Adopting a multipurpose inhibitor to control corrosion of ferrous alloys in cooling water systems

The heterocyclic compounds; 2,5-diphenylpyrazolo[ 1,5-c]pyrimidine-7(6H)thione (Phenyl), 5-methoxyphenyl-2-phenylpyrazolo[1,5-c]pyrimidine-7(6H)thione (Methoxy), 5-tolyl-2-phenylpyrazolo[1,5-c] pyrimidine-7(6H)thione (Tolyl), 5-tolyl-2-phenylpyrazolo[1,5-c]pyrimidine-7(6H)one (Inon), 2,5-diphenyl-3-iodopyrazolo[1,5-c]pyrimidine-7(6H)thione (Iodo) and 2,5-diphenyl-3-bromopyrazolo[1,5c]pyrimidine-7(6H)thione (Bromo) were screened by Tafel Extrapolation and Linear Polarization Resistance techniques to detect the possibility of inhibition the uniform corrosion of carbon steel in stagnant cooling water containing 200ppm chloride at 25 degrees C. The inhibition efficiencies of the studied compounds were found to decrease in the following order: Tolyl > Methoxy > Phenyl > Iodo > Bromo > Inon. The Tolyl compound was proved to be the most efficient inhibitor on carbon steel and therefore trialed on stainless steels 304 and 316 to examine its applicability as a multipurpose inhibitor at the same operating conditions. It was revealed that the Tolyl doses inhibit the pitting corrosion of both the stainless alloys. The Tolyl compound; therefore, functions as true multipurpose corrosion inhibitor for different ferrous alloys in industrial cooling water systems. For example, the percentage inhibition of 10 mmole L-1 of the Tolyl compound is 93.42%, 82.91% and 85.40% for carbon steel, 304SS and 316SS, respectively. (C) 2009 Elsevier B.V. All rights reserved.