Large diameter straight seam welded pipes are lighter in weight when the bending and torsional strengths are the same.

Large-diameter straight-seam welded pipes have hollow cross-sections and are widely used as pipelines for conveying fluids, such as pipelines for conveying oil, natural gas, coal gas, water and certain solid materials. Compared with solid steel such as round steel, large-diameter straight-seam welded pipes are lighter in weight when the bending and torsional strengths are the same. Alloy steel pipes are an economical cross-section steel, which is widely used in the manufacture of structural parts and mechanical parts, such as oil drill pipes, automobile transmission shafts, bicycle frames, and steel scaffolding used in construction. Using alloy steel pipes to manufacture annular parts can improve material utilization, simplify manufacturing processes, save materials and processing time, such as rolling bearing rings, jack sleeves, etc., which are currently widely made of steel pipes. Alloy steel pipes are also indispensable materials for various conventional weapons. Gun barrels and cannon barrels are made of steel pipes. Alloy steel pipes can be divided into round pipes and special-shaped pipes according to the different cross-sectional shapes. Since the circular area is the largest under the condition of equal circumference, more fluid can be transported by using a circular pipe. In addition, when the circular cross section is subjected to internal or external radial pressure, the force is more uniform. Therefore, most steel pipes are round pipes.