The mitigation of lateral buckling for subsea pipelines is achieved by making the pipe buckle at intended locations in preference to uncontrolled lateral buckles. At these engineered locations, the pipeline can be given enhanced characteristics (pipe tolerances, welds and Non-Destructive Examination (NDE) criteria). Alternatively, the buckle initiation equipment can be designed to distribute evenly the stress along the buckled pipeline and consequently reduce the maximum stress in the buckled pipeline section. As various parameters involved in the buckle formation process are uncertain (e.g. soil characteristics, residual horizontal imperfections after pipelay), a probabilistic approach is used to assess the likelihood that the pipeline will buckle at the intended locations.
Up to now, the existing guidelines focus on in-plane residual Out Of Straightness (OOS) whereas the impact of bathymetry (i.e. uneven seabed) is only addressed in a high level fashion, with no clear methodology.
The authors have therefore developed an original approach to account for the effects of bathymetry on the reliability of buckle formation. In a first step, the effects of bathymetry on buckle formation are discussed from a geotechnical and mechanical perspective. Then, the implementation of the buckling formation formulation in a probabilistic numerical subroutine is presented. Finally, a generic case study is considered to assess the impact of accounting for bathymetry on the buckle formation reliability analysis.