Liner Wrinkling in Mechanically Lined Pipes Under Cyclic Bending: Influence of Carrier Pipe Ovality and Wall Thickness Eccentricity

Abstract Mechanically lined pipes (MLPs) have been widely used in the oil and gas industry due to their low cost and excellent corrosion resistance. However, their thin corrosion-resistant liners are prone to wrinkling when exposed to the high plastic strains (1-3%) induced during reel-lay installation. To mitigate this instability, a thin adhesive layer between the liner and carrier pipe has been proposed, forming an adhesive-reinforced mechanically lined pipes (ARMLPs). Prior to full reel-lay numerical simulations, cyclic bending serves as a fundamental step, enabling parametric analysis and capturing the nonlinear mechanical response under controlled boundary conditions. A three-dimensional finite element model of (AR)MLP under cyclic bending is developed in this work, incorporating: i) solid and shell elements with a combined nonlinear isotropic/kinematic hardening model, ii) a bilinear traction-separation law for the adhesive layer and iii) initial geometric imperfections in the carrier pipe, while residual stresses are introduced through hydraulic expansion. The influence of the magnitude and orientation of carrier pipe initial ovality and wall thickness eccentricity on liner wrinkling evolution is systematically evaluated under repeated bending representative of reel-lay operations, and the critical number of cycles leading to wrinkling is identified. The results further demonstrate that ARMLPs maintain interlayer integrity and significantly delay local buckling even under severe imperfection scenarios. This work clarifies how manufacturing-induced imperfections affect structural stability during installation and provides mechanistic insight into liner wrinkling and buckling behavior.