The chemical cleaning treatments of industrial boilers are usually performed with hydrochloric acid solutions. Neverthless, for various reasons, in some cases it is suitable to use solutions of organic acids, such as citric acid or mixture of formic and hydroxyacetic acids, or complexing agents such as ethylenediaminetetracetic acid (EDTA) at different pH values. Literature reports a high number of papers on the corrosion inhibition of carbon steels or low-alloy steels in hydrochloric or sulfuric acid solutions, whereas data on corrosion inhibition of the same materials in organic solutions are less frequent. The present paper discusses corrosion rates and corrosion inhibition data of ARMCO iron and two steels (F11 and F22) commonly used for boiler tubes in thermoelectric units, in 3% citric acid solutions (pH 2.2), 3% ammoniated citric acid solutions (pH 3.5), in mixture of 1.5% formic and 1.5% hydroxyacetic acids and in 10% EDTA solutions (pH shifted to 5 with ammonium hydroxide solutions). Weight loss and electrochemical tests have been carried out for 6 hours, at 90°C. Among the compounds tested, heterocyclic substances containing nitrogen and sulfur, such as 2-mercaptopyrimidine and thiourea derivatives resulted partcularly efficient. On the contrary acetylenic derivatives, usually highly efficient in hydrochloric acid solutions, are not suitable for application in organic solutions.

Inhibitors for chemical cleaning of carbon steel in solutions of organic acids and complexing agents.

ZUCCHI, Fabrizio;GRASSI, Vincenzo;TRABANELLI, Giordano;
1995

Abstract

The chemical cleaning treatments of industrial boilers are usually performed with hydrochloric acid solutions. Neverthless, for various reasons, in some cases it is suitable to use solutions of organic acids, such as citric acid or mixture of formic and hydroxyacetic acids, or complexing agents such as ethylenediaminetetracetic acid (EDTA) at different pH values. Literature reports a high number of papers on the corrosion inhibition of carbon steels or low-alloy steels in hydrochloric or sulfuric acid solutions, whereas data on corrosion inhibition of the same materials in organic solutions are less frequent. The present paper discusses corrosion rates and corrosion inhibition data of ARMCO iron and two steels (F11 and F22) commonly used for boiler tubes in thermoelectric units, in 3% citric acid solutions (pH 2.2), 3% ammoniated citric acid solutions (pH 3.5), in mixture of 1.5% formic and 1.5% hydroxyacetic acids and in 10% EDTA solutions (pH shifted to 5 with ammonium hydroxide solutions). Weight loss and electrochemical tests have been carried out for 6 hours, at 90°C. Among the compounds tested, heterocyclic substances containing nitrogen and sulfur, such as 2-mercaptopyrimidine and thiourea derivatives resulted partcularly efficient. On the contrary acetylenic derivatives, usually highly efficient in hydrochloric acid solutions, are not suitable for application in organic solutions.
Carbon steels; Organic acids; Complexing agents; Chemical cleaning; Inhibitors
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11392/1196525
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