Corrosion rate of iron and iron–chromium alloys in CO 2 medium D.S. Carvalho a , C.J.B. Joia b , O.R. Mattos a, * a Laborato ´rio de Corrosa ˜o Prof. Manoel de Castro, EE/PEMM/COPPE, Universidade Federal do Rio de Janeiro—Cx. Postal 68505, CEP 21945-970, Rio de Janeiro, RJ, Brazil b PETROBRAS-CENPES, Cidade Universita ´ria, Q. 7 Ilha do Funda ˜o, CEP 21949-900, Rio de Janeiro, RJ, Brazil Available online 28 September 2005 Abstract Inthepresentpapercorrosionofiron(99.95%)andiron–chromiumalloys(1–5%Cr)were investigated by mass loss and ac impedance. These low-chromium content alloys have been proposed as an intermediate corrosion-performance material between C-steel and stainless steels to be used in oil plants. It was observed that small contents of chromium in the alloy decrease the corrosion attack only in very specific pH range 4 < pH < 5. InCO 2 medium, mass loss showed a linear behaviour with respect to time whereas in the presence of acetate the results were not monotonic. By ac impedance, it was found that R 1 p and R 1 t vary proportionally with respect to mass loss. A discussion concerning the online monitoring of the corrosion rate is presented. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: CO 2 corrosion; EIS; Acetate; NaCl; Iron and iron–chromium alloys 0010-938X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.corsci.2005.05.052 * Corresponding author. Tel.: +55 21 2562 8550; fax: +55 21 2290 6626. E-mail addresses: deysimar@metalmat.ufrj.br (D.S. Carvalho), omattos@metalmat.ufrj.br (O.R. Mattos). Corrosion Science 47 (2005) 2974–2986 www.elsevier.com/locate/corsci