SAFE JOINING TECHNOLOGY ON A GRAND SCALE FRIALEN XL Offprint No. 2/2011 Joining Large PE Pipes in No Time at All: A New Generation of Electrofusion A technical comparison between the new conical ring coupler and the traditional cylindrical coupler for PE pipes d 1000 and above by Dipl.-Ing. (FH) Robert Eckert Technical journal for piping system integrity and efficiency, 2/2011 Vulkan-Verlag GmbH, Essen www.frialen-xl.com
Water & Gas Distribution Joining Large PE Pipes in No Time at All: A New Generation of Electrofusion A technical comparison between the new conical ring coupler and the traditional cylindrical coupler for PE pipes d 1000 and above By Robert Eckert The conical ring 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 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 conical ring coupler. 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 630 mm, 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. 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 installer 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 fittings 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 conical ring coupler technology. This method achieves reproducible high fusion quality given. CRITERIA FOR PRACTICE-COMPLIANT DESIGN OF THE CYLINDRICAL ELECTROFUSION COUPLER UP TO d 1200 The practical demands become manageable also for cylindrical electrofusion couplers thanks to several special functions: FIG. 1: A non-violent assembly for cylindrical couplers is not possible because of tolerance conditions Special-Edition 2 / 2011 3
Water & Gas Distribution 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, the volume increase created during the FIG. 2: The outer fitting reinforcement prevents its expansion during fusion FIG. 3: Principal view of possible deformations of the pipe contour and their effects 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 technique 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 outof-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. out-of-roundness due to storage) are relieved, at the same time, the pipe remembers its almost ideally round contour of its produc- 4 2 / 2011 Special-Edition
tion 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. THE CONCEPT OF THE CONICAL RING COUPLER The new conical ring 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 conical ring coupler consists of three components: the outer coupler body and two fusion conical rings (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 conical ring is equipped with a heating coil in a meandering pattern both at the inner and outer surface. Axial flex grooves are integrated in the conical ring between these meanders. These flex grooves (Figure 6) make it possible to mechanically reduce the nominal diameter of the fusion conical ring. A large joint gap between the coupler and the pipe can be bridged. The coupler can thus be easily assembled with little force after one-time 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. In case of extreme out-of-roundnesses of the pipe, the radial flexibility of the fusion conical ring facilitates an easy sliding over. The pipe out-of-roundness is equalized because the conical ring and the coupler are contracted. Rounding clamps are thus not required as additional tools. FIG. 4: Functional principle of preheating FIG. 5: Conical ring coupler, consisting of two fusion conical rings and the coupler body. Bottom fusion conical ring before assembly, top bottom conical ring in final position 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 conical ring 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 conical ring (Figure 8). By assembling the conical ring to the fitting body, the shape of the pipe and the shape of the fitting body obtain an ideal condition. Special-Edition 2 / 2011 5
Water & Gas Distribution FIG. 6: Functioning of the fusion conical ring: The flex grooves permit a diameter reduction such that the joint gap between the pipe and the fusion conical ring is bridged FIG. 7: Assemblability depending on the actual diameter FIG. 8: The flexibility of the fusion conical ring facilitates sliding onto pipes with extreme out-ofroundness Conical ring activation The conical rings are pressed into the coupler body via premounted stud bolts using conventional ratchet wrenches or a pneumatic wrench. The internal diameter of the fusion conical ring 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 conical ring 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 conical ring 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 conical ring coupler are tested according to the requirements of the valid regulations and standards: DVGW GW335-B2: Plastics piping systems in the gas and water supply requirements and testing Part B2: Fittings made of PE 80 and PE 100 (2003) EN 12201-3: Plastics piping systems for water supply Polyethylene (PE) Part 3: Fittings (2003) EN 12201-5: Plastics piping systems for water supply Polyethylene (PE) Part 5: Fitness for purpose of the system (2003) 6 2 / 2011 Special-Edition
TAB.1: Overview: Comparison of the coupler concepts Comparison Conical ring coupler Cylindrical coupler Section through the joint Properties Fusion joint d1000 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 Reinforcement of the outer diameter to improve the joint quality Safe melt pressure build-up through constrained elongation Processing steps Removal of the oxide layer + + ++: Not required: zero gap through wedge tension ++: Not required + ++: One-time removal, independent of tolerances + --: Typically multiple scraping (10x and more given unfavourable tolerance condition) Restoration of pipe roundness ++: Not required --: Use of tools Assembly of the fitting body ++: Easy sliding on/over, almost independent of pipe condition --: Typically only after restoration of pipe roundness, high forces required to slide on Conical ring activation +: Simple and defined (not required) Fusion ++: Time saving approx. 2/3 --: Fusion may take several hours Cooling Typical processing time for HM coupler d1200 (example) ++: Little waiting time until pressure test / commissioning approx 2h --: High expenditure of time because of high energy input At least 1 working day ISO 4427-3: Plastics piping systems Polyethylene (PE) pipes and fittings for water supply Part 3: Fittings (2007) ISO 4427-5: Plastics piping systems Polyethylene (PE) pipes and fittings for water supply Part 5: Fitness for purpose of the system (2007) The demands made on a modern PE pressure piping system are met by the conical ring coupler technology. lindrical couplers. A reproducible good joint quality is achieved. Only a fracture of 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 conical ring coupler. Author Comparison of the conical ring coupler technology and cylinder coupler from d1000: Tab. 1 The conical ring coupler technology revolutionises the joining technology in the field of large pipes. The assemblability of the fitting is fundamentally simplified as compared to traditional cy- Dipl.-Ing. (FH) Robert Eckert FRIATEC AG, Mannheim Tel. +49 172 6425799 E-mail: robert.eckert@friatec.de, www.friatec.de Special-Edition 2 / 2011 7
SAFE JOINING TECHNOLOGY ON A GRAND SCALE FRIALEN XL Offprint No. 2/2011 FRIATEC Aktiengesellschaft Technical Plastics Division POB 71 02 61 D-68229 Mannheim Tel. +49 621 4 86-1431 Fax +49 621 479196 info-frialen@friatec.de www.frialen-xl.com www.frialen-xl.com FRIATEC AG TECHNICAL PLASTICS DIVISION / FRIALEN XL