L52284 Upheaval Buckling Limit State Function for Onshore Gas Pipelines

For buried pipelines a well established problem has been that of upheaval buckling. This occurs because the fluid is usually pumped through the pipes at elevated temperatures causing the pipeline to experience thermal expansion which, if restrained, leads to an increase in the axial stress in the pipeline possibly resulting in a buckling failure. A secondary phenomenon that has also been identified, particularly in loose sands and silts, involves floatation of pipelines through the backfill material, usually shortly after burial.

The upheaval buckling limit state function developed in this project employs the critical upheaval buckling force and applied compressive force due to temperature and pressure. It applies to pipe sections containing a hill-crest type of imperfection over which the pipeline is routed using a series of cold formed bends. The critical buckling force is calculated using an empirical equation developed by Boreas based on the results of parametric finite element analyses (FEA) on 252 design cases. The input parameters for the empirical equation are pipe diameter, diameter-over-wall-thickness (D/t) ratio, grade, pressure, soil download and imperfection angle. The development of the equation is described in a technical report prepared by Boreas.