Over-pressure damage to a storage tank in a refinery

The incident occurred during a temporary shutdown of the distillate hydro-treatment unit.
It 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, hydrogen at a pressure of 30 bars was allowed to enter the gasoline tank, causing an overpressure and substantial damage. The tank shell was lifted upwards by approximately 110 mm.

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 valves.
In this hydro-treatment unit, a valve in the start-up line to the high-pressure separator was branching off the line bringing the gasoline product from the crude oil distillation unit to the gasoline tank.
The high-pressure start-up line, carrying hydrogen at 30 bar, was opened before closing the line-to-tank valve.
The ICHEME report does not mention the ROOT CAUSE, but the operation error seems to hint 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.