| July 1, 1999 |
NKK Titanium-Clad Steel Sheet Used In Construction of Huge PontoonNKK recently completed the corrosion protection work on the splash zones of a steel pontoon on the Yumeshima side of the Yumeshima-Maishima Bridge, the world's first large-scale revolving pontoon bridge. Osaka City is funding construction of the bridge, which will link two manmade islands in Osaka Bay. NKK's work, awarded by a joint venture formed by Mitsubishi Heavy Industries, Kawasaki Heavy Industries and two other bridge construction companies, involved lining the large floating structure with its own titanium-clad steel sheet. Nippon Steel Corporation undertook the Maishima-side project. The Yumeshima-Maishima Bridge is an arched bridge, which can be opened halfway by tugboats to allow the passage of large ships. The bridge structure floats on two pontoons, the splash zones of which are protected by a titanium-clad steel sheet lining to improve their resistance to corrosion, thus extending the service life of the steel structures. The bridge is being built as part of a waterfront development program in Osaka, and is scheduled for completion during 2000. The titanium-clad steel sheet is a composite material made by bonding pure titanium to a carbon steel base sheet (base sheet thickness: 4mm, titanium cladding thickness: 1mm). It combines the structural strength of the base steel with the superior heat- and corrosion-resistant properties resulting from titanium cladding. It enables to line titanium to steel structures by welding carbon steel base sheet and due to its superb bonding strength, the composite sheet offers excellent bending workability. These advantages mean that whereas in the past it was necessary to protect steel structures against corrosion by means of heavy coating, it is now possible to simply line them with a titanium-clad steel sheet. Splash zones are required to withstand corrosion for a period of 50 years in a seawater environment, whereas heavy coatings and organic linings require regular maintenance and repair, which are costly and difficult when structures lie partially submerged in water. Use of the titanium-clad steel sheet--with its outstanding long-term corrosion resistance--offers a significant reduction in maintenance/repair costs. Therefore it was chosen for the current project. Each of the titanium-clad steel sheets used in the project measures 1.2m wide by 10-11m long. A total of 208 meters of the sheets weighing about 20 tons were used to line an area of about 500m2 . The use of the wide and long steel sheet allowed NKK to reduce the number of welding lines. Also, with the collaboration of the bridge construction companies, NKK applied a new construction method to mount the titanium-clad steel sheet after the completion of the main bridge structure. In addition to its already marketed titanium-clad steel plate, NKK established its unique titanium-clad steel sheet production system in 1997, and became the world's first manufacturer to commercialize a full range of hot-rolled titanium-clad steel products, from thick plate to sheet. The company plans to develop further application ranges of titanium-clad steel sheet and plate, with a view to applying them in future marine projects, including floating structures such as "Mega-float" platforms, bridges and other offshore public works. |
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