Det absolut vanligaste materialet vid nybyggnad av dricksvattenledningar var år 2008 polyeten. Flera VA-huvudmän i Sverige och Norge upptäckte dock att vissa av dessa ledningar gick sönder efter bara några få år i drift, trots det faktum att de skulle ha en drifttid på upp mot 150 år. Flera VA-bolag gick då ihop och skapade en branschorganisation under namnet 4S med syftet att stimulera till utveckling av ledningsmaterialet. Organisationen visste dock inte hur utbrett problemet med läckande PE-ledningar var och hade bara indikationer om bakomliggande orsaker. Det vill säga att PE-ledningar av stora dimensioner gick sönder efter få år i drift på grund av fel på skarven. Uppgiften med detta examensarbete var att ta fram ett statistiskt underlag som påvisar hur omfattande problemet var och kunna hitta samband som visar var och varför problemen uppkom. Ett frågeformulär som beskrev för VA-huvudmännen vilken information som eftersöktes för att kunna göra en bra undersökning sattes ihop och skickades ut. De data som sen inkom sammanställdes i ett dokument i programmet Excel för att få en enhetlig och övergripande bild. Resultaten som kom in visade sig dock ha stora brister och det var svårt att dra några statistiskt säkerställda slutsatser. Det fanns dock antydan till att problemet var på skarvar och i mindre dimensioner, oftast på servisledningar. Problembilden som uppkom under arbetets gång var att de data som tillhandahölls oftast var antingen bristfälligt eller obefintligt, och något VA-huvudmännen måste arbeta mer med. Det gick heller inte att se några ålderssamband, det vill säga att PE-ledningarna skulle gå sönder efter kort eller lång tid i drift. / The most common material used when producing new water pipes in Sweden in 2008 was polyethylene. A couple of pipe owners in Sweden discovered that pipes made out of PE who only had been operating a few years broke, despite the fact they are supposed to have a service life of 150 years. The pipe owners therefore created an organization named 4S with the target to develop the PE pipe system. The problem was that the organization did not know how widespread the problem with leaking PE pipes was and they only had indications of why it is caused. The objective with this project was to collect statistics to show how widespread the problem is and to find where and why the problem arises. A couple of question that described to the pipe owners what kind of data that was needed, on order to make a good examination, was put together and sent out. The data that came in was put together in an Excel document to get a better picture of the problem. The results that came in proved to have major flaws and it was difficult to draw statistically based conclusions. The results, however, showed a hint that the problem mainly was in the joints and in smaller dimensions. The biggest problem was that the received data most often was either inadequate or non-existent, and the pipe owners have to work harder improving the system. The statistics also cannot find any age related problem.

An advanced finite element (FE) model of the electrofusion welding of thermoplastic pipes has been developed using the ABAQUS FE package. The heat transfer analysis is coupled with thermal deformation analysis to include the time-dependent closure of the initial gap between the pipe and fitting. The effect of radial melt movement into the interface is modelled using a new `virtual material movement¿ technique. The predicted results (temperature distribution in the weld region, melt affected zones and gap closure time) are compared with experimental data and good agreement is found

At present, the fiber optic ducts are connected by a mechanical type of joint. In this method, two ducts cut in the right angle are pushed in from both sides of the joint, and takes approximately one second to joint ducts together. The problem with the existing joint technology is that if there is water inside of the joint, it will be damaged when the water freezes into ice, and then may cause leakage. There is a risk of explosion when compressed air to blow the fiber. Thus, a joint protection device (silicone rubber sleeve) was developed to seal the joint for protection utterly. However, this will cause the larger size of the entire joint and limit the number of single-duct joints next to each other in a multi-duct joint. Fiber optic ducts are made of High-Density Polyethylene, which is the best plastic for remelting and can be welded by using the electro-fusion welding method. Based on the thermoplasticity of this material, this thesis developed a plastic joint with a built-in conductive metal wire inside. The applied voltage will heat the wire, then remelt the duct surfaces to weld them together through the joint. The welding system uses a portable battery operating system, so there is no need to connect it to the grid. To prevent the battery from being damaged by supplying too much current, a capacitor bank is used to store high energy for the preheating joints. The system uses a microcontroller to control and monitor current and voltage to ensure uniform heating of the metal wire. Theemphasisof this thesis isplacedon the implementation of basic experiments to run the welding system. Multiple welding experiments show that the welding system can manually set parameters to control the welding current of different joints, thereby ensuring the welding quality. Using a 2.5Ω joint to weld ducts will approximately consume 120J from the battery, so a fully charged 42V, 4.4AH rechargeable battery can perform almost 5600 times of welding. The suitable range of joint resistance will decrease as the required energy consumption increases/ the welding time decreases.

Le soudage par électrofusion est la technique majoritairement utilisée pour assembler les tubes et les accessoires en polyéthylène utilisés sur le réseau gazier. Ses très bons résultats initiaux ont été ternis ces dernières années par un certain nombre de dysfonctionnements relevés tant sur le terrain qu'en laboratoire. Ils se traduisent par des soudures de qualité médiocre du fait de la présence de zones de très faible cohésion. L'objectif de ce travail est de développer des outils experts tant expérimentaux que numériques permettant d'optimiser les conditions de soudage par électrofusion. L'originalité de notre étude a été de développer un modèle éléments finis tridimensionnel prenant en compte les différents mécanismes et phénomènes physiques sous-jacents, responsables de la formation de la soudure. Le modèle permet de calculer le taux de transformation de la matière, de prendre en compte les enthalpies de fusion et de cristallisation, de calculer le taux d'interdiffusion des macromolécules à l'interface entre les différents corps à souder pour finalement prédire la qualité de la soudure en fonction des conditions de chauffage imposées. Pour valider le modèle numérique, tout en facilitant l'accès aux grandeurs expérimentales, nous avons conçu et réalisé un dispositif expérimental se présentant sous la forme d'une géométrie relativement simple et plane mais respectant les caractéristiques d'un accessoire réel. La confrontation entre résultats numériques et expérimentaux a permis de démontrer les capacités du modèle numérique à reproduire fidèlement la réalité. Les différents outils ont alors été utilisés pour étudier l'influence des conditions de soudage sur la soudure et pour étudier le soudage de géométries plus complexes telles que celles rencontrées dans les pièces industrielles. / The Electrofusion welding process is widely used to join polyethylene components in gas distribution networks. Even trusty as a technique, the field feedback points out some divergences whose influence on the long term performance of the weld. One of the well-known consequences of these divergences is the “sticking” (aka “cold weld”) that is the result of an uncompleted or even inexistent interdiffusion of the macromolecules of the materials to join. Most numerical simulations are two-dimensional whereas the process is usually three-dimensional both in terms of heat transfer and mechanical aspects. The main objective of the work was to develop a 3D finite element model and to validate it by comparing to a real situation the temperature evolution and the thermally affected areas in a simple planar welding geometry with the same dimensional characteristics as a real fitting chosen to make easier the instrumentation. The numerical model takes into account the fitting parameters such as polyethylene thermal and mechanical properties (i.e. melting and crystallization kinetics, phase transition, thermal expansion) and the electrical and geometrical settings. It computes a criterion based on the macromolecular interdiffusion theory able to determine whether a good welding occurred or not at the end of the welding cycle. The computed results (temperature, melted and cold areas and fracture surfaces) were compared with experimental data and gave very good agreement in terms of temperature, liquid phase fraction distribution and fracture surfaces. Finally the numerical model and the experimental process were used to study the influence of welding conditions on the weld itself and to study the welding of complex geometries such as the industrial fittings.