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Shawn Kenny, Ph.D., P.Eng.Assistant Professor
Faculty of Engineering and Applied ScienceMemorial University of [email protected]
ENGI 8673 Subsea Pipeline
Engineering
Lecture 15: Pipeline/Soil Interaction
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2 ENGI 8673 Subsea Pipeline Engineering – Lecture 15 © 2008 S. Kenny, Ph.D., P.Eng.
Lecture 15 Objective
to examine engineering models to analyse
geotechnical loads, pipeline/soil interactionand structural load effects for offshore
pipelines
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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
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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 stabilityRef: Langley (2005)
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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
Strengthparameters
Load-displacementbehaviour
Ref: BCOG (2001)
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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
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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
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8 ENGI 8673 Subsea Pipeline Engineering – Lecture 15 © 2008 S. Kenny, Ph.D., P.Eng.
Pipeline/Soil Interaction Analysis
Structural FiniteElement Procedures Standard tool
Rigid pipeline/structure
Soil load-displacement
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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)
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10 ENGI 8673 Subsea Pipeline Engineering – Lecture 15 © 2008 S. Kenny, Ph.D., P.Eng.
Trench Effects
Engineering Models
Load-Displacement
Centrifugemodels
Large-scalephysicalmodels
ContinuumFEA Ref: Phillips et al. (2004)
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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 operationsRef: C-CORE
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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 thermalexpansion for a buried pipeline
Design condition
Partial restraint
• Shore approach• Platform tie-in
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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 10
3Pa:= GPa 10
9Pa:= C K:= kN 10
3N:=
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 αT 1.15 105−
⋅ C1−
:=
Poisson's Ratio ν 0.3:=
Pipeline Route Length Lp 25km:=
Linepipe Density ρs 7850kg m3−
⋅:=
Concrete Coating Thickness tc 50mm:=
Concrete Coating Density ρc 3050kg m3−
⋅:=
OPERATATIONAL PARAMETERS
API Gravity API 38:=
Product Contents Density
ρcont 1000 kg⋅ m3−
⋅141.5
131.5 API+⋅:= ρcont 835 m
3−kg⋅=
Design Pressure (Gauge) Pd 10MPa:=
Safety Class (Sec.2 C200-C400) [L, M, H] SC "M":=
Design Pressure Reference Level h 5
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EN 8673 Subsea Pipeline Engineering Lecture 15Example 15-01
Winter 2008
GEOTECHNICAL PARAMETERS
Undrained Shear Strength Cu 25kPa:=
Adhesion Factor αsoil 0.25:=
DNV OS-F101 PARTIAL FACTORS AND DESIGN PARAMETERS
System Operations Incidental/Design Pressure Factor (Sec.3 B304) γinc_o 1.10:=
System Test Incidental/Design Pressure Factor (Sec.3 B304) γinc_t 1.00:=
Material Resistance Factor (Sec.5 C205 Table 5-4) γm 1.15:=
Safety Class Resistance Factor (Sec.5 C206 Table 5-5) γSC 1.138:=
Material Strength Factor (Sec.5 C306 Table 5-6) αU
0.96:=
Maximum Fabrication Factor (Sec.5 C307 Table 5-7)
αfab 1.00 FAB "SMLS"=if
0.93 FAB "HFW"=if
0.85 FAB "SAW"=if
:= αfab 1.00=
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EN 8673 Subsea Pipeline Engineering Lecture 15Example 15-01
Winter 2008
Diameter Fabrication Tolerance(Sec.7 G200 Table 7-17)
ΔDo max 0.5mm 0.0075 Do⋅,( ) FAB "SMLS"= Do 610mm≤∧if
0.01 Do⋅ FAB "SMLS"= Do 610mm>∧if
min max 0.5mm 0.0075 Do⋅,( ) 3.2mm,( ) FAB "HFW"= Do 610mm≤∧if
min 0.005 Do⋅ 3.2mm,( ) FAB "HFW"= Do 610mm>∧if
min max 0.5mm 0.0075 Do⋅,( ) 3.2mm,( ) FAB "SAW"= Do 610mm≤∧if
min 0.005 Do⋅ 3.2mm,( ) FAB "SAW"= Do 610mm>∧if
:= ΔDo 2.048 mm⋅=
Wall Thickness Fabrication Tolerance(Sec.7 G307 Table 7-18)
tfab 0.5mm FAB "SMLS"= tnom 4mm≤∧if
0.125 tnom⋅ FAB "SMLS"= tnom 4mm>∧if
0.125 tnom⋅ FAB "SMLS"= tnom 10mm≥∧if
0.100 tnom⋅ FAB "SMLS"= tnom 25mm≥∧if
3mm FAB "SMLS"=
tnom 30mm≥∧if 0.4mm FAB "HFW"= tnom 6mm≤∧if
0.7mm FAB "HFW"= tnom 6mm>∧if
1.0mm FAB "HFW"= tnom 15mm>∧if
0.5mm FAB "SAW"= tnom 6mm≤∧if
0.7mm FAB "SAW"= tnom 6mm>∧if
1.0mm FAB "SAW"= tnom 10mm>∧if
1.0mm FAB "SAW"= tnom 20mm>∧if
:= tfab 1.191 mm⋅=
Material Derating (Sec.5 C300 Figure 2)
ΔSMYS 0MPa ΔT 50C<if
ΔT 50 C⋅−( )30MPa
50 C⋅⎛ ⎝
⎞ ⎠
⋅⎡⎣
⎤⎦
50 C⋅ ΔT< 100C<if
30MPa ΔT 100 C⋅−( )40MPa
100 C⋅⎛ ⎝
⎞ ⎠
⋅+⎡⎣
⎤⎦
otherwise
:= ΔSMYS 10.00 MPa⋅=
ΔSMTS 0MPa ΔT 50C<if
ΔT 50 C⋅−( )30MPa⎛
⎝ ⎞⎠
⋅⎡⎣
⎤⎦
50 C⋅ ΔT< 100C<if
:= ΔSMYS 10.00 MPa⋅=
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EN 8673 Subsea Pipeline Engineering Lecture 15Example 15-01
Winter 2008
ENGINEERING ANALYSIS
PIPELINE GEOMETRIC PROPERTIESInside 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
π
4Do
2Do 2 tnom⋅−( )2
−⋅:= Ast 7.89 103
× mm2
⋅=
Concrete Area
Acπ4
Do 2 tc⋅+( )2 Do2−⋅:= Ac 5.08 104× mm2⋅=
Effective Outside Pipeline Area
Ae
π
4Do 2 tc⋅+( )2
⋅:= Ae 1.09 105
× mm2
⋅=
Inside Pipeline Area
Aiπ4
Di_o2⋅:= Ai 5.50 104× mm2⋅=
BUOYANCY FORCE (per meter basis)
BF g m⋅ ρw Ae⋅ ρc Ac⋅− ρs Ast⋅−( )⋅:= BF 1.03− kN⋅=
Buoyancy Force Check
BFchk "NEGATIVE BUOYANCY" BF 0<if
"FLOTATION" otherwise
:= BFchk "NEGATIVE BUOYANCY"=
External Hydrostatic Pressure
Pe ρw g⋅ hl⋅:= Pe 0.00 MPa⋅=
HOOP STRESS (THIN WALL THEORY)
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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
zπ Pd⋅ Ri_o
2⋅
f 1 2 ν⋅−
2 tnom⋅
Pd Ri_o⋅E⋅ αT⋅ ΔT⋅+
⎛
⎝
⎞
⎠⋅:= z 157.51 m=
Virtual Anchor Length Check
zchk "VIRTUAL ANCHOR OK" z 0.5 Lp⋅<if
"RECALCULATE" otherwise
:=
zchk "VIRTUAL ANCHOR OK"=
COMBINED STRESS STATE
Axial End Displacement
δend
Pd Ri_o⋅
2 E⋅ tnom⋅1 2ν−( )⋅ αT ΔT⋅+
⎡
⎣
⎤
⎦z⋅
f z2
⋅
4 π⋅ E⋅ Ri_o⋅ tnom⋅−:= δend 56 mm⋅=
Axial End Displacement [Equation 12 - Palmer and Ling (1981) OTC 4067]
δPalmer
π Ri_o⋅ E⋅ tnom⋅ αT ΔT⋅( )2⋅
f 1
Pd Ri_o⋅1
2ν−⎛
⎝ ⎞ ⎠
⋅
E tnom⋅ αT⋅ ΔT⋅+
⎡
⎢⎣
⎤
⎥⎦
2
⋅:= δPalmer 56 mm⋅=
Axial Stress (For X < Z)
x75 0.75 z⋅:=
σl_75
Pd Ri_o⋅
2tnom
f
2 π⋅ Ri_o⋅ tnom⋅x75⋅−:= σl_75 39.77− MPa⋅=
x1 1.00 z⋅:=
σl_1
Pd Ri_o⋅
2tnom
f
2 π⋅ Ri_o⋅ tnom⋅
x1⋅−:= σl_1 76.19− MPa⋅=
AXIAL STRESS (FOR X >= Z)
σl νPd Ri_o⋅
tnom
⋅ E αT⋅ ΔT⋅−:= σl 76.19− MPa⋅=
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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). “Pipelinegeotechnics – 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 PipelinesClose to Platforms.” Proc., OTC, OTC 4067, pp.17-24.
Palmer, A.C., Ellinas, C.P., Richards, D.M. and Guijt, J. “Design ofSubmarine Pipelines Against Upheaval Buckling.” Proc., OTC, OTC 6335,pp.551-560.
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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 TechnologyUpdate, JWEL Project No. BCV50229, October 19, 2001
DNV (2007). Submarine Pipeline Systems. OffshoreStandard, DNV OS-F101, October 2007, 240p.
Langley, D. (2005). “A Resourceful Industry Lands theSerpent”, 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.