抄録
A large-scale leakage happened from the discharge flange of water supply pump located at the Sasage pump station of Yokohama Waterworks bureau on July 10 in 2007. The motors in the pump station were submerged by water and inevitably stopped. Suspension of water supply or low pressure water supply reached to 22000 houses due to this accident. It took about six hours until the water supply was recovered by using another water supply routes. The investigation committee (headed by Professor Sekine of Yokohama National University) was formed. The investigation committee charged High Pressure Institute of Japan (in shorten HPI) to determine the root cause of the accident. HPI has formed the special group headed by Professor Sawa of Hiroshima University and the members described above. The group immediately started to investigate and take necessary measurements of the bolted flange joints in the facility. Then, the group interviewed the foreman engaged in the maintenance work, analyzed the operation data, carried out the experiment to measure the gasket behavior and examined the root cause. The group found that the main accident cause was due to the lower gasket stress caused by inadequate tightening of the bolts when the pump was overhauled in March 2007. The group summarized a written report of the whole activity of the special group to elucidate the accident cause and to propose the methods for preventing the leakage accident from bolted flange joints with gaskets.
