Corrosion behavior of V-N microalloyed X80 pipeline steel in a CO ₂ -saturated brine environment

The corrosion behavior of V-N microalloyed X80 pipeline steel in CO 2 -saturated brine was studied using immersion tests and electrochemical measurements. The microstructure consists of acicular and polygonal ferrite. The corrosion products exhibit a double-layer structure, with inner layer consisting of Cr-rich compounds and outer layer predominantly composed of FeCO 3 . With longer immersion, the layer thickens and densifies, reducing the corrosion rate from 5.29 mm/y to 1.15 mm/y, and electrochemical data show a positive shift in corrosion potential and reduced current density, confirming enhanced protectiveness. Alloying elements enrich selectively, Cr and Mo in the inner layer, Cu at the inner/outer layer interface, and V uniformly throughout. This uniform V distribution may be linked to V(C,N) precipitates and the deposition of V oxides.