X80管线钢在管道凹陷状态下的应变演变特征

Strain evolution characteristics of X80 line pipes with plain dents

高钢级管线钢管在施工和服役过程中会产生凹陷等缺陷,从而改变应力和应变分布特征,影响管道的服役可靠性。为此,以X80管线钢管为研究对象,采用ABAQUS有限元分析软件,分析了外部载荷作用下含单纯凹陷管道随凹陷深度变化的应变场分布特征,通过实物凹陷预制试验探明凹陷区应变分布和显微组织特征,结合有限元模拟结果讨论X80管线钢管含单纯凹陷状态下的应变分布规律。研究结果表明:①在相同内压条件下,不同凹陷深度下凹陷区的应变表现出相似的分布特征——应变量随着与凹陷中心距离的增加而增大,达到应变峰值后随距离的增大而快速减小;②应变量随着凹陷深度的增加而增大,并且在相同的内压及凹陷深度下,同一位置处的轴向应变大于径向应变;③凹陷深度越大,内压与深度对应变影响的叠加效应越大;④凹陷变形初期材料发生了应变硬化,随着变形的深入及凹陷半径的外延,材料应变响应能力增加,凹陷区底部和侧壁晶粒沿着变形最大的方向被拉长,晶格被扭曲,发生应变硬化,使得该区域位错密度增大,位错间产生相互作用,从而提高管线钢的强度。结论认为,该研究成果可以很好地预测凹陷过程中的应力应变演变规律,可以为机械损伤对管道服役安全影响研究提供理论基础和试验依据。

In the process of construction and service, high-grade line pipes will get defective, e.g. dents, which will change its stress and strain distribution characteristics and impact its service reliability. In this paper, a X80 line pipe was taken as the research object. The distribution characteristics of the strain field in the X80 line pipe with plain dents with the change of dent depth under external load were analyzed using the finite element analysis software ABAQUS. Then, the strain distribution and microstructure characteristics in the dent zone were explored by conducting prefabrication test on physical dent. Finally, combined with the finite element simulation results, the strain distribution laws of the X80 line pipe with plain dent were discussed. And the following research results were obtained. First, under the same internal pressure, the strain distribution characteristics in the dent zone at different dent depths are similar, i.e., the strain increases with the increase of the distance from the center of the dent, and decreases rapidly with the increase of the distance after the peak strain. Second, the strain increases with the increase of dent depth, and under the same internal pressure and dent depth, the axial strain is larger than the radial strain at the same location. Third, the greater the dent depth, the stronger the superposition effect of internal pressure and depth on the strain. Fourth, strain hardening occurs on the materials in the initial stage of the dent deformation. With the aggravation of deformation and the extension of dent radius, the strain response ability of materials increases, the grains at the bottom and side walls of the dent zone are elongated along the direction of maximum deformation, the lattice is distorted and strain hardening occurs. As a result, the dislocation density in this zone increases and the interaction occurs between dislocations, as a result, the strength of line steel is enhanced. In conclusion, the research results do well in predicting the stress–strain evolution laws in the process of dent, and provide a theoretical foundation and an experimental basis for studying the influence of mechanical damage on the service safety of pipelines.