On the use of high-density polyethylene additional pipes for water hammer control in multi-material pipeline systems

This study investigates high-density polyethylene additional pipes as passive compliant components for mitigating water hammer in predominantly HDPE and HDPE–steel pipeline systems. Experiments were conducted for different flow rates, pipe lengths, and connection locations relative to the valve and the material interface. In the predominantly HDPE system, the additional pipe mainly increased the oscillation period and had little effect on the first positive pressure maximum. In the HDPE-steel system, its effectiveness depended strongly on location: when installed near the valve, both investigated lengths reduced the first pressure maximum to approximately 62–68% of the reference value. A one-dimensional viscoelastic model with independently identified parameters for the main and additional HDPE pipes reproduced the measured pressure head histories with RMSE values of 1.01–1.74 m. The results show that mitigation depends more on connection location and short-time compliance than on pipe volume alone.