Developing a more accurate description of soil-pipe interaction for the design of high temperature pipelines

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1 Background references Developing a more accurate description of soil-pipe interaction for the design of high temperature pipelines David White Shell EMI Professor of Offshore Engineering Fraser Bransby Senior Principal Engineer, Fugro AG SUT Evening Technical Meeting, Perth June 25 White D.J., Westgate Z., Ballard J-C, de Brier C. & Bransby M.F. 25. Best practice geotechnical characterization and pipe-soil interaction analysis for HPHT flowline design. Proc. Offshore Technology Conference. Houston. OTC2626-MS Bransby, M.F., Borges Rodriguez, A., Zhou, H., Low, H.E. & White, D.J. 24. Sediment mobility effects on seabed resistance for unburied pipelines. Proc. Offshore Technology Conference. Paper OTC25287 Westgate Z.J. & White D.J. 25. Quantifying spatial variability in pipeline embedment for subsea pipeline design. Proc. Int. Conf. Offshore Mech. and Arctic Engng. OMAE White D.J., Leckie, S.H.F., Draper, S., Zakarian, E. 25. Temporal changes in pipeline-seabed condition and their effect on operating behaviour. Proc. Int. Conf. Offshore Mech. and Arctic Engng. OMAE Leckie, S., Draper, S., White, D.J., Cheng, L. & Fogliani N. 25. Lifelong embedment and spanning of a pipeline on a mobile seabed. Coastal Engineering. 95:-46. Hill A. & White D.J. 25. Pipe-soil interaction: Recent and future improvements in practice. Proc. Int. Symp. on Frontiers in Offshore Geotechnics (ISFOG). Time

2 Time Spatial variability Space Spatial variability Time 2

3 Axial PSI: General Model Consolidation Hardening Axial friction, F A /W Drained Undrained tan res (s u-int / no ) nc c/p Voids ratio, e Undrained From pipe weight Drained Mobilised strength s un (s u, ) s u R (s u,n ) Voids ratio, e ln R Cycle number Effective stress, Cycle number, n Effective stress, (Partial) Consolidation Hardening Consolidation Hardening: ISB Mobilised strength (s u, ) (s u,n ) Voids ratio, e Shear stress (kpa) 4 Cycles -2 Cycles 5-6 Cycles Boukpeti & White (25) Cycle number, n Effective stress, Horizontal displacement (mm)

4 Consolidation Hardening: FEA Consolidation Hardening: Experiment Axial friction, FA/W' mm dia..4 m length Soft kaolin clay Initially.D embedded.2. Example: Downslope Walking Typical short flowline on seabed slope. SAGE-Profile D software. White et al. (25) 5 Axial displacement, x (mm) Smith & White 24 5 Limiting Axial Friction Cases Pipeline, Bathymetry and Operating Parameters Value Pipeline diameter (m). Pipeline length (m) 4 Wall thickness (mm) 25 Submerged operating weight, W'op (kn/m) Seabed slope, ( ).5 Temperature range (startup to shutdown), T ( ) 8 Soil and PSI Parameters Value Undrained axial friction factor, FA/W'op = ud.4 Drained axial friction factor, FA/W'op = d.8 Mobilization distance, xmob (mm) Volumetric stiffness ratio, /. Coefficient of consolidation, cv (m2/yr).2 Accumulated pipeline walk [m] Yan et al (24).5 Solid line: analytical solution (Carr et al. 26) Dotted line: analytical solution with elastic correction Hollow dots: SAGE Profile FE simulations.5 No walking (FA/W =.8) White et al. (25)

5 With Consolidation Hardening Axial Equivalent Friction Factor, A Drained (Initial) Undrained White et al. (25) With Consolidation Hardening Accumulated pipeline walk [m].5.5 Solid line: analytical solution (Carr et al. 26) Dotted line: analytical solution with elastic correction Hollow dots: SAGE Profile FE simulations Acceptable walking No walking White et al. (25) Friction With Operational Effects Axial Equivalent Friction Factor, A Drained (Initial) Undrained Partial consolidation cases White et al. (25) Range of Walking Responses Accumulated pipeline walk [m].5.5 Acceptable walking? Acceptable walking? Acceptable walking No walking White et al. (25) 5

6 Consolidation Hardening: Field? (m) Time Hill & White (25) As-laid condition Intermittent self-burial and spanning Leckie et al. (25) Leckie et al. (25) 6

7 .2 m/s 2 m/s after 5 s. Impact on temperature profile 5 C Simon Leckie, Erich Zakarian OMAE D Spatial variability Space variability Westgate & White (25) KP (m) Pipe embedment, w/d 7

8 Breakout friction variability Lateral breakout friction, H brk /W' Actual P P KP (m) Westgate & White (25) Buckle initiation force variability Hobbs buckling force, P Hobbs (kn) Actual P P Westgate & White (25) KP (m) Buckle initiation force variability 25 Buckle initiation force variability 25 Hobbs buckling force, P Hobbs (kn) 2 5 Actual P P Westgate & White (25) KP (m) Hobbs buckling force, P Hobbs (kn) 2 5 Actual Envelope of possible P buckle initiation force P Westgate & White (25) KP (m) 8

9 More tolerable design frictions Conditional range Less onerous UB friction Full range Roberts & Taavale (OTC 24) See also: Gerginov et al. (OMAE 24), Bruton & Carr (OPT 25) Residual friction (tolerability) Breakout friction (initiation) Bransby et al. (OTC24) Concluding comments Design pipe-soil friction ranges mask temporal and spatial effects rise in axial friction Potential reduction in pipeline walking increase in thermal insulation and stability Potential improvement in corrosion and/or flow assurance Potential reduction in (secondary) stabilisation measures Spatial variability Less onerous buckling design via better PSI characterisation Developing a more accurate description of soil-pipe interaction for the design of high temperature pipelines David White Shell EMI Professor of Offshore Engineering Fraser Bransby Senior Principal Engineer, Fugro AG SUT Evening Technical Meeting, Perth June 25 9