Fire from a Hydro-Desulfurization Unit of a Refinery
In a refinery, a fire occurred at a new reactor for the vacuum distillate hydro-desulfurization unit. Internal gas (hydrogen, hydrocarbon, etc.) blew from a flange of upper piping in the reactor. It ignited producing 0.5-2 meters high flames.
Event Date
September 27, 1989
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Causes
Cause Comments
The tightening operation of hot bolting at start-up three months before was inadequate. This suggest a out cause related to operation. However, the cause could be also, or in addition due to lack of instruction and procedures. it this is the case, it would reveal organization shortcoming. The technical cause was considered to be a loose flange due to uneven tightening force with uneven thermal expansion of materials at 10-inch piping where gas flowed at 390 C and 10MPaG. Concretely, the following is pointed out:1. There was not a sufficient margin for tightening force on hot-bolting.2. The material of the upper part of the flange was SUS321 and at the lower part was 2-1/4Cr-1Mo with an overlay. Coefficients of thermal expansion differed.3. Furthermore, thermal expansion of piping acted in the direction of opening the flange.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
flange of a reactor
Storage/Process Medium
Location Type
Location description
Industrial Area
Operational Condition
Pre-event Summary
The reactor was new, but the operations was a standard operation.
Lessons Learned
Lessons Learned
Hot-bolting, after exceeding 360 C, should be done at every 30 C. Regulations of hot-bolting were reviewed and the management system for bolt-tightening force was strengthened. A special check team was set up for the flange of a high-temperature and high-pressure part of newly constructed piping and vessels. The team carried out periodic inspections.
Event Nature
Emergency Action
Event sequence: 19:55. In a reactor with a height of 13 m, vacuum distillate containing hydrogen blew from a flange of the upper piping. It ignited and produced a 0.5-2 m high flame. 20:00. An emergency call to the fire department was made and the emergency shutdown was started. Pressure was reduced from operating pressure of 10 MPa(g). 20:08. Public fire brigades arrived. For fear of a secondary disaster with hydrogen sulfide, they stood by without extinguishing the fire with water. 20:44. The fire extinguishment was confirmed. 20:45. The pressure in the reactor lowered to 0.6 MPa(g). Nitrogen gas was introduced into the system. 21:20. Pressure lowered to 0.3 MPa(g) or less. Cooling by feeding nitrogen gas was continued.
Release Type
Release Substance
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
Orignal source lost. RISCAD is closed