纵向连续冷弯管管段沉管下沟的可行性

Feasibility of lowering-in of longitudinally continuous cold-bends

【目的】沉管下沟是管道埋地敷设的主要方式之一,用连续冷弯管代替热煨弯头可以实现埋地管道纵向转弯,管道的最大应力是评判纵向连续冷弯管沉管下沟安全施工的关键指标。【方法】选取管径1 219 mm、壁厚22mm的X80管道为例,采用有限元方法建立纵向连续冷弯管管段沉管下沟数值模型,分析下沟过程中管道应力的变化规律,探讨下沟深度、连续冷弯角度、管沟开挖方向等对管道应力的影响。【结果】连续冷弯管的存在会加大下沟过程中管道的最大应力,且最大应力位置位于冷弯管起始边界附近;下沟过程中,管道上坡、下坡时产生的最大应力分别为压应力、拉应力,且同一上坡、下坡角度下的两种应力绝对值基本相当;从坡面向平面进行管沟开挖将会加大管道最大应力,且管道应力随下沟深度、连续冷弯角度的增加而增大。通过对管径1 219 mm、壁厚22 mm的X80管道的纵向连续冷弯管沉管下沟应力进行计算,得出在冷弯角度26°、下沟深度5 m内,管道的最大应力满足油气输送管道沉管下沟施工要求。为控制管道应力,可在冷弯管区域前、后100 m范围内进行分层开挖。【结论】管道下沟过程中应力受多个沉管参数的影响,依据下沟过程中最大应力的变化趋势,采取有效的控制措施即可实现纵向转弯管道的连续冷弯管管段沉管下沟施工。

[Objective] Lowering-in is a primary method for underground pipeline laying. Continuous cold bends are utilized in place of hotbending elbows at longitudinal turns along these buried pipelines. In this context, the maximum stress in the pipelines is considered a critical indicator for assessing safety when lowering longitudinally continuous cold bends into the trenches. [Methods] Taking X80 pipes with a diameter of 1 219 mm and wall thickness of 22 mm as an example, the Finite Element Method(FEM) was used to establish a numerical model for the lowering-in process of longitudinally continuous cold bends into the trench. The subsequent analysis focused on investigating the stress variations in the pipeline throughout the lowering-in process, aimed to discuss the impact of different factors such as lowering depth, angle of continuous cold bends, and the direction of trench excavation on pipeline stress levels. [Results] The presence of continuous cold bends resulted in an elevation of the maximum stress in the pipeline during the lowering-in operation, and the maximum stress was found near the initial boundary of the cold bends. In the lowering-in process, the pipeline's maximum stress was identified as compressive stress on the uphill and tensile stress on the downhill, with nearly identical absolute values at equivalent gradients. Trench excavation from a slope transitioning into a level section caused an escalation in the pipeline's maximum stress, directly correlating with increased lowering depths and angles of continuous cold bends. The stress calculations for longitudinal continuous cold bends constructed from X80 pipes with a diameter of 1 219 mm and wall thickness of 22 mm during the lowering-in process demonstrated that, at a turning angle of 26° and a lowering depth of 5 m, the resultant maximum stress in the pipeline complied with the established requirements for the lowering-in of oil and gas transmission pipelines. The implementation of layered excavation within a 100 m range preceding and following the cold bends was identified as an effective measure for managing pipeline stress levels. [Conclusion] Pipeline stress is influenced by multiple parameters during the lowering-in process. By analyzing the trends in maximum stress variation in this process, effective control measures can be employed to streamline the lowering-in of continuous cold bends at longitudinal pipeline turns.