Strain evolution characteristics of X80 line pipes with plain dents

Abstract

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.