Fire in the catalytic reformer operation

A fire occurred at the desulphurisation unit of a refinery during maintenance work. On the day of the incident, a distillation unit was shutdown for a steam air tightness test. A leak was found at the joint between the header and tube of the air-cooled heat exchanger. Nitrogen purging was carried out before the repair work. The header cover was then connected and tightened up using an electric torque wrench, when the fire broke out. Hydrogen gas, formed during the previous operation of the catalytic reforming unit, had entered the nitrogen gas system and ignited by a spark generated when the wrench was used.
The valve responsible for the presence of hydrogen in the system was the valve between the nitrogen supply pipe and the process gas pipe of the desulphuriser. The nitrogen supply pipe used for the routine maintenance and repair operation and the combustible gas piping were always connected. Since the in-between valve was left opened by mistake, hydrogen flowed into the nitrogen pipe.

After inspection of the nitrogen supply system, the cause of the hydrogen presence was found and the valve closed, what stopped the fire.

The INITIATING CAUSE was the presence of residual hydrogen in the shutdown system.
According to the shippai report, contributors to the ROOT CAUSE were:
(i) A lack of communication between shift teams during the repair operation.
(ii) The operating instructions were not clearly defining the use of the communication pipes (there were two connections) between the nitrogen purge system and the process gas.
(iii) Wrongly execution of the instructions received.
However, according to the report, the principal ROOT CAUSE was that there was no knowledge that flammable materials were still existing in the unit.

catalytic reformer, distilation unit, valve

Repair was ongoing

minor injury

When multiple pipes for multiple purposes are connected, accidents due to accidental opening are likely to occur. In particular, when the service piping is connected to the process. It should be avoided. If not possible, the operations have to be carefully managed by well-trained teams.

(1) To install a check valve in the nitrogen line.
(2) The nitrogen supply shall be connected and disconnected before, respectively after every repair or maintenance operation. Alternatively, “double block and bleeder valves” should be installed and operated.
(3) To review the items to be communicated to the maintenance and repair plug.
(4) To educate employees and contractors companies on gas detection.
Note: a Double Block & Bleeder valve consists of two block valves and in-between of a small-diameter valve (the bleeder), which allow for evacuation of one pipe line by keeping the other isolated.