输油管道超设计压力运行的几个关键问题

Several key aspects in operation of oil pipelines at a pressure higher than design pressure

为保证输油管道超设计压力运行的安全,针对钢管力学性能、管道临界缺陷尺寸、环焊缝质量验证3个影响管道承压的重要因素,在管道沿程压力计算基础上,开展了管材小试样屈服强度统计与试验、钢管实物屈服强度与小试样屈服强度差异性分析、管道临界缺陷尺寸计算与内检测精度分析、环焊缝性能验证方案的研究。研究表明:钢管实物屈服强度与管材最小要求屈服强度之比即为最大运行压力与设计压力之比;由于压力升高,管道运行时允许的缺陷尺寸减小,其中大于临界尺寸的缺陷应保证被现有管道内检测器发现,否则应降低运行压力从而增大临界缺陷尺寸值;超设计压力运行前,应进行一次相应强度的现场试压,排除环焊缝异常。

In order to ensure the safe operation of oil pipelines at a pressure higher than design pressure, a series of studies were conducted on three key factors （i.e. pipe mechanical property, pipeline critical defect size, and girth welds quality verification） influencing pipeline bearing capacity, after the pressures along pipelines were calculated. The yield strength of small specimen was calculated and tested, and the difference of yield strength between specimen and actual pipe was analyzed. The critical defect sizes of pipes were calculated and the internal inspection precision was analyzed. Moreover, girth welds quality verification programs were investigated. It is shown that the ratio of maximum operation pressure to design pressure is the ratio of actual yield strength to the required minimum yield strength of pipes. With the increasing of operation pressure, the allowable critical defect sizes during the operation of pipelines decrease. When the defect is over the critical size, the defect shall be detected by the detector inside the pipeline. Otherwise, it is necessary to decrease the operation pressure, so as to increase the size of the critical defect. Before any operation at a pressure higher than the design pressure, a field pressure test with the corresponding strength shall be performed, in order to eliminate abnormal girth welds.