buried flexible pipelines
DESCRIPTION
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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) [email protected] 0402 35 2313
THE DESIGN PROCESS Boundary 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
Soils & Soils Data Native Soil
– Classify – Modulus
Bedding – Type
Embedment – Material – Compaction – Geo-textile – Water Table
Backfill – Type – Compaction
Piles Testing
– Field – Laboratory
Trench Width & Depth
AS 2566.1 Minimum Embedment or Embankment Shape of trench
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
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 – Steady state pressure – Unsteady state pressure spikes – Hydrostatic test pressure
Structures Interfaces
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
Loading
Design loads due to trench & embankment fill
External hydrostatic loads Internal pressure Superimposed dead loads Superimposed live loads Other unsustained loads
Design Loads due to Trench & Embankment Fill
Superimposed Live Loads
Superimposed Live Loads
Other Unsustained Loads
1. Specialist Engineering
2. National Codes 3. Local Conditions 4. Risk Likelihood Consequences Responsibility Safeguarding
Earthquake Vibration/Shock Differential
Settlement Thermal Strain Subsidence Airport runways Railways
DESIGN FUNDAMENTALS AS2566.1 Buried Flexible Pipelines-Design Deflection Strength Internal Pressure Combined Loading Buckling
Hoop Stress Ring Bending Strain Creep Temperature Other Considerations
Deflection
Short term Long term Vertical & Horizontal
– Considered equal – Effect of excess side compaction
Modulus to use Acceptance criteria Measurement during installation
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
– True Ellipse Shape Factor Df=3.0 – Δhorizontal < Δvertical Shape Factor Df > 3.0
Internal Pressure
Steady State Unsteady State
– 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
Buckling
Ovalization Buckling External Pressure No substantial soil support-Timoshenko Substantial soil support –I.D. Moore
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
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%
Creep
Variation of Properties in Time Long term loading/Stress relaxation Reverse loading/Stress magnitude Repetitive loading/Fatigue
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
Mass of pipe contents
Thermal Strain Local buckling Fatigue Pavement
settlement
Materials Selection
Types Costs Class Characteristics Fittings & Valves
Modulus GRP Modulus
Thermoplastic Pipes
Materials - Types
GRP ABS PE PVC-U, PVC-M, PVC-O DICL MSCL
Materials Selection Costs – Supply
1. Pipe 2. Fittings 3. Supports
Costs – Installation 1. Standard of trades 2. Equipment 3. Jointing 4. Access 5. Testing
Costs - Whole of Life 1. Safety 2. Availability 3. Maintenance 4. Energy 5. Risks
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
Soil/Pipe Structure Design
Standardization Risk
– Likelihood – Consequences – Responsibility
Typical Material Characteristics
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
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
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
INSTALLATION
Trench Excavation Trench Shields Laying & Jointing Embedment &
Compaction
Thrust Blocks Hydrostatic
Testing
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
Trench Shields
When to use Remove in stages Affect on compaction Geotextile fabric Over excavation Wide trench
Trench Shields
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
Embedment & Compaction
Materials Dewatering Bedding Side Support Overlay Migration of fines
Pipeline Protection Prevention of
floatation Compaction trials Compaction controls Deflection controls Gauging
Thrust Blocks
Hydro-testing
Establish test pressure
Test standard Prepare test
equipment Prepare ITP’s Prepare test points
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
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
Tips, Tricks & Traps - Installation Variations from
design not engineered Surfaces not cleaned Aged solvent cement Pipe ends bevelled Damaged pipe UV degradation
Physical damage Solvent damage to
internal surface Use of incorrect
solvent Incorrect slings Foreign matter not
removed from trench
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
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
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
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
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
Questions 1. Is AS 2566 mandatory? 2. Can AWWA M45 be used? 3. Is FEA a viable alternative? 4. Who designs pipelines Civil, structural or
mechanical engineers?