Solid Particle Erosion in Long Radius Elbows and Straight Pipes
Authors: McLaury B.S. , Wang J. , Shirazi S.A. , Shadley J.R. , Rybicki E.F. 
Published: December 2007

Solid Particle Erosion in Long Radius Elbows and Straight Pipes B.S. McLaury, J. Wang, S.A. Shirazi, SPE, J.R. Shadley, and E.F. Rybicki, The Erosion/Corrosion Research Center, Department of Mechanical Engineering, The University of Tulsa

Abstract
Erosion is a severe problem during the production of oil and gas. Producers must have a method to limit the erosion to an acceptable level. One of the most common methods is the use of American Petroleum Institute Recommended Practice 14E (API RP 14E). However, API RP 14E does not account for many factors that influence the severity of erosion. This work is part of an ongoing study to develop erosion prediction models that extend API RP 14E to include these factors.
Previously, a mechanistic model to predict maximum penetration rates in standard radius elbows was presented by the present authors that accounts for a variety of parameters including sand and fluid properties as well as the respective flow rates. The mechanistic model could also be used to predict threshold flowstream velocities that would result in a specified tolerable amount of erosion. The current work has two goals:extend the mechanistic model to account for the radius of curvature of long radius elbows andcreate a mechanistic model that can predict penetration rates in straight pipes.
The modifications to the previous mechanistic model necessary to account for radius of curvature are presented and verified through a comparison with experimental data and results from a comprehensive erosion prediction model. A separate mechanistic model is also presented to predict erosion in straight pipes. The long radius elbow model is used to demonstrate the effect of elbow radius of curvature on the penetration rate. Results are also presented for both the long radius elbow and straight pipe models to show the effects of sand size, flowstream velocity, and pipe diameter on erosion penetration rate.

Introduction
Erosion is a major concern for many oil and gas companies. Sand produced along with the oil and gas impinges pipe walls, fittings, and valves resulting in erosion. Even wells that have only a small amount of sand can experience erosion. However, many companies are currently producing from wells that contain a relatively large amount of sand. Additionally, companies are being forced to drill wells in more severe environments. The depth of offshore wells is increasing which means more of the piping is becoming less accessible. Therefore, being able to predict erosion rates is extremely important. Companies would like to be able to predict erosion rates for a given design and set of operating conditions; this would enable them to evaluate various design configurations. Regardless of the design, a certain amount of erosion will occur, but the goal is to limit the erosion to an acceptable level.
API Recommended Practice 14E (RP 14E) is a common method used in the effort to limit erosion. This procedure determines a production velocity below which only a tolerable amount of erosion will occur,
(1)
The severity of erosion depends on numerous factors; however, API RP 14E only accounts for the fluid density,. In fact, API RP 14E accounts for fluid density incorrectly in the presence of sand. Furthermore, procedures for determining the coefficient, C, used in the calculation vary greatly especially if sand is present. The current work is aimed at providing an estimate of erosion rates for oilfield geometries.

Background
Erosion occurs in a variety of fittings, and one common fitting that is especially susceptible to erosion is the elbow. Since this is a common problem, many investigators have studied the effects of various parameters on the severity of erosion in elbows in an effort to reduce the erosion damage.
P. 977^