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The Effect of Monoethylene Glycol (MEG) on CO2 Corrosion Mechanisms

Ruiz, Roberto A.,
http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1511889934446601

Abstract Details

2017, Master of Science (MS), Ohio University, Chemical Engineering (Engineering and Technology).
The use of monoethylene glycol (MEG) is common in the oil and gas industry as it is injected in subsea flowlines to prevent hydrate formation. Albeit this is one of the main uses for this chemical in this industry, previous studies have indicated that the presence of MEG reduces the extent of corrosion of mild steel in CO2 and H2S dominated environments. Furthermore, MEG is reported to serve as a key component of pH-stabilization technique used for corrosion mitigation. Experimental work published over the last few years has provided valuable insight on the possible overall effect of MEG on uniform corrosion rates, however, wide gaps still remain especially related to mechanistic representation of the phenomenon involved. In this work, a systematic electrochemical study was performed on the effect of MEG on CO2 corrosion mechanisms of mild steel, in particular API 5L X65 (0.16wt. % Carbon). The scope of work covered the influence of temperature from 30 – 80ºC, of MEG content from 40 – 85wt. % and of pH 3.5 - 6 at atmospheric pressure for solutions saturated with CO2 and N2, respectively. Electrochemical techniques such as linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), and potentiodynamic sweeps were used to obtain corrosion rates, mixed potential (Ecorr), current density (Icorr), Tafel slopes and limiting currents. The experiments were performed in a typical three electrode set-up where a Rotating Cylinder Electrode (RCE) was used to study the effect of flow at rotation speeds of 100, 1000 and 2000RPM (equivalent to 0.2, 1.2 and 2.0m/s, respectively in a 4in pipeline). The completion of these experiments revealed that MEG reduces the corrosion rate by affecting in different ways both anodic and cathodic electrochemical reactions involved in CO2 corrosion mechanisms. By performing potentiodynamic sweeps, it was noted that the dissolution of iron was retarded with increasing glycol content in solution, inferring that MEG may adsorb on the metal surface and affect the kinetics of the anodic reaction. On the other hand, the effect of MEG on the net cathodic reaction, impacting both charge transfer and limiting current, seemed to be directly related to changes in solution chemistry and properties. Furthermore, it was noted that the electrochemical reactions (Fe dissolution, H+ and H2CO3 reductions) followed the expected Tafel behavior, and that the respective anodic and cathodic Tafel slopes were unaffected by the presence of MEG. Lastly, literature findings suggested changes in the reduction of water should be expected in the presence of MEG; however, this work found no variations in the reduction of water within the range of MEG content studied. While a mechanistic explanation on the effect of MEG on the anodic reaction remains elusive, all changes in the cathodic lines can be explained by differences in physico-chemical properties of the electrolyte. Upon completion of the experimental trials, a chemical and electrochemical model was developed to simulate CO2 corrosion in non-ideal solutions and validated using literature and experimental data. This MEG-H2O-CO2 corrosion model identified all the necessary changes in physical and electrochemical parameters needed for further implementation to the ICMT flagship in-house corrosion prediction software FREECORP™.
Marc Singer (Advisor)
Bruce Brown (Other)
Srdjan Nesic (Committee Member)
John Staser (Committee Member)
Rebecca Barlag (Committee Member)
166 p.
Chemical Engineering; Engineering; Petroleum Engineering
CO2 Corrosion; Monoethylene Glycol; MEG; Corrosion Mechanisms; Sweet Corrosion; Non-ideal Solutions; MEG-CO2 Corrosion; Hydrates

Recommended Citations

Citations

  • Ruiz, , R. A. (2017). The Effect of Monoethylene Glycol (MEG) on CO2 Corrosion Mechanisms [Master's thesis, Ohio University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1511889934446601

    APA Style (7th edition)

  • Ruiz, , Roberto. The Effect of Monoethylene Glycol (MEG) on CO2 Corrosion Mechanisms. 2017. Ohio University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1511889934446601.

    MLA Style (8th edition)

  • Ruiz, , Roberto. "The Effect of Monoethylene Glycol (MEG) on CO2 Corrosion Mechanisms." Master's thesis, Ohio University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1511889934446601

    Chicago Manual of Style (17th edition)

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This open access ETD is published by Ohio University and OhioLINK.