hydrogen fire in the hydro-desulphurisation unit of a refinery

A hot oil line (8-inch) in the hydrodesulphurisation unit failed due to fatigue cracking. Hot oil at 50 bar and 343°C sprayed across the roadway into the hydrogen units where ignition occurred. The pipe break was a guillotine -type, probably in the heat affected zone at 2 inches from a welding.
The intense fire around the pipe rack in the hydrogen plant caused a hydrogen line (16-inch) to rupture, adding a second blow torch to the fire. In successive order, more pipes ruptured with explosions.
After six-and-a-half hours, the fire was extinguished.
Damage was extensive. The three hydrogen units and the four HDS units were heavily damaged or destroyed.

The INITIATING CAUSE is fatigue cracking of the oil pipeline, which caused the failure of a hydrogen pipe.
Sources refer to probable fatigue cracking, possibly hydrogen assisted.
Before the loss, the line which failed was judged as having excessive vibration.

Failure of managing out-of-specification fatigue phenomena may be the root cause, or at least a contributing cause.

hydrogen (generation) unit

9 years earlier vibrations had been noted on the gas line which failed. The structure had been stiffened by means of gussets. An hypothesis is that this intervention had amplified/accelerated the fatigue phenomena which was caused the break of the line., together with blistering due to hydrogen attack.

Damage was extensive. The three hydrogen plants and the four HDS units were heavily damaged
or destroyed.
Other source report M$89(Excluding Production loss.)

The fire lasted 6h30