The subject needle valve was used primarily for manual filling to control the flow rate of hydrogen from storage banks to the 70MPa test system. The valve was installed on the exterior of the thermal chamber in ambient temperatures of -5C to +30C. The gas flowing through the valve was at conditioned temperatures of -40C to +50C. The valve was in service for approximately two years and 400 fill operations.
Failure occurred during a test under an open valve condition. When attempting to close the valve, the turning force increased and the technician was unable to completely close the valve. An upstream ball valve was closed to isolate the flow.
Investigation determined that internal galling has caused the failure rendering the needle valve unusable. The galling was caused by a stainless steel stem acting against a stainless steel seat. This failure mode had been observed before and the manufacturer had been previously notified. The valve was replaced with a new needle valve to continue with the test program. Additional discussion of best practices for equipment maintenance and integrity can be found in the Hydrogen Safety Best Practices Manual.