INSTALLATION ADVANTAGES OF DRISCOPLEX® 4000 / 4100 PIPE

HEAT FUSION OF POLYETHYLENE PIPE
Heat fusion of polyethylene pipe is proven, reliable and time-tested, with more than 50 years of success. The procedure is standardized, published in ASTM F2620, and there are thousands of trained operators throughout the nation. Compared to fusing other types of thermoplastic pipes, the process for polyethylene pipe is easier to learn, more forgiving and results in higher productivity rates. Joints have the same tensile strength as the pipe and no thrust blocks or restraints are required at fittings and bends. Polyethylene pipe can be fused and installed in subfreezing weather. See PP750, Heat Fusion Joining Procedures and Qualification Guide.

EXCEPTIONAL FOR TRENCHLESS INSTALLATIONS
DriscoPlex® pipe is flexible and tough. As a result, polyethylene pipes are well-suited for horizontal directional drilling, plowing, river and water crossings, pipe bursting and sliplining. Installers like the fact that polyethylene pipe is tough enough to stand up to rigors of field handling with higher impact resistance, greater ductility, more flexibility and higher resistance to RCP than its closest thermoplastic competitor. There is a wealth of technical publications for trenchless usage of polyethylene pipe including the Handbook of Polyethylene Pipe. See Chapter 11 “Pipeline Rehabilitation by Sliplining with PE Pipe,” Chapter 12, “Horizontal Directional Drilling,” and Chapter 16, “Pipe Bursting.

SMALL BEND RADIUS; BIG INSTALLATION ADVANTAGE
Installers often choose DriscoPlex® 4000 / 4100 pipe because of its flexibility and tight bend radius. The bend radius is the smallest radius to which a pipe can be bent without causing permanent damage. In open-cut and above-grade applications pipe may be strung around corners or over swales, often eliminating fittings. Polyethylene water mains can typically be laid around a cul-de-sac without the use of fittings. In trenchless applications, a more flexible pipe results in shorter insertions pits and reduced costs. For horizontal directional drilling, a tight bend radius greatly reduces laydown space, the area where pipe is placed prior to pullback. In tight suburban right-of-ways, it is often necessary to string pipe around corners or bends while awaiting pullback. Flexibility facilitates this and polyethylene pipe can be curved to a radius 1/10th of that of its closest thermoplastic pipe competitor. Thus, it is more convenient for the installer and less disruptive to the public by eliminating inconvenient street closures. In addition, this extra flexibility provides a safety factor against damage during pullback as the polyethylene pipe will almost always have a tighter bending radius than the drill rod used to install it. Thus, polyethylene pipe is protected from over-bending unlike other fused thermoplastic pipes. Bend radius should not be confused with the length of the pipe required to make a specific turn. Table 7 gives both the bend radius and the length required to make a 90°  bend. For additional information on bending see Technical Note PP819, Field Bending of PE Pipe.

SAFE PULL STRENGTH
Most trenchless methods using polyethylene pipe are pull-in or pullback techniques. Pull-in distance is often proportional to the pipe’s safe pull strength, which is the maximum tensile force that can be applied to the pipe with adequate assurance that the pipe will not be damaged or changed in any way that could affect its long term performance. The maximum safe tensile stress in DriscoPlex® PE4710 pipe for a 10 hour pull is 1300 psi. Table 8 lists the safe pull strength for DriscoPlex® 4000 / 4100 pipe.

HORIZONTAL DIRECTIONAL DRILLING RESOURCES
In developing plans for a directional drilling project, the designer must determine what DR to use. In addition to working-pressure considerations, DR selection depends on how much force will be required to pull the pipe back into the bore and on how much external force will be applied to the pipe during and afterward from the drilling slurry, soil and groundwater. Several resources are available to help the designer select an appropriate DR. Some of these resources offer additional and important information for planning a crossing. Resources include the following:

  • ASTM F1962, a standard guide for the design of a directional drilled crossing with PE pipe
  • PPI Handbook of Polyethylene Pipe, Chapter 12 Horizontal Directional Drilling 
  • ASCE MOP 108, Pipeline Design for Installation by Horizontal Directional Drilling 
  • Plastics Pipe Institute’s Technical Report 46, Guidelines for Use of Mini-Horizontal Directional Drilling for Placement of Polyethylene Pipe
  • PPI BoreAid Calculator , useful for making a preliminary evaluation of the DR requirements and the anticipated pullback force

BURIAL IN OPEN-CUT TRENCHING
The PPI Handbook of Polyethylene Pipe, Chapter 6, gives design guidance for open-cut trench installations of polyethylene pipes. HDPE pipe has been placed in landfills with cover depths well in excess of 100 feet. However, most municipal applications are significantly shallower. For the convenience of the designer, AWWA M-55, PE Pipe—Design and Installation, see Table 9, offers a safe design window. Pipe within the window meets the design deflection limits of M-55 and provide at least a 2:1 Safety Factor against buckling. For deeper depths or heavier loading, calculations are required. 

Like all piping materials, HDPE piping must be properly installed. DriscoPlex® 4000/4100 pipe should be installed in accordance with ASTM D 2774 Standard Practice for Underground Installation of Thermoplastic Pressure Piping and the Performance Pipe Field Handbook. HDPE is a flexible piping material that works together with its soil embedment to sustain the earth and live loads above it. Suitable embedment is required to provide support around the pipe, and embedment materials must be placed so that the pipe is properly surrounded. Under roadways, compacted coarse sands and gravels are preferred, but other materials may be used under the direction of the design engineer. For more information on installation of 12” and smaller diameter DriscoPlex® pipe see the Plastics Pipe Institute’s Polyethylene Piping Systems Field Manual for Municipal Water Applications. Installation by plowing and planting is covered in the Performance Pipe Field Handbook.

ADDITIONAL INSTALLATION CONSIDERATIONS

GROUND MOVEMENT AND SEISMIC RESISTANCE
A large number of water main breaks occur every year due to soil settlement, freeze and thaw cycles and shrinking or swelling of expansive soils; not to mention the occasional widespread damage that accompanies earthquakes. Polyethylene’s flexibility and its fusion joints make it considerably less susceptible to damage from ground movement. California gas utilities recognize polyethylene’s excellent record in enduring seismic events without damage.

MECHANICAL RESTRAINT AND THE POISSON EFFECT
While polyethylene pipe is self-restrained through the butt fusion joint, when it connects to a gasket jointed pipeline the polyethylene pipe must be anchored or the gasket joints upstream (or downstream) from the transition must be restrained to prevent pullout of the gasket joints. Additional information on how to design for this is covered in the Performance Pipe Technical Note "Mechanical Restraint and the Poisson Effect."

ABOVE GRADE AND AERIAL INSTALLATION
Performance Pipe black polyethylene pipe contains carbon black allowing indefinite above grade storage and use. Design considerations for above grade applications are available in the Performance Pipe Technical Notes Thermal Effects and Above Grade Pipe Supports.

VACUUM RESISTANCE (EXTERNAL PRESSURE)
Many pipelines operate under full or partial vacuum or experience negative internal pressures when subject to pressure surges. External pressure exceeding the internal pressure (external differential pressure) creates the same effect. Pipelines may be subject to external pressure during installation, submergence, grouting of sliplined pipe or directional drilling. All pipes have a limit to the amount of external differential pressure (or vacuum) they can withstand. Exceeding that limit will cause the pipe to collapse. Table 10 gives the allowable external differential pressure based on Equation 3-39 in Chapter 6 of the Handbook of Polyethylene Pipe with a safety factor of two against collapse and with 3 perecent ovality in the pipe assumed. Higher resistance to collapse can be achieved by embedding the pipe in soil, flowable fill, grout, or concrete. For additional temperatures, see the Performance Pipe Field Handbook.

FITTINGS, CONNECTIONS, AND REPAIR FITTINGS
Performance Pipe manufactures HDPE molded Fittings including tees and elbows in sizes through 8” diameter. Flange adapters for flange connections are available through 24” diameter. MJ Adapters for both DriscoPlex® 4000 and 4100 pipe are available through 12” diameter. Larger fittings are available through third party fabricators.

TRANSITION TO NON-POLYETHYLENE PIPES
Polyethylene pipe can be conveniently connected to metallic valves, pumps and even pipe. Normally the connection is made using a polyethylene Van Stone style Flange Adapter with a metallic backup ring which mates to a metallic flange or using a polyethylene Mechanical Joint (MJ) Adapter which mates to a DI mechanical joint bell. The MJ Adapter works with both IPS and DIPS polyethylene pipe. Acceptable methods also include metallic transition couplings that slide on, seal, and grip the polyethylene pipe or metallic transition couplings that slide on and seal but require additional external restraint rings. These types of couplings may require the use of an insert stiffener in the polyethylene pipe. DriscoPlex® 4000 pipe may be inserted directly into an MJ Bell. This requires placing an insert stiffener inside the end of the DriscoPlex® pipe and restraining the connection with an external ring or clamp on the DriscoPlex® pipe. When selecting mechanical couplings or components for use with DriscoPlex® pipe, make sure the mechanical coupling manufacturer recommends the particular part for HDPE pipe. For additional information on HDPE to non-HDPE pipe transitions, see

  • Plastics Pipe Institute’s Technical Note 36 General Guidelines for Connecting Potable Water HDPE Pressure Pipes to DI and PVC Piping Systems
  • Polyethylene Piping Systems Field Manual for Municipal Water Applications

TAPPING
A variety of heat fusion and mechanical fittings make hot or cold tapping a straightforward process. Heat fusion jointed products include saddle fusion tapping tees, electrofusion tapping tees and branch-saddles. A number of manufacturers produce metallic full body tapping saddles and sleeves for polyethylene pipe. Performance Pipe recommends that the manufacturer be contacted to make sure their saddles work with polyethylene pipes. Service saddles are available as well. These may come with double or extra wide straps, with spring washers or with both.

REPAIR
Polyethylene pipe has an excellent field record. However, circumstances may arise where repair is necessary. The most likely form of damage is impact or an underground strike, which is usually localized. A variety of repair clamps (both mechanical and electrofusion) and tapping saddles are available. If a section of pipe has to be removed, a new pup piece can be inserted using mechanical couplings, polyethylene flange adapters or electrofusion couplings.