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BURIED FLEXIBLE PIPELINES

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)

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BURIED FLEXIBLE PIPELINES

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  1. 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

  2. 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

  3. Soils & Soils Data • Native Soil • Classify • Modulus • Bedding • Type • Embedment • Material • Compaction • Geo-textile • Water Table • Backfill • Type • Compaction • Piles • Testing • Field • Laboratory

  4. Trench Width & Depth • AS 2566.1 Minimum • Embedment or Embankment • Shape of trench

  5. Trench Dimensions

  6. Structural Response to Loading

  7. 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

  8. Stiffness AS 2566.1

  9. 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

  10. Structures Interfaces • Differential Settlement • Soil swelling • Water Retaining • Shear Loading • Thermal Loading • Chaffing • Water seal in concrete

  11. 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

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

  13. Design Loads due to Trench & Embankment Fill

  14. Superimposed Live Loads

  15. Superimposed Live Loads

  16. 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

  17. DESIGN FUNDAMENTALSAS2566.1 Buried Flexible Pipelines-Design Hoop Stress Ring Bending Strain Creep Temperature Other Considerations • Deflection • Strength • Internal Pressure • Combined Loading • Buckling

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

  19. 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

  20. Internal Pressure • Steady State • Unsteady State • AS 2566.1 Requirements 1.25 • AS 2885 Requirement 1.10 • Other codes requirements

  21. Combined Loading • Combined external load and internal pressure • Re rounding effect

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

  23. 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

  24. 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%

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

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

  27. Other Considerations Mass of pipe contents Thermal Strain Local buckling Fatigue Pavement settlement • Anchor forces • Differential Settlement • Earthquake • Subsidence • Testing conditions • Corrosion

  28. Materials Selection Modulus GRP Modulus Thermoplastic Pipes • Types • Costs • Class • Characteristics • Fittings & Valves

  29. Materials - Types • GRP • ABS • PE • PVC-U, PVC-M, PVC-O • DICL • MSCL

  30. 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

  31. 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

  32. Typical Material Characteristics

  33. 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

  34. 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

  35. 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

  36. INSTALLATION Thrust Blocks Hydrostatic Testing • Trench Excavation • Trench Shields • Laying & Jointing • Embedment & Compaction

  37. 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

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

  39. Trench Shields

  40. 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

  41. Embedment & Compaction Pipeline Protection Prevention of floatation Compaction trials Compaction controls Deflection controls Gauging • Materials • Dewatering • Bedding • Side Support • Overlay • Migration of fines

  42. Thrust Blocks

  43. 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

  44. 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

  45. Tips, Tricks & Traps • Design • Installation • Testing • Product quality • Completion • In Service leaks

  46. 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

  47. 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

  48. 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

  49. 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

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