Corrosion rate of iron and iron-chromium alloys in CO2 medium

In the present paper corrosion of iron (99.95%) and iron-chromium alloys (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. In CO2 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 Rp-1 and Rt-1 vary proportionally with respect to mass loss. A discussion concerning the online monitoring of the corrosion rate is presented.