EP0636712B1 - Chemical cleaning process for metall workpieces - Google Patents

Chemical cleaning process for metall workpieces Download PDF

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Publication number
EP0636712B1
EP0636712B1 EP94401729A EP94401729A EP0636712B1 EP 0636712 B1 EP0636712 B1 EP 0636712B1 EP 94401729 A EP94401729 A EP 94401729A EP 94401729 A EP94401729 A EP 94401729A EP 0636712 B1 EP0636712 B1 EP 0636712B1
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compounds
process according
unsaturated
silica
amines
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French (fr)
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EP0636712A1 (en
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Béatrice Sala
Angel Gelpi
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Areva NP SAS
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Framatome SA
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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
    • 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
    • C23G1/14—Cleaning or pickling metallic material with solutions or molten salts with alkaline solutions
    • C23G1/19—Iron or steel
    • 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
    • C23G1/24—Cleaning or pickling metallic material with solutions or molten salts with neutral solutions
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
    • G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
    • G21F9/001—Decontamination of contaminated objects, apparatus, clothes, food; Preventing contamination thereof
    • G21F9/002—Decontamination of the surface of objects with chemical or electrochemical processes
    • G21F9/004—Decontamination of the surface of objects with chemical or electrochemical processes of metallic surfaces

Definitions

  • the present invention relates to the cleaning of parts metal on which a deposit has formed which is harmful to characteristics of the part, containing oxides (in particular iron oxide in the form of magnetite), following exposure to water, liquid and / or vapor phase high temperature. It relates more particularly to the chemical cleaning of such parts which have been exposed to high temperature water containing iron compounds and silicon, as well as other elements such as Na, Ca, X, Al, Zn, Cu, As, Sb, Tl, Pb, C, S, Ni, Cr, Sn.
  • oxides in particular iron oxide in the form of magnetite
  • the invention finds a particularly application important in the leaching of that of the faces of the tubes nuclear power plant steam generator which is exposed to the secondary circuit, where water containing polluting chemical elements of various origins, for example from condenser leaks, resins ion exchangers used for demineralization, water treatment and corrosion products of the secondary circuit. Deposits also form well on the straight parts of the exchange tubes and in the gaps, especially between tubes and spacers distributed along the tubes and intended to maintain them relative to each other as well as between the tubes and the tubular plate.
  • the invention is however also applicable to any metal part on which a comparable deposit has formed to those involved in such heat exchangers steam.
  • the analyzes carried out on samples of tubes of an exchanger carrying deposits has shown that the structure of these deposits was much more complex than never imagined it.
  • the deposit consists mainly of magnetite
  • the oxidized layer passivation conventionally developed during the phase final manufacturing of the exchange tubes, is destroyed under the alveolar silico-aluminate and it replaces one relatively thick non-protective layer.
  • this layer has a high chromium content and iron in the usual case where the exchange tubes are made of one of the nickel-chrome alloys containing also iron and other designated editing items by the brand "INCONEL". It is likely to exist also, with a lesser thickness, under the magnetite in the straight parts of the tubes.
  • the present invention aims to provide a method of cleaning of deposits likely to intervene in these conditions. To this end, it offers a cleaning process chemical treatment of metallic material parts bearing a deposit comprising compounds with a high silica content and metal oxides, in particular magnetite, according to claim 1.
  • additional species such as AlO - / 4, which give a negative ionic character to the surface deposit.
  • This negative nature can be automatically compensated for by the absorption of cations present in the aqueous phase, such as Ca 2+ , NH 4 , K + , or of cations originating from the corrosion of the metal part itself.
  • a feature that makes deposits particularly hard to tear is that the Si-O bond is one of strongest silicon bonds, since it comes immediately after Si-F in the order of energies decreasing.
  • the tube cleaning process begins with the elimination magnetite, by any of the methods known.
  • the second step is to remove deposits remaining, mainly containing siliceous compounds, by treatment with chemical compounds promoting delocalization of the electrons of Si-O-metal bonds and their weakening.
  • These compounds will be used in the aqueous phase, with a content of insertion compounds and a temperature of treatment chosen according to the compounds. In a way generally, it is best to work at the most high compatible with the physical or chemical stability of compounds.
  • heteropolyacids and their salts in particular alkaline molybdates.
  • the silica is thus maintained in the state of coordination +6 and its repolymerization is avoided.
  • boric acid can be added to maintain a pH between 1 and 5
  • F - ions can be added to promote the dissolution of silica.
  • This approach which amounts to an esterification, uses the fact that the silicon compounds having silanol Si-OH functions more acid than the alcohols-R-OH (R being a carbon radical, usually alkyl) give strong hydrogen bonds which cause condensations within the layer, in an acidic or basic medium, that is to say in the presence of H + or OH - ions. This is particularly the case for many organo-silicic compounds.
  • a representative reaction is of the kind: where R and R2 denote carbon radicals, generally alkyl such as R.
  • silica passes in particular to the state of polysiloxane.
  • the compounds finally obtained are fluid, even at low temperatures, since the elements of deposit do not have an excessive number of carbon atoms and do not lead to too long chains.
  • the silica layer is general re-passivation of the base metal. It may be done in a conventional way by oxidation with drying and dehydroxylation. Drying-oxidation can be carried out at 290-300 ° C for 24 to 48 hours with gas sweeping dry oxidant, for example consisting of dry air or air enriched with oxygen.
  • the treated specimens consisted of a "Inconel" section carrying various layers; in particular, most with a layer of about 100 ⁇ m of magnetite and, in some areas, a siliceous coating topped with a layer of magnetite.
  • these compounds can be used under form of aqueous ammonia solution with or without fluoride ammonium having an insertion role.
  • solutions were used with 1 mol per liter of ammonia, 20 to 300 g / l of phenol from 0 to 100 g / l of ammonium fluoride NH 4 F, for tests on Inconel test pieces previously coated with aluminosilicate gel and on samples from the steam generator of a French nuclear power plant containing deposits of magnetite and alumino-silicate.
  • the temperatures used varied from 80 to 150 ° C so as to obtain the best dissolution without corroding the base metal.
  • one test consisted in placing the solution and the test tube, already freed from magnetite, in a reactor containing a magnetic stirrer. The reactor was heated to 100 ° C and the vapors released were condensed in a column and returned to the reactor. After six hours, the test piece was rinsed in a 1 M NH 3 solution under hot conditions for 15 to 20 minutes, then rinsed in ethanol with ultrasonic stirring and finally dried with compressed air.
  • a 20% ethanol solution 10 g was prepared liter of boric acid and 100 g per liter of molybdate of ammonium in distilled water. The solution was again placed in a reactor and maintained at 80 ° C for seven hours. The test piece was then rinsed in ethanol with the application of ultrasound, then dried with compressed air. Observation by electron microscopy further revealed that the silica layer had been destroyed.
  • the first phase of the process is intended to eliminate the magnetite present on tubes and spacer plates.
  • the secondary circuit of the steam generator is filled with water whose temperature is increased, for example by circulation of high temperature water in the primary circuit.
  • the reagents EDTA
  • the water loaded with reagents is circulated, at a rate which will often be around 150 m 3 per hour for a typical steam generator of a nuclear power station, to drive the magnetite of the spacer plates. It is also advantageous to inject a nitrogen flow intended to activate the effect of the solution in the interstices between the tubes and the spacer plates.
  • the second step elimination of siliceous compounds, can follow immediately after the first as far where the products used for insertion or condensation, chosen from those mentioned above, are compatible with the products used during the first phase.
  • the secondary circuit of the steam generator is drained and then refilled and warmed up. Insertion or condensation components, intended to remove the siliceous deposit by solubilization, are injected. The solution is put into circulation with nitrogen injection to promote solubilization in interstices. After destruction of the layer and passage of silicates in solution, the generator is drained.
  • Passivation can be done by filling of water, warming up and injecting oxygen bubbles to bring the oxidation potential measured at the electrode to the saturated calomel, above 350 mV. Finally, the generator steam can be drained and dried before storage.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electrochemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Food Science & Technology (AREA)
  • Physics & Mathematics (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
  • Silicon Compounds (AREA)
  • Catalysts (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Description

La présente invention concerne le nettoyage de pièces métalliques sur lesquelles s'est formé un dépôt nuisant aux caractéristiques de la pièce, contenant des oxydes (notamment de l'oxyde de fer sous forme de magnétite), à la suite d'une exposition à l'eau, en phase liquide et/ou vapeur à haute température. Elle concerne plus particulièrement le nettoyage chimique de telles pièces qui ont été exposées à de l'eau à haute température contenant des composés de fer et de silicium, ainsi que d'autres éléments tels que Na, Ca, X, Al, Zn, Cu, As, Sb, Tl, Pb, C, S, Ni, Cr, Sn.The present invention relates to the cleaning of parts metal on which a deposit has formed which is harmful to characteristics of the part, containing oxides (in particular iron oxide in the form of magnetite), following exposure to water, liquid and / or vapor phase high temperature. It relates more particularly to the chemical cleaning of such parts which have been exposed to high temperature water containing iron compounds and silicon, as well as other elements such as Na, Ca, X, Al, Zn, Cu, As, Sb, Tl, Pb, C, S, Ni, Cr, Sn.

L'invention trouve une application particulièrement importante dans le lessivage de celle des faces des tubes de générateur de vapeur des centrales nucléaires qui est exposée au circuit secondaire, où circule de l'eau contenant des éléments chimiques polluants de diverses origines, provenant par exemple de fuites au condenseur, des résines échangeuses d'ions utilisées pour la déminéralisation, des produits de traitement de l'eau, et de la corrosion d'éléments du circuit secondaire. Des dépôts se forment aussi bien sur les parties droites des tubes d'échange et dans les interstices, notamment entre les tubes et les entretoises réparties le long des tubes et destinées à les maintenir les uns par rapport aux autres ainsi qu'entre les tubes et la plaque tubulaire.The invention finds a particularly application important in the leaching of that of the faces of the tubes nuclear power plant steam generator which is exposed to the secondary circuit, where water containing polluting chemical elements of various origins, for example from condenser leaks, resins ion exchangers used for demineralization, water treatment and corrosion products of the secondary circuit. Deposits also form well on the straight parts of the exchange tubes and in the gaps, especially between tubes and spacers distributed along the tubes and intended to maintain them relative to each other as well as between the tubes and the tubular plate.

L'invention est toutefois également applicable à toute pièce métallique sur laquelle s'est formé un dépôt comparable à ceux qui interviennent dans de tels échangeurs de vapeur.The invention is however also applicable to any metal part on which a comparable deposit has formed to those involved in such heat exchangers steam.

On sait depuis longtemps que la formation d'une couche oxydée, généralement sous forme de magnétite, à la surface des tubes d'échange, dégrade les performances de l'échangeur et de plus favorise la corrosion inter-granulaire et l'apparition de fissures sous contrainte. Il est en conséquence courant d'éliminer périodiquement la magnétite par lessivage des tubes. On connaít divers modes agents de nettoyage, agissant généralement par réduction, puis complexationde la magnétite. En particulier, on a utilisé un procédé de nettoyage par réduction à l'aide de N2H4, puis complexation du Fe2+ en un composé de Fe3+ à l'aide d'éthylène diamine tétraacétique. On ne décrira pas dans la présente demande les divers procédés bien connus qui existent.It has long been known that the formation of an oxidized layer, generally in the form of magnetite, on the surface of the exchange tubes, degrades the performance of the exchanger and moreover promotes inter-granular corrosion and the appearance of cracks. under constraint. It is therefore common to periodically remove magnetite by leaching from the tubes. Various modes of cleaning agents are known, generally acting by reduction, then complexation of the magnetite. In particular, a cleaning process was used by reduction using N 2 H 4 , then complexing of Fe 2+ into a compound of Fe 3+ using ethylene diamine tetraacetic. The various well-known methods which exist will not be described in the present application.

Les analyses effectuées sur des échantillons de tubes d'échangeur portant des dépôts ont fait apparaítre que la structure de ces dépôts était beaucoup plus complexe qu'on ne l'imaginait. Elles ont en particulier montré que, si le dépôt est majoritairement constitué de magnétite, il peut y avoir, localement, présence de silicates sur un silico-aluminate alvéolaire ayant une structure de gel solide, susceptible de contenir des produits carbonés dans la mesure où cet élément est présent dans le milieu. La couche oxydée de passivation, classiquement élaborée lors de la phase finale de fabrication des tubes d'échange, est détruite sous le silico-aluminate alvéolaire et il s'y substitue une couche relativement épaisse non protectrice. L'analyse a montré que cette couche présente une teneur élevée en chrome et en fer dans le cas habituel où les tubes d'échange sont constitués en l'un des alliages nickel-chrome contenant également du fer et d'autres éléments d'éddition désignés par la marque "INCONEL". Elle est susceptible d'exister également, avec une moindre épaisseur, sous la magnétite dans les parties droites des tubes.The analyzes carried out on samples of tubes of an exchanger carrying deposits has shown that the structure of these deposits was much more complex than never imagined it. In particular, they have shown that, if the deposit consists mainly of magnetite, there can locally have the presence of silicates on a silico-aluminate alveolar having a solid gel structure, likely to contain carbon products to the extent where this element is present in the middle. The oxidized layer passivation, conventionally developed during the phase final manufacturing of the exchange tubes, is destroyed under the alveolar silico-aluminate and it replaces one relatively thick non-protective layer. The analysis has shown that this layer has a high chromium content and iron in the usual case where the exchange tubes are made of one of the nickel-chrome alloys containing also iron and other designated editing items by the brand "INCONEL". It is likely to exist also, with a lesser thickness, under the magnetite in the straight parts of the tubes.

On connait déjà (DE-A-3 431 101) des solutions organiques permettant de dissoudre des produits de réaction contenant de l'acide silicique dans les sources d'eau potable. Ces solutions contiennent de l'acide fluorhydrique. On connait également (JP-A-58 092 499) un agent de désentartrage permettant d'éliminer un tartre silicique, constitué par une solution aqueuse contenant de l'acide hydroxyacétique, de l'acide polycarboxylique et un tensio-actif.We already know (DE-A-3 431 101) organic solutions for dissolving reaction products containing silicic acid in drinking water sources. These solutions contain hydrofluoric acid. We also know (JP-A-58 092 499) a descaling agent allowing to eliminate a silica scale, constituted by an aqueous solution containing hydroxyacetic acid, polycarboxylic acid and a surfactant.

La présente invention vise à fournir un procédé de nettoyage des dépôts susceptibles d'intervenir dans ces conditions. Elle propose dans ce but un procédé de nettoyage chimique de pièces en matériau métallique portant un dépôt comprenant des composés à teneur élevée en silice et d'oxydes métalliques, notamment de magnétite, suivant la revendication 1.The present invention aims to provide a method of cleaning of deposits likely to intervene in these conditions. To this end, it offers a cleaning process chemical treatment of metallic material parts bearing a deposit comprising compounds with a high silica content and metal oxides, in particular magnetite, according to claim 1.

Après lessivage des tubes pour les débarrasser de la magnétite et des composés siliceux, on effectuera en général une opération de repassivation qui peut être effectuée par oxydation superficielle avec séchage et déshydroxylation. On peut notamment utiliser un séchage à une température vers 300°C pendant 24 à 48 heures, en atmosphère oxydante sèche.After leaching the tubes to rid them of the magnetite and siliceous compounds, we will generally perform a repassivation operation which can be carried out by surface oxidation with drying and dehydroxylation. We can in particular use drying at a temperature around 300 ° C for 24 to 48 hours, in a dry oxidizing atmosphere.

Des caractéristiques secondaires de l'invention sont données dans les sous-revendications.Secondary features of the invention are given in the subclaims.

Avant de décrire davantage des modes possibles d'exécution de l'invention, il peut être utile de résumer le mode de formation le plus probable de composés siliceux dans le dépôt.Before describing further possible modes of execution of the invention, it may be useful to summarize the mode most likely formation of siliceous compounds in the deposit.

La silice à l'état dissous dans une phase aqueuse, sous la forme Si(OH)4, se fixe sur le métal avec intervention des ions OH présents à la surface du métal M, qui ont un effet catalytique. On peut schématiser les réactions sous la forme :

Figure 00030001
Silica in the dissolved state in an aqueous phase, in the form Si (OH) 4 , is fixed on the metal with the intervention of OH ions present on the surface of the metal M, which have a catalytic effect. We can schematize the reactions in the form:
Figure 00030001

Finalement, il se forme un dépôt comportant des liaisons du type :

Figure 00040001
Finally, a deposit is formed comprising links of the type:
Figure 00040001

Dans le réseau du dépôt ainsi constitué peuvent s'insérer des espèces supplémentaires, telles que AlO - / 4, qui donnent un caractère ionique négatif au dépôt de surface. Ce caractère négatif peut se compenser de façon automatique par l'absorption de cations présents dans la phase aqueuse, tels que Ca2+, NH4, K+, ou de cations provenant de la corrosion de la pièce métallique elle-même.In the network of the deposit thus formed can be inserted additional species, such as AlO - / 4, which give a negative ionic character to the surface deposit. This negative nature can be automatically compensated for by the absorption of cations present in the aqueous phase, such as Ca 2+ , NH 4 , K + , or of cations originating from the corrosion of the metal part itself.

Une caractéristique qui rend les dépôts particulièrement difficiles à arracher est que la liaison Si-O est l'une des liaisons du silicium les plus fortes qui soient, puisqu'elle vient immédiatement après Si-F dans l'ordre des énergies décroissantes.A feature that makes deposits particularly hard to tear is that the Si-O bond is one of strongest silicon bonds, since it comes immediately after Si-F in the order of energies decreasing.

Le procédé de nettoyage d'un tube commence par l'élimination de la magnétite, par l'un quelconque des procédés connus.The tube cleaning process begins with the elimination magnetite, by any of the methods known.

La seconde étape consiste en l'élimination des dépôts restants, contenant surtout des composés siliceux, par traitement avec des composés chimiques favorisant la délocalisation des électrons des liaisons Si-O-métal et leur affaiblissement.The second step is to remove deposits remaining, mainly containing siliceous compounds, by treatment with chemical compounds promoting delocalization of the electrons of Si-O-metal bonds and their weakening.

Dans la pratique on peut agir :

  • soit par insertion d'éléments provoquant un accroissement du nombre de coordination de la silice, typiquement à l'aide de composés électrophiles,
  • soit par condensation de groupements-OH sur la silice.
In practice we can act:
  • either by inserting elements causing an increase in the coordination number of silica, typically using electrophilic compounds,
  • or by condensation of OH groups on the silica.

Il est avantageux d'utiliser un milieu favorisant la complexation de la silice et évitant que Si(OH)4 ne revienne vers l'état SiO2 et ne se refixe sur le métal.It is advantageous to use a medium which favors the complexation of the silica and prevents Si (OH) 4 from returning to the SiO 2 state and from being re-fixed on the metal.

On détaillera maintenant ces deux modes de mise en solution.We will now detail these two modes of implementation solution.

Mise en solution aqueuse par insertion et accroissement du nombre de coordination de la siliceInsertion in aqueous solution and increase in coordination number of silica

On sait déjà qu'on peut obtenir des composés solubles au sein du réseau siliceux de la couche à détruire en y insérant :

  • OH- en milieu alcalin, pour former Si(OH)4,
  • F- en milieu acide, pour former notamment SiF6 2-.
We already know that we can obtain soluble compounds within the siliceous network of the layer to be destroyed by inserting:
  • OH - in an alkaline medium, to form Si (OH) 4 ,
  • F - in an acid medium, to form in particular SiF 6 2- .

En principe, on pourrait utiliser divers acides et bases fortes. Mais la concentration requise soulève un problème de corrosion de la plupart des supports métalliques à nettoyer. C'est notamment le cas des tubes en "Inconel". En revanche sont utilisables les systèmes insaturés ayant des propriétés électrophiles, parmi lesquels on peut citer :

  • 1°/ les systèmes insaturés conjugués tels que :
    • les groupements phényle substitués, par exemple mono-, di-, triphényl,
    • certains groupements à plusieurs noyaux benzéniques.
    Plus généralement les systèmes insaturés conjugués contiennent des groupements appartenant : aux composés organiques ayant au moins une fonction alcool; ou aux amines, ou leurs sels solubles.
  • 2°/ Les composés insaturés N-oxyde, tels que :
  • 2 hydroxypyridine - 1 oxyde.
    • In principle, various strong acids and bases could be used. However, the required concentration raises the problem of corrosion of most metal supports to be cleaned. This is particularly the case for "Inconel" tubes. On the other hand, unsaturated systems having electrophilic properties can be used, among which there may be mentioned:
  • 1 ° / unsaturated conjugate systems such as:
    • substituted phenyl groups, for example mono-, di-, triphenyl,
    • certain groups with several benzene nuclei.
    More generally, the conjugated unsaturated systems contain groups belonging to: organic compounds having at least one alcohol function; or amines, or their soluble salts.
  • 2 ° / N-oxide unsaturated compounds, such as:
  • 2 hydroxypyridine - 1 oxide.

    • De façon générale, on peut utiliser les composés insaturés N-oxyde ou systémes insaturés conjugués comportant des groupements électrophiles tels que : CO2H- C = N. In general, it is possible to use the unsaturated N-oxide compounds or unsaturated conjugated systems comprising electrophilic groups such as: CO 2 H- C = N.

    Ces composés seront utilisés en phase aqueuse, avec une teneur en composés d'insertion et une température de traitement choisies en fonction des composés. De façon générale, on a intérêt à travailler à la température la plus élevée compatible avec la stabilité physique ou chimique des composés.These compounds will be used in the aqueous phase, with a content of insertion compounds and a temperature of treatment chosen according to the compounds. In a way generally, it is best to work at the most high compatible with the physical or chemical stability of compounds.

    Il est avantageux d'ajouter à la phase aqueuse un produit complexant et on peut notamment utiliser dans ce but des hétéropolyacides et leurs sels, en particulier des molybdates alcalins. On peut citer l'heptamolybdate d'ammonium qui, en milieu acide de pH compris entre 1 et 5, réagit avec Si(OH)4 : 7 Si(OH)4+12 H6Mo7024,4 H2O + 174 H2O → 7H8Si(Mo2O7)8, 28 H2O It is advantageous to add a complexing product to the aqueous phase and it is possible in particular for this purpose to use heteropolyacids and their salts, in particular alkaline molybdates. Mention may be made of ammonium heptamolybdate which, in an acidic medium of pH between 1 and 5, reacts with Si (OH) 4 : 7 Si (OH) 4 12 H 6 Mo 7 0 24 4 H 2 O + H 2 O → 174 7 H 8 Si (Mo 2 O 7) 8 28 H 2 O

    La silice est ainsi maintenue à l'état de coordination +6 et sa repolymérisation est évitée.The silica is thus maintained in the state of coordination +6 and its repolymerization is avoided.

    Pour maintenir un pH entre 1 et 5, on peut ajouter de l'acide borique. Des ions F- peuvent être ajoutés pour favoriser la dissolutionh de la silice.To maintain a pH between 1 and 5, boric acid can be added. F - ions can be added to promote the dissolution of silica.

    Mise en solution aqueuse par condensation des groupements OH sur la siliceAqueous solution by condensation of the OH groups on silica

    Cette approche, qui revient à une estérification, utilise le fait que les composés de silicium ayant des fonctions silanol Si-OH plus acides que les alcools-R-OH (R étant un radical carboné, habituellement alkyl) donnent des liaisons hydrogène fortes qui provoquent des condensations au sein de la couche, en milieu acide ou basique, c'est-à-dire en présence d'ions H+ ou OH-. C'est notamment le cas de beaucoup de composés organo-siliciques.This approach, which amounts to an esterification, uses the fact that the silicon compounds having silanol Si-OH functions more acid than the alcohols-R-OH (R being a carbon radical, usually alkyl) give strong hydrogen bonds which cause condensations within the layer, in an acidic or basic medium, that is to say in the presence of H + or OH - ions. This is particularly the case for many organo-silicic compounds.

    Une réaction représentative est du genre :

    Figure 00070001
    où R et R2 désignent des radicaux carbonés, généralement alkyl comme R.A representative reaction is of the kind:
    Figure 00070001
    where R and R2 denote carbon radicals, generally alkyl such as R.

    On constate que la silice passe notamment à l'état de polysiloxane. Les composés finalement obtenus sont fluides, même à basse température, dans la mesure où les éléments de dépôt n'ont pas un nombre excessif d'atomes de carbone et ne conduisent pas à des chaínes trop longues.It is noted that the silica passes in particular to the state of polysiloxane. The compounds finally obtained are fluid, even at low temperatures, since the elements of deposit do not have an excessive number of carbon atoms and do not lead to too long chains.

    De nombreux composés organiques permettent d'obtenir de telles réactions de condensation.Many organic compounds make it possible to obtain such condensation reactions.

    Un certain nombre d'entre eux seront maintenant énumérés à titre d'exemples.

  • 1°/ Beaucoup de composés organiques ayant une ou plusieurs fonctions alcool, éventuellement couplées avec des insaturations, sont utilisables. On peut notamment citer les alcools méthylique, éthylique et butylique. Ces alcools peuvent être utilisés dans une très large plage de concentration, comprise entre 5 et 95 %. Toutefois on utilisera généralement une concentration comprise entre 5 et 30%. Le cis 2 butène 1-4 diol à 20 % favorise une désagrégation du réseau siliceux du gel.
  • 2°/ De nombreuses amines peuvent également être utilisées, ainsi que leurs sels solubles. On peut notamment citer des amines aromatiques et les sels solubles des amines tertiaires, en particulier les sels d'ammonium. Plus généralement, on recherchera des amines donnant naissance à des groupements de la forme :
    Figure 00080001
    • où --- désigne une liaison HA number of them will now be listed as examples.
  • 1 ° / Many organic compounds having one or more alcohol functions, possibly coupled with unsaturations, can be used. Mention may in particular be made of methyl, ethyl and butyl alcohols. These alcohols can be used in a very wide concentration range, between 5 and 95%. However, a concentration of between 5 and 30% will generally be used. The cis 2 butene 1-4 diol at 20% promotes disintegration of the siliceous network of the gel.
  • 2 ° / Many amines can also be used, as well as their soluble salts. Mention may in particular be made of aromatic amines and the soluble salts of tertiary amines, in particular the ammonium salts. More generally, we will look for amines giving rise to groups of the form:
    Figure 00080001
    •  where --- denotes an H bond

    Une fois la couche à base de silice détruite, il est en général nécessaire de repassiver le métal de base. Cela peut être fait de façon classique par oxydation avec séchage et déshydroxylation. Le séchage-oxydation peut être réalisé à 290-300°C pendant 24 à 48 heures avec balayage d'un gaz oxydant sec, par exemple constitué d'air sec ou d'air enrichi en oxygène.Once the silica layer has been destroyed, it is general re-passivation of the base metal. It may be done in a conventional way by oxidation with drying and dehydroxylation. Drying-oxidation can be carried out at 290-300 ° C for 24 to 48 hours with gas sweeping dry oxidant, for example consisting of dry air or air enriched with oxygen.

    On donnera maintenant quelques exemples de mise en oeuvre de l'invention sur des éprouvettes.We will now give some examples of implementation work of the invention on test pieces.

    Les éprouvettes traitées étaient constituées par un tronçon en "Inconel" portant diverses couches ; en particulier, la plupart portant une couche d'environ 100 µm de magnétite et, dans certaines zones, un revêtement siliceux surmonté d'une couche de magnétite.The treated specimens consisted of a "Inconel" section carrying various layers; in particular, most with a layer of about 100 µm of magnetite and, in some areas, a siliceous coating topped with a layer of magnetite.

    Exemple 1 : Condensation par les phénols (mono, di, tri)Example 1: Condensation by phenols (mono, di, tri)

    De façon générale, ces composés sont utilisables sous forme de solution aqueuse ammoniacale avec ou sans fluorure d'ammonium ayant un rôle d'insertion.In general, these compounds can be used under form of aqueous ammonia solution with or without fluoride ammonium having an insertion role.

    On a notamment utilisé des solutions à 1 mole par litre d'ammoniaque, 20 à 300 g/l de phénol de 0 à 100 g/l de fluorure d'ammonium NH4F, pour des essais sur des éprouvettes en Inconel préalablement recouvertes de gel d'aluminosilicate et sur des échantillons provenant de générateur de vapeur de centrale nucléaire française comportant des dépôts de magnétite et d'alumino-silicate.In particular, solutions were used with 1 mol per liter of ammonia, 20 to 300 g / l of phenol from 0 to 100 g / l of ammonium fluoride NH 4 F, for tests on Inconel test pieces previously coated with aluminosilicate gel and on samples from the steam generator of a French nuclear power plant containing deposits of magnetite and alumino-silicate.

    Les températures utilisées ont varié de 80 à 150°C de manière à obtenir la meilleure dissolution sans corroder le métal de base. Par exemple, un essai a consisté à placer la solution et l'éprouvette, déjà débarrassée de la magnétite, dans un réacteur contenant un agitateur magnétique. Le réacteur a été chauffé à 100°C et les vapeurs dégagées ont été condensées dans une colonne et retournées au réacteur. Au bout de six heures, l'éprouvette a été rincée dans une solution 1 M de NH3 à chaud, pendant 15 à 20 minutes, puis rincée dans l'éthanol avec agitation ultrasonique et enfin séchée à l'air comprimé.The temperatures used varied from 80 to 150 ° C so as to obtain the best dissolution without corroding the base metal. For example, one test consisted in placing the solution and the test tube, already freed from magnetite, in a reactor containing a magnetic stirrer. The reactor was heated to 100 ° C and the vapors released were condensed in a column and returned to the reactor. After six hours, the test piece was rinsed in a 1 M NH 3 solution under hot conditions for 15 to 20 minutes, then rinsed in ethanol with ultrasonic stirring and finally dried with compressed air.

    D'autres essais ont été réalisés en réacteur de verre pour les températures inférieures à 100°C et en autoclave pour les essais à température supérieure à 100°C. Les durées d'essai ont varié entre 2 h et 6 h. Le phénol, le pyrocathécol et le pyrogallol ont donné de bons résultats. Le pyrocathécol était utilisé à une teneur de 300 g à 25 g/l, entre la température d'ébullition et 150°C, avec et sans fluorure d'ammonium, pendant une durée de 4 h à 5 h.Other tests have been carried out in a glass reactor for temperatures below 100 ° C and in an autoclave for tests at temperatures above 100 ° C. The durations between 2 a.m. and 6 a.m. Phenol, pyrocathecol and pyrogallol have given good results. The pyrocathecol was used at a content of 300 g to 25 g / l, between boiling temperature and 150 ° C, with and without ammonium fluoride, for a period of 4 h to 5 h.

    L'observation en microscopie électronique à balayage a montré que la couche siliceuse avait été éliminée.Observation by scanning electron microscopy has shown that the siliceous layer had been removed.

    Des résultats similaires ont été obtenus avec d'autres composés similaires, par exemple le 1,2,3 triphenol.Similar results have been obtained with other similar compounds, for example 1,2,3 triphenol.

    Exemple 2 : Condensation par l'éthanol avec complexation par le molybdateEXAMPLE 2 Condensation with Ethanol with Complexation with molybdate

    On a préparé une solution à 20 % d'éthanol, 10 g par litre d'acide borique et 100 g par litre de molybdate d'ammonium dans l'eau distillée. La solution a encore été placée dans un réacteur et maintenue à 80°C pendant sept heures. L'éprouvette a ensuite été rincée dans l'éthanol avec application d'ultrasons, puis séchée à l'air comprimé. L'observation en microscopie électronique a encore révélé que la couche de silice avait été détruite.A 20% ethanol solution, 10 g was prepared liter of boric acid and 100 g per liter of molybdate of ammonium in distilled water. The solution was again placed in a reactor and maintained at 80 ° C for seven hours. The test piece was then rinsed in ethanol with the application of ultrasound, then dried with compressed air. Observation by electron microscopy further revealed that the silica layer had been destroyed.

    On décrira maintenant un mode possible de mise en oeuvre de l'invention pour le nettoyage chimique de la face externe des tubes d'un générateur de vapeur pour réacteur à eau sous pression.We will now describe a possible mode of implementation of the invention for chemical cleaning of the external face tubes of a steam generator for water reactor under pressure.

    La première phase du procédé est destinée à éliminer la magnétite présente sur les tubes et les plaques entretoises.The first phase of the process is intended to eliminate the magnetite present on tubes and spacer plates.

    Le circuit secondaire du générateur de vapeur est rempli d'eau dont la température est augmentée, par exemple par circulation d'eau à haute température dans le circuit primaire. Les réactifs (EDTA) sont injectés dans l'eau de remplissage portée au pH habituel pour le lessivage de la magnétite. L'eau chargée de réactifs est mise en circulation, à un débit qui sera souvent d'environ de 150 m3 par heure pour un générateur de vapeur type de centrale nucléaire, pour entraíner la magnétite des plaques entretoises. Il est avantageux d'injecter également un débit d'azote destiné à activer l'effet de la solution dans les interstices entre les tubes et les plaques entretoises.The secondary circuit of the steam generator is filled with water whose temperature is increased, for example by circulation of high temperature water in the primary circuit. The reagents (EDTA) are injected into the filling water brought to the usual pH for leaching the magnetite. The water loaded with reagents is circulated, at a rate which will often be around 150 m 3 per hour for a typical steam generator of a nuclear power station, to drive the magnetite of the spacer plates. It is also advantageous to inject a nitrogen flow intended to activate the effect of the solution in the interstices between the tubes and the spacer plates.

    La seconde étape, d'élimination des composés siliceux, peut faire immédiatement suite à la première dans la mesure où les produits utilisés pour l'insertion ou la condensation, choisis parmi ceux mentionnés ci-dessus, sont compatibles avec les produits utilisés au cours de la première phase. En cas d'incompatibilité, le circuit secondaire du générateur de vapeur est vidangé, puis rempli de nouveau et réchauffé. Les composants d'insertion ou de condensation, destinés à éliminer le dépôt siliceux par solubilisation, sont injectés. La solution est mise en circulation avec injection d'azote pour favoriser la solubilisation dans les interstices. Après destruction de la couche et passage des silicates en solution, le générateur est vidangé.The second step, elimination of siliceous compounds, can follow immediately after the first as far where the products used for insertion or condensation, chosen from those mentioned above, are compatible with the products used during the first phase. In the event of incompatibility, the secondary circuit of the steam generator is drained and then refilled and warmed up. Insertion or condensation components, intended to remove the siliceous deposit by solubilization, are injected. The solution is put into circulation with nitrogen injection to promote solubilization in interstices. After destruction of the layer and passage of silicates in solution, the generator is drained.

    La passivation peut être effectuée par remplissage d'eau, mise en température et injection de bulles d'oxygène pour amener le potentiel d'oxydation mesuré à l'électrode au calomel saturé, au-dessus de 350 mV. Enfin, le générateur de vapeur peut être vidangé et séché avant stockage.Passivation can be done by filling of water, warming up and injecting oxygen bubbles to bring the oxidation potential measured at the electrode to the saturated calomel, above 350 mV. Finally, the generator steam can be drained and dried before storage.

    Claims (11)

    1. Process for chemical cleaning of metal components carrying an iron oxide deposit upon a layer of compounds having a high silica content, including: eliminating the superficial metal oxides by complexation, possibly after reduction, then solubilizing the silica compounds by a reaction in aqueous medium for increasing the coordination number of silica with electrophilic compounds belonging to the group comprising the conjugated unsaturated systems and the unsaturated N-oxide compounds or by a reaction in aqueous medium for condensation with alcohols or amines, for weakening the bonds, in a medium which causes complexation of Si(OH)4.
    2. Process according to claim 1, characterized in that the unsaturated systems comprise substituted phenyl groups.
    3. Process according to claim 1, characterized in that the unsaturated compounds comprise a plurality of benzene rings.
    4. Process according to claim 1, 2 or 3, characterized in that the silica compounds are further maintained in solution by adding compounds complexing Si(OH)4 to the medium.
    5. Process according to claim 4, characterized in that said compounds are selected among molybdates.
    6. Process according to claim 5, characterized in that said compounds are ammonium molybdates.
    7. Process according to claim 1, characterized in that the unsaturated conjugated systems contain groups belonging to organic compounds having at least one alcohol function, to amines or to soluble salts thereof.
    8. Process according to claim 1, characterized in that an aromatic amine or a salt of a tertiary amine is used.
    9. Process according to claim 2, characterized in that the substituted phenyl groups belong to monophenyl, diphenyl and triphenyl.
    10. Process according to claim 1, characterized in that condensation is carried out by phenol, pyrocatechol or pyrogallol.
    11. Process according to any one of the preceding claims, characterized by a final step of passivation by oxidation and dehydroxylation.
    EP94401729A 1993-07-29 1994-07-27 Chemical cleaning process for metall workpieces Expired - Lifetime EP0636712B1 (en)

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    FR9309360A FR2708628B1 (en) 1993-07-29 1993-07-29 Method of chemical cleaning of metallic material parts.

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