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Learn the design process, materials, installation tips, and design fundamentals of buried flexible pipelines as per AS2566.1 standards. Gain insights on boundary conditions, loading, stiffness, thrust blocks, and structural response to ensure a safe and efficient pipeline system.
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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@yahoo.co.uk0402 35 2313
THE DESIGN PROCESSBoundary Conditions Water Table Design Loads Trench & Embankment Fill Superimposed Live Loads Other Superimposed Loads • Soils & Soil Data • Trench Width & Depth • Structural Response to Loading • Trench Details • Stiffness • Thrust Blocks • Structural Interfaces
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
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
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
Other Unsustained Loads Earthquake Vibration/Shock Differential Settlement Thermal Strain Subsidence Airport runways Railways • Specialist Engineering • National Codes • Local Conditions • Risk • Likelihood • Consequences • Responsibility • Safeguarding
DESIGN FUNDAMENTALSAS2566.1 Buried Flexible Pipelines-Design Hoop Stress Ring Bending Strain Creep Temperature Other Considerations • Deflection • Strength • Internal Pressure • Combined Loading • Buckling
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 • ABS 1% • GRP 0.18 to 0.6 % • PE 4.0% • PVC-U 1% • PVC-M 1% • 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 Mass of pipe contents Thermal Strain Local buckling Fatigue Pavement settlement • Anchor forces • Differential Settlement • Earthquake • Subsidence • Testing conditions • Corrosion
Materials Selection Modulus GRP Modulus Thermoplastic Pipes • Types • Costs • Class • Characteristics • Fittings & Valves
Materials - Types • GRP • ABS • PE • PVC-U, PVC-M, PVC-O • DICL • MSCL
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
Selection of Pipe Class Soil/Pipe Structure Design Standardization Risk Likelihood Consequences Responsibility • Design Pressure Steady State • Design Pressure Unsteady State • Vacuum Conditions • Industry Application & Environment
Fittings & Valves Jointing Gaskets Expansion Bellows Saddles Valves Isolation Check Air release Control • Valve classes do not meet all pipe classes • Injection moulded fittings- Size Limitation • Manufactured fittings-Larger Sizes • Tees • Bends
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 Thrust Blocks Hydrostatic Testing • Trench Excavation • Trench Shields • Laying & Jointing • Embedment & Compaction
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
Laying and Jointing Wrapped joints-GRP Welded joints-steel Flanges & Mechanical Joints-All Alignment & Bending Adjacent parallel pipes Crossing Pipelines Removal of temporary pegs and supports • 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
Embedment & Compaction Pipeline Protection Prevention of floatation Compaction trials Compaction controls Deflection controls Gauging • Materials • Dewatering • Bedding • Side Support • Overlay • Migration of fines
Hydro-testing Source of test water Disposal of test water Selection of test lengths Owner’s witness Records • Establish test pressure • Test standard • Prepare test equipment • Prepare ITP’s • Prepare test points
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 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
Tips, Tricks & Traps - Installation Resources Poor trench conditions Poor native soil Soil properties not measured routinely Inadequate access Water ingress Cleanliness • No detail drawings • Insufficient joints for erection • Incomplete insertion in joints • Inadequate time for welds or lay ups • Differential settlement
Tips, Tricks & Traps -Testing Records of test not prepared Person to witness test not available Resources not available Water supply Pump Gauges Data logger Temperature instrument Trained personnel • Lack of planning & procedure • Standard provisions not understood • Inexperienced testers • Test pressure unknown • Equipment not isolated • Procedure not agreed beforehand