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) geoffrey.stone@yahoo.co.uk 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?