Evaluation of Darcy–Weisbach Friction Factors of Fiberglass Pipes Based on Internal Surface Roughness Measurement

Assessment of energy head loss and the friction coefficient is a significant factor in fluid mechanics and the design of pipeline systems. Estimation of head loss and friction coefficient of FARATEC glass-reinforced plastic (GRP) pipes are considered by different profilometry methods in this study. It is based on surface roughness measuring by profilometry and special surface roughness instruments to compute the surface roughness and friction coefficient of GRP pipes. This method was used to compute the Darcy–Weisbach friction factor f of GRP pipes in the current range of flow velocities and pipe diameters based on Colebrook–White equation. In this method, surface roughness was measured by three instruments, and the friction factor f is computed numerically. The Surftest SJ-210 instrument obtained the best and most accurate surface roughness measurements among the other instruments. Also, Rz and Ra with λc, 0.8 and 2.5, respectively, are calculated as appropriate roughness parameters to evaluate the surface roughness of GRP pipe samples. All Darcy–Weisbach f coefficients and Moody diagrams were computed accurately and compared to reference friction factors. Therefore, the surface roughness and friction factor (f) of GRP pipes for commercial diameters are placed in the range of smooth pipes.