FIELD OF THE INVENTION The present invention relates to methods of inhibiting the corrosion of metallic surfaces of water- carrying systems, and to compositions for use in such a method, particularly in which the water of the system is oxygen bearing. More particularly, the present invention relates to the use of compositions in the presence of sodium chloride and/or calcium chloride brine systems.

BACKGROUND OF THE INVENTION Oxygen corrosion is, of course, a serious problem in any metal-containing aqueous system. The corrosion of iron and steel is of principal concern because of their extensive use in many types of industrial and municipal water systems. However, corrosion of copper and copper containing metals is also of concern and many systems use a combination of metals.

Brines are used in various industrial applications.

Of particular interest are the brines used in the cooling systems or chillers, as these are widely known. These systems are supposed to be closed loop but in practice due to leaks and operational requirements, they are practically oxygen saturated. These systems are, very aggressive for corrosion, and thus corrosion control is necessary.

Brine cooling systems, such as calcium chloride, sodium chloride and lithium chloride brines, have unique

corrosion problems, with sodium chloride and lithium chloride brine systems being particularly agressive towards carbon steel. If corrosion control is not used, piping and other components must be changed frequently.

In the past, generally, chromate-based products were used to inhibit corrosion in these brine systems. Chromates are soluble in these concentrated solutions and provide good corrosion protection. Subsequently, it was determined that chromium-containing products are hazardous to the environment and their use is being discontinued.

Replacement of chromates brine systems with alternatives is an ongoing process. Molybdates have been used but they are less cost-effective corrosion inhibitors. Nitrites have also been used, at very high concentrations.

A composition known as Belcor 575 is 2- hydroxyphosphono-acetic acid (HPA), is disclosed and available from Ciba Geigy. This product is a known corrosion inhibitor as disclosed in U. S. Patent No.

5,068,059. This product, HPA, is also known as a corrosion inhibitor in brines as disclosed in U. S. Patent Nos. 4,606,890 (Example 25) and 5,292,455, the disclosures of which are incorporated herein by reference in their entirety.

There are very many compositions that are known corrosion inhibitors for steel and other metals but are not known to be very effective in brine systems. For example, 2-phosphonobutane-1,2,4 tricarboxylic acid (PBTC), is disclosed in U. S. patent numbers: 3,886,207; 3,933,427; and 4,026,815.

Phosphonocarboxylic acid (POCA), is also known and <BR> <BR> <BR> <BR> is specifically phosphonate [ (acrylic acid) x ( AMPS) Y] n copolymer, such as Belclene 494 (AMPS is 2 acrylamido-2-

methylpropyl sulfonic acid). Also known is a similar product to POCA known as Bricorr 288, a polycarboxylic acid with a phosponate end cap that is a homopolymer (POCA homopolymer). These are known corrosion inhibitors in general applications but not in brine systems.

Azoles are also known corrosion inhibitors, such as the mercapto benzotriazoles (MBT), benzotriazoles (BT), tolyltriazoles, and mixtures thereof. Specific tolyltriazoles are the hydrogenated tolyltriazoles (e. g.

Cobratec 928) and sodium tolyltriazoles (NaTT).

There is still a need for improved corrosion inhibitors for brine systems, such as sodium chloride, lithium chloride, and calcium chloride brine systems, particularly cost effective ones.

SUMMARY OF THE INVENTION Disclosed in a first aspect of the present invention I) is a blend composition useful to inhibit the corrosion of metal surfaces that comprises; a) an effective amount of 2-phosphonobutane-1,2,4 tricarboxylic acid (PBTC) and b) an effective amount of hydroxyphosphono-acetic acid (HPA).

Disclosed in a second aspect of the present invention II) is a blend composition useful to inhibit the corrosion of metal surfaces that comprises ; a) an effective amount of a phosphono carboxylic acid homopolymer (POCA homopolymer) and b) an effective amount of a compound selected from the group consisting of 2- phosphonobutane-1,2,4 tricarboxylic acid (PBTC), hydroxyphosphono-acetic acid (HPA), and mixtures thereof.

Disclosed in a third aspect of the present invention III) is a blend composition useful to inhibit the corrosion of metal surfaces that comprises; a) an

effective amount of a phosponocarboxylic acid copolymer (POCA copolymer) and b) an effective amount of hydroxyphosphono-acetic acid (HPA).

The above compositions are also useful-in the process of corrosion inhibition in various brine systems, such as sodium chloride, lithium chloride, and calcium chloride brine systems.

Another aspect of the present invention for use in non-calcium chloride brine systems comprises a corrosion inhibitor and a small amount of calcium ions (preferably about 40ppm or more as calcium chloride), optionally in the presence of an azole. Wherein, the corrosion inhibitor is selected from the group consisting of PBTC, HPA, PAPEMP (polyamino polyether methylenephosphonate i. e. TRC-289), POCA homopolymer, and POCA copolymer. The small amount of calcium ions added to the system helps the corrosion inhibitor function as a corrosion inhibitor. Thus, when either corrosion inhibitor is used in non-calcium chloride brine systems it is combined with an amount of calcium ions to provide enhanced corrosion inhibition in the brine system.

DETAILED DESCRIPTION OF THE INVENTION The inventors have unexpectedly discovered various blend compositions that are very useful in the inhibition of corrosion of metal surfaces. These blend compositions are particularly useful in the metal corrosion inhibition of brine systems, such as sodium chloride and calcium chloride brine systems. The inventors have unexpectedly discovered very useful replacements of chromates in brine systems.

The inventors have also unexpectedly discovered that each of the above inhibitors, by themselves, provide improved corrosion inhibition to non-calcium chloride

brine systems when a small amount of calcium ions is added to the system (about 40ppm or more). Thus, when either PBTC, HPA, PAPEMP, POCA homopolymer, or POCA copolymer are combined with an amount of calcium ions in brine systems (e. g. sodium chloride and lithium chloride brine systems) improved corrosion inhibition is achieved.

A further improvement in corrosion inhibition is seen when a third component is added, either TTNa or Cobratec 928.

When treating these non-calcium chloride brines with the corrosion inhibitors of this last aspect of the present invention, the calcium ions are preferably added in the form of calcium chloride. The amount of calcium ions added or present in these systems is generally at least about 40ppm, preferably about 50 to 1000ppm, more preferably about 50 to 600ppm, with an amount of about 100 to about 300ppm calcium ions being most preferred.

Thus, the composition of the present invention that is useful to inhibit the corrosion of metal surfaces comprises; a blend selected from the group consisting of: I.) a) an effective amount of 2-phosphonobutane- 1,2,4 tricarboxylic acid (PBTC) and b) an effective amount of hydroxyphosphono-acetic acid (HPA); II.) a) an effective amount of a phosphonocarboxylic acid homopolymer (POCA homopolymer) and b) an effective amount of a compound selected from the group consisting of (PBTC), (HPA), and mixtures thereof; and III.) a) an effective amount of a phosponocarboxylic acid copolymer (POCA copolymer) and b) an effective amount of (HPA).

The composition according to the present invention has a synergistic effect upon the prevention of corrosion of metal surfaces when an effective amount of both a) and

b) are present in the system to be treated, even at very low levels. This amount is preferably at least about 100ppm of the total corrosion inhibitors. Amounts of all corrosion inhibiting compounds can be much higher than this, depending upon desired corrosion prevention levels.

However, due to costs and small incremental corrosion prevention, amounts much above 1000ppm are somewhat less preferred.

The weight ratio of a) to b) in each of the blends can vary significantly, so long as both a) and b) are present. However, this weight ratio of a) to b) preferably varies from about 1: 10 to 10: 1, more preferably at a weight ratio of about 40 to about 60 wt.

% a) and about 40 to about 60 wt. % b), with a ratio of a) to b) of about 50/50 being most preferred.

In the second aspect of the present invention II), the POCA homopolymer of a) is preferably a polycarboxylic acid with a phosponate end cap, more preferably a low molecular weight polymaleic acid, with Bricorr-288 being most preferred. In this aspect II), in which component b) can be a blend of PBTC and HPA, component b) is preferably a blend of PBTC and HPA and preferably in a weight ratio of PBTC to HPA that varies from 1: 10 to 10: 1.

In the third aspect of the present invention III), the POCA copolymer is preferably a low molecular weight phosphonate [ (acrylic acid) x (AMPS) y] n copolymer, such as Belclene 494 (AMPS is 2 acrylamido-2- methylpropyl sulfonic acid). In this phosphonate end capped POCA copolymer, x is preferably about 70 to about 90 wt. % of the monomer units, y is preferably about 10 to about 30 wt. % of the monomer units, and n is an integer between 2 and 50 (more preferably 4 to 20).

The composition according to the present invention preferably contains an azole c), in additional to the components a) and b). The azole of the composition according to the present invention is preferably selected from the group consisting of mercapto benzotriazoles (MBT), benzotriazoles (BT), tolyltriazoles, and mixtures thereof, wherein said tolyltriazoles are preferably selected from the group consisting of hydrogenated tolyltriazoles (Cobratec 928), sodium tolyltriazoles (NaTT), and mixtures thereof. The amount of the azole c) in said blend is preferably present in a concentration of about 1 to about 90 percent by weight.

In the composition according to the present invention the amount of component a) is preferably in a concentration of about 5 to about 90 wt. %, more preferably about 10 to about 89 wt. %, with an amount of about 40 to about 58 wt. % being most preferred. As with component a), component b) is also preferably in a concentration of about 5 to about 90 wt. %, more preferably about 10 to about 89 wt. %, with an amount of about 40 to about 58 wt. % being most preferred. The azole c) is preferably present in the composition, and in an effective amount. This amount is preferably about 1 to about 20 wt. %, more preferably about 2 to about 10 wt. %. Thus, the weight percent of all three components of the blend with respect to each other are preferably present in a concentration of about 10 to about 89 wt. % a), about 10 to about 89 wt. % b), and about 1 to about 20 wt. % of an azole c). This relative concentration is more preferably about 40 to about 58 wt. % a), about 40 to about 58 wt. % b), and about 2 to about 10 wt. % of an azole c). Wherein a concentration of about 48 wt. % a), about 48 wt. % b), and about 4 wt. % azole is most preferred.

The composition according to the present invention, the blend of a) and b), is preferably in a brine ina sufficient amount to inhibit the corrosion of the metal in contact with said brine. This composition is preferably added as a concentrate in a concentration in water and then diluted when added to the system and preferably contains less than 50 wt. % solids, more preferably about 42 wt. % solids.

The composition according to the present invention, the blend of a) and b) and optionally c), is preferably present in an aqueous system in a concentration of about 100 to 1000 ppm by weight. In calcium chloride brines this amount is more preferably about 100 to about 500 ppm, with about 150 to about 300 ppm being most preferred. The concentration of the components present in said aqueous system preferably ranges, with respect to each other from about 10 to about 500 ppm a), about 10 to about 500 ppm b), and about 1 to about 50 ppm of an azole c). This concentration of components is more preferably about 20 to about 300 ppm a), about 20 to about 300 ppm b), and about 5 to about 30 ppm of an azole; with about 50 to about 200 ppm a), about 50 to about 200 ppm b), and about 10 to about 20 ppm of an azole being most preferred.

The composition according to the present invention is a synergistic blend of a) and b), and optional c).

Thus the components a), b) and optional c) of the blend are each present in an aqueous system in a concentration in an amount that results in a synergistic combination such that the corrosion inhibition of a certain concentration of each component, when added together does not equal the actual corrosion inhibition of the equivalent blend of a) and b).

The above compositions are also useful in the process of corrosion inhibition in various brine systems, such as sodium chloride, lithium chloride, and calcium chloride brine systems. Thus, the method of inhibiting the corrosion of metal surfaces according to the present invention comprises; contacting said metal surfaces with an aqueous solution of a blend selected from the group consisting of: I.) a) an effective amount of 2-phosphonobutane- 1,2,4 tricarboxylic acid (PBTC) and b) an effective amount of hydroxyphosphono-acetic acid (HPA); II.) a) an effective amount of a phosphonocarboxylic acid homopolymer (POCA homopolymer) and b) an effective amount of a compound selected from the group consisting of (PBTC), (HPA), and mixtures thereof; and III.) a) an effective amount of a phosponocarboxylic acid copolymer (POCA copolymer) and b) an effective amount of (HPA).

The method according to the present invention for inhibiting the corrosion of metal surfaces in contact with an aqueous system preferably entails adding one or more of the above blends to said aqueous system itself.

In the case of non-calcium chloride brines, one or more of the components is added to the brine system in combination with at least 50ppm calcium ions, preferably in combination with an azole.

The method according to the present invention entails the inhibition of corrosion on metal surfaces, generally a combination of different metals. These above compositions are multi-metal corrosion inhibitors and can protect systems made up of a combination of metals.

These metal surfaces that are contacted with the blend of a) and b) are preferably made of iron, copper, aluminum

and their alloys, such as steel, brass, copper, and combinations thereof. Mild steel and high carbon steel are the most preferred due to significant corrosion inhibition of this metal with preferred blends.

The following examples are intended to illustrate the present invention but should not be considered as a limitation on the reasonable scope thereof.

Examples Experimental: General Set-up: Each closed system corrosion study was performed by immersing a rack of five 1.0 inch by 2.0 inch coupons of varying metallurgies in a glass reaction kettle containing 3.0 L of treated deionized water, and then blanketing the treated deionized water with saturated C02 scrubbed air. The air was fed through a gas sparge tube and an outlet tube was provided to enable a positive pressure of air for oxygen saturation. An Orbisphere Model 26060 Oxygen Analyzer with Sensor 2110 was used to measure the oxygen concentration. The kettles were nestled in a heating mantle connected to a variac. The variac was set to control the temperatures at 65.6° +/- 5°C. The pH was periodically measured, but not controlled.

Measurement of Coupon Corrosion Rates: The coupons were precleaned as outlined in CPT-203- CW,"Methods of Cleaning and Polishing Specimens Before Testing"and then weighed on a five place analytical balance. Next they were placed in an ASTM D1384 corrosion test rack in the following order by metallurgy: carbon steel, stainless steel, 90/20 Cu/Ni, Admiralty brass, and copper. Teflon spacers (3/16 inch) were placed between coupons, and between end coupons and the

brass legs. The center screw was covered with a Teflon insulating sleeve, before the coupons were slipped over it.

Following testing, coupons were recleaned as outlined in CPT-205-CW,"Methods For Cleaning Specimens After Testing"and then reweighed on the five place analytical balance. Corrosion rates are calculated using the weight loss method.

TABLE 1 Corrosion Studies in Calcium Chloride Brine Coupon Corrosion Rates Active Yellow Active Carbon Admiralty 90/10 Steel inhibitor Dose Metal Dose Steel Brass Cu/Ni (mg/L) inhibitor (mg/L) MPY MPY MPY Control None None None 3.7 4.1 0.8 Control None None None 5. 2 6. 0 1. 0 Cr 2000 None None 0. 9 0. 3 0. 5 BricorrTTNa153.13.92.1100 50EachTTNa154.04.81.8TRC-289/Belcor575 Belcor575 100 TTNa 15 3. 0 3. 2 1. 7 TRC-289 100 TTNa 15 3. 3 3. 5 2. 2 Bricorr288/Belcor 575 50 Each TTNa 15 2. 7 2. 6 1. 9 Bricorr288/TRC-289 50 Each TTNa 15 3. 9 4. 3 2. 6 Bricorr288 200 TTNa 30 2. 4 1. 3 1. 7 BelcorTTNa302.30.81.4200 Belcor 575/Bricorr 288 100 Each TTNa 30 2. 1 0. 8 1. 5 Bricorr288/TRC-289 100 Each TTNa 30 3. 0 3. 1 2. 1 Cobratec2003.00.20.4NoneNone 928 Bricorr 288 200 Cobratec 30 2.7 0.7 1.4 928 Belcor 575 200 Cobratec 30 1.7 1.1 1.3 928 Belcor 575/Bricorr 288 100 Each Cobratec 30 2.2 0.6 1.1 928 Bricorr 288/TRC-289 100 Each Cobratec 30 2.7 2.3 1.6 928 PBTC/Belcor 575 100 Each Cobratec 60 1.5 0.8 0.6 928 PBTC/Bricorr 288 100 Each Cobratec 50 2.5 0.5 0.7 928 PBTC 200 Cobratec 50 2.1 1.0 0.8 928 Belclene 494/100 Each Cobratec 50 1.6 1.2 1.2 Belcor 575 928 Belclene494 200 Cobratec 50 3.3 0.8 0.6 928 Belclene 494/100 Each Cobratec 50 2.5 1.0 1.0 Bricorr288 928 Conditions 65 degrees C, pH 8.0 25% Brine 7 days Aeration using air which had been washed with 5% NaOH One carbon steel coupon, one Admiralty brass coupon, and one 9010 CuNi coupon Carbon steel corrater tips

Results: CaCl2 Brine Corrosion Inhibition Studies TABLE 2 Active Dose (mg/L) With Carbon Admiralty 90/10 Inhibitor (s) 15 mg/L TTNa Steel Brass Cu/Ni Cr 2000 0.91 0.30 0.46 Bricorr 288 100 3.1 3.9 2.1 TRC-289/50 each 4.0 4.8 1.8 Belcor 575 Belcor 575 100 3.0 3.2 1.7 TRC-289 100 3.3 3.5 2.2 Bricorr 288/50 each 2.7 2.6 1.9 Belcor 575 Bricorr 288/50 each 3.9 4.3 2.6 TRC-289 Control None 3.7 4.1 0.79

TABLE 3 Carbon Admiralty 90/10 mg/L Actives Steel Brass Cu/Ni 200 Bricorr 288 + 30 TTNa 2. 35 1.25 1.71 200 mg/L Belcor 575 + 2.28 0.77 1.43 30 TTNa 100 Belcor 575 + 2.14 0.77 1.50 100 Bricorr 288 + 30 TTNa 100 Bricorr 288 + 2.95 3.14 2.07 100 TRC-289 + 30 TTNa 200 Bricorr 288 + 2.69 0.73 1.44 30 Cobratec 928 200 mg/L Belcor 575 + 1.71 1.05 1.30 30 Cobratec 928 100 Belcor 575 + 2.15 0.59 1.09 100 Bricorr 288 + 30 Cobratec 928 100 Bricorr 288 + 2.71 2.32 1.63 100 TRC-289 + 30 Cobratec 928 1

The test conditions were: 65°C+/-5°C pH 8.0 25% CaCl2 Test Solution Aeration With Air Which Has Been Washed With NaOH For CO2 Removal 9010 CuNi, Admiralty Brass, And Carbon Steel Coupons Carbon Steel Corrater Tips

The above tables illustrate a significant reduction in corrosion rates in calcium chloride brines for the preferred compositions when compared to the controls (no treatment). Further, the blends show synergism for multi-metal corrosion inhibition when compared to the single components (lower MPY) at adequate dosage, particularly when replacing a portion of the more expensive Belcor 575.

TABLE 4 Corrosion Studies in NaCI Brine (Coupon Corrosion Rates) MPY 25% NaCl + 25% Nazi + 25% NaCI + 25% NaCl + 25% NaCI 50 mg/L Ca+2 100 mg/L Ca+2 200 mg/L Ca+2 600 mg/L Ca+2 Treatment Adm Adm Adm Adm Adm (mg/L Actives) CS Brass CS Brass CS Brass CS Brass CS Brass No Treatment 10.3 13.1 6.1,6. 6 -, 9.1 7. 8 10.3 2000 Chromate 1.4 1. 1 - - 0. 8 2.1 50 TTNa 10. 2 4.8 200 HPA + 13.1 0.7 4.2 1.5 1.7 1.7 2.6 1.1 50TTNa' 500 HPA + 14. 9 3.6 6.1 1.6 2.7 1.0 2.3 1.9 50TTNa 100 HPA + 10.1 1. 8 - - 4. 3 1.4 50 TTNa 200 PBTC + 16.2 2. 8 - - - - 50 TTNa 500 PBTC + 11.8 1.4 - 50 TTNa 200 Bricorr 288 + 10.5 1.7 50TTNa 100HPA+ 11.1 0.7 6.2 1.6 0 7 3.8 2.0 +100PBTC 50 TTNa 250 HPA + 10.2 1.1 4.4 1.8 2.0 1.4 3.4 2.1 250 PBTC + 50TTNa 500 HPA + 12.2 2. 3 - - 2. 7 1.6 500 PBTC + 50 TTNa 100 HPA + 12.7 0.8 100 Bricorr 288 + 50 TTNa 250 HPA + 10.5 2.3 50 Bricorr 288 + 50TTNa 500 HPA + - - - - 3. 4 2.3 500 Bricorr 288 + 50 TTNa 100 HPA + 9.0 1.8 100Belclene 494 + 50 TTNa 250 HPA + 11.6 0.8 250 Beclene 494 + 50 TTNa 288+-6.42.2500Bricorr 500PBTC+ 50 TTNa Conditions: 2.85 L Brine in 3.0 L Resin Kettles pH 8. 0 65°C Aeration

TABLE 5 Corrosion Studies in 25% Lice2 Brine Treatment (mg/L Active) Carbon Steel Admiralty Brass 2.3None9.6 100 HPA + 100 PBTC + 50 TTNA + 100 Ca+2 6.9 0.9 Conditions: 2.85 L Brine in 3.0 L Resin Kettles pH 8. 0 65°C Aeration These tests were carried out in resin kettles.

Heating mantles were used as the heat source. Variacs were used to maintain a 65°C temperature. Condensers were used to maintain the water level. The air was washed with 5% NaOH to remove C02 prior to aeration of the test solution, in order to maintain the pH at 8.0.

The above tables illustrate a reduction in corrosion rates in non-calcium chloride brines for the preferred compositions when compared to the controls (no treatment). Further, the inventive compositions, with the addition of calcium ions, illustrates a significant reduction in corrosion rate (lower MPY).

TABLE 6 Background Information on inhibitors Inhibitor Supplier Structure Bricorr 288 Albright & Wilson H-[NaO2CCH-CHCO2Na] n-PO3Na2 n<5 (50% phosphonocarboxylic Chemical Corp. acidsalts) Belcor 575 (HPA) Great Lakes PO3H2-CH2-COOH (50% hydroxyphosphonoacetic Chemical Corp. acid) Belclene 494 (POCA) Great Lakes [Phosphonate Group]- [ [Carboxylic Acid] % (Phosphonocarboxylic Acid Chemical Corp. [AMPS] y] n Copolymer, 48.8% solids) Bayhibit AM (PBTC) Bayer or Calloway H2CCOOH-PO3H2CCOOH-H2C-H2CCOOH (50% 2-phosphonobutanetri-Chemical Corp. carboxylic acid) TRC-289 (PAPEMP) Petrolite (H203PH2C) 2NCH3CHCH2 (oCH2CH3CH) 2eN (c (32.9% Polyamino Polyether Chemical Corp. H2Po3H2) 2 Methylene Phosphonate)