1、 PPI TN-27/2009 Frequently Asked Questions HDPE Pipe for Water Distribution and Transmission Applications 2 PPI TN-27: Frequently Asked Questions HDPE Pipe for Water Distribution and Transmission Applications Foreword This report was developed and published with the technical help and financial supp
2、ort of the members of the PPI (Plastics Pipe Institute, Inc.). The members have shown their interest in quality products by assisting independent standards-making and user organizations in the development of standards, and also by developing reports on an industry-wide basis to help engineers, code
3、officials, specifying groups, and users. The purpose of this technical note is to provide answers to commonly asked questions about use of HDPE (high density polyethylene) piping systems for water applications. This report has been prepared by PPI as a service to the industry. The information in thi
4、s report is offered in good faith and believed to be accurate at the time of its preparation, but is offered without any warranty, expressed or implied, including WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. Any reference to or testing of a particular proprietary product shoul
5、d not be construed as an endorsement by PPI, which does not endorse the proprietary products or processes of any manufacturer. The information in this report is offered for consideration by industry members in fulfilling their own compliance responsibilities. PPI assumes no responsibility for compli
6、ance with applicable laws and regulations. PPI intends to revise this report from time to time, in response to comments and suggestions from users of the report. Please send suggestions of improvements to PPI. Information on other publications can be obtained by contacting PPI directly or visiting t
7、he web site. The Plastics Pipe Institute, Inc. http:/www.plasticpipe.org November 2009 3 PPI TN-27: Frequently Asked Questions HDPE Pipe for Water Distribution and Transmission Applications INDEX Page A. General 3 B. Engineering Properties similarly, the working pressure rating for PVC DR 18 is 120
8、psig per AWWA C900-07, Equation 4. As such, PE 4710 has a higher working pressure rating than PVC at these common conditions. A summary is shown below: Working Pressure Rating (WPR) for HDPE and PVC per answer to Q. 13 WPR for PVC DR 18 per C900-07 WPR for PE 4710 DR 17 per C901-08 120 psig 125 psig
9、 5 Also, based on AWWA C900-07, Example B.2 modified with 5 fps recurring surge velocity, the estimated number of cycles to failure for the DR18 PVC pipe is less than 1 million cycles and the Fatigue Life is about 20 years which is less than half of the 50 year Design Life that was required in the e
10、xample; in addition, the assumed 55 cycles per day may not be adequate; assuming 1 surge cycle every 15 minutes (96 cycles per day) and the 5 fps recurring surge velocity results in a Fatigue Life of about 11 years. On the other hand, IGN 4-37-02, “Design Against Surge and Fatigue Conditions for The
11、rmoplastic Pipes”, can be used to show that under the same conditions, an HDPE DR17 pipe has a fatigue life of 10,000,000 cycles or in excess of 100 years. This striking difference is due to HDPEs toughness and fatigue resistance. Q. 14 Where can I find engineering properties such as the modulus and
12、 tensile strength values for HDPE pipes? Engineering data for HDPE pipes may be found in Chapter 3 of the PPIs Handbook* of Polyethylene Pipe, 2nd ed. Q. 15 Do I have to be concerned with the long-term effects of creep? All plastic materials, including HDPE and PVC, are subject to creep. Proper desi
13、gn, such as using the long-term modulus of the material where appropriate, accounts for creep effects. Q. 16 Is there a flow loss in HDPE pipe due to the inner bead resulting from the butt fusion process? The fusion bead has very little effect on the flow as it is basically rounded and protrudes ver
14、y little on the inside surface of the pipe Secondly, the Hazen-Williams C-factor of 150 takes into account the inner bead. Field tests confirm that a 150 C- factor used in the Hazen- Williams equation properly calculates actual flow and that the bead is of no hydraulic significance for either pressu
15、re or flow. The Hazen-Williams Friction Factor, C, for PE pipe was determined in a hydraulics laboratory using heat fusion joined lengths of pipe with the inner bead present. Q. 17 Will sunlight adversely affect HDPE pipe? Sunlight is not a concern if black pipe is used. Carbon black, utilized in mo
16、st all HDPE pipe is the most effective ultraviolet stabilizer and therefore, black is the recommended pipe color for exposed long term service or storage. Pipe of this color will provide decades of outdoor use similar to that of black power-line cable jacketing. HDPE pipe produced in non-black color
17、s may also be supplied for outdoor exposure (storage and use) but its life expectancy is much less and is usually specified for a particular time period. Questions on this topic should be referred to the pipe manufacturer. Q. 18 What is the life expectancy of HDPE pipe in water applications? Many in
18、stallations of HDPE pipe in water applications are already reaching 50 years of successful service. The polyethylene pipe industry estimates a service life for HDPE pipe to conservatively be 50-100 years. This relates to savings in replacement costs for generations to come. Q. 19 Will HDPE pipe floa
19、t in water? Yes, HDPE pipe, due to its density being slightly less than water, will float even when full of water. When it is desired to ensure flotation of the line, various forms of collars, saddles, and strap-on flotation devices are available. For underwater anchored pipeline installations, it i
20、s important to specify the proper weights and spacing of the weights. Screw-anchors are a practical alternative. Whenever possible, an underwater pipeline should be installed in a trench with protective crushed rock cover. Refer to Chapter 10 of the PPI Handbook of Polyethylene Pipe, 2nd ed. Q. 20 W
21、hat is the max-min temperature range across which HDPE pipe for water pressure applications may be used? HDPE pipes typical operating temperature range is from -40oF (-400C) to 140oF (60oC) although some products may be pressure rated for service as high as 180oF (82oC). Since water freezes below 32
22、oF (00C) the practical lower temperature limit for water is 32oF (0oC). Consult with the pipe producer for information on applications. Q. 21 When using HDPE pipe, will the pipe deliver the same flow-rate as the modestly larger ID ductile-iron pipe with the same outside diameter? The inside surface
23、of HDPE pipe is devoid of any 6 roughness which places it in the “smooth pipe” category, a category that results in the lowest resistance to fluid flow. For water applications, HDPE pipes Hazen and Williams C factor for design is 150 and does not change over time. In contrast, the C factor for iron
24、pipe and other traditional piping products declines dramatically over time due to corrosion and tuberculation or biological build-up. In view of these advantages, it is often possible to utilize HDPE pipe of smaller inside diameter than Ductile Iron pipe, and still achieve or exceed the projects req
25、uired flow parameters. A detailed examination of the flow computations is encouraged. For flow factors and hydraulic design equations refer to Chapter 6 of PPIs Handbook of Polyethylene Pipe, 2nd ed. Q. 22 What is the maximum water pressure rating for HDPE pipe? The maximum rating depends on several
26、 factors, the material designation code from which the pipe is made, the DR of the pipe, and the design operating temperature of the application. Refer to the tables below for sample ratings and allowable pressures: The following table gives the Pressure Class per AWWA C901-08, the Pressure Rating a
27、nd Allowable Total Pressure During Surge for PE4710 pipe at 80o F. Sample Pipe Dimension Ratio (DR) Pressure Class Pressure Rating Allowable Total Pressure During Recurring Surge Allowable Total Pressure During Occasional Surge DR 9 250 psi 250 psi 375 psi 500 psi DR 11 200 psi 200 psi 300 psi 400 p
28、si DR 17 125 psi 125 psi 185 psi 250 psi The following table gives the Pressure Class per AWWA C901-08 and AWWA C906-07, the Pressure Rating and Allowable Total Pressure During for PE3608 pipe at 80oF. Sample Pipe Dimension Ratio (DR) Pressure Class Pressure Rating Allowable Total Pressure During Re
29、curring Surge Allowable Total Pressure During Occasional Surge DR 9 200 psi 200 psi 300 psi 400 psi DR 11 160 psi 160 psi 240 psi 320 psi DR 17 100 psi 100 psi 150 psi 200 psi Q. 23 What is the safe peak pressure (surge plus pumping) for HDPE pipe? AWWA C901 defines two types of surge pressure, recu
30、rring and occasional. The safe peak pressure or allowed total pressure for HDPE pipe is 1.5 times the pipes pressure rating for recurring surge, and 2.0 times the pipes pressure rating for occasional surge. For instance a DR 11 PE 4710 has a pressure rating of 200 psig at 80oF and can safely handle
31、total pressure during recurring surge of 300 psig and total pressure during an occasional surge of 400 psig. Refer to the answer under Q. 22 for additional data. Q. 24 What is the maximum flow velocity for HDPE Pipe? In a pumped system the maximum operating velocity is limited by the surge pressure
32、capacity of the pipe. The Plastics Pipe Institutes Handbook of Polyethylene Pipe states that “if surge is not a consideration, water flow velocities exceeding 25 feet per second may be acceptable.” Q. 25 How does surge pressure in HDPE pipe compare with DI or PVC pipe? Surge pressures in HDPE pipe a
33、re significantly lower than in DI pipe and lower than PVC pipe due to the lower value of dynamic modulus for HDPE. For example, a velocity change of 5 fps would cause a 51 psig surge in 7 HDPE DR 17 pipe, a 87 psig surge in PVC DR 18 pipe, and a 262 psig surge in DI Class 350 lined pipe. Lower surge
34、 pressures often means longer life for pumps and valves in an HDPE pipeline, as well as lower pressure class pipes. Q. 26 How does HDPE pipes capacity for recurring surge pressures (fatigue) compare to other pipes? HDPE has exceptional capacity for handling recurring surge pressures. For example, in
35、 AWWA standards recurring surge pressure must be subtracted from PVC pipes Pressure Class whereas PE has resistance up to 150% of its Pressure Class. Marshall and Brogden report on the cyclical fatigue strength of PVC and HDPE and their report shows, at a cyclical stress range of 10 MPa (1450 psi) s
36、ome PVC pipes failed at approximately 400,000 cycles whereas HDPE pipe reaches 10,000,000 million cycles before failure. Q. 27 What are the safe maximum and minimum burial depths for HDPE pipe? Safe burial depths vary and should be calculated. In lieu of calculations, AWWA states that for an embedme
37、nt soil with an E of 1000 psi and no surface water, HDPE pipes with DRs ranging from 7.3 to 21 can be safely buried from a depth of 2 ft to 25 ft where no traffic load is present and from 3 ft to 25 ft where H20 live load is present. However, most HDPE pipes can be buried to deeper depths, e.g. HDPE
38、 leachate collection pipe in landfills often have cover depths in excess of a hundred feet. Equations for calculating burial depth can be found in Chapter 6 of PPIs Handbook of Polyethylene Pipe, 2nd ed. Q. 28 Is HDPE pipe suitable for use under railroads? While HDPE pipe is structurally capable of
39、direct burial under railroads it is not recommended under a railroad mainline unless it is encased for safety reasons. In fact, many if not most railroad specifications require that pressurized pipes located beneath rail lines must be encased, and this requirement applies regardless of pipe material
40、. However, uncased direct burial may be considered for use under rail lines located within plant yards. Q. 29 Are thrust blocks required with HDPE pipelines? No. HDPE pipe and fittings joined by heat fusion are self-restrained in all applications, and therefore do not require thrust blocks, provided
41、 the entire system is fused. Thrust blocks may be required in cases where special gasketed mechanical fittings are used. This may be necessary to prevent separation of the gasketed joint just as it is required for gasketed PVC and ductile iron pipe in pressure applications. Detailed discussion of th
42、is topic can be found in Chapter 9 of PPIs Handbook of Polyethylene Pipe, 2nd ed. Publications available from the pipe manufacturer may also cover this subject. Q. 30 Can pipe-bursting technology be used on ductile-iron and cast-iron pipes? Yes, pipe bursting has proven to be a very valuable means o
43、f pipeline rehabilitation. The pipeline rehabilitation industry has adopted “pipe bursting” as the name of the process of rupturing brittle pipes (e.g., cast iron, clay, etc). A variation employed for ductile materials (i.e., ductile iron, steel, etc.), is called “pipe splitting”, which uses cutters
44、 to achieve enlargement of the host pipe. Preparation of the host pipe to receive the HDPE pipe is accomplished with a cone shaped head in both bursting and splitting processes. Refer to PPI Handbook of Polyethylene Pipe, 2nd ed., Chp 16. Q. 31 How does the impact strength of HDPE compare with other
45、 pipes? HDPE is a ductile material and has exceptional impact strength. HDPEs superior impact strength provides a piping system that is near impervious to impact damage and to damage from improper tapping. In the real world, engineers understand that pipes must be tough and resist impact and handlin
46、g damage. HDPE pipes are field tested and proven to be impact tough. Q. 32 Will the presence of hydrocarbons in soils in which HDPE pipe is buried affect the pipe or permeate through its wall into the water stream? AWWA has addressed concerns regarding hydrocarbon permeation by including a permeatio
47、n statement in all of its pipe standards including standards for polyethylene (PE) (C901-08 p. 6, C906-07 p. 6), polyvinyl chloride (PVC) (C900-07 p. 6, C905-97 p. 3), steel (C200-05, p. 7), ductile Iron (C110-03, p. 3), and others. Hydrocarbons do not degrade polyethylene but can diffuse through th
48、e wall of HDPE pipe in areas of gross contamination. The 8 exterior contact may affect saddle fusion connections, thus, after HDPE pipes have been exposed to grossly contaminated soils, mechanical connections may be preferred. In addition, while measures need to be taken to limit the impact of hydro
49、carbon permeation, the vast majority of HDPE water pipe installations will never be impacted by this problem. For more detailed discussion and information on this topic log on to: http:/plasticpipe.org/pdf/ppi-comment-permeation-hydrocarbons.pdf C. JOINING Q. 33 How are HDPE pipe segments joined and connected? HDPE pipe is easily and dependably joined using the standardized butt-fusion procedure. In this process matching ends of the pipes to be joined are aligned and heated with standard tools until the surfaces have become molten. When engaged under moderat
