Impact of Material Aging and Oxidation on Frequency-Dependent Wave Speed and Pressure Attenuation of HDPE Water Pipes

Plastic pipes in water distribution systems experience oxidation over time, but little is known of its impact on pipes’ hydraulic behavior under unsteady-flow conditions. The current research aims to establish the relationship between the level of plastic material oxidation and the dissipation and dispersion of pressure waves, which is fundamental for numerical modeling and wave-based pipeline condition assessment. Accelerated aging of high-density polyethylene (HDPE) pipes was conducted under controlled conditions. The remaining level of antioxidants and the extent of oxidation were quantified by determining the oxidation induction time (OIT) and carbonyl index (CI), respectively. The characteristics of wave dissipation and dispersion of the pipe sections were determined through calibrating the frequency-dependent wave speed and attenuation rate using pressure transients and a novel dual-sensor technique. The results demonstrated that, before the antioxidants were depleted, the OIT reduced with the progression of the aging process, but the wave speed and attenuation rate remained stable. After the depletion of antioxidants, noticeable oxidation occurred, the CI increased, the frequency-dependent wave speed reduced, and the attenuation rate increased.