ERW pipe due to the internal residual part of the rebar bending moment (residual bending moment or residual bending moment) caused by residual stress on the service performance of erw pipe has a significant impact, therefore, the industry on the welded steel pipe, the awareness and research of the problem of the residual bombs and explosions have been paid more and more attention. At present, when ordering steel pipe, the purchaser usually ensures clear and quantified residual rebound control of the erw pipe in order to ensure the safe and reliable operation of the pipelines (especially some important oil and gas pipelines) and adds the order to the more stringent steel pipe supplementary technical conditions. This practice has become a common practice. In the process of manufacture of erw pipe, the strip steel is fed into the roll voss fittings suppliers forming machine along a certain angle and direction. After the bending deformation of the three-roll bending machine, the sizing of the outer roll or inner roll, the inner and outer welding devices after welding and other processes, will remain in the finished tube blank remnants of part of the bending moment. This part of the rebound moment balances the torque required to keep the tube blank, and the tube itself is in a state of resilient recovery. If the billet is cut along its axial direction and the circumferential restraint is removed, the remaining rebound moment will be released freely, resulting in the rebound of the billet. This is the so-called welded pipe residual bombshell problem. ERW pipe is not welded after the cold expansion process, making the welded pipe after the despicable residual performance should be complex and diverse patterns, such as uneven distribution, the higher the peak, and the manufacturers of straight seam welded pipe residual stress greater differences. ERW pipe with a large residual tensile stress is to limit the use of welded steel pipe one of the main reasons.
On the other hand, due to the inhomogeneity of the residual stress distribution, there exists a higher residual tensile stress in the erw pipe, which is higher than the transport pressure high stress and pressure superimposed, in the presence of corrosive media, prone to stress corrosion damage or corrosion fatigue damage, resulting in early failure of the pipe: This is also considered the reliability of erw pipe than the UOE pipe two reasons for the low. And with the increase of delivery pressure and the increase of welded steel grade, the problem is more prominent. However, for external sizing, the bending curvature 1 / R2 formed when the strip is bent and deformed in the three-roll plate former of the former is greater than the bending curvature 1 / R of the finished tube. It is still possible to make the tube blank of?2 (Ro) in the small-diameter state welded by the constraint and control provided by a damping device (special design required) added to the spiral direction of the tube blank, before expansion to the specified diameter RO and the outer diameter of the tube to achieve the purpose of tube diameter. The resulting tube will have a circumferential negative elastic properties. That is to say, the external sizing former is used as a supplementary control by means of a restraint provided by a specially designed damping device. It is also possible to produce a tube blank with circumferential negative elastic properties. Although this damping device is still not really applied, the reasonableness and feasibility of this? Art assurance measures can not be denied, the above is the introduction of welded steel tube rebound characteristics.
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