The influence of pipeline steel strength level for the steel pipe strength

Pipeline steel strength has a significant impact on the work hardening ability of materials and Bauschinger effect. With the increase of the steel strength, the hardening index tends to decrease, namely the work hardening ability decreased, the Bauschinger effect strengthened. When the yield strength of pipeline is less than 450Mpa, work hardening effect is greater than the Bauschinger effect, thereby causing increased yield strength of steel tube test. When the yield strength of pipeline is greater than 450Mpa, the Bauschinger effect is greater than the strain hardening effect, thereby causing reduction in yield strength of steel tube test, but the yield strength tested after expanding is greater than the yield strength of the steel sheet

The change of tensile strength in the pipeline molding process is different from the change of yield strength. The tensile strength of steel pipe is always greater than the steel sheet. Such kind of trend of strength increasing of steel pipe are more evident for the low-strength steels, the increased tensile strength within 50Mpa. With the change in yield strength, steel pipe yield ratio also changed, and the steel yield ratio after expanding of steel pipe is always higher than the steel sheet.