Fire in the hydrogenation reactor of a alcohols an acids production plant

The event occurred at a chemical plant synthesising alcohols and acids by reactions between olefins and a H2 -CO gas mixtures. A pressure drop was noted on the on the primary hydrogenation reactor, caused by a leak from a thermally insulated pipe carrying hydrogen. The unit was depressurized, but 15 minutes later the hydrogen ignited generating a jet fire directed towards the inside of the unit.

The emergency plan was triggered, with four water jets cooling the unit. The fire was put under control by means of fire extinguishers do that the firefighters did not need to intervene.
No injury. Property damage and environmental impact (smoke) were limited.

The INITIATING CAUSE was the self-ignition of hydrogen released via a crack in a pipe.

The crack was probably caused by corrosion and consequent reduction of the stress-bearing section of the pipe. An investigation of the pipe revealed a 30 mm long crack perpendicular to the axis of the pipe in the outer part of an elbow, evidence of corrosion in the direction of the flange connecting to the condenser and internal corrosion at the elbow. The pipeline experienced corrosion and erosion, as well as out-of-specification stresses due to insufficient support, which weakened the elbow.
The ROOT CAUSE could be attributed to design shortcoming, aggravated by the incapacity of the inspection to detect reduction in wall thickness.

hydrogen pipe, hydrogenation reactor

DESCRIPTION OF THE PROCESS/COMPONENT
The purpose of the unit was to convert unsaturated fatty materials (such as oils, fats, or fatty acids) into high-purity alcohols. The alcohols were synthesised in 3 steps: high-pressure (280 bar) ozonisation, primary hydrogenation in presence of a catalyst, vacuum distillation and final hydrogenation.
The pipe which failed was a DN 50, 3.6 mm thickness pipe, with a nominal pressure of 40 bar.

Property damage and environmental impact (smoke) were limited.

2:40 The unit is depressurized
2:55 (15 minutes later) the hydrogen ignites by self-heating generating a torch fire directed towards the inside of the unit.
The emergency plan is triggered, with four water jets cooling the unit.
3:15 Fire under control by means of fire extinguishers.
3:10, The firefighters arrive to the scene but do not intervene
3:30 The emergency plan is called off .

Since the cause was failure to bear stress at a corroded pipe elbow, a thicker tube was used to replace the cracked pipe (5.6 mm thick instead of 3.6) and a suitable support was put in place to reduce stress at the elbow.