Study of the possible mechanisms of steel passivation in CO{sub 2} corrosion

Conference · Mon Nov 01 04:00:00 EST 1999

OSTI ID:697057

Gulbrandsen, E; Morard, J H ^[1]; Crolet, J L ^[2]

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1. Inst. for Energy Technology, Kjeller (Norway)
2. 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--
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
03 NATURAL GAS
36 MATERIALS SCIENCE
ACID CARBONATES
CARBON DIOXIDE
CARBON STEELS
CORROSION
CORROSION PRODUCTS
CORROSION PROTECTION
PASSIVATION