BURIED FLEXIBLE PIPELINESBURIED 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 PROCESSTHE DESIGN PROCESSBoundary ConditionsBoundary 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 DataSoils & Soils Data

Native Soil– Classify– Modulus

Bedding– Type

Embedment– Material– Compaction– Geo-textile– Water Table

Backfill– Type

– CompactionPiles

Testing– Field

– Laboratory

Trench Width & DepthTrench Width & Depth

AS 2566.1 MinimumEmbedment or EmbankmentShape of trench

Trench DimensionsTrench Dimensions

Structural Response to LoadingStructural Response to Loading

Stiffness AS 2566.1Stiffness AS 2566.12 year values of pipe stiffness suitable for good

soils50 year values of pipe stiffness should be used for

poor soils, uncontrolled installations or other higher risk applications

Stiffness AS 2566.1Stiffness AS 2566.1

Thrust BlocksThrust 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 InterfacesStructures Interfaces

Differential Settlement

Soil swelling Water Retaining Shear Loading Thermal Loading Chaffing Water seal in

concrete

Water TableWater 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

LoadingLoading

Design loads due to trench & embankment fill

External hydrostatic loadsInternal pressureSuperimposed dead loadsSuperimposed live loadsOther unsustained loads

Design Loads due to Trench & Design Loads due to Trench & Embankment FillEmbankment Fill

Superimposed Live LoadsSuperimposed Live Loads

Superimposed Live LoadsSuperimposed Live Loads

Other Unsustained Loads Other Unsustained Loads

1. Specialist Engineering

2. National Codes 3. Local Conditions4. Risk

Likelihood Consequences Responsibility Safeguarding

Earthquake Vibration/Shock Differential

Settlement Thermal Strain Subsidence Airport runways Railways

DESIGN FUNDAMENTALSDESIGN FUNDAMENTALSAS2566.1 Buried Flexible Pipelines-DesignAS2566.1 Buried Flexible Pipelines-Design

Deflection Strength Internal Pressure Combined Loading Buckling

Hoop Stress Ring Bending Strain Creep Temperature Other Considerations

DeflectionDeflection

Short termLong termVertical & Horizontal

– Considered equal– Effect of excess side compaction

Modulus to useAcceptance criteriaMeasurement during installation

StrengthStrength

Loads cause strain in pipe wallRing compression strains << ring bending

strainsAS 2566.1 predicts maximum tensile ring

bending strainsA Shape Factor adjusts strain values

– True Ellipse Shape Factor Df=3.0

– Δhorizontal < Δvertical Shape Factor Df > 3.0

Internal PressureInternal Pressure

Steady StateUnsteady State

– AS 2566.1 Requirements 1.25– AS 2885 Requirement 1.10– Other codes requirements

Combined LoadingCombined Loading

Combined external load and internal pressure

Re rounding effect

BucklingBuckling

OvalizationBucklingExternal PressureNo substantial soil support-Timoshenko Substantial soil support –I.D. Moore

Hoop StressHoop Stress

Stress in the wall due to pressureOnly criteria used for pipe class selectionDoes not take into account other stressesBasis of the Pipe Class SystemRelaxes with time for thermoplastic pipes Never Constant

Ring Bending StrainRing Bending Strain

Importance of StrainComparison of allowable strain in materials1. 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%

CreepCreep

Variation of Properties in TimeLong term loading/Stress relaxationReverse loading/Stress magnitudeRepetitive loading/Fatigue

TemperatureTemperatureThe design temperature may vary due to:-

•Ambient diurnal temperature variations•Flow rate•Fluid temperature range•Process conditions•Installation ambient temperature•Wall thickness

Other ConsiderationsOther Considerations

Anchor forcesDifferential

SettlementEarthquake SubsidenceTesting conditionsCorrosion

Mass of pipe contents

Thermal StrainLocal bucklingFatiguePavement

settlement

Materials SelectionMaterials Selection

TypesCostsClassCharacteristicsFittings & Valves

Modulus GRP Modulus

Thermoplastic Pipes

Materials - TypesMaterials - Types

GRPABS PEPVC-U, PVC-M, PVC-ODICLMSCL

Materials SelectionMaterials 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 Life1. Safety

2. Availability

3. Maintenance

4. Energy

5. Risks Costs - Standards

1. Authority

2. Industry

3. Acts

Selection of Pipe ClassSelection of Pipe Class

Design Pressure Steady State

Design Pressure Unsteady State

Vacuum Conditions

Industry Application & Environment

Soil/Pipe Structure Design

StandardizationRisk

– Likelihood– Consequences– Responsibility

Typical Material CharacteristicsTypical Material Characteristics

Fittings & ValvesFittings & 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 PipesModulus-GRP Pipes

Manufacturers establish values by test & calculation

Axial & longitudinal modulus differs

Values at various temperatures required for design

Strain rate changes valuesStandards such as ISO 14692

Modulus-Thermoplastic PipesModulus-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

INSTALLATIONINSTALLATION

Trench ExcavationTrench ShieldsLaying & JointingEmbedment &

Compaction

Thrust BlocksHydrostatic

Testing

Trench ExcavationTrench ExcavationExcavator bucket widthExcavated depthSoil removal, testing and stockpileShape of trenchPockets for pipeline projectionsThrust block preparationDewateringWelding machine accessAdjacent pipes

Trench ShieldsTrench Shields

When to use Remove in stages Affect on compaction Geotextile fabric Over excavation Wide trench

Trench ShieldsTrench Shields

Laying and JointingLaying 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 & CompactionEmbedment & Compaction

Materials Dewatering Bedding Side Support Overlay Migration of fines

Pipeline Protection Prevention of

floatation Compaction trials Compaction controls Deflection controls Gauging

Thrust BlocksThrust Blocks

Hydro-testingHydro-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 MethodsHydrotest Methods

Constant pressure test (No water loss) –DICL, MSCL, GRP & PVC

Constant pressure test (water loss) – PE, ABS, PP & PB

Pressure decay – PE & PBPressure rebound- DN ≤ DN315 ABS, PB

& PE

Tips, Tricks & TrapsTips, Tricks & Traps

DesignInstallationTestingProduct qualityCompletionIn Service leaks

Tips, Tricks & Traps - Tips, Tricks & Traps - DesignDesign

Design pressure may not include surgeTemperature profile not definedPipeline route/soils not adequately

surveyedConsultant expects sub contractor or

material supplier to do the detail designLower pipe class than necessary specifiedTemporary facilities not designed

Tips, Tricks & Traps - InstallationTips, Tricks & Traps - InstallationVariations from

design not engineeredSurfaces not cleanedAged solvent cementPipe ends bevelledDamaged pipeUV degradation

Physical damageSolvent damage to

internal surfaceUse of incorrect

solventIncorrect slingsForeign matter not

removed from trench

Tips, Tricks & Traps - InstallationTips, 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 Tips, Tricks & Traps -Testing-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 - Tips, Tricks & Traps - Product Quality – Inspection or QAProduct 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 -CompletionTips, Tricks & Traps -Completion

Resources & budgetSite clean upReinstatementHandover to ownerRecordsWork as Executed DrawingsQuality Assurance Sign-OffCertificate of Practical Completion

Tips, Tricks & Traps - Tips, Tricks & Traps - In Service Leaks & FailuresIn 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

QuestionsQuestions

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?