Effect of Cold Bending Process and Strain-Age on Properties of X80 Linepipe

Through the field cold bending and mechanical properties tests of Φ1219 mm × 22 mm X80 longitudinal submerged-arc welding line pipe, the effects of different bend radii consisting of 20D, 28D and 47D (D is the diameter of steel pipe) on properties of X80 linepipe were studied. The tests results indicate that the change of the transverse tensile property, roughness, hardness and bend performance of cold bends manufactured by various radius of curvature compare with the mother pipe is relatively small. When the radius of curvature is decreased, the transverse yield strength and yield ratio in intrados of bend increase slightly, but those in extrados of bend decrease in a little range. The changes of longitudinal tensile properties are bigger. When the radius of curvature is decreased, the yield strength and yield ratio in intrados of bend decrease obviously, but those in extrados of bend increase. The longitudinal tensile curves in different position of bend exhibit a rather large difference. After the strain-age for mother pipe and bends, the effects of material deformation in the pipe production process appear which result in that the transverse tensile strength and yield ratio increase obviously. The longitudinal tensile strength and yield ratio in different position of bend also present a increase tendency.