Ready For The Big One
THE MAGAZINE DEVOTED TO NICKEL AND ITS APPLICATIONS
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The Numazu Harbor waterway floodgate is the largest in Japan. It spans 40 metres from left bank to right
bank and the width of the connecting bridge is 3 metres.
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Large quantities of stainless clad steel plate were used in the structure.
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This is the first time in Japan that any structure has used such a large amount of double-sided clad
material.
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Japan's Numazu Harbour floodgate uses double-sided clad stainless steel
Nickel Magazine, July 2006 -- The floodgates used in Japan’s many flood control and irrigation works are essential to ensuring safe water usage, even in extreme conditions. Little wonder, then, that austenitic stainless steel is increasingly the material of choice in their construction.
Japan’s largest single-diameter floodgate is found in the Numazu Harbor Waterway. The structure was built on the waterway that joins the inner and outer harbours at the port city of Numazu in central Japan facing the Pacific to the south. The floodgate was built for protection against the tsunami which is expected to follow the anticipated Tokai earthquake, if and when that disaster happens. The gate weighs 923 tonnes, is 40 metres wide and 9.3 metres tall, and strides the waterway in one span. In the event that the tsunami does occur, the gate closes to prevent water from rushing in, thereby protecting the lives of about 9,000 people, as well as some 50 hectares of land that surround the port.
The floodgate is clad in S31600 stainless steel on both sides. The stainless provides a high resistance to corrosion and wear, and the inner steel provides high strength at a low cost. Steel that is coated with an anti-corrosive layer was considered, but must be recoated periodically; however, stainless steel does not require recoating, which is why maintenance-free stainless steel cladding was used on both sides of the Numazu floodgate. The main advantage to using stainless is that new coatings won’t have to be applied when earthquakes occur.
There are several ways of making double-sided stainless steel clad plate. The builders of the Numazu
floodgate used hot rolling, whereby one side of an ordinary steel plate is overlaid with a stainless steel
plate. After automatic welding of that one side in a vacuum chamber, the other side is overlaid and welded in
the same way. The metal piece is then heated and rolled to allow the formation of a metallurgical bond of the
different metals by diffusion.
The gate piece weighs 406 tons, with the double-sided stainless steel clad plate constituting a little under
half of that total. It is the first time in Japan that a floodgate, or indeed any structure, has used such a
large amount of double-sided clad material.
PHOTOS: Nickel Institute Japan
Tetsuyoshi Kohga |
