Experimental and Numerical Assessment of Liner Wrinkling and Triple Point Strain Localisation in Mechanically Lined Pipes

Abstract Mechanically Lined Pipes (MLPs) provide a robust solution for transporting corrosive hydrocarbons, yet their structural integrity is challenged by liner wrinkling and strain localisation at the triple point, the junction of the liner, outer pipe, and weld overlay. This study presents an evaluation of these phenomena through a full-scale bending test (FSBT) and finite element modelling (FEM). A rigorous validation process confirmed the model’s accuracy in predicting global moment capacity, wrinkling onset, and local strain evolution. The study compares the findings against Det Norske Veritas (DNV) Joint Industry Project (JIP) standards, highlighting the conservatism of the current Phase 4 guideline. Furthermore, an extended parametric study investigates the influence of weld overlay (WO) length (30 mm to 200 mm) on structural performance. Results indicate that while WO length has negligible impact on the onset of liner wrinkling, it influences local strain concentrations. Additionally, component-level moment analysis reveals that the liner’s contribution to stiffness degrades upon wrinkle formation, while the global capacity remains dominated by the outer pipe. These findings offer critical insights for optimising MLP design frameworks.