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Corrosion behaviour of aluminium sheet alloys and aluminium rivetted
bimetallic couples in eight Canadian atmospheres: summary of ten
years' results
NATIONAL R E S E A R C H COUNCIL CANADA
DIVISION O F BUILDING RESEARCH
T H E CORROSION BEHAVIOUR O F ALUMINIUM S H E E T ALLOYS AND ALUMINIUM R I V E T T E D B I M E T A L L I C C O U P L E S IN EIGHT CANADIAN A T M O S P H E R E S
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SUMMARY O F T E N YEARS' RESULTSN.K. J o h n s t o n , D. P. D o y l e , a n d H. P . G o d a r d A l u m i n i u m L a b o r a t o r i e s L i m i t e d , K i n g s t o n , O n t a r i o a n d E . V . G i b b o n s D i v i s i o n of Building Re s e a r c h , N a t i o n a l R e s e a r c h C o u n c i l , O t t a w a , O n t a r i o A joint r e p o r t of t h e A l u m i n i u m L a b o r a t o r i e s L i m i t e d a n d t h e D i v i s i o n of Building R e s e a r c h , N a t i o n a l R e s e a r c h C o u n c i l . I n t e r n a l R e p o r t No. 3 3 0 of t h e D i v i s i o n of B u i l d i n g R e s e a r c h OTTAWA A p r i l 1 9 6 6
P R E F A C E
T h e r e h a s b e e n a s h o r t a g e of published i n f o r m a t i o n on the a t m o s p h e r i c c o r r o s i o n b e h a v i o u r of d i f f e r e n t a r c h i t e c t u r a l m e t a l s a t v a r i o u s l o c a t i o n s a c r o s s C a n a d a . Such i n f o r m a t i o n is f r e q u e n t l y r e q u e s t e d by t h o s e r e s p o n s i b l e f o r t h e d e s i g n and m a i n t e n a n c e of buildings. Although s t u d i e s of t h i s n a t u r e have b e e n c a r r i e d out in the U . S . A . by t h e A m e r i c a n Society f o r T e s t i n g and M a t e r i a l s no s i m i l a r c o - o p e r a t i v e study involving m e t a l s u p p l i e r s , u s e r s , and r e s e a r c h o r g a n i z a t i o n s h a s u n t i l r e c e n t l y b e e n u n d e r t a k e n in C a n a d a . I n p a r t i a l f u l f i l l m e n t of t h i s n e e d and a s p a r t of t h e p r o g r a m of t h e A s s o c i a t e C o m m i t t e e on C o r r o s i o n R e s e a r c h and P r e v e n t i o n , e s t a b l i s h e d by t h e National R e s e a r c h Council i n 1950 t o s t i m u l a t e and c o o r d i n a t e c o r r o s i o n r e s e a r c h in C a n a d a , a n u m b e r of m e t a l s w e r e s e l e c t e d f o r t e s t i n g . T h e y w e r e exposed a t e i g h t outdoor s i t e s a c r o s s C a n a d a . T h e o v e r - a l l p r o g r a m included s e v e r a l m e t a l and o r g a n i c c o a t i n g s applied t o s t e e l s u b s t r a t e s . T h i s r e p o r t d e s c r i b e s t h e 1 0 - y e a r p e r f o r m a n c e a t t h e d i f f e r e n t s i t e s of t h r e e a l u m i n i u m a l l o y s and a l u m i n i u m r i v e t t e d b i m e t a l l i c c o u p l e s . O t h e r r e p o r t s c o v e r i n g the 1 0 - y e a r r e s u l t s on o t h e r m e t a l s will be i s s u e d l a t e r . T h e s p e c i m e n s of a l u m i n i u m a l l o y s w e r e f u r n i s h e d by A l u m i n i u m L a b o r a t o r i e s L i m i t e d , Kingston, who w e r e a l s o r e s p o n s i b l e f o r a s s e s s i n g t h e i r p e r f o r m a n c e and i n compiling t h i s r e p o r t . T h i s p a r t of the study w a s u n d e r the d i r e c t i o n of D r . H. P. G o d a r d , a m e m b e r of t h e f o r m e r A. C . C . R. P. with t h e a s s i s t a n c e of M r . N . K. Johnston and D. P. Doyle. T h e a r r a n g e - m e n t s f o r e x p o s u r e and e x a m i n a t i o n of s p e c i m e n s , and s o m e o v e r - a l l c o o r d i n a t i o n of the p r o g r a m w e r e c a r r i e d out u n d e r t h e d i r e c t i o n of M r . E. V. Gibbons of the Division of Building R e s e a r c h .
T h e Division i s indebted not only t o t h e c o m p a n i e s who have c o - o p e r a t e d in making t h i s s t u d y p o s s i b l e , but a l s o t o t h o s e who have c o n t r i b u t e d in the p r o v i s i o n and s e r v i c i n g of c e r t a i n of the e x p o s u r e s i t e s .
Ottawa A p r i l 1966
N. B. Hutcheon A s s i s t a n t D i r e c t o r
T H E CORROSION DEHAVIOUR O F ALUMINIUM S H E E T ALLOYS AND ALUMINIUM RIVETTED BIMETALLIC C O U P L E S IN EIGHT CANADIAN ATMOSPHERES - - SUMMARY O F T E N YEARS' RESULTS
N . K . J o h n s t o n , D. P. Doyle, and H . P . G o d a r d A l u m i n i u m L a b o r a t o r i e s L i m i t e d , King s t o n , O n t a r i o and E . V. Gibbons Division of Building R e s e a r c h , National R e s e a r c h C o u n c i l , O t t a w a , O n t a r i o In 1953, b e c a u s e of the i n c r e a s i n g n a t i o n a l t r e n d t o w a r d s i n d u s t r i a l i z a t i o n , t h e A s s o c i a t e C o m m i t t e e on C o r r o s i o n R e s e a r c h a n d P r e v e n t i o n (A. C . C. R . P. ) of t h e National R e s e a r c h Council ( N . R . C. ), O t t a w a , d e c i d e d t o u n d e r t a k e a p r o g r a m t o a s c e r t a i n t h e r e l a t i v e c o r r o s i o n b e h a v i o u r of v a r i o u s m e t a l s in a n u m b e r of t y p i c a l Canadian a t m o s p h e r e s . T h e p r o g r a m w a s c a r r i e d out by S u b c o m m i t t e e "C" of t h e A s s o c i a t e C o m m i t t e e . T h e s i t e s w e r e
s e t u p and o p e r a t e d by t h e Division of Building R e s e a r c h of the N. R . C. M a t e r i a l s t e s t e d in the f i r s t i n s t a n c e included s h e e t
s p e c i m e n s of a l u . m i n i u m , and a l u m i n i u m coupled t o c o p p e r , zinc and m i l d s t e e l , t h r e e low a l l o y s t e e l s , t h r e e s t a i n l e s s s t e e l a l l o y s , two m a g n e s i u m a l l o y s and r o l l e d z i n c . I n s u b s e q u e n t y e a r s , t o c o m p l e t e t h e e x p o s u r e p r o g r a m f o r t h e m a j o r a r c h i t e c t u r a l m e t a l , t h e following s p e c i m e n s w e r e a l s o included: c o p p e r , munt z m e t a l , l e a d a l l o y s and m o n e l . T h e a l u m i n i u m and r i v e t t e d b i m e t a l l i c couple s we r e supplied by A l u m i n i u m L a b o r a t o r i e s L i m i t e d . S p e c i m e n s of the o t h e r m e t a l s f o r t h i s f i r s t p o r t i o n of t h e p r o g r a m w e r e supplied by t h e S t e e l C o m p a n y of Canada L i m i t e d , A t l a s S t e e l L i m i t e d , Dominion M a g n e s i u m L i m i t e d , and t h e C o n s o l i d a t e d Mining and S m e l t i n g C o m p a n y of C a n a d a L i m i t e d . A l l m e t a l s p e c i m e n s w e r e 4 by 6 i n c h e s i n s i z e and w e r e held i n p l a c e with p o r c e l a i n i n s u l a t o r s a t 3 0 d e g r e e s t o t h e h o r i - z o n t a l , f a c i n g s o u t h . Twelve s p e c i m e n s of e a c h type of m e t a l w e r e s e t out i n i t i a l l y a t e a c h s i t e . T h i s e n a b l e d ' t h r e e s p e c i m e n s of e a c h type t o be r e m o v e d a f t e r e x p o s u r e p e r i o d s of o n e , t w o , f i v e , and t e n y e a r s . T h e s a m p l e s w e r e p r e p a r e d and weighed by e a c h p a r t i c i p a n t b e f o r e d i s p a t c h t o N. R . C . , and a f t e r e a c h e x p o s u r e p e r i o d t h e y w e r e r e t u r n e d by N. R. C. f o r photographing. T h e y
w e r e t h e n f o r w a r d e d t o t h e i r s o u r c e s f o r c l e a n i n g , r e - w e i g h i n g , and c o r r o s i o n e v a l u a t i o n . The individual r e p o r t s on t h e condition of t h e s a m p l e s e x p o s e d f o r one and two y e a r s have b e e n c o n - s o l i d a t e d and published ( 1 ).
The A. C. C. R. P. w a s d i s b a n d e d i n 1960, but t h e t e s t p r o g r a m w a s continued by t h e Division of Building R e s e a r c h . T h e r e s u l t s f o r t h e a l u m i n i u m a l l o y s a f t e r five y e a r s of e x p o s u r e a r e d e s c r i b e d i n a n A l u m i n i u m L a b o r a t o r i e s L i m i t e d r e p o r t i s s u e d i n 1960 ( 2 ) . T h i s p r e s e n t r e p o r t d e a l s with t h e t e n - y e a r r e s u l t s of t h e p o r t i o n of the p r o g r a m handled b y A l u m i n i u m L a b o r a t o r i e s L i m i t e d . DESCRIPTION O F MATERIAL T r i p l i c a t e s p e c i m e n s of a l u m i n i u m a l l o y s (Alcan 3 s - H 1 4 , 5 7 s -H34, and 6 5 s
-
T6) and b i m e t a l l i c r i v e t t e d couple s (of s i m i l a r o v e r - a l l s i z e with Alcan 3s-H14 a l u m i n i u m s h e e t and joined with 2 s a l l o y r i v e t s ) w e r e coupled t o c o p p e r , zinc, and m i l d s t e e l and e x p o s e d f o r 10 y e a r s a t e i g h t l o c a t i o n s a c r o s s Canada. Upon r e t u r n t o t h e l a b o r a t o r y the e x t e n t of c o r r o s i o n w a s d e t e r m i n e d by m e a s u r e m e n t of t h e d e p t h of pitting and weight l o s s . T h e c o m p o s i t i o n of t h e m e t a l s t e s t e d i s given in T A B L E I . T h e Alcan 3s-H14, 5 7 s - H - 3 4 and 6 5 s - T 6 a l u m i n i u m s h e e t s p e c i m e n s m e a s u r e d 4 by 6 by 0.064 i n c h e s . T h e r i v e t t e d c o u p l e s c o n s i s t e d e a c h of 3-3/8- by 4 - by 0 . 0 6 4 - i n c h s h e e t of 3s-H14 r i v e t t e d with A l c a n 2S a l l o y r i v e t s t o a 3 - 3 / 8 - by 4 - i n c h s h e e t of d i s s i m i l a r m e t a l . T h e s h e e t t h i c k n e s s e s of c o p p e r , z i n c , and s t e e l w e r e 0.032, 0 . 0 4 8 and 0.062 i n c h e s r e s p e c t i v e l y . T h e r i v e t t e d o v e r l a p of e a c h couple w a s 3/8 i n c h l e a v i n g t h e a s s e m b l e d s p e c i m e n 4 by 6 i n c h e s o v e r - a l l . DESCRIPTION O F T E S T SITES A c o m p l e t e d e s c r i p t i o n of t h e a t m o s p h e r i c t e s t s i t e s u s e d b y t h e National R e s e a r c h Council h a s b e e n published (3)..C
l*p Ottawa
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T h i s s i t e i s l o c a t e d on t h e p r o p e r t y of the M o n t r e a l Road L a b o r a t o r i e s of t h e N a t i o n a l R e s e a r c h Council. It i s on thee a s t e r n o u t s k i r t s of the City of Ottawa and c a n b e c l a s s e d s e m i - r u r a l .
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2 S a s k a t o o n
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T h i s i s a r u r a l s i t e l o c a t e d on the c a m p u s of t h e U n i v e r s i t y of S a s k a t c h e w a n on t h e o u t s k i r t s of S a s k a t o o n . 3 M o n t r e a l - T h i s i s a n i n d u s t r i a l s i t e l o c a t e d on the roof of at w o - s t o r e y building of t h e Canadian National R a i l w a y s in t h e P o i n t St. C h a r l e s d i s t r i c t n e a r 1801 L e b e r S t r e e t .
4 Halifax
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T h i s i s a m a r i n e i n d u s t r i a l s i t e l o c a t e d on the roof of a F e d e r a l P u b l i c building in downtown H a l i f a x , two c i t y b l o c k s f r o m t h e h a r b o u r .5 York Redoubt
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T h i s i s a r u r a l m a r i n e s i t e l o c a t e d on theAtlantic c o a s t . It i s a t a n e l e v a t i o n of 100 f e e t f r o m the o c e a n , about s e v e n m i l e s f r o m the c i t y of Halifax.
6
N o r m a n W e l l s-
T h i s i s a f a r n o r t h e r n s i t e l o c a t e d in t h e M a c k e n z i e R i v e r v a l l e y about 90 m i l e s s o u t h of the a r c t i c c i r c l e . 7 E s q u i m a l t ( R o c k y P o i n t )-
T h i s i s a m a r i n e s i t e on t h e w e s t c o a s t a t t h e s o u t h e a s t e x t r e m i t y of Vancouver I s l a n d , about 1 5 m i l e s f r o m the C i t y of V i c t o r i a . It i s a t a n e l e v a t i o n of 50 f e e t and about 1500 f e e t f r o m t h e o c e a n . 8 T r a i l--
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T h i s i s a s e m i - r u r a l s i t e l o c a t e d a t B i r c h b a n k i n t h e C o l u m b i a R i v e r Valley about6
m i l e s n o r t h of t h e City of T r a i l . It i s the outdoor t e s t s t a t i o n of t h e Consolidated Mining and S m e l t i n g C o m p a n y of C a n a d a .E a r l y m e t e o r o l o g i c a l d a t a and s u l p h u r dioxide c o n c e n t r a t i o n s a t e a c h s i t e w e r e given in a p r e v i o u s r e p o r t ( 1 ) . T h e l e a d p e r o x i d e method w a s u s e d t o m e a s u r e t h e s u l p h u r dioxide content of the a t m o s p h e r e . T h e i n s t r u m e n t u s e d in t h i s method d o e s not m e a s u r e t h e v o l u m e t r i c c o n c e n t r a t i o n of SO2 i n t h e a t m o s p h e r e d i r e c t l y , but p r e s e n t s a n i n t e g r a t e d m e a s u r e of the s u l p h u r dioxide " a c t i v i t y t ' d u r i n g a p e r i o d of e x p o s u r e . It w a s found t h a t t h i s i n s t r u m e n t w a s w e l l s u i t e d t o m e a s u r e the r e l a t i v e l e v e l s of SO2 a t t h e e x p o s u r e s i t e s when m e t a l s a r e u n d e r t e s t . A b r i e f c o n d e n s a t i o n of r e c e n t s u l p h u r dioxide d a t a u s i n g t h e l e a d p e r o x i d e method i s given i n T A B L E
II.
F i g u r e 1 i s a g r a p h i c a l r e p r e s e n t a t i o n of t h e a v e r a g e c o n c e n t r a t i o n of s u l p h y r dioxide a t e a c h t e s t s i t e .
E X P E R I M E N T A L P R O C E D U R E
All a l u m i n i u m s p e c i m e n s w e r e d e g r e a s e d and weighed b e f o r e e x p o s u r e . T h e two component s h e e t s of t h e r i v e t t e d c o u p l e s
w e r e weighed i n d i v i d u a l l y b e f o r e b e i n g a s s e m b l e d , e x c e p t f o r t h o s e e x p o s e d a t T r a i l ( s i t e n u m b e r 8 ) , w h e r e only t h e t o t a l weight of e a c h r i v e t t e d couple w a s r e c o r d e d . T h e s p e c i m e n s w e r e e x p o s e d f o r t e n y e a r s and t h e n r e t u r n e d t o A l u m i n i u m L a b o r a t o r i e s L i m i t e d , Kingston, f o r e x a m i n a t i o n . T h e s p e c i m e n s w e r e i n s p e c t e d v i s u a l l y , a f t e r which two of e a c h s e t of t h r e e r i v e t t e d c o u p l e s w e r e d i s a s s e m b l e d and c l e a n e d . C o n t r o l p a n e l s w e r e a l s o c l e a n e d t o d e t e r m i n e t h e weight of m e t a l l o s t by t h e c l e a n i n g p r o c e d u r e . T h e a l u m i n i u m coupons w e r e i m m e r s e d i n a hot s t r i p p i n g solution of c h r o m i c and p h o s p h o r i c a c i d s ( A S T M - B 137 - 4 5 ) , s c o u r e d gently with
s o a p i m p r e g n a t e d s t e e l wool p a d s ( B r i l l o ) , r i n s e d , and a i r d r i e d . T h e c o p p e r w a s i m m e r s e d i n a 10 p e r c e n t s u l p h u r i c a c i d s o l u t i o n , p o l i s h e d with B r i l l o p a d s , r i n s e d , and a i r d r i e d . T h e zinc w a s i m m e r s e d i n a 5 p e r cent a c e t i c a c i d s o l u t i o n , p o l i s h e d w i t h B r i l l o p a d s , r i n s e d , and a i r d r i e d . T h e m i l d s t e e l w a s i m m e r s e d in a Rodine ( 2 p e r c e n t ) inhibited w a r m 10 p e r cent h y d r o c h l o r i c a c i d s o l u t i o n , p o l i s h e d with B r i l l o p a d s , r i n s e d , a n d a i r d r i e d . T h e s p e c i m e n s w e r e t h e n weighed,again i n s p e c t e d v i s u a l l y , and pit d e p t h m e a s u r e m e n t s m a d e with a pit d e p t h m i c r o m e t e r . E a c h b i m e t a l l i c couple w a s e x p o s e d i n t r i p l i c a t e but only two of e a c h
s e t w e r e d i s a s s e m b l e d and c l e a n e d . T h e r e m a i n i n g c o u p l e s , along w i t h s i m i l a r s p e c i m e n s f r o m p r e v i o u s e x p o s u r e p e r i o d s w e r e r e t a i n e d f o r v i s u a l r e f e r e n c e . E X P E R I M E N T A L RESULTS ( 1 ) A l u m i n i u m Alloys The r e s u l t s of v i s u a l e x a m i n a t i o n s , b e f o r e and a f t e r c l e a n i n g , and t h e e x t e n t of pitting on t h e a l u m i n i u m s h e e t s p e c i m e n s e x p o s e d f o r ten y e a r s a r e given in T A B L E III. T A B L E IV h a s b e e n i n c l u d e d t o e n a b l e a convenient c o m p a r i s o n t o b e m a d e w i t h t h e r e s u l t s obtained a f t e r five y e a r s of e x p o s u r e ( 2 ) . Weight l o s s e s , and c o r r o s i o n r a t e s c a l c u l a t e d f r o m t h e m , a r e given in T A B L E V.
F i g u r e s 2 a n d 3 show t h e c o r r o s i o n r a t e s of t h e a l u m i n i u m a l l o y s a t e a c h s i t e f o r e x p o s u r e p e r i o d s of o n e , two, f i v e , and t e n y e a r s . T h e one - , t w o - , and f i v e - y e a r d a t a w e r e t a k e n f r o m e a r l i e r r e p o r t s ( 1 , 2).
( 2 ) R i v e t t e d B i m e t a l l i c C o u p l e s
T h e r e s u l t s of t h e v i s u a l e x a m i n a t i o n s b e f o r e a n d a f t e r c l e a n i n g and t h e e x t e n t of g a l v a n i c c r e v i c e c o r r o s i o n on t h e
r i v e t t e d b i m e t a l l i c c o u p l e s e x p o s e d f o r t e n y e a r s a r e g i v e n i n T A B L E S VI, VII, a n d VIII. M a x i m u m pit d e p t h s on r i v e t t e d b i - m e t a l l i c c o u p l e s a r e g i v e n i n T A B L E IX. Weight l o s s e s a r e g i v e n , a n d c o r r o s i o n r a t e s i n " m i l s p e r y e a r " ( m . p. y. ) a r e c o m p a r e d with u n c o u p l e d a l u m i n i u m in T A B L E X . I t should b e noted t h a t t h e t e r m " m i l s p e r y e a r t ' when u s e d t o c o m p a r e t h e c o r r o s i o n r a t e s of m e t a l s i s a c o m p a r i s o n of t h e a m o u n t of c o r r o s i o n and a s s u m e s t h a t c o r r o s i o n i s u n i f o r m on t h e s u r f a c e . T h i s i s n o t e n t i r e l y t r u e i n t h e c a s e of a l u m i n i u m s i n c e pitting o c c u r s . A g a i n f o r c o n v e n i e n c e t o c o m p a r e c h a n g e s i n a p p e a r a n c e w i t h t i m e t h e o b s e r v a t i o n s r e p o r t e d a f t e r five y e a r s of e x p o s u r e h a v e b e e n i n c l u d e d . F i g u r e s 4 t o 10 show t h e c o r r o s i o n r a t e s of a l u m i n i u m a t e a c h s i t e e x c e p t T r a i l ( s i t e n u m b e r 8 ) i n e a c h t y p e of a s s e m b l y f o r p e r i o d s of o n e , two ( I ) , five ( 2 ) , a n d t e n y e a r s . DISCUSSION ( 1 In c o n s i d e r i n g t h e r e s u l t s f r o m s i t e No. 4, t h e F e d e r a l B u i l d i n g i n H a l i f a x , i t s h o u l d be pointed out t h a t t h i s p a r t i c u l a r l o c a t i o n p r o v i d e s a n e n v i r o n m e n t t h a t i s not n o r m a l f o r t h i s g e n e r a l a r e a of H a l i f a x . P o l l u t i o n of t h e a t m o s p h e r e h e r e i s v e r y h e a v y d u e t o a l a r g e s m o k e s t a c k on the roof i n c l o s e p r o x i m i t y t o t h e e x p o s u r e r a c k s . T h e S O 2 c o n t e n t o v e r t h e p e r i o d 1954-1962 w a s 3 t o 4 t i m e s a s high a s t h a t a t t h e F i s h e r i e s B u i l d i n g l o c a t i o n ( a b o u t t h r e e c i t y b l o c k s a w a y ) i n a l l but t h e s u m m e r m o n t h s . T h e e f f e c t of t h i s is shown i n t h e c o m p a r i s o ~ l of c o r r o s i o n r a t e s f o r t h e t h r e e a l u m i n i u m a l l o y s a t t h e two s i t e s a s shown below.
.*, 1- F i s h e r i e s Duildir~rr F e d e r a l B u i l d i n g A l l o y
- - -
2 Y r . 5 Y r . l O Y r . 3 s 0 . 0 7 4 0 . 0 5 0 0 . 0 4 4 2 Y r . 5 Y r . 10 Y r . - - 0. 64 0 . 3 5 0. 24 ::< f r o m t e s t s c a r r i e d out by A l u m i n i u m L a b o r a t o r i e s L i m i t e dThe c o r r o s i o n r a t e s f o r the heavily polluted s i t e a r e 5 t o 6 t i m e s t h o s e for the m o r e n o r m a l location a t 10 y e a r s and higher f o r the e a r l i e r t i m e p e r i o d s .
It i s of i n t e r e s t that i n r e c e n t y e a r s (1963-1965) the SO2 content of the a t m o s p h e r e a t the F e d e r a l Building s i t e h a e been r e d u c e d c o n s i d e r a b l y and t e n d s t o a p p r o a c h equality with the F i s h e r i e e Building location in a l l but the m i d - w i n t e r months and even then i t i s l e s s than half the v a l u e s obtained previouely. A
continuation of the p r e s e n t values should r e s u l t i n a m a r k e d reduction in the c o r r o s i o n r a t e e of the a l u m i n i u m s a m p l e s . (2) The c o r r o s i o n behaviour of the t h r e e a l u m i n i u m alloye t e e t e d w a s s i m i l a r . Although the o n e - and t w o - y e a r rersults w e r e not conclusive, a t five y e a r s , and p a r t i c u l a r l y a t t e n y e a r s , the r e s u l t e show that the c o r r o s i o n r a t e of a l u m i n i u m in the a t m o r p h e r e a l m o s t a l w a y s d e c r e a s e s with t i m e .
( 3 ) Alcan 57s and 65s a l l o y s had slightly l o w e r c o r r o e i o n r a t e e than 3 s alloy i n s e v e r e i n d u s t r i a l a t m o s p h e r e s (Halifax and M o n t r e a l ) . Alcan 57s alloy w a s judged m o r e r e s i s t a n t t o euch a t m o s p h e r e 8 a f t e r five y e a r s but i t a p p a r e n t l y o f f e r s n o significant advantage o v e r
longer e x p o s u r e .
(4 Alcan 3 s alloy exposed i n r u r a l a t m o s p h e r e s l o s e e i t s a p p a r e n t e a r l i e r advantage o v e r the o t h e r a l u m i n i u m a l l o y s on long ( t e n y e a r s ) e x p o s u r e .
(5) As o b s e r v e d a f t e r five y e a r s , 3 s a l u m i n i u m a l l o y s , when coupled t o zinc, r e c e i v e a slight but m e a s u r a b l e a d v e r s e galvanic effect in r u r a l and m a r i n e a t m o s p h e r e s .
( 6 ) Copper and m i l d s t e e l , when coupled t o 3 s a l u m i n i u m alloy, c a u s e galvanic c o r r o s i o n t o a n e q u a l extent i n m a r i n e and i n d u s t r i a l a t m o s p h e r e s . Although m a r i n e a t m o s p h e r e s w e r e m o r e a g g r e s s i v e o v e r five y e a r s , the t e n - y e a r e x p o s u r e did not d e m o n s t r a t e t h i s d i f f e r e n c e .
(7) In F i g u r e 11 the t e n - y e a r panel weight 10s s e s of the 57s alloy p a n e l s a r e plotted a g a i n s t the a v e r a g e sulphur dioxide
c o n c e n t r a t i o n s a t e a c h s i t e o v e r the e x p o s u r e p e r i o d 1954-1964. It will be s e e n that t h e r e is a r e a s o n a b l e c o r r e l a t i o n between sulphur dioxide concentration and c o r r o s i o n a s m e a s u r e d by weight l o s s . A s o b s e r v e d a f t e r five y e a r s , t h e Halifax s i t e continues t o d e v i a t e f r o m the line.
( 1 ) T h e r a t e of c o r r o s i o n of a l u m i n i u m a l l o y s in t h e a t m o s p h e r e s , a s m e a s u r e d by weight l o s s , i s low, and d e c r e a s e s with t i m e of
e x p o s u r e .
( 2 T h e c o r r o s i o n of a l u m i n i u m a l l o y s i n t h e a t m o s p h e r e t a k e s t h e f o r m of l o c a l i z e d pitting o r e t c h i n g , t h e e x t e n t of which i s
p r o p o r t i o n a l t o t h e a g g r e s s i v e n e s s of t h e a t m o s p h e r e . Only i n a v e r y s e v e r e location
-
on a roof n e a r a building chimney (Halifax, s i t e No. 4 ) , d o e s g e n e r a l thinning of a l u m i n i u m s e c t i o n s o c c u r . ( 3 ) In C a n a d a , i n d u s t r i a l a t m o s p h e r e s a r e the m o s t a g g r e s s i v e t o a l u m i n i u m . M a r i n e a t m o s p h e r e s a r e c o n s i d e r a b l y l e s s a g g r e s s i v e , while r u r a l a t m o s p h e r e s a r e a l m o s t without effect on a l u m i n i u m .( 4
1
Of the t h r e e a l u m i n i u m a l l o y s t e s t e d , Alcan 57s and 6 5 s a r e m o s t r e s i s t a n t t o s e v e r e i n d u s t r i a l a t m o s p h e r e s . The t h r e e a l u m i n i u m a l l o y s ( 3 s ) 57S, and 6 5 s ) a r e about e q u a l l y r e s i s t a n t t o m a r i n e and r u r a l a t m o s p h e r e s .(5) C o p p e r and m i l d s t e e l c a u s e galvanic c o r r o s i o n of a l u m i n i u m
i n i n d u s t r i a l - m a r i n e ( w o r s t ) , i n d u s t r i a l , and m a r i n e a t m o s p h e r e s . Galvanic c o r r o s i o n of a l u m i n i u m i s negligible i n r u r a l a t m o s p h e r e s
.
(6) Zinc d o e s not c a u s e galvanic c o r r o s i o n of a l u m i n i u m , but i ns o m e i n s t a n c e s p r o t e c t s i t . R E F E R E N C E S
( 1 ) T h e c o r r o s i o n behaviour of t h e m a j o r a r c h i t e c t u r a l and s t r u c t u r a l m e t a l s in Canada: S u m m a r y of two y e a r r e s u l t s . National Re s e a r c h Council, Ottawa, A s s o c i a t e C o m m i t t e e on C o r r o s i o n R e s e a r c h and P r e v e n t i o n . 24 F e b r u a r y 1959.
( 2 ) Doyle, D. P. a n d Godard, H. P.
,
T h e c o r r o s i o n behaviour of a l u m i n i u m s h e e t a l l o y s and a l u m i n i u m b i m e t a l l i c r i v e t t e d c o u p l e s i n Canadian a t m o s p h e r e s : S u m m a r y of five y e a rr e s u l t s . A l u m i n i u m L a b o r a t o r i e s L i m i t e d , Kingston. R e p o r t
K - 1R-239-60-28, P r o g r e s s R e p o r t No. 1 , 23 S e p t e m b e r 1960. ( 3 ) Gibbons, E . V.
,
Outdoor e x p o s u r e s i t e s of t h e NationalR e s e a r c h Council. C h e m i s t r y i n C a n a d a , Vol. 12, No. 3, M a r c h 1960, p. 44-48.
T A B L E
ll
AVERAGE AMOUNT O F SULPHUR DIOXIDE IN T H E A T M O S P H E R E AT E A C H T E S T S I T E F R O M 1 9 5 4 - 1964 1 S i t e No. L o c a t i o n Mg s o 3 / d m / d a y 2 4 H a l i f a x 6. 36 3 M o n t r e a l 1 . 7 0 8 8 T r a i l 0 . 6 7 7 1 O t t a w a 0. 519 5 Y o r k Redoubt 0 . 2 7 5 2 S a s k a t oon 0 . 1 6 2 7 E s q u i m a l t 0 . 0 6 3 6 N o r m a n W e l l s 0 . 0 0 9
TABLE 4
APPEARANCE OF ALUMINIUM SPECIMENS EXPOSED FOR TEN YEARS
IN EIGHT CANADLGN ATMOSPHERES
E x t r a C o m m e n t s Thinned 3 m i l s Most affected M o r e pitted n e a r bottom Roughened slightly e a r t h w a r d Slightly b e t t e r t h a n 3s B e t t e r than 3s Most affected B r o a d e t c h type p i t s W o r s e than 3s l r r i d e s c e n t f i l m skyward No pitting No pitting No pitting I Site No. Halifax (4) M o n t r e a l (3) T r a i l (8) Ottawa (1) York Redoubt (5) Saskatoon ( 2 ) E s q u i m a l t (7 Norman Wells (6) Alcan Sheet Alloys 3s-H14 57s-H34 6 5 s - T 6 3s-H14 57s-H34 6 5 s - T 6 3s-H14 57s-H34 6 5 s - T 6 3s-H14 57s-H34 6 5 s - T 6 3 s - H l l 57s-H34 6 5s - T 6 3s-H14 57s -H34 6 5s - T 6 3s-H14 57s-H34 6 5 s - T 6 3s-H14 57s-H34 6 5 s - T 6 A p p e a r a n c e of S p e c i m e n s Skyward Uncleaned Blackened, s t u c c o effect Blackened, s t u c c o effect Blackened, s t u c c o effect Dulled, black s p o t s Dulled, b l a c k s p o t s Dulled, black s p o t s Dulled Dulled Dulled Smooth w e a t h e r e d Smooth w e a t h e r e d Smooth w e a t h e r e d Mottled Mottled Mottled Dulled Dulled Dulled Speckled Speckled Speckled Shiny Shiny Shiny E a r t h w a r d Uncleaned Uniform black f i l m Uniform black f i l m Uniform black f i l m G r e y f i l m G r e y f i l m G r e y f i l m Slightly dulled Slightly dulled Slightly dulled Mottled Mottled Mottled Mottled Mottled Mottled Mottled Mottled Mottled Mottled Mottled Mottled blackened blackened blackened Side Cleaned Very rough Rough Rough Tiny pits F e w tiny p i t s Many tiny p i t s S c a t t e r e d p i t s F e w s c a t t e r e d pits Many d e e p pits L i t t l e affected L i t t l e affected Little affected T i n y p i t s F e w tiny p i t s Many tiny p i t s Dulled Dulled Dulled Not affected Not affected F e w e t c h pits Unaffected Unaffected S m a l l b l i s t e r s Side Cleaned E x t r e m e l y rough V e r y rough V e r y rough Many l a r g e pits F e w p i t s Many p i t s Many s c a t t e r e d p i t s S c a t t e r e d p i t s Many d e e p p i t s T i n y p i t s F e w t i n y p i t s F e w p i t s Many tiny pits F e w tiny pits Many p i t s Mottled Mottled Mottled P i t t e d P i t t e d Many e t c h p i t s Unaffected Unaffected S m a l l b l i s t e r s
T A B L E IV A P P E A R A N C E O F ALUMINIUM S P E C I M E N S E X P O S E D F O R F I V E YEARS LN EIGHT CANADLAN A T M O S P H E R E S S i t e s H a l i f a x (4 M o n t r e a l ( 3 ) T r a i l ( 8 ) Ottawa ( 1 ) Y o r k Redoubt ( 5 ) S a s k a t o o n ( 2 ) E s q u i m a l t ( 7 ) N o r m a n W e l l s ( 6 ) F Alcan Sheet Alloys 3 s - H 1 4 57s-H34 6 5 s - T 6 3 s - H I 4 57s-H3.2 6 5 s - T 6 3 s - H 1 4 57s -H34 6 % - T 6 3 s - H 1 4 57s-H34 6 5 s - T 6 3 s - H 1 4 57s-H3-1 6 3 s - T 6 3 s - H 1 4 5 7 s - H 3 4 6 5 s - T 6 3 s - H 1 4 5 7 s - H 3 4 6 5 s - T 6 3s-H14 5 7 s - H 3 4 6 5 s - T 6 E x t r a C o m m e n t s 1 . 7 m i l s l o s t 1. 1 m i l s l o s t 2 . 4 m i l s l o s t Max. pit 1 m i l Max. p i t 5 m i l s Max. pit 5 m i l s Max. pit 6 m i l s Max. pit 7 m i l s Max. pit 7 m i l s A p p e a r a n c e of S k y w a r d U n c l e a n e d Rough s o o t y Rough s o o t y Rough s o o t y Rough w e a t h e r e d Rough w e a t h e r e d Rough w e a t h e r e d S m o o t h w e a t h e r e d S m o o t h w e a t h e r e d S m o o t h s p e c k l e d S m o o t h w e a t h e r e d S m o o t h w e a t h e r e d S m o o t h w e a t h e r e d S m o o t h w e a t h e r e d S m o o t h w e a t h e r e d S m o o t h w e a t h e r e d S m o o t h s p e c k l e d S m o o t h s p e c k l e d S m o o t h s p e c k l e d S m o o t h w e a t h e r e d S m o o t h w e a t h e r e d S m o o t h w e a t h e r e d Shiny Shiny M o t t l e d S p e c i m e n s Side C l e a n e d Rough g e n e r a l a t t a c k Rough g e n e r a l a t t a c k Rough g e n e r a l a t t a c k Dulled Dulled E t c h e d l i g h t l y E t c h e d l i g h t l y E t c h e d l i g h t l y E t c h e d a n d s p e c k l e d E x c e l l e n t E x c e l l e n t E x c e l l e n t Dulled Dulled E t c h e d l i g h t l y E x c e l l e n t F a i n t m o t t l e d F a i n t m o t t l e d Dulled Dulled S p e c k l e d E x c e l l e n t E x c e l l e n t E x c e l l e n t E a r t h w a r d Uncleaned Rough s o o t y Rough s o o t y Rough s o o t y Rough s l i g h t l y s o o t y Rough s l i g h t l y s o o t y Rough s l i g h t l y s o o t y S m o o t h w e a t h e r e d Rough w e a t h e r e d Rough s p e c k l e d Rough w e a t h e r e d Rough w e a t h e r e d Rough s p e c k l e d Rough w e a t h e r e d Rough w e a t h e r e d Rough s p e c k l e d S m o o t h s p e c k l e d S m o o t h s p e c k l e d S m o o t h s p e c k l e d S m o o t h w e a t h e r e d S m o o t h w e a t h e r e d S m o o t h w e a t h e r e d Shiny Shiny Shiny Side C l e a n e d Rough g e n e r a l a t t a c k Rough g e n e r a1 a t t a c k Rough g e n e r a l a t t a c k Mottled t i n y p i t s S p e c k l e d t i n y p i t s S p e c k l e d t i n y p i t s E t c h e d , t i n y p i t s E t c h e d , t i n y p i t s S p e c k l e d , t i n y p i t s Dulled Dulled S p e c k l e d Mottled Dulled S p e c k l e d F a i n t l y s p e c k l e d F a i n t l y s p e c k l e d F a i n t l y s p e c k l e d S p e c k l e d Mottled S p e c k l e d E x c e l l e n t E x c e l l e n t E x c e l l e n t
T A B L E V
T
LOSSES
AND CORROSION RATES OF ALUMINIUMSHEET
SPECIMENS EXPOSED F O R T E N YEARS
JN
EIGHT CANADIAN ATMOSPHERES'
-
S i t e Halifax (4 Mont r e a1 (3) T r a i l (8) Ottawa ( 1 ) York Redoubt (5) Sa skatoon (2) E s q u i m a l t (7) N o r m a n W e l l s (6) P a n e 1 N o . 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 Weight L o s s e s ,3s-
Wt. L o s s 4. 5550 5.8311 5. 3898 0. 3674 0.3625 0.3766 0.3345 0.3318 0.3300 0.1229 0.1246 0.1297 0.1461 0.1528 0.1652 0.0145 0.0231 0.0167 0.0290 0.0251 0.0260 0.0168 0.0119 0.01 55 m . p . y . 0.244 0.017 0.015 0.006 0.007 0.0009 0.001 0.0007 g r a m s and C o r r o s i o n 57s-H34 Wt. L o s s 3.9780 3.8198 3. 5184 0. 2848 0.2824 0.2844 0.2074 0.1974 0.2068 0.1161 0.1200 0.1219 0. 1529 0. 1551 0. 1453 0.0334 0.0253 0.0369 0.0421 0.0514 0.0535 0.0204 0.0301 0.0280 R a t e s , m . p.y.
m . p . y . 0.183 0.014 0,010 0.006 0.007 0.002 0.002 0.001-
Wt. L o s s 3.5632 3.6244 3.8650 0. 3200 0. 3348 0.3239 0.2023 0.1956 0.1889 0.1260 0.1205 0.1376 0. 1578 0.1590 0.1573 0.0185 0.0203 0.0187 0.0339 0.0396 0.0398 0.01 10 0.0120 0.0128 - m . p . y . 0.176 0.015 0.009 0.006 0.007 0,001 0.002 0.0006T A B L E VI
A P P E A R A N C E O F ALUMLNTUM-COPPER K I V E T T E D C O U P L E S
E X P O S E D F O R T E N YE.L\RS IN EIGHT CANADIAN A T M O S P H E R E S
7 -
- A l c a n S h e e t 3 s - H I 4 C o ~ ~ e r S h e e t1
i t S k y a r d E a r t h w a r d L a pi
L a p H a l i i a x (4) S e v e r e r o u g h e t c h i n z S e v e r e d e e p r o u g h Rough g e n e r a l S l i g h t l y e t c h i n g a t t a c k & p i t t i n g d i s c o l o u r e d S k v w a r d E t c h e d s l i q h t l y E a r t h w a r dI
E t c h e di
iLLontreal ( 3 ) S h i n y with s c a t t e r e d S o m e e t c h i n g Uneven g e n e r a l S l i g h t l y S l i g h t l y e t c h e d V e r y s l i g h t e t c h
t i n y p i t s a t t a c k d i s c o l o u r e d ! T r a i l ( 8 ) O t t a w a ( 1 )
i
S h i n y b u t s l i ~ h t l y'
S h i n y but s l i g h t d i s c o l o u r e d I1
e t c h i n ? S l i g h t l o s s of l u s t r e/
Y o r k Redoubt ( 5 )/
Shiny but s c a t t e r e d S l i 2 h t s c a t t e r e d! 1 rvith t i n y p i t s
1
p i t s I ! Uneven g e n e r a l a t t a c kI
S a s k a t o o n ( 2 ) S h i n y , m a n y t i n y p i t s Rough g e n e r a l a t t a c k Shiny1
S h i n y but s l i ~ h t 1 e t c h i n g U n a f f e c t e d S h i n y but s l i g h t e t c h i n g E s q u i m a l t ( 7 ) S o r m a n W e l l s ( 6 ) S h i n y but s o m e e t c h i n g S l i g h t l y d i s c o l o u r e dI
H a l i f a x (1) R o u g h g e n e r a l a t t a c k E t c h e d1
E X P O S E D F O R F I V E YEARS IN E I G H T CANADTAii A T M O S P H E R E S Shiny but v e r y s l i g h t e t c h i n g S h i n y , u n a f f e c t e d L R o u g h g e n e r a l a t t a c ki
X l o n t r e a l ( 3 ) E t c h e d , t i n y p i t sI
T i n y p i t s M o t t l e d U n a f f e r t e d V e r y s l i g h t e t c h i n g I U n a f f e c t e d II
E t c h e d l i g h t l y E t c h e d , t i n y p i t s1
T r a i l ( 8 )I
O t t a w a ( 1 ) V e r y s l i g h t e t c h i n gi
i I E t c h e d v e r y s l i g h t l y'
I Shiny S h i n y , u n a f f e c t e d E t c h e d l i g h t l y E x c e l l e n t G e n e r a l a t t a c k S h i n y but s l i g h t e t c h i n 5 Y o r k Redoubt ( 5 ) S a s k a t o o n ( 2 ) E s q u i m a l t ( 7 ) E t c h e d , t i n y p i t s E x c e l l e n t E x c e l l e n t 1 U n a f f e c t e d E t c h e d , t i n y p i t s E x c e l l e n t E x c e l l e n t N o r m a n W e l l s ( 6 ) S l i g h t e t c h i n g U n a f f e c t e d E x c e l l e n t Rough g e n e r a l a t t a c k Rough g e n e r a l a t t a c k S h i n y Rough u n e v e n a t t a c k R o u g h ; e n e r a 1 a t t a c k $ a r e a a t t a c k e d R o u g h g e n e r a l a t t a c k F a i n t s p e c k l e d e t c h E x c e l l e n t E t c h e d v e r y l i g h t V e r y s l i g h t e t c h i n p U n a f f e c t e d U n a f f e c t e d L i z h t e t c h i n g I I U n a f f e c t e d ! i E x c e l l e n t E x c e l l e n t E x c e l l e n t E x c e l l e n t E x c e l l e n t E x c e l l e n t E x c e l l e n t E x c e l l e n t R o u g h e t c h E t c h e d l i g h t l y E t c h e d l i g h t l y E t c h e d l i g h t l y E t c h e d l i g h t l y E t c h e d l i g h t l y E t c h e d l i z h t l y E t c h e d l i g h t l y Rough e t c h E x c e l l e n t E t c h e d l i g h t l y E x c e l l e n t E t c h e d l i g h t l y E x c e l l e n t E t c h e d l i g h t l y E x c e l l e n tTABLE VLI
APPEARANCE OF ALUMINIUM-ZINC RIVETTED COUPLES
EXPOSED FOR TEN YEARS IN EIGHT CANADIAN ATMOSPHERES
1 Site Halifax ( 4 ) Montreal (3) T r a i l (8) Ottawa ( 1 ) York Redoubt (5) Saskatoon ( 2 ) Esquimalt ( 7 ) Norman Wells ( 6 )
EXPOSED FOR FIVE Halifax ( 4 ) Montreal ( 3 ) T r a i l (8) Ottawa (1) York Redoubt ( 5 ) Saskatoon ( 2 ) Esquimalt ( 7 ) Norman Wells (6) Zinc Sheet Skyward B o r d e r etched rough B o r d e r etched lightly Almost unaffected Almost unaffected Almost unaffected Almost unaffected Almost unaffected Unaffected Rough etch Rough e t c h Rough e t c h Rough e t c h Rough e t c h Rough e t c h Rough etch Etched lightly E a r t h w a r d Rough etch Slight e t c h Etched light Liqht e t c h Light e t c h Very light e t c h Etched lightly Unaffected Rough etch Etched lightly Rough e t c h Etched lightly Etched lightly Etched lightly Etched lightly Excellent L a p Very rough e t c h Rough e t c h Etched light Rough e t c h Rough e t c h Light e t c h Etched lightly Etched v e r y lightly Alcan Sheet Skyward Rough g e n e r a l attack Shiny, a l m o s t unaffected Etched, tiny pits Shiny, a l m o s t unaffected Shiny, a l m o s t unaffected Shiny, unaffected Shiny, a l m o s t unaffected Shiny, unaffected YEARS I N EIGHT Rough g e n e r a l attack Etched lightly
Etched, tiny pits Excellent Etched lightly Excellent Excellent Excellent 3s-H14 E a r t h w a r d Rough g e n e r a l a t t a c k Etched, tiny pits Etched, tiny pits Dulled slightly Dulled slightly Shiny, a l m o s t unaffected Shiny, unaffected Shiny, unaffected CANADIAN ATMOSPHERES - L a p Shiny, unaffected Shiny, unaffected Shiny, unaffected Shiny, unaffected Shiny, unaffected Shiny, unaffected Shiny, unaffected Shiny, unaffected Rough g e n e r a l attack
Etched, tiny pits Etched, tiny pits Dulled Etched lightly Mottled Excellent Excellent Shiny Shiny Shiny Shiny Shiny Shiny Shiny Shiny F r i n g e a r e a etched Excellent Excellent Excellent Excellent Excellent Excellent Excellent
T A B L E VLZI
A P P E A R A N C E O F ALUMINIUM-STEEL R I V E T T E D COUPLES
EXPOSED F O R T E N YEARS IN EIGHT CANADIAN ATMOSPHERES
A l c a n S h e e t 3 s - H 1 l S t e e l S h e e t S k y w a r d S m o o t h e t c h e d S m o o t h e t c h e d Rough e t c h e d S m o o t h e t c h e d S m o o t h e t c h e d Unevenly e t c h e d S m o o t h e t c h e d S m o o t h e t c h e d E a r t h w a r d V e r y r o u g h V e r y rough V e r y r o u g h V e r y r o u g h V e r y r o u g h Rough V e r y r o u g h Slight a t t a c k L a p V e r y rough, p e r f o r a t e d V e r y rough V e r y rough V e r y rough V e r y rough V e r y r o u g h Rough Slight a t t a c k EXPOSED FOR F I V E YEARS IN EIGHT CANADIAN ATMOSPHERES
S i t e Halifax ( 4 ) M o n t r e a l ( 3 ) T r a i l (8) Ottawa ( 1 ) Y o r k Redoubt ( 5 ) S a s k a t o o n ( 2 ) E s q u i m a l t ( 7 ) N o r m a n W e l l s ( 6 ) Halifax ( 4 ) M o n t r e a l (3) T r a i l (8) Ottawa ( 1 ) York Redoubt ( 5 ) S a s k a t o o n ( 2 ) E s q u i m a l t (7) N o r m a n W e l l s ( 6 ) E a r t h w a r d Rough w e a t h e r e d Many tiny p i t s S c a t t e r e d etching Shiny, a l m o s t unaffected Shiny, a l m o s t unaffected Shiny, unaffected Shiny, a l m o s t u n a f f e c t e d Shiny, unaffected S k y w a r d Rough F e w tiny p i t s Slightly e t c h e d Shiny, a l m o s t unaffected Shiny, a l m o s t unaffected Shiny, unaffected Shiny, unaffected Shiny, unaffected L a p S e v e r e a t t a c k G e n e r a l a t t a c k S o m e d e e p p i t s
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with g e n e r a l a t t a c k E t c h e d , $ r o u g h Slight e t c h i n g G e n e r a l a t t a c k Slight etching - Rough g e n e r a l a t t a c k Rough g e n e r a l a t t a c k Shiny, few p i t s a r e a a t t a c k e d Rough g e n e r a l a t t a c k L i g h t e t c h in s p o t s Rough g e n e r a l a t t a c k F a i n t s p e c k l e d e t c h Rough g e n e r a l a t t a c k E t c h e d , tiny p i t s E t c h e d lightly E x c e l l e n t Etched, t i n y p i t s E x c e l l e n t Mottled E x c e l l e n t Rough s e v e r e Rough s e v e r e Rough s e v e r e Rough s e v e r e Rough s e v e r e Rough g e n e r a l Rough g e n e r a l Mild Rough g e n e r a l a t t a c k E t c h e d , tiny p i t s S p e c k l e d , tiny p i t s Dulled E t c h e d , tiny p i t s Mottled Mottled E x c e l l e n t Smooth e t c h e d Smooth e t c h e d Smooth e t c h e d S m o o t h e t c h e d Smooth e t c h e d Smooth e t c h e d S m o o t h e t c h e d Smooth e t c h e d Rough s e v e r e Rough g e n e r a l Rough s e v e r e Rough g e n e r a l Rough g e n e r a l Mild Rough g e n e r a l MildI
T A B L E IX
MAXIMUM D E P T H S O F CORROSION ( M E A S U R E D WITH P I T D E P T H M I C R O M E T E R 1
W N I U MAND DISSIMILAR M E T A L S H E E T S E X P O S E D A S R I V E T T E D C O U P L E S F O R T E N Y E A R S IN E I G H T CANADIAN A T M O S P H E R E S I S i t e H a l i f a x ( 4 ) P a n e l N o . 1 2 1 m i l s L a p 20 1 9 9 1 1 1 0 9 1 - 3 s - H 1 4
I
:
C o p p e r D e p t h , m i l s S k y 7 6 4. 5 6 4 . 5 2 3 - M o n t r e a l ( 3 ) T r a i l ( 8 ) O t t a w a ( 1 ) Y o r k R e d o u b t ( 5 ) S a s k a t o o n ( 2 ) E s q u i m a l t ( 7 ) N o r m a n W e l l s ( 6 ) S k y D e p t h , E a r t h 6 10 6 5 2 . 5 2 1 - 2 2 . 5 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2-
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-1 2 1 2 1 2 1 2 1 2 1 2 1 + 2 2 1 2 1 2 1 2 1 2 1 2 - 3 3 S k y 5 7 2 2 E a r t h 4 5 1 . 5 3:,
1 0 . 5 0 . 5 1---
1 . 5 5. 5 S t e e l D e p t h , m i l s 6 81
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L a p Z i n c-
D e p t h , E a r t h 3 . 5 2 . 5 2 2 S k y 1 3 1 3 1 3 1 6 1 5 1 6 1 9 3 6 - 5 4 4 8 m i l s L a p 1 . 5 2 . 5 4 2 0 . 5 0 . 5 0 . 5 2 2 0 . 5I ! :
6 7 . 5 8 9 2. 5 2 l II:.,
- - - 1 - E a r t h ' 1 4 1 61 :
- - 3. 5 1 MISSING L a p 1 01
p e r f o r a t i o n s:
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WEIGHT LOSSES AND CORROSION R A T E S O F ALUMINIUM S H E E T E X P O S E D AS B I M E T A L L I C C O U P L E S F O R T E N YEARS IN EIGHT CANADIAN A T M O S P H E R E S
