LH2 tanker venting on a highway

A liquid hydrogen tanker (with a water capacity of 2000 l) was passing a highway interchange, when the safety valve of the tank activated, releasing hydrogen gas. The drivers stopped first on the shoulder of the road near the junction for inspection. Then he moved to a service area for safety reasons. They performed a controlled release of the whole tank content, after having create a safety area around the tanker.
The probable cause of the valve activation was the increase of the internal pressure of the tank, due to the loss of thermal insulation provided by the vacuum between the two tank shells. The road vibrations had induced cyclic stress to the welded joint of the piping that penetrates from the inner container to the outer container. The welding failed to o fatigue, allowing hydrogen entering the vacuum layer between the inner \and the outer shell. With the vacuum deteriorating, its thermal insulation capacity faded as well with consequent temperature and pressure rise beyond the activation set point of the safety valve.
According to the inspection records, the tank had not been inspected at the legally prescribed inspection interval. Furthermore, the filling stations were filling the tanks without checking whether they had been properly and timely inspected.

[Note of HIAD validator: the KHK record provides a second cause. It is not known if these are two hypotheses to explain the loss of thermal insulations, or two different failures. “One of the plate fixing the inner shell of the tank inside the outer container broke due to fatigue, causing the inner shell to fall off inside the outer shell”.]

The INITIATING was the damage caused by road vibration to the welds of internal structures of the cryogenic tank, with consequent reduction or complete loss of its thermal insulation capacity.
The ROOT CAUSE was the lack of correct inspection and control. Probably also the original welds had not been designed to survive prolonged vibrations as those from roads travelling.

safety valve, vacuum shell

The report mentions that the cryogenic tank had been first filled and then loaded on the truck.

DESCRIPTION OF THE UNIT
This detail suggests a non-permanently installed tank. The value of only 2000 l of liquid hydrogen (only 100 kg) confirms that this was not really a LH2 tanker, but a smaller cryogenic vessel.