Influence of Acid Deposition on Atmospheric Corrosion of Metals: A

6 Influence of Acid Deposition on Atmospheric Corrosion of Metals: A Review Vladimir Kucera

Downloaded by UNIV OF CINCINNATI on February 18, 2015 | http://pubs.acs.org Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch006

Swedish Corrosion Institute, Box 5607, S-114 86 Stockholm, Sweden In outdoor atmospheres dry deposition of S-pollutants and especially of SO is of greatest importance. Dose response functions describing corrosion as function of SO and time of wetness are available for some materials as steel and zinc. NO in combination with SO has a synergistic corrosion effect especially indoors on electrical contact materials, copper and steel. The influence of acid precipitation may differ for different metals and depends also on the pollution level. The atmospheric corrosion of metals due to acid deposition is in most regions mainly a local problem restricted to areas close to the pollution source. A reduction of losses due to corrosion has been achieved in many Swedish cities by reduction of SO emissions and by introduction of district heating systems. 2

2

x

2

2

The i n c r e a s e d combustion o f f o s s i l f u e l s has c r e a t e d t h e problem o f a c i d i f i c a t i o n o f the e n v i r o n m e n t , which today i s c o n s i d e r e d t o be one o f the most s e r i o u s e n v i r o n m e n t a l p r o b l e m s . In S c a n d i n a v i a , where s c i e n t i s t s f i r s t gave warning o f t h e p r o b l e m , t h e l o n g d i s tance t r a n s p o r t o f p o l l u t a n t s from Europe and u n f a v o u r a b l e geol o g i c a l c o n d i t i o n s i n b i g areas make t h e s i t u a t i o n e s p e c i a l l y s e r i o u s . Among t h e e f f e c t s caused by a c i d i f i c a t i o n t h e c o r r o s i o n o f m a t e r i a l s belongs t o t h e f i r s t observed and b e s t documented. I t has thus been known f o r a l o n g time t h a t S - p o l l u t a n t s o r i g i n a t i n g from b u r n i n g o f f o s s i l f u e l s a c c e l e r a t e s i n t h e f i r s t p l a c e t h e a t m o s p h e r i c c o r r o s i o n o f c e r t a i n m e t a l s . T h e i r i n f l u e n c e was d e s c r i b e d e . g . i n Sweden's case study f o r t h e U.N. c o n f e r e n c e on human environment i n 1972, which was t h e f i r s t e f f o r t t o d e s c r i b e the g e n e r a l p i c t u r e o f t h e a c i d i f i c a t i o n problem Q J . More r e c e n t l y a l s o t h e i n f l u e n c e o f N - p o l l u t a n t s on the a t m o s p h e r i c c o r r o s i o n has a t t r a c t e d a t t e n t i o n . T h i s may be seen i n the l i g h t o f t h e f a c t t h a t d u r i n g t h e 1970s t h e wet d e p o s i t i o n o f s u l p h a t e i n Sweden remained by and l a r g e a t a c o n s t a n t l e v e l . The wet 0097-6156/86/0318-0104$06.00/ 0 © 1986 American Chemical Society

In Materials Degradation Caused by Acid Rain; Baboian, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

6. K U C E R A

105

Atmospheric Corrosion of Metals

deposition of n i t r a t e c e n t a y e a r (2).

by c o n t r a s t

i n c r e a s e d a t a r a t e o f 3-4 per


The c o r r o s i o n e f f e c t on c o n s t r u c t i o n s i n the atmosphere due t o a c i d i f i c a t i o n i s i n most areas m a i n l y o f l o c a l n a t u r e . It s h o u l d be s t r e s s e d , however, t h a t a c i d i f i c a t i o n o f s o i l and water can l e a d t o i n c r e a s e d c o r r o s i o n o f b u r i e d i n s t a l l a t i o n s and o f i n s t a l l a t i o n s i n water i n c l u d i n g water p i p e s ( 3 , _4). T h i s i s on the o t h e r hand m a i n l y a r e g i o n a l p r o b l e m , where the l o n g - r a n g e t r a n s p o r t o f a i r p o l l u t a n t s p l a y s an i m p o r t a n t r o l e . The f o l l o w i n g s u b d i v i s i o n may thus be u s e d .

C o r r o s i o n due t o acidification

X

C o r r o s i o n i n s o i l and water - r e g i o n a l p r o b lem - i n d i r e c t e f f e c t

Atmospheric c o r r o s i o n l o c a l problem, d i r e c t effect

In the p r e s e n t l e c t u r e a b r i e f r e v i e w w i l l be g i v e n o f the i n f l u e n c e o f a c i d i f y i n g a i r p o l l u t a n t s on the a t m o s p h e r i c c o r r o s i o n o f m e t a l s based m a i n l y on more r e c e n t r e s u l t s from Europe and e s p e c i a l l y from S c a n d i n a v i a . The d e p o s i t i o n p r o c e s s Both s u l p h u r and n i t r o g e n p o l l u t a n t s a r e e m i t t e d i n t o the a i r i n the form o f o x i d e s , SCL and NO r e s p e c t i v e l y , which may then f u r t h e r be o x i d i z e d d u r i n g the t r a n s p o r t i n the a i r . The p r o c e s s e s of d e p o s i t i o n of a i r p o l l u t a n t s a r e : a b s o r p t i o n o f gas on m a t e r i a l s u r f a c e s 1 - dry d e p o s i t i o n impaction of p a r t i c l e s J removal o f gas and a e r o s o l s by p r e c i p i t a t i o n - wet d e p o s i t i o n The relative s i g n i f i c a n c e of the individual deposition mechanisms f o r c o r r o s i o n o f m a t e r i a l s may v a r y i n d i f f e r e n t areas depending e . g . on the d i s t a n c e from the e m i s s i o n s o u r c e , and a l s o f o r d i f f e r e n t m a t e r i a l s depending on d i f f e r e n c e s i n c o r r o s i o n mechanisms and n a t u r e o f p r o t e c t i v e l a y e r s o f c o r r o s i o n p r o d u c t s . The i n f l u e n c e o f s u l p h u r p o l l u t a n t s The i n f l u e n c e o f m a i n l y S 0 on the c o r r o s i o n r a t e o f s e v e r a l m a t e r i a l s has been shown i n numerous n a t i o n a l exposure programs. D u r i n g the l a s t decades a number o f e m p i r i c a l r e l a t i o n s have been d e r i v e d from measurements o f a t m o s p h e r i c c o r r o s i o n r a t e s o f the most i m p o r t a n t s t r u c t u r a l m e t a l s and from measurements o f e n v i r o n mental f a c t o r s . The r e s u l t s are u s u a l l y p r e s e n t e d i n form o f e q u a t i o n s i n c l u d i n g p o l l u t i o n and m e t e o r o l o g i c a l parameters (j>). ?


106

MATERIALS DEGRADATION CAUSED BY ACID RAIN

Carbon_steel S e v e r a l i n v e s t i g a t i o n s have shown the d o m i n a t i n g e f f e c t o f S(L on the c o r r o s i o n r a t e , r e c e n t r e s u l t s from an i n t e r - N o r d i c and from a S w e d i s h - C z e c h o s l o v a k exposure may s e r v e as examples ( 6 , 2 ) · The f o l l o w i n g d o s e - r e s p o n s e f u n c t i o n s have been o b t a i n e d (FIG. 1 ) : 1 year:

K

R e

=

4.0 S 0 + 5 8

r = 0.98

4 years:

K

p e

=

8.0 S 0 +160

r = 0.94

2

2

w h e r e Κ = w e i g h t l o s s f o r s t e e l (g/m ) , SO2 = d e p o s i t i o n r a t e (mg/m .d) and r = c o r r e l a t i o n c o e f f i c i e n t . These i n v e s t i g a t i o n s show t h a t i n a broad range o f the temperate c l i m a t i c zone and i n S 0 p o l l u t i o n l e v e l s r e p r e s e n t a t i v e f o r Western and C e n t r a l Europe a s ^ w e l l as f o r Southern S c a n d i n a v i a most o f the v a r i a t i o n s i n the c o r r o s i o n r a t e may be e x p l a i n e d s o l e l y by the S 0 d e p o s i t i o n r a t e . In t h i s r e g i o n the average wetness c o n d i t i o n s do not d i f f e r t o a g r e a t e r e x t e n t . T h i s e x p l a i n s t h e f a c t t h a t time o f wetness i s not i n c l u d e d i n the dose response r e l a t i o n s h i p .


2

o

2

I t s h o u l d be p o i n t e d o u t , however, t h a t d u r i n g s h o r t e r time p e r i o d s , the v a r i a t i o n s o f wetness c o n d i t i o n s a r e v e r y e x t e n s i v e . P r e d i c t i o n s o f one o r t h r e e months s t e e l c o r r o s i o n needs a p a r t from the SO,, p o l l u t i o n d a t a a l s o a t l e a s t v a l u e s o f the time o f wetness as i l l u s t r a t e d by the f o l l o w i n g e q u a t i o n ( 1 0 ) : 1 month: K

p e

= 0 . 5 1 S 0 + 0 . 1 1 TOW - 9

r = 0.82

2

w h e r e Κ = w e i g h t l o s s f o r s t e e l (g/m ) , S0 = deposition rate (mg/m . d ) , TOW = time o f wetness (hours w i t h TW >80% and Τ > ° C ) , r = correlation coefficient. ?

9

The r e s u l t s from l e n g t h y exposure p e r i o d s are o f c o u r s e more r e l e v a n t f o r p r a c t i c a l purposes e . g . f o r c l a s s i f i c a t i o n o f the c o r r o s i v i t y o f atmosphere on a g i v e n l o c a t i o n o r f o r c o s t - b e n e f i t a n a l y s i s . In t h i s case the c o r r o s i o n r a t e may be a s s e s s e d from y e a r l y mean v a l u e s o f the c o n c e n t r a t i o n o f p o l l u t a n t s and from the t i m e - o f - w e t n e s s c l a s s e s t i m a t e d from m e t e o r o l o g i c a l measurements. Zinc Z i n c belongs t o the m a t e r i a l s t h a t e x e r t s a s t r o n g dependence o f the c o r r o s i o n r a t e on the c o n c e n t r a t i o n o f s u l p h u r p o l l u t a n t s . In s e v e r a l i n v e s t i g a t i o n s the c o r r o s i o n r a t e i n urban atmospheres was found t o be 2-6 times h i g h e r than i n r u r a l atmospheres ( 5 , 8 J . A l s o f o r z i n c d o s e - r e s p o n s e f u n c t i o n s o b t a i n e d i n the temperate c l i m a t i c zone show the d o m i n a t i n g i n f l u e n c e o f S 0 on i n l a n d s i t e s . The i n c l u s i o n o f time o f wetness i n the l i n e a r model d i d not f u r t h e r s i g n i f i c a n t l y improve the c o r r e l a t i o n . The f o l l o w i n g dose-response f u n c t i o n s have been o b t a i n e d i n the previously mentioned i n v e s t i g a t i o n ( F I G . 2 ) : 2

1 year:

K

Z p

= 0.13 S 0

2

+

7.21

r = 0.81


KUCERA

Atmospheric Corrosion of Metals

1200r

Steel

1000

800

600


400

200

100

F i g u r e 1. The weight l o s s o f s t e e l a f t e r 1, 2 , and 4 y e a r s ' e x posure as a f u n c t i o n o f S02 d e p o s i t i o n r a t e a t 7 t e s t s i t e s i n Sweden and C z e c h o s l o v a k i a ( 7 ) .

120

Zinc

1100

•

1 year

•

2 years

80

60

40

20

0

100 S0 deposition rate, mg/rrvd 2

F i g u r e 2 . The w e i a h t l o s s o f z i n c a f t e r 1, 2 , and 4 years* posure as a f u n c t i o n o f S 0 d e p o s i t i o n r a t e a t 7 t e s t s i t e s Sweden and C z e c h o s l o v a k i a "(7). ?


exin

108

M A T E R I A L S DEGRADATION C A U S E D BY ACID RAIN

4 years:K

= 0 . 6 6 S 0 + 14.20

Z n

r = 0.97

2

The c o r r o s i o n r a t e o f z i n c i s s t r o n g l y dependent on t h e wetness c o n d i t i o n s d u r i n g t h e e a r l y days o r weeks o f exposure ( 9 ) . T h e r e f o r e o f t e n no u s e f u l e q u a t i o n s f o r c o r r o s i o n can be found i n terms o f monthly averages o f environmental f a c t o r s ( 1 0 ) . The c o r r o s i o n r a t e o f z i n c may be e l e v a t e d d u r i n g t h e f i r s t y e a r o f exposure e s p e c i a l l y a t r u r a l s i t e s w i t h l a r g e amount o f p r e c i p i t a t i o n . T h i s so c a l l e d memory e f f e c t may e x e r t i t s i n f l u e n c e d u r i n g t h e f i r s t y e a r s o f e x p o s u r e . A f t e r some y e a r s o f exposure the c o r r o s i o n r a t e has d i m i n i s h e d and i n t h e l o n g run i t seems t o reach a v a l u e c o r r e s p o n d i n g t o t h e p o l l u t i o n l e v e l ( 6 J .


Copper I t i s a w e l l known f a c t t h a t f o r m a t i o n o f t h e green p a t i n a t a k e s a s u b s t a n t i a l l y s h o r t e r time i n urban than i n r u r a l atmosphere, where o f t e n v e r y l o n g time e l a p s e s b e f o r e t h e s u r f a c e i s covered by p a t i n a o r i n very pure atmospheres t h e s u r f a c e remains covered by a b l a c k o x i d e l a y e r . A l s o t h e c o r r o s i o n r a t e i n r u r a l atmos phere i s u s u a l l y lower (

Influence of Acid Deposition on Atmospheric Corrosion of Metals: A

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