Study of the possible mechanisms of steel passivation in CO{sub 2} corrosion
- Inst. for Energy Technology, Kjeller (Norway)
- Elf Exploration Production, Pau (France)
SuperProtective corrosion layers, frequently observed in CO{sub 2} corrosion tests, can be due to a passivation of the steel surface beneath the porous corrosion layers. By potentiodynamic scans on bare steel in CO{sub 2}/HCO{sub 3}{sup {minus}} solutions of various pH, an anodic peak and a passive domain are effectively observed. However the passivation pH of carbon steel lies within the pH range of the carbonate/bicarbonate buffer, and it should not normally be attained in the presence of CO{sub 2}. Possible passivation mechanisms are then discussed. Two alternative ways are essentially open: (1) the achievement of locally very high pH values, through the local disconnection of CO{sub 2} from bicarbonate (due to the rate limiting hydration of CO{sub 2} into H{sub 2}CO{sub 3} and the resulting depletion of H{sub 2}CO{sub 3} by cathodic reactions), followed by a further increase in pH due to the local generation of carbonate by the cathodic reduction of bicarbonate. (2) at lower pH, the involvement of mill scale and rust layers containing FeIII compounds. Then the permanent release of Fe{sup 3+} ions and their cathodic reduction can contribute to pass the critical current for passivation, when it cannot be supplied only by H{sup +} reduction.
- OSTI ID:
- 697057
- Report Number(s):
- CONF-990401-; TRN: IM9946%%443
- Resource Relation:
- Conference: Corrosion 1999 conference, San Antonio, TX (United States), 25 Apr 1999; Other Information: DN: 1 CD-ROM. Operating Systems: Windows 3.1, `95, `98 and NT; Macintosh; and UNIX; PBD: 1999; Related Information: Is Part Of Corrosion 99: Proceedings; PB: [3500] p.
- Country of Publication:
- United States
- Language:
- English
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