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									     Higher Performance
 Polyethylene Piping Materials
Understanding PE Designations and Coming
                Changes


       OHIO GAS ASSOCIATION
         Georg Fischer Central Plastics LLC
                   MARCH 2008
                  History
   Polyethylene was first discovered in
    1933. It wasn’t commercialized until
    many years later.
   First used as a piping material for oil
    field production in the mid-1950’s.
   Has become a highly engineered
    material with specific properties and
    capabilities for pressure piping.
         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.
               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
    Molecular Weight Distribution
   MWD is a key property that describes a material’s
    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.
Molecular Weight Distribution
    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.
         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
           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 1980’s 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.
    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.
       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 = >.925 to .940 g/cm                4= PENT Test > 10   hours
  06 = 625 psi
   PE             3 = >.940 to .947 g/cm               6= PENT Test > 100 hours
  08 = 800 psi
   PE             4 = >.947 to .955 g/cm               7= PENT Test > 500 hours
  10 = 1000 psi
    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
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.
Status of Standards Changes
       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).
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 1980’s 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.
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.
          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 don’t 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.
             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.
                           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 don’t 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
Current cell classification limits
     from ASTM D3350
       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.
 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.
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
                                       PE4710
        Questions and Answers….
Q. Why would anyone use one of the other grades like PE
    4408?
   A.   They probably won’t. 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 don’t they just get rid of the designations that we
    don’t use?
   A.   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.
          Questions and Answers
               continued…
Q. Why are we going through this?
   A. 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.
   B. 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.
          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 user’s 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.
         Questions and Answers
             continued….
Q. Is Central Plastics’ fitting material changing?
   A. 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.
   B. 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.
          Questions and Answers
              continued….
   What differences
    will I see?
    • Slight difference in
      fusion bead shape
      and texture.           PE 4710   PE 3408
      PE4710 sometimes
      appears “rougher”.

    • Molded fittings are
      not as glossy or
      shiny. May have
      swirls in finish.
                 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
The End

								
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