Spiral steel pipes are manufactured by coiling low-carbon carbon structural steel or low-alloy structural steel strips into a pipe billet at a specific spiral angle (known as the forming angle), followed by welding the seam to complete the pipe. This process enables the production of large-diameter steel pipes using narrower steel strips. The specifications of spiral steel pipes are expressed in terms of outer diameter and wall thickness. Welded pipes must undergo hydrostatic testing to ensure that their weld joints meet the required tensile strength and cold bending performance standards.
Steel pipes with an outer diameter-to-wall thickness ratio of less than 20 are classified as thick-walled spiral pipes. These pipes are primarily used in applications such as oil and gas drilling, petrochemical cracking, boiler piping, bearing pipes, and high-precision structural pipes for automobiles, tractors, and aviation.
The primary focus of production control for thick-walled spiral pipes is to enhance the ductility and toughness of the steel pipes, improve the cleanliness of molten steel, reduce harmful inclusions, and ultimately elevate the overall quality of the pipes. During production, a reasonable cooling system is adopted to prevent internal cracks, thereby improving pipe quality from multiple angles.
The production process of spiral pipes involves numerous steps, with the final step being the reduction of roll speed. Roll speed is a crucial parameter in the piercing process. As the roll speed increases from low to high, there exists a critical roll speed at which delamination begins to occur. At lower roll speeds, the pipe billet is prone to cavity formation, whereas at higher speeds, the billet and 45# structural spiral steel pipes may develop delamination defects. To eliminate these defects, the roll speed must be reduced below the critical speed where delamination initially occurs.
During the production of spiral pipes, it is essential to reasonably control the heating temperature. By measuring the hot ductility curve, the optimal heating temperature can be selected. Additionally, the pipe billet must be heated with sufficient soaking time to reduce deformation resistance and enhance the ductility and toughness of 45# structural thick-walled spiral pipes.
