Examination of the New Criteria Used to Designate the Latest Generation PE - PE 4710

1. Examination of the New Criteria Used to Designate the Latest Generation PE - PE 4710 Test Communication at DPC Sales Training Meeting Denver, CO 05-22-2013

2. What is PE 4710 ? • “Bi-modal” PE resin compounded for use in pressure pipe with use in Europe under ISO standards. • The ISO standards recommend a minimum design factor of 0.63 equivalent to a Safety Factor of 1.59. • It is adopted by many European Countries that then add their own additional DF or SF.

3. Design Factors for PE 4710 • Some PE Manufacturers and their trade association the PPI (Plastic Pipe Institute) would like to make PE pipe more competitive by reducing the wall thickness by 20 %.

4. Defining the Conversation with Standard Definitions • HDB ? • HDS ? • DF ? • SF ? • MARGIN OF SAFETY ?

5. Defining the Conversation with Standard Definitions • HDB = Hydrostatic Design Basis Is the long term categorized stress that results from testing pipe at different constant circumferential wall stress levels due to pipe internal pressure at room temperature (68-73 Deg. F.) in accordance with ASTM D2837.

6. Defining the Conversation with Standard Definitions • HDB is the projected circumferential wall stress that would cause failure in 10,000 hours (11.1 years). For PVC this is 4000 psi. For PE 4710 this is 1600 psi. For PE 3408 this is 1600 psi.

7. Defining the Conversation with Standard Definitions HDS = Hydrostatic Design Stress The actual maximum allowed constant circumferential stress in the wall of a pipe resulting from the operating pressure of the fluid in the pipeline when in service as recommended by AWWA.

8. Defining the Conversation with Standard Definitions DF = Design Factor Factor or fraction less that one that is multiplied by the HDB to give the allowable stress in the wall of the pipe so that. . . HDS = HDB(DF)

9. Defining the Conversation with Standard Definitions SF = SAFETY FACTOR Factor or number greater than one that is divided into HDB to give the reduced allowable stress in the wall of the pipe so that. . .. . . HDS = HDB/(SF)

10. Defining the Conversation with Standard Definitions SM = SAFETY MARGIN The degree or margin of safety between the HDB and the HDS or the actual operating stress and the stress indicated in the HDB pipe property.

11. Design Factors for PE 4710 • This would not be the first time that improved pipe due to improved material strength has resulted in thinner pipe walls. • Examples: • Cast Iron to Ductile Iron in C150 (1975) • Addition of PVCO in AWWA C909 (1998) • PE 3604 to PE 3608 in AWWA C906

12. Design Factors for PE 4710 • However, there is something very different about this latest HDPE proposal for PE4710 pipe. • The key material design property, HDB (Hydrostatic Design Basis) is not improved.

13. Design Factors for DI, PVC, PVCO, PE3608 • In all of the examples cited above, the thinner pipe walls were justified on the basis of a commensurate increase in the pipe material’s tensile strength and HDB. In every case the material strength increase enabled the water industry to maintain long and short term margins of safety of 1.0 or more, which can also be characterized as maintaining a design factor of 0.5 or safety factor of 2.0.

14. Design Factors for PE 4710 • But the new PE4710 material designation is not the result of any higher long term strength category or Hydrostatic Design Basis (HDB = 1,600 psi for both PE3608 and PE4710).

15. PE 3608 vs. PE 4710

16. Design Factors for PE 4710 • The PE4710 designation deviates from the water industry’s longstanding margin of safety by allowing a design factor of 0.63 (SF = 1.59) and thereby lowering the long term margin of safety to less than 1.0.

17. Design Factors for PE 4710 • PPI’s recommendation that the traditional design factor be increased from 0.5 to 0.63 for these new HDPE 4710 materials is solely based on these three criteria: • Maintain a ductile fracture mode to 50 yr. HDB intercept. • HDB data show less scatter (90% confidence) • Minimum PENT failure time of 500 hours

18. Design Factors for PE 4710 • The material be ductile* under sustained stress through an extrapolated 50-year intercept; * ”Ductile” is a description of the mode of failure as showing elongation as opposed to a “Brittle Failure”. The failure time given by the material property, HDB however is not improved.

19. Design Factors for PE 4710 • The lower confidence limit of the projected average value of the material’s long-term hydrostatic strength by ASTM D2837* is 90% instead of 85%. *Standard Test Method for Obtaining Hydrostatic Design Basis for Thermoplastic Pipe Materials or Pressure Design

20. Design Factors for PE 4710 • The minimum failure time under ASTM F1473 (PENT)* increase from 100 to 500 hours *Standard Test Method for Notch Tensile Test to Measure the Resistance to Slow Crack Growth of Polyethylene Pipes and Resins

21. Design Factors for PE 4710 • None of these new added criteria are measures of increased long or short term tensile strength. • The first two criteria merely narrow the allowable variation of the test results.

22. ASTM F1473 (PENT) • The last criterion is a test that determines the resistance to slow crack growth at 176°F of a notched, molded plaque of polyethylene stressed to 348 psi. • The test is not an indicator of long-term pipe performance. The increase from a minimum failure time of 100 to 500 hours has never been mathematically correlated with actual in-service pipe performance or longevity.