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.
Introduction
Today’s technology in surface engineering and pipe manufacturing has led to
the introduction of modern pipes. In the past the selection of the material for
the tubing was routine and basic, with most operators selecting carbon steel as
a de facto standard (Craig 1993). Now, there is a drastic shift from the use of
traditional carbon steel to pipes made with different alloys and internal
surface finishing. For example, the increase in the use of Chrome (Cr13) tubing
and internally plastic-coated pipes is because of their well-documented
longevity (Farshad et al. 2000). Piping manufacturers, to mitigate the various
problems associated with most operational phases of the chemical and petroleum
industries, developed new alloyed pipes with different surface characteristics
and specialized internal finishings (Arnold and Stewart 1986). Knowledge of the
internal surface-roughness value, ε, is especially important
economically in the design-optimization process of hydrocarbon production and
pipeline systems. Surface roughness influences the pipe flow characteristics by
creating unfavorable pressure and energy losses because of friction. Farshad
and Pesacreta (2003)pointed out that reports on research of physical
measurements, statistical analysis, and mathematical modeling of surface
roughness in new pipes are still scarce in the technical literature. Current
developments in profilometry and surface engineering have led to quick and
accurate measurements of the internal surface roughness of a pipe. This is a
very effective way of measuring and establishing the correct absolute surface
roughness of these pipes. Additionally, uncertainty is reduced when estimating
the friction factor necessary for calculating friction-pressure losses in
modern manufactured pipes.
© 2006. Society of Petroleum Engineers
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History
- Original manuscript received:
23 December 2004
- Revised manuscript received:
27 April 2006
- Manuscript approved:
28 April 2006
- Version of record:
20 September 2006
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