天然气管道局部等效应力及塑性变形评估

Evaluation on local equivalent stress and plastic deformation for natural gas pipeline

为了研究腐蚀及地面运动对埋地天然气管线安全性的协同影响,以X80管道为研究对象,模拟腐蚀缺陷及土壤力作用于管道之上,利用有限元方法对有腐蚀缺陷与预应变情况下的管道局部等效应力及塑性变形进行评估,结果表明腐蚀缺陷的深度对局部应力和应力分布影响非常明显,在失效压力预测中起着决定性作用。随着腐蚀深度的增加,应力集中增强,导致内表面和外表面的等效应力大小进一步分化,腐蚀深度的增加对管道内表面的等效应力的影响很大,但对有效塑性应变的影响却不大。模拟管道上施加有纵向应变的土壤力,不论拉伸与压缩的情况下,都会降低管道的失效压力,在施加拉伸预应变下的管道失效压力小于压缩预应变下的。塑性变形首先发生在外表面处,并扩展到腐蚀缺陷相邻区域,管道内表面也具有一定的塑性变形,但强度低。

In order to study the synergy influence of corrosion and ground movement to safety of buried natural gas pipeline,taking the X80 pipeline as a research object,it was assumed that the corrosion defect and soil force were applied on the pipeline. The local equivalent stress and plastic deformation of pipeline were evaluated in the presence of corrosion defect and pre-strain by using the method of finite element analysis. The results showed that the depth of corrosion defect has very obvious influence on the local stress and stress distribution,which plays a decisive role in the prediction of failure pressure. With the increase of corrosion depth,the stress concentration is enhanced,resulting in the further separation of equivalent stresses on the inner surface and the outside surface. The increasing of corrosion depth has a great influence on equivalent stress on the inner surface of pipeline,but has little influence on the effective plastic strain. When exerting the soil force with longitudinal strain on the simulating pipeline,it will reduce the failure pressure of pipeline regardless of tensile or compressive one.The failure pressure of pipeline under the tensile pre-strain is smaller than that under the compressive pre-strain. The plastic deformation starts from the outside surface,then expands to the adjacent area of corrosion defect. The inner surface of pipeline has somewhat plastic deformation,but at a low intensity.