Localised lateral buckling of partially embedded subsea pipelines with nonlinear soil resistance

Unburied partially embedded subsea pipelines under high temperature conditions tend to relieve their axial compressive force by forming localised lateral buckles. This phenomenon is traditionally studied as a kind of imperfect column buckling problem. We study lateral buckling as a genuinely localised buckling phenomenon governed by a different static instability, with a different critical load. No ad hoc assumptions need to be made. We combine this buckling analysis with a detailed state-of-the-art nonlinear pipe-soil interaction model that accounts for the effect of lateral breakout resistance. This allows us to investigate the effect of initial embedment of subsea pipelines on their load-deflection behaviour. Parameter studies reveal a limit to the temperature difference for safe operation of the pipeline, in the sense that for higher temperature differences a localised buckling mode has lower total energy than the straight unbuckled pipe. Localised lateral buckling may then occur if the pipe is sufficiently imperfect or sufficiently dynamically perturbed.