Behaiviour of PE Pipes

7/30/2019 Behaiviour of PE Pipes

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ADVANCES INPE PIPE MATERIALS

AND PERFORMANCE

Presented by

Daryl J.P. Tchir, P. Eng.

Senior Engineer, Standards

ATCO Gas

Presented May 7th, 2007 in Winnipeg


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Introduction

Todays presentation will shareinformation about:

Slow Crack Growth (SGC) & PENT Tests;

Rapid Crack Propagation (RCP) & S4Tests;

New PE Resin Options (PE 4710 / PE

100+); General Impacts on Installation;

Impacts on Large Diameter Mains.


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Introduction - Contd

This session has been developed to: Enhance the understanding of PE design

and material properties;

To ensure designs maximize pipe lifeexpectancy;

To discuss opportunities for cost savings.


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PART 1SGC & RCP PREDICTINGTHE LIFE OF PE MAINS

Presented by


Senior Engineer, Standards

ATCO Gas


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SCG & RCP

Two of the possible failure modes forPE pipe are Slow Crack Growth (SCG)and Rapid Crack Propagation (RCP).

SCG is much more common than RCP. Tests exist to predict the resistance to

SCG and RCP.

When SCG resistance improves, RCPresistance declines.


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Slow Crack Growth (SCG)

SCG occurs in PE pipe when molecular bondsbreak and small cracks grow to a critical lengthresulting in a pipe wall failure.

SCG failures happens over a relatively long

period of time.

Medium density pipe (PE 2406) has moreresistance to SCG failures than high density

pipe (PE 3408). SCG occurs in pipes of all sizes and wall

thicknesses.


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SCG Resistance Test

ASTM F1473, commonly referred to asthe PENT (Pennsylvania Elevated NotchToughness) test, is used to test for SCGresistance.

At an elevated temperature, a notchedpipe sample is subjected to a tensileload.

There are other tests to estimateSCG resistance such as ISO 13479(Notched Pipe Test NPT).


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SCG Resistance Test Contd

Early generation PE resins havePENT values of only as few minutes orseconds while modern resins can have

test times over 1000 hours.New tests are being developed to

estimate PENT and NPT values for pipe

with values over 1000 hours.


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SCG Failures

SCG Failures can be brittle or ductile.Brittle failures are less predictable and

indicate pipe is near the end of its useful

life.


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Ductile Failure


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Ductile Failure


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Brittle Failure


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Brittle Failure


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Rapid Crack Propagation(RCP)

RCP is a violent failure mode happeningover just a few seconds.

RCP failures are more likely in thicker

walled pipe sections and sections athigher operating stresses (largediameter pipes at greater risk).

RCP is also more likely to occur atcolder temperatures.


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Rapid Crack Propagation(RCP) Contd

High density pipe (PE 3408) is moreresistant to RCP than medium densitypipe (PE 2406).

RCP failures are far less common thanSCG failures.

The RCP failure is commonly triggered

by an impact event such as a rockimpingement or a hit line.


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Rapid Crack Propagation(RCP) Contd

The impact energy forms a crack thatpropagates rapidly along the pipe length.

The crack tip propagates faster than thedecompression wave permitting thecrack to run a great length beforearresting.

With many modern pipes, RCP is only

a concern when the pipe diameter isgreater than 4 inches (but wall thicknessis the critical dimension).


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RCP Resistance Test

The S4 (Small Scale Steady State) testis described in ISO 13477.

The S4 test can be correlated to a full

scale test (ISO 13478). This provides an estimate of the critical

pressure below which cracks will arrest

or the critical temperature above whichcracks will arrest.


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RCP Resistance Test Contd

The tests are costly and must berepeated to ensure good data.

There is some debate about the S4 test

and its relationship to the full scale test. There is some evidence to be concerned

about uniformity in S4 testing (discussed

in a paper at PPXIII).


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RCP Resistance Test Contd

(fictional data set)

Test Temperature

TestPressure

T1 T2 0C T3 Tc T5

P1

P2

P3

Pc

x

xx

o

oo

x xx ooooo

oClocheResults

Arrest Regime

ox x

oPropagation Regime


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RCP Failures

RCP Failures are always brittle.Pictures ???


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PE MoleculePolyethylene Backbone

Polyethylene Molecule with Branching Shown


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Molecular Weight Distribution


Molecular Weight

MDPE HDPE


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Effects of Molecular Branching

Distribution of the comonomer (shortchain branching) is important. It is best ifdistribution favors the high molecular

weight chains.Comonomer length is important (best if

uniform and shorter).

High molecular weight backbone isbetter.


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Effects of Antioxidantsand UV Stabilizers

Antioxidants and UV stabilizers areadded to the PE resin to rebuild brokenbonds.

Since gas companies first began usingPE pipe in about the late 1960s, therehave been many improvements to thestabilizers and the production of PE pipe.

Stabilizers called HALS (Hindered AmineLight Stabilizers) where introduced inabout 1995.


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HALS(Hindered Amine Light Stabilizers)

HALS have had the greatest impact onextending pipe life.

Much of the stabilizer in PE resin is

consumed during the heating cycle whilemanufacturing the pipe itself.

HALS survive the manufacturing

processes better and thus providegreater long-term protection.


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Review:SCG RCP Relationship

For each PE resin, improved RCPperformance comes at the cost of SCGperformance.

However; bimodal resins are able tohave better combined performancecharacteristics.

As a result, a well selected PE 100 resin

can have better SCG properties than aPE 2406 resin and better RCP propertiesthan a PE 3408 resin.


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Estimation of Pipe Life

SCG performance governs the estimateof pipe life expectancy.

Tests can be performed to determine the

Long-Term Hydrostatic Strength (LTHS)of PE pipe.

This results in the estimated life under a

sustained stress condition.


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LTHS Determination

LTHS is determined in accordance withASTM D 2837 by plotting the log valuesof hoop stress vs. the log value of time to

failure. Tests are done at 23

o

C.Points are plotted, then a line is

projected to 100,000 hours (11 years).

The value at 11 years is the LTHS(Long-Term Hydrostatic Strength)


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LTHS Determination - Contd


Time to Failure - Hours (Log Scale)

Stress

(Log

Scale)

10 100 1000 10,000 100,0001,000,000

LTHS HDB

100,000 hrs11.4 years18 data points to

10, 000 hrs (1.14 yrs)test @ 23 C

O


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Ductile to BrittleTransition Knee

The data from the LTHS test cannot beprojected indefinitely.

At some point, a ductile to brittle transitionoccurs.

At this transition a knee marks the rapiddecline in the observed slope of the plot.

To the left of the knee, pipe fails in a ductile

mode. To the right, it fails in a brittle mode.


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Ductile to BrittleTransition Knee - Contd



Stress

(Log

Scale)

10 100 1000 10,000 100,0001,000,000

KNEE

Ductile Failures

Brittle Failures


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Brittle failures are less predictable andcan occur at much lower stresses.

The occurrence of brittle failures is anindication that the pipe has reachedthe limit of its useful life.


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At normal operating temperatures, thebrittle knee is difficult to defineexperimentally.

Several years of data is required

(potentially more than 100 years of datafor some PE resins).

To estimate the location of the brittle

knee, a correlation has been developedfor PE pipe performance at differenttemperatures.


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Tests done at elevated temperaturesestablish the location of the brittletransition knee at lower temperatures.

This allows the tests to take place over arelatively short time period.

These tests were not conducted on

earlier PE resins.


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It is now apparent that some PE resinshave the brittle knee occurring within thedesired service life of the pipes.

This is evident by the number of brittlefailures that have been observed in earlygeneration PE resins.


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Correlation of PE PipePerformance to Temperature



Stress

(Log

Scale)

10

100

1000

10,000

100,000

1,000,000

40 CO

60 CO

23 CO

80 CO


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END OF PART 1

SGC & RCP PREDICTINGTHE LIFE OF PE MAINS

Any Questions ?????


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PART 2AN INTRODUCTION TOPE 4710 / PE 100+ MATERIAL

Presented by


Senior Engineer, StandardsATCO Gas


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What is PE 100+?

PE 100 is a European designation that isbased on the ISO 9080 standard.

PE 100 simply means that pipe has

an MRS value of 10 MPa. Likewise, PE 80 pipe has

an MRS value of 8 MPa.


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Why use PE 100+?

PE 100+

is capable of exhibiting thebest properties of MDPE (PE 2406)and HDPE (PE 3408).

PE 100+

is capable of better slow crackresistance than MDPE.

PE 100+ is capable of better RCP crack

resistance than HDPE. There is money to save.


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Molecular Weight

MDPE HDPE


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Molecular Weight

Bimodal HDPE


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What does MRS Mean?

MRS means:Minimum Required Strength

The MRS is categorized value that

represents an estimate of the long-termstrength of the pipe.

MRS values are calculated similar

to HDB values, but there are keydifferences. MRS values are alwayslower than HDB values.


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HDB Determination

HDB is determined in accordance withASTM D 2837 by plotting the log valuesof hoop stress vs. the log value of time tofailure. Tests are done at 23oC.

Points are plotted, then a line isprojected to 100,000 hours (11 years).

The value at 11 years is the LTHS(Long-Term Hydrostatic Strength)


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HDB Determination (Contd)



Stress

(Log

Scale)

10

100

1000

10,000

100,000

1,000,000

LTHS HDB

100,000 hrs11.4 years18 data points to

10, 000 hrs (1.14 yrs)test @ 23 CO


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HDB Determination (Contd)

The categorized 100,000 hour (11.4 yr)LTHS value is the HDB.

For example, an LTHS value between

1200 and 1530 psi is categorized asHDB = 1250 psi.

An LTHS value between 1530 and 1920

psi is categorized as HDB = 1600 psi.


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MRS Determination

MRS is determined in accordance withISO 9080 by plotting hoop stress vs.time at 20oC on a log- log scale.

MRS also considers the effect oftemperature. (Tests are conducted at 2other temperatures as well.)

Again, points are plotted, but a line isplotted representing the Lower PredictiveLimit (not the best-fit / average).


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MRS Determination (Contd)

The Lower Predictive Limit (LPL) isprojected to 50 years (not 11).

The 50 year value is then categorized.

A value between 8.0 and 9.9 MPa iscategorized as MRS = 8.0 MPa (PE 80)

A value between 10 and 11.19 MPa is

categorized as MRS = 10 MPa (PE100)


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MRS Determination (Contd)



Stress

(Log

Scale)

10 100100

0

10,000

100,000

1,0

00,000

LTHS MRS

50 years

30 data points to10,000 hrs (1.14 yrs)

test @ 20 C andtwo other temperatures

O

97.5 % LCLLower Confidence Limit


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HDB and MRS Compared



Stress

(Log

Scale)

10 100

1000

10,000

100,000

1,000,000

MRS

50 years

xx

HDB

11.4 years

97.5 % LCLLower Confidence Limit


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Why is MRS Better?

MRS gives consideration to temperature.MRS uses a lower confidence limit which

considers the quality of the data.

MRS requires more data points.Pipe can always be expected to perform

better than the categorized value.


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What is MRS Design?

MRS Design is a method of determininga safe hydrostatic design pressure.

MRS design calculations are similar to

the HDB design calculations used inCanada, but there are some keydifferences.


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MRS Design Methodology

In MRS design, the categorized long-term strength of the pipe is divided bydesign coefficients to obtain a safeoperating pressure.

In HDB design, the categorized long-term strength of the pipe is multiplied bydesign factors to obtain a safeoperating pressure.


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HDB Design Formula

P = {2S / (R-1)} F T

or

P = {2St / (D-t)} F T

where,

P = design pressure (psi or MPa)S = Hydrostatic Design Basis at 23 C, (psi or MPa)R = standard dimension ratio (SDR)D = maximum average outside diameter, (in. or mm)

t = minimum wall thickness, (in. or mm)

F = Service Design FactorT = Temperature Design Factor


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MRS Design Formula

P = 20*MRS / {(R-1)*C}

or

P = 20*MRS* t / {(D-t)*C}

where,

P = design pressure (Bar)MRS = Minimum Required Strength at 20 C (MPa)R = standard dimension ratio (SDR)D = maximum average outside diameter, (mm)

t = minimum wall thickness, (mm)

C = Overall Design Coefficient


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MRS Design Formula

P = 20*MRS / {(R-1)*C}or

P = 20*MRS* t / {(D-t)*C}

C is now in thebottom of the

equation replacingthe product F X T

2 becomes 20due to the unitsBar and MPa


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MRS Design Formula

The design factor is not simply theinverse of the design coefficient.

A design factor of 0.5 in the HDB designcalculation, yields different results thana design coefficient of 2.0 used in theMRS design calculation.

This is because the MRS and HDBestimates of strength are not equal.


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MRS Design Coefficients

The overall design coefficient is aproduct of several design coefficients.

C = CA X CM

C must be at least 2.0 per ISO 4437.Some regulatory authorities may also

specify a minimum value for C.


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MRS Design Coefficients

CM

= is the material coefficient andequals 1.25 for PE per ISO 12162.

CA is the application factor and isspecified by the design engineer.

CA must be at least 1.6 for C to equal2.0.


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MRS, HDB and PE 2406

PE 2406 pipe used by ATCO Gas hasan HDB value of 1250 psi (8.6 MPa).

PE 2406 pipe used by ATCO Gas hasan MRS value of 8.0 MPa.

The safe operating pressure for SDR 11pipe is 690 kPa per the HDB method or800 kPa (8 Bar) per the MRS method(F = 0.40 and C = 2.0).


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MRS, HDB and PE 3408

PE 3408 pipe, if used by ATCO Gas, hasan HDB value of 1600 psi (11.03 MPa).

PE 3408 pipe, if used by ATCO Gas, hasan MRS value of 8.0 MPa.

The safe operating pressure for SDR 11pipe is 860 kPa per the HDB method or800 kPa (8 Bar) per the MRS method(F = 0.40 and C = 2.0).


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Why is the MRS 8 for PE 3408?

If you were to buy PE 100 today, it wouldbe classified as PE 3408.

It would have an MRS value of 10 MPaand an HDB of 1600 psi.

However, most PE 3408 resins are notequivalent to PE 100. They are actuallyPE 80; just like PE 2406.

H PE 2406 d PE 3408


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How can PE 2406 and PE 3408both be MRS 8.0?

Many PE 3408 resins have an LTHSvalue just below 1600 psi.

They are therefore categorized asHDB = 1600 psi.

Many PE 2406 resins have an LTHSvalue near 1450 psi.

They are therefore categorized as

HDB = 1250 psi, even though they aremuch higher strength.

How can PE 2406 and PE 3408


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How can PE 2406 and PE 3408both be MRS 8.0? (contd)

PE 2406 is actually close in strength toPE 3408.

However, they are categorized verydifferently as 1250 psi and 1600 psi.

Following the ISO methodology, both arerated as MRS = 8.0 MPa.

What is Happening to


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What is Happening toDistinguish PE 100 Materials?

ASTM standards are being revised.

First, D3350 has just split the 3 in thedensity cell class to 3 and 4.

4 will be used to identify the higherdensity bimodal resins that are PE 100.

ASTM D2513 is in the process of

changing to recognize the change inASTM D3350.

What is Happening to Distinguish


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PE 100 Materials? (Contd)

Next, D3350 will be revised to add a 7 tothe slow crack growth resistance cellclass.

7 will be used to identify resins thathave a PENT test value > 500 hours.These are the high performance pipes.

ASTM D2513 will also need to change torecognize this change.



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What is Happening to DistinguishPE 100 Materials? (Contd)

Finally, the water industry is in theprocess of adopting a new design factor.

They are changing from F = 0.5 to 0.63of high performance materials.

This will change the 08 in PE 3408to a 10.

08 is the HDS, which is equal toFWater*HDB.



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What is Happening to DistinguishPE 100 Materials? (Contd)

PE 100 will be PE 4710 under ASTM.

4 = bimodal highdensity resin

7 = PENT test

> 500 hours

10 = HDS for water

of 1000 psi (F=0.63)



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What is Happening to DistinguishPE 100 Materials in Canada?

CSA is looking at changes to B137 andZ662.

B137.0 and 137.4 are looking atrevisions to include PE 100 resulting in 3cell classes for gas:

PE 2406, PE 3408, PE100

What does the future hold


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What does the future hold- for the U.S.?

PE 4710PE 3710PE 4710

PE 100+

(Bi-Modal)

PE 3608

or

PE 3710

PE 3408PE 3608

PE 3708 PE 3710PE 4708 PE 4710

PE 3408(HDPE)

PE 2606or

PE 2708

PE 2406PE 2606

PE 2706 PE 2708

PE 2406(MDPE)

FUTURE?TOMORROWTODAY

What does the future hold


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What does the future hold- for Canada?

PE 100

(PE 4710?)

PE 100+

(PE 3408)

PE 3408

(PE 3608)

PE 3408(HDPE)

PE 2406

(PE 2708)

PE 2406(MDPE)

FUTURE?TODAY


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Not all PE 100s are the Same!

Remember the + when you think ofPE 100. Not all PE 100 is superior.

Slow crack resistance still comes at theexpense of RCP crack resistance.

With bimodal PE 100 resins, the entirescale shifts allowing a better combinationof RCP and slow crack resistance butit does not guarantee it choose right.


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Where are the Savings?

The savings are in the pipe strength.

With PE 100 you pay 10% more pervolume but you buy 25% less volume.

This is because a larger SDR isacceptable.

SDR 17 permits the same 550 kPa or

80 psi MOP as SDR 13.5 in a PE 2406material.

Where are the Savings?


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Where are the Savings?(Contd)

You could even consider using323 mm SDR 21 PE 100 which has anMOP of 64 psi.

The wall thickness would be 15.4 mmcompared to 24.0 mm for SDR 13.5used today by many companies.

323 mm PE could be used to replacesome 323 mm steel projects.


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END OF PART 2

AN INTRODUCTION TOPE 4710 / PE 100+ MATERIAL

Any Questions ?????


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PART 3

USE OF NEW MATERIALS -IMPACT ON CONSTRUCTION

Presented by


Senior Engineer, StandardsATCO Gas


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What is the Catch?

Fusion Procedures

Fusion Training

Squeezing Procedures

Pipe Deflection from LoadingPipe Color

Change

What is the Catch?


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Fusion Procedures

We need to test our existing procedures.

PE 100 should fuse to PE 2406 withoutany problem (using conventional orelectrofusion).

We have already used a few PE 100Electrofusion fittings.

What is the Catch?


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Fusion Procedures

PE 100 has a slightly different bead

shape. It appears more pear shapedthan round (like an airplane wing).

We may need a new visual criteria asthe bead does not always roll back andtouch the pipe completely.

For yellow jacketed PE 100, visualinspection is more difficult (see sample).

What is the Catch?


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Fusion Procedures Bead Shape

PE 100 PE 2406

Bead does notsit down as well

Bead has aflatter appearance

What is the Catch?


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Fusion Procedures

Fusion beads have better visual

appearance using lower irontemperatures about 400 to 425OF.

PPI recommends 400 to 450OF in their

generic fusion procedure (TR-33).

At ATCO Gas, we specify an irontemperature range of 475 to 500OF.

What is the Catch?


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Fusion Procedures

PE 100 fuses better with slightly higher

interfacial pressure.

PE 100 can be conventionally fuseddirectly to PE 2406.

Electrofusion will be required if wallthickness is different (our rule).

What is the Catch?


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Fusion Training

Some fusion training will be required to

highlight the differences.

Not a small task - ATCO Gas has over600 qualified fusers.

Timing would need to be wellcoordinated.

Would likely train to PE 100 procedureand use on PE 2406 without problem.

What is the Catch?


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Squeezing Procedures

This should be no problem but still needs

confirmation for our climate.

PE 100 is used in the North EasternUnited States.

We need to ensure that our procedureswill work in both hot and cold conditions.

What is the Catch?


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Pipe Deflection - Loads

Currently, our soil loading model shows

some excessive deflections (> 5%) forour existing pipe when installed deeperthan normal or under heavy loads.

With bigger SDRs, larger deflections areconsidered acceptable (8.1% forSDR 32.5 Rinker and Driscoplex)

We need to investigate deflection even ifwe are not changing resins.

What is the Catch?


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Pipe Deflection - Loads

Europeans use SDR 17 PE 100.

Some companies have used SDR 21,but we need to investigate their results.

Good backfill practices are the best wayto reduce deflection.

What is the Catch?Pi C l


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Pipe Color

PE 100 is generally made black like

other high density pipes.

Black may be more difficult to locate.

The digging community in Alberta will notbe use to encountering live black gasmains in urban areas.

Pipe could be mistaken as conduit.

We will need to educate!



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Pipe Color

PE 100 is available in a yellow jacket.

Visual fusion criteria is harder to observebecause of the color blending.

Only one manufacturer makes thisproduct.



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Pipe Color

What is the Catch?

Ch


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Change

Change is always difficult to manage.

A few years ago, we introduced a newfitting line and experienced some of theissues that change brings.

We had to make some adjustments tovisual fusion criteria.

We also modified some procedures.

This would be no different.

C l i


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Conclusions

PE 100+ will result in savings.

PE 100+ eliminates RCP concerns on ago forward basis.

PE 100+ has been proven with over20 years usage in Europe.

Resin selection is important.

Remember to look for the +.

N t St


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Next Steps

Select a PE 100+ resin.

Begin fusion and squeeze procedurevalidation.

Install test projects.

Introducing Larger Diameter

PE into Your System


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PE into Your System

Higher strength Polyethylene made

today also has better performancecharacteristics. This creates theopportunity to install larger diameter PE

mains for gas distribution.

Concerns Introducing

New (Larger) PE Diameters


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New (Larger) PE Diameters

Some concerns include:

RCP Failures; Brittle Failures from SCG;

Pipe Capacity (Wall Thickness);

Pipe Deflection; Fitting Availability;

Training - Fusion;

Pipeline Isolation (Squeezing); Material Handling.

Concern:

RCP Failures


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RCP Failures

Use of a well selected PE 100 material

will eliminate RCP concerns.

Ensure S4 test data is available for theselected resin.

Specify a minimum Critical Pressure ormaximum Critical Temperature (or both)to ensure safe operation.

Concern:

RCP Failures (Contd)


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RCP Failures (Cont d)


Test Temperature

TestPressure

T1 T2 0C T3 Tc T5

Arrest Regime

Propagation

Regime

P1

P2

P3

Pc

PE 100+ PE 2406

Concern:

Brittle Failures from SCG


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Brittle Failures from SCG

Some resins appear to have no brittle

knee in the LTHS curves. These pipesare predicted to fail in a ductile mode.

Select pipe with a large PENT or NPT

value (greater than 1000 hours) toensure the brittle knee occurs wellbeyond 100 years.

Concern:

Pipe Capacity (Wall Thickness)


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Pipe Capacity (Wall Thickness)

Use of bimodal or high density resins

increases pipe strength and creates theopportunity to use thinner pipe walls:

SDR 11 for 125 PSI systems,

SDR 13.5 for 100 PSI systems, SDR 17 for 80 PSI systems,

SDR 21 for 64 PSI systems.

ISO formulas permit further opportunitiesbased on stress and temperature.

Concern:

Pipe Deflection


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Pipe Deflection

More needs to be done in this area.

Spanglers Modified Iowa Equation canbe used to calculate combined stressesfrom vehicles and soil as well as pipe

deflection. Field observations need to be compared

to calculated values.

Water industry or European gas industryexperiences may add insight.

Concern:

Fitting Availability


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Fitting Availability

More fittings are on the market today.

May have to accept a greater variety ofresins and resin categories to get thefittings you require.

Pipe is less flexible so straighteralignments are required. Pipe with bendsare more difficult to repair.

Allow for longer lead times. Inspectincoming stock to catch defects early.

Concern:

Training - Fusion


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Training - Fusion

If newer materials are selected, you may

require new procedures or new visual criteria. For hydraulic machines, remember that thinner

walled pipes require different fusion machinepressures.

Compare hydraulic fluid pressureand cross section of ramto:

desired interfacial pressureand cross section of pipe.

Concern:

Pipeline Isolation (Squeezing)


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Pipeline Isolation (Squeezing)

Sqeezing is a bonus. Steel systems

require valves anyway.

Conduct tests to decide if squeezing agiven pipe diameter and SDR is

desirable.

Thinner pipe walls make squeezingpossible for greater sizes.

Concern:

Material Handling


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Material Handling

Longer sticks of pipe will reduce fusion

costs, but are more difficult to handle.Consider a spreader bar for fork lifts.

This allows bundles to be lifts at several

points along their length.

Next Steps


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Next Steps

Investigate European experience with

SDR 21. Investigate pipe deflection criteria note

that there is limited data readily available

for PE pipe.Participate in CGA, CSA, AGA, and

ASTM committees where the

opportunities exist.


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END OF PART 3

USE OF NEW MATERIALS -IMPACT ON CONSTRUCTION

Any Questions ?????

References


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References

CSA Standards B137, Z662

ASTM Standards D2513, D2837, D3350, F1473 ISO Standards 4437, 9080, 10839, 12162,

13477, 13478, 13479

PPI Technical Reports TR-3, TR-4,TR-9, TR-33

Proceedings from Plastics Pipes XII, Milan Italy,April 2004

Proceedings from Plastics Pipes XIII,Washington D.C., U.S.A, October 2006

Documents

Behaiviour of PE Pipes