Vacuum-Jacketed Piping

Cryogenic liquid hydrogen piping systems should have minimum heat gain to reduce vaporization losses and to avoid formation of ice on the pipes from condensation of water vapor in the air. One good approach is to use vacuum-insulated piping.

Vacuum-jacketed piping must be designed to be adequately flexible to absorb thermal contraction without causing excess stress.

Flexible sections should be connected with adequate slack or compression when warm so they won't be excessively stretched when the system is cooled to operating temperature.

The jacket design should consider the thermal flexibility of the inner pipe and allow the jacket to follow its natural thermal displacement. The vacuum jacket should have its own pressure-relief system. The presence of ice on the jacket indicates that a leak may have occurred in the vacuum jacket.

Non-vacuum-jacketed insulation should be oxygen-compatible due to the possibility of liquid air formation. "Air will condense at liquid hydrogen temperatures and can become an oxygen-enriched liquid due to the vaporization of nitrogen. Oxygen-enriched air increases the combustion rate of flammable and combustible materials." (See Air Products reference at the right.)