Formic-carboxylic acid mixtures for removing iron oxide sclae from steel surfaces
First Claim
1. A method for removing iron oxide containing scale from interior surfaces of a steel vessel, comprising:
- circulating an aqueous cleaning solution through said vessel; and
contacting said scale with said aqueous cleaning solution at a temperature between about 150°
F. and a boiling point of said aqueous cleaning solution, for a time less than about 30 hours and under a reducing atmosphere so that removed iron remains in solution,said aqueous cleaning solution comprisingabout 0.5 to about 10.0 percent-by-weight in total of formic acid and at least one carboxylic acid selected from a group consisting of acetic, propionic, glycolic, lactic, malonic, fumaric, succinic, glutaric, malic, tartaric, gluconic and citric acids wherein a weight ratio of formic acid to carboxylic acid is from 4;
1 to 9;
1, andabout 0.1 to about 1.0 percent-by-weight of a corrosion inhibitor effective to limit corrosive attack of organic acids on steel to no more than about 0.015 lb/ft2 /day at the temperature of said contacting.
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Accused Products
Abstract
Methods and solutions useful for removing iron oxide-containing scale from the interior surfaces of steel. An aqueous cleaning solution containing formic acid and at least one carboxylic acid having at least two carbon atoms wherein the weight ratio of formic acid to higher carboxylic acid is greater than about 4:1 is contacted with the scale in the absence of an oxidizing agent. Preferred carboxylic acids are the mono-, di-, hydroxy-, and polyhydroxy-carboxylic acids having from two to six carbon atoms. More preferrably, the aqueous solution includes about 0.5-10.0 percent-by-weight in total of such acids wherein the weight ratio of formic acid to higher carboxylic acid is from about 4:1 to about 9:1, together with an effective amount of an organic acid corrosion inhibitor and, optionally, a scale dissolution accelerating agent. Preferrably, contact is under a reducing atmosphere, at a temperature in the range of about 150°-200° F. and a pH less than 7. More preferrably, the cleaning solution is circulated through the vessel for a time less than 30 hours. These high ratio formic/carboxylic acid solutions are capable of holding more iron in solution than low ratio solutions, especially in a reducing atmosphere where iron is maintained in the ferrous state.
24 Citations
25 Claims
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1. A method for removing iron oxide containing scale from interior surfaces of a steel vessel, comprising:
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circulating an aqueous cleaning solution through said vessel; and contacting said scale with said aqueous cleaning solution at a temperature between about 150°
F. and a boiling point of said aqueous cleaning solution, for a time less than about 30 hours and under a reducing atmosphere so that removed iron remains in solution,said aqueous cleaning solution comprising about 0.5 to about 10.0 percent-by-weight in total of formic acid and at least one carboxylic acid selected from a group consisting of acetic, propionic, glycolic, lactic, malonic, fumaric, succinic, glutaric, malic, tartaric, gluconic and citric acids wherein a weight ratio of formic acid to carboxylic acid is from 4;
1 to 9;
1, andabout 0.1 to about 1.0 percent-by-weight of a corrosion inhibitor effective to limit corrosive attack of organic acids on steel to no more than about 0.015 lb/ft2 /day at the temperature of said contacting. - View Dependent Claims (2)
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3. A method for removing iron oxide containing scale from interior surfaces of a steel vessel, comprising:
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contacting said scale with an aqueous cleaning solution comprising about 0.5 to about 10.0 percent-by-weight in total of formic acid and at least one carboxylic acid having from two to six carbon atoms and selected from a group consisting of mono-carboxylic acids, dicarboxylic acids, hydroxycarboxylic acids and polyhydroxycarboxylic acids wherein a weight ratio of formic acid to carboxylic acid is from 4;
1 to 20;
1; andabout 0.1 to about 1.0 percent-by-weight of a corrosion inhibitor effective to inhibit corrosive attack of organic acids on steel; and maintaining a reducing atmosphere in said vessel during said contacting so that removed iron remains in solution. - View Dependent Claims (4, 5)
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6. A cleaning solution useful for removing iron oxide containing scale from interior surfaces of a steel vessel, comprising:
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about 0.5 to about 10.0 percent-by-weight in total of formic acid and at least one carboxylic acid having from two to six carbon atoms and selected from a group consisting of mono-carboxylic acids, dicarboxylic acids, hydroxycarboxylic acids and polyhydroxycarboxylic acids wherein a weight ratio of formic acid to carboxylic acid is greater than 4;
1;about 0.1 to about 1.0 percent-by-weight of a corrosion inhibitor effective to inhibit the corrosive attack of organic acids on steel to no more than about 0.015 lb/ft2 /day at the cleaning temperatures; up to about 1.0 percent-by-weight of a scale dissolution accelerating agent selected from a group consisting of hydrofluoric acid and ammonium bifluoride; and balance being water. - View Dependent Claims (7)
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8. A method for removing iron oxide containing scale from interior surfaces of a steel vessel, comprising:
contacting said scale with an aqueous cleaning solution containing formic acid and at least one carboxylic acid having at least two carbon atoms wherein a weight ratio of formic acid to carboxylic acid is greater than 4;
1, said contacting occurring in absence of an oxidizing agent so that removed iron remains in solution.- View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
Specification