At around 5.50 am, flames and black smoke were emitted from the chimney connected to the three furnaces of a refinery’s distillation unit. Furthermore, a very sharp rise in temperature was noted on the convection outlet smoke exhaust duct (bright red colour – temperature measured of 900°C). The emergency shutdown procedure was activated including interruption of dispatch of the crude oil load and injection of smothering steam into the furnaces. These operations quickly contained the outbreak of fire without having recourse to the internal emergency resources that had been mobilised as a preventive measure.

Investigations carried out by the operator on the 3 furnaces revealed that one of the 6″ diameter tubes of the convection system of furnace F 5103 had a longitudinal opening that was approximately 150 mm across its upper generator. Loss of the tube’s containment released the crude oil circulating inside the tubes into the convection area. This caught fire generating the black smoke and flames noted at the top of the chimney.

The examination of the tube, which belonged to the first layer of the convection system (“shock tubes”), showed the presence of a deposit of coke on its inner wall. This deposit contributed to reduction of the heat exchange capacities causing abnormal heating of the wall of the tube (1 mm of deposited coke caused a rise in temperature assessed at 20°C) then its rupture due to “long-term creep”. Checks for the presence of coke on the convection system’s other tubes showed no other anomalies.

Additional measures recommended by the inspection authorities for classified facilities were prescribed, such as, the continuous control of the temperature of the lining of the “shock tubes” in the convection area with alarm transmission to the control room, monthly infrared thermography monitoring of the temperature of the lining of the tubes for all of the convection passes for the 3 smoke outlets of the furnaces, drafting of a procedure on the actions to take in the event of detection of high tube temperature, and study on the formation of coke on the inner walls of the crude oil distillation furnace tubes.

Following this incident, several units had to be progressively shut down due to loss of load. Operating losses were assessed at over 23,000 000 euros and material damage amounted to 920,000 euros.