隧道穿越段变形管道应力评估及应对措施

Stress assessment and control measures for deformed tunnel-crerossing pipeline section

【目的】山岭隧道穿越对于长输油气管道工程较为常见,当隧道内管道约束或补偿不足时,在输送内压与温度作用下,管道易发生较大变形,开展隧道穿越段变形管道应力评估显得尤为必要。【方法】综合利用理论计算、管道超声应力检测及有限元分析3种方法,对隧道穿越段变形管道应力进行计算;基于管道应力计算结果,合理布设管道应力监测点,高频动态监控隧道穿越段变形管道应力变化情况;基于管道应力动态监测数据,采用分阶段梯次释放管道应力的治理措施;根据治理前管道应力计算结果与治理中管道应力变化量(即管道应力监测数据),计算治理后的管道应力,从而评估管道的安全裕量。【结果】将评估方法应用于国家管网集团西气东输分公司某隧道穿越段变形管道,应力评估后发现变形管道处于高应力水平,应力集中点位于隧道入口和出口段管道处,在运行压力12 MPa、运行温度40℃的设计工况下,隧道出口处管道焊缝的当量应力占屈服应力比例为93.87%,不满足管道当量应力不大于0.9倍屈服应力的安全要求。通过非动火治理后,隧道入口段管道当量应力安全裕量由68.50 MPa增至181.14 MPa,而隧道出口段则由47.50 MPa增至183.66 MPa,应力释放效果较好。【结论】研究结果有助于长输油气管道隧道穿越段的设计与监测方案的制定。

[Objective] It is common for long-distance oil and gas pipelines to traverse mountain tunnels. The sections of pipelines passing through tunnels are susceptible to significant deformation due to internal pressure and temperature effects during the transmission process, especially when the constraints or compensatory mechanisms for the pipelines within the tunnels are inadequate. This tendency for deformation underscores the importance of conducting stress assessments on deformed pipeline sections crossing tunnels. [Methods]The study's proposed strategy begins with stress calculations for deformed tunnel-crossing pipeline sections using three approaches:theoretical calculations, ultrasonic stress detection, and finite element analysis. Subsequently, the process involves dynamically monitoring stress changes in these deformed pipelines at high frequencies, employing monitoring points strategically positioned based on calculation outcomes. The dynamic monitoring data is then utilized to develop control measures entailing the staged release of pipeline stress.Additionally, the pre-control pipeline stress calculation results and stress variations during the control process(i.e., pipeline stress monitoring data) are combined to determine the post-control calculated pipeline stress. These calculation outcomes serve as the foundation for assessing the pipeline's safety margin. [Results] The methodology was applied to the deformed pipeline section crossing a tunnel at PipeChina West-East Gas Pipeline Co. Ltd. The stress assessment revealed high stress levels in the deformed pipeline section, showing stress concentration at the tunnel entrance and exit. Under the design conditions with an operating pressure of 12 MPa and an operating temperature of 40 ℃, the equivalent stress in pipeline welds at the tunnel exit exceeded 93.87% of the yield stress, falling short of the safety limit of 0.9 times the yield stress for equivalent stress levels in pipelines. Following non-hot work treatment, the safety margin for equivalent stress at the tunnel entrance increased from 68.50 MPa to 181.14 MPa, while at the tunnel exit, it rose from 47.50 MPa to 183.66 MPa, showcasing a significant stress relief effect. [Conclusion] The research findings are valuable for establishing design and monitoring schemes for the tunnel-crossing sections of long-distance oil and gas pipelines.