Author(s): Mohamed Houcem Eddine Ben Arab; Moez Louati; Mohamed Salah Ben Habib Ghidaoui
Linked Author(s): Mohamed Houcem Eddine BEN ARAB, Moez LOUATI
Keywords: Time reversal; Sewage pipe system; Rising mains; Transient flows; Leak detection
Abstract: This paper concerns a case study of leak detection in real sewage rising mains in Hong Kong using transient-based time-reversal methods. Pressurized sewage transmission lines bring complexities to transient-based defect detection methods that are not encountered in water supply lines such as wave speed variability due to the presence of gases, air, and solids. The defects involve a real leak that occurred in Chung Hom Kok Road sewage rising main and simulated leaks in Chung Hom Kok Beach conveyance system. The simulated leak flows varied from 0.1 l/s to 1 l/s. Two transient generation mechanisms were used: a pump shutdown and rapid closure of a side discharge valve. Baseline (leak-free) transient response signals are measured in both systems. It is shown that the model-free time-reversal method which effectively cross-correlates the signal with and without a leak localizes the leaks to within the diffraction limit of half the probing wavelength (λ/2). The fact of λ_(pump)>>λ_(valve) meant that the leak resolution by the pump shutdown is poor in comparison to that of the valve closure. The challenges encountered during field tests are summarized and suggestions for good practice are proposed.