Abstract

The purpose of this paper is to present engineers and scientists with a simple means of determining the absolute surface rough ness, e, and relative roughness, e/D, for Cr13 pipes. An accurate determination of the frictional pressure drop in pipes due to fluid flow is required by practicing engineers and scien tists for the design of items such as well tubing strings, pipelines, and sales gas lines. An important factor in this frictional pressure drop is the relative/absolute roughness. In 1944, Moody 1 prepared a plot of relative roughness versus pipe diameter, D, for a number of materials. Moody did not provide surface roughness value for Cr13 pipes. At that time Cr13 pipes did not exist. Currently, Cr13 pipes are used worldwide 2. Consequently, relative/absolute roughness values of Cr13 pipes are needed to properly model the hydrodynamics. Relatively little work has been published on the standard surface roughness values in Cr13 pipes. Reports on research of physical measure ments, mathematical modeling studies and statistical analysis of surface roughness characterization 3 are still scarce. This research has focused on the development of a new set of surface roughness values and relative roughness chart along with its corresponding mathematical equation for Cr13 pipes.

Introduction

The use of Cr13 oil field tubular goods began, when the oil industry first became concerned with corrosion in gas condensate wells. Despite its practical relevance, relatively little work has been published on the measured absolute surface roughness of Cr13 pipes. Indeed, this aspect has received scant attention in the literature. In particular, reports on research of physical measurements, mathematical modeling studies, and statistical analysis of surface roughness in Cr13 pipes are still scarce 3.

Corrosion costs the industry billions of dollars each year 2. In order to control these costs, diligent effort has to be invested in corrosion considerations and selection of material. The introduction of corrosion resistant alloys in the oil, gas, petrochemical, and pipeline industries have brought revolution ary change in cutting down costs incurred by corrosion. In the past, the selection of the material for the tubing used to be routine and basic, with most operators selecting carbon steel. Today there is a drastic shift from the use of traditional carbon steel to Cr13 is taking place. For example, the increase in the use of Cr13 tubing is because the production engineers have realized that this alloy has long tubing life 4. The Cr13 tubing has already been presented in detail elsewhere 5 and will only be summarized here.

Cr13 Stainless-Steel Tubing

Under low temperature sweet environments containing carbon dioxide, low alloy steels are severely corroded accompanying a ring worm corrosion, but Cr13 steels are found to exhibit good resistance to such environments. No unfavorable field experi ence with regard to corrosion, sulfide stress corrosion or stress corrosion cracking has been reported so far for Cr13 stainless steel tubes in carbon dioxide containing environments. Though the Cr13 tubulars are resistant to carbon dioxide environment, care should be taken when the partial pressure of CO2 in the pipe is high. Similarly hydrogen sulfide also makes Cr13 susceptible to sulfide stress cracking.

Work By Moody

Moody's relative roughness chart has already been presented in detail elsewhere 6 and will only be summarized here. Moody furnished practicing engineers with a correlation for absolute roughness, e, and relative roughness, e/D, for any size of pipe of a given surface. Moody did not provide the relative roughness plot for Cr13 tubing, since at that time Cr13 pipes did not exist.

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