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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
3 ENGI 8673 Subsea Pipeline Engineering Lecture 15 2008 S. Kenny, Ph.D., P.Eng.
Overview
Geotechnical Loads Soil mechanical behaviour
Pipeline/Soil Interaction Load transfer mechanisms
Structural Load Effects Pipeline mechanical response
4 ENGI 8673 Subsea Pipeline Engineering Lecture 15 2008 S. Kenny, Ph.D., P.Eng.
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)
5 ENGI 8673 Subsea Pipeline Engineering Lecture 15 2008 S. Kenny, Ph.D., P.Eng.
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)
6 ENGI 8673 Subsea Pipeline Engineering Lecture 15 2008 S. Kenny, Ph.D., P.Eng.
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
7 ENGI 8673 Subsea Pipeline Engineering Lecture 15 2008 S. Kenny, Ph.D., P.Eng.
Structural Load Effects
Design Checks Limit States
SLS ULS
Stress Combined loading
criteria Strain
Rupture Local buckling
8 ENGI 8673 Subsea Pipeline Engineering Lecture 15 2008 S. Kenny, Ph.D., P.Eng.
Pipeline/Soil Interaction Analysis
Structural Finite Element Procedures Standard tool Rigid pipeline/structure Soil load-displacement
9 ENGI 8673 Subsea Pipeline Engineering Lecture 15 2008 S. Kenny, Ph.D., P.Eng.
Soil Load-Displacement Relationships
Axial
Transverse Lateral
Vertical Upward
Vertical DownwardRef: ALA (2001)
10 ENGI 8673 Subsea Pipeline Engineering Lecture 15 2008 S. Kenny, Ph.D., P.Eng.
Trench Effects
Engineering ModelsLoad-Displacement Centrifuge
models Large-scale
physicalmodels
Continuum FEA Ref: Phillips et al. (2004)
11 ENGI 8673 Subsea Pipeline Engineering Lecture 15 2008 S. Kenny, Ph.D., P.Eng.
Buried Performance
Thermal Flow assurance
Mechanical Uplift, flotation, subsidence during pipe lay Upheaval buckling during operations
Ref: C-CORE
12 ENGI 8673 Subsea Pipeline Engineering Lecture 15 2008 S. Kenny, Ph.D., P.Eng.
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:=
3/3/2008 Page 1 of 5
EN 8673 Subsea Pipeline Engineering Lecture 15Example 15-01
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=
3/3/2008 Page 2 of 5
EN 8673 Subsea Pipeline Engineering Lecture 15Example 15-01
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
EN 8673 Subsea Pipeline Engineering Lecture 15Example 15-01
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
EN 8673 Subsea Pipeline Engineering Lecture 15Example 15-01
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
18 ENGI 8673 Subsea Pipeline Engineering Lecture 15 2008 S. Kenny, Ph.D., P.Eng.
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.
19 ENGI 8673 Subsea Pipeline Engineering Lecture 15 2008 S. Kenny, Ph.D., P.Eng.
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