Weathering Steel for Saline Coastal Areas Developed
NKK has developed new weathering steel that requires no coating even in coastal areas with large amounts of airborne salt. Marketed as CUPLOY400-CL and CUPTEN490-CL, the new steel (containing1.5% nickel and 0.3% molybdenum as additives)has recently been chosen for two road bridge construction projects in Niigata and Mie prefectures. NKK's new steel is characterized by its complex additives of nickel and molybdenum. With conventional weathering steels in a salt-rich environment, it has been difficult to prevent the progression of corrosion from the concentration of chlorine ions permeating through rust layers on the steel surface.NKK has successfully optimized a combination of nickel and molybdenum to effectively prevent the concentration of chlorine ions, thus enhancing chlorine resistant properties. In addition to its excellent atmospheric corrosion resistance, the new steel, though added by alloys, offers remarkable mechanical properties, guaranteeing JIS SMA400 and 490. It also features good weldability due to the restrained carbon content, reducing work load by virtue of lower preheating temperature. As well, because initial rust streaming is minimal, appearance is enhanced. NKK has confirmed the new steel's superb chlorine resistant properties in field exposure tests conducted at several locations and also in tests using a model bridge structure built at the Tsu Works. In developing and commercially producing the steel, NKK collaborated with Kobe Steel for the welding materials and with Mitsuboshi Sangyo for high-strength bolts fitted for the steel. The new steel has been chosen for a single steel truss bridge (100m in length using 330 tons of steel) to be built in Niigata Prefecture and completed this August, and for a single non-synthetic steel-girder bridge (100m, 170 tons of steel) to go up this June in Mie Prefecture. Near seacoasts and other saline areas, ordinary steel is generally treated with heavy corrosion-protection coating, which costs about ¥10,000 per square meter. While the new weathering steel is priced some 35% higher than conventional weathering steels, the feature of not requiring heavy anti-corrosive coating means that initial corrosion protection costs are held to one-third of heavy coating methods. Moreover, since periodic recoating is not needed, the new steel can cut total life-cycle costs dramatically, including costs of long-term maintenance. |
