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Corrosion Science Vol. 33, No . 11, pp . 1809-1827, 1992 0010--938X/92 $5.00 + 0.00
Printed in Gre at Britain. ~ 1992 Pergamon Press Ltd
T H E I N F L U E N C E O F p H A N D C H L O R I D E
C O N C E N T R A T I O N O N T H E C O R R O S I O N B E H A V I O U R
O F A IS I 3 16 L S T E E L IN A Q U E O U S S O L U T I O N S
A . U . M A L I K , P . C . M A Y A N K U TT Y , N A D EE M A . S I D D IQ I , IS M A EE L N . A N D I J A N I a n d
SHAHREER AH ME D
Research D evelopm ent and Training Cen ter , Saline Water Conversion Corp orat ion (SWCC ),
P.O . B ox 8034, A1-Jubail-31951, Kingdom o f Saudi A rab ia
Abst ract - -The ef fect of chlor ide concentrat ion, pH, dissolved oxygen and temperature on the pi t t ing
behaviour of 316L SS in aqueous solutions has been investigated under dynamic and static condit ions.
W eight loss , metal lograph y and elect rochemical polar izat ion techniques have been emp loyed dur ing the
investigation. I t has been foun d that th e corro sion rate ge nerally increases l inearly with increasing CI
concentrat ion in the range 100-5000 ppm . W ith increasing pH , the cor rosion rate de creases, being highest
at pH 4 and lowest a t pH 9. The num ber and d epth of p i ts increase wi th increasing CI concentrat ion.
From the res ults of cyclic polariz ation studies i t is inferred that the p it t ing po tentia l , Epi is shifted to a
more negat ive potent ia l wi th increasing C I- concentrat ion and tem perature an d decreasing pH. I t has
been e stablish ed that low pH, high C I- co nten t and stagnancy are the conditions m ost suitable for
init iat ion and pro pag ation o f pit t ing in A1SI 316L stainless ste el .
I N T R O D U C T I O N
PITTIN G i s a l o c a l i z e d c o r r o s i o n a t t a c k o n m e t a l s a n d a l l o y s i n a q u e o u s e n v i r o n m e n t s .
I t i s a m a j o r c a u s e o f fa i l u re o f c h e m i c a l p r o c e s s i n g a n d d e s a l i n a t i o n p l a n t s , w a t e r
s t o r a g e t a n k s a n d p i p e l i n e s , p u m p s a n d v a l v e s , p e t r o l e u m r e f in e r i e s e t c . D u e t o t h e
l o c a l iz e d n a t u r e o f p i t t i n g c o r r o s i o n , t h e f o r m a t i o n o f p i t s is c o n f i n e d t o m u c h s m a l l e r
a r e a s c o m p a r e d t o th e o v e r a l l e x p o s e d s u r fa c e . B r o a d l y s p e a k i n g , t h e i n i t i a t i o n o f
p i t t i n g is t h e r e s u l t o f t h e b r e a k d o w n o f t h e p a s s i v e f il m o n t h e m e t a l d u e t o t h e
p r e s e n c e o f c e r t a i n a n i o n s s u c h a s C 1 - a n d t h e s u b s e q u e n t e s t a b l i s h m e n t o f an
e l e c t r o c h e m i c a l c e l l i n w h i c h t h e d a m a g e d s i te a c t s a s a n a n o d e a n d t h e p a s s i v e s i t e
a c ts a s a c a t h o d e . T h e b u i l d i n g u p o f c o r r o s i o n p r o d u c t s o n t h e m o u t h o f t h e p i t m a y
r e s u l t in t h e f o r m a t i o n o f a c r e v i c e , t h u s p r o d u c i n g m o r e a g g r e s s iv e c o r r o s i o n a t t a c k .
I r o n - b a s e a l l o y s , p a r t i c u l a r l y a u s t e n i t i c s ta i n l e s s s t e e l s , a r e m o s t p r o n e t o p i t t i n g in
d i s s o l v e d C O 2 - a n d C l - - c o n t a i n i n g e n v i r o n m e n t s s u c h as t h o s e o b s e r v e d in b r i n e
r e c y c le a n d b l o w d o w n p u m p s , f la sh c h a m b e r s a n d d e m i s t e r s o f d e s a l i n a t i o n p l an t s ,
a n d i n s t e a m b o i l e r s , f e e d w a t e r h e a d e r t u b e s a n d s t e a m t u r b i n e b l a d e s o f p o w e r
p l a n t s . 1 -5
T h e e f f e c t o f c h l o r i d e o n t h e p i t t in g s u s c e p t i b i l i t y o f v a r i o u s m e t a l s a n d a l l o y s a n d
e s p e c i a l ly s t a in l e s s s t e e l s h a s b e e n e x t e n s i v e l y i n v e s t i g a t e d b y n u m e r o u s r e s e a r c h e r s
a n d is r e v i e w e d i n a n u m b e r o f b o o k s , r e v i e w s a n d a r t ic l e s . 6-~3 P a r t i c u l a r i n t e r e s t h a s
b e e n s h o w n f o r t h e C I - d u e t o i t s p r e s e n c e in s ea w a t e r a s t h e m a j o r c o n s t i t u e n t a n d
i ts r o l e a s a n a c t i v e p i t t in g a g e n t . B e s i d e s t h e i n f lu e n c e o f t e m p e r a t u r e , f lo w v e l o c i t y ,
p H a n d C I - c o n c e n t r a t i o n [ C I - ] o n p i t t i n g , t h e s y n e r g ic e f f e c t o f a n i o n s s u ch a s
S O ] - , $ 2 0 32 - , C 1 0 4 e t c . h a v e a l s o b e e n s t u d i e d . S m i a l o w s k a 14 f o u n d t h a t a m a j o r i t y
Manuscript rec eived 25 Septem ber 1991.
1809
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1 8 1 0 A . U . M A LI K e t a l .
o f c o n s t r u c t i o n m a t e r i a ls s u f f e r p i tt i n g o n l y in s o l u t i o n s c o n t a i n i n g C i - o r o t h e r
h a l i d e i o n s . T h r e e m a i n r e a s o n s a r e g iv e n f o r t h e s p e c if i c e f f e c t s o f c h l o r i d e a n d i ts
a b i l i t y t o p r o d u c e p i t t i n g . F i r s t l y , t h e f o r m a t i o n o f a c h l o r i d e c o m p l e x w i t h c a t i o n
a n d h y d r o x i d e ; s e c o n d l y , a n i n c r e a s e o f h y d r o g e n i o n a c t i v it y in t h e p it e l e c t r o l y t e
a n d t h i r d l y , t h e f o r m a t i o n o f a sa l t l a y e r a t t h e b o t t o m o f p it s . T h e t h i r d fa c t o r
a p p e a r s t o e x p l a i n m o r e s p e c i f i c a l l y t h e r o l e o f h a l i d e s i n p it t i n g a t t a c k . I t i s
s u g g e s t e d t h a t t r a n s i t i o n f r o m p a s s i v i t y t o p i t t i n g c o n d i t i o n s c a n b e e x p l a i n e d b y a
c o m p e t i ti v e a d s o r p t io n m e c h a n i s m i n w h i c h c h l o r i d e io n s m o v e i n t o th e d o u b l e l a y er
( o x i d e / l i q u i d i n t e r f a c e ) , e v e n t u a l l y r e a c h i n g , a t a c r it ic a l p o t e n t i a l , E m it, c o r r e s p o n d -
i n g t o t h e [ C I -] r e q u i r e d t o d i s p l a c e t h e a d s o r b e d o x y g e n s p e c i e s . ~5-f? , N a s h i m u r a e t
a l . 1 7 1 8 f o u n d t h a t p i t i n i t i a t i o n i s s t r o n g l y r e l a t e d t o t w o d i f f e r e n t t y p e s o f b o u n d
w a t e r in a f il m . I t w a s f o u n d t h a t t h e p i tt i n g b e h a v i o u r o f a l l o y s c o v e r e d w i t h t h e
p a s s i v e f i lm i s l a r g e ly d e p e n d e n t o n t h e f i lm t h i c k n e s s a n d i o n s e l e c ti v i t y . D u r i n g
s t u d i e s 19 o n t h e e f f e c t s o f [ C I - ] o n p i tt i n g b e h a v i o u r o f s t e e l s l i n e a r r e la t i o n s h i p s
h a v e b e e n f o u n d t o e x i s t b e t w e e n p i t n u c l e a t i o n p o t e n t i a l v s l o g c h l o r i d e i o n
c o n c e n t r a t i o n , a n d l o g i n d u c t i o n t i m e v s l o g c h l o r i d e i o n c o n c e n t r a t i o n . T h e
t e m p e r a t u r e a p p e a r s t o b e a n i m p o r t a n t p a r a m e t e r i n i n f l u e n c i n g t h e p r o te c t i v i ty o f
t h e o x i d e s c a l e s .
A I S I 3 1 6 L is c o n s i d e r e d t o b e o n e o f t h e m o s t i m p o r t a n t o f s ta i n l e s s s te e l s f o r
m a r i n e e n v i r o n m e n t s a n d t h e r e f o r e i s w i d e l y u s e d a s a s t ru c t u ra l m a t e r i a l fo r
d e s a l i n a t i o n p l a n t s. E v e n t h i s a l l o y m a y f a i l u n d e r c o n d i t i o n s o f l o w p H , h i g h
c h l o r i d e c o n t e n t o r s t a g n a t i o n . 8 2 -21 R e l a t i v e l y f e w s t u d i e s h a v e b e e n c a r r ie d o u t t o
i n v e s t i g a t e t h e r o l e o f p H a n d s t a g n a n c y o n t h e p i tt i n g b e h a v i o u r o f a u s t e n i t ic s t e e l s .
T h e p r e s e n t c o m m u n i c a t i o n c o n t a i n s t h e r es u lt s o f a s tu d y e m p h a s i z in g t h e r o l e o f
p H , c h l o r i d e i o n c o n c e n t r a t i o n , s t a g n a n c y a n d t e m p e r a t u r e o n t h e p i tt i n g b e h a v i o u r
o f A I S I 3 1 6 L a u s t e n i t ic s t a i n l e ss s t e e l i n a q u e o u s c h l o r i d e s o l u t i o n s .
E X P E R I M E N T A L M E T H O D
C o m m e r c i a l g r a d e
A I S I 3 1 6 L
s t a i n l e s s s t e e l
( 1 7 . 1 C r , 1 1 . 3 N i , 2 . 1 M o , 0 . 0 2 C
a n d b a l a n c e F e , a l l i n
w t % ) , i n s h e e t a n d r o d fo r m s , w a s u s e d f o r th e s t u d i e s .
F o r i m m e r s i o n t e s t s , c o u p o n s o f a b o u t
5 c m 2
a r e a w e r e c u t f r o m t h e s h e e t a n d a b r a d e d s e q u e n t i a l l y
w i t h 1 8 0 , 3 2 0 , 4 0 0 a n d 6 0 0 g r it Si C p a p e r s . T h e a b r a d e d s p e c i m e n s w e r e c l e a n e d i n a n u l t r a s o n i c c l e a n e r
f o l l o w e d b y d ry i n g. T h e d r i e d s p e c i m e n s w e r e w e i g h e d p r io r to i m m e r s i o n .
F o r 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 s , c i r cu l a r f la t t e s t s p e c i m e n s o f
1 . 5 - 1 . 6 c m
d i a m e t e r w e r e u s e d . T h e
e x p o s e d a r e a o f t h e t es t s p e c im e n s w h i c h w a s s c r e w e d i n t h e s a m p l e h o l d e r w a s
1 c m2 .
E l e c t r o c h e m i c a l
p o l a r i z a t i o n s t u d i e s w e r e c a r r i e d o u t o n a n
E G & G m o d e l 3 4 2 - 2 so f t C o r r
m e a s u r e m e n t s y s t e m . T h e
s y s t e m w a s c o n s i s t e d o f m o d e l 2 7 3 p o t e n t i o s t a t / g a l v a n o s t a t , m o d e l 3 4 2 C o r r s o f t w a r e a n d m o d e l 3 0 I B M
P S - 2 .
A l l t h e e x p e r i m e n t s w e r e c a r r i e d o u t u s i n g a c o r r o s i o n c e l l
( E G & G
m o d e l K 0 0 4 7 ) w i t h s a t u r a t e d
c a l o m e l a n d g r a p h i t e a s r e f e r e n c e a n d c o u n t e r e l e c t r o d e s , r e s p e c t i v e l y . S e v e r a l s e r i e s o f e x p e r i m e n t s w e r e
c a r r i e d o u t i n o r d e r t o s t u d y t h e e f f e c t o f
[ C I - ] , p H
a n d s t a g n a n c y o n t h e p i t t i n g b e h a v i o u r o f
A I S I : 3 1 6 L
s t e e l u s i n g t e s t s o l u t i o n s u n d e r f o l l o w i n g c o n d i t i o n s :
p H
[ CI I ( p p m )
A r t i f i c i a l s e a w a t e r
I m m e r s i o n t i m e ( w e e k s )
C o n d i t i o n
T e m p e r a t u r e
D i s s o l v e d o x y g e n ( p p m )
4 , 7 a n d 9
0 , 1 0 , 1 0 0 , 3 0 0 , 5 0 0 , 1 0 00 a n d 50 0 0
C I 2 4 1 5 0
p p m
4 , 8 , 1 6 a n d 2 4
S t a ti c o r d y n a m i c
2 0 , 25 , 3 0 , 5 0 a n d 8 0 ( 2 C )
6 0 . 5
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7/23/2019 The Influence of PH and Chloride Concentration on the Corrosion Behavior of AISI 316L Steel in Aqueous Solutions
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p H an d [C I - ] an d t h e co r ro s i o n o f A IS I 3 1 6L s t ee l 1811
Prev i o u s ly w e i g h ed co u p o n s w ere i m mers ed i n te s t s o l u ti o n s fo r v a r io u s t i me i n t e rv a l s o f 1 , 2 , 4 an d 6
mo n t h s . Imm ers i o n t e st s u n d e r s t a ti c co n d i t i o n s w ere p e r fo rm ed fo l l o w i n g t h e A ST M G 3 1 -7 2 p ro ced u re .
S i mi l a r t e s ts w e re ca r r i ed o u t u n d e r d y n am i c co n d i t io n s u s in g a t h e rmo s t a t i c s h ak e r m o v i n g a t a s p eed o f
60 osc i l l a t ions min - 1. A t the end o f the t es t per iod s the coup ons w ere t aken ou t , washed in d i s t il l ed water ,
d r i ed an d t h e i r w e i g h ts w e re d c t e rm i n cd .
Fo l l o w i n g th e i mm ers i o n t e s t , m i c ro s tru c t u ra l ex am i n a t i o n o f a ll t h e t e s t s p ec i men s w as ca r r i ed o u t t o
assess the na tu re and ex ten t o f the local i zed a t t ack . Th e shap e , s i ze and dens i ty (d i s t r ibu t ion) o f the p it s
w ere d e t e rm i n ed me t a l l o g rap h i ca l l y u s in g an o p t io n a l m i c ro s co p e an d fo l lo w i n g A S T M G 4 6 -7 6 p ro -
ced u re .
O p en c i r cu i t p o t en t i a l (O CP) w ere meas u red u s i n g 3 1 6 L co u p o n a s a w o rk i n g e l ec t ro d e (W E ) an d
s a t u ra t ed ca l o me l (b e l o w 8 0 C) o r s i l v e r - s i lv e r ch l o r i d e a s a r e fe r en ce e l ec t ro d e . T h e O C P s t u d ie s w crc
carr i ed o u t w i th 100 , 300 , 500 , 1000 and 5(100 ppm ch lor ide so lu t ions o f pH 4 , 7 o r 9 and a t d i f feren t
t emp e ra t u re s . I t to o k 2 4 -4 8 h t o ach i ev e a co n s t an t p o t en t ia l co r r e s p o n d i n g t o o p en c i r cu i t co r ro s i o n
poten t i a l .
Po ten t iodyn am ic po lar i za t ion ex per im ents we re car r i ed ou t us ing a scan ra te o f 0 .1 m V s i
co mmen c i n g a t a p o t en t i a l ab o u t 2 5 0 mV mo re ac t i v e t h an t h e s t ab l e O CP. Be fo re s t a r t i n g t h e
polar i za t ion sca n , the spec ime n in the sam ple ho lder (W E) was l ef t in the ce l l fo r about 1 h to a t ta in a
s teady s t a te which i s shown by a cons tan t po ten t i a l and curren t a t the beg inn ing of the expe r ime nt . Thc
p o t cn t i o d y n am i c ru n s w ere p ro g ram me d s u ch th a t u p o n a t t a in i n g a cu r r en t d en s i ty o f 2 5 / t A cm
2,
the
scan d i rec t ion was reversed and the po ten t i a l s were scanned back to the s t ar t ing po ten t i a l .
Po lar i za t ion res i s t ance m easu rem ents w ere con ducted a t a scan ra te o f 0.1 mV s ~ wi th s tar t ing and
f in a l p o t en t i a ls co r r e s p o n d i n g t o - 2 0 an d + 2 1) mV (O C P) , r e s p ec t iv e l y . T h e max i m u m cu r r en t r an g e w as
0 . 1 / A c m
2
E X P E R I M E N T A L R E S U L T S
W eigh t lo ss s tud ie s
W e i g h t l o s s s t u d i e s s h o w e d t h a t n o p e r c e p t i b l e w e i g h t lo s s o c c u r s d u r i n g
i m m e r s i o n p e r i o d s o f u p t o 6 w e e k s i r r e s p e c t i v e o f [ C 1 - ] , p H a n d d y n a m i c o r s t a t i c
c o n d i t i o n s . E x t r e m e l y l o w w e i g h t l o s se s ( 5 0 - 7 0 k tg c m 2) w e r e n o t e d d u r i n g
i m m e r s i o n t i m e v a r y i n g f r o m 1 6 t o 2 4 w e e k s . T h e w e i g h t l o s se s r e c o r d e d w e r e
h i g h e s t a t p H 4 u n d e r s t a t i c c o n d i t i o n s a n d w e r e l o w e s t a t p H 7 u n d e r d y n a m i c
c o n d i t i o n s .
M e t a l l o g r a p h ic e x a m i n a t i o n s
U n d e r s i m i la r c o n d i t i o n s , a m a x i m u m n u m b e r o f p i t s w e r e f o u n d o n t h e
s p e c i m e n s i m m e r s e d i n s o l u t i o n s o f p H 4 a n d a m i n i m u m o n s p e c i m e n s i m m e r s e d i n
s o l u t i o n s o f p H 7 . U n d e r d y n a m i c c o n d i t i o n s ( w h e n t h e s o l u t i o n s w e r e a g i t a t e d
c o n t i n u o u s l y d u r i n g t h e e n t i r e p e r i o d s o f i m m e r s i o n t e s t ) t h e n u m b e r o f p i t s
o b s e r v e d o n t h e s u r f a c e o f t h e s p e c i m e n w a s s m a l l e r t h a n u n d e r s t a t i c o r s t a g n a n t
c o n d i t i o n s . I n g e n e r a l , t h e n u m b e r a n d d e p t h o f t h e p i ts i n c r e a s e d w i t h in c r e a s i n g
[ C I ] a n d i m m e r s i o n t i m e .
P i t d e p t h m e a s u r e m e n t s
T h e d e p t h o f t h e p i ts o n 3 1 6 L s p e c i m e n s w a s m e a s u r e d m i c r o s c o p i c a l l y . M i n i -
m u m a n d m a x i m u m p i t d e p t h s w e r e m e a s u r e d f o r a p a r t i c u l a r s p e c i m e n . A v e r a g e
d e p t h s w e r e d e t e r m i n e d b y c o n s i d e r i n g t h e d e p t h o f a ll t h e p i ts p r e s e n t . F i g u r e 1
s h o w s p l o t s o f m a x i m u m p i t d e p t h v s [C1 ] a n d d i f f e r i n g p H f o r t h e i m m e r s i o n p e r i o d
o f 4 m o n t h s . T h e p i t d e p t h i n c r e a s e s w i t h in c r e a s i n g [ C I ] . A p a r a b o l i c r e l a t i o n s h i p
a p p e a r s t o e x i s t b e t w e e n p i t d e p t h a n d c h l o r i d e c o n c e n t r a t i o n a s i n d i c a t e d b y t h e
l i n e a r n a t u r e o f p i t d e p t h v s [C 1 ]1/2 p l o t s ( F i g . 2 ) .
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1 8 1 2 A . U . M A L I K e t a l .
5 o o
3 0 0
cL 200
o
o pH 4 S
0 pH 7S
t - b
p H 9 S _ ~
I O 0
0 ~ I I I I I I
4 0 8 0 1 20 1 6 0 2 0 0 Z 4 0 2 8 0
C I - ( p p m )
M a x i m i m p i t d e p t h v s [ C 1 - ] f o r A I S I 3 1 6 L in C l - - c o n t a i n i n g a q u e o u s s o l u t i o n o f
[ c . 1 .
v a r i o u s p H v a l u e s u n d e r s t a t ic ( S ) a n d d y n a m i c ( D ) c o n d i t i o n s . I m m e r s i o n t i m e : 4 m o n t h s .
F i g u r e s 3 a n d 4 s h o w t y p i c a l o p t i c a l m i c r o g r a ph s o f t h e p i t s pr o d u c e d b y
p o t e n t i o d y n a m i c a n o d i c p o l a r i z a t i o n a t t w o d i f f e r e n t [ C I - ] . M o s t o f t h e p i t s a r e
g e n e r a ll y o f s m a ll d i a m e t e r ( < 5 0 ~ m ) .
E lec tr o chem i ca l measu r em en ts
Open c i r c u i t c o r r o s i o n po t en t i a l
F i g u r e s 5 - 7 s h o w s o m e t y p i c a l t i m e v s o p e n
c i r c u i t po t e n t i a l p l o t s f o r 3 1 6 L s t e e l i mme r s e d i n a q u e o u s s o l u t i o n s c o n t a i n i n g
vary ing [C1- ] a t pH 4 , 7 and 9 , a nd a t 30 , 50 and 80C. Th e indu c t ion t im e , t i, f or p i t
F r o . 2 .
5 0 0
[ ] S to t i c J
0 I I I I I I I
3 5 7' 9 11 13 15 17
1
[cl ]~
P l o t o f [ E l - ] 1/2 v s m a x i m u m p i t d e p t h f o r A I S I 3 1 6 L i m m e r s e d i n C l - - c o n t a i n in g
s o l u t i o n s o f
p H 4
u n d e r s t a t ic ( S ) a n d d y n a m i c ( D ) c o n d i t io n s .
3 0 0
"o
2OO
o
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FIG. 3.
FIG. 4.
P h o t o m i c r o g r a p h o f a c r os s s e c ti o n o f A I S I 3 1 6 L s p e ci m e n p i t te d p o t e n t i o -
d y n a m i c a l l y ( [C I ] : 5 0 0 0 p p m , p H 4 ) . x 4 0 0 .
P h o t o m i c r o g r a p h o f a c r o s s s e c t i o n o f A I S I 3 1 6 L s p e c i m e n p i t t e d p o t c n t i o -
dyn amic a l ly ([C1 ] : 1000 ppm , pH 7 , un de r de -a e ra t ed co nd i t i o n) . )
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E
o
5
(3-
FIG.
5.
p H a n d [ C I - ] a n d t h e c o r r o s io n o f A 1 S I 3 1 6 L s t e e l
2 0 0
100
-100
3 0 0
o 5 0 0
. 1 0 0 0
-2oo ~ 1 L _ _ _ i _ _ J . _ _ ~
0 4 8 12 16 20 24 23 32 36 40 44 48
T i m e ( h )
V a r i a t i o n o f O C P w i t h t i m e f o r A I S I 3 1 6 L i m m e r s e d i n a q u e o u s s o l u t i o n s o f
v a r y i n g
[ C I - ]
( in p p m ) a t
2 0 C ( p H 4 ) .
1815
i n i t ia t i o n h a s b e e n d e t e r m i n e d f r o m t h e p l o t s. A t a n y g i v e n t e m p e r a t u r e , ti i s a l i n e a r
f u n c t i o n o f [ C I- ] a n d c a n b e r e p r e s e n t e d b y t h e r e la t i o n s h i p:
l o g t = C + D l o g [ C I - ] .
B o t h C a n d D c o e f f i c i e n t s a r e t e m p e r a t u r e d e p e n d e n t . F i g u r e 8 s h o w s p l o t s f o r
l o g i n d u c t i o n t i m e f o r pi t i n i t ia t i o n v s l o g [ C I- ] a t p H 4 a n d a t d i f fe r e n t t e m p e r a t u r e s .
F ig u r e 9 s h o w s p l o ts o f l o g in d u c t i o n t i m e v s t e m p e r a t u r e a t t w o [ C l - ] c o n c e n -
t r a ti o n s . T h e p l o t s i n d i c a t e t h a t i n d u c t i o n t i m e f o r pi t i n i t ia t i o n , t d e c r e a s e s w i t h
i n c r e a s i n g [ C I - l ] a n d in c r e a s i n g t e m p e r a t u r e .
E
"6
F1o. 6.
40
O'
- 40
[J 30 C
-8 0 ,,, 50oc
o
80C
-120
- 1 6 0
- 2 0 0 . ~
0 4 8 12 16 20 24 28 32 36 40 44 48
T i m e
( h )
V a r i a ti o n o f O C P w i t h ti m e f o r
A I S I 3 1 6 L
i m m e r s e d i n 10 0 0 p pm
[C1- ]
a q u e o u s
s o l u t i o n s a t v a r i o u s t e m p e r a t u r e s
( p H 4 ) .
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1 8 1 6 A . U . M A L IK etal
8O
- _
/ o 4
~T o pH 9
- 2 0 0
0 4 8 12 16 20 24 28 32 36 40 44 48
T i m e (h)
FIG. 7. Var iat ion of OCP w i t h t i m e f o r A[S[ 316L i m m e r s e d i n 1 00 0 p p m C I - a q u e o u s
s o l u t io n s o f d i f f e r e n t pH v a l u e s a t 20C.
Polar izati on resistance P o l a r i za t i o n m e a s u r e m e n t s w e r e c a r r ie d o u t u s i n g 3 16 L
c o u p o n s i m m e r s e d i n c h l o r i d e - c o n t a i n i n g a q u e o u s s o l u t i o n s u n d e r c o n d i t i o n s o f
v a r y i n g t e m p e r a t u r e , p H a n d [ C I - ] . Ty p i c a l p o l a r iz a t i o n r e s i s t a n c e p lo t s a r e s h o w n
i n F i g s 1 0 - 1 2 . Ta b l e 1 l i s t s t h e c o r r o s i o n r a t e v a l u e s c o m p u t e d f r o m t h e p l o t s . Th e
c o r r o s i o n r a t e v a l u e s a s d e t e r m i n e d f r o m t h e p o l a r i z a t i o n r e s i s t a n c e e x p e r i m e n t s
w e r e b a s e d o n a n o d i c a n d c a t h o d i c T a fe l v a l u e s w h i c h w e r e o b t a i n e d f r o m p r e v i o u s l y
c a r r ie d o u t Ta f e l p l o t r u n s . Th e p o l a r i z a t i o n d a t a p r o v i d e t h e f o l l o w i n g i n f o r m a t i o n
r e g a r d i n g t h e b e h a v i o r o f 3 1 6 L i n c h l o r i d e - c o n t a i n i n g s o l u t i o n s : ( i ) a t p H 4 , t h e
2.0
FIG. 8.
i.8
1.6
1.4
12
~ - 1.0
...I Q8
0.6
0.4
Q2
[] 30 C
z~ 5 0 C
o 80 c
0 I I I
1 2 3
L o g CI -
L o g i n d u c t i o n t i m e f o r p i t i n i t i a t i o n v s l o g [ C I - ] a t v a r i o u s t e m p e r a t u r e s ( p H 4 ) .
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pH and [C1-] and the corrosio n of AISI 316L steel 1817
FIG. 9.
2.0
.J
1.8
1 . 6 -
1 . 4 -
1.2 -
1.0
-
0 . 8 -
0.6- -
0.4 --
0 .2 - -
01
0
1000 ppm
I I I I
20 4O 60 80 100
Tempereture (C)
Log induction ti me r or pit initiatio n vs temperaturc at 100 and 1000 pp m[ Ct ]
(pH4) .
TABLE 1. RE SULT S FROM POLARIZATION RESISTANCE MEASURE-
MENTS
Tem p [Cl ] pH E ..... Corro sion rate
C ppm mV MPY
20 100 4 -1 56 0.104
20 300 4 -1 20 0.116
20 500 4 -14 4 0.119
20 100(I 4 -168 0.135
20 5000 4 -1 85 0.148
30 1000 4 -203 0.143
5(1 1000 4 -127 0.154
80 1000 4 -93 0.295
20 1000 7 -50 0.071
30 1000 7 -15 0 0.051
50 1000 7 -12 2 0.03
80 1000 7 -200 0.169
20 1000 9 -2 31 0.011
30 1000 9 -2 19 0.041
50 1000 9 -238 0.(155
8(1 1000 9 - 287 0.163
25 24153* 7.3 -2 49 0.064
20 1000t 4 -3 43 0.049
20 1000t 7 -2 35 0.041
20 1000+ 9 -238 0.010
* Artificial sea water.
t De-aerated.
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1 8 1 8 A . U . M A L IK
e t a l .
FIG. 10.
- 1 4 5
- 1 5 6
- 1 6 7
- 1 7 8
- 1 8 9
I
- 0 . 0 4 4
100 p p m
1 0 0 0 p p m
. r ,
5 0 0 0 p p m
- 20 0 ' ' ,
- 0 .060 - 0 .028 - 0 .012 0 .00 4
I ( / c A m - 2 )
P o l a r i z a t i o n r e s is t an c e c u r v e s f o r A I S i 3 1 6 L i n a q u e o u s s o l u t i o n s o f v a r i o u s
c h l o r i d e c o n c e n t r a t i o n s a t p H 4 a n d 2 0 C .
FIG. II.
E
uJ
- 8 5
- 1 1 0
- 1 3 5
- -1 6 0
- 1 8
l 8 0 ~ C
.:
l
50 .
:...-
....
2 0 = C
3 0 C
r ~
-2 1( l i i I
- 0 . 1 0 - 0 . 0 6 -0 . 0 2 0 . 0 2 0 . 0 6
I ( # A c m -2 )
P o l a r i z a t i o n r e s is ta n c e c u r v e s fo r A I S [ 3 1 6 L i n 1 0 0 0 p p m C I - s o l u t i o n s o f p H 4
a n d a t d i f f e r e n t te m p e r a t u r e s
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FIG. 12.
0 . 1 6
- 1 4 5
1
- 1 6 3
- 1 8 1
E
w
- 1 9 9
- 2 1 7
- 2 3 5 ~ i
- 0 0 3 0 - 0 . 0 2 2 - 0 . 0 1 4 - 0 . 0 0 6
I ( ,Am 2 )
p H 7
pH4
p H 9
0,002
P o l a r i z a t io n r e s i s ta n c e c u r v e s f o r A I S I 3 1 6 L i n 1 00 0 p p m C l - s o l u t i o n s o f v a r io u s
p H v a l u e s a t 3 0 C .
0 . 1 5 -
0 . 1 4 -
0 . 1 3 -
0 . 1 2 -
0 . 1 1
-
. 1 1 . 4
A
E
o
8
o
(.~
Fro . 13 .
I I I I I I
1 .8 2 , 2 2 . G 3 . 0 3 , 4 3 , 8
L o g C l -
C o r r o s i o n r a t e v s lo g [ C I - ] a t 20 C a n d p H 4 .
p H a n d [ C I - ] a n d t h e c o r r o s i o n o f A I S I 3 1 6 L s t e el 1 81 9
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8 20 A . U . M A LIK e t a l .
0 . 3 0
0 . 2 6
A
> , 0 . 2 2
E
0 . 1 8
o
0.14.
8
~
0 . 1 0
L_
g , -
0.06
0 . 0 2
FIG. 14.
13 p H 4
,a, pH 9
zx
/x
~,
i I I
2 0 4 0 6 0 8 0 1 0 0
T e m p e r e t u r e ( C )
C o r r o s i o n r a t e v s t e m p e r a t u r e a t 2 0 C a n d p H v a l u e s 4 a n d 9 .
F1G. 15.
9 0 0
6 0 0
3 0 O
>
E
, , , 0
- 3 0 0
' 1 ' ' I ' ' 1 ' ' ' ~ . . . . . . . . I ' '~ . .. .
J
,
. - "
. . . . . . . . . . . . . - _ ~ . "
10 -3 10 -2 10 1 100 101 102 103
I ( /~A cm 2)
C y c l i c p o l a r i z a t i o n c u r v e f o r A I S I 3 1 6 L i n 1 0 0 p p m C I - s o l u t i o n o f p H 4 a t 3 0 (
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p H a n d [ C I - ] a n d t h e c o r r o s i o n o f A I S I 3 1 6 L s t ee l 1 82
FIG. 16.
6 0 0
4 0 0
2 0 0
E
U.I
- 200
' " i ' " , l ' " i ' " ' l ' " i ' " ' l ' " 1 ' " 9 ' " i ' " ' i " l '
7
J
- 4 0 0 , , ;, , , l < , : A . . . . . . [ , ~ l l , , , , ,
1 0 - 3 1 0 - 2 1 0 - 1 1 0 0 1 01 1 0 2 1 0 3
I ( / ~A
c m - 2 )
C y c l i c p o l a r i z a t i o n c u r v e f o r A I S 1 3 1 6 L i n 1 0 00 p p m C I - s o l u t i o n o f p H 4 a t
3 0 C .
F I~ . 17 .
E
W
1 5 0
5 0
- 5 0
- 1 5 0
2 5 0
. Z -
- i
a r - '
c
--- _
- 3 5 o . . . . . . J . . . . . i . i
. . . . . . . .
1 0 - 2 1 0 - 1 1 0 0 1 01 1 0 2
I (/.LA cm 2)
C y c l i c p o l a r i z a t i o n c u r v e f o r A I S 3 1 6 L in 1 0 0 0 p p m C I s o l u t i o n o f p H 4 at 8 0 C .
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1822 A . U . MALIKe t a l .
TABLE 2. RESULTS FROM CYCLIC POLARIZATIONSTUDIES
T e m p [ C l - ] p H g p i t g p r o t E p it - gp r ot E r
C ppm mV mV mV mV
20 100 4 759 -1 99 958 - -
20 300 4 502 -82 584 300
20 500 4 438 -100 538 280
20 1000 4 425 -77 502 250
20 5000 4 322 -140 462 200
30 1000 4 260 -62 322 67
50 1000 4 177 -29 206 20
80 1000 4 - 4 -38 34 0
20 1000 7 217 -49 266 233
30 1000 7 294 -4 298 66
50 1000 7 234 -4 8 282 82
80 1000 7 111 -27 138 133
20 1000 9 862 -186 1058 - -
30 1000 9 611 -2 79 990 - -
50 1000 9 389 -27 3 662 - -
80 1000 9 467 -37 5 842 - -
25 24153* 7.3 304 -230 534 - -
20 1000t 4 504 -79 578 200
20 1000t 7 427 -10 7 634 87.5
20 1000t 9 814 -216 1030 67
20 24153* 7.3 304 -230 534 75
* Art i f i c ia l sea water .
t
De -ae r a t e d .
c o r r o s i o n r a t e g e n e r a l l y i n c r e a s e s l i n e a r l y w i t h i n c r e a s i n g [ C I - ] i n t h e r a n g e
1 0 0 - 5 0 0 0 p p m ( F i g . 1 3 ) ; ( i i ) w i t h i n c r e a s i n g p H , t h e c o r r o s i o n r a t e d e c r e a s e s , b e i n g
h i g h e s t a t p H 4 . T h e r a t e s a t p H 7 a n d 9 a r e s i m i l a r i n m a g n i t u d e ; ( i i i ) i n g e n e r a l ,
c o r r o s i o n r a t e i n c r e a s e s w i t h i n c re a s i n g t e m p e r a t u r e b e i n g h i g h e s t a t 8 0 C a n d
l o w e s t a t 3 0 C ( F i g . 1 4 ) .
Cyc l i c po la r i za ti on
S o m e r e p r e s e n t a t i v e c y c l ic p o l a r i z a t i o n c u r v e s f o r 3 1 6 L i n
C l - - c o n t a i n i n g s o l u t i o n s a r e s h o w n i n F i g s 15 - 1 7 . A h y s t e r e si s l o o p is t r a ce d d u r i n g
r e v e r s e s c a n i n d i c a t i n g t h e p o s s i b i l i t y o f p i t ti n g . T a b l e 2 li s ts t h e v a l u e s o f p i t ti n g
p o t e n t i a l ( Ep it ) a n d p r o t e c t i o n p o t e n t i a l ( Ep ro t ), w h i c h a r e d e f i n e d a s t h e p o t e n t i a l
w h e r e t h e f o r w a r d a n d r e v e r s e s c a n s c r o s s . R e p a s s i v a t i n g p i t t i n g p o t e n t i a l ( E r ) i s
a l s o c o n s i d e r e d , w h i c h i s d e f i n e d a s t h e m o s t a c t i v e p o te n t i a l a t w h i c h t h e n u c l e a t i o n
o f u n s t a b l e ( i . e . r e p a s s i v a t i n g ) p i ts c a n o c c u r a n d i s c h a r a c t e r i z e d b y a r e v e r s i b l e
i n c r e a s e i n c u r r en t d e n s i t y ( C D ) . T h e s t a b l e n u c l e a t i o n p o t e n t i a l ( E p i t ) i s a s s e s s e d a s
t h a t a t w h i c h a c o n s i s t e n t i n c r e a s e i n C D o c c u r s , i n d i c a t i n g t h e i n i t i a t i o n o f n o n -
r e p a s s i v a t i n g p i ts . Epr ot i s t h e m o s t a c t i v e p o t e n t i a l a t w h i c h p i t p r o p a g a t i o n c a n
O c c u r .
I n g e n e r a l , p i t ti n g p o t e n t i a l , E pi t i s s h i f t e d t o a m o r e n e g a t i v e ( o r a c t i v e ) v a l u e
w i t h in c r e a s i n g [ C I - ] o r t e m p e r a t u r e .
A t a p a r t i cu l a r t e m p e r a t u r e a n d [ C I - ]
E p i t
s h i ft s to a m o r e n o b l e p o t e n t i a l w i t h
i n c r e a si n g p H . T h e e l e c t r o c h e m i c a l l y m e a s u r e d p i t p o t e n t i a l ,
Epi t
i s f o u n d t o b e a
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p H a n d [ C 1 - ]
a n d t h e c o r r o s i o n
o f A I S I 3 1 6 L
s t e e l
1823
900
8 0 0
7 0 O
6 0 O
E 5 0 0
~
4oo
3OO
2 0 0
1 0 0
FIG. 18.
I I
2 4
L o g C I - ( p p m )
P i t t i n g p o t e n t i a l
v s l o g [ C 1 - ] a t 2 0 C a n d p H 4 .
l in e a r f u n c t i o n o f t h e lo g a r i t h m o f [ C I - ] ( F i g . 1 8 ) . Th is li n e a r d e p e n d e n c e o f
E p i t o n
l o g [ C 1 - ] c a n b e r e p r e s e n t e d a s:
g p i t = A + B log [C1-] .
Bo t h t h e A a n d B c o e f fi c i e n t s a r e t e m p e r a t u r e d e p e n d e n t . F i g u r e 1 9 s h o w s t h e
d e p e n d e n c e o f
E p i t o n
t e m p e r a t u r e a t d i f f er e n t v a l u e s o f p H a t a fi x e d [ C l - ] . A s h i ft
o f E p i t i n t h e n e g a t i v e d i r e c t i o n u s u a l l y o c c u r s a s th e t e m p e r a t u r e i n c r e a s e s .
E
t.u
FIG. 19.
9 0 0
o o
7 0 0
6 0 0 [ ] p H 4
p H 7
5 0 0 o p H 9
4 O 0
2OO
100
0
- 1 0 0 I I I I
o 2 0 4 0 6 0 8 0 ~ o o
Tempereture ( C )
P i t t i n g po t e n t i a l v s t e m p e r a t u r e f o r
A I S I 3 1 6 L in 1 00 0 p p m C I s o l u t i o n o f
v a r i o u s p H v a l u e s a t
3 0 C .
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1 8 2 4 A . U . M A LI K e t a l .
D I S C U S S I O N
The immersion tests carried out on 316L coupons at different [C1-] concentra-
tions, pH and time intervals and under static and dynamic conditions show extremely
low weight losses (10-50/~g in typical 4-month runs). At a particular chloride
concentration and immersion time, the weight losses were more or less independent
of pH and immersion conditions (static or dynamic). The number and depth of the
pits increase with increasing immersion time. The maximum number of pits were
found on specimens immersed in solutions of pH 4. At pH 7 and 9, the pits were
generally shallow and the number was smaller, though some of them were deep.
Under dynamic conditions, the number of pits observed on the surface of the
specimen was much smaller than under stagnant conditions.
In the presence of C l- , austenitic stainless steels are subjected to local attack in
the form of pitting or crevice corrosion due to breakdown of the protective Cr20 3
film at random sites. 6 The pitting on the passive surface has been explained by the
competitive adsorption mechanism 15'16 in which chloride ions move into metal/oxide
film interface at the metal surface. At a particular chloride concentration, a critical
potential E p i t ) develops which is sufficient to displace oxygen from the protective
oxide layer. It appears from the present study that the low pH and stagnancy would
provide most favourable conditions for pit growth. In a typical case, at 30C and 4-5
ppm dissolved oxygen, the pits grow to maxima of 450 and 325 #m at pH 4 under
static and dynamic conditions, respectively, when 316L specimens were immersed in
300 ppm chloride solutions for 4 months. At higher pH values (7 and 9) the depth
rarely exceeded 70/~m. The pit depth has been found to be a parabolic function of
CI- concentration and therefore, with increasing [C1-] the rate of pit growth appears
to slow down.
The electrochemical studies on pitting corrosion were carried out at pH values of
4, 7 and 9. At a particular [C1-] and a given temperature, the corrosion rates were
3 2 0
300
280
260
I:: 24O
I,~ 220
200
180
160
0
FIG. 20.
1 I
2 4 6
Log Cl - (ppm)
R e p a s s i v a t i n g p o t e n ti a l v s l og [ C 1 -] f o r A I S I 3 1 6 L i n a q u e o u s s o l u t i o n o f p H 4
a n d a t 2 0 C .
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7/23/2019 The Influence of PH and Chloride Concentration on the Corrosion Behavior of AISI 316L Steel in Aqueous Solutions
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p H a n d [ C l - ] a n d t h e c o r r o s i o n o f A I S I 3 1 6 L s t e e l 1 82 5
900
8 0 0
7 0 0
600
E
uj~ 500
4 O O
30O
2O0
20
Flo . 21 .
I I
2 2 2 4 2 6
t i
P i t t in g p o t e n t i a l v s i n d u c t i o n t i m e f o r p it in i t ia t i o n in 1 0 00 p p m C I s o l u t i o n o f p H
4 and a t 20C.
f o u n d t o b e h i g h e s t at p H 4 a n d l o w e s t a t p H 9 . C o n s i d e r i n g t h e e f f e c t o f p H o n
p i t ti n g p o t e n t i a l , E p i , t h e p o t e n t i a l w a s f o u n d t o b e s h i ft in g to m o r e p o s i ti v e v a l u e s
w i t h i n c r e a s i n g p H . T h e c o r r o s i o n r a t e o f 3 1 6 L in a r ti fi c ia l s e a w a t e r ( [ C 1 -] 2 4 1 53
p p m a n d p H = 7 . 3 ) w a s s i m i la r t o t h a t i n 10 00 p p m C I - s o l u ti o n s o f p H 7 a n d 9 b u t
m u c h l o w e r t h a n t h a t i n a s o lu t io n o f p H 4 o f t h e s a m e c o n c e n t r a t i o n . T h e e f f e c t o f
c h l o r i d e c o n c e n t r a t i o n o n t h e s t a b l e p i t n u c l e a t i o n p o t e n t i a l , Epi t is c o n s i s t e n t w i t h
t h a t o b s e r v e d w i t h o t h e r s y s t e m s w h e r e b y t h e p o t e n t i a l v a r ie s l in e a r l y w i t h t h e
l o g a r i t h m o f C l - a c t i v i ty . L e c k i e a n d U h l i g 15 r e p o r t e d a 8 8 m V s h i f t i n t h e c r i ti c a l
n u c l e a t i o n p o t e n t i a l b y a 1 0 - f o l d i n c r e a s e in C I - a c t iv i ty in th e c o n c e n t r a t i o n r a n g e
0 . 0 1 -1 M ( 3 5 0 - 3 5 , 0 0 0 p p m ) . I n th e p r e s e n t s t u d y a s h if t o f a b o u t 2 0 0 - 3 0 0 m V w a s
o b s e r v e d b y a s i m i l a r i n c r e a s e i n t h e c o n c e n t r a t i o n r a n g e 1 0 0 - 50 0 0 p p m a t p H 4 . T h e
r e p a s s i v a t in g p o t e n t i a l , E r a l so v a r i e s l in e a r l y w i t h t h e l o g a r i t h m o f t h e c o n c e n -
t r a t i o n o f c h l o r i d e ( F ig . 2 0 ). H o w e v e r , n o s y s t e m a t i c v a r i a t i o n in p r o t e c t i v e
potent ial ,
E pro t , w a s f o u n d . A t [ C l - ] l e v e l s o f 1 0 0 p p m o r b e l o w n o r e p a s s i v a t i n g
p o t e n t i a l w a s o b s e r v e d . T h e i n d u c t i o n t i m e , ti, f o r p i t i n it i a ti o n m e a s u r e d u n d e r
o p e n c i r c u i t c o n d i t i o n s h a s b e e n f o u n d t o b e a l i n e a r f u n c t i o n o f p i t ti n g p o t e n t i a l ,
E p it , a n d f o l l o w s t h e r e l a t i o n s h i p :
Epi t = A + B log t
w h e r e A a n d B a r e t e m p e r a t u r e d e p e n d e n t c o e f f ic i e nt s ( Fi g. 2 1 ).
A t [ C 1 -] c o n c e n t r a t i o n s a t w h i c h s ta b l e n u c l e a t i o n w a s e v i d e n t ( 1 0 0 - 3 0 ,0 0 0 p p m )
e x t e n s i v e h y s t e r e s i s w a s o b s e r v e d u p o n s c a n r e v e r s a l w i th r e p a s s i v a t i o n o c c u r r i n g in
t h e v i c i ni t y o f th e O C P . T h e p i t t in g p o t e n t i a l , g p i t , w a s i n v a r i a b l y m o r e p o s i t iv e t h a n
t h e p r o t e c t i v e p o t e n t i a l ,
Eprot.
T h e d i f f e r e n c e b e t w e e n p i tt in g a n d p r o t e c t iv e
p o t e n t i a l s d e c r e a s e s w i t h i n c r e a s i n g [ C I - ] a n d is a l i n e a r f u n c t i o n o f lo g a r i t h m o f
[ C 1 -] ( F i g . 2 2 ). T h e o c c u r r e n c e o f p i t i n i ti a t io n p o t e n t i a l s i n th e t r a n s p a s s i v e r a n g e
c a n b e e x p l a i n e d i n te r m s o f t h e l o c a l i z e d b r e a k d o w n o f a s u r f a c e f il m o n 3 1 6 L th a t i s
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7/23/2019 The Influence of PH and Chloride Concentration on the Corrosion Behavior of AISI 316L Steel in Aqueous Solutions
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1826 A .U . MALIK t a l .
640
600
; 560
5 2 0
~ 480
FIG. 22.
440
4 0 0 I I
0 2 4
L o g C I - ( p p r n )
Difference of pitting potential and protective potential vs log [C I-] at 20C and
pH 4.
s o m e w h a t l es s p r o t e c t i v e ( i. e . s h o w s a h i g h e r r a t e o f g e n e r a l d i s s o l u t i o n ) t h a n t h a t
p r e v a l e n t i n th e p a s s iv e r e g i o n . A t p H 4 , u n d e r s i m i l ar c o n d i ti o n s o f t e m p e r a t u r e a n d
[ C l - ] , t h e r e p a s s i v a t i n g p o t e n t i a l , E r , a p p e a r s a t a m u c h h i g h e r p o s i ti v e p o t e n t i a l
t h a n a t p H 7 . N o r e p a s s i v a t i n g p o t e n t i a l w a s o b s e r v e d a t p H 9 . I t l e a d s t o t h e
c o n c l u s i o n t h a t a t p H 4 , th e n u c l e a t i o n o f r e p a s s i v a t i n g p it s o c c u r s a t o v e r p o t e n t i a l s
f a r b e l o w t h a t r e q u i r e d f o r s t a b l e p it t in g ; r e s u l t in g t h e r e b y in t h e o n s e t o f a d y n a m i c
p r o c e s s o f p it i n it ia t io n a n d r e p a s s iv a t i o n p r i o r t o t h e d e v e l o p m e n t o f p r o p a g a t i n g
p i t s .
C O N C L U S I O N
T h e p i t t i n g b e h a v i o u r o f A I S I 3 1 6 L in c h l o r i d e - c o n t a i n i n g s o l u t io n s i s g r e a t l y
i n f l u e n c e d b y t h e v a r i a t i o n in [ C 1 - ], p H , d i s s o l v e d o x y g e n , t e m p e r a t u r e a n d f l ow
c o n d i ti o n s . T h e e l e c t r o c h e m i c a l p o l a ri z a t io n e x p e r i m e n t s c a r r i e d o u t s h o w t h a t t h e
c o r r o s i o n r a t e , p i t t i n g p o t e n t i a l , E p i t , a n d r e p a s s i v a t i n g p o t e n t i a l , E r , a r e l i n e a r
f u n c t i o n s o f [ C l - ] . T h e i n d u c t i o n t i m e , ti, m e a s u r e d u n d e r o p e n c i r c u it c o n d i t i o n s ,
h a s a l so b e e n f o u n d t o b e a l i n e a r f u n c t i o n o f p i tt i n g p o t e n t i a l , E p i .
A n a n a l ys i s o f th e e x p e r i m e n t a l r e s u lt s in d i c a t e s t h a t in g e n e r a l , l o w p H , h i g h
[ C l - ] a n d s t a g n a n c y a r e t h e m o s t f a v o u r a b l e c o n d i t i o n s f o r i n i ti a t io n a n d p r o p a g a -
t i o n o f p i ts i n A I S I 3 1 6 L s t e e l .
R E F E R E N C E S
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CHONG,
D e s a l i n a t i o n 66, 147 (1987).
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ARY,
D e s a l i n a t i o n
55,229 (1985).
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UHLIG,
C o r r o si o n H a n d b o o k . W iley, New Y ork (1948).
-
7/23/2019 The Influence of PH and Chloride Concentration on the Corrosion Behavior of AISI 316L Steel in Aqueous Solutions
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p H a n d [ C 1 - ] a n d t h e c o r r o s i o n o f A I S I 3 1 6 L s t e e l 1 82 7
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SZKLARSKA-SMIALOWSKA,
i t t ing , C orros ion o f Meta ls . N A C E , H o u s t o n ( 1 9 8 6 ) .
13. Z.
SZKLARSKA-SM1ALOWSKA,
orros ion 2 7 ,2 2 3 ( 1 9 7 1 ) .
14. Z.
SZKLARSKA-SMIALOWSKA,
n d u s t r i a l P r o b l em s T r ea t m en t a n d Co n t r o l T ec h n i q u es . P e r g a m o n
P r e s s , O x f o r d ( t 9 8 7 ) .
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18. R. NISHMURA, Corros ion 4 3 ,4 8 6 ( 1 9 8 7 ) .
1 9 . J . H . W A N G , C . C . Su an d Z .
SZKLARSKA-SMIALOWSKA,
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