Relative Roughness Chart for Internally Coated Pipes (OCTG)

Abstract

Abstract The object of this paper is to furnish the engineer with a simple means of estimating the absolute surface roughness, e, and relative roughness, e/D, for internally coated pipes (OCTG). It is very important for design engineers in the oil and gas industry to know the values of surface roughness and relative roughness to properly select, design and install the tubing string. A tubing string is the critical part of the completion program. The tubing must be selected so that production operation can be carried out efficiently; it must be designed against failure from tensile forces, internal and external pressure and corrosive actions. In addition, it must be designed in such a way that maximum production rate and total optimization of the production system is achieved. In 1944, Moody 1 prepared a plot of relative roughness, e/D versus pipe diameter, D, for a number of materials. Moody's1 relative roughness correlation was based on experiments on pipes artificially roughened with sand grains. Moody 1 did not provide the relative roughness plot for internally coated pipes, nor did he perform a regression analysis of the data to provide functional forms of the equations relating relative roughness, e/D, as a function of pipe diameter, D. Currently, internally coated pipes are being utilized in the completion of oil and gas wells worldwide. Consequently, absolute surface roughness and relative roughness values of internally coated pipes are needed by practicing engineers to properly model the hydrodynamics and optimize the production rates in wells 2,3,4. It is important to emphasize that dimensional analysis suggests that the effect of surface roughness is not due to its absolute dimensions, but rather to its dimensions relative to the inside diameter of the pipe, e/D.