The sewer network has the important task of conveying wastewater and stormwater safely to treatment plants and discharge points. Like any other infrastructure, sewers have a limited service life. Trenchless rehabilitation of damaged sewers saves both time and money in comparison to traditional open trench rehabilitation methods. Sewer lining has emerged as the fastest growing rehabilitation method among trenchless technologies. In this process, a flexible tube made of carrier material soaked in reactive resin is inserted into the deteriorated sewer via manholes and cured in place. This creates a plastic pipe within the sewer pipe (CIPP = Cured in Place Pipe). This method was first used in London in 1971, and has since been widely used for over 50 years.

The increased adoption of this technology is yielding promising sewer renovation results. However, it also raises questions about the potential service life. According to manufacturers and the German Association for Water, Wastewater and Waste (DWA), the current technical service life assumption stands at 50 years. The materials and installation methods used have developed continuously over the past 30 years. Therefore, a 30-year-old sewer liner can only be compared to a 5-year-old one to a limited extent. Given the uncertainties surrounding the actual service life of sewer liners, a thorough investigation and, if necessary, reassessment of the service life specified in the regulations is imperative.

To ascertain the service life of CIPP liners, damage that shortens it and measures to ensure a long service life must be explored. In the SEMA Berlin 3 project, which is closely connected to and complements our SEMAplus tool, we address these issues with the help of three methods: a literature review, an analysis of damage to installed liners, and an interview campaign with operators of urban drainage systems, manufacturers of sewer liners, research institutes, consulting firms, and testing laboratories to gather information on their experiences and insights.

The investigation revealed a large number of influencing factors that impact sewer liners and their service life. The influences on a CIPP liner shown in Figure B include installation processes, environmental and operational factors, as well as decision-making processes related to strategic asset management. The service life of liners depends primarily on the quality of the installation. Ensuring a defect-free installation enhances the prospects of an extended service life for sewer liners. Just like with newly constructed sewers, CIPP liners should only be installed by trained and experienced installation companies, and comprehensive quality assurance should be carried out.