针对目前API Spec 5L-2009《管线钢管规范》中采用冷压平方法测试管线钢管屈服强度的不稳定性问题, 采用双肩圆试样拉伸、展平率法板试样拉伸、预拉伸至弹性极限Rp0.02板试样拉伸和预拉伸至弹性极限Rp0.01板试样拉伸四种方法对不同取样方向的管线钢管试样进行了拉伸试验, 并对四种方法测得的屈服强度结果进行分析比较。结果表明: 双肩圆试样拉伸法由于不是全厚度试样, 因而不能真实地反映管线钢管的屈服强度, 且试样加工比矩形平板状试样更为繁琐; 展平率法板试样拉伸方法由于同一取样角度只计算一个试样的展平率, 因而试验结果比较分散, 且需要采用滞后环法对试验数据进行处理, 工作量较大; 预拉伸至弹性极限板试样拉伸方法可以方便、准确地计算出管线钢管的屈服强度, 但预拉伸至弹性极限Rp0.02时的非比例伸长延伸率稍大, 因此建议采用预拉伸至弹性极限Rp0.01板试样拉伸的方法测试管线钢管的屈服强度。

Aimed at the instability problems of yield strength tested by cold-pressed method according to API Spec 5L-2009 “Specification for line pipe” for line pipes, four tensile test methods such as round bar specimens with double-shoulder, flat specimens with flat-spread ratio and flat specimens with pre-tension strain to elasticity limits of Rp0.02 and Rp0.01 were adopted to test the yield strength of line pipe specimens with different sampling directions, and test results of these four methods were compared and analyzed. The results show that since round bar specimens with double-shoulder are not full-thickness specimens, so yield strength gained by this method can not truly reflected the yield strength of the line pipes. At the same time, processing of round bar specimens with double-shoulder is more complex than that of rectangle cross-section specimens. Because the flat specimens with flat-spread ratio only calculate one specimen’s flat-spread ratio at the same angle, the test results are dispersed, and meanwhile using hysteresis loop method to process test dates requires more calculation. Flat specimens with pre-tension strain to elasticity limits method can conveniently accurately calculate the yield strength of line pipes, but percentage non-proportion extension to elasticity limits Rp0.02 is too large. Therefore it is suggested using flat specimens with pre-tension strain to elasticity limits Rp0.01 method to test the yield strength of line pipes.