Weathering steel (grade 09 cupcrni/Q355GNH), has also called ND steel, steel, belonging to the atmospheric corrosion steel, low alloy Gao Jiangnai contain small amounts of alloy elements, in the atmosphere with good corrosion resistance, low relative to the cost of stainless steel of high strength low alloy steel. Widely used in Bridges, buildings, vehicles, containers, all kinds of industry such as power transmission tower. Mainly on the basis of Cu - P, then add other alloying elements to improve the corrosion resistance of steel,

The present domestic only GB/T4171 weather resistance structural steel standard, there is no standard in special weather resistance of seamless tube. It is reported that there have been several large seamless steel tube company is working on weathering steel enterprise standards and popularization.