Carbon steel is commonly used as construction material of processing equipment due to its strength, ease of fabrication, and low cost. Nevertheless, carbon steel is susceptible to corrosion by process fluid, like nitric acid. However, corrosion effect can be reduced by inhibitor addition. Tannin is one of carbon steel corrosion inhibitors in acidic solution. Tannin is an organic compound which has hidroxyl and carboxyl functional groups, decomposed easily, and non-toxic. The aim of this research is to determine the effectiveness of tannin as a corrosion inhibitor for carbon steel in nitric acid solutions. The corrosion rate is determined using the Tafel method, whereas the corrosion mechanism is predicted by cyclic voltammetry. The results showed that tannin is ineffective to inhibit carbon steel corrosion in nitric acid solution. The carbon steel corrosion reaction in nitric acid solution, with or without tannin addition, is reversible, involving single step oxidation-reduction reaction, resulting stable corrosion product, and not forming any passivation.Keywords: carbon steel, corrosion, inhibitor, nitric acid, tannin
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