Design of Thermoplastic PipingDesign of Thermoplastic Piping

� Thermoplastic Pipe Design � Material Properties� Waterhammer Analysis� Issues arising in design, fabrication,

installation & testing

Thermoplastic Piping DesignThermoplastic Piping Design

Codes & Standards� Hydraulic Analysis� Selection of Pipe

Class� Fittings Class� Piping Layout

� Thermal: Expansion/Contraction

� Cold Cut & Pull� Unsustained Loads

– Wind

– Earthquake

– Ship Pitch & Roll

– Vibration

Role of the Thermoplastic Pipe Role of the Thermoplastic Pipe Customer & SupplierCustomer & SupplierWhat Customer Expects

� Material Properties� Design Criteria� Design Guidance� Material take off (MTO)� Applicable Standards� Final Inspection� Supplier to take the

design risk!!!

What Supplier avoids

� Taking the design risk� Taking the MTO risk

Thermoplastic Piping DesignThermoplastic Piping Design

� International and national standards do not define the design requirements adequately for thermoplastic pipe systems

� Hoop stress is the primary design parameter� Manufacturers heavily relied upon to provide design

assistance� Material properties vary between manufacturers and resin

used but are generally consistent to meet standards� Properties isotropic� Thermal strain significant for applications� NDE technology is not available� Testing is defined in material standards

Thermoplastic Piping DesignThermoplastic Piping DesignCodes and StandardsCodes and Standards� Australian standards are material specific for

products and cover above ground installation� ISO 15493 Plastics piping systems for industrial

applications — Acrylonitrile-butadienestyrene (ABS), unplasticized poly(vinyl chloride) (PVC-U) and chlorinated poly(vinyl chloride) (PVC-C) — Specifications for components and the system ―Metric series

� AS 4041 Pressure Piping Code� ASME B31.3 Chemical & Refinery Piping Code

The Selection of Pipe ClassThe Selection of Pipe Class

� Design Pressure Steady State

� Design Pressure Unsteady State

� Vacuum Conditions� Industry Application

& Environment

� Support distances for deflection

� Wear from abrasive slurries

� Standardization of classes on site

� Risk– Likelihood– Consequences– Responsibility

FittingsFittings

� Fittings do NOT meet all pipe classes� Injection moulded fittings� Manufactured fittings

– Tees– Bends

� Flanges- Composite Metallic and Plastic� Gaskets� Expansion Bellows� Saddles

Piping LayoutPiping Layout

� Piping connecting equipment

� Flexibility� Physical damage� Number and type

Fittings� Loads on nozzles� Horizontal or vertical� Straight lengths

– Flow metering– Pump suctions

� Supports– Use existing steelwork– Saddles-Local Stresses– Springs– Hangars– Concentrated weights

� Maintenance – Pipework– Equipment

� Erection� Access� Cost

ThermalThermal-- Expansion/ContractionExpansion/Contraction

� Coefficient of thermal expansion� Modulus affects loading� Friction� Use of elbows and bends� Stress intensification factors� Elastic follow up/strain concentration� Ratcheting

Cold Cut & PullCold Cut & Pull

� To reduce loads� Impact on stress cannot be included� Installed versus Service Temperature� Supports

Unsustained LoadsUnsustained Loads

� Specialist Engineering� National Codes � Local Conditions� Risk

- Likelihood

- Consequences

- Responsibility

- Safeguarding

� Earthquake– Building Influence

� Wind– Height of external

piping– Shading from buildings– Supports

� Vibration� Shock� Ship Pitch & Roll

– Ship’s Data

Waterhammer Analysis & DesignWaterhammer Analysis & Design

Benefits of Thermoplastic Pipe

� Low modulus hence low wavespeed (celerity) and hence low increased pressure

� Instantaneous stress property values

� Vacuum Resistance� Fatigue Resistance

Disadvantages of Thermoplastic Pipe

� Low pressure rating� Low surface

roughness delays pressure decay

� Longer valve closure times because reflection times increased

Material PropertiesMaterial Properties

� Modulus� Hoop Stress� Ring Bending Strain� Creep� Stiffness� Temperature

Variation

� Design Life� Toxicity & Taint� Abrasion Resistance� Chemical Resistance� Ultraviolet

Resistance� Comparison with

Other Materials

ModulusModulus

� Published at 20ºC only� Value determined by ASTM test

– Standard dog bone test specimen

– Fixed strain rate� Values at other temperatures required for design� Strain rate changes values � Resin properties changes values� Property affects wavespeed in surge events� Property needed to determine deflection and loads

Ring Bending StrainRing Bending Strain

� Importance of Strain� Comparison to other materials

– ABS 1%– Steel & DICL Not relevant– FRP 0.2 to 0.6 %– PE 4.0%– PVC-U 1% – PVC-O 1.3%

CreepCreep

� Variation of properties in time� Long term loading/stress relaxation� Reverse loading/stress magnitude� Repetitive loading/fatigue

TemperatureTemperatureThe design temperature may vary due to:-

• Ambient diurnal temperature• Flow rate• Fluid temperature range•Installation ambient temperature

Design LifeDesign Life

� Design life criteria 50 years� 50 year does not mean the pipe has a 50

year life� 50 Years is an arbitrary period to provide

comparative data� No matter how old it is the pipe will still

exhibit instantaneous properties similar to when it was made when subjected to high rates of strain

Abrasion ResistanceAbrasion Resistance

� Size distribution of particles

� Concentration of solids by volume

� Relative density of solids� Shape of particles� Sharpness of particles� Flow regime affecting

angle of impingement, sliding bed etc

� Temperature of fluid� Velocity of slurry� Chemical resistance

Some relationships predicting wear in pipelines:

Wear αααα Velocity (2.5-4.5)

E=6.1 dm^2.15*U^3.7

Where :-E= wear rate (at bottom of pipe,

mm/yeardm = mean particle size, U= mean slurry velocity, m/s

Chemical ResistanceChemical Resistance

� Offer high chemical resistance� Preferred materials for particular processes� Chemical resistance charts are a guide only� Contaminated fluids can be highly corrosive� Stress test recommended� No pickle & passivation as in stainless steel� No cathodic protection needed� No corrosion inhibitors

Comparison of MaterialsComparison of Materials

� Coefficient of Thermal Expansion

Tips Tricks & TrapsTips Tricks & Traps

� Design� Fabrication� Installation� Testing� Product quality

Design IssuesDesign Issues

� Design pressure does not include surge� Temperature profile not defined� Design layout not adequately drawn� Supplier has to provide more than

guidance in design� Consultant expects sub contractor to do

detail design� Lower class than necessary specified to

save costs

Fabrication IssuesFabrication Issues

� Inadequate detail drawings� Insufficient joints for erection� Incomplete insertion in solvent welded or electro

fusion joints� Inadequate time for butt fusion welds� Contaminated electro-fusion welds� Belief that all pipe can be site run rather than

designed

Installation IssuesInstallation Issues

� Spools forced to fit� Designed supports

missing or modified� Insufficient clearance

in clamps & guides� Variations from

design not engineered

� Surfaces not cleaned

� Physical damage� Other services

supported from pipes� Incorrect slings� Insufficient weld

time

Testing IssuesTesting Issues

� Excessive hydrotest pressures

� Lack of planning & procedure

� Standard provisions not understood

� Inexperienced testers� Test pressure unknown� Equipment not isolated

� Records of test not prepared

� Person to witness test not available

� Equipment not available– Water supply

– Pump

– Gauges

– Data logger

– Temperature instrument

Product QualityProduct Quality

� Virgin material or % regrind� Standard compliance� QA documents� Inspection at works or on site� If the price is low then you may not get

what you expect

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