Effect of operating temperature conditions in 21-year-old insulated pipe for a district heating network

Abstract

Since the insulated pipe in the district heating network should have a service life of more than 30 years based on EN253, the long-term thermal performance of PU foam is substantially important to guarantee sufficient shear strength. To examine the effect of operating temperature conditions on the degradation of PU foam in 21-year-old insulated pipe, two types of aged pipes were prepared from public office and general residence, since a large fluctuation in temperature profile with low average temperature is noted at the public office, while a small variation in temperature profile and high average temperature is noted at the general residence. The rate of thickness reduction in the cell wall of the aged PU foam is relatively faster at the public office than at the general residence since it underwent large fluctuation in operating temperature despite being exposed to low average temperature. In terms of the shear strength of the aged pipe, it exhibits relatively low shear strength at the public office compared to general residence, which reveals that the temperature fluctuation in the operating condition for the DH network tends to influence the degradation rate of the insulated pipe, substantially, compared to average exposed temperature.

Keywords

• Polyurethane (PU) foam
• District heating
• Degradation
• EN253
• Computer tomography (CT)
• Fourier transform infra-red (FTIR)