Title: Higher Performance Polyethylene Piping Materials Understanding PE Designations and Coming Changes OH
1Higher Performance Polyethylene Piping Materials
Understanding PE Designations and Coming
ChangesOHIO GAS ASSOCIATIONGeorg Fischer
Central Plastics LLC MARCH 2008
2History
- 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.
3Polyethylene 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.
4Key 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
5Molecular 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.
6Molecular Weight Distribution
7Medium 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.
8State-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
9Changes 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.
10What 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.
11Understanding 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
12What 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
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14PE 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.
15Status of Standards Changes
16PE4710 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).
17Will 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.
18PE 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.
19What 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.
20Potential 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.
21Cell 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
22Current 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.
24Can 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.
25What 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
26Questions 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.
27Questions 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.
28Questions 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.
29Questions 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.
30Questions 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
31Summary
- 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