leak from a dispenser of a mobile HRS

The accident occurred at a mobile hydrogen station during a fuelling test for a fuel cell vehicle. The day before, the gas detector in the dispenser detected a leak and the equipment was shut down. With a mobile detector and a helium leak test, the leak was found coming from the emergency shutdown valve of the dispenser. The valve manufacturer replaced the O-ring. The day after during a fuelling test, a leak was detected again. The leakage point was and found on the lower part of the emergency disconnect coupler on the fuelling nozzle side of the fuelling hose was leaking.

The INITIATING CAUSE was a small release of hydrogen from a damaged O-ring.

The ROOT CAUSE could not be identified with certainty and was believed to be one of the following:
1. The O-ring of the coupling valve was damaged during the previous work of dismantling and remounting of the emergency valve.
2. The sealing of the coupling was poor and during fuelling the application of a force on the coupling could have caused the movement and the damage of the O-ring.

emergency valve, dispenser

10 days before, a safety inspection was terminated and the operation restarted 3 days after.
10 vehicles had already been refuelled, when the first leak was detected during the refuelling of the 4th FCV of the day.

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.

This event is classified as incident because of the hydrogen release and the resources spent in improving the situation; however, considering that the safety system functioned as designed and that the leak was very small, system it is borderline with a near-miss classification.
The KHK report indicated that only at the lowest temperature of -40°C, the leak rate exceeded \the max allowed rate (2.1 10-5 Pa m3/s, instead of a max of 1.0 10-5 Pa m3/s).

The following general conclusion van be drown (modified in respect to the original KHK report):
(1) Leak testing is essential to detect any leaks before fuelling. However, as demonstrated by a similar incident (see HIAD_1207), they are not always effective in detecting loss of confinement if the conditions under tests differ too much from those experienced during refuelling. Leaking rate measured at room temperature were according to specification, while at -40 C resulted above maximum allowed.
(2) It is necessary to consider the whole assembly of the emergency disconnect coupler, the hose and fuelling nozzle, and the external force acting on them, to prevent that any force not considered in the design from being applied to the emergency disconnect coupler.
(3) An effective seal management is crucial in high-pressure gas equipment. This implies the correct choice and management of O-rings, with sealing power also at lower temperature and in a wide range of dynamic pressure. Moreover, correct control and care of the seal surface is important during the installation and replacement.

The facility has taken the following countermeasures to prevent a recurrence of the accident:
1. Changed the manufacturer of the emergency disconnect coupler and high-pressure hose.
2. The manufacturer created a checklist to prevent damage to the O-ring during assembly.
3. The manufacturer introduced a new helium leak test at 96.3 MPa and -40°C before product shipment.