Denting the oil pipelines by a rigid cylindrical indenter with conical nose by the numerical and experimental analyses

The present research discusses indentation process on the oil pipelines using a rigid indenter in the quasi-static condition by the experimental and numerical analyses. This article investigates influences of internal pressure, diameter and wall thickness of pipes and geometrical characteristics of rigid cylindrical indenters with conical nose such as cone angle, conical nose diameter and cylindrical part diameter on mechanical behavior of the circular steel pipes under concentrated lateral loading (denting). In the experimental part, some specimens made from the steel API5L L245 were prepared and they laterally compressed by a rigid cylindrical indenter with the conical nose to perform the indentation process on them. In the numerical part, some finite element models were prepared and indentation process was simulated on different models with various tube and indenter geometries in different conditions of internal pressure. By comparing the numerical and experimental results, precision and accuracy of the simulations were affirmed. The discussed results show that when tube diameter increases, bending moment arm of the concentrated applied load around the formed plastic hinge lines enhances; therefore, lower lateral load can create a certain plastic deformations in the tube wall; and also, total absorbed energy by the tube enhances. Results demonstrate that when a conical projectile with a certain mass and initial velocity laterally compresses a circular tube, increment of tube diameter causes reduction of probability of the tube failure. The results show that when cone angle of conical indenter decreases and reaches to a certain value that called critical angle, the penetration occurs during the indentation process. Furthermore, it is found that by increasing the diameter of cylindrical part of the indenter, lateral indentation load increases; and when applied internal pressure on the tube increases, ultimate lateral displacement of the indenter decreases; but, the maximum load for the tube wall fracture enhances.