Cooling water corrosion control method and composition

A composition for inhibiting corrosion in industrial cooling waters which contain hardness and have a pH of at least 8 which composition comprises:

• I. a phosphonate blend of 2-phosphonobutane-1,2,4-tricarboxylic acid and 1-hydroxyethylidene-1,1-diphosphonic acid, and
• II. a water-soluble non-crosslinked random terpolymer of 40 to 90 weight parts of an acrylic acid, 5 to 30 weight parts of methacrylic acid, and 5 to 50 weight parts of a t-butylacrylamide, based on a total of 100 weight parts of polymer, said polymer having a weight average molecular weight in the range of about 1,000 to 50,000, and the polymerized units of an acrylic acid and a t-butyl acrylamides are defined by the following formula:
• ##STR8## where m is in the range of about 10-700 and n is in the range of about 0.1 to 350, subject to the molecular weight limitations,
• R and R.sup.1 are individually selected from hydrogen and methyl;
• X is selected from hydrogen, sodium, potassium, calcium, ammonium, and magnesium moieties;
• and R.sup.2 and R.sup.3 are individually selected from hydrogen, and substituted and unsubstituted groups each containing a total of 1 to 8 carbon atoms, wherein the substituents on R.sup.2 and/or R.sup.3 are selected from alkyl, aryl, and keto groups, provided that either R.sup.2 and/or R.sup.3 is t-butyl, with the weight ratio of polymer:phosphonate blend being within the range of 0.2/1 to 2.1.