Rogue lateral buckle initiation at subsea pipelines

Abstract

Due to the pipelay vessel motions during installation of a subsea pipeline, as-laid direction of the pipeline changes along a nominally straight section of the route. In a High Pressure High Temperature (HPHT) pipeline, presence of rogue lateral Out of Straightness (OoS) can adversely influence the reliability of buckle initiation at engineered buckling sites e.g. sleepers. This implies the requirement to study the rogue buckle initiation to ensure unwanted buckles are not formed. This paper provides a framework to study the range of critical buckling force (CBF) of a rogue OoS which, so far has not been fully explored in the literature. A simplified and yet accurate pipe-soil interaction model for sandy seabeds, suitable for calculation of CBF is described. The built-in friction models in Abaqus FE software are not suitable for simulation of the lateral buckling as they cannot decouple axial and lateral force-displacement relationships. Therefore, a novel Finite Element (FE) modelling technique benefiting from a two-surface seabed capable of decoupling contact frictions at orthogonal directions is developed. This eliminates the need for developing complex user-defined friction subroutines. Different ways of characterising rogue lateral OoS are discussed and the best method is selected. Accordingly, and in a systematic process, pipe-soil interaction parameters, lateral OoS configuration parameters and pipeline stiffness which form the contributing parameters to the resistance against lateral buckling are identified.