As a relationship between the medium pipe and the casing, polyurethane foam plays an important role in district hvac pre-insulated pipes, both as thermal insulation and as a load bearing element. As a result, understanding how the foam behaves under multiaxial stresses is critical for network design as well as ageing predictions. Cell shape anisotropy in polymeric foams is known to cause anisotropy in mechanical properties. The microstructural anisotropy of PU foam from pre-insulated pipes, as well as its mechanical behaviour under compression in three orthogonal directions. Click here to learn more on pu pre insulated pipe malaysia.
We discovered that PU from pre-insulated pipes is orthotropic and exhibits greater anisotropy than PU slabs. The traditional bonded pipes under consideration exhibited a similar behaviour. However, despite the fact that no substantial variations in cell shape anisotropy were found when comparing the two flexible pipes in this study, a substantially different behaviour for the E modulus ratio was observed. This demonstrates that, while the manufacturing process has the greatest influence on cell shape anisotropy, other factors, such as cell size and cell size variability, must be considered to explain the difference in stiffness behaviour.
PU pre-insulated bonded pipes are available in a variety of processes and PU formulations. Rigid bonded steel pipes are the most common. They are batch-produced, with the PU injected between the service pipe and the casing. Service pipe and casing are manufactured separately. Flexible pipes, which have recently appeared on the market, are produced in a continuous process in which the PU is poured into a moving casting mould and the PU material flows around the moving pipe.
Details on the micro – structural and behaviour of the PU foam in DH pre-insulated pipes are not well understood, so design standards and calculation methods used in the sector are primarily for steel medium pipe [2,3]. While the ageing of PU foam in district heating pipes has been studied in recent years, the emphasis has been primarily on oxidation and thermal degradation [4,5,6], details on the microstructure and its relationship to the mechanical behaviour of the bonded pipe have largely gone unexplored. To optimise structural design, a thorough understanding of the mechanical behaviour of the basic materials is required. The traditional bonded pipes used in this study were made in batches by injecting PU insulating adhesive between the service pipe and the outer casing. The casing is made in a previous process, and one pipe is made at a time . The PU foam is blown with cyclopentane and meets the requirements of EN 253 . The manufacturer does not provide any additional information about the PU formulation.
Polyurethane foam in pre-insulated adhered pipes for district heating applications has a stronger cell shape, elastic modulus, and compressive strength anisotropy than PU foam slabs, particularly in traditional bonded pipes. This is due to the geometrical shape of the mould, the annular section between the medium pipe and the pipe casing, with a much smaller distance between the walls than rectangular moulds for slab production.