Over-pressure damage to a storage tank in a refinery

The incident occurred during a temporary shutdown of the distillate hydro-treatment unit.
The crude oil distillation units main column overhead product was pumped to a gasoline storage tank via the straight run gasoline rundown line.
When restarting the distillate hydro-treatment unit, a valve in the start-up line to the high pressure separator branching off the crude oil distillation unit main column overhead product line was opened before the line to tank was closed.

Hydrogen gas at a pressure of 30 bars consequently reached the tank, caused an overpressure and caused substantial damage. The tank shell was lifted upwards by approximately 110mm.

No one was injured in the incident and there was no leakage of liquid product.

The INITIATING CAUSE was an operation error, a wrong sequence of opening and closing of the valve connecting the storage tank to the high pressure section of the hydrocracker, with consequence entrance of hydrogen at 30 bars to the tank.

The ICHEME report (see reference) does not mention the root CAUSE, but the operation error seems to hints at inadequate operative instruction and risk assessment.

Distillation tank, hydro-treater

The incident occurred during a temporary shutdown of the distillate hydrotreater.

DESCRIPTION OF THE HYDROTREATING PROCESS
It aims at removing (approx. 90%) the liquid petroleum fractions contaminants such as nitrogen, sulphur, oxygen, and metals.
The process brings compressed hydrogen to react with organic compounds to remove oxygen (deoxygenation) and other heteroatoms (nitrogen, sulphur, and chlorine).

The roof of the distillation tank was damaged.

According to the ICHEME report (see reference) the following lesson learnt were drawn:
1) Consider training of operators for routes by which storage tanks can erroneously receive unwanted pressure and ensure that facilities and/or procedures prohibit this as far as possible.
2) The pressure of volatile hydrocarbons must always be considered as a possibility in any refinery storage tanks until shown to be otherwise. This is very important when considering dipping and sampling procedures (e.g., adequate relaxation time to dissipate static charge), and when giving clearance for tank entry and repair work.