On the buckling of mechanically lined pipes under combined tension and bending

During the installation of offshore pipelines, the pipe often encounters the joint action of bending and tension over a rigid curved surface. For example, in the S-lay installation, when the pipe passes over a stinger, it experiences the combined bending, tension, and the reactions from the support. In the case of a mechanically lined pipe, this combined loading tends to ovalize both tubes severely and separate the liner from the outer pipe, leading to flattening and even collapse. The paper deals with the buckling response of bi-material pipes bent over a rigid surface with tension, aiming to understand the extent to which lined pipes can be loaded before the buckling occurs. A custom numerical framework, including the quasi-two-dimensional and three-dimensional models, is presented. Two loading histories of bending and tension, namely kappa -> T and T ->kappa, are examined with lined pipes of perfect and imperfect geometries. The results show that tension, either applied before or after bending, affects the growth of ovalization and liner collapse, the extent of which depends on the load path followed. It is also demonstrated that bending with modest levels of internal pressure delays the onset of liner collapse, but the threshold pressure varies for different load paths.