Explosion and Fire in a Desulfurization Unit of a Refinery
At the time of the incident, the desulfurization unit was shut down for scheduled cleaning of a cooling tower with reintroduction of a gas mixture into the system at a high hydrogen content. The accident was caused by the complete rupture of an 8 heat-insulated carbon steel pipeline located along an upper rack and fed by a hydrocarbon/hydrogen mix. The event triggered an explosion whose pressure surge was evaluated by the site operator at approx. 60 mbar at a distance of 10 m. Since the leak was being fueled, the fire affected other pipelines as well as the exhaust valves connected to the flare system, which explains the persistence of several secondary fire outbreaks, finally extinguished 8 hours later. The quantities released were estimated by the operator to be less than 2 tones of liquid hydrocarbons and 50 kg of hydrogen.
Event Date
June 3, 2007
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Cause Comments
The rupture was due to external corrosion localized on the pipeline supporting structure. Over a section approx. 45 cm long on the lines lower half-circumference, the residual pipeline thickness equaled 3 mm on average vs. 6.5 mm originally, and eventually reached 1.2 mm in certain zones. The rupture occurred in two stages: an initial break, followed by propagation of the opening as a result of the high pressure of gases circulating inside the pipeline.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
Desulfurization unit in a refinery
Storage/Process Medium
Location Type
Location description
Industrial Area
Operational Condition
Pre-event Summary
The desulfurization unit was stopped for a programmed clean-up of an aero-cooling with circulation of a hydrogen-rich mixture.
Consequences
Number of Injured Persons
8
Number of Fatalities
1
Currency
Lessons Learned
Lessons Learned
The plant operator adopted the following measures, aiming at avoiding the reoccurrence of the event.The risk assessment was reviewed, for the gas lines with corrosion hazard, either under the heat insulation or at the supporting points. In the new risk assessment, the possibility of a pipe burst has to be taken into account under specific operative conditions: service pressure above 25 bar; presence of gaseous or mixed fluids; diameter exceeding 2; presence of hazardous fluid (H2, C2, C3, H2+H2S). Moreover, the plant operator also ensured the adequate implementation procedures and good state of heat insulation. Finally, a special examination was also carried out on pipes not being stored on skids.
Event Nature
Emergency Action
As hydrogen leak was continuous, the fire extended to other pipes resulting in some secondary fires which were controlled at 3h30 am.
Release Type
Release Substance
Release Amount (kg)
50.00
Ignition Source
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
Event no.33071 of the French database ARIA
https://www.aria.developpement-durable.gouv.fr/accident/33071/
(accessed December 2020)