WO1994005461A1 - Procede permettant d'enlever des contaminants de la surface de substrats - Google Patents

Procede permettant d'enlever des contaminants de la surface de substrats Download PDF

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Publication number
WO1994005461A1
WO1994005461A1 PCT/US1993/008038 US9308038W WO9405461A1 WO 1994005461 A1 WO1994005461 A1 WO 1994005461A1 US 9308038 W US9308038 W US 9308038W WO 9405461 A1 WO9405461 A1 WO 9405461A1
Authority
WO
WIPO (PCT)
Prior art keywords
salts
substrate
water
neutralized
metal substrate
Prior art date
Application number
PCT/US1993/008038
Other languages
English (en)
Inventor
Jack R. Cook
Loren L. Hatle
Original Assignee
Whitemetal, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US07/938,202 external-priority patent/US5317841A/en
Priority claimed from US08/031,695 external-priority patent/US5441441A/en
Application filed by Whitemetal, Inc. filed Critical Whitemetal, Inc.
Priority to AU50930/93A priority Critical patent/AU5093093A/en
Publication of WO1994005461A1 publication Critical patent/WO1994005461A1/fr

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24C—ABRASIVE OR RELATED BLASTING WITH PARTICULATE MATERIAL
    • B24C7/00—Equipment for feeding abrasive material; Controlling the flowability, constitution, or other physical characteristics of abrasive blasts
    • B24C7/0084—Equipment for feeding abrasive material; Controlling the flowability, constitution, or other physical characteristics of abrasive blasts the abrasive material being fed in a mixture of liquid and gas
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B08—CLEANING
    • B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
    • B08B3/00—Cleaning by methods involving the use or presence of liquid or steam
    • B08B3/02—Cleaning by the force of jets or sprays
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B08—CLEANING
    • B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
    • B08B7/00—Cleaning by methods not provided for in a single other subclass or a single group in this subclass
    • B08B7/02—Cleaning by methods not provided for in a single other subclass or a single group in this subclass by distortion, beating, or vibration of the surface to be cleaned
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24C—ABRASIVE OR RELATED BLASTING WITH PARTICULATE MATERIAL
    • B24C11/00—Selection of abrasive materials or additives for abrasive blasts
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24C—ABRASIVE OR RELATED BLASTING WITH PARTICULATE MATERIAL
    • B24C7/00—Equipment for feeding abrasive material; Controlling the flowability, constitution, or other physical characteristics of abrasive blasts
    • B24C7/0046—Equipment for feeding abrasive material; Controlling the flowability, constitution, or other physical characteristics of abrasive blasts the abrasive material being fed in a gaseous carrier
    • B24C7/0076—Equipment for feeding abrasive material; Controlling the flowability, constitution, or other physical characteristics of abrasive blasts the abrasive material being fed in a gaseous carrier the blasting medium being a liquid stream

Definitions

  • This invention relates to a method for the removal of surface contaminants from metal or concrete substrates, and more particularly to such a method in which an abrasive material is blasted in a pressurized water stream against the surface of such substrates for cleaning the surface.
  • Various coatings are applied to metal substrates. It is highly desirable that the metal substrate be effectively cleaned of contaminants prior to the application of the coating so that the useful coating life may be prolonged.
  • Contaminants include liquid halogens, sulfur compounds, and occasionally nitrogen compounds.
  • Such surface contaminants include water soluble salts, such as chlorides, sulfates and nitrates.
  • salts are iron salts (ferrous and ferric salts.)
  • Concrete is of course different from metals such as steel in that it is not chemically reactive with water soluble salts such as sodium chloride.
  • ferrous chloride is formed whenever steel or iron and soluble chloride in moisture are in contact. This reaction, in itself, is a strong corrodant of steel surfaces. Upon exposure to air, ferrous chloride oxidizes to ferric chloride, a hygroscopic salt with a natural affinity for moisture in the air. Trace amounts of either ferric or ferrous chloride remaining on the substrate accumulate moisture from the air resulting in the formation of a concentrated iron chloride solution on the surface of the steel substrate. Iron ions, chloride ions and water comprise an electrolytic solution that drives an electrochemical corrosion reaction.
  • Coatings applied over such a substrate fail in a short period of time due to the concentrated iron chloride solution on the substrate drawing water through the coating by osmosis and creating a blistering or disbondment of the coating. Rates of coating failure due to osmotic blistering are dependent on the thickness and porosity of the coating.
  • Concrete is a cast material that is porous by nature.
  • the porosity of concrete may provide water and air pockets extending from the surface into the material to a depth of one inch.
  • the amount of porosity varies with the method of casting of the cement and the type of finish applied. Hard troweling of the surface minimizes porosity.
  • Dry abrasive blasting can not efficiently remove localized sources of corrosion initiation sites (commonly referred to as corrosion cells) because an operator may not be able to see such contaminants and direct a dry grit blast against such corrosion initiation sites.
  • Efforts to develop methods for removal of these non-visible contaminants from substrates have been generally unsuccessful although several techniques have been tried with partial success, such as, for example, (1) dry blasting followed by water rinsing (several cycles), (2) hard grit wet abrasive blasting, (3) high pressure washing, and (4) acid washing followed by water rinsing.
  • the coating performance of concrete substrates is affected primarily by two problems.
  • One problem involves the formation of a thin layer of non-reactive materials on the surface of cured new concrete as a residue.
  • the residue forms a weak powdering material with little adhesive strength and therefore is not acceptable for the subsequent application of a coating material over the surface of the concrete.
  • the other problem is that uncleaned concrete of any age contains water soluble salts in the voids. These salts create the same hygroscopic condition that salt contaminants in steel create as a microscopic layer of water is always present on the substrate surface regardless of temperature and humidity conditions, due to the hydroscopic nature of the salt contaminants. Coatings applied over salt contaminated surfaces fail in a short period of time due to poor adhesion caused by osmotic blistering.
  • the present invention is particularly directed to a method for the removal of surface contaminants from metal substrates including as a first step the blasting with an abrasive, such as sodium bicarbonate, in a pressurized stream of water against the surface of the substrate with the water having a high purity. After the abrasive blast against the metal substrate, a pressurized high purity water wash is applied against the surface of the metal substrate in a second step. The water wash removes neutralized soluble salts, other surface contaminants, and any residual abrasive material.
  • the treatment of the surface of the metal substrate in accord with the process described above results in a superior cleaned surface that is free of any detectable ionic contaminants.
  • a variety of tests may be utilized to test the presence of soluble chemical salts such as ferrous sulfates, ferrous sulfides, ferrous chlorides, or sodium chloride. Some tests are effective to measure sodium chloride (Na Cl) but only to around forty parts per million (equivalent to 40 mg/m 2 or 4 ⁇ g/cm 2 ) based on a dilution of 10 ml of water per 100 square cm of substrate.
  • a preferred test for soluble iron salts (e.g. for steel structures) utilized for the present invention is effective for consistently providing a level of cleanliness below 1.5 milligrams of soluble contaminants per square meter of substrate area (1.5 mg/m 2 or 0.15 ⁇ g/cm 2 ).
  • a level of cleanliness below 40 mg/m 2 (4 ⁇ g/cm 2 ) for a majority of applications of the present invention.
  • a level of cleanliness below 100 mg/m 2 (10 ⁇ g/cm 2 ) may be satisfactory under certain conditions. While parts per million (ppm) have been utilized previously for test purposes, a weight/volume ration (mg/l) is preferred and 1.5 ppm is expressed as 1.5 milligrams per liter based on a dilution of 10 ml of water over a 100 square centimeter area of substrate.
  • Concentrations below the sensitivity of the test are negligible or "zero- detectable”.
  • a negligible or “zero-detectable" level, of substantially less than 1.5 milligram per square meter of substrate area (1.5 mg/m 2 ) of soluble chemical salts or residual ionic contaminants is confirmed by measuring with potassium ferricyanide paper for iron salts.
  • the test paper is prepared by saturating filter paper in a 5% by weight solution of potassium ferricyanide prepared from potassium ferricyanide crystal and an appropriate amount of distilled water. The test paper is then allowed to dry under ambient conditions. The surface of the substrate to be tested is sprayed with a fine mist of distilled water and a small piece of the freshly prepared test paper is then pressed against the sprayed surface. If a detectable level of soluble iron salts is present, blue dots will appear on the test paper.
  • the water used in the blast operation is deionized water as pure as possible with a ph range between six (6) and eight (8) and having a conductivity of between 0.5 and ten (10) micromohs/cm. Pure water by nature has a Ph close to neutral. Ionic contaminants (i.e., salts) on the surface of metals, such as steel or iron, tend to attract moisture which results in oxidation of the surface. (Rusting in the case of iron or steel). In order to remove the residual ionic contaminants or metal salts and oxidation products from the parent metal, an ultra pure water is used in water propelled abrasive cleaning of the substrate surface to avoid recontaminating the steel with impurities in the water.
  • Ionic contaminants i.e., salts
  • an ultra pure water is used in water propelled abrasive cleaning of the substrate surface to avoid recontaminating the steel with impurities in the water.
  • U.S. Patent No. 4,878,320 dated November 7, 1989 for an illustration of a suitable apparatus for water propelled abrasive cleaning, the entire disclosure of which is incorporated by this reference.
  • a suitable discharge nozzle is shown in U.S. Patent No. 4,878,320 for applying a high pressure stream of water and sodium bicarbonate particles.
  • a compressor provides pressurized supplies of water and air to the nozzle and a hopper provides a pressurized supply of sodium bicarbonate particles to the nozzle where the particles are propelled by a jet of water against the substrate surface.
  • One use of the present method has been for the cleaning of the interior surface of large cylindrical tanks, such as used in the oil and gas industry, prior to application of a coating on the tank.
  • An object of this invention is to provide a method for the removal of surface contaminants from metal substrates where the method is particularly adapted for the removal of water soluble iron salts including ferrous or ferric salts from the surface of a iron or steel substrate.
  • Another object of this invention is to provide such a method for the removal of surface contaminants from metal substrates utilizing a high pressure water blast system having a sodium bicarbonate abrasive material therein.
  • a further object of the invention is to provide such a water blast method utilizing an abrasive with water of superior purity of less than about five (5) micromohs/cm so that mechanical removal or chemical neutralization of ionic contaminants, such as iron chloride and sulfate salts, occurs.
  • the present invention is also particularly directed to a method for the removal of surface contaminants from concrete substrates including as a first step the blasting with an abrasive, such as sodium bicarbonate, in a pressurized stream of water against the surface of the substrate with the water having a high purity.
  • an abrasive such as sodium bicarbonate
  • a pressurized high purity water wash is applied against the surface of the concrete substrate in a second step.
  • the abrasive scrubbing action in the first step removes any surface residue on the concrete and displaces soluble salts from the pores of the concrete.
  • the second step utilizing the high purity water wash readily dissolves and removes the water soluble salts, other surface contaminants, and any residual abrasive material.
  • the treatment of the surface of the concrete substrate in accord with the process described above results in a superior cleaned surface that is free of any detectable ionic contaminants and prepares the concrete surface for application of a suitable coating for enhancing the coating life.
  • One particular use of the present method for removing surface contaminants from concrete substrates is on concrete surfaces on which acid etching has been performed to achieve the desired surface profile on horizontal concrete surfaces.
  • Acid etching is usually accomplished with hydrochloric or muriatic acid although sulfamic, phosphoric, or citric acid may be used for etching under various conditions.
  • the acid etching process creates water soluble salts which are in addition to the soluble salts already present in the concrete.
  • the residual unreacted acid together with the soluble salts formed by the reaction and those previously existing in the concrete must be completely removed. Testing of the cleaned surface is performed to confirm the results.
  • an abrasive material such as sodium bicarbonate, and water of a high degree of purity
  • the water used in the blast operation is deionized water as pure as possible with a ph range between six (6) and eight (8) and having a conductivity of between 0.5 and ten (10) micromohs/cm.
  • Pure water by nature has a Ph close to neutral.
  • Ionic contaminants i.e., salts
  • an ultra pure water is used in water propelled abrasive cleaning of the substrate surface to avoid recontaminating the concrete with impurities in the water.
  • a further object of the invention is to provide such a water blast method utilizing an abrasive with water of superior purity of less than about five (5) micromohs/cm so that mechanical removal or chemical neutralization of ionic contaminants occurs.
  • Figure 1 is an elevational view, partly schematic, illustrating the method of the invention for removing surface contaminants from the inner surface of a steel tank prior to application of a coating;
  • FIG 2 is a schematic view of a wet abrasive blast system used in Figure 1 with the method of the present invention
  • Figure 3 is a schematic view illustrating the sequential steps involved in carrying out the method of the invention. Description Of The Invention
  • a workman W is shown within the interior of a steel or concrete cylindrical tank generally indicated at 10 which has an inner surface 12 to be treated and cleaned for removing surface contaminants prior to application of a coating.
  • inner surface 12 may have already been preliminarily cleaned as by conventional dry abrasive blasting, such as sand blasting, etc. Alternatively, such preliminary cleaning may be performed by wet abrasive blasting, high pressure water blasting, hand tools, etc.
  • the workman W grips a nozzle 14 connected to suitable supply lines for the application of high pressure water and an abrasive material from a predetermined orifice against the surface of the metal substrate.
  • Nozzle 14 has a propulsion chamber with high pressure water supplied through line 16 to such propulsion chamber.
  • Abrasive preferably sodium bicarbonate, is supplied with a stream of pressurized air through line 18 to the propulsion chamber of nozzle 14.
  • a water supply 20 supplies water of a superior purity to a control station 22.
  • a high pressure water pump 24, driven by an air supply 16 supplies pressurized water through line 16 to nozzle 14 at a pressure generally between 500 psi and 10,000 psi (preferably between 1,500 psi and 5,000 psi).
  • a supply of water soluble abrasive, preferably sodium bicarbonate, is shown at 28 in a supply hopper or "pot”. Air under pressure passes from air supply 30 through a dryer 32 and a regulator valve 34 to hopper 28. Air to convey the abrasive to nozzle 14 is supplied from air supply 16 and regulator valve 38 to supply line 18.
  • a metering valve 40 is provided for metering the abrasive material from hopper 28 to line 18.
  • a pressure differential of around 2-5 psi is provided between the pressure in hopper 28 and the pressure in conveying line 18 to provide a suitable abrasive flow by gravity and differential pressure from hopper 28 to conveying line 18.
  • Dryer 32 insures that no liquid phase water is present in the air supply to hopper 28. While a dried air supply is illustrated for pressurization of hopper 28, it is to be understood that other gases may be used satisfactorily such as nitrogen, argon, or hydrogen, for example.
  • a dryer at the output of air supply 16 may be provided to dry air applied to conveying line 18, but dry gas applied to air line 17 is not essential whereas dry gas applied to hopper 28 via line 19 is essential to prevent clogging of the water soluble abrasive at the exit line 21 of the hopper.
  • Pressure regulators 34 and 38 are coupled to each other through line 42 having a pressure control 44 therein so that the internal pressure in hopper 28, which contains sodium carbonate particles, is always greater than the pressure in line 18.
  • Figure 3 illustrates diagrammatically the steps involved in the method of the present invention in which high pressure water of a superior purity and sodium bicarbonate are first applied against the surface of a steel substrate having contaminants including ferrous or ferric salts.
  • the mechanical action of the abrasive against containments may remove such contaminants to a certain purity level.
  • Such step may also involve a chemical action comprising a neutralization action by the sodium bicarbonate of any remaining ionic contaminants (i.e. water soluble iron salts).
  • the first step of wet abrasive blasting may include mechanical abrasion of the contaminants or chemical neutralization of contaminants or both mechanical abrasion and chemical neutralization.
  • a pressurized washing with the superior purity water at a pressure generally between 200 psi and 20,000 psi is provided against the substrate to remove the neutralized soluble salts and other surface contaminants.
  • a test is provided on the surface of the substrate to confirm the absence of any iron salts of an amount greater than ten micrograms per square meter (10 ⁇ g/cm 2 or 100 mg/m 2 ).
  • a potassium ferricyanide test is conducted. It is understood that the test is capable of testing the absence of any iron salts of an amount greater than one and one-half milligrams per square meter (1.5 mg/m 2 or 0.15 ⁇ g/cm 2 ) although such a high degree of cleanliness is not required in many applications.
  • the substrate comprised an eight (8) foot diameter steel pipe.
  • Water of a purity of 5 micromohs/cm at a pressure of 3,000 psi propelled a sodium bicarbonate abrasive material in a blast from a discharge nozzle against the surface of the pipe.
  • the bicarbonate of soda to water ratio was about two (2) pounds of sodium bicarbonate for one (1) gallon of water.
  • a production rate of around 240 square feet was achieved per nozzle hour.
  • a neutralizing reaction occurred between the water soluble iron salts and the bicarbonate of soda.
  • a wash step was initiated with a pressure of about 8,000 psi with a water purity of 5 micromohs/cm at a production rate of around 750 square feet per nozzle hour.
  • the cleaned substrate surface was then tested by the aforementioned potassium ferricyanide test and a "zero-detectable" level under 1.5 milligrams of soluble iron salts per square meter (1.5 mg/m 2 or 0.15 ⁇ g/cm 2 was confirmed.
  • the sodium bicarbonate material used in the above examples is designated as a regular coarse granular sodium bicarbonate in accord with the following specifications.
  • Figure 3 also illustrates diagrammatically the steps involved in the method of the present invention in which high pressure water of a superior purity and sodium bicarbonate are first applied against the surface of a concrete substrate.
  • the mechanical action of the abrasive against containments may remove such contaminants to a certain purity level.
  • Such step may also involve a chemical action comprising a neutralization action by the sodium bicarbonate of any remaining ionic contaminants.
  • the first step of wet abrasive blasting may include mechanical abrasion of the contaminants or chemical neutralization of contaminants or both mechanical abrasion and chemical neutralization.
  • a pressurized washing with the superior purity water at a pressure generally between 200 psi and 20,000 psi is provided against the substrate to remove the neutralized soluble salts and other surface contaminants.
  • a test may be provided on the surface of the substrate to confirm the absence of any salts of a predetermined amount, for example, greater than one (1 ) equivalent ppm.
  • the process described above solves two coating related problems with respect to cast concrete.
  • the first problem concerns the fact that new cured concrete has "laitance" on the surface.
  • Laitance is not a part of the concrete matrix, but is a thin layer of non- reactive materials in the cement which are present as a surface residue.
  • Laitance forms a weak powdery material with little adhesive strength.
  • Laitance is removed from a concrete surface by the process described above.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Cleaning By Liquid Or Steam (AREA)

Abstract

L'invention concerne un procédé permettant d'enlever des sels solubles dans l'eau d'un substrat métallique dans un système de sablage humide dans lequel un abrasif au bicarbonate est propulsé dans un flot d'eau sous pression contre la surface du substrat métallique afin de préparer cette dernière avant l'application d'un revêtement. Ledit procédé se décompose en plusieurs étapes conformément à la figure 3 au cours desquelles de l'eau sous pression pour sablage à haute pression et un abrasif au bicarbonate de sodium sont d'abord appliqués à l'aide d'un pistolet (14) sur la surface du substrat métallique, ce qui permet d'enlever et de neutraliser les sels solubles dans l'eau. De l'eau sous pression sans abrasif est ensuite appliquée à l'aide du pistolet (14) sur la surface du substrat métallique afin de nettoyer cette dernière et d'enlever les sels neutralisés. On procède ensuite à un test au ferricyanure afin de vérifier que lesdits sels ont été enlevés.
PCT/US1993/008038 1992-08-28 1993-08-26 Procede permettant d'enlever des contaminants de la surface de substrats WO1994005461A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU50930/93A AU5093093A (en) 1992-08-28 1993-08-26 Method for removal of surface contaminants from substrates

Applications Claiming Priority (6)

Application Number Priority Date Filing Date Title
US07/938,202 1992-08-28
US07/938,202 US5317841A (en) 1992-08-28 1992-08-28 Method for removal of surface contaminants from metal substrates
US928393A 1993-01-26 1993-01-26
US08/009,283 1993-01-26
US08/031,695 US5441441A (en) 1992-08-28 1993-03-15 Method for removal of surface contaminants from concrete substrates
US08/031,695 1993-03-15

Publications (1)

Publication Number Publication Date
WO1994005461A1 true WO1994005461A1 (fr) 1994-03-17

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PCT/US1993/008038 WO1994005461A1 (fr) 1992-08-28 1993-08-26 Procede permettant d'enlever des contaminants de la surface de substrats

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AU (1) AU5093093A (fr)
WO (1) WO1994005461A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1995030781A2 (fr) * 1994-05-05 1995-11-16 Sjunnesson Sales Acc Procede permettant d'eliminer des ions chlorure ou un compose les contenant d'une surface contaminee par ces substances
DE10042806A1 (de) * 2000-08-30 2002-03-28 Wap Reinigungssysteme Reinigungsmittel für die Hoch- und Niederdruckreinigung

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3950642A (en) * 1975-05-27 1976-04-13 Metal Improvement Company, Inc. Method of inspecting shot peened surfaces for extent of coverage
US4020857A (en) * 1976-04-13 1977-05-03 Louis Frank Rendemonti Apparatus and method for pressure cleaning and waxing automobiles and the like
US4258505A (en) * 1978-03-04 1981-03-31 Metallgesellschaft Aktiengesellschaft Method of and apparatus for the surface cleaning of workpieces
US4583329A (en) * 1984-02-09 1986-04-22 Water Research Centre High pressure jets
US4729770A (en) * 1986-04-11 1988-03-08 Pyrene Chemical Services Limited Processes and compositions for abrasive blast cleaning
US4878320A (en) * 1987-12-04 1989-11-07 Whitemetal, Inc. Abrasive feed system
US5123206A (en) * 1987-12-04 1992-06-23 Whitemetal, Inc. Wet abrasive blasting method

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3950642A (en) * 1975-05-27 1976-04-13 Metal Improvement Company, Inc. Method of inspecting shot peened surfaces for extent of coverage
US4020857A (en) * 1976-04-13 1977-05-03 Louis Frank Rendemonti Apparatus and method for pressure cleaning and waxing automobiles and the like
US4258505A (en) * 1978-03-04 1981-03-31 Metallgesellschaft Aktiengesellschaft Method of and apparatus for the surface cleaning of workpieces
US4583329A (en) * 1984-02-09 1986-04-22 Water Research Centre High pressure jets
US4729770A (en) * 1986-04-11 1988-03-08 Pyrene Chemical Services Limited Processes and compositions for abrasive blast cleaning
US4878320A (en) * 1987-12-04 1989-11-07 Whitemetal, Inc. Abrasive feed system
US5123206A (en) * 1987-12-04 1992-06-23 Whitemetal, Inc. Wet abrasive blasting method

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1995030781A2 (fr) * 1994-05-05 1995-11-16 Sjunnesson Sales Acc Procede permettant d'eliminer des ions chlorure ou un compose les contenant d'une surface contaminee par ces substances
WO1995030781A3 (fr) * 1994-05-05 1996-03-07 Sjunnesson Sales Acc Procede permettant d'eliminer des ions chlorure ou un compose les contenant d'une surface contaminee par ces substances
DE10042806A1 (de) * 2000-08-30 2002-03-28 Wap Reinigungssysteme Reinigungsmittel für die Hoch- und Niederdruckreinigung

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