Experimental and numerical investigation into the influence of galling on liner wrinkling behaviour in mechanically lined pipes

• FSBT and FEM validated the mechanical response of MLPs with natural galling. • Galling triggered wrinkling, reducing onset strain by 32% without global loss. • Galling height and circumferential position are dominant instability drivers. • Proposed framework improves DNV predictions and reduces design conservatism. Mechanically lined pipes (MLPs) are widely used in offshore pipelines because they combine the structural capacity of carbon steel with the corrosion resistance of a CRA liner. However, their integrity can be compromised by liner wrinkling, a local instability that occurs when compressive bending strains act on the thin CRA liner. Liner wrinkling is sensitive to geometric imperfections, as small manufacturing-induced surface defects can trigger early strain localisation. While the influence of large imperfections such as dents has been documented, the destabilising effect of smaller imperfections, such as those caused by galling, remains poorly understood. This study addresses this knowledge gap through a combined experimental–numerical investigation. A full-scale bending test (FSBT) was performed on an MLP specimen containing galling indications, and the results were used to validate a finite element model that incorporated the measured defect geometry. Comparison with a galling-free pipe showed that although galling has negligible impact on global bending stiffness, it acts as a critical trigger for liner wrinkling, reducing the onset strain by 32% and shifting the wrinkle initiation to the defect location. A parametric study further demonstrated that galling height and circumferential position relative to the maximum compressive fibre are the dominant drivers of instability. Building on these insights, a new performance-based design framework is proposed by introducing calibrated modification factors into the existing DNV-JIP wrinkling equation. This framework links manufacturing quality, imperfection severity, and internal pressure to structural capacity, providing an accurate and less conservative basis for predicting wrinkling resistance in engineering design.