Influence of carrier pipe ovality and wall-thickness eccentricity on liner wrinkling in mechanically lined pipes under monotonic bending

To achieve a balance between corrosion resistance and economic efficiency, bimetallic lined pipes, particularly mechanically lined pipes (MLPs), have become an important solution for oil and gas transportation from shallow to ultra-deep waters. During reel-lay installation, the pipe undergoes severe plastic bending, under which the liner may detach from the carrier pipe and further develop wrinkling or even pronounced local buckling. Manufacturing defects are regarded as one of the key factors governing liner stability. To better understand this issue, a nonlinear finite element framework is established in this study to investigate the effects of manufacturing-induced initial ovality and wall-thickness eccentricity of the carrier pipe on the stability of MLPs under monotonic bending. The effects of carrier-pipe imperfections are strongly orientation-dependent. For D C / t C = 22 , pure ovality has a relatively limited influence on wrinkling onset, with a maximum reduction in the onset strain of approximately 6%, whereas wall-thickness eccentricity exerts a much stronger and highly orientation-dependent influence, with the onset strain reduced by up to approximately 31% in the most unfavorable orientation. When ovality and eccentricity are combined, the most unfavorable configuration produces a reduction of approximately 34%. Increasing D C / t C , together with the associated increase in liner D L / t L , generally promotes earlier instability and the transition toward a coupled liner–carrier buckling mode. These findings provide further insight into the mechanisms through which manufacturing defects influence the stability of MLPs and may serve as a useful numerical reference for the installation assessment of imperfect MLP systems.