Hydrogen Explosion at a Refinery
The accident occurred at a distillate dewaxing Unit (MDDW) of the refinery, during the operation of regeneration of the catalyst. To perform this operation, both temperature and pressure have to be increased. After approximately six hours after having reached the correct regeneration conditions, the 10 inches pipe at the bottom to one of the two reactor experienced a guillotine break, and hot gas was released from both ends. The gas released consisted of 81% of hydrogen, 9.5% of methane and some light hydrocarbons. It rapidly ignited (0.7 sec), causing an explosion. A shock wave from the resulting explosion expanded through the adjacent neighbourhood, causing varied degrees of blast damage to residential homes. The ensuing flash fire spread up to 230 feet west of the tank farm.
Event Date
November 4, 2009
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Cause Comments
The immediate cause of the accident was the corrosion of pipe, inducing thinning of the pipe wall. The corrosion went uninspected for years. The metallurgical analysis (see references) identified the same kind of suffixation corrosion already found in accidents in other plants; sulfur compounds in the process stream corroded a steel piping segment, causing the pipe walls to become severely thin. While sulfidation is a well-known damage mechanism at refineries that requires regular inspection and monitoring, the segment that failed has no record of ever being inspected.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
distillate dewaxing unit, catalytic bead
Storage/Process Medium
Location Type
Location description
Industrial Area
Pre-event Summary
Catalytic dewaxing is a particular hydrocracking process used to improve cold flow properties of middle distillates and lubricants by cracking normal paraffins. The pipe failure occurred at the exit of the one of the two catalyst bed reactors of the distillate dewaxing Unit, on the line bringing the gas to the heat exchanger. The unit was undergoing hot hydrogen regeneration of the catalyst at the time of the explosion. Catalyst regeneration is a procedure performed periodically, in which the normal liquid hydrocarbon feed stops and a hydrogen-rich gas mixture is fed through the catalyst bed. The process occurs at a temperature (800 F, 370 C), higher than the operative temperature (700 F, 430 C).
Lessons Learned
Lessons Learned
The accident was due to pipe walls being thinned due to corrosion that went undetected for years (no inspection record were found). Regular and adequate inspection is hence key to prevent such event.
Event Nature
Emergency Action
Unknown
Release Type
Release Substance
Release Amount (kg)
43.00
Ignition Source
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Flame Type
Source Category
References
References
Final Metallurgical Analysis report by Exponent, June 19, 2013, subcontracted by CSB,
https://www.csb.gov/silver-eagle-refinery-flash-fire-and-explosion-and-…
(accessed November 2020)
Statement by Investigations Supervisor Don Holmstrom and CSB Chairman John Bresland, 11.17.2009,
https://www.csb.gov/silver-eagle-refinery-flash-fire-and-explosion-and-…
(accessed November 2020)