Corrosion protection of mild steel in cooling water systems with green polymeric inhibitor, tannic acid

Tannin is one of the promising green inhibitor from natural polymers due to its natural and renewable source and it has high biodegradability under aerobic and anaerobic conditions, which makes it safe for disposal compared to inorganic corrosion inhibitors such as chromates, nitrites, zinc salts or oxides. The present work is designed to investigate and gain further understanding of the inhibition mechanism of tannin as green inhibitor for the corrosion of mild steel in acidic media (0.5 M H₂SO₄ and 1 M HCl solutions), decarbonized and sea water via electrochemical techniques. In the first part, acidic medias are examined in absence of and with varying amount of tannin in order to observe the optimum dosage of the inhibitor and adsorption isotherm plots were investigated in order to gain information about corrosion protection mechanism. In the second part, decarbonised and sea water are examined in absence and presence of tannin at varying pH values in order to observe the optimum dosage of the inhibitor. Thin Layer Choromotography (TLC) was conducted for the characterization of solutions and to examine the structure effective for the corrosion inhibition. In the last part, pilot plant studies, simulating closed cooling systems have been carried out to investigate the behaviour of the tannin for corrosion inhibition under practice-like conditions.