BURIED FLEXIBLE PIPELINES
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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@yahoo.co.uk 0402 35 2313
THE DESIGN PROCESS
Boundary Conditions
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Soils & Soil Data
Trench Width &
Depth
Structural Response
to Loading
Trench Details
Stiffness
Thrust Blocks
Structural Interfaces
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Water Table
Design Loads Trench
& Embankment Fill
Superimposed Live
Loads
Other Superimposed
Loads
Soils & Soils Data
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Native Soil
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– Classify
– Modulus
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Bedding
– Type
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Embedment
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Material
Compaction
Geo-textile
Water Table
Backfill
– Type
– Compaction
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Piles
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Testing
– Field
– Laboratory
Trench Width & Depth
AS 2566.1 Minimum
 Embedment or Embankment
 Shape of trench
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Trench Dimensions
Structural Response to Loading
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
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
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– Steady state pressure
– Unsteady state pressure spikes
– Hydrostatic test pressure
Structures Interfaces
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Differential
Settlement
Soil swelling
Water Retaining
Shear Loading
Thermal Loading
Chaffing
Water seal in
concrete
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
Superimposed Live Loads
Superimposed Live Loads
Other Unsustained Loads
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2.
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4.
Specialist
Engineering
National Codes
Local Conditions
Risk
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Likelihood
Consequences
Responsibility
Safeguarding
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Earthquake
Vibration/Shock
Differential
Settlement
Thermal Strain
Subsidence
Airport runways
Railways
DESIGN FUNDAMENTALS
AS2566.1 Buried Flexible Pipelines-Design
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Deflection
Strength
Internal Pressure
Combined Loading
Buckling
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Hoop Stress
Ring Bending Strain
Creep
Temperature
Other Considerations
Deflection
Short term
 Long term
 Vertical & Horizontal
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– 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 << ring bending
strains
 AS 2566.1 predicts maximum tensile ring
bending strains
 A Shape Factor adjusts strain values
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– True Ellipse Shape Factor Df=3.0
– Δhorizontal < Δvertical Shape Factor Df > 3.0
Internal Pressure
Steady State
 Unsteady State
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– AS 2566.1 Requirements 1.25
– AS 2885 Requirement 1.10
– Other codes requirements
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
1. ABS 1%
2. GRP 0.18 to 0.6 %
3. PE 4.0%
4. PVC-U 1%
5. PVC-M 1%
6. 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
Other Considerations
Anchor forces
 Differential
Settlement
 Earthquake
 Subsidence
 Testing conditions
 Corrosion
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Mass of pipe
contents
 Thermal Strain
 Local buckling
 Fatigue
 Pavement
settlement
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Materials Selection
Types
 Costs
 Class
 Characteristics
 Fittings & Valves
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Modulus GRP
Modulus
Thermoplastic Pipes
Materials - Types
GRP
 ABS
 PE
 PVC-U, PVC-M, PVC-O
 DICL
 MSCL
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Materials Selection
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Costs – Supply
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1. Safety
2. Availability
3. Maintenance
4. Energy
5. Risks
1. Pipe
2. Fittings
3. Supports
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Costs – Installation
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2.
3.
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5.
Standard of trades
Equipment
Jointing
Access
Testing
Costs - Whole of Life
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Costs - Standards
1. Authority
2. Industry
3. Acts
Selection of Pipe Class
Design Pressure
Steady State
 Design Pressure
Unsteady State
 Vacuum
Conditions
 Industry
Application &
Environment
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Soil/Pipe Structure
Design
 Standardization
 Risk
– Likelihood
– Consequences
– Responsibility
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Typical Material Characteristics
Fittings & Valves
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Valve classes do not
meet all pipe classes
Injection moulded
fittings- Size
Limitation
Manufactured
fittings-Larger Sizes
– Tees
– Bends
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Jointing
Gaskets
Expansion Bellows
Saddles
Valves
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Isolation
Check
Air release
Control
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
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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
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When to use
Remove in stages
Affect on compaction
Geotextile fabric
Over excavation
Wide trench
Trench Shields
Laying and Jointing
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Join on the bank and lay
Lay in trench and join
Rubber ring joints PVCU, PVC-M, PVC-O,
GRP, DICL & MSCL
Solvent welded jointsABS, PVC-U & PVC-M
Fusion butt weld-PE, PB
& PP
Electro-fusion
couplings-PE
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Wrapped joints-GRP
Welded joints-steel
Flanges & Mechanical
Joints-All
Alignment & Bending
Adjacent parallel pipes
Crossing Pipelines
Removal of temporary
pegs and supports
Embedment & Compaction
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Materials
Dewatering
Bedding
Side Support
Overlay
Migration of fines
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Pipeline Protection
Prevention of
floatation
Compaction trials
Compaction controls
Deflection controls
Gauging
Thrust Blocks
Hydro-testing
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Establish test
pressure
Test standard
Prepare test
equipment
Prepare ITP’s
Prepare test points
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Source of test water
Disposal of test water
Selection of test
lengths
Owner’s witness
Records
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
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
Variations from
design not engineered
 Surfaces not cleaned
 Aged solvent cement
 Pipe ends bevelled
 Damaged pipe
 UV degradation
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Physical damage
 Solvent damage to
internal surface
 Use of incorrect
solvent
 Incorrect slings
 Foreign matter not
removed from trench
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Tips, Tricks & Traps - Installation
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No detail drawings
Insufficient joints for
erection
Incomplete insertion
in joints
Inadequate time for
welds or lay ups
Differential
settlement
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Resources
Poor trench
conditions
Poor native soil
Soil properties not
measured routinely
Inadequate access
Water ingress
Cleanliness
Tips, Tricks & Traps -Testing
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Lack of planning &
procedure
Standard provisions
not understood
Inexperienced testers
Test pressure
unknown
Equipment not
isolated
Procedure not agreed
beforehand
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Records of test not
prepared
Person to witness test not
available
Resources not available
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Water supply
Pump
Gauges
Data logger
Temperature instrument
Trained personnel
Tips, Tricks & Traps -
Product Quality – Inspection or QA
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Non conformance with drawings
Pipe ovality
Lining thickness
Socket dimensions
Surface defects
Fabricated fittings
– Cracks at weld
– Dimensions
– Orientation
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
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Pipe burst
Flanged joints leak
Solvent welds leak
Rubber ring joints
leak
Fusion welds leak
Fittings
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Buckling of thin wall
pipe
Thrust blocks
Waterhammer
Over pressure
Pipe shear
Fatigue & vibration
Questions
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2.
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4.
Is AS 2566 mandatory?
Can AWWA M45 be used?
Is FEA a viable alternative?
Who designs pipelines Civil, structural or
mechanical engineers?