| Case Name |
Leakage and explosion of hydrogen at outlet piping of a reactor in the indirect hydrodesulfurization unit of a fuel oil |
| Pictograph |
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| Date |
March 6, 1989 |
| Place |
Kurashiki, Okayama, Japan |
| Location |
Refinery |
| Overview |
A cap of piping at the outlet of a heat exchanger in the furthermost downstream at the reactor outlet side of an indirect desulfurization unit of a fuel oil corroded, and an opening occurred at the cap. Hydrogen that leaked exploded, oil leaked out from the heat exchanger due to the explosion, an oil fire also occurred, and the damage spread. The causes of corrosion might be the following three: The concentration of corrosive substances of injection water in the original process was high. The concentration of corrosive substances increased due to remolding of the heat exchangers. The shape of the cap was dead end piping. |
| Incident |
During normal operation of an indirect desulfurization unit of fuel oil at a refinery, hydrogen leaked from a cap of an outlet header at a reactant condenser (a fin-fan cooler of eight runs) "A" which was the furthest downstream of a series of heat exchanger groups in the reactor outlet side of the plant exploded. Refer to Fig.2. |
| Processing |
Manufacture |
| Individual Process |
Reaction |
| Process Flow |
Fig3.Unit process flow
|
| Chemical Reaction |
Other (hydro-desulfurization) |
| Substance |
Hydrogen, Fig4 |
| Vacuum gas oil |
| Type of Accident |
Leakage, explosion, fire |
| Sequence |
At about 00:32 on March 6th 1989, a whooshing sound was heard. Soon after that there were a fire and an explosion. A power failure happened at the same time in the control room and in the field. An emergency shutdown was carried out immediately.
At about 03:55, fire engines turned out. Water spraying for cooling nearby facilities was carried out.
At about 06:30, there were prospects of extinguishing the fire. |
| Cause |
An opening occurred at one of the caps of the T type piping at the outlet of reactant condenser "A" in the furthermost downstream of a series of heat exchanger groups at the outlet of the indirect desulfurization reactor, and high-pressure hydrogen leaked through the opening. The leaking gas remained, was ignited by static electricity, and exploded. Other heat exchangers were also damaged by the blast, fuel oil inside escaped, and there was an oil fire. Due to the thermal effects of the flames, equipments and structures were damaged, and the damage spread. |
| Response |
An operator shut down the plant immediately after the accident. The fire brigade turned out and cooling water was sprayed on peripheral equipment. In addition, foam fire extinguishing was carried out and the fire was extinguished. |
| Countermeasures |
1. The management system of operations and facilities should be strengthened at the hydrodesulfurization unit to grasp abnormal phenomena such as local corrosion and to respond properly.
2. The safety review system for remodeling o installation of new facilities should be strengthened. Besides, safety of other existing facilities should be re-evaluated.
3. As a request, all refineries with the same kind of desulfurization unit should check dead end piping areas of the accident point thoroughly. Simultaneously, it is desirable to do a safety review of operational and facilities management. |
| Knowledge Comment |
1. It is a fact that if you do not make a very careful study, safety aspects might be disregarded, even if the initial purpose of remodeling is achieved.
2. No conditions are completely the same in the similar great number of plants having the same process. Safe handling of plants would be difficult without fully understanding each of its characteristics.
3. Dead-end piping is the cause of various problems, so careful attention would be necessary to areas of dead end piping. |
| Background |
Scale was deposited at the cap section of the outlet piping of the heat exchanger. Corrosion caused by corrosive substances such as ammonium hydroxide and chlorine which was included in the injection water of the process progressed and decreased the thickness of the cap section. In addition, a dummy support was being welded to the cap section, so thermal stress might also be a cause. It is very characteristic that the concentration of corrosive substances was controlled at a higher level at the plant in comparison with that at a similar plant of another company. In 1985, the addition of a heat exchanger and rearrangement of heat exchangers at the outlet of the reactor were carried out to rationalize energy recovery. Therefore, the concentration of corrosive substances at the heat exchanger outlet increased. According to general opinion at that time, no one believed the wall thickness at the part would be reduced by corrosion, so the part was not selected for wall thickness measurements. Therefore, it was not possible to discover the decrease of thickness at an early stage.
The cap section was at the end of an outlet header of eight heat exchangers and the exit of the collecting pipe of heat exchangers, and had a dead end.
In the dead end part, a replacement of fluid is difficult, and concentrations of corrosive substances would increase locally.
The piping's structure seems also to be a cause. |
| Incidental Discussion |
The accident is considered as an example at a chemical plant still contains the area of experience engineering. Is there an engineering method in which such an accident never occurs? The same kind of accident will occur again if safety depends only on experience and investigation ability of the engineers. |
| Reason for Adding to DB |
Example of accident that occurred due to insufficient anticipation of influences of remodeling |
| Scenario |
| Primary Scenario
|
Insufficient Analysis or Research, Insufficient Practice, Lack of Imagination, Poor Value Perception, Poor Safety Awareness, Inadequate Risk Recognition, Ignorance, Insufficient Knowledge, Insufficient Collection of Related Information, Planning and Design, Poor Planning, Unsuitable for Operatiom Condition, Failure, Abrasion, Corrosion, Secondary Damage, External Damage, Leakage/Explosion/Fire, Bodily Harm, Injury, 3 person injured, Loss to Organization, Economic Loss, Direct Monetary Damage 480 million yen
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| Sources |
Yuji Kawamura. Investigation on explosion accidents at Fuel oil indirect desulfurization unit in Mizushima petroleum complex. Fire and explosion accident examples. Japan Soc. for Safety Engineering. pp.90-96(2002)
Chugoku International Trade and Industries Office. Investigation report of Fuel oil indirect desulfurization unit explosion accident at N petroleum M Refinery in Okayama Pref. (1989)
High Pressure Gas Safety Inst. Of Japan. Fuel oil indirect desulfurization unit hydrogen gas explosion. Accident Examples of Petroleum Refinery and Petrochemical unit. pp.51-53(1995)
Assoc. for Safety Technics of Dangerous Materials. Accident case of dangerous material. Dangerous material accident case seminar. pp.57-58(1996)
|
| Number of Injuries |
3 |
| Physical Damage |
Piping, a fin-fan cooler, instrumentation devices and a structure etc, installed near the high-pressure separator burned out. At the factory, windows of 57 buildings in a 1 km radius were damaged. Outside the factory, windows of six buildings within a 2.5 km radius were damaged, and 14,000 cubic meters of hydrogen and 30 kL of vacuum gas oil burned out. |
| Financial Cost |
¥ 480 million (Accident cases of dangerous material) |
| Multimedia Files |
Fig2.Outlook of outlet header
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Fig4.Chemical formula
|
| Field |
Chemicals and Plants
|
| Author |
KOBAYASHI, Mitsuo (Office K)
TAMURA, Masamitsu (Center for Risk Management and Safety Sciences, Yokohama National University)
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