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Title: Higher Performance Polyethylene Piping Materials Understanding PE Designations and Coming Changes OH


1
Higher Performance Polyethylene Piping Materials
Understanding PE Designations and Coming
ChangesOHIO GAS ASSOCIATIONGeorg Fischer
Central Plastics LLC MARCH 2008
2
History
  • Polyethylene was first discovered in 1933. It
    wasnt commercialized until many years later.
  • First used as a piping material for oil field
    production in the mid-1950s.
  • Has become a highly engineered material with
    specific properties and capabilities for pressure
    piping.

3
Polyethylene Molecule
  • Polyethylene is made from ethylene gas, composed
    of two double-bonded carbon atoms and four
    hydrogen atoms.
  • In a reactor, the double carbon bond is broken,
    which allows the carbon atoms to bond with others
    in long chains.

4
Key Properties
  • Comonomer
  • Branch placing along molecule length
  • Density
  • Crystallinity-amount of side chain branching
    affects the ability of the molecules to organize
    and pack together The shorter/fewer branches,
    the higher the density.
  • Molecular Weight
  • Describes molecule length

5
Molecular Weight Distribution
  • MWD is a key property that describes a materials
    molecule weight to number average.
  • A broad MWD (both long and short chains) results
    in better crack resistance and toughness.
  • A narrow MWD (shorter,uniform chain lengths)
    processes better, but has less ability to resist
    slow crack growth.
  • The ideal MWD is referred to as being bi-modal.
    It has a blend of both long and short chains,
    with side branching in the higher molecular
    weight portion, resulting in good processability
    (fusion characteristics) and excellent resistance
    to environmental stress cracking.

6
Molecular Weight Distribution
7
Medium Density / High Density
  • Early production used a high pressure reactor
    process that resulted in lots of side branching.
    Since a large number of side branches reduces the
    ability of the chains to pack together, the
    result is LOW DENSITY PE (LDPE). It is very
    ductile (amorphous), but not very stiff.
  • Medium Density PE (MDPE), like PE2406, has fewer,
    shorter side branches. It is still ductile, but
    packs together more densely. Because of the
    increased density, it can withstand more
    short-term pressure.
  • High Density PE (HDPE) uses a comonomer in the
    reactor process, such as butene or hexene, to
    control side branching and results in the highest
    density. Short term properties, such as
    elongation and burst strength increase, but the
    material becomes more brittle (crystalline).
    Because of this, older HDPE materials typically
    did not resist slow crack growth failure as well
    as MDPE.

8
State-of-the-art HPDE
  • Recent improvements in the performance of HPDE
    have led to dramatic changes in PE piping
    materials.
  • Bi-modal PE4710 materials possess properties of
    both MDPE and HDPE.
  • Excellent slow crack growth resistance
    properties.
  • Higher pressure capabilities
  • Greater short-term properties

9
Changes are coming
  • PE 4710 is the next step in the evolution of
    improved polyethylene materials for pressure
    piping. The last similar change was in the late
    1980s when PE 2306 and PE 3306 materials changed
    to the PE 2406 and PE 3408 materials that we know
    today.
  • Although the goal is to recognize and utilize
    the higher performing material known as PE4710,
    the changes also include other new material
    designations PE2606, PE2708, PE3608, PE3708,
    PE3710, PE4608, and PE4708.

10
What does PE XXXX Mean?
  • PE designations, such as PE 2406, PE3408, and
    PE100 are more than simply the color of a resin.
  • While typically PE 2406 resins are yellow and
    PE3408 is black, color is not related to the
    designation.
  • The letters PE indicate Polyethylene.
  • The numbers are codes for density, slow crack
    growth resistance, and hydrostatic design stress.
    These values come from a completely separate,
    but more complicated, classification system in
    ASTM D3350.

11
Understanding the Code.
  • Example PE 2406,PE3408,PE4710
  • PE 2 4 06
  • PE 3 6 08
  • PE 4 7 10
  • Polyethylene Density
    Slow Crack Growth Resistance Design
    Stress
  • PE 2 gt.925 to .940 g/cm? 4 PENT Test
    gt 10 hours 06 625 psi
  • PE 3 gt.940 to .947 g/cm? 6 PENT Test
    gt 100 hours 08 800 psi
  • PE 4 gt.947 to .955 g/cm? 7 PENT Test
    gt 500 hours 10 1000 psi

12
What does PE XXXX Mean?
  • The PE designations are established by PPI
    (Plastics Pipe Institute) and are listed in PPI
    TR-4.
  • All polyethylene materials are not the same, so a
    common designation system was needed to indicate
    that important property requirements are met for
    PE used for pressure piping applications.
  • These designations were created as a way to
    identify and distinguish PE materials based on
    their properties.
  • Anyone can access PPI documents for free at
    www.plasticpipe.org

13
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14
PE 4710 is currently being added to ASTM
standards.
  • ASTM Standards are being revised to accommodate
    the higher performance materials. Some are
    complete, many are still being revised.
  • Old cell classification system in ASTM D 3350
    could not accommodate higher performance
    materials. Cells were split and added to allow
    for the new values.
  • Cell class change will also affect PE 2406
    designation by adding PE2606 and PE 2708.

15
Status of Standards Changes
16
PE4710 has a higher performance/pressure rating
than PE 3408.
  • Improved slow crack growth resistance over PE
    3408.
  • Will allow for increased design factors .63
    instead of .5 for water(160 psi rating becomes
    200 psi). Pending revision of current piping
    standards.
  • Pressure rating for GAS will not change until DOT
    192 regulations are revised, but is intended for
    use with the proposed .4 design factor. SDR 11
    PE4710 125 psi, PE2708 100 psi (Previously
    PE2406).

17
Will require dual marking of product short-term.
  • Fittings will be marked PE3408/PE4710 and
    PE2406/PE2708 to ensure compliance with DOT
    regulations.
  • Similar to change in the 1980s from PE 2306 to
    PE 2406 and PE 3306 to PE 3408.
  • Old designations (PE 3408 and PE 2406) will
    eventually stop being used, but for now, must be
    included on pipe and fitting markings until DOT
    Part 192 is revised.
  • PE 100 will not be referenced on imperial sized
    product going forward unless specifically
    requested.

18
PE 4710 and PE 100 are the same material, but...
  • ISO MRS system (PE63, PE80, PE100) was not
    compatible with ASTM system. MRS designation
    system does not classify slow crack growth
    resistance properties.
  • PE 4710 was adopted in the US instead of PE 100
    to keep the familiar four-digit PE XXXX
    designation system. Adding PE 4710 was thought
    to be the best way to identify material
    properties and to reduce confusion by users.

19
What problems can be expected?
  • A general confusion and misunderstanding is
    expected.
  • While most of the industry is probably aware of
    PE 4710 and the changes to ASTM standards, some
    may not be.
  • Some may not be aware that PE 4710 and PE 100 are
    the same material. Fittings are labeled PE 4710
    (not PE 100) because we dont want to confuse the
    issue any more than necessary.
  • Old specifications by cell classification and
    material designation will no longer be correct.
  • PE 4710 is perfectly suitable for use in these
    specifications, however the specification might
    need to be reviewed and updated.

20
Potential problems
  • Specifications that call for a specific cell
    classification based on the old PE 3408.
  • It is very important to understand the
    differences in the old ASTM D3350 standard for
    cell classification and the new version. Cell
    classifications, when using the old system, may
    be the same. See the next slide for examples of
    cell class differences when the same material is
    classified using both versions.

21
Cell Classification
  • A cell classification is a six digit code given
    to the material based on a value for six specific
    properties. The code comes directly from ASTM
    D3350. Some users of polyethylene may not
    completely understand what the differences are in
    materials, they may simply assume that if the
    cell classes dont match, they are not
    compatible. Below is a comparison of cell
    classifications for the same material using ASTM
    D3350 old (pre January 2005) and new versions
  • Fitting Material Old New
  • PE 2406 (K38-20-160) 234363E 234373E
  • PE 3408 (K44-08-123) 345464C 345464C did not
    change
  • PE 4710 (XS 10 B) 345564C 445574C or 445576C
    (PE 100)
  • PE 4710 (TUB 121 N3000) 345564C 445574C or
    445576C (PE 100)
  • Example of a cell classification CELL PROPERTY
  • 1st 4 Density
  • 2nd 4 Melt Index
  • 3rd 5 Flexural Modulus
  • 4th 5 Tensile Strength
  • 5th 7 Slow Crack Growth Resistance (PENT
    value)
  • 6th 4 Hydrostatic Design Basis (or MRS
    rating if PE 100)
  • Letter C Color or UV Stabilizer

22
Current cell classification limits from ASTM D3350
23
What if an old PE 3408 cell classification is
specified?
  • In the long-term it is necessary to revise or
    change the specifications, but we can reference
    previous editions of ASTM D3350 and classify
    material as both PE 3408 and PE4710 depending on
    the date of the print edition being referenced.
    The PE 4710 material used by Central Plastics
    today has a
  • Cell classification of 345464C per ASTM D3350-02a
    and is PE 3408.
  • Cell classification of 445574C per ASTM D3350-05
    and is PE 4710.

24
Can PE 4710 fittings be used in a natural gas
application?
  • Yes, but they must still be marked PE3408. Pipe
    and Fittings will be dual marked as PE 2406/PE
    2708 and PE3408/PE 4710 until DOT 192 regulations
    have been updated to recognize the new standards.
    Pressure ratings have not changed for gas piping
    applications.

25
What other material designations can be expected?
  • PE 2406 will split into 3 designations, PE 3408
    will split into 6 designations
  • PE 2406 PE2406 PE 3408 PE3408 PE2606 PE3608
    PE2708 PE3710 PE4408 PE4608 PE
    4710

26
Questions and Answers.
  • Q. Why would anyone use one of the other grades
    like PE 4408?
  • They probably wont. Some designations were
    simply a by product resulting from the
    restructuring of the ASTM standards. PE4408
    would indicate a higher density material with a
    relatively poor PENT performance.
  • Q. So why dont they just get rid of the
    designations that we dont use?
  • Standards are a result of industry cooperation
    and participation through a voting process.
    There was concern that some manufacturers or
    users might suddenly find that they were phased
    out of the market, so the standards could not be
    changed to down grade an existing material.
    Instead, the cells were split or added which
    resulted in theoretical, but unlikely, additional
    designations. What was once a PE3408 is still at
    least a PE3408, but may also qualify as a PE3608.

27
Questions and Answers continued
  • Q. Why are we going through this?
  • The end result will be increased design
    pressures, which have many benefits to the piping
    industry. In order to compete with PVC, for
    example, the pipe wall thickness to achieve a 160
    psi pressure rating using the increased design
    factor changes from DR 11 to DR 14.
  • A similar benefit will be realized in the gas
    industry. The increase from .32 to .4 design
    factor means that PE2406/PE2708 SDR 11 can
    operate at 100 psi, as opposed to 80 psi.
    Smaller diameters or wall thicknesses can be
    used, or higher pressures can be used lower the
    cost a piping system.
  • The result is a slightly higher per/pound cost of
    pipe, but a lower per/foot cost if the higher
    pressure capability is utilized.

28
Questions and Answers continued..
  • Q. What about fusion compatibility?
  • A. PE 4710 pipe and fittings have been qualified
    to PPI TR-33 and TR-41 generic fusion procedures
    on a myriad of commercially available pipe and
    are compatible for use with those procedures,
    just as old PE 3408 pipe and fittings were.
    There are no changes in Central Plastics
    recommendations for using the generic procedures.
  • Specific fusion combinations, such as PE4710 to
    PE2406, should be endorsed by the pipe and
    fitting manufacturers. It is the users
    responsibility to ensure that they have qualified
    their installers to a procedure.
  • B. Electrofusion fittings have also been
    qualified in PE 4710 to the same commercially
    available pipes. There are no changes to any
    electrofusion installation procedures.

29
Questions and Answers continued.
  • Q. Is Central Plastics fitting material
    changing?
  • Our PE 2406 fittings material is not changing.
    We will continue to use the same formulation that
    we have for many years. The material designation
    will change from PE 2406 to PE 2708. The
    material achieves the highest designation for
    PENT hours and an 800 psi maximum HDS. We will
    continue to mark fittings as PE 2406/ PE 2708 for
    as long as the market requires.
  • Our PE 3408 fittings material is changing. As
    part of our plan that has been in place for many
    months, we are nearing completion of a conversion
    of all black fittings to PE 4710 / PE 100
    material. We will no longer use a material that
    cannot achieve a PE 4710 rating in molded
    products.

30
Questions and Answers continued.
  • What differences will I see?
  • Slight difference in fusion bead shape and
    texture. PE4710 sometimes appears rougher.
  • Molded fittings are not as glossy or shiny. May
    have swirls in finish.

PE 4710
PE 3408
31
Summary
  • PE4710 has improved mechanical properties and
    durability.
  • Can replace PE2406 without sacrificing slow crack
    growth resistance.
  • Increased pressure rating or
  • Increased flow capacity at same pressure
    Example DR11 to DR13.5 provides 12 flow capacity
    increase.
  • Lower system cost.
  • Fusion compatibility with existing materials

32
The End
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