Release from the Storage of a Hydrogen Production Plant
The accidental hydrogen release occurred when testing the storage system connected to a PEM electrolyzer. The leak test consisted in filling the storage with hydrogen at step-wise increase of pressure. After the step at 3 bar (0.3 MPa), which did not reveal any leak, the storage was pressurised up to 5 bar (0.5 MPa). At that moment a hissing sound occurred from the storage at the outside of the building indicating a leak. The production of hydrogen was stopped and all shut-off valves were closed automatically.Since the leak took place on the 'storage side of the shut-off valves, the leaking continued. The operator decided then to let the storage bleed out. Afterwards, the location of the leak was found and isolated by closing of nearby manual valves. The leak was located on a flanged connection near the storage. Bolts on this flange were found loose after the incident. The exact cause of the leak could not be identified. A possible explanation was that the torqued connection might have become loos when installing the vent line due to the manoeuvring of the pipe. The vibration of the leak could have further loosen the bolts. The gasket was replaced, the bolts were retightened and torqued and the storage was leak tested up to 33 bar (3.3 MPa) without any other leaks.Approximately 224Nm were released in 60 minutes.
Event Date
December 5, 2021
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Cause Comments
The leak was most likely caused by the maneuvering of the piping during the installation of the vent line. The case showed that the storage system did not have a depressurization system by its own.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
Flanged connection of storage vessel
Storage/Process Medium
Actual Pressure
0
Design Pressure
3
Location Type
Location description
Unknown
Operational Condition
Pre-event Summary
The event took place during the commissioning stage of the hydrogen installation. The storage was beingfilled with hydrogen up to a pressure of 5 bar.DESCRIPTION of the FACILITY2.5 MW (1.25 MW stacks x2) electrolyzer connected to a wind farm
Lessons Learned
Lessons Learned
The safety system in place worked as planned. However, since the leak was located on the 'storage side' of the shut-off valves, the leaking continued till emptying of the storage system. After that, as immediate corrective measure, the gasket was replaced, the bolts were retightened and torqued and the storage testing restarted. As long term measure correcting the initial design, it was decided to add an automated depressurisation system to the storage, to release pressure in case of a malfunctioning or failure.
Event Nature
Emergency Action
The alarm was given by the hissing sounds. The production of hydrogen was then stopped and all shut-off valves were closed automatically. Thereport does not says if the production stop was the action of an operator, or was triggered by an automatic system. it is highly probably that the 'hissing sound' did not triggered any of the preventing/mitigating automatic system in place.
Release Type
Release Substance
Hydrogen Release Concentration (%)
100.00
Release Duration (s)
3600
Release Rate (kg/s)
20.00
Release Amount (kg)
224.00
Release Pressure (bar)
0.50
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
Own report available but confidential