Fire in a desulphurisation unit of a refinery

The event occurred at the flanges on the outlet of a desulphurization reactor, which was working under about 300 degrees C. The flanges and bolts were cooled down by a large amount of rainwater which had got into the rain-cover around the flanges.
This caused the material to shrink and made the flanges too tight, putting too much stress on the ring gaskets which deformed and damaged.
As a result, hydrogen gas and light oil mist leaked out and ignited spontaneously, causing damage to pressure gauges and insulation of pipes.

INITIATING cause was a too high thermo-mechanical stress on flange of a reactor, due thermal gradient induced by rain water.

Possible ROOT CAUSES could be an inadequate risk assessment or safety design, and inadequate operative processes, which failed to protect the installation from rain.

hydro-desulphurization unit, flanges and gaskets

The operative condition were as usual, but there was a heavy rain several hours before the accident, and a large quantity of rainwater flowed in between the rain cover and the heat-insulating sheet metal.

A pressure gage and piping heat insulation were damaged by fire.

There are many cases where insufficient attention is paid to the specific locations of each valve, and its possible lifetime damage patterns. It is only after that an incident took place, that plant management realises the inadequacy of installations.

1. Measures to prevent rainwater from flowing around the flange shall be taken.
2. Similar parts of the plant shall be checked as well, and countermeasures should be taken.
3. The procedure of flange tightening force shall be reviewed.