15 - pipeline-soil interaction[1]

8/3/2019 15 - Pipeline-Soil Interaction[1]

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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



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




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 stabilityRef: Langley (2005)




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)




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 FiniteElement 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 Models

Load-Displacement

Centrifugemodels

Large-scalephysicalmodels

ContinuumFEA Ref: Phillips et al. (2004)




Buried Performance

Thermal

Flow assurance

Mechanical

Uplift, flotation, subsidence during pipe lay

Upheaval buckling during operationsRef: C-CORE




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



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




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=




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



:= 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⋅=




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)




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⋅=




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.




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.

15 - pipeline-soil interaction[1]

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