the engineering world of thermoplastic piping

Presented By Geoffrey D Stone C.Eng FIMechE; CP Eng FIEAust RPEQ

Design Detail & Development

http://waterhammer.hopout.com.au/                 Skype address geoffrey.stone@yahoo.co.uk

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

installation & testing

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

What 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

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

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

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

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

Tees Bends

Flanges- Composite Metallic and Plastic Gaskets Expansion Bellows Saddles

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

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

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

Specialist engineering required

National codes apply 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

Benefits of Thermoplastic Pipe

Low modulus hence low wave speed (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

Modulus Hoop stress Ring bending strain Creep Stiffness Temperature

variation

Design life Toxicity & taint Abrasion resistance Chemical

resistance Ultraviolet

resistance Comparison with

other materials

Data is published at 20ºC only Values determined by ASTM test

Standard dog bone test specimen Fixed strain rate

Values at other temperatures required for design Strain rate changes modulus value Resin properties changes values Short term property needed to determine

maximum loads and transient pressures Long term property used to determine maximum

deflection

Importance of Strain Comparison thermoplastic materials

ABS 1% FRP 0.2 to 0.6 % PE 4.0% PVC-U 1% PVC-O & PVC-M1.3%

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

The design temperature may vary due to:-

• Ambient diurnal temperature• Flow rate• Fluid temperature range•Installation ambient temperature•Exothermic chemical reaction

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

year life span 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

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 Velocity (2.5-4.5)

E = 6.1 dm2.15 . U 3.7

Where :- E = wear rate (at bottom of

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

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

Coefficient of Thermal Expansion

Design Fabrication Installation Testing Product quality

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 pipe class than necessary specified

to save costs

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 Lack of training or supervision

Spools forced to fit Designed supports

missing or modified Insufficient

clearance in clamps & guides

Variations from design not engineered

Surfaces contaminated

Physical damage Other services

supported from pipes

Incorrect slings Insufficient weld

time Lack of training or

supervision

Excessive hydrotest pressures

Lack of planning & procedure

Standard provisions not understood

Inexperienced testers Test pressure unknown Equipment not isolated Premature testing

Records of test not prepared

Person to witness test not available

Equipment not available Water supply Pump Gauges Data logger Temperature

instrument

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