Damage to the insulation sell of a LH2 tank

During the warm-up phase of a large liquid hydrogen sphere, the annular space was over-pressurised and perlite insulation was expelled through the evacuation nozzle and the burst diaphragm. Air had leaked into the annular space some weeks earlier and repairs had been carried out. However, the air had solidified in the annular space. During the warm-up, the air vaporised and caused a pressure build-up. The vessel sustained minor damage.

[Ordin, NASA (1974)]

Leak points had been found in the external shell and sealed approximately six weeks prior to this event. The event was due to a lack of design considerations for monitoring/ evaluating the tank conditions during warmup. The hazards involved in making temporary re­pairs in the evacuation system were not iden­tified.
Therefore, the ROOT CAUSES were shortcoming in repairing procedures and n asesing the related risks.

LH2 vessel

leaks in the external shell of the vessel had been repaired six week before.

Minor damage to the vessel

This is a rare case of deterioration of the annular space serving the insulation of a LH2 vessel, due to overpressure. It happened during the warming up of the vessel (which was highly probably almost empty), a procedure starting with the reduction of the vacuum in the insulation shell.
A possible escalation could have been the over-pressurisation of the internal shell due to too rapid heat inlet. Nevertheless, since the final goal of the operation as to bringing the vessel to room temperature, it is expected that venting system would have been able to deal with a higher hydrogen flow than the one planned. The vessel was anyhow equipped with pressure relief devises in case of internal over-pressurisation.