Spiral pipe forming methods and causes internal stress

Spiral welded steel pipe in the petrochemical, heat pipe network and urban water supply and drainage works and piling pipe construction and other fields have a wide range of applications, especially in the long-distance transportation of oil pipeline and natural gas pipelines are more widely used. Oil, gas pipeline network almost all spiral welded steel pipe, with high security, durability and economic rationality. Since the diameter of the spiral welded steel sheet width generally not limited, by a variety of different specifications of the plate width coil manufacture, so no wide plate width of the plate. This gives plate manufacturing, transportation convenience, the use of flat steel strip ratio much lower price, suitable for China's actual situation. Spiral welded steel pipe there is a problem produce elastic recovery after welding steel pipe, steel pipe previously exposed to the equivalent one circumferential tensile stress, the stress will produce stress corrosion and reduced ability of the pressure tube.

Spiral welded steel pipe using a continuous forming, welding fabrication method, is now widely used within and outside deck holds two kinds of molding method, forming rolls and rolls made within (or outside hold rolls) composed of a shaper plate along the arrow fed to the forming device in the direction, while forming the side weld. Molding can be obtained by adjusting the different sizes of the pipe. In order to prevent excessive bending, forming rolls three points of contact with the plate height is generally not much difference, manufacturers have adopted an insufficient amount molding, pipe made within the radius of curvature is to rely on roll (or external hold rolls) formed by the radius of curvature that in within each roll (or external hold rolls) in the elastic and plastic plates are actually mixed deformation. Spiral welded steel pipe cut open along the generatrix direction, there must be a certain amount of circumferential openings, namely the existence of certain steel pipe bomb complex quantity, steel residual stress exists. Since the existence of internal stress, steel external tensile stress, so this will reduce the ability of the pressure tube, increasing the external pipe corrosion, to adversely affect the use of steel. Many studies have discussed in detail the tone type parameters (forming roll positional parameters) on the amount of complex pipe bomb, but the actual parameters and by the whole steel welded steel tube mill parameters, can only be imprecise quantitative analysis. In fact at the various spiral pipe manufacturers are relying on experience, probably forming roller position adjusting parameters, and then producing a steel pipe, steel pipe is cut open along the bus to check whether the amount of the opening meet customer requirements. Is not very important for the steel (such as water pipes) is not limited to the opening size of the steel pipe.