Hydraulic and Technological Investigations of a Phenomenon Responsible for Increase of Major Head Losses in Exploited Cast-Iron Water Supply Pipes

The paper presents results of investigations of influence of major head losses on exploitation properties of water supply pipes after 30-year exploitation. The tested materials were cast-iron pipes with the internal diameter of 150 mm. A flowability drop coefficient ηt with average value of 0.45 was determined. Using the measured values of pressure difference Δp determined the absolute roughness of internal walls of the pipes after 30-year exploitation, which was referred to the new pipelines. The absolute roughness for the exploited pipes was equal to k = 27.6 mm, whereas for the new ones it was significantly lower and equal to k = 0.9 mm. Additionally, an analysis of the chemical and mineral composition of sediments gathered in the investigated pipelines was also performed. The top layer of the sediments was dominated by the compounds of a character of the iron hydroxide: goethite (α-FeOOH) and lepidocrocite (γ-FeOOH), whereas the internal layer was supplemented by the gypsum and sulfur, which was proven by the investigations performed with the use of scanning electron microscope (SEM). The sediment gathered within the pipes is the main reason of ca. 30-fold increase of the absolute roughness, which resulted in the flowability drop of the exploited water supply pipes