Using coating roughness to control pipe-soil friction and influence pipeline global buckling behaviour

Submarine on-bottom High Pressure / High Temperature pipelines are susceptible to buckling and walking phenomena to relieve axial stress built up in the pipeline through thermal expansion. Axial stress is dependent on the friction coefficient between seafloor soils and pipeline coatings and has a controlling influence on the instigation of buckles. Typical approaches to influencing the formation and distribution of buckles is the placement of sleepers or sliders to promote or discourage lateral deformation. Herein, an alternative methodology is proposed where variation of the pipe-soil interaction friction coefficient axially can promote analogous behaviour. Recent experimental investigations have characterised friction coefficients for polypropylene, a typical pipe coating material, with typical real-world surface textures and also with enhanced textures designed to improve interface shear strength. Finite element analysis using Abaqus was used in this paper to model an approximately 5 km on-bottom pipeline subject to operational loads typical of HPHT systems. The results show that pipe-soil friction has the expected impact on axial stress build up and buckle properties, but also that axial variation of PSI friction has a significant impact on the distribution and magnitude of buckles.