Defect Evolution in Sewer Pipes: Enhancing Deterioration Models

Deterioration models for sewer pipes often rely only on aggregated pipe-level data (pipe condition), without considering individual defects and their evolution. Is-it worth considering individual defects to improve deterioration models? A preliminary answer is to know if it is possible to model the evolution of individual defects. This study presents a methodology for analysing defect transitions in multi- inspected sewer pipes to gain insights into the aging and deterioration processes at the defect level. Using inspection data provided by Berliner Wasserbetriebe, covering 242,920 pipes and nearly 1.9 million observations, incl. defects encoded according to EN 13508-2, defect transitions were analysed across 24,734 inspection pairs. Defects between inspection pairs for each pipe and position are mapped, creating a transition matrix and knowledge graph to highlight defect inter-dependencies. The results reveal plausible transitions, such as gradual surface degradation from increased roughness to missing pipe wall parts, with varying durations, but also transitions that may reflect inspection uncertainties. Future work will incorporate defect severity classes and explore how these insights can enhance machine learning models through feature engineering or domain-informed approaches.