In article , Brian Lawson says...

Wow!! That's amazing! What sort of relative humidity would there be
in the area. I would have thought that as the exterior surfaces of
the flex line began to cool, that it would form a heavier and heavier
layer of "ordinary" frost from the ambient room air.

Really cold exposed transfer lines don't really frost from
water vapor, the amount of gas condensing on them seems to
prevent that. Basically they just get 'wet' looking and
start dripping. Obviously when one is transferring cryogenic
fluids for real the use of a flexible vacuum-insulated
transfer stick is required.

The good story I read about the apollo rocket program was that
the engines were all tested on the ground, and the exposed
flex lines would frost up to a large degree. The frost provided
significant mechanical damping to the stainless bellows lines.

The second time the rocket was flown, an engine failed
because the flex line had a resonant oscillation, and fatigued
during operation, and fractured open. Dampers were added.

Note, temperatures are from memory, I don't have a chart handy.

Appx boiling points of:

LO2: 90K
LN2: 77K
Liq Neon: 27K
LH2: 20K
LHe-4: 4K
LHe-3: 3.5K

Jim

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