The ullage volume specified for a cryogenic vessel should always be respected. With the addition of heat, liquid hydrogen can expand 23 times greater than the expansion of water when heated. Overfilling a cryogenic vessel can lead to entrainment of liquid in the pressure-relief system and the possibility of over pressurization.
Pressure-relief devices should be designed to discharge upward and unobstructed to the open air to prevent any impingement of escaping gas upon the vessel, adjacent structures, or personnel.
Pressure-relief devices and vent piping should be designed and located so that moisture cannot collect, freeze, or interfere with proper operation of the device.
Hydrogen storage and handling facilities must be equipped with pressure-relief devices (PRDs), which could be:
- rupture disks
- pressure-relief valves
- breaking pin devices
The PRD protects pressurized equipment from exceeding the maximum allowable working pressure.
If the PRD fails to function as designed, an overpressure condition could occur within the vessel or piping and possibly result in equipment failure.
Pressure-relief valve settings should be checked and then verified by a second party.