| Case Name |
Fire of ethylene leaked from mounting part of a rupture disk of a polymerization reactor at a high-pressure polyethylene plant |
| Pictograph |
|
| Date |
November 26, 1991 |
| Place |
Ichihara, Chiba, Japan |
| Location |
Chemical factory |
| Overview |
On November 26th, 1991. In a polyethylene manufacturing plant applying a low-density, high-pressure method, de-pressurizing work was carried out to stop the polymerization section. When the reactor pressure dropped from 245 MPa to 65 MPa, ethylene gas leaked from the rupture disk mounting part, and a fire occurred. The cone ring at the mounting part of the rupture disk was not set properly, and ethylene gas leaked. The leaking gas was ignited by static electricity (speculation), and a fire occurred. |
| Incident |
Ethylene gas leaked from the mounting portion of a rupture disk during stopping of operation of the polymerization section at a polyethylene plant. The leaked gas ignited and a fire occurred. Refer to Fig2.
Rupture disk: A kind of safety device against a pressure rise. A flat plate with a weak part. The pressure is released by rupture of the part in case of an abnormal rise of pressure. |
| Processing |
Manufacture |
| Individual Process |
Maintenance |
| Process Flow |
Fig3.Unit process flow
|
| Chemical Reaction |
Polymerization |
| Substance |
Ethylene, Fig4 |
| Type of Accident |
Leakage, fire |
| Sequence |
08:37 on November 26th, 1991. For changing the screen pack of an extruder with switching the product grade, the stop operation of the polymerization section started. The operating pressure was lowered from the usual pressure of 245 MPa to 223 MPa. The supply of catalysts was stopped, and an operation for lowering pressure to 65 MPa was carried out.
About 08:50. Ethylene gas leaked from the rupture disk mounting position, and the gas detector was activated. At that time, the leaked gas was considered to have ignited. The thermometer indication rose. At 300 °C, the sequence of safety valves operated. Immediately, fire extinguishing operations such as cutting-off the gas supply were carried out.
09:05. Extinguishing and treatment were completed.
Screen pack: There is a cutter in the last stage of the extruder for pellets, and the screen pack is a special mesh mounted upstream. For replacing the screen pack, stopping of the polymerization is required because the first extruder is connected directly to the polymerization section in the high-pressure polyethylene plant. |
| Cause |
Ethylene gas leaked from the west side flange of the rupture disk.
The cause of leakage: The working face of the west side cone ring of the rupture disk was only about 2 mm (normally 4-6 mm), because the initial setting might have been bad.
The cause of ignition: As there is no direct ignition source in the vicinity, it was considered that ignition was caused by static electricity. |
| Response |
Cutting off the gas. Fire extinguishing activities. |
| Countermeasures |
1. Ensuring initial setting of the straight pipe on tightening the flange. A concrete checklist is reexamined and is corrected.
2. Eleven places where cone rings are renewed at a turnaround shutdown were overhauled and, the cone rings were changed. |
| Knowledge Comment |
If there are some problems with a piping connection, sometimes a failure might not happen immediately. Air tight tests are valid under the condition that all piping parts are correctly constructed in the correct procedure. In this case, a failure did not occur soon after mounting of the rupture desk-a failure occurred during a pressure-lowering procedure. |
| Background |
A lack of ability of the plumber or the site inspector who could not find the improper setting was the background of the accident. Connection using a cone ring is special work and is difficult. |
| Reason for Adding to DB |
Example of leakage and fire caused due to inadequate mounting of a rupture disk |
| Scenario |
| Primary Scenario
|
Carelessness, Insufficient Precaution, Carelessness of Operator, Usage, Maintenance/Repair, Repair, Malfunction, Poor Hardware, Leak, Secondary Damage, External Damage, Fire, Loss to Organization, Economic Loss, Direct Monetary Damage 3 million yen
|
|
| Sources |
High Pressure Gas Safety Inst. of Japan. High pressure gas protection overview. pp.186-187(1992).
High Pressure Gas Safety Inst. of Japan. Polyethylene manufacturing plant. Fire in protection wall of polymerization process. Accident examples of Petroleum refinery and Petrochemical units. pp.131-135(1995).
|
| Physical Damage |
25 square meters of heat insulating material, a thermometer, a gasket, lighting devices, cables, and 700 kg of ethylene burned. |
| Financial Cost |
¥ 3 million (Accident examples of Petroleum refinery and Petrochemical units) |
| Multimedia Files |
Fig2.Plant layout drawing
|
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Fig4.Chemical formula
|
| Field |
Chemicals and Plants
|
| Author |
DOBASHI, Ritsu (School of Engineering, The University of Tokyo)
TAMURA, Masamitsu (Center for Risk Management and Safety Sciences, Yokohama National University)
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