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Congratulations! You have successfully finished this module. Next you will have the opportunity to review the newly acquired knowledge with an interactive questionnaire. You can navigate back to any point in the lessons if you wish to review a specific point or subject. Stay curious! |
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Nov 03, 2016 This module is devoted to the pipe bursting as a special method of the replacement of pipelines. In addition, the module looks at the material and equipment requirements and the effects that pipe bursting has on the pipeline itself as well as its surrounding environment. Upon the successful completion of this module, you will be able to:
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This lecture deals with the theoretical background of the topic of welding of polyethylene pipes, as well as the practical steps and limiting conditions that have to be considered. The aim is to outline the requirements that must be met for quality assurance and the consequences of non-compliance. |
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Nov 04, 2016
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Nov 04, 2016 The image below presents the classification of plastic materials into groups and sub-groups, based on similar characteristics. (Image: Classification of plastics according to [Jürge05] [Image: S&P GmbH]) |
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Nov 04, 2016 Plastics can be grouped into three main categories, based on their arrangement of the chain molecules and their properties. These groups and their schematic view are presented in the image below. (Image: Schematic view of the arrangement of the chain molecules in plastics and their properties according to [Bos00] [Image: S&P GmbH]) |
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Nov 04, 2016 A schematic view of the structure of plastics van be visualized in the image below. (Image: Schematic view of the structure of plastics according to [Bos00] [Image: S&P GmbH]) |
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Nov 04, 2016
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Nov 04, 2016 The table below presents a general overview of the chemical resistance of various plastic materials. (Table: General chemical resistance of plastics according to [Bos00]) |
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Nov 04, 2016 The main plastics for pipe production are listed as follows:
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Polyethylene belongs to the thermoplastics, i.e. to the plastics that superficially fuse (plasticise) when heated and solidify when cooled. Structure of polyethylene Polyethylene (PE) consists of long chains (macromolecules) whose basic components (monomers) contain ethylene, which is extracted of mineral oil or natural gas. These chains are produced by so-called polymerisation. Polymerisation is a chemical reaction process in which molecules give up … |
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The below image differentiates between low and high pressure polyethylene. (Image: PE modification [Grondo95]) |
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This table presents the various properties of polyethylene, as well as advantages and limits of the different types of polyethylene.
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The quality of welded joints depends on the qualification of the welders, on the machines and devices used, as well as on the compliance with welding regulations. The welding seam can be examined by non-destructive and/or destructive testing. |
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The length of the molecular chains has a strong influence on the weldability. Therefore, the different chain lengths should be as equal as possible in order to achieve homogeneous flowing properties. If there are very high molecular weights, as with PE 100 (an ultra high-molecular polyethylene- PE- HD -UHMW), the chain reaches such a length that the molecular chains in thermoplastic state cannot slide down anymore due to the many entanglements with … |
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(Image: Temperature) Polyethylene has a very wide thermoplastic range between about 280 °F and 570 °F (140 °C and 300 °C). However, experience shows that polyethylene has the best (long term-) strength in heating element butt welding at a welding temperature of 390 °F and 430 °F (200 °C to 220 °C). (Image: Condition range of polyethylene according to [SKZ] [Image: S&P GmbH]) (Image: Attention!) Lower or higher temperatures, respectively, have negative … |
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Why is the welding load important? The welding load serves to bring the plastified join partners into contact in such a way that the molecular chains are sufficiently mixed and that the semi-crystalline structures, which determine the strength of the polyethylene, can develop. The necessary welding load (specific jointing pressure) for polyethylene is determined by the formula presented below, and has to be converted for the corresponding welding surfaces (… |
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