The present application claims priority of Mexican patent application number MX/a/2022/004099 filed Apr. 4, 2022.
The present disclosure relates to the field of experimental devices which perform corrosion and biocorrosion studies on different metals exposed to fluids, which simulate flow patterns found in hydrodynamic pipeline conditions.
The internal corrosion process of metallic materials is due to the physicochemical and electrochemical interaction of the different fluids they carry, which bring with them microorganisms capable of inducing biocorrosion. The phenomenon of corrosion and biocorrosion is determined and analyzed by means of the electrochemical method with an arrangement of three electrodes: working, reference and auxiliary, as shown in
The electrochemical flow cell documented in industrial reference A50T110 (Radiometer Analytical, “C145/170, Flow Cell A50T110”) is a glass cell with a volume capacity of 250 mL. The cell is designed with a three-electrode array (including accessories) to perform electrochemical tests in flow condition as shown in
Additionally, there are several patents associated with inventions for electrochemical studies with flow condition: US399606A (L H. Thaller, “Electrically rechargeable REDOX flow cell”, US patent application US399606A, Dec. 7, 1976); US20150236363A1 (G. D. Polcyn, N. Bredemeyer, C. Roosen, D. Donst, P. Toros, P. Woltering, D. Hoormann, P. Hofmann, S. Köberle, F. Funck, W. Stolp, B. Langanke, “Flow-type electrochemical cell”, US patent application US20150236363A1, Sep. 3, 2012); WO1998/32008 (U. Bilitewski, W. Mascheroder, M. Stiene, I. Rohm, “Electrochemical flow cell”, German Pat. Application WO1998/32008, Jul. 23, 1998); US3151052A (E.P. Arthur, H. L. Friedman, “Electrochemical flow cell”, US Pat. Application US3151052A, May 17, 1962); US4413505A (W. R. Matson, “Electrochemical flow cell, particularly use with liquid chromatography”, US Pat. Application US 2010/0155262 A1, Mar. 9, 1981); however, most use an electrochemical cell with a two-electrode arrangement and homogeneous solutions. Sometimes the cell is designed for small volumes of solution, in order to carry out organic synthesis reactions or for energy production [1-6].
T. Hong, W. P. Jepson, “Corrosion inhibitor studies in large flow loop at high temperature and high pressure”, Corros. Sci., 43 (2001) 1839-1849; G. Koster, M. Ariel, “Electrochemical flow cell”, J. Electroanal. Chemistry Interfacial Electrochem., 33 (1971) 339-349; L. D. Syntrivanis, F. J. del Campo, J. Robertson, “An electrochemical flow cell for the convenient oxidation of Furfuryl alcohols”, J flow Chemistry, 8 (2018) 123-128; J. Genesca, R. Olalde, A. Garnica, N. Balderas, J. Mendoza, R Duran, “Electrochemical evaluation of corrosion inhibitors in CO2 containing brines. An RCE and flow-loop comparison, NACE Corrosion Conference 2010, paper No. 10162, pp. 1-15; T. Hong, Y. H. Sun, W. P. Jepson, “Study on corrosion inhibitor in large pipelines under multiphase flow using EIS”, Corros. Sci., 44 (2002) 101-112; X. Wang, J. Xu, C. Sun, M. C. Yan, “Effect of oilfield produced water on corrosion of pipeline”, Int. J. Electrochem. Sci., 10 (2015) 8656-8667 [7-12].
In the electrochemical flow cells of the present disclosure (e.g., flow cell of
The electrochemical flow cells of the present disclosure solve the technical problem of obtaining the best electrochemical response for corrosion and biocorrosion studies using homogeneous solutions in immiscible two-phase and/or multiphase systems such as hydrocarbon and associated water mixture. This electrochemical flow cells of the present disclosure did not previously exist in the prior art because only the design of a conventional electrochemical cell for carrying out corrosion and biocorrosion studies in single-phase or miscible solutions was considered. These electrochemical flow cells icannot be deduced from other prior disclosures because they allow the study and understanding of the corrosion and biocorrosion process of any type of metallic material in immiscible two-phase and/or multiphase mixed solutions and suggests other ways to combat the corrosion process in pipelines affected by interior corrosion and biocorrosion. Among the problems or challenges presented by the corrosion phenomenon is the adsorption-fixation and growth of microorganisms in the form of a biofilm, and the consequent electrochemical imbalance on the metal surface inside a pipeline, in the presence of a fluid with different corrosive agents. These may include but are not limited to water with nutrients, such as seawater, injection water or congenital water (these latter two are commonly referred to as production water), and under hydrodynamic conditions and different temperatures. Until now, internal corrosion in lines and pipelines through which oil and its derivatives are transported, has been studied and related to the presence of sweet and sour media [10-12], its concentration is increasing in current crude oils; however, the participation of other contaminants in this process such as saline media is still unknown for Mexican crude oils. The internal protection process of pipelines that transport hydrocarbons is affected by variations in the concentrations of corrosive species, significant changes in the flow pattern, flow regime and the influence of temperatures in the range of 45 to 60° C. [13,14]. At present, biocorrosion problems continue to be a topic of great scientific and industrial interest because corrosion mechanisms are related to sulfate-reducing microorganisms, organic acid producers, metal reducers and exopolymer generators, as well as high salt concentrations and temperatures at different hydrodynamic pipeline conditions [15-18]. In the electrochemical flow cells of the present disclosure, the design, construction, assembly and testing of an electrochemical flow cell for conducting corrosion and interior biocorrosion studies simulating different fluids with hydrodynamic pipeline conditions is described.
In order to contribute to the knowledge and study of the corrosion and biocorrosion damage mechanism inside pipelines, a solution recommended by the ASTM international standard [19] has been reported that simulates the electrolytes present in saline environments using electrochemical cell designs with different hydrodynamic conditions present in pipelines [1-16]. For example, Hong and co-workers [11] reported the study of the corrosion process in a 15 m long acrylic pipe section with an inner diameter of 101.6 mm subjected to the action of a multiphase flow. This study consisted of the use of a saline solution with CO2 and the dosage of a molecule that inhibits the corrosion process at different flow conditions, 40° C. and 0.136 MPa, using the electrochemical impedance spectroscopy (EIS) technique. Thus, electrochemical characterization was carried out on a three-electrode array located in a special section of the electrochemical system. In this case, the working electrode was made of 1018 carbon steel. The auxiliary and reference electrodes were 316 L stainless steel. All electrodes had an exposed area of 0.785 cm2 (10 mm diameter). In addition, 10 mV of perturbation potential and a frequency window from 5 kHz to 20 mHz were used to plot the EIS spectra. The results of this work showed real and imaginary impedance semicircles of depressive type and diffusion phenomena. Moreover, as a function of exposure time, the real impedance value increased gradually. However, the electrochemical arrangement designed in this work does not correspond to a pipe system, because a three-electrode arrangement using metallic materials such as 1018 steel and 316 L stainless steel was used. In addition, the temperature employed in this work is at the limit used in acrylic vessels. The literature review indicates that there is a lack of information or knowledge on the susceptibility to biocorrosion of pipeline steels and the corrosivity of the associated water for pipelines under hydrodynamic conditions and temperatures. These are important factors for the material choice, design and construction of an electrochemical cell for the investigation of the use of pipe steels in the absence and presence of biofilms. By designing and implementing the electrochemical and gravimetric technique in an electrochemical flow cell and a recirculation system with coolant for temperature control, it will be possible to simulate conditions as close as possible to those of pipeline operation.
Therefore, the design, construction, and assembly of an electrochemical flow cell for corrosion and biocorrosion studies on American Petroleum Institute (API) steels exposed to different fluids with hydrodynamic pipe conditions are recommended. Thus, an electrochemical flow cell was designed to adapt an electrochemical system with a three-electrode array with flow and temperature control systems. The cell is designed to perform at least two independent and/or combined flow systems: in the first one, the fluid is transported through a hydraulic pump, and in the second one, the fluid is activated by means of a magnetic stirrer (especially for case studies with emulsions). In addition, the cell offers a recirculation system for temperature control. In order to carry out electrochemical and gravimetric tests, three types of working electrodes were machined from pipeline steel with different geometries and exposure areas. Therefore, in the present disclosure, the results of electrochemical impedance spectroscopy spectra and corrosion rates obtained by polarization and weight loss curves obtained at different electrode exposure times, subjected to various hydrodynamic and temperature conditions, both in the absence and presence of microorganisms are reported. Furthermore, the procedure to prepare electrolytes simulating associated water and the experimental method to carry out electrochemical tests and corrosion and biocorrosion studies are described. The results obtained demonstrate that the exposure time of the X52 steel in contact with a saline medium containing microorganisms generate important modifications in the development of the biocorrosion of this type of steel, and the user is able to identify the experimental conditions that will be used to continue with the systematic study of this phenomenon in other types of API grade steels exposed to other types of environments found in oil and gas pipelines. Some environments involve the associated water obtained in the field, solutions prepared by means of recommended standards, new coatings, and new microorganisms subjected to different flow and temperature conditions. It is important to mention that the corrosion effect is assessed using electrochemical methods complimented with standardized and non-standardized laboratory tests. Thus, the corrosiveness of a fluid with and without a bacterial strain is performed under stagnant condition where the electrochemical responses are confused. This is because the microorganisms tend to form a compact biofilm system on steel surface that block the charge transfer such that a passivation trend might occur. Therefore, the passivation effect causes the underestimation of the corrosive effect of the microorganisms due to their physiological and biological nature. In the field, it is rare to find the fluid under static conditions, so the design of the electrochemical flow cell of the present disclosure considers both laminar and turbulent flow, promoting the formation of biofilms under flow regimes that are more in line with reality inside a pipeline. In addition, the electrochemical cell is designed to study the corrosion and biocorrosion process of steels in the presence of hydrocarbon-in-water or water-in-hydrocarbon emulsions, when the double hydrodynamic system is applied.
This section describes the design, construction, and an example of the start-up and validation of an electrochemical flow cell of the present disclosure. This includes obtaining and analyzing experimental data from different working electrode geometries exposed in a corrosive medium recommended by ASTM D1141 [19]. A saturated calomel reference electrode is used with a platinum wire as auxiliary electrode (counter electrode). As an example, for obtaining the electrochemical responses and experimental data by weight loss, three steel coupons were machined as working electrodes including the following geometries: the first is an API X52 steel cylinder of 1.0 cm length and 0.635 cm in diameter, offering an exposed area of 0.316 cm2; the second is a section of steel pipe 8 cm long and 1.0 cm internal diameter, offering an exposed internal area of 25.13 cm2; the third is a 2.5 cm ×0.5 cm×0.2 cm rectangular carbon steel bar with two 0.4 cm diameter holes to hold it on an electrode holder, offering an exposed area of 3.45 cm2. It is important to mention that the reference electrode is placed in a Luggin capillary in order to avoid contamination of the porous membrane of the reference electrode.
The criteria for the design and construction is based on the knowledge of electrochemical and biocorrosion processes that occur in pipeline steels which are exposed to a flow. The procedure to carry out the design and assembly of an electrochemical flow cell considers the following steps:
The electrochemical cell is designed and constructed of Pyrex glass with a solution capacity of 700 milliliters. It includes a movable lid designed to adapt and hermetically seal the electrodes (working, auxiliary and reference), as well as the cell itself. Furthermore, the electrochemical cell, peristaltic pump, stirring grid, recirculation system with coolant for temperature control, and potentiostat-galvanostat are mounted in strategic locations.
The advantages and limitations of the electrochemical cell are described below:
As an example, the overall dimensions of the electrochemical cell system are as follows:
The electrochemical cell is equipped with a peristaltic pump, hoses, a magnetic stirrer and a stirring grid to recirculate and stir the solution under study. In addition, the cell has a glass shell located on the outside of the cell body, a recirculation bath, hoses and other accessories for temperature control in the electrochemical system. The electrochemical cell should preferably be placed near an exhaust hood so that in case of gas emission it can be discharged safely.
Refor a pipe section=VDρ/μ (1)
ReRDE or RCE=2r2ω(1/v) (2)
τRDE o RCE=0.0791ρω2r2Re−0.3 (3)
where RDE is the rotating disk electrode, RCE is the rotating cylinder electrode, τ is the shear stress (N/m2); ω is the angular velocity (rad/s); r is the cylinder radius (cm); v is the kinematic viscosity (m2/s). In Table 1 the Reynold's number and shear stresses are presented as a function of fluid velocity for an API X52 steel disk of diameter 0.635 cm with an exposed area of 0.316 cm2 using a sour water solution with ρ=1025 kg/m3 and μ=0.00065 kg/ms (v=1.046 m2/s). The second working electrode is a section of steel pipe 8.0 cm long and with a 1.0 cm internal diameter, providing an exposed internal area of approximately 25.13 cm2. As can be seen, both the fluid velocity and the diameter of the working electrodes generate considerable shear stresses on the surface of the working electrode. However, in field practices, the value of Re will depend on the flow rate of the transported hydrocarbon, the physicochemical properties of the hydrocarbon and the diameter of the pipeline.
Table 2 presents the calculation of the Re number for a 30-inch internal diameter pipeline at different flow rates, where the pipeline area is 0.435 m2, the internal diameter is 0.7445 m, and μ=1.046 m2/s. It is important to note that the fluid velocity of 100 and 160 thousand barrels per day (TBD) generates Re values similar to those calculated in the working electrodes, that is why it is important to design this flow cell to simulate as much as possible the effect of the corrosion and biocorrosion process under flow conditions.
For the elaboration of the third working electrode holder, a solid Teflon rod was fabricated. The working electrode (corrosion coupon) is made of API X52 steel of 2.5 cm×0.5 cm×0.15 cm. This electrode was drilled to obtain two 0.4 cm diameter holes to hold it with an electrode holder, offering an exposed area of 3.45 cm2.
In order to carry out the validation of the electrochemical cell, a synthetic seawater solution recommended by ASTM D1141 [19] was used as the electrolytic medium.
Determination of electrochemical parameters, gravimetric tests and analysis of corrosion rate values were carried out on working electrode surfaces of 0.316 cm2 for the disk, 25.13 cm2 for the pipe section and 3.45 cm2 for the corrosion coupon in contact with a seawater solution and the addition of a microorganism for biocorrosion studies.
The materials used in the development of this work are the following:
The equipment that were run for the electrochemical testing stage were the following:
Ultrasonic bath.
The used reagents were:
The electrochemical evaluation is carried out using a potentiostat-galvanostat.
The recommended methodology for obtaining open circuit potential spectra, electrochemical impedance and polarization curves (Tafel curves) is described below:
Recommended procedure for the determination of corrosion rates by coupon weight loss:
Methodology for the determination of the corrosion rate by weight loss of the coupons after the gravimetric test. Taking into account the difference in weight of the coupons (initial weight—final weight), it is possible to determine the values of the corrosion rates. NACE TM0169 and NACE RP0775 [21,22] recommend using the following equation (4) for the determination of the corrosion rate (CR) in millimeters/year (mm/year):
where Wi is the initial weight of the working electrode (g) and Wf is its final weight (g); A denotes the total surface area of the tube under test in contact with the fluid in (mm2); ρ is the density of the metallic material (g/cm3); and t is test duration time in days.
The electrochemical characterization of three types of working electrodes exposed in synthetic seawater was carried out in order to validate the adaptation of an electrochemical flow cell for corrosion and biocorrosion studies simulating hydrodynamic conditions and operating temperatures found in typical pipelines.
Table 6 shows the CR values obtained on two types of steels exposed to seawater at 4.075×10−5 m3/s, at 38° C. and three hours of exposure, both in the absence and in the presence of the microorganism.
Number | Date | Country | Kind |
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MX/A/2022/004099 | Apr 2022 | MX | national |