Steel tubes, as an essential component of steel products, are classified into two major categories: seamless steel tubes (made from round billets) and welded steel tubes (made from plates or strip billets), based on their manufacturing processes and the shapes of the tube billets used.
Cold-rolled formed steel allows for local buckling of the cross-section, enabling full utilization of the load-bearing capacity after buckling of the member. In contrast, hot-rolled steel sections do not permit local buckling of the cross-section.
The causes of residual stresses in hot-rolled and cold-rolled steel sections differ significantly, leading to vastly different distributions across their cross-sections. The residual stress distribution in cold-formed thin-walled steel sections is of a bending type, whereas in hot-rolled or welded steel sections, it is of a membrane type.
There is little difference between the two types of steel tubes in terms of finished products, as they are generally manufactured to standard specifications. Mechanical properties are also similar, with the primary differences lying in the manufacturing processes and the resulting precision. Typically, cold-drawn steel tubes exhibit higher dimensional accuracy and surface finish.
Welded steel tubes, also known as welded pipes, are produced by curling and welding steel plates or strips. The production process of welded steel tubes is simple, efficient, and versatile, requiring less equipment and capital investment. However, their strength is generally lower than that of seamless steel tubes.
Welded steel tubes are further classified into straight seam welded pipes and spiral welded pipes based on the form of the weld seam. Spiral welded pipes generally have higher strength than straight seam welded pipes, allowing for the production of larger-diameter pipes from narrower materials. They also enable the production of pipes with different diameters from the same width of material. However, compared to straight seam pipes of the same length, spiral welded pipes have a weld seam length increased by 30-100%, and their production speed is lower. Therefore, smaller-diameter welded pipes are mostly produced using straight seams, while larger-diameter pipes are predominantly produced using spiral welding.
