The electrochemistry of 13% chromium stainless steel in oilfield brines

The electrochemistry of a 13% Cr stainless steel (API5CT L80-13Cr) in 3% NaCl containing acetate and either acetic acid or carbon dioxide at 333 K is explored using RDE voltammetry. The reduction of proton, carbonic acid and acetic acid occur simultaneously, immediately negative to the corrosion potential. Acetic acid gives a well formed reduction wave and the current densities increase with the equilibrium concentration of acetic acid in the medium; in the plateau region, the reduction is mass transport controlled. Despite this reduction process, the corrosion resistance and passivation current density are independent of the acetic acid concentration. It is confirmed that the 13% Cr stainless steel is much more resistant to corrosion that X65 carbon steel and, unlike the carbon steel, its rate of corrosion does not vary with acetic acid concentration. The properties of the passivating film appear to dominate the behaviour of the 13% Cr stainless steel.