WL123 HIGH-PERFORMANCE PE4710

Transcription

1 What is High-Perfrmance PE4710 Plyethylene? High-perfrmance plyethylene is an imprved plyethylene cmpund fr pressure pipe that is designated PE4710. Cmpared t cnventinal pressure piping materials such as PE3408, several imprtant perfrmance characteristics are significantly enhanced. Higher density Higher density increases tensile strength, stiffness and chemical resistance. PE3408 materials (D 3350 cell classificatin ) have base resin densities abve t gm/cc, and with 2% carbn black, density is t gm/cc. PE4710 materials (D 3350 cell classificatin ) have base resin densities abve t gm/cc, and with 2% carbn black, density is abve t gm/cc. HDB Substantiatin at 50 years ASTM D 2837 and PPI TR-3 are used t determine the hydrstatic design basis, HDB, fr thermplastic pressure piping materials (including PVC, CPVC, PP, PE, ABS, PB, PA, etc.). HDB requires testing multiple pipe lts fr up t 10,000 hurs, and then perfrming a mathematical extraplatin that estimates material strength at 100,000 hurs. ASTM D 2837 requires an analysis f the pipe test data t shw that the estimated strength will be crrect at least 85% f the time. The ASTM D 2837 methd des nt accmmdate a knee r dwnturn in the stress rupture curve that indicates a transitin t slw crack grwth type failures. Therefre, PE materials must als underg additinal validatin pipe tests t prve that a transitin t SCG des nt ccur befre 100,000 hurs. T qualify as PE4710, additinal testing and analysis must shw that a transitin t SCG (a knee in the stress rupture curve) des nt ccur befre 438,000 hurs (50 years) a 4 t 1 increase and must shw that the estimated strength will be crrect at least 90% f the time a 33% reductin in permissible pipe test data variability. Up t fifty-fld increase in SCG resistance PE3408 materials (D 3350 cell classificatin ) have PENT (ASTM F 1473) SCG resistance f at least 10 hurs. PENT test research empirically crrelated hurs PENT SCG resistance t 100 years in pressure gas service. PE4710 materials (D 3350 cell classificatin ) must have at least 500 hurs PENT SCG resistance, a 50 t 1 increase WL Plastics PE4710 cmpunds typically exceed 2500 hurs prviding greatly imprved SCG resistance cmpared t PE3408 cmpunds. This means that the ptential fr SCG failure, the lng-term failure mde fr PE pipe, is extremely remte. These higher perfrmance specificatins can nly be met by high perfrmance materials. The High-Perfrmance PE4710 Advantage PE4710 pipe is pressure rated higher than PE3408 pipe fr the same DR, r fr PE3408 and PE4710 pipes that have cmparable pressure ratings, PE4710 prvides a flw capacity increase. Table 1 Cmparative Pipe Pressure Ratings fr Water at 80 F and Lwer, psi DR PE4710 PR PE3408 PR Table 2 PE4710 vs. PE3408 Water Flw Capacity Increase, % System Pressure, psi PE4710 Capacity Increase vs. PE3408, % WL Rev Aug 2011 Supersedes all previus editins 2011 WL Plastics Crp Page 1 f 6

2 Why PE4710 has a higher pressure rating In Nrth America, pipe pressure rating is determined using the hydrstatic design stress, HDS, fr the material and the applicatin. HDS is the HDB multiplied by a design factr, DF, fr an applicatin. T avid cnfusin with safety factrs that are usually divisrs applied t reduce shrt term mechanical strength, a design factr multiplier is used. Design factrs can vary fr different applicatins and regulatry requirements. As the thermplastic pipe industry began abut a half century ag, the PPI Hydrstatic Stress Bard develped design factrs t address reductins t labratry derived design stress ratings t address uncertainty in material, pipe manufacture, handling, installatin, applicatin perating characteristics, and unknwn factrs. The result was a 0.50 design factr fr thermplastic pressure water pipe service that is used thrughut Nrth America fr mst thermplastic pressure piping materials. It was develped by determining cmpnent design factrs fr water applicatin as fllws: 1.00 starting basis 0.25 fr materials variability frm lt t lt, and fr variability in testing and test methds 0.05 fr extrusin quality variatin 0.10 t extend the HDB frm 11.4 years t 50 years 0.20 fr pressure surge variatins (based n PVC water hammer capacity) 0.20 fr handling and installatin 0.20 fr unknwn factrs When summed, the verall design factr frm these cmpnents is 2.00, the inverse being Over the years, the 0.50 DF has prved t be cnservative and generally satisfactry fr thermplastic water piping materials including PVC, CPVC, ABS, PP and cnventinal PE, and fr general thermplastic pressure piping applicatins. Hwever, as presented abve, PE4710 materials demnstrate a higher level f perfrmance, superir ductility and resistance t fracture at higher stress. These higher perfrmance prperties allw higher internal pressure withut risk f service life reductin. Nevertheless, PE4710 materials must demnstrate higher perfrmance by qualifying against higher PPI standards fr a 0.63 design factr fr water and cmparable applicatins. Using the same technical basis as that used fr the 0.50 DF, the 0.63 DF is derived as fllws: 1.00 starting basis 0.25 fr materials fr variability in testing, test methds, and lt t lt material variatins Significantly higher requirements fr HDB pipe test data quality and analysis and substantiatin t prve ductility beynd 50 years reduce material variability and d nt require a design factr cmpnent that extends the HDB t a 50-year value fr extrusin quality variatin Lt t lt material variatins are reduced resulting in materials having mre cnsistent prcessability, thus reducing the extrusin quality variability design factr cmpnent fr peratin, handling, installatin and unknwn factrs The riginal 0.50 design factr allcates 0.20 fr surge allwance, 0.20 fr handling and installatin and 0.20 fr unknwn factrs. Hwever, the 0.20 surge allwance is based n limiting PVC surge pressure t prevent bursting and disjining. In cntrast, high perfrmance PE materials tlerate far higher surge pressure and piping jints are fully restrained. Fr a typical 100 psi water system, PE4710 prvides fr WL Rev Aug 2011 Supersedes all previus editins 2011 WL Plastics Crp Page 2 f 6

3 mmentary surge pressures abve the steady pressure rating frm instantaneus water velcity changes up t 10 fps. The remaining allwances fr handling, installatin, and unknwn factrs, are cmbined at PE4710 materials have higher density, higher mlecular weight, and higher SCG resistance, which prvide greater tughness and better resistance t abrasin, chemicals, and imprved elevated temperature perfrmance. This ensures that PE4710 pipes are cnservatively rated fr the applicatin, and that higher pressure ratings frm the 0.63 design factr are derived withut increased risk. This derivatin yields a cnservative verall water service design factr fr PE4710 f 1.60 (0.63 DF) withut increased risk f premature failure r reductin in service life ptential. Thermplastic pipes are pressure rated using the HDB, DF and DR f the pipe as fllws: 2 HDB DF PR = ( DR 1) 2 HDS = ( DR 1) Thus pressure ratings fr PE4710 and PE3408 DR 11 pipes fr ambient temperature water at are: PE4710 DR 11: PR = = 200 psi ( 11 1) PE3408 DR 11: PR = = 160 psi (11 1) PE4710 vs. PE100 Reality vs. Myth A mythlgy has develped arund PE100 in Nrth America primarily frm unfamiliarity and lack f understanding. PE100 is an ISO designatin fr a grade f pressure rated PE material. The designatin means simply that the material is plyethylene, PE, and that the material qualifies fr a 10 MPa (100 bar, 1450 psi) MRS rating at 20 C (68 F); nthing mre; nthing less. There are als PE80 and PE63 plyethylene materials that have MRS ratings f 8.0 MPa (80 bar, 1160 psi) and 6.3 MPa (63 bar, 914 psi) respectively at 20 C (68 F). MRS, minimum required strength, is a categrized lng-term strength rating similar t HDB, but it is develped using ISO standards 9080 and 12162, which tgether are rughly similar t ASTM D Hwever, MRS and HDB are nt the same. Sme f the differences between ISO and ASTM methds fr characterizing lng-term material strength are: Rating temperature MRS at 20 C (68 F) vs. HDB at 73 F (23 C) All thermplastics have greater strength at lwer temperatures. Rating time MRS at 50 years (438,300 hurs) vs. HDB at 11.4 years (100,000 hurs) MRS and HDB lng-term material strength ratings are bth based n statistical prjectins (estimates) f strength at a future time. ISO uses a mre cmplex statistical frmula, and extends its estimate further int the future, but as statistical estimates are extended farther and farther int the future, predictin accuracy and reliability decrease. Fr bth ISO and ASTM methds, the future strength prjectin is n lgarithmic scales, that is, each scale pint increase is 10 t 1 1, 10, 100, 1000, 10,000, 100,000, 1,000,000, etc. Bth methds require test data up t 10,000 hurs, and typically prjectins t the next scale pint (10 times further) have gd reliability. T increase prjectin reliability beynd the first scale pint, ISO applies slightly tighter limits n data variability, and determines the MRS value at a lwer cnfidence limit; HDB is a mean (average) value. Validatin ISO permits a ductile-brittle transitin knee within the rating perid; ASTM des nt The ISO 9080 frmula fr estimating lng-term strength in the future allws the use f brittle (SCG) failure data and ductile failure data, and permits a knee r dwnturn in the stress-rupture curve befre the prjected rating time. The ASTM D 2837 methd requires validatin t demnstrate that a knee in the stress rupture curve WL Rev Aug 2011 Supersedes all previus editins 2011 WL Plastics Crp Page 3 f 6

4 des nt ccur within the rating time. Substantiatin demnstrates that the stress rupture curve extends t 50 years befre the nset f SCG failure. MRS and HDB are nt the same, and d nt translate This is because the statistical methds used t determine MRS and HDB ratings are different. Hwever, the same material can be rated under bth systems. A PE3408 may be a PE80 r a PE100 under the ISO system; likewise, a PE100 may be a PE4710 r a PE3408 under the ASTM system. MYTH PE100 s are high perfrmance PE materials. PE100 identifies nly a material and a strength rating. Nthing in the PE100 designatin r the ISO stress rating methd identifies high perfrmance prperties r sets high perfrmance requirements. The PE4710 designatin, hwever, can nly be achieved by meeting high perfrmance requirements. Only the very best PE100 materials may qualify as PE4710. MYTH PE100 pipe has a higher pressure rating ISO applies a minimum design cefficient divisr f 1.25 fr MRS rated PE, but als advises the system designer t increase the design cefficient fr service cnditins, installatin and handling. Using the minimum design cefficient alne takes nly material variability int accunt; thus, it can be grssly inadequate fr field cnditins. When cmpared t the additinal design factr cmpnents that are incrprated int the Nrth American 0.50 design factr fr cnventinal thermplastic materials, adding necessary design factr cmpnents fr extrusin variability (0.05), handling and installatin (0.20), unknwn cnditins (0.20), and adjusting MRS t 23 C (0.03), the design cefficient fr PE100 in water service under field cnditins shuld be at least 1.73 (0.58 DF) applied t the ISO MRS. (Nte an additinal 0.20 cmpnent fr surge pressure is included in the Nrth American 0.50 DF.) When the ISO pressure rating is adjusted t the same temperature, and the ISO design cefficient includes cmpnents that address field applicatin cnditins that are already included in the Nrth American DF, PE100 pipe pressure ratings are cmparable t thse fr PE3408 pipe. Table 3 Cmparative PE Pipe Pressure Ratings fr Water at 23 C (73 F), psi DR PE PE PE Hw is High-Perfrmance PE4710 Prduced? Plyethylene material perfrmance is dependent n the mlecular structure f the material. Plyethylene mlecules are lng carbn-carbn chains with side chain branches. Mlecular weight, MW, is the ttal weight f the atms in the mlecule chain including side chain branches. PE pipe materials are prduced in plymer reactrs. During prductin, mlecule length (weight) will vary. The verall variatin f mlecular weight is statistically described as a mlecular weight distributin, MWD. A typical MWD curve has a characteristic bell shape. WL Rev Aug 2011 Supersedes all previus editins 2011 WL Plastics Crp Page 4 f 6

5 Fr many years, plyethylene reactr technlgy prduced unimdal plyethylene materials, that is, the MWD curve is bell shaped with ne peak. Over the past decade, hwever, new technlgy has develped fr using tw plymer reactrs t prduce plyethylene having a unique bimdal mlecular weight distributin and enhanced physical prperties. Plyethylene prperties are dependent n interrelatinships amng density, mlecular weight, mlecular weight distributin and the lcatin and type f side chain branches n the PE mlecule. Increasing density yields higher shrt-term strength, but reduces lng-term strength; increasing mlecular weight imprves lng-term strength, but reduces the ability t prcess int pipe and jin the pipe by heat fusin. Brader MWD (a wider bell) imprves prcessability, and lastly, the type and lcatin f side chain branches n the PE mlecule affects resistance t slw crack grwth, the lng-term failure mde fr PE pipe. Figure 1 Unimdal and Bimdal Mlecular Weight Distributin 1 It was discvered that prcessing PE in a single reactr (unimdal technlgy) typically placed side chain branches n the shrter mlecules where SCG resistance was least affected. A new technlgy fr high-perfrmance bimdal PE4710 materials uses tw plymer reactrs in series. With this new technlgy, side chain branches are typically placed n lnger mlecules, yielding huge gains in SCG resistance. Tenfld and higher imprvements in SCG resistance can be realized. Further, with the new dual-reactr bimdal technlgy, density can be increased which increases tensile strength and chemical resistance; lng-term strength is maintained and can even be significantly imprved. Figure 2 Dual Reactr Bi-Mdal PE4710 Technlgy 1 WL Rev Aug 2011 Supersedes all previus editins 2011 WL Plastics Crp Page 5 f 6

6 Figure 3 Unimdal and Bimdal Physical Prperty Relatinships 1 S What s Next? PE4710 high-perfrmance materials are the next evlutin in plyethylene pipe higher pressure ratings, increased flw capacity, and imprved lng-term perfrmance all withut cmprmising traditinal benefits f flexibility, leak-tight heat fusin jining, chemical resistance and ease f installatin. With the establishment f perfrmance characteristics and requirements fr PE4710 materials, material and pipe specificatins are being updated t include PE4710, and then cdes fr applicatins such as gas and water will be updated. Lastly, PE4710 prducts cannt be prperly applied withut technically sund, crrect infrmatin. Educatin must be prvided s that the industry may understand and knw hw t prperly apply PE4710 prducts fr maximum benefit. WL Plastics, resin suppliers, the Plastics Pipe Institute, standards writing rganizatins such as ASTM and AWWA, certifiers such as NSF, cde bdies and ther rganizatins are wrking t prvide the benefits f highperfrmance PE4710 pipe t custmers in Nrth America and internatinally. This publicatin is intended fr use as a piping system guide. It shuld nt be used in place f a prfessinal engineer s judgment r advice and it is nt intended as installatin instructins. The infrmatin in this publicatin des nt cnstitute a guarantee r warranty fr piping installatins and cannt be guaranteed because the cnditins f use are beynd ur cntrl. The user f this infrmatin assumes all risk assciated with its use. WL Plastics Crpratin has made every reasnable effrt t ensure accuracy, but the infrmatin in this publicatin may nt be cmplete, especially fr special r unusual applicatins. Changes t this publicatin may ccur frm time t time withut ntice. Cntact WL Plastics Crpratin t determine if yu have the mst current editin. Cpying withut change permitted. ISO 9001:2008 Certified CASPER PLANT: 2075 Nrth Pyrite P. O. Bx 1120 Mills, WY Custmer Service: Fax: CEDAR CITY PLANT: 4660 W. Highway 56 P. O. Bx 627 Cedar City, UT Custmer Service: Fax: ELIZABETHTOWN PLANT: 2151 West Park Rad Elizabethtwn, KY Custmer Service: Fax: BOWIE PLANT: 1110 Old Wise Rad P.O. Bx 32 Bwie, TX Custmer Service: Fax: CROSSFIELD PLANT: PO Bx Western Drive Crssfield, AB T0M 0S0 Canada Custmer Service: Fax: Figures 1, 2 and 3 curtesy Lyndell Basell Chemical Cmpany. WL Rev Aug 2011 Supersedes all previus editins 2011 WL Plastics Crp Page 6 f 6