Fire of a mixture of hydrogen and hydrocarbons in a refinery

The fire occurred on the tube plate gaskets of 3 of the 4 exchangers loaded with catalytic reforming effluent. The fuel (500°C and p=30 bar) was a mixture of 30% hydrocarbons and 70% hydrogen.

After depressurisation of the unit and nitrogen flushing (some problems to access the valves), the exchangers being cooled (overall flow 600 m³/h on 3 units), the fire was controlled until extinction by nitrogen injection.

The accident was apparently due to incorrect tightening of the threaded rods; only 1/5 were correctly tightened on one of the heat exchangers involved. Three threaded rods break and the gasket surfaces were poorly prepared.

The INITIATING cause was the release of hydrogen at a flange
The root (or interm4ediate) cause was the wrong execution of the flange joint (incorrect tightening, bad quality of the gasket surface)

heat exchanger of the catalytic reforming unit

The tightening procedure is reviewed (hot tightening procedure: 340 °C and 8 bar) before the
charge is introduced again.

The flange tightening process was reviewed and improved.