Re: How cold can I go...

[avest@magnus.acs.ohio-state.edu (Albert Lee Vest)]

>Joel,
>
>I would suggest you contact some materials type people.  From my limited 
>understanding, it isn't so much how cold these things get (maybe your 
>application is outside this assumption), rather how the temperature is
cycled.  

Quite right.  Welds, if they fail, will fail because of stress.  Stress
comes from mechanical load exerted (bending, twisting, tensile, or
compressive) and from differential thermal expansion.  The latter is
enhanced by a higher the rate of temperature change, sometimes with
catastrophic consequences (as in the movie Alien III).

Also, steels go through a transition from ductile (high toughness) to
brittle (low toughness) as the temperature drops below a certain point.
Different alloys have different critical temperatures.  Toughness is
important in determining resistance to breakage, and crack growth rates.
Stress cycling of all kinds (but especially when locally tensile) tends to
cause cracks to grow, and they grow faster in brittle materials.

>The Materials people should be able to help you.
>
>Rob Gunter
>ORNL

As a "materials type person" (BS. Met. E, 1985), I couldn't remain silent
any longer, even though I consider myself rusty on the specifics of steel
metallurgy. I hope my babblings weren't too confusing.
Albert Lee Vest                   Radiation Safety
Health Physicist   Environmental Health and Safety
(614)292-0122            The Ohio State University
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