Classifications

• • 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

Definitions

• This invention relates to a method of simultaneously removing iron and copper scales from ferrous metal surfaces, and to compositions useful therefor.
• 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 complexors degrade and are ineffective at temperatures above about 160°F (71 0 C).
• a composition for simultaneously removing iron and copper scales from a ferrous metal surface which comprises water; one or more organic chelating acids which dissolve iron; one or more reducing agents selected from erythorbic acid, and alkali metal salts and ammonium salts of erythorbic acid; and as copper complexor, one or both of thiourea and hexahydropyrimidine-2-thione.
• the invention also includes a method of simultaneously removing iron and copper scales from a ferrous metal surface which comprises contacting said scale-containing ferrous metal surface with a composition of the invention, and maintaing said contact for a time and at a temperature sufficient for said scales to be dissolved.
• 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.
• suitable such acids are hydroxyacetic acid, formic acid, malic acid, citric acid, ethylenediaminetetracetic acid (EDTA), nitrilotriacetic acid, and mixtures of such acids.
• EDTA ethylenediaminetetracetic acid
• nitrilotriacetic acid and mixtures of such acids.
• 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 of from 1% to 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 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 75°F (24°C) to about 150°F (66°C).
• the reducing agents utilised in the compositions are selected from the group consisting of erythorbic acid, alkali metal salts of erythorbic acid, ammonium salts of erythorbic acid and mixtures thereof and are preferably included in the compositions in an amount in the range of from about 0.25% to about 5% by weight of the compositions.
• the reducing agent is sodium erythorbate and is present in the aqueous compositions in an amount of 1% by weight of the compositions.
• the copper complexing compounds utilized in the compositions of this invention are thiourea and hexahydro- pyrimidine-2-thione. A mixture of the two can be used.
• the copper complexor is preferably included in the aqueous composition in an amount of from 0.25% to 3% by weight of the compositions.
• the copper complexor is a mixture of hexyhydropyrimidine-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 composition in an amount of about 2% by weight of the composition, formic acid present in the composition in the 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.
• ferrous metal corrosion inhibitors can be included in the compositions of this invention, as for example, dibutyl-thiourea, quaternary alkyl pyridinium salts, alkylbenzene sulfonate and heavy aromatic naphtha.
• the most preferred ferrous metal corrosion inhibitor for use in accordance with this invention is a low chloride inhibitor mixture comprised 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 nonionic ethoxylated alcohol and 5% by weight ethoxylated amine.
• the corrosion inhibitor is preferably included in the aqueous composition in an amount of from about .05% to about 6% by volume of the composition.
• 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 composition 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 environment does not result.
• the temperature of the aqueous composition during the contact of the scale-containing surfaces can be as low as 75°F (24°C) while still efficiently removing scale from the surfaces up to as high as about 150°F (66° C ).- At temperatures above about 150°F (66°c), degradation of the copper complexors begins to take place.
• the most preferred contact temperature is about 140°F (60°C).
• 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 75°F (24°C) to about 150°F (66°C) in a single stage treatment.
• Aqueous solutions containing 2% by weight hydroxyacetic 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 1 below and the solutions are maintained at such temperatures for time periods of six hours.
• 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. The results of these tests are given in Table I below.
• the corrosion inhibitor is a commercially available mixture comprised 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 nonionic ethoxylated alcohol and 5% by weight ethoxylated amine.
• 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 140°F (60°C) 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.
• boiler tube sample A 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 a magnetite, copper metal and hydroxyapatite [Ca 5 (PO 4 ) 3 OH].
• the scale on boiler tube sample B consists of magnetite, copper and nickel.
• Example 1 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 corrosion 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 maintained at a tmperature of 75°F (24°C) for six hours with one minute of stirring each hour. One percent by weight copper complexor only is added to the second solution which is also maintained at 75 F (24°C) for a six-hour time period.
• 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 maintained at a tmperature of 75°F (24
• the third solution is heated to 190°F (88°C) 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.

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• 1983
  • 1983-08-26 EP EP83304969A patent/EP0104012A3/de not_active Withdrawn
  • 1983-09-20 CA CA000437060A patent/CA1204372A/en not_active Expired
  • 1983-09-21 ES ES525797A patent/ES525797A0/es active Granted

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