Re: How cold can I go...

[don@radpro.uchicago.edu]

It would seem to me that your experience might count.  

SS is often used for LN2 dewars because of its low thermal conductivity.
It is probably also used for liquid helium transfer tubes etc.  NASA
probably uses a lot of SS plumbing etc. in its liq. fuel rockets, & would
have a lot of experience with cryogenic behavior of SS.

The problem is not so much with the SS, but with the welds.  SS has 
a very different (lower, I think) coefficient of thermal expansion
than ordinary steels, and the type 300 series (austenitc?) differ significantly
from the type 400 series (martensitic) stainless steels.  The welding rod
material's coefficient of expansion _could_ differ from the SS by quite
a lot - but your experience suggests not.  If the wall material & the 
welding material have similar coeff. of expansion, there should be little 
stress from the thermal cycling.  Find out what type of SS the walls & the
welds are made of & (if they're different types, e.g., type 304 (very common)
& type 316 (common)) thier expansion coeff.s  The manufacturer should have 
this data.  If not, more than you ever cared to know about SS will be
contained in one of the volumes of the Metals Handbook pub. by the 
ASM (American Soc. for Metals?  I can look it up if you need it.)

___________________________________________________________________

Don Jordan                          Tel. (312) 702-6299
Office of Radiation Safety          Fax        702-4008
The University of Chicago           email: don@radpro.uchicago.edu
1101 East 57th Street, Room 11
Chicago, Illinois  60637  
           -- Opinions expressed are soley the author's --