This is a repository copy of Investigating pitting in X65 carbon steel using potentiostatic polarisation.

Appropriate material selection for injection pipelines and tubing for carbon dioxide geologic storage is fundamental to ensure asset integrity and reduce cost. This paper evaluates the corrosion behaviour of X65, 1Cr, 3Cr and 5Cr, which have the potential to be utilised as injection pipeline/tubing materials. The influence of steel Cr content on the general and localised corrosion behaviour is investigated at time periods from 6 to 192 hours at C The evolution, morphology and chemistry of corrosion products on the surface of each material were evaluated using a combination of Scanning Electron Microscopy, Energy Dispersive X-Ray Spectroscopy and X-Ray Diffraction and related to their overall corrosion protection. Results indicate that prior to the formation of protective films on the steel surfaces, the resistance of the materials to corrosion increase with increasing Cr content (Corrosion resistance: X65<1Cr<3Cr<5Cr). However, as corrosion products evolve, the protection afforded to the different steels varies significantly and decreases with increasing Cr content. X65 becomes the material with the lowest general corrosion rate by the end of the 192 h experiments and 5Cr exhibits the highest corrosion rate (ranking of corrosion resistance: X65>1Cr>3Cr>5Cr). In terms of the corrosion products on X65, both inner amorphous and outer crystalline corrosion layers consist of FeCO3. For the Cr-containing steels, the outer layer also comprises FeCO3, but the inner layer is enriched with Cr, and is predominantly amorphous Cr(OH)3. The extent of localised corrosion (determined using surface profilometry) is noticeably less for X65 compared to the Crcontaining steels. The paper raises questions about the benefits that low Cr steels offer towards extending component design life compared to carbon steel under the test conditions considered here.

This is a repository copy of Electrochemical response of micro-alloyed steel under potentiostatic polarization in CO saturated brine ₂ .

No abstract

Corrosion products that form on carbon steel in sweet (CO 2 ) environments can protect the steel by retarding interactions between the substrate steel and a corrosive electrolyte. Such protective films could become damaged at local sites leading to potential differences and the emergence of galvanic currents with the consequence of pitting in certain envfironments. The large protected surface (with a higher positive potential) becomes a cathode while the tiny exposed surface (with a lower positive potential) becomes the anode. Films formed in a Ca 2+ -rich environment often comprise mixed calcium and iron carbonates in the form, Ca x Fe (1−x) CO 3 . This work utilized an artificial pit to investigate pitting under Ca x Fe (1−x) CO 3 film conditions. Mixed carbonate films were grown on cathode discs (25-mm diameter) for 96 h at pH 7.5, 50°C. Freshly polished anode pins were screwed onto the cathode disc and the galvanic currents were measured for 24 h. The anode/cathode area ratios were varied by using pins of 1, 2, and 3 mm diameter. Scanning electron