Transient response of hybrid and homogeneous pipelines: Laboratory experiments

The replacement of deteriorated pipe segments in aging water distribution networks often results in hybrid pipelines, consisting of segments of different materials of comparable length. The fact that short segments of polymeric material have a strong effect on the transient response of metallic pipelines authorizes to consider it important to examine the transient behavior of hybrid pipelines. To this end, transient tests were carried out on a high-density polyethylene (HDPE)+ cast iron (CI) hybrid pipeline at the Water Engineering Laboratory (WEL) of the University of Perugia, Italy. As a reference, tests were also carried out on a homogeneous HDPE pipeline with the same total length. The results of the laboratory tests showed that the value of the pressure local extremes (i.e., pressure peaks) was much higher in the homogeneous pipeline than in the hybrid one. On the contrary, the number of pressure peaks is much smaller in the homogeneous pipeline than in the hybrid one. Such features have been explained by analyzing the mechanisms of interaction of pressure waves at the in-series junction between the two different materials.