Estimation of Equivalent Sand–Grain Roughness for Coated Water Supply Pipes

Abstract

The Colebrook equation gives the Darcy-Weisbach friction factor for fluid flow in pipes as a function of sand-grain roughness and the Reynolds number. Values of equivalent sand-grain roughness (k) have been obtained for various ductile iron pipes coated with different anticorrosion materials through fluid flow experiments, and the results show that the value of k calculated by the Colebrook equation varies significantly with the Reynolds number. Considering the uncertainty in the hydraulic data due to errors during lab measurements, the paper shows how to estimate a reasonable value of k based on a systematic analysis of uncertainties for a pipe of given diameter, length, flow discharge, and head loss, as well as width, height, and head above the crest of sharp-edged weirs used for flow measurement. The values of k for three pipe cases were estimated, and rules pertaining to uncertainty in the relevant parameters and the Reynolds number are summarized with quantitative relation expressions. A sensitivity analysis of the estimation of k and some important practical findings are also provided.