The Study of the Corrosion Behavior of Gas Nitriding Treated L80 Steel in Simulated Environment for the Slotted Liners of SAGD

  • Author / Creator
    Chen, Xueyuan
  • The oil sand in Alberta province is mainly extracted by Steam Assisted Gravity Drainage (SAGD) technique which employs the slotted liners as the primary sand screening system. However, the slotted liners made of L80 carbon steel suffer from severe corrosion and erosion problems in the downhole environment containing aggressive species. However, conventional protection methods, such as inhibitors and cathodic protection methods are not applicable to this environment. Gas nitriding, as a well-established surface treatment method, has been widely applied in metallurgical processes to form an erosion resistance surface layer in extreme environment since this treatment grows a high hardness layer of ceramic iron nitrides (Fe-N) on the surface of carbon steel. Iron nitrides are also believed to have great potential to boost the corrosion resistance in various environment, but the corrosion behavior and the stability of GN carbon steel is seldom studied in any environment similar to the one that slotted liners have. Therefore, gas nitriding (GN) was selected as a coating candidate for liners in this thesis. The lab-scale GN treatment in tube furnace on L80 carbon steel was optimized by varying nitriding time, temperature and ammonia gas flowrate to grow a thick, compact and pure compound layer on L80. The corrosion behavior of GN treated L80 will be tested in the simulated environment by using various electrochemical tests such as Potentiodynamic Polarization (PD) curves and Electrochemical Impedance Spectroscopy (EIS). The surface characterization techniques such as digital microscope (DM), Scanning Electron Microscope (SEM), Energy-Dispersive X-ray Spectroscopy (EDX) and X-ray Diffraction (XRD) are also employed to investigate the microstructure, morphology and compositions of GN treated L80. With a treatment at 40 mL/min of flowrate at 530 °C for 15 h, GN treated L80 achieved a significantly decreased corrosion rate of 0.023 mm/year in the simulated environment with iii saturated carbon dioxide (CO2) at 20°C. The significantly decreased corrosion rate was about one order of magnitude lower than that of L80 without treatment tested in the same environment. The longer GN duration increased the thickness of the compound layer but the temperature and flowrate were treated as a pair for the optimized dissociation rate to produce a compact compound layer. Double-layer equivalent circuit was used to fit the EIS data and the results suggested that the Rp, 3.96 × 105 Ω·cm2, of GN treated L80 tested in the simulated environment was very close to that of alloy 800, which is one of the corrosion resistant materials applied in oil sand industry, and two orders of magnitude larger than that of L80. GN treated L80 was believed to be a more suitable material for the application of slotted liners due to wider and more stable passivation zone shown in PD curve. The XRD results showed that the surface composition of GN treated L80 did not have significant change before and after the immersion test, while the SEM and EDX provided the same confirmative evidence that both of the compositional and dimensional stability of GN treated L80 maintained after 24 h immersion test. From the potentiostatic polarization test at the applied potential of + 0.2 V vs. Ag/AgCl, the stable and decreased current density indicated that GN treated L80 not only had stable corrosion resistance in the simulated environment but also had lower overall corrosion rate than the value predicted by PD test. Therefore, GN treated L80 had significantly improved corrosion resistance of L80 in the simulated environment and it was a competitive candidate for the application as a corrosion resistant material for the slotted liners of SAGD system.

  • Subjects / Keywords
  • Graduation date
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.
  • Language
  • Institution
    University of Alberta
  • Degree level
  • Department
    • Department of Chemical and Materials Engineering
  • Specialization
    • Materials Engineering
  • Supervisor / co-supervisor and their department(s)
    • Luo, Jingli (Chemical and Materials Engineering)
  • Examining committee members and their departments
    • Liu, Qi (Chemical and Materials Engineering)
    • Etsell, Thomas (Chemical and Materials Engineering)
    • Luo, Jingli (Chemical and Materials Engineering)
    • Li, Leijun (Chemical and Materials Engineering)