| Case Name |
Leakage and fire of LPG caused due to inadequate repair work at a gasification-desulphurization plant |
| Pictograph |
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| Date |
November 25, 1991 |
| Place |
Kawasaki, Kanagawa, Japan |
| Location |
Refinery |
| Overview |
On November 23rd, 1991, a pinhole was found at the lower nozzle of a level gauge in a LPG washing column of gasification-desulphurization unit for a vacuum residue in a refinery in Kanagawa Prefecture. Welding was carried out by the box-in method, which is a method that does not require stopping operation. The opening was suddenly expanded on the 25th, and a large amount of LPG blew out, which was ignited by a welding spark. Selection of the repair method and management were inadequate. |
| Incident |
A fire occurred during repair work at a LPG washing column of a gasification-desulphurization unit for vacuum residue oil in a refinery. A pinhole was found in short piping connected to a bottom level gage at the lower nozzle of the same tower. The repair work started by the box-in method as an emergency repair while operation continued. The pinhole opening expanded during repair work, LPG in the washing column spouted out and was ignited by an electric welding spark, and a fire occurred. As a safety countermeasure, steam condensate was filled into the bottom to seal it with water from the opening to the upper part, however, both water and LPG spouted out.
The operating condition was 14 atm and 38 °C.
Using the box-in method, the leakage in the piping should be stopped from the outside by wrapping the leak part in larger diameter piping.
Box-in method; Refer to Fig2. |
| Processing |
Manufacture |
| Individual Process |
Maintenance |
| Substance |
LPG (Liquefied petroleum gas) |
| Type of Accident |
Leakage, fire |
| Sequence |
On November 23rd, 1991, about 10:40. A manufacturing section operator found a leak from piping connected to the level gauge at the lower part of the washing column during a scheduled patrol.
Afternoon. Emergency repair methods were studied. It was judged that water sealing was possible, and welding repair was done using the box-in method.
About 20:00. Water sealing started with high-pressure water at the bottom of the tower. Repair using the box-in method started.
On November 24th about 02:30. Mounting of the circumference box was completed, but there was a water leakage.
About 10:30. The second attempt at repairing started using the box-in method.
About 16:00. Repair was completed, but there was a leak at the weld.
On November 25th about 10:20. The third attempt at repairing using the box-in method started.
14:40. A fire occurred.
14:50. An emergency shutdown was carried out. |
| Cause |
The piping was remarkably thin due to corrosion from inside and outside. Scale adhering to the surface was detached because a water seal and a welding repair were carried out repeatedly. Therefore, the opening suddenly expanded and LPG blew out. The gasified LPG was ignited by a welding spark. The first repair work did not stop the leakage, and the second and third attempts at repairing were made. This inappropriate work was also one of the causes. |
| Countermeasures |
1. Leakage prevention. (Strengthen material inspection, protect against corrosion, etc.).
2. Strengthen the management system. (Equipment test data is used immediately for facilities).
3. Strengthen safety education. (Including subcontractors' employees).
4. Improve repair methods.
5. Improve equipment of facilities. |
| Knowledge Comment |
The repair method and the situation nearby have to be sufficiently investigated when making a repair with hot work without stopping a plant, and sufficient safety countermeasures are required during repair work.
J Changing of the repair method is also necessary in case the repair does not go well. |
| Background |
1. Corrosion in piping.
(1) STPG38 equivalent was used instead of SUS304 as the piping material.
(2) A local cell was formed because the carbon steel piping was connected to both ends of a stainless steel valve, and corrosion was promoted.
(3) No protective coating was applied.
2. Inadequate construction method.
(1) Repair work was continued for 8.5 hours, although the time for repairing was limited to 4 hours because the condensed LPG accumulates on the sealing water. The water level seemed to drop because it was controlled at level gauge reading of 40%.
(2) Strength confirmation of the repaired part was insufficient. Thickness measurement was not possible near the opening, and corrosion was not examined. In such a situation, welding was repeated many times at a small area of about 170 mm in length.
It is speculated that there were some problems in selecting the repair method to reduce cost and to shorten the repair period. |
| Reason for Adding to DB |
Example of leakage and fire caused due to corrosion |
| Scenario |
| Primary Scenario
|
Poor Value Perception, Poor Safety Awareness, Insufficient Recognition of Risk, Misjudgment, Misperception, Mis-Convincement, Organizational Problems, Inflexible Management Structure, Schedule the First, Planning and Design, Poor Planning, Poor Planning of Repair, Failure, Abrasion, Erosion, Failure, Large-Scale Damage, Leakage, Secondary Damage, External Damage, Fire, Bodily Harm, Death, Bodily Harm, Injury
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| Sources |
High Pressure Gas Safety Inst. of Japan. High-pressure gas protection overview. pp.171-173, 186-187(1992).
High Pressure Gas Safety Inst. of Japan. Gas recovery equipment, Fire at cracked gas recovery plant washing column. Accident examples of Petroleum refinery and Petrochemical units. pp.67-75(1995).
Kawasaki City Fire fighting station. Matsuo Yoshida. Accident prevention at petrochemical plant-case studies. Dangerous material accident case seminar. pp.39-45(1993).
Kawasaki City Fire fighting station Prevention division Safety section. Outline of fire at gasification-desulfurization plant gasification part of T petroleum Co., Ltd. K refinery. Material of the Kawasaki City complex safety countermeasure committee.
|
| Number of Deaths |
1 |
| Number of Injuries |
1 |
| Physical Damage |
Instruments and light fixtures were damaged by fire. Mixed gas of 0.75 ton was lost. |
| Financial Cost |
¥ 1 million (Material of the Kawasaki City Complex safety countermeasure committee) |
| Multimedia Files |
Fig2.Figure showing repairs
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| Field |
Chemicals and Plants
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| 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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