Factors of Influencing on Tensile Strength Test of High Grade Pipeline Steels

The factors,including index selection,sample size and sample shape,influenced on the tensile strength test of the X80,X100 and X120 high grade pipeline steels were investigated by means of optical microscope and tensile tester.The results show that Rt0.5 used for the pipeline steel whose grade was greater than X80 could not accurately characterize the material yield strength,while Rp0.2 and Rt0.6 were more reasonable.The smaller the size of the round bar specimen,the lower the Rt0.5,Rp0.2,Rt0.6 and tensile strength obtained by the tensile test.Due to the Bauschinger effect,the transverse tensile sample should adopt round bar shape for the X80 and X100 pipeline steel,and rectangular shape for the X120 pipeline steel.