Corrosion inhibition
United States Patent 3868217
Use of mono-, di-, and triphosphoric acid esters of triethanol amine and mixtures thereof to inhibit the corrosion of metals by oxygen-bearing waters.
US Patent References:
Product for and process of treating metallic articles before coating
Frasch - March 1956 - 2737498
Corrosion inhibited phosphoric acid composition
Fisher - July 1966 - 3260673
Composition and method for treating surfaces
Burt - August 1968 - 3397150
TRIETHANOLAMINE SALTS OF MONO- AND DINONYL PHENOL (ETHOXYLATE) PHOSPHATE ACID ESTERS
Davis - January 1969 - 3422166
AMINE/PHOSPHATE COMPOSITION USEFUL AS CORROSION AND SCALE INHIBITOR
Larsen - January 1974 - 3787319
Product for and process of treating metallic articles before coating
Frasch - March 1956 - 2737498
Corrosion inhibited phosphoric acid composition
Fisher - July 1966 - 3260673
Composition and method for treating surfaces
Burt - August 1968 - 3397150
TRIETHANOLAMINE SALTS OF MONO- AND DINONYL PHENOL (ETHOXYLATE) PHOSPHATE ACID ESTERS
Davis - January 1969 - 3422166
AMINE/PHOSPHATE COMPOSITION USEFUL AS CORROSION AND SCALE INHIBITOR
Larsen - January 1974 - 3787319
Application Number:
05/468347
Publication Date:
02/25/1975
Filing Date:
05/09/1974
View Patent Images:
Export Citation:
Assignee:
Calgon Corporation (Robinson Township, PA)
Primary Class:
Other Classes:
252/392, 252/394, 252/389.210
International Classes:
C23F11/10; C23F11/167; C23F11/14; C23F11/16
Field of Search:
21/2.7A,2.5A 252/148,390,389A,392,394
Primary Examiner:
Richman, Barry S.
Assistant Examiner:
Lovercheck, Dale
Attorney, Agent or Firm:
Katz, Martin Westlake Harry L. E.
Parent Case Data:
This application is a continuation-in-part of U.S. Ser. No. 347,009, filed Apr. 2, 1973 and now abandoned.
Claims:
I claim
1. A method of inhibiting the corrosion of metals in a water system which comprises maintaining in the water of said system at least about 10 mg/l of a phosphoric acid ester of triethanol amine.
2. A method as in claim 1 which further comprises maintaining in said system at least about 1 mg/l of a member selected from the group consisting of thiazoles and triazoles.
3. A method as in claim 2 wherein the thiazole is mercaptobenzothiazole.
4. A method as in claim 2 wherein the triazole is benzotriazole.
1. A method of inhibiting the corrosion of metals in a water system which comprises maintaining in the water of said system at least about 10 mg/l of a phosphoric acid ester of triethanol amine.
2. A method as in claim 1 which further comprises maintaining in said system at least about 1 mg/l of a member selected from the group consisting of thiazoles and triazoles.
3. A method as in claim 2 wherein the thiazole is mercaptobenzothiazole.
4. A method as in claim 2 wherein the triazole is benzotriazole.
Description:
This invention relates to the use of the mono-, di-, and triphosphoric acid esters of triethanol amine N(CH 2 CH 2 O(PO 3 ) n ) 3 where n=1-3 and mixtures thereof, alone or in combination with certain triazoles, thiazoles and mixtures thereof, for inhibiting corrosion of metals by oxygen-bearing waters.
Oxygen corrosion is, of course, a serious problem in any metal-containing water 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. Copper and its alloys, aluminum and its alloys, and galvanized steel are also used in water systems and are subject to corrosion. The use of similar corrosion inhibitors is disclosed in U.S. Pat. No. 3,260,673 to Fisher, and No. 3,397,150 to Burt, et al., and No. 3,422,166 to Pitman.
I have found that the mono-, di-, and triphosphoric acid esters of triethanol amine and mixtures thereof are effective corrosion inhibitors without the necessity of adding zinc, chromates or other additives. These esters effectively inhibit the corrosion of metals in water systems when they are added in amounts of from about 10 to 100 mg/l either alone or in combination with from about 1 to 10 mg/l of an effective triazole or thiazole, as for example, mercaptobenzothiazole or benzotriazole.
The following table shows the results of experiments which demonstrate the effectiveness of a mixture of the mono-, di-, and triphosphoric acid ester of triethanol amine and the water-soluble salts thereof in inhibiting metallic corrosion. These tests were run in synthetic Pittsburgh water. Steel electrodes were used in polarization test cells with the initial pH at 7.0. Inhibitor concentrations were calculated on the basis of active material. The amount of corrosion that had taken place was determined from the current density at the intersection of an extrapolation of the so-called "Tafel" portion of the anodic polarization curve with the equilibrium or "mixed" potential value, usually referred to as the corrosion potential, "E corr ." Application of Faraday's Lay allows a computation of a direct mathematical relationship between the current density of E corr , expressed in amperes per square centimeter and a more useful corrosion rate expression such as milligrams of steel consumed per square decimeter of surface per day (m.d.d.) and mils per year (m.p.y.). This relationship is such that a current density value of 4.0×10 - 7 amperes/cm 2 = 1.0 mg/dm 2 /day. Further, the m.p.y. value is calculated from the usual formula: m.p.y. = m.d.d. × (1.44/density, using a density value of 7.87 g/cm 3 for steel.
Table I ______________________________________ Corrosion Rate mg/l m. d. d. m. p. y. ______________________________________ 0 150 27.2 10 71 13.0 15 33 6.0 20 21 3.8 25 4.6 0.84 30 2.5 0.46 40 2.8 0.51 50 3.2 0.58 75 1.0 0.18 100 0.4 0.07 ______________________________________
The following test provided corrosion rate data under field conditions. Pilot plant size cooling tower-heat exchanger test equipment (CTHE) was used to simulate large industrial recirculated cooling water systems. The makeup water for this experiment was a synthetically prepared tap water similar in analysis to Pittsburgh, Pennsylvania tap water. The pH of the water in the operating system was controlled to 7.0 ± 0.1 by feeding a dilute solution of sulfuric acid on demand from an automatic pH control system. This simulation also included flow velocities of 2 - 5 ft./sec., natural concentration of the minerals in the water to about five times their concentration in the makeup water (5×) by evaporation, several different metals exposed (but not galvanically coupled), three successive heat transfer surfaces, etc. This system is highly instrumented and provides substantial data relating to the performance of inhibitors since one can evaluate not only test coupons, but also steel and admiralty brass heat transfer surfaces, and continuously record instrumental corrosion rate data (Corrater instrument, Magna Corp., Santa Fe Springs, Calif.). The aforenoted mixture of phosphate ester of triethanol amine was maintained at 30 - 60 mg/l during this test.
Corrosion rates on steel during this 3-1/2 week long test (the test ran continuously, 24 hrs./day, for twenty-four consecutive days) were 1.5 to 3.5 m.p.y. on test coupons; the recording Corrater chart showed a very stable value of 1.5 ± 0.5 m.p.y. The heat transfer surfaces of the heat exchanger tubes were clean and essentially free of any corrosive attack.
The copper alloy specimens initially showed corrosion rates of 0.5 - 0.9 m.p.y. Since this is a bit high for copper alloys, 1 - 2 mg/l of a specific copper corrosion inhibitor, sodium mercaptobenzothiazole was fed to the system. This reduced the copper alloy corrosion rates to an acceptable rate of less than 0.1 m.p.y. Benzotriazole would be equally effective in this application. Both products are compatible with the ester and can be used interchangeably in a commercial preparation.
Oxygen corrosion is, of course, a serious problem in any metal-containing water 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. Copper and its alloys, aluminum and its alloys, and galvanized steel are also used in water systems and are subject to corrosion. The use of similar corrosion inhibitors is disclosed in U.S. Pat. No. 3,260,673 to Fisher, and No. 3,397,150 to Burt, et al., and No. 3,422,166 to Pitman.
I have found that the mono-, di-, and triphosphoric acid esters of triethanol amine and mixtures thereof are effective corrosion inhibitors without the necessity of adding zinc, chromates or other additives. These esters effectively inhibit the corrosion of metals in water systems when they are added in amounts of from about 10 to 100 mg/l either alone or in combination with from about 1 to 10 mg/l of an effective triazole or thiazole, as for example, mercaptobenzothiazole or benzotriazole.
The following table shows the results of experiments which demonstrate the effectiveness of a mixture of the mono-, di-, and triphosphoric acid ester of triethanol amine and the water-soluble salts thereof in inhibiting metallic corrosion. These tests were run in synthetic Pittsburgh water. Steel electrodes were used in polarization test cells with the initial pH at 7.0. Inhibitor concentrations were calculated on the basis of active material. The amount of corrosion that had taken place was determined from the current density at the intersection of an extrapolation of the so-called "Tafel" portion of the anodic polarization curve with the equilibrium or "mixed" potential value, usually referred to as the corrosion potential, "E corr ." Application of Faraday's Lay allows a computation of a direct mathematical relationship between the current density of E corr , expressed in amperes per square centimeter and a more useful corrosion rate expression such as milligrams of steel consumed per square decimeter of surface per day (m.d.d.) and mils per year (m.p.y.). This relationship is such that a current density value of 4.0×10 - 7 amperes/cm 2 = 1.0 mg/dm 2 /day. Further, the m.p.y. value is calculated from the usual formula: m.p.y. = m.d.d. × (1.44/density, using a density value of 7.87 g/cm 3 for steel.
Table I ______________________________________ Corrosion Rate mg/l m. d. d. m. p. y. ______________________________________ 0 150 27.2 10 71 13.0 15 33 6.0 20 21 3.8 25 4.6 0.84 30 2.5 0.46 40 2.8 0.51 50 3.2 0.58 75 1.0 0.18 100 0.4 0.07 ______________________________________
The following test provided corrosion rate data under field conditions. Pilot plant size cooling tower-heat exchanger test equipment (CTHE) was used to simulate large industrial recirculated cooling water systems. The makeup water for this experiment was a synthetically prepared tap water similar in analysis to Pittsburgh, Pennsylvania tap water. The pH of the water in the operating system was controlled to 7.0 ± 0.1 by feeding a dilute solution of sulfuric acid on demand from an automatic pH control system. This simulation also included flow velocities of 2 - 5 ft./sec., natural concentration of the minerals in the water to about five times their concentration in the makeup water (5×) by evaporation, several different metals exposed (but not galvanically coupled), three successive heat transfer surfaces, etc. This system is highly instrumented and provides substantial data relating to the performance of inhibitors since one can evaluate not only test coupons, but also steel and admiralty brass heat transfer surfaces, and continuously record instrumental corrosion rate data (Corrater instrument, Magna Corp., Santa Fe Springs, Calif.). The aforenoted mixture of phosphate ester of triethanol amine was maintained at 30 - 60 mg/l during this test.
Corrosion rates on steel during this 3-1/2 week long test (the test ran continuously, 24 hrs./day, for twenty-four consecutive days) were 1.5 to 3.5 m.p.y. on test coupons; the recording Corrater chart showed a very stable value of 1.5 ± 0.5 m.p.y. The heat transfer surfaces of the heat exchanger tubes were clean and essentially free of any corrosive attack.
The copper alloy specimens initially showed corrosion rates of 0.5 - 0.9 m.p.y. Since this is a bit high for copper alloys, 1 - 2 mg/l of a specific copper corrosion inhibitor, sodium mercaptobenzothiazole was fed to the system. This reduced the copper alloy corrosion rates to an acceptable rate of less than 0.1 m.p.y. Benzotriazole would be equally effective in this application. Both products are compatible with the ester and can be used interchangeably in a commercial preparation.