Surface-Roughness Design Values for Modern Pipes

Abstract

Summary The purpose of this paper is to present practicing engineers and scientists with a new means of estimating the absolute surface roughness values, ε, and relative roughness, ε/d, which are specific to modern pipes with specialized internal finishes. Our research thrust has developed new relative-roughness-design equations, values, and derived charts. Currently, the friction-pressure losses in pipes are being evaluated by practicing engineers by use of Moody's relative-roughness chart (Szilas 1975; Economides et al. 1994). Moody (1944) prepared a relative-roughness chart for a number of common piping materials. Relative roughness provides a simple means for estimating friction factors to be used in computing the friction-pressure losses in piping systems. An accurate determination of the frictional fluid-pressure drop in pipes is required for design purposes. Currently, these newly developed pipes are used worldwide for various applications, and their surface-roughness values are needed to properly model the hydrodynamics (Farshad et al. 2001; Brown 1984). Recently, Farshad and Rieke (2005) published a new relative-roughness chart for the modern manufactured oil-country tubular goods (OCTG). Moody did not provide equations for his relative-roughness chart. Equations are the foundation for establishing such correlation charts. In our research, a new set of nonlinear mathematical models was successfully regressed and developed to accurately describe the log/log relationship between pipe diameter and relative roughness. In this paper we provide a set of new equations for our charts. The new equations developed can be used directly in computer models and simulators for frictional pressure-drop calculations.