CA1204372A - Methods and compositions for simultaneously removing iron and copper scales from ferrous metal surfaces - Google Patents
Methods and compositions for simultaneously removing iron and copper scales from ferrous metal surfacesInfo
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- CA1204372A CA1204372A CA000437060A CA437060A CA1204372A CA 1204372 A CA1204372 A CA 1204372A CA 000437060 A CA000437060 A CA 000437060A CA 437060 A CA437060 A CA 437060A CA 1204372 A CA1204372 A CA 1204372A
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
- C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
- C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
- C23G1/08—Iron or steel
- C23G1/088—Iron or steel solutions containing organic acids
Abstract
\
Abstract of the Disclosure Methods and compositions for simultaneously removing iron and copper scales from ferrous metal surfaces are provided.
The compositions are comprised of water, one or more organic chelating acids which dissolve iron, a reducing agent selected from the group consisting of erythorbic acid, alkali metal salts of erythorbic acid, ammonium salts of erythorbic acid and mixtures thereof and a copper complexing compound selected from the group consisting of thiourea, hexahyrdopyrimidine-2-thione and mixtures thereof. The compositions are utilized by contacting scale-containing ferrous metal surfaces therewith at temperatures in the range of from about 75°F to about 150°F.
Abstract of the Disclosure Methods and compositions for simultaneously removing iron and copper scales from ferrous metal surfaces are provided.
The compositions are comprised of water, one or more organic chelating acids which dissolve iron, a reducing agent selected from the group consisting of erythorbic acid, alkali metal salts of erythorbic acid, ammonium salts of erythorbic acid and mixtures thereof and a copper complexing compound selected from the group consisting of thiourea, hexahyrdopyrimidine-2-thione and mixtures thereof. The compositions are utilized by contacting scale-containing ferrous metal surfaces therewith at temperatures in the range of from about 75°F to about 150°F.
Description
This invention relates to methods and compositions for simultaneously removing iron and copper scales from ferrous metal surfaces.
In the operation of high pressure steam generating equipment utilized in electric power generation and other applications, the interiors of boiler tubes generally always gradually become encrusted with scale deposits consisting primarily of ferric oxide, e.g., magnetite (Fe304) and hematite (Fe203). Copper oxide scale is also usually present and copper metal is often plated directly onto the boiler tube walls.
Removal of iron and copper scales from boiler tubes and other scale-containing ferrous metal surfaces has been accomplished heretofore by contacting the scale-containing surfaces with acidic formulations to dissolve the scales.
One such acidic composition which has found wide usage in removing iron scales from industrial boiler and other heating surfaces is an aqueous mixture of hydroxyacetic acid and formic acid. However, the hydroxyacetic-formic acid mixture has here-tofore had to be used at high temperatures, i.e., about 200Fwith constant agitation in order to efficiently remove the scales. Because of the high temperatures involved, copper complexing chemicals have not been included in the composition, and consequently, a separate step has been required for removing copper scales. That is, the aqueous mixture of hydroxyacetic and formic acids has been removed from contact with a scale-containing surface after iron scales thereon have been dissolved and a second composition containing a copper complexor has then been brought into contact with the scale-containing surface at a lower temperature to remove copper scales. This two-step procedure has been necessitated by the fact that the copper ~J~
i~Z~437Z
complexors degrade and are ineffective at temperatures above about 160F.
By the present invention methods and compositions for simultaneously removing iron and copper scales from ferrous metal surfaces are provided. In accordance with the invention, scale-containing surfaces are contacted with the compositions at temperatures in the range of from about 75F
to about 150~F and maintained in such contact for a time period sufficient to dissolve the scales.
The scale-removing compositions of the present invention are comprised of water, an organic chelating acid or mixture of organic chelating acids which dissolve iron, a reducing agent selected from the group consisting of erythorbic acid, alkali metal salts of erythorbic acid, ammonium salts of erythorbic acid and mixtures thereof and a copper complexing compound selected from the group consisting of thiourea, hexahydropyrimidine-2-thione and mixtures thereof.
Any organic acid or mixture of organic acids having low pH (a pH of less than 7 at room temperature) which chelate iron can be used in the compositions of this invention.
Examples of suitable such acids are hydroxyacetic acid, formic aeid, malic acid, eitric acid, ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid, and mixtures of such acids. Of the various organic iron chelating acids which can be used, a mixture of hydroxyacetic acid and formic acid is preferred.
The organic iron chelating acid or acids utilized in the aqueous scale-removing compositions of this invention are preferably present in an amount in the range of from about 1% to about 10% by weight of the compositions. The preferred acids, i.e., hydroxyacetic acid and formic acid are preferably present in the aqueous compositions in a weight ratio of ~Z04372 hydroxyacetic to formic acid of about 2:1.
The erythorbic acid and/or salt reducing agent functions in the compositions of this invention to increase the rate of dissolution of iron by the organic chelating acid or acids utilized whereby iron scales can be effectively removed from ferrous surfaces by the compositions at low temperatures, i.e., temperatures in the range of from about 75F to about 150F. This in turn allows copper complexing compounds to be included in the compositions whereby both iron and copper scales are simultaneously removed by the compositions. As indicated above, the reducing agents utilized in the compositions are selected from the group consisting of erythorbic acid, alkali metal salts of erythorbic acid, ammonlum salts of erythorbic acid and mixtures thereof and are included in the compositions in an amount in the range of from about 0.25% to about 5% by weight of the com-positions. Most preferably, the reducing agent is sodium erythorbate and is present in the aqueous compositions in an amount of about 1% by weight of the compositions.
The copper complexing compounds utilized in the compositions of this invention are selected from the group consisting of thiourea, hexahydropyrimidine-2-thione and mixtures of such compounds. The copper complexor or mixture is included in the aqueous composition in an amount in the range of from about 0.25% to about 3% by weight of the com-positions. Preferably, the copper complexor is a mixture of hexahydropyrimidine-2-thione and thiourea consisting of 60 parts by weight hexahydropyrimidine-2-thione and 40 parts by weight thiourea present in the aqueous composition in an amount of about 1% by weight.
A particularly preferred composition of this invention is comprised of water, hydroxyacetic acid present in the com-~Z04372 position in an amount of about 2% by wei~ht of the composition,formic acid present in the composition in an amount of about 1% by weight of the composition, sodium erythorbate present in the composition in an amount of about 1% by weight, and a mixture of 60 parts by weight hexahydropyrimidine-2-thione and 40 parts by weight thiourea present in the composition in an amount of about 1% by weight~
Various ferrous metal corrosion inhibitors can be included in the compositions of this invention, as for example, dibutyl thiourea, quaternary alkyl pyridinium salts, alkyl-benzene sulfonate and heavy aromatic naphtha. The most pre-ferred ferrous metal corrosion inhibitor for use in accordance with this invention is a low chloride inhibitor mixture com-prised of 15% by weight heavy aromatic naphtha-, 40% by weight ethylene glycol, 8% by weight dibutyl thiourea, 12% by weight acetic acid, 10% by weight alkyl pyridine, 10% by weight non-ionic ethoxylated alcohol and 5% by weight ethoxylated amine.
The corrosion inhibitor is preferably included in the aqueous compositi~n in an amou~t in the range of from about .05% to about 6% by volume of the composition.
In carrying out the methods of the present invention for simultaneously removing iron and copper scales from ferrous surfaces, a composition of the present invention is brought into contact with an iron and copper scale-containing ferrous metal surface at a temperature and for a time sufficient for the scales to be dissolved by the composltion and thereby removed from the surface. The composition containing the dissolved scales is removed from contact with the surface and disposed of in the usual manner whereby pollution of the en-vironment does not result.
As mentioned above, the temperature of the aqueouscomposition during the contact of the scale-containing sur-12(~437z faces can be as low as 75F while still efficiently removingscale from the surfaces up to as high as about 150F. At temperatures above about 150F, degradation of the copper complexors begins to take place. The most preferred contact temperature is about 140F.
- As is well understood by those skilled in the art, the cleaning compositions can be brought into contact with the scale-containing surfaces in a static condition, or as is preferred, the compositions can be circulated over the surfaces. The compositions effectively dissolve deposits containing iron and copper at temperatures in the range of from about 75F to about 150F in a single stage treatment.
In order to facilitate a clear understanding of the methods and compositions of the present invention, the follow-ing examples are given.
Example 1 Aqueous solutions containing 2% by weight hydroxy-acetic acid, 1% by weight formic acid and 0.1% by volume of a corrosion inhibitor are prepared. One hundred milliliter portions of the solutions are placed in glass beakers, 2 grams of powdered iron oxide (technical grade magnetite) are added thereto and dry pre-weighed 1020 mild steel corrosion coupons are placed in the solutions. Various quantities of sodium erythorbate are added to some of the test solutions, the solutions are heated to the temperatures given in Table I
below and the solutions are maintained at such temperatures for time periods of six hours. During the six-hour periods the test solutions are stirred for one minute each hour and at the termination of the six hour periods, the solutions are analyzed for dissolved iron (by atomic absorption analysis) and the weight losses of the corrosion coupons are determined.
~Z0437Z
The results of these tes-ts are given in Table I below.
The corrosion inhibitor is a commercially available mixture comprised cf 15% by weight heavy aromatic naphtha, 40% by weight ethylene glycol, 8% by weight dibutyl thiourea, 12% by weight acetic acid, 10% by weight alkyl pyridine, 10%
by weight nonionic ethoxylated alcohol and 5% by weight ethoxylated amine.
Table I
Magnetite Dissolution Tests in Aqueous Hydroxyacetic-Formic Acid Solutions with and without Sodium Erythorbate Sodiuml Mild Steel - Magnetite2 Test Erythorbate Temperature Corrosio2n Rate Dissolved No. % F lbs/ft /day Grams Percent 1 0 120 0.002 0.015 0.75
In the operation of high pressure steam generating equipment utilized in electric power generation and other applications, the interiors of boiler tubes generally always gradually become encrusted with scale deposits consisting primarily of ferric oxide, e.g., magnetite (Fe304) and hematite (Fe203). Copper oxide scale is also usually present and copper metal is often plated directly onto the boiler tube walls.
Removal of iron and copper scales from boiler tubes and other scale-containing ferrous metal surfaces has been accomplished heretofore by contacting the scale-containing surfaces with acidic formulations to dissolve the scales.
One such acidic composition which has found wide usage in removing iron scales from industrial boiler and other heating surfaces is an aqueous mixture of hydroxyacetic acid and formic acid. However, the hydroxyacetic-formic acid mixture has here-tofore had to be used at high temperatures, i.e., about 200Fwith constant agitation in order to efficiently remove the scales. Because of the high temperatures involved, copper complexing chemicals have not been included in the composition, and consequently, a separate step has been required for removing copper scales. That is, the aqueous mixture of hydroxyacetic and formic acids has been removed from contact with a scale-containing surface after iron scales thereon have been dissolved and a second composition containing a copper complexor has then been brought into contact with the scale-containing surface at a lower temperature to remove copper scales. This two-step procedure has been necessitated by the fact that the copper ~J~
i~Z~437Z
complexors degrade and are ineffective at temperatures above about 160F.
By the present invention methods and compositions for simultaneously removing iron and copper scales from ferrous metal surfaces are provided. In accordance with the invention, scale-containing surfaces are contacted with the compositions at temperatures in the range of from about 75F
to about 150~F and maintained in such contact for a time period sufficient to dissolve the scales.
The scale-removing compositions of the present invention are comprised of water, an organic chelating acid or mixture of organic chelating acids which dissolve iron, a reducing agent selected from the group consisting of erythorbic acid, alkali metal salts of erythorbic acid, ammonium salts of erythorbic acid and mixtures thereof and a copper complexing compound selected from the group consisting of thiourea, hexahydropyrimidine-2-thione and mixtures thereof.
Any organic acid or mixture of organic acids having low pH (a pH of less than 7 at room temperature) which chelate iron can be used in the compositions of this invention.
Examples of suitable such acids are hydroxyacetic acid, formic aeid, malic acid, eitric acid, ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid, and mixtures of such acids. Of the various organic iron chelating acids which can be used, a mixture of hydroxyacetic acid and formic acid is preferred.
The organic iron chelating acid or acids utilized in the aqueous scale-removing compositions of this invention are preferably present in an amount in the range of from about 1% to about 10% by weight of the compositions. The preferred acids, i.e., hydroxyacetic acid and formic acid are preferably present in the aqueous compositions in a weight ratio of ~Z04372 hydroxyacetic to formic acid of about 2:1.
The erythorbic acid and/or salt reducing agent functions in the compositions of this invention to increase the rate of dissolution of iron by the organic chelating acid or acids utilized whereby iron scales can be effectively removed from ferrous surfaces by the compositions at low temperatures, i.e., temperatures in the range of from about 75F to about 150F. This in turn allows copper complexing compounds to be included in the compositions whereby both iron and copper scales are simultaneously removed by the compositions. As indicated above, the reducing agents utilized in the compositions are selected from the group consisting of erythorbic acid, alkali metal salts of erythorbic acid, ammonlum salts of erythorbic acid and mixtures thereof and are included in the compositions in an amount in the range of from about 0.25% to about 5% by weight of the com-positions. Most preferably, the reducing agent is sodium erythorbate and is present in the aqueous compositions in an amount of about 1% by weight of the compositions.
The copper complexing compounds utilized in the compositions of this invention are selected from the group consisting of thiourea, hexahydropyrimidine-2-thione and mixtures of such compounds. The copper complexor or mixture is included in the aqueous composition in an amount in the range of from about 0.25% to about 3% by weight of the com-positions. Preferably, the copper complexor is a mixture of hexahydropyrimidine-2-thione and thiourea consisting of 60 parts by weight hexahydropyrimidine-2-thione and 40 parts by weight thiourea present in the aqueous composition in an amount of about 1% by weight.
A particularly preferred composition of this invention is comprised of water, hydroxyacetic acid present in the com-~Z04372 position in an amount of about 2% by wei~ht of the composition,formic acid present in the composition in an amount of about 1% by weight of the composition, sodium erythorbate present in the composition in an amount of about 1% by weight, and a mixture of 60 parts by weight hexahydropyrimidine-2-thione and 40 parts by weight thiourea present in the composition in an amount of about 1% by weight~
Various ferrous metal corrosion inhibitors can be included in the compositions of this invention, as for example, dibutyl thiourea, quaternary alkyl pyridinium salts, alkyl-benzene sulfonate and heavy aromatic naphtha. The most pre-ferred ferrous metal corrosion inhibitor for use in accordance with this invention is a low chloride inhibitor mixture com-prised of 15% by weight heavy aromatic naphtha-, 40% by weight ethylene glycol, 8% by weight dibutyl thiourea, 12% by weight acetic acid, 10% by weight alkyl pyridine, 10% by weight non-ionic ethoxylated alcohol and 5% by weight ethoxylated amine.
The corrosion inhibitor is preferably included in the aqueous compositi~n in an amou~t in the range of from about .05% to about 6% by volume of the composition.
In carrying out the methods of the present invention for simultaneously removing iron and copper scales from ferrous surfaces, a composition of the present invention is brought into contact with an iron and copper scale-containing ferrous metal surface at a temperature and for a time sufficient for the scales to be dissolved by the composltion and thereby removed from the surface. The composition containing the dissolved scales is removed from contact with the surface and disposed of in the usual manner whereby pollution of the en-vironment does not result.
As mentioned above, the temperature of the aqueouscomposition during the contact of the scale-containing sur-12(~437z faces can be as low as 75F while still efficiently removingscale from the surfaces up to as high as about 150F. At temperatures above about 150F, degradation of the copper complexors begins to take place. The most preferred contact temperature is about 140F.
- As is well understood by those skilled in the art, the cleaning compositions can be brought into contact with the scale-containing surfaces in a static condition, or as is preferred, the compositions can be circulated over the surfaces. The compositions effectively dissolve deposits containing iron and copper at temperatures in the range of from about 75F to about 150F in a single stage treatment.
In order to facilitate a clear understanding of the methods and compositions of the present invention, the follow-ing examples are given.
Example 1 Aqueous solutions containing 2% by weight hydroxy-acetic acid, 1% by weight formic acid and 0.1% by volume of a corrosion inhibitor are prepared. One hundred milliliter portions of the solutions are placed in glass beakers, 2 grams of powdered iron oxide (technical grade magnetite) are added thereto and dry pre-weighed 1020 mild steel corrosion coupons are placed in the solutions. Various quantities of sodium erythorbate are added to some of the test solutions, the solutions are heated to the temperatures given in Table I
below and the solutions are maintained at such temperatures for time periods of six hours. During the six-hour periods the test solutions are stirred for one minute each hour and at the termination of the six hour periods, the solutions are analyzed for dissolved iron (by atomic absorption analysis) and the weight losses of the corrosion coupons are determined.
~Z0437Z
The results of these tes-ts are given in Table I below.
The corrosion inhibitor is a commercially available mixture comprised cf 15% by weight heavy aromatic naphtha, 40% by weight ethylene glycol, 8% by weight dibutyl thiourea, 12% by weight acetic acid, 10% by weight alkyl pyridine, 10%
by weight nonionic ethoxylated alcohol and 5% by weight ethoxylated amine.
Table I
Magnetite Dissolution Tests in Aqueous Hydroxyacetic-Formic Acid Solutions with and without Sodium Erythorbate Sodiuml Mild Steel - Magnetite2 Test Erythorbate Temperature Corrosio2n Rate Dissolved No. % F lbs/ft /day Grams Percent 1 0 120 0.002 0.015 0.75
2 0 140 0.003 0.030 1.5
3 0 160 0.003 0.023 1.15
4 0 180 0.003 0.037 1.85 1 120 0.001 0.214 10.7 6 1 140 0.001 0.265 13.25 7 1 160 0.002 0.344 17.2 8 1 180 0.003 0.400 20.0 9 2 120 0.001 0.237 11.85 2 140 0.001 0.355 17.75 11 2 160 0.002 0.419 20.95 12 2 180 0.003 0.451 22.55 1 The percent number indicated is the number of grams of sodium erythorbate per 100 milliliters of solution.
Amount of dissolved magnetite is determined by atomic absorption analysis of spent solvent. This value is corrected for coupon weight loss.
From Table I it is readily apparent that an aqueous solution of hydroxyacetic and formic acids dissolves a greater quantity of magnetite at higher temperatures. However, it is also readily apparent that the inclusion of sodiu~ erythorbate in an aqueous solution of hydroxyacetic and formic acids brings i20437z about an increase in the dissolution of magnetite. For example, at 120F the inclusion of 1% by weight sodium erythorbate results in a 14-fold increase in the quantity of magnetite dissolved (tests 1 and 5). A 2% concentration of sodium erythorbate results in a 16-fold increase in the dissolution of magnetite (tests 1 and 9). At 140F, a solution without sodium erythorbate dissolves twice as much magnetite as does the same solution at 120F (tests 1 and 2). The same aqueous solution with 1% sodium erythorbate at 140F results in an 18-fold increase in magnetite dissolution as compared to the solution without sodium erythorbate at lZ0F (tests 1 and ~).
Thus, the inclusion of sodium erythorbate in the aqueous hydroxyacetic-formic acid solutions brings about an increase in the rate of dissolution of magnetite which is far greater than the effect of heat alone on the rate of dissolution.
-- Example 2 One hundred milliliter portions of aqueous solutions containing 2% by weight hydroxyacetic acid, 1% by weight formic acid and 0.1% by volume of the corrosion inhibitor described in Example 1 are placed in glass beakers. Sodium erythorbate and/or copper complexor are combined with some of the solutions and 2 grams of powdered iron oxide (technical grade magnetite) and 0.1 gram of copper powder are combined with the solutions.
Dry pre-weighed 1020 mild steel corrosion coupons are placed in the solutions and the solutions are heated and maintained at temperatures of 140F for time periods of six hours with one minute of stirring each hour. At the termination of the six-hour test periods, the solutions are analyzed (by atomic absorption analysis) for dissolved iron and copper and the weight losses of the corrosion coupons are determined.
The results of these tests are given in Table II below.
1;Z(~4372 Table II
Copper and Magnetite Dissolution in Aqueous Hydroxyacetic-Formic Acid Solutions with and without Sodium Erythorbate and Copper Complexor at 140F for 6 Hours Additive Results . . _ _ . . . _ .
Sodium Copper Magnetite Copper Test Erythorbate Complexor Dissolved Dissolved No. % % Grams Percent Percent 13 0 0 0.029 1.45 0.0010 14 0 1% "A" 0.045 2.25 0.0240 0 1% "A" 0.037 1.85 0.0215 16 1 0 0.270 13.5 0.0015 17 1 1% "A" 0.334 16.7 0.0235 18 1 1% Thiourea 0.456 22.8 0.0223 19 2 1% "A" 0.363 18.15 0.0247 2 1% Thiourea 0.373 18.65 0.0222 1 Copper complexor "A" is a mixture consisting of 60% by weight hexahydropyrimidine-2-thione and 40% by weight thiourea.
Amounts of dissolved magnetite and copper are determined by atomic absorption analysis of spent solvent. The value of dissolved magnetite is corrected for coupon weight loss.
3 The percent number indicated is the number of grams of additive per 100 milliliters of solution.
From Table II it can be seen that the addition of a copper complexor to an aqueous solution of hydroxyacetic acid, formic acid and sodium erythorbate does not diminish the ability of the solution to dissolve magnetite at 140F (see tests 6 and 10 of Table I and 17, 18, 19 and 20 of Table II) but, in fact, increases the amount of magnetite dissolved. The addition of the copper complexor to an aqueous solution of hydroxyacetic and formic acids in the absence of sodium erythorbate (tests 13, 14 and 15), produces a small increase in the dissolution of magnetite, but the dissolution of copper lZ04372 is greatly increased. When sodium erythorbate and copper complexor are both present in the aqueous solution (tests 17, 18, 19 and 20), greatly improved dissolution of both magnetite and copper are obtained as compared to when neither additive or only one is present, i.e., tests 2, 6, 10, 13, 14, 15 and 16~
Example 3 Small sections of boiler tube containing iron and copper scale are placed in glass beakers, each of which con-tains 225 milliliters of an aqueous solution containing 2%by weight hydroxyacetic acid, 1% by weight formic acid and 0.1% by volume of the corrosion inhibitor described in Example 1. Some of the solutions also contain sodium erythorbate and copper complexor. The solutions are heated to temperatures of 140F and maintained at such temperatures for time periods of 24 hours. At the terminations of the 24-hour test periods, the solutions are analyzed by atomic absorption analysis for iron and copper content and the boiler tube sections are inspected for the presence of scale.
The test sections of boiler tube are cut from two boiler tube samples designated herein as boiler tube sample A
and boiler tube sample B. The scale on boiler tube sample A
consists of magnetite, copper metal and hydroxyapatite [Ca5tP04)30H]. The scale on boiler tube sample B consists of magnetite, copper and nickel.
The results of these tests are set forth in Table III below.
iZ~4372 Table III
Scale Removal by Aqueous Hydroxyacetic-Formic Acid Solutions with and without Sodium Erythorbate and Copper Complexor at 140F for 24 Hours Formulation Results Boiler Sodium Copper Tube Test Erythorbate Complexor Tube Sample No. % % _ % Cu % Fe Appearance A 21 0 0 0.00019 0.28 copper pl~ted A 22 0 1 0.0078 0.45 not clean 3 A 23 1 1 0.0093 0.39 tube clean B 24 0 0 0.0010 0.39 copper plated B 25 0 1 0.0280 0.33 hot side not clean2 B 26 1 1 0.0230 0.29 90% clean4 A mixture consisting of 60% by weight hexahydropyrimidine-2-thione and 40% by weight thiourea.
All copper removed but about 40% iron oxide was still on tube section.
3 All scale removed.
All copper removed, but about 10% iron oxide was still on tube section.
.
From Table III it can be seen that the formulation containing sodium erythorbate and copper complexor is effective in removing iron and copper scale.
Example 4 One hundred milliliter portions of an aqueous solution containing 2% by weight hydroxyacetic acid, 1% by weight formic acid and 0.1% by volume of the corro3ion inhibitor described in Example 1 are placed in three beakers. Two grams of powdered iron oxide are combined with each solution. One percent by weight sodium erythorbate and 1% by weight copper complexor (60% by weight hexahydropyrimidine-2-thione and 40% by weight thiourea) are combined with the first solution which is main-tained at a temperature of 75F for six hours with one minute ~Z1~3~Z
of stirring each hour. One percent by weight copper complexor only is added to the second solution which is also maintained at 75F for a six-hour time period. The third solution is heated to 190F and is maintained at such temperature for a six~hour time period. At the terminations of the six-hour time periods, the solutions are analyzed for dissolved iron.
The results in these tests are shown in Table IV below.
Table IV
Iron Dissolution in Aqueous Hydroxyacetic-Formic Acid Solutions with and without Sodium Erythorbate and Copper Complexor Sodium CopperMagnetite Test Erythorbate ComplexorTemperature Dissolved No. % % F %
27 1 1 75 0.026 28 0 1 75 0.012 29 0 0 190 0.027 2 The percent number indicated is the number of grams of additive per 100 milliliters of solution.
Amounts of dissolved magnetite and copper are determined by atomic absorption analysis of spent solvent. The value of dissolved magnetite is corrected for coupon weight loss.
~ = .
From Table IV it can be seen that the solution con-taining sodium erythorbate and copper complexor ef,fectively dissolves magnetite at 75F.
Amount of dissolved magnetite is determined by atomic absorption analysis of spent solvent. This value is corrected for coupon weight loss.
From Table I it is readily apparent that an aqueous solution of hydroxyacetic and formic acids dissolves a greater quantity of magnetite at higher temperatures. However, it is also readily apparent that the inclusion of sodiu~ erythorbate in an aqueous solution of hydroxyacetic and formic acids brings i20437z about an increase in the dissolution of magnetite. For example, at 120F the inclusion of 1% by weight sodium erythorbate results in a 14-fold increase in the quantity of magnetite dissolved (tests 1 and 5). A 2% concentration of sodium erythorbate results in a 16-fold increase in the dissolution of magnetite (tests 1 and 9). At 140F, a solution without sodium erythorbate dissolves twice as much magnetite as does the same solution at 120F (tests 1 and 2). The same aqueous solution with 1% sodium erythorbate at 140F results in an 18-fold increase in magnetite dissolution as compared to the solution without sodium erythorbate at lZ0F (tests 1 and ~).
Thus, the inclusion of sodium erythorbate in the aqueous hydroxyacetic-formic acid solutions brings about an increase in the rate of dissolution of magnetite which is far greater than the effect of heat alone on the rate of dissolution.
-- Example 2 One hundred milliliter portions of aqueous solutions containing 2% by weight hydroxyacetic acid, 1% by weight formic acid and 0.1% by volume of the corrosion inhibitor described in Example 1 are placed in glass beakers. Sodium erythorbate and/or copper complexor are combined with some of the solutions and 2 grams of powdered iron oxide (technical grade magnetite) and 0.1 gram of copper powder are combined with the solutions.
Dry pre-weighed 1020 mild steel corrosion coupons are placed in the solutions and the solutions are heated and maintained at temperatures of 140F for time periods of six hours with one minute of stirring each hour. At the termination of the six-hour test periods, the solutions are analyzed (by atomic absorption analysis) for dissolved iron and copper and the weight losses of the corrosion coupons are determined.
The results of these tests are given in Table II below.
1;Z(~4372 Table II
Copper and Magnetite Dissolution in Aqueous Hydroxyacetic-Formic Acid Solutions with and without Sodium Erythorbate and Copper Complexor at 140F for 6 Hours Additive Results . . _ _ . . . _ .
Sodium Copper Magnetite Copper Test Erythorbate Complexor Dissolved Dissolved No. % % Grams Percent Percent 13 0 0 0.029 1.45 0.0010 14 0 1% "A" 0.045 2.25 0.0240 0 1% "A" 0.037 1.85 0.0215 16 1 0 0.270 13.5 0.0015 17 1 1% "A" 0.334 16.7 0.0235 18 1 1% Thiourea 0.456 22.8 0.0223 19 2 1% "A" 0.363 18.15 0.0247 2 1% Thiourea 0.373 18.65 0.0222 1 Copper complexor "A" is a mixture consisting of 60% by weight hexahydropyrimidine-2-thione and 40% by weight thiourea.
Amounts of dissolved magnetite and copper are determined by atomic absorption analysis of spent solvent. The value of dissolved magnetite is corrected for coupon weight loss.
3 The percent number indicated is the number of grams of additive per 100 milliliters of solution.
From Table II it can be seen that the addition of a copper complexor to an aqueous solution of hydroxyacetic acid, formic acid and sodium erythorbate does not diminish the ability of the solution to dissolve magnetite at 140F (see tests 6 and 10 of Table I and 17, 18, 19 and 20 of Table II) but, in fact, increases the amount of magnetite dissolved. The addition of the copper complexor to an aqueous solution of hydroxyacetic and formic acids in the absence of sodium erythorbate (tests 13, 14 and 15), produces a small increase in the dissolution of magnetite, but the dissolution of copper lZ04372 is greatly increased. When sodium erythorbate and copper complexor are both present in the aqueous solution (tests 17, 18, 19 and 20), greatly improved dissolution of both magnetite and copper are obtained as compared to when neither additive or only one is present, i.e., tests 2, 6, 10, 13, 14, 15 and 16~
Example 3 Small sections of boiler tube containing iron and copper scale are placed in glass beakers, each of which con-tains 225 milliliters of an aqueous solution containing 2%by weight hydroxyacetic acid, 1% by weight formic acid and 0.1% by volume of the corrosion inhibitor described in Example 1. Some of the solutions also contain sodium erythorbate and copper complexor. The solutions are heated to temperatures of 140F and maintained at such temperatures for time periods of 24 hours. At the terminations of the 24-hour test periods, the solutions are analyzed by atomic absorption analysis for iron and copper content and the boiler tube sections are inspected for the presence of scale.
The test sections of boiler tube are cut from two boiler tube samples designated herein as boiler tube sample A
and boiler tube sample B. The scale on boiler tube sample A
consists of magnetite, copper metal and hydroxyapatite [Ca5tP04)30H]. The scale on boiler tube sample B consists of magnetite, copper and nickel.
The results of these tests are set forth in Table III below.
iZ~4372 Table III
Scale Removal by Aqueous Hydroxyacetic-Formic Acid Solutions with and without Sodium Erythorbate and Copper Complexor at 140F for 24 Hours Formulation Results Boiler Sodium Copper Tube Test Erythorbate Complexor Tube Sample No. % % _ % Cu % Fe Appearance A 21 0 0 0.00019 0.28 copper pl~ted A 22 0 1 0.0078 0.45 not clean 3 A 23 1 1 0.0093 0.39 tube clean B 24 0 0 0.0010 0.39 copper plated B 25 0 1 0.0280 0.33 hot side not clean2 B 26 1 1 0.0230 0.29 90% clean4 A mixture consisting of 60% by weight hexahydropyrimidine-2-thione and 40% by weight thiourea.
All copper removed but about 40% iron oxide was still on tube section.
3 All scale removed.
All copper removed, but about 10% iron oxide was still on tube section.
.
From Table III it can be seen that the formulation containing sodium erythorbate and copper complexor is effective in removing iron and copper scale.
Example 4 One hundred milliliter portions of an aqueous solution containing 2% by weight hydroxyacetic acid, 1% by weight formic acid and 0.1% by volume of the corro3ion inhibitor described in Example 1 are placed in three beakers. Two grams of powdered iron oxide are combined with each solution. One percent by weight sodium erythorbate and 1% by weight copper complexor (60% by weight hexahydropyrimidine-2-thione and 40% by weight thiourea) are combined with the first solution which is main-tained at a temperature of 75F for six hours with one minute ~Z1~3~Z
of stirring each hour. One percent by weight copper complexor only is added to the second solution which is also maintained at 75F for a six-hour time period. The third solution is heated to 190F and is maintained at such temperature for a six~hour time period. At the terminations of the six-hour time periods, the solutions are analyzed for dissolved iron.
The results in these tests are shown in Table IV below.
Table IV
Iron Dissolution in Aqueous Hydroxyacetic-Formic Acid Solutions with and without Sodium Erythorbate and Copper Complexor Sodium CopperMagnetite Test Erythorbate ComplexorTemperature Dissolved No. % % F %
27 1 1 75 0.026 28 0 1 75 0.012 29 0 0 190 0.027 2 The percent number indicated is the number of grams of additive per 100 milliliters of solution.
Amounts of dissolved magnetite and copper are determined by atomic absorption analysis of spent solvent. The value of dissolved magnetite is corrected for coupon weight loss.
~ = .
From Table IV it can be seen that the solution con-taining sodium erythorbate and copper complexor ef,fectively dissolves magnetite at 75F.
Claims (20)
1. A method of simultaneously removing iron and copper scales from a ferrous metal surface comprising:
contacting said scale-containing ferrous metal surface with a composition comprised of water, an organic chelating acid or mixture of organic chelating acids, having a pH of less than 7 at room temperature, from about 0.25% to about 5% by weight of a reducing agent which increases the rate of iron dissolution by said organic chelating acid or acids selected from the group consisting of erythorbic acid, alkali metal salts of erythorbic acid, ammonium salts of erythorbic acid and mixtures thereof and from about 0.25%
to about 3% by weight of a copper complexor selected from the group consisting of thiourea, hexahydropyrimidine-2-thione and mixtures thereof; and maintaining said contact for a time and at a temperature from about 75°F to about 150°F sufficient for said scales to be dissolved.
contacting said scale-containing ferrous metal surface with a composition comprised of water, an organic chelating acid or mixture of organic chelating acids, having a pH of less than 7 at room temperature, from about 0.25% to about 5% by weight of a reducing agent which increases the rate of iron dissolution by said organic chelating acid or acids selected from the group consisting of erythorbic acid, alkali metal salts of erythorbic acid, ammonium salts of erythorbic acid and mixtures thereof and from about 0.25%
to about 3% by weight of a copper complexor selected from the group consisting of thiourea, hexahydropyrimidine-2-thione and mixtures thereof; and maintaining said contact for a time and at a temperature from about 75°F to about 150°F sufficient for said scales to be dissolved.
2. The method of claim 1 wherein said organic acid or mixture of organic acids is selected from the group consisting of hydroxyacetic acid, acetic acid, formic acid, malic acid, citric acid, EDTA, and nitrilotriacetic acid.
3. The method of claim 2 wherein said organic acid is a mixture of hydroxyacetic acid and formic acid.
4. The method of claim 3 wherein said scale-containing ferrous metal surface is contacted with said aqueous com-position at a temperature in the range of from about 75°F to about 150°F.
5. The method of claim 3 wherein said reducing agent is sodium erythorbate and said copper complexor is a mixture of thiourea and hexahydropyrimidine-2-thione.
6. The method of claim 1 wherein said aqueous com-position is further characterized to include a ferrous metal corrosion inhibitor comprised of a mixture of heavy aromatic naphtha, ethylene glycol, dibutyl thiourea, acetic acid, alkyl pyridine, nonionic ethoxylated alcohol and ethoxylated amine.
7. The method of claim 1 wherein said organic chelating acid or mixture of acids is present in said composition in an amount in the range of from about 1% to about 10% by weight of said composition, said reducing agent is present in said composition in an amount in the range of from about 0.25% to about 5% by weight of said composition and said copper com-plexor is present in said composition in an amount in the range of from about 0.25% to about 3% by weight of said composition.
8. The method of claim 1 wherein said organic chelating acid is a mixture of hydroxyacetic acid and formic acid and said hydroxyacetic acid is present in said composition in an amount of about 2% by weight of said composition, said formic acid is present in said composition in an amount of about 1%
by weight of said composition, said reducing agent is present in said composition in an amount of about 1% by weight of said composition, and said copper complexor is present in said com-position in an amount of about 1% by weight of said composition.
by weight of said composition, said reducing agent is present in said composition in an amount of about 1% by weight of said composition, and said copper complexor is present in said com-position in an amount of about 1% by weight of said composition.
9. The method of claim 8 wherein said reducing agent is sodium erythorbate and said copper complexor is a mixture of thiourea and hexahydropyrimidine-2-thione.
10. The method of claim 9 wherein said copper complexor mixture consists of 60 parts by weight hexahydropyrimidine-2-thione and 40 parts by weight thiourea.
11. The method of claim 10 wherein said scale-containing ferrous metal surface is contacted with said aqueous com-position at a temperature of about 140°F.
12. A composition for simultaneously removing iron and copper scales from a ferrous metal surface at a temperature in the range of from about 75°F to about 150°F comprising water, an organic chelating acid or mixture of organic chelating acids having a pH of less than 7 at room temperature and which dissolve iron, from about 0.25% to about 5% by weight of a reducing agent selected from the group consisting of erythorbic acid, alkali metal salts of erythorbic acid, ammonium salts of erythorbic acid and mixtures thereof and from about 0.25% to about 3% by weight of a copper complexor selected from the group consisting of thiourea, hexahydropyri-midine-2-thione and mixtures thereof.
13. The composition of claim 12 which is further charac-terized to include a ferrous metal corrosion inhibitor.
14. The composition of claim 13 wherein said corrosion inhibitor is comprised of a mixture of heavy aromatic naphtha, ethylene glycol, dibutyl thiourea, acetic acid, alkyl pyridine, nonionic ethoxylated alcohol and ethoxylated amine.
15. The composition of claim 14 wherein said organic chelating acid is a mixture of hydroxyacetic acid and formic acid.
16. The composition of claim 15 wherein said reducing agent is sodium erythorbate and said copper complexor is a mixture of thiourea and hexahydropyrimidine-2-thione.
17. The composition of claim 16 wherein said copper complexor mixture consists of 60 parts by weight hexahydro-pyrimidine-2-thione and 40 parts by weight thiourea.
18. The composition of claim 13 wherein said organic chelating acid or mixture of organic chelating acids is present in said composition in an amount in the range of from about 1% to about 10% by weight of said composition, said reducing agent is present in said composition in an amount in the range of from about 0.25% to about 5% by weight of said composition and said copper complexor is present in said composition in an amount in the range of from about 0.25% to about 3% by weight of said composition.
19. The composition of claim 13 wherein said organic chelating acid is a mixture of hydroxyacetic acid and formic acid, said hydroxyacetic acid being present in said composi-tion in an amount of about 2% by weight of said composition, said formic acid being present in said composition in an amount of about 1% by weight of said composition, said erythorbic acid reducing agent is sodium erythorbate present in said composition in an amount of about 1% by weight of said composition, and said copper complexor is a mixture of thiourea and hexahydropyrimidine-2-thione present in said composition in an amount of about 1% by weight of said com-position.
20. The composition of claim 19 wherein said copper complexor mixture consists of 60 parts by weight hexahydro-pyrimidine-2-thione and 40 parts by weight thiourea.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US42099882A | 1982-09-21 | 1982-09-21 | |
| US420,998 | 1982-09-21 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1204372A true CA1204372A (en) | 1986-05-13 |
Family
ID=23668765
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000437060A Expired CA1204372A (en) | 1982-09-21 | 1983-09-20 | Methods and compositions for simultaneously removing iron and copper scales from ferrous metal surfaces |
Country Status (3)
| Country | Link |
|---|---|
| EP (1) | EP0104012A3 (en) |
| CA (1) | CA1204372A (en) |
| ES (1) | ES8503728A1 (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2157322B (en) * | 1984-03-29 | 1987-10-21 | Diversey Limited | Removal of iron oxide deposits |
| US4810405A (en) * | 1987-10-21 | 1989-03-07 | Dearborn Chemical Company, Limited | Rust removal and composition thereof |
| CN1047409C (en) * | 1997-03-07 | 1999-12-15 | 沈阳市巨龙防腐技术研究所 | Normal-temp copper pickling corrosion inhibitor |
| DE10346192B4 (en) * | 2003-10-02 | 2009-08-06 | Thyssenkrupp Presta Teccenter Ag | Method for rust removal of molded parts and use of the method |
| ATE384807T1 (en) * | 2004-09-25 | 2008-02-15 | Chemetall Gmbh | METHOD FOR REMOVAL OF LASER SCALE |
| CN112516793A (en) * | 2020-11-10 | 2021-03-19 | 东华理工大学 | Method for reducing Fe (III) EDTA by using sodium iso-VC and method for removing NO in waste gas by using EDTA |
| CN113337827A (en) * | 2021-06-07 | 2021-09-03 | 山东惠中新材料科技有限公司 | Environment-friendly rust remover |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2040546B1 (en) * | 1970-08-14 | 1971-12-02 | Hagen Feldmann | Aqueous solution of an aliphatic carboxylic acid to remove ocher deposits or deposits |
| US3730901A (en) * | 1972-04-27 | 1973-05-01 | Halliburton Co | Composition and method for removing copper containing iron oxide scales from ferrous metals |
| JPS53731B2 (en) * | 1973-07-31 | 1978-01-11 | ||
| DE2457235A1 (en) * | 1974-12-04 | 1976-06-10 | Peter Vodicka | Protecting descaled pickled or cleaned metal articles - against attack by ferric cations by redn. using metals or water soluble cpds. |
-
1983
- 1983-08-26 EP EP83304969A patent/EP0104012A3/en not_active Withdrawn
- 1983-09-20 CA CA000437060A patent/CA1204372A/en not_active Expired
- 1983-09-21 ES ES525797A patent/ES8503728A1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| EP0104012A2 (en) | 1984-03-28 |
| EP0104012A3 (en) | 1985-08-21 |
| ES525797A0 (en) | 1985-03-01 |
| ES8503728A1 (en) | 1985-03-01 |
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