Leak from a CGH2 tube trailer

A tube trailer carrying compressed hydrogen was travelling along a city road, when the drivers heard an abnormal sound from behind. They stopped and discovered that hydrogen was leaking from the threaded joint of a pipe connecting all the tubes to the manifold. They tightened the joint, but the leak did not stop, therefore it was decided to transfer hydrogen to another tube trailer.
The reason of the leak was the O-ring of the joint, which did not fit properly. All tube trailers of the same type were modified by installing a valve to each of the tubes.

The INITIATING CAUSE was a defective O-ring causing a leak on a joint.
According to the KHK report, the was an inspection failure, which had not been able to identify the wrong O-ring and the ensure tightness the joint before departure. Since the leak was heard only when travelling, road vibration could have been a contributing factor. Since there was no possibility to isolate the tubes from the general manifold, the fundamental ROOT CAUSE is a shortcoming in design, which did not take into account all possible accidental scenarios.

O-ring, threaded joint

There were 22 long tubes on the trailer

Since the O-ring was defective and therewas no possibility to isolate the tubes from the common manifold, it was decided to transfer hydrogen to another tube trailer.

Timeline of Accident:
• May 23, 9:30 AM: The station opened for business, with a monthly inspection scheduled.
• May 23, 10:35 AM: Filling of hydrogen into the FCV began.
• May 23, 10:37 AM: The gas detector in the dispenser detected a leak, and the equipment was shut down.
• May 23, 11:00 AM: The station was closed, and a hydrogen leak test was conducted, but no leak was detected.
• May 23, 19:20 PM: A filling test was conducted using the FCV, and a leak was detected from the emergency shutdown valve.
• May 24, 11:00 AM: The tightening torque of the emergency shutdown valve was checked, and it was found to be below the specified value.