| Case Name |
Leakage and explosion of hydrogen caused by using SUS304 in a chloride atmosphere and poor welding at a hydrogenated reduction plant. |
| Pictograph |
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| Date |
May 30, 1992 |
| Place |
Kawasaki, Kanagawa, Japan |
| Location |
Chemical factory |
| Overview |
An explosion occurred at a plant where p-nitrophenetole (PNP) is reduced to p-phenitidine with hydrogen. A PNP drum supplying PNP to a hydrogen reduction reactor burst into flames, and part of the insulation was damaged and fell off. Upper part of the PNP drum and piping that connected the PNP drum and the reduction reactor were destroyed by the fire. There were eight penetration cracks at welds of piping from the PNP drum to the reduction reactor. The valve was not completely closed, and hydrogen and toluene flowed back from the reduction reactor to the PNP drum. Leaked hydrogen accumulated underneath the insulation cover, and was ignited by a static electric spark. The causes of the leakage were considered to be inappropriate selection of piping material and inadequate welding. |
| Incident |
At a p-phenitidine manufacturing plant where hydrogen reduction of p-nitrophenetole (PNP) was performed, an explosion occurred. A PNP drum for supplying PNP to a hydrogen reduction reactor, burst into flames, and part of the insulation was damaged and fell off. Upper part of the PNP drum and piping that connected the PNP drum and the reduction reactor were destroyed by the fire. Hydrogen and toluene flowed backward from the PNP drum to PNP supply piping, and leaked under the insulation. Hydrogen and toluene accumulated, ignited, and exploded. The explosion occurred around piping from the PNP drum (Fig3, 3 page, left D-108) to the reduction reactor (R-401A). |
| Processing |
Manufacture |
| Individual Process |
Reaction |
| Process Flow |
Fig2.Reactor schematic diagram
|
| Chemical Reaction |
Reduction |
| Substance |
Hydrogen, Fig3 |
| Sequence |
09:30 on May 30th, 1990; Charging toluene and catalyst, and next PNP to the reduction reactor started.
14:00 Charging finished. Nitrogen purging of the reactor was performed.
15:20 Hydrogen displacement in the reactor started.
About 15:30 Whistling was heard from somewhere around the PNP drum. The cause of the whistling was checked but it was not clear. Steam was supplied to the jacket of the reduction reactor, and a temperature rise started.
15:40 Hydrogen displacement was completed.
15:48 A reduction reaction started.
16:05 Flames spouted from upper and lower parts of the PNP drum.
16:10 The fire was extinguished by employees.
16:15 A fire brigade confirmed the fire was extinguished.
(History of the plant)
The plant was approved as a manufacturer of dangerous materials on December 25th, 1990. The accident occurred a year and a half after the start of operation. |
| Cause |
There were 40 cracks in the welded part of piping (SUS304 3 inches) connecting the PNP drum and the reduction reactor, among which eight were penetration cracks. In addition, the valve between the PNP drum and the reduction reactor was not completely closed. This was the cause of a back-flow of hydrogen and toluene from the reduction reactor, which leaked through the penetration cracks to a space underneath the insulation. Hydrogen and toluene filled the space between the PNP drum surface and an insulation cover, were ignited by static electric sparks and exploded. |
| Response |
1. An emergency shutdown of the entire factory.
2. Fire extinguishing by employees.
3. Thorough inspection of similar facilities. |
| Countermeasures |
1. All similar piping was replaced with that made of SUS316L, and welds were inspected with X-rays.
2. Valves with an air flow meter were installed to be monitored from a central control room.
3. Valves were replaced with those that are easily checked for an open/closed state.
4. Inspection windows were made on piping with insulation for daily checks.
5. The pressure and temperature of steam trace of a supply line of the PNP drum were lowered.
6. The standards of operation procedure and education for employees were prepared and carried out without exception. |
| Knowledge Comment |
1. Not all stainless steels are resistant to chlorine corrosion. Careful selection of the kind of stainless steel is essential because it is possible that corrosive chlorine or hydrochloric acid is produced by some unexpected reactions.
2. When part of the system experienced a problem, not only that part but also related parts should be examined carefully to prevent accidents. |
| Background |
1. There was incomplete fusion at all welded parts of the piping. Inadequate construction and construction management were suspected.
2. A mistake in selecting piping material was suspected. SUS316L, which is resistant to corrosive characteristics of chlorine, should have been used instead of SUS304. However, it is not sure whether the corrosive nature of p-nitrochlorobenzene was recognized or not.
3. Valve operation management was not adequate.
4. Other reports indicate that the piping had already experienced leakage twice in the past, and part of the piping was replaced with SUS 316L. The accident would have not occurred if the whole piping had been replaced at that time. There must have been negligence or a serious mistake in judgment. |
| Reason for Adding to DB |
Example of explosion caused due to improper selection of piping material. |
| Scenario |
| Primary Scenario
|
Ignorance, Insufficient Knowledge, No Consideration about Erosion Property of Raw Material, Organizational Problems, Poor Staff, Poor Experiment of Staff, Hydrogen Reduction Reaction, Planning and Design, Design Misuse, Mal Material Selection, Production, Hardware Production, Piping Construction, Usage, Maintenance/Repair, Inspecton, Regular Operation, Erroneous Operation, Valve was not Closed Tightly, Failure, Fracture/Damage, Crack, Secondary Damage, External Damage, Explosion
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| Sources |
High Pressure Gas Safety Inst. of Japan. High-pressure gas protection overview. p.231(1994)
National dangerous object safe association. Explosion caused by hydrogen leakage from pipe crack. 100 cases of accidents 100-No.2- at dangerous facilities. pp.29-30(1994)
Kawasaki City. Fire fighting station. Prevention division. Peace section. Outline of explosion and fire accident at K industry Co., Ltd. Material of the Kawasaki City complex safety countermeasure committee.
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| Physical Damage |
A PNP storage and piping, etc, were partially destroyed by fire. |
| Multimedia Files |
Fig3.Chemical formula
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| Field |
Chemicals and Plants
|
| Author |
YOSHINAGA, Jun (Graduate School of New Frontier Sciences, The University of Tokyo)
TAMURA, Masamitsu (Center for Risk Management and Safety Sciences, Yokohama National University)
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