Fire on a hydrogenation reactor of a refinery

A weld on a 1 inch diameter instrument tapping from a Octafiner reactor overhead line fractured, resulting in a small but intense fire, lasting about 50 minutes until the unit was nitrogen purged.

The fire was always under control and the fire fighting effort was directed solely to cooling the surrounding metal with fire steam lances. Plant Inspection reported that the failure was due to hydrogen embrittlement of the heat affected zone of the tapping and probably resulted from improper or no stress relieving of the connection during construction.

The INITIATING CAUSE was the failure of a weld on an instrument line of the reactor.
The fracture was due to hydrogen embrittlement, probably worsened by the presence of non-design stress probably due to an inadequate heat treatment for relieving welding stress.
The ROOT CAUSE could then be attributed to manufacturing shortcoming, possibly together with choice of non-optimal materials. Nothing is known on the inspection procedures which could identify degradation in its early stage.

octafining reactor pipe, weld

PRCOESS

DESCRIPTION OF THE PROCESS
The Octafiner process is catalytic hydrogenation process. It is a patented technology aiming at upgrading heavy oils and distillates into lighter, higher-value products. This process is used to remove sulfur, nitrogen, and metals, and to saturate aromatics, which improves the quality of the product.

The fire was always under control and the fire fighting effort was directed solely to cooling the surrounding metal with fire steam lances. The fire stoppedwhen the reactor was nitrogen-purged (which implies that it was shutdown first).

The emergency measures taken were effective in containing the emergency and avoiding escalation. Probably the fact that the fire was small helped in not affecting surrounding component. The measure which solved the emergency was the purging by nitrogen, which stopped the fire.