Fire on a hydrogen compressor in a refinery

The incident occurred at a refinery unit for the desulphurisation of a light heavy oil.
This unit was equipped with three hydrogen compressors. Two of them were usually operated and the third was kept in standby. On the day of the accident, due to the malfunctioning of one of the two operating compressors, it was decided to switch to the standby compressor.
The pre-start-up inspection of this compressor did not reveal any problem. However, at the start-up, its recycling buffer burst, releasing hydrogen which caught fire.

The INITIATING CAUSE was a loss of confinement due to corrosion.
The buffer tank ruptured at normal operating conditions (66 barg, 66 ° C, in presence of hydrogen sulphide). This tank, which had the function of damper, had experienced a humid hydrogen sulphide gas environment for many years. The rupture occurred by stress corrosion cracking caused by the hydrogen sulphide gas.
The ROOT CAUSE was due to inadequacies in material selection, design, and maintenance inspection of the failed component.

H2 buffer tank (damper),
Hydrogen compressor

The desulphurisation unit was equipped with 3 hydrogen recycling compressors. Two of them were usually operated and the third was kept in standby. On the day of the accident, one of the two operating compressors started malfunctioning. Therefore, it was decided to switch to the standby compressor.
The pre-start-up inspection of this compressor did not reveal any problem.

DESCRIPTION OF THE PROCESS
The makeup side of the hydrogen suppy delivered 8900 std m3/h 15 bar at ambient tempearture.
At the compressor, the process gas was brought from 69 bar (64 C) to 82 bar (80 C), with a flow of ca. 52,000 std m3/h.

Flying debris was scattered within a radius of 29 m. Total damage to the slate roof of a high-pressure gas compressor house.
Damage to the hydrogen compressor, to the steel floor gratings, and to the wall of a shed.

The unit was depressurised and the fire extinguished after 1h, due to hydrogen depletion.

An improved component/system design should take into account the chemical environment when in use. The following improvements should be considered:
1. For this type of components, corrosion prevention measures are required, principally by design, by using better fit-for-purpose materials.
2. The mitigation of the effect of stress corrosion on the integrity of components could be achieved by measure preventing excessive mechanical/chemical stress transients, such as using shock absorbers.
3. The inspections should be improved, by developing effective methods to monitor ageing of components under complex boundary operative conditions. Detecting incremental damage at microstructural level is a difficult task, nevertheless critical to assess component integrity.