WO1996039549A1

WO1996039549A1 - Method for inhibiting metal corrosion in large scale water systems

Info

Publication number: WO1996039549A1
Application number: PCT/US1996/006158
Authority: WO
Inventors: Ronald Liudas Oleka; Sandra Lynn Edmondson; Peter Fung; Vladimir Jovancicevic
Original assignee: Betzdearborn Inc.
Priority date: 1995-06-05
Filing date: 1996-05-02
Publication date: 1996-12-12

Abstract

A method inhibiting metal corrosion in a closed water system such as is found in industrial, commercial and institutional systems which utilizes a formulation comprising at least one water soluble fatty acid salt of the formulae R COOX and R1 (COOX)¿n? wherein R is alkyl C6-18, or hydroxyalkyl (6-18), R?1¿ is alkyl C¿2-18? or hydroxyalkyl C2-18, X is a salt forming cation and n is 2 or 3. The corrosion inhibiting salt(s) is present in an amount 1 to 1000 parts per million parts of the aqueous treatment system. Other additives for helping to reduce corrosion of metal such as benzoates, silicates, nitrates, molybdates, triazole and the like may also be present.

Description

Method For Inhibiting Metal Corrosion In Large Scale Water Systems

This invention relates to a method for inhibit¬ ing metal corrosion in a closed water system such as is found in industrial, commercial or institutional systems, including without limitation HVAC systems of hospitals, universities, office towers, factories, shopping malls and the like. More particularly, the invention relates to a method for inhibiting metal corrosion in such a system by- maintaining therein an effective amount of at least one water soluble fatty acid salt as hereinafter more particu¬ larly defined. The invention further relates to certain corrosion inhibiting compositions, the aqueous formulations containing the same and the systems produced therefrom by dilution with water.

The corrosion inhibiting formulations for use in the aforesaid closed water systems comprise at least one water soluble fatty acid salt selected from salts having the formulae

RCOOX and

wherein R is straight or branched chain alkyl having at least 6 carbon atoms and preferably 6 to 18 carbon atoms or hydroxyalkyl having at least 6 and preferably 6 to 18 carbon atoms, X is a cation (ammonium, alkali metal, amine or any other basic compound which forms a salt with said fatty acid) , R¹ is alkyl or hydroxyalkyl having at least 2 carbon atoms, and preferably 2 to 18 carbon atoms and n is 2 or 3 and optionally at least one additive selected from the group of alkali metal borates, alkali metal molybdates, hydrocarbyl triazoles, silicates and amines such as ethylenediamine, morpholine, pyridine and pyrolidine.

The corrosion inhibiting compositions of the invention, in addition to their effectiveness for their intended purpose are also environmentally acceptable because of their low toxicity and reduced adverse effect when discharged into a waste stream. While a variety of corrosion inhibitors have been proposed, many of the conventional corrosion inhibitors have themselves been found to cause problems when employed in corrosion inhib¬ iting formulations. For example phosphate compounds have been found to be good corrosion inhibitors but attendant problems may result from the use of phosphate compounds. For example, the dilution of a corrosion inhibiting formulation containing phosphate corrosion inhibitors with hard water will cause the precipitation of insoluble alkali earth phosphate salts from the aqueous corrosion inhibiting aqueous solutions. The precipitation causes rapid depletion of the phosphate in solution and in turn causes a decrease in corrosion protection. In addition, the precipitating solids will scale and eventually have detrimental effects on the system. The use of various anti-precipitation additives in phosphate containing anti- corrosion formulations has been proposed, however, the uses of such additives increases the overall cost of the formulation. In addition, several governmental authori¬ ties have banned the use of phosphates in aqueous systems because of their detrimental effects to the environment when the water in the system has to be discharged. Other conventional corrosion inhibitors have problems associated with their use in aqueous corrosion inhibiting systems, as for example, the amine and nitrite compounds which are often employed as corrosion inhibitors may form dangerous nitroso compounds particularly when they are used togeth¬ er.

It would therefore be advantageous to develop a metal corrosion inhibiting formulation for use in a closed water system which provides adequate protection for a variety of metals without requiring the use of organophos- phates, amines and/or nitrites or heavy metal compounds such as chromates and molybdates.

Special requirements and considerations come into play in treating such large scale closed water systems. There are significant differences between such systems and for example automobile cooling systems, other internal combustion engine systems, boilers and the like which have been well documented. Closed systems are constituted of a water filled closed loop, typically constructed of steel pipes in which there is minimal air contact with the water in the system.

Air contact, however, can and does occur as for example if the system has a sump open to the air. The corrosion inhibitor(s) employed therefore have to be stable against decomposition and/or oxidation and above all are required to be effective to present oxidation of metal i.e., corro¬ sion. The metal of most concern is typically mild steel although corrosion protection for brass, solder, copper, cast iron, aluminum, magnesium and their alloys is also important as components of the systems such as valves, heat exchangers, etc. are constructed from these metals. Another major factor to be considered in con¬ nection with water treatment for large scale closed systems as contemplated herein is that these systems, many times, sit with uncirculated water for prolonged periods i.e., for months, when the system for example a heating system is shut down in the hot summer months and a cool- ing/chiller system is shut down for the cold winter months. The non-circulating water during these time periods remains stagnant. The corrosion inhibitor employed must be effective both in a flowing and in a non- flowing or static condition.

Still another area of concern for closed system water treatment is that the corrosion inhibitor used for example, in a building's hot water heating system and/or air conditioning chiller system must be stable in perfor- mance for prolonged periods of time, by which is meant years. It is most desirable to treat the system once and for the system to require minimal additional treatment or monitoring over this extended period. Systems of the type contemplated herein are frequently very complicated in construction and can contain miles of steel pipe, for example when installed in a large building complex. Leaks and water losses do occur. These leaks in turn reduce the amount of corrosion inhibitor in the system. Such leaks of the treated water in the system which took place heretofore and when the heretofore available corrosion inhibiting agents such as chromates and hydrazine were utilized, gave rise to health concerns because of the recognized toxicity of these materials and because they are suspected of being carcinogens . Alkali metal molybdate based formulations have also been proposed for use in closed aqueous systems and have been found to be effective as corrosion inhibitors . Even though such molybdates are much less toxic than the chromates and hydrazine, many communities have imposed waste discharge limits with respect thereto as molybdenum is perceived and is classified as a toxic heavy metal. Nitrites and borate-nitrites have heretofore been employed as corrosion inhibitors in closed systems and particularly have been used together with amine compounds . Their use is characterized by a relatively high inorganic solids content which gives rise to a solids buildup in the case where a leak has occurred. Such solids can cause caustic crevice corrosion at fitting connections and also on the external surfaces of the equipment as they usually are highly alkaline. The use of nitrites is furthermore undesirable as they are microbio¬ logical nutrients and their discharge can cause eutrophication. Treatment solutions containing nitrites are frequently unstable in use as there are microorganisms present in the system which consume the nitrites decreasing or eliminating the corrosion inhibitor from the system. The heretofore conventional use of phosphorus containing compounds in the formulations is also undesir¬ able as such compounds support microbiological growth in as much as they constitute an essential nutrient for microorganisms . The proposed use of organophosphorus compounds has also been found to be undesirable as the organophosphorus compounds eventually convert to phosphate which in turn gives rise to precipitates of insoluble alkaline earth metal phosphate salts by reaction with the soluble calcium present in the water. This precipitation causes rapid depletion of the phosphate in the treatment solution resulting in a decrease in corrosion protection.

In addition, the precipitating solids will scale and eventually plug the passages of the system. This is the case with the use of many of the organic phosphonates such as hydroxyphosphonoacetic acid (HPA) , 1-hydroxyethylidene-

1, 1-diphosphonic acid (HEDPA) or 2-phosphonobutane-l, 2, 4- tricarboxylic acid (PBTC) and other organophosphonates. Prior Art

U.S. Patent No. 4,759,864 describes the use of C₆-Ci2 aliphatic monobasic acids or their alkali metal salts in automotive antifreeze formulations. U.S. Patent No. 5,269,956 is directed to corro¬ sion inhibiting compositions including potassium, an aliphatic monocarboxylate having at least 5 carbon atoms, hydrocarbyl triazole and one or more of the group of sili¬ cates, phosphates or borates useful in heat transfer fluids, antifreezes and for corrosion inhibition in motor vehicle engines.

In U.S. Patent No 4,851,145 the combination of alkylbenzoic acid with monobasic and dibasic fatty acids is disclosed for use in corrosion inhibiting antifreeze formulations. Canadian Patent No. 1,118,990 describes corrosion inhibitors for closed water systems comprising at least one molybdate and at least one amine such as morpholine and ethylenediamine. There may also be present a supplementary inhibitor such as benzotriazole, sodium polymethacrylate or a copolymer of a sulphonatated polystyrene and malic anhydride.

Canadian Patent No. 1,116,026 relates to inher¬ ently bactericidal metal working fluids having corrosion inhibiting activity composed of boric acid, an alkali tetraborate, an alkanol amine, pelargonic acid, a non¬ ionic surfactant and water. The compositions are metal working fluids and for this application must be used in such high concentration as would render them unsuitable for large scale closed water treatment systems. Several of the above-noted references disclose the use of monobasic fatty acids and dibasicarboxylic acids. The sole reference directed to closed water systems (Canadian Patent 1,118,990) however does not, but rather teaches the use of a combination of molybdate and amine as a corrosion inhibitor for closed water systems. The references dealing with fatty acid and dicarboxylic - acid use teach their use in automative antifreezes and metal-working fluids where they are used in much higher concentrations than that taught herein.

Water treatment for closed water systems has different requirements as compared to water treatment applicable to automotive internal combination engines or metal working or antifreeze applications and the common practices of the latter are not applicable to the former.¹

It is the object of the instant invention to provide a corrosion inhibiting concentrate formulation for closed water systems, an aqueous corrosion inhibiting system produced therefrom by dilution with water which contains no phosphates, molybdates, chromates, hydrazine, high solids content, nitrites, etc., yet which remains effective in preventing corrosion of a variety of metals in both static and active, i.e., flowing liquid conditions and to provide a method for corrosion protection for various metals and processes involving industrial, commer¬ cial and institutional closed water systems which avoids the disadvantages of the heretofore available methods . Summary of the Invention The present invention is directed to a method for inhibiting metal corrosion in a closed water treatment system by supplying to and maintaining therein an effective amount of at least one water soluble fatty acid salt selected from salts having the formulae

The NALCO Water Handbook, sec. ed. McGraw-Hill 1988, Chapter 37, pp. 37.1-37.13. Betz Handbook of Indu¬ strial Water Condi tioning, 7th ed. , 1976, Chapter 26, pp. 185-191 and pp. 223-225. RCOOX and R¹ (COOX) _n

wherein R is straight or branched chain alkyl having at least 6 carbon atoms and preferably 6 to 18 carbon atoms or hydroxyalkyl having at least 6 and preferable 6 to 18 atoms, X is a cation such as ammonium, alkali metal, amine or any other basic compound which forms a salt with the fatty acid, R¹ is alkyl or hydroxyalkyl having at least 2 carbon atoms and preferably 2 to 18 carbon atoms and n is 2 or 3 and optionally at least one additive which may be a corrosion inhibitor, selected from the group of alkali metal borates, alkali metal molybdates, hydrocarbyl triazoles, silicates, morpholine, ethylenediamine, pyridine and pyrrolidine.

Typical straight chain alkyl groups are hexyl, octyl, decyl, nonyl dodecyl, hexadecyl and octadecyl. Examples of branched chain alkyl groups include ethylhexyl, trimethylhexyl, and ethylnonyl. The hydroxy alkyl groups are analogous to the aforenoted alkyl groups except for the presence of the hydroxy groups. While monohydroxyalkyl groups predominate, dihydroxyalkyl groups such as in malic acid and tartaric acid and trihydroxyalkyl groups are equally suitable. Mixtures of two or more of the salts of the various acids can also be used.

The acids are used in the form of their water soluble salts i.e., X in the formulae is a salt forming cation. Illustrative salts are the sodium, potassium. lithium, ammonium and amine salts. Particularly useful salts include the alkali metal, ammonium, alkylolammonium (e.g. monoethanol ammonium or triethanol ammonium salts) . When X is an amine, it corresponds to the formula ( R ) ₃N

wherein each R¹¹ is independently hydrogen, Cι_ι₀ alkyl or C₂-ιo hydroxyalkyl. When each of R¹¹ is hydrogen, the cation is ammonium. (R^ι:L)₃N can also be a primary, secondary or tertiary monoamine. In some instances at least one of R¹¹ is di- or tri- (hydroxyalkyl) and (R^1:I)₃N is then for example diethanolamino, diethylaminoethanol or triethanolamino. (R¹¹) can also be designate an alicyclic group as for example cyclohexylamino, cyclopropylamino, and cyclopentylamino. (R¹¹)₃N can also represent a heterocyclic group as for example morpholino, pyridino, pyrrolidino and the like. The salts of dicarboxylic and tricarboxylic acids which are used in formulating the corrosion inhibitors of the present invention are represented by the formula R¹(COOX)_n, wherein X has the meaning as set forth above and R¹¹ is straight or branched chain alkyl having 2 or more carbon atoms and preferably not more than 18 carbon atoms . Illustrative examples of straight chain alkyl are ethyl, propyl, butyl, pentyl, hexyl, octyl, onyl, decyl, undecyl, dodecyl, hexadecyl and octadecyl and of the branched chain alkyl are ethylhexyl, trimethylhexyl, and the like. Illustrative of hydroxyalkyl groups are hydroxyethyl, hydroxypropyl, hydroxyhexyl and the like.

Illustrative instances of acids preferred for use herein include: valeric, caproic, caprylic, capric, pelargonic, heptanoic, octanoic, isovaleric, 2-ethyl- hexanoic, nonanoic, sebacic, dodecanedioic, neodecanoic, succinic, undecanedioic, isononanoic, trialkylacetic, tartaric acid, palmitic, stearic, malic, citric, malonic, glutaric and adipic, and the like.

The corrosion inhibiting compositions of the invention are water soluble and can be used in the form of aqueous compositions including therein a substantial percentage of water. More particularly, they can be utilized per se or in the form of concentrates to be diluted with water on site.

In accordance with the invention the aqueous system has incorporated therein a corrosion inhibiting amount of at least one of the above described monocaboxylic and/or dicarboxylic acid salts. A corrosion inhibiting amount preferably is from about 1 part to about 1000 parts of corrosion inhibitor per million parts of the aqueous treatment system, more preferably about 50 parts to about 500 parts and most preferably about 300 parts of corrosion inhibitor per million parts of the aqueous treatment system.

The aqueous systems of the present invention also can contain other additives, singly or in combination to help reduce corrosion, and include additives such as alkali metal hydroxides, benzoates, silicates, nitrates, molybdates, hydrocarbyl triazoles and the like.

The triazole component may be any hydrocarbyl triazole such as tolyltriazole 2-methylbenzotriazole, mercaptobenzotriazole and benzotriazole.

The borate can be a tetraborate such as sodium tetraborate, also known as borax, potassium tetraborate and mixtures thereof, boric acid, or an alkali metal borate such as potassium borate.

The silicate component must be water soluble and may be one or mixtures of the following: sodium- metasilicate pentahydrate, sodium-metasilicate nonahydrate, sodium orthosilicate pentahydrate, anhydrous sodium silicate and the like.

The nitrate component typically is an alkali metal nitrate such as potassium nitrate. The molybdate is also typically an alkali metal molybdate such as sodium molybdate.

In addition, different anti-scaling and dispers¬ ing polymers, copolymers, terpolymers and tetramers of acrylic acid may be present in the aqueous treatment solution. Illustrative of the monomer groups which can be present are those derived form maleic anhydride, sulphonated styrene, AMPS, polymethacrylate(s) and hydro- lyzed polyacrylamides. This type of additive is well known to the art for their ability to: (1) inhibit, retard or prevent objectionable scale formation on high temperature heat exchange surfaces, as would be likely to occur in hot water heating systems using unsoftened make-up water, and

(2) retard crystal growth of calcium, magnesium and iron deposits. Such crystalline deposits are particularly detrimental to the performance of pump seals and heat exchange surfaces.

The polymers or copolymers are water soluble and include without limitation the water soluble salts of copolymers of acrylic acid and maleic acid including for example, the alkali metal, ammonium and substituted ammonium salts. Soluble acrylate/maleate copolymers of this type are known materials and are described in European Patent Application No. 66915 published Dec.l, 1982.

Other conventional additives may additionally be present such as nitrite, borate - nitrite, chromate, amines, hydrazine, phosphate and phosphonate compounds, however their inclusion may not be desirable for the reasons noted earlier.

The optional components generally represent less than about 200 ppm, preferably about 15 to about 100 ppm of the components introduced into the closed water treatment system and in the concentrate, from about 1 to about 40%, preferably 5 to 20% by weight of the other non aqueous components.

The preferred composition for the method of the invention comprises:

(a) from about 1 to about 30% by weight of at least one of the water soluble monocarboxylic acids R COOX and water soluble dicarboxylic acids R¹(COOX)_n wherein R, R¹, n and X are as previously defined. (b) from 0% to about 40% by weight of at least one of alkali metal hydroxides, benzoates, silicates, ni¬ trates, molybdates, hydrocarbyl triazoles, acrylic polymers and copolymers,

(c) the balance of the composition comprising water The method of the invention is practiced by introducing into the water of a closed system such as the HVAC system of a building complex and maintaining therein an amount of the composition effective to inhibit corro¬ sion of metal in that water environment. The materials are either mixed together and added to the water or are mixed together and added to a relatively small amount of water to form a concentrate which is then added to the water in the system.

The following examples more fully describe the corrosion inhibitor compositions the invention and illus¬ trate how they are used. These examples are merely illus¬ trative of the invention and should not be construed as limiting in any way the scope thereof. EXAMPLE 1: STATIC SOLUTION CORROSION TESTS (TABLES 1 TO 4)

The water used was tap water from Lake Ontario. All tests contained a buffering amount of the amine morpholine or sodium metaborate. These tests were all initially at a pH of about pH 9.4. The beakers were open to air and any liquid loss was made up with deionized water so that no additional salts were introduced. Metal test coupons were submerged and allowed to sit in this treated tap water in open beakers at room temperature for approximately one month at which time the submerged metal coupons were removed and the corrosion rate was determined and expressed as metal loss penetration in thousandths of inches (mils) per year (MPY) . ASTM procedure D2688-90 was followed in the preparation, processing and MPY determinations of the metal coupon test pieces. All of the metal test pieces were of the same size and dimensions and of the same metallurgy. ASTM 1010 mild steel was used. The lower the MPY value achieved the more success¬ ful the corrosion inhibitor. Realizing a low corrosion rate is most desirable for the mild steel test piece because closed systems are primarily constructed using this grade of steel for the piping. The corrosion rate was also tested using aluminum and copper as corrosion of these metals is also an issue in closed systems. All of the monocarboxylic, dicarboxylic and tricarboxylic acid materials used were neutralized with the appropriate amount of sodium or potassium hydroxide to obtain a neutralized salt in solution. Morpholine or sodium metaborate was then added to obtain a pH of 9.4 which was the standard test pH and used for all the tests. Maintaining the same pH for all of the tests is important as it is well known that the pH of an aqueous solution significantly affects the corrosivity to metals especially in the case of mild steel.

Table 1 shows the results of static beaker corrosion tests which contained the recited level of ingredients and which included linear C₆, C₈, and do fatty acid, (caproic, caprylic and capric) and other inhibitors as indicated.

Table 1 also provides the corrosion values obtained with the known morpholine plus sodium molybdate based inhibitor treated water and of morpholine alone. 225 ppm morpholine was used in the test as this was the quantity required to obtain a pH of 9.4 in this test protocol. If the tap water was left at its normal pH of 7.5, the mild steel corrosion rate would be approximately 10 MPY over this time period, A corrosion rate of less than 1 MPY on the steel piece is most desirable.

The mixture of caproic, caprylic, capric acid (C₆, C₈, Cio respectively) was used as it is a readily available material. From Table 1, it can be appreciated that corro¬ sion inhibition on the mild steel and the aluminum test coupons is realized with an increasing concentration of these fatty acids. An effective total dosage of between 50 and 345 ppm of these fatty acids gives excellent corrosion inhibition on steel and aluminum at the de¬ scribed static conditions. As mentioned previously, obtaining corrosion inhibition at static (no flow) conditions is extremely desirable and is difficult to obtain with many other corrosion inhibitors. TABLE 1 STATIC CORROSION INHIBITION USING WATER SOLUBLE FATTY ACID SALTS

TEST # CONCENTRATION OF COMPO¬ MPY MPY MPY CORRO¬ NENTS ON ON SION RATE ON

MILD ALU¬ COPPER STEEL MINUM

1 _**

225 ppm morpholine 4.3 n.t 0.33

2 1.5 ppm caproic acid 2.5 1.3 0.05 28 ppm caprylic acid 20 ppm capric acid

225 ppm morpholine 15 ppm tolyltriazole

3 3 ppm caproic acid <0.03 1.4 <0.02 56 ppm caprylic acid 40 ppm capric acid 270 ppm morpholine 15 ppm tolyltriazole

4 6 ppm caproic acid <0.03 0.55 <0.02 112 ppm caprylic acid

80 ppm capric acid 300 ppm morpholine

15 ppm tolyltriazole

5 10 ppm caproic acid <0.03 0.3 <0.02 193 ppm caprylic acid 224 ppm capric acid 300 ppm morpholine

15 ppm tolyltriazole

6 300 ppm morpholine 0.14 0.01 n.t 195 ppm sodium molyb¬ date dihydrate (Na₂Mo0₄.₂H₂θ) 15 ppm tolyltriazole

n t. not tested Table 2 describes tests carried out with the water adjusted to pH 9.4 with sodium metaborate. This was done to establish if this practical buffering method had any significant effect on corrosion rates when using fatty acids. The corrosion inhibition by the C₈ and Cι₀ fatty acid mix is slightly inferior in the sodium metaborate pH adjusted solutions compared to the morpholine pH adjusted solutions. Example 11 establishes that citric acid, a tricarboxylic acid, is an effective corrosion inhibitor for mild steel. It is to be noted that increased corro¬ sion inhibition could be realized by increasing the fatty acid salt concentration.

TABLE 2: STATIC CORROSION INHIBITION WITH WATER SOLUBLE

FATTY ACID SALTS

TEST # CONCENTRATION OF COM¬ MPY ON MPY MPY PONENTS MILD ON CORRO¬

STEEL ALU¬ SION MINUM RATE ON COPPER

7 1.5 ppm caproic acid 3.3 1.8 0.04 28 ppm caprylic acid 20 ppm capric acid

180 ppm Na₂B₂θ₄.4H₂0 15 ppm tolyltriazole

8 3 ppm caproic acid 0.08 1.4 <0.02 56 ppm caprylic acid 40 ppm capric acid 210 ppm Na₂B₂θ₄.4H₂0 15 ppm tolyltriazole

9 6 ppm caproic acid <0.03 0.7 <0.02 112 ppm caprylic acid

80 ppm capric acid 210 ppm Na₂B₂θ₄.4H₂0

15 ppm tolyltriazole

10 10 ppm caproic acid <0.03 0.7 <0.02 193 ppm caprylic acid 224 ppm capric acid 210 ppm a₂B₂θ₄.4H₂0 15 ppm tolyltriazole

11 345 ppm citric acid 0.18 n.t. n.t.

15 ppm tolyltriazole

TABLE 3 shows the corrosion inhibiting proper¬ ties of various concentrations of various other monocarboxylic fatty acids using the same static condi¬ tions described in Table 1. Table 3 demonstrates the efficacy of these various fatty acids. The fatty acid concentration in all of these tests was 345 parts per million.

Comparing the data in Tables 1 to 3, it can be seen that some fatty acids are more effective than others.

In general, the trend indicates a longer fatty acid carbon chain yields more effective steel and aluminum corrosion inhibition.

TABLE 3

TEST CONCENTRATION OF MPY ON MPY ON MPY CORROSION COMPONENTS MILD ALUMI¬ RATE ON COP¬ #

STEEL NUM PER

12 345 ppm pelargonic acid 0.02 0.3 0.02 300 ppm morpholine 15 ppm tolyltriazole

13 345 ppm heptanoic acid 1.7 0.96 <0.02 300 ppm morpholine 15 ppm tolyltriazole

14 345 ppm isovaleric acid 3.3 0.89 <0.02 300 ppm morpholine 15 ppm tolyltriazole

15 345 ppm isononanoic 1.67 1.0 <0.02 acid

300 ppm morpholine 15 ppm tolyltriazole

Table 4 sets forth the corrosion rates obtained using various pure dicarboxylic acids, commercially available mixtures of dicarboxylic acids and mixtures of dicarboxylates and monocarboxylates. A comparative 345 ppm concentration of the mixed and pure dicarboxylic acid and of the mixtures of various mono dicarboxylic acids was used.

A commercially available mixture of, primarily, three dicarboxylic acids, comprising 36% dodecanedioic acid 41% undecanedioic acids, 7% sebacic acid and 13% other dibasic acids was employed in the test reported in Table 4. From the data in Table 4, it can be seen that this combination of dicarboxylic acids is an extremely effective static corrosion inhibitor for steel at a rela- tively low concentration and is synergistic in its perfor¬ mance compared to various pure dicarboxylic and monocarboxylic acids.

From the data reported in Tables 3 and 4, it can also be appreciated that there is an unexpected synergistic corrosion inhibition when sebacic acid and isononanoic acid (3,5, 5-trimethylhexanoic acid) are combined.

Very desirable static corrosion inhibition is also seen when mixtures of sebacic acid and commercially available trialkyl acetic acids in which each hydrogen of the acetic acid has been replaced by an alkyl group were tried. The resulting quaternary alpha carbons of these acids and all of their derivatives are reported to have a much higher thermal, oxidative and hydrolytic stability compared to the linear fatty acids. The combination used in Test #21 mixture of neodecanoic acids with, primarily, 10 carbon atoms. The acids used in Text #20 a mixture of acids having from 9 to 13 carbon atoms.

Tests 22 and 23 utilized 50 and 100 ppm tartaric acid concentrations respectively. The salt of this dicarboxylic acid is also a very good static corrosion inhibitor especially at the higher 100 ppm concentration. TABLE 4

TEST CONCENTRATION OF MPY ON MPY ON MPY CORRO¬

COMPONENTS MILD ALUMI¬ SION RATE

#

STEEL NUM ON COPPER

16 345 ppm sebacic acid 2.8 3.3 <0.02 300 ppm morpholine 15 ppm tolyltriazole

17 100 ppm dodecanedioic acid 2.4 n.t. n.t. 270 ppm morpholine 15 ppm tolyltriazole

18 100 ppm acid mixture^* <0.02 n.t. n. t. 270 ppm morpholine 15 ppm tolyltriazole

19 100 ppm sebacic acid 0.02 0.67 <0.02 245 ppm isononanoic acid 300 ppm morpholine 15 ppm tolyltriazole

20 261 ppm acid mixture^** <0.02 n.t. n. . 84 ppm sebacic acid

300 ppm morpholine 15 ppm tolyltriazole

21 261 ppm acid mixture^*** <0.02 n.t. n.t. 84 ppm sebacic acid

300 ppm morpholine 15 ppm tolyltriazole

22 50 ppm tartaric acid 3.1 0.65 0.02 300 ppm morpholine 15 ppm tolyltriazole

23 100 ppm tartaric acid 0.3 0.53 <0.02 300 ppm morpholine 15 ppm tolyltriazole

Mixture of dodecanedioc, undecanedioc and sebacic acids.

Mixture of neodecanedioic acids having from 9 to 13 carbon atoms.

Mixture of neodecanedioic acids having primarily 10 carbon atoms. EXAMPLE 2: HOT WATER TEST RIG

It is very desirable for the closed system treatment to be able to maintain its efficacy at elevated water temperatures of up to 100° Celsius. Test evaluations at a water temperature of 80° celsius were carried out to investigate the carboxylic acid compound(s) performance at this water temperature. The tests were carried out on a small seven liter internal volume recirculating system loop which was constructed from 1 inch internal diameter ASTM 316 stainless steel piping. Lake Ontario tap water was always used as the water source. This hot water was recirculated across the metal test pieces at one foot per second velocity. The hot water temperature was achieved by flowing the water across a stainless steel immersion heater, which had its heating capacity controlled using a rheostat. The metal test pieces and the MPY determinations were carried out as described in Example 1.

The test exposure period for the metal test pieces was approximately three days. Tables 5 and 6 set out the test results using various water treatments and concentrations of the mono- and dicarboxylic acids and mixtures of these acids using the hot water test rig described above. Tests conducted utilizing the above described hot water test rig and using untreated Lake Ontario water yielded a mild steel corrosion rate of greater than 20 MPY on the standard test pieces . Treatment yielding less than one MPY on the steel piece are desirable.

As set forth with respect to Example 1, the carboxylic acids are neutralized with the appropriate amount of sodium or potassium hydroxide to yield a neutral solution pH and then the appropriate amount of morpholine or metaborate is added to obtain a final solution pH of 9.4 at room temperature.

Test 24 shows the corrosion rate obtained on this test rig using a known, existing commercial closed system formulation.

From the results in Tables 5 and 6 it appears obvious that many dicarboxylic and monocarboxylic acids and their mixtures are effective steel corrosion inhibi- tors in a closed system.

TABLE 5: HOT WATER TEST RIG RESULTS

TEST # CONCENTRATION OF MPY ON MPY ON MPY COMPONENTS MILD ALUMINUM CORROSION

STEEL RATE ON COPPER

24 150 ppm morpholine 0.6 44 0.15 105 ppm a₂B₂θ₄.4H₂0 195 ppm Na₂Mo0₄.2H₂0 9 ppm tolyltriazole

25 51 ppm tartaric acid 0.3 76 <0.15 300 ppm morpholine 15 ppm tolyltriazole

26 300 ppm morpholine <0.1 14 <0.15 204 ppm tartaric acid 15 ppm tolyltriazole

27 100 ppm tartaric acid <0.1 44 n.t.

10 ppm caproic acid 193 ppm caprylic acid 224 ppm capric acid 300 ppm morpholine 15 ppm tolyltriazole

28 10 ppm caproic acid 0.6 52 0.15 193 ppm caprylic acid 224 ppm capric acid 300 ppm morpholine

15 ppm tolyltriazole

29 6 ppm caproic acid 0.6 4.4 n.t 113 ppm caprylic acid

80 ppm capric acid 300 ppm morpholine

15 ppm tolyltriazole

TABLE 6: HOT WATER TEST RIG RESULTS

TEST CONCENTRATION OF MPY MPY MPY CORRO¬ # COMPONENTS ON ON SION RATE

MILD ALU¬ ON COPPER STEEL MINUM

30 270 ppm morpholine 0.2 23 0.18 200 ppm acid mixture^* 15 ppm tolyltriazole

31 300 ppm morpholine 2.0 22 0.18 100 ppm isononanoic acid 100 ppm acid mixture* 15 ppm tolyltriazole

32 216 ppm Na₂B₂θ₄.4H₂0 0.2 42 <0.15 204 acid mixture* 15 ppm tolyltriazole

33 270 ppm morpholine 1.9 18 <0.15 102 ppm acid mixture* 15 ppm tolyltriazole

34 108 ppm a₂B₂θ₄.4H₂0 0.8 18 0.21 102 ppm acid mixture* 15 ppm tolyltriazole

35 300 ppm morpholine 0.1 20 <0.15 345 ppm acid mixture* 15 ppm tolyltriazole

36 210 ppm Na₂B₂θ₄.4H₂0 0.2 35 0.20 345 ppm acid mixture* 15 ppm tolyltriazole

Mixture of dodecanedioic, undecanedioic and sebacic acids.

Claims

1. Method for inhibiting metal corrosion in a closed water system such as is found in industrial, commercial and institutional installations, which comprises introducing into and maintaining in the water of such a system, an effective amount of at least one water soluble fatty acid salt selected from the group of salts having the formulae

RCOOX and R¹(COOX)_n wherein R is straight or branched chain alkyl having at least 6 carbon atoms or mono-, di-, or tri-hydroxyalkyl having at least 6 carbon atoms, X is selected from the group consisting of ammonium, alkylolammonium, alkali metal and amine cations, R¹ is alkyl having at least 2 carbon atoms or mono-, di-, or tri-hydroxyalkyl having at least 2 carbon atoms and n is 2 or 3.

2. Method according to claim 1 wherein R is straight or branched chain alkyl or mono-, di-, or tri- hydroxyalkyl, each alkyl having from 6 to 18 carbon atoms.

3. Method according to claim 1 wherein R¹ is straight or branched chain alkyl or mono-, di, or tri- hydroxyalkyl, each having from 2 to 18 carbon atoms.

4. Method according to claim 1 which comprises introducing into and maintaining in the water of said system at least one other additive selected from the group consisting of alkali metal borates, alkali metal molybdates, hydrocarbyl triazoles, alkali metal silicates, amines and acrylic and methacrylic polymers.

5. Method according to claim 4 wherein said amine is selected from the group consisting of ethylenedi- amine, morpholine, pyridine and pyrrolidine.

6. Method according to claim 1 wherein X has the formula

(Rⁿ)₃N wherein each R¹¹ is independently selected from the group consisting of hydrogen, Ci-Cio alkyl, C₂-Cι₀ hydroxyalkyl, and cycloalkyl, and when R¹¹ is taken together with the nitrogen atom to which they are attached, (R )₃N is a heterocyclic moiety.

7. Method according to claim 6 wherein said heterocyclic moiety is a member selected from the group consisting of morpholino, pyridino, and pyrrolidino.

8. Method according to claim 1 wherein each of said salts is the same or a different member selected from the group consisting of metal salts, ammonium salts, and alkylolammonium salts.

9. Method according to claim 1 wherein said fatty acid salt is a salt of an acid selected from the group consisting of valeric caproic, caprylic, capric, pelargonic, heptanoic, octanoic, isovaleric, 2- ethylhexanoic, nonanoic, succinic, dodecanedioic, neodecanoic, undecanedioic, isononanoic, trialkylacetic, palmitic, stearic, malic, citric, malonic, glutaric and adipic acids.

10. Method according to claim 1 wherein said fatty acid salt is maintained in said system in an amount of from 1 part to about 1000 parts of said salt per about one million parts of water.

11. Method according to claim 1 wherein said fatty acid salt is maintained in said system in an amount of about 50 to about 525 parts of said salt per about one million parts of water.

12. Method according to claim 1 wherein said fatty acid salt is maintained in said system in an amount of about 300 parts of said salt per about one million parts of water.

13. Method according to claim 1 which comprises additionally maintaining in said system an effective amount of at least one member selected from the group consisting of anti-scaling agents and dispersing agents.

14. Method according to claim 4 which comprises maintaining said alkali metal borate in said system in an amount of about 100 to about 210 parts per million parts of water.

15. Method according to claim 4 which comprises maintaining said hydrocarbyl triazole in said system in an amount of about 15 parts per million parts of water.

16. Method according to claim 4 which comprises maintaining said amine in said system in an amount of about 240 to about 300 parts per million parts of water.

17. Method according to claim 4 which comprises as a first step forming an aqueous concentrate comprising at least one water soluble fatty acid salt as defined in claim 1, at least one member selected from the group consisting of alkali metal borates, alkali metal molybdates, hydrocarbyl triazoles, silicates, amines, and acrylates and water.

18. Method according to claim 4 which comprises introducing into said system a mixture of salts of caproic acid, caprylic acid and capric acid, morpholine and tolyltriazole.

19. Method according to claim 4 which comprises introducing into said system a mixture of the salts of caproic acid, caprylic acid and capric acid, sodium borate and tolyltriazole.

20. Method according to claim 4 which comprises introducing into said system a mixture of the salt of pelargonic acid, morpholine and tolyltriazole.

21. Method according to claim 4 which comprises introducing into said system a mixture of the salt of heptanoic acid, morpholine and tolyltriazole.

22. Method according to claim 4 which comprises introducing into said system a mixture of the salts of sebacic acid and isononanoic acid, morpholine and triazole.

23. Method according to claim 4 which comprises introducing into said system a mixture of the salt of tartaric acid, morpholine and tolyltriazole.

24. Method according to claim 4 which comprises introducing into said system a mixture of the salts of tartaric acid, caproic acid, caprylic acid and capric ac¬ id, morpholine and tolyltriazole.

25. Method according to claim 4 which comprises introducing into said system a mixture of morpholine, a mixture of neodecanedioc acids having 9 to 13 carbon atoms and tolyltriazole.

26. Method according to claim 4 which comprises introducing into said system a mixture of Na₂B₂θ .4H₂0, a mixture of decanedioic, undecanedioic and sebacic acids and tolyltriazole.

27. Method according to claim 4 which comprises introducing into said system a mixture of the salts of neodecanoic acids having from 9 to 13 carbon atoms, the salt of sebacic acid, morpholine and tolyltriazole.

28. Method according to claim 4 which comprises introducing into said system a mixture of the salts of neodecanoic acids having primarily 10 carbon atoms, the salt of sebacic acid, morpholine and tolyltriazole.

29. Method according to claim 4 which comprises introducing into said system an amount of fatty acid salt sufficient to provide a concentration of about 1 to about 1000 ppm of said fatty acid salt per one million parts of water and of said additive of about 15 to about 500 parts per one million parts of water.

30. A concentrate for inhibiting metal corrosion in a closed water system such as is found in industrial, commercial and institutional installations having a concentration of a fatty acid salt as defined in claim 1 sufficient to provide about 50 to about 500 parts of said salt per one million parts of water in said system and from about 15 to about 500 parts per million parts of water in said system of at least one additive selected from the group consisting of alkali metal borates, alkali metal molybdates, hydrocarbyl triazoles, alkali metal silicates, amines and polymeric dispersants, in water.