Release from a hydrogen truck

A hydrogen leak took place on a trailer carrying compressed hydrogen, located inside the fenced perimeter of a hydrogen station. According to the company managing the hydrogen delivery and refuelling station, the leak did not pose any risk to people or the environment.
A preliminary assessment identified a faulty valve source of the leak, but it was unclear at that time if it was a single defect or a systemic (i.e. design) problem. Following a detailed investigation in close cooperation with the trailer and valve suppliers, the company determined that the root cause of the valve malfunction was due to a set of improperly tightened bolts, causing an O-ring to burst.

Approximately one month later, addtional malfunctioning were found on the same valves on othr eight trailers.

The INITIATING CAUSE The was a non-further specified defective valve.

The assembly error was not detected by valve supplier quality control nor by the tube trailer suppliers’ quality inspection, but only when the all assembly was operating.

This, and the fact that more valves were found defective, suggest as ROOT CAUSE an improper tightening procedure damaging the O-ring , an installation error or a manufacturing defect.

O-ring, bolts (presumaby from a flange), compressed hydrogen tube

DESCRIPTION OF THE UNIT
Various wesites provide the following technical data :
Capacity = 1,100 kg of hydrogen
Nominal pressure = 30 MPa
129 onboard type 4 compressed hydrogen cylinders, mounted vertically in racks and connected via piping and a shut-off valve.
The trailers can be used as swap modules into the company hydrogen refuelling stations using or as delivery to customers.

The company decided to suspend the use of its 12 hydrogen trailers until all relevant valves have been controlled. The grounding of the trailer fleet had a negative impact on the distribution of hydrogen to customers and refuelling stations.
Following verification that the fault was not systematic, the company redeployed the trailers.
Mitigating actions will be implemented at both trailer supplier and valve supplier to eliminate recurrence of the near miss.