170
exposure t o tellurium.
T e s t s near reasonable design stresses have been i n
progress several thousand hours.
Type 304L s t a i n l e s s steel, nickel-200,
and Inconel 600 have been i n test several thousand hours, b u t have not been examined metallographically. The r e a c t i o n products of t e l l u r i u m with
W I
a
nickel-200 and INOR-8 are b a s i c a l l y n i c k e l t e l l u r i d e s , b u t t h e only detectable product on s t a i n l e s s s t e e l is an oxide of t h e Feg04 type. Tube b u r s t tests of INOR-8 were run with t h e o u t s i d e of t h e tubes i n helium o r s a l t environments.
Some of t h e tubes were e l e c t r o p l a t e d
with t e l l u r i u m before t e s t i n g .
The test environment had no d e t e c t a d l e
e f f e c t , but the tubes p l a t e d with t e l l u r i u m f a i l e d i n s h o r t e r t i m e s than those not p l a t e d .
Metallographic examination revealed i n t e r g r a n u l a r
cracks about 10 mils deep along almost every g r a i n boundary of t h e p l a t e d specimens.
Some of t h e s t a i n l e s s steel tubes are s t i l l i n t e s t , b u t t h e
rupture lives of those t h a t have f a i l e d are equivalent f o r p l a t e d and unplated specimens. The o t h e r type of s t r e s s e d test t h a t has been run is one with controlled strain l i m i t s .
Thermal stresses commonly occur i n components
such as h e a t exchangers where high h e a t fluxes develop and t r a n s i e n t s are frequent. exchangers.
-,
Thermal s t r a i n s of +0.3% are a n t i c i p a t e d f o r MSBR h e a t
.
Our f i r s t test has u t i l i z e d a Te-plated Hastelloy N speci-
men s t r a i n e d between limits of +-0.16%. The rupture l i f e w a s s h o r t e r than a n t i c i p a t e d on t h e b a s i s of tests with t e l l u r i u m , and numerour i n t e r granular cracks were present on t h e o u t s i d e where t h e t e l l u r i u m w a s plated. SUMMARY
These tests show t h e t e l l u r i u m causes t h e formation of i n t e r g r a n u l a r cracks i n INOR-8 and t h a t t h e s e cracks are deeper i f t h e material is s t r e s s e d and exposed t o t e l l u r i u m simultaneously than they would be i f the material were exposed t o t e l l u r i u m and then s t r e s s e d .
Although t h e
d i f f u s i o n rate of t e l l u r i u m i n INOR-8 has been measured, t h e r o l e of t
stress i n a c c e l e r a t i n g crack propagation makes t h e d i f f w i o n measurements of questionable value i n estimating t h e e x t e n t of cracking i n service. Only elements of t h e S, Se, and T e family were found t o cause i n t e r granular cracking in’INOR-8.
id