Аnalysis of the Actual Condition of Pre-Insulated Pipelines of District Heating Systems After Operation

The article discusses issues related to the actual condition of pre-insulated (PI) pipelines of district heating systems (DHS). Some of the pipelines in operation are approaching their estimated service life, so the issue of their further use is relevant. The aging of the heating supply pipelines occurs due to various processes associated with both operating temperature regimes and oxidation. The durability of polymer materials used in pre-insulated pipes can be assessed through empirical or predictive methods. For six batches of PI pipes that were in operation at different times in the Minsk DHS, tests were carried out according to standardized parameters in order to determine their actual values. For most of the samples presented, the values of the average cell size, thermal insulation density, compression strain stress and the number of closed pores significantly meet the requirements of STB 2252–2012 for new pipes. The value of the thermal conductivity coefficient is in the range of 0.030 to 0.037 W/(m·K), which is 10 % higher than the required value for new pipes. Values of the shear strength limit of the pre-insulated pipe construction in many tests was less than 0.12 MPa, indicating a potential risk of failure in the thermal insulation structure of the pipe. Besides, there is no specific correlation with either the service life of the pipes or the temperature regime.