Corrosion inhibitors

Abstract

Corrosion and scale-inhibiting compositions which are useful in recirculating aqueous systems comprise a mixture of a phosphate compound, a phosphonate compound comprising 1-hydroxyethylidene-1,1-diphosphonic acid or nitrilotris(methylene)triphosphonic acid, an aryl triazole, and a salt of a metal selected from the group consisting of molybdenum, tungsten and chromium. In the preferred embodiment of the invention, the phosphate compound is present in a weight percent ratio in the range of from about 2.5:1 to about 4:1 weight percent per weight percent of the metal salt. An example of an effective anti-corrosion composition comprises a mixture of sodium tripolyphosphate, 1-hydroxyethylidene-1,1-diphosphonic acid, benzotriazole and sodium molybdate, said composition being present in an amount of from about 5 to about 5,000 ppm.

Dependencies are inferred from the claim text.