A chemical plant experienced a valve failure during a planned shutdown for maintenance that caused hydrogen to leak from a valve and catch fire. Four chemical reactor chambers in series were being emptied of liquid using hydrogen gas as part of a maintenance procedure. Two heater valves were opened allowing 3000 psi hydrogen to flow in reverse direction to purge the reactor system for approximately 25 minutes. At completion of the purging process, a "light" thud was heard as the reactor empty-out valves are being closed. Smoky vapor was observed coming out of one of the reactor empty-out valves and the valve closing was stopped by the operator. The operator summoned a second operator for help at which time a second "loud" thud was heard with a much larger light and dark gray vapor cloud observed coming from the leaking valve. Both operators evacuated the area and proceed to shut off the fuel supply and lower the reactor system hydrogen pressure.
Approximately two minutes after the start of this incident, the vapor cloud from the valve was replaced by a large yellow and green flame that initially engulfed a nearby separator and tank. Plant personnel began emergency fire response procedures that included closing valves to shut off hydrogen and natural gas supplies, starting the local fire fighting deluge system, bringing in an additional large fire hose, and making an emergency call to the off-site fire department. Plant personnel quenched the fire prior to arrival of the fire department. Full emergency response and incident command was established until area was declared safe. An estimated 40 lbs of hydrogen gas was released in this incident. No personnel were injured in this incident but some minor damage to nearby equipment occurred.
After the incident, the leaking valve was removed and replaced. The leaking valve was disassembled for forensic analysis. The cause of the valve failure was determined to be a packing leak in the reactor empty-out valve. The remaining valve packing was sent to vendor for failure analysis. The metallurgy of the leaking valve components was verified as being correct. Valve installation standards, specification, and records were retrieved but there was no vendor specification or standard for the valve packing.
- Process Equipment
- Process Vessels
An important aspect of the reliability of a valve is the condition of the stem seal which tends to deteriorate with time and wear. Valves used in hydrogen service should be packed with the correct valve packing material and periodically checked for leaks as part of a regular maintenance program.