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7/28/2019 Dexter 1986 Aquacultural-Engineering
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AquaculmralEngineering 5 (1986i 333-3 45
M a t e r ia l s S c i e n c e in A q u a c u it u r al E n g i n e e r in g
Stephen C. Dexter
College of M arine Studies, University of D elaware. Lewes, Delaware 1995 8. USA
A B S T R A C T
The pert ine nt s trength an d &trabi l i~ ' propert ies o f metal l ic and
non m etal l ic m ater ials used in the construct ion o f aquacul tural sys tems
are ou tl ined . Re cen t advances in max imiz ing the per formance o f
mater ials fo r c om po ne nts such as nets, cages , f loats a nd screens use d in
f loat ing sy s tems are reviewed. Ma ter ials req uirements are discussed jbr
r ig id versus f l ex ib le sys tems and for min imiz ing prob lem s in mar ine
systems cau sed by biofouling. C om po ne nts o f f ix ed s tructures such as
water in take and supply l ines , pumps and pond sys tems are also con-s idered. Ma ter ials select ion fo r aquacu l tural sys tems is d iscussed in
terrns of t rade-off~ betw een durabi l i ty a nd perform anc e on th e one
hand and cap i ta l and main tenance cos t s on the o ther . New deve lop-
ments in bo th meta l l i c and nonmeta l l i c compos i t e mater ia l s and in
seawater resistant stainless steels may benefi t aquacultural engineering
in th e j~Lture.
I N T R O D U C T I O N
O v e r t h e p a st d e c a d e , t h e r e h as b e e n a t r e m e n d o u s g r o w t h o f i n te r e st
i n a v a r i e t y o f t y p e s o f m a r i c u l t u r e s y s t e m s . A l o n g w i t h t h i s g r o w t h ,
h o w e v e r , t h e r e h a s n o t b e e n a c o m m e n s u r a t e i n c r e a se i n t h e ap p l ic a -
t i o n o f a d v a n c e s i n m a t e r i a l s s c i e n c e t o t h e e n g i n e e r i n g o f m a r i c u l t u r e
s y s t e m s . T h e p u r p o s e o f t h is p a p e r is t o r e v i e w w h a t h a s b e e n
r e c o r d e d i n t h e r e c e n t m a r i c u l t u r e a n d r e l a t e d l i t e r a t u r e c o n c e r n i n g
m a t e r i a l s s e l e c t i o n a n d m a t e r i a l s p e r f o r m a n c e , g iv e a n o v e r v i e w o f t h e
p e r t i n e n t p r o p e r t i e s o f s t r u c t u r a l m a t e r i a l s o f i n t e r e s t i n t h e c o n s t r u c -
t i o n o f m a r i c u l t u r e s y s t e m s , a n d t o d i s c u s s s o m e o f th e i s su e s in v o l v e d
i n m a t e r i a l s s e l e c t i o n .
333
Aquacultural Engineering 0 1 4 4 -8 6 0 9 /8 6 /S 0 3 .5 0 - © E l sev ie r Ap plied Sc iencePublishers Ltd. England, 1986. Printed in Great Britain
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334 S . C D e x t e r
Four principal journals were searched for articles discussing
materials and their selection for, and/or performance in, aquacultureand mariculture systems. These four journals were: Aquaculture(1976-84), Journal of Shellf ish Research and Journal of WorldMaricuhure Socieo' (1981-84) and Aquacuhural Engineering(1982-84). This search revealed that a wide variety of metallic and
nonmetallic structural materials are in common use in mariculture
systems. The new developments in advanced materials utilization have
been in the areas of materials used mostly for containing the
organisms being cultured, or for protecting them from predators, or
for providing a suitable substratum for attachment and growth of theorganisms, or a combination of these. The primary issues addressed
have been the durability of the materials in terms of their resistance to
corrosion and other types of degradation in the aquatic environment,
their compatibility with the cultured organisms and their relative costand maintenance requirements.
Neudecker (1982) has discussed the use of galvanized iron con-
tainers for growing oysters on square mesh plastic netting stapled tooak frames, as opposed to the earlier plastic tray system, in German
coastal waters. Heavy fouling encrustations were a major problem atsome of their test sites. Systems for the culture of Sydney Rock
Oysters in New South Wales estuarine waters have been described by
Wisely et al. (1979, 1983). They describe a galvanized steel cage
system fitted with either galvanized wire or high density polyethylene
plastic mesh for the floors and walls.Pfister and Romaire (1983) described experiments on the catch
efficiency of crawfish traps as a function of trap design and the use of
PVC plastic coated versus galvanized wire. They concluded that traps
made with plastic coated wire cost about $90 more than those made
with galvanized wire. The increase in commercial life of the trap from
one to two }'ears for the galvanized wire traps to three to five years for
the plastic coated wire traps, however, more than compensated for the
increase in cost.
A considerable amount of work has been done to improve the
corrosion and fouling resistance of fish cage systems. Biofouling canbe a particularly serious problem for marine aquaculture systems
operating on a continuous basis. Fouling on nets, cages, floats and
intake screens increases weight and drag, reduces buoyancy and water
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Materials sc ience in aquac u lm ra l eng ineering 3 3 5
f l o w a n d c o m p e t e s w i t h t h e c a s h c r o p f o r a v a i l a b l e n u t r i e n t s . A
n u m b e r o f n e t s y s t e m f ai l u re s in l ar g e c o m m e r c i a l m a r i n e a q u a c u l t u r e
o p e r a t i o n s h a v e a l r e a d y o c c u r r e d , w i t h b i o fo u l i n g b e i n g a m a j o r c o n -
t r i b u t o r ( H u g u e n i n a n d A n s u i n i , 1 9 7 5 ).
H u g u e n i n a n d A n s u i n i ( 1 9 7 8 ) h a v e r e v i e w e d t h e t e c h n o l o g y ,
e c o n o m i c s a n d p r o b l e m s a s s o c i a t e d w i t h v a r i o u s c o m m o n l y u s e d fi sh
cage sys tems . The i r r ev iew covers the use o f : (1 ) f l ex ib le cages used
b o t h a s in d i v i d u a l u n i ts a n d a s n e s t e d s y s t e m s , m a d e m o s t ly f r o m
n y l o n a n d o t h e r s y n t h e t i c n e t t i n g a n d k n o t l e s s m e s h ; (2 ) r i n d c a g e
s y s t e m s m a d e w i t h g a l v a n i z e d , v i n y l - c o a t e d g a l v a n i z e d a n d
c o p p e r - n i c k e l a l l o y m e s h , a n d g a l v a n i z e d , w o o d , a l u m i n u m a n d f i b -e r g l a s s s t r u c t u r a l m e m b e r s ; a n d ( 3 ) v a r i o u s m o o r i n g a n d f l o a t a t i o n
m a t e r i a l s a n d c o n f i g u r a t i o n s . D e s i g n r e q u i r e m e n t s , i n c l u d i n g t h o s e
requ i rements fo r cor ros ion and fou l ing res i s tances , a re o f ten s i t e spe -
c ific , a n d d e p e n d o n a v a r i e t y o f p a r a m e t e r s s u c h a s t y p e o f e x p o s u r e
( river , e s tua ry , bay , l agoon o r ope n ocean) , wa te r qua l i ty and temp era -
t u re , p r o b a b i l it y o f s t o r m o c c u r r e n c e s a n d m a r g i n o f s a f e ty b a l a n c e d
a g a i n s t c o n s e q u e n c e s o f s y s t e m f a i l u r e . A s e x a m p l e s o f r e c u r r i n g
mate r ia l s - re la ted p rob lems wi th these types o f sys tems they c i t e : (1 )
b io fou l ing , wi th the consequen t inc rease in bo th we igh t and d rag ; (2 )cor ros ion o f the meta l l i c componen ts ; and (3 ) u l t ra -v io le t de te r io ra -
t i o n o f p o l y m e r i c c o m p o n e n t s . T h e l a t t e r t w o p h e n o m e n a d e c r e a s e
s y s t e m s e rv i c e l if e a n d i n c r e a s e m a i n t e n a n c e a n d r e p l a c e m e n t c o st s,
n o t t o m e n t i o n l o ss o f p r o d u c t a n d r e v e n u e s i n t h e c a s e o f la r ge s ca l e
sys tem fa i lu re .
I n o r d e r t o i n c r e a s e s y s t e m r e l ia b i l it y a n d p r o v i d e h i g h e r s t re n g t h
for hand l ing inc reas ed p ro du c t loads in the l a rge r cages , severa l types
of r ig id , fou l ing res i s tan t cages a re be ing deve loped . Ansu in i and
H u g u e n i n ( 1 9 7 8 ) h a v e d e s c r i b e d a p r o t o t y p e l o w - m a i n t e n a n c e c a g es y s t e m c o n s i s t i n g o f a f i b e r g l a s s f r a m e c o v e r e d w i t h 9 0 - 1 0
c o p p e r - n i c k e l e x p a n d e d m e t a l m e s h . T h e s e c a g e s w e r e f o u n d t o h a v e
b o t h o p e r a t i o n a l a n d e c o n o m i c a d v a n t a g e s o v e r t h e m o r e c o m m o n l y
u s e d n y l o n n e t b a g s y s t e m s . T h e b e n e f i t s i d e n t i f i e d i n c l u d e d r e d u c e d
m a i n t e n a n c e a n d r e p l a c e m e n t c o s ts , r e d u c e d p r o b a b i l i t y o f s y s t e m
s t ru c t u r a l f a il u re , a n d i n c r e a s e d p r o d u c t i v i t y f r o m i m p r o v e d w a t e r c ir -
cu la t ion due to a reduc t ion in ne t c logg ing by fou l ing . O th er fea tu res
o f c a g e s y s t e m c o n s t r u c t i o n w e r e h o t d i p p e d g a l v a n i z e d s t e e l w e l d -
ments used a t h igh s t ress po in t s o f the f ibe rg lass f rame , fa s teners o f
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336 S. C De x t e r
copper-nickel or monel electrically isolated from the galvanized
components by plastic bushings to avoid galvanic corrosion problems,
and a floatation system of treated wood and polystyrene boxes
sheathed with 10 mils (254 k~m) of 90-10 copper-nickel to provide
fouling resistance and protection from slush ice.
In their analysis of system economics, Ansuini and Huguenin
(1978) found that converting from a flexible cage system to modular
rigid cage system doubled the containment cost per unit volume, and
then upgrading from galvanized to copper alloy mesh added another
50% surcharge. Despite the higher acquisition cost, however, the
increased performance of the copper alloy cages resulted in aprojected yearly cost including maintenance and replacement of about
40% less for the rigid copper alloy cages as compared to the nylon net
cages. Moreover, they found that the greater fouling resistance of the
copper-nickel cages allowed a greater water flow into the cage
interior, and thus better utilization of the food available in the water.
A different approach to fouling control has been taken by Blair e t
a l . (1982). They utilized a partially submerged rectangular cage based
on a rigid polypropylene frame with mesh panels of either plastic or
copper-nickel held to the frame with strips of hardwood and nylonnuts and bolts. The cage could be rotated by inflation and deflation of
neoprene bladders located along each of the four corners of the
rectangle. At any given time, the mesh side currently out of the water
could be removed for maintenance and cleaning. Biofouling was thus
controlled with this cage system by stepwise 90 ° rotations at weekly
intervals. The total maintenance time for this setup was reduced by a
factor of about 25 compared with that for a conventional flexible net
system at the same location over a period of eight months in Dunstaff-
nage Bay, UK.Far less has been written in the aquaculture and mariculture litera-
ture about materials selection for fixed structures, such as water intake
and supply lines, pumps, pond systems and the like. Bouck (1981) has
contrasted the construction and maintenance of a seawater intake and
supply system built from PVC pipe with a more conventional system
of concrete-lined ductile iron pipe. Many references are made to the
use of PVC for pipes, lines and valves; fiberglass for building or lining
tanks and trays; and concrete for tanks and ponds (McVey, 1983).
Some papers mention the materials of construction in passing, othersmake no mention of them at all. Rarely is there given any rationale for
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Materials science in aquaculmral engineering 3 3 7
s e l e c t i o n o f t h e m a t e r i a l s b e i n g u s e d , o r a c r it ic a l a n a ly s i s o f t h e p e r -
f o r m a n c e o f t h e s e m a t e r ia l s i n s er v ic e . T h i s l a ck o f i n f o r m a t i o n is
p r o b a b l y d u e t o t h e f a c t t h a t t h e m a t e r i a l s r e q u i r e m e n t s f o r s u c h
s y s te m s a r e r e l a ti v e ly s im p l e , a n d t h e m a i n p r o b l e m s f a c e d b y t h e
m a r i c u l t u r e i n d u s t r y h a v e b e e n b i o l o N c a l a n d b i o c h e m i c a l , r a t h e r
t h a n m a t e r i a l s r e l a t e d .
A g r e a t d e a l o f i n f o r m a t i o n , h o w e v e r , i s a v a i l a b l e i n t h e m a t e r i a l s
s c i e n c e li t e ra t u r e a b o u t t h e m a t e r i a ls t h a t w o u l d n o r m a l l y b e u s ed in
aquaculture/mariculture s y s t e m s . T h e t y p e o f i n f o r m a t i o n a v a i l a b l e
a n d t h e s o u r c e s f r o m w h i c h it c a n b e o b t a i n e d w i ll b e b r i ef ly r e v i e w e d
i n t he ne x t s e c t i on .
C H A R A C T E R I S T I C S O F C A N D I D A T E M A T E R I A L S
A s u m m a r y o f m a n y o f t h e p e r t i n e n t p r o p e r t i e s o f b o t h m e t al li c a n d
n o n m e t a l l i c s t r u c t u r a l m a t e r i a l s o f i n t e r e s t i n m a r i c u l t u r a l s y s t e m s i s
g i ve n i n T a b l e s 1 , 2 , a n d 3 . A l a r ge vo l um e o f l i t e r a t u r e e x i s ts f r om
w h i c h th e d a t a i n t h e s e ta b l es w e r e t ak e n . A n u m b e r o f s u m m a r y
v o l u m e s , w h i c h t h e r e a d e r s h o u l d c o n s u l t fo r f u r th e r i n f o r m a t i o n o nt h e p r o p e r t i e s o f t h e s e m a t e r i a l s a n d t h e i r r e s i s t a n c e to d e t e r i o r a t i o n
in n a t u r a l a q u e o u s e n v i r o n m e n t s , in c l u d e : L a Q u e , 1 9 7 5 ; F i n k a n d
B o y d , 1 9 7 8 ; D e x t e r , 1 9 7 9 ; S c h u m a c h e r . 1 9 7 9 ; A m e r i c a n S o c ie t y f o r
M e t a ls ( A S M ) , 1 9 8 1 ; C o b u r n , 1 9 8 4 ; a n d U h l ig a n d R e v i e , 1 9 8 5 .
T h e m e t a l s a n d a l lo y s l is te d in T a b l e 1 r a n g e f r o m s t r u c t u r a l s te e ls
a n d a l u m i n u m a l l o y s t h a t a r e i n e x p e n s i v e , b u t r e q u i r e p r o t e c t i v e
m e a s u r e s a g a i n s t e l e c t r o c h e m i c a l c o r r o s i o n i n o r d e r to o b t a in a r e a so n -
a b l e s e r v i c e li f et im e , to c o p p e r a l l o y s t h a t a re m o r e c o r r o s i o n r e s is t a n t
a n d h a v e s o m e a n t i f o u l i n g p r o p e r t i e s , t o t h e s t a i n l e s s s t e e l s a n d s u p e r -
a l l o y s , w h i c h h a v e g r e a t l y i n c r e a s e d c o r r o s i o n r e s i s t a n c e s , b u t a l s o
h i g h e r i n i t i a l c o s t s . L o w c o s t s t r u c t u r a l s t e e l c o r r o d e s m o r e o r l e s s
u n i f o r m l y o v e r its e n t i r e e x p o s e d s u r f a c e , b u t i t d o e s s o in a p r e d i c t -
a b l e m a n n e r t h a t c a n u s u a l ly b e a c c o u n t e d f o r i n th e d e s ig n o f a
s y s t e m .
T h e c o r r o s i o n r a t e o f s te e l i n a e r a t e d n a t u r a l w a t e rs d e p e n d s
p r i m a r i l y o n t h e c o n c e n t r a t i o n o f d i s s o l v e d o x y g e n , a n d s e c o n d a r i l y
o n t h e t e m p e r a t u r e a n d s a li n it y o f t h e w a t e r. T h e e f fe c ts o f f r e sh a n d
s e a w a t e r c h e m i s t r ie s o n t h e c o r r o s i o n t y p e a n d r a te o f s te e l a n d o t h e r
s t r u c t u r a l a l l o y s h a s b e e n r e v i e w e d b y D e x t e r a n d C u l b e r s o n ( 1 9 8 0 ) .
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3-*0 S.C. Dexter
I n d e a e r a t e d e n v i r o n m e n t s c o n t a i n i n g su lf a te s , t h e c o r r o s i o n r a te o f
s t e e l w i l l b e p r i m a r i l y a f u n c t i o n o f t h e a c t i v i t y o f s u l f a t e - r e d u c i n g
b a c t e r i a ( s e e U h l i g a n d R e v i e , 1 9 8 5 ).
T h e c o r r o s i o n r a t e o f s t e e l c a n u s u a l l y b e c o n t r o l l e d t o w i t h i n
a c c e p t a b l e l im i t s b y t h e u s e o f c o a t i n g s t o g e t h e r w i t h c a t h o d i c p r o t e c -
t io n . C o a t i n g s f u n c t i o n b y i s o l a t in g t h e u n d e r l y i n g m e t a l f r o m t h e c o r -
r o s iv e e n v i r o n m e n t . C a t h o d i c p r o t e c t i o n i s a n e l e c t r o c h e m i c a l
t e c h n i q u e b y w h i c h a n e l e c t r o c h e m i c a l c u r r e n t i s s u p p l i e d t o t h e c o r-
r o d i n g s t r u c t u r a l m e t a l (s t ee l i n th is c a s e ) b y m e a n s o f a p o w e r s u p p l y
a n d a n a u x i li ar y e l e c t ro d e . T h e c a t h o d i c p r o t e c t i o n c u r r e n t is a p p l i e d
i n a d i r e c t i o n s o a s t o o p p o s e , a n d n e g a t e , t h e n a t u r a l ly o c c u r r i n g c o r -r o s i o n c u r r e n t . C o a t i n g s u s e d t o g e t h e r w i t h c a t h o d i c p r o t e c t i o n
r e d u c e t h e s u r fa c e a r e a o f b a r e m e t a l t o b e p r o t e c t e d . T h i s r e d u c e s
t h e a m o u n t o f e l e c t r i c a l c u r r e n t t h a t n e e d s t o b e s u p p l i e d b y t h e
c a t h o d i c p r o t e c t i o n s y s t em , t h u s m a k i n g it m o r e e c o n o m i c to o p e r a te .
C o n v e r s e l y , as t h e c o a t i n g d e t e r i o r a t e s o v e r t i m e , th e c a t h o d i c p r o t e c -
t i o n s y s t e m a u t o m a t i c a l l y p r o t e c t s t h e m e t a l a t d e v e l o p i n g f la w s in t h e
coa t i ng .
T h e c o p p e r a n d c o p p e r - n i c k e l a ll o y s i n T a b l e 1 a ls o t e n d t o
c o r r o d e i n a u n i f o r m a n d p r e d i c t a b l e m a n n e r . I n a d d i t i o n , a s t h e yc o r r o d e , t h e y r e l e a s e c u p r o u s i o ns i n t o t h e b o u n d a r y l a y er o f w a t e r i n
w h i c h t h e y a re i m m e r s e d . I n s u f fi c ie n t c o n c e n t r a t io n s , t h e s e c u p r o u s
ion s a re tox ic to m ar in e fou lim,~ or~anisms,~ g iv ing r i s e to the an t i -
f o u l i n g p r o p e r t i e s o f t h e s e a l l o y s . I t w a s e s t i m a t e d b y L a Q u e i n t h e
1 9 3 0 s ( se e L a Q u e , 1 9 7 5 ) th a t th e m i n i m u m c o r r o s i o n r a t e t ha t w o u l d
r e le a s e e n o u g h c o p p e r i o n s to m a k e t h e a l lo y a n t if o u l in g w a s 5 m g p e r
1 0 0 c m - " o f e x p o s e d s u r f a c e a r e a p e r d ay ' o f e x p o s u r e . T h i s c o r r e -
s p o n d s t o a u n i f o r m s u r fa c e p e n e t r a t i o n o f a b o u t 0 - 0 0 0 8 in (0 "0 2 m m )
y e a r - j . I f f o r a n y r e a s o n t h e c o r r o s i o n r at e o f e v e n p u r e c o p p e r fa llsbe l ow t ha t r a te , t he m e t a l w i l l l o s e i ts an t i f ou l i ng p r ope r t i e s . T h us , i f a
c o p p e r - n i c k e l a l l o y i s c h o s e n f o r a p a r t i c u l a r a p p l i c a t i o n b e c a u s e o f
i t s a n t i f o u l i n g p r o p e r t i e s , i t w i l l b e c o u n t e r p r o d u c t i v e t o a t t e m p t t o
r e d u c e i ts c o r r o s i o n r a te b y u s e o f c o a ti n g s o r c a t h o d i c p r o t e c t i o n .
T h e v a r i o u s r e q u i r e m e n t s o f a n,,' l a rg e e n g i n e e r i n g s y s t e m u s u a l l y
d i c t a t e t h a t s e v e r a l d i f f e r e n t m a t e r i a l s o f c o n s t r u c t i o n w i l l b e n e c e s -
s ary . T h u s d i f f e re n t m e t a l s a re o f t e n p u r p o s e l y jo i n e d t o g e t h e r i n e l e c-
t r i ca l con t ac t . T h i s g i ves r i s e t o t he pos s i b i l i t y t ha t one o f t he me t a l s
w i l l b e d a m a g e d b y g a l v a n i c c o r r o s i o n . T h i s p r o b l e m c a n u s u a l l y b e
s o l v e d b y r e c o g n i z i n g w h e r e i t m a y o c c u r , p r e d i c t i n g w h i c h m e t a l w il l
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Materials science in aqu acu lmr al engineering
TABLE 2Galva mc Ser i e s o f M eta ls an d Al loys in Seawa te r ( a f t e r Dexte r . 1 979)
341
Allov Potential range on
saturated calomel scale (l')
Gra phi t e (o r g raph i t e - con t a in ing p l ast ic ) + 0 -30 t o + 0 -20
Plat inum + 0"35 to + 0.20
Ha ste l loy C- 27 6 + 0" 10 to - 0 .04
Una l loyed t i tan ium + 0" 06 t o - 0 -05
304 and 31 6 s ta inless s tee l (pass ive) 0-00 to - 0 .15
M one l 400 - 0" 04 t o - 0 . 14
9 0 - 1 0 c o p p e r - n i c k e l - 0 "2 1 t o - 0 . 28
C op pe r - 0"28 to - 0"36
304 and 316 s ta inless s tee l (ac t ive) - 0 .35 to - 0 .57
AISI 1020 s teel - 0 .60 to - 0 .70
Alum inum a l loys - 0 . 70 t o - 0 . 90
Z i n c - 0 - 9 8 t o - 1 .0 3
M agnesium - I '60 to - 1"63
b e d a m a g e d a n d a p p l y i n g a n a p p r o p r i a t e c o r r o s i o n p r e v e n t i o n
m e a s u r e . P r e d i c t i o n o f w h i c h m e t a l w i l l b e d a m a g e d w h e n d i s s i m i la rm e t a l s a r e j o i n e d t o g e t h e r i s d o n e b y m e a n s o f a g a l v a n i c s e r i e s , s u c h
a s t h e o n e s h o w n in T a b l e 2 f o r m e t a ls a n d a l lo y s in s e a w a t e r . W h e n
t w o m e t a l s f r o m t h a t t a b le a r e p l a c e d in c o n t a c t i n s e a w a t e r , t h e o n e
t o w a r d t h e b o t t o m o r a c t i v e e n d o f t h e li s t w i l l s u f f e r a c c e l e r a t e d c o r -
r o s i o n . T h e d e g r e e o f a c c e l e r a t i o n d e p e n d s o n t h e r e l a t i v e e x p o s e d
a r e a s o f t h e t w o m e t a l s a n d o n t h e i r d i s t a n c e o f s e p a r a t i o n o n t h e
c h a r t . T h u s , a n a l u m i n u m a l lo y w i l l b e s e v e r e l y d a m a g e d b y c o n t a c t
w i th a c o p p e r a l l o y , a n d e v e n m o r e s o b y c o n t a c t w i th a g r a p h i t e -
c o n t a i n i n g p l a s t i c , w h i l e o n l y m o d e r a t e l y d a m a g e d b y c o n t a c t w i th t h e
s a m e e x p o s e d a r e a o f s te e l. F o r d e t a i l e d i n s t r u c t i o n s in h o w t o u s e t h e
g a l v a n i c s e r i e s s e e D e x t e r ( t 9 7 9 ) o r U h l i g a n d R e v i e ( 1 9 8 5) . G a l v a n i c
c o r r o s i o n c a n b e t u r n e d t o a d v a n t a g e b y p u r p o s e l y a p p l y i n g a c o a t i n g
o f a n a c t i v e m e t a l t o a s t ee l s t r u c t u r e t h a t n e e d s t o b e p r o t e c t e d . Z i n c
c o a t i n g s o n s t e e l ( g a l v a n i z i n g ) p e r f o r m t hi s f u n c t i o n . T h e z i n c
c o r r o d e s p r e f e r e n t i a l l y , a c t i n g as a s a c r i f i c ia l a n o d e , a n d s u p p l y i n g a
c a t h o d i c c u r r e n t t o p r o t e c t t h e s t e e l.
T h e a l u m i n u m , s t a i n le s s s t e e l a n d s u p e r a l l o y s i n T a b l e 1 d o n o t
c o r r o d e u n i f o r m l y i n a q u e o u s e n v i r o n m e n t s . W h e n t h e y c o r r o d e a t
a ll , th e y d o s o b y l o c a l i z e d f o r m s o f a t t a c k s u c h a s p i t t i n g , c r e v i c e c o r -
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Materials science in aquacultural engineering 343
r o s i o n a n d s tr e ss c o r r o s i o n c r a c k i n g . T h e s e ~ ' p e s o f c o r r o s i o n a r e
m o r e d a n g e r o u s t h a n i s u n i f o r m c o r r o s i o n b e c a u s e t h e y a r e m o r e
d i f f ic u l t t o de t e c t a n d c a n l e a d t o f a i l u r e o f a s t r u c t u r e w i t h li tt le w a r n -
i n g a n d w i t h l i t t l e o v e r a l l l o s s o f m e t a l . T h e b e s t d e s i g n p r o c e d u r e i n
t he s e c a s e s i s t o a vo i d u s i ng a l l oys t ha t a r e s u s c e p t i b l e t o l oc a l i z e d
c o r r o s i o n i n a g i v e n e n v i r o n m e n t . E x a m p l e s a r e t h e s u b s t i t u t i o n o f
s t ai n le s s s te e l ty p e 3 1 6 L f o r t y p e 3 t 6 t o a v o i d i n t e r g r a n u l a r c o r r o s i o n
o f w e l d m e n t s , a n d t h e u s e o f t y p e 2 9 - 4 o r a s u p e r a l l o y in p la c e o f 3 0 4
a nd 316 i n c a s e s w he r e t he l a t t e r t w o a l l oys ha ve i n s u f f i c i e n t r e s i s t -
a n c e t o p it ti n g o r c r e v i c e c o r r o s i o n .
S e v e r a l n o n m e t a l l i c m a t e r i a l s c o m m o n l y u s e d i n m a r i c u l t u r es y s te m s a r e s h o w n i n T a b l e 3 . D e g r a d a t i o n o f s u c h m a t e ri a ls i n n a tu r a l
a q u e o u s e n v i r o n m e n t s n o r m a l ly t ak e s p l a ce b y o n e o f t w o m e c h a n i s m s ,
T h e f ir st is w e a t h e r in g . T h i s i n v o lv e s a c o m b i n a t i o n o f w e t / d r y ( a n d
s o m e t i m e s f r e e z e / t h a w ) c y c li n g a n d u l tr a - v io l e t ir r a d i a t io n f r o m s u n -
lig h t. T h e s e c o n d i n v o lv e s w a t e r a b s o r p t i o n a n d t h e c o n s e q u e n t
c h a n g e s i n d i m e n s i o n s a n d p h y s i ca l a n d m e c h a n i c a l p r o p e r t ie s . S u c h
c h a n g e s i n p r o p e r t i e s a r e u s u a l ly , b u t n o t a l w a y s , d e t r i m e n t a l , a n d c a n
r a n g e f r o m i n s ig n i fi ca n t t o a 3 0 - 5 0 % r e d u c t i o n . M a n y o f t h e s e
m a t e r i a l s h a v e s p e c i a l p r o p e r t i e s t h a t m a k e t h e m a t t r a c t i v e f o r c e r t a i na p p l ic a t io n s . T h e f o a m s , w o o d s a n d p o l y p r o p y l e n e a r e li g ht er t h a n
w a t e r a n d c a n s e r v e a s fl o a t a t io n m a t e r i a ls . P o l y e t h y l e n e a n d t e f lo n
a r e c h e m i c a l l y i n e rt , n o n t o x i c a n d h a v e v e r y l o w w a t e r a b s o r p t i o n .
N y l o n , o n t h e o t h e r h a n d , ab s o r b s 7 - 1 0 % w a t e r o v e r a p e ri o d o f
s e v e r a l m o n t h s i m m e r s i o n . A s t h i s a b s o r p t i o n o c c u r s , t h e m a t e r i a l
s w e l ls a n d t h e m e c h a n i c a l p r o p e r t i e s d e c r e a s e . S w e l li n g c a n b e a
p r o b l e m i n c a s e s w h e r e c l o s e d i m e n s i o n a l t o l e r a n c e s m u s t b e m a i n -
t a i n e d , b u t it c a n a l so b e b e n e f i c i a l. S w e l l in g o f n y l o n f a s t e n e r s u n d e r
w a t e r c a n h e l p p r e v e n t t h e i r l o o s e n i n g u n d e r v i b r a t i o n a l l o a d i n g .K e v l a r f ib e r s h a v e t h e h i g h e s t st r e n g th - a n d m o d u l u s - t o - w e i g h t r at io s
o f a n y m a t e r i a l a v a i l a b le f o r m a k i n g c a b l e s . C o n c r e t e is a h i g h ly v e r s a -
t il e m a t e r i a l a n d is m a d e e v e n m o r e s o b y v i r t u e o f its c o m p a t i b i li t y
w i t h t h e s t e e l b a r s u s e d f o r r e i n f o r c e m e n t . S t e e l a n d c o n c r e t e h a v e
v e r y n e a r l y t h e s a m e t h e r m a l e x p a n s i o n c o e f f i c i e n t s , a n d s t e e l d o e s
n o t c o r r o d e i n t h e al k a li n e e n v i r o n m e n t o f w a t e r s a t u r a te d c o n c r e t e
( p H 1 2 ) . O n l y w h e n t h e c o n c r e t e b e g i n s t o d e t e r i o r a t e , o r t h e p o r e
w a t e r b e c o m e s c o n t a m i n a t e d w i th h ig h c o n c e n t r a t i o n s o f c h l o r i d e
i o n s ( f r o m s e a w a t e r o r r o a d d e i c i n g s a lt s) d o e s c o r r o s i o n o f t h e r ei n -
f o r c i ng s t e e l be g i n .
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344 ~ C D e x ~ r
M A T E R L A L S S E L E C T I O N A N D N E W D E V E L O P N L E N T S
T h e r e a r e a l w a y s t r a d e - o f f s i n v o l v e d i n th e p r o c e s s o f m a t e r ia l s s e le c -
t io n . T h e m a t e r ia l s t h a t a r e t h e m o s t c o r r o s i o n r e s i s t a n t a r e u s u a ll y t h e
m o s t e x p e n s i v e . A n i m p o r t a n t a s p e c t o f m a t e r i a ls s e l e c ti o n t h at is n o t
o f t e n g i v e n s e ri o u s c o n s i d e r a t i o n is t h e q u a l it y o f t h e p e r s o n n e l t h a t
w i ll b e u s i n g a n d m a i n t a i n i n g t h e s t r u c t u r e d u r i n g i ts s e r v ic e l if e ti m e .
I n g e n e r a l , i t m a y b e s a i d t h a t t h e m o r e t h e s e p e o p l e k n o w a b o u t
p o t e n t i a l c o r r o s i o n p r o b l e m s a n d h o w t o s o l v e t h e m , t h e m o r e f r e e -
d o m o n e h a s t o s e l e c t l e s s t h a n i d e a l m a t e r i a l s c o m b i n a t i o n s f r o m a
c o r r o s i o n p o i n t o f v ie w . C o n v e r s e ly , if t h e s e p e o p l e k n o w a n d / o r c a r el it tl e a b o u t m a t e r i a l s a n d c o r r o s i o n t h e n t h e d e s i g n e r is w e l l a d v i s e d t o
e l i m i n a t e t h e p o t e n t i a l p r o b l e m s i n t h e d e s i g n s ta g e b y s p e c i ~ 'i n g h ig h
q u a li ty , c o r r o s i o n r e s i s t a n t a n d c o m p a t i b l e m a t e r i a l s sy s t e m s .
E x p e r i e n c e h a s t a u g h t th a t h ig h l y i n a p p r o p r i a t e m a t e r ia l s c o m b i n a -
t i o n s s u c h a s a l u m i n u m a l l o y s i n con t a c t w i t h l a r ge ba r e a r ea s o f s t a i n -
l e s s s t e e l a l l o y s i n s e a w a t e r c a n b e m a d e t o w o r k f o r a n a c c e p t a b l y
l o n g ti m e i f t h e p e o p l e i n c h a r g e o f m a i n t e n a n c e k n o w w h a t t h e p ro b -
l e m s a re a n d w i ll b e m e t i c u l o u s i n t h e i r d e t a il e d m a i n t e n a n c e p r o c e -
d u r e s . I f t h i s t y p e o f p e r s o n n e l i s n o t a v a i l a b l e , h o w e v e r , s u c h am a t e r ia l s c o m b i n a t i o n s h o u l d b e a v o i d e d . A n y t im e t h a t ex t e n s iv e
m a i n t e n a n c e p r o c e d u r e s w i ll b e d i f fi cu l t o r u n d e s i r a b l e , o r t h e p r o p e r
p e r s o n n e l w i l l n o t b e a v a i l a b l e , o r t h e c o n s e q u e n c e s o f a s t r u c t u r a l
f a i l u r e w i l l b e u n a c c e p t a b l e , t h e d e s i g n e r s h o u l d c h o o s e t o o p t i m i z e
t h e i n h e r e n t d u r a b i l i t y o f t h e s t r u c t u r e b y b u i l d i n g i t f r o m a s i n g l e
m a t e r i a l ( to avo i d ga l van i c e f fec t s ) t ha t i s a s co r r o s i o n r e s i s t an t as pos -
s ib le .
I n c l o s i n g , i t s h o u l d b e m e n t i o n e d t h a t e n g i n e e r s a n d d e s i g n e r s
d e a l i n g w i t h m a r i c u l t u r e s y s te m s s h o u l d b e a w a r e o f n e w d e v e l o p -m e n t s i n t h e f i e ld o f m a t e r i a l s t e c h n o l o g y . T w o o f t h e s e i n p a r ti c u l a r
a r e t h e r a p id d e v e l o p m e n t o f n o n m e t a l l i c c o m p o s i t e m a t e ri al s a n d t h e
r e c e n t c o m m e r c i a l a v a i l a b i l i t y o f s e v e r a l n e w s t a i n l e s s s t e e l a l l o y s
h a v i ng e n h a n c e d s e a w a t e r c o r r o s i o n r es is ta n c e. N o n m e t a ll ic c o m -
p o s i te s c a n b e f o r m u l a t e d w i th h i g h l y f a v o r a b l e m e c h a n i c a l p r o p -
e r ti e s , i n c l u d i n g h i g h s t r e n g t h - t o - w e i g h t r at io s , a n d t h e y a r e n o t
s u s c e p t ib l e t o e l e c t r o c h e m i c a l c o r r o s i o n . T h e p r o p e r t i e s a n d
i m p r o v e d c o r r o s i o n b e h a v i o r o f th e n e w s ta i n le s s al lo y s (s e e t y p e 2 9 - 4
i n T a b l e 1 ) h a v e b e e n s u m m a r i z e d b y S t r e i c h e r ( 1 9 8 3 ) . T h e s e n e w
a l lo y s h a v e c o s t s s im i l a r to t h e c o n v e n t i o n a l 3 0 0 s e r ie s s t ai n le s s st e e ls
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c o u p l e d w i t h c o r r o s i o n r e s i s t a n c e s c l o s e to t h o s e o f th e s u p e r a l l o y s .
S u c h d e v e l o p m e n t s m a y p r o v e a d v a n t a g e o u s t o t he m a r i c u l u re
i n d u s tr y , in t h e f u t u r e .
R E F E R E N C E S
A mer i can So c i e t y fo r Me t a l s (1 9 8 1 ) . T h e M e t al s H a n d b o o k - - 1 9 81 E d i ti o n ,
A SM, Me t a l s Pa rk , O h i o .
A n s u i n i , F . J . & H u g u en i n , J . E . (1 9 7 8 ) . T h e d es i g n an d d ev e l o p men t o f afou l ing res i s t an t mar ine f i sh cage sys tem, Proc. l \Tnth W orld M aricu l ture
S o c i e~ Mee t i n g , p. 737.Blai r, A . , Cam pb el l , R. & G ran t , P. T. ( L9 8 2 ). A s u b m ers i b l e f is h cag e t h a t c an
b e r o t a t e d o n t h e s u r f a c e t o r e m o v e b i o f o u l i n g a n d f o r o t h e r p u r p o s e s .A q u a cu l t u r e , 29 , 177 .
Bo u ck , G . R . ( 1 9 81 ). E as i ly co n s t ru c t e d e co n o m i ca l s eaw a t e r i n t ak e an d s u p -p ly sys tem . J . Wor ld M ar icu lmr e Soc . , 12 , 51 .
Coburn , S . K . (ed . ) (1984) . C o r r o s io n S o u r ce B o o k , A m e r i c a n S o c i e t y f o rMeta l s , Meta l s Park , Ohio .
Dexter , S. C. (1979). Handbook o f Ocea t -zograph ic Eng ineer ing Mater ia l s ,
W i l ey In t e r s c i en ce , N ew Y o rk .
Dexter , S . C. & Culberson , C. H. (1980) . Global var i ab i l i ty o f na tu ra l sea-water . Materials t~epforrnance, 19, 16.
Fink. F. W. & Boyd, W. K. (1978). Corros ion o f meta l s in mar ine ep~viron-
men t s , M C I C R e p o r t N o . 7 8 - 3 7 , M e t a l s a n d C e r a m i c s I n f o r m a t i o n C e n -t er , Ba t te l le Co l u m b u s L ab o ra t o r i e s .
Hu guen in , J . E . & A nsu in i , F . J . (1975) . T he adv an tag es and l imi ta tions o fu s i n g co p p e r ma t e r i a l s i n mar i n e aq u acu l t u re , Proc. O cea ns '75 Con fer-ence, I E E E , p . 4 4 4 ,
H u g u en i n , J . E . & A n s u i n i , F . J . ( 1 9 7 8 ) . A r ev i ew o f t h e t ech n o l o g y an deco n o m i cs o f mar i n e f i sh cag e s y st ems . A q u a cu l t u r e , 15, 151.
La Q ue , F . L . (1975) . Ma r in e C o r r o s io n, J o h n W i l e y a n d S o n s , N e w Y o r k.
7/28/2019 Dexter 1986 Aquacultural-Engineering
http://slidepdf.com/reader/full/dexter-1986-aquacultural-engineering 14/14
346 S.C. Dexter
McVey, J. P. (ed.) (1983). H an db oo k of Maricul ture, ~bL 1 - CnlstaceanAquacul ture , C R C P r e ss , B o c a R a t o n , F lo r id a .
Ne u d eck e r , T . ( 1 9 8 2 ). N ew o y s te r o n -g ro w in g co n ta in e r f o r G e rm an m ar icu l -tu r e o p e ra t io n s . Aq uac ultural Engineering, 1, 193.
Pf is te r, V. A. & Ro m aire , R . P . (1983) . C atch e f f ic iency and re ten t ive ab il ityo f co m m erc ia l c r awf ish t r ap s . Aq ua culm ral Engineering, 2, 10 I .
S c h u m a c h e r , M . ( e d . ) ( 1 9 7 9 ) . Seawater Corros ion Ha ndb ook , N o v e s D a t aCo rp o ra t io n , Pa rk Rid g e , New Je rsey .
S t r e ich e r , M. A . ( 1 9 8 3 ) . An a ly s i s o f c r ev ice co r ro s io n d a ta f ro m two seawa te rexp osu re tes ts on s ta in less a lloys. Materials Performance, 22, 37.
Uhlig , H. H. & Revie , R. W. (1985) . Corrosion and Corrosion Control, 3 rded n , Wi ley In te r sc i en ce , New Yo rk .
W ise ly , B., Ho l l iday , J . E . & B enn et t , W. (1979) . E xpe r ime nta l de epw ater cu l -t u r e o f t h e S y d n e y R o c k O y s t e r ( Crassostrea Commercialis). Aquaculture.18, 191.
Wisely, B. , Hol l iday , J. E . & B enn et t , W. (1983) . E xpe r im enta l de epw ater cu l -tu r e o f t h e Sy d n ey Ro ck Oy s te r . VI . Co m m erc ia l o y s t e r cag e sy s t em s .Aquacul ture , 3 0 , 2 9 9 .