hydrogen leak in the hose of a dispenser

This incident occurred at a 70MPa hydrogen refuelling station. After completing a filling test, the pressure in the filling hose suddenly dropped. A worker heard the hissing sound of a hydrogen release. By using a portable gas leak detector, the worker discovered a hydrogen leak at the filling hose, near the connection to the dispenser. The facility was manually shut down.
There were no casualties. The only property damage was the breakage of one filling hose.

Details
A filling test was being conducted to check the durability of a plastic filling hose. 945 fillings per year were the target, corresponding to the expected number of the annual filling during the first phase of hydrogen mobility development. The goal of the test was to confirm that he hose was able to function for a year without replacement needed.
After completing the filling operation, cracks appeared near the dispenser side connection part of the plastic filling hose, causing a leak of the hydrogen retained inside the hose. A 1.4 mm long crack was on the outer surface of the inner layer, a 2.5 mm long crack on the inner surface of the inner layer, and a 1.5 mm x 2.0 mm through hole in the outer layer.
This hose failed after 130 filling cycles.

INITIATING CAUSE was crack in the filling hose.
Post-incident investigation showed that the cracks develops as a combination of hydrogen, cold temperature and bending fatigue at the tensile side.
The ROOT CAUSE is therefore design-related.

hose

A similar incident had occurred 3 October 2013. The investigation concluded that that repeated low-temperature filling tests with the filling hose in a bent state contributed to the occurrence of cracks in the inner layer of the filling hose. As corrective measure, the length of the filling hose upstream of the emergency breakaway coupling was changed from the previous 1,700 mm to 1,100 mm. The mounting structure was modified so that the minimal bending radius of the filling hose became from 200 mm, the double of the previous 100mm. In addition, it was decided to conduct a filling test by removing the filling hose every 100 fillings and gradually increasing the number of fillings while checking the soundness of the hose's inner layer.

DESCRIPTION OF THE FACILITY
HRS production capacity = 12,936 m³/day (1160 kg/day)
Nominal pressure = 70MPa
Hydrogen refuelling temperature range: -40°C ~40°C
Hose had diameter = 16mm, hose length = 1100mm. Its inner layer of the hose was made of a resin, and the external layer made of a special high strength fibre.

Only damage, the hose

(1) The rubber and resin materials used in hydrogen environments have a non-uniform structure. This makes difficult manufacturing quality control and the laboratory determination of accurate lifetime values of the hoses. It is therefore necessary to adopt safety margins, which take into account the broad variation of hose performances.
(2) Post-incident investigation revealed that tests performed with a medium different from hydrogen were not able to reproduce the cracks developed in a hydrogen environment. Tests with hydrogen set additional requirement to the testing infrastructure, and are therefore more expensive. Nevertheless, especially for component design purpose, it is advisable to perform the tests in conditions as near as possible the real operative environment.

The cause of the crack development in the hose was a combination of low temperature, high pressure, and bending (tensile side). These conditions cannot be modified, because required by the operation of the hydrogen refuelling station.
Therefore, it was decided to use each hose only 100 times, instead of the 945 times as originally planned. In addition, the minimum hose bending radius was increased to 300mm.