Ageing of plastic pipes in urban drainage systems

Plastic materials, such as PVC and HDPE, have become dominant construction materials for sewer systems, mainly due to their reputed chemical resistance. Nonetheless, plastic sewer pipes have operated for decades in a hostile environment, raising concern among sewer managers over the longevity of their drainage systems. Therefore, the main aim of this research was to expand the knowledge about the ageing and failure mechanisms of plastic (especially PVC) sewer pipes and thereby contribute to more efficient sewer management. This research was conducted in three main parts, each part being based on the findings of the previous one. The first step was a literature study into ageing of PVC pipes and an analysis of inspection data from four Dutch municipalities. This resulted in an interesting discrepancy: although the literature indicates that PVC is a durable material with a theoretical lifespan of at least 100 years, the inspection images show that PVC pipes show numerous defects even shortly after installation and that the number of defects increases over time. This discrepancy formed the basis for the second step in this research: the excavation and extensive testing of PVC pipes with defects found in practice through inspections in order to determine the cause of the defects. The main causes of failure were found to be low-quality installation and excavation activities in the direct vicinity of the pipes. However, testing also showed that PVC ages physically, which means that the pipe material gradually becomes more brittle. This last aspect formed the basis for the third part of this research, the development of a non-destructive vibro-acoustic technique that can estimate the physical ageing of plastic pipes in practical conditions.