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Localized Corrosion Initiation of Steel in CO2 Environments

Gao, Xin
http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1596657895973621

Abstract Details

2020, Doctor of Philosophy (PhD), Ohio University, Chemical Engineering (Engineering and Technology).
The objective of this dissertation research was to investigate initiation mechanisms for CO2 localized corrosion on mild steel, encompassing the effects of chloride, oxygen, and acetic acid. In CO2 corrosion, iron in steel will be oxidized to ferrous ions under deareated conditions. The ferrous and carbonate ions can combine to form FeCO3 and precipitate once exceeding the solubility limit. When the precipitation of FeCO3 occurs evenly on the steel surface it forms a compact and protective layer. This acts as a diffusion barrier hindering the mass transfer of electrochemical species and covers/blocks the surface making it unavailable for corrosion, which enhances the resistance of mild steel to further uniform CO2 corrosion. However, there are various scenarios where localized corrosion may occur. When the environment becomes more aggressive, the FeCO3 could be partially removed. This leads to localized regions of the bare steel surface that become exposed to the corrosive solution and, subsequently, localized corrosion could be initiated. To study CO2 localized corrosion, two-stage experiments were performed: (1) a uniform protective FeCO3 layer was first formed on a carbon steel with high initial FeCO3 saturation; (2) localized CO2 corrosion scenarios were then developed by adding additional salts (NaCl or NaClO4), oxygen or acetic acid to challenge the protective FeCO3 layer. The experiments were conducted in a two-liter glass cell with a three-electrode system, working electrode (X65 carbon steel), reference electrode (Ag/AgCl saturated electrode), and counter electrode (platinum). Electrochemical measurements (linear polarization resistance) were carried out to observe electrochemical behaviors and calculate the corrosion rates. Weight loss was also used to determine general corrosion rates. Fe2+ concentration was measured using spectrophotometry in order to study the solubilization of FeCO3. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and profilometry by infinite focus microscopy (IFM) were used to determine pitting. The results in non-ideal solutions showed that no localized corrosion was initiated by introducing more salt. The introduction of acetic acid resulted in localized corrosion. When oxygen was introduced, severe pitting occurred. A new water chemistry model based on Oddo & Tomson’s equation was proposed by the author. Based on EQCM results, a new model to calculate the solubility constant of iron carbonate in non-ideal solution at 80℃ was developed based on Sun & Nesic model.
Srdjan Nesic (Advisor)
191 p.
Chemical Engineering; Materials Science
Chloride; acetic acid; oxygen; water chemistry; iron carbonate; localized corrosion; ionic strength; EQCM

Recommended Citations

Citations

  • Gao, X. (2020). Localized Corrosion Initiation of Steel in CO2 Environments [Doctoral dissertation, Ohio University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1596657895973621

    APA Style (7th edition)

  • Gao, Xin. Localized Corrosion Initiation of Steel in CO2 Environments. 2020. Ohio University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1596657895973621.

    MLA Style (8th edition)

  • Gao, Xin. "Localized Corrosion Initiation of Steel in CO2 Environments." Doctoral dissertation, Ohio University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1596657895973621

    Chicago Manual of Style (17th edition)

ohiou1596657895973621
434
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This open access ETD is published by Ohio University and OhioLINK.