Designing cryogenic ducts

Attention is given to the materials, design principles, and control system features which have been developed in order to meet the performance requirements of the Space Shuttle Orbiter Main Engine's ten liquid hydrogen recirculation and replenishment ducts. Liquid hydrogen flows through these ducts at a rate of 1.5 lb/sec, at a pressure of 55 psia. In choosing materials, careful consideration was given to mechanical properties, thermal conductivity and specific heat, surface reflectivity, and outgassing rates. Inconel 718 exhibits the best balance of properties for use in such cryogenic ducting.