Functionally stable piping systemsThe department of Building Technology and Mechanics in Gothenburg is one of Sweden's leading institutions for research into the durability of buried distribution systems for district heating and cooling, gas and water. The emphasis in recent years has been on optimisation of materials, designs and methods of laying, in order to minimise investment costs.
District heating pipes
Many projects concerned with district heating pipes have been carried out in close conjunction with Chalmers University of Technology and the Swedish district heating sector. They have included everything from long-term performance of joints and electrical moisture monitoring systems to the sensitivity of outer sheaths to cracking. The work is ongoing, with the following current areas of interest:
Durability of mastic/hot-melt-sealed shrink joints – Joints of this type are very widely used, but there are no established methods for evaluating their long-term performance, and so it is difficult for users to select between different brands and types.
A double-sealed shrink joint
Laying pipes under roads in residential areas – Substantial savings could be made if district heating pipes could be laid less deeply beneath roads: environmental, through reduced need for transport and the use of excavators, and economic, mainly through time savings. There are many factors that indicate that at least small pipes could be laid a lot less deeply under streets carrying only light traffic, without either the pipes or the streets being damaged.
Foamed PET instead of PUR for thermal insulation – Polyurethane (PUR) is today by far the most commonly used material for thermal insulation of district heating pipes. It has excellent thermal and mechanical properties, but is a thermoset plastic that contains health-hazardous components. PET, or polyethylene terephthalate, is considerably less environmentally harmful, and has the advantage of being able to be produced from recycled raw material.
Our work on plastic pipes is carried out in conjunction with sector organisations and raw material and product manufacturers. Current working areas are:
Durability of unpressurised pipes –
Unpressurised pipes, such as sewage and drain pipes, face very different loads than pressurised pipes for water or gas. The design load is pressure from the backfill of the trench, which is a lot less critical than a constant positive internal pressure. Recently, interest has turned to the potential for using cheaper and poorer-quality raw materials for these types of pipes, which means that there is a need to investigate their load resistance and strength.
External damage to pressurised pipes – Non-excavation methods of laying pipes are being increasingly used. Pipes are pressed or pulled through the ground, without excavating a trench. However, such rough handling of the pipes means that they are likely to be damaged by scratches, pressure from stones etc.
A pipe being laid in a trench for onward non-excavation driving.