Load bearing capacity of API X65 pipe with dent defect under internal pressure and in-plane bending

Abstract

► Opening bending had a higher load bearing capacity than closing bending. ► TES moment decreased with increasing dent depths and internal pressures. ► Max moment in the closing bending mode increased with increasing internal pressures. The objective of this study was to investigate the effect of the dent magnitude on the collapse behavior of a dented pipe subjected to a combined internal pressure and in-plane bending. The plastic collapse behavior and bending moment of the dented pipe containing several dent dimensions were evaluated using elastic–plastic finite element (FE) analyses. The indenters used to manufacture the dents on the API 5L X65 pipe were hemispherical rods with diameters of 40, 80, 160 and 320 mm. Dent depths of 19, 38, 76, 114 and 152 mm were introduced to the pipe with a diameter of 762 mm and a wall thickness of 17.5 mm. A closing or opening in-plane bending load was applied to the dented pipes pressurized under an internal pressure equivalent to atmospheric pressure as well as pressures of 4, 8, and 16 MPa. The FE analyses results showed that the plastic collapse behavior of the dented pipes was significantly governed by the bending mode and the dent geometry. Moment-bending angle curves for the dented pipe were obtained from computer simulations and evaluated with a variety of factors in the FE analyses. The load bearing capacity of the dented pipes under the combined load was evaluated by TES (Twice Elastic Slope) moments. The load bearing capacity of the pipe containing up to a 5% dent depth of the outer diameter was not reduced in comparison to that of the plain pipe. The opening bending mode had a higher load bearing capacity than the closing bending mode under the combined load regardless of dent depth. The TES moment decreased with increasing dent depth and internal pressure regardless of the bending modes.