Geothermal Frequently Asked Questions

Any technical information contained herein is provided for convenience only, without any warranty or guarantee of any kind, either express or implied; furthermore, no party should rely on any such technical information without prior independent verification. "Technical information" includes any technical advice, recommendations, testing, or analysis, including, without limitation, information as it may relate to the selection of a product for a specific use and application.

Design

Yes. PlexCalc® II will do many of the calculations that are in the Performance Pipe Engineering Manual and the PPI Handbook of Polyethylene Pipe. Use the Questions and Feedback form to order our literature on CD-Rom. The CD contains PlexCalc® II.
Pressure ratings are given in PP401, Pressure Ratings for Municipal and Industrial Pipes as well as on Size and Dimension Sheets for each specific product.
Normally it is not a concern for buried municipal water or sewer pipelines. Soil will provide sufficient restraint against movement. However, thermal effects must be considered for above grade or aerial pipelines. The unrestrained expansion/contraction coefficient for PE pipes is approximately 9 x 10-5 in/in-oF. See Technical Note PP814 Thermal Effects for more information.
  1. Safe burial depths vary and should be calculated. In lieu of calculations AWWA says 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.
  2. Most pipes can be buried to deeper depths. Equations for calculating burial depth may be found in Chapter 6 of the PPI Handbook of Polyethylene Pipe.
Design information for HDPE pipe is located on the Download Page of Performance Pipe’s website. You will find links to Technical Notes, the Engineering Manual, and the Field Handbook. There is also a link to the Plastics Pipe Institute’s Handbook of Polyethylene Pipe. Other resources include AWWA Manual M-55 and various ASCE publications including MOP 108 Pipeline Design for Horizontal Directional Drilling and MOP 112 Pipe Bursting Project
This information is given in the Size and Dimension Sheets, found in the Submittals section of our website.
Generally there are better ways to handle temperature change in an above grade or aerial pipeline than using expansion joints. See Technical Note PP814, "Thermal Effects".  If an expansion joint is used, the joint should be specifically manufactured for use with HDPE pipe. Use of an improper expansion joint such as one designed for steel pipe could damage the PE pipe.

Engineering Properties

PE has exceptional capacity for handling recurring surge pressure. For instance, AWWA standards demonstrate that PE has resistance up to 150% of its pressure class under recurring surge pressure . Additionally, in a report on the cyclical fatigue strength of PVC and HDPE, Marshall and Brogden found that at a cyclical stress range of 10 Mpa (1450 psi), HDPE pipe reached 10,000,000 million cycles before failure.
No. PE pipe does not tuberculate. Tuberculation is caused by ferrous seeking bacteria in iron, cast iron, or ductile iron pipes. PE is immune to this attack.
Engineering data for HDPE and PE pipes may be found in Chapter 3 of the Plastics Pipe Institute’s Handbook of Polyethylene Pipe which may be found at www.plasticpipe.org. Engineering information may also be found in the various Performance Pipe Technical Notes. Look on the Download Page for a link to Technical Notes.
An Army Corps of Engineers study reported that PE pipe wore at a rate of 3 to 5 times less than steel pipe in sand slurry. Best results are obtained with PE when the flow is turbulent to keep particles suspended. See Chapter 6 of the PPI Handbook of PE Pipe for slurry applications.
  1. PE is a ductile material and has exceptional impact strength. As an example, AWWA publishes an Izod Impact resistance value of 10-12 ft-lbf/in for HDPE and of 0.65 ft-lbf/in. for PVC. PE superior impact strength provides a piping system that is near impervious to impact damage and to damage from improper tapping.
  2. In the real world, engineers understand that pipes must be tough and resist impact and handling damage. PE pipes are field tested and proven to be impact tough.

General

DR stands for dimension ratio, which is the average outside diameter of a PE pipe divided by its minimum wall thickness. A standard dimension ratio (SDR) is a specific DR based on an 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 the converse is not true.
Yes. Every day more utilities realize the advantages of trenchless technology. More trenchless projects are being installed than in the past because of cost savings. Savings 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).
Aside from the low cost of PE pipe, long term savings may be realized due to PE pipe’s fusion joints and corrosion resistance. Leakage rates for fused PE systems are far lower than for gasket jointed DI or PVC systems. PE pipe is resistant to corrosion. It will not undergo tuberculation and is unaffected by “hot” soils or electrogalvanic corrosion, thus PE pipes last longer in the ground. Additional savings may be realized by trenchless installation. Go to www.PEpipe.org for more information.
A fusion joined pipeline may be thought of as a continuous pipeline without joints. On the other hand, gasket joints are a 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 subtrench consolidation occurs, if significant thermal change occurs, or if gaskets are blown out due to surge pressures. Fused joints are generally considered superior to gasket joints for leak prevention.
Yes. It is safe when manufactured, used, or incinerated. It helps preserve water and electricity as there is no water loss through its fused joints. No toxins are released during the creation or disposal of PE pipe.
HDPE stands for high density polyethylene.

Hydraulics

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.”
AWWA C906 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 DR17 pipe which has a pressure rating of 100 psi can safely handle total pressure during recurring surge of 150 psi and total pressure during an occasional surge of 200 psi.
The C factor for HDPE butted fused pipe was found experimentally to be about 155. A conservative design value is 150. DI manufacturers publish an initial value of 140 for cement lined DI pipe. Many engineers assume that this value will be reduced over the life of a pipeline due to corrosion and use design values of 120 or 100. Such a reduction is not required for HDPE pipe. AWWA M-55 states that “No allowance for corrosion and therefore, no subsequent lowering of the flow capacity need be considered when using PE pipe.”
No. The Hazen Williams C factor of 155 was determined with pipe that was fused together and thus contained inner fusion beads.
Surge pressures in HDPE pipe are significantly lower than in DI pipe and lower than PVC pipe due to the lower value of dynamic modulus for HDPE. For example, in a typical 8” line a velocity change of 5 fps would cause a 51 psi surge in HDPE DR17 pipe, a 87 psi surge in PVC DR18 pipe, and a 262 psi surge in DI Class 350 lined pipe. Lower surge pressures often mean longer life for pumps and valves in an HDPE pipeline, as well as lower pressure class pipes.

Installation

See Performance Pipe Technical Note PP802, “Leak Testing”.
See Performance Pipe Technical Note PP803, “Pull-in Applications”.
See Performance Pipe's Field Handbook found under Engineering Information on the Download Page. Information is also given in the PPI Handbook of Polyethylene Pipe, Chapter 2.
AWWA M-55 states that “minor scratches or scuffing will not impair serviceability” and that “pipe with gouges or cuts in excess of 10 percent of the product wall should not normally be used.”
No. When transitioning from an HDPE pipeline into a DI or PVC pipeline with unrestrained gasket joints, it is necessary to provide restraint. See Performance Pipe Technical Note PP813 Mechanical Restraint and Poisson Effect for details.
HDPE pipe does not undergo galvanic corrosion; therefore, it may be safely installed in hot soils that would attack metal pipes without any cathodic protection.
Yes.
There are no hazardous fumes associated with the cutting of HDPE pipe.
Yes. The same embedment materials are generally suitable; however, the specific parameters of the application may influence this somewhat. For instance, very high DR pipes in shallow cover subjected to a live load may require a higher level of compaction for the embedment material than required by a lower DR PE pipe or stiffer pipe.
  1. PE pipes can be safely bent to a radius about 1/10th that of the same size PVC pipe. See Performance Pipe Technical Note PP819, “Field Bending of DriscoPlex® Pipe”.
  2. HDPE pipe can be cold bent to the dimensions shown below for a long term application based on the pipe DR. (The pipes may be bent to a tighter radius during installation see Technical Note PP819)

 Pipe DR

Minimum Long Term Cold
Bending Radius

 9 or less  20 times pipe OD
 11 and 13.5  25 times pipe OD
 15.5, 17, and 21  27 times pie OD
 26  34 times pipe OD
 32.5  42 times pipe OD
 41  52 times pipe OD
 Fitting or flange present in bend  100 times pipe OD

Joining

Fusion time depends on the pipe size and DR as well as field conditions. Larger diameter and heavier wall pipes take longer to fuse as more time is required to heat and cool the pipe. For instance, 6” DR11 pipe might take 10 to 12 minutes including the time to allow the joint to cool under pressure.
No. Heat fusion (which includes butt fusion, socket fusion, and electrofusion) and mechanical joints are the only permitted methods for joining HDPE pipe.
Manufacturers of fusion equipment include McElroy Manufacturing, Connectra Fusion Technologies, Ritmo America, and Wegner Welding. The equipment is readily available through distributors.
Yes. You have to protect the joint during cold weather fusion from wind, moisture, and blowing snow so that the heater plate uniformly heats the end of the pipes. Guidelines for cold weather fusion are given in PP750, Heat Fusion Joining Procedures and Qualification Guide found on the Download Page.
ASTM F2620 addresses heat fusion of HDPE pipes. Also, see Performance Pipe PP750, Heat Fusion Joining Procedures and Qualification Guide for information on fusing DriscoPlex® pipe products. Fusion information on Performance Pipe historical products such as Driscopipe® and Plexco® pipe can be found on the Download Page
  1. Yes. Polyethylene pipe has been heat fused for almost fifty years in a wide range of service applications. The window of conditions that are acceptable for good quality fusion joints is broad, and the long term performance is documented in actual field applications as well as in long term testing. PE pipe joints are standardized through ASTM fusion procedures as well as recognized in AWWA, PPI, ASME, and other industry standards.
  2. There are new technologies that attempt to mimic the advantages of PE fused joints for other pipe materials. However, these materials do not have the history, the proven performance, and the industry peer reviewed standardization of PE pipe fusion joints.

Manufacturing

A complete line of molded PE fittings including tees and MJ adapters up to 8” IPS and molded PE flange adapters up to 18” are available from Performance Pipe. For more information, see our Fittings page. Additional fittings and sizes are available through other PE suppliers.
In 2005, ASTM allowed the introduction of new codes for PE pipes. Prior to that time HDPE had a material designation code of PE3408. Under the new system, material with a PE3408 code is classified either as PE3608 or PE4710. To facilitate a smooth transition manufacturers are allowed to dual mark pipe as PE3408/3608 or PE3408/4710. For details on this transition, see Technical Note PP816 PE3608 and PE4710 Materials Designation Codes and Pipe Pressure Ratings.
PE coils are available in diameter sizes up to 6”. Typical coil lengths are 500 ft. and 1000ft. Availability varies with pipe diameter.

Mechanical

Yes, a soft pig should be used.
If the ditch can be dewatered and the pipe dried off, fusion repair may be used. Otherwise, a mechanical repair is recommended.

Generally speaking, many saddle manufacturers have saddles/sleeves specifically made for use with HDPE pipe, and they are typically the same as those used with PVC pipe and sometimes the same as those used with ductile iron pipe. Service saddles often include double straps or extra wide straps and Belleville (spring) washers for use with HDPE pipe so that the tension on the strap remains constant once the nuts are properly torqued. As for tapping sleeves, some manufacturers such as JCM indicate that as long as it is a full sleeve in accordance with AWWA C110/111, it can be used on HDPE pipe. Check with the manufacturer for specific information.

 

The most common method is to use a PE MJ adapter to connect the PE pipe end in a DI MJ bell using the bolt and gland kit supplied by the PE MJ manufacturer. See Technical Note PP812 MJ Adapter Connections for more information. Connections may also be made using a flange adapter which is essentially a HDPE Van Stone style flange with a backup ring. See Technical Note PP811 PE Flange Adapter for details. DIPS sizes of HDPE pipe may be inserted directly into an MJ bell with a restraint ring and stiffener for the HDPE pipe. When jointing HDPE pipe to a DI pipeline either the DI joints must be restrained or the transition connection must be anchored. See Technical Note PP813 Mechanical Restraints and Poisson Effects.
Yes. For PE pipe, connections to butterfly valves are usually made with Beveled Flange Adapters. This prevents interference between the valve and the inside diameter of the pipe.
No. Tapped threads are not recommended for use on PE. The industry standards for service taps to HDPE mains recommend the use of saddle fusion tapping tees, electrofusion tapping tees, Fuse-A-corps, branch-saddles, and certain metal mechanical clamps.
  1. When external third-party damage does occur, there are several repair methods. Punctures in PE pipe may be repaired using electrofusion repair saddles or mechanical repair clamps.
  2. If the damage is sufficiently extensive that a pipe section must be removed, the pipe section may be replaced with a spool piece of the pipe connected on each end to the exiting pipe using mechanical fittings, electrofusion couplings, or flanged connections. Refer to the PPI Handbook on HDPE Pipe Repair and Maintenance.
HDPE pipe can be cold or hot/wet (under pressure) tapped using piping products presently available. Saddle fusion tapping tees, electrofusion tapping tees, Fuse-A-Corps, and branch-saddles are readily available in the industry. There are also bolt-on mechanical connections qualified for use with HDPE pipelines as well.
Insert stiffeners are normally used when inserting HDPE pipe into a PVC bell or DI MJ bell. The stiffener ensures compression of the gasket to the PE pipe. Stiffeners are also typically used in FM MJ adapters and in some large diameter MJ adapters. Check with the MJ adapter manufacturer for their specific recommendations.
PE is considered to be a re-roundable pipe and the cold ring clamps of a McElroy fusion machine may be used to re-round larger pipe. When desired, expandable stiffeners are available. They can be inserted into the pipe and then expanded with a triangular wedge. Romac makes these for pipes up to 12”. Cascade Waterworks sells these up to 20” DIPS.