of the techniques used to join the piping components and appurtenances PE pipe or fittings are joined to each other by heat fusion or with mechanical fittings.
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PE Pipe Joining Procedures Polyethylene Joining Procedures 5 – 3Thermal Heat Fusion Methods IntroductionThere are three types of heat fusion joints currently used in the industry; Butt, Saddle, and Socket Fusion. Additionally, there ar e two methods for producing the socket and saddle heat fusion joints. One method, used for all three types of joints , uses special heating tools for heating the parts to be joined. The other method, fie lectrofusionfl, is used only for socket and saddle-type joints. Heat is generated by induc ing electric current into a conductor that is a part of the electrofusion fitting. The principle of heat fusion is to heat two surfaces to a designated temperature, then fuse them together by applicat ion of a sufficient force. This force causes the melted materials to flow and mix, ther eby resulting in fusion. When fused according to the pipe and/or fitting manufacturers’ procedures, t he joint area becomes as strong as or stronger than the pipe it self in both tensile and pressure properties. As soon as the joint cools to near ambient temperat ure, it is ready for handling. The following sections of this chapter provide a general procedural guideline for each of these heat fusion methods.Butt Fusion Figure 5.1 A Standard Butt Fusion Joint The most widely used method for joining indi vidual lengths of polye thylene pipe is by heat fusion of the pipe butt ends as illustrat ed in Figure 5.1. This technique, which precludes the need for specially modified pipe ends or couplings, produces a permanent, economical and flow-efficient connecti on. Field-site butt fusion may be made readily by trained operators using spec ially developed butt fusion machines (see Figure 5.2) that secure and precisely al ign the pipe ends for the fusion process. 327-357.indd 3281/16/09 10:01:59 AM
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PE Pipe Joining Procedures Polyethylene Joining Procedures 5 Р4 The six steps involved in making a butt fusion joint are: 1. Securely fasten the components to be joined 2. Face the pipe ends 3. Align the pipe profile 4. Melt the pipe interfaces 5. Join the two profiles together 6. Hold under pressure Figure 5.2 ΠTypical Butt Fusion Mach ine for Smaller Diameter Pipe (Butt Fusion machines are available to fuse pipe up to 65 inches in diameter) NOTE: This is a general discussion. Pipe and fitting manufacturers have established qualified fusion procedures (15) which should be followed precisely when using their specific products. Refer to PPI Technical Report TR-3 3 for the Generic Butt Fusion Joining Procedure for Polyethylene Pipe. 327-357.indd 3291/16/09 10:01:59 AM
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PE Pipe Joining Procedures Polyethylene Joining Procedures 5 – 5Optional Bead Removal In some pipe system usage, engineers may elect to remove the inner or outer bead of the joint. External beads are removed wit h run-around planing tool s, which are forced into the bead, then drawn aro und the pipe. Power planers may also be used, but care must be taken not to cut into the pipe™s outside surface. It is uncommon to remove internal beads, as they have little or no effect on flow, and removal is time consuming. Internal bead s may be removed from pipes after each fusion with a cutter fitted to a long pole. Since the fusion must be completely cooled before bead removal, assembly time is increased slightly. Saddle/Sidewall Fusion Figure 5.3. Standard Saddle Fusion Joint The technique to join a saddle to the sidewall, illustrated in Figure 5.3, consists of simultaneously heating both the external surface of the pi pe and the matching surface of the “saddle” type fitting with concave a nd convex shaped heating tools until both surfaces reach proper fusion temperature. Th is may be accomplished by using a saddle fusion machine that has been designed for this purpose. 327-357.indd 3301/16/09 10:02:00 AM
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PE Pipe Joining Procedures Polyethylene Joining Procedures 5 – 7Socket Fusion Figure 5.4 — Standard Socket Fusion Joint This technique consists of simultaneously heat ing both the external surface of the pipe and the internal surface of the socket fi tting until the material reaches fusion temperature; inspecting the melt pattern; inserting the pipe end into the socket; and holding it in place until the joint cools. Figur e 5.4 illustrates a typical socket fusion joint. Mechanical equipment is available to hold the fitting and should be used for sizes larger than 2fl CTS to attain the increased force r equired and to assist in alignment. Follow these general steps when performing socket fusion: 1. Select the equipment 2. Square and prepare the pipe ends 3. Heat the parts 4. Join the parts 5. Allow to cool Equipment Selection Select the proper size tool faces and heat the tools to the fusion temperature recommended for the material to be joined. For many years, socket fusion tools were manufactured without benef it of any industry standardization. As a result, variances of heater and socket depths and di ameters, as well as depth gauges, do exist. More recently, ASTM F1056 (7) was written, establis hing standard dimensions for these tools. Therefore, mixing various manufacturers’ heating tools or dept h gauges is not 327-357.indd 3311/16/09 10:02:00 AM
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PE Pipe Joining Procedures Polyethylene Joining Procedures 5 – 10 minimum). Exercise caution to avoid cont amination of the scraped pipe surfaces. There are tools available to assist the operator in this procedure. Clamp the Fitting and Pipe(s) (if required by the manufacturer) Place the pipe(s) and fitting in the clamping fixtur e to prevent movement of the pipe(s) or fitting. Give special att ention to proper positioning of t he fitting on the prepared pipe surfaces. Apply Electric Current Connect the electrofusion control box to th e fitting and to the power source. Apply electric current to the fitting as specified in the manufacturer’s instructions. Read the barcode which is supplied with the electrofusi on fitting. If the control does not do so automatically, turn off the cu rrent when the proper time ha s elapsed to heat the joint properly.Figure 5.6 — Typical El ectrofusion Control Box and Leads with Clamps and Fittings Cool Joint and Remove Clamps Allow the joint to cool for the recommended time. If usi ng clamps, premature removal from the clamps and any strain on a joint that has not fully cooled can be detrimental to joint performance. Heat Fusion Joining of Unlike Polyethylene Pipe and Fittings Research has indicated that polyethylene pipe and fittings m ade from unlike resins can be heat-fused together to make satisfactory joints. Some gas companies have been heat-fusion joining unlike polyethylenes for many years with success. Guidelines for heat fusion of unlike materials are outlined in TN 13, issued by the Plastics Pipe 327-357.indd 3341/16/09 10:02:00 AM
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