Release from a vessel at a HRS

The release occurred at a composite pressure vessel on the roof of a refuelling station (in the form of a ISO-container). The leak occurred on a treated connection to the vessel. The vessel working pressure was 950 bar and it contained approximately 9 kg of hydrogen. The leak occurred through the intended "leak detection hole", with a diameter of approximately 1 mm.

The leak was identified in the remote control room. How the leak was identified is not known but could be unexpected pressure loss in vessel. Since the leak was located before the first valve, the gas was released through the vent stack. The hydrogen inventory of the entire facility was 80 kg. All gas was emptied to stop the leak.
The cause of the leak was believed to be vibrations from the compressor that caused the screwed connection to loosen. To reduce the risk of the same occurring again, additional pipe support was mounted.
The rescue service was never notified.

No harm to people or property due to no ignition, but a downtime until the facility before restart.

The INITIATING CAUSE was the loosening of a screwed connection
The ROOT CAUSE was probably the vibrations induced by the compressor. This suggest some shortcoming in the mechanical design of the facility.

connection

DESCRIPTION OF THE FACILITY
The high pressure vessel was part of a renewable hydrogen production plant made up of a PV farm and a water electrolyser.

80 kg of hydrogen were released

(1) Vibrations are often the cause of loosening of screwed connections. This occurs regularly on trailer due to road vibrations, but it can also occur on stationary system as the one affected in this case, due the vibrations of moving parts from the compressor stages. It is unclear if standardised tests aiming at ensuring a minimal tightness of the connection under determined vibrational modes exist.
(2) The report does not provide details of the pressure control system available at the facility. Therefore it is unclear why the whole hydrogen inventory had to be released through the vent, in absence of isolation valve which could isolate the leak.

To reduce the risk of the same occurring again, additional pipe support was mounted, aiming gat reducing the (amplitude of the) vibrations.