Method for preventing corrosion in water-carrying systems

Claim 1

In the inhibition of corrosion and scale formation in a water-carrying system wherein to the water there is added about 5 to 100 g/m 3 of a phosphonocarboxylic acid of the formula ##STR9## in which R is hydrogen, an alkyl, alkenyl or alkinyl radical having up to 4 carbon atoms, a phenyl, cycloalkyl or phenylalkyl radical, or the radical ##STR10## R' is hydrogen, an alkyl radical having up to 4 carbon atoms or a carboxyl radical; and X is ##STR11## the improvement which consists essentially of further adding to the water about 0.05 to 100 ppm, constituting about 5 to 500% by weight of the phosphonocarboxylic acid, of at least one member selected from the group consisting of a benzimidazole derivative selected from the group consisting of Δ .sup. -2-(ε-aminopentyl)-imidazoline, Δ 2 -1-(β-aminoethyl)-2-(ε-aminopentyl)-imidazoline, Δ 2 -2-(ε-aminopentyl)-thiazoline, 2-(βamino-β-methylpropyl)-benzimidazole, 2-(δ-aminobutyl)-benzimidazole, 2-(ε-aminopentyl)-benzimidazole, 2-(λ-aminoundecyl)-benzimidazole, 2-(ε-methylaminopentyl)-benzimidazole, 2-(ε-aminopentyl)-1-phenylbenzimidazole, 2-(ε-aminopentyl)-5-methylbenzimidazole, 2-(γ-phenylaminopropyl)-5-methylbenzimidazole, 2-(γ-aminopropyl)-benzthiazole, 2-(β-amino-β-methylpropyl)-benzthiazole, 2-(ε-aminopentyl)-benzthiazole, 2-(γ-methylaminopropyl)-benzthiazole, and 2-(ε-dimethylaminopentyl)-benzimidazole, polyacrylamide with a molecular weight of about 30,000 to 2,000,000, polyethyleneimine with a molecular weight of about 100,000 to 1,000,000, polyvinylpyrrolidone with a molecular weight of about 20,000 to 800,000, and lignin sulfonate.