

p i p e l i n e s , c o u l d be t h r e a t e n e d by t h i s cu mu la ti ve movement and

may need a p p r o p r i a t e d e s i gn p r o v i s i o n s t o accommodate these

d i sp l ac em en t s i n s e i s m i c a l l y- a c t i v e areas .

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D . OTHER ENVIRONMENTAL CONCERNS

The . P o r e g o i n g p a r t s o f S e c t i o n I 1 h a ve f o c u s e d o n t h e

p r i n c i p a l i s s u e s i n t h e d e s i g n o f A r c t i c o f f s h o r e p i p e l i n e s .

T h e r e a r e s e v e r a l a d d i t i o n a l e n v i r o nm e nt a l f a c t o r s wh ic h must

b e c o n s i d e r e d i n t h e t o t a l d e s i g n f r a m e w o r k and w hich pose

f o r m i d a b l e c h a l l e n g e s i n t h e c o n s t r u c t i o n and o p e r a t i o n o f

s uc h p i p e l i n e s . I t is t h e r e f o r e a p p r o p r i a t e t o review t h e s e

f a c t o r s f o r a n o v e r a l l a p p r e c i a t i o n o f t h e p o t e n t i a l d i f f i -

c u l t i e s i n s u ch a n e nd ea vo r .

1. L o c a t i o n

Re mo te ne ss a nd i n a c c e s s i b i l i t y a r e f u n d a m e n t a l c h a r a c-

t e r i s t i c s o f t h e Al a sk an A r c t i c . T h e n o r t h e r n c oa s t a l areas

a r e s e v e r a l h un dr ed m i l e s f rom i n d u s t r i a l a nd s u p p ly c e n t e r s

a nd t h e f ew r o u t e s o f t e n a re made impassable by w e a t h e r . A s

a c on se qu en ce o f t h i s i s o l a t i o n , l o g i s t i c e f f o r t s w i l l r e q u i r e

e x c e p t i o n a l p l a n n i n g a n d s c h ed u l i n g t o e n s u r e t h a t n e ce s sa r y

s u p p l i e s a nd e qu i pm en t a r e a v a i l a b l e when n e ed e d. P r e s e n t l y ,

m o s t l a r g e and heavy i t e m s must b e t r a n s p o r t e d t o t h e N or th

S l o p e by b a r g e d u r i n g t h e b r i e f o pe n- w at e r p e r i o d . T h i s mode

o f t r a n s p o r t i s e n t i r e l y d e p en d en t upon t h e n or t h wa r d r e t r c a t

o f p a c k i c e w hich a l l o w s b a r g e t r a f f i c t o move a r o u n d P o i n t

B a r r o w a n d c o n t i n u e eastward t o t h e main s t a g i n g areas a t

P r u d h o e Ba y . The r e t r e a t o f t h e p ac k i c e is v e r y u n p r e d i c t a b l e

as is t h e d u r a t i o n of t h e o p en- w at er p e r i o d a l o n g t h e c oa s t .

Wester ly summer storms c an d r i v e t h e p a ck i c e b a c k i n t o t h e

coast i n a mat ter o f h ou r s . I f t h i s o c c u r s t ow ar d t h e e nd of

t h e summer s e a s o n , t h e p ac k i c e may remain c l o s e t o s h o r e

t h r ou gh t h e w i n t e r a nd p re v e n t f u r t h e r n a v i g a t i o n .

The i s o l a t i o n o f t h e Be a u f o r t coas t u n d o u b t e d l y w i l l

a f f e c t p i p e l i n e d e ve lo pme nt s t r a t e g i e s i n many o t h e r w a ys .

The a b i l i t y t o r e s p o n d t o e m e r g e n c i e s , f o r e x am p le , w i l l be

i m p a i r e d b y t h i s f a c t o r . C on se qu en t l y , i t may be n e c e s s a r y

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t o s to ck a v e r y e x t e n s i v e s u p p l y of s p a r e p a r t s on t h e N or th

Slope t o p r o v i d e a more t i m e l y r e s p o n s e t o breakdowns, l e a k s ,

e t c . From a d e s ig n s t a n d p o i n t , p i p e l i n e s e q ui pp ed w i t h h i g h l y

r e l i a b l e o r redundant components are a l s o i m p o r t a n t i n t h i s

r e g a r d .

2. Weather

The seve re Arc t i c w e a t h e r is a major obs tac le t o p ipe-

l i n e c o n s t r u c t i o n a nd m ai n te na nc e. G e ne r a l c l ima t i c condi-

t i o n s a re charac te r ized by co ld te mpe ra t ur es (b ot h summer and

w i n t e r ) , s m a l l a nn ua l p r e c i p i t a t i o n , a nd s t r o n g p e r s i s e n t

winds. The a b i l i t y of humans and machinery t o f u n c t i o n e f f i-

c i e n t l y u nd er t hese c o n d i t i o n s is i m p a i r e d g r e a t l y .

Tempera ture i s p robably t h e s i n g l e g r ea t e s t f a c t o r which

a f f e c t s Arc t i c work ing co nd i t io ns and human e f f i c i en cy . Tab le

2-3 i l l u s t r a t e s t y p i c a l t e mp er a t ur e c on d i t io n s a t t h r e e N o r t h

Sl o p e c oa s t a l l o c a t i o n s .

Th e s u b- f r e e z i n g t e m p e r a t u r e s w h i c h e x i s t t h r o u g h most

of t h e y e a r are e x a gg e r a te d s e v e r e l y by p e r s i s t e n t w in ds which

make the e q u i v a l e n t c h i l l temperature much lower. A t B a r r o w ,

f o r example, calm c o n d i t i o n s a re o b s e rv e d o n l y 1 . 3 percen t of

t h e t i m e . F i g u r e 2-21 is a series of p r o b a b i l i t y c u r v e s f o r

e q u i v a l e n t c h i l l t e m p e r a t u r e s i n each month. T h e s e c u r v e s

were d e v e l o p e d u s i n g h o u r l y v a l u e s of t e m p e ra t u r e a n d corres-

ponding s u r f a c e wind r ep o r t s f o r B a r r o w . However, t h e y are

g e n e r a l l y a p p l i c a b l e t o most Nor th Sl o p e co as t a l areas . The

c u rv e s i l l u s t r a t e t h e h i g h p r o b a b i l i t y of e n c o u n t e r i n g d a ng e r -

o u s t e m p e ra t u r e s a t a l l t i m e s of t h e year .

With respect t o p i p e l i n e development , l o w t e m p e r a t u r e s ,

o r l o w e f f e c t i v e t e m pe r a t ur e s , ha ve s e v e r a l i m p l i c a t i o n s . The

s e l e c t i o n of m a t e r i a l s , f o r example, may be i n f l u e n c e d b y t e m-

p e r a t u r e b ec aus e of p o t e n t i a l prob lems w i t h b r i t t l e f r a c t u r e .

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T a b l e 2-3. North Slope Temperatures

S u m m e r W i n t e r

Daily Daily Daily Daily Mean Numberof Days

Record Below

OC

(OF) Annual

Seasonal Seasonal Seasonal Seasonal Record

FreezingMaximum Minimum Maximum Minimum High Low

0 0C ( F )Location OC ( O F ) OC ( O F ) OC ( O F ) OC ( O F )

tu

Barter Island 9 ( 4 8 ) -8 (16 ) -5 ( 2 3 ) -32 (- 26) 24 (75) -50 (-59) 311n

-3

U m i a t 18 ( 6 4 ) -10 (13) -6 ( 2 1 ) -38 (- 36) 29 (85) -53 (- 63) ---

Barrow 7 (45 ) -10 ( 1 3 ) 6 (21 ) - 31 (- 24) 25 (78)-

49 (-56) 324

Source: Swift et al, 1974


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60

50

40

30

20

10

cr

0

-10

- 2 0

- 30

-40

-50

-60

-70

-800.5 5 10 20 50

Figure 2-21. Percent Probab

Equivalent Chill Temperature at Barrow,

2-58

80 98

Iity of Occurrence --

99 .9

Alaska Searby & Hunter, 1971)


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O pe r a t i ng m ac h ine ry s uc h as pumps, compr es s or s , and v a l v e s

l i ke w i s e must ha ve l ow- t e m p e r a t u r e c a p a b i l i t y a n d d e m o n s t r a t e d

r e l i a b i l i t y f o r Arct ic u s e . P i p e l i n e c o n s t r u c t i o n w i l l be

s t r o n g l y i n f l u e n c e d by t e m p e r a t ur e . D u ri n g w i n t e r , w o r ke r s

mu st b e p r o t e c t e d a g a i n s t extremes t h ro u gh t h e u s e of e nc l o-s u r e s a ro un d work areas o r w i t h b u lk y c l o t h i n g i n e xp os ed

l o c a t i o n s . The l a t t e r s o l u t i o n t e n ds t o r e d u c e e f f i c i e n c y

a nd may r e qu i r e a d d i t i on a l m e a su r e s t o e n s u r e a d eq u at e q u a l i t y

c o n t r o l .

A f i n a l c on ce rn r e g a r d i n g Arc t i c weather r e l a t e s t o

weather f o r e c a s t i n g . R e l i a b l e f o r e c a s t i n g i s most i m por t a n t

f o r summer l o g i s t i c s a nd d u r i n g t h e c o n s t r u c t i o n p e r i o d . Un-

f o r t u n a t e l y , p r e s e n t s t a n d a r d s f o r Arc t i c f o r e c a s t i n g a re v e r ypoor i n c om pa ri so n w i t h temperate r e g i o n s . H i s t o r i c a l weather

d a t a are i ncomple t e and there is a l a c k of r e p o r t i n g meteoro-

l o g i c a l s t a t i o n s , e s p e c i a l l y o f f s h o r e . F ur th er mo re , remote

s e n s i n g s y s te m s , c a p a b l e o f o b t a i n i n g h i g h r e s o l u t i o n da ta

u n de r c o n d i t i o n s of c l o u d s an d d a r k n e s s p r e v a l e n t i n t h e

Arc t ic , h av e n o t b e en d e p l o ye d i n o p e r a t i o n a l we a t h er s a t e l-

l i t e s (Weeks, 1 9 7 8 ) .

3 . Low V i s i b i l i t y and O p t i c a l Phenomena

A major f a c t o r wh ic h i n f l u e n c e s b o t h s u r f a c e an d a i r

l o g i s t i c s i n t h e Arct ic is v i s i b i l i t y . Low v i s i b i l i t y due t o

d a r k n e s s , c l o u d s , f o g , a n d o t h e r opt i ca l phenomena i s a common

c o n d i t i o n a l o n g t h e Arct ic c oa s t .

Dur ing t h e w i n t e r m on th s, t h e s un is c o n t i n u o u s l y below

t h e h o r i z o n from mid-November t o mid- J a nua ry . D ur ing t h e l a t e

f a l l a nd e a r l y s p r i n g m on th s, d a y s a r e c o m p a r a t i v e l y s h o r ta l t h o u g h t h e r e is s u f f i c i e n t t w i l i gh t t o c a r r y o n a number of

a c t i v i t i e s w i th o u t a r t i f i c i a l l i g h t .

C l o u d i n e s s is a p r e v a l e n t c o n d i t i o n a l o n g t h e e n t i r e

Arct ic coas t . More t h a n 60 p e r c e n t of t h e days a r e c l oudy o n

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I

o nl y i n areas s u c h as Barrow and Prudhoe Bay where t h e r e is a

s i g n i f i c a n t a m o u n t of m a r i ne s h i p p i n g . S i n c e i t is a n t i c i p a t e d

t h a t m o s t , i f n o t a l l , Arctic s u bm ar i n e p i p e l i n e s w oul d be

b u r i e d , t h e t h r e a t of danger appea rs min ima l .

Danger from m a r i n e l i f e such as whales a l s o would a p p e a r

t o pos e a v e r y remote t h r ea t t o p i p e l i n e s . Al though t h e r e are

cons ide rab le numbers of w h a l e s found i n t h e Arct ic d u r i n g

summer months, they are an u nl i k e l y t h r e a t for b u r i e d p i p e l i n e s .

E . SUMMARY

Arc t i c p i p e l i n e s face a number of p o t e n t i a l h a z a r d s

un ique t o t h e r e g i on i n a d d i t i o n t o t h e normal hazards encoun-

t e r e d i n temperate l a t i t u d e s . The p rob l em s w hi ch p o s e t h emost s e r i o u s e n gi n e e r i n g c h a l l e n g e s i n c l u d e i c e scour , pe rma-

f r o s t , f r o s t h ea ve , s t r u d e l s c o u r , a nd coas t a l e ro s i o n . Se v-

e r a l of t he s e problems s u c h as p e r ma f r o s t and f r o s t heave have

been en cou n t e r e d i n Arc t i c t e r r e s t r i a l p i p e l i n e p ro je c t s and

appropr i a t e e n g i n e e r i n g s o l u t i o n s h a v e be en d e ve l op e d t o d e a l

w i t h them. The remaining problems can be m i t i g a t e d or, i n some

i n s t a n c e s , a v oi d ed c o mp l et e l y by j u d i c i o u s r o u t e s e l e c t i o n .

Pr obl ems i n common w i t h t empe ra t e zones i nc l ude wave andc u r r e n t a c t i v i t y , s e i s m i c i t y , a nd s ed im en t g e o t e c h ni c a l p ro pe r -

t ies s u c h as i n s t a b i l i t y . The o ce a no g ra p hi c h a z ar d s i n t h e

Arct ic h av e no t b ee n e v a l u a t e d f u l l y b u t appear t o b e s ubs t a n-

t i a l l y less s e v e r e t h a n t h o s e i n t h e Gulf of Mexico, f o r

example. The most r e c e n t seismic h i s t o r y of t h e area shows

t h a t there have been some moderate e ar t hq ua ke s i n t h e v i c i n i t y

of t h e proposed Be au for t lease area. A n a l y s i s of t h e s e ear th-

q u a k e s i n d i c a t e s t h a t t h e y would produce s m a l l a c c e l e r a t i o n s

and o t h e r low-magni tude ground mot ions wi th in t h e lease areab o u n d a r i e s . L imi t ed g e o t e c h n i c a l i n f o r ma t i o n s u g g e s t s t h a t

there a r e no major hazards for p i p e l i n e c o n s t r u c t i o n . The

n e a r - s u r f a c e s e d i m e nt s h a ve h i g h l y - v a r i a b l e e n g i n e e r i n g proper-

t i e s , b u t appear to be g e n e r a l l y s t a b l e .

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111. PIPELINE SYSTEMS FAILURE ANALYSIS

A . INTRODUCTION

The f a i l u r e d a t a a d dr e ss e d i n t h i s sect ion is a s s o c i a t e d

w i t h b o t h o n s h o re a n d o f f s h o re o i l / g a s p i p e l i n e s . The b u l k o ft h e d a t a r e f l e c t s t h e on sh or e h i s t o r y . The o f f s h o r e d a t a are

l i m i t e d and are on ly f rom t h e Gulf of Mexico. An overview of

t h i s i nf or m at i on w a s a ss em b le d be c a u se many o f t h e s e f a i l u r e

modes could occur i n a d di t io n t o t h e p o s tu l a t e d f a i l u r e modes

u n i q u e t o Arctic o f f s h o r e p i p e l i n e s ( d i s cu s s ed i n S e ct i o n 1V.D

w i th p r i n c i p a l ones d e p i c t e d i n F i g u r e 4-5).

The p r im ar y c a us e s o f p i p e l i n e f a i l u r e s i n t h e U ni t ed

S t a t e s , as c l a s s i f i e d by t h e Dep art men t o f T r a n s p o r t a t i o n ,are o u t s i d e f o r c e s , corrosion, c o n s t r u c t i o n d e f e c t s , material

f a i l u r e s , a nd o t h e r r e as o ns . The f a i l u r e i nf o rm at io n i n t h i s

s e c t i o n i n c l ud e s d a t a from d i f f e r e n t sources which cannot be

p r e c i s e l y compared because o f r e p o r t i n g d i f f e r e n c e s . However,

t h e i n f o r m a t i o n d o e s p r o v i d e a gene ra l background o f causes of

p i p e l i n e f a i l u r e s .

1. T yp es o f Fa i l u r e s R e p or t e d

B e fo r e t h e f a i l u r e s ca n b e d i sc u s s e d , i t is essent ia l t o

d e f i n e t h e t y p e o f p i p e l i n e f a i l u r e s r e p o r t ed . The US D ep ar t-

ment of T ra ns po r t a t io n r e q u i r e s c e r t a i n p i p e l i n e f a i l u r e s t o

b e r e p o r t e d .

G a s P i p e l i n e s . F o r gas t r a n sm i s si o n p i p e l i n e s and cer-

t a i n gas g a t h e r i n g s y s te m s w i t h i n m ost c i t y l i m i t s , f a i l u r e s

m e e t i n g t h e c r i t e r i a i n t h e T i t l e 49 o f t h e Code o f F e d e ra l

Regu la t i ons (CFR) P a r t s 191 . 5 and 191 .15 mu s t b e r e p o r t e d onForm DOT-F-7100.2. These p a r t s c a l l for t h e t e l e ph o n i c n o t i c e

a nd t h e w r i t t e n f ol lo w- u p , r e s p e c t i v e l y , a n d a gas p i p e l i n e

f a i l u r e is d e f i ne d un de r t h e s e p a r t s g e n e r a l l y as any l e ak t h a t :

3-1


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c au se d d e a t h o r p er s o na l i n j u r y r e q u i r i n g

h o s p i t a l i z a t i o n ; o r

r e q u i r e d t a k i n g a n y segment of a t r a n s m i s s i o n

l i n e ou t of s e r v i c e ; o r

r e s u l t e d i n g a s i g n i t i n g ; or

caused es t imated damage of $5,000 o r mo re; o r

i n t h e ju dg me nt o f t h e o p e ra t o r w a s s i g n i f i c a n t

en ough f o r t e l e p h o n i c not ice even though not

meeting any c r i t e r i a i n a-d above; or, as p a r t

o f t h e w r i t t e n r e p o r t ;

r e q u i r e d i mm ed ia te r e p a i r o f a t r a n s m i s s i o n

l i n e ; o rw a s a t e s t f a i l u r e w h il e t e s t i n g for gas or

another medium.

I t s h o ul d b e n o t ed t h a t t h e a bo ve i n d i v i d u a l l e a k or

test f a i l u r e r e p o r t s h av e be en u s e d i n t h i s r e p o r t t o c ompare

t o t h e i n d i v i d u a l o f f s h o r e l e a k r e p o r t s f rom t h e Gulf o f

Mexico. There i s a l s o an Annua l Report of Gas Transmis s ion

and Gathering Systems (DOT-F-7100.2-1) which w a s used i n p r e-

p a r i n g Tab le 3-

1.

L i q u i d P i p e l i n e s . With r e g a r d t o l i q u i d p i p e l i n e s , a

f a i l u r e t h a t r e s u l t s i n a l o s s of commodi ty re su l t ing i n any

o f t h e f o l lo w in g g e ne r a l s i t u a t i o n s f u r t h e r d e fi n e d i n P a r t

195.50 m u s t . b e r e p o r t e d on DOT Form 7000-1:

( a ) e x p l o s i o n or f i r e n ot i n t e n t io n a l l y set by

t h e carr ie r

(b) l o s s o f 50 or m o r e b a r r e l s of l i q u i d

( c ) e s ca p e t o t h e a tm os ph er e o f more than 5 b a r r e l s

a day o f h i gh l y v o l a t i l e l i q u i d s

3-2


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( d ) dea th

( e ) bodi ly harm

( f ) p roper ty damage of a t least $1,000 t o o t h e r

than t h e c a r r i e r ' s f a c i l i t i e s

( g ) p roper ty damage of a t o t a l of $5,000 or more

t o ca r r i e r ' s and others .

I t should be noted t h a t t he re are a l so a d d i t i o n a l te le-

phonic not ice repor t ing requi rements fo r l i q u i d releases t h a t

p o l l u t e any stream, r i v e r , l a ke , r e s e r v o i r , or o t h e r s imi la r

body of water. However, t he re are no annua l repor t ing requi re-

m e n t s fo r l i q u i d p i p e li n e s and th er ef or e no annual t o indiv id -

u a l leak comparisons are made i n t h i s r e po r t f o r l i q u i d

p i p e l i n e s .

2 . Information Sources

Because of a l a c k o f f a i l u r e h i s t o r i e s a v a i l a b l e concern-

. i ng t h e f e w kilometers of Arctic subsea pi pe l i ne s now i n place,

d a t a on o t h e r US p i p e l i n e s are p resented t o g ive a h i s t o r i c a l

background on f a i l u r e s . I t should n o t be construed t h a t t h e

causes of f a i l u r e of t h e temperate zone p i p e l i n e s mentioned

i n t h i s s e c t i o n are necessar i ly app l i cab le t o cur r en t o r f u t u r ep i p e l i n e s i n t h e Arctic. However, there is a s t r o n g i n d i c a t i o n

t h a t t h e same problems a f f e c t a l l p i p e l i n e s w i t h t h e degree of

s e v e r i t y dependent on locat ion and t y p e of commodity t r a n s -

por ted .

and t r a n sm i s s i o n (gas ) o r g a t h e r i n g a n d t r u n k ( l i q u i d o i l )

p i p e l i n e s i n t h e US .

A l l f i g u r e s c i t ed i n t h i s s e c t i o n apply t o ga the r ing

Offshore . O ff s h o re gas and o i l f a i l u r e data are from U S

Geological Survey (USGS) f o r t h e Gulf of Mexico area. F a i l u r ecauses appear i n t h e USGS data verbatim from leak repor t forms.

For t h e charts appea r ing in t h i s s e c t i o n , t h e of f sho re causes

were d i v i d e d i n t o categories s imi lar t o t h o s e i n t h e DOT f i g u r e s .

3-3


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The number o f o f f s h o r e f a i l u r e s p e r y e a r f rom 19 70 t o 1978,

i n c l u s i v e , range from 10 t o 31 which is n o t a l a rge enough

f i e l d t o e s t a b l i s h m ea ni ng fu l t r e n d s . T h i s can b e compared

agains t combined i n d i v i d u a l o n sh o re o i l a nd g a s p i p e l i n e

f a i l u r e r a t e s ( i n c l u d i n g t e s t f a i l u r e s ) whi ch r a n g ed f r om 700

t o 1 ,0 18 pe r yea r between 1971 and 1976, i n c l u s i v e . Conse-

q u e n tl y , t h e o f f sh o r e f a i l u r e s h ave s t a t i s t i c a l l y much l ess

s i g n i f i c a n c e . A l s o , t h e USGS f i g u re s d o n o t c o v e r a l l o f f-

s h o r e p i p e l i n e s i n t h e G ul f of M exico. S t a t e g o ve rn me n ts a nd

t h e US Bureau of Land Management have j u r i s d i c t i o n over about

7 ,300 m i l e s o f t h e a pp ro x i ma t e l y 1 2 , 0 0 0 m i l e s of p i p e l i n e s i n

t h e G u l f .

G a s P i p e l i n e s . C o m p i l a t i o n s of DOT Forms F7100.2

( i n d i v i d u a l l e a k o r t e s t f a i l u r e r e p o r t ) a nd d a t a p re s e nt e d

i nAn A n a l y s i s o f R e po r ta b le I n c i d e n t s f o r Natural G a s Trans-

m i s s i o n and Gat her i ng L in es 1970 Through 1975 by t h e American

Gas A s s o c i a t i o n (AGA) p ro v i d e f a i l u r e t o t a l s , c a u s e s a n d o t h e r

d a t a c o n c e r ni n g g a s l i n e f a i l u r e s .

O ns ho re g a s p i p e l i n e m il e ag e f i g u r e s are b a se d o n AGA

d a t a . D i f f e r i n g mileage f i g u r e s were p u b l i s h e d by t h e AGA

( i n its p u b l i c a t i o n , G a s F a c t s ) , by t h e O i l and G a s J ou r n a l

(OGJ) i n i ts August 13, 1 9 7 9 i s s u e , a n d b y DOT i n 7100.2-

1

d a t a . I t a p p e a r s t h a t t h e OGJ f i g u r e s are based on o n l y 103

o f t h e a p p r ox i m at e ly 150 p i p e l i n e s i n s e r v i c e . The DOT gas

t r a n sm i s s i o n m i l e a g e s t a t i s t i c s are w i t h i n 2 p e r c e n t of t h e

AGA f i g u r e s b u t t h e DOT g a t h e r i n g l i n e mileage is only abou t

35 p e r c e n t o f t h e A G A ' s f i e l d and g a t h er i ng t o t a l . I t a p p e a r s

t h a t t h e l a t t e r d i s c r e p a n c y is c au se d by t h e l i m i t e d e x t e n t

of t h e j u r i s d i c t i o n a l a u t h o r i t y o f t h e DOT. Consequen t ly ,

AGA g a s p i p e l i n e mi le ag e f i g u r e s are u se d i n t h i s r e p o r t .

L iq ui d P i p e l i n e s . F or l i q u i d l i n e s , summaries o f DOT

Form 7000-1 f ro m 19 70 t o 1 9 76 , i n c l u s i v e , and d a t a i n a special

s t u d y by t h e N a t i o n a l T r a n s p o r t a t i o n S a f e t y Boar d (NTSB) t i t l e d

3-4


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Sa f e

S e r v i c e L i f e fo r Liqu id Pe t ro leum Pipe l ines" are used.

Mileage data are from t r i e n n i a l DO1 Mineral Indust ry and DOE

Energy Data r e p o r t s .

3. F a i l u r e s P e r 1 , 00 0 Mi1,es

Fig u re 3-1 shows p i pe l i ne mileage i n t h e Un it ed S t a t e s .

The t o t a l number of f a i l u r e s per year and t h e mi le ag e f o r t h a t

year h av e been t r a n s l a t e d i n t o f i g u r e s r e p r e se n t i n g f a i l u r e

t o t a l s p er year p e r 1 ,00 0 m i l e s o f p i p e l i n e (F ig u re s 3-2, 3-3,

3- 4). The f i gu re s permit a rough comparison of t h e th r ee

ca t ego r ie s (o f f shor e gas and l i qu i d , onshore gas , and onshore

l i q u i d l i n e s ) . However, t h e f a c t t h a t t h e r e a r e d i f f e r e n t

criteria f o r d e f i n i n g and r e p o r t i n g l e a k s i n g as an d l i q u id

l i n e s cannot be overlooked.

Onshore. Gulf of Mexico gas and l i q u i d l i n e s show an

in cr ea si ng number of f a i l u r e s between 1974 and 1978 with a

sharp peak i n 1975 t o 4 . 4 f a i l u r e s p e r 1 ,0 00 m i l e s (F ig u re

3-2). Offshore mi leage f i gu re s bef o re 1974 are not immediately

a v a i l a b l e .

G a s Pip e l ine s . Onshore gas l i n e s show a high of 2 .21

and a l o w o f 1 . 52 f a i l u r e s p e r 1,000 m i l e s i n t h e p e r io d 1970-76. An overa l l d e c l i n e i n f a i l u r e s p e r 1 ,0 00 m i l e s occurred

dur ing the 1970-76 per iod (F ig ure 3-3).

L iq ui d P i p e l i n e s , Onshore l i q u i d o i l p i p e l i n e s a l s o

show a. s t e a d y d e c l i n e s i n c e 1970 (F ig u re 3-4) r each in g a l o w

o f 0 . 93 f a i l u r e s p e r 1 ,0 00 m i l e s i n 1976.

3-5


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5

4

3

2

330 ,

325

320

t

-I--*---

/

0

-1

--

'70 ' 71 I 72 '73 ' 74 ' 75 I76 I77 I78

Onsh or e Gas Gatheri ng and Transmi ssi on Pipel ines (AGA, 1979)

DataUnavailable

/ *

*

@

mmm@

)O

e**

1

3ct.

2 30

225

220

215

3-6


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4.0

3.5

3.0

W

I

2.5

2.0

1.5

1974

888888888888888888

8881

1975 1976 1977 197

'::USGS

approved lines,Gulf of Mexico

Figure 3-2. Offshore" Gas and Oi l Pipel ine Failure s per 1,000 Mi les (USGS,1979)


18/60

Failures per 1,000 miles-_

-

w

I

00

Figure3-3, Onshore Gas Pipeline Failures per 1OOO Miles (DOT, 1978; AGA, 1979)


19/60

Failur.esper 1, 000 miles

1.6

1.5

1.4

1.3

w

I

c 1.2

1.1

1.0

0.91970 1971 1972 1973 1974 1975

Figure 3-4. Onshore Liquid Oil Pipeli ne Failures per 1,000 Miles

(DOT, 1979; DO1 , 1968, 1974; DOE, 1977)

19


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B. MODES OF FAILURE

1. Major Cau ses o f Fa i lu r e

Outs ide force ( a l s o descr ibed as equipment rupture) ,

co r r o s io n , an d tlunknownttor " other " r easo n s are t h e three

leasing c a us es of p i p e l i n e f a i l u r e ( F i g ur e s 3-5, 3-7 and 3-

8).

Sin ce 19 70 , o u t s id e f o r c e is c l e a r l y t h e dominant cause of

o ns ho re ga s a nd l i q u i d p i p e l i n e f a i l u r e s b u t fo r o f f s h o r e gas

and l i q u i d l i n e s , t h e three l e a d i n g c a t e g o r i e s o f c a u se s v ar y

i n r a n k in g from ye a r t o y e a r .

a. Outside Forces . P i p e l i n e r u p t u r es , a lmo st wi th

excep t ion generated by m a n ' s a c t i v i t i e s , are a major cause

of p i p e l i n e f a i l u r e s . T y p i c a l examples o f ou ts id e fo rc esare: onshore , excavat ing equ ipment, and o f f sho re , sh ip

an ch o r s an d f i sh in g t r a w l boards . For subsea Arctic app l i-

c a t i o n s , e x t e r n a l i m p a c t s c o u l d be l i m i t e d r easonab ly t o i ce

s c ou r a nd, t o a lesser e x t e n t t h a n i n temperate w a t e r s , s h i p

anchors .

Gas P i p e l i n e s . A University of Oklahoma report for

t h e DOT, "Analysis and Management of a P i p e l i n e S a f e t y I n f o r -

Mation System," concluded t h a t fo r onshore gas t r an smis s io nl i n e s , o n e o u t s id e force ( o r e x t e r n a l impact) l eak is equiva-

l e n t t o ap pr ox ima tely 95 co r r o s io n leaks i n terms o f p o t e n t i a l

danger . The conclus ion w a s based on a comparison of individ-

ual and annual DOT inc ide n t r e po r t s f rom 1970 t o 1973 a n d .

involved a weigh t ing fa c t o r formula t oo complex t o be d esc r ib ed

here. The 1 : 9 5 r a t i o w a s determined by d i v i d i n g t h e weigh t ing

f ac tor o f o u t s i d e f o r c e (18 .0) by t h a t o f co r r o s io n ( 0 .1 9 ) i n

Table 3-1.

L iq u id P ip e l i n es . Cor ro s io n w a s t h e l ead in g cau se

and equ ipment rup tur ing l ine w a s t h e second lead ing cause of

o ns ho re l i q u i d p i p e l i n e f a i l u r e s ( F ig u r e 3-8).

3-10


21/60

w

I

c

c

Percentage ofannua1 failure totals

70

60%

50%

4@ 0

3w0

20%

10%

0

b

44

b b

4

b

b

4

4

4

*

b

4

4

4

0

b

\

X

b

4

b

4

0

4

0

4

0.4

4

P

4

*.

.'.,

4

4 .

4

4

4

0

0

0

4

.

z

E

%

++++

Corrosion

*****- Outside Force

-

UnknownLJ

zero readings may indicate a lack of reports and not necessarily a lack of failures

1970 1971 1972 1973 1974 1975 1976 1977 -1978-

XUSGS

approved line s, Gulf of Mexico

Figure 3-5. Major Causes of Offshor e' Gas and Oil Pip eline Fail ures (USGS, 1979)


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Percentage ofannual,failure totals

25%

20%

15%

I

10

5%

0

-Mater ia l Fai lu re

- . - Other

-Actual or SuspectedWeather Damage

-- Constr ucti on Defecfailures

1970 1971 1972 1973 1974 1975 1976 1977 1978

'kUSGS

approved l ines, Gulf of Mexico

F i g u r e 3-6. M i n o r Causes of Offshore" Gas and Oil Pipeline Failur es (USGS, 1979)


23/60

0

1970 1971 1972 1973 1974 1975

Outside Force........

Material Failure- _

+++++ Corrosion

i c

Other-

A Const ruct ion Defec

Figure 3-7. Causes of Onsho re Gas Pipe line Failures (DOT, 1977)


24/60

Percentage ofannual failure totals

oTo It

1970 1971 1972 1973 1974 1975 1976

.* .0

Equipment

+++++ Corrosion

Rupturing Line

Other

Defective Pipe

- .-

--Defective Welds

- - - Incorrect,Operations

Figure 3-8. Causes of On shore Liquid Pipeline Fai lures (DOT, 1978)


25/60


26/60

Liqu id P i p e l i n e s . Onshore petroleum l i n e d a t a i n d i-

cate a d e c l i n i n g corros ion- c a u s e d f a i l u r e r a t e , Corros ion

f a i l u r e s f o r 1978 are about h a l f of t h e 1970 r a t e ( F i g u r e 3- 8).

Summaries of DOT Form 7000-1 e x t e r n a l c o r r o s i o n d a t a from 1970

t o 1977 show mixed r e s u l t s when var io us means of co r ro s i on

p r o t e c t i o n are compared. Coated pi pe w i t h c a t h o d i c p r o t e c t i o n

an d b a r e p ip e w i t h c a t h od i c p r o t e c t i o n h av e t h e h i g h e s t p er -

cen tag es of e x t e r n a l c o r r o s i o n f a i l u r e s f o r 1974 t h ro ug h 1 97 8.

N o d a ta on t h e number of m i l e s of each t y p e of co r ros i on p ro-

t e c t i o n is a v a i l a b l e n or are e x p l a n a t i o n s o f why t h e r e s u l t s

d i f f e r from t h e g a s l i n e da t a above .

c .Unknown

and "Other " Causes. A s t h e l a s t o f t h e

l e a di n g c a us es of p i p e l i n e f a i l u r e s , unknown and o t h e r

c a u s e s a r e , by n a t u r e , t h e most d i f f i c u l t t o d et e rm in e b ec au se

of a l a c k of d a t a .

Of f shore . A s shown i n Fi gur e 3-5, unknown causes

vary f rom 8 p e r c e n t t o 40 p e r c e n t an nu a l l y . However, t h e

small number o f i nc id en ts r epo r te d (see Subsec t ion 2 , I n f o r -

mation Sources) makes c on cl us io ns d i f f i c u l t , i f n o t imp o s s ib l e .

G a s P i p e l i n e s . Unknown o r o t h e r cau s es are n o t

a major cause o f onshore gas l i n e f a i l u r e s .

L iq ui d P i p e l i n e s . F a i l u r e s a t t r i b u t e d t oo t h e r

c a u s e s a r e i n c r ea s in g an d are t h e t h i r d l a r g e s t c au se of

f a i l u r e s from 1 970 t o 19 76 . .

2 . Minor Causes of Fai lure

Material f a i l u r e , i n c o rr e c t o pe r at i on fly carrier per-

s o n n e l , c o n s t r u c t i o n defects, weather , d e f e c t i v e w e l d s and

. other (gas and o f f s h o r e o n l y ) each account for approximately

20 p e r c e n t or less o f o n sh or e and o f f s h o r e p i p e l i n e f a i l u r e s

( F i g u r e s 3-6, 3-7 and 3-8). Offshore o t h e r cau s es are l i s t e d

i n Tab le 3-2w i t h v e r b a t im d es c r ip t io n s f r o m a U S G S Gulf of

3-16


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Table 3-2. Offshore O i l / G a s P i p e l i n e "Other " Causes

Desc r ip t ions of causes from USGS records f o r Gulf of Mexico

Year N o . o f Fa i l u r e s D e s c r i n t i o n of Cause

1970 0

1971 1 Severe ly k inked. Sp l i t a t kink.

1972 2 1) G a s reg ula tor malfunct ioned. H.P.P. malfunct ioned. Pipe

rup tured .

2 ) Suspect pre viou s damage t o f / l due t o c o n s t ru c t i o n .

1973

1974

1975

1976

1977

1978

2 1) Bul l p lug cove r ing 1/2 needle va lve in open posi t ion had

a h o l e i n i t . Poss ib ly caused by t ra wling.

2 ) Abrasion - rubb ing aga ins t ano the r p ipe .A t l a n t i c R i c h f i e l d ' s 8 l i n e r i p pe d o f f t h e C obi a l i n e a t t h e

subsea t i e- i n .

1) P / 1 k in k a f t e r t r y i n g t o move it away from 0 deco s w e l l

6 i n SS Block 119.

2 ) Mechanical f a i l u r e .

3) Lack of communication between operator.

( i l l e g i b l e )

P a r a f f i n p l u g p i p e l i n e s .


28/60

Mexico f a i l u r e r e p o r t c o m p i l a ti o n . I n F ig u r e 3- 6 , t h e p e rc en t-

a g es o f m inor c a u s e s o f o f f s h o r e f a i l u r e s f l u c t u a t e wi d el y.

When co n s id e r in g d a t a on o f f s h o r e l i n e s p r e s en ted h e r e , t h e

cau t io n g iv en e a r l i e r a bo ut t h e t o t a l number of f a i l u r e s n o t

b e i n g l a rge enough t o e s t a b l i s h a t r en d s h o u ld b e k ep t i n mind.

C . FAILURE COUNTERMEASURES FOR SUBSEA ARCTIC APPLICATIONS

S ub sea g a s and l i q u id p e t r ol eu m p i p e l i n e s i n t h e Arc t i c

are l i k e l y t o have c o r r os i o n a nd o u t s i d e f o r c e as t h e p r ime

p o t e n t i a l c a us e s of f a i l u r e . Because o f envi ronment- r e la ted

d i f f i c u l t i e s menti oned elsewhere i n t h i s r e p or t ( S e c t i on s I 1

and I V ) , f a i l u r e s i n subsea Arct ic areas are m o r e d i f f i c u l t

t o c on te nd w i t h t h a n i n t empera te areas . Consequent ly , pre-

v en t io n of f a i l u r e s c o u l d be of utmost impor tance . Prompt

d i s co v er y o f f a i l u r e s t h a t o c c ur d e s p i t e p r e c a u t i o n s a l so

would be of va l ue . However, i t is beyond t h e scope o f t h i s

r e p or t t o e va l u t e any t r a d e o f f s between env i ronmen ta l p ro tec-

t i o n an d p ip e l in e eco n o mics .

1. I mp ac t P r o t ec t io n

Ice s c o u r is t h e most f o r midab le imp ac t h aza r d a f f e c t in g

a s u b s e a p i p e l i n e . A s d i s c u s s e d i n S e c t i o n 11, t h e d e p t h ,f requency and locat ion o f s co u r in g is not known f u l l y . Pre-

v en t i o n of p i p e l i n e impact fr om i c e cou ld be accomplished b y

t r e n ch i n g b e lo w t h e a n t i c i p a t e d s co u r d ep t h ( S e c t i o n 1 V . D ) .

More r e se ar ch on sco ur dep t hs wou ld be of va lu e. Damage from

a n c ho r s and f i s h i n g a c t i v i t i e s pr o ba b l y would be small because

of t h e i ce cover which pre ve nt s s h i p movement f o r much of each

y e a r . During the open-water season , sea t r a f f i c is no t ex-

p ec t e d t o be of major consequence. Marking of p i p e l i n e l o ca-

t i o n s on maps shoul d be s u f f i c i e n t w a r n i n g .

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2 . Corros ion P revent ion

Coa t i ng a nd c a t hod i c p ro t e c t i on , as r e q u i r e d i n Par t s

192 and 195 s i nc e t h e e a r l y 7 0 1 s would be e s s e n t i a l for sub-

sea Arctic steel p i p e l i n e e x t e r n a l c o r r o s i o n p re ve n t i on . The

p o t e n t i a l f o r e x t e r n a l c o r r o s i o n would be similar for both gas

and l i q u i d pet roleum pi pe l i ne s . Arguments between impressed

cur ren t and s a c r i f i c i a l anode c a t h o d i c p r o t e c t i o n q u a l i t y are

moot because of t h e mai nt en an ce d i f f i c u l t i e s t h a t would be

encountered i f an impressed current s y s t e m were chosen. O t h e r -

wise , ex te rn a l cor ros ion probably would no t be aided o r hinder -

ed by t h e subsea Arct ic environment as compared t o a temperate

z on e l o c a t i o n . Although d i f f i c u l t t o accomplish, a s a t i s f ac to r y

e l ec t r i ca l ground for c o r ros i on c on t ro l c a n be ob t a i ne d i n

pe rmaf ros t .

I n t e r n a l c o r ros i on and erosion problems would be s i m i l a r ,

i f n o t i d e n t i c a l , t o c on t e mpora ry i n s t a l l a t i ons ;in tempera te

areas. Analyses of t h e commodity t o be car r i ed would be valu-

a b l e i n de t ermi ni ng t h e need, i f a n y , f o r i n t e r n a l p r o t e ct i o n .

I n t e r n a l p ipe c oa t i ng , a nd / o r sweeteningt1 of sour gas or o i l

before c o n t a c t w i t h t h e p i p e l i n e are p o t e n t i a l s o l u t i o n s i n

c u r r e n t p rac t ice .

G e n e r a l l y , t h e ma jo r d i f f e r e n c e i n c o r r o s i o n p r e ve n t io n

between temperate zone p i p e l i n e s and t h o s e b en ea th t h e Arctic

seas would be t h e p o s s i b l e desire t o r ed uc e t h e frequency of

corrosion- c a u s e d f a i l u r e s i n t h e l a t t e r as low as pos s ib le .

Judging from t h e h i g h i nc idence of cor ros ion- c au se d f a i l u r e s

i n t h e US , and presumably elsewhere i n temperate areas , con-

s iderab le p r og re s s coul d be real ized i n t h i s f i e l d .

3. Inspect ion and Moni tor ing

Reduction, i f no t p r e ve n t i on , of p i p e l i n e f a i l u r e s can

be aided by s c r up u l ou s i n s p e c t i o n d u r i n g f a b r i c a t i o n an d

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i n s t a l l a t i o n and by f r equen t and thorough monitoring of t h e

s y s t e m d u r i n g o p e r a t i o n . A w e l l-p l an ned program f o r preven-

t i v e maint en an ce is neces sa ry t o con t inued suc ces s fu l opera-

t i o n . Un f o rtu n a t e ly , env i ro nmen tal co n d i t i o n s and t r enched

l i n e s , i f u sed , gr e a t l y hamper monitoring and maintenance

e f f o r t s . Such cons ide ra t ion s may j u s t i f yoverdes ign ing

and excess ive care d ur i ng i n s t a l l a t i o n of p i p e l i n e s t o com-

pe ns a t e f o r t h e po ss ib le lack of access d u r in g o p e r a t i o n .

E x i s t i n g an d proposed changes i n inspec t ion and moni to r ing

requirements appear i n S e c t i o n V I of t h i s r e p o r t .

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I V . UNIQUE REQUIREMENTS OFARCTIC OFFSHORE PIPELINES

The Arctic env i ronmen t , d i scussed i n S e c t i on 1 1 , p r e s e n t s

some u n iq ue r e qu i re m en t s f o r o f f s h o r e p i p e l i n e d e s i g n , con-

s t r u c t i o n and o p e ra t i o n . The d i s c u s s i o n i n t h i s s e c t i o n is arev iew of key requirements which , i f n o t c o n s i d e r e d i n a p ipe-

l i n e p r o j e c t , c ou ld a f f e c t i t s s t r u c t u r a l i n t e g r i t y , s a f e t y

and environmental impact. The d isc uss ion o f t h e s t a t e- of- t h e-

a r t o f Arctic o f f s h o r e p i p e l i n e s p r e s e nt e d i n S e c t i on I covered

p r e s e n t t echnology and some o f t h e problems encounte red , and

r e f e r e n c e w i l l be made t o t h a t a n d o t h e r s e c t i o n s where

a p p r o p r i a t e .

A . MATERIALS

S t e e l is t h e p r e f e r r e d mater ia l f o r Arctic a p p l i c a t i o n s

because of h i g h s t r e n g t h , s u i t a b l e low- t emp er atu re p r o p e r t i e s

( r e s i s t a nc e t o crack p r opag a t i on ) and g o o d w e ld ab i l i t y . T i t l e

4 9 ( P a r t 1 9 5. 1 12 ) p e r mi t s o n ly s t e e l f o r new l i q u i d p i p e l i n e s ;

however, f o r gas p i p e l i n e s ( P a r t 192) t h e r e g u l a t i o n w i l l

allow t h e u s e of cast i r o n o r d u c t i l e i r o n p i p e s , a l though

t h e u s e i s p r i m a r i l y i n gas d i s t r i b u t i o n s y st e m s. O th er

a l l o y s are n o t co mp e t i t i v e w i th s t e e l f o r l a rge d iameter orh i g h p r e s s u r e p i p e . Although aluminum a l l o y s and t i t a n i u m

a l l o y s ca n h av e t h e same t o u g h n e s s r a t i o as s t e e l , t h e i r

s t r e n g t h is much lower a t co mp ara t ive l e v e l s . Th e r e f o r e ,

t h i c k w a l l s are r e q u i r e d for large a luminum pipes because

t h e s t r e n g t h is about h a l f t h a t of h igh- grade s t e e l , and t h e

t h e r m a l e x p a n s i o n c o e f f i c i e n t is t h ree t i m e s as grea t , l e ad -

i n g t o a p o t e n t i a l l y- h i g h t h e r m a l stress. Also , weld ing o f

aluminum p i pe l i ne se c t io ns wou ld be more d i f f i c u l t and c o s t l y .

I n a d d i t i o n t o t h e u s u a l s p e c i f i e d minimum y i e l d stress

( SMYS ) , t h e s a f e t y s t a n d a r d s f o r Arctic p i p e l i n e s should con-

s i d e r s t e e l behav io r a t low tempera tu res . Once i n s t a l l e d on

t h e sea bot tom, such p i p e l i n e s w i l l en co u n te r a r e l a t i v e l y

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impacted by a c a l i b r a t e d pend ulu m. An a b s o r b e d f r a c t u r e

impact energy of 205 (15 f t- l b ) g e n e r a l l y is c o ns i de r ed t o

be t h e minimum a c c e p t a b l e l e v e l f o r p l a i n carbon s t e e l s a t

some s p e c i f i e d t e m p e ra t u r e ( s e e Fi g u r e 4- 1). However, t h e

Charpy acceptance test h a s be en f o un d t o be l i m i t e d i n evalu-a t i n g materials s u s c e p t i b i l i t y t o p rema ture b r i t t l e f r a c t u r e .

The re are cases where s t e e l s were c o n s i d e r e d t o b e d u c t i l e

a t a g i v e n s e rv i c e t e m p e ra t u r e b e c a u s e t h e Ch arpy s p e ci m en s

e xh i bi t ed d u c t i l i t y a t t h i s t em pe ra tu re . I n s e r v i c e , b r i t t l e

f r a c t u r e o f t h e s t e e l o c c u r r e d . The d i f f e r e n c e w a s e x p l a i n e d

on t h e b a s i s t h a t s t a n d a r d Charpy t e s t i n g may n o t a c c u r a t e l y

d e te r mi n e t h e d u c t i l e - t o -b r i t t l e t r a n s i t i o n t e m p e r a t u r e . To

compensa te , t h e Charpy test s pe ci me n h a s be e n f a t i g u e p r e -

c r ac ke d t o b e t t e r r e l a t e r e s u l t s t o t h e n i l - d u c t i l i t y tempera-

t u r e (NDT), which is d e f i n e d i n ASTM STDE208-69.

The NDT is d e f i n e d t o b e t h e t e m p e r a t u r e a t which a

s m a l l f l aw may pr op aga te a t stresses n ea r t h e y i e l d stress.

NDT+60F (NDT+15'C)

i s cons ide r ed t h e t empera t u re above which

no u n s t a b l e c l e a v a g e c r a c k p r o p a g a t i o n c a n oc c u r a t stresses

a p p ro a c h i n g t h e SMYS. O t h e r b r i t t l e - f r a c t u r e criteria used

i n c o n j u n c t i o n w i t h t h e C h a r p y test are ba sed on f r a c t u r e

appea rance such as t h e d ro p w e i g h t t ea r test (DWTT); l i n e a r

e l a s t i c f r a c t u r e m ec ha ni cs s u c h as t h e c r i t i c a l stress i n t e n-

s i t y v a l u e ; o r e l a s t i c -p l a s t i c f r a c t u r e mechanics such as t h e

J- i n t e g r a l or c r i t i c a l cr ac k ope ning disp lac emen t (COD).

Charpy-V Notch and DWTT impact tests w e r e u s e d i n t h e

s e l e c t i o n o f mater ia l f o r t h e T r a n s A l a s k a P i p e l i n e Sy s t e m

from Prudhoe Bay t o P or t Valdez ( O i l and G a s J o u r n a l , 1 9 7 4 ) .

P a n a r c t i c G a s L i n es r e q u i r e d a 345 ( 2 5 f t - l b ) Charpy impact

v a l u e a t minus 50C (minus6 0 F )

(Pa lmer , 1979) .

Two i mp or ta nt f i e l d o p e r a t i o n s i n p i p e l i n e c o n s t r u c t i o n

w i l l b e a f f e c t e d by Arc t i c e n vi ron m en t : p i p e b e n d i ng a nd g i r t h

w e l d in g . To m in im iz e t h e e f f e c t o f l ow t e m p e ra t u r e s , s uc h

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Transition ,Zone

Increasing Temperatu re->

Figure 4-1. Charpy Transi ti on Temperatur e (Azmi, 1978)

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opera t ions usua l ly have been per fo rmed w i t h a prehea ted p i p e

or i n a p r o t e c t i v e e nc l osu r e (Hanamoto, 1978, TAPS experience.).

In view of t h e p a r t i c u l a r importance of flaw-free bends and

welds f o r Arctic o f f sh o r e p ip e l in es , and t h e d i f f i c u l t y of

access, 100-percent non- d es t r uc t iv e t e s t i n g o f b o th sh o uld be

r eq u i r ed .

The s a f e t y s t an d a r d s fo r Arctic o f f s ho r e p i p e l i n e material

sh o u ld sp ec i f y a des ign requi rement f o r c rack -propagat ion resis-

t a n c e a t t h e lowest an t i c i pa te d s er v i ce tempera tu re (LAST) and

a t t h e h i g h e s t stresses encountered du r ing pi pe handl ing and

f i e l d operations. However, t h e des igner shou ld be free t o

select t h e mater ia l- acc ept anc e method, and a way should be l e f t

open f o r f u t u r e material improvements.

B. PRESSURE-TEST PROCEDURES

P r e s s u r e- t es t p rocedures f o r milder cl imates are w e l l -

e s t a b l i s h e d from experience w i t h many thousands of m i l e s of gas

and o i l p i p e l i n e s b u i l t bo th onshore and of f sho re . Spec i a l

p r o v i s i o n s must be made, however , f o r p ressu re- t es t in g under

Arctic co n d i t i o n s su ch as those exper ienced dur ing t h e TAPS

an d Pan a r c t i c p i p e l i n e c o n s t r u c t i o n s .

Because t h e s h o r t Arct ic summer p e r i o d is t h e only t i m e

when temperatures are above f reezing, many construct ion and

i n s t a l l a t i o n a c t i v i t i e s , i nc l ud in g p i p e l i n e pr e ss u re t e s t i n g ,

w i l l ha ve t o be done i n win ter a t sub- f r eez ing tempera tu res .

P a s t e x pe r i en c e on i n s t a l l e d p i p e l i n e s i n d i c a t e s t h a t a 24-hour

h y d ro t e s t is p r e f e r a b l e t o a gas t e s t when o pe ra ti ng above t h e

NDT. Compared t o gases, non- compress ible l i qu i ds p rov ide

greater test s a f e t y , easier leak d e t e c t i o n , a n d smaller p r e s s u r e

va r i a t io ns when sub jec te d t o t e m p e r a t u r e d i f f e r e n t i a l s . If

water is u se d f o r t e s t i n g a t s ub - z e r o t emp er a tu r e s , it must i n-

c l u d e a f r eez ing-po int de pr es san t . c o n s i d e r a t i o n should be

given t o any environmental impact r e s u l t i n g f rom t h e d i s p o s a l

o r storage of t h a t medium.

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I n a d d i t i o n t o any onshore pressure- t e s t of p i pe s e c t i o n s ,

a p i p e l i n e i n s t a l l e d i n a t r ench shou ld be tested a f t e r b e i ng

covered w i t h f i l l material. Cons idera t ion also should be given

t o an a d d i t i o n a l p r e s s ur e t e s t before t h e p i pe is covered.

Although t h e a d d i t i o n a l t e s t would involve increased cost and

r e q u i r e a d d i t i o n a l t i m e , i t may be desirable i n v iew of t h e

d i f f i c u l t i e s i n vo lv ed w i t h p o s s i b l e r e p a i r s of a b u r i e d p i p e .

Ice cover and l i m i t e d a c c e s s i b i l i t y w ar ra nt t h a t a l l r easonab le

s teps be t a k en pr omp tl y du r i n g p i p e l i n e i n s t a l l a t i o n t o a s s u r e

t r o u b l e- f r e e f u t u r e o p e r a t i o n s . S a f e t y s t a n d a r d s for Arctic

o f f s h o r e p i p e l i n e s s h o u l d re f lec t appropr ia te p r e s s u r e- t e s t

requirements .

C . PIPELINE DES IGN AND CONSTRUCTION

Environmental hazards d i scu s sed i n Sec t io n 1 1 , and

specia l c o n s t r u c t i o n a nd i n s t a l l a t i o n p r oc e du re s prepared by

R . J . Brown and Associates, and adopted on th e Pana rc t i c o f f-

shore gas l i n e i n t h e Canadian Arctic Sea d i scu s sed i n Sec t io n

I , g ave an i n s i g h t i n to p ro blems p e cu l i a r t o t h e design and

co n s t r u c t io n o f Arctic o f f sh o r e p i p e l i n e s .

In view of these , requirements f o r p i p e l i n e d e s i g n , con-

s t r u c t i o n and i n s t a l l a t i o n must c o n si d e r :

0 Unique heat t r a n s f e r probl ems a s s o c i a t e d with

of f sho re and onshore permaf ros t (Sec t i on 11.

C.2).

0 A d e t a i l e d and r e a l i s t i c l o g i s t i c s p la n f o r

unexpected con t in genc ies due t o remoteness

of t h e a r e a , t r a ns p o rt a t i o n d i f f i c u l t i e s

a n d s c a r c i t y of l oca l manpower and equipment.

0 The e f f e c t of h o s t i l e environment (low t e m-

p e r a t u r e , poor v i s i b i l i t y ) on o pe r at o r

e f f i c i e n c y and a b i l i t y t o perform work under

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u n p ro t ec t ed co n d i t i o n s . T h e re f o r e , t r a i n i n g

programs more s t r i n g e n t t h an t h o s e fo r s imilar

work i n temperate climates might be necessary .

The need f o r special equipment f o r permaf ros t

t r en ch in g , for some d i ve r l es s oper a t i ons , and

f o r i ce c u t t i n g , may r e q u i r e e a r l i e r des ign

and development.

U s e of s t r i n g e n t s a f e t y m ea sur es t o p re ve nt

f i r e and /or exp los ion i f heated en c lo su r es

are used f o r some operat ions .

Ut i l i z a t i o n o f advanced n o n- des t ruc t ive

i n s p ec t i o n t ec hn iq ue s u s i n g h y d r o s t a t i c t e s t s ,

such as aco u s t i c emis s io n as a means of loca t-

i n g defects and e s t i m a t i n g t h e l e v e l o f s e v er -

i t y of t h e defect.

p i p e l i n e c o n s t r u c t o r w i t h U n i t e d Sta tes and/or Canadian

Arctic ex p e r i en ce b u i ld in g a p i p e l i n e would be cognizant of

t h e sp ec i a l r eq u i r emen t s l i s t e d above. In t h a t case, a l l t h a t

migh t be r e q u i r e d i n t h e s a f e t y s t a n d a r d s would be a g en e r a l

i n t r o d u c to r y comment r eg a r d in g t h e items mentioned above.

D. EXTERNAL LOADS

I n d i s c u s s i n g e x t e r n a l loads on Arct ic of fshore p i p e l i n e s ,

a t t e n t i o n w i l l be focused on t h e effects of pe r ma f r os t , ice-

imposed l o a d s , wave an d cu r r en t ac t i o n , s e i smic i ty , and thermal

expansion or c o n t r a c t i o n . (The l a s t cou ld be cons idered e i t h e r

a n e x t e r n a l o r an i n t e r n a l l o a d . ) Each of these loads may add

t o t h e r ad i a l and/or ax i a l stresses i n t h e p ipe an d th e r e f o r eshou ld be c o n s i d e r e d i n t h e p i p e l i n e d es ig n .

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1. Permafrost

The d i scu s s io n o f su bsea pe r maf r os t i n t h e Beauf o rt Sea

( Sec t io n I I . C . 2 ) noted t h a t ice- r ich permafros t e x i s t s i n a

non- con tinuous f ash ion i n t h e sha l low waters of t h e Arctic

Ocean, and t h a t i t becomes cont inuous and close t o t h e s u r f a c e

nea r and on t h e shore . Consequen t ly , an o f f s hore Arctic pipe-

l i n e i n s t a l l e d i n a tr en ch may enco unter dis con tin uous perma-

f r o s t w i t h i n t h e dep th of t h e t r e n c h i n s h a ll o w waters and

w i l l cr oss con t inuous permafros t i n its onshor e approach. The

s u bs e a p e rm a fr o st , b e i n g c l o s e t o 0 C (32F) ( sea water temper-

a t u r e is approximately minus 1 . 8 O C ) , is n e a r i ts thawing point

and its eq u i l i b r iu m is determined by temperature and water

s a l i n i t y . T h u s , a small amount of heat a d d i t i o n or e x t r a c t i o nmay change t h e p h y s i c a l cha r ac t e r i s t i c s o f t h e permafros t

d r a s t i c a l l y , making i t t h e most d i f f i c u l t t e r r a i n problem

(Phukan, 1979). I n g en e r a l , d i s tu r b ed p e r maf r o s t e i t h e r w i l l

thaw i f heat is added ( a s w i t h a heated o i l p i p e ) , or w i l l

grow by f r e e z i n g i f heat is e x t r a c t e d ( w i t h a c h i l l e d - g a s

p i p e l i n e , f o r i n s t a n c e ) .

The t hawing of ice- rich f ine- g ra in ed s o i l s u s u a l l y is

accompanied by su r fa ce weaken ing and se t t l emen t . The se t t l e-ment w i l l be caused by t h e volume decrease of ice thawed i n t o

water and by t h e t h a w c o n s o l i d a t i o n of t h e s o i l . Thaw con-

s o l i d a t i o n h a s been c a l c u l a t e d ( C r o r y , 1973) from measured

v a l u e s o f specific weight of dry- frozen, and dry- thawed s o i l .

The r e s u l t i n g s u bs i d en c e ca n create down-drag loads on a p ipe

and must be cons idered i n p ip e l in e des ign (Huck, 1979). I n

d i sco n t in u o u s ice- r ich s o i l s i t u a t i o n s , a w a r m o i l p i p e cou ld

behave l i k e a beam immersed i n a d e n s e f l u i d w i t h suppor t a t

i n t e r v a l s a l o n g its l e n g t h (Walker, 1978). The l e n g t h of t h e

unsupported p i p e spans , and t h e d e f l e c t i o n of t h e p i p e w i l l

determine t h e r e s u l t i n g stresses. A mathematical model of

such a p i p e has been de sc r ibe d (Walker, 1 9 7 8 ) , and p ipe stresses

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due t o bending, s a g , temperature d i f f e r e n t i a l , and i n t e r n a l

p r e s s u r e were c a l c u l a t e d .

If th e thawing of permafrost r e su l t s i n formation of

s l u r r y w it h a very l o w shea r stress, a gas p ipe o r an empty

o i l p i p e l i n e may have a p o s i t i v e buoyancy and, wi thout adequate

overburden weight, w i l l t end t o f l o a t and move upward. To

prevent t h i s , a p ipe may be anchored t o t h e sea bottom o r pro-

vided with weight coa t ing (usua l ly concrete) s u f f ic i e n t t o

i n s u r e a ne gat iv e buoyancy under t h e most a dverse co ndit ions .

A p o t e n t i a l thaw subsidence problem w a s encountered i n

t h e c o n s tr u c t i on of t h e T ra n s Alaska p ip e l i ne . There, i n

regions of p o t e n t i a l l y u ns t a b l e permafros t , t h e p ipe w a s ele-

va t ed on ve r t i ca l suppor t members which were cooled by heat

p ipes t o prevent loca l permafrost degradat ion, A s imi la r

s o l u t i o n may not be p os s i b l e f o r Arctic o f f s h o r e p i p e l i n e s .

Other means, s uch as p ipe i n s u l a t i o n o r gr anu la r bedding

material ( J a h n s , 1973) would have t o be provided f o r p i p e l i n e

s a f e t y when cross ing thaw- sensi t ive s o i l d . The effect of p ipe

insu l a t i on on t h e s ize of a thaw plug forming around a p ipe is

i l l u s t r a t e d i n F igu re 4-2. The importance of thaw subsidence

on pipe i n t e g r i t y can be i l l u s t r a t e d by a n i n c i d e n t w i t h t h eTrans Alaska O i l Pipeline. Thawing of a n ice l e n s below t h e

d i t c h i n one of its bur ied s e c t i o n s r e s u l t e d i n a sagging of

t h e p ip e , followed by wrinkl ing and r u p t u r e ( O i l and G a s

Journal , Ju ly 1979) .

Frost heave can occur when a p i p e l i n e , having a tempera-

t u r e below f re ez ing , crosses s a t u r a t e d s o i l s w i t h high water

pore pr essu res . Any unfrozen Water w i l l t en d t o freeze around

t h e p ipe forming a f r o s t bulb. The increase i n t h e volumewith phase change from water t o i c e , and t h e migrat ion of water

t o t h e f r o zen / u n f r o zen i n t e r f a c e , may cause formation of segre-

gated i ce l e n s e s , as shown i n t h e upper p a r t of Figure 4-3,

and r e s u l t s i n f r o s t heave. The increase i n ice volume would

4-9


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E

s

E 50

0

4

3

2

1

0

F i g u r e 4 - 2 . Depth of Thaw for Insulated

4-10

and Bare Pipe at 2 and 3 Years

(Jahns, 1973)


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(see Sec t io n I ) , may n o t be feas ib le i n those p a r t s of t h e

Beaufor t Sea no t p ro tec ted by o f f s h o r e i s l a n d s .

I n t h e sp r in g b reak - u p p e r io d , or i n t h e freeze- up dur ing

t h e f a l l , a c c e s s i b i l i t y by barges is n o t p rac t ica l . Thus,

p ipe- l a y in g i n t h e Arctic o f f s h o r e r e q u i r e s c a r e f u l p l a n n i n g

and prov is ion of contingency f o r many op er at i on s. These in-

c l u d e t r a n s p o r t a t i o n , f i e l d work, p i p e l i n e i n s t a l l a t i o n , and

check-out procedures. The t echno logy t o do t h e work is a v a i l-

ab le , b u t it shou ld be used i n an imagina t ive , innovat ive and

well-planned manner.

Ice s c o u r , d i s c u s s e d i n d e t a i l i n S ec t io n I I . B , is a rea l

hazard t o p i p e l i n e s i n sha l low p a r t s of t h e Beaufor t Sea. As

i l l u s t r a t e d i n Fi gu re 2-

7 ( Sec t io n I I . B . 3 ) , t h e dep th o f s cour

and its frequency are a f u n c t i o n of water de pt h, sc ou rs becom-

i n g deeper b u t less f r eq u en t i n deeper waters. Some o f t h e

moving blocks of i ce , w i t h large mass and i n e r t i a , c o u ld scrape

t h e sea bot tom, a f f e c t i n g t h e s a f e t y o f p i p e l i n e s a nd cables

u n l e s s spec ia l p r o t e c t i o n is provided ( Sec t i on I ) .

Ice a c c r e t i o n , as related t o p i p e l i n e s y s t e m s , may affect

t h e o p e r a t i o n of pumping s t a t i o n s by b locking compressor i n l e t s ,

a problem en co u n te r ed i n t h e Prudhoe Bay development. The r a t e

of i c e accret ion depends on a i r , on sea water temperature and

o n t h e wind force, as shown i n Fi gur e 4-4. Ice accret ion is

d i sc u ss e d f u r t h e r i n pa r t 5.2 of t h i s s e c t i o n . P i p e l i n e f a i l -

ure modes due t o permafrost and i ce a re shown i n Fig u r e 4-5.

3 . Waves and Cu r r en t s

Waves and currents i n t h e Beaufor t Sea w e r e d i s c u s s e d i n

Sec t io n I I . A , which s a i d t h e normal waves and currents are

small when compared w i t h mi d- l a t i t u d e areas. Table 2-1 shows

estimates of maximum (storm) wave h e i g h t s for v a r i ou s r e t u r n

pe r io ds . These v a lu es are a l s o c o n s id e r a bl y lower than those

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Ice Scour\

;(-' I- - --I' \.\- - ---

Frost Heave

1

I . . . Frozen- Soil

IceImpact

at Shoreline

I * .

Subsidence

- .

Figure 4-5. Arctic Offshore Pipeline Failure Modes Due to Ice and Permafrost


47/60

expe cted i n o t h e r OCS locat ions . P i p e l i n e b u r i e d i n t h e gr ound

or o t h er w i se p r o t e c t e d a g a i n s t i ce f o r c e s woul d n o t b e a f f e c t e d

by waves and c u r r e n t s ex ce p t i n t h e s u r f zone . Here, a p i p e

may b e s u b j e c t e d t o s o i l mass movement or ve r t i c a l erosion o f

s e v e r a l f e e t p e r y e a r , as r e p o r t e d i n t h e Outer C o n t i n e n t a l

Shelf Environmental Assessment Program (OCSEAP Synthesis Report,

1978) . I n t h e n e ar - shore area o f f t h e s u r f z o n e , waves a l s o

may induce cyc l i ng stresses i n t h e sea bottom whi ch may ca us e

a p r o g r e s s i v e b u i l d u p of p o re p r e s s u r e , l e a d i n g t o s o i l l i q u e-

f a c t i o n and l o s s o f s u pp o rt f o r a p i p e c r o s s i n g such a r e g i o n

(Seed and Rahman, 19 77) . Cons eque ntl y, du ri ng i ts p e r i o d of

o p e r a t i o n al l i f e , t h e b u r i a l d ep th must be l a r g e enough t o

p r e v e n t p i p e exposure i n a l l s u c h l o c a t i o n s .

P e r h a p s t h e most s i g n i f i c a n t e f f e c t o f waves and c u r r e n t s

w ou ld b e d u r i n g t h e p i p e- l a y i n g o p e ra t i o n . The t e c h no l o g y o f

d e a l i n g w i t h t h i s pr ob lem w a s e s t a b l i s h e d i n t h e Gu lf of Mexico

a nd N or th S ea o p e r a t i o n s . The a d d i t i o n a l h a z ar d o f f l o a t i n g

ice i n t h e Arct ic o f f s h o r e may r e q u i r e some f u r t h e r p r e c a u t i o n s

and con t ingency measures.

4 . S e i s m i c i t y

The seismic c h a r a c t e r i s t i c s of t h e B ea u fo r t S ea o f f s h o r e

have been reviewed i n S e c t i o n I I . C . 4 . I n t h e s o u th e r n p a r t o f

Alaska ( t h e Anchorage, Por t Va ldez area) h i g h- i n t e n s i t y , seis-

m i c e v e n t s w e r e r e c o rd e d , and h ad t o be c o n s i d e r e d i n t h e

d e s i g n of t h e T r a n s A l a s k a p i p e l i n e . On t h e o t h e r h and , t h e

e s t i m a t e d s e i s m i c i t y o f t h e B e a u fo r t Sea i s of low magnit ude,

w i t h a p r e d i c t e d 100-year return period and maximum l a t e r a l

a c c e l e r a t i o n s o f o n l y 0 . 12 g ( E I A , 1 9 7 9 ). No a c t i v e f a u l t s

w e r e i d e n t i f i e d i n t h e B e a uf o r t S e a o f f s h o r e . C o ns e qu e nt l y,p i p e l i n e s d es ig n ed t o w i t hs t a nd t h e e x t e r n a l l o a d s di s c u s s e d

p r e v i o u s l y sh ou l d b e able t o resist p r e d i c t e d seismic e v e n t s .

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5 . Thermal Expansion or Contract ion of a Pipe

Although thermal expansion or contraction may not be

considered an e x t e r n a l l o a d i n a bu r i ed and r e s t r a i n e d p i p e ,

such stresses w i l l be generated as a r e s u l t of p ipe- t o- so i l

in te rac t ion . Luscher e t a1 (1979) ana lyzed the case of f u l l y-

r e s t r a ined , the rma l ly- expanding p ipe l ine s . The l o n g i t u d i n a l

force F1 genera ted in such a case is:

F1 = As x ( E x u x AT -V X U H + 0 . 5 x U H )

F1

=

As (EaAT

- v u H + 0 . 5aH)

As - Pipe w a l l cross- sec t ion area

E - Pipe material modulus of e l a s t i c i t y

a - Pipe material c o e f f i c i e n t of thermal expansionAT - Temperature d i f f e r e n t i a l

v - Poi s son ' s r a t i o

aH

- Hoop stress caused by a n e t i n t e r n a l p r es s u re

The first t e r m i n t h e above equation represents thermal

f o r c e , t h e second t h e Poisson ' s r a t i o effect, and t h e t h i r d

t h e ax ia l f o r ce caused by i n t e r n a l p r e s s u r e .

As a r e s u l t o f t h e longi tudina l compress ive force , a

p ipe may buckle i n t h e d i r e c t i o n o f l eas t r e s t r a i n t . The

i n t e r a c t i o n of t h e surrounding s o i l dur ing t h e overbending,

sidebending and sagbending of a p ipe has been s tudied (Luscher

e t a l , 1979). The p i p e movement w i l l be r e s t r a i n e d by t h e

combination of i ts own w e i g h t , t h e overburden weight, and by

s o i l shear strength. Once a bend starts i n a b u r i ed p i p e l i n e ,

large r ad ia l forces can develop which are resisted by t h e

surrounding s o i l . To quote Luscher e t a1 (1979):

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I

...as r a d i a l disp lacements occur a t t h e b en d,t h e p i p e t e n d s t g move lon gi tu di na l l y through

t h e s o i l toward t h e bend, and i n so doing

mobilizes l o n g i t u d i n a l s h e a r stresses which

reduce t h e long i tud ina l and hence t h e t r a n s-

v e r s e force at t h e bend. S a t i s f a c t o r y des ign

of t h e bends r e q u i r e s t h a t t h e a c t u a l r a d i a l

bend force is i n e q u i l ib r i u m w i t h t h e resist-

i n g forces provided by t h e sur rounding s o i l ,

a nd t h a t p i p e stresses and p i p e s t r a i n s are

with in a l lowable l i m i t s f o r r easo n ab le p i pe

displacements.

Should t h e compressive stresses i n t h e bend exceed t h e

y i e l d s t r e n g t h of t h e p i p e mater ia l , a wr in k l in g of t h e p i p e

may occur . US s a f e t y s tandards a l low no wr ink le bends in

h ig h ly- s t r e s sed p i pe s (above 30% of SMYS, Sec. 192.315 and

above 20% of SMYS , Sec. 195.212) . T h er e f o r e , s a f e design must

en su r e a maximum bend curvature below t h e c r i t i c a l c u r v a t u r e

of wrink l ing . For such a n a n a l y s i s , s o i l p r o pe r t i e s and t h e

l o c a t i o n of p o s s i b l e thaw su b s id en ce ( o r f r o s t heave) areas

must be known.

In a r e c e nt f a i l u r e i n v e s t i g a t i o n of t h e TAPS ( O i l and

G a s J o u r n a l , J u l y 1 9 7 9 ) , i t w a s p o s t u l a t e d t h a t t h e l i n e s ag ge d,

wr inkled and f r a c t u re d because o f t h e e x i s t e n c e of unknown ice

lenses below t h e p i p e . These thawed even tua l ly , and t h e p i p e ,

covered w i t h a heavy overburden, sagged and buckled.

The geometry of a n unbur ied p i p e u s u a l l y a l l o w s s u f f i -

cient movement s o t h a t thermal stresses are n o t s i g n i f i c a n t .

I n a coo led p i p e ( p ip e t emper a tu re lower i n o p e r a t i o n

t h a n d u r i n g i n s t a l l a t i o n ) t h e first t e r m i n t h e e q u a t i o n i n D 5

w i l l be n eg a t iv e . T h e r m a l l y induced compressive stresses i n

t h e p i p e then w i l l be lower o r even may disappear . Thus, t h e

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The co n s t r u c t io n o f t h e TAPS and t h e Pru dhoe Bay p ro-

d u c t i o n f a c i l i t i e s h a s p r o v i d e d v a l u a b l e e x p e r i e n c e i n Arctic,

l o g i s t i c s ( Jah ns , 1978) . Mar ine t r an sp or t by barges th rough

t h e Beaufo r t Sea is economica l , bu t it r e l i e s on an ice-free

water p a t h i n summer. I n some y e a r s , t h i s may n o t o c c u r .

For b a r g e unload ing , causeways may provide the sa fe s t and

l eas t economica l ly damaging means o f heavy l oad t r a n s f e r t o

onshore si tes.

Both f ixed wing a i r c r a f t ( H e r cu le s 130, Twin O t t e r ) and

This mode

h e l i c o p t e r s ( B e l l 205) f r e q u e n t l y were used f o r t r a n s p o r t o f

l o a d s ( up t o 20 t o n s i n t h e case of t h e H e r c u l e s ) .

is e x pe n si v e , r e q u i r e s c o n s t r u c t i o n of l a n d i ng s t r i p s or p ads ,

and is s e n s i t i v e t o weather c o n d i t i o n s .

R o l l i g o n s are t h e o ff - road veh ic le s most u sed on t h e

North S lope . They can c r o s s t h e t u n dr a a f t e r i t d r i e s , a n d

c a n o p e r a t e o n i ce as t h i n as 0.6m ( 2 f t ) because of t h e low

g r o u n d p r e s s u r e t h e y e x e r t .

E xc ep t f o r l i m i t e d us e o f t h e Canadian B e l l Voyager and

a i r- cu s h ion ed b a r g es , a i r - c u sh i on v e h i c l e s( A C V ' s )

have had

r e l a t i v e l y l i t t l e u s e i n A las kan o i l / g a s o p e r a t i o n s .

E x i s t i n g t r a n s p o r t a t i o n m e a n s are now adequa te t o suppor t

e xp lo ra t or y a c t i v i t i e s , b u t are n o t s u f f i c i e n t f o r year - round

s u p p o r t o f o p e r a t io n s i n o f f s h o r e o i l / g a s f i e l d s . For t h a t

pu rpose , c o n s t r u c t i o n of ad d i t io na l permanent r oad s , causeways ,

and perhaps a w i de r u s e of m ore r e l i a b l e A C V ' s would be r equ i red .

Tab le 4- 1 p r e s e n t s a l i s t i n g o f t r a n s p o r t a t i o n m e a n s , concerns ,

and gaps s t i l l e x i s t i n g i n t e chn o lo g y an d b a s e l in e d a t a .

Summarizing t h e t r an s p o r t a t i o n p ro blem, f o u r modes of-

t r a n s p o r t c an be co n s id e r ed :

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TYPE

MARINE

ICESURFACE

AIR

AMPHIR

rous

A L L -

WEATHERYEAR -

AROUND

EXAMPLES

SURVEY SI.iIF S0

SUPPLY BARGES

0 TRUCKSSLEDS

0 ROLLIGON

F t X E D - W I N G

0 I-1ELICOPTER

0 ACV

0

CAUSEWAYS

Table 4-1. Logistics Support

CONCERNS

0 SUMMERICE0 ODER. COST

HAZARDS

0 ICE THICKNESS@ SNOW DRIFTING

ICEMOVEMENTRIDGING

0 RUNWAY0 WEATHER

DOWNTIMECOST

0 RELLABILITY0 I E RIDGE

CROSSING

0fCE PRESSURE

0 ICE OVERRIDE0 WAVE EROSION0 GRAVEL AVAIL.

MAR INE BIOTA

0

11IDGE-C;ROSSIN GTECHNIQUES

0 IMPROVE13

0

RE L I ARJL I T Y

INCR EASF; >GND. CLEARANCE

JMP14OVED

I C E

FORECAST

0

I E PJIESS

O V ill R I I)EO C E A N O -

C R A '1 11C

LIFE

a U E N T H I C


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I

0 Marine, By Sh ip s, Barges and Tan ker s. The

co n s t r a i n t on t h i s mode is t h e s h o r t s ea so n

(approx imate ly 60 d ay s ) and t h e s h a l lo wn es s

of t h e water i n t h e g e n t l y s l o p i n g B ea u fo r t

Sea which p ut s a l i m i t a t i o n on t h e d r a f t o ff l o a t i n g v e ss e l s .

0 T e r r e s t r i a l- Over land , There are c o n s t r a i n t s

on t h i s mode of t r anspor ta t ion . F rom l a t e

s p r i n g u n t i l t h e e a r l y f a l l ( June t o e a r l y

O ct ob er ) t r a v e l a c r o s s t h e t u nd r a w i t h ' heavy-

wheeled a n d t r a c k e d v e h i c l e s is n o t p e r m i t t e d .

The f r a g i l i t y of t h e thawed ac t i ve vegega t ion

layer above t h e permafros t would be a f f e c t e dby t h e passage o f any high-ground-pressure

wheels or t r a c k s . Only a i r cu s h io n v eh ic l e s

an d s p ec i a l l o w-ground-pressure r o l l i g o n s

cou ld be cons idered .

0 T e r r e s t r i a l Over Snow or Ice . T h i s mode of

t r a n s p o r t a t i o n is p o s s i b l e i n w i n t e r when t h e

sea ice is t h i c k enough t o sup por t moving

loads . Add i t iona l suppor t a l s o may be ga ineda t some l o c a t i o n s by c o n s t r u c t i n g i ce roads

or i c e ag g r eg a t e p ad s p e r mi t t i n g w i n t e r t r a n s-

p o r t a t i o n of equipment and s u p p l i e s .

0 A i r . One c o n s t r a i n t i n t h i s mode of t r a n s p o r -

t a t i o n us ing f ixed -wing a i r c r a f t or h e l i c o p t e r s

i s weather ( v i s i b i l i t y , wind, p r e c i p i t a t i o n ) .

A second is t h e a v a i l a b i l i t y of landing and

t a ke o ff s t r i p s , f o r fi xed -wing a i r c r a f t , whichi n w i n t e r c o u ld be b u i l t on i c e , b u t i n summer

would require a subs tan t ia l amoun t of sand and

g r a v e l .

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G . COMMUNICATIONS

The communication between of f shore and onshore f a c i l i t i e s

r e l a t ed t o p i p e l i n e o p e r a t i o n concerns s a f e t y and s t r u c t u r a l

i n t e g r i t y of p i p e l i n e and a s s o c i a t e d equipment; p i p e l i n e per-

formance and o i l / g a s f low con t r o l ; and per sonnel s a fe t y and

h e a l t h .

In view of t h e d i f f i c u l t y i n t r a n s po r t a t i on and accessi-

b i l i t y discussed above , r e l i a b l e communication channels, im-

perv ious t o Arct ic weather cond i t ions are impor tant . Because

of t h i s , i t would be prudent t o prov ide a backup t o t h e p r i m a r y

communications system, an approach usually taken by p i p e l i n e

o p e r a t o r s . For i n s t a n c e , t h e TAPS communications s ys t e m con-

sists of p r imary microwave s ta t ions , a network backed up w i t h

s a t e l l i t e- t r a n s m i t t e d s i g n a l s ( M e r r e t t , 1 9 7 9 ) , and radio. I n

t h e proposed Alaskan Arctic G a s P i p e l i ne p r o j e c t , t h e communi-

cation concept used microwave s ys t e m s c o n s i s t i n g of f i v e

primary communication sites and four repeater si tes , one

located between each o f t h e p r ima ry s i t e s (Alaskan Arctic Gas

P i p e l i n e C o . 1974) . A s i mi l a r a p p r o a c h , u t i l i z i n g some of t h e

microwave chann els of t h e TAPS w a s proposed by Alcan G a s .

I n t h e ope ra t i on of pumping s t a t i o n s , development is

under way t o automate some of t h e f u n c t i o n s t o r e d u c e t h e

number of pe rson nel i n remote out po st s (Schaferman, 1974) .

Any automated f u nc t i o n would need r e l i a b l e t r an smis s io n of

s i g n a l s t o and from a c o n t r o l c e n t e r .

The r equ i red technology and exper ience i n communications

i n t h e Arctic environment is a v a i l a b l e , a n d i t would be desir-

able f o r p i p e l i n e s a f e t y s t a n d a r d s t o emphasize t h e importance

of t h i s f u n c t i on and t o stress t h e r e l i a b i l i t y aspects .

4-24


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I

H . SURVEILLANCE AND MONITORING

The s t a t u s o f t ec hn ol og y f o r s u r v e i l l a n c e a nd mo n it o ri n g

w a s d e s c r i b e d b r i e f l y i n S e c t i o n I . F . P er fo rma nc e o f t h e s e

f u n c t i o n s f o r Arctic o f f s h or e p i p e l i n e s is c ons t r a i ne d by

se ver e envi ronmenta l con di t ion s . Approximately 80 pe r ce n t of

t h e t i m e , t h e Beaufor t Sea is covered w i t h non- s t a t i ona ry i ce .

Consequent ly , t h e most p r a c t i c a l way t o p er f or m s u r v e i l l a n c e

f o r any leaks is by a e r i a l means. However, g a s le ak ag e from

a p i p e would no t be v i s i b l e u n l e s s i n s u f f i c i e n t l y l a r g e

volume t o form a vapor c l oud c a pa b l e o f fo r c i n g i t s way through

ice cracks. A n o t h e r p o s s i b i l i t y is t h a t a v i s i b l e d e p r e s s i o n

might be formed i f t h e leakage w a s s u f f i c i e n t t o r up t ur e t h e

i c e . M oni t or i ng o f p r e s su r e and f l ow- ra te measurements onb o t h a n of f sho re p l a t fo rm a nd a n onshore gas r e c e i v i n g p o i n t

a l s o would i n d i c a t e a ma j o r l e a k , bu t no t i ts l oc a t i on . P rob-

ably minor gas leaks would no t be de tec ted i n w i n t e r and would

no t be found u n t i l unde rw a te r i n s pe c t i on w a s feasible.

O i l leakage would be eas i e r t o detect even i n t h e w i n t e r

se a son , If t h e i ce cover is porous and s u b j e c t t o c r a c k l i n g

d u r i n g i t s movement, o i l cou ld f in d i ts way t o t h e su r f a c e and

be v i s i b l e u n t i l covered b y snow. O i l accumulated under i c ewould be detectable i n t h e f u t u r e when i n f r a- r e d s e n s o r s , r ad a r ,

or s o n i c d e v i ce s are deve loped more f u l l y .

The effect o f c o r r o s i o n can be monitored by pumping a

p ig w i t h t h e f l u i d , e qu ip ped w i t h s e n s o r s t o meas ur e w a l l

t h i c kne s s . Reduct ion i n t h i c k n e s s t h u s can be d e t e c t e d b e f o r e

c a us i ng t h e l e ak .

During summer months (August, September) ice-free waters

may e x i s t in t h e p i p e l i n e c o r r i d o r s . I n t h e f o r e s e e a b l e

f u t u r e , s u c h areas would be c on f i ne d t o s ha l l ow waters u p t o

a 20m (66 f t ) de p t h . These are t h e t r a c t s earmarked by the

fe de ra l government t o be so l d by t h e s t a t e of Alaska i n t h e

4-25


56/60


57/60

I

expec ted du r ing wh ich a l a y b a r g e can be u s ed ( F ig u r e 2- 4).

If t r ench ing and p ipe- l ay in g i s done from i c e , t h e o p e r a t i o n .

w i l l b e l i m i t e d by i ce movement which i n c r ea s e s i n mag n i tu d e

w i t h t h e d i s t an ce f r o m t h e s h o r e l i n e ( S e c t i o n 1 I . B ) . I n t h e

Nor th Sea , p i pe- l a y i n g o p e r a t i o n s f r e q u e n t l y are cu r t a i l ed by

s to r ms , b u t a warning of s e v e r a l h o u r s u s u a l l y is p rovided .

On t h e o t he r hand, i ce movement i n t h e Arctic canno t ye t be

p r e d i c t e d w i t h s u f f i c i e n t a c c ur a c y, a nd t h e warning t i m e may

be s h o r t or n i l .

The same comments apply t o o p e r a t i o n a l p i p e r e p a i r s .

Equipment r equ i red sho u ld be immedia tely av a i l ab l e t o t ake

advantage of t h e f r ee water i n summer o r t h e n e a r - s t a t i o n a r y

t h i c k ice i n t h e l a t e w i n t e r . In some cases a p i p e may n o t

b e r e p a i r e d f o r a p e r i o d o f weeks o r mo nths , and t h i s s h o u ld

be t a k e n i n t o a cc ou nt i n c o n s i d e r i n g t h e economics of an

Arctic o f f s h o r e p i p e l i n e . Dua l p i p e l i n e s m ig ht be j u s t i f i e d .

I n summing u p, t h e t ec hn ol o gy f o r p i p e l i n e i n s t a l l a t i o n

i n t h e Arctic o f f s h o r e is a v a i l a b l e , b u t c a r e f u l p l a nn i ng and

l o g i s t i c s u p p o r t is n eces s a r y f o r s a f e and economic p e r f o r -

mance.

J. ENVIRONMENTAL CONSIDERATIONS

1. G a s and O i l Leaks

The e n vi r o nm e nt a l i mp ac t of p i p e l i n e i n s t a l l a t i o n ,

o p e r a t i o n , and p o s s i b l e g a s or o i l leaks caused by a f a i l u r e

i n t h e p i p e l i n e i s c o n s i d e r e d f o r a l l US o f f s h o r e p i p e l i n e s .

The un ique p rob lem assoc ia ted w i t h Arct ic o f f s h o r e i n s t a l l a-

t i o n s is t h e d e t e c t i o n , c on ta in me nt a nd c o l l e c t i o n of any o i l

l e a k i n i ce- covered or i c e- i n

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