Read on for answers to the most common butt welding questions.
Q. 1 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 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. There are several other well established heat fusion procedures used to join HDPE pipe such as electrofusion, which is exceptionally well suited for the assembly of pipe to fittings, or for making tie-ins or repairs, and saddle fusion which is used for the attachment of service fittings to HDPE mains. More details of some of these heat fusion procedures can be found in ASTM standards such as F2620, Standard Practice for Heat Fusion Joining of Polyethylene Pipe and Fittings, AWWA Manual M55, “PE Pipe – Design and Installation, and in Chapter 9 of PPI’s Handbook of Polyethylene Pipe, 2nd ed. In addition, most of the pipe / fittings producers publish literature covering their recommendations for heat fusion joining of their products. Apart from the heat fusion process of joining HDPE pipe, it can also be joined successfully with a variety of mechanical style fittings. Details of these joining systems can also be found in Chapter 9 of the Handbook mentioned above or by consulting directly with the pipe manufacturer.
Q. 2 How long does it take to make a butt fusion joint in HDPE pipe?
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.
Q. 3 Can HDPE pipe be fused and installed in sub-zero weather conditions?
Yes, but the operator and fusion machine must be protected from the, wind, moisture or blowing snow so that the heater plate uniformly heats the ends of the pipes. Please refer to the pipe manufacturer’s recommendations for fusing and installing HDPE pipe under these conditions or the cold weather guidance in ASTM F 2620, Standard Practice for Heat Fusion Joining of Polyethylene Pipe and Fittings. For situations in which weather conditions prohibit fusion joining, mechanical connections should be considered.
Q. 4 What inspection criteria are used to assure quality heat-fusion joints?
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. . Refer to ASTM F2620, Standard Practice for Heat Fusion Joining of Polyethylene Pipe and Fittings. 9
Q. 5 Is extensive training required to operate a fusion machine?
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.
Q. 6 How do heat fusion operators become qualified (or trained)?
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.
Q. 7 Where do I get the equipment to fuse HDPE pipes?
A list of the of fusion equipment manufacturers can be obtained by contacting PPI The HDPE pipe distributor or pipe manufacturer may also be able to supply information in answer to this question..
Q. 8 Can HPDE service tubing be joined with mechanical couplings?
Yes, mechanical couplings are commonly used on HDPE sizes 2” and below and come in a variety of installation methods such as stab type or interference fit. To maintain homogenous, leak free, and corrosion resistant HDPE service tubing systems, couplings molded from HDPE resins are preferred versus metallic (brass) couplings. Mechanical couplings molded from HDPE can offer significant excavation and labor cost savings and in general, require very little training and tooling to install. These service tubing fittings provide joints with the same integrity and life expectancy as fusion; however, some mechanical joints require the use of restraint devices, while other mechanical coupling products include stiffeners to prevent pullout of the final joint. Additional detail on the form and function of these products is available in the PPI Handbook 2 nd ed., Chapters 9 and 15. Also, refer to PPI Technical Note TN22, PPI Guidelines for Qualification Testing of Mechanical Couplings for PE Pipes in Pressurized Water or Sewer Service.
Q. 9 Are gaskets required between the faces of HDPE flange adapters?
Generally it is not recommended or necessary that a gasket be used when making connections that involve two mating HDPE flanges for water pressure applications operating at 80 psi or less. However, special tightening of the bolting system is required and that may include re-tightening of the bolts in 4-hours to 24-hours after the initial torque. PPI publishes a technical note, TN 38 that deals with this subject in considerable detail and with other options for flanged connections made between HDPE and other pipe materials. It is strongly recommended that the design engineer/contractor refer to this document when faced with issues of design or assembly of any flanged connection involving HDPE pipe.
Q. 10 How is HDPE pipe connected and joined to PVC pipe?
Methods of joining HDPE pipe to PVC pipe vary with the size and style of PVC. Common methods include slip-joint anchor fittings, gasketed joint adapters, and flange connections. HDPE to PVC transition fittings are also available from certain fittings manufacturers; also, refer to PPI TN-36, General Guidelines for Connecting HDPE Potable Water Pressure Pipes to DI and PVC Piping Systems, for additional information.
Q. 11 How can HDPE pipe be connected to other pipe products such as ductile iron pipe or valves?
For pressure applications, HDPE transition fittings, HDPE mechanical-joint adapters, gasketjoint adaptors, HDPE flanges, and standard metal couplings with internal stiffeners are recommended. The most common method is to use an HDPE MJ (mechanical joint) adapter to connect the HDPE pipe end in a DI MJ bell using the bolt and gland kit supplied by the HDPE MJ manufacturer. DIPS sized HDPE pipe may be inserted directly into an MJ bell with a restraint ring and insert stiffener for the HDPE pipe. When joining HDPE pipe to a DI pipeline either the DI joints must be restrained or the transition connection must be anchored. More details of these mechanical joining systems can be found in Chapter 9 of PPI’s Handbook* of Polyethylene Pipe, 2nd ed. and PPI TN-36, General Guidelines for Connecting 10 HDPE Potable Water Pressure Pipes to DI and PVC Piping Systems. Information on these systems may also be obtained from the pipe manufacturer.
Q. 12 Can butterfly valves be used with flanged HDPE pipe?
Yes. In some cases, depending on the butterfly valve dimensions, butterfly valve flange adapters, or standard flange adapters with tapered ID spacers are required in order for the valve to open & close freely. Consult with your flange adaptor or mechanical-joint adaptor supplier to insure dimensional compliance.
Q. 13 What is the recommended practice for joining HDPE pipe to mechanical joint valves and fittings?
An HDPE mechanical joint (MJ) adapter is fused to the HDPE pipe. The HDPE MJ adaptor is inserted into the metal MJ bell, with the standard gasket in place. The bolts through the gland are evenly tightened in a star pattern to complete the MJ connection.
Q. 14 What HDPE fittings are available for HDPE pipe?
Fittings are available in sizes from ½” 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.
Q. 15 Are there HDPE valves available?
Yes, there are several manufacturers offering HDPE valves; at present, 16” is the largest size available for water applications.
Q. 16 Are stiffeners recommended for Mechanical-Joint (MJ) Adapters?
Yes, several manufacturers recommend stiffeners for all diameters; other manufacturers offer MJ adapters with stiffeners for diameters 12” and larger. For diameters above 12”, seasonal thermal contraction and creep under radial gasket pressure can decrease the nose diameter of the MJ adapter. But while the gasket thickness is the same for 4” to 24” pipe diameters, the reduction in the nose diameter of the adapter caused by a drop in temperature becomes larger with increase in diameters. As a result, there is a greater loss of compression (and sealing capacity) of the rubber gasket in the larger sizes. Hence, stiffeners are recommended in larger diameters above 12”. More information on this subject as well as results of various tests is available in PPI’s technical note TN22, PPI Guidelines for Qualification Testing of Mechanical Couplings for PE Pipes in Pressurized Water or Sewer Service, at www.plasticpipe.org. Consult with individual HDPE MJ adapter manufacturers for engineering information.
Q. 17 Will the existing municipal warehouse inventory of ductile iron fittings go to waste if I switch to an all HDPE piping system?
No. With the use of HDPE mechanical joint adapters, polyethylene pipe and ductile iron fittings are completely compatible. However, due to the flexibility and tighter bending radius that can be achieved with HDPE pipe, fewer fittings may be required.
Q. 18 How are service connections tapped onto HDPE pipe mains?
HDPE pipe can be cold or hot (under pressure) tapped using piping products presently available. Saddle fusion tapping tees, electrofusion tapping tees, electrofusion corp saddles, and branch-saddles are readily available. There are several bolt-on mechanical connections qualified for use with HDPE pipelines as well. With this variety of fittings, tapping is a straightforward procedure. More information on this topic is available in Chapter 9 of PPI’s Handbook of Polyethylene Pipe, 2nd ed.
Q. 21 Can a bolt-on tapping saddle/sleeve be used with HDPE pipe?
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 11 accordance with AWWA C110/111, it can be used on HDPE pipe.
Q. 22 Can HDPE pipe be direct threaded using the same tapping tools commonly used to tap PVC or ductile iron pipe?
No. Tapped threads are not recommended for use on HDPE piping products. The industry standards for service taps to HDPE mains recommend the use of saddle fusion tapping tees, electrofusion tapping tees, branch-saddles, and certain metal mechanical clamps.
Q. 23 Does HDPE pipe split in the same manner that can occur when PVC pipe is improperly tapped?
No. Due to the ductile nature of HDPE and the design of fittings used for tapping, no splitting will occur when properly “hot” tapping HDPE pipe.
Q. 24 Can HDPE pipe be joined by solvent coupling joints?
No. At this time, there are no known adhesives or solvent cements that are suitable for pressure sealing or that have sufficient strength characteristics to join HDPE pipes. Heat fusion, which includes butt fusion, electrofusion, saddle fusion and mechanical joints are the only methods for joining HDPE pipe.
If you haven’t seen one and want to, let me know on +61 (0)3 89753888, rob@worldpoly.com, or +61 (0)418356959.
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