腐蚀减薄对X80钢管机械损伤凹陷过程中应力应变的影响

Effect of Corrosion Thinning on Stress and Strain of X80 Steel Tube in Mechanical Depression Process

石油管道运行过程中的机械损伤和腐蚀问题对石油管道工程安全性具有重要影响。对于X80钢管,热轧制和热卷管工艺使其表层晶粒细化,在腐蚀状态下的变形过程中各位置会产生不同的应变响应。针对腐蚀造成的管壁减薄对凹陷过程的应力应变分布的影响情况,采用模拟和实验方法研究了不同凹陷深度对钢管应力应变的影响,分析了凹陷区组织及硬度的变化规律。结果表明:腐蚀减薄后使得表层细晶退化,对管体机械损伤凹陷过程影响显著,最大应力出现在腐蚀凹坑边缘。当凹陷深度≥5%D时,应变增幅较单纯凹陷急速增大,腐蚀造成的管壁减薄损伤部位在发生凹陷变形时,管体的应力应变集中于腐蚀坑边缘且急剧增大。在管线钢变形过程中,位错大部分聚集并缠结于晶界处,腐蚀减薄后形成了表面缺陷,产生位错钉扎;高密度位错导致抗裂纹扩展性降低,致使管道的承载能力降低,这是腐蚀凹坑边缘缺陷集中造成管道失效的主要原因。

The mechanical damage and corrosion problem during the operation of oil pipelines have an important impact on the safety of petroleum pipeline engineering.For X80 steel tube,the hot rolling and hot coiling process refine the surface grain,different position has different strain responses during the deformation in the corrosive state.For the effect of wall thinning caused by corrosion on the stress and strain distribution during sagging,the effects of different sag depths on the stress and strain of steel tubes were studied by simulation and test methods and the variation rules of microstructure and hardness in the depression area were analyzed.The results show that the fine grain of the surface layer is degraded after corrosion thinning,which has a significant effect on the mechanical damage process of the pipe body.The maximum stress appears at the edge of the corrosion pit.When the depth of the depression is more than 5%D,the strain increase amplitude is bigger than that of the simple depression.When the sag is at the wall damage position caused by corrosion,the stress,strain of the tube concentrates on the edge of the corrosion pit and increases sharply.During the deformation process of pipeline steel,most of the dislocations are gathered and entangled at the grain boundary.After corrosion thinning,the surface defects appear,the dislocation pinning occurs,and high-density dislocations lead to the reduction of crack propagation resistance and reduce bearin g capacity of pipeline,which is the main reason for the pipeline failure caused by concentrated defects in corrosion pits edge.