Remaining service life of preinsulated bonded pipes—A key element of transformation strategies and future district heating systems in Germany

Abstract

The decarbonisation and the transformation of existing District Heating (DH) systems requires high investments. For the DH utilities the implementation must take place during ongoing operation, while ensuring security of supply. In this context, it is becoming increasingly important to know the remaining service life of DH pipes when developing transformation strategies and planning the future DH systems. The pipelines of the heating networks in Germany are designed for a minimum service life of 30 years and can be operated even longer, depending on the pipe system and operational conditions. The remaining service life of buried preinsulated bonded pipes is carried out using material testing according to EN 253 (2018) combined with calculating material’s fatigue according to EN 13941-1 (2018) and AGFW FW 401 (2007). In this research work the remaining service life of four sections of preinsulated pipes in the DH network in Duisburg is determined comparing the results of material testing with the calculations of material’s fatigue. Besides the material tests according to EN 253 (2018), thermogravimetric analysis (TGA) and the apparent activation energy determined from TGA is used to estimate the remaining service life of the rigid polyurethane foam (PUR). For the pipes investigated, the service life is determined by the decrease in the properties of the PUR. The results imply that sections can be operated for another 6 up to 14 years and reach a service life of remarkable 50 years under local conditions. Status assessment and the remaining service life of DH pipes are a key element of DH utilities transformation strategies. In order to gain reliable results there is a need to improve knowledge on determining the remaining service life. The TGA is a promising approach for improving the PUR’s service life analysis especially since the previously valid methods of the old EN 253 have been withdrawn. The described approach using current standards and improved new methods in the field will accelerate the use of research results to DH utilities.