ferrous pipeline corrosion processes (3 of 4) 150-230

8/12/2019 Ferrous Pipeline Corrosion Processes (3 of 4) 150-230

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SECTION V

CONSTRUCTION, MAINTENANCE, AND INSPECTION

1. Cons t ruc t i on

Probably the m o s t c r i t i c a l s t a g e i n c o r r o si o n c o n t r o l i s

t h e c o ns t r u c t io n o f t h e p i p e l i n e . T h is i n c l u d es t r e n c h in g ,

l a y i n g , and c o nn e ct i ng t h e p i p e ; c o a t i n g ; f i l l i n g t h e t r e n c h ;

z

and i n s t a l l i n g c a th o d ic p r o t e ct i o n . O f cours e , be f ore one can

i n t e l l i g e n t l y p la n a c o r r o s i o n p r o t e c t i o n s ys te m, it is a dv i s-

a b l e t o make a c o r ros i on s u rve y on t he pa t h the p i p e l i n e w i l lt ake . 'The importance of s o i l r e s i s t i v i t y , s o lu t e s , m o i s t u r e ,e tc . , on c o r ros i v i t y ha s be e n no t e d p re v i ous l y . It i s almoste s s e n t i a l t o have d e t a i l e d s p e c i f i c a t i o n s f o r a l l a s pe c t s o ft h e c o r r o s i o n p r o t e c t i o n s ys te m a s p a r t of t h e c o n s t r uc t i o n

c o n t r a c t .The prevalence of in te r f e r en ce be tween cas ings under road -

ways and roadbeds and ca thodica l ly pro tec ted p ipe l ine ; h a s been

m e n t i o n e d e a r l i e r ( 2 2 , 6 6 9 c a s i n g s s h o r t e d and 302 Leaks ins idecas i ngs repo rt ed by th e companies sur vey ed) . The research and

tes t r e s u l t s r e p o r t e d i n R ef er en ce 559 i n d i c a t e c o n s i d e r a b l e

p ro g r e ss toward e l i m i n a t i o n of t h e r e qu i re me n t f o r c a s i n g p i pe-

l i ne s unde r roa dbe ds , i . e . , there i s e v id e nc e t o s u p p o r t t h ec o n t e n t io n t h a t c a si n g s are unne c es sa ry f o r s a f e t y and a r e

h ar mf ul i n terns of c o n t ro l l i n g c o r ros i on . The f o l l o d i n g comment

f rom t he que s t i onna i r e i s of i n t e r e s t i n t h i s r eg ar d:" A l l

s t a t e s should adopt a law s i m i i a . r t o C z l i f s r n i a ' s t ha r , wouldno t r e q u i r e ca si ng s. Our company, Lor o x e , has ' lad shor te dcasinqs. 4.t t h e t i m z t h e s e l > n e s w-re _aici, :eused the best

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i n s u l a t o r s a n d seals a v a i l a b l e . F o r i n s t a n c e , o n 390 m i l e s of

20-22- inch p i pe i n s i de 26- inch cas ing w e had over 2,800 f ee t o f

c o a t e d l i n e s h o r t e d t o t h e c a s i n g " (Q495).F o ll owi ng va r i o us s t a g e s o f c on s t r uc t i on , t horough i n s pe c-

t i o n s are de s i ra b l e . Both good ins t r ument s and w e l l t r a i n e d

i n s p e c t o r s are necessa ry . Electrical methods can be used t o

d et er mi ne i f p r o p e r i n s u l a t i o n or connect ion between j o i n t s

has been obta ined , whichever i s d e s i r e d ( 2 2 7 ) . I n s p e c t i o n of

c o a t i n g s i s p a r t i c u l a r l y impor t an t . To minimize ca thodic pro-

t e c t i o n c u r r e n t re q ui r em e nt s , g r e a t care must be taken t o re-

p a i r a l l h o l id a y s. H ol id ay s i n i n s u l a t i n g c o a t i n g s are normal ly

de t e c t e d by " j e e p i n g , " i n which a h i g h v o l t a g e e l e c t r o d e i spassed over t h e c oa t i ng . A ho l i da y i s i n d i c a t e d by c u r r e n t

passage , a s d e t e c t e d by s u i t a b l e i n s t ru me n t a t i on . Although

s p e c i f i c v o l t a g e d i f f e r e n c es are sometimes recommended ( e . g . ,403), t h e r e a l l y i m p o r t a n t q u a n t i t y i s t h e electric f i e l d . Thef i e l d must be s u f f i c i e n t t o c a u se a d i s c ha rge t h rough a i r , b u t

n o t so l a r g e as t o damage t he coa t i ng . A f i e l d o f 1 2 0 V / m i la c r o s s t h e c o a t i n g h a s been recommended (6 86 ) . Some e n g i ne e r s

recommend c he c k i ng t he c oa t i n g a ga i n j u s t a f t e r l a y i ng t h e p i pe-

l i n e i n t h e d i t c h a nd b e fo r e c o v er i ng .

A lt hough e l a b o r a t e t r e nc h d re s s i ngs are n o t n e c e s s a r y , i t

i s g e n e r a l l y d e s i r a b l e t o remove l a r g e r o ck s t o avoid damage

t o t h e c o a ti n g . U s e o f ro c k s h i e l d s i s v e r y p o o r p r a c t i c e be-

cause they may provide good con di t ion s f o r mic rob io l ogi ca l

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

One ga s company recommended i n s t a l l a t i o n of a Mg anode

c

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" i n s pe c t i on s ys t e m" (555) . A Mg anode w a s i n s t a l l e d on t h e p ip e

d ur in g t h e f i r s t day of c o n s t r u c t i o n a nd t h e p i p e p o t e n t i a l was

r e a d a t the end of each day of c o n s t r u c t i o n . A sudden drop i n

p o t e n t i a l s i g n a l e d c o n t a c t wi t h f o r e i g n s t r u c t u r e s , s h o r t e d cas-

i n g s , or l a r g e s e c t i o n s of u nc oa te d or poo r ly c oa t ed p i pe . This

w a s p a r t i c u l a r l y u s e f u l i n l a y i n g submarine p i p e l i n e s .

The c ond i t i ons under wh ich p l a n t a pp l i e d c oa t i n gs or o v e r -t h e- d i t c h a p p l i e d c o a t i n g s were p r e f e r r e d a r e l i s t e d i n Tables

36 and 37, r es pe c t iv e l y , f o r t h e companies sur ve ye d. Some re p-

r e s e n t a t i v e s t a n d ar d s and s p e c i f i c a t i o n s f o r c o a ti n g s and t h e i r

a p p l i c a t i o n are l i s t e d i n Table 3 8 .

TABLE- 35CONDITIONS UNDER W H I C H PLANT APPLIED COATINGS ARE PREFERRED

Con di ti on Number of Companies

All c o n d i t i o n s 6 2

S m a l l jobs 35

Urban areas, poor r i g h t of way, and where

submarine c on s t ru ct io n methods are used 27

Whenever economical 1 5

S m a l l s i z e s 15Wi nt e r t i me c ond i t i ons 1 0

F l a t t e r r a i n 7

N e w c o n s t r u c t i o n 5

When using thin f i l m epoxy o r po l ye t hy l e ne c oa t i n gs

When proper handling i s a s s u r e d 3

Cased highway crossings 2

Rugged te r ra in 2

Ce n t r i fu ga l l y s pun p i pe

When used f o r pumping st a t i o n pi pi ng 1

5

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TABLE 3 7CONDITIONS UNDER WHICH OVER-THE-DITCH APPLIED COATINGS A m PREFERRED

Condition Number of Companies

None 76

Open cou ntr y, cr os s count ry 29

Large jobs, long l i n e s 25Large pipe s i z e s 1 8

Where considered economical 18

1 6A t f i e l d j o i n tsRocky rugged terrain 1 5

Summertime condi t ions 11

Jobs requir ing l i t t l e handling of th e coated p ipe

Recoating on replacement 9

1 0

Short runs, odd s i z e s , o r extremely heavy se cti on s 8

Under a l l condi t ions8

New c ons truc t ion p ro j e c t s 7

I n t h e v i c i n i t y of pumping s t a t i o n s 1When work is done by an experienced contractor 1

Table 39 l i s t s t he f i e l d p ra c t i c e s u sed by t h e companies

surveyed to ensure good coatings.

TABLE 39

FIELD PRACTICES USED TO ENSURE GOOD COATINGS

Practice N u m b e r of Companies

F ie ld inspec t ing 356

Holiday detect ing 3 2 2

Rock shielding 248

Sand bac kf i l l ing i n rock areas 279

Most of the companies surveyed used high molecular weight

polyethylene jacketed copper ca b l e fo r ca thodic pro tec t ion con-

ductors . The t h e r m i t process was used by 309 companies t o at tach

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TABLE 38

STANDARDS AND SPECIFICATIONS FOR COATINGSType of

Parme te r s Coat ing Organ izat i on Date Ref .A pp l i c a t i on

A pp l i c a t i on

A p p l i c a t i o n , i n s p e c t i o n

Appl ica t ion procedures

Adhesion

Adhesion

Composi t ion, weight ,s t r e n g t h , s a t u r a t i o n

F u n g i r e s i s t a n c e

Leakage conductance

M a t e r i a l s , a p p l i c a t i o n ,inspec t ion main tenance

Materials, a p p l i c a t i o n

Material t h i c k n e s s , tear

Coal t a r NACE

Various U K

Coal t a r NACEenamel for marinee nv i rons

Coal t a r and N R P C Aaspha l t enamels

P a i n t s ASTM

Bituminous AWWA

Asbestos NACEf e l t

Plas t i c ASTM

I n s u l a t i n g NACE

Mastics NACE

Wrapped, m a s t i c The Asphalti n t e r i o r a s p ha l t I n s t i t u t e

F ib r ou s g l a s s NACEs t r e n g t h , b r e a k i n g s t r e n g t h , r e i n f o r c e d

p l i a b i l i t y , p o r o s i t y p i p e wrap

P r o p e r t i e s ,t es t methods, Waxuse

NACE

S t r e n g t h , p l i a b i l i t y , Bituminous NACEp o r o s i t y s a t u r a t e d

glass p ipe wrap

1 9 5 7

1 9 6 6

1 9 5 7

1 9 6 7

1 9 6 7

1 9 6 6

1 9 6 2

1 9 6 3

1 9 5 7

1 9 5 7

1 9 5 8

1 9 6 21 9 6 7

1 9 6 1

1 9 6 2

Surf ace p r e p a r a t i o n P a i n t s Swedish s t a n d - 1 9 6 7T e s t i n g , a p p l i c a t i o n , A sp h al t NACE 1 9 5 3composi t ion 1 9 5 8

Thickness , b e n d a b i l i t y , I n s u l a t i n g AGA 1 9 7 0i m p a c t r e s i s t a n c e ,

a r d s A s s o c .

- w e a t he r i ng , a b ra s i onr e s i s t a n c e , p e n e t r a t i o n ,t he rma l a g i ng , c a t hod i c

L. d i s b o n d i n g , s o i l stress,

w a t e r pe n e t r a t i on , c apa-c i t a n c e

Thickness , un i formi ty , Zn, Cdsmoothness , b r igh tness ,s u r fa c e f i n i s h

We ight s (pe r a r e a ) In s u l a t i ng

6177

82,708

6173

480

7 1 8

5 8 8

6188

719

6 1 9 1

6179

7 2 0

61926 1 9 0

6182

6192

7 3 1

61786 1 8 0

7 0 0

UK,USA,Germany 1 9 6 3 2 4 3

1 9 6 6 4 8 1NAPCA

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t h e co n d u c t o r t o t h e p i pe (Table 4 0 ) . F o r h i g h s t r e n g t h (X52 orabove) steel p i p e t h e t h e r m i t p r o c e s s w a s l i m i t e d g e n e r a l l y t o a

15-gra m c a r t r i d g e . One hundred and th r e e companies app ar en t l y

have used X-52 or above h i g h s t r e n g t h steel p ip e .

TABLE 40

METHODS CURRENTLY USED FOR ATTACHING CONDUCTOR TO PIPE

Method N u m b e r of Companies

Thermi t p rocess 309

Solder 23

Conductor brazed t o steel couponwelded t o p i p e 87

Bol t ed connec t ion 4 6

Other 2 2

2 . Maintenance

D e t e r i o r a t i o n b eg in s when a p i p e l i n e i s completed. I n addi-

t i o n t o n a t u r a l p r o ces se s such a s l i g h t n i n g , man o f t e n acceler-

a t e s t h e p r o ces s w i t h v a r i o u s ea rt h-mov ing mac hine s which damage

co a t i n g s an d m e t a l . Thus, re gu la r main tenance i s n eces sa r y t o

k ee p t h e p i p e l i n e o p e r a t i ng . I n t h e c r u d e s t me thod, r e p a i r isi n i t i a t e d o n l y when l eak s man i f e s t t hemse l ves . Tab le 4 1 l i s t s

t h e methods used t o r e p a i r c o r r o s i o n l e a k s b y t h e c ompanies i n

t h e su r v ey .

Repai r may co n s is t of r ep l a c i n g o l d p i p e s ec t i o n s w i t h new

p i p e . As p o i n t ed o u t ea r l i e r new pipe i s a n od i c w i th r e s p e c t

t o o l d p i p e , a nd so sh o u l d b e p r o t e c t e d by co a t i n g and /o r

c a t h o d ic p r o t e c t i o n . Table 42 l i s t s t h e f a c t o r s t h a t t h e su r -

veyed companie s t ak e i n t o co n s i d e r a t i o n i n t h e r ep l acemen t cr

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abandonment of cor roded p ipe .

TABLE 4 1

METHODS USED TO REPAIR CORROSION LEAKS

Method Number of Companies

Clamps 226

Replacement 204

Weld leak 85

A N S I B 3 1 . 8 p rocedures 11

Welded pa tches and o ther devices 1 0

I n s e r t p l a s t i c i n t e r n a l l y 9

Abandonment 4

Reduce l i n e p re s s u re 4

Redwood o r oak pl ug fo llo wed by pa t c h 3

D r i l l , t a p , a nd p l ug 1

Recaulk j o i n t s 1

Table 4 3 shows t h e cri ter ia use d fo r r e pl a c eme n t f o r t he

water sys tem of a l a r g e c i t y . T h i s i s a s y st e ma t i c r a t i o n a l

approach tha t could be ex tended t o gas and o i l systems.

I n t e r n a l c o a t i n g s may be a p p l ie d , p a r t i c u l a r l y i n l a r g e

d i a me t e r l i ne s . I n one method f o r l e a k r e pa i r of ga s l i n e s

a suspens ion of r u b b e r p a r t i c l e s i s pumped through t h e p i p e s*

a nd p l ugs t he l e a ks ( 7 2 3 ) . The companies surveyed re po rt ed

v a r y i n g e x p e r ie n c e and p r e fe r e n c e r e g a r d i n g t h e e f f e c t i v e n e s s

of a v a i l a b l e c ommercial s e a l a n t s i n r e p a i r i n g c o r r o s i o n l e a k s .


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TABLE 42

FACTORS TAKEN I N T O CONSIDERATION I N THE FU3PLACEMRnTTOR ABANDONMENT OF CORRODED PIPE

F a c t o r s Number of Companies

Leak h i s tory

Locat ion of c o r rode d p i pe

Condi t ion of p i p e

Age of pipe

O pe ra t i ng p re s s u re

P r e s e n t and f u t u r e p l a n s f o r p i p e

C o st o f r e p a i r v e r s u s cost t o r e p la c e

D e p t h / S i z e of p i t s and spacingS a f e t y c o n s i d e r a t i o n s

Ex t e n t of Corros ion

EconclmicsS o i l res i s t i v i t y / s o i l TypeType of pipe

S i z e of p i p e

V i s u a l i n s p e c t i o n / a p p e a r a n c eF e a s i b i l i t y of c a t ho d i c p r o t e c t io n

Damage t o area and inconvenience of inoperab le l ine

P i p e p o t e n t i a l

W a l l t h i c k n e s s

Ana lys i s o f sample se c t io n

1 42

7 6

6 8

67

47

46

45

4 1

39

37

36

26

2 2

2 1

1 8

1 4

9

8

6

1

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TABLE 4 3C R I T E R I A FOR REPLACEMENT OF 12- I N C H AND SMALLER MAINS (9685)

A. Length - The s tud y le ng th used w i l l be approximate ly 600f e e t , or one block t he long way, o r t w o b loc ksthe shor t way .

B. Poin t s Requi red - A minimum of 1 0 p o i n t s w i l l be r e q u i r e dt o j u s t i f y r e l a y i n g .

C. B a s i s f o r P o i n t s

1. Genera l Cons idera t ions

.

a.

b.

C .

Age of Main

1. ove r 80 y e a r s o l d2 . 51 - 80 y e a r s o l d3 . 2 1 - 5 0 y e a r s old4 . 0 - 20 years o l d

H i s t o r v of Leaks and Breaks1. P i p e w a l l c o r r o s i o n leak2 . B e a m break o r j o i n t l e a k

Standards

Mat er i a l o r workmanship n ot con-formi ng t o s t a nda rds

2 . H v d r a u l i c Cons i de ra t i onsa.

b.

C .

Divergency from t h e Standard Gi rd

1. Two o r more s i z e s2 . One s i z e

S m a l l S i z e Mains

3 p o i n t s2 p o i n t s1p o i n t0 p o i n t s

2 p o i n t s2 p o i n t s

2 p o i n t s

2 p o i n t s1p o i n t

1. 4 " main2 . 2" or smal ler mains3 . 3 " main

3 p o i n t s2 p o i n t s1 p o i n t

Car ry ing Capac i ty

To be r e co n di t io n ed i f less t ha n 5 o r h e r p o i n t sFlow co ef f i c i en t s (Hazen Wi l l iams I'C'') :1. L e s s than 752 . 75 - 1 0 03 . More than 1 0 0

2 p o i n t s1p o i n t0 p o i n t s


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TABLE 4 3 ( con t inued)

Head Loss p e r 1 , 0 0 0 Feet (Peak Hour Con dit ion s)a.

1. More t h a n 5 f e e t2. L e s s t h a n 5 f e e t

2 p o i n t sp o i n t s

3. Corros ion Cons idera t ions

a. Actua l Cor ros ion of t h e Main - (5 f t r un ni ng l e ng t h )

1. P i t s m o r e t h an 75% of t h e w a l lt h i c k n e s s 5 p o i n t s

2 . P i t s 50 - 75% of t h e w a l l t h i c k n e s s 3 p o i n t s3 . . P i t s less t han 50% of t h e w a l lt h i c k n e s s 0 p o i n t s

b. S o i l Re sis tan ce i n Ohm Cm

1. L e s s t h a n 1 , 0 0 02. 1 , 0 0 0 - 2 ,0003 . Over 2 ,000

3 p o i n t s1p o i n t0 p o i n t s

c. Galvanized Pipe 2 p o i n t s

4 . S p ec i a l C o n s i d e r a t i o n s

Any one of t h e f o l lowing c i rcu msta nces may, i n themselves ,be s u f f i c i e n t c r i t e r i a f o r main r e pl ac em en t.

1. Divergency f rom s ta nda rd dep th2. Extreme e x t e r n a l l o a d i n g

3 . I n sp ec t i o n

Tab l e 44 i n d i c a t e s t h e f re qu en cy o f s u r v e i l l a n c e o r tests

performed by t h e 373 op er at in g companies surveyed. Other tha n

annual measurements of p i p e- t o- s oi l p o t e n t i a l a t t es t s t a t i o n s ,

c u r r e n t i n t e r f e r e n c e , and l i n e c u r r e n t m ea su re me nt s, m o s t of

the measurements are u n sch ed u led , u sed i n f r e q u e n t l y , o r used

on ly on occas ions when the oppor tun i ty p resen t s i t s e l f .

V ar i o u s i n sp ec t i o n r e t h o d s have been des igned t o l o c a t eproblems b e f o r e l e a k s develop. S e v e r a l of t h e s e are aimed

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TABLE 44

FREQUENCIES OF SURVEILLANCE METHODS

Type of Surveillance T e s t A* B T Q1 Q2 S 1 S 2 01 W M U R X 0 2Ae r ob i c ba cteria 0 3 0 0 0 0 0 0 0 0 3 2 1 8 4 2 0Anaerobic bacteria 2 1 0 0 1 0 0 0 0 0 40 30 50 0

Coating conductance survey ( local 7 1 0 0 0 0 0 0 1 0 68 22 45 4

Coating conductance survey ( lon glin e) 1 2 1 0 0 0 0 0 0 1 0 68 1 8 45 4

Coating Discont inuity Survey (Pearson) 1 0 0 0 1 0 0 2 0 1 8 2 2 5 7 80 0 0 0 0 1 0 55 20 33 Ear th cur rent t e s t ( pi p e v i c i n i t y ) 6 1 0

Line current measurement 77 6 0 0 0 0 1 0 1 4 71 43 32

Surface potent i a l surveyP c l o s e i n t e r v a l 2 1 7 2 0 4 0 0 0 1 1 94 44 36

0 1 0 0 0 0 1 6 5 2 1 2 6Continuous 1 0 1 01 9 1 38 1 0 1 0 0 0 3 38 11 5 3 2

( a t test s t a t i o n s )0 0 0 0 0 0 0 2 8 4 2 9Redox potential 0 0 00 0 0 0 0 1 1 105 7 5 4 1s o i l r e s i s t i v i t y s ur ve y 11 1 00 0 0 0 0 0 0 40 18 54 Chemical analyses 1 1 0

Curr ent i n t e r f e r ence 59 4 0 0 1 1 0 0 3 5 89 90 11Other 0 2 1 0 0 0 0 0 0 1 7 3 1 3

B e l l hole inspect i on 7 0 0 0 0 0 0 0 1 0 1 7 3 1 9 2 1 8 6

(coating and pipe c o n d i t i o n )

rpulPipe- to- soi l potent -ial survey

*A = Annually W = WeeklyB = Biannually M = Monthly

T = Tr ienn ia l ly U = UnscheduledQl = Quar t e r lyQ2 = Quinquennially X = I n f r equen t lyS1 = S e x e n n i a l l y 0 2 = Other than the aboveS2 = Septennial ly01 - Octennially

i i = O n occasions when oppor tuni ty presents i t s e l f


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a t the coating, which may be t h e p a r t o f t h e s y st em m o s t vu l ne r -

a b l e t o problems. The g e n e r a l c o n d i t i o n of an i n s u l a t i n g coat-

i n g o n b u r i e d p i p e l i n e s i s i n d i c a t e d by t h e a v e r a g e c u r r e n t den-

s i t y r e q ui r ed f o r c a th o di c p ro t e c t i o n or by t h e l ea ka ge conduc-

t a n c e of t h e c o a t i n g ( 6 1 9 1 ) . A l a rge gas p ipe l ine company

c lass i f ies p i p e as " b a r e " i f 1 ampere or more i s r e q u i r e d p e rm i l e of 3- i nc h e qu i va l e n t p i pe ( Q 4 0 3 ) . S p e c i f i c c o a t i n g d e-f e c t s may be loca ted by sev er a l ins t ruments . One of t he mos t

common i s t h e P ea rs on h o l i d a y d e t e c t o r ( 6 0 ) . G e ne ra l l y , a n

o p e r a t o r w al ks a l o n g t h e p i p e l i n e w h i l e a ud io- f r e que nc y c u r r e n t

i s conducted t o ground through m e t a l cleats i n h i s s ho es . A

s e c ond ope ra t o r w a l k s 20 f e e t be hi nd w i t h a n a u d i o d e t e c t o r .

Sudden i nc re as es i n s i gn a l occur when even a s m a l l h o l i d a y i s

p r e s e n t . Experience i s need ed t o u nd e rs t an d t h e s i g n a l f l u c t u a -

t i o n s a nd t o l o c a t e f l aw s i n t h e c o a t i n g ( 6 0 8 ) .

A s u r f a c e p o t e n t i a l s ur ve y i s u s e f u l f o r r e v e a l i n g "ho t

s p o t s " i n s yst e ms no t ha vi ng c a t h od i c p ro t e c t i on . In one p ro-

c e dure t w o CuS04 e l e c t r o d e s are c onne c t e d t o a po te n t i ome te r( 6 0 1 ) . The rear e l e c t r o d e i s p la ce d d i r e c t l y over t h e l i n e and

t h e l e a d e l e c t r o d e e xt en de d d i r e c t l y over th e p ipe . The elec-

t r o d e s are t h e n " leap- f rogged" one s e p a r a t io n d i s t a n c e u n t i l

t h e s u r v e y i s completed. Cor roding se c t io ns of p ip e are i n d i c-

a t e d by s ha r p p e a k s or changes of p o l a r i t y . -Po te n t i a l surveys may also b e performed by p a s s i n g a r o l l i n g

e l e c t r o d e a lo n g t h e p i p e , w i t h t h e o t h e r s i d e o f t h e p o te n t io-

m e t e r c on ne cte d d i r e c t l y t o t h e p i pe . I f a r e c o r d e r i s a t t a c h e d

by g e a r s t o t h e r o l l i n g e l ec t r o d e , t h en p o t e n t i a l v e r su s d i s t a n c e

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i s a u t o m a t i c a l l y d i s p l a y e d . I t ha s be en po i n t e d ou t t h a t pot en-

t i a l s u r v e y s c a n n o t d e t e c t s m a l l , l o c a l i z e d c o r r o s i o n c e l l s ,

which would be expec ted on ba re p ip e l in es ( 6 1 7 2 ) .

C a r e must be taken when e lec t r i ca l co nt a ct must be made d i r -*

e c t l y t o t h e p i p i ng . P ro be s c au se h o l i da y s , a nd i f b r i g h t metal

i s c r e a t e d by s c r a t c h i n g it may cor ro de ra p i d l y , be ing anodic . A

b e t t e r approach i s t o i n s t a l l t e s t r e f e r e n c e l e a d s on t h e p i p i n g

a t t h e t i m e o f c o n s t r u c t i o n .

U n f o r t u n a t e l y , methods r e q u i r i n g e lec t r i ca l c o n ta c t t o t h es o i l are d i f f i c u l t t o u s e when t h e p i p e p a s se s u nd er c o n c r e t e

or rock. Thus, methods have been dev ised no t re qu ir in g elec-

t r i c a l c o n t a c t o f a n e l e c t r o d e t o t h e s o i l . I n o ne method,

pick- up loops a r e e mployed t o detect t h e m a gn et ic f i e l d g e n er -

ated by c u r r e n t f lowing i n t h e p i pe . Sudden drops i n o u t p u t

w i t h d i s t a n c e s i g n i f y c u r r e n t l e a k ag e t hr ou gh t h e c o a t i n g ( 4 0 3 ) .

A t t h i s t i m e , t h e b e s t i n d i c a t o r of p i p e l i n e c o r r o s i o n

a p pe a rs t o b e close m o ni t or i ng and i n t e r p r e t i n g of t h e p i p e

p o t e n t i a l s . S inc e it i s c u r r e n t l e a v in g a b u r i ed s t r u c t u r e

t h a t cause s c orr os i on , th e optimum measurement would be t he

d e t e r m i n a t i o n o f t h e c u r r e n t l e a v i n g t he s t r u c t u r e . I n t h e

n e a r f u t u r e it may be pos s i b l e t o measure t he cu r r en t f low

p a t t e r n s i n t h e p i p e by a magnet ic grad iomete r . The use of a

magne tic grad iomete r may a l low th e de te c t io n of t h e v a r i a t i o n

c ha ng es i n t h e m ag ne ti c f i e l d of t h e p i p e c u r r e n t a nd p i n p o i n t

l o c a t i o n , d i r e c t i o n , an d a mp li tu de of c u r r e n t f low. A ddi t ion-

a l l y , t h i s i n st r u m en t c an c o nc e iv a bl y be used a t speeds from 20

t o 200 m i l e s p e r hour e x t e r n a l t o o r i n t h e p i p e l i ne ( 7 9 9 ) .

*In t e rv i e w w i t h A. W. Peabody, 1 9 7 0 .1 4 7


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The indus t ry i s i n need of easy- to- u se , a c c u r a t e i n s t r u m e n t s

t h a t combine as many c o r r o s i o n r e l a t e d f a c t o r s ( s o i l r e s i s t i v i t y ,

pT:, p i p e p o t e n t i a l , etc.) as would be pract ical ( Q 2 5 2 , Q 2 2 0 ,Q 5 0 5 , 4 6 0 6 , Q8.2, Q 4 9 0 , Q 6 9 9 ) . Automated surveys and remotei n s t r u m e n t s w i l l become m o r e d e s i r a b l e w i th f u t u r e i n c r e a s es

i n c a t ho d i c p r o t e c t i o n a nd i n t e r f e r e n c e ( Q 2 8 2 ) .H y d r o s t a t i c t e s t i n g c a n b e u s e d t o detect l e a ks a nd corro-

s i o n weakened areas ( 5 9 8 , 5 9 9 ) . P r o g r e s s i v e l y smaller f l aws

are d e t e c t e d as p r e s s u r e i s i n c r e a s e d . S u r p r i s i n g l y , t h e hy dr o-

s t a t i c proof t e s t acts f a vo ra b l y on s u rv i v i n g f l a w s , p roba bl y

by c a us i n g p l a s t i c deformat ion a t t h e t i p of c r a ck s and p i t s

( 5 9 9 ) . Thi s de c re a s e s t he stress c o n c e n t r a ti o n t h e r e and i n t r o -

d uc es f a v o r a b l e r e s i d u a l stresses -- mechanical stress r e l i e f .

P i p e l i n e i n t e r i o r s ca n a l s o be moni t ore d fo r c o r ros i on .

A magne t ic survey ins t rument has been developed which t r a v e l s

i n t h e l i n e and l o c a t e s p i t t i n g and g e n e ra l m e ta l loss ( 3 3 5 ) .

S ma ll d ia m et e r t e l e v i s i o n cameras have been de vel oped which

t ravel i n t h e l i n e . U l t r a s o n i c t h i c k n e s s d e t e c t o r s may e i t h e r

be u s e d i n t e r n a l l y or e x t e rn a l l y on e xpos ed p i pe s .

Leaks may be de te ct ed i n several ways. The leas t d e s i r a b l e

method, b u t very commonly used , i s to no te l eakage when a s u f f i -c i e n t amount has t a ke n p l a c e t o be a p p ar e n t . I n l on g p i p e l i n e s

l a r ge l e a ks a r e sometimes no t i c e d by d i s c r e p a n c ie s i n i n v e n to r y

or t r a n s p o r t e d p r o d u c t , i . e . , less p roduc t e m i t s f rom the p ipe-l i n e t ha n i s i n t r o d u c e d . Leaks can be l o c a t e d by c l o s i n g o f f

s e c t i o ns o f t h e p i pe s yst e m a nd obs e rv i ng p re s s u re dec ay i n

s e c t i o n s c o n t a i n i n g l e a k s . G a s l e a k s are s o m e t i m e s l oc a t e d by

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" s n i f f i n g " i n s t rum en t s wh ich de t e c t gas . Di s co l o ra t ion o f vege-t a t i o n is a l s o u se d as a l e a k i n d i c a t o r .

The theory and fundamenta ls o f l eakage t e s t in g a r e d i scu ssed

i n Reference 812. T e s t c a t e g o r i e s , r e a so ns f o r t e s t i n g , c h o i c e

of procedures , t e s t p l ann ing , f low c h a r a c t e r i s t i c s , and guide-

l i n e s f o r w r i t i n g s p e c i f i c a t i o n s are i nc luded , A d e t a i l e d d e s-

c r i p t i o n of test methods is given which cover s th e u se of

s t an d a r d s , mass sp ec t r o me t e r s , g a s d e t e c t o r s , p r e s su r e and flow

m ea su re me nts , b u bb le d e t e c t i o n , r a d i o a c t i v e t r a c i n g , h a l i d e

t o r ch e s , so n i c met ho ds , e l ec t r o mag n e t i c ene rg y ab so r p t i o n ,

c he mi ca l i n d i c a t o r s , h i gh p o t e n t i a l d i s c h a r g e s , i o n i z e d g a s e s ,

t h er m a l c o n d u c t i v i t y ga g es , a nd s e v e r a l s p e c i a l a p p l i c a t i o n s .

An ex t en s i v e l i s t i n g o f c h a r a c t e r i s t i c s and so u r ces of commer -

c i a l l y a v a i l a b l e l e a k d e t e c t o r s i n c l ud e s a d dr e ss e s of manufac-

t u r e r s , c o d e symbol s f o r t y p e s of equipment , t ra de names, and

c h a r a c t e r i s t i c s of t h e e qu ip me nt. P r o p e r t i e s o f t r a c e g a s es

and safety measures f o r t h e i r use a r e a l s o d i s c u s s e l l .

r

Supp lementa l obser va t ion s dur ing th e i nsp ec t io n of corro-s i o n l eak s b y t h e surveyed companies a r e shown i n Tab le 4 5 .

The " o t h e r " o b s e r v a t i o n (Par t E) c o n s i s te d of p i pe p o t e n t i a l s ,

s t r a y c u r r e n t s , l o c a t io n and d ep th of p i t s , e l e c t r i c a l c o nt in-

u i t y of g a s k e t e d j o i n t s , s o i l r e s i s t i v i t y , and t h e review of

c a t h o d ic p r o t e c t i o n r e p o r t s t o d e t er m i ne i f t h e r e ha d b ee n any

d e t e r i o r a t i o n o r i n t e r r u p t io n of c a th o di c p r o t ec t i o n p r i o r t o

l eak s .

Many companies have developed correlat ions (Tab le 45 , P a r t

F ) with leak f requency and wi th some of the observat ions made

1 4 9


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TABLE 4 5

SUPPLEMENTAL OBSERVATIONS ON THE INSPECTION OF CORROSION LEAKSN u m b e r of Companies- Observat ions Y e s N o

(A) General Condi t ion Df Coa t i ng , i nc l ud i ngBond t o P i p e 30 4 20

(B) So i l Type and/or Texture 282 40( C ) Soi l Mois ture 236 71(D) Proximity of O t he r P i pe l i ne s or S t r u c t u r e s

( P o s s i b i l i t y of C at ho di c I n t e r f e r e n c e ) 269 50

(E) Other 79 33(F) Have Any of t h es e Obser vati ons Been

C o r r e l a t e d w i t h Leak Frequency? 109 2 1 4

dur in g l ea k ins pec t io ns . One of t h e most common methods us ed

t o d ev el op c o r r e l a t i o n s was t o f i l e a r e p or t when a l e a k had

been r e p a i r e d . The c o n t e n t s of t h e r e p o r t g e n e r a l l y i n d i c a t e d

t h e t ype o f l e a k , l oc a t i on on t he pe ri me t e r o f t h e p i pe , t ype

of c o r ros i on c a us i ng t h e l e a k , s o i l t ype , s o i l r e s i s t i v i t y ,

amount of c a t hod i c p ro t e c t i on , t ype o f r e p a i r made, etc. The

l e a k s w e r e p l o t t e d by geographic l o c a t i o n on a y e a r l y b a s i s .

Over a p e r i o d of t i m e h o t s p o t s w e r e l oc a t e d a nd s o i l resis-

t i v i t i e s w e r e known by areas, so t h a t f u t u r e p i p i n g c o u l d b e

i n i t i a l l y l a i d w i t h a d eq u at e p r o t e c t i o n a p p l i e d a nd o l d p i p i n gcould be economical ly scheduled f o r r e p l a c e me n t be fo re s e r i ous

problems a ros e . A second coirunonly used system, which i s ve rymuch l i k e t he f i r s t s ys t em, was t o r e c o rd t h e s o i l r e s i s t i v i t y

when a l e ak was re pa i r ed and main ta in a graph p l o t t in g l eak s

as a fu n ct io n of s o i l r e s i s t i v i t y . A s i n t h e p re v i ous s ys te m,

t h i s gave a b a s i s f o r judgment when a s e c t i o n of p i p e shoul

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be r e c o n d i t i o n e d or r ep laced and a l so i n d i c a t e d l e v e l s of p r ot e c-

t i o n re qu i red on new p ip in g by geogra ph ica l area acco r d i n g t o t h e

s o i l r e s i s t i v i t y . The t h i r d s ys te m w a s t o p l o t cumula t ive l eak-

ag e as a f u n c t i o n o f t i m e on semilog graph paper and augment

p r e v e n t i v e measures when a s h a r p i n c r e a s e i n t h e s l o p e of t h egraph w a s observed . A t h e o r e t i c a l l y b e t t e r method would b e t o

p l o t cumula t ive l eakag e as a f u n c t i o n o f t i m e on log- log graph

pape r as i n d i ca t e d by Equat ion 1 0 . The log- l og p l o t s h ou l d be

l i n e a r a nd may g i v e v a l i d e x t r a p o l a t i o n s o f f u t u r e l e a k s . I t

sh o u l d b e n o t ed t h a t l e ak d a t a o n t h e number of l e a k s r e p a i r e d

d ur i ng e ve ni ng s h i f t s a r e a p t t o be i n f l a t e d .

A s t andard record sys t em shou ld be deve loped by t h e i n d u s t r y

a s s o c i a t i o n s t h a t w i l l a l l o w s t a t i s t i c a l co r r e l a t i o n s b e t w een

c o r r o s i o n v a r i a b l e s a nd o t h e r v a r i a b l e s s uc h as l eak f r equency

on a r e g i o n a l o r n a t i on w id e basis ( Q 2 5 0 , 0114 . An e xc e l l e n texample on t h i s t y p e of co r r e l a t i o n on 22 , 000 m i l e s of coa ted

p i p e l i n e s i s r e p o r t e d i n R e fe re nc e 4 7 4 .

Two t y p i c a l l e a k r e p o r t s are shown i n Tab les 46 and 4 7 .

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TABLE 46

UNDERGROUND PIPE INSPECTION REPORT Q 6 8 5 )Make Sep arat e Report f o r Each Siz e, Kind , and Individual Line

~

Trunk Feeder Dist r ibutor

Size C a l v a n i zed

-

C a s tKind: Steel C.A. Conc. I ronDate Laid:

PIPE DATA

-. _ . 7

MAINS SOIL RESISTIVITY

Ohm-CMLocation

Remarks

Na ti vePIPE TO SOIL POTENTIALS

No sca le , N o p i t s Pe r f e c tGraphi t izat ion or Scale o r p i t t i n g t o

p i t t i n g._ zc / 3 t h r u 1 / 3 t h r u p ipe w a l l

I Protecteds p e c t e a

Bare SpotsPockets

Sagging

LEAKAGE PROTECTIVE COATING DATACondition

Pipe Wall Taints F i t t i n g sTap. Good Fair Poor

wailGraphi t izat ion or

p i t t i n g from 1/ 3 t o2/3 thru w a l lGraphi t izat ion or

p i t t i n g 2/3 o r moreth r u w a l lGraphi t izat ion or

p i t t i n g th r u pipe

CONDITION OF F I P E_-l a s s Cast I ron S t e e l

S ca l e o r p i t t i n gfrom 1 / 3 t o 2/3 t h r uw a l lScale or p i t t i n g

2/3 or more thr uw a l l

Perforat ions

BondMoisture Present Under

E

_ _ _ .~~-No gr aphi t i za t i on ICoating: Y e s NOI

w a l l I I

TypeRed RockDec. G r a n iShale

Grave1

SandLoamClayS i l tP e a t

t e GrayBlack

Y e l l o wBrownRedI3lueGreen

Date

REPLACEMENT DATA

AgeLeaks

Min. 2 /y r . -3 in5 yrs)P i t t i n gS o i l R e s i s t i v i t yGalvanized Pipe

CATHODIC PROTECTIONSize

SOIL DATACheckAll Applicable Ite

Agglomeration

ManyBouldersStones

FewPe bb1esHard Lumps

Texture PackingFine Loose

Medium Medium

Coarse Hard

Inspected by:

L


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20/81

SECTION V I

ECONOMICS

Economics are t h e scale by which t h e e f f e c t s of c o r r o s i o n

and the methods of c o n t r o l l i n g c o r r o s i o n are measu r ed . I d ea l l y ,

enough economic data w o u l d b e av a i l ab l e t o en ab l e o ne t o c a l c u l a t et h e o p t i m a l c o u r s e of a c t io n f o r a l l c o n c ei v a b le s i t u a t i o n s . Un-

h a p p i l y , t h e r e i s a real p a u c i t y of d a t a a v a i l a b le , and.much ofwhat i s pu b l i sh ed i s p robably based on s p e c u l a t i o n and unsup-

p o r t e d estimates. N o economic informat ion w a s u ne a rt he d i n t h e

r e p l i e s t o t h e q u e s t i o n n a ir e .

Cor ros ion i s expens ive . Valuab le p rod uc t s are l o s t when

p i p e l i n e s l e a k . L o s t pumping t i m e i s nev er recove red . Escaped

p r o d u c t s may r u i n c r o p s , i n j u r e w i l d l i f e , d e s p o i l n a t u r a l bea u t y ,

and damage property. C o s t s could and should be ass igne d t o prop-

e r t y damage and haz ard s . Toxic , f lammable , and ex plo siv e prod ucts

c o n s t i t u t e h a z a r d s t o human l i f e and well-be ing . The damage re-

s u l t i n g f r o m a l e a k de pends on t h e p r e s s u r e i n t h e p i p e l i n e , t h e

f l u i d it car r ies , and t h e l o c a t i o n of the p i p e l i n e . Leaks are

expens ive t o l o ca t e an d t o r e p a i r . When p i p e s e c t i o n s mus t b e

r ep l aced , f l o w i s i n t e r r u p t ed w i t h co n seq u en t loss i n r e ve nu e .

It h as b een e s t i ma t ed t h a t t h e e x t r a pumping c o s t s d ue t o r u s t on

t h e i n t e r i o r of p i p e s amounts t o $40 , 000 , 000 /yea r i n t h e U . S .( 4 9 3 ) .

A 1 9 5 0 survey i n Arkansas , Kansas , W e s t Texas, and Ne w

Mexico r e v e a l e d t h a t 4 4 p e r c e n t of t h e s o u r c r u d e o i l w e l l s were

eco n o mi ca l ly a f f e c t ed by co r r o s i o n ( 6 1 8 5 ) . I n A r kansas t h e corro-

s i o n costs averaged $1250 p e r well p e r y e a r . I n Kansas, t h e

1 5 4


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average w a s a bou t $ 2 0 0 0 and i n West Texas-New Mexico $ 2 7 0 . U s eof t h e c o r r o si o n i n h i b i t o r s r ed uc ed t h e c o s t s t o $100 , $225, and

$220 p e r w e l l p e r y e a r , r e s p e c t i v e l y , f o r c o r r o s i o n c o n t r o l p l u s

r em a in in g c o r r o s i o n c o s t s . C o r ro s io n c o u l d c o s t a bo u t $1000 p e r

y e a r p e r w e l l i n s w e e t o i l w e l l s when the s a l t water c o n t e n t i s

above 4 0 p e r c e n t ( 5 5 3 ) . I n a 1963 surve y (6193) of 8919 o i l and

g a s w e l l s , t h e r a t i o of r e p o r t e d s a v i ng s t o c o r r o s i o n c o n t r o l

c o s t s w a s a bou t 5 : l . Much l a r g e r r a t i o s were f ou nd i n o f f s h o r eope ra t i on s . N e ve r t h e l e s s , many op e ra t o r s have made l i t t l e or no

a t t e m p t t o c o n t r o l c o r r o s i o n .

I n u se o f c o a t i n g s t h e i m p o r ta n t f a c t o r i s r e a l l y t h e c o s t /e f f e c t i v e ne s s r a t i o o r t h e r a t i o of s av in gs t o c o s t over t h e l i f e

of t h e p i pe . To ob t a i n va l i d c ompar is ons on suc h a b a s i s i s no t

s impl e , however . I f a l l c o a t in g s c o s t t h e s a m e on a vo l ume t r i c

b a s i s t h e n one c ou l d s imply p r e p a r e specimens having t h e same

t h i c k n e s s -- b u t c o s t s va ry widely. One canno t compare c o a t i n g sp r ep a re d so t h a t t h e c o s t p e r u n i t l e n gt h i s t h e same because t h e

e f f e c t i v e n e s s o f a c o a t i n g i n c r e a s e s w i t h t h i c k n e ss , b u t i n a n

unpredic tab le manner . A t ho r ou g h s t u d y would u t i l i z e a range of

t h i c kn e s s f o r e a c h t ype o f c oa t i ng a nd t he n c ompare t h e minima i n

c o s t / e f f e c t i v e n e s s ( o r maxima i n s a v i n g s / c o s t ) of e a c h . Th i s ha sno t y e t been done. There are l i t t l e pu b l i s he d d a t a on e i t h e r c o s t

of a pp l i c a t i on a nd ma in t enanc e o r on s a v i ngs .

The c o s t s f o r c o n t ro l o f i n t e r n a l c o r r os i on i n two average

s our c rude o i l g a th e r i n g l i n e s are compared i n Refere nce 793. I t

w a s c on cl ud ed t h a t c o n c r et e l i n i n g s and c o r r o s i o n i n h i b i t o r s

a p pe a re d m ost ec on om ic al i n t h e l a r g e r , l o n g e r l i n e s . C o nc re te

I -:-3 5


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l i n i n g s , i n t e r n a l p l a s t i c c o a t i n g s , a nd p l a s t i c pi p e ap pe are d

m o s t e co no mi ca l f o r s h o r t e r , smaller l i n e s . P r o t e c t i v e m ea su re s

p rovided s av i n g s of 9 c e n t s t o 25.5 ce n t s per foot o f p i p e p e r

y ea r .

The cost o f c a t h o d i c p r o t e c t i o n de pe nd s g r e a t l y o n t h e q u a l-

i t y of t h e c o a t i n g , t h e i s o l a t i o n , a nd t h e m ec ha ni ca l j o i n t bonds

( 1 5 8 ) . The C a s t I r o n P i pe R es ea rc h As s o c i a t i o n h a s a s s e r t e d t h a tc a t h o d ic p r o t e c t i o n of p i p e sys tems adds a t leas t 1 0 p e r c e n t t o

4

t h e t o t a l p r o j e c t cost ( 7 8 9 ) . P re su ma bl y, t h i s f i g u r e i s fo r

b a r e cast i r o n p i pe . The i n s t a l l a t i o n c o s t of c a t h o d i c p r o t e c t i o n

on b a r e o i l s t o r a g e t a nk b o tt om s was f ou nd t o be abou t 3 per ce n t

o f t h e t an k b ot to m i n v es t ment ( 7 9 3 ) . The t o t a l an n ua l o p e r a t i n g

expense was abou t 1 .25 per ce n t o f one r e pa i r j ob o r about 25

p e r c e n t o f t h e annua l r e p a i r cost w i t h o u t p r o t ec t i o n . P ay ou t f o r

c a t h o d ic p r o t e c t i o n w a s e s ti m at e d a t 1 .5 y e a r s . I n s t a l l a t i o n of

ca t h o d i c p r o t ec t i o n on modern co a t ed p i p e l i n es i s claimed t o cost

less t han 0.5 per cen t of t h e t o t a l cos t s , wi th main tenance and

o p e r a t i n g costs l e s s t han $28 per m i l e y e a r ( 4 9 2 ) . A t o t a l cost

of 4 .2 c e n t s / f t w a s e s t i m a t e d f o r 30 y e a r s o f p r o t e c t i o n of a100,000- foot long, 5 /8 - inch OD p i p e l i n e ( 4 7 4 ) .

G al van i c ca t h o d i c p r o t e c t i o n r edu ced t h e ma i n ten an ce costs

p e r o ve rhau l of U . S . Navy d e s t r o y e r s by $ 1 0 , 0 0 0 t o $ 2 0 , 0 0 0 ( 4 9 1 ) .B a r e o f f s h or e p i p e l i n e w a s p r o t e c t e d by z i n c b r a c e l e t s fo r an

e s t i m a t e d cost of $40 /mi l e /yea r as compared t o $ 1 0 0 / m i l e / y e a r f o r *an impressed - cur ren t sys t em (728) . For an e s t i ma t ed 40 y e a r s Of

p r o t e c t i o n t h e cost of t h e b r a c e l e t s w a s 0. 5 p e r c en t of t h e p i p e-

l i n e . I t w a s claimed t h a t t h e l o w e s t t o t a l costs are o b t a i n ed by

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ca thodic pro tec t ion combined wi th "reasonably" c o at e d l i n e s ( 7 9 3 ) .

"Reasonab le" a ppe a r s t o mean a n a dhe re n t i n s u l a t i n g c oa t i ng o fl ong l i f e t i me b u t w i t hou t a ny a t t e mpt s t o make it h o l i d a y- f r e e .

Some p i p e s ys te m o p e r a t o r s i n s t a l l c a t h o d i c p r o t e c t i o n a t some

t i m e a f t e r l a y i n g t h e p i pe . I t h a s b een e s t i m a t e d t h a t o n l y a b ou t

1 5 p e r c e n t of a p i p e system w i l l be s u b j e c t t o r a p i d c o r r o s i o n

( 6 0 1 ) . One procedure i s t o perform a s u rv e y o f p i p e p o t e n t i a l a nd

p r o t e c t on l y t h o s e areas c o n t a i n i n g "ho t s p o t s . " The payout peri -od f o r t h e cost o f t h e s u r ve y an d t h e c a t h o d i c p r o t e c t i o n w a s

found t o be 2 t o 5 ye a r s . A t o t a l o f $258 /mi le /yea r w a s saved ono ne l i n e o v er a 6-ye a r pe r i od .

Another procedure i s t o i n s t a l l c a t ho di c p ro t e c t i o n t o an

area on ly when lea ks have a l re ad y developed. With bar e pi pe i t

h a s bee n f ou nd t o be c h e a pe r t o a p p ly c a t h o d i c p r o t e c t i o n t h a n t o

r e p l a c e t h e l i n e w i t h new c oa t e d p i pe (59 2) . A lt hough s a v i ngs

w e r e r e a l i z e d by c at h od i c p r o t e c t i o n a f t e r several y e a r s , a l a r g e

g a s company fou nd t h a t more money would have been s ave d by a p p l i-

c a t i on be fo re l e a k s had devel oped (58 9) .

I n c a l c u l a t i n g c o s t s and s a v in g s o f v a r i o u s p r o t e c t i o n

met hods , one must no t o n l y a t t e m pt t o a c c oun t fo r a l l d i r e c t

and i n d i r e c t e xp en se s, b u t a l s o t a k e i n t o a c co un t t h e t i m e v a l u e

of money. Seve ra l d i f f e r e n t methods of accompl i sh ing t h i s have

been used ( e . g . , 591, 493, 7 0 5 ) . T h e e f f e c t of a c c o u n t i n g f o ri n t e r e s t a nd d e s i re d p r o f i t i s t o i n c r ea s e t h e c o s t of p r e s e n t

c a p i t a l i n v e s t m e n t s as compared t o expenses oc cur r ing l a t e r .


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SECTION V I 1OTHER PROBLEMS ASSOCIATED WITH CORROSION OF PIPELINES

1. Tra in i ng of Corros ion Engineers and Technic ia ns

According t o Reference 305 few engineer ing gradua tes have

r e c ei v e d any t r a i n i n g i nc o r r o s i o n c o n t r o l . A s a r e s u l t t h e ac-

q u i s i t i o n o f t h e n e c es sa r y s k i l l s t o p er fo r m w e l l as a c o r r o s i o n

e n g i n e e r i s l a r g e l y a p e r s o n a l r e s p o n s i b i l i t y . A m a t e u r . b u n g l i n gi s common i n c o r r o s i o n c o n t r o l w ork, p a r t i c u l a r l y i n c a t h o d i c

-p r o t e c t i o n ; t o h e l p a l l e v i a t e t h i s s i t u a t i o n , t h e B r i t i s h Associa-

t i o n o f Cor ros i on Eng i ne e r s w a s formed t o p rov ide e d u c a t i o n i n

c o r r o s i o n c o n t r o l and p r o f e s s i o n a l q u a l i f i c a t i o n s t a nd a r d s.

A v a r i e t y of w e l l s u b sc r i b ed s h o r t c o u r s e s are o f f e r e d i n a l l

p a r t s of t h e U . S .

However, th e r e a ppears t o be a ne e d fo r more c our s e s a t more a d -

vanced l e ve l s . Evening cour ses are given by some u n i v e r s i t i e s .

NACE w i l l s oon pub l i s h a ba s i c c o r r os i o n c ou r s e .

Many books and papers are a v a i l a b le f o r s e l f - t e a c h i n g , as i l l u s -

t r a t e d by t h e r ef e r e n c e s f o r t h i s r e p o r t . I nf or ma l i n fo r ma t io n

f l o w among p r a c t i c i ng c o r ros i on e ng i ne e r s i s p robably as g r e a t as

i n any o t h e r t e c h n i c a l s p e c i a l t y , and i s p a r t i c u l a r l y n o t i c e a b l ea t l o c a l NACE me e t ings . N e ve r t he l e s s , one s e ns e s a real d e f i c i e n -

cy of unde r s t a nd i ng o f fundamen t al and t he o re t i c a l a s p e c t s of

c o r r o s i o n c o n t r o l , a l th o ug h r e g a rd f o r c o r r o s i o n c o n s u l t a n t s i s *

somewhat mixed. Ni ne ty - f ive of t h e surveyed companies used con-

s u l t a n t s i n t h e i r c or ro s i on c o n t r ol e f f o r t s ..

U nfor t una t e l y , no s a t i s f a c t o r y method o f de t e rmi n i ng o r

c e r t i fy i n g c ompe te nc e o f c o r ros i on e n g i ne e r s a nd t e c hn i c a l p e r -

s o nn e l e x i s t s i n t h e U ni te d S t a t e s . The fac t t h a t c o rr o si o n

1 5 8


25/81

con t ro l has deve loped as an a r t r a t h e r t h a n a s c i e n c e i s exem-

p l i f i e d by t h e e x t e n s i v e u se of undef ined t e r m s and misnomers;

e . g . , p i p e t o soi l p o t e n t i a l i s g e n e r a l l y used f o r t h e p o t e n t i a lbetween a b u r i e d p i p e and a h a l f ce l l l oca t ed on t h e s o i l s u rf a ce ;

a sa t u r a t ed co p p e r - c op pe r s u l f a t e h a l f c e l l i s one i.n which thec op pe r s u l f a t e , r a t h e r t h a n t h e c op pe r , i s s a t u r a t e d ; terms such

as "zero swing" are u se d w i t ho u t p r e c i s e d e f i n i t i o n .

.

-Table 48 l i s t s t h e pub l i ca t i ons and in fo rmat ion s ources wh ich

were t hough t t o co n t r i b u t e t h e mos t t o t h e r e sp on d i ng co mp an ie s'

co r ros ion con t ro l p rogram.

TABLE 48

PUl3LICATIONS AND I N F O R N A T I O N SOURCES W H I C H HAVE BEEN FOUNDTO CONTRIBUTE RlOST TO CORROSION CONTROL PROGEIAPIS:dumber of ConFanies

Source '& los t 2nd 3rd 4 t hAiier ican G a s Assoc ia t ionA v e r i c a n P et ro le um I n s t i t u t eCommit tees / f l ee t ingsConsu l t an t s

E l ec t r o ch emi ca l S o c i e t y

Yonth1 Magaz i nesNACE Pub1ic a t i o n sN a t i o n a l Bureau of Standards

P a c i f i c C oa st G a s Assoc ia t ion

S h o r t C o u r s e s / S e n i n a r sText Books

2 11 9 1

1 1 9 037 53 29 914 9 14 6r 0 0 1

31 G ? 38 2 8

54 36 21 60 0 1 11 1 0 3

1 3 8 60 35 8

1 7 2 1 11 2


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2. In t e r fe rence wi th Smal l P ip ing Sys t ems

While t h e p i p e l i n e i n d u s t r y has been h i g h l y s u c c e s s f u l i nm i n i r t i z i n g co r r o s i o n cau sed by ca t h o d i c i n t e r f e r en ce b e t w een i t smembers, t h e r e r ema i n s a s u b s t a n t i a l q u a n t i t y of p i p e i n cus tody

o f o p e r a t o r s o f s m a l l water and g as compani es , r an ch es , i n d u s t r i a l

p l a n t s , r e s t a u r a n t s , o t h e r b u s i n e s s e s , home owners, etc . , which

i s s u b j e c t e d t o i n t e r f e r e n c e . To comprehend t h e hazard , i t i so n l y n eces sa r y t o p o i n t o u t t h a t 30 microamperes are s u f f i c i e n t

t o cause a l e a k i n one ye a r i f t h e p i t i n a 1 / 8 - i n c h p i p e w a l lhas the form of a p a r a b o l o i d a l segment w i t h d e p t h and s u r f a c e

r a z i u s eq u a l t o t h e w a l l t h i c k n e s s o f t h e p i p e . F u r t h e r , op e r -

a t i n g p i p e l i n es may b e su b j ec t ed t os m a l l ,

u n d e t e c t e d i n t e r f e r e n c ec u r r e n t s . C at ho di c i n t e r f e r e n c e may be a n t i c i p a t e d u n d e r t h ef o l l o w i n g co n d i t i o n s .

a . I f t h e s u r fa c e or deep w e l l anode i s less t h an 1 0 0 0 feet

d i s t a n t f r o m t h e p i p e l i n e of concern .

b. I f t h e o f f en d ed p i p e i s i n f e r i o r i n c o a t in g as measured

by conductance , and (1) c r o s s es t h e p r o t e c t ed p ip e o r ( 2 ) p a r a l l e l sw i t h i n 1 5 d i a m e te r s of t h e p r o t e c t e d p i p e .

The foregoing are n o t p e rf or mance r u l e s b u t are i n d i c a t o r s for

concern .

3 . Grounding of Elec t r ic C i r c u i t s o n Water Pipe

St ra y cu r r en t s caused by g rounding o f e lec t r i ca l c i r c u i t s on

water p i p e s are a co r r o s i o n h aza r d t o a l l underground p ip ing .

Th is common pr a c t i c e p en al iz es t h e owner of t h e p i p in g . F or t h e

owner it i s e c on om i ca l ly b e t t e r t o pay t h e i n i t i a l c o s t of i n-

s t a l l i n g a separa t e g round ing electrode t h an t o have a

1 6 0


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d e t e r i o r a t e d p i p i n g s y st em a t a l a t e r d a t e . I t i s a l s o s a f e r t o

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

4. Mechanical Damage t o P ip in g

Mechanical damage t o p ip in g has been es t a b l i s he d as one of

t h e ma j o r causes of p i p e l i n e a c c i d e n t s . When a p i p e l i n e i s rup-

t u r ed b y n e c h a n i c a l equ ipment , t he cause i s obv ious . A more in-s id ious p rob lem ar i ses when mechanical eq u i p men t co n t ac t s p i p i n g

and damages th e coa t in g and /o r p ipe wi thou t ru p tu r in g it. A t

a l a t e r t i m e c o r r o s i o n t a k e s i t s t o l l a nd a n ot he r a c c i d e n t o r l e a k

i s chalked up t o c o r r o s i o n .5, Improper U s e o f C a t h o d ic P r o t ec t i o n

I t has been no ted t h a t t he re has been some in ep t i tu de among

t h o s e e nga ged i n ' c o r r o s i o n m i t i g a t i o n t h ro u gh c a t h o d i c p r o t e c t i o n ;

t h i s i ncompe tence i s m a n i f e s t e d i n real o r i n c i p i e n t f a i l u r e s

rang ing f rom one t o many inc iden ces . They inc lud e:

a. Del ibera t e r es i s t ance coup l ing be low g round o f anode and

c a t h o d e c a b l e s t o match t h e c u r r e n t an d v o l t ag e o u t p u t w i t h t h er ec t i f i e r c a p a c i t y .

b . Connect ing and o p e r a t i n g r e c t i f i e r s i n reverse p o l a r i t y ,

i . e . , w i t h t h e c a t h o d i c c a b l e from t h e p i p e l i n e c o nn e ct ed t o t h ep o s i t i v e t e r m i n a l o f t h e r e c t i f i e r .

c. Cath od ic a l ly p r o t ec t i ng unbonded mechan ica l ly coup led

p i p e i n c l u d i n g l eaded c a s t i r o n j o i n t s .


28/81

SECTI ON VI11GAPS I NTHE TECHNOLOGY AND COMCLUSI ONS

f he f ol l owi ng concl usi ons have been dr awn f r omt he col l ect i vei nf ormat i on of t he l i t erat ure sear ch, t he quest i onnai re r esul t s,

per sonal i nt ervi ews, meet i ngs at t ended, and per sonal exper i ence.

On exi st i ng pi pel i nes, i t may not be pract i cabl e t o t ot al l y

el i mi nat e al l cor rosi on. The goal i s r at her t o br i ng cor r osi on

t o an accept abl e l evel f or t he l owest cost . Thi s i s not t o say

t hat al l owi ng a f ew l eaks to devel op i s consi der ed "accept -abl e, i n vi ew of t he pot ent i al hazard to l i f e and proper t y.On t he ot her hand, i t i s not r at i onal t o i nsi st on el i mi nat i ng

al l cor rosi on when a r easonabl e cor r osi on cont r ol pr ogr amwi l l

prevent cor r osi on l eaks dur i nq t he usef ul l i f e of a pi pel i ne.Much coul d be l earned about cor rosi on mechani sms under

aut hent i c f i el d condi t i ons by det ai l ed exami nat i on of cor r oded

pi pel i nes. Pi t s and cracks and surr oundi ng envi r ons shoul d be

par t i cul ar l y i nvest i gat ed. Thi s shoul d i ncl ude mi cro pH measure-ment s, mi croscopi c exami nat i on cf t he cor r osi on pr oduct , X- ray

anal ysi s of sol i d cor r osi on pr oducts, met al l ogr aphi c sect i oni ng

and mi croscopi c exami nat i on, chemi cal anal yses, bact er i ol ogi cal

cul t ures, etc. Much woul d. be gai ned i f t he i ndust ry knew mor e

about t he basi c corrosi on i nechani sms associ at ed wi t h pi pel i nes.St eel pi pe sel domf ai l s by uni f ormcor rosi on. I t. f ai l s pre-

domi nant l y by l ocal i zed et t ack i n t he f ormof pi t s. The pi t s

ar e i ni t i at ed by some sor t of i nhomogenei t y. Chl ori de i on seemsto be par t i cul ar l y i mpl i cat ed as a causat i ve agent f or pi t t i ng,

as wel l as f or crevi ce cor rosi on.

c

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S t r a y di rec t c u r r e n t s f ro m e lec t r ic r a i l w a y s , h i g h v o l t a g e

d i r e c t c u r r e n t (HVDC) power t r a n s mi s s i o n , pick- up from o v e r h e a dAC power l i n e s , and c a t h o d i c p r o t e c t i o n have caused and w i l l

c o n t i n u e t o c a us e s e r i o u s c o r r o s i o n p ro bl em s. I d e a l l y , e l e c t r i c

r a i l w a y s and power t r a n s mi s s i o n l i n e s s h ou l d n o t c o n t a c t t h e

s o i l , much less u se s o i l r e t u r n f o r any po r t i o n of the power.F u r t h e r s t u d i e s on t h e e f f e c t of KVDC are need ed, and methods of

r e du ci n g t h e c o r ro s i on e f f e c t s o f HVDC need t o be developed.

i n f l u e n c e o f AC on cor ros ion has no t been wel l e x p l o re d , b u t i s

The

known t o cause some c o r r o s i o n .

power t o water l i n e s s h o u ld be d i s c o n t i n u e d .

The p rac t i ce of grounding AC

C a t h o d i c p r o t e c t i o n i n t e r f e r e n c e i s genera l ly be ing hand ledw e l l by p r i v a t e groups b u t w i l l con t inue t o be a p e r s i s t e n t

problem.

h igh dens i ty o f underground meta l l i c s t r u c t u r e s creates seve re

i n t e r f e r e n c e prob le ms a nd may b e i n e f f e c t i v e du e t o e l e c t r i c a l

shie ld ing. Methods f o r a v oi d i ng i n t e r f e r e n c e a nd s h i e l d i n g i n

C a t h o d i c p ro t e c t i o n of p i p e s i n areas c o n t a i n i n g a

some s u ch s i t u a t i o n s d o n o t a p p ea r t o b e a v a i l a b l e o r k nown.

U n q ua l i fi e d c a t h o d i c p ro t e c t i o n e n t h u s i a s t s may u n w i t t i n g l y

create i n t o l e r a b l e c o r r o s i o n h a z a rd s t o u nbonded me c ha n i ca l l y

c ou pl ed un der gr ou nd f a c i l i t i e s . Anodes discharging 1 0 o r m o r e

amperes 0 5 current may create a h a za rdo u s g r a d i e n t w i t h i n ar a d i u s of 1 0 0 0 f ee t . Endangered s t ru c t u r es may inc lu de g round

w i r e s , r e i n f o r c i n g b a r s i n c o n c r e t e, and t h e l i k e , i n a d d . i t i o nt o l e a d c ov er ed c a b l e s a nd u t i l i t y p i p i ng .

The va r ious types of mec ha ni ca l c o r ro s i o n e f f e c t s i n t h eunderground environment are n o t well unders tood . I n p a r t i c u l a r ,

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n o c e r t a i n method i s known f o r av o i d in g ca t a s t r o p h i c f a i l u r e by

stress c r ack i n g of h i g h s t r e n g t h steels. Hard s p o t s i n t h e

p i p e due t o manufacture and welding should be avoided . I t i s

n o t ev en c e r t a i n t h a t stress c r ack i n g i s l i m i t e d t o h i g h s t r e n g t h

steels. There i s some ev idence t h a t ca thod ic p ro tec t ion may

cause hydrogen embri t t lement of some steels, b u t more fundamental

knowledge i s bad ly needed. C a u s t i c e rnbr i t t l ement c r ac k i n g may

take p lace downst ream from compressor s t a t io n s when ca t hod ic

p r o t e c t i o n i s a p p l i e d , b u t t h i s p o s s i b i l i t y h as n o t been ade-

q u a t e l y i n v e s t i g a t e d .

Twenty-two l eaks w e r e a t t r i b u t e d t o h y d r o g e n b l i s t e r i n g by

t h e su rve yed compani es. Hydrogen i s g en e r a t ed both by corrosion

i n an ac i d env ir on ment and by ca t h o d i c p r o t ec t i o n , e s p e c i a l l y a th i g h p o t e n t i a l s . Metals w i t h v o i ds a nd i n c l u s i o n s a r e p a r t i c u -

l a r l y s u s ce p t i b le .

I n t e r g r a n u l a r c o r r o s io n of man y s t a i n l e s s steels i s r a p i d

when t h e t he r ma l c y c l e of w el di ng g e n e r a t e s c e r t a i n t y p e s of i n-

homogenei t ies .

Temperature has an effect on co r r o s i o n . I n f r o zen soi ls , no

c o r r o s i o n of steel p i l i n g s was observed . Th i s cann o t be e x t r a p-

o l a t e d t o t r a n s p o r t a t i o n of pe t ro leum i n cold envi ronments ,

s i n c e t h e p i pes would be h ea t ed i n such cases. Stress c o r r o s i o n

c r ack i n g i s more common i n p ipe le ad in g f rom compressor s t a t i o n s ,

.l

presumably because of e l e v a t e d t e mp e r at u r es t h e r e .

Al though co r ros ion occurs on a l l steel b u r i e d underground,

t h e c o r r o s i o n ra te can be n z g l i g i b l y low. It has been foundt h a t leaks i n a p i p e l i n e occur p redominant ly i n soils l o w i n

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r e s i s t i v i t y . P i t t i n g o f p i p e l i n es i n s t a t i s t i c a l l y u n i f o r m s o i l s

w a s f ou nd i n a t least one i n s t a n c e t o o c cu r o n l y a t p o i n t s where

t h e r e s i s t i v i t y was below about 1 2 0 0 ohm-cm. Noncorrosive soi l

i s g e n e r a l l y i n d i c a t e d by a h ig h r e s i s t i v i t y , 5 0 0 0 ohm-cm o r

h i g h e r . I t s hou ld be no t e d , how ever , t h a t r e s i s t i v i t y may c ha nge,

f o r example by a p p l i c a t i o n o f c he mi ca l f e r t i l i z e r s . T he re i s a

growing r e a l i z a t i o n t h a t o t h e r f a c t o r s , i n c l u d i n g t h e change i n

s o i l r e s i s t a n c e , t h e ch em ic al s p e c i e s i n t h e s o i l , t h e m o i st u r e ,

a nd t h e t e x t u r e , c an also i n f l u e n c e c o r r o s i o n .

Ch l o r i de i on i s known t o accelerate co rro s io n. Hydrogen su l -

f i d e accelerates c o r r os i o n and c an c aus e s u l f i de stress c r a c k i n g .

Carbon d i ox i d e p re s s u re s ove r 3 0 p s i i n w e t o i l a nd g a s c a us e

cor r os io n . Calcium io n and low carbona t e conc ent r a t io ns are

o f t e n b e n e f i c i a l i n t h a t C a C 0 3 p r o t e c t i v e scales can be formed.The s p l a s h a nd t i d a l z ones i n seawater are t h e most c o r r os i v e

marine envi ronment . Fur the rmore, ca thodi c pr o t ec t i on i s i n e f f e c-

t i v e t h e r e . F or p i p e i n seawater , however , no co at in gs are nec-e s s a ry w i t h c a t hod i c p r o t e c t i on be ca use t h e c u r r e n t c a us ed he avy

p r o t e c t i v e d e p o s i t s t o form. The bes t co at in gs have been found

t o be formed a t l ow e r c u r r e n t d e n s i t i e s < 1 5 0 mA/ sq f t ) and t oc o ns i s t p r i m a r i l y o f c al c i um c a rbona t e . One c a n cause s i m i l a r

de p os i t s t o fo rm on bu r i e d p i pe by a ddi ng ca l ci um b i c a rbona t e

t o t h e b a c k f i l l and zipplying c a t ho d i c p r o t e c t i o n .I t i s known t h a t p roduc t s of mi c r o b i o l o g i c a l m e t a b o l i s m can

accelerate c o r r o s i s r l .mat ion unde r a na e rob i c c ond i t i o ns a nd a c c e l e r a t e c o r r os i o n . The

e x t e n t t o w hich mic ro-o rg an ism s c o n t r i b u t e t o p i p e l i n e c o r r o s i o n

S u l f a t e r e duc i ng bac ter ia cause H2S f o r-

165__-. I -


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i s uncer ta in . Very l i t t l e good f i e l d d a t a are a v a i l a b l e . T h e r e

t e n d s t o be a s i g n i f i c a n t p o l a r i z a t i o n of o p in i on on t h i s s u b j e c t .

The us e of b i oc i de s ha s bee n l i mi t e d .In t h e a tmos phere, c o r ros i on i s a c c e l e r a t e d by m o i s t u r e ,

wind-blown sea sa l t , s u l f u r d i o x i d e , and t o some extent , ozone.

The combined effect o f d i l u t e s u l f u r i c a c i d a nd ozone i s worse

than the sum of t h e i r i n d iv i d ua l e f f e c t s .

Al though no fe r rous m e t a l i s untouched by cor ros ion , the

e x t e n t of c o r r o s i o n i s s i g n i f i c a n t l y i n f lu e n c ed by t h e e x a c t

composi t ion of t h e metal and by thermal and mechanical t rea tments .

U nfo r t una t e l y , most of t h e ad d i t iv es which markedly improve cor ro -

s i o n r e s i s t a n c e are p robably t o o expens ive f o r use i n l a r g e p ipe-

l i n e s y s t e m s .

Welds are n ot ed t o be p a r t i c u l a r l y s u s c e p t i b l e t o c o r r o s i o n .

Greater unders tanding of t h e e f f e c t o f w el di ng c o n d i t i o n s on c o r -

r o s i o n i s needed. The in f l ue nc e of m e t a l inhomogene i t i e s i ss c a r c e l y u nd e rs t oo d , b u t i s probably s e r i o u s . Methods of p ro-

duc ing p ipes could probably be developed t o a void such problems.

Al th ou gh most c o r r o s i o n o c c u r s e x t e r n a l l y , i n t e r n a l c o r r o s i o n

i s also a problem when moi s t ure and c h l o r i d e i o n , hydrogen su --f i d e , or carbon d ioxide are p r e s e n t . T h i s h a s b e e n c o n t r o l l e d

by removing moi s tu re , adding i n h i b i t o r s , o r c o a t i n g . P ro pe r i n -h i b i t o r s a r e s e l e c t e d e m p i r i c a ll y . The mechanism o f i n h i b i t o ra c t i o n i s poo r ly u n d e r s t s z d . I n p a r t i c u l a r , it i s n o t y e t pos-s i b l e t o c o n fi d e nt l y s p e c i f y an i n h i b i t o r f o r a ny g i a e n a p p l i-c a t i o n . Q u a n t i t a t i v e i n v e s t i g a t i o n s of i n h i b i t o r e f f e c t i v e n e s s

a nd a pp l i c a t i on p roc e dure s are needed and should be pub l i she d i n


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t h e open l i t e r a t u r e . I t i s impor t an t t o n o t e t h a t many i n h i b i t o r s

accelerate c o r ro s i on i f t h e i r c o nc e nt r at io n i s too l o w .

The c o r r o s i o n f a i l u r e ra te o f u n p r ot e c te d p i p e l i n e s t e n d s t o

i n c r e a s e w i th t i m e . A widely used method o f co r ros ion co n t ro l i s

t h e a p p l i c a t io n of coa t ings . Al though metal c o a t i n g s are e f f e c -Pi t i v e under some c o n d i t i o n s , t h i c k o r g a n i c c o a t i n g s are g e n e r a l l y

favored f o r underground use where p ro te c t io n i s r e q u i r e d f o r l o n g

p e r i o d s . These c o a t i n g s are i d e a l l y w a t e r impervious , electr ic-

a l l y i n s u l a t i n g and t ou gh. G e ne r al ly , t i g h t a d h e s i o n t o t h e p i pei s a l s o r eq u i r ed , a l t h o u g h good r e s u l t s have b een r ep o r t ed w i t h

loose f i t t i n g p l a s t i c s h e a th s . The r eq ui re me nt f o r water perm-

e a b i l i t y i s p robab ly even more severe when the c o a t i n g i s n o tbonded t o t h e p i p e . I t s ho ul d be n o t ed t h a t no p e r f e c t c o a t i n g

material e x i s t s , a n d so con t inued search fo r improved materials

i s j ustif ied .The most common circ umst ance f o r l e a ks developed i n co at ed

p i p e w a s p h y s i c a l damage of t h e c o a t i n g . The second most common

ci rcumstance w a s co r r o s i o n a t improper ly app l i ed coa t ings . Micro-

organ i sms a t t ack m o s t , if n o t a l l , o r g a n i c c o a t i n g s . T h e r ef o r e,one c a n n o t assume t h a t once a p i p e i s c o a t e d , i t r emains e f fec-t i v e l y c o at e d f o r e v e r . I n s pe c t io n and r e p a i r are n eces sa r y n o t

m l y when l ay in g p ip e , bu t also p e r i o d i c a l l y t h e r e a f t e r . Themaintenance requi rements are p robably p a r t i c u l a r l y s e v e r e when

c a t h o d i c p z . = t e c t i o n i s n o t e r i p l o y e d s i m u i t a n e o u s l y .*Although se ldom used for. p i p p s ca r r y i n g g as an d o i l , c o n c r e t e

c o a t i n g s car, p r ov i de e f f e c t i v e cea r ros ion conLro l . C o n c r e t e ' se f f e c t i v e n e s s i s l a r g e l y due t o i t s h igh pH. Agair., p rop e r

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a p p l i c a t i o n i s r e q u i r e d i n c l u d i n g c h oo si ng t h e p r o p e r c o n c r e t e

mix.

I n c a t h o d i c p r o t e c t i o n , c o r r o s i o n i s reduced by making the

p i p e n e g a t i v e w i t h r e s p e c t t o t h e a d j a c e n t s o i l . C a th o di c p r o-

t e c t i o n i s n o t a panacea f o r a l l c o r r os i o n p robl ems. N e i t he r ist h e p r o pe r a p p l i c a t i o n of c a t h o d i c p r o t e c t i o n a t r i v i a l m at te r .

I n c r e a s e d c o r r o s i o n d ue t o c a t h o d i c p r o t e c t i o n h a s a c t u a l l y been

1

observed when steel was co n t i nu o u s ly o r i n t e r m i t t e n t l y heated

and in te rm i t t e n t l y we t ted . Such con di t ion s would be expec ted on

p i p e s j u s t downstream from compressor s t a t i o n s i n a r e a s where t h e

s o i l i s i n t e r m i t t e n t l y d r y and w e t . Ca t hod i c p ro t e c t i o n c a n i n -

crease t h e l e a k r a t e a t f i r s t when a p p l i e d t o o ld p ipe by loosen-

i n g a d he r en t r u s t scale which prev ious ly covered small h o l e s .

Ca thodic pro te c t io n may e i t h e r be accompli shed by ex t e r na l l y

a p p l i e d DC power o r by a t t achment of s a c r i f i c i a l a no de s, su ch a s

Mg, Zn, o r A l , which are slo wly consumed. E i t h e r method works

when prop er ly i n s t a l l e d and main ta ined .

T h e o r e t i c a l c o n s i d e r a t i o n s g i v e r e a s o n t o s u s pe c t t h a t h i gh e r

t ha n norma l c a t ho d i c p ro t e c t i o n v o l t a ge s may be r e q u i r e d t o s up-

p r e s s a c t i v e s u l f i d e c o r r o s i o n i f , indee d , it i s p o s s i b l e a t a l l .

T h i s a p pa r en t n e c e s s i t y i n t u r n i f iduces e x c e s s i v e a p p l i e d v o l t a g e st h a t t en d t o de s t o ry a nd t o l o os e n t h e c o a t i n g , t h u s s t a r v i n g

bo t h t h e disbonded. and remote a r e a s cf c u r r e n t , f u r t h e r r e q ui r i ngadded c u r r e n t . T h is c y c l i c p r o c es s l e a d s u l t i m a t e l y t o loss i nc o n t ro l o f c a t hod i c p ro t e c t i o n , and l e a k s may de ve lop bo t h i n

p rox i mi ty t o t h e p o i n t of c u r r e n t d r 3 i n a g e and a t remote a r e a s .


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The d i f f i c u l t y i n a ch i e vi n g a c c e p t a b l e p r o t e c t i o n w i th

co at in gs a lo ne has c aused many companies t o supplement coa t-

i ng s wi th ca t hod i c p r o te c t i on . On t h e o t h e r h an d, cathodic

p r o t e c t i o n used a lone can g e n e r a l l y p rov ide adequa te p r o t e c t i o n ,

e x c e p t t h a t l a r g e c u r r e n t s are r e q u i r e d a nd i n t e r f e r e n c e w it h

s t ru c t u r es t h a t may be nearby i s l i k e l y . When used w i t h coat-

i ng s , on ly enough cu r re n t i s r e q u i r e d t o p r o t e c t a r e a s where

ho le s have deve loped i n th e coa t ing s . Thus , c oa t ings and

c a t h o d i c p r o t e c t i o n are o f t e n u se d i n c o nj u nc t io n .

t h e dat a f rom th e surveyed companies in di ca te d a lower corro-

s i o n l e a k rate w i t h co a ted and ca t h o d i ca l l y p r o t ec t ed p i p e

than wi th unp rotec ted p ip e, some le aks d id develop on pro-

t e c t ed p ipe s . Thus th e co n t r o l measures do n o t ap pea r t o be

t o t a l l y e f f e c t i v e . I n many cases, t h i s may r e f l e c t improper

u se of e i t h e r c o a t i n gs o r c a t h o d i c p r o t e c t i o n , o r b ot h.

U s e of ca t h o d i c p r o t ec t i o n and co a t i n g s t o g e t h e r i s n o t

wi thou t p roblems. Cathod ic p ro tec t io n may cause d isbonding

of th e coa t in g . Cav i t i es under d isbonded c o a t i n c ; a r e i d e a lf o r c r ev i ce co r ros ion and microb i o log ica l co r ros i on . To a

l a r g e e x t e n t , c a th o di c p r o t e c t i o n is i n e f f e c t i v e i n d is bo nd ed

a r e a s . C at ho di c p r o t e c t i o n i n c r e a s e s p H i n t h e s ur ro un di nge l e c t r o l y t e , which can cause sapon i f i ca t ion and des t ruc t ionof b i t m i n o u s and s i l i c o n e c o a t i n g m a t e r i a l s . The e x t e n t t owhich ca t h o d i c p r o t ec t i o n w i l l damage o l d co at ing s i s un-

known.

t i o n of c a t h o di c p r o t e c t i o r t o 016 p i p i n g n o t p r ev i ou s l y

Even though

This is important when one i s co n s i d e r i n g ap p l i ca-

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p r o t e c t e d . A t e s t on a s e c t i o n o f t h e o l d p i pe would p roba b ly

be necessa ry i n each ca se .

The p re s e n t me thods o f ve r i fy i n g c a t hod i c p ro t e c t i on are i m-

p e r f e c t . Th i s i s proven by t h e f a c t t h a t c o r r o s i o n l e a k s occ ur

e ve n w i t h c a t ho d i c p ro t e c t i o n . The re a ppe a r s t o be n o e n t i r e l y

s a t i s f a c t o r y c r i t e r i o n f o r v e r i f y i n g t h a t c a t h od i c p r o te c t i o n h as

been achieved . P o t e n t i a l s cannot be made too n e g a t i ve o r c o a t-

i ng s a r e d i sbonde d. M o s t of the surveyed companies used a p i p e

p o t e n t i a l o f 0.85 v o l t re la t ive t o t h e copper s u l f a t e e l e c t r od e

as t h e i r c r i t e r ion f o r c a t h o d i c p r o t e c t i o n . Al th ou gh s a t i s f a c -

t o ry i n many i n s t a nc e s , t h e u se o f a f i x e d p ip e p o t e n t i a l i s

known t o be d e l e t e r i o u s under c e r t a i n c o n d i t i o n s . The second

m o s t common c r i t e r i o n used by t h e surveyed companies w a s a 300

mV d i f f e r e n c e between t he e ne rg i z e d a nd t h e o r i g i na l ope nc i r c u i t p o t e n t i a l s , which i s s i m i l a r t o t h e f i x e d p i p e p o t e n t i a l

c r i t e r i o n i n a d v an t ag e s and d i s a dv a n ta g e s.

The i n s t a n ta n e o u s open c i r c u i t p o t e n t i a l ( t h e p o l a r i z a t i o n

p o t e n t i a l ) and o t h e r p o s s i b l e p r o t e c t i o n cr i te r ia have been poor ly

e xp l o i t e d . The re i s a need f o r a c r i t i c a l r e vi e w o f p os s i b l e

p r o t e c t i o n cr i te r ia , s t a t i s t i c a l methods f o r an aly ses and of

c o r r e l a t i o n s w i t h bs.sic e lec t rochem: -ca l concept s .Improved methods a r e badly needed bot h f o r d e t e c t i r . g s m a l l

leaks and f o r d e t e c t i n g areas which w i l l s o o n f a i l . A s t a n d a r d

record sys tem should be d e v e l o p e d t h a t w i l l a l l o w c o r r e l a t i o n s

between l e a k frequency and such va:r,abJ.es as s o i l p r o p e r t i e s ,c o a t i n g p r o p e r t i e s , c a th o d ic p r o t e c t i o n c o n d i t i on s , l o c a t i o n ,

etc. A c curat e l e a k r e c o rds a r e va l ua b l e ai d may serve a number


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of purposes i n c l u d i n g p r e d i c t i n g f u t u r e l e a k s , l o c a t i n g areas

f o r r e c o n d i t i o n i n g o r c a t h od i c p r o t e c t i o n and i n d i c a t i n g p r e-

c a u t i o n s t o ta ke when l ay i n g new pi pe . The re co rd s, however,

s ho ul d c l e a r l y i n d i c a t e c a u s e s so t h a t damage by ot h e r s may no t

be confused w i t h l e a k s caused by c o r r o s i o n a l one ..

Ca s i ngs a round p i pe s unde r roa dbe ds a nd r a i l roa d t r a c ks ha ve

been shown t o be no t on l y unne c es s a ry i n most cases, b u t d e l e t e -

r i o u s f r o m a c o r r o s i o n s t a n d p o i n t as w e l l . When t h e m e t a l cas-

i n g s are s h o r t e d t o t h e p i p e , c a t h o di c p r o t e c t i o n i s i n e f f e c t i v e .

Much money i s be ing n e e d l e s s l y wasted on unnecessa ry c a s i n g s .

One of t h e gr e a t es t needs i s f o r more d at a on th e economics

of c o r r o s i o n c o n t r o l . T h i s i s p a r t i c u l a r l y n o t i c e a b l e i n d i s-

c us s i ons o f c oa t i ng s , where one wi s he s t o maximize t h e r a t i o of

s a v i n gs t o c o s t . I d e a l l y , t h e optimum c o a t i n g t h i c k n e s s f o r

e a c h t ype of co a t i ng should be known on t h i s ba s i s . E s t i m a t e s

f o r i n s t a l l a t i o n o f c a t h o d i c p r o t e c t i o n r an g e from less t ha n 0 .5

p e r c e n t t o o v e r 1 0 p e r c e n t of t h e t o t a l p r o j e c t c o s t , and y e t

a c t u a l c o s t s are almost n e v e r r e p o r t e d .

Shor t courses and seminars w e r e f e l t t o be t h e mos t impor tan ti n fo rma t i on s ou rc e fo r t he s u rve yed c ompa ni es ' c o r ros i on c o n t ro l

programs. T h i s r e f l e c t s t h e f a c t t h a t c e r r o s i o n e n g i n e e r i n g i s. n o t t rea ted as a s e p a ra t e a cademic d i s c i p l i n e i n t h e u n i v e r s i t i e s .

Thus , the a r t and sc ien ce of c c r r o s i o n c o n t r o l i s l e a r n e d "o n t h ej o b " by e x p e r i e n c e , s e l f- s t u d y , i t l e e t i n g s , s h Q r t courses , andevening cou rses . There seems t o be a geed f o r more sh or t cou rseswhich go in to 6 . e t a i l on s p e c i f i c a s p e c f s of c o r r o s i o n c o n t r o l ,e . g . , a c a t h o d i c p r o t e e t i o i l c o u r s e , a basic e l e c t r o c h e m i s t r y

17 1


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c o u r s e , a c o a t i n g s c o u r s e , etc . However, co rr os io n cou rse s a lo ne

do no t c ons t i t u t e a de qua t e ba c kground fo r a c o n p e t e n t c o r r o s i o ne n g - n e e r . Experience, good judgment, and a s o l i d fundamen ta lt e c h n i c a l e d u c a t i o n are also needed.

Because degrees are n o t g r a n t e d i n c o r r o s i o n e n g i n e e ri n g ,

t h e r e i s nee d fo r an a de qua te method o f j udg ing t h e qua l i f i c a t i on s

of c o r r os i o n e ng i ne e r s and t e c hn i c i a n s . The p re s e n t met hods a r e

no t a de quat e . Competence o f p r a c t i c i ng e ng i ne e r s , c on s u l t a n t s ,

and t e c hn i c i a ns v a r i e s w ide ly a nd i s d i f f i c u l t t o e v a l u a t e .

Nationwide expansion of c o r ros i on c on t ro l p rog ra ms i n t h e n e a rf u t u r e would be hinder ed by t h e l a c k of s u f f i c i e n t numbe r s of

t r a i n ed and competen t pe rsonne l .

Much of t h e research l i t e r a t u r e a v a i l a b l e on co r r o si o n i s

too s op h i s t i c a t e d a nd compli c at e d f o r u se by t he op e ra t i ng c o m-

p a n i e s . More r e s e a r c h d i r e c t e d t ow ar d t h e s p e c i f i c c o r r o s i o n

problems of t h e p i p e l i n e i n d u st r y i s needed.

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APPENDIX I

EXAMPLE ABSTRACT RETRIEVAL RUN

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*ABSTRACT RETRIEVAL RUN

COLUMN CODE KEYWORDS

11- 1 2 1 UXDERGROUND1 3- 1 4 30 ANAEROBIC BACTERIAL CORROSION

7- 8 10 CARBON STEELS

SOURCE STATEMENT - THE FOLLOWING I N AN ABSTRACT * * * COMMENT - )INDICATES THAT WHAT FC LLOW S I S A COMMENT W R I TTI I i J E3Y MRI. NACEI S THE SOURCE OF THE OTHER ABSTRACTS.

REPORT NO CL AS SI FI CAT IO N CODE

538 538101010 130 0 02010 I V E R S O N , W . 1 9 6 8MICROBIAL CORROSION, W . P . I V E R S O N , NB S A D- 6 7 0 5 0 1 ( 1 9 6 8 ) A P R .***COMMENT- S T U D I E S OF EF FEC T OF MICROORGANISMS, PARTICULARLYSULFATE REDUCERS (DESU LFOBI VRIO) , ON MARINE CORROSION WEREI NI T IA T ED . THE IN AB IL IT Y OF SULFATE REDUCERS TO GROW ON THEAGAR SURFACE T F MEDIA APPEARS TO BE DUE TO THE PRES ENCE O F THEFERROUS SAL T USED AS AN INDIC ATO R FOR HYDROGEN S UL FI DE . EVID ENCE

INDICATES THAT PHOSPHATE MAY BE AN ELECTRON ACCEPTOR I N THECATHODIC DEPOLARIZAT ION OF ST EE L. IRON PHOS PHIDE AND D I V I V I A N I T EWERE PRODUCED BY DESULFOBIVRIO GROWING I N CONTACT WITH MILD STEEL.

THE ORGANISM REDUCES PHOSPHATE I N THE PRESENCE OF HYDROGEN TOFORM A VOLATILE PHOSPHOROUS CONTAINING COMPOUND WHICH I S NOTPHOSP HINE. LIG HT INCREASES THE CORROSION RATE OF STEE L ASIND ICA TE D BY POL ARI ZAT ION MEASUREMENTS. THE CATHODIC PROT ECT IONC 3 R R I 3 N T S REQUIRED TO MAINTAIN A POTENTIAL O F 0.8 VOLTS ON A STEELSPECIMEN I N IN DI RE CT SUNL IGHT WAS FOUND TO BE 1 . 5 TIMES THATREQUIRED I N THE DARK.

5 4 9 5 4 9 3 0 1 0 1 0 1 3 0 0 020 0 I V E R S O N , W . 1 9 6 9ANAEROBIC CORROSION OF MILD ST EE L BY D E S U L F O V ; ' r , l t I i ) , W . P . V E R S O N ,

NBS, NACE CONF . HOUSTON, ( 1 9 6 9 ) . * * * C O M M E N T E X P C R I M E N T S WITHBAC TE RIA PRODUCE CATHODIC DEPO LARI ZATI ON. PHOSPHATE I S ALSO

REDUCED TO PRODUCE F E 2 P AND A GASEOUS PHOSPHOROUS COMPOUND, NOTPH OS PH IN E. HOWEVER, THE CORROSION RATES ATTRIBUTABL E TO CATHODIC

DEPOLARIZATION DO NOT ACCOUNT FOR HIGH CORROSION RATES SOMETIMESOBSERVED I N THE F I E L D . THES E MAY BE DUE TO FORMATION OF

DIFFERENTIAL OXYGEN CELLS, THE ACTION OF H 2 S , OR ALTERNATEANAEROBIC AND AEROBIC CONDITIONS TO PRODUCE SULFURIC ACID.

BENZYL VIOLOGEN IN PLACE OF so4 HAVE PROVER THAT ANAEROBIC

5015 50156010 0 130 060101G G A N S E R , P . 1 9 6 4CATHODIC P R O T E C T I O K FOR AN UNCOATED GAS DISTRIBUTION SYSTEM,P. GANSER, A COLLECTION O F PAPER S ON '3YDERGROUND P I P E L I N ECORROSION, V. 8 , P . 2 4 1- 2 5 3 , ( 1 9 6 4 ) . * * * I N V E S T I G A T I C N O F ANPRINICPAL CAUSE TO BE ANAEROBIC BAC TE RIA . CATHODZC PROT ECTI ON

WAS INSTALLED TO KILL MICRO BES. TO MAKE L I N E CONDUCTIVE A NEW

INCREASING L 3 A K RATE OF UNDERGROUND MAINS INDICATED THE

*T h i s i s an example of a very selective A b s t r a c t R e t r i e v a l R u n .The run i s n o t c o m p l e t e . A t y p i c a l run may select several hund-red p e r t i n e n t abs t r ac t s .

1 7 4


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TECHNIQUE WAS DEVISED FOR SPOT WELDING CONDUCTORS ACROSS P I P ECONNECTIONS USING ONLY A VERY SMALL ( 4 INCHES BY 1 8 I N C H ES)OPENING. OPERATING COST INCLUDING EL EC TR IC IT Y, MAINTENANCE

AND ENGINEERING COST I S 4 . 6 C E N T S / F T . O F P I P E .5102 5 1 0 2 1 0 7 0 0 1 3 0 0 0 2 0 0 3 U T L I N , K . R . V E R N O N , W . H . 1 9 5 2I N V ESTI G A TI O N S ON UNDERGROUND CORROSION. K.R. BU TL IN , W. H. J.VERNON AND L.C. W H I S K I N . IRON STEEL I N S T . SP ECI AL REPT. NO.4 5 , 29-38 ( 1 9 5 2 ) , WATER + WATER ENG., 5 6 , NO. 6 7 1 , 15- 18 ( 1 9 5 2 )JAN. ***FUNDAME NT AL ST UD IE S ON SULFATE-REDUCING q A C T E R I A , ANDANAEROBIC CONDITIONS ARE DESCRIBED. DETAILS OF F IE L D TE ST SON BARE AND PROTECTED BURIE D IRON P I P E S ARE GIVE N. SPE CIME NS

OF COPPER, LEAD, AND GALVANIZED STE EL P I P E ARE INCLUDED I NTESTS NOW I N PROGRESS.***

II

' I N V ESTI G A TI O N S O F TH E EFFEC TS O F THESE BACTERIA O N I R O N I N

.

5598 55983070 0 13030 0 2 0 0 M I N C H I N , L . 1954CORROSION O F P I P E S BY BACTERIA. L . T . MINC HIN. GAS AGE,1 1 4 , 8 , 4 5 - 4 7 , 1 0 1 - 1 0 2 , 1 0 4 ( 1 9 5 4 ) O C T . 7 . * * * E U R O P E A N SURVEYOF MICROGIOLOGICAL ANAEROBIC CORROSION WITH SPECIAL REFERENCETO EXPE RIEN CE I N LOW COUNTRIES . TABL E, PHOTOGRAPHS. 7

REFERENCES.

6 1 2 3 61233070 0 1 3 0 3 0 2 0 2 0 0 S T A R K E Y , R . W R I G H T , K . M . 1 9 4 7ANAEROBIC CORROSION OF IRON I N S O I L WITH PARTICULAR CONSIDERA-TI O N O F THE S O I L REDOX POTENT IAL AS AN IN DICAT OR O F CORROSIVE-

N E S S . R . L . S T A R K E Y AND K . M . WRIGHT AGA. CONDENSATION CORROSION3, 227- 232 ( 1 9 4 7 ) M A Y . * * * D I S C U S S I O N I S PRESENTED ON THEANAEROBIC CORROSION O F IRON I N SOIL, DATA PRESENTED ON THECHARACTERIS TICS O F CORRODED IRON AND ST EE L SURFACES, OR IG INO F SU L FI D E I N S O I L , C H A RA C TERI STI CS O F B AC TER I A CA USIN G

ANAEROBIC CORROSION, IMPORTANCE O F SULFATE R E D U C T . I O N ,MECHANISM OF THE PROCESS O F MICRO- BIOLOGICAL A N A E I

ferrous pipeline corrosion processes (3 of 4) 150-230

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