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Mechanical Effects of Flow on CO2 Corrosion Inhibition of Carbon Steel Pipelines

Li, Wei
http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1461751721

Abstract Details

2016, Doctor of Philosophy (PhD), Ohio University, Chemical Engineering (Engineering and Technology).
Transportation of multiphase fluids using carbon steel pipelines is ubiquitous in the oil and gas industry. These pipelines are prone to internal corrosion when exposed to an aqueous CO2 environment. The mitigation of CO2 corrosion can be achieved by the use of organic corrosion inhibitors or by reliance on formation of protective corrosion product layers. However, the mechanisms for their potential failure in flow conditions are still being debated. Wall shear stress induced by turbulent multiphase flow is considered an important parameter in CO2 corrosion as it has been claimed to be responsible for the removal of protective corrosion product layers and corrosion inhibitor films. In this study, a floating element wall probe was used to directly measure the wall shear stresses in single-phase and horizontal gas-liquid two-phase flow, instead of the more common indirect measurement of the wall shear stress. Wall shear stress measurements were complemented by high speed video camera recordings of the flow field. In single-phase pipe and channel flow, the wall shear stress was in good agreement with empirical shear stress calculations. In two-phase pipe flow, video-recorded observations confirmed that the high wall shear stress pulses captured by the probe in the slug flow pattern were in sync with the passage of liquid slugs; the highest measured wall shear stress values were of the order of 100 Pa. Wall shear stress values in the slug body varied along the inner pipe circumference with the top of the pipe having the highest values and the bottom of the pipe having the lowest values. The maximum wall shear stress measured was about 2 to 4 times higher than the calculated mean wall shear stress in the slug body, obtained by using the mixture velocity, which can serve as a guideline for slug flow modeling. Findings suggest that the wall shear stress alone, produced in single-phase and multiphase flow patterns covered in the present study, is insufficient to mechanically damage the protective corrosion product layers or corrosion inhibitor films. In addition, corrosion experiments with an imidazoline-based inhibitor were performed on X65 pipeline steel in a thin channel flow cell (TCFC). Local flow velocities were up to 28 m/s with wall shear stresses up to 4.8 kPa. Electrochemical measurements, surface analysis and computational fluid dynamics (CFD) were used as diagnostic tools. Localized corrosion was observed on a protrusion in the flow cell and depended on local flow conditions and inhibitor concentration. Overall, the wall shear stress was unable to affect performance of corrosion inhibitors. However, the low static pressure at the protrusion caused cavitation with bubble collapse leading to accelerated desorption of inhibitor from the steel surface, which explained the localized corrosion. An excess amount of inhibitor was found to mitigate localized corrosion by cavitation.
Srdjan Nesic (Advisor)
Marc Singer (Committee Member)
Douglas Green (Committee Member)
Lauren McMills (Committee Member)
Yoon-Seok Choi (Committee Member)
David Young (Committee Member)
200 p.
Chemical Engineering; Engineering
CO2 corrosion; Carbon steel; Wall shear stress; Gas-liquid slug flow; Flow visualization; Corrosion inhibition; Cavitation

Recommended Citations

Citations

  • Li, W. (2016). Mechanical Effects of Flow on CO2 Corrosion Inhibition of Carbon Steel Pipelines [Doctoral dissertation, Ohio University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1461751721

    APA Style (7th edition)

  • Li, Wei. Mechanical Effects of Flow on CO2 Corrosion Inhibition of Carbon Steel Pipelines. 2016. Ohio University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1461751721.

    MLA Style (8th edition)

  • Li, Wei. "Mechanical Effects of Flow on CO2 Corrosion Inhibition of Carbon Steel Pipelines." Doctoral dissertation, Ohio University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1461751721

    Chicago Manual of Style (17th edition)

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