Q/
ORNL/ zms- 57 8 2
C o n t r a c t N o . W-7405-eng-26 METALS
The Corrosion Resis
G E W I C S D-fVLSPQN
of
J. R. Keiser, J. H. D
Date Published
316 Stainless S t e e l t a L i z n, and D. L. Manning
- April
1977
QPlCE This document contains information of a preliminary nature. It is subject to revision O F correction and therefore does not represent a final report.
.......................... ............................ ....................... ....................... ........................... ..............................
THE CORROSION RESISTANCE OF TYPE 396 STAINLESS STEEL TO Li2BeFb nd D. LI.M a
J . R. K e i s
orrela t e d
WI
A corrosion e as-recei
was observ
a l t further
blanket mat
t-
eactors w i l
a t i o n of n e u t h fabrication,
roduction of
nl.ess s t e e l
have r e s u l t
t-wall. mate
i o n f o r the
ket capable
are limite
CI
k e s material
b e a r i n g eompa
e
Because
may impose
t, s t r o n g c o n s i d e r a t i
1.
8
re
2 t h e s a l t s TdiF and BeF2 f o r a b l a n k e t of a f u s i o n r e a c t o r w i t h a s t a i n l e s s
s t e e l f i r s t wall.
The p u r p o s e of t h i s paper i s t o r e p o r t on t h e c o r r o s i o n
r e s i s t a n c e of t y p e 316 s t a i n l e s s s t e e l t o %i2BeFt+.
There are p o t e n t i a l problems a s s o c i a t e d w i t h t h e u s e of Li.F-BeF2 as a combined c o o l a n t - b r e e d i n g material.
These i n c l u d e t h e e f f e c t i v e
b r e e d i n g and t h e e f f i c i e n t r e c o v e r y of t r i t i u m , t h e e f f e c t on t h e salt:
of induced e l e c t r i c f i e l d s and o f t r a n s m u t a t i o n p r o d u c t s , and t h e compatib i l i t y of t h e s a l t w i t h t h e component i t c o n t a c t s .
The % r i t i . u m b r e e d i n g
r a t i o of t h i s s a l t i s n o t a s h i g h as i s t h a t of l i t h i u m , and some d e s i g n s would probably r e q u i r e t h e a d d i t i o n of a n e u t r o n mml..ti-plier such as beryllium. A n o t I i e ~problem coul-d b e t h e e l s c t ~ i f~i .e l d induced i n t h e c ~ n i d u c t i n g
s a l t when
i t
containment
f l o w s through t h e i n t e n s e magnetic f i e l d s r e q u i r e d f o r plasma T h i s p o t e n t i a l d i f f e r e n e e o c c u r r i n g hetwcen the salt and
t h e p i p e wall could b e g r e a t enough to e l e c t r o l y z e t h e salt and t h u s
cause s e v e r e c o r r o s i o n problems f o r the metallic c o n t a i n e r
e
Means OP
r e d u c i n g the e f f e c t of t h e induced f i e l d to a t o l e r a b l e level. have been s u g g e s t e d by Horneyer.
According t o him, e l e c t r o l y t i c c o r r o s i o n could
b e minimized by a v o i d i n g , a s much as p o s s i b l e , h i g h f l u i d v e l o c i t i e s
p e r p e n d i c u l a r t o t h e magnetic f i e l d .
Solution of t h i s problem w i l l
most probably have t o b e a r e s u l t of e n g i n e e r i n g d e s i g n changes r a t h e r
t h a n through a d d i t i o n s or m o d i f i c a t i o n s t o t h e s a l t ,
An a d d i t i o n a l c o n c e r n w i l l be t h e c o r r o s i v e e f f e c t of t h e salt on A s seen from t h e f r e e e n e r g i e s of formati-on in
the. s t a i n l e s s s t e e l .
T a b l e 1, L i F and BeF2 a r c much more s t a b l e t h a n t h e f l u o r i d e s of the major c o n s t i t u e n t s of s t a i n l e s s s t e e l , E e , Ni, and Cr.
Consequently,
no s i g n i f i c a n t r e a c t i o n of t h e s a l t components w i t h the m e t a l l i c c o n t a i n e r i s e x p e c t e d ; however,
i m p u r i t i e s i n the s a l t may cause c o r r o s i o n ,
t i e s expected t o b e p x c s c n t a r e HP and N i F 2 ,
Impuri-
and t h e s e w i l l c a u s e
r e a c t i o n s of the? t y p e :
2W. R. G r i m e s and S t a n l e y Carter, “MoPten Salt Blanket F l u i d s i n C o n t r o l l e d Ftasion R e a c t o r s pp 161--9(4 i n The Chemistry of Fusiovi TechnoZogy D. M. Gruen, e d . Ylenan P r e s s , New York, 1972.
3W. G. Horneyer
flTherrnal and Chemical A s p e c t s of t h e Thernnoniiclear
Blanket Problem,� T e c h n i c a l Report 4 3 5 , M. 1, T . Research L a b o r a t o r y of
E l e c t r o n i c s (1965).
,
3
T a b l e 1.
Foma
of F l u o r i d e
LiF
-448
-107
---e,10
---98
@rFz
-7 5
FeF2
--67
HF
-66
NiF2
-5 5
MOF6
-5 0
aC. F , B dynamics of M 15, 6 2 4 , P , C
MF2
+
Cr
ions of i m p u r i I l y b u t w i l l s1
o additional.
690801 (196’3)
e
ould be Ni o ntainer w i l l i m p u r i t i e s are
d t o t h e system, a a r e not exp
hours these
of a r e d u e t
e t h e corrosive
p u r i t i e s by s.
n e u t r o n react e of o x i d a n t s in t
The t r a n
r e p r e s e n t axlo e
elemental
C8
are expected
T h e reactions o f l i t h i u m ,
7LiF
4-
n
3
-f
H e -E. ,WF f n c
(3)
are, of c o u r s e , d e s i r e d became t h i s is thc means of p r o d u c i n g t h e
tritium f u e l .
Hocdcver, t h e TF p ~ o d ~ ecan d react w i t h t h e s t a i n l e s s
steel. c o n t a i n e r t o form metals f l u o r i d e s as shown i n ~ q (1). .
Transmutation of b e r y l l i u m c a n occur i n either of
6
The ,Ke undergoes beta decay w i t 1 1 an O.$-sec
~ W Q ways:
h a l f - l i f e yir?l.di.ng f a r t h e
r i g h t s i d e of Kquation 6,
‘The f l u o r i n e produced i n these beryll.ium t r a n s m u t a t i o n reac t i a n s
can react w i t h t h e s t a i n l e s s s t e e l c o n t a i n e r , c o n s t i t u t i n g a n o t h e r source of c o r r o s i o n .
The o t h e r t r a n s m u t a t i o n of t h e s a l t cornponents i s that o â‚Ź f l u o r i n e :
The
16
,N
-~undergoes
beta d e c a y w i t h a b o u t a 7-sec ha8f-l.ife
yielding
16
0,
which can be expected to r e a c t w i t h t h e containment metal c a u s i n g a d d i tional. c o r r o s i o n .
The net r e s u l t of all.. three tuansrnritation r e a c t i o n s
i s the product.i.on o f s u b s t a n c e s that w i l l cause ear-rosion of t h e s t a i n l e s s
5 s t e e l containment a l l o y nt and p o s s i b
One means of
p s o f clliminat-ing t
. T2
this c o r r o s i o n
This buffer
and a s o l u b l e f
01pre.s i n s a l t and can
One o t h e r problem a
tritium from the s a l t ,
in the form of Tz bec
b l y make i t e:
o b e c a p a b l e of (
cting with the f I t of the s a l t .
t h e u s e of LizBe
the recovery
8
er r e q u i r e d t o
ity of TF w i t h s t a i n l e s s s t e e l
the tritium f r
and tritium
me
r i f a CizBeFt, b sel,
n-
A great de
redox b u f f e r h a s been a
with molten s
as a r e s u l t of work f a r t h e
The f u e l salt
e n S a l t Breeder R e sed of L i F and E3
f e r t i l e mat
Cause of r e x . h preparation
i s a c t u a l l y fou
e containment
i n both t h e her t h e s e compo
of t h e f u e l t addition of
a w e serious
f an o x i d i z i
t sf material
containment
s i n some U ( I I
nd, converse1 of U ( I V ) to
u
11) r a t i o migh
t i c swings in th
a
se of t h i s b e n t i a 1 w i l l . take
6
reactor
6
t h a t c o u l d make t h e s a l t s u f f i c i e n t l y "reduciiig'l t o p r a c t i c a l l y e l i m i n a t e t h e c o r r o s i o n caused by i m p u r i t i e s and t r a n s m u t a t i o n p r o d u c t s is beryllium,
Typical. r e a c t i o n s c o u l d be:
To d e t e r m i n e t h e s u i t a b i l i t y o f s t a i n l e s s s t e e l f o r c o n t a i n i n g Li2BeF4, c o r r o s i o n measurements have been made w i t h sa1.t i n t h e a s - r e c e i v e d c a n d i t i o n and i n t h e r e d u c i n g c o n d i t i o n reached by a d d i n g b e r y l l i u m t o it EXPERIMENTAL METHODS
The e x p e r i m e n t a l assembly used f o r t h i s c o ~ r o s i o nwork, cal.l.ed
a thermal-convection
l o o p , i s shown in F i g . 1.
The l o o p p o r t i o n of
t h e assembly i s c o n s t r u c t e d of t y p c 316 s t a i n l e s s s t e e l t u b i n g and i s h e a t e d on t h e bottom and one v e r t i c l e s i d e .
Cooling t h e o t h e r t w o
s i d e s c a u s e s t h e m o l t e n s a l t i n t h e t u b i n g to f l o w because o f t h e v a r i a t i o n i n d e n s i t y of t h e salt w i t h temperature,
the s a l t i s about 1 m l m i n ,
The v e l . o c i t y of
Other i m p o r t a n t f e a t u r e s of t h e I S O ~ are
t h e removable c o r r o s i o n specimens and t h e accesses f o r i n s e r t i o n o f
e l e c t r o d e s f o r voltammetry measurements and f o r a d d i t i o n of material to t h e s a l t i n t h e I-oop o r removal of salt samples from t h e 100p.
S i x t e e n c o r r o s i o n specimens a r e
IISFZ.w ~ ,i t h
e i g h t i n s e r t e d i n the h o t
l e g (heated v e r t i c a l s e c t i o n ) and e i g h t i n t h e c o l d keg ( c o o l e d verticle section).
T h es e specimens a r e removed from. t h e l o o p e v e r y
500 h r f o r weighing and examination..
When t h e irivestigationas t o b e
made w i t h a p a r t i c u l a r s e t s f spcci.rnens a r e completeds s e v e r a l of the speci.mens a r e examined m e t a l l o g r a p h i c a l l y a n d , i f b7arwanted
electron m i c r o p r o b e .
w i t h the
These r e s u 1 . t ~reveal at which t e m p e r a t u r e w e i g h t
7
ORWL-DWG
68-598TR3
SAMPLER
1
FLUSH
TANK
1
I
TANK
ion t
8
g a i n s o r l o s s e s have occi.mred, and t h e microprobe examination i d e n t i f i e s which components of t h e specimen material. have been t r a n s p o r t e d ,
One of t h e most s i g n i f i c a n t improvements i n thermal-convec t i o n
l o o p operation h a s been the a p p l i c a t i o n of v o l t a n m e t r y
potential volta
e
Controlled-
e t r y i s a modern e l e c t r o c h e m i c a l t e c h n i q u e , w1-nicl-n
may be used t o examine t h e n a t u r e of an electrochcnaical r e a c t i o n i n d i f f e r e n t media, such as aqueous and nonaqueous s o l u t i o n s a n d highFor measurements i n mol.ten L ~ ~ B E F, Ithe .~
t e m p e r a t u r e salt systems *
electrodes c o n s i s t e d of the 1 . 0 0 ~i t s e l f , which s e r v e d as the c o u n t e r
e l e c t r o d e , and two i r i d i u m e l e c t r o d e s , which were the quasi-refermce
and working e l e c t r o d e s .
These e l e c t r o d e s were t y p i c a l l y 25-nm
l e n g t h s of 1.8-gage i r i d i u m wires welded t o 3-mm-OD (118-in.)
risers.
TIE
(1-in.)
ni-ckel
e1.ectrode area exposed t o the m e l t was 10 t o 20 m m 2 -
T R ~
voltammograms were ~ e c ~ r d eversiis d the i r i d i u m qziasli-reference e l e c t r o d e
(IK QRE), which i s p o i s e d a t t h e equi.l.ibrium p o t e n t i a l (Eeq ) of t h e
melt.
I n this mamner rel.atiwe chan.ges i n t h e o x i d a t i o n p o t e n t i a l . o f
t h e s a l t anid of t h e c o n c e n t r a t i o n of c e r t a i n i m p u r i t i e s and p r o d u c t s c a n be measured o n - l i n e .
COKI-OS~CIII
The e q u i l i b r i u m p o t e n t i a l o f t h e
s a l t is a measure of the tendency of t h e m e l t t o r e a c t w i t h o x i d i z a b l e
materials t h a t i t c o n t a c t s .
For m e l t s that a r e n o t p o i s e d by a redox
b u f f e r r e l a t i - v e changes i n t h e equiSi.briurr1 p s t e , n t i a l a r e c o n v e n i e n t l y observed by determining v o l . t a m e t r i c a l - I * yt h e potential d i f f e . r e n c e (AE)
between t h e m e l t e q u i l i b r i u m potential.. and t h e c a t h o d i c l i m i t of t h e
melt, which f o r E ~ ~ B ~ iFs Lthe , r e d w t i . o ~ nof b e r y P l i u m ( I 1 ) .
We d e f i n e
t h e c a t h o d i c l i m i t f o r these measurements a s t h e p o t e n t i a l a t 80 n ~ 4
c e l l current.
Other r e f e r e n c e markers may a l s o b e used as l o n g a s t h e
same c o n d i t i o n s a r e m a i n t a i n e d ,
A d e c r e a s e i n A&’, r e s u l t i n g i n a
c a t h o d i c s h t f t i n Eeq f o r example, indicates that t h e melt h a s beconlle l e s s o x i d i z i n g ; and a n i n c r e a s e i n AI7 i n d i c a t e s t h a ~t h e o p p o s i t e h a s occurred
A voltammetric s c a n t h a t shows t h e c a t h o d i c l i m i t r e l . a t i v e
t o Eeq i s i1l.usltrated i.n F i g . 2,
9
80
60
40
20
F i g , 2.
L i 2BeF4 i n I,
n Final L i m i t
r e d u c t i o n of
mmogram shown i n
h e i g h t s of t h e t w o waves
t o about 1 3 r e s u l t s of a v o l t a m m e t r i
due t o i r o n has
the same h e i g h t .
It is a
k potential of
eral weeks a f t e r that
le the chro
t o note t h a t cathodic shif
of t h e analyse
tential v o J t a
1.0
Fig. 4 *
Reduction. of Chromium in Loop NCL 31,
11
16 stainless
were f i r s t exp
"on loop cont
t a i n l e s s stee
190 ppm Fe, 60 e of 650째C and 500 and 1000 ans of v o l t a
,a
Following thi
.
It and a n e
beryllium
t a i n l e s s steel
These s p e c i
ng af t h e cond n a t i o n of t h e
h e f i r s t 500
t significant
d occurred, m
b e c a u s e of r e a c t i o n s with
.
F i g u r e 5 shows t
st and l o w e s t temp
12 weight l o s t by t h e h o t t e s t specimen d u r i n g t h e f i r s t 508 h r , i f w e assume t h a t t h e material w a s l o s t u n i f o r m l y f r o m t h e s u r â‚Ź a c e ,
c o r r e s p o n d s t o a c o r r o s i o n r a t e of a b o u t 10 ym ( 8 . 4 m i l ) p e r year.
ow ever, i n p r e v i o u s W Ow~i t P h s t a i n l e s s steel i n fluoricie salts
c o n t a i n i n g U F 4 as an o x i d i z i n g s p e c i e s , c o r r o s i o n d i d n o t r e s u l t i n uniform removal of material; r a t h e r , a porous s t r u c t u r e w a s found (Fig. 6 ) .
The 1000-hr e x p o s u r e of
OUT
specfinens w a s n o t l o n g e n ~ i ~ g l i
f o r e x t e n s i v e c o r r o s i o n t o occur, b u t F i g . 'I i n d i c a t e s that material w a s n o t removed u n i f o r m l y from t h e h o t t e r specimen.
Consequently, t h e
d e p t h of a t t a c k c a n b e expected t o exceed that c a l c u l a t e d f o r uniform m a t e r i a l removal.
Futhermore, i n t h e s a l t of a f u s i o n r e a c t o r , impuri-
t i e s would b e p ~ o d u c e d c o n t i n u o u s l y and i n s i g n i f i c a n t q u a n t i t i e s , and these i m p u r i t i c s would be m u r e o x i d i z i n g t h a n t h e i m p u r i t i e s found i n t h i s experimental s a l t .
Thus, c o r r o s i o n of s t a i n l e s s s t e e l i n a
L-usion r e a c t o r coiz'hd b e a s e r i o u s prohl-cm i f no e f f o r t i s made t o buffer the salt.
Y-'3 277
13 Y- 134722
. 7.
Type 316
TO e v a l u a t e t h e e f f e c t i2BeF4, a p i e c e o
wed t o r e a c t .
As s
cally, indicating
ts i n d i c a t e d t A new s e t of Examination w e i g h t chan
e w e i g h t changes f a smaller f o r t h e s
ecimens Expos
r on t h e c o x r o s s inserted i n t
e equilibrium made l e s s o x i d i t i o n t o be les ed t o t h i s r e
ter 500 and of d e t e c t i o n .
en temperatu he reducing s
h r than i n t F i g u r e 5 shows t h a t o t h e f i r s t 500-
ium w a s removed from
e t o the red
n the hottest
increasing we
f time.
Thi
c u r r e d becaus
urn w a s remov
the salt wer
urn and t h e sa
i v e l y more ox
n a low corr continuously o r a t least e of t y p e 316 s t a i n l .
a range acceptable f o r f
ium would have
If t h a t were done eF4 s a l t c o u l d b e
14 ORNL-DWG
-4.1 5
77-3822
- 1.10 >
0
v
d 5 -4.05
t-
z
w
)-.
B
t 5 J-.
-1.00
-0.95
<
-----e-
-0.90
0
t
Be ADDITION
20
4Q 60 TIME (days)
400
F i g . 8. V a r i a t i o n of the L i m i t f o r TAZBeFb S a l t i n NCL 3 1 . CONCTAJS IONS
The c o n c l u s i o n s t h a t can be drawn from t h i s r e s e a r c h are:
1.
The o x i d a t i o n p o t e n t i a l o f t h e s a l t can be c o n t r o l l e d by
a d d i t i o n s o f a r e d u c i n g metal, 2.
V o l t a m e t r i c t e c h n i q u e s p r o v i d e o n - l i n e measurement o f the
o x i d a t i o n p o t e n t i a l of t h e s a l t and t h e c o n c e n t r a t i ~of ~ ~i m p u r i t i e s i n the salt.
3.
High c o r r o s i o n r a t e s a r e encountered i n i t i a l . 1 - y i n s a l t w i t h
a normal i m p u r i t y c o n c e n t r a t i o n .
4.
The c o r r o s i o n r a t e of t y p e 316 s t a i n l e s s s t e e l i n Li2ReF1,
s a l t w a s reduced s i g n i f i c a n t l y by t h e d i r e c t a d d i t i o n of b e r y l l i u m metal t o t h e s a l t ,
95
T h e a u t h o r s would
Soar o p e r a t i n g t h e thermal-c * ing, S. Peter n o f t h e manu
e f f o r t s of E . S. Lawrence DJStefano and J . L. Scott 1 G 0 1 l . i h e ~f o r f i n a l e
17
IBUTION 1-2
.
3. 4. 5.
6. 7.
8.
11
.
12. 13.
16.
17 * 20
21. 22.
23. 23.
C e n t r a l Research L i Document Referen Laboratory Rec o r a t o r y Rec L Patent O f ?A. G . Alsmiller S . Bettis H. Bryant D. Cannon J. F. Clarke R, E. Clausing S I D. Clinton E. Cunningha a A* Dandl J. H. DeVan P. F r a a s sion Energy D sion Energy D A. Gabriel M. L , Grossbeck P . M. Haubenre M, R. Hill J. A. Horalc
. .
.
O f f ice
64, 65. 66. 67.
W.C.T.
J , S, W J. R, W
W. M, Wells
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WESTINGHOUSE ELECTRIC COKPQKATPON, R e s e a r c h and D e v e l o p m e n t C e n t e r , Yittsburg, PA
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