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I EVALUATION OF THE SPERRY ULTRASONIC I WHEEL INSPECTION UNIT I
R, W, Smith
AEC RESEARCH &
DEVELOPMENT REPORT
BNWL-1302
UC-37, Ins t ruments
EVALUATION OF THE SPERRY ULTRASONIC
WHEEL INSPECTION UNIT
R. W. Smith N. L. Johnson
Nondes t ruc t i ve T e s t i n g Department Systems and E l e c t r o n i c s D i v i s i o n
February 1970
BATTELLE MEMORIAL INSTITUTE PACIFIC NORTHWEST LABORATORIES
R i c h l and, Washington 99352
P r i n t e d i n the U n i t e d S ta tes o f America Avai 1 ab le from
Clear inghouse f o r Federal S c i e n t i f i c and Technica l I n fo rma t i on Na t i ona l Bureau o f Standards, U.S. Department o f Commerce
S p r i n g f i e l d , V i r g i n i a 221 51 P r i ce : P r i n t e d Copy $3.00; M i c r o f i c h e $0.65
EVALUATION OF THE SPERRY ULTRASONIC
WHEEL INSPECTION UNIT
R. W. Smith N. L. Johnson
ABSTRACT -
The Sperry wheel u l t r a s o n i c i n s p e c t i o n u n i t , Model 50D467, was
eva lua ted f o r remote s u r v e i l l a n c e o f the FFTF pressure vessel du r i ng
r e a c t o r shutdown. Faci 1 i t i e s f o r t e s t i n g t ransducers and t ransducer
components i n the FFTF environment were developed. A number o f m a t e r i a l s
were t e s t e d f o r use i n the p r o j e c t e d FFTF environment.
The Sperry wheel has t h ree drawbacks which make i t u n s u i t a b l e f o r
use i n the FFTF environment. These are: 1 ) i t cannot be used on a d r y
sur face, 2) a number of t he components w i l l n o t t o l e r a t e the p r o j e c t e d
environment, and 3) the acous t i c no i se l e v e l i s t o o h i g h f o r FFTF
su rve i 1 lance.
iii
19 Comparison of Transducer Backing Members: ( a ) Standard Sperry Wheel Transducer. (b) Lavi t e Backed Transducer. (c ) Sintered . . . . . . . . . . . . . . . . . . . . . . . . Metal BackingMember 28
20 A Closer View of the Transducer of Figure 19. Showing the . . . . . . . . . . . . . . . . . . . . . . . . . . . . Damping Rate 29
. . . . . . . 21 Ultrasonic Velocity of Sperry Fluid Versus Temperature 35
22 Ultrasonic Wave Velocity of Polyglycol E-200 Versus Temperature . . 36
. . . . . 23 Ultrasonic Velocity of Polyglycol P-400 Versus Temperature 37
24 Ul trasoni c Wave Velocity of Polyglycol P-1200 Versus Temperature . . 38
. . . . . 25 Ultrasonic Wave Velocity of Dowtherm A Versus Terr~perature 39
. . . 26 Ultrasonic Wave Velocity of Ambliflo H-149 Versus Temperature 40
27 Ul trasoni c Wave Veloci ty of Fl uorosi 1 i cone FS-1265 Fl uid Versus . . . . . . . . . . . . . . . . . . . . . . . . . . . . Temperature 41
. . . . 28 Ultrasonic Wave Velocity of Dow 710 Fluid Versus Temperature 42
29 Device Used to Measure Ultrasonic Velocities of Fluids a t High Temperatures . . . . . . . . . . . . . . . . . . . . . . . . . 43
30 Rectangular Samples for Compati bi l i ty Tests of Sil a s t i c 52 and 82 . 47
. . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Small Furnace 50
. . . . . . . . . . . . . . . . 32 Temperature Profile of Small Furnace 51
. . . . . . . . . . . . . . . . . . . . . . . . . . . 33 LargeFurnace 52
. . . . . . . . . . . . . . . . 34 Temperature Profile of Large Furnace 53
35 Dynamic Tester . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
. . . . . . . . . . . . . . . . . . . . . . . . . . . 36 Test Standards 55
EVALUATION OF THE SPERRY ULTRASONIC
WHEEL INSPECTION UNIT
R. W. Smith N. L. Johnson
INTRODUCTION
Our i n v e s t i g a t i o n s p e c i f i c a l l y i nvo l ves e v a l u a t i n g t h e Sperry
Model 50D467 h i g h temperature, u l t r a s o n i c wheel* (F i gu re 1) f o r t he
Fast F l ux Tes t F a c i l i t y (FFTF) i n - s e r v i c e i nspec t i on , s u b s t i t u t i n g
improved m a t e r i a l s where poss ib le , and recomnendi ng modi f i ca t i ons and
addi ti onal development i f deemed necessary. Th is u n i t was proposed
by westinghouse(' ) f o r i n s p e c t i o n o f vessel be1 t welds and p r imary
p i p i n g d u r i n g r e a c t o r shutdown. Ba t te l le -Nor thwes t was requested
t o eva lua te t h i s u n i t f o r FFTF s u r v e i l lance, (2,3) as the p ro jec ted
FFTF environment exceeds t h e design speci f i c a t i ons o f t he Sperry wheel.
Th i s r e p o r t out1 i n e s our eva lua t i on procedures, r e p o r t s t h e
eva lua t i on r e s u l t s and descr ibes t h e f a c i l i t i e s which we developed
t o t e s t t ransducers i n t he p r o j e c t e d FFTF environment.
* Autoniation I n d u s t r i e s , Danbury D i v i s i o n , Danbury Conn.
SUMMARY AND CONCLUSIONS
We eva lua ted t h e Sperry u l t r a s o n i c wheel i n s p e c t i o n u n i t which was
proposed f o r t h e remote i n s p e c t i o n o f t h e FFTF r e a c t o r vessel and p i p i n g
d u r i n g r e a c t o r shutdown. Tes t f a c i 1 i t i e s f o r e v a l u a t i n g t he u l t r a s o n i c
i n s p e c t i on u n i t were developed.
The h igh temperature Sperry u l t r a s o n i c wheel u n i t has t h r e e major
drawbacks which make i t unsu i t ab le f o r use i n t he p r o j e c t e d FFTF
env i ronmen t. These are :
The i n s p e c t i o n u n i t cannot be used on a d r y sur face.
A number o f t he components w i l l n o t t o l e r a t e t he p r o j e c t e d
FFTF environment. These i n c l u d e 1 ) a velumoid gasket, 2) a
t e f l o n i n s u l a t e d coax ia l cable, 3) a t e f l o n e l e c t r i c a l connector,
4) a t e f l o n back ing r i n g f o r t he a x l e seals , 5 ) t he ax le
seals , 6 ) t he cable sea l , 7) t he t ransducer component,
8) the coup lan t f l u i d , and 9 ) t h e s i l i c o n rubber t i r e .
The acous t i c no i se l e v e l i s above acceptable l i m i t s f o r
FFTF vessel su rve i 1 lance.
We demonstrated t h e f e a s i b i 1 i t y o f d r y coup1 i n g u l t r asound i n t o
s t a i n l e s s s t e e l . However, our t e s t s show t h a t a pressure o f t he o r d e r
o f 150 p s i i s necessary t o d r y couple u l t r asound from a 50 durometer
rubber i n t o 304 s t a i n l e s s s t e e l hav ing a 125 p in . su r face f i n i s h . It
i s n o t poss ib l e t o app ly more than 5 p s i w i t h t he Sperry wheel.
We were ab le t o f i n d improved m a t e r i a l s f o r a1 1 o f t he unsu i t ab le
components. We f e e l t h a t a l l o f these components, w i t h t he excep t ion o f
t h e t i r e , w i l l operate f o r a t l e a s t severa l hours a t 500 OF. Compared
t o p r o j e c t e d ope ra t i ng temperatures, we cons ider gamma r a d i a t i o n t o be
a minor problem. I n ou r op in ion , a f l u i d f i l l e d wheel i n s p e c t i o n u n i t
cou ld be operated i n t h e p r o j e c t e d FFTF environment by c o o l i n g t h e
coup l ing f l u i d below 400 OF. Our r e s u l t s i n d i c a t e t h a t , above 400 OF,
elastomers s u i t a b l e f o r use i n t he t i r e a re n o t compat ib le w i t h any o f
t he coup l ing f l u i d s which were tested.
Our recmmendat i ons f o r r e p l a c i n g the unsu i t ab le components are:
1 ) E l i m i n a t e the velumoid gasket, o r rep lace i t w i t h a meta l gasket.
2) S u b s t i t u t e s t a i n l e s s s t e e l sheathed cable w i t h ceramic i n s u l a t i o n f o r t he t e f l o n i n s u l a t e d cable.
3) Replace the t e f l o n e l e c t r i c a l connector w i t h a ceramic i n s u l a t e d connector.
4) Rep1 ace the t e f l o n backup r i n g wi t h a meta l r i n g .
5 ) S u b s t i t u t e commercial ly a v a i l a b l e V i t on ax le sea ls f o r t h e s tandard u-cup a x l e seals .
6) Use a V i t on o - r i n g t o seal around t he coax ia l cable.
7) Mod i fy the t ransducer component by us ing a ceramic back ing member t o rep lace the s tandard s l a t e - f i 1 l e d epoxy member.
8) Replace t he coup lan t f l u i d w i t h po lypropy lene oxide. A second choice f o r the coup lan t f l u i d would be Dow 710 f l u i d , a s i l i c o n e o i l . The po l y - propylene ox ide has lower u l t r a s o n i c a t t enua t i on and s l i g h t l y b e t t e r c m p a t i b i li ty w i t h the elastomers tested, w h i l e Dow 710 f l u i d outgases much l e s s due t o r a d i a t i o n .
9 ) Use S i l a s t i c 52, a Dow Corning s i l i c o n rubber, f o r t he t i r e . O f t he m a t e r i a l s tes ted , S i l a s t i c 52 i s themost s a t i s f a c t o r y i n terms o f the FFTF requirements. V i t o n o r F l u o r e l compounds have b e t t e r h i gh temper- a tu re c o m p a t i b i l i t y w i t h the coup lan t f l u i d s , however, they have h i g h halogen contents .
The acous t i c no i se i n t he Sperry wheel i s caused by r e f l e c t i o n s o f
the sound wave i n s i d e t h e wheel. Redesign o f t he wheel, t a k i n g s teps t o
min imize these r e f l e c t i o n s , cou ld s u b s t a n t i a l l y reduce t h i s no ise.
I t i t s p resen t form, the Sperry wheel i s n o t s u i t a b l e f o r the s u r v e i l -
l ance o f the FFTF r e a c t o r vessel , and a ma jo r redes ign o f the wheel would
be r e q u i r e d t o make i t useable.
I t i s f e l t t h a t a d d i t i o n a l development work should eva lua te o t h e r
t ransducer concepts as w e l l as the f l u i d f i l l e d wheel t ransducer , w i t h
cons ide ra t i on o f t h e FFTF we ld i n s p e c t i o n requirements such as we ld conf ig-
u r a t i ons , d e f e c t s i z e and o r i e n t a t i o n , t ransducer p o s i t i o n i n g capabi 1 i ty , e t c . A d d i t i o n a l t ransducer c o n f i g u r a t i o n s which cou ld be cons idered are:
1. S o l i d wedge t ransducer
2. S o l i d wheel t ransducer
3. F l u i d f i l l e d wedge
EVALUATION
The projected FFTF environment requires tha t an inspection unit 5 function properly for an extended period in a 10 R / h r gamma f ie ld a t
500 O F . The unit must be operated remotely and can present no danger of
halogen contamination which could induce s t ress corrosion cracking i n the
vessel. Also, no residue can be l e f t a f t e r the inspection; therefore, the
inspecti on uni t cannot be ul trasoni cal ly coupled to the pressure vessel
with a f luid. We evaluated the Sperry wheel, which was suggested for
this application by Westinghouse, on the basis of the above requirements.
These requirements exceed the design specifications for the Sperry wheel.
The high temperature Sperry wheel inspection unit , Model 50D467, i s
essentially an ultrasonic transducer (2.25 MHz nominal frequency) mounted
inside a f luid f i l l e d silicone rubber t i r e . The transducer i s mounted on
the axle of the wheel and i s held in a fixed position relat ive to the
t e s t surface while the wheel rotates freely. The transducer i s coupled
t o the t i r e with a mixture containing 50% water and 50% ethylene glycol.
In operation the wheel i s rolled over the area t o be inspected. Normally,
water i s used t o ultrasonically couple the t i r e with the t e s t surface and
t o cool the unit. The wheel specifications are given in Appendix A .
The beam incident angle of the transducer can be varied in both the
side and the forward/reverse directions. The side angle i s variable from
0" to 50" and the forward/reverse angle i s variable from -15" to +15".
Both angles are measured from perpendicular to the t e s t surface. The
commonly used mode of testing with the Sperry wheel i s shear wave inspec-
tion. The shear wave i s generated in the t e s t specimen by mode conversion
of the longitudinal wave a t the specimen surface. The refracted wave
angle in the t e s t specimen i s determined by the ultrasonic velocities of
the couplant f luid and the t e s t material, according to Snell ' s law.
Incident angles above the c r i t i ca l angle for longitudinal waves are
comnonly used since then only shear waves will be present in the specimen,
making t e s t resul ts easier to interpret.
TEST PROCEDURES
The Sperry wheel t ransducer was t e s t e d f o r accuracy and s e n s i t i v i t y ,
and the i n d i v i d u a l wheel components were eva lua ted f o r s e r v i c e i n t h e
p r o j e c t e d environment. Recommendations were made f o r replacement
ma te r i a l s . The i n v e s t i a a t i o n procedure i s summarized be1 ow.
1. Procure the Sperry wheel , Model 50D467, and develop the
f a c i 1 i ti es r e q u i r e d t o t e s t and eva l ua te t h i s t ransducer
f o r the p r o j e c t e d environment.
2. Conduct a 1 i t e r a t u r e search f o r t he e f f e c t s o f r a d i a t i o n and
temperature on m a t e r i a l s and components used i n t he wheel.
3. Evaluate t h e wheel components f o r s e r v i c e i n t h e p r o j e c t e d
environment on t he bas i s o f i n f o r m a t i o n i n t he l i t e r a t u r e .
4. Tes t t he wheel components and rep lace inadequate components
wi t h s a t i s f a c t o r y s u b s t i t u t e s .
5. Design and f a b r i c a t e a s tandard t e s t b l o c k t o t e s t t h e
sensi ti v i ty o f t he u l t r a s o n i c wheel u n i t .
6. Determine the s e n s i t i v i t y o f t h e u l t r a s o n i c wheel u n i t .
7. Determine the accuracy and reproduc i b i li t y o f t he u l t r a s o n i c
wheel un i t.
8. Determine the e f f e c t of specimen sur face f i n i s h on t he
s e n s i t i v i t y o f the u l t r a s o n i c wheel u n i t .
9. Tes t the u l t r a s o n i c wheel u n i t a t 500 O F .
The i n v e s t i g a t i o n proceeded i n t h i s sequence, genera l l y . I tem 9 was
n o t completed because t he wheel u n i t d i d n o t meet t he requirements f o r
t h i s a p p l i c a t i o n . The major problems w i t h the wheel u n i t i n i t s p resen t
fo rm are t h a t i t wi 11 n o t operate i n a 500 O F environment, i t cannot be
used on a d r y sur face , and i t has a h i g h no i se l e v e l which makes i t
d i f f i c u l t t o use e f f e c t i v e l y .
A d e t a i l e d account o f the eva lua t i on procedures i s i nc l uded i n t he
f o l l ow ing sec t ions . The t o p i c s are n o t d i scussed i n t he ch rono log i ca l
o rde r o f the i n v e s t i g a t i o n 1 i s t e d above, b u t r a t h e r i n t h e i r approximate
o rde r o f importance.
TRANSDUCER SENSITIVITY
The response o f t h e Sperry wheel u n i t t o t h e d e f e c t s d r i l l e d v e r t i -
c a l l y i n t o t h e 32 u i n . su r f ace t e s t b l ock (see T e s t F a c i l i t i e s s e c t i o n )
i s i l l u s t r a t e d by F igures 2 and 3. The t e s t setups f o r these measurements
a re shown i n F igure 4. The Sper ry wheel was wate r coupled t o t h e t e s t
su r f ace and d r i v e n by a Nor tec NDT-100 pu l se r . A 45" (approx imate ly )
shear wave was generated i n t h e s t a i n l e s s s t e e l . F i gu re 4a shows t h e
t e s t c o n f i g u r a t i o n f o r F i gu re 2. I n t h i s t e s t the u l t r asound was
r e f l e c t e d o f f t h e back su r f ace o f t h e t e s t p l a t e once be fo re reach ing t h e
t e s t ho le . The u l t r a s o n i c pa th l e n g t h was about 5 i n . one way i n t h e
s t a i n l e s s s t e e l . Fo r t h e r e s u l t s shown i n F i gu re 3 t h e sound was
r e f l e c t e d o f f t h e back su r f ace t w i c e (F i gu re 4b), t r a v e l i n g about 10 i n .
one way i n t he s t a i n l e s s s t e e l . F i gu re 4c i s a photograph o f t he t e s t
setup.
The n o i s e i n t h e Sperry wheel i s caused by r e f l e c t i o n s i n s i d e t he
wheel and makes t h e u n i t d i f f i c u l t t o use e f f e c t i v e l y . I t would be
d i f f i c u l t t o d e t e c t t h e 1/16 i n . d iameter t e s t h o l e if we d i d n o t know
1 ) t h a t i t was t h e r e and 2 ) i t s exac t l o c a t i o n . A f u t u r e t ransducer
des ign u t i l i z i n g t h e wheel concept should min imize t h i s no ise.
Attempts t o use t h e Sper ry wheel on a d r y su r f ace were n o t success-
f u l . We cou ld n o t app ly enough pressure t o g e t good a c o u s t i c coup l i ng
between t h e t i r e and t he t e s t b lock. However, us i ng a convent iona l 5 MHz
PZT t ransducer and a f l a t p i ece o f s i l i c o n rubber we were ab le t o couple
sound q u i t e e f f e c t i v e l y i n t o a 250 p i n . su r f ace (see F igu re 5) . No l i q u i d
coup1 a n t was necessary. The 1 / 4 i n , d iameter 1 ongi t u d i n a l t ransducer was
pressed a g a i n s t t h e su r f ace o f t h e s t a i n l e s s s t e e l t e s t b l ock w i t h a 1/16
i n . t h i c k p iece of s i l i c o n rubber sandwiched between t he t ransducer and
t he block. F igures 6a and 6b show the response t o t he f l a t bot tom o f a
118 i n . d iameter and a 1/16 i n . d iameter t e s t ho le , r e s p e c t i v e l y . The
t ransducer i s " l o o k i n g " through 1-112 i n . o f s t a i n l e s s s t e e l . A pressure
P R E S S U R E , p s i g
3 2 rms S U R F A C E - S I L A S T I C 5 2
S I L A S T I C 5 2
I I I
FIGURE 7. U l t r a s o n i c Coupl ing Versus Pressure f o r S i l a s t i c 52 and S i l a s t i c 82 S i 1 i cone rubbers
ampl i tudes o f these curves a re a t t r i b u t e d p r i m a r i l y t o t ransducer a l i g n -
ment which was a problem du r i ng t he experiment. A t ransducer m i s a l i g n -
ment o f 1.25" reduces the r e t u r n s i g n a l by 30%. F igure 8 shows t he
coupl ing/pressure r e l a t i o n s h i p f o r S i l a s t i c 52 on a 63 u i n . sur face.
Several curves were ob ta ined f o r each b l o c k a t d i f f e r e n t l o c a t i o n s on
t he b locks. The d i f f e r e n c e s a re a t t r i b u t e d t o t ransducer a l ignment and
-
-
S I L A S T I C 5 2 5 0 D U R O M E T E R ON 6 3 p I N . S U R F A C E
1 I
P R E S S U R E , p s i g
FIGURE 8. Dry Coupl ing U l t rasound f rom S i l a s t i c 52 i n t o a 63 win. S t a i n l e s s S tee l Sur face
t o l o c a l v a r i a t i o n s i n t h e su r f ace f i n i s h . The h i g h and low curves f o r
bo th S i l a s t i c 82 and 52 on a 250 p in . su r f ace were compared i n F igu re 9.
Note t h a t S i l a s t i c 52 couples a t about 150 p s i , w h i l e t h e knee i n t h e
curves f o r S i 1 as ti c 82 a re never reached.
- Y-x-x- X
S I L A S T I C 5 2 2 5 0 rms
-
S I L A S T I C 8 2 2 5 0 rms
I I 1 0 0 2 0 0
P R E S S U R E , p s i g
FIGURE 9. Comparison o f t h e U l t r a s o n i c Coupl ing P rope r t i es o f S i l a s t i c 52 and S i l a s t i c 82
The pressure r e q u i r e d t o d r y couple u l t r asound across the s t a i n l e s s
s t e e l / s i li cone rubber i n t e r f a c e was determined w i t h the apparatus shown i n
F igure 10. Th i s dev ice was clamped t o t he t e s t b l ock w i t h the s i l i c o n e
rubber touch ing the sur face o f t he t e s t b lock . The t ransducer was coupled
t o the s i l i c o n e rubber w i t h wate r o r a h i g h temperature f l u i d , and a i r
S U R E
FIGURE 10. Devi ce f o r Measuring U l t r a s o n i c Coupl ing Pressure
pressure above t h e f l u i d f o r c e d the s i l i c o n e rubber a g a i n s t t he t e s t b lock .
The pressure o f t he s i l i c o n rubber a g a i n s t t h e t e s t b l o c k was v a r i e d by
a d j u s t i n g t h e a i r pressure above the f l u i d . A Wallace and T ie rnan 0-300
p s i abso lu te pressure gauge measured t h e a i r pressure.
To measure the degree o f coup l i ng between t h e s i l i c o n e rubber and t h e
t e s t b lock , t h e t r ansduce r was opera ted pulse-echo, and t he amp l i tude o f
the f i r s t r e f l e c t i o n o f f t he back su r f ace was noted. F i gu re 11 shows t he
response o f a 5 MHz 1 / 4 i n . d iameter PZT-5 t ransducer operated i n t h i s t e s t
setup. The i m p o r t a n t r e f l e c t i o n s are i nd i ca ted on t he photograph.
I N C I D E V A R I
0 "
/ ( a ) T E S T P I E C E
0 "
15"- 1 5 '
E A M
1
FIGURE 12. Beam Incident Angle Adjustments (a ) Side Angle, (b ) Forward/Reverse Angle
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echo, and the sound was r e f l e c t e d o f f the 1/2 in . d iameter b a l l bear ing .
The t ransducer was mounted a t the cen te r o f the accu ra te l y c a l i b r a t e d
D r i n g , w i t h t he b a l l bear ing mounted on the D r i n g . A f t e r s e t t i n g the
b a l l a t some angle, the r e t u r n s i g n a l was peaked by a d j u s t i n g t h e
t ransducer angle.
Inaccurac ies i n the I n s p e c t i on Angle
A temperature change i n the u l t r a s o n i c coup l ing f l u i d used i n an
u l t r a s o n i c wheel u n i t can cause a s h i f t i n the i n s p e c t i o n angle i n the
t e s t specimen i f the u l t r a s o n i c v e l o c i t y o f the coup lan t f l u i d i s temper-
a tu re dependent. Most f l u i d s do have an u l t r a s o n i c v e l o c i t y which
decreases w i t h temperature. It i s t h e r e f o r e necessary t o know the
temperature dependence o f t he v e l o c i t y t o c o r r e c t f o r t h i s s h i f t . The
magnitude o f t h i s temperature- induced beam s h i f t was c a l c u l a t e d and i s
shown i n F igure 16. I iere, the inc rease i n the shear wave angle i n s t a i n -
l e s s s t e e l induced by a 10 O F i nc rease i n the coup lan t temperature i s
p l o t t e d as a f u n c t i o n o f the shear wave angle i n the s t a i n l e s s s t e e l . A
cons tan t shear wave v e l o c i t y i n the s t a i n l e s s s t e e l and a temperature o f
500 O F i s assumed, and t h e v e l o c i t y versus temperature curve o f one o f
the p o t e n t i a l coup l i ng f l u i d s i s used. Th i s curve i n d i c a t e s t h a t a
temperature induced s h i f t i n the beam angle can be s i g n i f i c a n t ,
p a r t i c u l a r l y a t l a r g e i n s p e c t i on angles.
The u l t r a s o n i c v e l o c i t y o f t he coup lan t f l u i d a l s o a f f e c t s the
magnitude o f the i n s p e c t i on angle e r r o r caused by mechanical t o l e rance
i n the system. The p o s s i b l e e r r o r i n the i n s p e c t i o n angle i s l a r g e r w i t h
a low v e l o c i t y f l u i d than w i t h a h i g h e r v e l o c i t y f l u i d . Th i s e r r o r was
c a l c u l a t e d and i s shown i n F igure 17 where the angu la r beam s h i f t o f a
shear wave i n s t a i n l e s s s t e e l caused by a lo s h i f t i n t he i n c i d e n t beam
i s p l o t t e d as a f u n c t i o n o f t he angle o f t he shear wave i n the s t a i n l e s s .
Th is curve i s e s s e n t i a l l y the e r r o r i n the shear wave angle caused by a
lo e r r o r i n the i n c i d e n t wave. Two curves a re shown, one f o r a f l u i d
v e l o c i t y o f 0.030 in . /psec and one f o r a f l u i d v e l o c i t y o f 0,060 i n . / ~ s e c .
The e r r o r increases w i t h decreasing u l t r a s o n i c v e l o c i t y and w i t h l a r g e
i n s p e c t i on angles.
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2 0 " 4 0 " 6 0 "
A N G L E OF U L T R A S O U N D I N S T E E L
FIGURE 16. Change i n the Angle o f a Shear Wave i n S ta in less S tee l Caused by a 10 O F Change i n Temperature o f Couplant
2 0 " 4 0 " 6 0 "
A N G L E O F U L T R A S O U N D I N S T E E L
FIGURE 17. Change i n the Shear Wave Angle i n S ta in less Stee l Caused by a 1 O F Change i n the I n c i d e n t Angle
Thus, the u l t r a s o n i c v e l o c i t y o f the coup l ing f l u i d used i n t he u l t r a -
son i c wheel u n i t has a s i g n i f i c a n t e f f e c t on the accuracy o f the u n i t .
Because o f t h i s , the v e l o c i t y o f any p o t e n t i a l coup l ing f l u i d was measured
as a f u n c t i o n o f the f l u i d temperature. Th is measurement i s discussed i n
a l a t e r s e c t i o n on F l u i d s and Elastomers.
TRANSDUCER COMPONENTS
Transducer components were i n i t i a l l y eva lua ted on t he bas i s of a
1 i t e r a t u r e search and manufacturers ' speci f i c a t i ons. Ques t ionab le p a r t s
were then tested, and recommendations were made f o r rep1 acement ma te r i a1 s
which would operate s a t i s f a c t o r i l y i n t h e p r o j e c t e d environment.
We conducted a l i t e r a t u r e search t o suppor t t h e e v a l u a t i o n e f f o r t .
We ob ta ined i n f o r m a t i o n about r a d i a t i o n and temperature to le rances of
m a t e r i a l s used i n the wheel components, s p e c i f i c a l l y t he o rgan ic m a t e r i a l s
and p i e z o e l e c t r i c c r y s t a l s .
For the organi c m a t e r i a1 s the most severe env i ronmental parameter
i s the 500 OF temperature. Most o f the o rgan ic m a t e r i a l s can t o l e r a t e
the p r o j e c t e d r a d i a t i o n l e v e l much l onge r than they w i l l t o l e r a t e the h i g h
temperature. I n f o r m a t i on about t he u l t r a s o n i c p r o p e r t i e s o f o rgan ic
m a t e r i a l s a t h i gh temperature and about the c o m p a t i b i l i t y o f the components
a t h i gh temperature i s g e n e r a l l y n o t a v a i l a b l e i n the l i t e r a t u r e o r f rom
the manufacturer. Consequently, a s i g n i f i c a n t t e s t i n g e f f o r t was requi red.
Rad ia t ion damage t o p i e z o e l e c t r i c c r y s t a l s and ceramics has n o t been
e x t e n s i v e l y s tud ied , and i n f o r m a t i o n i n the l i t e r a t u r e i s n o t conc lus ive.
From a p r e l i m i n a r y r e p o r t by ~ e s s e l m a n ' ~ ) i n 1963, i t appears t h a t PZT i s
r e l a t i v e l y r a d i a t i o n r e s i s t a n t and a t t he p r o j e c t e d dose l e v e l s , r a d i a t i o n
damage would n o t be a problem. We conducted a t e s t (descr ibed under
Transducer) which a l s o i n d i c a t e s t h a t r a d i a t i o n damage t o the PZT-5 a c t i v e
element i n the u l t r a s o n i c wheel u n i t w i l l be n e g l i g i b l e .
Component Eva1 u a t i on
The u l t r a s o n i c wheel u n i t was disassembled, and the i n d i v i d u a l t rans-
ducer components were eva lua ted f o r use i n the FFTF environment. Our
eva lua t i on was based on i n fo rma t i on ob ta ined i n a l i t e r a t u r e search, on
i n f o r m a t i o n s u p p l i e d by Sperry and o t h e r manufacturers , and on ou r t e s t
r e s u l t s . The most severe ope ra t i ng parameter proved t o be the 500 OF
ope ra t i ng temperature. Most o f the components had enough r a d i a t i o n
t o l e rance , and we were ab le t o f i n d s a t i s f a c t o r y s u b s t i t u t e s f o r those
t h a t d i d no t .
The s tandard wheel components whi ch a re unsa t i s f a c t o r y f o r t h i s
a p p l i c a t i o n a re (see F igu re 18) : 1 ) a velumoid gasket, 2) a t e f l o n
i n s u l a t e d coax ia l cab le , 3) a t e f l o n e l e c t r i c a l connector, 4) a t e f l o n
backup r i n g f o r the u-cup a x l e sea ls , 5 ) the u-cup a x l e sea ls , 6 ) an o-
r i n g used t o sea l around t h e coax ia l cab le ( n o t shown), 7) the t ransducer
component, 8 ) the s tandard f l u i d coup lan t used i n s i d e the t i r e , and
9 ) s i l i c o n rubber t i r e . We can recommend repladements which wi 11 t o l e r a t e
t he p r o j e c t e d environment f o r a1 1 o f these components excep t t h e s i l i c o n e
rubber t i r e , and we can recommend an improved t i r e m a t e r i a l which w i l l
t o l e r a t e t h e environment i f c o o l i n g i s p rov i ded f o r t h e coup l i ng f l u i d .
The s p e c i f i c p a r t s a re eva lua ted i n the f o l l o w i n g paragraphs. D e t a i l e d
t e s t i n g and e v a l u a t i o n o f e lastomers and coup l i ng f l u i d s i s d iscussed i n
a separate sec t i on , F l u i d s and Elastomers.
Velumoid Gasket
The velumoid gasket has a maximum use fu l temperature o f 300 OF. A t
500 OF t h e m a t e r i a l chars and q u i c k l y becomes useless. Th i s gaske t serves
no impo r tan t f u n c t i o n i f the t ransducer i s used i n a d r y environment. It
cou ld be rep laced w i t h a meta l gasket, however.
T e f l o n Par ts
The t e f l o n p a r t s , namely the c o a x i a l cab le , the backup r i n g f o r the
a x l e sea l , and t he e l e c t r i c a l connector w i l l s t and t h e 500 OF temperature.
However, the p r o j e c t e d gamma r a d i a t i o n l e v e l w i l l q u i c k l y cause them t o
f a i 1. A s u i t a b l e replacement f o r t he s tandard cab le i s a s t a i n l e s s s t e e l
sheathed c o a x i a l cab le , s i m i l a r t o t h e type manufactured by E l e c t r o n i c
Spec ia l t i e s . A c o i l o f t h i s cab le would a l l o w repeated ad justment o f t he
t ransducer angle. Standard h i gh temperature cab le connectors, s u p p l i e d
de r were observed p e r i o d i c a l l y . No s i g n i f i c a n t change was no ted a f t e r a 8 5 t o t a l dose o f 4 x 10 R. The dose r a t e was 5 x 10 R/hr.
Since the Cu r i e temperature o f PZT-5A i s about 690 OF, t h i s m a t e r i a l
can w i t h s t a n d the 500 OF temperature s a t i s f a c t o r i l y . We operated PZT-5A
t ransducers a t 500 "F t o measure t he u l t r a s o n i c v e l o c i t y o f t h e coup l i ng
f l u i d s , as d iscussed i n t h e s e c t i o n on Elastomers and F lu i ds .
The l ead -z i r cona te l e a d - t i t a n a t e (PZT-5) p i e z o e l e c t r i c ceramic used
as the a c t i v e t ransducer element i n t he Sperry u l t r a s o n i c wheel u n i t i s
s a t i s f a c t o r y ; however, the m a t e r i a l used t o back the t ransducer (Hysol
type I s l a t e f i l l e d epoxy) w i l l n o t w i t h s t a n d temperatures above 250 OF.
Therefore, the t ransducer was redesigned.
Impo r tan t requi rements f o r the t ransducer back ing member are t h a t i t
w i t hs tand t he 500 OF temperature, t h a t i t be compat ib le w i t h the coup l i ng
f l u i d , and t h a t i t be h i gh l y a t t e n u a t i v e t o u l t rasound . For t h i s app l i ca -
t i o n , i t i s a l s o d e s i r a b l e t h a t t he a c o u s t i c impedance o f t h e back ing
member match as c l o s e l y as p o s s i b l e the impedance o f t h e PZT-5 a c t i v e
element, t o m in im ize t ransducer r i n g i n g .
Three m a t e r i a l s were t e s t e d as p o s s i b l e replacements f o r the s tandard
t ransducer back ing member used i n t he Sperry wheel. These m a t e r i a l s were
1) s i n t e r e d me ta l , 2) l a v i t e , a h i gh temperature ceramic, and 3) po ly im ide .
The l a v i t e back ing members were the most s a t i s f a c t o r y , as t he po l y im ide
samples cracked on hea t i ng , and the s i n t e r e d meta ls d i d n o t have a
s u f f i c i e n t l y h i g h a t t e n u a t i o n t o u l t rasound .
The l a v i t e back ing members were machined o u t o f t h e ceramic and then
f i r e d t o harden them. The t ransducer a c t i v e element was fas tened t o t he
back ing member w i t h Sauerei sen cement.
The s i n t e r e d meta l back ing members were made by s i n t e r i n g m i x tu res o f
powdered meta ls and i n s u l a t o r s toge ther . M i x tu res o f a1 uminum, tungs ten
and s i l i c o n d i o x i d e i n a copper m a t r i x were used. It i s p o s s i b l e t o a d j u s t
t he a c o u s t i c impedance w i t h t h i s technique by va r y i ng t he re1 a t i v e amounts
of tne component m a t e r i a l s . Table 1 shows the acous t i c impedances f o r a
group o f m a t e r i a l s prepared by s i n t e r i n g . The acous t i c impedances range 5 5 2 f rom 33 x 10 t o 55 x 10 g/cm -sec. The u l t r a s o n i c a t t e n u a t i o n f o r these
m a t e r i a l s was t o o low, however.
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TABLE 1. Acoust i c Impedance o f S i n t e r e d Backing Ma te r i a1
Long i t ud ina l S i n t e r e d P a r t i c l e Acous t i c Impedance,
Metal Formulat ion Size, p g/cm2-sec
50% Copper 44 20% Tungsten 44-54 15% A1 umi n um 10-44 15% S i 1 i con d i ox ide 10
70% Copper 4 4 10% Tungsten 44-54 10% A1 umi n um 10-44 10% S i l i c o n d i o x i d e 10
75% Copper 25% Tungsten
85% Copper 15% Tungsten
90% Copper 4 4 10% S i 1 i con d i o x i de 10
80% Copper 4 4 20% S i l i c o n d i o x i d e 10 85% Copper 44 15% S i l i c o n d i o x i d e 50-200
BNWL- 1 302
Elastomer Pa r t s
The e lastomer components used i n the Sperry wheel a re two Buna N u-
cup pack ing sea ls used t o sea l around t he ax les, A Buna N o - r i n g which
sea ls around the coax ia l cable, and t he s i l i c o n e rubber (Union Carbide
K1305B) ti re. Since t he maximum recommended s e r v i c e temperature f o r
Buna N compounds i s 250 OF, t h i s m a t e r i a l w i l l n o t w i t h s t a n d the p r o j e c t e d
environment. The s tandard t i r e i s n o t compat ib le w i t h coup lan t f l u i d s a t
500 OF. S u i t a b l e replacements f o r these m a t e r i a l s a re d iscussed i n the
s e c t i o n on F l u i d s and Elastomers.
Sperry F l u i d
A m i x tu re o f 50% water and 50% e thy lene g l y c o l (Sperry f l u i d ) i s used
t o f i l l the s i l i c o n e rubber t i r e . Th i s m ix tu re u l t r a s o n i c a l l y couples t he
t ransducer w i t h t he ti re. Sperry f l u i d b o i 1s a t a temperature under 300 OF
and i s , there fo re , n o t a s u i t a b l e f l u i d f o r t h i s app l i ca t i on . Replacements
f o r the Sperry f l u i d are d iscussed i n the s e c t i o n on F l u i d s and Elastomers.
F l u i d s and Elastomers
As no ted above, the s tandard e las tomer components and t h e coup1 i n g
f l u i d are n o t s u i t a b l e f o r ope ra t i on a t 500 OF. We conducted a market
survey and t e s t i n g program t o f i n d s a t i s f a c t o r y s u b s t i t u t e s f o r these
ma te r i a l s . I n t h i s way we were ab le t o 1 ) determine the f e a s i b i l i t y o f
mod i f y i ng the Sperry wheel f rom a m a t e r i a l s s tandpo in t , and 2 ) eva lua te
a number o f m a t e r i a l s f o r use i n o t h e r t ransducer con f i gu ra t i ons .
C r i t e r i a f o r S e l e c t i o n o f F l u i d s and Elastomers
Elastomers f o r use i n an u l t r a s o n i c wheel i n s p e c t i o n u n i t f o r t h i s
a p p l i c a t i o n must have 1 ) c o m p a t i b i l i t y w i t h any coup lan t f l u i d used,
2) h i g h res i s tance t o gamma r a d i a t i o n , and 3) the a b i l i t y t o t o l e r a t e
temperatures up t o 500 O F . I n a d d i t i o n , e lastomers f o r the t i r e shou ld
have 4) the a b i l i t y t o conform i n t i m a t e l y t o a 250 p in . su r face f i n i s h ,
5 ) low halogen con ten t , and 6 ) low a t t e n u a t i o n t o u l t rasound.
Important properties of an ultrasonic couplant f luid for this applica- tion are 1 ) thermal s t ab i l i t y and low vapor pressure a t 500 O F or above,
2 ) low attenuation to ultrasound, 3 ) compatibility w i t h the other trans- ducer components, 4) low halogen content, and 5) an ultrasonic velocity of 0.030 in./psec or higher a t 500 O F . Most of these properties for both the fluids and the elastomers are not specified by the manufacturer or discussed i n the l i terature . Consequently, an extensive testing e f fo r t was required to determine these unknown parameters.
Market Survey
An extensive market survey was conducted to find elastomers and fluids suitable for use in a fluid-fi l led ultrasonic inspection u n i t . Manufactur- e rs of fluids and elastomers were asked to recomnend materials which would meet the requi rements outlined above. These manufacturers included a number of companies engaged in compounding elastomers for speci a1 appl i ca- t ions, as well as manufacturers of base polymers.
E 1 as tomers
The 500 O F temperature requi rernent eliminates most e l as tomers from further consideration. The only elastomers which are generally used a t this temperature are fluorocarbon rubbers (Vi ton, Fl uorel ) , f l uorosi 1 i cone rubbers, and silicone rubbers. Even these materials are generally not recommended for long term use a t 500 O F with organic fluids. The low halogen content required for the t i re eliminated the fluorocarbon and f l uorosilicone rubbers from consideration as t i r e materials (they should be useful seal materials, however).
Samples of the materials which were recommended by manufacturers were obtained and tested for this application along w i t h the standard elastomers used in the ultrasonic wheel unit. These materials include:
1. Vi ton A , a fluorocarbon , Parker compound 77-545
2. S i l i cone rubbersparker compound S604-7
3. S i las t ic 52, a silicone rubber,Dow Corning
4. S i las t ic 82, a silicone rubber,Dow Coming
5. S i l i c o n e rubber,Union Carbide K1305B, t h e m a t e r i a l used
i n the s tandard h i g h temperature t i r e
6. Buna N rubber, the m a t e r i a l used i n the s tandard seals .
A1 1 o f these elastomers were t e s t e d f o r compat ibi 1 i ty w i t h the
coup lan t f l u i d s a t h i gh temperature, and the halogen con ten t o f the
s i 1 i cone rubbers was determined. These p r o p e r t i e s are discussed i n 1 a t e r
sect ions.
The e f f e c t o f gamma r a d i a t i o n on the elastomers i s i n d i c a t e d i n
Table 2. I t i s f e l t t h a t these m a t e r i a l s would be use fu l t o r a d i a t i o n 7 l e v e l s o f 10 R. Some o f these data were ob ta ined from Har r ing ton , ( 5
as noted. Data on the Parker S604-7 and the Union Carbide K1305B s i l i c o n e
rubbers were ob ta ined by p u l l i n g i r r a d i a t e d o - r ings on an I n s t r o n t e n s i l e
t e s t i n g machine.
As w i t h the elastomers, the h i gh environmental temperature i s t he
most impo r tan t f a c t o r i n e v a l u a t i n g coup l ing f l u i d s f o r t h i s a p p l i c a t i o n .
Most f l u i d s have a h i g h vapor pressure o r decompose a t 500 OF. The f l u i d s
considered f o r t h i s a p p l i c a t i o n are l i s t e d i n Table 3 by chemical name as
w e l l as t r ade name. These f l u i d s were eva lua ted by measuring t h e i r u'i t r a -
son i c v e l o c i t y , halogen content , and c o m p a t i b i l i t y w i t h elastomers. For
the two b e s t f l u i d s , An ib i f l o and Dow 710, the u l t r a s o n i c a t t e n u a t i o n
was measured, and t h e gas evolved du r i ng i r r a d i a t i o n was determined.
V e l o c i t y Measurements. The u l t r a s o n i c v e l o c i t i e s o f t he coup l i ng
f l u i d s as a f u n c t i o n o f temperature are shown i n F igures 21 through 28.
Since an open system was used f o r the v e l o c i t y measurements, the tempera-
t u r e was k e p t below the f l a s h p o i n t o f the f l u i d s . Note t h a t w i t h t he
excep t ion o f Sperry f l u i d the u l t r a s o n i c v e l o c i t y decreases 1 i n e a r l y w i t h
i nc reas ing temperature.
The v e l o c i t i e s were measured i n a furnace i n an open s t a i n l e s s s t e e l
beaker w i t h the dev ice shown i n F igure 29. Th is apparatus has two 5 MHz
PZT-5 c r y s t a l s ( a t r a n s m i t and a rece i ve c r y s t a l ) so ldered t o s t a i n l e s s
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TABLE 2. Ef fect o f Gamna Rad ia t ion on the Proper t ies o f Elastomers
% Increase I n % Increase I n U l t in ia te Tensi l e
Mater i a1 Dose, R E longat ion a t Break S t reng th
S i l a s t i c 8 0 ' ~ ) 3 x l o 6 6
30 60 90
S i l a s t i c 5 0 ' ~ )
V i t on A-2(a) 5 5 0
100
Uni on Carbi de 10 -28 - 9 K1305B 100 -78 -36
1000 o - r ings broke eas i l y
Parker S604-7 10 - 5 ~4 1 100 -56
1000 o - r ings broke e a s i l y
a. These data were taken from R. Harr ington, P a r t 11: E f f e c t o f Gamma
Rad ia t ion on Heat-Resistant Elastomers, Rubber Age, Vol. 82, No. 3,
De~ernber~ l957. The newer compounds, S i l a s t i c 82 and S i l a s t i c 52
have s i m i l a r p rope r t i es t o S i l a s t i c 80 and S i l a s t i c 50.
TABLE 3. Fluids Evaluated f o r Use in the Sperry Wheel
Chemical Name Trade Name
Polypropylene oxi de
Polypropylene glycol
Polypropylene glycol
Polyethylene glycol
26.5% diphenyl i n diphenyl ox i de
F luoros i l icone o i l
S i l i cone oi 1
A mixture of 50% water 50% e thylene glycol
Ambiflo
Polyglycol P-400
Polyglycol P-1200
Polyglycol E-200
Dowtherm A
DOW FS-1265
Dow 710 f l u i d
Sperry f l u i d
BNWL- 1302
100 1 5 0
TEMPERATURE, OF
FIGURE 21. U l t r a s o n i c Veloci t y of Sperry F l u i d Versus Temperature
BNW L- 1 302
T E M P E R A T U R E , O F
FIGURE 25. U l t r a s o n i c Wave V e l o c i t y o f Dowtherm A Versus Temperature
BNWL- 1 302
