Buckling of dented bi-material pipe under bending Part I: Experiments and simulation

Abstract

As a cost-effective solution for transporting corrosive hydrocarbons, mechanically lined pipe has been used in many offshore and onshore projects. The bonding between the carbon steel carrier and the non-corrosive liner is commonly achieved by mechanical expansion. As typical pipeline damage, the local dent brings deformation to the bimetallic composite, which is expected to undermine the structural integrity. This work investigates the influence of a local dent on the plastic responses and stability of a lined pipe system during bending. Part I presents the results of the experiments and numerical analysis involving a set of small-scale lined tubes. The lined tubes, made of carbon steel Grade GB45 (AISI 1045) and copper Grade T2, are manufactured using a custom hydraulic expansion facility. The products have finished diameters of 50 mm and an overall D/t of 16.5, with 1.0 mm thickness for the liner. A minor transverse dent is introduced to the specimen using a cylindrical indenter. The dented tube is subsequently bent to collapse in a four-point bending facility. It is found that the local dent tends to induce early collapse of both the outer tube and the liner, resulting in a noteworthy reduction of the bending capacity of the composite. Initially, the local dent grows stably instead of collapsing right away. With increasing bending, the liner develops a major buckle and several satellite dimples around it. Subsequently, the manufacture, indentation, and the succeeding bending to collapse are simulated using a custom numerical framework, and the experimental results are reproduced reasonably well. Part II will use the validated numerical model to conduct an extensive parametric study of the important variables of the problem for full-scale lined pipes.