Effect of corrosion inhibitors on the rate of carbon steel dissolution in chloride solution under alternating current

• T.A. Nenasheva and A.I. Marshakov

A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 119071 Moscow, Russian Federation

Abstract: The study covers the effect of two inhibitory organic formulations and sodium nitrite on the AC corrosion rate of carbon steel in 3.5% NaCl aqueous solution. The weighing method was used to determine the corrosion rates at the free corrosion potentials or after electrode polarization at a potential of intense metal dissolution. It has been shown that the efficiency of the inhibitors studied decreases under alternating current. The degree of protection varies in the range from 30 to 70% depending on the alternating current density (peak potential values). It is assumed that the decrease in degree of inhibitory protection in the case of AC corrosion is due to a decrease in the efficiency of inhibitors over time under conditions of intense metal dissolution. It has been shown that the concentration of Fe(Ⅱ) compounds in the AC corrosion products grows proportionately with an increase in the steel mass loss. In the presence of organic inhibitors, the concentration of Fe(Ⅱ) compounds grows considerably and no linear correlation with the mass loss of steel is observed. It is assumed that the “oxide-free” metal passivation in the presence of organic corrosion inhibitors may be the reason of the increase in the amount of Fe(Ⅱ) compounds in the AC corrosion products.

Keywords: corrosion, alternating current, carbon steel, chloride electrolyte, organic corrosion inhibitors, nitrite, mass loss, potentiostatic polarization, coulometric oxidation, passivation

Int. J. Corros. Scale Inhib., 2021, 10, no. 3, 1110-1127
doi: 10.17675/2305-6894-2021-10-3-16

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