The Influence of Mono Ethylene Glycol (MEG) on CO2 Corrosion of Carbon Steel at Elevated Temperatures (80 to 120oc)

Thunyaluk Pojtanabuntoeng, Mobin Salasi, Rolf Gubner

Corrosion Centre for Education, Research & Technology School of Chemical and Petroleum Engineering, Curtin University, Bentley, 6102,

Australia

ABSTRACT Monoethylene glycol (MEG) is injected in the pipelines to prevent hydrate formation, and subsequent pipeline blockage. Recent investigations indicated that presence of MEG could impede CO2 corrosion of carbon steel, although many aspects remain unknown.

In the current study, experiments were conducted at 80 oC (176 oF), atmospheric pressure, and 100 oC (212 oF), and 120 oC (248 oF) at pCO2 of 10 bar. Test solutions had different ratios of MEG/Ultra-pure water with 3 wt. % NaCl concentration. Electrochemical techniques such as linear polarization resistance (LPR), Electrochemical Impedance Spectroscopy (EIS) and Tafel polarization were employed to investigate the corrosion rate and phenomenon. Corroded surface of the samples were characterized using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) techniques.

This research aims to provide an improved insight on contribution of MEG on CO2 corrosion of carbon steel, at elevated temperatures.

Keywords: CO2 corrosion, MEG, Monoethylene glycol

INTRODUCTION CO2 corrosion of carbon steel pipelines has been studied for many years and effect of various parameters; such as pH, temperature and water chemistry, is thoroughly researched [1–3]. Study of carbon steels in CO2 saturated conditions can be complicated in the presence of different chemicals added into the system. In wet gas transportation pipelines, the hydrate formation is the common concern and mono ethylene glycol (MEG) is the preferred thermodynamic hydrate inhibitor [4]. Nonetheless, MEG effect on CO2 corrosion of carbon steel is not well understood [5].

It was reported that presence of MEG changed the physico-chemical properties of the aqueous phase [6–8]. The density of solution increased almost linearly, while the viscosity increased exponentially [6]. Same study showed that CO2 solubility decreased when MEG concentration increased to about 60 wt.%. However, further addition of MEG into the solution (more than 60 wt%) increased the CO2 solubility. Another study demonstrated that the CO2 solubility in MEG/water mixture was a function of salt concentration [7]. At high salt concentration (> 6 mole NaCl/kg solvent), CO2 solubility increases with MEG concentration. Additionally, the diffusivity of CO2 in the solution mixture decreases with increasing MEG concentration [6].

Addition of glycol to wet gas pipeline may influence CO2 corrosion in two ways [9]. Firstly, it lowers the dew point of water and consequently could reduce the severity of Top-of-the-Line Corrosion (TLC). Secondly, it was reported that the corrosion rate at the bottom of the line decreases when glycol mixes with the water phase [9–12]. This study only focuses on when

1

Paper No.

4176

©2014 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084.The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.

the pipeline steel is fully immersed in the aqueous phase, thus the effect of MEG on TLC will not be discussed.

Gulbrandsen and Morard [10] noticed that MEG altered the anodic half reaction of the corrosion process (dissolution of iron). They related that to the possible adsorption of MEG on the steel surface. The influence of other parameters in combination with MEG, such as the presence of O2 [13], H2S [14], and the corrosion inhibitors [10], [11] was also researched. However, there appeared to be many unanswered questions on how MEG changes the CO2 corrosion mechanism [5].

The effect of MEG on CO2 corrosion has been investigated only at temperatures below 80 oC (176 oF). The temperature encountered in wet gas transportation pipelines and in the MEG regeneration process is often higher than 80 oC (176 oF). Therefore, it is important to investigate the corrosion behaviour of carbon steel at elevated temperature. The aim of the present study is to analyse the effect of elevated temperatures on CO2 corrosion of carbon steel in the presence of MEG.

EXPERIMENTAL Table 1 shows test conditions for this study. Three concentrations of MEG, resembling what is often observed in the MEG regeneration process: a) in the absence of MEG, b) rich MEG (50 wt.% MEG), and c) lean MEG (80 wt.% MEG). Lean MEG represents fresh MEG solution introduced to the pipelines. After it is mixed with brine or produced water, the MEG content decreases, and is referred to as rich MEG.

When MEG is added to the pipelines, brine or produced water is diluted and the overall salinity of the mixture decreases. Kvarekval et al. [14] demonstrated that varying NaCl concentration from 0 to 82 g/L affected the corrosion behaviour of carbon steel in 50 wt.% MEG. In that study, the aim was to investigate the MEG influence on corrosion properties irrespective of the salt content. Therefore, concentration of NaCl present in total mixture was always kept constant (3 wt.%). Analytical grade NaCl† was added based on the total volume of test solution to achieve the 3 wt.% concentration. Test solutions were prepared by mixing the ultra-purity water (solution resistivity = 18.2 MΩ) and laboratory grade MEG† at the aforementioned ratios.

Test setups and procedures

A conventional one-litre glass cell was used for the tests conducted at the atmospheric pressure. The counter electrode was a platinum coated mesh, and the reference electrode was Ag/AgCl. The working electrode was made of carbon steel grade UNS G10300 (composition by wt.%: 0.37 C, 0.80 Mn, 0.282 Si, 0.012 P, 0.001 S, 0.089 Cr, 0.012 Ni, 0.004 Mo, 0.004 Sn, 0.01 Al, and Fe (balance)), with an exposed surface area of 0.196 cm2. To limit the exposed area to only one surface, the sample was embedded in an epoxy resin. Sample was polished with 600 grit SiC papers, rinsed with ultra-purity water, ultrasonically cleaned in ethanol, and then dried with stream of air.

After solution was transferred into the test cell, it was deoxygenated with CO2 (high purity grade, 99.99%) for 2 hours, while heated to the desired temperature. CO2 was continuously sparged throughout the test.

† Chem Supply

2

©2014 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084.The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.

A 2-L autoclave was used for tests at 10 bar partial pressure of CO2 (Figure 1a). The autoclave was manufactured from UNS N10276‡. The body of the autoclave was acting as the counter electrode in the electrochemical measurements. A UNS N10276 rod, electrically insulated from the autoclave, was used as the pseudo-reference electrode. Tafel polarization results obtained using the pseudo-reference electrode was compared against the independent experiment with the Ag/AgCl, acting as the reference electrode. As shown in Figure 2, the Tafel curves were in good agreement. The working electrode was made of carbon steel grade UNS G10300 with an exposed surface area of 0.33 cm2 embedded in a polyether ether ketone (PEEK) rod. The photograph of the sample is shown in Figure 1b. Prior to tests, the samples were prepared as described earlier.

For high pressure tests, the solution was initially sparged with CO2 for 2 hours. Then the sample was installed at the holder and autoclave was fully closed. The autoclave was pressurized and depressurized 5 times to achieve the minimum oxygen concentration. Ultimately, the autoclave was pressurized to the final pCO2 of 10 bar and heated to the test temperature. CO2 supply was then disconnected from the autoclave.

Electrochemical measurements Electrochemical measurements were carried out using a potentiostat§. Corrosion rate of the samples were recorded using linear polarization resistance technique (LPR) every 15 minutes for 18 hours. Potential of the samples was scanned from ±10 mV vs. the open circuit potential (OCP) at the scan rate of 10 mV/min. Afterwards, electrochemical impedance spectroscopy (EIS) was carried out from a frequency of 10 kHz to 0.01 Hz with the rms amplitude of ± 5 mV. Prior to the termination of these tests, Tafel polarization was carried out at the scan rate of 10 mV/min, starting from 200 mV below the OCP and was continued up to 300 mV above the OCP.

The corrosion rates were calculated according to Stern-Geary equation. Polarization resistance was extracted from the LPR curves and the B values were calculated from the Tafel polarization scans.

During the tests conducted in the autoclave, one carbon steel sample with a surface area of 1.27 cm2 was also inserted inside the autoclave. The aim was to observe whether the presence of MEG can influence the precipitation of FeCO3.

pH measurement The presence of MEG can interfere with the liquid junction potential of the pH electrode, and may result in inaccurate pH readings. The deviation of the measurements increases with MEG concentration and temperature. This error was compensated using the procedure outlined by Sandengen et al. [15]. The deviation in pH (∆pH) caused by the presence of MEG is shown in Table 3. The effect of NaCl on the ∆pH was assumed to be negligible. Only compensated pH values are reported in this paper.

RESULT AND DISCUSSION

Water chemistry of MEG/Glycol mixtures When CO2 dissolves in water (Eq. 1), it forms carbonic acid (Eq. 2) which dissociates to H+, bicarbonate ions, and carbonate ions (Eq. 3 and Eq. 4). All four reactions (Eq 1-4) are in equilibrium with each other. It was suggested that MEG mainly influences the chemical

‡ Hasteloy C-276 § Gamry Reference 600TM

3

©2014 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084.The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.

potential of ionic species involved in Eq. 1 to Eq. 4 [10]. MEG does not contribute in the carbonic acid formation (Eq. 2), but may interfere with the carbonic acid and bicarbonate dissociation reactions (Eq. 3 and Eq. 4). This in turn can shift the equilibrium and result in the change of the solution pH.

Table 4 shows pH measurement of the solutions saturated with CO2, at different MEG concentration at 80oC (176 oF) and atmospheric pressure. It can be seen that the pH increases with MEG concentration, which is similar to the results obtained at 25 oC [10].

𝐶𝑂2(𝑔) ↔ 𝐶𝑂2(𝑎𝑞) Eq. 1

𝐶𝑂2(𝑎𝑞) +𝐻2𝑂(𝑎𝑞) ↔ 𝐻2𝐶𝑂3(𝑎𝑞) Eq. 2

𝐻2𝐶𝑂3(𝑎𝑞) ↔ 𝐻+(𝑎𝑞) +𝐻𝐶𝑂3−(𝑎𝑞) Eq. 3

𝐻𝐶𝑂3−(𝑎𝑞) ↔ 𝐻+(𝑎𝑞) + 𝐶𝑂32− Eq. 4

Influence of temperature EIS results show that, presence of MEG increases the solution resistance of MEG/water mixtures, even though the NaCl content was the same in all tests (Figure 3). An increase in the solution resistance was taken into account in corrosion rate calculations. It can be seen in Figure 3b and c that the charge transfer resistance (Rct) increases with MEG concentration. At 120 oC (248 oF), the addition of more than 50 wt.% MEG had less significant effect of Rct than at lower temperatures.

Figure 4a depicts the corrosion rates obtained from LPR measurement at 80 oC. It is observable that the corrosion rate decreases with increasing MEG concentration, which is consistent with the EIS results. The results indicate that significant amount of MEG (80 wt.% MEG) is required to achieve a noticeable reduction in corrosion rate.

At a particular MEG concentration, corrosion rates obtained at 100 oC are similar to those at 120 oC (248 oF) (Figure 4b). A sharp decrease in corrosion rate is observed when solution contains 50 wt.% MEG, compared to when no MEG was present in the solution. Increasing MEG from 50 wt.% to 80 wt.% only slightly reduces the corrosion rates at 100 oC (212 oF), and no corrosion rate reduction can be seen at 120 oC (248 oF).

Comparison with the CO2 corrosion prediction model The effect of glycol on CO2 corrosion rate was estimated by de Waard et al. [9] as shown in Eq. 5. Glycol factors at different MEG concentration were calculated from Eq. 5. Predicted corrosion rate at different MEG concentration was obtained from corrosion rate in the absence of MEG and the glycol factor at that particular MEG concentration. The comparison shows good agreement when temperature is 80 oC (176 oC). However, at 100 oC (212 oF) and 120 oC (248 oF), the glycol factor underestimates the corrosion rate of carbon steel when 80 wt.% of MEG was present.

𝑔𝑙𝑦𝑐𝑜𝑙 𝑓𝑎𝑐𝑡𝑜𝑟 = 101.6(log(100−𝑤𝑡%𝐺𝑙𝑦𝑐𝑜𝑙)−2) Eq. 5

Possible corrosion mechanism in the presence of glycol Figure 5a to c shows polarization curves after ~18 hours of immersion at different test conditions. Anodic Tafel slope (ba) is ~70 mV/decade at both 100 oC (212 oF ) and 120 oC

4

©2014 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084.The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.

(248 oF) and is relatively constant for all MEG concentrations. It was reported earlier that ba increased from 40 mV/decade to 90 mV/decade at 25 oC (77 oF), when MEG concentration was increased to more than 70 wt. % [10]. This may imply that the iron dissolution mechanism (anodic reaction) at high temperature is independent of MEG concentration.

Nesic et al. [2] described the dissolution mechanism of iron in CO2 containing solution at pH < 4 (Eq. 6 to Eq. 11), that dissolved CO2 forms an intermediate species (ligand) with the steel as an initial step (Eq. 6). Water molecules then react with the intermediate species and catalyse the dissolution reaction. It should be pointed out that the proposed mechanism was for a pure water system, which could be applicable to MEG/water system. High concentration of MEG in the bulk and at the steel surface, reduces the concentration of water and CO2 in contact with the steel surface. This may slow down the rates of intermediate steps, involving CO2 and water (i.e. Eq. 6, Eq. 7, and Eq. 9). Subsequently these equations may become the rate determining step. This could explain the reduction in corrosion rate in the presence of MEG.

𝐹𝑒 + 𝐶𝑂2 → 𝐹𝑒𝐿 Eq. 6

𝐹𝑒𝐿 + 𝐻2𝑂 ↔ 𝐹𝑒𝐿𝑂𝐻𝑎𝑑 +𝐻+ + 𝑒− Eq. 7

𝐹𝑒𝐿𝑂𝐻𝑎𝑑 ↔ 𝐹𝑒𝐿𝑂𝐻𝑎𝑑+ + 𝑒− Eq. 8

𝐹𝑒𝐿𝑂𝐻𝑎𝑑+ +𝐻2𝑂 ↔ 𝐹𝑒𝐿(𝑂𝐻)2𝑎𝑑 +𝐻+ Eq. 9

𝐹𝑒𝐿(𝑂𝐻)2𝑎𝑑𝑟𝑑𝑠�� 𝐹𝑒𝐿(𝑂𝐻)2𝑠𝑜𝑙 Eq. 10

𝐹𝑒𝐿(𝑂𝐻)𝑠𝑜𝑙 + 2𝐻+ ↔ 𝐹𝑒2+ + 𝐶𝑂2 + 2𝐻2𝑂 Eq. 11

Precipitation of FeCO3 in the presence of MEG Figure 6 shows surface analysis (Backscatter SEM images and EDS) of samples after about 20 hours of immersion at 100 oC (212 oF). Given the same exposure time, the sample immersed in 80 wt.% MEG is mainly bare steel and FeCO3 precipitation does not occur in this condition, while in 50 wt.% MEG or in its absence, FeCO3 presents. However, at 120 oC (248 oF), FeCO3 precipitates on test samples immersed in all tested MEG concentration. This could be relevant to the lower FeCO3 solubility and the faster precipitation rate at higher temperature (120 oC, 248 oF).

The observation at 100 oC (212 oF) seems to be in contrast with what was previously reported, that the FeCO3 super saturation increases in the presence of MEG, and FeCO3 solubility decreases with MEG [16]. A separate study conducted at 60 oC (140 oF ) found that the induction time before FeCO3 precipitates increases with MEG concentration [17]. Because of short exposure time in this work (~20 hours), it might be the reason why FeCO3 is not observed at 100 oC (212 oF). Long term experiments are required to ascertain the influence of MEG on the precipitation of FeCO3.

CONCLUSIONS Series of experiments have been conducted to better understand the influence of MEG on CO2 corrosion. It was found that:

− At elevated temperatures, MEG reduces corrosion rates in all test conditions without any pH adjustment, but not significant enough to be relied on as the primary corrosion mitigation method.

5

©2014 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084.The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.

− Corrosion rate reduction factor by glycol proposed by de Waard is in good agreement with the experimental results obtained at 80 oC (176 oC) and 0.56 bar of CO2. However, it underestimates corrosion rates at 100 oC (212 oF ) and 120oC (248 oF) in the presence of 80 wt.% MEG at a higher pressure.

− Current results show that the presence of MEG influences the precipitation of FeCO3. Formation of iron carbonate film reduces the CO2 corrosion rate of carbon steel. Therefore, further investigation is required to conclude whether presence of MEG can hinder the formation of the iron carbonate layer.

ACKNOWLEDGEMENT The authors would like to acknowledge School of Chemical and Petroleum Engineering, Curtin University for their facility and financial support. The authors also thank Curtin University Electron Microscope Facility for the use of their facility and technical support.

REFERENCE

[1] M. B. Kermani and A. Morshed, “Carbon Dioxide Corrosion in Oil and Gas Production—A Compendium,” Corrosion, 59, 8(2003): p. 659–683.

[2] S. Nesic, N. Thevenot, J. L. Crolet, and D. M. Drazic, “Electrochemical Properties of Iron Dissolution in the Presence of CO2 - Basic Revisited,” in CORROSION/96, paper no. 3 (Houston, TX: NACE, 1996), p. 23.

[3] C. DeWaard and D. Milliams, “Carbonic acid corrosion of steel,” Corrosion, 31, 5(1975): p. 177–181.

[4] S. Brustad, K. Løken, and J. G. Waalmann, “Hydrate Prevention Using MEG Instead of MeOH : Impact of Experience fFrom Major Norwegian Developments on Technology Selection for Injection and Recovery of MEG,” in Offshore Technology Conference, 2005, paper no.17355.

[5] S. Nesic and W. Sun, “Corrosion in Acid Gas Solutions,” in Shrier’s Corrosion, Elsevier Science, 2010, pp. 1270–1298.

[6] M. H. Oyevaar, R. W. J. Morssinkhof, and K. R. Westerterp, “Density, Viscosity, Solubility, and Diffusivity of CO2 and N2O in Solutions of Diethanolamine in Aqueous Ethylene glycol at 298 K,” Journal of Chemical Engineering Data, 34 (1989): p. 77–82.

[7] H. Lu, A. T. Kan, and M. B. Tomson, “Effects of Monoethylene Glycol on Carbonate Equilibrium and Calcite Solubility in Gas/Monoethylene Glycol/NaCl/Water Mixed Systems,” SPE Journal 15, 3 (2010): p. 714–725.

[8] A. T. Kan, H. Lu, and M. B. Tomson, “Effects of Monoethylene Glycol on Carbon Dioxide Partitioning in Gas/Monoethylene Glycol/Water/Salt Mixed Systems,” Industrial & Engineering Chemistry Research, 49, 12 (2013): p. 5884–5890.

[9] C. De Waard, U. Lotz, and D. E. Milliams, “Predictive Model for CO2 Corrosion Engineering in Wet Natural Gas Pipelines,” Corrosion Engineering 47, 12 (1991): p. 976–985.

[10] E. Gulbrandsen and J.H. Morard, “Why Does Glycol Inhibit CO2 Corrosion,” in CORROSION/98, paper no. 221 (Houston, TX: NACE, 1991), p. 21.

6

©2014 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084.The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.

[11] I. Ivonye, C. Wang, X. Hu, and A. Neville, “Corrosion Study of Carbon Steel in The Presence of Monoethylene Glycol (MEG) and Corrosion Inhibitors in Acid,” in CORROSION/2013, paper no. 2349 (Houston, TX: NACE, 2013), p. 15.

[12] J. J. Gonzalez, M. E. Afonso, and G. Pellegrino, “Corrosion of Carbon Steels in Monoethylene Glycol,” in CORROSION/2000, paper no. 00498 (Houston, TX: NACE, 2000), p. 13.

[13] J. Kvarekval, S. Olsen, and S. Skjerve, “The Effect of O2 on CO2 Corrosion in pH Stabilised Gas/Condensate Pipelines,” in CORROSION/2005, paper no. 05305, (Houston, TX: NACE, 2005), p. 21.

[14] J. Kvarekval and A. Pederson, “An Electrochemical Study of Corrosion Inhibition of Carbon Steel in Sour Glycol Solutions,” in CORROSION/2013, paper no. 2447, (Houston, TX: NACE, 2013), p. 17.

[15] K. Sandengen, B. Kaasa, and T. Østvold, “pH Measurements in Monoethylene Glycol (MEG) + Water Solutions,” Industrial & Engineering Chemistry Research 46, 14 (2007): p. 4734–4739.

[16] A. Dugstad, R. Nyborg, and M. Seiersten, “Flow Assurance of pH Stabilized Wet Gas Pipelines,” in CORROSION/2003, paper no. 03314 (Houston, TX: NACE, 2003), p. 19.

[17] E. Flaten, G. Watterud, J.-P. Andreassen, and M. Seiersten, “Precipitation of Iron and Calcium Carbonate in Pipelines at Varying MEG Contents,” in SPE International Oilfield Scale Conference, 2008, paper no. 114089.

7

©2014 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084.The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.

a) b)

Figure 1: a) Photograph of a 2-L autoclave used for elevated temperature and pressure conditions; 1) CO2 inlet, 2) CO2 outlet, 3) Thermocouple, 4) Pressure gauge, 5) Safety relief valve, 6) Pseudo reference electrode (rod made from UNS N10276), 7)

Working electrode (UNS G10300 embedded in PEEK), 8) Counter electrode (autoclave body made from UNS N10276), and 9) Drain, b) Front view of test sample (working

electrode) .

Table 1 Test matrix

Table 2 Comparison of the pH reference value standards (pHRVS) and the measured values

(pHmeasured) for water/MEG solution at 80 oC (176 oF)

MEG/ wt% pHrvs pHmeasured ΔpH 0 4.16 4.20 -0.04

50 4.93 4.76 0.17 80 5.64 5.18 0.46

Parameters Conditions Temperature, oC (oF) 80 (176) 100 (212) 120 (248)

pCO2, bar 0.56 10 MEG, wt%. 0, 50, 80

Test duration, hours 18 Material UNS G10300

Measurement techniques LPR, Tafel polarization, EIS

1

2

3 4

5

6 9

7

8

15.5 mm

6.5 mm

8

©2014 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084.The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.

Figure 2: Comparison of potentiodynamic polarization curves of samples obtained with 2 different reference electrodes; 1) Ag/AgCl and 2) UNS N10276 rod. Solution was

80 wt.% water and 20 wt.% MEG, Temperature = 80 oC (176 oF), pCO2 = 0.56 bar, measurements after 18 hours.

Table 3: pH values of 3 wt.% NaCl solution with varying MEG concentration saturated with CO2

at 80 oC (176 oF)

cMEG/ wt.% pHmeasured pHcorrected 0 4.02 4.02

50 4.12 4.125 80 4.44 4.612

a) T = 80 oC (176 oF), pCO2 = 0.56 bar

b) T = 100 oC (212 oF), pCO2 = 10 bar

c) T = 120 oC (248 oF), pCO2 = 10 bar

9

©2014 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084.The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.

Figure 3: Comparison of Nyquist plots of samples immersed in various concentration of MEG at various temperature and pressure. Immersion time = 18 hours.

a) b)

Figure 4: Corrosion rates after 18 hours obtained from linear polarization resistance technique, a) T = 80 oC (176 oF) pCO2 = 0.56 bar, b) T = 100 oC (212 oF), pCO2 = 10 bar

and T = 120 oC (248 oF), pCO2 = 10 bar

Table 4 Comparison between corrosion rates obtained from LPR and the estimations using

glycol reduction factor proposed by de Waard et al.[9].

Temperature/ oC (oF)

pCO2/ bar

cMEG/ wt.%

CRLPR/ mm/yr

Glycol factor (Eq. 5)

Predicted corrosion rate*/

mm/yr 80 (176) 0.56 0 10.39 1.00 10.39

20 5.27 0.70 3.69 50 3.48 0.33 1.15 80 1.00 0.08 0.08

100 (212) 10 0 14.54 1.00 14.54 50 3.60 0.33 1.19 80 3.40 0.08 0.35

120 (248) 10 0 15.25 1.00 15.25 50 3.10 0.33 1.02 80 3.18 0.08 0.24

*Predicted corrosion rate are the product of the glycol factor and the corrosion rate in the absence of MEG.

10

©2014 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084.The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.

Figure 5: Tafel polarization curves after ~18 hours of immersion in varying MEG/water concentration at a) 80 oC (176 oF), 0.56 bar pCO2, b) 100 oC (212 oF), 10 bar pCO2, c)

120 oC (248 oF), 10 bar pCO2.

a

c

b

11

©2014 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084.The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.

a)

b)

c)

Figure 6: SEM-Backscattered images (left) and EDS spectrum (right) of samples exposed to different concentration of MEG at 100oC (212 oF), 10 bar pCO2 for 20 hours.

a) 0 wt.% MEG, b) 50 wt.% MEG, c) 80 wt.% MEG.

+

+

+

12

©2014 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084.The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.

a)

b)

c)

Figure 7: SEM-Backscattered images (left) and EDS spectrum (right) of sample exposed to different concentration of MEG at 120oC (248 oF), 10 bar pCO2 for 20 hours. a) 0 wt.% MEG, b) 50 wt.% MEG, c) 80 wt.% MEG.

+

+

+

13

©2014 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084.The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.