Pressure-relief devices must be provided in piping wherever liquid hydrogen could be trapped between closures.
Below-ground piping should be laid in open trenches with removable grating. Cryogenic liquid hydrogen piping must be adequately insulated so it will not freeze the ground.
Piping systems must have sufficient flexibility to prevent excessive stresses caused by thermal expansion or contraction, which could lead to leaks.
For information on low-temperature concerns or material selection for cryogenic liquid hydrogen piping systems, please see Material Selection for Cryogenic Liquid Storage Vessels.
The large temperature difference between ambient and cryogenic conditions (300° F or more) results in significant thermal contraction of most materials, which must be accommodated for in designs for cryogenic service.