Rotating Cylinder Electrode Study on the Influenceof Turbulent Flow, on the Anodic and Cathodic

Kinetics of X52 Steel Corrosion, in H2SContaining Solutions

Ricardo Galván-Martínez(1), Juan Mendoza-Flores(2), Rubén Durán-Romero(2)

and Juan Genescá-Llongueras*(1)

(1) Dpto. Ingeniería Metalúrgica. Facultad Química. Universidad Nacional Autónoma de México (UNAM). Ciudad Universitaria.04510 México DF (México).

(2) Instituto Mexicano del Petróleo. Dirección Ejecutiva de Exploración y Producción. Corrosión. Eje Central L.Cárdenas # 152. México DF 07730. México

Efecto del flujo turbulento sobre la cinética de corrosion de un acero API X52 en soluciones acuosasque contienen H2S.

Efecte del flux turbulent sobre la cinètica de corrosió d’un acer API X52 en dissolucions aquoses que contenen H2S.

Recibido: 6 de junio de 2005; aceptado: 7 de julio de 2005.

AFINIDADREVISTA DE QUÍMICA TEÓRICA Y APLICADA

EDITADA POR LA ASOCIACIÓN DE QUÍMICOS E INGENIEROS

DEL INSTITUTO QUÍMICO DE SARRIÁ

Afinidad (2005), 62 (519), 448-454

448

Rotating Cylinder Electrode Study on the Influenceof Turbulent Flow, on the Anodic and Cathodic

Kinetics of X52 Steel Corrosion, in H2SContaining Solutions

Ricardo Galván-Martínez(1), Juan Mendoza-Flores(2), Rubén Durán-Romero(2)

and Juan Genescá-Llongueras*(1)

(1) Dpto. Ingeniería Metalúrgica. Facultad Química. Universidad Nacional Autónoma de México (UNAM). Ciudad Universitaria.04510 México DF (México).

(2) Instituto Mexicano del Petróleo. Dirección Ejecutiva de Exploración y Producción. Corrosión. Eje Central L.Cárdenas # 152. México DF 07730. México

Efecto del flujo turbulento sobre la cinética de corrosion de un acero API X52 en soluciones acuosasque contienen H2S.

Efecte del flux turbulent sobre la cinètica de corrosió d’un acer API X52 en dissolucions aquoses que contenen H2S.

Recibido: 6 de junio de 2005; aceptado: 7 de julio de 2005.

Dedicado al Prof. Dr. Lluís Victori, S.J.,en ocasión de su 70 aniversario

RESUMEN

En este trabajo se presentan los resultados obtenidosdurante el estudio del mecanismo y de la cinética decorrosión de un acero API X52 en soluciones acuosasque contienen H2S bajo condiciones de flujo turbulento,utilizando un electrodo de cilindro rotatorio (ECR). Elestudio se ha realizado a cinco diferentes velocidadesde rotación: 0 (condiciones estáticas), 1000, 3000, 5000y 7000 rpm. Se ha encontrado que bajo condiciones deflujo turbulento aumenta significativamente la velocidadde corrosión y el mecanismo de corrosión está contro-lado por el proceso de difusión que tiene lugar en la reac-ción catódica.

Palabras clave: Acero API X52. Electrodo cilindro rota-torio. Flujo. H2S. Transferencia masa.

Dedicated to Prof. Dr. Lluís Victori, S.J.,on the occasion of his 70th birthday

SUMMARY

This work presents the electrochemical kinetics resultsmeasured during the corrosion of API X52 pipeline steelimmersed in aqueous environments, containing dissol-ved hydrogen sulfide (H2S) under turbulent flow condi-tions. In order to control the turbulent flow conditions, aRotating Cylinder Electrode (RCE) was used. Five diffe-rent rotation rates were studied: 0 (or static conditions),

1000, 3000, 5000 and 7000 rpm. It was found that the tur-bulent flow increases the corrosion rate and the corro-sion mechanism for X52 steel exhibits a significant depen-dence on mass transfer on the cathodic kinetics.

Key words: API X52. Flow. Hydrogen sulfide. Mass trans-fer. RCE.

Dedicat al Prof. Dr. Lluís Victori, S.J.,amb motiu del seu 70è aniversari

RESUM

En aquest treball, es presenten els resultats obtingutsdurant l’estudi del mecanisme i de la cinètica de corro-sió d’un acer API X52 en dissolucions aquoses que con-tenen H2S sota condicions de flux turbulent, utilitzant unelèctrode de cilindre rotatori (ECR). L’estudi s’ha realit-zat a cinc velocitats diferents de rotació: 0 (condicionsestàtiques), 1000, 3000, 5000 i 7000 rpm. S’ha trobat quesota condicions de flux turbulent augmenta significati-vament la velocitat de corrosió i el mecanisme de corro-sió està controlat pel procés de difusió que té lloc en lareacció catòdica.

Mots clau: Acer API X52. Elèctrode cilindre rotatori. Flux.H2S. Transferència massa.

* Corresponding author:genesca@servidor.unam.mx

INTRODUCTION

In the oil industry, H2S has been associated to damagesby corrosion and stress corrosion cracking (SCC) inducedby sulphides or hydrogen.(1) H2S gas can dissolve in aque-ous solutions turning them in corrosive solutions, knownas «sour».(2, 3) The increment of temperature and/or pres-sure can increase the aggressiveness of H2S solution tocarbon steel. Corrosion of steel in H2S containing solutionscan be represented according to:(4-6)

Fe + H2Saq ⇒ FeS + H2 (1)

The majority of studies on the corrosion of steels in envi-ronments containing dissolved H2S, have been carried outunder static conditions(7). The main objective of these stu-dies, is the determination of the resistance of different alloysto combined conditions of corrosion and mechanical stres-ses. In many real situations, H2S corrosion occurs underflowing conditions, for example, in transport of hydrocar-bons in pipelines(7). Therefore, the influence of flow on thecorrosion processes is an important issue to be conside-red in the design and operation of industrial equipment.The most common type of flow conditions found in indus-trial processes is turbulent; however, few corrosion stu-dies in controlled turbulent flow conditions are available.With the increasing necessity to describe the corrosion ofmetals in turbulent flow conditions some laboratoryhydrodynamic systems have been used with different degre-es of success(8-10). Among these hydrodynamic systems,rotating cylinder electrodes (RCEs), pipe segments, con-centric pipe segments, submerged impinging jets and clo-se-circuit loops have been used and have been importantin the improvement of the understanding of the corrosionprocess taking place in turbulent flow conditions(10-17). Theuse of the rotating cylinder electrode (RCE), as a labora-tory hydrodynamic test system, has been gaining popula-rity in corrosion studies(18-19). This popularity is due to itscharacteristics, such as, its operation mainly in turbulentflow conditions, its well-defined hydrodynamics, ease ofassembly and disassembly, smaller volume of fluid used,and easier flow and temperature control(20, 21).It has been found that for a RCE enclosed in a concentriccell, the transition between the laminar and turbulent flowoccurs at values of Reynolds number (Re) of 200 approxi-mately(8, 9, 21). The RCE in corrosion laboratory studies is a use-ful tool for the understanding of mass transfer processes,effects of surface films, inhibition phenomena, etc(2, 3, 22) takingplace in turbulent flow conditions. However, the use of theRCE has been questioned by some researchers(23), due tothe differences found between the values of corrosion ratesmeasured on pipe flow electrodes and on the RCE. Thereasons for this difference are still not well understood.However, some works have provided ideas on the expla-nation of this apparent difference(24-26).Dimensionless analysis using mass transfer concepts sho-wed that the corrosion when controlled by diffusion ofone of the species between the bulk fluid and the surfa-ce, could be modeled completely by the rate of masstransfer of the rate limiting species and the Re and Schmidtnumbers (Sc) (27-29). In general, the effect of flow can beused to determine if corrosion is under activation, diffu-sion or mixed control.

EXPERIMENTAL

Test Environment

All experiments were carried out at 20 °C and at the atmosp-heric pressure of Mexico City (0.7 bar). Two aqueous solu-tions were used: (a) NACE brine specification 1D196(30) and

(b) 3.5 % NaCl solution. These two test environments wereselected due to the fact that, most of the H2S corrosionlaboratory testing is carried out in one of these solutionsand the electrochemical behavior has not been reported.In order to remove oxygen from the solution, N2 gas (99.99%)was bubbled into the test solution for a period of 20 minu-tes. The measured dissolved O2 content was lower to 10ppb. After oxygen removal H2S gas (99.99%) was bubbledinto the test solution until saturation was reached. The mea-sured saturation pH was 4.2 for NACE brine and 4.1 for the3.5 % NaCl brine.

Experimental Set up

An air-tight three-electrode electrochemical glass cell wasused. Cylindrical working electrodes were used in all expe-riments. These cylinders were made of API X52 steel(31). Thetotal exposed area of the working electrodes was 5.68 cm2

and 3.4 cm2 for static and dynamic conditions, respecti-vely. As reference electrode a saturated calomel electro-de (SCE) was used. A sintered graphite rod was used asauxiliary electrode. Prior to each experiment, the steel wor-king electrode was polished up to 600 grit SiC paper, cle-aned in deionised water and degreased with acetone. Allelectrochemical tests were carried out on clean samplesand in freshly prepared test solutions.Hydrodynamic conditions were controlled using a Perking-Elmer EG&G Model 636 Rotating Cylinder Electrode (RCE)system. In dynamic conditions, the rotation speeds testedwere 1000, 3000, 5000 and 7000 rpm.

Electrochemical Measurements

A SolartronTM SI 1280B Potentiostat / Galvanostat was usedin all the electrochemical tests. Potentiodynamic polariza-tion curves were recorded at a sweep rate of 1 mV persecond. In order to minimize the effect of the solution resis-tance a Lugging capillary was used.

EXPERIMENTAL RESULTS AND DISSCUSION

Previous work on these systems has shown that the corro-sion mechanism for carbon steel exhibits a significantdependence on mass transfer. This has lead various wor-kers to suggest the use of dimensionless analysis as ameans of relating laboratory-scale experiments to plant-scale corrosion behavior.For an accurate study of the influence of flow velocity uponthe corrosion rate of fluids in motion, the hydrodynamicconditions must be well-defined. The Reynolds number(Re), a dimensionless number dependent on the fluid velo-city or the electrode rotation rate, as the case may be, den-sity and viscosity of the fluid, and a characteristic dimen-sion is used to define the type of flow.At low velocities, i.e. at low Re, a stable or laminar flow isencountered. Assuming the fluids under consideration tobe Newtownian and incompressible in nature, the shearstress at any point in a laminar flow is given by

duτw = µ ––––– (2)

dy

If the velocity is increased, at a critical Reynolds number(ReCRIT), the flow becomes turbulent and an additionalmechanism of momentum mass transfer appears, whichis caused by rapid and random fluctuations of velocityabout its average value. The ReCRIT for the transition bet-ween laminar and turbulent flow will vary depending on thegeometry and ReCRIT for pipe flow has been experimentallyfound to be around 2100.The Reynolds number for the RCE (ReRCE) is given by theexpression:

449

uRCE dRCE uRCE dRCE ρReRCE = –––––––––– – = –––––––––––––– (3)

ν µ

Where uRCE is the peripheral velocity of the RCE, dRCE is theRCE diameter, ν is the kinematic viscosity of the environ-ment, µ is the viscosity of the environment (1 x 10–3 kg m–1

s–1 considered for both environments) and ρ is the densityof the environment (1.024 x 103 kg m–3 considered for bothenvironments). Figure 1 shows the correlation between therotation rate of the electrode and the equivalent Reynoldsnumber.Figure 2 shows the measured values of corrosion poten-tial (Ecorr) as a function of Reynolds number. Ecorr was obtai-ned on the API X52 steel cylindrical samples immersed inNACE brine and 3.5% NaCl solution saturated with hydro-gen sulfide (H2S) at different rotation rates (0, 1000, 3000,5000 and 7000 rpm) and 20 °C. This Figure shows that themeasured values of the Ecorr are affected by the incrementof the rotation rate. In both NACE brine and 3.5% NaClsolution, as the ReRCE (and therefore the rotation rate) incre-ases, Ecorr also increases. The measured Ecorr correspondingto the 3.5% NaCl solution increased from a value of –0.768V (at 0 rpm) to a value of –0.700 V (at ReRCE = 5.34 x 104,equivalent to 7000 rpm) approximately. The measured Ecorr,corresponding to the NACE brine, increased from a valueof –0.750 (at 0 rpm) to a value of –0.695 V (at ReRCE = 5.34x 104, equivalent to 7000 rpm) approximately.In order to obtain an estimation of the corrosion currentdensities (icorr) for each system, an extrapolation of the cat-hodic and anodic branches of the polarization curves wasmade for each case, in a region of ± 0.150 V of overpo-tential, approximately, with respect to the correspondingvalue of Ecorr.Figure 3 shows the estimated values of icorr for both 3.5%NaCl and NACE brines, as a function of the calculated ReRCE.This Figure demonstrates that there is a clear influence offlow on the measured corrosion rate.Figure 4 shows the cathodic polarization curves (CPC)obtained on API X52 steel cylindrical electrodes, in theNACE brine saturated with H2S at 20 ºC and at 0.7 bar, asa function of the rotation rate. In this Figure it is possibleto see that all CPC (at all rotation rates) have a region whe-re a diffusion process is influencing the overall cathodiccurrent. It is clear that the measured cathodic current isaffected by the rotation rate of the electrode. At a cons-tant value of E, as the rotation rate of the electrode incre-ases the measured values of current density also increa-se. It is important to note that these features can suggest

450

Figure 1. Equivalence of rotation rate of the electrode andcalculated Reynolds Number.

Figure 2. Corrosion potential (Ecorr) as a function of the dif-ferent rotation rates of the cylindrical electrode in 3.5%NaCl and NACE solutions at 20 ºC and 0.7 bar.

Figure 3. Measured values of icorr as a function of ReRCE.

Figure 4. Cathodic polarization curves as a function of dif-ferent rotation rates. API X52 Steel cylindrical electrodeimmerse in NACE brine saturated with H2S at 20 ºC and 0.7bar.

that a diffusion process is taking place on the surface ofthe cylindrical electrode.If H+ ions are considered to be the main diffusing speciesin the environment, it is possible to calculate the cathodiccurrent density due to H+ reduction (ilim,H+). In order to dothis, the expression proposed by Eisenberg, Tobias andWilke(32) was used:

ilim,H+ = 0.0791 n F CH+ d–0.3RCE ν–0.344 DH+

0.644 u0.7RCE (4)

Where: n = number of electrons; F = Faraday constant; CH+

= bulk concentration of H+; dRCE = RCE diameter; ν = kine-matic viscosity; DH+ = diffusion coefficient and uRCE = RCEperipheral velocity. This expression indicates a direct rela-tionship of the calculated limiting current density (ilim,H+) tothe peripheral velocity of the RCE (uRCE), to a power of 0.7Figure 5 compares the different measured and calculatedcurrent densities as a function of uRCE to a power of 0.7 inNACE brine. The values of cathodic current densities (ic)were taken from the corresponding cathodic polarizationcurves in Figure 4, at a constant potential of –0.860 V (SCE).The estimated values of corrosion current densities (icorr)correspond to NACE brine showed in Figure 3. The valuesof cathodic limiting densities (ilim) for H+ diffusion were cal-culated with equation (4).This analysis demonstrates that the measured cathodiccurrent is affected by flow and this current can be asso-ciated to the diffusion of H+ ions from the bulk of the solu-tion to the surface of the electrode, where they reduce toH2 gas. It also demonstrates that the flow dependency ofthe icorr can be associated to this diffusion process.Figure 6 shows the cathodic polarization curves (CPC)obtained on the X52 steel cylindrical samples, in 3.5% NaClsolution saturated with H2S at 20 ºC and at 0.7 bar, at dif-ferent rotation rates. These cathodic curves show a simi-lar behaviour to that one observed in Figure 4. All CPCs (atall rotation range) show a region where a diffusion processis influencing the overall cathodic current. It is clear thatthe measured cathodic current is affected by the rotationrate of the electrode. At a constant value of potential, asthe rotation rate of the electrode increases the measuredvalues of current density also increase.

Figure 7 compares the different measured and calculatedcurrent densities as a function of uRCE to a power of 0.7 in3.5% NaCl solution. The values of cathodic current densi-ties (ic) were taken from the corresponding cathodic pola-rization curves in Figure 6, at a constant potential of –0.860V (SCE). The estimated values of corrosion current densi-ties (icorr) correspond to 3.5% NaCl solution showed in Figure3. The values of cathodic limiting densities (ilim) for H+ dif-fusion were calculated with equation (4).The analysis of this Figure 7 confirms the influence of flowon the cathodic kinetics. As the rotation rate of the elec-trode increases the measured cathodic current also incre-ases. It is also possible to suggest that the measured cat-hodic current can be associated to the diffusion andreduction of H+ ions. It is also demonstrated that the flowdependency of the icorr can be associated to this diffusionprocess.

451

Figure 5. API X52 steel immersed in NACE brine saturatedwith H2S at 20 ºC and 0.7 bar. Cathodic current densities(ic) read at -0.860 V (SCE) on the CPCs in Figure 4; calcu-lated limiting current density(29) for the diffusion of H+ (ilim,H

+)and corrosion current density (icorr), as a function of the RCEperipheral velocity (uRCE), to a power of 0.7. H+ diffusioncoefficient = 1.04 ( 10–8 m2 s–1, H+ concentration = 0.0794mol m–3; RCE diameter = 0.012 m; kinematics viscosity = 1x 10–6 m2s–1.

Figure 6. Cathodic polarization curves as a function of dif-ferent rotation rates. API X52 Steel cylindrical electrodeimmerse in 3.5% NaCl solution saturated with H2S at 20 ºCand 0.7 bar.

Figure 7. API X52 steel immersed in 3.5% NaCl solutionsaturated with H2S at 20 ºC and 0.7 bar. Cathodic currentdensities (ic) read at –0.860 V (SCE) on the CPCs in Figure6; calculated limiting current density(29) for the diffusion ofH+ (ilim,H+) and corrosion current density (icorr), as a functionof the RCE peripheral velocity (uRCE), to a power of 0.7. H+

diffusion coefficient = 1.04 x 10–8 m2 s–1, H+ concentration =0.0794 mol m–3; RCE diameter = 0.012 m; kinematics vis-cosity = 1 x 10–6 m2s–1.

Silverman(14) has suggested that the method of quantitati-vely relating the mass transfer relations must also ensurethat the interaction between the alloy surface and the trans-fer of momentum is equivalent for both pipe and rotatingcylinder geometries. Then, for the same alloy and envi-ronment, laboratory simulation allow to duplicate the velo-city-sensitivity mechanism found in the plant geometry.The shear stress is one such measure of the alloy surface-fluid interaction. The shear stress at the wall can be esti-mated for many geometries so that the following equationmay be written(32, 33)

τLAB = τPLANT (5)

Then, for a given system, the mechanism by which fluidvelocity affects corrosion rate in the plant is proposed tobe identical to that which affects corrosion rate in the labo-ratory.Figures 8 to 11 show the dimensionless number analysisas a function of the wall shear stress (τw) and the Reynoldsnumber (Re). The H+ ions are considered to be the mainactive specie in the environment, in this analysis.Figures 8 and 9 compare the measured cathodic currentdensity (ic) and the corrosion current density (icorr) as a func-tion of the wall shear stress (τW,RCE) in NACE and 3.5% NaClsolution. The expression used in the calculation of τW,RCT forthe RCE was(14, 15, 23, 34-37):

τW,RCE = 0.079 Re–0.3RCE ρu2

RCE (6)

Figure 8 shows ic and icorr as a function of τW,RCE in NACEbrine. In this Figure it is possible to see that as measuredic and icorr increases the τW,RCE also increases. These resultssuggest that the corrosion rate increases as the wall she-ar stress increases.Figure 9 shows ic and icorr as a function of τW,RCE in NACEbrine. This Figure shows the same behavior that the Figure8, because the measured ic and icorr increase when the τW,RCE

also increases. These results also suggest that the corro-sion rate increase as the wall shear stress (τw) increases.Figure 10 shows the mass transfer coefficient of H+ ion, inthe form of a dimensionless group, Sherwood number, (Sh)as a function of the Reynolds number (ReRCE). The Sherwoodnumber for the RCE (ShH+, RCE) is given by the expression(25):

ilim,H+ dRCEShH+ = –––––––––––––– (7)

n F DH+ CH+

In Figure 10 it is possible to see that the Sherwood num-ber (mass transfer coefficient in form of dimensionless num-ber) increases as the ReRCE increases. The mass transfer coefficient corresponding to H+ ions forRCE (kH+, RCE) is shown in Figure 11. kH+, RCE is presented as afunction of Reynolds number (ReRCE). The mass transfer ofH+ is given by the following expression(18, 25, 38):

ilim,H+

kH+ = ––––––––––– (8)n F CH+

Where the kH+, RCE is given in m s–1.

452

Figure 8. Cathodic current densities (ic) read at –0.860 V(SCE) on the CPCs in Figure 4 and corrosion current den-sity (icorr), as a function of the Wall Shear Stress (τW, RCE). APIX52 steel immersed in NACE brine saturated with H2S at20 ºC and 0.7 bar.

Figure 9. Cathodic current densities (ic) read at –0.860 V(SCE) on the CPCs in Figure 6 and corrosion current den-sity (icorr), as a function of the Wall Shear Stress (τW, RCE). APIX52 steel immersed in 3.5% NaCl solution saturated withH2S at 20 ºC and 0.7 bar.

Figure 10. Sherwood number of the specie H+(ShH+) as afunction of the Reynolds number. API X52 steel immersedin NACE brine and 3.5% NaCl solution, saturated with H2Sat 20 ºC and 0.7 bar.

Figure 11 shows the same behavior that the Figure 10,because the mass transfer coefficient increases when theReRCE also increases. The behaviour show in Figures 10 and 11 can suggestthat the mass transfer coefficient (ShH+ and kH+) is flowdependent, because it increases as the rotation rate alsoincreases.Figure 12 shows the measured anodic polarization cur-ves (APC) obtained on API X52 steel cylindrical electro-des immersed in the NACE brine, saturated with H2S at20 ºC and 0.7 bar, for different rotation rates. In this figu-re, it is possible to observe that the anodic Tafel slopes(ba) are high. This fact indicates a passivation process,taking place on the surface of the electrode. It is impor-tant to note that the APCs measured from 3000 to 7000rpm are not as influenced by rotation rate of the elec-trode.

Figure 13 shows the APC obtained on API X52 steel cylin-drical electrodes, immersed in the 3.5% NaCl solution satu-rated with H2S, at 20 ºC and 0.7 bar, for different rotationrates. In this figure, it is also possible to observe that theanodic Tafel slopes (ba) are high. These observations alsosuggest a passivation process taking place on surface ofthe electrode. It is important to note that the measuredAPCs are influenced by the rotation rate of the electrode.Figure 14 show the estimated anodic Tafel slopes (ba) as afunction of ReRCE, on API X52 steel cylindrical electrodesimmersed in NACE brine and 3.5% NaCl solution, saturatedwith H2S at 20 ºC and 0.7 bar. The slopes were calculatedon each anodic polarization curve, in the region from + 0.150V of overpotential, to the corresponding Ecorr. All the esti-mations of the Tafel slopes, in the NACE brine, were higherthan 0.180 V/decade. The calculated Tafel slopes, in the3.5% NaCl solution, also were higher than 0.180 V/decade.

453

Figure 11. Mass transfer coefficient of the specie H+ (kH+)as a function of the Reynolds number. API X52 steel immer-sed in NACE brine and 3.5% NaCl solution, saturated withH2S at 20 ºC and 0.7 bar.

Figure 12. Anodic polarization curves as a function of dif-ferent rotation rate. API X52 steel cylindrical electrodeimmerses in NACE brine saturated with H2S at 20 ºC and0.7 bar.

Figure 14. Calculated anodic Tafel slopes as a function ofReynolds number. API X52 steel cylindrical electrode immer-ses in NACE brine and 3.5% NaCl solution saturated withH2S at 20 ºC and 0.7 bar.

Figure 13. Anodic polarization curves as a function of dif-ferent rotation rate. API X52 steel cylindrical electrodeimmerses in 3.5% NaCl solution saturated with H2S at 20ºC and 0.7 bar.

CONCLUSIONS

1. In both test environments (NACE brine and 3.5% NaClsolution), the cathodic polarization curves show a regionthat is influenced by a diffusion process, at all rotationrates.

2. All cathodic polarization curves are affected by the rota-tion rate of the cylindrical electrode. In general, whenthe rotation rate of the cylindrical electrode increases,the measured cathodic current density also increases.

3. The cathodic process taking place on the surface of theelectrode can be associated to the diffusion of H+ ions,from the bulk of the solution towards the surface of theelectrode, and their reduction to H2 gas at the surface.

4. In NACE brine and 3.5% NaCl solution, the measuredcathodic current density values (at a constant E), are ingood correlation with the theoretical limiting currentdensity values, calculated by the Eisenberg, Tobias andWilke expression for H+ ions (ilim,H+).

5. All the anodic polarization curves show a high anodicTafel slope (ba). This fact can be associated to a passi-vation process, taking place on the surface of the cylin-drical electrode.

6. The anodic polarization curves corresponding to 3000,5000 and 7000 rpm obtained in NACE brine are not affec-ted by the rotation rate.

7. In both test environments (NACE brine and 3.5% NaClsolution), the cathodic current density and the corro-sion current density increase as the wall shear stressincreases.

8. The mass transfer coefficient (kH+ and ShH+) is flow depen-dent, because it increases as the rotation rate also incre-ases.

ACKNOWLEDGMENTS

The authors would like to thank the National Council ofScience and Technology (CONACYT) for the grant awar-ded to Mr. Galvan-Martinez, required to develop this workand to Mexican Petroleum Institute, IMP, for financial sup-port (FIES).

BIBLIOGRAFÍA(1). M.S. CayardS, R.D. Kane: Corrosion 53 (1997) 227. (2). R. Galvan-Martinez, J. Genesca-Llongueras, J. Mendoza-Flores, R. Duran-Romero: «Effects of Turbulent Flow onthe Corrosion Kinetics of X52 Pipeline Steel, in AqueousSolutions Containing H2S», CORROSION/2003, Paper no.03641, (Houston. TX: NACE, 2003).(3). S. Arzola-Peralta, J. Genesca-Llongueras, J. Mendoza-Flores, R. Duran-Romero: «Electrochemical Study on theCorrosion of X70 Pipeline Steel in H2S Containing Solutions»,CORROSION/2003, Paper no. 03401, (Houston. TX: NACE,2003).(4). Colwell J. A.; Payer J. H.; Boyd W. K.: «Performance ofSteel in High Pressure Environments containing low H2SConcentrations», CORROSION/86, Paper no. 168 (Houston.TX: NACE, 1986).(5). N. Seki, T. Kotera, T. Nakasawa: «The Evaluation ofEnvironmental Condition and the Performance of Line pipeSteels under Wet Sour Gas», CORROSION/82, Paper no.82131 (Houston. TX: NACE, 1982).(6). S.P. Ewing: Corrosion 11 (1955) 51.

(7). T.Y. Chen, A.A. Moccari, D.D. Macdonald: Corrosion 48(1992) 239.(8). B. Poulson: Corros. Sci., 23 (1983) 391.(9). B. Poulson: Corros. Sci., 35 (1993) 655.(10). B. Poulson: J. Appl. Electrochem., 24 (1994) 1.(11). G. Liu, D.A. Tree, M.S. High: Corrosion 50 (1994) 584.(12). U. Lotz: «Velocity Effect In Flow Induced Corrosion»,CORROSION/90, Paper no. 27 ((Houston. TX: NACE, 1990)(13). G. Schmitt, W. Bruckhoff, K. Faessler, G. Blummel: Mater.Perform., 29 (1991)85.(14). D.C. Silverman: Corrosion 40 (1984) 220.(15). D.C. Silverman: Corrosion 44 (1988) 42.(16). D.C. Silverman: «Rotating Cylinder Electrode - AnApproach For Predicting Velocity Sensitive Corrosion»,CORROSION/90, Paper No. 13 (Houston. TX: NACE, 1990)(17). A.A. Wragg: The Chemical Engineer (1977) 39.(18). S. Nesic, G.T. Solvi, J. Enerhaug: Corrosion 51 (1995)773.(19). S. Nesic, G.T. Solvi, J. Enerhaug: «Comparison Of TheRotating Cylinder And Pipe Flow Test For Flow SensitiveCO2 Corrosion», CORROSION/95, Paper no. 130, (Houston.TX: NACE, 1995)(20). D.R. Gabe: J. Appl. Electrochem., 4 (1974) 91.(21). D.R. Gabe, F.C. Walsh: J. Appl. Electrochem, 13 (1983)3.(22). J. Mendoza-Flores, R. Duran-Romero, E. Garcia-Ochoa:«Effects of Turbulent Flow on the Efficiency of TriazoleBased Inhibitors», CORROSION/2002, Paper no. 02491(Houston. TX: NACE, 2002)(23). K.D. Efird, E.J. Wright, J.A. Boros, T.G. Hailey: Corrosion49 (1993) 992.(24). J. Mendoza-Flores, S. Turgoose: «Influence of ElectrodeLength on the Measurement of Cathodic Kinetics of SteelCorrosion in CO2 Containing Solutions, Under TurbulentFlow Conditions», CORROSION/2002, Paper no. 02490(Houston. TX: NACE, 2002)(25). J. Mendoza-Flores: «Kinetic Studies of CO2 CorrosionProcesses Under Turbulent Flow», PhD Thesis, UMIST,Corrosion and Protection Centre, Manchester, 1997.(26). S. Turgoose, J.L. Dawson, J.M. Palmer, T. Rizk:«Boundary Layer Effect In Turbulent Flow Testing», CORRO-SION/95, Paper no. 95112, (Houston. TX: NACE, 1995).(27). B.T. Ellison, W.R. Schmeal: J. Electrochem. Soc. 125(1978) 524.(28). S.W. Dean, G.D. Grab: «Corrosion of Carbon Steel byConcentrated Sulfuric Acid», CORROSION/84, Paper no.147, (Houston. TX: NACE, 1984).(29). T.K. Ross, G.C. Wood, I. Mahmus: J. Electrochem. Soc.113, 4 (1966) 127.(30). NACE 1 D196: «Laboratory Test Methods for EvaluatingOilfield Corrosion Inhibitors», (Houston. TX: NACE, 1996).(31). «API, Specification for Line Pipe», API Specification 5L,forty-second Edition, API, July 2000.(32). M. Eisenberg, C.W. Tobias, R.C. Wilke: J. Electrochem.Soc., 101 (1954) 306.(33). W.M. Kays: «Convective Heat and Mass Transfer» (NewYork, NY: McGraw Hill Book Co., 1966).(34). K.D. Efird, E.J. Wright, J.A. Boros, T.G. Hailey: «CorrosionControl for Low-Cost Reliability», 12th InternationalCorrosion Congress, Proceeding, Vol. 4, Houston, TX,U.S.A., September 19-23, 1993, p. 2662.(35). B.V. Johnson, H.J. Choi, A.S. Green: «Effects of LiquidWall Shear Stress on CO2 Corrosion of X52 Steel SimulatedOilfield Production Environments», CORROSION/91, Paperno. 573 (Houston. TX: NACE, 1991).(36). K. Denpo, H. Ogawa: Corrosion 49, 6 (1993) 442.(37). K.G. Jordan, P.R. Rodes: «Corrosion of Carbon Steel byCO2 solution: The Role of Fluid Flow», Corrosion/95, paperno. 125, (Houston. TX: NACE, 1995).(38). S. Nesic, J. Bienkowski, K. Bremhorts, K.-S. Yang:Corrosion 56, 10 (2000) 1005.

454