Corrosion of Metals in Sea Water - Advances in Chemistry (ACS...
1 downloads
229 Views
2MB Size
Corrosion of Metals in Sea Water FREDERICK W. FINK
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on September 5, 2015 | http://pubs.acs.org Publication Date: January 1, 1960 | doi: 10.1021/ba-1960-0027.ch005
Battelle Memorial Institute, 505 King Ave., Columbus 1, Ohio
The Office of Saline Water is directing a large number of investigations into the feasibility of new processes for producing fresh water starting with sea or brackish water as a source. It is desired that these plants last for 20 years or more. This paper points up ways in which the economic waste resulting from corrosion in saline water plants can be avoided. The article is based on a review of the corrosion literature and on consultations with marine experts in the field. Of the many materials for distillation plants, steel is the most important. It can be used to handle sea water below 250° F., if proper steps are taken such as the removal of all air (oxygen) from solution. For severe service and better performance metals like titanium, Hastelloy C, Monel, cupro-nickels, aluminum, aluminum brass, or Admiralty brass are used.
T h e ocean, w h i c h covers more t h a n 7 0 % of the earth's surface, is considered b y m a n y t o b e a c h a l l e n g i n g f r o n t i e r . S u c h g o v e r n m e n t agencies as t h e N a v y , t h e D e p a r t m e n t of t h e I n t e r i o r , t h e B u r e a u o f M i n e s , t h e M a r i t i m e C o m m i s s i o n , t h e D e p a r t m e n t o f A g r i c u l t u r e , etc., h a v e r e c o g n i z e d t h e i m p o r t a n c e of t h e sea f r o m t h e i r o w n s p e c i a l v i e w points for m a n y years. G o v e r n m e n t activities, such as the demonstration plants of the Office o f S a l i n e W a t e r t o c o n v e r t sea w a t e r t o f r e s h w a t e r , t h e 7 m i l e d e e p - s e a - d i v i n g " B a t h y s c a p h e " under N a v y sponsorship, a n d plans f o r studying hydrofoil ships, p r o v i d e e x a m p l e s o f n e w e r a c t i v i t i e s c o n n e c t e d w i t h t h e sea. T h e l a t e s t n u c l e a r - p o w e r e d s u b m a r i n e s c a n v i s i t m o s t p a r t s o f t h e oceans, e v e n those u n d e r t h e ice. P r i v a t e i n t e r e s t s are engaged i n i n t e n s i v e studies r e l a t e d t o t h e ocean. One c a n m e n t i o n t h e o i l - a n d s u l f u r - m i n i n g i n d u s t r i e s w i t h t h e i r T e x a s t o w e r s , some of w h i c h a r e f a r o u t t o sea. N e w t y p e s of t e l e p h o n e a n d p o w e r cables a n d p i p e l i n e s are b e i n g p l a c e d o n t h e sea b o t t o m . S h o r e - b a s e d o p e r a t i o n s b y c h e m i c a l c o m p a n i e s a r e m a k i n g use o f sea w a t e r t o o b t a i n m a g n e s i u m , b r o m i n e , a n d sea s a l t . P h a r m a c e u t i c a l s a r e being extracted from sea-growing vegetation a n d f r o m marine animals. M a n y shoreb a s e d i n s t a l l a t i o n s use sea w a t e r f o r c o o l i n g a n d , i n some s p e c i a l cases, f o r s a n i t a t i o n o r for fire-protection services. T h i s i n c r e a s e d a c t i v i t y o n t h e sea, i n t h e sea, a n d u n d e r t h e sea focuses a t t e n t i o n o n t h e n e e d f o r k n o w l e d g e o f t h e b e h a v i o r o f m e t a l s i n these e n v i r o n m e n t s . I t has b e e n k n o w n f o r y e a r s t h a t sea w a t e r w i l l a t t a c k m o s t o f t h e c o m m o n m e t a l s . I n some service c o n d i t i o n s , c e r t a i n l i v i n g o r g a n i s m s i n t h e sea cause m a r i n e f o u l i n g o n t h e e x p o s e d m e t a l surfaces l e a d i n g t o c o r r o s i o n o r i n t e r f e r e n c e w i t h f u n c t i o n i n g of t h e e q u i p m e n t . 27
In SALINE WATER CONVERSION; Advances in Chemistry; American Chemical Society: Washington, DC, 1960.
28
ADVANCES IN CHEMISTRY SERIES
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on September 5, 2015 | http://pubs.acs.org Publication Date: January 1, 1960 | doi: 10.1021/ba-1960-0027.ch005
Corrosîvîty of Sea Water A q u e o u s c o r r o s i o n i s e l e c t r o c h e m i c a l i n n a t u r e a n d i n v o l v e s t h e passage of e l e c t r i c c u r r e n t s . T h e c u r r e n t enters t h e s o l u t i o n a t l o c a l anodes a n d leaves t h e s o l u t i o n a t c a t h o d i c areas o n t h e m e t a l . I n t h e case o f steel, f e r r o u s i o n s e n t e r t h e s o l u t i o n a t t h e anode a n d hydrogen is deposited a t the cathode. V e r y p u r e w a t e r , because o f i t s h i g h r e s i s t i v i t y , m a k e s d i f f i c u l t t h e passage o f c o r r o s i o n c u r r e n t s t h r o u g h t h e s o l u t i o n f r o m a n o d i c t o c a t h o d i c areas. F o r a m b i e n t t e m p e r a t u r e s , h i g h l y p u r i f i e d w a t e r , free f r o m d i s s o l v e d o x y g e n , i s n o t c o r r o s i v e t o m e t a l s s u c h as steel. T h e a d d i t i o n o f s o d i u m c h l o r i d e t o w a t e r f o r m s a s o l u t i o n w h i c h tends t o b e c o r r o s i v e t o steel a n d o t h e r c o m m o n m e t a l s . H o w e v e r , i f t h e s o l u t i o n i s c o m p l e t e l y a i r free, i t s c o r r o s i v i t y m a y n o t b e m u c h g r e a t e r t h a n t h a t o f p u r e w a t e r . S e a w a t e r c o n t a i n s , i n a d d i t i o n : s u l f a t e , b i c a r b o n a t e , b r o m i d e , a n d fluoride i o n s . L a b o r a t o r y experience i n d i c a t e s t h a t , a t t h e same p H , s u l f a t e s o l u t i o n s t e n d t o b e less c o r r o s i v e t h a n s i m i l a r c h l o r i d e s o l u t i o n s . T h e presence o f b i c a r b o n a t e ions i n w a t e r , f r o m d i s s o l v e d C 0 , p r o m o t e s some c o r r o s i o n a t t a c k o n m a n y m e t a l s . I t also s h o u l d be m e n t i o n e d t h a t t h e p H o f s e a w a t e r n o r m a l l y ranges f o r m 7.50 t o 8.25, i n d i c a t i n g t h a t some free h y d r o x y l i o n s are a l w a y s p r e s e n t . B r o m i d e s a n d fluorides a r e v e r y c o r r o s i v e ; b u t , b e i n g p r e s e n t o n l y i n s m a l l a m o u n t s , t h e i r effects i n sea w a t e r p r o b a b l y a r e m a s k e d b y t h e v e r y h i g h c h l o r i d e c o n t e n t . I n e x p e r i m e n t a l w o r k , a c o n t i n u o u s s u p p l y o f f r e s h , c l e a n sea w a t e r i s essent i a l i f t h e effects o f s u c h m i n o r c o n s t i t u e n t s o n t h e c o r r o s i o n o f a m e t a l a r e t o b e evaluated. O n e m i g h t e x p e c t sea w a t e r t o b e c o r r o s i v e because t h e s o l u t i o n is a g o o d e l e c t r o l y t e , i t c o n t a i n s ions k n o w n f r o m experience t o p r o m o t e t h e a t t a c k o n c o m m o n m e t a l s , i t contains dissolved oxygen w h i c h promotes t h e attack—e.g., b y reacting w i t h nascent hydrogen formed a t t h e c a t h o d e — a n d i t contains a m u l t i t u d e of forms of organic life, some o f w h i c h affect m e t a l c o r r o s i o n . N a t u r a l processes, o p e r a t i n g b o t h a t t h e s u r f a c e a n d a t g r e a t d e p t h s , r e s u l t i n m o s t of t h e ocean b e i n g s t i r r e d c o n t i n u o u s l y . I t i s f o u n d t h a t t h e r e l a t i v e p r o p o r t i o n s o f d i s s o l v e d salts a r e v i r t u a l l y t h e same e v e r y w h e r e , a l t h o u g h t h e t o t a l salt c o n t e n t (salinity) m a y show appreciable variations w i t h geography. T h e more i m p o r t a n t ions f o u n d i n a sample of N o r t h Pacific Ocean surface water, as r e p o r t e d b y L y m a n a n d A b e l ( 5 ) , a r e t a b u l a t e d b e l o w . 2
Per Cent
Cations Na+ Mg+ Ca K+ Sr+ •
+ 2
2
2
Anions ciSO4-
1.056 0.127 0.040 0.038 0.001 S u m 1.262
H3BO3, undissociated
2
HCO3-
Br" F-
T o t a l 3.449
Per Cent 1.898 0.265 0.014 0.0065 0.0001 S u m 2.184 0.003
N a t u r a l vs. S y n t h e t i c S e a W a t e r . I t i s n o t a l w a y s r e a l i z e d t h a t n a t u r a l sea w a t e r i s a c o m p l e t e l y different m e d i u m f r o m s y n t h e t i c sea w a t e r f r o m t h e c o r r o s i o n s t a n d p o i n t . A p r i m a r y f a c t o r i s t h e presence o f b i o l o g i c a l effects i n n a t u r a l sea w a t e r t h a t are n o t p r e s e n t i n t h e s y n t h e t i c m i x t u r e . O n e effect i s t h a t b i o - f o u l i n g o f t h e m e t a l s u r f a c e o f t e n p r o m o t e s l o c a l i z e d a t t a c k . W h e n a b a r n a c l e o r m u s s e l a t t a c h e s i t s e l f t o a p l a t e o f stainless steel i n sea w a t e r , a differential aeration corrosion cell is formed. Intense local p i t t i n g results w h i c h m a y l e a d t o c o m p l e t e p e r f o r a t i o n i n a r e l a t i v e l y s h o r t t i m e . I n o n e case a 0 . 7 5 - i n c h t h i c k stainless steel p l a t e w a s p e r f o r a t e d b e n e a t h a b a r n a c l e base a f t e r 9 m o n t h s o f i m m e r s i o n in sea w a t e r .
In SALINE WATER CONVERSION; Advances in Chemistry; American Chemical Society: Washington, DC, 1960.
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on September 5, 2015 | http://pubs.acs.org Publication Date: January 1, 1960 | doi: 10.1021/ba-1960-0027.ch005
FINK—CORROSION OF METALS IN SEA WATER
29
A v a r i e t y o f a n i m a l s a n d p l a n t s , as w e l l as colonies of m i c r o o r g a n i s m s , m a y d e p o s i t f r o m n a t u r a l sea w a t e r o n t o t h e m e t a l s u r f a c e . T h e l i f e processes a n d d e c o m position products m a y contribute directly to attack o n the metal. F o u l i n g m a y o b s t r u c t flow i n h e a t e x c h a n g e r s a n d p i p e s , l e a d i n g t o s u c h c o r r o s i v e effects a s a r e c a u s e d b y overheating or i m p i n g e m e n t at local high-water velocities. S o m e o r g a n i s m s e n t e r a m a r i n e p i p i n g s y s t e m i n t h e i r l a r v a l stages, t h e n a n c h o r t h e m s e l v e s t o sites s u c h as i n t e r i o r t u b e w a l l s . I f these l a r v a e a r e a l l o w e d t o g r o w , t h e l o c a l t u r b u l e n c e m a y r e s u l t i n severe c o r r o s i o n . T h e o r g a n i s m s m a y b e k i l l e d b y c h l o r i n a t i o n , b y flooding t e m p o r a r i l y w i t h f r e s h w a t e r , b y h o t s e a w a t e r , o r b y t o x i c m a t e r i a l s s u c h as s o d i u m p e n t a c h l o r o p h e n o l . E v e n when t h e organisms are killed, t h e i r d e c o m p o s i n g b o d i e s m a y s t i l l c l o g t h e s e a - w a t e r s y s t e m a n d cause c o r r o s i o n . T w o facts concerning t h e corrosion behavior of metals i n sea w a t e r s t a n d o u t : A l t h o u g h there is v a r i a t i o n i n temperature, salinity, a n d content of l i v i n g o r g a n i s m s , t h e rates o f a t t a c k — e s p e c i a l l y f o r s t e e l — a r e o f t h e same o r d e r o f m a g n i t u d e a t m a n y different l o c a t i o n s t h r o u g h o u t t h e w o r l d . T h e r e l a t i v e o r d e r o f resistance o f m e t a l s as d e t e r m i n e d b y t h e i r c o r r o s i o n rates i n n a t u r a l sea w a t e r i s n o t r e a d i l y s i m u l a t e d w i t h s y n t h e t i c s e a - w a t e r p r e p a r a t i o n s i n the laboratory. F a c t o r s i n S a l t W a t e r C o r r o s i o n . Because of expediency, a n d i n spite of t h e s i t u a t i o n discussed a b o v e , m u c h w o r k h a s b e e n d o n e i n t h e l a b o r a t o r y w i t h saline s o l u t i o n s m a d e u p t o s i m u l a t e sea w a t e r . H a c h e (3) has c a r r i e d o u t s o m e v e r y i n t e r e s t i n g e x p e r i m e n t s c o n c e r n i n g t h e c o r r o s i o n o f steel i n s o d i u m c h l o r i d e s o l u t i o n s . I n F i g u r e 1, H a c h e s h o w s t h e effect of t e m p e r a t u r e o n t h e c o r r o s i o n o f i r o n b y a i r saturated a n d deaerated solutions containing 30 grams per liter of pure N a C l i n d o u b l y d i s t i l l e d w a t e r . T h e effect of o x y g e n i n i n c r e a s i n g c o r r o s i o n u p t o a b o u t 5 0 ° C . ( 1 2 2 ° F . ) i s seen. A b o v e t h i s t e m p e r a t u r e , t h e s o l u b i l i t y o f o x y g e n i s v e r y l i m i t e d . I t is f o r t h i s r e a s o n t h a t t h e c u r v e s b e c o m e t h e s a m e . I n t h e r a n g e f r o m 1 0 ° t o 5 0 ° C . (50° t o 1 2 2 ° F . ) , t h e corrosion increases at t h e rate o f a b o u t 5 % p e r ° C . S u c h a t e m perature dependence h a d been reported earlier b y P a l m a e r ( 7 ) .
Dissolved Iron, mg.
Figure I. Effect of temperature and aeration on the corrosion of iron in 3% sodium chloride solution F i g u r e 2 i l l u s t r a t e s c o r r o s i o n b e h a v i o r a n d o x y g e n s o l u b i l i t y as a f u n c t i o n o f t h e s a l i n i t y of t h e s o l u t i o n a t a fixed t e m p e r a t u r e . I t i s t o b e n o t e d t h a t a s m a l l v a r i a t i o n i n s a l i n i t y i n t h e n e i g h b o r h o o d o f t h e n o r m a l 3 . 5 % c o n t e n t o f sea w a t e r h a s n o effect o n o x y g e n s o l u b i l i t y a n d l i t t l e effect o n c o r r o s i o n r a t e .
In SALINE WATER CONVERSION; Advances in Chemistry; American Chemical Society: Washington, DC, 1960.
ADVANCES IN CHEMISTRY SERIES
30
ι -
s
d
c issolv
i
:
\
gen Oxy
I
Λ)
I
(
I
ν _
I
Ν
Saturation
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on September 5, 2015 | http://pubs.acs.org Publication Date: January 1, 1960 | doi: 10.1021/ba-1960-0027.ch005
F a c t o r s i n S e a - W a t e r C o r r o s i o n . T h e effects o f t e m p e r a t u r e a n d s a l i n i t y i n sea w a t e r a r e b e l i e v e d t o b e s i m i l a r t o those f o u n d i n s a l t w a t e r , discussed a b o v e . G o o d q u a n t i t a t i v e i n f o r m a t i o n is n o t y e t r e a d i l y a v a i l a b l e . H a c h e (S) c o n c l u d e d t h a t l i g h t h a s a n i n h i b i t i n g effect o n c o r r o s i o n b y sea w a t e r a n d t h a t t h e r e s u l t s o f c o r r o s i o n tests c o n d u c t e d i n t o t a l d a r k n e s s were less p r o n e t o scatter.
; \
\
\
\
\ ~
\ \
i
\ ν
ϊ 0.02
005
0.1
0.25
0.50 Sodium
Figure 2.
I
2
5
10
20 30
5060
100
200
360
Chloride, g. per I.
Variation of corrosion as a function of salinity at 24° C.
M a n y o t h e r p a r a m e t e r s t e n d t o influence t h e c o r r o s i o n o f m e t a l s i m m e r s e d i n sea w a t e r . W h e n t w o m e t a l s o f different p o t e n t i a l s a r e g a l v a n i c a l l y c o u p l e d , t h e a c c e l e r a t i o n of t h e a t t a c k o n t h e less n o b l e m e t a l o f t h e t w o i s o b s e r v e d f r e q u e n t l y . A s m a l l a r e a o f a n a n o d i c m e t a l c o u p l e d t o a l a r g e a r e a o f a second m e t a l t h a t i s c a t h o d i c can be p a r t i c u l a r l y dangerous. A useful guide t o help predict unfavorable c o m b i n a t i o n s i s t h e g a l v a n i c series of m e t a l s i n sea w a t e r (9). T h e reverse s i t u a t i o n — n a m e l y , a small cathode coupled t o a n anode that is large i n area—often proves satisfactory i n service. S o m e m e t a l s d e p e n d o n f o r m a t i o n o f a p r o t e c t i v e film f o r c o r r o s i o n resistance i n sea w a t e r . A f r e s h s u p p l y o f o x y g e n b r o u g h t t o t h e s u r f a c e o f t h e m e t a l t e n d s t o p r o m o t e t h e c o r r o s i o n r e a c t i o n i n some cases, a n d i n o t h e r s i t h e l p s f o r m d e s i r e d p r o t e c t i v e films. I f a c r i t i c a l v e l o c i t y o f flowing sea w a t e r i s exceeded, t h e film m a y b e e r o d e d a w a y . T h e v e l o c i t y f o r u s e f u l c o r r o s i o n resistance i s l o w f o r c o p p e r , h i g h e r f o r a l u m i n u m , c u p r o - n i c k e l s , a n d a l u m i n u m b r o n z e s , a n d h i g h e s t f o r stainless steels, Hastelloy C, and titanium. P r o t e c t i v e films o n m e t a l s also c a n b e d e s t r o y e d a n d c o r r o s i o n a c c e l e r a t e d b y t h e i m p i n g e m e n t o f a h i g h - v e l o c i t y s t r e a m o f sea w a t e r o n t o t h e m e t a l l i c s u r f a c e . T h e i n l e t e n d s o f condenser t u b e s , a r e f r e q u e n t l y a t t a c k e d ( F i g u r e 3,a). J e t tests h a v e been devised f o r r a n k i n g t h e susceptibility of metals to such impingement attack. A corrosion cell is f o r m e d between t h e bare surface d i r e c t l y under t h e j e t (anode) a n d the a d j a c e n t filmed s u r f a c e ( c a t h o d e ) . T h e s e j e t tests g i v e m o r e d e p e n d a b l e i n f o r m a t i o n , i f n a t u r a l sea w a t e r i s c o n t i n u o u s l y s u p p l i e d t o t h e e q u i p m e n t . U s u a l l y , t h e c o r r o s i o n - f a t i g u e l i m i t o f a m e t a l i n sea w a t e r i s l o w e r t h a n i n f r e s h w a t e r . R e p e a t e d flexing a l l o w s t h e c o r r o s i o n t o p r o c e e d a t t h e b r e a k s i n t h e p r o t e c t i v e film w h e r e a c t i v e m e t a l i s e x p o s e d . C a v i t a t i o n c o r r o s i o n i s c a u s e d b y r e p e a t e d p o u n d i n g r e s u l t i n g f r o m r a p i d collapse of v a p o r b u b b l e s . O n a m e t a l s u r f a c e w h e r e t h e r e i s a v i o l e n t flow o f w a t e r , s u c h a s t h a t o f a s h i p ' s p r o p e l l e r , t h e p r e s s u r e a t some a r e a m a y b e r e d u c e d t o w h e r e l o c a l i z e d boiling forms bubbles of vapor. A t a n o t h e r s i t e , these b u b b l e s s u d d e n l y c o l l a p s e .
In SALINE WATER CONVERSION; Advances in Chemistry; American Chemical Society: Washington, DC, 1960.
FINK—CORROSION OF METALS IN SEA WATER
31
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on September 5, 2015 | http://pubs.acs.org Publication Date: January 1, 1960 | doi: 10.1021/ba-1960-0027.ch005
T h e r e s u l t a n t h a m m e r i n g m a y , i n t i m e , cause t h e s u r f a c e l a y e r t o f a i l a n d pieces o f m e t a l t o f l a k e off. T h e a c t i v e m e t a l sites, t h u s exposed, m a y i n t u r n b e r a p i d l y a t t a c k e d b y sea w a t e r . I t h a s b e e n f o u n d d i f f i c u l t t o d e v e l o p a l a b o r a t o r y test t h a t w i l l a c c u r a t e l y s i m u l a t e c a v i t a t i o n a t t a c k as i t o c c u r s i n a c t u a l m a r i n e s e r v i c e .
Crevice corrosion
Figure 3.
Corrosion in sea water
σ. Inlet impingement attack due to excessive turbulence b. Concentration cells T h e i m p o r t a n c e of bio-fouling t o corrosion has already been mentioned. Marine f o u l i n g i s l i k e l y t o o c c u r i n a l l t h e oceans f r o m t h e A r c t i c t o t h e T r o p i c s , e s p e c i a l l y d u r i n g t h e breeding period. I n n o r t h e r n waters, fouling occurs o n l y d u r i n g t h e s u m m e r , w h e r e a s i n t h e T r o p i c s i t i s p r a c t i c a l l y c o n t i n u o u s . C o p p e r a n d some of i t s a l l o y s , high i n copper, n o r m a l l y are n o t susceptible. H o w e v e r , a n y treatment t h a t prevents t h e t o x i c c o p p e r ions f r o m f o r m i n g m a y r e s u l t i n a t e n d e n c y f o r c o p p e r t o f o u l . C o r r o s i v e a t t a c k o n some m e t a l s a c t u a l l y m a y b e s t i f l e d b y f o u l i n g . F o r m a n y m e t a l s , l o c a l i z e d a t t a c k c a n b e m o r e serious u n d e r f o u l e d areas ( F i g u r e 3 , 6 ) . A t v e l o c i t i e s of 2 t o 3 feet p e r second o r m o r e , m e t a l s u s u a l l y a r e n o t a p t t o f o u l . O n c e t h e o r g a n i s m s b e c o m e a t t a c h e d , as d u r i n g a s h u t - d o w n o r o f f - p e r i o d o f a p l a n t , e x t r e m e l y h i g h v e l o c i t i e s m a y be needed t o dislodge t h e m at t h e s t a r t - u p . D i f f e r e n t i a l a e r a t i o n c a n p l a y a n i m p o r t a n t role i n p r o d u c i n g a c c e l e r a t e d a t t a c k o n m e t a l s i n s e a w a t e r — f o r e x a m p l e , a t c r e v i c e s . T h e s e crevices m a y b e f o r m e d b y l o o s e l y a t t a c h e d m a r i n e o r g a n i s m s , b y d e b r i s , o r b y c l o s e - f i t t i n g surfaces t o w h i c h s e a w a t e r h a s r e s t r i c t e d access ( F i g u r e 3 , 6 ) . T h e c o r r o s i o n b e h a v i o r tends t o f o l l o w m u c h t h e same p a t t e r n i n c l e a n sea w a t e r t h e w o r l d o v e r . I f t h e r e i s p o l l u t i o n , i t m a y cause a n u n b a l a n c e o f t h e p H , c h a n g e t h e m a r i n e o r g a n i s m c o n c e n t r a t i o n , decrease t h e d i s s o l v e d o x y g e n , o r a l t e r t h e i o n i c b a l a n c e of sea w a t e r . P o l l u t i o n n o r m a l l y r e s u l t s i n saline w a t e r s ' b e c o m i n g c o n s i d e r a b l y m o r e aggressive t o o n e o r m o r e m e t a l s . Specific tests m u s t b e m a d e t o d e t e r m i n e t h e a p p l i c a b i l i t y of a m e t a l i n each t y p e of p o l l u t e d water. Sulfides, w h i c h are often found m s u c h w a t e r s , t e n d t o p r o m o t e c o r r o s i o n of b o t h f e r r o u s a n d n o n f e r r o u s m e t a l s .
In SALINE WATER CONVERSION; Advances in Chemistry; American Chemical Society: Washington, DC, 1960.
32
ADVANCES IN CHEMISTRY SERIES
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on September 5, 2015 | http://pubs.acs.org Publication Date: January 1, 1960 | doi: 10.1021/ba-1960-0027.ch005
Scale F o r m a t i o n b y S e a W a t e r . A s s e a w a t e r i s h e a t e d ( j i ) , i t s s c a l e - f o r m i n g constituents t e n d t o become supersaturated. Scale crystals w i l l be deposited a t t h e p o i n t o f highest t e m p e r a t u r e , w h i c h m a y b e t h e m e t a l s u r f a c e t h r o u g h w h i c h heat i s being introduced. T h e bicarbonate i o n is p a r t l y transformed t o carbonate i o n a n d t o c a r b o n d i o x i d e . T h e c a r b o n a t e i o n reacts w i t h c a l c i u m , w h i c h p r e c i p i t a t e s as c a l c i u m c a r b o n a t e . A s t h e sea w a t e r i s h e a t e d s t i l l f u r t h e r , t h e r e m a i n i n g c a r b o n a t e i o n i n t h e w a t e r decomposes t o free c a r b o n d i o x i d e a n d h y d r o x y l i o n s . T h e l a t t e r c o m b i n e w i t h m a g n e s i u m w h i c h p r e c i p i t a t e s as m a g n e s i u m h y d r o x i d e . B o t h o f these s c a l e - f o r m i n g r e a c t i o n s c a n b e i n h i b i t e d b y s l i g h t l y a c i d i f y i n g the i n c o m i n g sea w a t e r . A s t h e sea w a t e r i s n e a t e d s t i l l h i g h e r , a p o i n t i s r e a c h e d a t w h i c h c a l c i u m s u l f a t e w i l l p r e c i p i t a t e . T h i s r e a c t i o n i s m u c h less r e a d i l y p r e v e n t e d t h a n t h e first t w o , a n d i t is r e p o r t e d t o o c c u r o n l y a b o v e 325° F . i n sea w a t e r h e a t e d u n d e r p r e s s u r e . T h u s , t h e r e a r e t h r e e m a j o r scale c o m p o n e n t s i n sea w a t e r : calcium carbonate, magnesium hydroxide, a n d calcium sulfate. F r o m t h e s t a n d p o i n t o f c o r r o s i o n p r o t e c t i o n , a s l i g h t a m o u n t o f m i n e r a l scale f o r m a t i o n — i f the thickness can be controlled—is desirable. T h i s helps t o e x p l a i n w h y , i n some cases, sea w a t e r i s f o u n d t o b e less c o r r o s i v e t h a n a b r i n e of s o d i u m c h l o r i d e w i t h t h e same s a l i n i t y . H o w e v e r , i n a p p l i c a t i o n s w h e r e heat is b e i n g t r a n s f e r r e d across the m e t a l w a l l , t h e presence of scale m a r k e d l y affects t h e efficiency. I n distillation units, a m e t h o d of corrosion control based o n i n t e n t i o n a l mineral-scale f o r m a t i o n w o u l d thus lead t o greater fuel consumption. T h e s e scales also c a n b e p r o d u c e d e l e c t r o l y t i c a l l y b y a p p l y i n g c a t h o d i c c u r r e n t t o t h e m e t a l s u r f a c e i m m e r s e d i n sea w a t e r . A s a r e s u l t o f t h e h y d r o x y l ions f o r m e d a t t h e c a t h o d e , t h e film o f sea w a t e r a t t h e m e t a l s u r f a c e b e c o m e s h i g h l y a l k a l i n e a n d scale is p r e c i p i t a t e d .
Metals Used în Sea Water F e r r o u s - B a s e M e t a l s . S T E E L . S t e e l finds w i d e use i n sea w a t e r , e s p e c i a l l y as a s t r u c t u r a l m a t e r i a l s u c h as f o r s h i p s , off-shore d r i l l i n g t o w e r s , p i l i n g f o r p i e r s a n d d o c k s , a n d sea w a l l s . I t i s also u s e d as p i p i n g t o h a n d l e sea w a t e r . C o m p a r e d t o o t h e r m e t a l s , steel i s one o f t h e least e x p e n s i v e m a t e r i a l s of c o n s t r u c t i o n . Steel is the basic m a t e r i a l of construction for m a n y sea-water plants. E v e n though i t m a y c o r r o d e i n some sections o f a p l a n t , s u c h as a d i s t i l l a t i o n u n i t , i t s l o w i n i t i a l cost m a y r e s u l t i n l o w e r o v e r - a l l costs i f g o o d design a n d g o o d c o r r o s i o n - c o n t r o l p r a c t i c e s are f o l l o w e d . T h e r a t e o f a t t a c k f o r i m m e r s e d c o n d i t i o n s i s f a i r l y u n i f o r m i n u n p o l l u t e d sea w a t e r a n d averages a b o u t 5 m i l s p e r y e a r . G e n e r a l a t t a c k , w h e n i t o c c u r s , h a s b e e n observed t o be a linear f u n c t i o n of t i m e — t h a t is, i t continues a t a f a i r l y u n i f o r m rate, despite a n a c c u m u l a t i o n of corrosion products o r m a r i n e g r o w t h . O f t e n , h o w e v e r , steel i s s u b j e c t t o p i t t i n g a t t a c k b y sea w a t e r . T h e deepest a t t a c k o n steel i s r e p o r t e d t o b e a b o u t 10 t o 15 m i l s p e r y e a r . T h e presence o f m i l l scale on the steel—especially w h e n i t covers a large p o r t i o n of the exposed area—significantly increases t h e r a t e o f p i t t i n g , a n d p e n e t r a t i o n s o f a b o u t 2 0 m i l s p e r y e a r c a n b e e x p e c t e d . T h i s i s a r e s u l t o f t h e m i l l scale s e r v i n g as l a r g e c a t h o d e s t o t h e s m a l l , b a r e a n o d i c areas. P i t t i n g a t t a c k o f t e n t a p e r s off w i t h c o n t i n u e d e x p o s u r e . A recent p a p e r b y F o r g e s o n , S o u t h w e l l , a n d A l e x a n d e r (2) gives t h e r e s u l t s o f a n 8 - y e a r exposure o f s t r u c t u r a l steels t o t r o p i c a l sea w a t e r . I t w a s f o u n d t h a t s m a l l a d d i t i o n s o f c o p p e r d i d n o t a l t e r t h e c o r r o s i o n o f m i l d steel. Steels c o n t a i n i n g 2 a n d 5% of n i c k e l were d e f i n i t e l y i n f e r i o r t o m i l d steel o n t h e basis o f b o t h g e n e r a l a n d l o c a l a t t a c k . Steels c o n t a i n i n g 3 a n d 5% o f c h r o m i u m w e r e m o r e r e s i s t a n t t h a n m i l d steel f o r t h e first 3 y e a r s , b u t t h e n c o r r o d e d s i g n i f i c a n t l y m o r e t h a n m i l d steel d u r i n g t h e r e m a i n i n g 5 y e a r s . T h e a m o u n t o f p i t t i n g also w a s g r e a t e r f o r c h r o m e steels d u r i n g t h e l a t t e r p e r i o d . F o r c o m p l e t e i m m e r s i o n , m i l d steel i s p r e f e r r e d . I n o t h e r e x p e r i m e n t s c o n d u c t e d i n S a n D i e g o H a r b o r , C a l i f o r n i a , t h e r a t e o f p i t t i n g f o r m i l d steel w a s f o u n d t o b e as h i g h as 60 m i l s p e r y e a r (8).
In SALINE WATER CONVERSION; Advances in Chemistry; American Chemical Society: Washington, DC, 1960.
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on September 5, 2015 | http://pubs.acs.org Publication Date: January 1, 1960 | doi: 10.1021/ba-1960-0027.ch005
FINK—CORROSION OF METALS IN SEA WATER
33
W R O U G H T I R O N . W r o u g h t i r o n has f o u n d c o n s i d e r a b l e a p p l i c a t i o n i n m a r i n e - b a s e d s t r u c t u r e s a n d i n p i p i n g . W h i l e w r o u g h t i r o n , a c c o r d i n g t o s o m e sources, a p p e a r s t o be m o r e r e s i s t a n t t h a n m i l d steel t o g e n e r a l a n d l o c a l i z e d c o r r o s i o n b y sea w a t e r , t h e r e is n o g e n e r a l a c c e p t a n c e o f t h i s m a t e r i a l b y o p e r a t o r s o f m a r i n e p l a n t s . A d v a n t a g e is s o m e t i m e s t a k e n o f i t s d i r e c t i o n a l p h y s i c a l p r o p e r t i e s w h e r e c o r r o s i o n resistance also is needed. I t s h o u l d b e m e n t i o n e d t h a t f o r t h e same i n i t i a l cost a m u c h t h i c k e r w a l l c a n b e p u r c h a s e d i n a cast i r o n o r a steel p i p e t h a n f o r one o f w r o u g h t i r o n . Until directly comparable engineering d a t a are developed i n t h e economic use of w r o u g h t i r o n vs. steel o r cast i r o n i n s e a - w a t e r p l a n t s , m a n y e x p e r i e n c e d m a r i n e o p e r a t o r s h e s i t a t e t o s p e c i f y i t i n p l a c e o f o t h e r less e x p e n s i v e f e r r o u s m a t e r i a l s . A n o l d e r f o r m o f w r o u g h t i r o n , as p r o d u c e d i n E n g l a n d , c o n t a i n e d s l a g l a y e r s . T h e s e l a y e r s , w h e n s u i t a b l y o r i e n t e d , w e r e f o u n d i n some c o r r o s i o n e n v i r o n m e n t s t o prevent p i t t i n g attack f r o m progressing deeply into t h e m e t a l . W h i l e this behavior a c c o u n t s f o r t h e l o n g e r l i f e t i m e of t h e a n c i e n t f o r m o f t h e m a t e r i a l , i t does n o t f o l l o w (according t o m a r i n e specialists) t h a t t h e m o d e r n fibrous f o r m of w r o u g h t i r o n w i l l g r e a t l y o u t l a s t steel i n i d e n t i c a l s e a - w a t e r s e r v i c e . C A S T I R O N . T h e i r o n phase i n cast i r o n i s r e a d i l y a t t a c k e d b y sea w a t e r , as i s t h e case f o r m i l d steel. I f t h e l a y e r of g r a p h i t e l e f t w i t h t h e c o r r o s i o n p r o d u c t i s dense a n d compact, f u r t h e r corrosion tends t o be stifled. I f the layer is porous, corrosion m a y be accelerated b y t h e galvanic action between t h e graphite a n d t h e i r o n beneath. T h e a t t a c k t h e n a p p r o a c h e s a r a t e s i m i l a r t o t h a t f o u n d f o r t h e p i t t i n g o f m i l d steel. A l u m i n u m a n d A l u m i n u m A l l o y s . A l u m i n u m c a n b e e m p l o y e d i n sea w a t e r as a resistant m a t e r i a l of construction. Experiments at Fort Belvoir, Virginia, a n d elsewhere, i n d i c a t e t h a t b y p r o p e r c o r r o s i o n - c o n t r o l p r a c t i c e s , a l u m i n u m c a n b e u s e d f o r a n e n t i r e p l a n t w h i c h processes s e a w a t e r . T h e sea water entering t h e plant s h o u l d b e free o f a l l m e t a l l i c i o n s , e s p e c i a l l y c o p p e r o r n i c k e l . I t i s e s s e n t i a l , i n s u c h a p l a n t , t h a t n o c o p p e r - b a s e a l l o y s b e u s e d a t a l l a n d t h a t g a l v a n i c couples t o m o s t other metals be avoided. T o o b t a i n longer lifetime i n sea-water service, a l u m i n u m - c l a d t u b i n g is r e c o m m e n d e d . P r o p e r l y chosen, t h e c l a d d i n g acts as a s a c r i f i c i a l m e t a l a n d t h e a t t a c k w i l l n o t p e n e t r a t e i n t o t h e base m e t a l u n t i l m o s t o f t h e c l a d d i n g h a s b e e n c o n s u m e d b y c o r r o s i o n . T h e a l u m i n u m u s u a l l y chosen f o r c l a d d i n g i s b o t h m o r e c o r r o s i o n r e s i s t a n t a n d s l i g h t l y a n o d i c t o t h e base a l l o y . T h e f a c t t h a t a m e t a l i s m o r e a n o d i c t h a n a n a d j a c e n t o n e i n t h e g a l v a n i c series f o r s e a w a t e r does n o t n e c e s s a r i l y i m p l y i t w i l l corrode a t a higher rate w h e n exposed u n c o u p l e d . A l u m i n u m a l l o y s h a v e b e e n u s e d t o f a b r i c a t e h e a t i n g coils f o r t a n k e r s i n w h i c h c r u d e o i l a n d s e a - w a t e r b a l l a s t a r e a l t e r n a t e cargoes. Savings i n weight a n d i n losses due t o c o r r o s i o n a r e r e p o r t e d t o b e v e r y f a v o r a b l e c o m p a r e d w i t h m i l d steel. Stainless Steels. I n s p e c i a l c i r c u m s t a n c e s , u n d e r c a r e f u l l y c o n t r o l l e d c o n d i t i o n s , some grades o f stainless steel h a v e g i v e n g o o d service i n sea w a t e r . M o s t a u t h o r i t i e s s t r o n g l y r e c o m m e n d c a u t i o n i n t h e use o f stainless steel f o r s e r v i c e i n sea w a t e r . I n heat e x c h a n g e r s e r v i c e , stainless steels c a n b e u s e d a t m u c h h i g h e r v e l o c i t i e s t h a n most c o m m o n metals. T h e r e i s , nevertheless, t h e ever-present possibility t h a t s t r e s s - c o r r o s i o n c r a c k i n g m a y t a k e p l a c e . T h i s b e c o m e s m u c h m o r e l i k e l y as t h e m e t a l t e m p e r a t u r e i s r a i s e d . A n y p o i n t s a t w h i c h h i g h stress a n d h i g h c h l o r i d e c o n c e n t r a t i o n s o c c u r are p a r t i c u l a r l y p r o n e t o t h i s t y p e o f f a i l u r e . S t a i n l e s s steel also i s s u s c e p t i b l e t o c r e v i c e c o r r o s i o n a n d d e p o s i t a t t a c k . D i f f e r e n t i a l a e r a t i o n cells, f o r m e d b e t w e e n s t a g n a n t a n d w e l l - a e r a t e d areas o n t h e m e t a l surface, m a y promote r a p i d attack. It is found that T y p e 316, containing m o l y b d e n u m , is more resistant t o t h e i n i t i a t i o n o f p i t s . H o w e v e r , once a p i t i s s t a r t e d , t h e r a t e o f p e n e t r a t i o n m a y b e o f t h e same o r d e r as f o r a m o l y b d e n u m - f r e e a l l o y . S i n c e t h e process side i n a h e a t e x c h a n g e r m a y d e m a n d stainless steel, as i n t h e case o f a m a r i n e - b a s e d c h e m i c a l p l a n t t h a t has b e e n f o r c e d t o use sea w a t e r f o r c o o l i n g p u r p o s e s , i t i s necessary t o c o n s i d e r m e a s u r e s f o r o b t a i n i n g o p t i m u m s e r v i c e . T h e c o o l i n g w a t e r s h o u l d b e free f r o m solids w h i c h c o u l d d e p o s i t o n t h e t u b e s . T h e
In SALINE WATER CONVERSION; Advances in Chemistry; American Chemical Society: Washington, DC, 1960.
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on September 5, 2015 | http://pubs.acs.org Publication Date: January 1, 1960 | doi: 10.1021/ba-1960-0027.ch005
34
ADVANCES IN CHEMISTRY SERIES
v e l o c i t y s h o u l d n o t b e a l l o w e d t o d r o p m u c h b e l o w 5 feet p e r second. C r e v i c e areas a n d s t a g n a n t areas s h o u l d b e m i n i m i z e d o r e l i m i n a t e d b y d e s i g n . R e s i d u a l a n d service stresses s h o u l d b e h e l d t o t h e l o w e s t possible l e v e l s . U n d e r s u c h c a r e f u l l y c o n t r o l l e d c o n d i t i o n s , stainless steel c o u l d g i v e g o o d s e r v i c e . S t a i n l e s s steel p u m p i m p e l l e r s are g i v i n g excellent service i n sea w a t e r . T h e same m a y b e s a i d f o r stainless steel s h i p p r o p e l l e r s n o w i n u s e o n c o a s t a l vessels. I n b o t h cases, i t i s essential t h a t t h e stainless steel n o t b e l e f t f o r l o n g p e r i o d s b e t w e e n r u n s i n s t a g n a n t sea w a t e r . S t a i n l e s s steel g e n e r a l l y w i t h s t a n d s p o l l u t e d sea w a t e r a n d p o l l u t e d b r a c k i s h w a t e r b e t t e r t h a n c o p p e r - b a s e a l l o y s . S u b s t i t u t i n g a n a u s t e n i t i c stainless screen f o r s i l i c o n b r o n z e t r a s h r a c k s h a s r e s u l t e d i n g r e a t l y i m p r o v e d service a t a west coast p o w e r p l a n t . N o r m a l l y stainless steel screens, because o f t h e crevices i n v o l v e d ( w h e r e t h e w i r e s c r o s s ) , a r e n o t r e c o m m e n d e d f o r use i n sea w a t e r . T h i s a l t e r a t i o n o f t h e u s u a l c o r r o s i o n m e c h a n i s m , p r e s u m a b l y r e l a t e d t o t h e h y d r o g e n sulfide c o n t e n t o f p o l l u t e d sea w a t e r , needs t o b e s t u d i e d . M o n e l . E x t e n s i v e use f o r h a n d l i n g sea w a t e r i s p r o v i d e d b y M o n e l . I t has g i v e n excellent service i n heat e x c h a n g e r s , p i p i n g , s h e a t h i n g t o p r o t e c t steel a t t h e h a l f - t i d e zone, v a l v e s , p u m p i m p e l l e r s , a n d fittings i n g e n e r a l . M o n e l has b e e n u s e d i n f a b r i c a t i n g d i s t i l l a t i o n u n i t s . I n o n e t y p e , a M o n e l heat e x c h a n g e r " b a s k e t " c a n b e m a d e t o flex i n o r d e r t h a t t h e s e a - w a t e r scale w i l l d r o p off, t h u s r e s t o r i n g i t s t h e r m a l efficiency. T h i s service i s c o n s i d e r e d m u c h t o o severe f o r m o s t m e t a l s . M o n e l s h a f t s , s u c h as t h e h a r d e r Κ M o n e l , a r e r e s i s t a n t t o c o r r o s i o n f a t i g u e i n s e a - w a t e r service. M a r i n e e x p e r i e n c e , i n g e n e r a l , considers M o n e l o n e of t h e best a l l - a r o u n d m e t a l s f o r h a n d l i n g sea water. C o p p e r - B a s e A l l o y s . T h e r e i s a w i d e r a n g e of c o p p e r - b a s e a l l o y s t h a t h a v e g i v e n g o o d service i n sea w a t e r . A d m i r a l t y b r a s s , 7 0 C u - 2 9 Z n - 1 S n , p l u s a n i n h i b i t o r s u c h as a r s e n i c , h a s f o u n d w i d e use as condenser t u b e s i n m a r i n e - b a s e d p l a n t s u s i n g sea w a t e r f o r c o o l i n g . W h i l e i t i s n o t so r e s i s t a n t as t h e c u p r o - n i c k e l s , i t o f t e n seems t o b e p r e f e r r e d because o f t h e l o w e r i n i t i a l cost. A n o t h e r w i d e l y u s e d a l l o y i n c o o l i n g - w a t e r service i s a l u m i n u m b r a s s , 76 C u - 2 2 Z n - 2 A l . T h e a l u m i n u m c o n t e n t i m p r o v e s t h e resistance t o v e l o c i t y a n d i m p i n g e m e n t . T h i s a l l o y seems t o b e m o r e s u s c e p t i b l e t o p i t t i n g t h a n some o f t h e o t h e r c o p p e r a l l o y s i n s t a g n a n t sea w a t e r . A r s e n i c is a d d e d as a n i n h i b i t o r of d e z i n c i f i c a t i o n . T h e h i g h - t i n b r o n z e s — e . g . , 9 0 C u - 1 0 S n — a r e k n o w n t o h a v e excellent l i f e t i m e i n sea w a t e r as condenser t u b e s . U n d o u b t e d l y , t h e i r cost has r e s t r i c t e d t h e w i d e r u s e o f these r e s i s t a n t a l l o y s . O r d i n a r y copper is n o t recommended f o r sea-water plants i f t h e water velocities are m u c h g r e a t e r t h a n 2 feet p e r second. I t remains to be demonstrated whether c o p p e r c a n b e e m p l o y e d i n c o n t a c t w i t h c o m p l e t e l y d e a e r a t e d sea w a t e r a t m u c h higher velocities. CUPRO-NICKELS. A t t h e p r e s e n t t i m e , m o s t m a r i n e o p e r a t o r s agree t h a t t h e c u p r o - n i c k e l s are t h e m o s t u s e f u l m a t e r i a l o f c o n s t r u c t i o n f o r s e a - w a t e r p l a n t s . S i n c e W o r l d W a r I I , t h e 9 0 C u - 1 0 N i a l l o y m o d i f i e d w i t h a b o u t 1.5% o f i r o n h a s b e c o m e well established. T h e l o w e r n i c k e l c o n t e n t r e s u l t s i n a cost a d v a n t a g e o v e r t h e 70 C u - 3 0 N i a l l o y . A l l o y s c o n t a i n i n g 7 0 C u - 3 0 N i o r 8 0 C u - 2 0 N i , e a c h w i t h a d d e d i r o n , are p r e f e r r e d b y some designers t o w i t h s t a n d m o r e severe c o n d i t i o n s . T h e c u p r o - n i c k e l s h a v e b e e n w i d e l y a c c e p t e d as t h e best a v a i l a b l e a l l o y f o r c o n d e n s e r t u b e s . F o r h a n d l i n g h o t sea w a t e r , t h e r e has been s o m e f a v o r a b l e e x p e r i e n c e w i t h c u p r o - n i c k e l for p u m p s a n d heat exchangers. T i t a n i u m . U n l i k e o t h e r m e t a l s , t i t a n i u m n o r m a l l y does n o t p i t , i s n o t s u s c e p t i b l e t o stress c o r r o s i o n , i s free f r o m l o c a l c o r r o s i o n u n d e r f o u l i n g o r g a n i s m s , i s free f r o m impingement a n d c a v i t a t i o n attack a t velocities w h i c h attack copper-base alloys, a n d is n o t s u s c e p t i b l e t o sulfide a t t a c k i n c o n t a m i n a t e d s e a w a t e r . Experiments with w a t e r v e l o c i t i e s a t 20 t o 50 feet p e r second s h o w n o a t t a c k o n t i t a n i u m . T i t a n i u m a n d i t s a l l o y s a r e s a i d t o b e less s u s c e p t i b l e t o m i n e r a l s c a l i n g i n sea w a t e r t h a n m o s t o t h e r m e t a l s . ( T h e c o r r o s i o n p r o d u c t s o n a m e t a l , s u c h as steel, p r o b -
In SALINE WATER CONVERSION; Advances in Chemistry; American Chemical Society: Washington, DC, 1960.
FINK—CORROSION OF METALS IN SEA WATER
35
a b l y h e l p t o a n c h o r sea-scale deposits.) Although thermal conductivity is low, the o v e r - a l l efficiency, t a k i n g f u l l a d v a n t a g e o f t h e v e r y h i g h v e l o c i t i e s p e r m i t t e d , c a n b e greater t h a n w i t h m a t e r i a l used a t present i n sea-water applications i n v o l v i n g h i g h rates o f h e a t t r a n s f e r .
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on September 5, 2015 | http://pubs.acs.org Publication Date: January 1, 1960 | doi: 10.1021/ba-1960-0027.ch005
Methods of Protection Protective Coatings. A v a r i e t y o f p r o t e c t i v e coatings i s a v a i l a b l e f o r steel i n sea-water service. F o r such applications as ships' hulls, n o r m a l practice i s t o a p p l y compatible antifouling paint over t h e corrosion-resistant primer coating system. F i g u r e 4 s h o w s p a n e l s w h i c h h a v e r e s i s t e d f o u l i n g f o r a y e a r o r m o r e as c o m p a r e d w i t h a d j a c e n t p a n e l s w h e r e t h e e x p e r i m e n t a l c o a t i n g is n o t p r o t e c t i v e .
Figure 4.
Experiments at Battel le's Daytona Beach Marine Station
σ. Effect of cathodic protection on paint systems 6. Antifouling paint studies Cathodic Protection. Steel c a n be protected b y cathodic current, supplied e i t h e r f r o m s a c r i f i c i a l anodes o r a n e x t e r n a l d i r e c t c u r r e n t source. T h e m e t h o d is effective f o r c o m p l e t e l y i m m e r s e d s t e e l — i . e . , f o r surfaces o n s t r u c t u r e s b e l o w t h e low-tide level. C u r r e n t consumption c a n be greatly reduced b y a p p l y i n g a suitable p a i n t s y s t e m t o t h e steel b e f o r e i t i s i m m e r s e d i n s e a w a t e r . S u c h a p a i n t s y s t e m should be alkali resistant.
In SALINE WATER CONVERSION; Advances in Chemistry; American Chemical Society: Washington, DC, 1960.
36
ADVANCES IN CHEMISTRY SERIES
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on September 5, 2015 | http://pubs.acs.org Publication Date: January 1, 1960 | doi: 10.1021/ba-1960-0027.ch005
A l u m i n u m c a n be c a t h o c l i c a l l y p r o t e c t e d , b u t c a u t i o n m u s t b e e m p l o y e d . I f t h e r e is t o o m u c h a l k a l i d e v e l o p e d as a r e s u l t of too h i g h a c a t h o d i c c u r r e n t , t h e a l u m i n u m w i l l b e a t t a c k e d . F i g u r e 4 shows a c a t h o d i c - p r o t e c t i o n e x p e r i m e n t b e i n g c o n d u c t e d a t Battelle's marine station. W a t e r Treatment. M a n y years have been spent i n developing corrosion i n h i b i t o r s for o r d i n a r y waters. O n l y a v e r y few such treatments have been studied f o r use i n sea w a t e r . F o r a o n c e - t h r o u g h p l a n t , c o r r o s i o n p r e v e n t i o n b y t h e u s e o f i n h i b i t o r s u s u a l l y is f o u n d t o b e t o o c o s t l y . I f sea w a t e r i s first d e a e r a t e d , o n l y a s m a l l a m o u n t of c o r r o s i o n i n h i b i t o r , i f a n y , p r o b a b l y w o u l d b e n e e d e d t o p r e v e n t a t t a c k o n steel, o r c o p p e r - b a s e a l l o y s . F o r a l u m i n u m , o x y g e n i s n e e d e d t o p r o m o t e a p r o t e c t i v e film. M o s t of t h e i n t e r e s t , so f a r , h a s been i n d e v e l o p i n g w a t e r t r e a t m e n t s f o r scale prevention, not corrosion prevention.
Design Consideration in Heat Exchangers I n choosing materials f o r sea-water, heat exchanger, o r evaporator service, m a n y f a c t o r s — s u c h as cost, a v a i l a b i l i t y , efficiency, as w e l l as c o r r o s i o n — m u s t be c o n s i d e r e d . M a t e r i a l s a v a i l a b l e i n w r o u g h t f o r m s , s u c h as t u b i n g a n d sheet, h a v e b e e n h i g h l i g h t e d i n t h i s r e v i e w . A l l o f these m e t a l s c a n b e f a b r i c a t e d b y w e l l - e s t a b l i s h e d m e t h o d s including welding. W h i l e the t h e r m a l conductivity for t h e alloys varies considerably, t h e p r o p e r t y o f i n t e r e s t t o t h e designer i s t h e o v e r - a l l r a t e o f h e a t t r a n s f e r i n s e r v i c e . F o r efficiency, t h i n p r o t e c t i v e films o n t h e s u r f a c e a r e t o b e p r e f e r r e d t o h e a v y d e p o s i t s of scale a n d c o r r o s i o n p r o d u c t s . W h e r e s p a c e a n d w e i g h t a r e i m p o r t a n t , s u c h as o n b o a r d s h i p , a n e x p e n s i v e m a t e r i a l ( s u c h as t i t a n i u m ) m i g h t cost less i n t h e l o n g r u n because o f i t s f r e e d o m f r o m m a i n t e n a n c e expense. H e a t Exchangers U s i n g C o o l i n g W a t e r . T u b u l a r - t y p e heat exchangers used i n m a r i n e service are a m o n g the m o s t critical i n a distillation p l a n t . One troublesome a r e a i n a t u b e a n d s h e l l - t y p e h e a t e x c h a n g e r i s a t t h e i n l e t ends o f t h e t u b e s . I m p i n g e m e n t c o r r o s i o n , w h i c h i s c a u s e d b y h i g h - v e l o c i t y t u r b u l e n t flow, i s e n c o u n t e r e d m o s t f r e q u e n t l y o v e r t h e first 6 i n c h e s of t h e i n l e t ends o f t h e t u b e s ( F i g u r e 3 , a ) . Beyond t h i s p o i n t , t h e flow u s u a l l y t e n d s t o b e l a m i n a r unless t h e r e i s some o b s t r u c t i o n i n t h e tube. I m p i n g e m e n t a t t a c k a t t h e i n l e t ends c a n b e m i n i m i z e d b y p r o v i d i n g a s u i t a b l e a m o u n t o f c a t h o d i c c u r r e n t . W h i l e t h i s c u r r e n t does n o t e n t e r t h e t u b e ends t o a n y g r e a t d e p t h , i t p r o t e c t s t h e first few i n c h e s . T h e c u r r e n t m a y b e p r o v i d e d b y s a c r i f i c i a l anodes made f r o m i r o n , zinc, a l u m i n u m , o r m a g n e s i u m . I f s a c r i f i c i a l anodes a r e u s e d i n c o n d e n s e r w a t e r b o x e s , i t i s d e s i r a b l e t o select a t y p e t h a t w i l l last f o r several years. P u r e zinc o r specially f o r m u l a t e d zinc anodes h a v e r e g a i n e d f a v o r i n r e c e n t y e a r s w i t h some o p e r a t o r s . H i g h - p u r i t y z i n c i s s a i d t o be s e l f - r e g u l a t i n g a n d does n o t r e q u i r e a r e s i s t a n c e t o c o n t r o l t h e c u r r e n t . I n s o m e cases, t h e t u b e sheet a n d t u b e ends also a r e c o a t e d t o r e d u c e t h e c u r r e n t d r a i n o n t h e anodes. A n o t h e r m e t h o d o f p r o v i d i n g p r o t e c t i v e c u r r e n t i s t o use t h e heads o r w a t e r b o x e s as s a c r i f i c i a l anodes. T h e s e w a t e r boxes, w h e n m a d e o f h e a v y steel o r o f cast i r o n , p r o v i d e g a l v a n i c p r o t e c t i o n t o t h e t u b e ends a n d t u b e sheet as t h e y c o r r o d e . I n c i d e n t a l l y , t h e s m a l l a m o u n t of i r o n i n t r o d u c e d i n t o sea w a t e r b y s u c h corrosion, o r b y i n t e n t i o n a l chemical a d d i t i o n , i s considered beneficial b y some a u t h o r i ties f o r p r o m o t i n g p r o t e c t i v e films o n c o p p e r - b a s e a l l o y s . R e d u c e d a t t a c k c a n also be a c c o m p l i s h e d b y flaring t h e t u b e ends t o f a c i l i t a t e s t r e a m l i n e flow. I t i s essential t h a t the cross-over area i n the head o r channel b e larger t h a n the cross-sectional area of t h e t u b e s t o r e d u c e t u r b u l e n c e . M u n r o (6) r e c o m m e n d s 1 2 5 % f o r t h e c r o s s - o v e r area i n water boxes f o r sea-water service. A l s o f r o m t h e s t a n d p o i n t of turbulence, side e n t r y i s p r e f e r r e d t o a x i a l e n t r y a t t h e f r o n t e n d o f t h e c o n d e n s e r . I f t h e f e r r o u s heads o r w a t e r b o x e s i n a c o n d e n s e r a r e l i n e d w i t h a p r o t e c t i v e c o a t i n g , o r w i t h a m e t a l s u c h a s M o n e l , t h e i n l e t t u b e ends w i l l n o l o n g e r r e c e i v e
In SALINE WATER CONVERSION; Advances in Chemistry; American Chemical Society: Washington, DC, 1960.
FINK—CORROSION OF METALS IN SEA WATER
37
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on September 5, 2015 | http://pubs.acs.org Publication Date: January 1, 1960 | doi: 10.1021/ba-1960-0027.ch005
c a t h o d i c p r o t e c t i o n f r o m the i r o n t o c o p p e r a l l o y c o u p l e . I m p i n g e m e n t a t t a c k a t t h e t u b e ends m a y b e e x p e c t e d t o b e m o r e severe. S a c r i f i c i a l anodes, as a l r e a d y d e s c r i b e d , p r o b a b l y w i l l b e needed. F o r p a i n t e d w a t e r boxes, t h e a n o d e d e s i g n a n d p l a c e m e n t m u s t be c a r e f u l l y designed. T o o m u c h c u r r e n t m a y r e s u l t i n b l i s t e r s o n t h e p a i n t c o a t i n g a n d u n d e s i r a b l e m i n e r a l scale o n the t u b e i n l e t s e c t i o n . T h e r e a r e r e p o r t s t h a t pieces of d i s l o d g e d p a i n t c o a t i n g h a v e caused s u d d e n p l u g g i n g o f condenser t u b e s w i t h s e r i o u s loss of c o o l i n g c a p a c i t y . I n c e r t a i n c h e m i c a l p l a n t s , t h e process s o l u t i o n b e i n g c o o l e d i s u n d e r pressure o r i s v e r y c o r r o s i v e . I t i s f o u n d e x p e d i e n t i n some cases t o p u t t h e Ιολν-pressure s e a w a t e r o n the s h e l l side o f t h e h e a t e x c h a n g e r . U n d e r these c o n d i t i o n s , t h e steel s h e l l w i l l suffer m o r e r a p i d a t t a c k because o f g a l v a n i c c o u p l i n g t o t h e c o p p e r - b a s e a l l o y tubing. H o w e v e r , only the outer tubes are " s e e n " b y the shell i n this couple. Never theless, t h i s r e p r e s e n t s a l a r g e c a t h o d e . F o r e a c h c o n d e n s e r - t u b e a l l o y , t h e r e i s a r e c o m m e n d e d m a x i m u m as w e l l as m i n i m u m v e l o c i t y i n s e a - w a t e r s e r v i c e . S i l t o r o t h e r fine solids i n t h e c o o l i n g w a t e r i s a c o m p l i c a t i n g f a c t o r . I t m a y b e h e l p f u l t o raise t h e m i n i m u m v e l o c i t y t o t h e p o i n t w h e r e t h e s i l t is a l w a y s m a i n t a i n e d i n s u s p e n s i o n . I n b r a c k i s h w a t e r s , t h e same g e n e r a l c o r r o s i o n p r i n c i p l e s m a y a p p l y as f o r sea w a t e r . E x p e r i e n c e has also s h o w n t h a t t h e r e m a y b e c o n s i d e r a b l e v a r i a t i o n f r o m p l a n t t o p l a n t i n t h e p e r f o r m a n c e o f m e t a l s , e v e n w h e r e t h e c o o l i n g w a t e r comes o u t o f t h e same g e n e r a l source s u c h as a deep b a y o r e s t u a r y . T h e r e a r e c o a s t a l sites w h e r e t h e s a l i n i t y m a y s h o w v e r y m a r k e d seasonal f l u c t u a t i o n . P r o t e c t i v e film f o r m a t i o n i s essential f o r l o n g l i f e t i m e i n condenser t u b i n g . T u b e s i n s t a l l e d a t t h e season o f t h e y e a r w h e n c o n d i t i o n s are m o s t f a v o r a b l e t o f o r m p r o t e c t i v e films t e n d t o g i v e l o n g e r s e r v i c e . T h e use o f s a c r i f i c i a l anodes f o r p r o t e c t i o n o f t h e heads o f t h e h e a t e x c h a n g e r m a y n o t b e so effective i n b r a c k i s h w a t e r . T h e w a t e r m a y b e v e r y c o r r o s i v e because o f p o l l u t i o n o r c o n t a m i n a t i o n , e v e n w h e n t h e s a l i n i t y i s r e l a t i v e l y l o w . M o r e anodes, w i t h closer s p a c i n g , n o r m a l l y a r e needed t o g i v e sufficient p r o t e c t i o n i n b r a c k i s h w a t e r t h a n i n sea w a t e r . E v a p o r a t o r s a n d H e a t E x c h a n g e r s for H a n d l i n g H o t Sea W a t e r . R e l a t i v e l y l i t t l e i n f o r m a t i o n is a v a i l a b l e o n m a t e r i a l s o f c o n s t r u c t i o n f o r e l e v a t e d - t e m p e r a t u r e s e r v ice w i t h sea w a t e r . U s u a l l y , o n e also m u s t c o n s i d e r t h e a t t a c k b y flue gas, s t e a m , o r o t h e r m e d i u m o n the o t h e r side o f t h e m e t a l b a r r i e r . C u p r o - n i c k e l s are r e c o m m e n d e d f o r c o n s i d e r a t i o n i n e v a p o r a t o r s e r v i c e , e s p e c i a l l y if sea w a t e r i s t o b e h a n d l e d a t 2 0 0 ° F . o r h i g h e r . M o n e l s h o u l d g i v e g o o d s e r v i c e . T h e r e i s some i n t e r e s t i n u s i n g e i t h e r T y p e 316 stainless steel o r A l l o y 20. B e c a u s e o f the d a n g e r o f stress c o r r o s i o n , p r e c a u t i o n s m u s t b e t a k e n w i t h these l a t t e r t w o m a t e r i a l s . H a s t e l l o y C is s a i d t o b e v e r y r e s i s t a n t t o h o t sea w a t e r . F r o m a corrosion viewpoint, the m e t a l w i t h the most outstanding promise f o r seaw a t e r heat exchangers i s t i t a n i u m . L a b o r a t o r y e x p e r i m e n t s s t a r t i n g w i t h s e a w a t e r , a n d h e a t i n g u n d e r pressure t o a b o v e t h e c r i t i c a l t e m p e r a t u r e , h a v e i n d i c a t e d t i t a n i u m t o be g r e a t l y s u p e r i o r t o H a s t e l l o y C a n d M o n e l , u n d e r these c o n d i t i o n s ( 4 ) . A l l i n d i c a tions suggest t h a t t i t a n i u m is the m o s t r e s i s t a n t o f t h e c o m m e r c i a l l y a v a i l a b l e m e t a l s to sea w a t e r a t t e m p e r a t u r e s u p t o 7 5 0 ° F . A t t h e p r e s e n t t i m e , i t i s r e c o m m e n d e d t h a t t h e h e a t - t r a n s f e r surfaces o f e v a p o r a t o r s a n d t h e h e a t exchangers f o r h a n d l i n g h o t sea w a t e r b e m a d e o f 7 0 % c o p p e r , 3 0 % n i c k e l a l l o y w i t h 0 . 7 % i r o n . T h i s a l l o y has g i v e n excellent service i n heat e x c h a n g e r s a b o a r d ships under a wide v a r i e t y of service conditions. P u m p s . M a t e r i a l s of construction f o r p u m p s v a r y w i t h the t y p e of service. A t l o w e r v e l o c i t i e s , sea w a t e r has b e e n h a n d l e d s u c c e s s f u l l y i n p u m p s u s i n g casings m a d e f r o m cast i r o n . C a s t i r o n c o n t a i n i n g a f e w p e r cent o f n i c k e l i s r e p o r t e d t o b e finer g r a i n e d a n d t o h a v e s m a l l e r g r a p h i t e flakes. T h i s m a y e x p l a i n i t s s u p e r i o r p e r f o r m a n c e f o r s e a - w a t e r service c o m p a r e d w i t h o r d i n a r y cast i r o n . A f t e r a y e a r o r t w o i n sea w a t e r , a r e s i d u a l l a y e r o f g r a p h i t e f o r m s o n t h e c a s t i r o n surface. I f a cast-iron p u m p casing becomes g r a p h i t i z e d , the p o t e n t i a l relationship is r e v e r s e d a n d t h e c a s i n g m a y b e c o m e c a t h o d i c t o t h e b r o n z e i m p e l l e r . T h e l a t t e r
In SALINE WATER CONVERSION; Advances in Chemistry; American Chemical Society: Washington, DC, 1960.
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on September 5, 2015 | http://pubs.acs.org Publication Date: January 1, 1960 | doi: 10.1021/ba-1960-0027.ch005
38
ADVANCES IN CHEMISTRY SERIES
can n o w be expected t o corrode a t a higher rate. M a n y operators prefer a more r e s i s t a n t m a t e r i a l f o r t h e c a s i n g , s u c h as M o n e l , a b r o n z e , o r a c u p r o - n i c k e l . T h i s a v o i d s t h e a b o v e p r o b l e m w i t h cast i r o n . A l t h o u g h i m p e l l e r s a r e c o m m o n l y m a d e o f one o f t h e b r o n z e s , m a n y o p e r a t o r s p r e f e r M o n e l a n d S M o n e l because o f t h e l o n g e r service o b t a i n e d . S e v e r a l i n s t a n c e s o f c o r r o s i o n c r a c k i n g o f a u s t e n i t i c stainless steel p u m p shafts h a v e b e e n r e p o r t e d . I t i s f o u n d t h a t p u m p s h a f t s of Κ M o n e l g i v e excellent s e r v i c e i n sea water. T h e lifetime of the p u m p , p a r t i c u l a r l y the impeller, is greatly extended i f i t is o p e r a t e d b e l o w i t s r a t e d c a p a c i t y f o r f r e s h w a t e r w h e n i t i s u s e d f o r sea w a t e r . F o r h a n d l i n g h o t sea w a t e r , C a r p e n t e r 2 0 i m p e l l e r a n d casings h a v e b e e n u s e d w i t h success. C u p r o - n i c k e l also h a s b e e n u s e d f o r p u m p s h a n d l i n g h o t sea w a t e r . I m p i n g e m e n t o r E r o s i o n - C o r r o s i o n . A c o n s i d e r a b l e n u m b e r of f a i l u r e s i n s e a w a t e r service t e n d t o o c c u r o n t h e d o w n s t r e a m side o f v a l v e s , fittings, b r a n c h c o n n e c t i o n s , e t c . E x c e s s i v e l y h i g h s e a - w a t e r v e l o c i t i e s a n d t u r b u l e n c e were i n v o l v e d . I t i s n o t c o n s i d e r e d g o o d p r a c t i c e t o c o n t r o l r a t e s of flow b y t h r o t t l i n g a t t h e v a l v e , since this introduces turbulence just b e y o n d t h e v a l v e . V a l v e s should be used for isolation s e r v i c e . G o o d h y d r a u l i c d e s i g n i s essential f o r l o n g l i f e t i m e i n a p l a n t f o r h a n d l i n g sea w a t e r . V e l o c i t i e s i n pipe's, etc., s h o u l d b e i n t h e r a n g e r e c o m m e n d e d f o r t h e m a t e r i a l i n sea water. Intake t o P l a n t . C l e a n sea w a t e r ( o r b r a c k i s h w a t e r ) free f r o m s u s p e n d e d m a t t e r is essential f r o m a n o p e r a t i o n a l s t a n d p o i n t . S h e l l fish, t r a s h , etc., i f a l l o w e d i n t o t h e w a t e r s y s t e m i n t h e p l a n t , m a y b e c o m e l o d g e d a t c r i t i c a l p o i n t s , s u c h as h e a t e x c h a n g e r tubing.
Conclusions F o r e c o n o m y i n c o n s t r u c t i o n a n d o p e r a t i o n of p l a n t s f o r h a n d l i n g s a l i n e w a t e r , particular attention m u s t be p a i d to corrosion factors. Steel can be used i n m a n y a p plications, i f i t i s protected b y the use of coatings o r is given cathodic protection. A l l o w a n c e also c a n b e m a d e i n t h e d e s i g n f o r t h e c o r r o s i o n o f steel. I f i t does n o t c o n f l i c t w i t h o t h e r d e s i g n f a c t o r s , i n c o m i n g sea w a t e r s h o u l d b e d e a e r a t e d t o c o n t r o l steel c o r r o s i o n . C o r r o s i o n i n h i b i t o r s a n d c h e m i c a l t r e a t m e n t m a y b e e m p l o y e d t o reduce t h e attack, b u t frequently this method is too costly. A l a r g e n u m b e r o f c o p p e r - b a s e a n d n i c k e l - b a s e a l l o y s ( s u c h as c u p r o - n i c k e l s , M o n e l , a n d a l u m i n u m b r a s s ) h a v e b e e n u s e d i n s e a - w a t e r service w i t h success. S p e c i a l m a t e r i a l s s u c h as H a s t e l l o y C , I l l i u m , a n d t i t a n i u m a r e a v a i l a b l e f o r e x t r e m e l y c o r r o s i v e s i t u a t i o n s . T h e e v i d e n c e , so f a r , i n d i c a t e s t i t a n i u m t o b e o u t s t a n d i n g a n d t o r a n k a b o v e o t h e r c o m m e r c i a l l y a v a i l a b l e m e t a l s i n c o r r o s i o n resistance u n d e r c o n d i t i o n s i n v o l v i n g h i g h temperature, velocity, a n d other adverse e n v i r o n m e n t a l conditions. C h l o r i n a t i o n t o a residual of 0.5 p . p . m . is w i d e l y used. I t is r e q u i r e d t o prevent f o u l i n g o f t h e M o n e l o r b r o n z e i n t a k e screens, t h e d u c t s , p i p e s , e t c . , t h r o u g h o u t t h e s y s t e m . E x p e r i e n c e h a s s h o w n t h a t c h l o r i n a t i o n , unless c a r e f u l l y c o n t r o l l e d t o l o w r e s i d u a l s , t e n d s t o increase t h e c o r r o s i v i t y o f saline w a t e r s . S a c r i f i c i a l anodes f r e q u e n t l y a r e u s e d t o p r o t e c t t h e r o t a t i n g steel f r a m e w h i c h s u p p o r t s the M o n e l screens a t t h e p l a n t i n t a k e . R e c e n t l y , a l u m i n u m has been demonstrated t o be a v e r y useful m a t e r i a l of c o n s t r u c t i o n f o r s e a - w a t e r p l a n t s . S p e c i a l care m u s t b e t a k e n w i t h a l u m i n u m t o a v o i d c o n t a c t w i t h m o s t o t h e r m e t a l s . H e a v y m e t a l ions i n t h e i n c o m i n g s e a w a t e r , s u c h as c o p p e r , m u s t b e r e m o v e d b e f o r e t h e w a t e r enters a n a l u m i n u m i n s t a l l a t i o n t o p r e v e n t l o c a l a t t a c k s u c h as p i t t i n g . W i t h greatly increasing interest i n t h e ocean for m a n y purposes, t h e corrosion experts w i l l be increasingly active i n h e l p i n g t o design corrosion-resistant a p p a r a t u s a n d plants for sea-water service.
In SALINE WATER CONVERSION; Advances in Chemistry; American Chemical Society: Washington, DC, 1960.
FINK—CORROSION OF METALS IN SEA WATER
39
Acknowledgment T h e a u t h o r is indebted t o a large n u m b e r of specialists who generously c o n t r i b u t e d t i m e , experience, a n d ideas t o t h i s p a p e r . T h e author v e r y m u c h appreciates t h e s u p p o r t of t h e Office o f S a l i n e W a t e r o n a p r o j e c t c l o s e l y r e l a t e d t o t h e s u b j e c t o f t h i s paper.
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on September 5, 2015 | http://pubs.acs.org Publication Date: January 1, 1960 | doi: 10.1021/ba-1960-0027.ch005
Literature Cited (1) B a d g e r , W. L., a n d Associates, Inc., Ann Arbor, Mich., "Critical R e v i e w of L i t e r a t u r e o n F o r m a t i o n a n d P r e v e n t i o n of Scale," Research a n d D e v e l o p m e n t P r o g r . R e p t . N o . 25, Office of Saline W a t e r , July 1959. (2) Forgeson, B. W . , S o u t h w e l l , C . R., A l e x a n d e r , A. L., Corrosion 16, No. 3 (1960). (3) H a c h e , Α., Rev. mét. 53, No. 1 (1956). (4) L a s e r s o n , G. L., et al., "Extraction of F r e s h W a t e r f r o m Sea W a t e r in the S u p e r c r i t i c a l S t a t e , " t o the Office of Saline W a t e r , by N u c l e a r D e v e l o p m e n t Associates, Inc., W h i t e P l a i n s , N. Y., NDA 32-2, p. 36, July 31, 1954. (5) L y m a n , J o h n , Abel, R. Β., J. Chem. Educ. 35, 113-5 (1958). (6) M u n r o , J. D., Proc. Am. Petrol. Inst. 34, 19 (1954). (7) P a l m a e r , W . , J. lutte contre corrosion, 18-24 (1938). (8) P e t e r s o n , M. H., W a l d r o n , L. J., "An I n v e s t i g a t i o n of t h e C o r r o s i o n R a t e of Mild Steel in San D i e g o H a r b o r , " Natl. Assoc. C o r r o s i o n E n g r s . , 16th A n n . C o n f . , D a l l a s , T e x . , M a r c h 14-18, 1960. (9) U h l i g , H. H., ed., " C o r r o s i o n H a n d b o o k , " p . 416T, E l e c t r o c h e m i c a l S o c i e t y , 1948. RECEIVED for review July 15, 1960. A c c e p t e d July 28, 1960.
In SALINE WATER CONVERSION; Advances in Chemistry; American Chemical Society: Washington, DC, 1960.
