| Case Name |
Leakage and fire of hydraulic oil caused due to restriction of piping with a support at a thermal power station |
| Pictograph |
|
| Date |
November 28, 1997 |
| Place |
Kawasaki, Kanagawa, Japan |
| Location |
Power plant |
| Overview |
Near a generator turbine at a three-story power plant building of T Co., small smoke rose and was extinguished. At a restart of the power plant after a turnaround shutdown, hydraulic oil leaked through the flange at the hydraulic oil piping for the high-pressure steam adjusting valve, and the leaked oil caught fire after having penetrated hot insulation of the steam piping. The leak of hydraulic oil originated from a support that could not absorb the expansion of piping caused by a temperature rise. |
| Incident |
A turnaround shutdown for a power generator finished, and a test run started. Hydraulic oil leaked from a flange of hydraulic piping used for controlling a high-pressure adjusting valve that adjusts the quantity of high-pressure steam sent to a turbine for power generation. It was thought that oil permeated into heat insulation of the main steam piping which was installed beneath the control piping, then ignited. Refer to Fig2. |
| Processing |
Consumption and usage |
| Substance |
Hydraulic oil |
| Type of Accident |
Fire |
| Sequence |
On November 21st, 1997; at start-up after turnaround shutdown maintenance, oil was supplied to turbine bearing hydraulic oil piping. There was no problem,
On November 22nd; the turbine bearing hydraulic oil piping was pressurized at 0.16 MPaG. There was no problem.
On November 23rd; the turbine bearing hydraulic oil piping was pressurized at 0.54 MPaG. There was still no problem.
On November 28th; a boiler started. After adjustment, a power generation turbine started. An operator on patrol found ignition about 20 hours after the boiler started, and extinguished the fire with a fire extinguisher. Then, a block valve of the hydraulic oil piping was closed, and the leakage stopped. In addition, the generator stopped.
The leaked hydraulic oil piping was a part of the turbine bearing hydraulic oil piping system. |
| Cause |
1. The cause of a leak of hydraulic oil
a. A U-band support of 3/4 inch control hydraulic oil piping was mounted on a metal fitting welded to two-inch hydraulic oil piping for a high-pressure adjusting valve which controlled turbine supply steam. Movement of the control hydraulic oil piping was restricted at that position.
b. The distance between one of the supports and the bend of the control hydraulic oil piping was short, which became a factor that restricted piping transfer in the horizontal direction.
c. Due to thermal effects, an actuator of the high-pressure adjusting valve to which control piping was connected, moves in the horizontal direction when the turbine is driven. However, as movement of the control oil piping (3/4 inches) had been restricted, stress was applied at the joint, and hydraulic oil leaked through a gap at the joint.
2. Causes of fire
Leaked hydraulic oil dropped onto the concrete foundation for the steam turbine via a rod of the main steam piping spring support, and sank into heat insulation, and it was ignited by a high temperature of the external
surface of the main steam piping. |
| Response |
An operator on patrol found and extinguished the fire using a fire extinguisher. Public and private fire-fighters turned out. |
| Countermeasures |
Design was changed to give flexibility to the support so that it could follow the movement of the valve. Countermeasures for hydraulic oil permeating into heat insulation were taken. |
| Knowledge Comment |
1. Even if lube is not a dangerous material under the fire protection law, it is a flammable liquid, and should be treated like a dangerous material under the law.
2. The accident occurred after a turnaround shutdown. The support for small piping seemed to be fastened with a U-bolt without any care. The role of the piping support is not only fixing but also keeping an adequate relation between a moving part and a fixed part. Sufficient attention is required to the support. Although the accident seems small, its cause was fundamental. |
| Background |
A repair error with inadequate management seems to be the main cause. The main steam valve moved after the operation restart due to effects of temperature rising, and attached piping had to follow this movement, but a designer or a worker seems to have forgotten this during a turnaround shutdown. The supports of small piping were often decided according to field instructions, but in this case there seemed to be insufficient education and/or insufficient attention. |
| Reason for Adding to DB |
Example of accident caused due to poor installations of a piping support |
| Scenario |
| Primary Scenario
|
Ignorance, Insufficient Knowledge, Insufficient Experience, Poor Value Perception, Poor Safety Awareness, Insuficient Education/Training for Safety, Planning and Design, Poor Planning, Poor Design, Malfunction, Poor Hardware, Poor Piping Support, Failure, Fracture/Damage, Leakage, Secondary Damage, External Damage, Fire
|
|
| Sources |
Kawasaki City Fire station, Prevention division, Peace division, Outline of fire at turbine oil supply equipment of K power station, T power Co. Material of Kawasaki City Complex safety countermeasure committee (1997).
|
| Physical Damage |
500 mL of hydraulic oil leaked. Burning of heat insulation and some of the hydraulic oil. |
| Multimedia Files |
Fig2.Sketch of leakage position
|
| Notes |
The properties of hydraulic oil (FBK56): Flash-point: 256°C, Ignition-point; 468°C. In the current fire protection law, materials with the flash-point of over 250°C are excluded from dangerous materials. Although it is not a dangerous material under the Fire Protection Law, it still has dangerous properties. |
| Field |
Chemicals and Plants
|
| Author |
KOSEKI, Hirosi (National Research Institute of Fire and Disaster)
TAMURA, Masamitsu (Center for Risk Management and Safety Sciences, Yokohama National University)
|
