BURIED FLEXIBLE PIPELINES

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BURIED FLEXIBLE PIPELINES

• The Design Process- Boundary Conditions
• Design Fundamentals-AS2566.1
• Materials
• Installation AS 2566.2
• Tips, Tricks Traps

Presented by Geoffrey D Stone C.Eng FIMechE CP
Eng FIEAust RPEQ Principal Blenray Pty Ltd (
Design Detail Development) geoffrey.stone_at_yahoo.
co.uk 0402 35 2313
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THE DESIGN PROCESSBoundary Conditions

• Soils Soil Data
• Trench Width Depth
• Structural Response to Loading
• Trench Details
• Stiffness
• Thrust Blocks
• Structural Interfaces

• Water Table
• Design Loads Trench Embankment Fill
• Superimposed Live Loads
• Other Superimposed Loads

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Soils Soils Data

• Native Soil
• Classify
• Modulus
• Bedding
• Type
• Embedment
• Material
• Compaction
• Geo-textile
• Water Table

• Backfill
• Type
• Compaction
• Piles
• Testing
• Field
• Laboratory

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Trench Width Depth

• AS 2566.1 Minimum
• Embedment or Embankment
• Shape of trench

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Trench Dimensions
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Structural Response to Loading
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Stiffness AS 2566.1

• 2 year values of pipe stiffness suitable for good
  soils
• 50 year values of pipe stiffness should be used
  for poor soils, uncontrolled installations or
  other higher risk applications

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Stiffness AS 2566.1
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Thrust Blocks

• Not required for fully welded systems as in ABS,
  PP, PVC-U, PB or PE
• Required for rubber ring systems as used for
  DICL, MSCL, GRP PVC-U/O/M
• Design basis
• Steady state pressure
• Unsteady state pressure spikes
• Hydrostatic test pressure

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Structures Interfaces

• Differential Settlement
• Soil swelling
• Water Retaining
• Shear Loading
• Thermal Loading
• Chaffing
• Water seal in concrete

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Water Table

• Water hydrostatic level applies load onto
  pipe-refer AS2566
• Rising water applies uneven load onto pipe and
  the pipe may buckle or exceed its strain limit
• Water may cause flotation of empty pipe and
  special embedment may be necessary
• High water table increases construction
  difficulty
• Safety
• Dewatering
• Quality

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Loading

• Design loads due to trench embankment fill
• External hydrostatic loads
• Internal pressure
• Superimposed dead loads
• Superimposed live loads
• Other unsustained loads

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Design Loads due to Trench Embankment Fill
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Superimposed Live Loads
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Superimposed Live Loads
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Other Unsustained Loads

• Specialist Engineering
• National Codes
• Local Conditions
• Risk
• Likelihood
• Consequences
• Responsibility
• Safeguarding

• Earthquake
• Vibration/Shock
• Differential Settlement
• Thermal Strain
• Subsidence
• Airport runways
• Railways

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DESIGN FUNDAMENTALSAS2566.1 Buried Flexible
Pipelines-Design

• Deflection
• Strength
• Internal Pressure
• Combined Loading
• Buckling

• Hoop Stress
• Ring Bending Strain
• Creep
• Temperature
• Other Considerations

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Deflection

• Short term
• Long term
• Vertical Horizontal
• Considered equal
• Effect of excess side compaction
• Modulus to use
• Acceptance criteria
• Measurement during installation

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Strength

• Loads cause strain in pipe wall
• Ring compression strains ltlt ring bending strains
• AS 2566.1 predicts maximum tensile ring bending
  strains
• A Shape Factor adjusts strain values
• True Ellipse Shape Factor Df3.0
• ?horizontal lt ?vertical Shape Factor Df gt 3.0

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Internal Pressure

• Steady State
• Unsteady State
• AS 2566.1 Requirements 1.25
• AS 2885 Requirement 1.10
• Other codes requirements

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Combined Loading

• Combined external load and internal pressure
• Re rounding effect

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Buckling

• Ovalization
• Buckling
• External Pressure
• No substantial soil support-Timoshenko
• Substantial soil support I.D. Moore

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Hoop Stress

• Stress in the wall due to pressure
• Only criteria used for pipe class selection
• Does not take into account other stresses
• Basis of the Pipe Class System
• Relaxes with time for thermoplastic pipes
• Never Constant

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Ring Bending Strain

• Importance of Strain
• Comparison of allowable strain in materials
• ABS 1
• GRP 0.18 to 0.6
• PE 4.0
• PVC-U 1
• PVC-M 1
• PVC-O 1.3

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Creep

• Variation of Properties in Time
• Long term loading/Stress relaxation
• Reverse loading/Stress magnitude
• Repetitive loading/Fatigue

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Temperature

• The design temperature may vary due to-
• Ambient diurnal temperature variations
• Flow rate
• Fluid temperature range
• Process conditions
• Installation ambient temperature
• Wall thickness

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Other Considerations

• Anchor forces
• Differential Settlement
• Earthquake
• Subsidence
• Testing conditions
• Corrosion

• Mass of pipe contents
• Thermal Strain
• Local buckling
• Fatigue
• Pavement settlement

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Materials Selection

• Types
• Costs
• Class
• Characteristics
• Fittings Valves

• Modulus GRP
• Modulus Thermoplastic Pipes

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Materials - Types

• GRP
• ABS
• PE
• PVC-U, PVC-M, PVC-O
• DICL
• MSCL

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Materials Selection

• Costs - Whole of Life
• Safety
• Availability
• Maintenance
• Energy
• Risks
• Costs - Standards
• Authority
• Industry
• Acts

• Costs Supply
• Pipe
• Fittings
• Supports
• Costs Installation
• Standard of trades
• Equipment
• Jointing
• Access
• Testing

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Selection of Pipe Class

• Design Pressure Steady State
• Design Pressure Unsteady State
• Vacuum Conditions
• Industry Application Environment

• Soil/Pipe Structure Design
• Standardization
• Risk
• Likelihood
• Consequences
• Responsibility

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Typical Material Characteristics
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Fittings Valves

• Valve classes do not meet all pipe classes
• Injection moulded fittings- Size Limitation
• Manufactured fittings-Larger Sizes
• Tees
• Bends

• Jointing
• Gaskets
• Expansion Bellows
• Saddles
• Valves
• Isolation
• Check
• Air release
• Control

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Modulus-GRP Pipes

• Manufacturers establish values by test
  calculation
• Axial longitudinal modulus differs
• Values at various temperatures required for
  design
• Strain rate changes values
• Standards such as ISO 14692

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Modulus-Thermoplastic Pipes

• Published figures normally are strain rate at
  20ºC
• Value determined by ASTM test
• Standard dog bone test specimen
• Fixed strain rate
• Values at various temperatures required for
  design
• Strain rate changes values

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INSTALLATION

• Trench Excavation
• Trench Shields
• Laying Jointing
• Embedment Compaction

• Thrust Blocks
• Hydrostatic Testing

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Trench Excavation

• Excavator bucket width
• Excavated depth
• Soil removal, testing and stockpile
• Shape of trench
• Pockets for pipeline projections
• Thrust block preparation
• Dewatering
• Welding machine access
• Adjacent pipes

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Trench Shields

• When to use
• Remove in stages
• Affect on compaction
• Geotextile fabric
• Over excavation
• Wide trench

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Trench Shields
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Laying and Jointing

• Join on the bank and lay
• Lay in trench and join
• Rubber ring joints PVC-U, PVC-M, PVC-O, GRP,
  DICL MSCL
• Solvent welded joints-ABS, PVC-U PVC-M
• Fusion butt weld-PE, PB PP
• Electro-fusion couplings-PE

• Wrapped joints-GRP
• Welded joints-steel
• Flanges Mechanical Joints-All
• Alignment Bending
• Adjacent parallel pipes
• Crossing Pipelines
• Removal of temporary pegs and supports

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Embedment Compaction

• Materials
• Dewatering
• Bedding
• Side Support
• Overlay
• Migration of fines

• Pipeline Protection
• Prevention of floatation
• Compaction trials
• Compaction controls
• Deflection controls
• Gauging

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Thrust Blocks
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Hydro-testing

• Establish test pressure
• Test standard
• Prepare test equipment
• Prepare ITPs
• Prepare test points

• Source of test water
• Disposal of test water
• Selection of test lengths
• Owners witness
• Records

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Hydrotest Methods

• Constant pressure test (No water loss) DICL,
  MSCL, GRP PVC
• Constant pressure test (water loss) PE, ABS, PP
  PB
• Pressure decay PE PB
• Pressure rebound- DN DN315 ABS, PB PE

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Tips, Tricks Traps

• Design
• Installation
• Testing
• Product quality
• Completion
• In Service leaks

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Tips, Tricks Traps - Design

• Design pressure may not include surge
• Temperature profile not defined
• Pipeline route/soils not adequately surveyed
• Consultant expects sub contractor or material
  supplier to do the detail design
• Lower pipe class than necessary specified
• Temporary facilities not designed

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Tips, Tricks Traps - Installation

• Physical damage
• Solvent damage to internal surface
• Use of incorrect solvent
• Incorrect slings
• Foreign matter not removed from trench

• Variations from design not engineered
• Surfaces not cleaned
• Aged solvent cement
• Pipe ends bevelled
• Damaged pipe
• UV degradation

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Tips, Tricks Traps - Installation

• No detail drawings
• Insufficient joints for erection
• Incomplete insertion in joints
• Inadequate time for welds or lay ups
• Differential settlement

• Resources
• Poor trench conditions
• Poor native soil
• Soil properties not measured routinely
• Inadequate access
• Water ingress
• Cleanliness

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Tips, Tricks Traps -Testing

• Lack of planning procedure
• Standard provisions not understood
• Inexperienced testers
• Test pressure unknown
• Equipment not isolated
• Procedure not agreed beforehand

• Records of test not prepared
• Person to witness test not available
• Resources not available
• Water supply
• Pump
• Gauges
• Data logger
• Temperature instrument
• Trained personnel

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Tips, Tricks Traps - Product Quality
Inspection or QA

• Non conformance with drawings
• Pipe ovality
• Lining thickness
• Socket dimensions
• Surface defects
• Fabricated fittings
• Cracks at weld
• Dimensions
• Orientation

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Tips, Tricks Traps -Completion

• Resources budget
• Site clean up
• Reinstatement
• Handover to owner
• Records
• Work as Executed Drawings
• Quality Assurance Sign-Off
• Certificate of Practical Completion

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Tips, Tricks Traps - In Service Leaks
Failures

• Pipe burst
• Flanged joints leak
• Solvent welds leak
• Rubber ring joints leak
• Fusion welds leak
• Fittings

• Buckling of thin wall pipe
• Thrust blocks
• Waterhammer
• Over pressure
• Pipe shear
• Fatigue vibration

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Questions

• Is AS 2566 mandatory?
• Can AWWA M45 be used?
• Is FEA a viable alternative?
• Who designs pipelines Civil, structural or
  mechanical engineers?