leak from a dispenser of a HRS

The accident occurred during the filling of hydrogen into a fuel cell vehicle (FCV) at a hydrogen station.
The gas detector in the dispenser detected a leak, and the equipment was shut down. A test was performed, but it was unable to find a leak. A filling test was then executed, and the leak was finally identified on the emergency shutdown valve.
The tightening torque of the emergency shutdown valve was checked, and it was found to be below the specified value.

The INITIATING CAUSE was a small release of hydrogen from a valve.

The ROOT CAUSE could not be identified with certainty, and was believed to be one of the following:
1. Loosening of the tightening torque: The tightening torque may have decreased due to temperature and pressure changes or external vibrations, resulting in a leak.
2. Performance of the emergency shutdown valve: The valve may have been defective due to manufacturing defects or damage during assembly.

emergency valve, dispenser

DESCRIPTION OF THE FACILITY
High-Pressure Gas Production Capacity: 12,366 m3/day
Normal Operating Pressure: 70.0 MPa
Normal Operating Temperature: -40 to 40°C

The location is classified as CONFINED, because the leaking valve was installed in an enclosed section of the dispenser.

No personal injury, no property damage.
Only a very small release of hydrogen.

During this event, the safety measures worked as designed. The leak test performed to identify the location of the leak did not find any, while the following filling ‘real’ test was allowed to identify its exact location. This fact may indicate a difference between test conditions and real fillings. Indeed, the leak test is performed under static pressure conditions, while the filling occur with a dynamic pressure profile.

The following are the wo lessons learnt mentioned I the KHK report.
(1) In equipment that handles high-pressure hydrogen, it is essential to regularly check the tightening torque of joints to prevent leaks.
(2) In equipment that handles high-pressure hydrogen, it is crucial to ensure that the emergency shutdown valve is properly manufactured and assembled to prevent leaks.

The facility has taken the following countermeasures to prevent a recurrence of the accident:
1. The facility will conduct regular checks of the tightening torque of all threaded joints every 4 months.
2. The defective valve will be replaced with a new one from a different manufacturer.
3. The facility will consider introducing a leak test using FCV filling to detect any leaks that may not be detected by static pressure tests.