Pipeopsy: A Novel Method for Status Assessment of District Heating Pipes in Operation

AbstractThis study presents a novel status assessment method for district heating (DH) pipelines in operation, which we call “Pipeopsy” (a biopsy for pipes). The method evaluates adhesion strength between the service pipe and polyurethane (PUR) insulation, which is a crucial property for the durability of DH pipes and the extent of degradation of PUR foam closest to the service pipe. This method is based on three parts: (1) measuring adhesion strength and taking samples of the foam, (2) analyzing the foam in a laboratory using Fourier-transform infrared (FTIR) spectroscopy, and (3) restoring pipeline by replacing the foam and sealing the casing by welding polyethylene plugs in the holes. Temperature dependence and measurement accuracy of the shear strength test method have also been examined, as well as correlation with the standard axial shear strength test method. The shear strength of the aged pipes shows no temperature dependence, while the quotient between the value produced with the plug method and axial method is 3.1. Compared with the standard test methods, the advantages of Pipeopsy involve small cost, less damage to pipes, and the use of simple mobile tools for taking samples and performing measurements. Importantly, testing can be performed without shutting down the operation of DH pipelines. Furthermore, the method provides not only the information on adhesion strength but also information on the extent of chemical degradation in PUR. This combination of information provides a more detailed picture of the status of pipes and can be used to make a prediction about the remaining lifetime. Pipeopsy produces many results in a short time, and better statistics, which provide a solid basis for decision-makers focused on the maintenance of DH pipes or for applying artificial intelligence. Practical ApplicationsDistrict heating (DH) pipes consist of a steel pipe surrounded by insulating foam and a casing. This design requires satisfactory adhesion between the components to achieve good long-term performance. The use of DH pipes in a reliable and cost-effective way as long as possible requires planned and selective replacement of worn-out parts. A prerequisite to accomplish this is reliable information about the functional status and remaining service life of different parts of existing networks. Pipeopsy is a new field test method that provides valuable information on whether adhesion strength between insulation foam and steel pipe is at a satisfactory