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Investigation on the efficiency of corrosion inhibitor in CO2 corrosion of carbon steel in the presence of iron carbonate scale
Accepted Manuscript Investigation the Efficiency of Corrosion Inhibitor in CO2 Corrosion of Carbon Steel in the Presence of Iron Carbonate Scale Mehdi Javidi, Reza Chamanfar, Shima Bekhrad PII:
S1875-5100(18)30510-9
DOI:
https://doi.org/10.1016/j.jngse.2018.11.017
Reference:
JNGSE 2769
To appear in:
Journal of Natural Gas Science and Engineering
Received Date: 2 June 2018 Revised Date:
15 October 2018
Accepted Date: 15 November 2018
Please cite this article as: Javidi, M., Chamanfar, R., Bekhrad, S., Investigation the Efficiency of Corrosion Inhibitor in CO2 Corrosion of Carbon Steel in the Presence of Iron Carbonate Scale, Journal of Natural Gas Science & Engineering, https://doi.org/10.1016/j.jngse.2018.11.017. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Investigation the Efficiency of Corrosion Inhibitor in CO2 Corrosion of Carbon Steel in the Presence of Iron Carbonate Scale Mehdi Javidia, Reza Chamanfarb, Shima Bekhradb Associate Professor, Department of Materials Science and Engineering, School of
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a
Engineering, Shiraz University, Shiraz,7134851154, Iran. (Corresponding Author) Tel: +98-71-36133266 Fax: +98-71-32307293
Graduated as Master of Science, Department of Materials Science and Engineering, School
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b
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Email: [email protected]
of Engineering, Shiraz University, Shiraz, 7134851154, Iran Tel: +98-71-36133266
Email: [email protected], [email protected]
Abstract
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In this work, the inhibition efficiency of an imidazoline derivative corrosion inhibitors in CO2 corrosion of carbon steel was investigated in the presence of iron carbonate scale and hydrogen sulfide. The use of corrosion inhibitors is one of the most common controlling techniques for CO2 corrosion of carbon steel in oil and gas industry. One of the imidazoline
EP
derivatives was used as a corrosion inhibitor which protects the surface through the film formation mechanism. The investigation material was API 5L X65 carbon steel which was
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cut from a wet gas transmission pipeline. The internal surface of the pipe was covered with iron carbonate as corrosion product. In order to investigate the inhibitor efficiency, Tafel polarization and electrochemical impedance spectroscopy were done in CO2-saturated 3.5 wt.% sodium chloride solution. According to the results, the existence of iron carbonate film reduced the inhibition efficiency. Furthermore, it was found that in the presence of H2S gas, the inhibition efficiency was decreased due to the decrease in inhibitor adsorption on the surface.
Keywords: CO2 Corrosion, H2S Gas, Inhibitor Efficiency, Iron Carbonate, Surface Scales.
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ACCEPTED MANUSCRIPT 1. Introduction One of the most critical problems in oil and gas industries is a type of corrosion due to presence of CO2 gas, called sweet corrosion. This phenomenon occurs after dissolution of CO2 in aqueous phase which produces carbonic acid followed by decrease in pH of the solution. Because of economic reasons most of the pipes and equipment used in oil and gas
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industries are made from different types of carbon steel instead of stainless steel, which has a lower corrosion resistance against CO2 corrosion. CO2-Corrosion reaction is an
electrochemical reaction which its anodic half-cell reaction is the dissolution of iron and the cathodic half-cell reaction is a mixture of hydrogen evolution and direct carbonic acid
CO2 g → CO2 (aq) CO2 aq + H2O → H2CO3
Cathodic reactions H+ +
→1/2 H2
H2CO3 → H+ + HCO3-
Anodic reaction
(1) (2)
(3) (4) (5) (6)
(7)
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Fe →Fe2+ + 2e-
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HCO3- → H+ + CO32-
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H2CO3 + 2e- → H2+CO32-
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corrosion mechanism is shown by Equations 1 to 8 [4-8]:
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reduction. The rate of each reaction depends on solution pH [1-3]. The step by step CO2
Total reaction
Fe + CO2 + H2O → FeCO3 + H2
(8)
On the other hand, when gaseous H2S is present, it dissolves in the aqueous phase and contributes in electrochemical reactions. Equations 9 to 14 show the reactions by which FeS can be formed as corrosion product [9]: ↔
+
(9) 2
ACCEPTED MANUSCRIPT +
+
(10)
⇔ ⇔ ⇔
+
(11)
+
(12)
+
(13)
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↔
Thus FeS can be formed on the electrode surface via Reaction 14: ⇔
+
+ 1−
(14)
CO2 corrosion is affected by numerous parameters such as pH [10-12], temperature [13-15],
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CO2 partial pressure [13], flow velocity [3, 13], corrosion products [16] and H2S concentration [17, 18]. Variety of these parameters leads to difficulties in controlling the
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corrosion rate, thus it is essential to select a suitable controlling method. One of the most practical and useful methods is employing of corrosion inhibitors in corroding systems [19]. Corrosion inhibitors are chemicals that once injected to a corrosive environment in small concentration, adsorb on the surface chemically or physically and decrease the corrosion rate effectively [20, 21]. It is the mechanism of film forming corrosion inhibitors. However, other type of inhibitors affects the corrosion phenomenon via different mechanism. Nitrogen-based
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organic compounds such as imidazoline, amides, amidomines, amines, and salts are some commercial type of inhibitors that have been effectively utilized in oil and gas industry[22]. Imidazoline and its derivatives are generally utilized in order to protect carbon steel in CO2-
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containing solutions. Selecting a suitable inhibitor is half the way of protection of pipelines, the second half is monitoring the inhibitor performance and the parameters that affect it such
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as foaming [23].
Many papers were published on corrosion inhibitors in different corrosive environments, but in most of these studies, samples with fresh surface were investigated. However, in practice depending on service conditions the surface of the pipeline may be covered with corrosion products like iron carbonate film and iron sulfide and these films might affect inhibitor performance [24]. In 2006, Foss et al. [25] conducted a study on scale inhibitor interactions with oxide layers on the surface of carbon steel. The results indicated that when scale inhibitors are present, the rate of corrosion increases due to the precipitation of a less protective layer in comparison with a state in which there is no inhibitor in the system. In 2008, Foss et al.[26] in another study investigated the relation between surface wettability,
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ACCEPTED MANUSCRIPT corrosion rate and inhibitor performance. In their study partly protective ferrous carbonate (FeCO3) covered carbon steel specimens were used. They found that presence of corrosion product decreases the efficiency of corrosion inhibitor as a result of less adsorption of inhibitor on the surface. In 2008 Paolinelli [27] conducted a study on the relationship between microstructure, surface condition and inhibition efficiency of inhibitors in sweet
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corrosion. The results showed a decrease in the inhibitor efficiency due to pre-corrosion, but they found that this effect depends on microstructure of steel. In 2011, Liu et al. [28]
investigated the interaction of inhibitors and presence of corrosion products on N80 steel surface in a saturated atmosphere of CO2 and salt. Based on their research, the inhibitor
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efficiency is dependent on two parameters: first the size of the inhibitor molecule and the second reaction of the inhibitor with scales which may be synergistic or antagonistic. In 2017, Chen Zhang [24] investigated the impact of pre-corrosion on CO2 corrosion performance of
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inhibitor in the CO2/H2S saturated brine solution. The results revealed that pre-corrosion process decreases the performance of inhibitor as corroding species might diffuse to surface via diffusion path available through porosities in the corrosion product layers. In this paper, the influence of iron carbonate corrosion product, which formed during the service life of an API 5L X65 carbon steel pipeline which transmitting wet natural gas, on
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inhibition efficiency of an imidazoline derivatives corrosion inhibitor was studied. The effect of H2S gas concentration has also been considered on the inhibitor performance. It is the novelty of this work which investigates the effect of iron carbonate corrosion product which
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formed in field service condition.
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2. Research Methodology
2.1. Material characterization The specimens of the studied material were cut from a piece of API 5L X65 carbon steel pipeline which experience wet natural gas transmission conditions for 12 years. The pipe's chemical composition was characterized by the use of an optical emission spectroscopy (OES, Foundry-Master Pro). The service conditions and also characteristics of the surface scale of the pipeline, including its chemical composition and also thickness, were discussed in the previous work of the authors [29]. 2.2. Electrochemical measurements 4
ACCEPTED MANUSCRIPT The investigations were carried out on bare and iron carbonate scale covered specimens with and without the presence of inhibitor. Bare samples were polished by emery paper (up to 1000 grit SiC paper) then washed by ethanol and finally dried with hot air. The electrolyte for electrochemical studies was 3.5% wt. NaCl solution which purged with CO2 gas to produce a CO2-saturated solution. The investigated corrosion inhibitor in this study was an amine-based
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imidazoline derivatives inhibitor with TX-1100 commercial name (Travis Iran Co.) which inhibits the corrosion via film formation mechanism. Based on the company specifications a concentration of 50 ppm inhibitor in aqueous phase was used as the optimized concentration. Thus, after saturation of the solution with CO2 gas, the inhibitor was added to the solution
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with 50 ppm concentration. Then the samples were put in a cell to experience 24 h pre-
corrosion condition. Such a treatment was done to ensure of the inhibitor film formation on the surface. It is necessary to note that pre-corrosion was also performed on samples without
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the presence of the corrosion inhibitor to have a same treatment so that the resulted data can be compared.
In order to consider the effect of different concentrations of H2S on the inhibition efficiency, three concentrations of 50, 100 and 150 ppm of H2S in the aqueous phase were investigated. The reaction of sulfuric acid with sodium sulfate was employed to dissolve H2S gas into the
+
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CO2-saturated solution via following the stoichiometry of Reaction 15 [30-32]: →
+
(15)
On the other hand, to verify the desired concentration of dissolved H2S in the solution, the
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iodometric titration technique which proposed by NACE TM 0284-2016 was used. According to this test method, the concentration of dissolved H2S in aqueous solution can be
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evaluated by Equation 16: ! "
%$ #
&
'=
) * +
× 17040
(16)
A = Normality of standard iodine solution (equivalents/L) times the volume used (L) B= Normality of standard sodium thiosulfate solution (equivalents/L) times the volume used (L) C = Volume of test solution sample (L) The result of the titration technique revealed a close proximity between the desired dissolved H2S concentration and the calculated concentration in such a manner that in case of dissolving 50 ppm H2S in CO2-saturated solution, the result of titration showed the presence 5
ACCEPTED MANUSCRIPT of 47 ppm dissolved H2S. The value of the pH was found to be 4.0 for CO2-saturated solution, and was changed to 2.8 and 2.5 after dissolving 100 and 200 ppm H2S, respectively. All the electrochemical tests were conducted in a three-electrode double-jacketed glass cell which was filled with 450 ml CO2-saturated brine. The Ag/AgCl and platinum electrode were selected as the reference electrode and counter electrode, respectively. Before each
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electrochemical test, the samples have been pre-corroded in the solution for 24 h then open circuit potential (OCP) was monitored for 1800 s. The electrochemical impedance
spectroscopy (EIS) test was performed in the frequency range of 100 kHz to 0.01 Hz with applying a sinusoidal perturbation AC potential with amplitude of ± 10 mV. Electrochemical
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parameters from EIS tests were obtained through fitting the EIS data with ZViewTM Software (3.4 Scribner Associates Inc.).
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Then inhibitor efficiency, η, was calculated from the charge transfer resistance by using charge transfer resistance (Rct ) with the Equation 17:
η=
012 - 012 Rct
×100
(17)
where Rct and Rct° are charge transfer resistance with and without the presence of inhibitor in
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the solution, respectively [33].
Tafel polarization test was performed after EIS measurements in the potential range of -300 mV to 300 mV versus OCP at a scan rate of 1 mV/s and electrochemical parameters obtained through fitting curves with Ivium Software (Ivium Technologies B.V.). Subsequently
18: i corr° - icorr
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η=
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inhibitor efficiency,η, was evaluated from corrosion current density (icorr) regarding Equation
(18)
i corr°
where i corr° and icorr are corrosion current density without and with the presence of corrosion inhibitor, respectively. All electrochemical measurements were performed at 40 °C and the reported data are the average of at least three measurements.
2.3. Phase composition and surface investigation After performing electrochemical experiments the surface of samples were investigated with scanning electron microscopy (SEM, Cambridge Stereo-scan S360) and the chemical 6
ACCEPTED MANUSCRIPT composition of surface scales was investigated via X-ray diffraction (XRD) with Cu-Kα radiation (λ = 1.5406 Å) and the obtained patterns were analyzed by X'pert Highscore Plus Software (PANalytical B.V.).
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3. Results and discussion 3.1. Chemical composition of the scale
As mentioned in the experimental section, the phase composition of the surface scale of the samples was studied in the previous work of the authors. It was revealed that the surface scale
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consists of mainly iron carbonate (siderite) with the rhombohedral crystal structure and
FeCO3 chemical formula and also the minor amount of FeS (Mackinawite) was detected. The absence of iron's peak in the X-ray sweep of Fig. 2. b indicates that the diffracted beam
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passage from the steel substrate was prevented because of the presence of thick iron carbonate surface scale [34]. Furthermore, it was found that iron carbonate layer is a uniform scale with a 200 µm thickness which can protect the surface against corroding spices. The protectiveness of the film is widely influenced by environmental parameters such as
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temperature, fluid flow, steel composition, and microstructure, etc. [35].
3.2. Potentiodynamic polarization measurement Potentiodynamic polarization investigations were performed for bare and iron carbonate scale
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covered samples with and without the presence of inhibitor in different H2S concentration at 40 °C and the results are shown in Figure 1. Also, the electrochemical parameters were
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obtained by fitting polarization curves with Ivium Software and are showed in Table 1. According to Figure 1 and Table 1, one can realize that the corrosion current density of bare samples was decreased significantly in the presence of inhibitor. The efficiency of the inhibitor was found to be 99.86 % which proves the inhibiting action of the inhibitor and formation of inhibitor film. On the other hand, Figure 1.c and 1.d and also the data presented in Table 1 reveal the decrease in corrosion current density because of corrosion inhibitor in the presence of iron carbonate scale. However, the decrease in corrosion current density and corresponding inhibition efficiency (88.3 %) was not comparable as the decrease which was found for the bare sample. Thus, the inhibitor efficiency decreased in the presence of surface layers [16, 24, 27]. 7
ACCEPTED MANUSCRIPT By considering the data presented in Figure 1 and Table 1 it can be concluded that by increasing H2S concentration in the solution, corrosion current density of the bare samples is decreased. This is due to formation and precipitation of mackinawite (FeS(s)) as corrosion product on the surface in the presence of H2S in trace amounts [31, 36, 37]. On the other hand, by comparing corrosion current density and inhibition efficiency of the bare samples in
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different concentration of H2S an increase in corrosion current density and a decrease in the inhibition efficiency can be observed. This is due to the formation of FeS on the surface which prevents the adsorption of inhibitor film on the surface.
By considering the data presented in Table 1, one soon realizes that increasing the H2S
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concentration from 50 to 100 ppm declines the corrosion current density. However, the
corrosion current density increases by rising the H2S concentration from 100 to 150 ppm .
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This variation in corrosion current density can be observed for the bare and also iron carbonate scale covered samples. Such a decrease in corrosion rate of carbon steel can be attributed to the formation of FeS corrosion product on the surface of the samples. The XRD pattern presented in Figure 2 reveals the presence of FeS on the surface of both bare and iron carbonate scale in 50 ppm H2S concentration. On the other hand, the SEM cross-sectional view of the samples which is presented in Figure 3, shows the formation of FeS on the bare
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and also iron carbonate scale covered sample in case of the increase in H2S concentration from 50 to 100 ppm. However, by increasing H2S concentration from 100 to 150 formation of
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cracks on FeS film was observed.
3.3. Electrochemical impedance spectroscopy measurements
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The EIS experiments were conducted for bare and iron carbonate scale covered samples with and without the presence of inhibitor in different H2S concentration and the resulted data are shown in Figure 4 and 5 and the extracted electrochemical data are presented in Table 2. Furthermore, Figure 6 shows equivalent circuits used for fitting EIS curves to investigate electrochemical parameters. The corresponding physical models are also represented in the figure and the related sample conditions are described in the figure caption. Electrochemical parameters obtained by fitting the curves are reported in Table 2 and Equation 17 was used in order to calculate the inhibition efficiency. By considering the data presented in Figures 4. a and 4.b one can see that when inhibitor is present the diameter of the capacitive loop increased for bare samples which mean corrosion 8
ACCEPTED MANUSCRIPT rate has been decreased. On the other hand, by comparing Figure 5. a and 5.b it was revealed that when surface scales are present, the capacitive loop diameter, which is corresponding to charge transfer resistance, was increased however this increase is less than the increase which was observed for the bare sample. This phenomenon indicates that inhibition efficiency has been decreased in the existence of scale on the surface which is in good agreement with the
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results obtained in polarization test investigation. According to Figure 5.a, for iron carbonate scale covered samples in spite of the bare
samples, it was seen that by increasing H2S concentration the capacitive loop diameter was decreased which may be due to cracking of the film because of increase in its thickness by
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FeS formation [39]. Figure 4.c and 4.d are showing Bode phase plots of the bare samples when inhibitor film is present and FeS as corrosion product and Figure 5.c and 5.d also show
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Bode phase plots for the iron carbonate scale covered samples in the presence of inhibitor and H2S in the solution. Both of these curves are shown at least two-time constants. The Lowfrequency time constant indicates corrosion process on the steel surface and the highfrequency one could be related to the film covering the surface [38]. By considering the data presented in Table 2, one can conclude that for all samples in the presence of inhibitor, the charge-transfer resistance increases which indicates that an inhibitor
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film is formed on the surface. On the other hand, for the bare sample, the charge transfer resistance increases by increasing H2S concentration, in the absence of inhibitor, which can be related to the inhibition effect of FeS film as corrosion product. This is attributed to the
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presence of H2S in trace concentration in the solution and coverage effect mechanism [36, 40]. While, by increasing H2S concentration in the solution in the presence of inhibitor, charge transfer resistance was decreased which was related to poor adsorption of inhibitor
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film on the surface due to more FeS formation [24]. For iron carbonate scale covered samples, it was found that by increasing H2S concentration, the iron carbonate scale was deteriorated and charge transfer resistance was decreased and consequently corrosion rate was increased due to formation of cracks in the surface film by FeS growth.
4. Conclusions In this investigation the influence of iron carbonate scale as corrosion product on inhibition efficiency of imidazoline derivatives corrosion inhibitor in CO2-saturated 3.5 wt.% NaCl solution was studied. The effect of H2S gas concentration has also been considered on the 9
ACCEPTED MANUSCRIPT inhibitor performance. It was found that in the presence of iron carbonate surface scale, the inhibition efficiency of the inhibitor phase was decreased due to decrease in adsorption of inhibitor on the surface. Furthermore, it was revealed that inhibition efficiency decreased by increase in H2S concentration in the solution due to surface film cracking as a result of FeS formation and growth. Finally, it was concluded that in the presence of trace concentration of
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H2S in CO2-saturated 3.5 wt.% NaCl solution, the corrosion rate of the bare samples
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decreases in the absence of corrosion inhibitor due to precipitation of FeS scale.
Nomenclature
Solution resistance
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Rs Rf
Inhibitor film resistance
Charge transfer resistance
CPEdl
Constant phase element of the double layer capacitor
CPEf
Inhibitor film constant phase element
CPEScale
Scale constant phase element
RScale
Scale resistance
Warburg impedance
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W
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Rct
References 1. 2.
3. 4.
Kunal, K.C., A Study of Inhibitor - Scale Interaction in Carbon Dioxide Corrosion of Mild Steel. 2004, Ohio: Usa. P. 1-121. Amri, J., On Growth And Stifling of Localized Corrosion Attacks in CO2 and Acetic Acid Environments : Application to the Top-of-Line Corrosion of Wet Gas Pipelines Operated in Stratified Flow Regime, in Institut Polytechnique De Grenoble. 2010, University of Stavanger - Norway: France. P. 1-253. Nesic, S., J. Postlethwaite, And S. Olsen, An Electrochemical Model for Prediction of CO2 Corrosion. S. Nesic, J. Postlethwaite, And S. Olsen, Paper, 1995(131). Dugstad, A. Fundamental Aspects of CO2 Metal Loss Corrosion-Part 1: Mechanism. in Corrosion 2006. 2006. Nace International. 10
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7.
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6.
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Liu, D., Et Al., Interaction of Inhibitors With Corrosion Scale Formed on N80 Steel in CO2 -Saturated Nacl Solution. Materials And Corrosion, 2011. 62(12): P. 11531158. Javidi, M. And S. Bekhrad, Failure Analysis of A Wet Gas Pipeline Due to Localised CO2 Corrosion. Engineering Failure Analysis, 2018. 89: P. 46-56. Ma, H., Et Al., An Ac Impedance Study of the Anodic Dissolution of Iron In Sulfuric Acid Solutions Containing Hydrogen Sulfide. Journal of Electroanalytical Chemistry, 1998. 451(1): P. 11-17. Ma, H., Et Al., The Influence of Hydrogen Sulfide on Corrosion of Iron Under Different Conditions. Corrosion Science, 2000. 42(10): P. 1669-1683. Taheri, H., Et Al., The Effect of H2S Concentration and Temperature on Corrosion Behavior of Pipeline Steel A516-Gr70. Caspian Journal of Applied Sciences Research, 2012. 1(5): P. 41-47. Hosseini, M.G. And A. Ahadzadeh, Electrochemical Ampedance Spectroscopy. 2012, Iran: Iran Corrosion Congress. Palacios, C. And J. Shadley, Characteristics of Corrosion Scales on Steels In A CO2Saturated Nacl Brine. Corrosion, 1991. 47(2): P. 122-127. Kahyarian, A., M. Singer, And S. Nesic, Modeling of Uniform CO2 Corrosion of Mild Steel In Gas Transportation Systems: A Review. Journal of Natural Gas Science And Engineering, 2016. 29: P. 530-549. Lee, K.-L.J. And S. Nesic, The Effect of Trace Amount of H2S On CO2 Corrosion Investigated By Using The Eis Technique, In Corrosion. 2005, Nace International: Usa. P. 1-16. Plennevaux, C., Et Al., Contribution of CO2 on Hydrogen Evolution And Hydrogen Permeation In Low Alloy Steels Exposed To H2S Environment. Electrochemistry Communications, 2013. 26: P. 17-20. Abelev, E., Et Al., Effect of H2S On Fe Corrosion In CO2-Saturated Brine. Journal of Materials Science, 2009. 44(22): P. 6167-6181. Tait, W.S., An Introduction To Electrochemical Corrosion Testing For Practicing Engineers And Scientists. 1994: Pairodocs Publications. Lee, K.-L.J., A Mechanistic Modeling of CO2 Corrosion of Mild Steel In The Presence of H2S. 2004, Ohio: Usa. P. 1-220.
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Figure captions
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28.
Figure 1: Tafel polarization curve for a). Bare samples without inhibitor; b). Bare samples with inhibitor; c). Samples with iron carbonate scale without inhibitor; d). Samples with iron carbonate scale without inhibitor. All in CO2-saturated 3.5 wt.% NaCl solution containing 0, 50, 100, 150 ppm H2S concentration. Figure 2: The XRD pattern: a) Bare sample. b). Iron carbonate scale covered samples. Both in CO2-saturated 3.5 wt.% NaCl solution containing 50 ppm H2S concentration. Figure 3: SEM cross-sectional view photomicrographs. a, b , c). Bare samples. d, e, f). Iron carbonate scale covered samples. Both in CO2-saturated 3.5 wt.% NaCl solution containing 50, 100,150 ppm H2S concentration, respectively.
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ACCEPTED MANUSCRIPT Figure 4: a, b). Nyquist diagram curves and c, d). Bode phase plot for the bare samples without and with inhibitor; in CO2-saturated 3.5 wt.% NaCl solution containing 0, 50, 100, 150 ppm H2S concentration. Figure 5: a, b). Nyquist diagram curves and c, d). Bode phase plot for the iron carbonate scale covered samples without and with inhibitor; in CO2-saturated 3.5 wt.% NaCl solution containing 0, 50, 100, 150 ppm H2S concentration.
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Figure 6: The equivalent circuits used for fitting EIS data. a). Bare samples b). Bare samples with inhibitor film in CO2-saturated 3.5 wt.% NaCl solution containing 0, 50, 100, 150 ppm H2S concentration or Iron carbonate scale covered samples with inhibitor in CO2-saturated 3.5 wt.% NaCl solution containing 0 ppm H2S concentration or Iron carboante coverd samples without inhibitor in CO2-saturated 3.5 wt.% NaCl solution containing 0, 50 ppm H2S; c). Iron carboante covered samples without inhibitor in CO2-saturated 3.5 wt.% NaCl solution containing 100, 150 ppm H2S, or Iron carbonate scale covered samples with inhibitor in CO2-saturated 3.5 wt.% NaCl solution containing 50, 100, 150 ppm H2S.
Table captions
Table 1: Electrochemical parameters obtained from Tafel polarization curves for bare and iron carbonate covered samples with and without the presence of inhibitor in 0,50,100,150 ppm H2S concentration.
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Table 2: Electrochemical parameters obtained from EIS analysis for bare and iron carbonate scale covered samples with and without the presence of inhibitor in 0,50,100,150 ppm H2S concentration.
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Table 1: Electrochemical parameters obtained from Tafel polarization curves for bare and iron carbonate covered samples with and without the presence of inhibitor in 0,50,100,150 ppm H2S concentration. Ecorr (V,vs.Ag/AgCl)
Corrosion rate (mm/year)
H2S Inhibitor
Bare
With iron carbonate
Bare
With iron carbonate
Bare
With iron carbonate
Without
1.08×10-4
1.78×10-5
-0.674
-0.652
1.257
0.205
1.48×10-7
2.08×10-6
-0.610
-0.354
0.017
0.024
1.84×10-5
2.80×10-5
4.89×10-7
9.08×10-6
1.39×10-5
2.53×10-5
2.35×10-6
1.43×10-5
(ppm)
0
Without
50
Without
100 With
Without
150
2.81×10-6
-0.672
0.213
0.325
-0.626
-0.346
0.005
0.105
-0.654
-0.667
0.161
0.293
-0.638
-0.361
0.027
0.166
6.01×10-5
-0.641
-0.672
0.319
0.718
3.13×10-5
-0.692
-0.405
0.032
0.391
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EP
With
2.75×10-5
-0.650
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With
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With
SC
concentration
Efficiency (%)
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i corr (A/cm2)
Bare
With iron carbonate
99.86
88.30
97.34
67.57
83.09
43.47
89.87
47.92
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Table 2: Electrochemical parameters obtained from EIS analysis for bare and iron carbonate scale covered samples with and without the presence of inhibitor in 0,50,100,150 ppm H2S concentration.
Bare
Inhibitor
Without With
Rs (Ω.cm2)
Rct (Ω.cm2)
Y0 (sn/cm2.Ω)
n
Rfilm (Ω.cm2)
Y0 film (sn/cm2.Ω)
n
η (%)
2.25 12.10
140.7 29617.0
4.47×10-4 5.49×10-6
0.82 0.66
-
-
-
99.52
15.09 94.00
1553.0 10422.0
4.03×10-5 7.36×10-6
0.65 0.42
71.85 1312.00
7.01×10-8 1.68×10-9
1.00 1.00
85.09
6.32 4.17
560.0 7350.0
3.81×10-4 1.63×10-6
0.90 0.80
76.00 452.00
8.78×10-4 2.49×10-5
0.77 0.59
92.34
15.83 34.33
241.0 1130.0
6.13×10-4 1.46×10-5
0.42 0.28
20.00 166.00
4.27×10-4 3.42×10-5
0.63 0.48
78.67
4.89 8.87
1000.0 4265.0
3.31×10-4 2.61×10-6
0.81 0.79
33.00 135.00
7.97×10-4 6.37×10-5
0.80 0.55
76.55
With iron carbonate
Without With Without
Bare With
50 With iron carbonate Bare
Without With Without
100 With iron carbonate
Without With Without
Bare 150
3.23 74.00
321.0 570.0
4.66×10-4 2.43×10-5
0.46 0.51
-
-
-
43.68
1.80 1.00
389.0 2500.0
7.66×10-4 6.16×10-5
0.75 0.59
102.00 68.00
8.26×10-4 2.29×10-4
0.81 0.57
84.44
75.0 137.0
9.28×10-4 2.22×10-4
0.28 0.33
-
-
-
45.25
EP
With
TE D
With
M AN U
0
Without With
AC C
With iron carbonate
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Sample
SC
H2S concentration (ppm)
9.70 72.00
AC C
EP
TE D
M AN U
SC
RI PT
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AC C
EP
TE D
M AN U
SC
RI PT
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AC C
EP
TE D
M AN U
SC
RI PT
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AC C
EP
TE D
M AN U
SC
RI PT
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AC C
EP
TE D
M AN U
SC
RI PT
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EP
TE D
M AN U
SC
RI PT
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EP
TE D
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SC
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Investigating CO2 corrosion inhibitor efficiency in presence FeCO3 scale and H2S. Samples were cut from wet gas transmission pipeline with FeCO3 corrosion product. In the presence of FeCO3 scale on the surface the inhibitor efficiency decreased. H2S addition to solution decreased inhibitor efficiency because of less adsorption. Increasing H2S concentration increased corrosion and decreased inhibitor efficiency.
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• • • • •
S1875-5100(18)30510-9
DOI:
https://doi.org/10.1016/j.jngse.2018.11.017
Reference:
JNGSE 2769
To appear in:
Journal of Natural Gas Science and Engineering
Received Date: 2 June 2018 Revised Date:
15 October 2018
Accepted Date: 15 November 2018
Please cite this article as: Javidi, M., Chamanfar, R., Bekhrad, S., Investigation the Efficiency of Corrosion Inhibitor in CO2 Corrosion of Carbon Steel in the Presence of Iron Carbonate Scale, Journal of Natural Gas Science & Engineering, https://doi.org/10.1016/j.jngse.2018.11.017. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Investigation the Efficiency of Corrosion Inhibitor in CO2 Corrosion of Carbon Steel in the Presence of Iron Carbonate Scale Mehdi Javidia, Reza Chamanfarb, Shima Bekhradb Associate Professor, Department of Materials Science and Engineering, School of
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a
Engineering, Shiraz University, Shiraz,7134851154, Iran. (Corresponding Author) Tel: +98-71-36133266 Fax: +98-71-32307293
Graduated as Master of Science, Department of Materials Science and Engineering, School
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b
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Email: [email protected]
of Engineering, Shiraz University, Shiraz, 7134851154, Iran Tel: +98-71-36133266
Email: [email protected], [email protected]
Abstract
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In this work, the inhibition efficiency of an imidazoline derivative corrosion inhibitors in CO2 corrosion of carbon steel was investigated in the presence of iron carbonate scale and hydrogen sulfide. The use of corrosion inhibitors is one of the most common controlling techniques for CO2 corrosion of carbon steel in oil and gas industry. One of the imidazoline
EP
derivatives was used as a corrosion inhibitor which protects the surface through the film formation mechanism. The investigation material was API 5L X65 carbon steel which was
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cut from a wet gas transmission pipeline. The internal surface of the pipe was covered with iron carbonate as corrosion product. In order to investigate the inhibitor efficiency, Tafel polarization and electrochemical impedance spectroscopy were done in CO2-saturated 3.5 wt.% sodium chloride solution. According to the results, the existence of iron carbonate film reduced the inhibition efficiency. Furthermore, it was found that in the presence of H2S gas, the inhibition efficiency was decreased due to the decrease in inhibitor adsorption on the surface.
Keywords: CO2 Corrosion, H2S Gas, Inhibitor Efficiency, Iron Carbonate, Surface Scales.
1
ACCEPTED MANUSCRIPT 1. Introduction One of the most critical problems in oil and gas industries is a type of corrosion due to presence of CO2 gas, called sweet corrosion. This phenomenon occurs after dissolution of CO2 in aqueous phase which produces carbonic acid followed by decrease in pH of the solution. Because of economic reasons most of the pipes and equipment used in oil and gas
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industries are made from different types of carbon steel instead of stainless steel, which has a lower corrosion resistance against CO2 corrosion. CO2-Corrosion reaction is an
electrochemical reaction which its anodic half-cell reaction is the dissolution of iron and the cathodic half-cell reaction is a mixture of hydrogen evolution and direct carbonic acid
CO2 g → CO2 (aq) CO2 aq + H2O → H2CO3
Cathodic reactions H+ +
→1/2 H2
H2CO3 → H+ + HCO3-
Anodic reaction
(1) (2)
(3) (4) (5) (6)
(7)
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Fe →Fe2+ + 2e-
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HCO3- → H+ + CO32-
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H2CO3 + 2e- → H2+CO32-
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corrosion mechanism is shown by Equations 1 to 8 [4-8]:
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reduction. The rate of each reaction depends on solution pH [1-3]. The step by step CO2
Total reaction
Fe + CO2 + H2O → FeCO3 + H2
(8)
On the other hand, when gaseous H2S is present, it dissolves in the aqueous phase and contributes in electrochemical reactions. Equations 9 to 14 show the reactions by which FeS can be formed as corrosion product [9]: ↔
+
(9) 2
ACCEPTED MANUSCRIPT +
+
(10)
⇔ ⇔ ⇔
+
(11)
+
(12)
+
(13)
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↔
Thus FeS can be formed on the electrode surface via Reaction 14: ⇔
+
+ 1−
(14)
CO2 corrosion is affected by numerous parameters such as pH [10-12], temperature [13-15],
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CO2 partial pressure [13], flow velocity [3, 13], corrosion products [16] and H2S concentration [17, 18]. Variety of these parameters leads to difficulties in controlling the
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corrosion rate, thus it is essential to select a suitable controlling method. One of the most practical and useful methods is employing of corrosion inhibitors in corroding systems [19]. Corrosion inhibitors are chemicals that once injected to a corrosive environment in small concentration, adsorb on the surface chemically or physically and decrease the corrosion rate effectively [20, 21]. It is the mechanism of film forming corrosion inhibitors. However, other type of inhibitors affects the corrosion phenomenon via different mechanism. Nitrogen-based
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organic compounds such as imidazoline, amides, amidomines, amines, and salts are some commercial type of inhibitors that have been effectively utilized in oil and gas industry[22]. Imidazoline and its derivatives are generally utilized in order to protect carbon steel in CO2-
EP
containing solutions. Selecting a suitable inhibitor is half the way of protection of pipelines, the second half is monitoring the inhibitor performance and the parameters that affect it such
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as foaming [23].
Many papers were published on corrosion inhibitors in different corrosive environments, but in most of these studies, samples with fresh surface were investigated. However, in practice depending on service conditions the surface of the pipeline may be covered with corrosion products like iron carbonate film and iron sulfide and these films might affect inhibitor performance [24]. In 2006, Foss et al. [25] conducted a study on scale inhibitor interactions with oxide layers on the surface of carbon steel. The results indicated that when scale inhibitors are present, the rate of corrosion increases due to the precipitation of a less protective layer in comparison with a state in which there is no inhibitor in the system. In 2008, Foss et al.[26] in another study investigated the relation between surface wettability,
3
ACCEPTED MANUSCRIPT corrosion rate and inhibitor performance. In their study partly protective ferrous carbonate (FeCO3) covered carbon steel specimens were used. They found that presence of corrosion product decreases the efficiency of corrosion inhibitor as a result of less adsorption of inhibitor on the surface. In 2008 Paolinelli [27] conducted a study on the relationship between microstructure, surface condition and inhibition efficiency of inhibitors in sweet
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corrosion. The results showed a decrease in the inhibitor efficiency due to pre-corrosion, but they found that this effect depends on microstructure of steel. In 2011, Liu et al. [28]
investigated the interaction of inhibitors and presence of corrosion products on N80 steel surface in a saturated atmosphere of CO2 and salt. Based on their research, the inhibitor
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efficiency is dependent on two parameters: first the size of the inhibitor molecule and the second reaction of the inhibitor with scales which may be synergistic or antagonistic. In 2017, Chen Zhang [24] investigated the impact of pre-corrosion on CO2 corrosion performance of
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inhibitor in the CO2/H2S saturated brine solution. The results revealed that pre-corrosion process decreases the performance of inhibitor as corroding species might diffuse to surface via diffusion path available through porosities in the corrosion product layers. In this paper, the influence of iron carbonate corrosion product, which formed during the service life of an API 5L X65 carbon steel pipeline which transmitting wet natural gas, on
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inhibition efficiency of an imidazoline derivatives corrosion inhibitor was studied. The effect of H2S gas concentration has also been considered on the inhibitor performance. It is the novelty of this work which investigates the effect of iron carbonate corrosion product which
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formed in field service condition.
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2. Research Methodology
2.1. Material characterization The specimens of the studied material were cut from a piece of API 5L X65 carbon steel pipeline which experience wet natural gas transmission conditions for 12 years. The pipe's chemical composition was characterized by the use of an optical emission spectroscopy (OES, Foundry-Master Pro). The service conditions and also characteristics of the surface scale of the pipeline, including its chemical composition and also thickness, were discussed in the previous work of the authors [29]. 2.2. Electrochemical measurements 4
ACCEPTED MANUSCRIPT The investigations were carried out on bare and iron carbonate scale covered specimens with and without the presence of inhibitor. Bare samples were polished by emery paper (up to 1000 grit SiC paper) then washed by ethanol and finally dried with hot air. The electrolyte for electrochemical studies was 3.5% wt. NaCl solution which purged with CO2 gas to produce a CO2-saturated solution. The investigated corrosion inhibitor in this study was an amine-based
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imidazoline derivatives inhibitor with TX-1100 commercial name (Travis Iran Co.) which inhibits the corrosion via film formation mechanism. Based on the company specifications a concentration of 50 ppm inhibitor in aqueous phase was used as the optimized concentration. Thus, after saturation of the solution with CO2 gas, the inhibitor was added to the solution
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with 50 ppm concentration. Then the samples were put in a cell to experience 24 h pre-
corrosion condition. Such a treatment was done to ensure of the inhibitor film formation on the surface. It is necessary to note that pre-corrosion was also performed on samples without
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the presence of the corrosion inhibitor to have a same treatment so that the resulted data can be compared.
In order to consider the effect of different concentrations of H2S on the inhibition efficiency, three concentrations of 50, 100 and 150 ppm of H2S in the aqueous phase were investigated. The reaction of sulfuric acid with sodium sulfate was employed to dissolve H2S gas into the
+
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CO2-saturated solution via following the stoichiometry of Reaction 15 [30-32]: →
+
(15)
On the other hand, to verify the desired concentration of dissolved H2S in the solution, the
EP
iodometric titration technique which proposed by NACE TM 0284-2016 was used. According to this test method, the concentration of dissolved H2S in aqueous solution can be
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evaluated by Equation 16: ! "
%$ #
&
'=
) * +
× 17040
(16)
A = Normality of standard iodine solution (equivalents/L) times the volume used (L) B= Normality of standard sodium thiosulfate solution (equivalents/L) times the volume used (L) C = Volume of test solution sample (L) The result of the titration technique revealed a close proximity between the desired dissolved H2S concentration and the calculated concentration in such a manner that in case of dissolving 50 ppm H2S in CO2-saturated solution, the result of titration showed the presence 5
ACCEPTED MANUSCRIPT of 47 ppm dissolved H2S. The value of the pH was found to be 4.0 for CO2-saturated solution, and was changed to 2.8 and 2.5 after dissolving 100 and 200 ppm H2S, respectively. All the electrochemical tests were conducted in a three-electrode double-jacketed glass cell which was filled with 450 ml CO2-saturated brine. The Ag/AgCl and platinum electrode were selected as the reference electrode and counter electrode, respectively. Before each
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electrochemical test, the samples have been pre-corroded in the solution for 24 h then open circuit potential (OCP) was monitored for 1800 s. The electrochemical impedance
spectroscopy (EIS) test was performed in the frequency range of 100 kHz to 0.01 Hz with applying a sinusoidal perturbation AC potential with amplitude of ± 10 mV. Electrochemical
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parameters from EIS tests were obtained through fitting the EIS data with ZViewTM Software (3.4 Scribner Associates Inc.).
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Then inhibitor efficiency, η, was calculated from the charge transfer resistance by using charge transfer resistance (Rct ) with the Equation 17:
η=
012 - 012 Rct
×100
(17)
where Rct and Rct° are charge transfer resistance with and without the presence of inhibitor in
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the solution, respectively [33].
Tafel polarization test was performed after EIS measurements in the potential range of -300 mV to 300 mV versus OCP at a scan rate of 1 mV/s and electrochemical parameters obtained through fitting curves with Ivium Software (Ivium Technologies B.V.). Subsequently
18: i corr° - icorr
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η=
EP
inhibitor efficiency,η, was evaluated from corrosion current density (icorr) regarding Equation
(18)
i corr°
where i corr° and icorr are corrosion current density without and with the presence of corrosion inhibitor, respectively. All electrochemical measurements were performed at 40 °C and the reported data are the average of at least three measurements.
2.3. Phase composition and surface investigation After performing electrochemical experiments the surface of samples were investigated with scanning electron microscopy (SEM, Cambridge Stereo-scan S360) and the chemical 6
ACCEPTED MANUSCRIPT composition of surface scales was investigated via X-ray diffraction (XRD) with Cu-Kα radiation (λ = 1.5406 Å) and the obtained patterns were analyzed by X'pert Highscore Plus Software (PANalytical B.V.).
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3. Results and discussion 3.1. Chemical composition of the scale
As mentioned in the experimental section, the phase composition of the surface scale of the samples was studied in the previous work of the authors. It was revealed that the surface scale
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consists of mainly iron carbonate (siderite) with the rhombohedral crystal structure and
FeCO3 chemical formula and also the minor amount of FeS (Mackinawite) was detected. The absence of iron's peak in the X-ray sweep of Fig. 2. b indicates that the diffracted beam
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passage from the steel substrate was prevented because of the presence of thick iron carbonate surface scale [34]. Furthermore, it was found that iron carbonate layer is a uniform scale with a 200 µm thickness which can protect the surface against corroding spices. The protectiveness of the film is widely influenced by environmental parameters such as
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temperature, fluid flow, steel composition, and microstructure, etc. [35].
3.2. Potentiodynamic polarization measurement Potentiodynamic polarization investigations were performed for bare and iron carbonate scale
EP
covered samples with and without the presence of inhibitor in different H2S concentration at 40 °C and the results are shown in Figure 1. Also, the electrochemical parameters were
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obtained by fitting polarization curves with Ivium Software and are showed in Table 1. According to Figure 1 and Table 1, one can realize that the corrosion current density of bare samples was decreased significantly in the presence of inhibitor. The efficiency of the inhibitor was found to be 99.86 % which proves the inhibiting action of the inhibitor and formation of inhibitor film. On the other hand, Figure 1.c and 1.d and also the data presented in Table 1 reveal the decrease in corrosion current density because of corrosion inhibitor in the presence of iron carbonate scale. However, the decrease in corrosion current density and corresponding inhibition efficiency (88.3 %) was not comparable as the decrease which was found for the bare sample. Thus, the inhibitor efficiency decreased in the presence of surface layers [16, 24, 27]. 7
ACCEPTED MANUSCRIPT By considering the data presented in Figure 1 and Table 1 it can be concluded that by increasing H2S concentration in the solution, corrosion current density of the bare samples is decreased. This is due to formation and precipitation of mackinawite (FeS(s)) as corrosion product on the surface in the presence of H2S in trace amounts [31, 36, 37]. On the other hand, by comparing corrosion current density and inhibition efficiency of the bare samples in
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different concentration of H2S an increase in corrosion current density and a decrease in the inhibition efficiency can be observed. This is due to the formation of FeS on the surface which prevents the adsorption of inhibitor film on the surface.
By considering the data presented in Table 1, one soon realizes that increasing the H2S
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concentration from 50 to 100 ppm declines the corrosion current density. However, the
corrosion current density increases by rising the H2S concentration from 100 to 150 ppm .
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This variation in corrosion current density can be observed for the bare and also iron carbonate scale covered samples. Such a decrease in corrosion rate of carbon steel can be attributed to the formation of FeS corrosion product on the surface of the samples. The XRD pattern presented in Figure 2 reveals the presence of FeS on the surface of both bare and iron carbonate scale in 50 ppm H2S concentration. On the other hand, the SEM cross-sectional view of the samples which is presented in Figure 3, shows the formation of FeS on the bare
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and also iron carbonate scale covered sample in case of the increase in H2S concentration from 50 to 100 ppm. However, by increasing H2S concentration from 100 to 150 formation of
EP
cracks on FeS film was observed.
3.3. Electrochemical impedance spectroscopy measurements
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The EIS experiments were conducted for bare and iron carbonate scale covered samples with and without the presence of inhibitor in different H2S concentration and the resulted data are shown in Figure 4 and 5 and the extracted electrochemical data are presented in Table 2. Furthermore, Figure 6 shows equivalent circuits used for fitting EIS curves to investigate electrochemical parameters. The corresponding physical models are also represented in the figure and the related sample conditions are described in the figure caption. Electrochemical parameters obtained by fitting the curves are reported in Table 2 and Equation 17 was used in order to calculate the inhibition efficiency. By considering the data presented in Figures 4. a and 4.b one can see that when inhibitor is present the diameter of the capacitive loop increased for bare samples which mean corrosion 8
ACCEPTED MANUSCRIPT rate has been decreased. On the other hand, by comparing Figure 5. a and 5.b it was revealed that when surface scales are present, the capacitive loop diameter, which is corresponding to charge transfer resistance, was increased however this increase is less than the increase which was observed for the bare sample. This phenomenon indicates that inhibition efficiency has been decreased in the existence of scale on the surface which is in good agreement with the
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results obtained in polarization test investigation. According to Figure 5.a, for iron carbonate scale covered samples in spite of the bare
samples, it was seen that by increasing H2S concentration the capacitive loop diameter was decreased which may be due to cracking of the film because of increase in its thickness by
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FeS formation [39]. Figure 4.c and 4.d are showing Bode phase plots of the bare samples when inhibitor film is present and FeS as corrosion product and Figure 5.c and 5.d also show
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Bode phase plots for the iron carbonate scale covered samples in the presence of inhibitor and H2S in the solution. Both of these curves are shown at least two-time constants. The Lowfrequency time constant indicates corrosion process on the steel surface and the highfrequency one could be related to the film covering the surface [38]. By considering the data presented in Table 2, one can conclude that for all samples in the presence of inhibitor, the charge-transfer resistance increases which indicates that an inhibitor
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film is formed on the surface. On the other hand, for the bare sample, the charge transfer resistance increases by increasing H2S concentration, in the absence of inhibitor, which can be related to the inhibition effect of FeS film as corrosion product. This is attributed to the
EP
presence of H2S in trace concentration in the solution and coverage effect mechanism [36, 40]. While, by increasing H2S concentration in the solution in the presence of inhibitor, charge transfer resistance was decreased which was related to poor adsorption of inhibitor
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film on the surface due to more FeS formation [24]. For iron carbonate scale covered samples, it was found that by increasing H2S concentration, the iron carbonate scale was deteriorated and charge transfer resistance was decreased and consequently corrosion rate was increased due to formation of cracks in the surface film by FeS growth.
4. Conclusions In this investigation the influence of iron carbonate scale as corrosion product on inhibition efficiency of imidazoline derivatives corrosion inhibitor in CO2-saturated 3.5 wt.% NaCl solution was studied. The effect of H2S gas concentration has also been considered on the 9
ACCEPTED MANUSCRIPT inhibitor performance. It was found that in the presence of iron carbonate surface scale, the inhibition efficiency of the inhibitor phase was decreased due to decrease in adsorption of inhibitor on the surface. Furthermore, it was revealed that inhibition efficiency decreased by increase in H2S concentration in the solution due to surface film cracking as a result of FeS formation and growth. Finally, it was concluded that in the presence of trace concentration of
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H2S in CO2-saturated 3.5 wt.% NaCl solution, the corrosion rate of the bare samples
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decreases in the absence of corrosion inhibitor due to precipitation of FeS scale.
Nomenclature
Solution resistance
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Rs Rf
Inhibitor film resistance
Charge transfer resistance
CPEdl
Constant phase element of the double layer capacitor
CPEf
Inhibitor film constant phase element
CPEScale
Scale constant phase element
RScale
Scale resistance
Warburg impedance
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EP
W
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Rct
References 1. 2.
3. 4.
Kunal, K.C., A Study of Inhibitor - Scale Interaction in Carbon Dioxide Corrosion of Mild Steel. 2004, Ohio: Usa. P. 1-121. Amri, J., On Growth And Stifling of Localized Corrosion Attacks in CO2 and Acetic Acid Environments : Application to the Top-of-Line Corrosion of Wet Gas Pipelines Operated in Stratified Flow Regime, in Institut Polytechnique De Grenoble. 2010, University of Stavanger - Norway: France. P. 1-253. Nesic, S., J. Postlethwaite, And S. Olsen, An Electrochemical Model for Prediction of CO2 Corrosion. S. Nesic, J. Postlethwaite, And S. Olsen, Paper, 1995(131). Dugstad, A. Fundamental Aspects of CO2 Metal Loss Corrosion-Part 1: Mechanism. in Corrosion 2006. 2006. Nace International. 10
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23.
24.
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26. 27.
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10.
SC
9.
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8.
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7.
EP
6.
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33. 34. 35.
36.
37.
38. 39. 40.
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32.
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31.
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30.
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Liu, D., Et Al., Interaction of Inhibitors With Corrosion Scale Formed on N80 Steel in CO2 -Saturated Nacl Solution. Materials And Corrosion, 2011. 62(12): P. 11531158. Javidi, M. And S. Bekhrad, Failure Analysis of A Wet Gas Pipeline Due to Localised CO2 Corrosion. Engineering Failure Analysis, 2018. 89: P. 46-56. Ma, H., Et Al., An Ac Impedance Study of the Anodic Dissolution of Iron In Sulfuric Acid Solutions Containing Hydrogen Sulfide. Journal of Electroanalytical Chemistry, 1998. 451(1): P. 11-17. Ma, H., Et Al., The Influence of Hydrogen Sulfide on Corrosion of Iron Under Different Conditions. Corrosion Science, 2000. 42(10): P. 1669-1683. Taheri, H., Et Al., The Effect of H2S Concentration and Temperature on Corrosion Behavior of Pipeline Steel A516-Gr70. Caspian Journal of Applied Sciences Research, 2012. 1(5): P. 41-47. Hosseini, M.G. And A. Ahadzadeh, Electrochemical Ampedance Spectroscopy. 2012, Iran: Iran Corrosion Congress. Palacios, C. And J. Shadley, Characteristics of Corrosion Scales on Steels In A CO2Saturated Nacl Brine. Corrosion, 1991. 47(2): P. 122-127. Kahyarian, A., M. Singer, And S. Nesic, Modeling of Uniform CO2 Corrosion of Mild Steel In Gas Transportation Systems: A Review. Journal of Natural Gas Science And Engineering, 2016. 29: P. 530-549. Lee, K.-L.J. And S. Nesic, The Effect of Trace Amount of H2S On CO2 Corrosion Investigated By Using The Eis Technique, In Corrosion. 2005, Nace International: Usa. P. 1-16. Plennevaux, C., Et Al., Contribution of CO2 on Hydrogen Evolution And Hydrogen Permeation In Low Alloy Steels Exposed To H2S Environment. Electrochemistry Communications, 2013. 26: P. 17-20. Abelev, E., Et Al., Effect of H2S On Fe Corrosion In CO2-Saturated Brine. Journal of Materials Science, 2009. 44(22): P. 6167-6181. Tait, W.S., An Introduction To Electrochemical Corrosion Testing For Practicing Engineers And Scientists. 1994: Pairodocs Publications. Lee, K.-L.J., A Mechanistic Modeling of CO2 Corrosion of Mild Steel In The Presence of H2S. 2004, Ohio: Usa. P. 1-220.
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Figure captions
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Figure 1: Tafel polarization curve for a). Bare samples without inhibitor; b). Bare samples with inhibitor; c). Samples with iron carbonate scale without inhibitor; d). Samples with iron carbonate scale without inhibitor. All in CO2-saturated 3.5 wt.% NaCl solution containing 0, 50, 100, 150 ppm H2S concentration. Figure 2: The XRD pattern: a) Bare sample. b). Iron carbonate scale covered samples. Both in CO2-saturated 3.5 wt.% NaCl solution containing 50 ppm H2S concentration. Figure 3: SEM cross-sectional view photomicrographs. a, b , c). Bare samples. d, e, f). Iron carbonate scale covered samples. Both in CO2-saturated 3.5 wt.% NaCl solution containing 50, 100,150 ppm H2S concentration, respectively.
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Figure 6: The equivalent circuits used for fitting EIS data. a). Bare samples b). Bare samples with inhibitor film in CO2-saturated 3.5 wt.% NaCl solution containing 0, 50, 100, 150 ppm H2S concentration or Iron carbonate scale covered samples with inhibitor in CO2-saturated 3.5 wt.% NaCl solution containing 0 ppm H2S concentration or Iron carboante coverd samples without inhibitor in CO2-saturated 3.5 wt.% NaCl solution containing 0, 50 ppm H2S; c). Iron carboante covered samples without inhibitor in CO2-saturated 3.5 wt.% NaCl solution containing 100, 150 ppm H2S, or Iron carbonate scale covered samples with inhibitor in CO2-saturated 3.5 wt.% NaCl solution containing 50, 100, 150 ppm H2S.
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Table 1: Electrochemical parameters obtained from Tafel polarization curves for bare and iron carbonate covered samples with and without the presence of inhibitor in 0,50,100,150 ppm H2S concentration.
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Table 2: Electrochemical parameters obtained from EIS analysis for bare and iron carbonate scale covered samples with and without the presence of inhibitor in 0,50,100,150 ppm H2S concentration.
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Table 1: Electrochemical parameters obtained from Tafel polarization curves for bare and iron carbonate covered samples with and without the presence of inhibitor in 0,50,100,150 ppm H2S concentration. Ecorr (V,vs.Ag/AgCl)
Corrosion rate (mm/year)
H2S Inhibitor
Bare
With iron carbonate
Bare
With iron carbonate
Bare
With iron carbonate
Without
1.08×10-4
1.78×10-5
-0.674
-0.652
1.257
0.205
1.48×10-7
2.08×10-6
-0.610
-0.354
0.017
0.024
1.84×10-5
2.80×10-5
4.89×10-7
9.08×10-6
1.39×10-5
2.53×10-5
2.35×10-6
1.43×10-5
(ppm)
0
Without
50
Without
100 With
Without
150
2.81×10-6
-0.672
0.213
0.325
-0.626
-0.346
0.005
0.105
-0.654
-0.667
0.161
0.293
-0.638
-0.361
0.027
0.166
6.01×10-5
-0.641
-0.672
0.319
0.718
3.13×10-5
-0.692
-0.405
0.032
0.391
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Efficiency (%)
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i corr (A/cm2)
Bare
With iron carbonate
99.86
88.30
97.34
67.57
83.09
43.47
89.87
47.92
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Table 2: Electrochemical parameters obtained from EIS analysis for bare and iron carbonate scale covered samples with and without the presence of inhibitor in 0,50,100,150 ppm H2S concentration.
Bare
Inhibitor
Without With
Rs (Ω.cm2)
Rct (Ω.cm2)
Y0 (sn/cm2.Ω)
n
Rfilm (Ω.cm2)
Y0 film (sn/cm2.Ω)
n
η (%)
2.25 12.10
140.7 29617.0
4.47×10-4 5.49×10-6
0.82 0.66
-
-
-
99.52
15.09 94.00
1553.0 10422.0
4.03×10-5 7.36×10-6
0.65 0.42
71.85 1312.00
7.01×10-8 1.68×10-9
1.00 1.00
85.09
6.32 4.17
560.0 7350.0
3.81×10-4 1.63×10-6
0.90 0.80
76.00 452.00
8.78×10-4 2.49×10-5
0.77 0.59
92.34
15.83 34.33
241.0 1130.0
6.13×10-4 1.46×10-5
0.42 0.28
20.00 166.00
4.27×10-4 3.42×10-5
0.63 0.48
78.67
4.89 8.87
1000.0 4265.0
3.31×10-4 2.61×10-6
0.81 0.79
33.00 135.00
7.97×10-4 6.37×10-5
0.80 0.55
76.55
With iron carbonate
Without With Without
Bare With
50 With iron carbonate Bare
Without With Without
100 With iron carbonate
Without With Without
Bare 150
3.23 74.00
321.0 570.0
4.66×10-4 2.43×10-5
0.46 0.51
-
-
-
43.68
1.80 1.00
389.0 2500.0
7.66×10-4 6.16×10-5
0.75 0.59
102.00 68.00
8.26×10-4 2.29×10-4
0.81 0.57
84.44
75.0 137.0
9.28×10-4 2.22×10-4
0.28 0.33
-
-
-
45.25
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With
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With
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0
Without With
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With iron carbonate
RI PT
Sample
SC
H2S concentration (ppm)
9.70 72.00
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Investigating CO2 corrosion inhibitor efficiency in presence FeCO3 scale and H2S. Samples were cut from wet gas transmission pipeline with FeCO3 corrosion product. In the presence of FeCO3 scale on the surface the inhibitor efficiency decreased. H2S addition to solution decreased inhibitor efficiency because of less adsorption. Increasing H2S concentration increased corrosion and decreased inhibitor efficiency.
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