virtual anchor length - kbr
TRANSCRIPT
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Gas Speak Colloquium 2011
Determination of Soil Restraint Properties and Calculation of Virtual Anchor Lengths in Buried Pipelines
Daniel TianMechanical Engineer
KBR
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Introduction
• What is Pipe Soil Interaction?• What is Pipe-Soil Interaction?– Behavior of buried pipeline in the surrounding soil– Pipe and soil together form the engineered systemPipe and soil together form the engineered system
• Soil Restraint Propertiesp– Relationship between soil resistance and pipe movement
• Virtual Anchor Length– Pipe section moving relative to the soil near directional change
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Why now?
• Risk based pipeline design approach (AS2885)
• Challenges facing pipeline designin Australia– Higher pressures– Larger diameters
Telfer Brooklyn-Lara Iona-Orford QueenslandTelferPipeline
Brooklyn LaraPipeline
Iona OrfordPipeline
QueenslandCSG Pipeline
Size (DN) 250 500 450 1050
Length (km) 443 65 101 Over 1000g ( )
MAOP (MPag) 10.2 10.2 15.3 10.2 / 15.3
WT (mm) 4.7 7.9 9.1 14.1 / 18.7
Material API 5L X60 API 5L X70 API 5L X70 API 5L X70Material API 5L X60 API 5L X70 API 5L X70 API 5L X70
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Onshore Pipeline Uplift, Uzbekistan
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Subsea Oil Pipeline Failure, Brazil, 2000
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Purpose of Calculating Pipe-Soil Interaction
• Soil restraint input into Pipe Stress Analysis (AutoPipe or Caesar II)• Virtual anchor length to define model boundary• Virtual anchor length to define model boundary
– Above-Ground Facilities - Buried Pipeline Sectionsp
(soil restraint is the fundamental part)
Compressor Station Major Water CrossingCompressor Station Major Water Crossing
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Determination of Soil Restraint Properties
Longitudinal TransverseActual
Vertical Upward Vertical Downward
Elastic-Plastic Soil Springp g
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Determination of Soil Restraint Properties
Soil and Pipe Properties:• Unit Weight ()
Elastic-Plastic Soil Springs:• Soil Stiffness (K1)
• Undrained Shear Strength (Su)• Angle of Internal Friction ()• Pipe Diameter (D)
• Ultimate Soil Resistance (P1)
ALAPipe Diameter (D)• Depth of Cover (H)
ALA
AutoPipe
Peng
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ALA Method for Calculating Pipe-Soil Interaction
• Widely recognised and applied
• Advanced soil modeller in Caesar II
• Based on laboratory and field i t l i ti tiexperimental investigations
• Formulas available for design factors• Formulas available for design factors
• Limitation:Limitation:– Under-estimate vertical upward
resistance (Appendix B)(Appendix B)
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AutoPipe Method for Calculating Pipe-Soil Interaction
• Detailed in AutoPipe Technical Reference Manual
• Based on laboratory and field i l i i iexperimental investigations
Li it ti• Limitations:– Design factors need to be
determined from tables and charts
(Pipe-Soil Appendix)
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Peng’s Method for Calculating Pipe-Soil Interaction
• First published in 1978
• Basic Soil Modeller in Caesar II
• Limitations:P li i ti ti– Preliminary estimation
– Based on theoretical soil mechanics
(Chapter 10)
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KBR Pipe-Soil Interaction Calculation Sheet
• Each of the 3 established methods• Each of the 3 established methods has strengths and weaknesses.
• Compare results from 3 methods and choose which method is suitableand choose which method is suitable for a particular application
• Calculate input data for stress software package
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Typical Soil Properties
Soil TypeSoftClay
NormalClay
StiffClay
LooseSand
MediumSand
DenseSandy y y
Dry Unit Weight(kg/m3)
1600 1800 2000 1600 1800 2000
UndrainedShear Strength
(kP )5 25 100 0 0 0
(kPa)Internal Friction
Angle (°)0 0 0 25 30 40
• To be used when soil data is not available for critical locations
Angle ( )
• Soft clay – worst design case for unknown soily g
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DN1000, 1.2m Cover, Soft Clay Condition, Various Methods
Vertical Upward
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DN1000, 1.2m Cover, Soft Clay Condition, Various Methods
Transverse
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DN1000, 1.2m Cover, Soft Clay Condition, Various Methods
Longitudinal VerticalDownward
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Calculation of Virtual Anchor Length in Buried Pipeline
• Distance from bend, tee or A/G-U/G transition to the point where pipe axial strain is completely suppressed by soil.
La
Virtual Anchor Length La = Co A [ε E + (0.5 - v) SHP] / Plong
Elastic Factor
Stress -Thermal
Expansion
Stress -Pressure
Elongation
LongitudinalSoil Resistance
Expansion Elongation
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Virtual Anchor Lengths under Different Soil Conditions
DN1000, 1200mm Cover, 55°C DT, 10.2MPag DP
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Applications
Anchor Block Requirementat Pig Trap
MajorW tWater
Crossing
Overbend atTop of Hill
Depth of Cover ChangeDepth of Cover Change
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Pipeline Design Engineer’s Responsibility
• Know how to use the right engineering design toolsengineering design tools
• Do some research and understand pipe-soilunderstand pipe-soil interaction
• Make sound engineering• Make sound engineering judgement
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Questions?
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Disclaimer
These materials contain information of a general nature and are provided for discussion purposes only. They do not in any p p p y y yway represent engineering advice and KBR does not warrant the accuracy, completeness or currency of the information in these materials. Any person who uses or relies on these materials doesthese materials. Any person who uses or relies on these materials does so entirely at their own risk.