120403102 pipeline soil interaction

Shawn Kenny, Ph.D., P.Eng.Assistant ProfessorFaculty of Engineering and Applied ScienceMemorial University of [email protected]

ENGI 8673 Subsea Pipeline Engineering

Lecture 15: Pipeline/Soil Interaction

2 ENGI 8673 Subsea Pipeline Engineering Lecture 15 2008 S. Kenny, Ph.D., P.Eng.

Lecture 15 Objective

to examine engineering models to analysegeotechnical loads, pipeline/soil interaction and structural load effects for offshore pipelines


Overview

Geotechnical Loads Soil mechanical behaviour

Pipeline/Soil Interaction Load transfer mechanisms

Structural Load Effects Pipeline mechanical response


Design Considerations Installation

Pipeline embedment On-bottom roughness

Mechanical response, free spans Intervention

Pre-sweep, clearance Trenching

Natural in-fill, mechanical backfill Rock dump

Operations Thermal expansion Lateral and upheaval buckling On-bottom stability

Ref: Langley (2005)


Geotechnical Loads Soil Mechanics

Seabed Surveys Remote sensing In-situ testing and sample recovery Index and laboratory testing

Key Issues Soil type Strength

parameters Load-

displacementbehaviour

Ref: BCOG (2001)


Pipeline/Soil Interaction Engineering Tools

Guidance documents ALA, DNV, NEN

Numerical models Structural Continuum

Physical models Full-scale Large-scale Centrifuge

Key Issues Load transfer mechanisms Stress or strain based design Model uncertainty

Ref: C-CORE


Structural Load Effects

Design Checks Limit States

SLS ULS

Stress Combined loading

criteria Strain

Rupture Local buckling


Pipeline/Soil Interaction Analysis

Structural Finite Element Procedures Standard tool Rigid pipeline/structure Soil load-displacement


Soil Load-Displacement Relationships

Axial

Transverse Lateral

Vertical Upward

Vertical DownwardRef: ALA (2001)


Trench Effects

Engineering ModelsLoad-Displacement Centrifuge

models Large-scale

physicalmodels

Continuum FEA Ref: Phillips et al. (2004)


Buried Performance

Thermal Flow assurance

Mechanical Uplift, flotation, subsidence during pipe lay Upheaval buckling during operations

Ref: C-CORE


Example 15-01

Calculate the virtual anchor point, axial strain and end deflection due to thermal expansion for a buried pipeline

Design condition Partial restraint

Shore approach Platform tie-in

EN 8673 Subsea Pipeline Engineering Lecture 15Example 15-01

Winter 2008

Example 15-01

Calculate the anchor point, axial strain and end deflection due to thermal expansion for a buried offshore pipelinelocated outside the 500m excursion limit.

DEFINED UNITS

MPa 106Pa:= kPa 103Pa:= GPa 109Pa:= C K:= kN 103N:=

PIPELINE SYSTEM PARAMETERS

Nominal Outside Diameter Do 273.1mm:=Initial Selection Nominal Wall Thickness (Sec.5 C203 Table 5-3) tnom 9.525mm:=External Corrosion Protection Coating Thickness tcpc 0mm:=Fabrication Process (Sec.7 B300 Table 7-1) [SMLS, HFW, SAW] FAB "SMLS":=Corrosion Allowance (Sec.6 D203) tcorr 3mm:=Elastic Modulus E 205GPa:=Specified Minimum Yield Stress (Sec.7 B300 Table 7-5) SMYS 450MPa:=Speciifed Minimum Tensile Stress (Sec.7 B300 Table 7-5) SMTS 535MPa:=Coefficient of Thermal Expansion T 1.15 10

5 C 1:=Poisson's Ratio 0.3:=Pipeline Route Length Lp 25km:=Linepipe Density s 7850kg m

3:=Concrete Coating Thickness tc 50mm:=Concrete Coating Density c 3050kg m

3:=OPERATATIONAL PARAMETERS

API Gravity API 38:=Product Contents Density

cont 1000 kg m 3 141.5131.5 API+:= cont 835 m3 kg=

Design Pressure (Gauge) Pd 10MPa:=Safety Class (Sec.2 C200-C400) [L, M, H] SC "M":=Design Pressure Reference Level href 5m:=Temperature Differential T 50 C:=Maximum Water Depth hl 0m:=Seawater Density w 1025kg m

3:=Hydrotest Fluid Density t 1025kg m

3:=

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Winter 2008

GEOTECHNICAL PARAMETERS

Undrained Shear Strength Cu 25kPa:=Adhesion Factor soil 0.25:=

DNV OS-F101 PARTIAL FACTORS AND DESIGN PARAMETERS

System Operations Incidental/Design Pressure Factor (Sec.3 B304) inc_o 1.10:=System Test Incidental/Design Pressure Factor (Sec.3 B304) inc_t 1.00:=Material Resistance Factor (Sec.5 C205 Table 5-4) m 1.15:=Safety Class Resistance Factor (Sec.5 C206 Table 5-5) SC 1.138:=Material Strength Factor (Sec.5 C306 Table 5-6) U 0.96:=Maximum Fabrication Factor (Sec.5 C307 Table 5-7)

fab 1.00 FAB "SMLS"=if0.93 FAB "HFW"=if0.85 FAB "SAW"=if

:= fab 1.00=

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Winter 2008

Diameter Fabrication Tolerance(Sec.7 G200 Table 7-17)

Do max 0.5mm 0.0075 Do, ( ) FAB "SMLS"= Do 610mmif0.01 Do FAB "SMLS"= Do 610mm>ifmin max 0.5mm 0.0075 Do, ( ) 3.2mm, ( ) FAB "HFW"= Do 610mmifmin 0.005 Do 3.2mm, ( ) FAB "HFW"= Do 610mm>ifmin max 0.5mm 0.0075 Do, ( ) 3.2mm, ( ) FAB "SAW"= Do 610mmifmin 0.005 Do 3.2mm, ( ) FAB "SAW"= Do 610mm>if

:= Do 2.048 mm=

Wall Thickness Fabrication Tolerance(Sec.7 G307 Table 7-18)

tfab 0.5mm FAB "SMLS"= tnom 4mmif0.125 tnom FAB "SMLS"= tnom 4mm>if0.125 tnom FAB "SMLS"= tnom 10mmif0.100 tnom FAB "SMLS"= tnom 25mmif3mm FAB "SMLS"= tnom 30mmif0.4mm FAB "HFW"= tnom 6mmif0.7mm FAB "HFW"= tnom 6mm>if1.0mm FAB "HFW"= tnom 15mm>if0.5mm FAB "SAW"= tnom 6mmif0.7mm FAB "SAW"= tnom 6mm>if1.0mm FAB "SAW"= tnom 10mm>if1.0mm FAB "SAW"= tnom 20mm>if

:= tfab 1.191 mm=

Material Derating (Sec.5 C300 Figure 2)

SMYS 0MPa T 50C


Winter 2008

ENGINEERING ANALYSIS

PIPELINE GEOMETRIC PROPERTIES

Inside Pipeline Diameter (Operations Case)

Di_o Do 2. tcorr 2. tfab:= Di_o 264.72 mm=Inside Pipeline Radius (Operations Case)

Ri_o 0.5 Di_o:= Ri_o 132.36 mm=Effective Outside Pipeline Diameter

De Do 2. tcpc+ 2. tc+:= De 373.10 mm=Pipeline Steel Area

Ast

4Do

2 Do 2 tnom( )2 := Ast 7.89 103 mm2=Concrete Area

Ac

4Do 2 tc+( )2 Do2 := Ac 5.08 104 mm2=

Effective Outside Pipeline Area

Ae

4Do 2 tc+( )2:= Ae 1.09 105 mm2=

Inside Pipeline Area

Ai

4Di_o

2:= Ai 5.50 104 mm2=

BUOYANCY FORCE (per meter basis)

BF g m w Ae c Ac s Ast( ):= BF 1.03 kN=Buoyancy Force Check

BFchk "NEGATIVE BUOYANCY" BF 0


Winter 2008

Distance to Virtual Anchor Point - Assumes constant temperature (conservative) - Equation 9 of Palmer and Ling (1981) OTC4067

z Pd Ri_o2

f1 2 2 tnom

Pd Ri_oE T T+

:= z 157.51 m=

Virtual Anchor Length Check

zchk "VIRTUAL ANCHOR OK" z 0.5 Lp= Z)

l Pd Ri_o

tnom E T T:= l 76.19 MPa=

EQUIVALENT STRESS CHECK

eq h2

h l l2+:= eq 293.73 MPa=eqchk "EQUIVALENT STRESS OK" eq 0.9 SMYS


Reading List http://www.fugro.com/survey/offshore/gcs.asp

ALA (2001). Guideline for the Design of Buried Steel Pipe. July 2001, 83p.[2001_ALA_Design_Guideline.pdf]

Cathie, D.N., Jaeck, C., Ballard, J.-C. and Wintgens, J.-F. (2005). Pipeline geotechnics state-of-the-art. Frontiers in Offshore Geotechnics, ISFOG, ISBN 0 415 39063 X, pp.95-114[2005_Cathie_PSI.pdf]

Palmer, A.C. and Ling, M.T.S. (1981). Movements of Submarine Pipelines Close to Platforms. Proc., OTC, OTC 4067, pp.17-24.

Palmer, A.C., Ellinas, C.P., Richards, D.M. and Guijt, J. Design of Submarine Pipelines Against Upheaval Buckling. Proc., OTC, OTC 6335, pp.551-560.


References http://en.wikipedia.org/wiki/Geotechnical_engineering http://en.wikipedia.org/wiki/Soil_mechanics BCOG (2001). BC Offshore Oil & Gas Technology

Update, JWEL Project No. BCV50229, October 19, 2001 DNV (2007). Submarine Pipeline Systems. Offshore

Standard, DNV OS-F101, October 2007, 240p. Langley, D. (2005). A Resourceful Industry Lands the

Serpent, Journal of Petroleum Technology, 57(10), 6p. Phillips, R. A. Nobahar and J. Zhou (2004). Trench

effects on pipe-soil interaction. Proc. IPC, IPC 04-0141, 7p.

ENGI 8673 Subsea Pipeline EngineeringLecture 15 ObjectiveOverviewDesign ConsiderationsGeotechnical Loads Soil MechanicsPipeline/Soil InteractionStructural Load EffectsPipeline/Soil Interaction AnalysisSoil Load-Displacement RelationshipsTrench EffectsBuried PerformanceExample 15-01Example 15-01 (cont)Example 15-01 (cont)Example 15-01 (cont)Example 15-01 (cont)Example 15-01 (cont)Reading ListReferences

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