Steel with a hollow section whose length is much greater than its diameter or circumference. According to the cross-sectional shape, it is divided into round, square, rectangular and special-shaped steel pipes; according to the material, it is divided into carbon structural steel pipe, low alloy structural steel pipe, alloy steel pipe and composite steel pipe; according to the use, it is divided into transportation pipeline, engineering structure, Steel pipes for thermal equipment, petrochemical industry, machinery manufacturing, geological drilling, high-pressure equipment, etc.; according to the production process, they are divided into seamless steel pipes and welded steel pipes, among which seamless steel pipes are divided into hot-rolled and cold-rolled (drawn) There are two types, welded steel pipes are divided into straight seam welded steel pipes and spiral seam welded steel pipes.
Steel pipes are not only used to transport fluids and powdery solids, exchange heat energy, and manufacture mechanical parts and containers, but they are also a kind of economical steel. Using steel pipes to manufacture building structural grids, pillars and mechanical supports can reduce weight, save 20 to 40% of metal, and enable factory-like mechanized construction. Using steel pipes to manufacture road bridges can not only save steel and simplify construction, but also greatly reduce the area of protective coating, saving investment and maintenance costs.
(1) Specifications: The specifications of spiral steel pipes should be stated in the import and export trade contract. Generally, it should include the standard grade (type code), the nominal diameter of the steel bar, the nominal weight (mass), the specified length and the tolerance value of the above indicators, etc. Our country's standards recommend a series of spiral steel pipes with nominal diameters of 8, 10, 12, 16, 20, and 40mm. The length of supply is divided into two types: fixed length and double length. The fixed length selection range of rebar exported from my country is 6~12m, and the fixed length selection range of rebar produced in Japan is 3.5~10m.
(2) Appearance quality: ① Surface quality. Relevant standards stipulate the surface quality of rebar, requiring that the ends should be cut straight, the surface should be free of cracks, scars, folds, and harmful defects in use; ② The allowable value of the overall dimension deviation. The requirements for the curvature of rebar and the geometry of steel bars are stipulated in relevant standards. As stipulated in our country's standards, the curvature of straight steel bars shall not be greater than 6mm/m, and the total curvature shall not be greater than 0.6% of the total length of the steel bars.
