YES. HDPE pipes certified for potable water applications are produced from pressure rated polyethylene compounds approved by NSF for public drinking water service.
High Density Polyethylene
HDPE pipe provides the lowest life cycle cost when compared to other systems due to significantly reduced or no leakage, increased billable dollars, water conservation, fewer new water treatment plans, reduced maintenance crews, reduced seasonal water main breaks, and no loss in flow capacity over the long term.
DR stands for Dimension Ration which is the average outside diameter (note: DR is also used for pvc pipe) divided by the minimum wall thickness. A Standard Dimension Ratio (SDR) is a specific DR based on ANSI preferred number series. The use of SDR’s enables manufacturers to produce pipe to a set of standardized DR’s. SDR’s include 9, 11, 13.5, 17, 21, 26, and 32.5. All SDR’s are DR’s, but not all DR’s are SDR’s.
A fusion joined pipeline may be thought of as a continuous pipeline without joints. On the other hand, gasket joints are a potential source of leakage and lost water in many water systems. Leaks may occur if the gasket is improperly installed, if dirt or grit sticks to the gasket, if the gasket is not properly lubricated, if negative pressure (vacuum) occurs in the pipeline, if ground movement or sub-trench consolidation occurs, if significant thermal change occurs and if gaskets are blown out due to surge pressures. Fused joints are far superior to gasket joints for leak prevention.
Everyday more utilities realize the advantages of trenchless technologies. More trenchless projects are being installed than in the past because of cost savings. Savings can result from quicker installations, faster permitting and design time, fewer disruptions to business and residents, less damage to parks and tress, and less disturbance to road beds (and subsequent road repair.)
No. All pipes expand and contract with change in temperature. The key is management of the resultant thermal strain. As with all materials, expansion and contraction must be taken into consideration when designing a HDPE piping system. Buried pipelines usually do not move due to soil friction. However, thermal effects must be considered for above grade applications. The unrestrained coefficient of thermal expansion for HDPE pipe is approximately 9x10-5 in/in/oF. Information regarding thermal calculations for restrained and un- restrained above-ground and slip-lined pipelines can be found in PPI’s Handbook of Polyethylene Pipe, 2nd ed.
No. When HDPE pipe is buried, the temperature of the system becomes much more stable than an above ground pipeline and therefore will exhibit far less dimensional change. In most systems, buried HDPE pipe does not move after it is buried.
All plastic materials, including HDPE and PVC, are subject to creep. Proper design, such as using the long-term modulus of the material where appropriate, accounts for creep effects.
The fusion bead has very little effect on the flow as it is basically rounded and protrudes very 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 pressure 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.
Sunlight is not a concern if black pipe is used. Carbon black, utilized in most 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 colors 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.
Many installations 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.
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 is 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.
HDPE pipe’s 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 32oF (00C) the practical lower temperature limit for water is 32oF (0oC). Consult with the pipe producer for information on applications.
Yes, The inside surface of HDPE pipe is devoid of any roughness which places it in the “smooth pipe” category, a category that results in the lowest resistance to fluid flow. For water applications, HDPE pipe’s Hazen and Williams C factor for design is 150 and does not change over time. In contrast, the C factor for iron 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 project’s required flow parameters. A detailed examination of the flow computations is encouraged.
The maximum water pressure depends on several factors, the material designation code from which the pipe is made, the DR of the pipe, and the design operating temperature of the application.
AWWA C901 defines two types of surge pressure, recurring and occasional. The safe peak pressure or allowed total pressure for HDPE pipe is 1.5 times the pipe’s pressure rating for recurring surge, and 2.0 times the pipe’s 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 total pressure during recurring surge of 300 psig and total pressure during an occasional surge of 400 psig.
In a pumped system the maximum operating velocity is limited by the surge pressure capacity of the pipe. The Plastics Pipe Institute’s Handbook of Polyethylene Pipe states that “if surge is not a consideration, water flow velocities exceeding 25 feet per second may be acceptable.”
HDPE has exceptional capacity for handling recurring surge pressures. For example, in AWWA standards recurring surge pressure must be subtracted from PVC pipe’s 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) some PVC pipes failed at approximately 400,000 cycles whereas HDPE pipe reaches 10,000,000 million cycles before failure.
Safe burial depths vary and should be calculated. In lieu of calculations, AWWA states that for an embedment soil with an E’ of 1000 psi and no surface water, HDPE pipes with DR’s 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 leachate collection pipe in landfills often have cover depths in excess of a hundred feet.
No. HDPE pipe and fittings joined by heat fusion are self-restrained in all applications, and therefore do not require thrust blocks, provided 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.
HDPE is a ductile material and has exceptional impact strength. HDPE’s 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 handling damage. HDPE pipes are field tested and proven to be impact tough.
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 moderate pressure, the melt faces flow together forming a monolithic, homogeneous joint that, as the material cools, yields joints that are as strong as or stronger than the pipe itself.
The time required to make a butt fusion joint is dependent upon the pipe wall thickness and diameter, and the field weather conditions. The thicker the pipe being joined the longer it takes to make a butt fusion joint, due to heating and cooling time requirements. An estimate on 6” DR11 pipe would be about 4 to 5 minutes to load the pipe, face it, heat it and apply the fusion force. An additional 5 to 6 minutes would be required to let the joint cool under pressure. A rough guide is to approximate 1-1/2 to 2 minutes per diameter-inch per joint. Alternatively, the use of certain other proven and validated industry fusion technologies may shorten the cooling time.
First, insure the fusion joint is made in accordance with PPI and/or the pipe/fitting manufacturer’s fusion procedure guidelines. This could be accomplished by recording either manually or by an electronic data logging device the critical parameters of each fusion joint and by comparing this data to the approved standard to prevent an improperly fused joint from being buried in the ground. Second, the time proven method used for field inspection of fusion joints is visual examination of the melt bead. Many pipe manufacturers provide printed or video examples of melt beads illustrating quality and sub-standard heat-fusion joints.
Most people can be trained quickly to properly fuse HDPE pipe; for assistance, refer to PPI TN42, Recommended Minimum Training Guidelines for PE Pipe Butt Fusion Training Operators for Municipal and Industrial Projects.
Some pipe manufacturers and authorized distributors of pipe, fittings and fusion equipment conduct training and operator qualification programs year round, both on-site and at their facilities. Details of a suggested training program are outlined in a PPI publication TN42, entitled, “Recommended Minimum Training Guidelines for PE Pipe Butt Fusion Training Operators for Municipal and Industrial Projects.” The PPI or pipe manufacturer’s recommended fusion joining procedures must be followed to assure a quality joint is produced.
Fittings are available in sizes from 1⁄2” to 65”. Molded elbows, tees and concentric reducers are standard up to 12”. Fabricated fittings that include elbows, equal tees, reducing tees, laterals, crosses, concentric reducers, and eccentric reducers are usually stocked up to 24”. Fabricated fittings up to 65” that include elbows, equal tees, reducing tees, laterals, crosses, concentric reducers, and eccentric reducers are available by custom fabrication. Flanges, mechanical-joint adapters, outlet branch saddles, pull heads, gasket joint adapters, MIPT, FIPT and Weld End connections are available in most sizes.