Two fitting failures were experienced for fueling equipment filling systems. Both fittings were installed in the system thermal chamber experiencing ambient temperatures of -40C to +50C. They were connected in high-pressure lines used for 70MPa hydrogen fueling.

The first fitting, a 0.25-inch NPT hose connection, was in service for approximately one year with no signs of leakage. The failure was noticed when the system was pressurized during a filling sequence. The failure was discovered by an audible hissing noise during leak checking. The system was depressurized and the fitting removed and replaced. The system was re-pressurized with no further leakage.

When attempting to reconnect a second fitting, a double-ferrule high-pressure connection, the fitting in question would not re-seal. The nut would not spin freely on the tubing and had created gouge marks. The fitting was replaced and no further leakage occurred.

Incident Date
Sep 19, 2007
  • Vehicle & Fueling Systems
  • Fueling Dispenser
  • Piping/Fittings/Valves
  • Piping
Damage and Injuries
Probable Cause
When Incident Discovered
Lessons Learned

For the use of mechanical fittings in hydrogen service, administrative controls should be in place, as in this case, to ensure that leak testing is conducted on a regular basis. It should never be assumed that every fitting is tight. Additional discussion of best practices for fittings and joints can be found in the Hydrogen Safety Best Practices Manual.