| Case Name |
Gas oil leakage from the tip valve of a bottom-loading tank lorry |
| Pictograph |
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| Date |
May 22, 1999 |
| Place |
Kawasaki, Kanagawa, Japan |
| Location |
Refinery |
| Overview |
A leak occurred at a lorry station when the loading arm was disconnected from the lorry for bottom loading. A small piece from a broken special pin reached at the poppet valve in the tip valve. So, the tip valve did not close tightly. The special pin that fixed a shaft and a link broke due to repeated stress. Moreover, the driver could not take a suitable measure due to a lack of education on emergencies, so the leak spread |
| Incident |
Loading of gas oil into a tank lorry of the bottom-loading type was completed. Then, the driver disconnected a tip valve (automatic adapter) of the tank lorry from a coupler of the loading arm tip. Gas oil leaked from the tip valve of the tank lorry. |
| Processing |
Manufacture |
| Individual Process |
Transfer |
| Process Flow |
Fig2.Unit process flow
|
| Substance |
Gas oil |
| Type of Accident |
Leakage |
| Sequence |
At 05:05 on May 22nd, 1999, a tank lorry arrived at the lorry station.
At 05:15, the tank lorry was placed at the directed loading spot, and the driver started loading preparations.
At 05:20, he started loading of three kinds of oil into the directed hatch.
At about 05:30, loading of gas oil finished. He disconnected a coupler of the loading arm of gas oil. Gas oil leaked from the tip valve of the lorry. As the leakage did not stop, he was convinced the problem was a block valve at the bottom of the tank, and operated the block valve with turning a switch 5 or 6 times. Although the leakage did not still stop, the lorry station's field operator stopped loading into the other tank lorries by operating an emergency shutdown valve. The driver stopped the bottom valve with the emergency shutdown valve at the rear of the lorry. The leak stopped. The inside of the tip valve was checked. Then a metal piece was found at the lower part of the tip valve seat. The metal piece was removed by opening the inner valve. It was confirmed that the valve closed perfectly. |
| Cause |
With a metal piece trapped in the valve seat of the tip valve, there was not a perfect close-out condition. The metal piece was immediately proven to be a special pin of the shaft presser foot at the coupler side. |
| Response |
1. The coupler was replaced with spare parts, and loading was finished.
2. The leaked gas oil was poured into the oily sewer with soapsuds and water, and it was recovered as waste oil. |
| Countermeasures |
1. All loading arm couplers for bottom loading were checked, and all the special pins were changed.
2. As for the type of special pin, changing to a tapered pin with a round bar from a rolled plate type will be studied. The structure of the coupler was changed, as the stress would not placed on the special pin.
3. "The emergency response procedure" for drivers was restudied, and a "note" was added on leakage accident prevention in loading work. Safety education for drivers was carried out based on this revised edition.
4. The cause and the countermeasures of this accident were explained to all of the company staff at the lorry station and the staff of the subcontractor in charge of on-land shipping, and retraining was carried out. |
| Knowledge Comment |
1. The accident might have happened due to a failure in a very small part of a small part from the viewpoint of the entire system. Sufficient study is required even for that kind of details.
2. Stress, especially repeated stress, arises where there is a driven part. |
| Background |
1. The special pin of the coupler at the loading arm side was damaged. The tip valve did not close perfectly, because a part of the damaged piece bit into the valve seat of the lorry side tip valve when the loading arm was disconnected.
2. The cause of failure of a special pin is estimated as follows. The turning force of the shaft from a switching handle operation of the coupler put bending stress on the special pin through the link. It occurred repeatedly, and the stress was concentrated at the root of the protrusion of the special pin acting as a supporting point. Moreover, through the inner fluid, the link of the shaft vibrated axially, and repetition stress was generated at the special pin. Due to the stress working in two directions, the special pin was gradually broken from the outside roll, and the breakage finally occurred.
3. There was a 300 L leak. The cause was the bottom valve opening, because the operator carried out switching operation for the bottom valve several times, and not only gas oil in the loading piping area but also gas oil flowed from the hatch. |
| Incidental Discussion |
There might not be many reports of problems caused by repeated stress at a special pin of the coupler. This accident might be the first report. The stress level the designer considered was probably small. However, the actual stress level might be larger than considered because of small differences in methods of attachment and fluid vibrations, etc. By looking at the results of using a practical unit like this, improvements will be gradually made. |
| Reason for Adding to DB |
The possibility of a large problem occurring from small parts with insufficient strength |
| Scenario |
| Primary Scenario
|
Unknown Cause, Occurrence of Unknown Phenomenon, No Responsibility of User, Planning and Design, Poor Planning, Poor Design of Manufacturer, Failure, Fracture/Damage, Breakage, Bad Event, Mechanical Event, Bite the Foreign Matter, Secondary Damage, External Damage, Leakage
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| Sources |
Kawasaki City, Fire fighting station, Prevention division, Peace section. Gas oil leakage accident from tip valve of the bottom-loading tank lorry. Material of the Kawasaki City complex safety countermeasure committee (1999)
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| 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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