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Nov 04, 2016 In order to get heated, the joining areas have to lie flat against the heating element under low pressure. For this purpose, the pressure is reduced to almost zero (≤ 0.02 N/mm2). During the heating process, the heat enters into the areas to be welded. As a result, the required welding temperature is reached. (Image: Heating element butt welding ? adjusting the joining areas) (Image: Temperature sequence and pressure curve in the adjusting and heating-… |
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Nov 04, 2016 After heating-up, the joining areas are to be removed from the heating element. The heating element is to be taken out without damaging or soiling the heated joining areas. The joining areas are to be brought together quickly until they almost meet. The relocating time is to be kept as short as possible as otherwise the plastified areas cool down. This would have negative effects on the quality of the welding seam. (Image: Heating element butt welding - … |
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Nov 04, 2016 The areas to be welded are supposed to connect with a velocity of near zero. The necessary joining pressure is preferably applied in linear increase and is, for instance, 0.15 ± 0.01 N/mm2 for PE. Sudden use of full pressure would press the hot plastic material out of the welding zone which would result in an inadequate weld factor [Simona11]. The jointing pressure has to be maintained during the cooling-off period. (Image: Heating element butt welding - … |
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Nov 04, 2016 Reference values for the heating element butt welding of PE pipes and fittings are provided by the pipe manufacturers. These values are generally applicable at an external temperature of about 70°F (20 °C). (Table: Guidance values for the heating element butt welding of pipes, pipelines and sheets made of HDPE at an external temperature of about 70 °F (20°C) and moderate air flow) |
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Nov 04, 2016
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Nov 04, 2016 The following list of equipment is necessary for the heating element butt welding process:
(Image: Equipment for heating element butt welding [FI-Huern]) |
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Nov 04, 2016 (Image: Temperature) The welding area is to be protected from unfavourable climatic influences (e.g. moisture and temperatures below +40 °F (+5 °C)). The following measures may help to achieve this:·
In order to prevent stresses due to differing temperatures such as the influence of the sun, temperature equalisation should be achieved by covering the region of the welding seams on time. |
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Nov 04, 2016
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Nov 04, 2016 The visual inspection serves to examine butt weldings with regard to the following aspects:
(Image: Welding bead) |
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Nov 04, 2016 During PE welding processes, different failures may occur, which can be detected by means of ultrasonic non-destructive testing. Incomplete fusion at the interior surface, exterior surface or in the cross section, displaced joints may be detected using this testing procedure. (Image: Conventional sliplining process with annular space [FI-Teerb] - Testing the welded seam) (Image: Conventional sliplining process with annular space [FI-Teerb] - View on … |
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Nov 04, 2016
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Nov 04, 2016 What type of information needs to be documented during the welding process? Welding work has to be monitored. The type and extent of supervision has to be agreed upon between the contract partners. It is recommended to document the information about the welding method used in welding protocols or on data media. (Image: Documentation) Welding protocol
As the welder knows the nominal values from the … |
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Nov 04, 2016 What are the most important causes of heating element butt welding failure?
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Nov 04, 2016 The external and internal welding beads that are formed can be removed if desired. If the weld bead requires finishing, this is best done before cooling, when approximately 2/3 of the cooling time is complete. There is a danger that cutting work on the cold bead will cause notches [Simona11]. (Image: Device for removing the internal welding bead for HD-PE pipes [FI-WIDOS]) (Image: Arrangement for removing the internal welding bead for HD-PE pipes (Locheisen) … |
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Nov 04, 2016 The following measures must be taken to assure the required quality of the heating element butt welding work. (Table: Quality assurance measures during heated element butt welding) |
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Nov 14, 2016 (Table: US standards and regulations for PE pipe joining procedures) |
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Nov 04, 2016 (Table: Standards and regulations for heated tool welding (as of 12/2005) [FI-Steina]) |
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(Image: Attention!) Clamping pipe ends axially and cutting them to length square to the pipe axis A pipe separation that is not square may lead to the fact that parts of the electrofusion coils are not covered by the pipe, which may cause excessive heat, uncontrolled formation of melting material and auto-ignition [Friatec04]. Right (Image: Electrofusion welding – square pipe separation according to [FI-Friat]) Wrong (Image: Electrofusion welding pipe separation (… |
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Removing the oxidation layer The oxidation layer that forms on the pipe surface by solar radiation during storage, has to be removed from the pipe before any welding procedure, otherwise a homogeneous connection of the materials would be hindered. In order to remove the oxidation layer, peeling devices have to be used that guarantee a reproducible quality of the joining layer. (Image: Removal of the oxide layer by a peeling device on the construction … |
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