Correlation Corrosion Mass

8/3/2019 Correlation Corrosion Mass

1/25

C or r os i on S c i e n c e , 1968 , V o l . 8 , p p , 173 to 193 . Pe r gam on p r e s s . Pr in ted i n Gr e a t B r i ta i n

S TE EL PIP E C O R R O S I O N U N D E R F L O WC O N D I T I O N S - -I . A N I S O T H E R M A L C O R R E L A T I O N F O R A

M A S S T R A N S F E R M O D E L*B. K. MAHATO, S. K. VOORA and L. W. SHEMILT

Department of Chemical Engineering, University of New Brunswick,Fredericton, New Brunswick, CanadaAbstraet--A critical review of the existing literature on the effect of velocity on the corrosion of Feand steel in water has been made. Based on a doubl e resistance model with one resistance significantlytime-dependent, the analytical form required to portray the corrosion amount-time relationshipfor the steel pipe-water system has been established. A modified mass transfer coefficient withdeterminable relationship to the Re number for flow conditions has been obtained. An adequatesemi-empirical correlation for corrosion rate, either in usual units or in a dimensionless form, as afunction of Re nu mber and a dimensionless diffusion group has been obtained for isothermal flowconditions.This correlation, based on corrosion as an unsteady state mass transfer process, adequatelyrepresents new data on corrosion of steel pipe at 150F in natural water, as well as available datafrom other laboratories.R6sum6----On a fait une revue crit ique de ce qui a 6t6 publi6 sur l'effet de la vitesse d'6coul emen t d'ea usur la corros ion du fer et de l'acier. A part ir d 'un mod~le b. double rdsistance den t u ne est' fonc tion dutemps, on a r6alisd l'6quation qui donne la valeur du montant de la corrosion en fonction du tempspour le syst/~me d'un conduit d'eau en acier.

On a obtenu un coefficient modifid d'6change de masse en fonction du nombre de Reynolds etdes cond itions de l'&:oulement. Une relation semi-empirique qui ddter mine le taux de corros ion enfonction du hombr e de Reynolds et d'un nombre de diffusion (non-dimensionelle) a dt6 obtenu po urcondition isotherme. Cette dquation, bas6e sur un mod~le qui voit la corrosion comme 6tant unproc6dd de transfer de masse variable avec le temps, d6termine suffisamment bien les valeursexpdrimentales obtenues pour la corrosion d'un tuyau d'acier par eau naturelle ~ 150F, et aussiautres valeurs obtenues par divers chercheurs.Zusammenfassung--Es wird ein kritischer 0berbl iek iiber die vorhand ene Literatur gegeben, die denEinflug der Str6mungsgeschwindigkeit auf die Ko rrosio n von Eisen und Stahl in Wasser behandelt.Auf der Grundla ge eines Zwei-Widerstan d-Modells, bei dem ein Wider stand deutlich zeitabh,~ngigist, wird die analytische Form des Korrosionszeitablaufs fi.ir den Angriff yon Stahlrohren dutc hWasser aufgestellt. Ein abgew andelter Stoffiibergangskoeflizient, der in de3niert er Weise yon derReynolds -Zahl abhiingt, wird fiir unterschiedliche Str6mun gsbedin gungen erhalten. Ein angemessener,halb empirischer Zusammenhan g zwischen der Korrosionsgeschwindigkeit und der Reynolds-Zahlsowie einer dimensionslosen Diffusionszahl wird fiir isotherme Str6mun gsbedingungen angegebensowohl in den iiblichen Einheiten als auch in dimensionsloser Form.Dieser Zusammenhang, der die Korrosion als einen instation~ren Stoffiibergang darstellt,entsp richt gut Messun gen der Ko rro sio n von Stahlrohre n in natiirlichen W/issern bei 150F und auchden Ergebnissen, die in anderen Laboratorien erhalten wurden.

The Russian abstract for this Manuscript will appear as a loose insert in the next issueof this Volume.

*Manus cript received 28 July 1967.173


2/25

174 B.K. MAHATO,S. K. VOORAand L. W. SHEMILT

I N T R O D U C T I O NT i m p r a c t i c a l i m p o r t a n c e o f t h e c o r r o s i o n o f F e h a s l e d t o a v a s t l i t e ra t u r e i n t h e f ie ld .I n t h e c as e o f c o r r o s i o n i n a q u e o u s e n v i r o n m e n t th e i m p o r t a n t v a r i a b l e s re c o g n i z e dh a v e b e e n t h e a m o u n t o f d i s s o lv e d O , t e m p e r a t u r e , f l o w c o n d i t i o n s , p H , m e t a lc o m p o s i t i o n , d u r a t i o n o f e x p o s u r e , a n d c o m p o s i t i o n o f w a t e r . 1 W h i l e m a n y i n v e st i g a-t i o n s o f t h e s e i m p o r t a n t f a c t o r s h a v e b e e n c a r r i e d o u t , t h e c o r r e l a t i o n o f s o m e o r a l l o ft h e m h a s n o t b e e n a d e q u a t e l y a c h i e v e d . T h i s i n v e s t i g a t i o n r e p o r t s o n a n i n i t i a le f f o r t t o c o r r e l a t e th e f a c t o r s o f a m o u n t o f d i ss o l v e d O , f lo w r at e s , a n d d u r a t i o n o fe x p o s u r e . T h e a d d i t i o n o f t h e t e m p e r a t u r e p a r a m e t e r i s a l so c o n t e m p l a t e d , a s isv a r i a t i o n i n w a t e r c o m p o s i t i o n . A t t h i s s t a g e i t i s a s s u m e d t h a t m e t a l c o m p o s i t i o na n d w a t e r c o m p o s i t io n a r e m a i n t a i n e d c o n s t a n t a n d t h is p a p e r r e p o r t s a n i s o th e r m a li nve s t i ga t i on .

I t i s w i d e l y r e c o g n i z e d t h a t t h e c o r r o s i o n o f F e m a y b e a c c o u n t e d f o r b y a na n o d i c r e a c t i o n , e q u a t i o n 1 a n d a c a t h o d i c r e a c t i o n e q u a t i o n 2 , i ll u s tr a ti n g t h e b a s i ce l e c t ro c h e m i c a l n a t u r e o f t h e c o r r o s i o n p h e n o m e n a . 2

F e ---> F e ++ + 2e (1)2 H + + 2e ---> H2. (2)

I n t h e p r e s e n c e o f O , d e p o l a r i z a t i o n o f t h e c a t h o d i c p r o d u c t s t a k e s p l a c e a c c o r d i n gt o e q u a t i o n 3 .

02 + H~O + 2e --> 2O H -. ( 3 )I n m o s t s i t u a t i o n s i t i s t h e c a t h o d i c r e a c t i o n a n d t h e s u b s e q u e n t d e p o l a r i z a t i o n b yo x y g e n t h a t t e n d t o c o n t r o l t h e r a t e a t w h i c h F e c o r r o d e s . H o w e v e r , e q u a t i o n 3 isg e n e r a ll y so r a p i d t h a t O c o n c e n t r a t i o n a t t h e c a t h o d i c s u r f a c e a p p r o a c h e s z e r o . I t i st h e r e f o r e a cc e p t e d t h a t t h e r a t e o f O d e p o l a r i z a t i o n d e p e n d s o n t h e r a t e o f t h ed i f fu s i o n o f O t h r o u g h t h e r e s i s ta n t f il m s a t t h e s u r f a c e o f th e m e t a l . O n e o f t h ed i f fu s i o n b a r ri e r s i s d u e t o t h e c o r r o s i o n p r o d u c t , o f t e n l a r g el y c o n si s ti n g o f F e ( O H ) 2a c c o u n t e d f o r b y c o m b i n i n g e q u a t i o n s 1 a n d 3 :

F e + H 20 + 02 ---> F e ( O H ) 2 ( 4 )F e ( O H ) 2 + H ~ O + O 2 --~ F e ( O H h ( 5 )

F e r r o u s i o n i s c o n v e r t e d t o t h e f e r ri c s t a te b y f u r t h e r o x i d a t i o n a s i n e q u a t i o n 5 a n d


3/25

Steel pipe corrosion under flow conditions 175m o s t o r d i n a r y r u s t i s c o m p r i s e d o f t h e h y d r a t e d f e r r ic o x id e . F r e q u e n t l y a b l a c k l a y e ro f m a g n e t i c h y d r o u s f e r r o u s f e r r i te ( F e a O 4 . n H 2 0 ) f o r m s b e t w e e n F e ~O 3 a n d F e O .H e n c e i t is c o n s i d e r e d t h a t r u s t f il m s n o r m a l l y c o n s i s t o f t h r e e l a y er s, o f i r o n o x i d e i nd i f f e r e n t s t a te s o f ox i d a t i on , x

E x a m i n a t i o n o f t h e c o r r o s io n p r o c e ss c a n b e m a d e f r o m o n e o r m o r e o f f o u r t y p eso f m e a s u r e m e n t s . F i r s t l y , the w e i gh t l o s s o f m e t a l i t s e l f w i ll be a c om pl e t e i nd i c a t i o no f th e a m o u n t o f c o r r o s i o n , w h i l e s e c o n d l y t h e g r o w t h o f c o r r o s i o n p r o d u c t f i'.m w il lg i ve a n i n d i r e c t i n d i c a t i o n o f t h e a m o u n t o f c o r r o s i o n . T h i s l a t t e r c a n b e r e l a t e dd i r ec t ly t o a m o u n t o f c o r r o s i o n o n l y i f t h e r e is n o l os s o f c o r r o s io n p r o d u c t i n t o t h ea q u e o u s e n v i r o n m e n t , a n d p r o v i d e d t h a t i ts c h e m i ca l c o m p o s i t io n is c o m p l e te l y a n da c c u r a t e l y k n o w n . E l e c t r o c h e m i c a l m e t h o d s i n c l u d e m e a s u r e m e n t s o f c o r r o s i o nc u r r e n t a n d c o r r o s i o n p o t e n ti a l. T h e f o u r t h a p p r o a c h is in t e r m s o f m e a s u r e m e n t o ft he t r a ns f e r o f t he c a t h od e r e a c t a n t , i .e . d i s so l ve d O i n w a t e r , a nd he nc e e s s e n t ia l l ya m a s s t r a n s f e r m e a s u r e m e n t .T h e e q u i v a l en c e o f w e ig h t lo ss , a m o u n t o f c o r ro s i o n p r o d u c t f o r m e d , a n d Ot r a n s f e r o r u p t a k e i s d i r e c t a n d o b v i o u s . N u m e r o u s i n v e s t i g a t i o n s h a v e b e e n m a d e o ft h e r e l a ti o n s h i p b e t w e e n t h e s e a n d t h e e l e c t r o c h e m i c a l m e a s u r e m e n t o f c o r r o s i o nc u r r e n t s a n d o f p o l a r i z a ti o n , a-9 a l t h o u g h l it tl e s u c ce s s h a s a p p a r e n t l y b e e n a c h i e v e d i na c h i e v i n g q u a n t i t a t i v e c o r r e l a t i o n w i t h o v e r a l l s p e c i m e n o r c o r r o s i o n p o t e n t i a l .

I r r e sp e c t i v e o f t h e m e a s u r e m e n t m e t h o d , t h e r e s u lt s o f c o r r o s i o n t e st s a r e u s u a ll ye x p r e s s ed i n re l a t i o n t o t h e t i m e o f e x p o s u r e . T h e g r o w t h o f c o r r o s i o n p r o d u c t fi lmw i t h ti m e , f o r e x a m p l e , h a s b e e n r e p r e s e n te d b y m a n y m a t h e m a t i c a l e x p r e ss i o n s, a n dE va ns 1 ha s p r o v i d e d a t h e o r e t i c a l ba s i s f o r t he s e l a w s o f f i lm g r o w t h w i t h a ge ne r a ls e t o f c u r v e s re p r e s e n t i n g t h e v a r io u s e q u a t i o n s w h e r e t h e a m o u n t o f c o r r o s i o n i se q u a t e d t o t h e O u p t a k e .

T h e a d d e d p a r a m e t e r s e l e c t e d f o r s p e c i a l c o n s i d e r a t i o n i n t h i s i n v e s t i g a t i o n i st h a t o f t h e v e l o c i ty o r f l ow s i t u a t io n i n th e a q u e o u s e n v i r o n m e n t .

A r e v ie w o f l i te r a t u r e d e a li n g w i t h t h e c o r r o s i o n o f F e w h e n v e l o c i ty a n d f l u i df l o w is a v a r i a b l e s h o w s m a n y a p p a r e n t c o n t r a d i c t i o n s . F r i e n d u - a a o b s e r v e d t h ec o r r o s i o n r a t e o f F e i n a n a t u r a l w a t e r t o d e c r e a s e w i th i n c r e a s i n g v e l o c i ty u n t i la b o v e 8 f t ]s i t w a s a l m o s t z e r o , w h i le S p e l l e r a n d K e n d a l l 14 f o u n d t h e r a t e l o w u n d e rl a m i n a r f l o w c o n d i t i o n s , r a p i d l y i n c re a s in g i n t h e t r a n s i ti o n r a n g e , a n d m o r e s l o w l yi n c r e a s i n g u n d e r t u r b u l e n t f l o w c o n d i t i o n s .

W h i t m a n 15 s t a t e d t h a t t h e c o r r o s i o n r a t e s s h o u l d i n c r ea s e a t h i g h e r f l o w r a te sd u e t o a n i n c r e a s e in O d i f f u si o n a n d b r e a k i n g d o w n o f t h e p r o t e c t i v e f il m s o n t h em e t a l s u r fa c e s. W i l so n 18 e m p h a s i z e d t h e e f f ec t o f v e l o c i t y a s a n i m p o r t a n t f a c t o r i ng o v e r n i n g t h e t h i c k n e s s o f t h e f il m t h r o u g h w h i c h O m u s t d i f fu s e i n t h e c o r r o s i o np r oc e s s . E va ns 1 i nd i c a t e d t ha t g r e a t e r t u r bu l e nc e d ue t o h i gh ve l oc i ti e s r e s u l t s in m or eu n i f o r m O c o n c e n t r a t i o n a n d m o s t l i k el y d el ay s t h e i n it ia t io n o f c o r r o s io n o n ap r e v io u s l y u n c o r r o d e d s u rf a ce .

C o x a n d R o e t h e l i x7 o b t a i n e d d a t a f o r s t e el s p e c im e n s i n a e r a t e d n a t u r a l w a t e r( C a m b r i d g e , M a s s ., U . S . A . ) b y v a r y i n g t h e r o t a t i o n a l s p e e d o f th e s p e c i m e n a n d t h eO c o n t e n t i n t h e w a t e r , a n d f o u n d t h a t c o r r o s i o n r a t e i n c r e a s e d w i t h t h e i n c r e a s e d Oc o n t e n t ( u p t o 6 p p m ) a n d i n c r e a s ed p e r i p h e r a l v e l o c i t y ( u p t o 1 .2 ft /s ) .

R o e t h e l i a n d B r o w n as f u r t h e r r e p o r t e d t h a t t h e c o r r o s i o n r a t e s i n c r e a s e d t o am a x i m u m , a s t h e r o t a t i o n a l v e l o c i ti e s o f t h e i r s te e l sp e c im e n s , i n o x y g e n a t e d w a t e r ,


4/25

176 B. K. M.AHATO,S. K. VOORA an d L. W. SI-IF,MILT

i n c r e as e d , t h e n d e c r e a s e d to a v e r y l o w v a l u e a n d i n c r e a se d a g a i n t o a s o m e w h a t h i g h e rva l ue a t ve r y h i gh ve l oc i t ie s .F r e s e 19 s h o w e d t h a t F e t e n d s t o b e c o m e p a ss i v e w i t h h i g h O c o n c e n t r a t i o n a n dt h e c o r r o s i o n r a t e s m a y d r o p t o l o w v a lu e s . S p e ll e r2 obs e r v e d t h a t t he e f f e c t o f v e l oc i t yw a s t o b r i n g O i n t o m o r e i n t i m a t e c o n t a c t w i t h t h e c a t h o d i c s u r fa c e s . T h i s r e s u l t ed i na c t iv e o x i d a t i o n a n d f o r m a t i o n o f p r o t e ct i v e F e ( O H ) 3 fi lm n e a r e r t o t h e r e a c t i o n p o i n t s ,t hus s t i f l i ng t he c o r r o s i on r e a c t i on .W o rm w el1 21 r e p o r t e d t h a t c o r r o s i o n r a t e s w e r e d e t e r m i n e d l a r g e ly b y t h e r a t e o f Os u p p l y t o t h e m e t a l s u r fa c es . H a t : h a n d R i c e 2z o b s e r v e d t h a t t h e c h a n g e i n t h e Oc o n c e n t r a t i o n g r a d i e n t n e a r t h e m e t a l s u r f a c e w a s d u e t o t h e e f fe c t o f v e l o c i ty . I ns p i te o f v e r y h i g h v e lo c i ti e s t h e O c o n c e n t r a t i o n a t t h e m e t a l s u r f a c e w a s o n l y s l ig h t l yg r e a t e r t h a n a t m o d e r a t e v e l o ci ti e s, a n d t h u s t h e c o r r o s i o n r a t e w a s i n c r e a s ed b u t as m a l l a m o u n t .

C o h e n ~3 s h o w e d t h a t i n n a t u r a l w a t e r ( O t t a w a , O n t . , C a n a d a ) p i p e c o r r o s i o ni n c r ea s e d w i t h v e l o c i ty u p t o 4 . 5 f t/ s a n d t h e n d e c r e a s e d w i t h t h e f u r t h e r i n c r e as e o fflOW.C o p s o n u f o u n d t h a t c o r r o s i o n , i n g e n e r al , i n c r e a s e d w i t h i n c r e as e i n v e l o c i ty , b u tt he e f f e c t w a s s om e t i m e s t he op pos i t e . S t r e i c he r z5 e x p l a i n e d t h e d r o p i n c o r r o s i o n r a t e so f s te e l a t h i g h e r v e lo c i ti e s a s d u e t o p a s s i v a t io n b r o u g h t a b o u t b y t h e i n c r e a s e d Os u p p l y . U h l i g 2 h a s r e p o r t e d e x t e n si v e ly o n t h e e f f e ct o f O p a s s i v a t i o n a t h i g h Oc o n c e n t r a t i o n .El ia s sen e t a l . 2 e ,2 7 p r e s e n t e d f u n d a m e n t a l h y d r a u l i c c o n c e p t s a s a p p l i e d t o c o r r o s i o na n d t h e r a t e o f t r a n s f e r o f i n t e r a c t i n g c h e m i c a l s in f l o w o v e r p l a te s , r o t a t i n g d i s ksa n d t h r o u g h p i pe s . H e i n d i c a t e d t h a t t h e v e l o c i t y o f t h e w a t e r, d e g r e e o f t u r b u l e n c e ,g e o m e t r y o f pi p es , a n d o t h e r p h y s i c a l f a c to r s h a v e a d i r e c t i n fl u e n ce o n t h e m o v e m e n to f d is s o lv e d O a n d i o n s t h r o u g h o u t t h e f l u id . T h e s e f a c t o r s i n t u r n e x e r t e f fe z t s o n t h ef o r m a t i o n o f c o r ro s i o n p r o d u c ts , a n d o n d e p o l a r i z a t i o n a n d t h u s o n t h e c o r r o s i o nr e a c t i o n i ts e lf .

D e y 28 o b s e r v e d t h e l o w e s t a m o u n t o f c o r r o s i o n i n b l a c k F e p i p e s p e c i m e n s ,c a r r y i ng V a nc ou ve r ( C a na d a ) c i t y w a t e r , f o r t he h i ghe s t l e ve l o f f l ow r a t e s (i .e . 4 . 5c o m p a r e d t o 0 . 75 , 1 .5 a n d 3 . 0 f t /s ) a t 9 0 F a n d 1 3 0 F , i r re s p e c ti v e o f t e s t d u r a t i o n .H e a t t r i b u t e d t h i s t o t h e p a s s i v a ti n g e f f e c t o f O .

B u t l e r a n d I s o n "9 i n v e s t ig a t e d c o r r o s i o n o f m i l d s t e el p i p e s p e c i m e n s i n f l o w i n gw a t e r o f T e d d i n g t o n ( E n g l a n d ) m a i n s a n d p r e s e n t e d d a t a f o r d i f fe r e n t f l o w r a t e s a n dd i f f er e n t t e m p e r a t u r e s . T h e y f o u n d t h a t t h e c o r r o s i v i t y o f w a t e r is l a rg e l y g o v e r n e db y i ts s c a le - f o r m i n g p r o p e r t ie s a n d a n i n c r e as e i n b o t h s p e e d o f f lo w a n d t e m p e r a t u r ep r o m o t e s t h e d e p o s i t i o n o f a p r o t e c t i v e s ca l e.

R o s s a n d H i t c h e n a s h o w e d t h e i m p o r t a n c e o f w a t e r v e l o c i t y i n t h e d e p o l a r i z a t i o no f c a t h o d i c p r o c es s e s b y a s t u d y o n t h e s h o r t - t e r m e l e c t r o c h e m i c a l b e h a v i o u r o fF e , C u a n d C a r r a n g e d i n a n n u l a r c o u p l e s a n d e x p o s e d t o d i s t i l l e d w a t e r . A ne x p l a n a t i o n o f t h e r e su l ts i n t e rm s o f th e l i q u i d b o u n d a r y l a y e r a t t h e m e t a l s u r f a c ew a s s u g g e s t e d b u t n o t e v a l u a t e d .

B u t l e r a n d S t r o u d a~ s t u d i e d t h e c o r r o s i o n r a t e o f m i l d s t e el t u b e s b y h i g h p u r i t yw a t e r a n d o b s e r v e d t h a t t h e c o r r o s i o n r a t e i n c r e a s e d w i t h i n c r ea s i n g s p e ed o f f l o w t o am a x i m u m v a l u e a t a b o u t 3 . 3 f t / s ; a n y f u r t h e r i n c r e a se r es u l t e d i n a d e c r e a s e d c o r r o s i o nr a t e .


5/25


6/25

1 78 B . K . MAHATO, S . K . V O O R A a n d L . W . S HE M IL T

PIG. I .

Y////

t "2 I 0 2 /( /Y2 Yl w a t e rf low

I . d a m p e d t u r b u l e n c e l a y e r2 . c o r r o s i o n p r o d u c t l a y e r

I I

, II I

6 C b " ' " "

o" ~ci "- ' ;% ,

>d i s t a n c e f r o m wal l

Physical mo del for t ransfer of dissolved 0 for F corros ion process.

d n _ ( D , 4 - ~) ( C b - - C i )d t Y x (6)

( In D v ( C i - - Cw)d t Y 2 (7 )

The resistance, Y2 offered by the corrosion product layer is given by equation 8,assuming it to vary as the amount of corrosion product (or amount of O trans-ferred) and with a resistance coefficient which is independent o f time.

t- k ~ d t = k n . ( 8 )Y~ = d dt

0

The total mass flux is then obtained as in equation 9, which on integration gives aparabolic form, equation 10.

t in D , C bd t D , Y lk n 4 - - (9)D v + ~

a n 2 + { 3 n = t . ( 1 0 )

The mass transfer rate in terms of the coefficients a and [3 is given by equation 11with coefficients defined in equations 12 and 13.


7/25

Steel pipe corrosion under flow conditions 179dn 1d t 2 a n + f~ (11)

ka - - - - "(12)2 D~Cb

_ y x ( 1 3 )Cb ( Dv + ~)T h e c o n v e n t i o n a l o v e r a ll m a s s t r a n s f e r c o e f f ic i en t K o ( e q u a t i o n 1 4) m a y t h e n b ere li a ted to the coe f f ic ien t s c t and ~3 a s in eq ua t io n 15 .

dn- - = K o A C = K o C b ( 1 4 )d t1Ko = (15)C b ( 2 u n q- ~ )

C o n s i d e r i n g t h e t w o m a s s t r a n s f e r c o ef f ic i en t s i n s er ie s (e q u a t i o n I 6 ) , a n d w i t h t h ec o r r o s i o n p r o d u c t l a y e r p r o v i d i n g t h e g r e a t e r r e s is t a n c e ( e q u a t i o n 1 7), t h e s i g n i f ic a n tm a s s t r a n s f e r c o e ff i ci e n t K ~ m a y t h e n b e f o u n d i n t e r m s o f s y st e m p r o p e r t i e s ( e q u a t i o n18).

1 _ 1 + 1 = C b f ~ - { - C b 2 c t n (16)/('1Ko = K 2 w h e n K 2 < < K t (17)_ 1 1 _ D ~ I ( 1 8 )

, - - - - . - -K 2 2C b( ~ n k nI n t h i s f o r m , h o w e v e r , i t d e p e n d s o n t h e t o t a l a m o u n t o f O t r a n s f e r r e d , a n d i s b e t t e rd e f i n e d a s a m o d i f i e d t i m e - i n d e p e n d e n t m a s s t r a n s f e r c o e f f i c ie n t K 2.

K ~ - - D v ( 1 9 )kI n t h i s f a s h i o n , m e a s u r e m e n t o f c o r r o s i o n a m o u n t s , r e l a t e d t o t i m e a s i n e q u a t i o n 1 0,c a n b e u s e d t o p r o v i d e a m a s s t r a n s f e r c o e f fi c ie n t .

A P P A R A T U S A N D P R O C E D U R E F O R C O R R O S I O N M E A S U R E M E N T ST h e r e - c ir c u l a t in g f l o w a p p a r a t u s ( F i g . 2 ) c o n s i s t e d o f a b e a t i n g t a n k , p u m p

d i s t r i b u t o r a n d c o l l e ct i n g r e s er v o i r s, w i t h t h e n e c e s s a ry v a lv e s a n d f l o w m e t e r s . T h ed i s t r i b u t o r a n d c o l l e c t i n g r e s e r v o i r s c o u l d a c c o m m o d a t e s e v e r a l t e s t s e c t i o n s s i m u l -t a n e o u s l y . A l l m a t e r i a l s u s e d w e r e e i th e r p o l y e t h y l e n e o r n e o p r e n e , w i t h t h e e x c e p t i o n


8/25

1 8 0 B . K . M A H A T O , S . K . V O OR A a n d L . W . S H E r m L r

1 4

12 - ' - . . - iJI I

I I 0 ~ 6' r '8 7 9 I I

I

T

FIG. 2. Schem atic diagram o f the recirculating corrosion test apparatus.I. Distributor tank. 2. Flow stabilizer. 3. Test section. 4. Silver-silver chloride electrode .5. Collecting tank. 6. Thermom eter. 7. Supply tank. 8. Level indicator. 9. Air bubbler.10. Feedback line. 11. Compressed air line. 12. Feed water line. 13. Sampling point.14. Sam ple cooler. 15. Byp ass line . 16. Lead ing to drain. 17. Flow me ter.

o f v a l v e s a n d p u m p w h i c h w e r e l in e d w i t h H e r e s i t e . E a c h t e s t s e c t io n w a s p r e c e d e dw i t h a f lo w s ta b il iz e r a n d a d i a p h r a g m v a lv e f o r m a n u a l c o n t r ol . T h e w a t e r t e m p e r a t u r ew a s c o n t r o l l e d t o w i t h i n 0 .5 F . A b o u t 1 2 p e r c e n t o f t h e v o l u m e o f th e s y s t e m w a t e rw a s r e p l a c e d d a i l y b y f r es h w a t e r .

T h e t e s t s ec t io n s w e r e c o m p o s e d o f s ix o r t w e l v e ~ i n. d i a . ( s c h e d u le 4 0 ) b l a c kF e p i p e s p e c i m e n s , e a c h 3 i n. l o n g . T h e s p e c i m e n s w e r e c o n n e c t e d w i t h c o u p l i n g sa n d s e p a r a t e d b y a c ry l i c w a s h e r s . T h e y w e r e c a r e f u l l y m o u n t e d , a n d s p e c i a ll y r e a m e dt o p r e v e n t a n y d i st u r b a n c e o f t h e fl o w p a t t e rn . A b o u t h a l f o f t h e s p e c i m e n s w e r ec o n n e c t e d e l e c tr i c al ly to a p o t e n t i o m e t e r . A A g - A g C I e l e c tr o d e f o r r e f e re n c e p u r -p o s e s w a s i n s e r te d in t h e c o l l e c ti n g r e s e r v o ir . D u r i n g t h e t e s t r u n s , t h e p o t e n t i a l sw e r e r e c o r d e d p o t e n t i o m e t r i c a l l y a t f r e q u e n t i n t e r v a l s . T h e w a t e r u s e d w a sF r e d e r i c t o n c i t y t a p - w a t e r , w h i c h is w e l l w a t e r w i t h a t o t a l a l k a l i n it y , a s C a C O s , o fa b o u t 8 0 p p m , a t o t a l d i s s o l v e d s o l id s o f 10 0- -1 50 p p m , a n d p H ,- , 7 .2 . D a i l y s a m p l e so f w a t e r w e r e t a k e n d u r i n g t h e t e s t r u n a n d a n a l y s e d f o r F e c o n t e n t , O c o n t e n t , a n dp H .

A l l s p e c i m e n s w e r e c a r e f u l l y m a r k e d a s t o l o c a t i o n a n d w e r e c a r e f u l ly c le a n e d a n dw e i g h e d b e f o r e u s e. A t t h e e n d o f a d e f in i te t e s t p e r i o d t h e s p e c i m e n s w e r e r e m o v e d ,d r i e d a n d r e w e i gh e d . T h e c o r r o s i o n p r o d u c t s w e r e th e n r e m o v e d , t h e s p e c im e nc a t h o d i c a l l y c l e a n e d ~9 a n d w e i g h e d . M o s t t e s ts w e r e p e r f o r m e d o n t w e l v e s p e c i m e n sa l t h o u g h i n s o m e c a s e s o n l y s i x w e r e u s e d . A l l r e s u l t s w e r e a v e r a g e d a n d s t a n d a r d


9/25

Steel pipe corr osion under flow condit ions 181

d e v i a t i o n s o b t a i n e d . F l o w r a t e s w e r e c o r r e c t e d t o p i p e R e n u m b e r s ( R e = DtUp/[ . tba s e d on i n i t i a l p i pe d i a m e t e r s .

T h i s r e p o r t c o v e r s te s ts c a r r i e d o u t a t 1 5 0 F a t a s e ri es o f f o u r f l o w r at e s a n d f o rv a r i e d t e s t d u r a t i o n s u p t o 2 5 d a y s .

R E S U L T S A N D D I S C U S S I O NT h e s t a n d a r d d e v i a t i o n s o b t a i n e d f o r t h e w e i g h t l o s s m e a s u r e m e n t s w e r e n e v e r

g r e a t e r t h a n 8 p e r c e n t a n d u s u a l l y l e s s t h a n 5 p e r c e n t . N o c o n s i s t e n t v a r i a t i o nr e l at i v e t o t h e s p e c i m e n p o s i t i o n w a s n o t e d . N o a p p r e c i a b l e b u i l d - u p o f F e i n th ew a t e r a n d n o s i g n i f ic a n t c h a n g e i n p H w e r e f o u n d , a n d t h e d i s s o lv e d O c o n t e n t w a sc l o se t o s a t u r a t e d c o n d i t i o n s t h r o u g h o u t t h e te s t d u r a t i o n s . B l a n k t e s ts o n t h e m e t h o do f c a t h o d i c c l e a n i n g i n d i c a t e d a n i n s ig n i f ic a n t w e i g h t l o s s.

V i su a l a n d m i c r o s c o p i c in s p e c ti o n o f t h e c o r r o s i o n p r o d u c t s s h o w e d a p o r o u s ,r u s t - c o l o u r e d p r e c i p i ta t e u n d e r l a i d b y a f i ne , d e n s e , g r a n u l a r , b l a c k f i lm i n a g r e e m e n tw i t h u s u a l o b s e r v a t i o n s u n d e r s i m i la r s i tu a t io n s . T h e s u r f a c e ro u g h n e s s c h a r a c t e ri s t ico f th e c o r r o s i o n p r o d u c t v a r i e d w i t h e a c h f lo w r a t e a n d e a c h t e s t p e r i o d . I n a l m o s t a llc a se s c o r r o s i o n w a s q u i t e u n i f o r m o v e r t h e s p e c im e n s u r f a c e. T h e c o r r o s i o n p r o d u c ts u r f a c e w a s w a v y i n a p p e a r a n c e w i t h s ig n i f ic a n t p e a k s a n d v a l le y s , t h e p e a k s p r o -j e c t in g i n t h e d i r e c t i o n o f fl o w . F i g u r e s 3 a n d 4 g i v e s o m e i n d i c a t i o n o f t h e e f f ec t o ff lo w r a te a n d o f t es t d u r a t i o n o n t h e e x t e r i o r f o r m o f t h e c o r r o s i o n p r o d u c t .

7000

-Q

0=ooa :a .

o~ no

o(. 1

Zo

200~

O

F[o. 5. Relationship

O W I I I |0 1 0 0 0 2 0 0 0 3 0 0 0 4 ooo

A M O U N T O F C O R R O S I O N , m d

between the amount of corrosion product and the amountof corrosion.


10/25


11/25

.trc af the corrosion product layer. Test periodm p e r a t u r c 1 5 0 FI O ; ( c ) R c 2 6 , 2 1 0 : ( c l ) R e 2 6 , 2 1 0 .


12/25

1 8 2 B . K . M A H A TO , S . K . V O O RA a n d L . W . S H EM IL T

6 0 0 C

i 4 5 0 C

0 3 0 0 0

D 1 5 0 0o

I I I I I I

0 -

Re 26210

0 I 1 I I I I0 4 8 1 2 1 6 2 0 2 4

T I M E , D A Y SF IG . 6 . E f fe c t o f d u r a t i o n o n t h e a m o u n t o f c o r r o s i o n a t 1 5 0 F.

1 i I 1 ( ~ 1 i I ( ~

o 4 0 0 0

Zo qD @) 3 0 0 0e .o J, , 2 0 0 0o~- ReZ 39320o 1 0 0 05.~ 1 3 1 1 0

o 65500 I I I I I I I

0 2 4 6 8 I0 12 14T I M E , D A Y S

F IG . 7. E f fe c t o f d u r a t i o n o n t h e a m o u n t o f c o r r o s i o n f o r d i f fe r e n t fl o w ra t e s a t 1 5 0 F .

The corrosion product had a composition that closely approximated to hydratedferric oxide. In Fig. 5, the reference lines indicate the stoichiometric relationshipbetween pure Fe and the theoretical corrosion product of hydrated ferric oxideFeOOH and of ferrous oxide, FeO. The experimental data agree very closely with theformer.The average weight losses as MD (mg/dm2) are shown as function of time inFigs 6 and 7, with the Re number corresponding to the fluid velocity as a parameter;


13/25

Steel pipe corros ion under flow condit ions 183

Eo.

E teo

12 Q

6O

ll ! 1 !

I

J ! !0 4 8 ;~ 16 2 ' 0 '4T IME , d a y sFIG. 8, Effect of durat ion on the speci~qc cor ros ion rate at 150F.

the solid lines correspond to the parabolic corrosion equation (equation 10). The bestvalues of the coefficients ct and ~ were obtained from the experimental data by themethod of least squares. The corrosion rates as MDD (rag/drug/day) v~ere thenobtained using equation 11, and the results plotted as specific corrosion rates, i.e.MDD/ppm of dissolved O, are shown in Fig. 8. The corrosion rates fall rapidly in theinitial periods and then gradually level off until they decrease slowly and regularlywith time. Within the range investigated, the velocity increases the corrosion ratesfor the same corresponding test duration. These results are qualitatively consistentwith the model proposed above, in that higher Re numbers should decrease theresistance factor in the so-called damped turbulence zone, thus increasing the rate ofO transfer to the cathodic areas. The lack of agreement noted amongst earlier workersis understandable from two standpoints. In the first instance the hydrodynamics weremixed and ill-defined. Secondly a simple relationship between corrosion rate andvelocity does not exist; the crossover of the curves shown in Figs 6 and 7 is evidenceof this. Some clarification ensues when a specific corrosion rate plot (Fig. 8) is used.

Examples of the measured potentials relative to the Ag/AgCI electrode, as afunction of time are shown in Fig. 9. The data plotted are average values of from threeto six specimen potentials belonging to the same test section. Average deviations fromthe average however are quite high. The sudden change in potential shown partway through the test period is due to the disturbance of the test section when half ofthe specimens were replaced. This same disturbance did not occur in undisturbedtest sections and is similar to results noted by others. 39, 3o

The general relationship between the potentials and the corrosion rates is clear.The rapid change of potential in the anodic direction corresponds to the high initialcorrosion rate. The potentials then become gradually more cathodic with time andapproach a constant value. This latter tends to be higher (more positive) at highervalues of Re numbers. The correspondence between corrosion potentials and corrosion


14/25

184 B .K . MAHATO,S. K. VOOP.Aand L. W. SHEMILT

F I G . 9 .

6 0 07 0 (

~ j 8 0 0~ . 9 0 0

d:>u~ E

"7t/ )_1mI- -ZLUI- -0n

5 0 C6 0 0

R e 13110

i i i I i i i i i i , i , ,5 6 9 12

6 o o) 9-----I. .r.t- _..O -~"JC ,7 0 0 /aoo O Re 2 6 2 1 0| i i i i i i i i , f , i , ,0 6 12 18 2 4

T I M E D A Y S

Average specimen. Potential w.r . t , s i lver-silver chloride electrod e (ACE )c u r v ~ .

r a t e s i s e x e m p l i f i e d w h e n b o t h a r e p l o t t e d o n t h e s a m e t i m e s c a l e . F r o m t h e t i m e w h e nt h e p o t e n t ia l s r e a c h t h ei r m a x i m u m a n o d i c v a l u e f o r t h e d u r a t i o n o f t h e te s t, v e r ys i m i l a r cu r v e s r e s u lt . T h i s i n d i c a t e s t h e s e l f -a d j u s t i n g n a t u r e o f t h e a n o d i c a n dc a t h o d i c a r e a p o t e n t i a l s s o a s t o p r o d u c e a c o r r o s i o n c u r r e n t e x a c t l y s u f f i c i e n t t oc o n s u m e t h e O a s i t b e c o m e s a v a i l a b l e a t t h e m e t a l s u r f a c e. 1o A c l e a r p o r t r a y a l o f t h i sm a y b e s h o w n b y r e p l o tt i n g th e d a t a i n a n a l t e r na t iv e f o r m . S i n c e th e t i m e - d e p e n d e n te q u a t i o n f o r t h e a m o u n t o f c o r r o s i o n i s ct W 2 - F [3 W = t , t h e n t h e r e c i p r o c a l o f t h es q u a r e o f t h e c o r r o s i o n r a t e w i ll b e l in e a r w i t h t im e . F i g u r e 1 0 s h o w s b o t h t h i sr e c i p r o ca l s q u a r e a n d t h e r e c ip r o c a l s q u a r e o f t h e p o t e n t i a l s ( a v e r a g e p o t e n t i a l s b u tw e i g h t e d f o r th e n u m b e r o f s p e c i m e n s i n v o l v e d ) o n a t im e b a s e . T h e p o t e n t i a l r e su l tss h o w a f a i r l y u n i f o r m s c a t t e r i n g a b o u t t h e c o r r o s i o n r a t e l i n e .T h e p o t e n t i a ls o f i n d iv i d u a l sp e c im e n s r e la t iv e t o t h e A g - A g C 1 s h o w l a rg ed i f fe r e n c es a n d t h e r e f o r e t h e a v e r a g e p o t e n t i a l i s o f l im i t e d v a l u e . N o n e t h e l e s s t h ec o r r e s p o n d e n c e h e r e w i t h c o r r o s i o n r a t e i s c o n s i d e r e d s i g n i f i c a n t .

V a l u e s f o r t h e m o d i f i e d m a s s t r a n s f e r c o e f f i c i e n t K ' w e r e c a l c u l a t e d f r o m t h es m o o t h e x p e r i m e n t a l d a t a a n d p l o t t e d a g a i n s t R e n u m b e r ( F i g . 1 1 ) . T h e r e l a t i o nm a y b e e x p r e ss e d e x p o n e n t i a l ly a n d h a s b e e n t h u s e v a lu & t e d a s

K~ = 6"31 . 106 R e TM. ( 2 0 )T h e m o d e l p r o p o s e d a b o v e , w h i c h a s s i s t s i n r e l a t i n g t h e m o d i f i e d m a s s t r a n s f e r

c o e f f i c i e n t t o t h e a c t u a l c o r r o s i o n m e a s u r e m e n t s , i s b a s e d o n a n u n s t e a d y - s t a t e m a s s


15/25

Steel pipe corrosion under flow conditions 185

3 2 5 . . . . tr a te / ]O S f ID po tential ~ 2 4 0 0

i . ~ ( ) 1 , .

, , 5 ~ ~ l ' ' , oT I M E , d a y s.F I G . 1 0 . R e l a t i o n s h i p b e t w e e n c o r r o s i o n p o t e n t i a l a n d c o r r o s i o n r a te .

ox

F IG . 11 .

3020

10S

6

0

i6 8 | 0 2 0 3 0 4 0 5 0

R e y n o l d s n u m b e r x 10 .3E f f ec t o f K e o n t h e m o d i f i e d m a s s t r a n s fe r c o e t ~ c ie n t .

t rans fer proces s. The rate o f 0 t rans fer is bas ica l ly a fun ct ion o f t emperature , timeand f low rate . Us ing the phys ica l propert ies o f th i s sys tem, these bas ic var iables mayb e t ra n s f o rm ed i n t o re l a t ed d i m en s i o n l e s s g ro u p s


16/25

B. K. -TO, S.K . VOORAand L. W. SHEMILT

T IM E , d a y s .FIG.12. Effect of exposure time on the overall mass transfer coefficient for differentflow rates.

Th e left-hand side of the equation gives the ratio of chemical reaction rate to m oleculardiffusion rate, and the independent variable groups are respectively Re number, anunsteady-state diffusion group representing the ratio of diffusive mass transport tobulk mass transport, Schmidt number, porosity of corrosion product (which isessentially a function of the Re num ber an d the reaction rate group) a nd a dimension-less temperature group. For an isothermal system this reduces to two dependentvariable groupings as in equation 22. This may be rewritten showing a functionaldependence (equation 23). By substitution of the overall mass transfer coefficientKO rom equationl24, the final dimensionless relationship is obtained (equation 25).


17/25

Steel pipe corrosion under flow conditions 187d W d nR - - - - - - - - K o C h ( 24 )d t d t

D, = a . f ( R e ) . q ~ 'K o D J \ D ~ / ( 2 5 )T h e f u n c t i o n a l r e l a t i o n s h i p o f t h e u n s t e a d y - s t a t e d i f f u s io n g r o u p w i t h t h e r e c i p r o c a l

o f t h e s q u a r e o f t h e m a s s t r a n s f e r c o e f f ic i e n t c a n b e o b t a i n e d b y p l o t t i n g t h e l a t t e ra g a i n s t t i m e , t . T h i s i s s h o w n i n F i g . 1 2 a n d i n d i c a t e s a s t r o n g d e p e n d e n c e o n R en u m b e r . A p l o t o f a f ( R e ) a g a i n s t t h e R e n u m b e r i t s e lf c o u l d i n d i c a t e th e p r o b a b l er e la t io n s h i p o f t h e R e n u m b e r f u n c t i o n w i th l IKe , a nd F i g . 13 s how s a r e a s on a b l es t r a i gh t l i ne r e l a t i ons h i p .

I n F i g . 12 t he p l o t o f 1 / K ~ vs . t g i ve s a s t r a i gh t l ine r e l a t i ons h i p f o r e a c h R en u m b e r i n d i c a t in g t h e l i n e a r n a t u r e o f t h e u n s t e a d y s t a t e d if f u si o n g r o u p . A s a r e s u l t,e q u a t i o n 2 5 m a y b e r e w r i t t en , w i t h t h e i n t r o d u c t i o n o f a t e r m r t o i n d i c a t e t h e s tr a i g h tl ine r e l a t i ons h i p .

i .K~I __ \D,/(D'~za f ( R e ) - \(tD~D' + r ) (26)

T h e s l o p e i s t h e n e q u a l t o a " f (Re) /Dv, a n d t h e i n t e r c e p t i s a . f ( R e ) . ( D a / D , ) Z . r .

F IG . 1 3 .

40

20

o-- '10x~ 8

, | , i | I

i I I I I I4 6 8 10 2 40R e y n o l d s n u m b e r X I0 "s

Determination of the functional relationship of R.e num ber (equ ation 27).


18/25

1 88 B . K . M A H A T O , S . K . V O O RA a n d L. W. SHEMILT

F r o m t h e s l o p e a n d i n t e r c e p t v a l u e s it w a s p o s s i b l e t o o b t a i n a n a v e r a g e v a l u e o f 0 -1 3f o r r f o r t h e r a n g e o f R e n u m b e r s s t u d i e d . T h e s t r a i g h t l in e r e l a t i o n s h i p f r o m F i g . 1 3 i s

a . f ( R e ) = P R e a . ( 2 7)S u b s t i t u t i o n t h e n p u t s t h i s i n t h e f o r m o f e q u a t i o n 2 8 w h i c h i n v o l v e s t h e r a t e a s ad i f fe ren t ia l ( R = d W/ dt ).

R D , _ _ 1D,Cb

dW D~Cbo r - - - ~ -dt Dt

p Req/t D,

1Re7 , D ,, +

( 2 8 )

( 2 9 )

I n t e g r a t in g e q u a t i o n 2 9 g i ve s e q u a t i o n 3 0 f o r t h e t o t a l a m o u n t o f c o r r o s i o n , IV , a s af u n c t i o n o f t im e .

Fxo. 14 .

1 ;: E

io noR,8 :ouu=oi -z-. ioq [

6000I I

O

G

3 0 0 0

GR e

O 9 5 S 0 1 3 1 1 0Q ) 2 6 2 1 0

3 9 3 2 0T = l S o F

O ~0 5OO IOO0 1 5 0 0

DoC o r r e l a t io n b e t w e e n t h e a m o u n t o f c o r ro s i o n a n d ~ ( R e , D v t / D t 2 ) a t 1 5 0 F .


19/25

Steel pipe corrosion under flow conditions 189

, , , , : ~ < ~ o , , , < o - o . , , r , ' , o , )~ , ,, r - , - } ( 3 0 )U n d e r i s o th e r m a l c o n d i ti o n s t h e c o n s t a n c y o f a n u m b e r o f t h e p r o p e r t ie s i n e q u a t i o n3 0 l e a d s t o

, + . _ - . , . , < : - . , , r e , , > . , ) o . ~ , o . qL \ D I + - - " (31)T h e v a lu e s o f th e c o n s t a n t s w h i c h p e r t a i n f o r a p a r t i c u la r t u b e d i a m e t e r a n dt e m p e r a t u r e c a n t h e n b e o b t a i n e d f r o m t h e s m o o t h e d e x p e r i m e n t a l d a t a a n d s u b -s t it u te d . T h e r e s u l t a n t e q u a t i o n 3 2 g i v es c o r r o s i o n a m o u n t a s a f u n c t i o n o f R en u m b e r a n d t i m e .

W = 5 .21 R e '535 [(0-96t + 0 .31) '5 -0 .56] ( 3 2 )T h i s i s p l o t t e d a s a s t r a i g h t l in e i n F ig . 1 4 a n d t h e a c t u a l e x p e r i m e n t a l v a l u e s f o r

W a g r e e f a i r l y w e l l w i t h t h i s s t r a i g h t l i n e c o r r e l a t i o n .S i m i l a r c a l c u l a t i o n s o n r e c e n t w o r k b y E l i as s e n 28.~7 a t a m u c h l o w e r t e m p e r a t u r e

a r e p r e s e n t e d i n F i g . 1 5 . C o n s i d e r a b l y b e t t e r a g r e e m e n t i s s h o w n a p p a r e n t l y b e c a u s e

I S ' ~ R eO 6 " 3 7 0

l t . 7 4 0 ! 9 " ! 00

S .O 0 0 ~ 2 5 ' 4 7 0T = 68 F

E- 4 . 0 0 0zO(/ )

O~ . 3 0 0 0 , !OU

Z0

0 0 I 3 5 7 9( b , - ~ t )FIG. 15. Correlation between the amo unt of corrosion and the q) (Re, Dvt/D,') at 150F.


20/25

190 B. K. M A H A T O , S. K. VOORA an d L. W. SHEM1LT

T A B L E 1 . C O R R O S I O N O F F e I N N A T U R A L W A T E R

EnvironmentSuspended specimen apparatus

Method of Variables investigatedSpecimen measure-ment Temp. F Flow rate Durati on Reference

Natural water Fe foil Wt. lossNatur al water Cold- Wt. loss(Cambridge, Mass., U.S.A.) rolledsteelNatural water Mild Wt. loss(Cambridge, Mass., U.S.A.) steelcouponNatur al water Fe Wt. loss(Iowa City, U.S.A.) couponNatural water Fe Wt. loss(Middletown, Ohio, U.S.A.) rodsDistilled water Cold- Wt. JossrolledsteelDistilled water Mild Wt. losssteelDistilled water (CO2-r 02) Steel Wt. lossNatural water Mild Wt. loss(Pittsburgh, P.A., U.S.A.) steelColorado River water Black Wt. lossironNatural water Mild Wt. loss(Great Lakes) steel and

potentialNatural water Cast Wt. loss(Great Lakes) FeDistilled water Pure Fe Wt. loss

R.T. 0"02- --8 ft/s72-104 -- 12 d1332

70 0.04 - 2-14 d 337"05 ft/sR.T. - - 24 h 34R.T. 100-500 1-60 d 35cm/min95 - - 24 h 36

77 - - 8 d140, 194 - - 5 h82 0-240 10 d

c m / s51--60 1-15 ft/ s 14 dR.T. 0.085- 2-16 d0-14 ft/sR .T . 0.2-2 ft/s --

122-567 - - 163 d

1937222538

3940

TABLE 2. C O R R O S I O N O F E e I N N A T U R A L W A T E R

EnvironmentRotating specimen apparatus

Method of Variables investigatedSpecimen measure-ment Temp. F Flow rate Duration Reference

Distilled waterNatural water(Cambridge, Mass.,U . S . A . )Natural water(Cambridge, Mass.,U.S.A.)Natural water(Cambridge, Mass.,U.S.A.)Distilled waterArtificial sea-water

Mild steel Wt. loss 70 0-7-6 ft/s 2-14 dcouponChr ome steel W ater R.T. 230 rpm 40 rain

Low-car bon Water R.T. 0-342 rpm 29 hannealedsteelMild steel Wt. loss 73 0-1.2 ft/s 5-7 dcouponMild steel Wt. loss R.T. 13-260 rpm - -Mild steel Wt. loss 77 1500 rp m 100 dand potential

3341

18

17

2142


21/25

FI G. 3 . Tr ans mi s s i on el ec t ron mi c r ogr aph of t he t hor n-s haped depos i t s s t r ipped f r omth e s u r f a c e by pl as t i c r epl i c a.

FI G. 4 . El ec t ron di f fr ac t i on pat t er n c ar r es ponding t o Wi l e obt ained f r om t he t hor n-s haped c r y s t al s of Fi g. 3


22/25

FIG. I. Transmission elcctrnn micrograph of oxide Tim fOrmed on Ti in hoikingCl wt. ;> H,SO, for 24 II.

FIG. 2. Electron diffraction patterns of rutile and anatase ob tained from the oxidefi lm of Fig, I.


23/25

Stee l p ipe cor ros ion under f low condi t ionsTABLE 3. CORROSIONOF Fe IN NATURALWATER

191

Env i r onm e n tP ipe spe c im e n a ppa r a tus

M e tho d o f Va r i a b le s i nve s tiga t edS pe c im e n m e a su r e -m e n t T e m p . F F l o w r a t e D u r a t i o n ReferenceNa tu r a l wa te r(P i t t sburgh, Pa . , U.S .A. )Na tu r a l wa te r( Wa sh ing ton , D . C . ,U . S . A . )N a t u r a l w a t e r( O t t a wa , C a na da )S yn the t i c wa te r(Mass . , U.S .A. )Synthe t ic wate r

M i ld s t ee l W a te r 60 - 170(, , ~- di a.) an aly sisW r ough t F e Wt . l o s s R . T .(2" dia . )M ild s tee l W t. lossM ild s tee l W t. lossMild s tee l W t. loss

Na tu r a l wa te r M i ld s t ee l W t . l o s s( Va nc ouve r , C a na da ) a nd po te n t i a lNa tu r a l wa te r M i ld s t e el W t . l o s s( Te dd ing ton , Eng la nd) a nd po te n t i a lDis t i l led wate r Fe--Cu cou ple Poten t ia lNa tura l wa te r M ild s tee l W t. loss( F r e de r i c ton , N . B . a nd po te n t i a lC a n a d a )Na tura l wa te r M ild s tee l W t. loss( F r e de r i c ton , N . B . , a nd po te n t i a lC a n a d a )Hig h pur i ty wate r Mild s tee l W t. lossNa tu r a l wa te r M i ld s t ee l Wt . l o s s( F r e de r i c ton , N . B . , a nd po te n t i a lC a n a d a )

68-1006868

90-13072-131

6815 0

125-170

72-131100

0.1-8 f t / s 25-50 1430 ft/s 10 y 43

0-12 f t / s 5 d 230 . 1 2 5 - 42 d 264 f t /s0 , 1 2 5 - 42 d 274 f t /s0 .75- 25 d 284"5 ft/s5~140 I t/ 70 d 29m inR e = 4 0 5 0 - - 3 00-45- 25 d 442"7 ft/s0"45- 40 d 452'7 f t /s2 '4 - 70 d 31400 f t/s0"45 210 d 462 '7 f t / s

o n l y t h e s m o o t h e d d a t a w e r e u s ed , t h e a c t u a l e x p e r i m e n t a l r e s u lt s n o t b e i n g r e p o r t e d .T h e c o n s t a n t s i n t h e c o r r e s p o n d i n g e q u a t i o n f o r E l i a ss e n ' s d a t a o f co u r s e a r e c o n s id e r -a b l y d i f f e r en t b e c a u s e o f t h e d i f f er e n c e in t e m p e r a t u r e a n d p h y s i c a l p r o p e r t i e s o f th es y s te m . O f t h e e x p e r i m e n t a l w o r k c a r r i ed o u t u n d e r h y d r o d y n a m i c a l l y de f in a b l ec o n d i t i o n s ( T a b l e 3 ), t h a t o f S p e l l e r a n d K e n d a l l 14 g a v e i n i t ia l c o r r o s i o n r a t e s o n l y ,a n d t h a t o f E l l in g e r a n d W a l d r o n 4s o n l y f in a l c o r r o s i o n a m o u n t s . S i m i l a r l y t h e w o r ko f C o h e n 2s a n d o f D e y 28 d i d n o t p r o v i d e s u ff ic i en t d a t a f o r t h e t y p e o f a n a l y s i s c a r r i e do u t h e r e . T h e l a t t e r w o r k 2s a s w e l l a s o t h e r r e s u l t s f r o m t h i s l a b o r a t o r y 45,46 c a n b ea p p l i e d , h o w e v e r , i f t h e a n a l y s i s is b r o a d e n e d t o i n c l u d e t e m p e r a t u r e a s a v a r i a b l e ,a n d t h i s w i ll b e d e a l t w i t h i n a l a t e r p a p e r . T h e w o r k o f B u t l e r a n d I s o n ~9 w a s b a s e do n a w a t e r w i t h a n e x c e e d i n g l y h i g h d i s s o l v e d s o l i d s c o n t e n t w h i c h o f c o u r s e n e g a t e dt h e b a s i c a s s u m p t i o n s o f t h e c h e m i c a l r e a c t io n s f o r m i n g t h e c o r r o s i o n p r o d u c t( e q u a t i o n s 4 a n d 5 ). N o n e t h e l e s s p r e l i m i n a r y c a l c u l a t i o n s o n t h e i r d a t a i n d i c a t e t h a t as i m i l a r c o r r e l a t i o n t o t h a t r e p o r t e d h e r e w i ll b e v a l i d . T h i s t y p e o f c o r r e l a t i o n c a nt h e r e f o r e b e c o n s i d e r e d a s h a v i n g c o n s i d e r a b l e e x p e r i m e n t a l j u s t i f ic a t i o n , a n d c a n b eu s e d t o p r e d i c t c o r r o s i o n a m o u n t s o f st e el p i p e i n w a t e r o v e r a c o n s i d e r a b l e r a n g e o ff l o w r a t e s .


24/25

1 9 2 B . K . MAHATO,S. K . VOORA and L. W . SHEMILTA c k n o w l e d g e m e n t s - - T h e a u t h o r s w i s h to t h a n k D r . F . R . S t e w a r d f o r m o s t h e l p f u l d i s c u s s io n s o n t h ec o r r e l a t i o n s p r e se n t e d h e r e , a n d t h e S t e el C o m p a n y o f C a n a d a w h o s u p p l i e d t h e p i p e u se d f o r t h et e s ts . T h e f i n a n c ia l a s s i st a n c e o f th e N a t i o n a l R e s e a r c h C o u n c i l o f C a n a d a i s g r a t e f u ll y a c k n o w l e d g e d .

R E F E R E N C E S1 . H . H . U H U G , Co rro s io n a n d c o rro s io n c o n t ro l . J o h n W i l e y , N e w Y o r k ( 1 9 6 3 ) .2 . H . H . U H U G , T h e c o r r o s io n h a n d b o o k . J o h n W i l e y , N e w Y o r k ( 1 9 4 8 ) .3 . U . R . EVANS an d T . P . HOAR , P r o c . R . S o c . , L o n d . (Ser ies A) 137, 343 (1932) .4 . W. R. WnrrNEx, , d . A m . c h e m . S o c . 2 5 , 394 (1903).5 . R . B . M E A ~ a n d R . H . B R O W N , Tra n s . e l e c t ro c h e m . S o c . 74, 495 (1938).6 . R . H . B R O W N a n d R . B . M E A ~ , Tra n s . e l e c t ro c h e m . S o c . 81, 455 (1942).7. M. A. STREICHER,J . e l e c t ro c h e m . S o c . 96, 170 (1949).8 . R . B . MEmaS an d R . H . B R OWN,J . e l e c t ro c h e m . S o c . 97, 75 (1950).9 . T . P . HOAR an d J . G . H ~ r s , J . I ro n S t e e l I n s t . 182, 124 (1956).10 . U. R. EVANS, T h e c o r r o s i o n a n d o x i d a t i o n o f m e t a l s . E d w a r d A r n o l d , L o n d o n ( 1 9 6 0 ) .1 1 . J . N . FmEND, J . c h e m . S o c . 119, 932 (1921).12 . J . N. FRIEND, T r a n s . A m . e l e c tr o c h e m . S o c . 40, 63 (1921).

13 . J . N. FmErCa, J . I r o n S t e e l I n s t . 11, 62, 128 (1922).14. F. N. SPELLERa n d V . V . K r r ~ A L L , I n d . E n g n g C h e m . 15, 134 (1923).1 5 . W. G . WHrrMAN, C h e m . R e v . 2, 419 (1925).1 6 . R . E . W m s o s , I n d . E n g n g C h e m . 15, 127 (1923). ,1 7 . C . L . C o x an d B . E . R o ~rHEta , I n d . E n g n g C h e m . 2 3 , 1012 (1931).1 8 . B . E . R O ~ r l E U a n d R . H . B R O W N , I n d . E n g n g C h e m . 2 3 , 1010 (1931).19 . F . G. FRESE, I n d . E n g n g C h e m . 30, 83 (1938).20. F. N. SPELLER,J . N e w E n g l . W a r . W k s . A s s . 52, 231 (1938).21. F. J. WOmW~VELL, . I r o n S t e e l I n s t . 154, 219 (1946).2 2 . G . B . H ATC H an d O . R IC E, I n d . E n g n g C h e m . 37, 752 (1945).23 . M . C o a E N , J . e l e c t r o c h e m . S o c . 93, 26 (1948).2 4 . H . R . C o Pso N, I n d . E n g n g C h e m . 4 4 , 1745 (1952) .25. L. STREICHER,J . A m . W a r . W k s A s s . 4 8 , 219 (1956).26. R. ELIASSErq,C. PEREDA, A. J . ROMEOand 1L T. Sr, .~atcoE,J . Am . W a t . 1 4 "k s Ass . 4 8 , 1005 (1956) .27 . A. J . ROMEO, R. T. SKmt,a~. and R. EtaASSErq,P r o c . A m . S o c . C i r . E n g r s Paper 1702, Ju ly (1958) .2 8. W . R . D E Y , M . A . S c . T h e s i s , U n i v e r s i t y o f B r it i s h C o l u m b i a , 1 95 9.2 9 . G . B t r rLER an d H . C . K . ISON,J . a p p l . Ch e m . 10, 80 (1960).3 0 . T . K . R o ss an d B . P . L . Hr rC HEN, Co rro s . S c i . 1, 65 (1961).3 1 . G . B t r rLER an d E . G . STR OUD,J . a p p l . Ch e m . 15, 325 (1965).3 2 . G . E . W mTMAN, R . P . R USSELan d V . J . AL~ER Y, I n d . E n g n g C h e m . 16, 665 (1924).33 . R . P . RUSSEL, E. L. Cr tAPPEL an d A. WroTE, I n d . E n g n g C h e m . 19, 65 (1927).34 . W. L. DENMAN an d E . B AR LOW,I n d . E n g n g C h e m . 22, 36 (1930).35. R. F. PASSANOan d F . R . NAt3 LEY,P r o c . A m . S o c . T e s t . M a t e r . 33, 387 (1933).36. C. S. BORGMAN,I n d . E n g n g C h e m . 29, 815 (1937).3 7 . G . T . S~ '.APE~AS an d H . H . U r ILm, I n d . E n g n g C h e m . 24, 748 (1942).3 8. R . V . S K O L ~ a n d T . E . L A ~ O N , Co rro s io n 13, 139t (1957).39 . E. L. LARSONan d R . V . SKOLD,J . A m . W a r . W k s . A s s. 50, 1429 (1958).4 0 . W . E . R U T H E R a n d R . K . H A R T , Co rro s io n 19, 127t (1963).4 1 . H . O . F O R ~ T , B . E . R o F . r a s u a n d R . H . B r t ow N , In c l . En g n g Ch e m . 22, 1197 (1930).4 2. F . W O ~ W L L , 3". a p p l . Ch e m . 3, 164 (1953).4 3 . G . A . ELUNG ER an d L . J . WALDR ON,P a p e r T r a d e J . 127, 27 (1948).4 4 . S . K . VOOR A, M.Sc . Th es is , U n iv e r s i ty o f Ne w B ru n swick , F red er ic to n , 1 9 64 .4 5 . B . K . M A H AT O , M . S c . T h e s i s , U n i v e r s i t y o f N e w B r u n s w i c k , F r e d e r i c t o n , 1 96 4.4 6 . B . K . M A r lA r O, P h . D . T h e s i s , U n i v e r s i t y o f N e w B r u n s w i c k , F r e d e r i c t o n , 1 96 7.47 . V. G. LEXqCH,P h y s i c o c h e m i c a l H y d r o d y n a m i c s . P r e n t i c e - H a l l , I n c . , N e w Y o r k ( 19 62 ).48 . G. S. GARDNER, Co rro s io n 19, 81t-90t (1963) .

C ,:C~"D~:

N O T A T I O NC o n c e n t r a t i o n o f O i n t h e m a i n s t r e a m , p p m o r g m o l e / l.C o n c e n t r a t i o n o f O a t t h e i n t e r f a c e a t t h e s o li d w a l l a n d d a m p e d t u r b u l e n c e l a y e r ,p p m o r g m o l e / l .C o n c e n t r a t i o n o f O a t t h e m e t a l w a l l s u r f a c e , p p m o r g m o l e ] l .P i p e d i a m e t e r , e r a .


25/25

S t ee l p i p e c o r r o s i o n u n d e r f lo w c o n d i t i o n s 1 93

K , , K 1 , K 2 , K l - :k:n:P:p:q:R:R e :r"T :t :U :W :Ya:Ys:

8 :~. :p :p, p':

D i f f u s i o n c o e f f i c ie n t o f O i n w a t e r , c m l / s .F u n c t i o n s .A s d e f in e d i n e q u a t i o n s 1 5 - 19 .R e s i s t a n c e c o e f f i c ie n t , c m 3 / g m o l e .M o l e s o f O t r a n s f e r r e d u n i t a r ea , g m o l e s / c m 2.P o r o s i t y .C o e f f i c i e n t , e q u a t i o n 2 7 .E x p o n e n t , e q u a t i o n 2 7 .R e a c t i o n r a t e , g m o l e / c m - ~ / s - 1.R e n u m b e r b a s e d o n i n i ti a l p i p e d i a m e t e r .A s e q u a t i o n 2 6 .T e m p e r a t u r e , F .T i m e , d a y .V e l o c i t y, c m / s .A m o u n t o f c o r r os i o n , m g / d m z.R e s i s t a n c e t o t h e t r a n s f e r o f O t h r o u g h t h e d a m p e d t u r b u l e n t l a y er , er a .R e s i s t a n c e t o t h e t r a n s f e r o f O t h r o u g h t h e c o r r o s i o n p r o d u c t l a y e r , c m .A s d e f i n e d i n e q u a t i o n 1 2.A s d e f i n e d i n e q u a t i o n 1 3.A b s o l u t e v i sc o s it y , g c m - 1 s - x.F l u i d d e n s i t y , g / c m 3.E d d y d i f f u s i o n c o e ff i c ie n t , c m l / s .F u n c t i o n s .

Documents

Correlation Corrosion Mass