Classification of steel pipes
The steel pipes are divided into seamless steel pipes and welded steel pipes, among which the welded steel tubes can be divided into ERW steel pipes, LSAW steel pipes and SSAW spiral steel pipes.
|Seamless steel pipe wall thickness is relatively thick, diameter thickness is relatively small. However, the pipe diameter is limited and its application is also limited. And the production cost, especially the production cost of large diameter seamless steel tube is relatively high.
|The ERW steel pipe has good shape, uniform wall thickness, the internal and external burr produced by welding is scraped by corresponding cutter, and the quality of welding seam is strictly controlled by online nondestructive testing, with high degree of automation and low production cost. But the wall thickness is relatively thin, the pipe diameter is relatively small, the wall thickness is generally not more than 12mm, the pipe diameter is generally not more than 610mm, the steel structure is particularly suitable for the production of pipe rack structure.
|The LSAW steel pipe adopts the double-sided submerged arc welding process, and the welding quality is high and the welding seam is short under the static condition, so the probability of defects is very small. Steel tube through the full - length diameter, good shape, accurate size. The range of wall thickness and diameter of steel tube is wide, with the range of pipe diameter up to 406-1829mm and the range of wall thickness up to 6.0-60mm. The degree of automation of LSAW steel pipe is higher, compared with seamless steel pipe, the production cost is lower. It suitable for bearing columns of steel structures such as buildings, Bridges, dykes, offshore platforms, etc, and super-large span building structure and the mast structure of electric pole tower which is required to resist wind and earthquake.
|SSAW steel pipe can be used to produce larger welded tubes from narrower billets. The blank of the same width can also be used to produce welded pipes with different diameters. However, the spiral welding seam of the spiral steel pipe is distributed, and the welding seam is long, especially when the welding seam is in the dynamic condition, it leaves the forming point before it has time to cool down, so it is easy to generate welding hot cracks. The direction of the crack is parallel to the weld, axis and pipes with a certain Angle, generally between 30 and 70 °. This Angle is just consistent with the shear failure Angle, so its bending, tensile, compressive and torsional properties are far less than LSAW steel pipe. Meanwhile, due to the limitation of welding position, the saddle-shaped and fish-ridged welds will affect the appearance. Therefore, it is necessary to strengthen the nondestructive testing of spiral welded steel pipes to ensure the welding quality. Otherwise, spiral steel pipes should not be used in important steel structures.