Small leak from a CGH2 trailer

When a CGH2 tube trailer was backing into the terminal stall and getting ready to unhook the tractor a leak was detected on one of the cylinders. It was reported immediately to owner of the trailer and is responsible for its maintenance. When the company expert arrived at the site, they found the top tube was leaking. With soap solution they identified the location of the leak on the valve to rupture disc adapter fitting (piping).

The trailer had been inspected by drivers and an instructor before departing from the loading terminal, verifying pressures. During the trip to the delivery site, the drivers had conducted several inspections to ensure correct and stable pressures. No leaks were detected during those inspections. It can be concluded the condition for the leak established during the travel, and that the leak had slowly developed until the moment it could be finally detected by inspection.

The INITIATING CAUSE was the loosening of a threaded connection of a valve, probably due to road travel vibrations.

The ROOT CAUSE is not provided, however, an effective design should be able to take into account road vibrations on a road vehicle.

connection

DESCRIPTION OF THE UNIT
The PHMSA source provides a amount of released hydrogen in GCF, which has been converted into kg using the conversion formula provided by PHMSA.
The techncial data of the trailer are not provided. From the website of the supplier, it results that each tube could have:
Nominal pressure of 2400 psi or 1630 psi ( 165 or 182 bar).
Dimensions: 6.2 m or 7.3 m in lenght and a water volume of of 246 or 286 l.

Depending on the number of tubes on the trailers, the nominal hydrogen transport capacity could varies between 60 to 200 kg.

The leakage was probably detected by checking pressure stability. The location was found by the soap method. Nothing is known on the corrective measure.

The inspection procedure demonstrated its effectiveness. It was therefore recommend continuing to conduct complete and comprehensive pr- and post-trip inspections and to guarantee that maintenance is completed as scheduled.