Hydrocarbons fire in a refiner

During a work tour on a refinery, an employee noticed a fire at the level of a flange at the inlet of the grille of an exchanger, located at the outlet of a reactor of the catalytic reforming unit.

The plant operator detected a lack of uniformity of torque on the bolts. Two years before, during a shutdown period, some parts of the exchanger had been removed for inspection. The flange on the heat exchanger side was not easily accessible. During reassembly, the presence of a pipe tee near the flange made it difficult to tighten with a bolting machine. The faulty tightening (1.5 mm opening) could have led to the leakage of high-octane gasoline, mixed with hydrocarbon gases and hydrogen. Without a hot spot nearby, this 500°C fluid could have spontaneously ignited on contact with air.
The plant operator tightened the flange and modified procedures to specify the use of a suitable wrench for the configuration. The operator also planned to carry out independent checks on the quality of the connections made.
(ARIA database)

The INITIATING cause was the ignition of leaked mixture of hydrocarbons, including hydrogen. The INTERMEDIATE or ROOT CAUSE could have been the lack of tightness of a flange caused by a not-properly tightening of the bolts. Finally, A CONTRIBUTING or ROOT CAUSE was the difficulty of re-assembling of the system due to design.

reformer, heat exchanger, flanges, bolts

The quality of the event description does not allow for a detailed lesson learnt. nevertheless, better operative/maintenance procedures and a (better) reporting system shall be part of it.

The plant operator modified procedures to specify the use of a suitable wrench for the configuration.
The operator also planned to carry out independent checks on the quality of the connections made.