US2927068A - Inhibiting corrosion - Google Patents

Inhibiting corrosion Download PDF

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US2927068A
US2927068A US704818A US70481857A US2927068A US 2927068 A US2927068 A US 2927068A US 704818 A US704818 A US 704818A US 70481857 A US70481857 A US 70481857A US 2927068 A US2927068 A US 2927068A
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coating
water
solution
sodium
phosphoric acid
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Glenn A Marsh
Schaschl Edward
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Pure Oil Co
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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
    • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F13/00—Inhibiting corrosion of metals by anodic or cathodic protection
    • C23F13/02—Inhibiting corrosion of metals by anodic or cathodic protection cathodic; Selection of conditions, parameters or procedures for cathodic protection, e.g. of electrical conditions
    • C23F13/06—Constructional parts, or assemblies of cathodic-protection apparatus
    • 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
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
    • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
    • C23C22/07—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing phosphates
    • C23C22/23—Condensed phosphates
    • 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
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
    • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
    • C23C22/24—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing hexavalent chromium compounds
    • C23C22/33—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing hexavalent chromium compounds containing also phosphates
    • 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
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/73—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals characterised by the process
    • 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
    • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F13/00—Inhibiting corrosion of metals by anodic or cathodic protection
    • C23F13/02—Inhibiting corrosion of metals by anodic or cathodic protection cathodic; Selection of conditions, parameters or procedures for cathodic protection, e.g. of electrical conditions
    • C23F13/04—Controlling or regulating desired parameters
    • 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
    • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F2213/00—Aspects of inhibiting corrosion of metals by anodic or cathodic protection
    • C23F2213/30—Anodic or cathodic protection specially adapted for a specific object
    • C23F2213/31—Immersed structures, e.g. submarine structures
    • 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
    • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F2213/00—Aspects of inhibiting corrosion of metals by anodic or cathodic protection
    • C23F2213/30—Anodic or cathodic protection specially adapted for a specific object
    • C23F2213/32—Pipes

Definitions

  • This invention relates to cathodic protection of ferrous metal structures submerged under water or buried underground, and is more particularly directed to a method of treating such structures prior to submerging or burying them in order to reduce the amount of current necessary to give adequate cathodic protection against corrosion.
  • cathodic protection it is common practice to apply cathodic protection to :structures such as pipe lines buried underground or submerged under water, as well as to structures such as drilling platforms erected in water and ships used in salt water. It is also common practice to wrap, coat or encase ferrous'metal structures which are buried or submerged in order to prevent corrosion. Such methods are expensive. Where coating or wrapping is not practiced, the amount of current required to aiford necessary cathodic protection is usually prohibitive.
  • Our invention resides in coating the surface with a slution of an alkali metal hexametaphosphate, drying the coating, and then applying a second coating of a solution of an alkali metal chromate or dichromate and a phosphoric acid, and drying the second coating prior to submerging or burying the pipe.
  • Other objects of the invention will become manifest from the following description and the accompanying drawing, of which the single ligure is a graph showing rate of corrosion of test specimens when protected in accordance with this invention as compared with specimens which are not so protected.
  • the structure to be protected such as pipe or piling
  • the clean structure is then coated with a solution, preferably freshly prepared, of an alkali metal hexametaphosphate, preferably sodium hexametaphosphate.
  • a solution of any desired concentration may be used but we prefer Va solution ⁇ of about 5-20% by weight sodium hexametaphosphate.
  • the solution is applied to the structure by brushing, spraying, dipping, or any other suitable manner.
  • the specimen may be left in the solution for a period of l-100 minutes at a temperature ⁇ of about 40l20 F.
  • a dilute, aqueous solution containing about 0.5-1% of sodium dichromate and inthe neighborhood of about 0.l1% of ⁇ phosphoric acid.
  • Dilute solutions should be used so that when the coating is dried it will be very thin, weighing less than 1 gram per sq. ft.
  • the temperature of the solution should be maintained at about 40-120 F., and where immersion is used, the period of immersion will be about 1-100 minutes. Preferred conditions of immersion are l20 F. fora period of 5-10 minutes.
  • the structure to be protected is one which is partially corroded or rusted
  • the structure to be protected is clean, only a ⁇ single coating with the hexametaphosphate and with the dichromate-phosphoric acid solution is required,
  • an ordinary rusted steel specimen was wire-brushed to remove loose rust and then degreased by scrubbing with carbon tetrachloride.
  • the degreased specimen was immersed for 15 minutes at room temperature in a freshly prepared 20% solution of hexametaphosphate, after which it was removed, drained and allowed to dry in air. After the specimen was dried it was immersed for l0 minutes in an aqueous solution at F., containing 0.67% by weight of sodium ⁇ dichromate and 0.5% by weight of 85% phosphoric acid. The specimen was removed from the second solution, drained, and dried in air.
  • Curve A represents the results obtained using a probe which had been coated in the manner just described in connection with the previous example, but to which no cathodic protection was applied.
  • Curve B shows the results obtained with a probe which had not been coated but to which a cathodic protection of l m.a./ sq. ft. current density had been applied.
  • ⁇ Curve C shows the results obtained when the probe was coated in the manner described in connection with the previous example and to which cathodic protection current had been applied lat a current density of l ma./ sq. ft. In this test the current was interrupted for one hour during each 24 hours.
  • Phosphoric acid-l-HZO added iron lings in excess, after bubbles stopped; filtered through coarse lter paper; added 100 cc. of HiPOl; then added 10 cc. of manganous chloride).
  • Disodium Phosphate 0.1% Monosodium Phosphate. 99.00% Water.
  • Silicone (Mfg. by'Dow Corning). Silicone (Mfg. by G.E.)
  • Our invention is equally eiective in protecting khotv,rolled and cold'rolled steel and in protecting other ferrous metal alloys.
  • the coatings are veasy and inexpensive to apply, it 'being necessary only to coat the entire surface to beprotected and permit each coating to dry before applying the .subsequent coating or before .mmersing or burying the structure. Whereas it is often necessary to use in the neighborhood of 30-50lma./sq. ft. current density to protect uncoated structures, we are able to fully protect structures which have been coated ⁇ in accordance with our invention by the application of as little as 1 ina/sq. ft. of current density. in applying our invention to a structure to be protected, We prefer after burying or submerging the structure to initially apply a higher current density of the order of l0-20 ma./sq. ft. and gradually decrease the current density to the minimum required to aiord protection as indicated by corrosionmeter tests.
  • the sodium hexametaphosphate is an aqueous solution containing 5-20% of sodium hexametaphosphate and the second solution is an aqueous solution containing about 0.67% sodium dichromate and about 0.5% phosphoric acid by weight.

Description

March l', 1960 G. A. MARSH ETAL INHIBITING coRRosIoN Filed Dec. 23, 1957 nmkdoo wm wm C# (SBHONIOHDIN V* NOISOHHOQ IN VENTOR.
GLEN/v A MARSH BY EDWARD soHAQcHL ATTORNEY United States Patent INHIBITIN G CORROSION Glenn A. Marsh and Edward Schaschl, Crystal Lake, Ill., assignors to The Pure Oil Company, Chicago, Ill., a corporation of Ohio Y Application December `23, 1957, Serial No. 704,818
7 claims. (c1. V24m- 147) This invention relates to cathodic protection of ferrous metal structures submerged under water or buried underground, and is more particularly directed to a method of treating such structures prior to submerging or burying them in order to reduce the amount of current necessary to give adequate cathodic protection against corrosion.
It is common practice to apply cathodic protection to :structures such as pipe lines buried underground or submerged under water, as well as to structures such as drilling platforms erected in water and ships used in salt water. It is also common practice to wrap, coat or encase ferrous'metal structures which are buried or submerged in order to prevent corrosion. Such methods are expensive. Where coating or wrapping is not practiced, the amount of current required to aiford necessary cathodic protection is usually prohibitive.
We have discovered an inexpensive method `of treating such structures prior to burying underground or sub- `merging in water which is inexpensive and enables adequate cathodic protection to be obtained with approximately 2-20% of the currentwhich is ordinarily required for uncoated structures.
Our invention resides in coating the surface with a slution of an alkali metal hexametaphosphate, drying the coating, and then applying a second coating of a solution of an alkali metal chromate or dichromate and a phosphoric acid, and drying the second coating prior to submerging or burying the pipe.
It is 4an object of our invention to provide an -inexpensive method for protecting ferrous metal structures buried underground or submerged under water against corrosion. It is another object of our invention to provide an inexpensive coating on ferrous metal structures which will enable buried or submerged structures to be cathodically protected against corrosion by a small amount of current. Other objects of the invention will become manifest from the following description and the accompanying drawing, of which the single ligure is a graph showing rate of corrosion of test specimens when protected in accordance with this invention as compared with specimens which are not so protected.
In accordance with our invention, the structure to be protected, such as pipe or piling, is wire-brushedor sanded to remove loose rust, and then tiegreased by scrubbing with carbon tetrachloride or equivalent grease solvent. The clean structure is then coated with a solution, preferably freshly prepared, of an alkali metal hexametaphosphate, preferably sodium hexametaphosphate. A solution of any desired concentration may be used but we prefer Va solution `of about 5-20% by weight sodium hexametaphosphate. The solution is applied to the structure by brushing, spraying, dipping, or any other suitable manner. Where the coating is performed by dipping or immersing, the specimen may be left in the solution for a period of l-100 minutes at a temperature `of about 40l20 F. We prefer to maintain the solution at about 60-90" F. and allow the structure to rerice main immersed for about 5-15 minutes, after which it is dried in air and then given a second coating with a solution of an alkali metal chromate or dichromate, such as sodium or potassium dichromate, containing a phosphoric acid, such as meta, ortho, or pyro-phosphoric acid. We prefer to use a dilute, aqueous solution containing about 0.5-1% of sodium dichromate and inthe neighborhood of about 0.l1% of` phosphoric acid. Dilute solutions should be used so that when the coating is dried it will be very thin, weighing less than 1 gram per sq. ft. In coating with the dichromate-phosphoric acid solution the temperature of the solution should be maintained at about 40-120 F., and where immersion is used, the period of immersion will be about 1-100 minutes. Preferred conditions of immersion are l20 F. fora period of 5-10 minutes.
Where the structure to be protected is one which is partially corroded or rusted, it has been found expedient to repeat the hexametaphosphate coating after coating with the dichromate-phosphoric acid solution, and drying, and to also repeat the dichromate-phosphoric acid coating after the second hexametaphosphate coating and drying. Where the structure to be protected is clean, only a `single coating with the hexametaphosphate and with the dichromate-phosphoric acid solution is required,
In order to demonstrate the invention, an ordinary rusted steel specimen was wire-brushed to remove loose rust and then degreased by scrubbing with carbon tetrachloride. The degreased specimen was immersed for 15 minutes at room temperature in a freshly prepared 20% solution of hexametaphosphate, after which it was removed, drained and allowed to dry in air. After the specimen was dried it was immersed for l0 minutes in an aqueous solution at F., containing 0.67% by weight of sodium `dichromate and 0.5% by weight of 85% phosphoric acid. The specimen was removed from the second solution, drained, and dried in air. The treatment just described with the two solutions was repeatedon the specimen, after which the specimen was immersed in aerated, agitated water and cathodic protection was applied at a current density of 3 milliamperes per sq. ft. of surface area. No visible corrosion occurred over a period of a 30-day test period.
In order to further demonstrate the efcacy of the method constituting our invention, a series of experiments were performed, the results of which are graphically represented in the drawing. In these tests corrosion test- -probes of the type similar lto those sold by Labline, Inc. and disclosed in their Bulletins Nos. 52 and 5205, and claimed in our copending application Serial No. 528,032, led August 12, 1955 and also in application of Lynn E. Ellison, Serial No. 631,697, led December 3l, 1956, Patent No. 2,824,283, in which the test element was made of mild steel, were used in the tests, and loss of thickness was read directly on the corrosion meter. The results in these tests are shown in the drawing by plotting a loss in thickness in micro-inches against time. The slope of the curve at any point is the corrosion 4rate at that particular time. Curve A represents the results obtained using a probe which had been coated in the manner just described in connection with the previous example, but to which no cathodic protection was applied. Curve B shows the results obtained with a probe which had not been coated but to which a cathodic protection of l m.a./ sq. ft. current density had been applied. `Curve C shows the results obtained when the probe was coated in the manner described in connection with the previous example and to which cathodic protection current had been applied lat a current density of l ma./ sq. ft. In this test the current was interrupted for one hour during each 24 hours. In a similar test, represented by curve D, the current was applied continuously without interruption. The results 3 as depicted in the drawing show that not only does the combination of coating and low :current-density eathodic protection aiord substantially complete protection against corrosion, but, it further shows that interruption of the current does not have a serious detrimental effect on the protection afforded. Maximum protection is obtained, however, when the current is continuous.
A further series of tests was run to `determine whether other solutions when used in conjunction with lov/density cathodie current would protect rusted steel against corrosion. The vario-us solutions used in lthese tests and the 4combinations in which the solutions were used for coating the probes are given in the following Tables I and II.
TABLE I Solutions used in tests Identication Composition 50% EQOA-50% Formula 30 alcohol. 10% NaOH.
5% Chromie Acid. 10% Chromic Acid.
Cone. HNOa. 30% HNOQ. 2% Versene Fe3.
5% Sodium Hexametaphosphate. 20% Sodium Hexametaphosphate. Straight HaPO4. 50-50 HgPOi-l-Formula 30 alcohol.
20% Sodium Hydroxide. y A 20% Sodium Hydroxide saturated in Sodium Nitrite. Water Glass. Water Glass 90%-l-Calcium Chloride 10% plus 500 g.
dist. water. Saturated sodium chromate. 50-50 Satd. potassium dichromate-H3P04.
Saturated potassium dichromate solution, 500 cc.l1
cc. sulfuric acid. 50-50 Phosphoric acid-l-distilled water plus 10 g. iron filings. i
50-50 H3PO4+Formula 30 alcohol (added 10 g. manganous sulfate).
50-50 Phosphoric acid-l-water solution (to 200 cc. o this added zinc granules until just saturated with zinc, then added 20 cc. phosphoric acid).
350 g.850 g. Phosphoric acid-l-HZO (added iron lings in excess, after bubbles stopped; filtered through coarse lter paper; added 100 cc. of HiPOl; then added 10 cc. of manganous chloride).
250 g.-250 g. HgPOl-l-water (added zinc granules in excess, after bubbles stopped; poured oi the solution leaving zinc behind. Then added 50 ce. H3PO4. Then added l cc. manganous chloride).
Saturated Calcium Chloride-l5% HgPOl.
% Tri-Sodium Phosphate.
% Potassium Permanganate.
5% Ammonium Persulfate.
50-50 (20% Sodium Hydroxide saturated with Sodium Nitrite)water glass. {50% Water Glass.
50% NaOH. 50% Water Glass-5% (20% NaOH) 45% water. 5% Water Glass-95% (20% NaOH). 5% Water Glass, 45% (20% NaOH) 50% water. Calcium Chloride. 10% Copper Sulfate. Mercurio Nitrate. 5% Sodium Arsenite. Saturated Sodium Chromate. Saturated sodium bicarbonate. 0.67% Sodium Dichromate. 0.5% Phosphoric Acid. 98.83% Water. 0.2% Sodium Nitrite. 0.2% Diammonium Hydrogen Phosphate. 99.6% Water. 0.5 Sodium Nitrite. 0.5% Diammonium Hydrogen Phosphate. 99.0% Water. 0.7% Sodium Nitrite. 0.7% Diammonium Hydrogen Phosphate. 98.6% Water. 0.5% Sodium Nitrite. 0.25% Disodium Phosphate.
% Monosodium Phosphate.
99.00% Water.
0.5% Sodium Nitrite.
0.37% Disodium Phosphate.
0.13% Monosodium Phosphate.
99.00% Water.
Saturated Trisodium phosphate` Sodium Nitrite 0.5%.
0.5% Diammonium Phosphate.
{0.5% Sodium Nitrite.
0.5% Diammonium Phosphate. 99.00% Water.
0.5% Sodium Nitrite.
0.5% Disodium Phosphate. 0.1% Monosodium Phosphate. 99.00% Water.
TABLE @continued Identcation Composition 0.5% Sodium N itrlte. 41 0.25% Disodium Phosphate.
.25% Water. .5% Sodium Nitrite. .1% Dlsodium Phosphate. 0.4% Monosodium Phosphate. 99.00% Water. 43 {1% Dritilm.
"""""""" 99%Hexane.
Silicone (Mfg. by'Dow Corning). Silicone (Mfg. by G.E.)
Gora
TABLE II Solution applied as coating and order in which applied to test specimen Second First Coating Coating Coating 'In no case were the solutions effective in affording p rotection except in the two tests in which the probe was initially coated with the sodium hexametaphosphate solution and then coated with'the sodium dichromatephos phoric acid solution.
Our invention is equally eiective in protecting khotv,rolled and cold'rolled steel and in protecting other ferrous metal alloys.
The coatings are veasy and inexpensive to apply, it 'being necessary only to coat the entire surface to beprotected and permit each coating to dry before applying the .subsequent coating or before .mmersing or burying the structure. Whereas it is often necessary to use in the neighborhood of 30-50lma./sq. ft. current density to protect uncoated structures, we are able to fully protect structures which have been coated `in accordance with our invention by the application of as little as 1 ina/sq. ft. of current density. in applying our invention to a structure to be protected, We prefer after burying or submerging the structure to initially apply a higher current density of the order of l0-20 ma./sq. ft. and gradually decrease the current density to the minimum required to aiord protection as indicated by corrosionmeter tests.
What is claimed is:
l. In a process for cathodically protecting ferrous metal structures, submerged in water or buried beneath the ground, against corrosion, the steps of coating the bare metal structure with a solution of alkali metal hexametaphosphate, drying the coating, then coating the structure with a second solution containing a phosphoric acid and an alkali metal salt of the group consisting of alkali metal chromates and dichromates, drying the coating before submerging or burying the structure, contacting said coating with the water or ground, and cathodically protecting the structure by applying thereto a current having a density equal to a small fraction of that required to protect the uncoated structure against corrosion.
2. Process in accordance with claim 1 in which the structure is cleaned and degreased prior to applying the solution of alkali metal hexametaphosphate thereto.
3. Process in accordance with claim 2 inV which the alkali metal hexametaphosphate is sodium hexametaphosphate.
4. Process in accordance with claim 3 in which the second solution is a dilute solution of phosphoric acid and sodium dichromate.
5. Process in accordance with claim 4 in which the sodium hexametaphosphate is an aqueous solution containing 5-20% of sodium hexametaphosphate and the second solution is an aqueous solution containing about 0.67% sodium dichromate and about 0.5% phosphoric acid by weight.
6. A process according to claim 1 in which the current density is about 1 milli-ampere per square foot.
7. A process according to claim 1 in which the current density is initially 10-20 milli-amperes per square foot and is gradually decreased to the minimum current density required to afford substantially complete cathodic protection as indicated by corrosion rate measurements.
Reereuces Cited in the le of this patent UNTED STATES PATENTS 2,163,984 Pekovic June 27, 1939 2,337,856 Rice Dec. 28, 1943 2,499,261 Rosenbloom Feb. 28, 1950 2,787,557 Christensen et al. Apr. 2, 1957

Claims (1)

1. IN A PROCESS FOR CATHODICALLY PROTECTING FERROUS METAL STRUCTURES, SUBMERGED IN WATER OR BURIED BENEATH THE GROUND, AGAINST CORROSION, THE STEPS OF COATING THE BARE METAL STRUCTURE WITH A SOLUTION OF ALKALI METAL HEXAMETAPHOSPHATE, DRYING THE COATING THEN COATING THE STRUCTURE WITH A SECOND SOLUTIOIN CONTAINING A PHOSPHORIC ACID AND AN ALKALI METAL SALT OF THE GROUP CONSISTING OF ALKALI METAL CHROMATES AND DICHROMATES, DRYING THE COATING BEFORE SUBMERGING OR BURYING THE STRUCTURE, CONTACTING SAID COATING WITH THE WATER OR GROUND, AND CATHODICALLY PROTECTING THE STRUCTURE BY APPLYING THERETO A CURRENT HAVING A DENSITY EQUAL TO A SMALL FRACTION OF THAT REQUIRED TO PROTECT THE UNCOATED STRUCTURE AGAINST CORROSION.
US704818A 1957-12-23 1957-12-23 Inhibiting corrosion Expired - Lifetime US2927068A (en)

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3958049A (en) * 1971-11-04 1976-05-18 Rodco, Inc. Method of inspecting and treating sucker rod
US4714529A (en) * 1985-12-16 1987-12-22 General Motors Corporation Method of coating metal surfaces in oil-based lubricants
US4808281A (en) * 1988-06-27 1989-02-28 General Motors Corporation Phosphate coating complex metal surfaces
US4828655A (en) * 1988-02-18 1989-05-09 General Motors Corporation Method of forming molybdenum/iron phosphate surface coating material

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2163984A (en) * 1935-12-09 1939-06-27 Petkovic Valentin Anton Process for the preparation of a rust-preventing coating on metallic objects
US2337856A (en) * 1942-10-27 1943-12-28 Hall Lab Inc Process of retarding the corrosion of metal by water
US2499261A (en) * 1945-11-23 1950-02-28 Hall Lab Inc Compositions and methods for depositing amorphous metal-phosphate coatings on metal surfaces
US2787557A (en) * 1954-05-11 1957-04-02 Koppers Co Inc Marine organism resistant composition and method of coating structural articles therewith

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2163984A (en) * 1935-12-09 1939-06-27 Petkovic Valentin Anton Process for the preparation of a rust-preventing coating on metallic objects
US2337856A (en) * 1942-10-27 1943-12-28 Hall Lab Inc Process of retarding the corrosion of metal by water
US2499261A (en) * 1945-11-23 1950-02-28 Hall Lab Inc Compositions and methods for depositing amorphous metal-phosphate coatings on metal surfaces
US2787557A (en) * 1954-05-11 1957-04-02 Koppers Co Inc Marine organism resistant composition and method of coating structural articles therewith

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3958049A (en) * 1971-11-04 1976-05-18 Rodco, Inc. Method of inspecting and treating sucker rod
US4714529A (en) * 1985-12-16 1987-12-22 General Motors Corporation Method of coating metal surfaces in oil-based lubricants
US4828655A (en) * 1988-02-18 1989-05-09 General Motors Corporation Method of forming molybdenum/iron phosphate surface coating material
US4808281A (en) * 1988-06-27 1989-02-28 General Motors Corporation Phosphate coating complex metal surfaces

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