Method and composition for inhibiting corrosion in aqueous systems

[0003] Metals are widely used in the construction of equipment associated with aqueous systems. By “aqueous systems” it is meant any system containing metals which contain or are or contacted with aqueous fluids on a regular basis. Water-based fluids are typically fluids that contain at least about 50 weight percent water, the remainder being solids (suspended and/or dissolved) and/or nonaqueous fluids. The term aqueous fluids is intended to include not only water-based fluids, but also fluids that are predominantly non-aqueous but have sufficient water present, at least about 5 weight percent water, so that water soluble treatment components may be effectively employed to limit corrosion. Such non-aqueous fluids may be miscible or immiscible with water.

[0004] Typical aqueous systems include, but are not limited to, open recirculating cooling systems which obtain their source of cooling by evaporation, closed loop cooling systems, boilers and similar steam generating systems, heat exchange equipment, reverse osmosis equipment, oil production systems, flash evaporators, desalinization plants, gas scrubbers, blast furnaces, paper and pulp processing equipment, steam power plants, geothermal systems, food and beverage processing equipment, sugar evaporators, mining circuits, bottle washing equipment, soil irrigation systems, closed circuit heating systems for residential and commercial use, aqueous-based refrigeration systems, down-well systems, aqueous machining fluids (e.g. for use in boring, milling, reaming, broaching, drawing, turning, cutting, sewing, grinding and in thread-cutting operations, or in non-cutting shaping, spinning, drawing, or rolling operations), aqueous scouring systems, aqueous glycol anti-freeze systems, water/glycol hydraulic fluids, ferrous-surface pre-treatment, polymer coating systems, and the like. Various types of water may be utilized in such systems, for example fresh water, brackish water, sea water, brines, sewage effluents, industrial waste waters, and the like.

[0005] The aqueous systems that may be treated using the compositions of this invention may contain dissolved oxygen, such as might be obtained from absorbing oxygen from ambient air, or they may be substantially or completely oxygen free. Further, the aqueous system may contain other dissolved gases such as carbon dioxide, hydrogen sulfide, or ammonia, or they may be substantially or completely free of such gases.

[0006] There may be several different types of corrosion encountered in aqueous systems. For example, aqeuous systems may have uniform corrosion over the entire metal surface. The aqueous system may also have localized corrosion, such as pitting or crevice corrosion, where the corrosion is found only in certain locations on the metal surface. Often, control of localized corrosion may be the critical factor in prolonging the useful life of the metal equipment in the aqueous system. In particular, aqueous systems which contain high levels of aggressive anions such as chloride and sulfate are particularly prone to both generalized and localized attack. These aggressive anions may be present in the water source used for the aqueous system at levels that cause problems, or they may be concentrated to harmful levels in the aqueous system because they are part of a system that evaporates water such as an evaporative cooling system.

[0007] Localized corrosion may pose even a greater threat to the normal operation of the system than general corrosion because such corrosion will occur intensely in one location and may cause perforations in the system structure carrying the fluid stream. Obviously, these perforations may cause leaks which require shutdown of the entire aqueous system so that repair can be made. Indeed, corrosion problems usually result in immense maintenance costs, as well as costs incurred as a result of equipment failure. Therefore, the inhibition of metal corrosion in aqueous systems is critical.

[0008] In the descriptions that follow, we utilize the terms oligomer, polymer, co-oligomer, and co-polymer. By oligomer we mean materials produced by the polymerization of a single monomer where the number of monomer units incorporated in the product is between 2 and about 10. By polymer, we mean materials produced by the polymerization of a single monomer without restriction on the number of monomer units incorporated into the product. By co-oligomer, we mean materials produced by the polymerization of more than one type of monomer (including 2, 3, 4, etc. different monomers) where the total number of monomer units incorporated in the product is between 2 and about 10. By co-polymers, we mean materials produced by the polymerization of more than one type of monomer (including 2, 3, 4, etc. different monomers) without restriction on the number of monomer units incorporated into the product.

[0009] We have discovered that certain tetrazolium compounds given by the generalized formula:

[0010] wherein R₁, R₂and R₃can be various organic and inorganic substituents, e.g., from the group consisting of lower alkyl, branched lower alkyl, aryl, substituted aryl, alkylaryl, substituted alkylaryl and heterocyclic substituted aryl with the proviso that none of R₁, R₂or R₃contain more than 14 carbon atoms, and n may be 1 or 2, synergistically combine with a wide range of compounds to provide effective general and localized corrosion protection for metals in aqueous systems. If the components chosen to be combined with the tetrazolium compounds are also scale and/or deposition inhibitors, the combinations will also provide scale and/or deposition inhibition for these aqueous systems.

[0011] Anions and/or cations may be associated with the above structure to balance the charge depending upon the substitutions employed. If R₁, R₂and R₃are all neutral, then the structure shown in the above formula will be positively charged and anionic species will be needed.

[0012] Examples of such tetrazolium compounds that may be utilized according the this invention include Nitroblue Tetrazolium chloride (3,3′-(3,3′-Dimethoxy-4,4′-biphenylene)-bis-[2-p-nitrophenyl-5-phenyl-2H-tetrazolium chloride]), hereafter referred to as NBT, Distyryl Nitroblue Tetrazolium Chloride (2,2′-Di-p-nitrophenyl-5,5′-distyryl-3,3′-[3,3′-dimethoxy-4,4′-biphenylene]ditetrazolium chloride), hereafter referred to as DNBT, Tetranitroblue Tetrazolium chloride (3,3′-(3,3′-Dimethoxy-4,4′-biphenylene)-bis-[2,5-p-nitrophenyl-2H-tetrazolium chloride]), hereafter referred to as TNBT, and Iodonitro tetrazolium chloride (2-(4-Iodophenyl)3-(4-nitrophenyl)-5-phenyltetrazolium chloride) hereafter referred to as INT.

[0013] Examples of compounds that may be combined with the tetrazolium compounds to provide synergistically improved corrosion protection include: inorganic phosphates, such as orthophosphates or polyphosphates, borates, nitrites, and compounds that release a metal anion in water, where the metal anion is selected from the group consisting of molybdates, tungstates, vanadates, metavanadates, chromates or mixtures thereof.

[0014] Additional materials that may be combined with the tetrazolium compounds include polycarboxylates. The polycarboxylates may be simple aliphatic compounds containing between 4 and about 20 carbon atoms which are multiply substituted with carboxylate groups (e.g., C₄-C₁₅α,ω-dicarboxylates or compounds such as 1,2,3,4-butanetetracarboxylic acid) or may be polymeric compounds. The polymeric polycarboxylates may be homopolymers or copolymers (including terpolymers, tetrapolymers, etc.) of ethylenically unsaturated monomers that contain a carboxyl group. Examples of such polymeric polycarboxylates include polyacrylic acid, polymaleic acid, and polymaleic anhydride. Additionally, the polycarboxylates may be hydrocarbyl polycarboxylates as disclosed in U.S. Pat. No. 4,957,704, herein incorporated by reference.

[0015] Additional materials which may be combined with the tetrazolium compounds of the present invention include alkyl hydroxycarboxylic acids or a mixture of such alkyl hydroxycarboxylic acids having the formula:

[0016] HOOC—(R_B1)_a—(R_B2)_b—(R_B3)_c—R_B4

[0017] where a, b, and c are integers from 0 to 6 and (a+b+c)>0 where R_B1, R_B2, R_B3comprise C═O or CYZ, where Y and Z are separately selected from the group of H, OH, CHO, COOH, CH₃, CH₂(OH), CH(OH)₂, CH₂(COOH), CH(OH)COOH, CH₂(CHO) and CH(OH)CHO, so selected that the molecule has a minimum of one OH group when written in its fully hydrated form and R_B4is either H or COOH, including the various stereoisomers and chemically equivalent cyclic, dehydrated, and hydrated forms of these acids and hydrolyzable esters and acetals that form the above compounds in water or the water soluble salts of such alkyl hydroxycarboxylic acids. Examples of such hydroxycarboxylic acids include tartaric acid, mesotartaric acid, citric acid, gluconic acid, glucoheptonic acid, ketomalonic acid and saccharic acid.

[0018] Additional materials which may be combined with tetrazolium compounds include aminohydroxysuccinic acid compounds (or mixtures of such aminohydroxysuccinic acid compounds) such as those disclosed in U.S. Pat. No. 5,183,590, herein incorporated by reference. Suitable aminohydroxysuccinic acids include those selected from the group consisting of compounds of the generalized formulas:

[0019] wherein R_C1is H or C₁to C₄alkyl, optionally substituted with —OH, CO₂H, —SO₃H, or phenyl, C₄to C₇cycloalkyl, or phenyl which is optionally substituted with —OH or —CO₂H, and R_C2is H, C₁to C₆alkyl, optionally substituted with H or —CO₂H (specifically including the moiety —CH(CO₂H)CH(OH)(CO₂H)); and

[0020] wherein R_C2is as above, and Z_Cis selected from the group consisting of

[0021] i) —(CH₂)wherein k is an integer from 2 to 10,

[0022] ii) —(CH₂)₂—X_C—(CH₂)₂— wherein X_Cis —O—, —S—, —NR_C3—, wherein R_C3is selected from the group consisting of H, C₁to C₆alkyl, hydroxyalkyl, carboxyalkyl, acyl, —C(O)OR_C4wherein R_C4is selected from the group consisting of C₁to C₆alkyl or benzyl and a residue having the general formula:

[0023] wherein R_C2is as above,

[0024] iii) a residue having the generalized formula:

[0025] wherein Y is H, C₁to C₆alkyl, alkoxy, halogen, —CO₂H, —SO₃H, m is independently 0 or 1, and p is 1 or 2, and

[0026] iv) a residue having the generalized formula:

[0027] wherein R_C5and R_C6are independently H or C₁to C₆alkyl, Q is H or C₁to C₆alkyl, s is 0, 1 or 2, t is independently 0, 1, 2, or 3, q is 0, 1, 2, or 3, and r is 1 or 2 or water soluble salts thereof. Preferred examples of such aminohydroxysuccinic acid compounds include iminodi(2-hydroxysuccinic acid), N,N′-Bis(2-hydroxysuccinyl)-1,6-hexanediamine, and N,N′-Bis(2 hydroxysuccinyl)-m-xylylenediamine, or the water soluble salts thereof.

[0028] Additional materials which may be combined with the tetrazolium compounds include the carboxyamine compounds which are reaction products of carboxylating agents such as epoxysuccinic acid with amines comprising a plurality of nitrogen atoms such as polyethylene polyamines as disclosed in the International Patent Application WO 96/33953, herein incorporated by reference.

[0029] Additional materials which may be combined with the tetrazolium compounds include polyepoxysuccinic acids (referred to as PESAs) of the general formula:

[0030] where l ranges from about 2 to about 50, preferably 2 to 25; M_Tis hydrogen or a water soluble cation such as Na⁺, NH₄⁺, or K⁺ and R_Tis hydrogen, C_1-4alkyl or C_1-4substituted alkyl (preferably R_Tis hydrogen). The use of PESAs in treating aqueous systems has been disclosed in U.S. Pat. Nos. 5,062,962 and 5,344,590. A corrosion inhibition process utilizing a combination of an orthophosphate, a polyepoxysuccinic acid, an acrylic acid/allyl hydroxy propyl sulfonic acid polymer, and an azole has been disclosed in U.S. Pat. No. 5,256,332, herein incorporated by reference.

[0031] Modified polyepoxysuccinic acids of the general formula:

[0032] wherein R_D1, when present, is H, a substituted or non-substituted alkyl or aryl moiety having a carbon chain up to the length where solubility in aqueous solution is lost, or a repeat unit obtained after polymerization of an ethylenically unsaturated compound; R_D2and R_D3each independently are H, C₁to C₄alkyl or C₁to C₄substituted alkyl; Z_Dis O, S, NH, or NR_D1, where R_D1is as described above, u is a positive integer greater than 1; f is a positive integer; and M_Dis H, a water soluble cation (e.g., NH₄⁺, alkali metal), or a non-substituted lower alkyl group having from 1 to 3 carbon atoms (when R_D1is not present, Z_Dmay be M_DO₃S, where M_Dis as described above) may also be effectively combined with the tetrazolium compounds of the present invention. Use of such compounds have been disclosed in U.S. Pat. Nos. 5,871,691 and 5,489,666, herein incorporated by reference. Examples of such modified polyepoxysuccinic acids include derivatives according to the above formula where R_D1is meta-CH₂—C₆H₄—CH₂—(m-Xylylene), Z_Dis —NH—, both R_D2and R_D3are H, f is 2, and M_Dis Na. Practical examples are typically mixtures where the individual molecules have a range of u, and are hereafter referred to as m-Xylylenediamine/PESA derivatives.

[0033] Additional compounds that may be combined with the tetrazolium compounds include 2,3-dihydroxybenzoic acid and 1,10-phenanthroline.

[0034] Additional compounds that may be combined with the tetrazolium compounds include monophosphonic acids having the generalized formula:

[0035] wherein R_Fis a C₁to C₁₂straight or branched chain alkyl residue , a C₂to C₁₂straight or branched chain alkenyl residue, a C₅to C₁₂cycloalkyl residue, a C₆to C₁₀aryl residue, or a C₇to C₁₂aralkyl residue, and where R_Fmay additionally be singly or multiply substituted with groups independently chosen from hydroxyl, amino, or halogen; and diphosphonic acid compounds having the generalized formula:

[0036] wherein R_Kis a C₁to C₁₂straight or branched chain alkylene residue, a C₂to C₁₂straight or branched chain alkenylene residue, a C₅to C₁₂cycloalkylene residue, a C₆to C₁₀arylene residue, or a C₇to C₁₂aralkylene residue where R_Kmay additionally be singly or multiply substituted with groups independently chosen from hydroxyl, amino, or halogen, or water soluble salts thereof. A preferred example of such a diphosphonic acid is 1-hydroxyethane-1,1-diphosphonic acid (HEDP).

[0037] Additional materials which may be combined with the tetrazolium compounds include phosphonocarboxylic acids (or mixtures of such phosphonocarboxylic acids) such as those disclosed in U.S. Pat. Nos. 3,886,204, 3,886,205, 3,923,876, 3,933,427, 4,020,101 and 4,246,103, all herein incorporated by reference. Preferred are those phosphonocarboxylic acids defined by the following generalized formulas:

[0038] where R_H1is H, alkyl, alkenyl, or alkinyl radical having 1 to 4 carbon atoms, an aryl, cycloalkyl, or aralkyl radical, or the radical selected from the following:

[0039] where R_H2is H, alkyl radical of 1 to 4 carbon atoms, or a carboxyl radical; and X_His selected from the following:

[0040] and where the —PO₃H₂group is the phosphono group

[0041] or water-soluble salts thereof. An example of such a preferred phosphonocarboxylic acid is 2-phosphonobutane-1,2,4-tricarboxylic acid.

[0042] Additional materials which may be combined with the tetrazolium compounds include hydroxyphosphonocarboxylic acids (or mixtures of such hydroxyphosphonocarboxylic compounds) such as those disclosed in U.S. Pat. Nos. 4,689,200 and 4,847,017, both herein incorporated by reference. Suitable hydroxyphosphonocarboxylic acids includes those having the generalized formula:

[0043] wherein R_Eis H, a C₁to C₁₂straight or branched chain alkyl residue, a C₂to C₁₂straight or branched chain alkenyl residue, a C₅to C₁₂cycloalkyl residue, a C₆to C₁₀aryl residue, or a C₇to C₁₂aralkyl residue, X_Eis an optional group, which when present is a C₁to C₁₀straight or branched chain alkylene residue, a C₂to C₁₀straight or branched chain alkenylene residue, or a C₆to C₁₀arylene residue or water soluble salts thereof. A preferred example of such a hydroxyphosphonocarboxylic acid is 2-hydroxy-phosphonoacetic acid.

[0044] Additional materials which may be combined with the tetrazolium compounds include aminophosphonic acids such as those disclosed in U.S. Pat. Nos. 3,619,427, 3,723,347, 3,816,333, 4,029,696, 4,033,896, 4,079,006, 4,163,733, 4,307,038, 4,308,147 and 4,617,129, all herein incorporated by reference. Suitable aminophosphonic acids include those having the generalized formula:

[0045] where R_G2is a lower alkylene having from about one to about four carbon atoms, or an amine, hydroxy, or halogen substituted lower alkylene; R_G3is R_G2—PO₃H₂, H, OH, amino, substituted amino, or R_Fas previously defined; R_G4is R_G3or the group represented by the generalized formula:

[0046] where R_G5and R_G6are each independently chosen from H, OH, amino, substituted amino, or R_Fas previously defined; R_G7is R_G5, R_G6, or the group R_G2—PO₃H₂with R_G2as previously defined; v is an integer from 1 to about 15; and w is an integer from 1 through about 14 or water soluble salts thereof. An example of such an aminophosphonic acid is diethylenetriamine penta(methylenephosphonic acid).

[0047] Additional materials which may be combined with the tetrazolium compounds include water soluble phosphonomethyl amine oxides (or mixtures of such water soluble phosphonomethyl amine oxides) such as those disclosed in U.S. Pat. Nos. 5,051,532, 5,096,595, and 5,167,866, all herein incorporated by reference. Suitable phosphonomethyl amine oxides include those having the generalized formula:

[0048] wherein either R_A1is selected from the group consisting of hydrocarbyl, and hydroxy-substituted, alkoxy-substituted, carboxyl-substituted and sulfonyl-substituted hydrocarbyl; and R_A2is selected from the group consisting of hydrocarbyl, and hydroxy-substituted, alkoxy-substituted, carboxyl-substituted and sulfonyl-substituted hydrocarbyl, —CH₂PO₃H₂, and

[0049] or R_A1and R_A2together form an alicyclic ring having 3 to 5 carbon atoms in the ring or a water-soluble salt of said phosphonomethyl amine oxide. Hydrocarbyl includes alkyl, aryl, and alkaryl groups which do not render the amine oxide insoluble in water. A preferred example of such a phosphonomethylamine oxide is N,N-bis-phosphonomethylethanolamine N-oxide, hereafter referred to as EBO.

[0050] Additional materials which may be combined with the tetrazolium compounds include polymeric amine oxides as described in U.S. Pat, No. 5,629,385, herein incorporated by reference, polyether polyaminomethylene phosphonates and polyether polyamino methylene phosphonate N-oxides, as described in U.S. Pat. Nos. 5,338,477 and 5,322,636, respectively, both herein incorporated by reference, and iminoalkylenephosphonic acids, as described in U.S. Pat. No. 5,788,857, herein incorporated by reference.

[0051] Additional materials which may be combined with the tetrazolium compounds include phosphorus-containing carboxylate materials (hereafter, P-carboxylates) which are telomeric, co-telomeric, polymeric or co-polymeric compounds that include at least one organic phosphorus group and multiple carboxylate groups. Optionally, these materials may also include other substituent groups when the P-carboxylates are produced from monomers which contain substituents other than carboxylate. The phosphorus may be present as an end group, in which case it may be a phosphono or end-type phosphino-type moiety, or may be incorporated into the compound as a phosphino moiety in which the phosphorus is directly bonded to two carbon atoms, a configuration sometimes referred to as a “dialkyl” phosphino moiety. These possibilities are shown schematically below.

[0052] X may be hydrogen or a cationic species such as an alkali metal ion, an ammonium ion, or a quaternized amine radical. Y may be the same as X or additionally may be a substituted or non-substituted akyl, aryl, or akylaryl residue, where the substitutions may or may not contain carboxylate. Y must be chosen so as to maintain adequate solubility of the compound in water. The carbon atoms shown are part of the carbon backbone of the telomer, co-telomer, polymer, or co-polymer, this backbone containing at least two carboxyl groups and optionally other phosphorus incorporations and optionally other non-carboxyl substitutions.

[0053] Preferred are P-carboxylates having number average molecular weights under 10,000, and particularly preferred are oligomeric or polymeric P-carboxylates of low number average molecular weight, e.g., 2,000 or less, and especially 1,000 or less. It is particularly preferred that 2 or more carboxylates are substituted on a linear alkyl residue, in order of preference, in a 1,2-(adjacent) or a 1,3-substitution arrangement. The P-carboxylates may contain the phosphorus substitution or substitutions predominantly or exclusively as phosphono species, predominantly or exclusively as end-type phosphino species, predominantly or exclusively as dialkylphosphino species, or contain a mixture of these substitution types on an individual molecule and/or in the mixture of molecules generated by a particular preparative process. The various preparative processes used for P-carboxylates may also generate various inorganic phosphorus species as part of the synthetic process. Such mixtures of P-carboxylates and the associated inorganic phosphorus species when combined with tetrazolium compounds are considered to be within the scope of this invention.

[0054] Non-limiting examples of the preparation of P-carboxylates suitable for use in this invention and their use as corrosion and/or scale control agents alone and in combination with other water treatment agents in aqeuous systems are disclosed in U.S. Pat. Nos. 2,957,931, 4,046,707, 4,088,678, 4,105,551, 4,127,483, 4,159,946, 4,207,405, 4,239,648, 4,563,284, 4,621,127, 4,681,686, 5,023,000, 5,073,299, 5,077,361, 5,085,794, 5,160,630, 5,216,099, 5,229,030, 5,256,302, 5,256,746, 5,294,687, 5,360,550, 5,376,731, 5,386,038, 5,409,571, 5,606,105, 5,647,995, 5,681,479, and 5,783,728 and European Patents 283191A2, 360746B1, 569731A2, 681995A3, 786018A1, 792890A1, 807635A1, 807654A2, and 861846A2, all herein incorporated by reference. As may be appreciated by examination of these patents, a variety of preparative processes are suitable for producing P-carboxylates useful for this invention. It is not the object of this invention to specify any particular process or method for making the P-carboxylates suitable for use in this invention. In general, they may be produced by reacting a phosphorus containing material with one or more polymerizable monomers, at least one of which contains carboxyl groups or groups which can be made to generate a carboxyl in the final compound (after the polymerization process) by further reactions such as hydrolysis, oxidation, and the like, such monomers being hereafter referred to as carboxyl monomers. The processes disclosed in the art typically involve reaction of a phosphorus-containing material with one or more unsaturated monomers, at least one of which is a carboxyl monomer, to generate P-carboxylate oligomers or polymers. Examples of suitable carboxyl monomers include acrylic acid, maleic acid, maleic anhydride, methacrylic acid, itaconic acid, crotonic acid, vinyl acetic acid, fumaric acid, citraconic acid, mesaconic acid, acrylonitrile, methacrylonitrile, alpha-methylene glutaric acid, cyclohexenedicarboxylic acid, cis-1,2,3,6-tetrahydrophthalic anhydride, 3,6-epoxy-1,2,3,6-tetrahydrophthalic anhydride, 5-norbornene-2,3-dicarboxylic anhydride, bicyclo[2.2.2]-5-octene-2,3-dicarboxylic anhydride, 3-methyl-1,2,6-tetrahydrophthalic anhydride, and 2-methyl-1,3,6-tetrahydrophthalic anhydride. Preferred carboxyl monomers are acrylic acid, maleic acid, itaconic acid, and maleic anhydride.

[0055] Although it is preferred that P-carboxylate materials contain a major proportion of residues that bear carboxyl groups, it may be advantageous to utilize co-oligomeric or co-polymeric P-carboxylates that contain residues that are derived from at least one carboxyl monomer and a minor proportion (under 50 percent by weight of the total product) of residues obtained from at least one other monomer that is not a carboxyl monomer. A wide variety of suitable non-carboxyl monomers exist, including, for example, 2-acrylamido-2-methylpropanesulfonic acid (commercially available as AMPS™ from the Lubrizol Corporation), 2-hydroxy-3-(2-propenyloxy)propanesulfonic acid, 2-methyl-2-propene-1-sulfonic acid, allylsulfonic acid, allyloxybenzenesulfonic acid, styrenesulfonic acid, vinylsulfonic acid, allylphosphonic acid, vinylphosphonic acid, isopropenylphosphonic acid, phosphoethyl methacrylate, hydroxyalkyl and C₁-C₄alkyl esters of acrylic or methacrylic acid, acrylamides, alkyl substituted acrylamides, allyl alcohol, 2-vinyl pyridine, 4-vinyl pyridine, N-vinylpyrrolidone, N-vinylformamide, N-vinylimidazole, vinyl acetate, hydrolyzed vinyl acetate, and styrene.

[0056] Specifically included within the category of P-carboxylates are phosphonic polymers having the generalized formula:

[0057] wherein X_Jis H, an alkali metal atom, an alkaline earth metal atom, or an ammonium or amine residue; and R_J1is a copolymer residue comprising two different residues

[0058] wherein z is an integer ranging from 2 to 100, and wherein, in the first residue, R_J2is —COOH, and in the second residue, R_J2is —CONHC(CH₃)₂CH₂SO₃X_J, wherein X_Jis as hereinbefore defined.

[0059] Non-limiting examples of P-carboxylate materials suitable for use in this invention include Belsperse 161, Belciene 400, Belclene 494. Belclene 500 (all commercially available products of FMC corporation), phosphonosuccinic acid, and Bricorr 288 (a product of Albright and Wilson). Bricorr 288 is described as a composition which consists essentially of up to 50% by weight of a phosphonosuccinic acid, based on the weight of the composition, a phosphonated dimer of alkali metal maleate, not more than a minor proportion by weight, based on the weight of the dimer, of higher phosphonated oligomers of maleate; and from about 0.5 to about 5% by weight of the composition of an alkali metal phosphate.

[0060] Additional materials which may be combined with the tetrazolium compounds include long chain fatty acid derivatives of sarcosine (or mixture of such fatty acid sarcosine derivatives) or their water soluble salts. An example of such a derivative is N-Lauroylsarcosine.

[0061] The tetrazolium compounds of this inventions may also be combined with water soluble alkali metal silicates. Such silicates are well known in the art as corrosion inhibitors for both ferrous metals and aluminum, both in systems where the fluid is predominantly water as well as in glycol-based aqeuous systems typically used as antifreeze coolants for internal combustion engines. The sodium silicates may be represented generically by the formula Na₂O.xSiO₂.yH₂O where x is in the range of about 1 to about 3.5. Commerical sodium silicate solutions in which the mole ratio of silica to soda is about 3.3 may be used. More alkaline solutions having an SiO₂:Na₂O mole ratio as low as about 1:1 or less alkaline solutions having a an SiO₂:Na₂O mole ratio up to about 3.5:1 can also be used. Other alkali metal silicate salts, especially potassium silicate may also be employed. When using water soluble alkali metal silicates in the practice of the current invention, it may be advantageous to combine the silicates with other inhibitors and/or silica stabilizers. Examples of such suitable combinations are disclosed in U.S. Pat. Nos. 3,711,246, 4,085,063, 4,404,114, 5,137,657, 5,262,078, 5,578,246, and 5,589,106, all herein incorporated by reference.

[0062] The tetrazolium compounds of this inventions may also be combined with water soluble monofluorophosphate salts. The use of such salts as corrosion inhibitors for metallic sufaces has been disclosed in U.S. Pat. Nos. 4,132,572 and 4,613,450, both herein incorporated by reference. As disclosed in U.S. Pat. No. 5,182,028, herein incorporated by reference, such salts also have utility for calcium carbonate scale control and in iron and manganese stabilization.

[0063] A wide variety of additional aqueous system corrosion inhibitors suitable for combination with the tetrazolium materials in this invention are known in the art. Non-limiting examples of such inhibitors may be found in Corrosion Inhibitors, C. C. Nathan, ed., NACE, 1973; I. L. Rozenfeld, Corrosion Inhibitors, McGraw-Hill, 1981; Metals Handbook, 9^thEd., Vol. 13—Corrosion, pp. 478497; Corrosion Inhibitors for Corrosion Control, B. G. Clubley, ed., The Royal Society of Chemistry, 1990; Corrosion Inhibitors, European Federation of Corrosion Publications Number 11, The Institute of Materials, 1994; Corrosion, Vol. 2—Corrosion Control, L. L. Sheir, R. A. Jarman, and G. T. Burstein, eds., Butterworth-Heinemann, 1994, pp. 17:10-17:39; Y. I. Kuznetsov, Organic Inhibitors of Corrosion of Metals, Plenum, 1996; and in V. S. Sastri, Corrosion Inhibitors: Principles and Applications, Wiley, 1998. Such inhibitors include amines (e.g., morpholine, cyclohexylamine, benzylamine), alkanolamines, ether amines, diamines, fatty amines and diamines, quaternized amines, oxyalkylated amines, akyl pyridines; tetrazoles such as those disclosed in U.S. Pat. No. 5,744,069, herein incorporated by reference; imidazoline and substituted imidazolines, amidoamines, polyamines, including polyakylenepolyamines such as those disclosed in U.S. Pat. No. 5,275,744, herein incorporated by reference, alkyl derivatives of benzene sulfonic acid, benzoates and substituted benzoates (e.g., p-tert-butylbenzoic acid as disclosed in U.S. Pat. No. 5,275,744, herein incorporated by reference), aminobenzoates, salicylates, dimer-trimer acids, petroleum oxidates, borogluconates; lignins, tannins, and the sulfonated and/or carboxylated derivatives thereof (e.g., lignosulfonates); straight chain C₅-C₁₁monocarboxylates, amine salts of carboxylic acids and mercaptocarboxylic acids such as those disclosed in U.S. Pat. No. 5,779,938, herein incorporated by reference; amino acids, polyamino acids, and derivatives thereof such as those disclosed in U.S. Pat. Nos. 4,971,724, 5,531,934, 5,616,544, 5,750,070, and 5,785,896 herein incorporated by reference; hydroxyether acids and related lactone compounds such as those disclosed in U.S. Pat. No. 5,055,230 herein incorporated by reference, N-acyl sarcosines, N-acyliminodiacetic acids; triazine di- and tri-carboxylic acids such as those disclosed in U.S. 4,402,907, herein incorporated by reference, and phospho- and phosphate esters (e.g., of ethoxylated alcohols) such as those disclosed in U.S. Pat. Nos. 3,873,465, 3,932,303, 4,066,398, and 5,611,991, herein incorporated by reference.

[0064] In the practice of this invention is may be advantageous to employ additional agents to enhance or add additional functionality to the combinations of this invention. Suitable additional agents include dispersants, copper corrosion inhibitors, aluminum corrosion inhibitors, water soluble metal salts and their chelates, scale and deposit control agents, sequestering agents, anti-foams, oxidizing and non-oxidizing biocides, non-ionic and ionic freezing point depressants, pH adjusting agents, inert and active tracers, water insoluble and soluble lubricants, surfactants, calcium hardness adjusting agents, and coloring agents.

[0065] Dispersants are often needed to maintain system cleanliness when the aqueous system contain suspended particulate matter. A wide variety of polymeric and non-polymeric dispersants are known in the art which may be used in the practice of this invention. Preferred are a) water-soluble sulfonated polymers or copolymers obtained from the polymerization of one or more ethylenically unsaturated monomers, at least one of which contains sulfonate functionality, or the water soluble salts thereof or b) copolymers of diiosbutylene and maleic anhydride with molecular weights <10,000 or the water soluble salts thereof. Particularly preferred is about a 3:1 weight ratio copolymer of acrylic acid and allyl hydroxy propyl sulfonate ether or the water soluble salts thereof.

[0066] Additional agents that may be combined with the tetrazolium compounds of this invention include copper corrosion inhibitors, including heterocyclic ring type copper inhibitors such as azole compounds. As is well known in the art, azoles are typically used to provide corrosion protection for copper-based alloys. However, as is also known in the art, in certain systems azoles and similar heterocyclic ring type copper inhibitors additionally provide corrosion protection for ferrous-based metals and/or aluminum, and the use of such materials for these purposes is considered to be within the scope of this invention. As one skilled in the art may readily appreciate, the use of copper inhibitors in the practice of this invention may enhance the performance of the compositions of this invention in protecting a particular metal system and/or may extend the applicability to multi-metal systems.

[0067] Suitable azole compounds include triazoles, tetrazoles, pyrazoles, imidazoles, isoxazoles, oxazoles, isothiazoles, and thiazoles, all optonally substituted with alkyl, aryl, aralkyl, alkylol, and alkenyl radicals, including those disclosed in U.S. Pat. Nos. 2,618,608, 2,742,369, and 2,941,953 and summarized in U.S. Pat. No. 4,101,441, all herein incorporated by reference. Examples of suitable azoles and related heterocylic ring compounds include benzotriazole, tolyltriazole, alkyl or alkoxy substituted benzotriazoles, including n-butyl and hexyloxy substituted benzotriazoles, wherein the substitution occurs on the 4 or 5 position of the benzene ring, 2-mercaptobenzothiazole, 2-mercaptobenzotriazole,1,2,3-triazole, 4-phenyl-1,2,3-triazole, 1,2-napthotriazole, 4-nitrobenzotriazole, pyrazole, 6-nitroindazole, 4-benzylpyrazole, 4,5-dimethylpyrazole, 3-allylpyrazole, imidazole, adenine, guanine, benzimidazole, 5-methyl benzimidazole, 2-phenyl imidazole, 2-benzyl imidazole, 4-allylimidazole, 4-(betahydroxy ethyl)-imidazole, purine, 4-methylimidazole, xanthine, hypoxanthine, 2-methyl imidazole, isoxazole, benzisoxazole, 3-mercaptobenzisoxazole, oxazole, 2-mercapto oxazole, 2-mercaptobenzoxazole, isothiazole, 3-mercaptoisothiazole, 2-mercaptobenzisothiazole, benzisothiazole, thiazole, 2,5-dimercaptothiadiazole, 2,5-dimercaptobenzotriazole, 5,5′-methylene-bis-benzotriazole, and 4,5,6,7-tetrahydrobenzotriazole. Additional suitable azoles include those disclosed in U.S. Pat. Nos. 3,985,503, 4,298,568, 4,734,257, 4,744,950, 4,874,579, 5,217,686, and 5,236,626, all incorporated herein by reference, and 1-phenyl-5-mercaptotetrazole as disclosed in U.S. Pat. No. 5,156,769, herein incorporated by reference. Suitable azoles include mixed compositions such as a tolyltriazole composition which includes at least 65% of the 5-methylbenzotriazole isomer by weight as disclosed in U.S. Pat. No. 5,503,775, herein incorporated by reference. Particularly suitable are halogen-tolerant azoles which give improved corrosion performance, no objectionable odor, and reduced biocide comsumption when halogen-based oxidizing biocides (e.g., chlorine) are used in the aqueous system. Non-limiting examples of such halogen-tolerant azoles are disclosed in U.S. Pat. Nos. 5,772,919, 5,863,463 and 5,863,464, herein incorporated by reference, and include chloro-tolyltriazole, bromotolyltriazole, mono-halobenzotriazole, di-halo-benzotriazole, and mixtures of mono-halo and di-halo-benzotriazoles.

[0068] Preferred azoles are tolyltriazole, benzotriazole and halogen-tolerant azoles, especially chloro-tolyltriazole.

[0069] Additional agents that may be combined with the tetrazolium compounds of this invention include aluminum corrosion inhibitors. Preferred are water soluble nitrate salts, particularly sodium nitrate, and the combination of nitrate salts with alkali metal silicates.

[0070] Additional agents that may be combined with the tetrazolium compounds of this invention include water-soluble metal salts of metals chosen from the group zinc, manganese, aluminum, tin, nickel, yttrium, and the rare earth metals (atomic numbers 57 to 71) and/or organic metal chelates of such metals, where the organic chelant is chosen to impart a desired level of water solubility of the metal ion. As is known in the art, such metal salts and chelates may be utilized to provide additional corrosion protection. The metal salt can be obtained from manganese in the +2 oxidation state, such as wherein the manganese salt state is the sulfate, chloride, acetate, or nitrate salt.

[0071] The use of zinc ions as a corrosion inhibitor is well known in the art, especially in combination with other water treatment agents such as phosphates, phosphonates, P-carboxylates, carboxylates and hydroxycarboxylates. Preferred sources of zinc ions are the sulfate, chloride, acetate, or nitrate zinc salts and the zincate ion obtained by dissolving zinc oxide in base. Particularly preferred are the sulfate and chloride salts and the zincate ion.

[0072] The use of manganese ion in water treatment in combination with aminophosphonates and with P-carboxylates has been disclosed in U.S. Pat. No. 4,640,818 and in European Patent 283191A2, respectively, both herein incorporated by reference. The use of yttrium and cations of the metals of the lanthanum series having atomic numbers from 57 to 71 and/or organics chelates thereof for corrosion inhibition in aqeuous systems has been disclosed in U.S. Pat. Nos. 4,749,550 and 5,130,052, both herein incorporated by reference. The preferred lanthanum salts are those of lanthanum, praseodymium, and neodymium, and commercially available materials which contain mixtures thereof. The metal salt can be obtained from lanthanum or a mixture of rare earth metals containing lanthanum, with the lanthanum salt or mixture of rare earth metal salts containing lanthanum being independently chosen from the sulfate, chloride, acetate or nitrate salts.

[0073] Additional agents that may be combined with the tetrazolium compounds of this invention include scale and deposit control agents. Although many of the previously described combinations of this invention provide both corrosion and scale and/or deposit control (particularly for calcium carbonate scales), there may instances where additional agents must be utilized to control scaling and/or deposition for particular species (e.g., barium sulfate or calcium oxalate). Agents appropriate for control of a variety of such species are known in the art.

[0074] Additional agents that may be combined with the tetrazolium compounds of this invention include sequestering agents. Such agents are needed to prevent metallic (e.g., iron, copper) or alkaline earth ions from fouling the aqueous system or from interfering with the proper functioning of corrosion inhibitors or other agents in the system. Such sequestering agents are known in the art and in some cases may be selected to be effective on a specific ion. Non-limiting examples of suitable sequestering agents include ethylenediaminetetra(acetic acid) nitrolotriacetic acid, and N,N-di(2-hydroxyethyl)glycine or water soluble salts thereof.

[0075] Additional agents that may be combined with the tetrazolium compounds of this invention include anti-foams. Examples of suitable antifoaming agents include silicones (e.g., polydimethylsiloxanes), distearylsebacamides, distearyladipamide and related products derived from ethylene oxide or propylene oxide condensations, and fatty alcohols, such as capryl alcohols and their ethylene oxide condensates.

[0076] Additional agents that may be combined with the tetrazolium compounds of this invention include biocides. The use of biocides may be necessary to control microbiological growth in both the aqueous system and in the feed sources for the compositions of this invention. Both oxidizing and non-oxidizing biocidal agents may be utilized for these purposes. Suitable oxidizing biocides include chorine, hypochlorite, bromine, hypobromite, chlorine and/or bromine donor compounds (e.g., bromochlorohydantoin), peracetic acid, inorganic peroxides and peroxide generators, chlorine dioxide, and ozone. Suitable non-oxidizing biocides include amines, quaternary ammonium compounds (e.g., N-alkyl dimethylbenzylammonium chloride), 2-bromo-2-nitropropane-1,3-diol, β-bromonitrostyrene, dodecylguanidine hydrochloride, 2,2-dibromo-3-nitrilopropionamide, gluteraldhyde, chlorophenols, sulphur-containing compounds such as sulphones, methylene bis thiocyanates and carbamates, isothiazolones, brominated propionamides, triazines (e.g. terbuthylazine, and triazine derivatives such as those disclosed in U.S. Pat. No. 5,534,624 herein incorporated by reference), phosphonium compounds, organometallic compounds such as tributyl tin oxide, and mixtures of such biocides. A preferred non-oxidizing biocide is a mixture of (a) 2-bromo-2-nitropropane-1,3-diol (BNPD) and (b) a mixture of about 75% 5-chloro-2-methyl-4-isothiazolin-3-one and about 25% 2-methyl-4-isothiazolin-3-one, the weight ratio said BNPD (a) to said mixture (b) being about 16:1 to about 1:1 as disclosed in U.S. Pat. No. 4,732,905, herein incorporated by reference.

[0077] Additional agents that may be combined with the tetrazolium compounds of this invention include freezing point depressants. Such agents are needed for aqueous systems such as refrigeration, dehumidification, and internal combustion engine coolant systems. The depressants may be ionic or non-ionic in nature. Non-limiting examples of suitable ionic agents include calcium chloride, sodium chloride, lithium bromide, and lithium chloride. Examples of suitable non-ionic agents are water-soluble alcohols such as ethylene glycol, propylene glycol, ethanol, glycerol, isopropanol, methanol, and mixtures thereof.

[0078] Additional agents that may be combined with the tetrazolium compounds of this invention include pH adjusting agents. Non-limiting examples of suitable agents include sodium hydroxide, potassium hydroxide, lithium hydroxide, hydrochloric acid, sulfuric acid, nitric acid, carbon dioxide, ammonia, organic acids such as oxalic acid, alkali metal carbonates, and alkali metal bicarbonates.

[0079] When the compositions of this invention are used in aqueous systems that involve moving contact between a surface and a metal (e.g., such as encountered in systems containing pumping equipment or in applications involving metal machining or forming), it may be desirable to employ a lubricant to improve the performance of the machining operation or to decrease wear of the contacting and/or metal surface. Such lubricants may be water soluble or water insoluble. Suitable water insoluble organic lubricants such as naturally occurring or synthetic oils include those disclosed in U.S. Pat. No. 5,716,917, herein incorporated by reference. Suitable water soluble lubricants include those disclosed in U.S. Pat. Nos. 3,720,695, 4,053,426, 4,289,636, 4,402,839, 4,425,248, 4,636,321, 4,758,359, 4,895,668, 5,401,428, 5,547,595, 5,616,544, and 5,653,695, herein incorporated by reference. Some lubricants (e.g., those disclosed in U.S. Pat. Nos. 4,405,426 and 5,401,428, all herein incorporated by reference) may additionally impart improved corrosion inhibition performance to the compositions of this invention.

[0080] It may be advantageous either in the formulation of stable product containing a mixture of the components of this invention or in the application of the compositions of this invention to a particular aqueous system (particularly those systems in which significant proportions of nonaqueous fluids are present) to additionally employ surfactants. Such surfactants may be anionic, cationic, amphoteric or non-ionic in nature and are well known in the art. Such agents may be added to the compositions of this invention for a variety of functions (e.g., as emulsifiers, dispersants, hydrotroping agents, anti-foaming agents, lubricants, corrosion inhibitors). The process of selecting appropriate surfactants for accomplishing a given purpose is well known to those skilled in the art. It is particularly desirable to utilize surface active agents when utilizing additives to the compositions of this invention which have limited solubility in water (e.g., when employing water insoluble organic lubricants or supplementary corrosion inhibitors based on marginally soluble materials such as fatty acid derivatives).

[0081] Additional agents that may be combined with the tetrazolium compounds of this invention include calcium hardness adjusting agents. It is well known in the art that the efficacy of many aqueous system corrosion inhibitors, particularly those commonly used to treat open recirculating cooling system, is dependent upon the presence of a certain minimum level of dissolved calcium in the water. Although the efficacy of the compositions of this invention is somewhat independent of dissolved calcium, it may be advantageous in the practice of this invention to increase the dissolved calcium concentration in the system. Non-limiting examples of suitable calcium hardness adjusting agents include the bicarbonate, carbonate, chloride, sulfate, and acetate salts of calcium as well as calcium hydroxide and calcium oxide.

[0082] Additional agents that may be combined with the tetrazolium compounds of this invention include coloring agents. Non-limiting examples of the use of such agents include improving product appearance, aiding in product identification, and serving as additives on which automatic feed control systems which utilize calorimetric methods can be controlled. Non-limiting examples of such agents include water soluble dyes.

[0083] Suprisingly, it has been found that the tetrazolium compounds combine synergistically with a wide range of known scale and/or corrosion inhibitors to provide greatly increased performance for both generalized corrosion and pitting. The combinations are effective over a range of calcium hardness and pH, including low hardness waters. In some cases, a reduction of one order of magnitude or more in the corrosion rate occurs when employing the combination compared to the treatment without using a tetrazolium compound, even when keeping total active treatment levels constant.

[0084] The tetrazolium compounds of this invention are known to be reducible species. While the mechanistic details have not been studied in depth and are not fully understood, it is believed that one important element of the corrosion inhibiting effect of the novel compositions of this invention is the reduction of the soluble tetrazolium compound to a relatively insoluble and protective film at the surface of the corroding metal. The reduction may be a multi-step process, and the protective film may contain several of the intermediate reduction products. Potentially, some of these intermediate reduction products may not be part of the protective film, but may be still capable of further reduction to form a corrosion-inhibiting film. Such corrosion-inhibiting intermediate reduction products of the tetrazolium compounds are also considered to be within the scope of this invention.

[0085] The protective action of the tetrazolium compound works in concert with the protective action of the additional water treatment agent to provide effective aqueous system corrosion control. In many cases the additional water treatment agent also provides protection against water formed scales and deposits, and for these cases, the combinations of this invention are effective for the control of both corrosion and scaling/deposition. The additional water treatment agent may impart other desirable properties to the composition (e.g., the ability to disperse particulate matter). However, it is possible for certain water treatment agents (e.g., oxygen scavengers) to cause the reduction of the tetrazolium compound directly in solution, making the tetrazolium compound itself or potential corrosion-inhibiting intermediate reduction products unavailable to form a protective film at the metal surface. Consequently, water treatment agents that substantially reduce tetrazolium compounds in aqueous solution under the particular conditions of use are not suitable for use with this invention. The conditions of use include such considerations as the relative proportions of tetrazolium compound and the tetrazolium-reducing water treatment agent (e.g., the use of an amount of a reducing water treatment agent that did not substantially reduce the amount of tetrazolium compound present would still fall within the scope of this invention). The conditions of use also would include the absolute concentrations of both tetrazolium compounds and other species, temperature, time, the presence or absence of additional oxidizing and/or reducing agents or other compounds that might alter the interaction between the tetrazolium compound and the tetrazolium-reducing water treatment agent, the presence or absence of catalytic surfaces (e.g., metal surfaces), and the like. One skilled in the art may readily determine if a particular agent substantially reduces the tetrazolium compound under the conditions of use. Because the reduction products of the tetrazolium compounds are generally highly colored while the parent materials are not, simple methods of making this determination include visual inspection and colorimetry.

[0086] In a preferred embodiment of the present invention, from about 0.5 to 10,000 parts per million of a combination of a tetrazolium compound and an aqueous system treatment material is added to the aqueous system in need of treatment, with from about 10 to 1000 parts per million of said combination being particularly preferred. The weight ratio of the other aqueous system treatment material to tetrazolium compound is preferably from about 100:1 to 1:20, with a weight ratio of from about 20:1 to 1:1 particularly preferred.

[0087] The pH of the aqeuous system in which the compositions of this invention may be applied ranges from about 5 to about 12. The pH is preferably in the range from about 6 to about 10.

[0088] The components of this invention may be dosed into the aqeuous system at an effective concentration by a slug feed or by blending with the aqueous fluid as the system is being filled. When used to treat aqueous systems in which one or more of the treatment components are discharged from the system or are consumed by chemical or physical processes within the system and thus require replenishment to maintain treatment effectiveness (e.g., open cooling systems), the compositions of this invention may be fed to the system on a continuous basis, on an intermittent basis, or using a combination of the two (e.g., utilizing a continuous low level feed supplemented by slug feeds as needed). Depending upon the application, it may be advantageous to combine the compositions of this invention together into a single treatment fed from one feed supply source, or, alternatively, to separate the components into two or more treatment sources, each source independently being fed continuously or intermittently into the system at a rate needed to maintain adequate concentrations in the system. Single or multiple feed points to the aqueous system for each treatment source may be utilized.

[0089] The timing and rate of treatment feed may be controlled by a variety of methods known in the art. One suitable method is to utilize metering pumps or other feed system devices which may be variously configured to feed continuosly at a fixed rate, on a time schedule, on signals generated by other system components such as makeup or blowdown pumps, or on signals generated by an analog or computer-based feed control system. Non-limiting examples of suitable feed systems have been disclosed in U.S. Pat. Nos. 4,648,043, 4,659,459, 4,897,797, 5,056,036, 5,092,739 and 5,695,092. The feed control systems may utilize signals corresponding to the concentration of one or more of the treatment components, to the concentration of one or more inert or active tracer materials added to the treatment, to the value of one or more measures of system performance (e.g., values obtained from corrosion rate meters, scaling monitors, heat transfer monitoring devices, analytical devices that detect the amount corrosion product in the water such as total or dissolved iron or other metal constituent, and the like), to the value of one or more of the physical characteristics of the system (e.g., temperature, flow rate, conductivity), to the value of one or more chemical characteristics of the system (e.g., pH, calcium hardness, redox potential, alkalinity) or to combinations of these signals to feed and maintain levels of treatment adequate for effective performance in a particular aqueous system. Alternatively, it may be advantageous in some systems to employ a controlled release (also referred to as gradual release or time release) delivery system for some or all the compounds of this invention. In such controlled release systems the material or materials to be fed are impregnated or are otherwise incorporated into a controlled release system matrix. Suitable controlled release delivery systems include those in which the matrix is exposed to the fluid in the aqeuous system or to a fluid stream being fed to the aqeuous system and the treatment components are gradually released into the system by the action of various processes (e.g., diffusion, dissolution, osmotic pressure differences) and which may further be designed to vary the release rate in response to aqeuous fluid characteristics such as temperature, flow rate, pH, water hardness, conductivity, and the like. Non-limiting examples of such controlled release delivery systems have been disclosed in U.S. Pat. Nos. 3,985,298, 4,220,153, 5,316,774, 5,364,627, and 5,391,369.

[0090] When feed systems are employed that utilize measured concentrations of treatment or tracer components, such concentrations may be determined by continous, semi-continuous, or batch type analytical techniques including spectroscopic methods (UV, visible emission, visible absorption, IR, Raman, fluorescence, phosphorescence, etc.), electrochemical methods (including pH, ORP, and ion selective electrode measurements), chromatographic methods (GC, LC), methods that rely on antibody binding or release, chemical based analytical/colorimetric methods such as those commercially avaiable from the Hach Company, and the like. A suitable spectrophotometric method is described in U.S. Pat. No. 5,242,602, herein incorporated by reference. A suitable method for regulating the in-system concentration of a water treatment agent is disclosed in U.S. Pat. No. 5,411,889. U.S. Pat. No. 5,855,791, herein incorporated by reference, discloses suitable methods for determining the feed rates of corrosion and fouling inhibitors based on certain performance monitors and system characteristics.

[0091] The tracer compounds that may optionally be employed may be compounds that serve no particular treatment function, referred to as inert tracers, or may be water treatment compounds that are also readily monitored, such treatment compounds being referred to as active tracers. Suitable tracers include soluble lithium salts such as lithium chloride, transition metals such as described in U.S. Pat. No. 4,966,711, herein incorporated by reference, and fluorescent inert tracers such as described in U.S. Pat. No. 4,783,314, herein incorporated by reference. Suitable fluorescent inert tracers include the mono-, di-, and trisulfonated naphthalenes (e.g., water soluble salts of naphthalene sulfonic acid or of naphthalene disulfonic acid). Suitable active tracers include fluorescently tagged polymers such as described in U.S. Pat. No. 5,171,450, herein incorporated by reference, and polymers containing a photo-inert, latently detectable moiety which will absorb light when contacted with a photoactivator, as described in U.S. Pat. No. 5,654,198, herein incorporated by reference, azole-based copper corrosion inhibitors such as tolyltriazole, and water soluble molybdate and tungstate salts.

[0092] Although many of the compounds combined with the tetrazolium compounds are known corrosion inhibitors, they are generally known to be effective only under particular conditions of calcium hardness and pH. For example, certain phosphonocarboxylates such as 2-phosphono-butane-1,2,4-tricarboxylic acid (PBTC) are generally effective as corrosion inhibitors only at pHs exceeding 8 and in waters containing significant calcium hardness (i.e., >200 mg/l as CaCO₃). As will be demonstrated, combinations of PBTC with the tetrazolium compounds are very effective at pH 7.6 in a water containing only 100 mg/l calcium as CaCO₃. Similar results are seen with other combinations. It is particularly advantageous in many aqueous systems to have treatments that are “robust” with respect to the pH and hardness of the water, i.e., that perform well over a wide range to these conditions.

[0093] Use of the tetrazolium compound can significantly reduce the total treatment dosage needed to effectively limit corrosion in the aqueous system. Many of the combinations of the tetrazolium compounds are with materials that are primarily or exclusively utilized as scale and/or deposition inhibitors. However, the combinations are effective for both scaling/deposition and corrosion control.

[0094] The corrosion inhibition activity of the treatments in the present invention were evaluated using the Beaker Corrosion Test Apparatus (BCTA). The BCTA consists of a 2 liter beaker equipped with an air/CO2 sparge, 1010 low carbon steel (LCS) coupon(s), a 1010 LCS electrochemical probe, and a magnetic stir bar. The test solution volume was 1.9 liters. Air/CO₂sparging is continuous during the test. The reference electrode and counter electrode used in making the electrochemical corrosion measurements are constructed of Hastelloy C22. The beaker is immersed in a water bath for temperature control. Electrochemical corrosion data were obtained periodically on the probe during the test using a polarization resistance technique. All tests were conducted at 120° F., using a 400 RPM stir rate. Unless otherwise noted, the test duration was 18 hours. Two values are reported for each test; EC(avg), the average value of the electrochemically measured corrosion rate during the test, and EC(18 hour), the value of the corrosion rate at the end of the test. The latter value is thought to be more indicative of the longer term corrosion rate expected.

[0095] In all tests the coupon(s) immersed in the beaker during the test is photographed. For some tests, the pit depths on the coupons are measured using a microscopic technique (see ASTM G 46-94, section 5.2.4). For these pit measurement tests, two coupons are used and up to 20 pits per coupon are measured (up to 10 per side).

[0096] Unless specifically noted otherwise, the test water contains 100 mg/l Ca (as CaCO₃), 50 mg/l Mg (as CaCO₃), 100 mg/l chloride, and 100 mg/l sulfate. Using this water, tests were conducted at pHs of 8.6, 7.6, and 6.8. The corresponding “M” alkalinities at these pHs were 110, 32, and 4 mg/l (all as CaCO₃).

[0097] It is relatively difficult to control ferrous metal corrosion in this test water. The relatively low calcium hardness makes it difficult for inhibitors which depend on calcium to function effectively. The relatively high sulfate and chloride levels (for the given calcium level) makes the water aggressive to ferrous metals, particularly with respect to pitting corrosion.

[0098] To prevent calcium carbonate and/or calcium phosphate deposition from occurring during the test, many of the tests were conducted using 5 mg/l of a Polyepoxysuccinic Acid (PESA) with a degree of polymerization of about 5 and 5 mg/l active of a copolymer of acrylic acid and allylhydroxypropylsulfonate ether sodium salt (AA/AHPSE) added to the test water. For some tests, only 5 mg/l of AA/AHPSE copolymer was used.

[0099] Both addition and substitution (constant inhibitor level) tests were conducted. In former type of test, a low level of a tetrazolium compound (2 to 5 mg/l) was added to a second composition. In the latter test, the second composition was reduced by a given amount (3 to 5 mg/l) and replaced by the same amount of tetrazolium compound.

[0100] BCTA results for tests conducted at pH 8.6 are shown in Table 1. The tetrazolium compound utilized for these tests was NBT. Belcor 575 is hydroxyphosphonoacetic sold by FMC. Bricorr 288 is a mixture of phosphonosuccinic acid, the phosphonated dimer of maleic acid, phosphoric acid, and a minor proportion by weight of higher phosphonated oligomers of maleic acid sold by Albright and Wilson. Dequest 2060 is diethylenetriamine penta(methylenephosphonic acid) sold by Monsanto. Bayhibit AM is 2-phosphonobutane-1,2,4-tricarboxylic acid sold by Bayer. Goodrite K-752 is a polyacrylate sold by B. F. Goodrich.

[0101] As can be seen from Table 1, in all cases except for Bricorr 288, the addition or substitution of low levels of NBT synergisticially improves corrosion performance. Such factors as, e.g., particular test conditions may have contributed to the Bricorr 288 result in this case.

[0102] Corrosion results for tests conducted at pH 7.6 with both AA/AHPSE and PESA present are shown in Table 2. Results with AA/AHPSE only are shown in Table 3. In these waters, an EC(18) of 3 mpy or less is considered to be an acceptable corrosion rate for most industrial applications. In some cases shown in Table 3, the corrosion rates with the tetrazolium compound present are not acceptable. However, the synergistic improvement of the combination of first component with the tetrazolium compound is obvious, and one skilled in the art may readily determine both the effective total amount of inhibitor needed as well as the relative proportions of the tetrazolium compound and other component that are needed to obtain the corrosion protection needed for the application of interest.

[0103] The trends noted above for results at pH 8.6 are also seen at pH 7.6. Results for tests with Bricorr 288 are shown in graphical form in FIG. 1 to more clearly illustrate the synergistic improvement obtained by utilizing the tetrazolium compound NBT in combination with this material.

[0104] Corrosion results for tests conducted at pH 6.8 are shown in Table 4. The pattern previously identified holds at this pH also.

[0105] Pit depth results for varying exposure times for tests at pH 8.6 with tartaric acid are shown in Table 5. As the results show, addition of NBT is very effective at limiting the growth of pits. Pitting is a particular problem for non-phosphorus inhibitors such as tartaric acid.

[0106] Pit depth and pit count data for tests at pH 7.6 with orthophosphate are shown in Table 6. These results show that NBT is effective both at reducing pit depths and pit densities.

[0107] Shown in Table 7 are pitting data obtained at 10 mg/l total added inhibitor which further demonstrate the pit growth inhibiting property of NBT. Although pit densities were higher in the treatments containing NBT, pit depths were significantly lower. The significant impact of NBT on general corrosion rate can clearly be seen in the case of Bayhibit AM.

[0108] The hardness and pH of waters in aqueous systems such as cooling towers and the like can vary widely. It is greatly advantageous to have inhibitor formulations which can function effectively over a wide hardness range and pH range while inhibiting both corrosion and deposition. It is of further advantage in certain systems that must use uncycled water which typically has low calcium (<100 mg/l Ca as CaCO₃) and is relatively neutral pH (6.5-7.5) that the inhibitors used need not rely on alkaline pH, high hardness conditions to function effectively, as is the case with many of the treatments currently in use. Examples of such systems are closed loop cooling systems once through cooling systems, hot water heating systems, and the like. The following examples further establish the wide-ranging effectiveness of inhibitor formulations containing a tetrazolium compound and the improvement obtained over materials known in the art when a tetrazolium compound is utilized in conjunction with other components described in this disclosure.

[0109] Low pH, Low Hardness

[0110] Table 8 shows results from a water containing 15 mg/l Ca as CaCO₃, 7.6 mg/l Mg as CaCO₃, 71 mg/l Cl, 48 mg/l SO₄, with 5 mg/l active AA/AHPSE at pH 7.0. A significant decrease in corrosion rate is observed when 5 mg/i NBT is added.

[0111] Lower pH, Higher Hardness

[0112] Results of BCTA tests conducted at pH 6.8 in a water containing 500 mg/l Ca as CaCO₃, 250 mg/l Mg as CaCO₃, 7 mg/l MAlk as CaCO₃, 354 mg/l chloride, and 500 mg/l sulfate are shown in Table 9. All tests contained 5 mg/l active AAIAHPSE. Conditions of this kind are often encountered in open recirculating cooling systems where the source (makeup) water has been concentrated several times due to evaporation and sulfuric acid has been added to maintain relatively low pH. In these series of tests the total inhibitor concentration was kept constant or nearly constant for each pair of comparisons (with and without NBT). In each case, replacement of part of the inhibitor or inhibitor blend with NBT resulted in a significant improvement in corrosion performance. As previously noted, not all combinations with the tetrazolium compound provide acceptable corrosion performance, but the combination in all cases improves performance. One skilled in the art may readily determine the appropriate levels and ratios needed to obtain satisfactory performance in a particular aqueous system.

[0113] Higher pH, Moderate Hardness Water

[0114] Table 10 shows the results from a pH 8.6 test water that contains 360 mg/l Ca as CaCO₃, 180 mg/l Mg as CaCO₃, 255 mg/l Cl, 220 mg/l SO₄, and 300 mg/l Malk as CaCO₃. All tests contain 5 mg/l active AA/AHPSE. Conditions of this kind are often encountered in open recirculating cooling systems where the source (makeup) water has been concentrated several times due to evaporation and the pH has been controlled to be in the mid-pH 8 range to make it easier to control ferrous corrosion. The effectiveness of the addition of a tetrazolium compound under these conditions is apparent from these results.

[0115] Data obtained with NBT and three additional tetrazolium compounds: Distyryl Nitroblue Tetrazolium Chloride (DNBT), Tetranitro Blue Tetrazolium Chloride (TNBT), and 2-(4-Iodophenyl)-3-(4-nitrophenyl)-5-phenyltetrazolium chloride (INT) at pH 7.6 are shown in Table 11. The test water is the same as for Example 2. Other than the DNBT combination with Belclene 200, the synergistic interaction of the combination of a tetrazolium compound with other materials disclosed in this invention is evident.

[0116] While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications of this invention will be obvious to those skilled in the art. The appended claims and this invention generally should be construed to cover all such obvious forms and modifications which are within the. true spirit and scope of the present invention.