JOINTING OF LARGE BORE PE PIPES: THINK BIG AND EVEN BIGGER!

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1 JOINTING OF LARGE BORE PE PIPES: THINK BIG AND EVEN BIGGER! Robert Eckert FRIATEC AG, Germany Abstract A New Generation of Electrofusion: A technical comparison between the new wedge coupler and the traditional cylindrical coupler for PE pipes d1000 (40 ) and above. FRIATEC has developed a totally new concept of electrofusion jointing method for large bore PE pipes, d1000 mm (40 ) and above. The new method completely revolts existing practice with respect to easy installation, fast progress and minimal energy consumption. Compared with standard EF fittings in large dimensions the new technique allows a dramatically reduction in processing time, eases installation and does not require additional devices on site. Basic design criterion of the fittings is maximum reliability in processing of the joint under rough site conditions as well as durable operation of the pipe system. The presentation introduces the new concept, shows the advantages of the new method and highlights processing with respect to practical and economical aspects. PRACTISE-RELATED CHALLENGES WITH REGARD TO LARGE PIPE JOINTS PE pipes have been installed in piping systems for the most diverse applications for more than fifty years. They are increasingly used in very large dimensions above d 630mm, mainly for the transport of potable water as well as irrigation and drainage. But increasing diameters also result in increasing demands on a manageable joining technology. Here, the traditionally used techniques, such as e.g. electrofusion butt welding and electrofusion, increasingly reach their limits. Electrofusion makes high demands on the roundness of the pipes and the narrow fitting tolerances of the joining partners. But these demands are contrary to the actual conditions in practice because increasing diameters also mean increasing tolerances. With regard to large dimension ranges, the concept of today s usual cylindrical electrofusion fitting thus requires a considerable extra processing effort (Fig. 1). As a consequence, increased demands are made on the expert knowledge of the fitter and the diligence during installation. The communication of knowledge within the scope of the standard welder training is thus no longer sufficient. Apart from the quality of the component parts and the matched equipment, a special training as well as application-technical supervision by specialists are required to be able to produce reliable large pipe joints. Compensation of an extreme joint gap and integrated restoration of the pipe s roundness: These features were implemented for the new wedge coupler technology. This method achieves reproducible high fusion quality given simultaneous enormous acceleration of the entire processing process.

manageable also for cylindrical electrofusion couplers thanks to several special functions: Reinforcement of the outer diameter of the coupler to improve the fusion quality (Figure 2), reliable melt

2 Figure 1: A non-violent assembly for cylindrical couplers is not possible because of tolerance conditions. Figure 2: The outer fitting reinforcement prevents its expansion during fusion CRITERIA FOR PRACTICE-COMPLIANT DESIGN OF THE CYLINDRICAL ELECTROFUSION COUPLER UP TO D1200 The practical demands become manageable also for cylindrical electrofusion couplers thanks to several special functions: Reinforcement of the outer diameter of the coupler to improve the fusion quality (Figure 2), reliable melt pressure built-up through constrained elongation of the coupler body Preheating for a high joint gap bridging capacity, in addition: matched use of installation aids and devices OUTER REINFORCEMENT The decisive parameter for fusion joints is apart from temperature and time the pressure acting in the melt during fusion. In electrofusion welding, the volume increase created during the conversion of the state of aggregation solid liquid is used. The joint gap is filled by the created melt, the joining pressure is built up due to a further volume increase. The forces created here result in an enlargement of the coupler s diameter depending on the size of the annular gap between coupler and pipe. If the elongation is permitted, the melt pressure is reduced at the same time. The outer reinforcement (Figure 2) of the coupler prevents the elongation during the fusion process under the acting melt pressure. The mesh reinforcement at first remains resilient and progressively counteracts the increasing elongation. A stiff, inflexible reinforcement in contrast could provoke melt release, i.e. an impermissible pressure reduction. The effect of the reinforcement can often be well observed in practice: After cooling of the joint, the coupler shrinks again, in contrast to the mesh reinforcement. The reinforcement comes loose from the coupler at some points and thus indicates reliably that the reinforcement has been active in the joining process and that an optimal melt pressure was given. Typical defect patterns in case of lacking reinforcement are marked shrinkage holes in the fusion zone.

PREHEATING METHOD Avoidable mistakes in the processing of large pipes are mainly the result of shape deviations: Out-of-roundness and flattening at the outer diameter.

3). If the out-of-roundness of the pipes cannot be avoided as a whole, the fitting must provide for a corresponding resistance to shape deviations.

3 PREHEATING METHOD Avoidable mistakes in the processing of large pipes are mainly the result of shape deviations: Out-of-roundness and flattening at the outer diameter. Storage and transport influences may cause these deviations from the ideally round shape of the pipe, above all with regard to the net weight or linear distributed loads as bearing reactions (Figure 3). If the out-of-roundness of the pipes cannot be avoided as a whole, the fitting must provide for a corresponding resistance to shape deviations. The preheating method was thus developed to improve the fit ratios for coupler components. Both the storage on the ground as well as the displaced arrangement of pipe layers in a wooden crate may result in local flattenings at the outer pipe diameter. In butt welding, this might result in an impermissible displacement; in electrofusion welding, this might result in excessive clearances between the coupler and the pipe. A large gap between the pipe and the installed coupler as annular gap or also in locally defined areas may result in an insufficient build-up of the melt pressure in the extreme case. In order to counteract these deviations which are hardly to be completely avoided in practice -, their negative influence is taken into consideration when designing the coupler: By preheating the joining zone below the melt temperature before starting the fusion process, the joint gap is reduced (Figure 4). This utilises the specific material properties of the material polyethylene: The relatively large thermal elongation of PE results in a volume increase, pipe and fitting approach each other, the joint gap is reduced. Stress relief under the influence of heat and memory effect: Frozen stresses (as e.g. outof-roundness due to storage) are relieved, at the same time, the pipe "remembers" its almost ideally round contour of its production process and tries to restore it. The memory effect of plastics has been known for decades and is used in many areas, e.g. medical engineering. The heat applied to the connecting area below the melt temperature increases the energetic level in the joint area before the joining process and thus improves the condition for the following fusion process. Figure 3: Principal view of possible deformations of the pipe contour and their effects Figure 4: Functional principle of preheating

extremely simplified. Because a "zero gap situation is achieved after assembly, the fusion times are reduced by approx. 2/3. A preheating is thus no longer required.

4 THE CONCEPT OF THE WEDGE COUPLER The new wedge coupler technology revolutionises the joining technology in the field of large pipes. As a result of the mechanical compensation of extremely large gap ratios between coupler and pipe, assembly of the coupler, above all as slide over couplers to integrate a fitting piece, can be extremely simplified. Because a "zero gap situation is achieved after assembly, the fusion times are reduced by approx. 2/3. A preheating is thus no longer required. The wedge coupler consists of three components: the outer coupler body and two fusion wedges (Figure 5). The coupler body is equipped with a tapered joining area on both inner surfaces. As pressure-retaining component part, it is designed for an operating pressure PN / PFA of 10 bar. The tapered fusion wedge is equipped with a heating coil in a meandering pattern both at the inner and outer surface. Axial flex grooves are integrated in the wedge between these meanders. These flex grooves (Figure 6) make it possible to mechanically reduce the nominal diameter of the fusion wedge. A large joint gap between the coupler and the pipe can be bridged. The coupler can thus be easily assembled with little force after onetime scraping, independent of the tolerance condition of the pipe. A complete sliding over, which is required for the standard application the integration of a fitting piece into the existing pipeline - is now possible with hitherto not achieved ease. Figure 5: Wedge coupler, consisting of two fusion wedges and the coupler body. Bottom fusion wedge before assembly, top bottom wedge in final position. Figure 6: Functioning of the fusion wedge: The flex grooves permit a diameter reduction such that the joint gap between the pipe and the fusion wedge is bridged. In case of extreme out-of-roundnesses of the pipe, the radial flexibility of the fusion wedge facilitates an easy sliding over. The pipe out-of-roundness is levelled because the wedge and the coupler are contracted. Rounding clamps are thus not required as additional tools.

PROCESSING REMOVAL OF THE OXIDE LAYER A scraper tool was specifically designed for large pipes for the machining of the joint area, which is very easy to operate using especially little effort.

5mm is sufficient to remove the oxide layer and contaminations on the surface of the pipe and thus to create a fresh PE joining surface.

maximum gaps and last but not least the risk of an accident caused by electrical current are thus a thing of the past.

5 PROCESSING REMOVAL OF THE OXIDE LAYER A scraper tool was specifically designed for large pipes for the machining of the joint area, which is very easy to operate using especially little effort. A one-time swarf removal given an equal swarf thickness of approx. 0.5mm is sufficient to remove the oxide layer and contaminations on the surface of the pipe and thus to create a fresh PE joining surface. Multiple scraping requiring great effort to create a diameter fitting cylindrical couplers or even the use of an electrical plane with the known risks of uneven swarf removal, the creation of local maximum gaps and last but not least the risk of an accident caused by electrical current are thus a thing of the past. ASSEMBLY OF THE FITTING BODY The fitting can be pushed over the pipe body with little effort and without necessitating any further measures. Because of the larger internal diameter in unclamped condition of the wedge coupler, extreme tolerance conditions of the outer pipe diameter do not play any significant role with regard to the assemblability (Figure 7). A large pipe out-ofroundness can be managed using the flexible fusion wedge (Figure 8). By assembling the wedge to the fitting body, the shape of the pipe and the shape of the fitting body obtain an ideal condition. Figure 7: Assemblability depending on the actual diameter Figure 8: The flexibility of the fusion wedge ring facilitates sliding onto pipes with extreme out-of-roundness

6 WEDGE ACTIVATION The coupler wedges are pressed into the coupler body via pre-mounted stud bolts using conventional ratchet wrenches or a pneumatic wrench. The internal diameter of the fusion wedge is thus reduced and the heating coil zones engage to the pipe and coupler body in a close fit and without gaps. As a result of the wedge effect, the pipes to be joined are tension-proof locked in place. Fusion, is of course, at first only possible at one coupler side. FUSION Because of the mechanical gap compensation, all joining zones are mutually positioned virtually without any clearance. Because the major part of the fusion energy for cylindrical couplers is used to close the gap, the wedge coupler not only offers significant energy savings but above all reduction of the fusion time to a minimum. COOLING A reduced energy input and a short fusion time result in less through heating such that the connection can be commissioned under operating pressure after very short cooling periods. TESTS Fusion joints of the wedge coupler are tested according to the requirements of the valid regulations and standards: DVGW GW335-B2 (2003): Plastics piping systems in the gas and water supply - requirements and testing - Part B2: Fittings made of PE 80 and PE 100 EN (2003): Plastics piping systems for water supply - Polyethylene (PE) Part 3: Fittings EN (2003): Plastics piping systems for water supply - Polyethylene (PE) Part 5: Fitness for purpose of the system ISO (2007): Plastics piping systems - Polyethylene (PE) pipes and fittings for water supply - Part 3: Fittings ISO (2007): Plastics piping systems - Polyethylene (PE) pipes and fittings for water supply - Part 5: Fitness for purpose of the system The demands made on a modern PE pressure piping system are met by the wedge coupler technology.

thicknesses to absorb the + + internal pressure load Long pipe insertion depths serve the + + pipe guiding Broad fusion zones for a reliable joint + + Broad internal cold zone eliminates the effect

7 COMPARISON OF THE WEDGE COUPLER TECHNOLOGY AND CYLINDER COUPLER FROM D1000 Tab.1: Overview: Comparison of the coupler concepts Comparison Wedge coupler Cylindrical coupler Section through the joint Properties Figure 9: Fusion joint d1000 Figure 10: Fusion joint d1000 Solid wall thicknesses to absorb the + + internal pressure load Long pipe insertion depths serve the + + pipe guiding Broad fusion zones for a reliable joint + + Broad internal cold zone eliminates the effect of sunken pipe ends + + Preheating for a high gap bridging capacity ++: Not required: zero gap + through wedge tension Reinforcement of the outer diameter to improve the joint quality ++: Not required + Safe melt pressure build-up through constrained elongation Processing steps Removal of the oxide layer ++: One-time removal, independent --: Typically multiple scraping (10x of tolerances and more given unfavourable tolerance condition) Restoration of pipe roundness ++: Not required --: Use of tools Assembly of the fitting body ++: Easy sliding on/over, --: Typically only after restoration almost independent of pipe of pipe roundness, high forces condition required to slide on Wedge activation +: Simple and defined (not required) Fusion ++: Time saving approx. 2/3 --: Fusion may take several hours Cooling ++: Little waiting time until --: High expenditure of time because pressure test / commissioning of high energy input Typical processing time for HM coupler d1200 (example) approx 2h At least 1 working day SUMMARY The wedge coupler technology revolutionises the joining technology in the field of large pipes. The assemblability of the fitting is fundamentally simplified as compared to traditional cylindrical couplers. A reproducible good joint quality is achieved. Only a fracture of

8 the hitherto required time is necessary for processing. The assembly is made according to clearly defined and simple rules. Anybody able to assemble a flange will also be able to handle the clamping system of the wedge coupler.

Joining Large PE Pipes in No Time at All: A New Generation of Electrofusion

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