Rotating Cylinder Electrode Study on the Influence of ... - DePa - UNAM

2 downloads 0 Views 1MB Size Report
En este trabajo se presentan los resultados obtenidos durante el estudio del mecanismo y de la cinética de corrosión de un acero API X52 en soluciones ...
AFINIDAD REVISTA DE QUÍMICA TEÓRICA Y APLICADA EDITADA POR LA ASOCIACIÓN DE QUÍMICOS E INGENIEROS DEL INSTITUTO QUÍMICO DE SARRIÁ

Rotating Cylinder Electrode Study on the Influence of Turbulent Flow, on the Anodic and Cathodic Kinetics of X52 Steel Corrosion, in H2S Containing Solutions (1)

(2)

(2)

Ricardo Galván-Martínez , Juan Mendoza-Flores , Rubén Durán-Romero (1) and Juan Genescá-Llongueras* (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 acuosas que 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.

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

Rotating Cylinder Electrode Study on the Influence of Turbulent Flow, on the Anodic and Cathodic Kinetics of X52 Steel Corrosion, in H2S Containing Solutions (1)

(2)

(2)

Ricardo Galván-Martínez , Juan Mendoza-Flores , Rubén Durán-Romero (1) and Juan Genescá-Llongueras* (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 acuosas que 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 obtenidos durante el estudio del mecanismo y de la cinética de corrosión de un acero API X52 en soluciones acuosas que contienen H2S bajo condiciones de flujo turbulento, utilizando un electrodo de cilindro rotatorio (ECR). El estudio se ha realizado a cinco diferentes velocidades de rotación: 0 (condiciones estáticas), 1000, 3000, 5000 y 7000 rpm. Se ha encontrado que bajo condiciones de flujo turbulento aumenta significativamente la velocidad de corrosión y el mecanismo de corrosión está controlado por el proceso de difusión que tiene lugar en la reacción catódica. Palabras clave: Acero API X52. Electrodo cilindro rotatorio. 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 results measured during the corrosion of API X52 pipeline steel immersed in aqueous environments, containing dissolved hydrogen sulfide (H2S) under turbulent flow conditions. In order to control the turbulent flow conditions, a Rotating Cylinder Electrode (RCE) was used. Five different rotation rates were studied: 0 (or static conditions),

448

1000, 3000, 5000 and 7000 rpm. It was found that the turbulent flow increases the corrosion rate and the corrosion mechanism for X52 steel exhibits a significant dependence on mass transfer on the cathodic kinetics. Key words: API X52. Flow. Hydrogen sulfide. Mass transfer. RCE.

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

RESUM En aquest treball, es presenten els resultats obtinguts durant l’estudi del mecanisme i de la cinètica de corrosió d’un acer API X52 en dissolucions aquoses que contenen H2S sota condicions de flux turbulent, utilitzant un elèctrode de cilindre rotatori (ECR). L’estudi s’ha realitzat a cinc velocitats diferents de rotació: 0 (condicions estàtiques), 1000, 3000, 5000 i 7000 rpm. S’ha trobat que sota condicions de flux turbulent augmenta significativament la velocitat de corrosió i el mecanisme de corrosió està controlat pel procés de difusió que té lloc en la reacció catòdica. Mots clau: Acer API X52. Elèctrode cilindre rotatori. Flux. H2S. Transferència massa.

* Corresponding author: [email protected]

INTRODUCTION In the oil industry, H2S has been associated to damages by corrosion and stress corrosion cracking (SCC) induced (1) by sulphides or hydrogen. H2S gas can dissolve in aqueous solutions turning them in corrosive solutions, known (2, 3) as «sour». The increment of temperature and/or pressure can increase the aggressiveness of H2S solution to carbon steel. Corrosion of steel in H2S containing solutions (4-6) can be represented according to: Fe + H2Saq ⇒ FeS + H2

(b) 3.5 % NaCl solution. These two test environments were selected due to the fact that, most of the H2S corrosion laboratory testing is carried out in one of these solutions and 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 minutes. The measured dissolved O2 content was lower to 10 ppb. After oxygen removal H2S gas (99.99%) was bubbled into the test solution until saturation was reached. The measured saturation pH was 4.2 for NACE brine and 4.1 for the 3.5 % NaCl brine.

(1) Experimental Set up

The majority of studies on the corrosion of steels in environments containing dissolved H2S, have been carried out (7) under static conditions . The main objective of these studies, is the determination of the resistance of different alloys to combined conditions of corrosion and mechanical stresses. In many real situations, H2S corrosion occurs under flowing conditions, for example, in transport of hydrocar(7) bons in pipelines . Therefore, the influence of flow on the corrosion processes is an important issue to be considered in the design and operation of industrial equipment. The most common type of flow conditions found in industrial processes is turbulent; however, few corrosion studies in controlled turbulent flow conditions are available. With the increasing necessity to describe the corrosion of metals in turbulent flow conditions some laboratory hydrodynamic systems have been used with different degre(8-10) es of success . Among these hydrodynamic systems, rotating cylinder electrodes (RCEs), pipe segments, concentric pipe segments, submerged impinging jets and close-circuit loops have been used and have been important in the improvement of the understanding of the corrosion (10-17) process taking place in turbulent flow conditions . The use of the rotating cylinder electrode (RCE), as a laboratory hydrodynamic test system, has been gaining popula(18-19) rity in corrosion studies . This popularity is due to its characteristics, such as, its operation mainly in turbulent flow conditions, its well-defined hydrodynamics, ease of assembly and disassembly, smaller volume of fluid used, (20, 21) and easier flow and temperature control . It has been found that for a RCE enclosed in a concentric cell, the transition between the laminar and turbulent flow occurs at values of Reynolds number (Re) of 200 approxi(8, 9, 21) mately . The RCE in corrosion laboratory studies is a useful tool for the understanding of mass transfer processes, (2, 3, 22) effects of surface films, inhibition phenomena, etc taking place in turbulent flow conditions. However, the use of the (23) RCE has been questioned by some researchers , due to the differences found between the values of corrosion rates measured on pipe flow electrodes and on the RCE. The reasons for this difference are still not well understood. However, some works have provided ideas on the expla(24-26) nation of this apparent difference . Dimensionless analysis using mass transfer concepts showed that the corrosion when controlled by diffusion of one of the species between the bulk fluid and the surface, could be modeled completely by the rate of mass transfer of the rate limiting species and the Re and Schmidt (27-29) numbers (Sc) . In general, the effect of flow can be used to determine if corrosion is under activation, diffusion or mixed control.

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

An air-tight three-electrode electrochemical glass cell was used. Cylindrical working electrodes were used in all expe(31) riments. These cylinders were made of API X52 steel . The 2 total exposed area of the working electrodes was 5.68 cm 2 and 3.4 cm for static and dynamic conditions, respectively. As reference electrode a saturated calomel electrode (SCE) was used. A sintered graphite rod was used as auxiliary electrode. Prior to each experiment, the steel working electrode was polished up to 600 grit SiC paper, cleaned in deionised water and degreased with acetone. All electrochemical tests were carried out on clean samples and in freshly prepared test solutions. Hydrodynamic conditions were controlled using a PerkingElmer EG&G Model 636 Rotating Cylinder Electrode (RCE) system. In dynamic conditions, the rotation speeds tested were 1000, 3000, 5000 and 7000 rpm. Electrochemical Measurements A SolartronTM SI 1280B Potentiostat / Galvanostat was used in all the electrochemical tests. Potentiodynamic polarization curves were recorded at a sweep rate of 1 mV per second. In order to minimize the effect of the solution resistance a Lugging capillary was used.

EXPERIMENTAL RESULTS AND DISSCUSION Previous work on these systems has shown that the corrosion mechanism for carbon steel exhibits a significant dependence on mass transfer. This has lead various workers to suggest the use of dimensionless analysis as a means of relating laboratory-scale experiments to plantscale corrosion behavior. For an accurate study of the influence of flow velocity upon the corrosion rate of fluids in motion, the hydrodynamic conditions must be well-defined. The Reynolds number (Re), a dimensionless number dependent on the fluid velocity or the electrode rotation rate, as the case may be, density and viscosity of the fluid, and a characteristic dimension is used to define the type of flow. At low velocities, i.e. at low Re, a stable or laminar flow is encountered. Assuming the fluids under consideration to be Newtownian and incompressible in nature, the shear stress at any point in a laminar flow is given by du τw = µ ––––– dy

(2)

If the velocity is increased, at a critical Reynolds number (ReCRIT), the flow becomes turbulent and an additional mechanism of momentum mass transfer appears, which is caused by rapid and random fluctuations of velocity about its average value. The ReCRIT for the transition between laminar and turbulent flow will vary depending on the geometry and ReCRIT for pipe flow has been experimentally found to be around 2100. The Reynolds number for the RCE (ReRCE) is given by the expression:

449

Figure 1. Equivalence of rotation rate of the electrode and calculated Reynolds Number.

uRCE dRCE uRCE dRCE ρ ReRCE = ––––––––––– = –––––––––––––– ν µ

(3)

Where uRCE is the peripheral velocity of the RCE, dRCE is the RCE diameter, ν is the kinematic viscosity of the environ–3 –1 ment, µ is the viscosity of the environment (1 x 10 kg m –1 s considered for both environments) and ρ is the density 3 –3 of the environment (1.024 x 10 kg m considered for both environments). Figure 1 shows the correlation between the rotation rate of the electrode and the equivalent Reynolds number. Figure 2 shows the measured values of corrosion potential (Ecorr) as a function of Reynolds number. Ecorr was obtained on the API X52 steel cylindrical samples immersed in NACE brine and 3.5% NaCl solution saturated with hydrogen sulfide (H2S) at different rotation rates (0, 1000, 3000, 5000 and 7000 rpm) and 20 °C. This Figure shows that the measured values of the Ecorr are affected by the increment of the rotation rate. In both NACE brine and 3.5% NaCl solution, as the ReRCE (and therefore the rotation rate) increases, Ecorr also increases. The measured Ecorr corresponding to the 3.5% NaCl solution increased from a value of –0.768 4 V (at 0 rpm) to a value of –0.700 V (at ReRCE = 5.34 x 10 , equivalent to 7000 rpm) approximately. The measured Ecorr, corresponding to the NACE brine, increased from a value of –0.750 (at 0 rpm) to a value of –0.695 V (at ReRCE = 5.34 4 x 10 , equivalent to 7000 rpm) approximately. In order to obtain an estimation of the corrosion current densities (icorr) for each system, an extrapolation of the cathodic and anodic branches of the polarization curves was made for each case, in a region of ± 0.150 V of overpotential, approximately, with respect to the corresponding value 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 of flow on the measured corrosion rate. Figure 4 shows the cathodic polarization curves (CPC) obtained on API X52 steel cylindrical electrodes, in the NACE brine saturated with H2S at 20 ºC and at 0.7 bar, as a function of the rotation rate. In this Figure it is possible to see that all CPC (at all rotation rates) have a region where a diffusion process is influencing the overall cathodic current. It is clear that the measured cathodic current is affected by the rotation rate of the electrode. At a constant value of E, as the rotation rate of the electrode increases the measured values of current density also increase. It is important to note that these features can suggest

450

Figure 2. Corrosion potential (Ecorr) as a function of the different 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 different rotation rates. API X52 Steel cylindrical electrode immerse in NACE brine saturated with H2S at 20 ºC and 0.7 bar.

that a diffusion process is taking place on the surface of the cylindrical electrode. + If H ions are considered to be the main diffusing species in the environment, it is possible to calculate the cathodic + current density due to H reduction (ilim,H+). In order to do this, the expression proposed by Eisenberg, Tobias and (32) Wilke was used: ilim,H = 0.0791 n F CH dRCE ν –0.3

+

+

–0.344

0.644

DH

+

0.7

uRCE

(4)

Where: n = number of electrons; F = Faraday constant; CH + = bulk concentration of H ; dRCE = RCE diameter; ν = kinematic viscosity; DH = diffusion coefficient and uRCE = RCE peripheral velocity. This expression indicates a direct relationship of the calculated limiting current density (ilim,H ) to the peripheral velocity of the RCE (uRCE), to a power of 0.7 Figure 5 compares the different measured and calculated current densities as a function of uRCE to a power of 0.7 in NACE brine. The values of cathodic current densities (ic) were taken from the corresponding cathodic polarization curves 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 values + of cathodic limiting densities (ilim) for H diffusion were calculated with equation (4). This analysis demonstrates that the measured cathodic current is affected by flow and this current can be asso+ ciated to the diffusion of H ions from the bulk of the solution to the surface of the electrode, where they reduce to H2 gas. It also demonstrates that the flow dependency of the 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% NaCl solution saturated with H2S at 20 ºC and at 0.7 bar, at different rotation rates. These cathodic curves show a similar behaviour to that one observed in Figure 4. All CPCs (at all rotation range) show a region where a diffusion process is influencing the overall cathodic current. It is clear that the measured cathodic current is affected by the rotation rate of the electrode. At a constant value of potential, as the rotation rate of the electrode increases the measured values of current density also increase.

Figure 7 compares the different measured and calculated current densities as a function of uRCE to a power of 0.7 in 3.5% NaCl solution. The values of cathodic current densities (ic) were taken from the corresponding cathodic polarization curves in Figure 6, at a constant potential of –0.860 V (SCE). The estimated values of corrosion current densities (icorr) correspond to 3.5% NaCl solution showed in Figure + 3. The values of cathodic limiting densities (ilim) for H diffusion were calculated with equation (4). The analysis of this Figure 7 confirms the influence of flow on the cathodic kinetics. As the rotation rate of the electrode increases the measured cathodic current also increases. It is also possible to suggest that the measured cathodic current can be associated to the diffusion and + reduction of H ions. It is also demonstrated that the flow dependency of the icorr can be associated to this diffusion process.

Figure 5. API X52 steel immersed in NACE brine saturated with 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+ (29) + lated limiting current density for the diffusion of H (ilim,H ) and corrosion current density (icorr), as a function of the RCE + peripheral velocity (uRCE), to a power of 0.7. H diffusion –8 2 –1 + coefficient = 1.04 ( 10 m s , H concentration = 0.0794 –3 mol m ; RCE diameter = 0.012 m; kinematics viscosity = 1 –6 2 –1 x 10 m s .

Figure 7. API X52 steel immersed in 3.5% NaCl solution saturated with H2S at 20 ºC and 0.7 bar. Cathodic current densities (ic) read at –0.860 V (SCE) on the CPCs in Figure (29) 6; calculated limiting current density for the diffusion of + H (ilim,H+) and corrosion current density (icorr), as a function + of the RCE peripheral velocity (uRCE), to a power of 0.7. H –8 2 –1 + diffusion coefficient = 1.04 x 10 m s , H concentration = –3 0.0794 mol m ; RCE diameter = 0.012 m; kinematics vis–6 2 –1 cosity = 1 x 10 m s .

+

+

+

Figure 6. Cathodic polarization curves as a function of different rotation rates. API X52 Steel cylindrical electrode immerse in 3.5% NaCl solution saturated with H2S at 20 ºC and 0.7 bar.

451

Figure 8. Cathodic current densities (ic) read at –0.860 V (SCE) on the CPCs in Figure 4 and corrosion current density (icorr), as a function of the Wall Shear Stress (τW, RCE). API X52 steel immersed in NACE brine saturated with H2S at 20 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 density (icorr), as a function of the Wall Shear Stress (τW, RCE). API X52 steel immersed in 3.5% NaCl solution saturated with H2S at 20 ºC and 0.7 bar.

ilim,H+ dRCE ShH = –––––––––––––– n F DH CH

(14)

Silverman has suggested that the method of quantitatively relating the mass transfer relations must also ensure that the interaction between the alloy surface and the transfer of momentum is equivalent for both pipe and rotating cylinder geometries. Then, for the same alloy and environment, laboratory simulation allow to duplicate the velocity-sensitivity mechanism found in the plant geometry. The shear stress is one such measure of the alloy surfacefluid interaction. The shear stress at the wall can be estimated for many geometries so that the following equation (32, 33) may be written τLAB = τPLANT

τW,RCE = 0.079 Re RCE ρuRCE 2

452

+

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

+

ilim,H+ kH = ––––––––––– n F CH

(8)

+

+

–1

Where the kH , RCE is given in m s . +

(6)

Figure 8 shows ic and icorr as a function of τW,RCE in NACE brine. In this Figure it is possible to see that as measured ic and icorr increases the τW,RCE also increases. These results suggest that the corrosion rate increases as the wall shear stress increases. Figure 9 shows ic and icorr as a function of τW,RCE in NACE brine. This Figure shows the same behavior that the Figure 8, because the measured ic and icorr increase when the τW,RCE also increases. These results also suggest that the corrosion rate increase as the wall shear stress (τw) increases. + Figure 10 shows the mass transfer coefficient of H ion, in the form of a dimensionless group, Sherwood number, (Sh) as a function of the Reynolds number (ReRCE). The Sherwood (25) number for the RCE (ShH , RCE) is given by the expression : +

+

(5)

Then, for a given system, the mechanism by which fluid velocity affects corrosion rate in the plant is proposed to be identical to that which affects corrosion rate in the laboratory. Figures 8 to 11 show the dimensionless number analysis as a function of the wall shear stress (τw) and the Reynolds + number (Re). The H ions are considered to be the main active specie in the environment, in this analysis. Figures 8 and 9 compare the measured cathodic current density (ic) and the corrosion current density (icorr) as a function of the wall shear stress (τW,RCE ) in NACE and 3.5% NaCl solution. The expression used in the calculation of τW,RCT for (14, 15, 23, 34-37) the RCE was : –0.3

(7)

+

+

Figure 10. Sherwood number of the specie H (ShH+) as a function of the Reynolds number. API X52 steel immersed in NACE brine and 3.5% NaCl solution, saturated with H2S at 20 ºC and 0.7 bar.

Figure 11. Mass transfer coefficient of the specie H (kH+) as a function of the Reynolds number. API X52 steel immersed in NACE brine and 3.5% NaCl solution, saturated with H2S at 20 ºC and 0.7 bar.

Figure 12. Anodic polarization curves as a function of different rotation rate. API X52 steel cylindrical electrode immerses in NACE brine saturated with H2S at 20 ºC and 0.7 bar.

Figure 11 shows the same behavior that the Figure 10, because the mass transfer coefficient increases when the ReRCE also increases. The behaviour show in Figures 10 and 11 can suggest that the mass transfer coefficient (ShH+ and kH+) is flow dependent, because it increases as the rotation rate also increases. Figure 12 shows the measured anodic polarization curves (APC) obtained on API X52 steel cylindrical electrodes immersed in the NACE brine, saturated with H2S at 20 ºC and 0.7 bar, for different rotation rates. In this figure, 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 important to note that the APCs measured from 3000 to 7000 rpm are not as influenced by rotation rate of the electrode.

Figure 13 shows the APC obtained on API X52 steel cylindrical electrodes, immersed in the 3.5% NaCl solution saturated with H2S, at 20 ºC and 0.7 bar, for different rotation rates. In this figure, it is also possible to observe that the anodic Tafel slopes (ba) are high. These observations also suggest a passivation process taking place on surface of the electrode. It is important to note that the measured APCs are influenced by the rotation rate of the electrode. Figure 14 show the estimated anodic Tafel slopes (ba) as a function of ReRCE, on API X52 steel cylindrical electrodes immersed in NACE brine and 3.5% NaCl solution, saturated with H2S at 20 ºC and 0.7 bar. The slopes were calculated on each anodic polarization curve, in the region from + 0.150 V of overpotential, to the corresponding Ecorr. All the estimations of the Tafel slopes, in the NACE brine, were higher than 0.180 V/decade. The calculated Tafel slopes, in the 3.5% NaCl solution, also were higher than 0.180 V/decade.

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

Figure 14. Calculated anodic Tafel slopes as a function of Reynolds number. API X52 steel cylindrical electrode immerses in NACE brine and 3.5% NaCl solution saturated with H2S at 20 ºC and 0.7 bar.

+

453

CONCLUSIONS

(7)

1. In both test environments (NACE brine and 3.5% NaCl solution), the cathodic polarization curves show a region that is influenced by a diffusion process, at all rotation rates. 2. All cathodic polarization curves are affected by the rotation rate of the cylindrical electrode. In general, when the rotation rate of the cylindrical electrode increases, the measured cathodic current density also increases. 3. The cathodic process taking place on the surface of the + electrode can be associated to the diffusion of H ions, from the bulk of the solution towards the surface of the electrode, and their reduction to H2 gas at the surface. 4. In NACE brine and 3.5% NaCl solution, the measured cathodic current density values (at a constant E), are in good correlation with the theoretical limiting current density values, calculated by the Eisenberg, Tobias and + Wilke expression for H ions (ilim,H ). +

5. All the anodic polarization curves show a high anodic Tafel slope (ba). This fact can be associated to a passivation process, taking place on the surface of the cylindrical electrode. 6. The anodic polarization curves corresponding to 3000, 5000 and 7000 rpm obtained in NACE brine are not affected by the rotation rate. 7. In both test environments (NACE brine and 3.5% NaCl solution), the cathodic current density and the corrosion current density increase as the wall shear stress increases. 8. The mass transfer coefficient (kH+ and ShH+) is flow dependent, because it increases as the rotation rate also increases.

ACKNOWLEDGMENTS The authors would like to thank the National Council of Science and Technology (CONACYT) for the grant awarded to Mr. Galvan-Martinez, required to develop this work and to Mexican Petroleum Institute, IMP, for financial support (FIES).

BIBLIOGRAFÍA (1)

. M.S. CayardS, R.D. Kane: Corrosion 53 (1997) 227. . R. Galvan-Martinez, J. Genesca-Llongueras, J. MendozaFlores, R. Duran-Romero: «Effects of Turbulent Flow on the Corrosion Kinetics of X52 Pipeline Steel, in Aqueous Solutions Containing H2S», CORROSION/2003, Paper no. 03641, (Houston. TX: NACE, 2003). (3) . S. Arzola-Peralta, J. Genesca-Llongueras, J. MendozaFlores, R. Duran-Romero: «Electrochemical Study on the Corrosion 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 of Steel in High Pressure Environments containing low H2S Concentrations», CORROSION/86, Paper no. 168 (Houston. TX: NACE, 1986). (5) . N. Seki, T. Kotera, T. Nakasawa: «The Evaluation of Environmental Condition and the Performance of Line pipe Steels under Wet Sour Gas», CORROSION/82, Paper no. 82131 (Houston. TX: NACE, 1982). (6) . S.P. Ewing: Corrosion 11 (1955) 51. (2)

454

. 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 - An Approach 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 The Rotating Cylinder And Pipe Flow Test For Flow Sensitive CO2 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 Triazole Based Inhibitors», CORROSION/2002, Paper no. 02491 (Houston. TX: NACE, 2002) (23) . K.D. Efird, E.J. Wright, J.A. Boros, T.G. Hailey: Corrosion 49 (1993) 992. (24) . J. Mendoza-Flores, S. Turgoose: «Influence of Electrode Length on the Measurement of Cathodic Kinetics of Steel Corrosion in CO2 Containing Solutions, Under Turbulent Flow Conditions», CORROSION/2002, Paper no. 02490 (Houston. TX: NACE, 2002) (25) . J. Mendoza-Flores: «Kinetic Studies of CO2 Corrosion Processes 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», CORROSION/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 by Concentrated 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 Evaluating Oilfield 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» (New York, NY: McGraw Hill Book Co., 1966). (34) . K.D. Efird, E.J. Wright, J.A. Boros, T.G. Hailey: «Corrosion Control for Low-Cost Reliability», 12th International Corrosion 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 Liquid Wall Shear Stress on CO2 Corrosion of X52 Steel Simulated Oilfield Production Environments», CORROSION/91, Paper no. 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 by CO2 solution: The Role of Fluid Flow», Corrosion/95, paper no. 125, (Houston. TX: NACE, 1995). (38) . S. Nesic, J. Bienkowski, K. Bremhorts, K.-S. Yang: Corrosion 56, 10 (2000) 1005.