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An Alternative to API 14E Erosional Velocity Limits for Sand-Laden Fluids Mamdouh M. Salama Conoco Inc., 1000 South Pine Street, P.O. Box 1267, Ponca City, OK 74602-1267 Fellow ASME

The current practice for eliminating erosional problems in piping systems is to limit the flow velocity 共 Ve兲 to that established by the recommended practice API RP 14E based on an empirical constant (C-factor) and the fluid mixture density 共 ␳ m兲 as follows:Ve ⫽ C/ 冑␳ m. The API criterion is specified for clean service (noncorrosive and sand-free), and it is noted that the C-factor should be reduced if sand or corrosive conditions are present. The validity of the equation has been challenged on the basis that the API RP 14E limits on the C-factor can be very conservative for clean service and is not applicable for conditions when corrosion or sand are present. Extensive effort has been devoted to develop an alternative approach for establishing erosional velocity limits for sand-laden fluids. Unfortunately, none of these proposals have been adopted as a standard practice because of their complexity. This paper will review the results of these studies and proposes an alternative equation that is as simple as the API 14E equation. This alternative equation has the following form: Ve⫽SD冑␳m/冑W. The value of the S-factor depends on the pipe geometry, i.e., bend, tee, contraction, expansion, etc. Using the units for mixture flow velocity 共 Ve兲 in m/s, fluid mixture density 共 ␳ m兲 in kg/m3, pipe diameter (D) in mm and sand production (W) in kg/day, the value of the S-factor is 0.05 for pipe bends. The accuracy of the proposed equation for predicting erosion in pipe bends for fluids containing sand is demonstrated by a comparison with several multi-phase flow loop tests that cover a broad range of liquid-gas ratios and sand concentrations. 关S0195-0738共00兲00202-8兴

Introduction Erosion is defined as the removal of material from a solid surface by the repeated application of mechanical forces. These forces are induced by solid particles, liquid droplets, or cavitation. Liquid impingement erosion occurs when liquid drops or liquid jet repeatedly impact the solid surface. Erosion may be attributed to removal of the metal, the inhibited film, and/or protective corrosion scales. In order to avoid erosion damage, the current oil industry practice for sizing process piping, flow lines, pipelines, and tubing is to limit the flow velocity to the maximum erosional velocity as calculated by the following API RP 14E equation 关1,2兴: V e⫽

C

冑␳ m

(1)

V e ⫽ fluid erosional velocity, ft/s C ⫽ empirical constant ␳ m ⫽ gas/liquid mixture density at flowing pressure and temperature, lb/ft3 C is 100 for continuous service and 125 for intermittent service. Consideration should be given to reducing these values if solids production 共sand兲 is anticipated. In the latest API RP 14E 关2兴, higher C-values of 150 to 200 may be used when corrosion is controlled by inhibition or by employing corrosion-resistant alloys. The original API criterion 关1兴 is specified for clean service 共noncorrosive and sand-free兲, and it is noted that the C-factor should be reduced if sand or corrosive conditions are present. Contributed by the Petroleum Division and presented at the Offshore Technology Conference, Houston, Texas, May 4–7, 1998, of THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS. Manuscript received by the Petroleum Division, March 23, 1999; revised manuscript received March 3, 2000. Associate Technical Editor: C. Sarica.

However, no guidelines are provided for these reductions. It has been argued by several investigators that the API RP 14E relation is extremely conservative under these conditions and this led to the changes in the 1991 edition 关2兴. However, the recent changes 关2兴 imply that a C-factor of 100 is acceptable for corrosive systems and a C-factor of 150 to 200 is acceptable for inhibited systems. In this paper, the basis for the API RP 14E equation will be investigated and the current industry practice in its application will be examined. The paper will then focus on examining the validity of the API 14E equation for sand-laden fluids and present several models that are being advanced by the industry to predict sand erosion in piping systems. A new simplified model will be proposed and its accuracy will be examined using a large number of two-phase 共liquid-gas兲 flow loop experiments.

Basis of the API RP 14E Erosional Velocity Equation The basis and the source of this API RP 14E equation 关1,2兴 have been the subject of speculation in several papers and reports. Several suggestions were offered for the basis of this equation. These suggestions are summarized in Table 1. A detailed discussion on these suggestions is presented by Salama 关3兴. Although several authors attempted to rationalize the validity of the C-factor limit, none of the references succeeded in providing evidence supporting the use of a C-factor of 100 or 150 to avoid erosion. Both Salama and Venkatesh 关4兴 and Heidersbach 关5兴 suggested that the API equation was based on limits on pressure drop in pipes. As an extension to this argument to two-phase flows, Salama 关3兴 suggested the following equation that relates pressure drop in two-phase horizontal pipes to the API C-factor and showed that predictions made by this equation compare very well with those made using Beggs and Brill model 关6兴 for several twophase flow conditions

Journal of Energy Resources Technology Copyright © 2000 by ASME

冉

冊

␦P 0.00045 1.62 ⫽ C ␦L D 1.2

(2)

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Table 1 Speculations regarding the origin of API RP 14E erosional velocity equation

Information in the table taken from 关4,5,7–15兴.

where ␦ P/ ␦ L⫽pressure drop per unit length 共psi/ft兲 D⫽Pipe diameter 共in.兲 C⫽API C-factor⫽V m 冑␳ m V m ⫽mixture velocity 共ft/s兲 ␳ m ⫽mixture density 共lb/ft3兲

Application of the API RP 14E Erosional Velocity Equation Although the source and validity of the API 14E erosional velocity equation is being questioned by many, its use within the oil industry is widespread. However, many companies are using higher values for the C-factor than suggested in the API RP 14E document. Deffenbaugh and Buckingham 关9兴 reported that Mobil does not limit flow velocities, and Arco uses a C-factor of 200 for continuous service and C-factor of 250 for intermittent service when corrosion is controlled and if sand can be avoided. Deffenbaugh and Buckingham also presented data developed by Arco on velocity effect of inhibited systems 共with and without solids兲 on carbon steel and 316 stainless steel for pipes, elbows, and chokes. The results showed that for a straight pipe section, no erosion/ corrosion was observed for C-factors up to 500. For other components, no erosion/corrosion was reported for C-factors up to 300, even with sand. Heidersbach 关5兴 reported that Phillips does not use API 14E to determine production rates. Erichsen 关16兴 reported that one North Sea operator produced from a condensate well at a velocity of 286 ft/s 共C-factor of 726兲 for 1050 days 共@2.9 yr兲 until a failure occurred in the AISI 4140 carbon steel tubing at the flow coupling. The failure of the coupling was attributed to liquid impingement caused by the fluids exiting the 2-in. downhole safety valve into the 3.9-in. tubing. The flow coupling was replaced by L80-13 Cr material and no failure was reported, but the velocity was also reduced. Erichsen also reported that another North Sea operator has used a C-factor of 300 as upper limit for Gullfaks subsea water injectors completed with L80-13 Cr tubing. One should not, however, be surprised if corrosion failure occurs in this system at the joints because of the susceptibility of 13 Cr to crevice corrosion and pitting. Results by Camacho 关17兴 showed no erosion damage, in most experiments, for N-80 steel after repeated impact by liquid slug at a velocity of 100 ft/s, which corresponds to a C-factor of 800. When erosion damage was observed, it was attributed to the presence of microscopic solid particles in the liquid. Three-month 72 Õ Vol. 122, JUNE 2000

tests were conducted at a velocity corresponding to a C-factor between 220 and 260 in a seawater flow loop containing fiberglass pipes and pipe bends of CuNi and stainless steel 关18兴. The tests were concluded without any erosion damage in the fiberglass, CuNi, or stainless steel. Single 共distilled water兲 and two-phase 共water and nitrogen兲 flow loop test results on simulated tubular joints 关19兴 showed that, providing corrosion can be suppressed, a C-factor of 400 can be used without any concern for erosion. The results show that there is no difference between erosion/corrosion rate for a C-factor of 40 and that of 400. The results also show that at a C-factor of 400, carbon steel showed no signs of erosion when corrosion was suppressed by cathodic protection. High corrosion rates were, however, observed when the steel joints were not cathodically protected. This high corrosion rate was unexpected because the oxygen level was very low. However, experimental results 关20兴 have confirmed that corrosion rates in a deaerated system can be high when the pH value is low, which was the situation in this case. Since corrosion rates can be influenced by flow velocity, C-factor values higher or lower than 100 are possible, depending on the operating condition. Even for systems that rely on inhibitors to suppress corrosion, the use of a C-factor of 150 to 200 as suggested by API RP 14E 关2兴 can be risky unless the inhibitor is evaluated using a flow loop testing at the operating C-factor. In many cases, inhibitors that provide good protection under stationary conditions lose their effectiveness at higher velocities, even at C-factors lower than 100 关21兴. However, there are inhibitors that maintain their effectiveness even at a C-factor of 400 关21兴. Therefore, extreme care must be taken in selecting inhibitors for systems operating at high C-factors.

Sand Erosion Unlike erosion in sand-free systems where erosion rate is related to two parameters, i.e., mixture density and flow velocity, erosion due to sand is influenced by several factors including fluid characteristics 共flow rate, composition, density, viscosity兲, sand characteristics 共concentration, impact velocity, impact angle, number of particles hitting the surface, shape/sharpness, hardness, size distribution, density兲, component geometry 共bend, tee, choke, joint兲, and material properties 共hardness, microstructure兲. There Transactions of the ASME

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exists an extensive database that can be used to characterize erosion rate of different materials. These data are generally presented using the following equation: E r ⫽AV np F 共 ␣ 兲

(3)

where E r is erosion ratio measured as the ratio between the mass of metal loss and the mass of sand hitting the target material. A and n are experimentally determined constants that depend on the material properties. For ductile materials the value of n is in the range of 2 to 3. For brittle material, n can be as high as 6. V p is the impact velocity of the sand particle on the metal surface. This velocity depends on the flow conditions, the geometry of the component, and sand properties 共density and size兲. F( ␣ ) is a function whose value varies between 0 and 1, depending on the impact angle. The function depends on the target material ductile/brittle behavior. The value of F( ␣ ) is maximum for ductile materials such as steel at impact angles of 20 to 40 deg, and for brittle materials such as ceramics at 90 deg. The difficulty in calculating erosion rates is in predicting the proper values of particle impact angle, ␣, and velocity, V p , whose values depend on: fluid density, fluid viscosity, sand particle diameter, sand density, pipe diameter, and pipe geometry 共elbow, tee, choke, etc.兲. Also, the amount of sand hitting the target is influenced by the flow conditions, sand concentration, and the geometry of the component; therefore, it may not be the same as the total amount of sand in the flow. One can account for these factors through the use of computational fluid dynamic 共CFD兲 analyses and particle tracking simulation models. There are four main models that have been developed within the industry for predicting sand erosion in piping systems. These models are based on work done by Salama and Venkatech 关4兴, Kvernvold of DNV 关22兴, Shirazi et al. of Tulsa University 关28兴, and Lockett et al. of AEA 关24兴. All models are limited to erosion predictions in simple pipe geometries, such as pipe bends and tees. Salama and Venkatech’s model 关4兴 is a closed-form equation whose predictions are accurate for mainly gas systems. The model was verified using sand erosion data in air flow. This model suggests the following equation for erosion prediction in steel with yield strength of 50 to 80 ksi: ER⫽S m

WV 2 D2

(4)

where ER is erosion rate in mpy, W is sand flow rate in lb/day, V is fluid flow velocity in ft/s, D is pipe internal diameter in in., S m is a geometry-dependent constant. Salama and Venkatech 关4兴 suggested the following values for Sm : S m ⫽ 0.038 共for pipe bends兲 S m ⫽ 0.019 共for tees兲 Svendeman and Arnold 关25兴 recommended the same equation proposed by Salama and Venkatech 关4兴, but proposed different values for S m . Their values for gas systems are as follows: S m ⫽ 0.017 共for long radius elbow兲 S m ⫽ 6⫻10⫺4 共for plugged tees兲 The AEA model 关24兴 which is based entirely on experimental correlations, is available in a spread sheet form and has the following form: ER⫽F 共 aV ln ⫹be ⫺cV l 兲

(5)

where a, b, and c are functions of the gas velocity; F is a function of several nondimensional groups that relates values from experiments to the values under the process conditions. The models developed by DNV 关22兴 and Tulsa University 关23兴 are similar in their attempts to incorporate flow conditions in the Journal of Energy Resources Technology

erosion prediction model. The Tulsa model relies on empirical formulas to account for particle tracking, while the DNV model allows actual calculations, though simplified, of the trajectories of the sand particles. While all other models predict a single value that corresponds to the maximum erosion rate, the DNV model predicts erosion rate distribution along a pipe bend based on calculations of impact velocity and angle at all locations. The models developed by Salama and Venkatesh 关4兴, DNV 关22兴, and Tulsa University 关23兴 incorporate the standard erosion equation, Eq. 共3兲, but the values of the constants are different. While the value of n in Salama and Venkatesh’s model is 2, the value is 1.73 in the Tulsa University’s model and 2.6 in the DNV’s model. Although each model claims to be verified based on experimental data, their predictions for the same case can vary by two orders of magnitude. Resolution of these differences is critical because, while one model shows that certain operating conditions are acceptable, another model shows them unacceptable, which makes it necessary to reduce production rate.

Proposed Sand Erosion Model Extensive effort has been devoted to develop an approach for establishing velocity limits for sand-laden fluids. Unfortunately, none of these proposals have been adopted as a standard practice because of their complexity. There is a need for a reliable, yet simple, equation, as simple as the API RP 14E equation, to establish erosion rate or erosional critical velocity for fluids containing sand. Although the equation proposed by Salama and Venkatesh 关4兴 is simple, it is not very accurate when applied to two-phase 共gas-liquid兲 flow systems. When proposing their equation, Eq. 共4兲, they suggested that the fluid properties have an effect on erosion rate, but they selected the constant of the equation based on calibration with sand erosion in air. Not surprising that their equation becomes increasingly conservative as the liquid-gas ratio increases, i.e., as the mixture density ( ␳ m ) increases. In addition, they did not account for the sand particle size which is known to have an effect on erosion rate for particles less than 400 microns. Above 400 microns, the effect of sand particle size becomes negligible because of the different competing parameters of particle weight, drag and number of particles per unit sand weight. The new equation being proposed in this paper is based on modifying Eq. 共4兲 by incorporating the effect of fluid mixture density and particle diameter as follows: E p⫽

2 d 1 Vm 2 Sp D ␳m

(6)

The accuracy of Eq. 共6兲 is demonstrated by comparing its predictions with measured erosion rates in pipe bends from flowloop experiments conducted under different flow conditions, liquid-gas ratios, sand size, pipe size, and by different investigators. The results of this comparison are presented in Table 2 and shown in Fig. 1. The value of S p , as well as the value of other constants that will be derived later by reformatting Eq. 共6兲, are given in Table 3. It must be noted that almost all the experimental data used in validating this model were derived from erosion tests in liquid 共water兲 and gas 共air or nitrogen兲; thus, the effect of viscosity on erosion rates for liquids having the same density has not been fully quantified. It is, however, expected that the erosion rate will be lower for liquids that have higher viscosity while having the same density. Equation 共6兲 can be rewritten to predict erosion rate 共mm/yr兲 in terms of sand production rate 共kg/day兲 as follows: ER⫽

2 d 1 WV m 2 Sm D ␳m

(7)

For oil and gas production, typical sand size is 250 micron and in general erosion rate in the order of 0.1 mm/yr 共4 mpy兲 is considered tolerable. Therefore, the erosional velocity limit can be given in the following form: JUNE 2000, Vol. 122 Õ 73

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Table 2 Measured and predicted erosion rates using Eq. „6…

V e ⫽S

D 冑␳ m

冑W

(8)

Sometimes, operators establish operating conditions based on a certain tolerable sand concentration. Equation 共7兲 can be rewritten in terms of sand concentration as follows: ER⫽

冉 冊

1 3 M dV m Sc

(9)

Typically, a tolerable sand concentration of 5 ppm is specified and a sand size of 250 micron is considered. Considering a tolerable erosion rate of 0.1 mm/yr 共4 mpy兲, the critical erosional mixture velocity for elbows is: V e ⫽11.7 m/s. 74 Õ Vol. 122, JUNE 2000

Although it is more convenient to treat erosion predictions as a deterministic phenomenon, the probabilistic approach is more appropriate because of the many uncertainties of erosion calculations. These uncertainties are associated with both the input parameters and the predictive models. Uncertainties in the input parameters include uncertainty in the calculation of flow velocity, uncertainty associated with the forecast of production data, uncertainty of fluid properties, uncertainty of sand size distribution, and physical uncertainty of pipe diameter and wall thickness. This is in addition to the obvious uncertainty in the predictive model itself. It is critical to properly account for these uncertainties, particularly, when erosion predictions are used as basis for placing limitations on production rate and/or serving as the sole input in Transactions of the ASME

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Table 2. (Continued)

Information in the table taken from 关26–30兴.

establishing the inspection frequency of production and process systems.

Proposed Erosional Velocity Limits The accuracy of the form of Eq. 共6兲 is clearly demonstrated as shown in Fig. 1. The value of the constant S p and the other related constants for the different pipe geometries can be derived based on experimental results as given in Table 3 or by detailed CFD analysis for the required geometry. Based on the extensive experimental data base presented in Table 3, it is recommend that the value of the constants should be limited to those identified for elbows. The constants are validated based on tests conducted by four independent laboratories. The constants based on the work by Journal of Energy Resources Technology

Fig. 1 Correlation between empirical model predictions and measured sand erosion rate in bends

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Table 3 Values of sand erosion constants

Information in the table taken from 关26–30兴.

Bourgoyne 关30兴 appear to be high, and therefore cannot be used without further validation. In the proposed equation, the effect of pipe bend radius was not considered because test results did not show a major difference between erosion in 1 1/2 and 5 D elbows. For plugged tee, both CFD analysis and limited experimental work suggest that the erosion rate is lower than that for elbows. But the effect decreases as the liquid to gas ratio increases. This observation is also illustrated by Bourgoyne’s work 关30兴. Using Eq. 共8兲 as the basis, the following is the recommended equation for establishing erosional velocity limits for oil and gas production: V e⫽

D 冑␳ m 20冑W

(10)

Conclusions and Recommendations 1 For solid-free, noncorrosive fluids, providing pressure drop is not a concern, the maximum flow rate can be established using the following form of API RP 14E equation: V⫽

400

冑␳ m

where V is the maximum fluid velocity limit in ft/s, ␳ m is the gas-liquid mixture density at flowing pressure and temperature in lb/ft3. 2 For sand-free, corrosive fluids, inhibitors exist that are effective at flow velocities corresponding to C-factors higher than 300. However, it is very important that the effectiveness of the inhibitor be evaluated in a flowloop at these high velocities. For multiphase pipelines, the effectiveness of the corrosion control program depends on the proper transport of the inhibitors in the pipeline. 3 For sand-laden fluids, the maximum flow rate limit can be established using the following equation: V e⫽

D 冑␳ m 20冑W

4 At high flow rates, the presence of sand enhances the corrosion of steel in both uninhibited and inhibited solutions due to erosive wear of protected corrosion product and/or depolarization of anodically/cathodically controlled corrosion process by plastic deformation of the metal surface. At low flow rates where sand settling occurs, sand has no effect on corrosion rates in uninhibited solutions, but it can have a profound effect on the rates in inhibited solutions.

Acknowledgment The author would like to thank the management of Conoco for their permission to publish this paper. The author would also like 76 Õ Vol. 122, JUNE 2000

to express his appreciation to Oddmund Kvernvold of DNV, Tim Locket of AEA, and Sia Shirazi of Tulsa University for their input.

Nomenclature 共Units are as stated here, unless noted otherwise in the text of the paper.兲 Erosion measurements E r ⫽ erosion ratio in kg/kg, which is ratio between mass of metal loss and mass of sand hitting target material E p ⫽ erosion parameter in mm/kg, which is ratio between penetration in metal and mass of sand hitting target material ER ⫽ erosion rate in mm/y, which is rate of penetration in metal by erosion Sand W ⫽ sand flow rate in kg/day M ⫽ sand concentration ppm 共by weight兲, which is the ratio of mass of sand to mass of fluid d ⫽ sand size in micron 共typical value 250 micron兲. 共Note: The effect of d on ER becomes negligible above 400 micron. Therefore, for d⬎400, the limit of 400 is used.兲 ␳ s ⫽ sand density in kg/m3 共typical value 2650 kg/m3兲 Fluids V l ⫽ liquid superficial velocity in m/s V g ⫽ gas superficial velocity in m/s V m ⫽ fluid mixture velocity in m/s ⫽ V l ⫹V g V e ⫽ erosional velocity limit, m/s ␳ l ⫽ liquid density in kg/m3 ␳ g ⫽ gas density in kg/m3 ␳ m ⫽ fluid mixture density in kg/m3 ⫽ ( ␳ l V l ⫹ ␳ g V g )/V m Pipe geometry D ⫽ pipe internal diameter in mm Constants C ⫽ empirical constant specified by API 14RP 14E to predict the erosional velocity limit, V e 共in ft/s兲 S ⫽ geometry-dependent constant, specified in this paper for typical operating conditions 共tolerable erosion rate of 0.1 mm/yr 共4 mpy兲 and sand size of 250 micron兲 to predict erosional velocity limit, V e 共m/sec兲 S p ⫽ geometry-dependent constant, specified in this paper and used to predict E p in terms of flow parameters Transactions of the ASME

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S m ⫽ geometry-dependent constant, specified in this paper and used to predict ER given sand rate 共W兲 and other flow parameters S c ⫽ geometry-dependent constant, specified in this paper and used to predict ER given sand concentration 共M兲 and other flow parameters 共Note that the parameters S,S p ,S m ,S c are all related. As an example: S m equals 365/S p to convert E p to ER.兲

References 关1兴 API, 1981, ‘‘API RP 14E Recommended Practice for Design and Installation of Offshore Production Platform Piping Systems,’’ 3rd Edition, American Petroleum Institute, Washington, DC, p. 22. 关2兴 API, 1991, ‘‘API RP 14E Recommended Practice for Design and Installation of Offshore Production Platform Piping Systems,’’ 5th Edition, American Petroleum Institute, Washington, DC, p. 23. 关3兴 Salama, M. M., 1998, ‘‘An Alternative to API 14 E Erosional Velocity Limits for Sand Laden Fluids,’’ Proc., Annual Offshore Technology Conference, OTC Paper 8898. 关4兴 Salama, M. M., and Venkatesh, E. S., 1983, ‘‘Evaluation of API RP 14E Erosional Velocity Limitations for Offshore Gas Wells,’’ Proc., 15th Offshore Technology Conference, Paper OTC 4485. 关5兴 Heidersbach, R., 1985, ‘‘Velocity Limits for Erosion-Corrosion,’’ Proc., 17th Offshore Technology Conference, Paper OTC 4974. 关6兴 Beggs, H. D., and Brill, J. P., 1973, ‘‘A Study of Two-Phase Flow in Inclined Pipes,’’ J. Pet. Technol., 25, No. 5, pp. 607, 617. 关7兴 Rybicki, E., 1987, private communication, University of Tulsa, Tulsa, OK. 关8兴 Engel, O. G., 1955, ‘‘Water Drop Collisions with Solid Surfaces,’’ J. Res. Natl. Bur. Stand., 54, No. 5, pp. 281–298. 关9兴 Gipson, F., 1989, ‘‘Petroleum Production Engineering, Pits and Pieces,’’ Manual of Southwest Petroleum Short Course, Texas Tech University, April 17–20. 关10兴 Deffenbaugh, D. M., and Buckingham, J. C., 1989, ‘‘A Study of the Erosional/ Corrosional Velocity Criterion for Sizing Multi-Phase Flow Lines,’’ Southwest Research Institute Final Report, Project No. 04-2433, prepared for the Minerals and Management Service, U.S. Department of the Interior. 关11兴 Smart, J. S., 1990, ‘‘A Review of Erosion Corrosion in Oil and Gas Production,’’ Corrosion 90, Paper 10, NACE. 关12兴 Coker, A. K., 1990, ‘‘Understand Two-Phase Flow in Process Piping,’’ Chem. Eng. Prog., 86, No. 11, Nov. pp. 60–65. 关13兴 Coulson, J. M., and Richardson, J. F., 1977, Chemical Engineering, 1, 3rd Edition, p. 91, Pergamon Press. 关14兴 Smart, J. S., 1991, ‘‘The Meaning of the API RP 14E Formula for Erosion/

Journal of Energy Resources Technology

Corrosion in Oil and Gas Production,’’ Corrosion 91, Paper 468, NACE. 关15兴 Patton, C. C., 1993, ‘‘Are We Out of the Iron Age Yet?,’’ Corrosion 93, Paper No. 56, NACE. 关16兴 Erichsen, H., 1988, ‘‘Nipple, Lock, and Flow Coupling Recommendations and Subassembly Description for North Sea Wells,’’ private communications, Norske Conoco a.s. 关17兴 Camacho, R. A., 1988, ‘‘The Design, Construction, and Testing of a Liquid Impingement Apparatus and a Study of Metal Surfaces Eroded by Liquid Impingement,’’ M. S. thesis, The University of Tulsa, Tulsa, OK. 关18兴 Saetre, O., 1991, ‘‘Testing of Composite Pipes in High Velocity Seawater,’’ Volume III, Part B Proc., 10th International Conference on Offshore Mechanics and Arctic Engineering, ASME, eds., M. M. Salama et al., pp. 577–583. 关19兴 Salama, M. M., 1996, ‘‘Velocity Limits for Multi-Phase Piping,’’ unpublished internal report, Conoco Inc.. 关20兴 Salama, M. M., 1993, ‘‘Erosional Velocity for Water Injection Systems,’’ Materials Performance, NACE, 32, No. 7, pp. 44–49. 关21兴 Greving, D., 1991, ‘‘Effect of Flow Velocity on the Performance of Selected Oil Field Corrosion Inhibitors in Vertical Tubing, Under Two-Phase Flow Conditions,’’ M. S. thesis, Mechanical Engineering, University of Tulsa, Tulsa, OK. 关22兴 Kvernvold, O., 1998, ‘‘ERBEND 2—Erosion in Pipe Bends,’’ Det Norske Veritas 共DNV兲, Norway. 关23兴 Shirazi, S. A., McLaury, B. S., Shadley, J. R., and Rybicki, E. F., 1995, ‘‘Generalization of the API RP 14E Guidelines for Erosive Services,’’ J. Pet. Technol., 47, No. 8, pp. 693–698. 关24兴 Lockett, T. J., Beech, P. M., Birchenough, P. M., McCarthy, P., Dawson, S. G. B., and Worraker, W. J., 1997, ‘‘Erosion/Corrosion in Sweet Multiphase Systems,’’ AEAT Report No. 1174, AEA Technology plc., UK. 关25兴 Svendeman, S. J., and Arnold, K. E., 1994, ‘‘Criteria for Sizing Multi-phase Flow Lines for Erosive/Corrosive Services,’’ SPE Prod. Facil. 关26兴 Birchenough, P. M., Dawson, S. G. B., Lockett, T. J., and McCarthy, P., 1995, ‘‘Critical Flow Rates Working Party,’’ Report No. AEA-TSD-0348, AEA Technology, UK. 关27兴 Kvernvold, O., and Sandberg, R., 1993, ‘‘Production Rate Limits in TwoPhase Flow Suystems: Erosion in Piping Systems for Production of Oil and Gas,’’ Technical Report No. 93-3252, Det Norske Veritas 共DNV兲, Norway. 关28兴 Tolle, G. C., and Greenwood, D. R., 1977, ‘‘Design of Fittings to Reduce Wear Caused by Sand Erosion,’’ API OSAPER Project No. 6, American Petroleum Inst., Texas A&M Research Foundation. 关29兴 Weiner, P. D., and Tolle, G. C., 1976, ‘‘Detection and Prevention of Sand Erosion of Production equipment,’’ API OSAPER Project No. 2, American Petroleum Inst., Texas A&M Research Foundation. 关30兴 Bourgoyne, A. T., 1989, ‘‘Experimental Study of Erosion in Diverter Systems Due to Sand Production,’’ Proc., SPE/IADC Drilling Conference, New Orleans, LA, SPE/IADC 18716.

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