输油管道强度试压最高应力研究
A Study on Maximum Stress of the Strength Test on Oil Pipelines
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摘要: 管道试压后残存裂纹的疲劳扩展是影响管道正常使用寿命的主要因素之一。从管道缺陷的断裂特性入手, 分析了试压应力对管道残存裂纹扩展寿命的影响,管道试压高应力过载峰对试压后裂纹扩展速率产生明显的延缓作用, 过载峰愈高, 延缓作用愈大; 同时过载峰又增大了裂纹尺寸, 造成管道承压能力逆转。加速裂纹扩展速率。定量分析表明, 当表面裂纹的长度与深度的比值较小时,承压能力逆转量较小, 对裂纹扩展速率影响不大; 而裂纹尺寸较大的情况却正是需要通过试压来排除的。由此得出试压应力越高,裂纹寿命越长, 管道工作寿命越长的结论, 结合裂纹剩余寿命的计算分析和目前国内管材的实际情况,确定出管道强度试压的最高应力为管材的屈服极限。Abstract: The fatigue propagation of residual cracks after the pipeline being pressure tested is one of the main factors affecting normal pipeline service life. Starting with fracture characteristics of the defects in pipeline, the paper analyzes the influence of test pressure stress on the propagation life of the residual cracks in pipeline. It points out that the overload peak of the high stress from test pressure has a considerable delay effect on crack propagation rate after pressure test: the higher the overload peak, the greater the delay effect; and that the overload peak enlarges the crack size, resulting in the reversal of pipe's load-bearing capacity and the accelaration of crack propagation. The quantitative analysis shows that at smaller lengthdepth ratio of surface cracks, the reversal of load-bearing capacity is minimum, and the influence on crack propagation rate is also quite small. And what to be surmounted through pressure test is the occurrence of large sized cracks. Therefore, it is concluded that the higher the stress from test pressure, the longer the crack life and the longer the pipeline service life. In the light of the calculation of crack's residual life and the actual conditions of the current pipes in China, the paper points out that the maximum stress of strength test on pipeline shall be the yield limit of the pipe.