Bending and buckling of internally-pressurized steel lined pipes

During offshore installation, steel lined pipes are subjected to severe plastic bending, resulting in detachment of the thin-walled liner pipe from the outer pipe and eventually, the formation of local buckling in the form of short-wave wrinkles that menace the structural integrity of the pipeline. The paper focuses on the mechanical behaviour of mechanically lined pipes subjected to monotonic bending, considering for the presence of low and moderate levels of internal pressure, aimed at preventing or delaying wrinkle formation, and improving structural performance. The problem is solved numerically, accounting for geometric non-linearities, local buckling phenomena and elastic-plastic material behaviour for both the liner and the outer pipe. Two types of lined pipes are examined, with and without mechanical bonding between liner and outer pipe referred to as tight-fit and snug-fit lined pipe, respectively. The results demonstrate that the bending performance of lined pipes, under low or moderate internal pressure levels, is significantly improved. The influence of initial geometric imperfections on liner pipe buckling is also examined, showing the imperfection sensitivity of bi-material pipe bending behaviour.