Explosion at a pipeline of a petrochemical plant

A gas mixture (25% nitrogen, 73% of hydrogen, 2% methane) leaked, due to the ejection of the check valve from its connection with the inlet pipe. A large amount of the gas mixed with air and ignited, probably due to sparks generated by the ejected check hitting a metal pipe. It followed an explosion and a fire. Its pressure wave hit a gas pipeline causing its fracture and a fire. After about 1 hour and 30 minutes the fire was under control. The shockwave from the explosion caused a gas pipe at the back of the workshop to crack and leak, causing a large fire.

The INITIATING cause of the incident was the sudden falling-off of the check valve, due to a large deviation of the dimension of the small diameter of the inner flange thread. Its diameter was too small and eventually lead to the separation of two connections.
The ROOT CAUSE was related to quality control not properly done and failure in inspection.

check valve, pipe

2 fatalities, 11 injured persons (out of which 6 were severely injured). Damage estimated around 57K Euro

The plant operator has to establish and implement a qualification system for purchased components.
This will allow the early detection of wrong or not certified materials. Moreover, an inspection system has to be in place, to assess additional risks related to components replacements and repair.