Dynamic Versus Static Lateral Buckling of Subsea Pipelines

The current demand for hydrocarbon products has led to the development of High Pressure / High Temperature (HP/HT) reservoirs previously thought to be uneconomical. These marginal fields are usually developed via satellite wells tied back to existing processing facilities. For long tiebacks to HP/HT wells, where HIPPS are not employed, pipeline systems needs to be designed for full wellhead shutin pressures. Pipelines left un-trenched on the seabed surface are susceptible to lateral buckling under operating conditions. Lateral buckling (or snaking) of subsea pipelines represents a stability problem that is amenable to solution by numerical methods, such as Finite Element Analysis (FEA). Two different approaches have been adopted in the application of FEA to lateral buckling of subsea pipelines: non-linear static and implicit dynamic analysis. An overview of lateral buckling is presented, including the merits and limitation of analytical and numerical methods. The cause and effect of initial imperfections is examined as well as methods of including imperfections within an analysis. Numerical methods are investigated in terms of local and global modelling techniques and the effects of "feedin" to a buckle location are discussed. Static and dynamic solutions to FEA are investigated in terms of solution accuracy and numerical stability. An example of a typical pipeline section subjected to functional loading and prone to lateral buckling is included. The results from static and dynamic solutions, including the effects of fishing gear interaction, are compared in terms of lateral displacements due to temperature and pressure loading. The merits of the different solution techniques are examined in terms of accuracy and numerical stability. The effects of initial imperfections due to pipelay on the type of analysis adopted for lateral buckling are also discussed.