Buckle formation process is a key subject for the design of subsea pipelines laid on the seabed and operating under high pressure and high temperature (HP/HT) conditions. When the controlled lateral buckling methodology is adopted triggers are placed along pipeline route in order to increase the buckle formation probability in specific locations, sharing pipeline expansion between these sites and reducing the level of stress and strain in each buckle.
Despite of its importance, buckle formation process is influenced by several parameters such as the seabed bathymetry, engineered triggers, lateral out-of-straightness (OOS) and pipe-soil interaction. While the first two items above can be defined with reasonable accuracy at previous stages of design, lateral OOS will only be known with tolerable confidence after pipeline installation. The level of uncertainty related to pipe-soil interaction is also considerable since pipeline embedment and friction factors are estimated using equations that include empirical correlations and field collected data. In addition these parameters are influenced by the installation process. Due to these uncertainties, conservative premises are usually assumed in order to obtain a robust pipeline thermo-mechanical design.
After pipeline installation and/or start of operation an investigation can be performed in order to confirm the assumptions considered in the design. This paper presents a comparison of premises adopted during design stage of a pipeline based on the controlled lateral buckling methodology and the feedback obtained with the post-lay survey performed. After a brief introduction, pipeline embedment, global buckling at crossings, lateral OOS and sleepers’ height are some of the subjects addressed. Finally, conclusions and recommendations are presented in order to support future similar projects.
Localised lateral buckling of partially embedded subsea pipelines with nonlinear soil resistance