buried flexible pipelines
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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?
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