EP2122011A1

EP2122011A1 - Use of an aqueous neutral cleaning solution and method for removing rouging from stainless steel surfaces

Info

Publication number: EP2122011A1
Application number: EP09705741A
Authority: EP
Inventors: Marc Philippe Vernier
Original assignee: Ateco Services AG
Current assignee: Ateco Services AG
Priority date: 2008-02-01
Filing date: 2009-01-30
Publication date: 2009-11-25
Anticipated expiration: 2029-01-30
Also published as: WO2009095475A1; CH699016B1; DK2122011T3; EP2090676A1; EP2122011B1; ATE521732T1

Abstract

The invention relates to a method for removing films and deposits from stainless surfaces, especially from stainless metal surfaces such as they are used in process stations and production units in the pharmaceutical, food and biotechnological industries, and to aqueous cleaning solutions which contain a reducing agent and at least one complexing agent for use in said method.

Description

USE OF A WASSERING NEUTRAL CLEANING LOSS AND METHOD FOR REMOVING ROUGING COVERS ON STAINLESS STEELS

The invention relates to methods for removing surface changes which occur on surfaces of stainless metallic materials in the form of coatings and deposits of oxidic iron, in particular on surfaces of stainless steels, as used in process and Produktionsaniagen in the pharmaceutical, food and biotechnology industry frequently used, as well as aqueous cleaning solutions containing a reducing agent and a complexing agent for use in these methods.

Process / production equipment used in the manufacture and processing of active pharmaceutical ingredients, pharmaceutical forms, biotechnologically derived active ingredients, foods, etc., as well as systems and equipment used in the manufacture and distribution of these products, as well as systems and equipment, which are operated with ultrapure water, purified water and pure steam, are usually made of stainless steels based on stainless steel alloys. Examples include stirred tanks, storage tanks, storage tanks, fermenters, dryers, Abfüiϊanlagen, autoclaves, SferiÜsationsbehäiter, Gefriertrockπer, washing machines, CIP ~ plants, ultrapure water generators, Reinstdampferzeuger, Verteilieitungen for the media (purified water, ultrapure water, pure steam, products) etc.

Despite the use of high quality materials such as stainless steels (eg CrNiMo steels, grade AiSI 316L, AiSI 316Ti or AIS! 904L), color changes in the wetted surfaces, which are also known as "rouging" in the pharmaceutical industry, can usually be observed after some time Shipments of typical brown-red particles to the final product or the final product.

Surface changes on stainless metallic surfaces can occur in very different forms. These are often precipitates of oxidic iron compounds, which can occur in the form of fine red-brown particles of iron oxide or iron hydroxide and usually shares of Cr ₁ Ni and Mo included. These particles usually have a powdery consistency and therefore adhere only loosely to the surface. They are therefore easily mechanically abradable, but often leave a visible discoloration of the metallic surfaces, in other forms occur these surface changes in the form of adherent deposits or deposits, which then can not be mechanically removed, but must be subjected to chemical treatment. These newly created surface layers can have a color spectrum from yellow, biow, red, brown to black.

The occurrence of these surface changes entails, in particular in the area of pharmaceutical product manufacturing and the food processing industry, the risk of undesired contamination due to the detachment of heavy metal particles which are distributed in other systems and thus can adversely affect the purity and the quality of the production or process products.

Depending on the intensity and conditions of the operation, these surface changes may occur for the first time a few months after commissioning of a system. In other cases, it may take years for such changes to be observed for the first time.

As far as the formation of these surface changes known under the name "rouging" is concerned, there are currently no reliable scientific results of research iron oxide-rich corrosion layer, with the emergence and transport of corrosion particles in the system as an additional effect.

This roughening phenomenon is characterized by the appearance of a typical iron oxide or iron hydroxide layer on the surface of the stainless steel material, these typical hematite or magnetite layers containing Cr, Ni and Mo intercalated, indicating a layered Aufiösung tendency of the Edeistahlmaterials. The Rougingschichten are usually between 0.1 - 10 microns, with only the thinner coatings are to be designated as Rougekontaminationen, massive deposits on the other hand correspond more Rostkontaminatioπen.

It has been shown that the described changes occur more intensively in systems that are operated with ultrapure water or media-carrying ultrapure water or with ultrapure (water) steam, with increased temperatures being the process of Surface changes seem to accelerate. The formation of these surface changes is also influenced by the atmospheric conditions prevailing in the respective systems, the prevailing media conditions (eg pH <7), the material quality (alloy composition) and the surface quality. Depending on the operating time and conditions, different levels of deposits / deposits occur.

The cause of rouging is evidently a local depassivation of the chromium oxide protective layer of the Edeistahloberflächen caused by the breakdown of said protective layer at discrete surface points due to the above parameters, as well as the failure of a sufficient for a repassivation amount of oxygen.

This mechanism of local depassivation is favored by the significantly reduced amount of dissolved oxygen in hot waters (WFi> 70 ° C or steam) and by a greatly increased ionic capacity due to the purity of said waters.

Among other things, the elevated temperatures cause iron atoms to diffuse to the surface and react with the oxygen present there to form oxide and hydroxide.

In order to enable trouble-free rebuilding of the chromium oxide-rich passive layer as well as to reduce the risk of carry-over of heavy metal particles and the risk of contamination of the products produced in the process / production plants, complete removal and removal of the iron oxide-rich rouging or rust contamination layers is required Simultaneous protection of the stainless steel surfaces. These deposits / deposits must therefore be cleaned periodically using mechanical or wet chemical cleaning methods or combinations thereof.

Mechanical cleaning methods, in which the loosely adhering to the surface particles are removed, for example, with hooves of wipes, are limited in the rain! on easily accessible areas. A removal of the more permanent discoloration, as well as adherent deposits and deposits can not be achieved. In wet-chemical cleaning processes, the deposits / deposits are to be chemically removed. For this purpose, almost exclusively crude solutions containing inorganic acids are currently used. Purification techniques based on neutral cleaning solutions, as sometimes suggested for the removal of rust deposits on cold or hot water pipe systems and black steel containers, have not hitherto been considered for use in the removal of rouging deposits on media contacted stainless steel surfaces. Such neutral cleaning agents are described, for example, in US Pat. No. 6,310,024, US Pat. No. 5,587,142, US Pat. No. 4,789,406 for cleaning boiiem, instantaneous water heaters, etc, for removing rust and / or caustic deposits.

EP 1,621,521 and EP 1 300,368 disclose the use of neutral detergents to remove deposits from cold water bearing systems, particularly water supply facilities such as drinking water tanks. Rouging deposits on media-contacting stainless steel surfaces of process / production plants operated with ultrapure water have a different quality than the rust and lime deposits described in the above-mentioned prior art, which occur on blackstones or on non-metallic surfaces, in practice The complete elimination of rouging on stainless steel surfaces has proven to be extremely cumbersome and difficult, leading to popular wisdom that it is imperative to use strong and highly concentrated mineral acids, despite the numerous known disadvantages.

The use of concentrated mineral acids can namely z.T. involve significant risks, both in terms of transportation and use as part of the cleaning solution itself. In addition to the corrosive and highly corrosive action of an acid such as concentrated hydrochloric acid, sulfuric acid or phosphoric acid, their vapors can cause massive irritation of the respiratory system.

Organic acids, for example oxalic acid and / or citric acid are also used in part for cleaning off the deposits / deposits. However, organic acids do not have the digestibility of highly concentrated mineral acids, so often mixtures of organic and inorganic acids are used. In some cases, complex acid binders, eg EDTA or NTA, are added to these acid mixtures. A major drawback of such acid mixtures is that they do not specifically remove the deposits / deposits in the form of oxidic iron compounds, but also partially solubilize the heavy metals contained in the stainless steel alloy. Inappropriate Handling is thus the danger that the Oberfiäche the process / Produktionsanfagen is attacked and thereby adversely affect the surface properties. In addition, these cleaning solutions contain after use in the rain! a high Schwermetailanteii, so that the solutions must then be disposed of consuming and professional.

In order to compensate for these disadvantages, in practice, the cleaning solutions used in the rouging decontamination have been given specific additives to mitigate the negative effects of the concentrated mineral acids on the stainless steel surfaces and elaborate complex process control and control protocols to ensure a minimum residence time of the cleaning solution To achieve the EdeJstahloberflächen with maximum cleaning effect, as for example in the "Techicai Bulletin" of the company Henkel (Article Nr, 26 / Rev, 00, 2003).

It is therefore an object of the present invention to provide a simple and gentle process which is easy to control in process control for the complete removal of rouging deposits based on oxidic iron compounds on medially contacted surfaces of stainless metallic materials, in particular on surfaces of stainless chromium / nickel steel materials, in particular made of stainless chrome / nickel / molybdenum steels, especially stainless chrome / nickel! and / or chromium / nickel / molybdenum steels of grade AISI 304 (* 1.4301), AIS] 304L (1.4307, 1.4306), AlSi 316 (1.4401), AIS 316L (1.4404, 1.4435), AISI 316 Ti (1.4571) and AIS! 904L (1.4539). [* 1.xxxx = according to DIN 10027-2], but in particular a method for the removal of Oberfiächenveränderungen on surfaces manufactured from said materials processing and production equipment, in particular of process and production plants with ultrapure water or media-carrying ultrapure water or operated with ultrapure water and eg in the pharmaceutical, food and bäσtechnoiogischen industry application and avoids the known disadvantages of the currently majority-used method.

This task could surprisingly by the use of neutral aqueous

Cleaning solutions are dissolved, which contain a reducing agent in combination with at least one complexing agent and allow working in the neutral pH range.

In a specific embodiment, the present invention relates to a process for the complete removal of oxidic iron compounds Rouging coatings on surfaces, in particular on surfaces in contact with the media, of stainless metallic materials, in particular on media-contacting surfaces of materials made of stainless chromium / nickel steels, in particular of stainless chromium / nickel / molybdenum steels, in particular of stainless chromium / nickel and / or chromium / nickel Grade molybdenum AlSI 304 ( ^* 1.43Ö1), AISI 304L (1.4307, 1.4306), AISi 316 (1.4401), AISi 316L (1.4404, 1.4435), AlSI 316 Ti (1.4571) and AISI 904L (1.4539). p .xxxx = according to DIN 10027-2],

The present invention thus relates to a method for the complete removal of rouging-based surface changes on stainless metallic materials, in particular on media-contacted stainless metallic materials, in particular on materials of stainless chromium / nickel steels of the above quality classes, which is characterized in that said surfaces treated with an aqueous solution containing a reducing agent and at least one Komplexbtldner in the neutral pH range and the said cleaning solutions for use in such a method. Also encompassed by the present invention is a process for the repassivation of selectively destroyed chromium oxide-rich passive layers on stainless steel surfaces, in particular on media-contacting stainless steel surfaces, which is characterized in that the Rougingab- deposits formed on said surfaces, with an aqueous solution containing a Reduktionsmitte! and treating at least one complexing agent at neutral pH values and completely removing said deposits and subsequently treating them with an aqueous solution containing an oxidizing agent and preferably at least one complexing agent capable of forming the passivation layer protecting the stainless steel.

The present invention further relates to a method for preventing contamination of manufacturing or process products that are produced in process and Produktionsanfagen which are made of stainless metallic materials, in particular stainless steels, in particular stainless chrome / nickel! Steels, in particular of stainless chromium / nickel / molybdenum steels, in particular of stainless chrome / nickel! and / or chromium / nickel / molybdenum steels of grade AiSi 304 ( ^* 1.4301), AISi 304L (1.4307, 1.4306), AISI 316 (1.4401), AISI 316L (1.4404, 1.4435), AISI 316 Ti (1.4571) and AISi 904L ( 1.4539). [* 1.xxxx = according to DiN 10027-2], but preferably in process and production plants that use ultrapure water or media-carrying ultrapure water or ultra-pure water (water) vapor be operated, in particular at elevated temperatures in the range of 40 ° C to 90 ⁰ C, in particular in a range of 50 ⁰ C to 85 ° C. Said contaminations are caused by particles or constituents, in particular particles or constituents which are dissolved by oxidic iron compounds, which detach from the changed surface and can then be distributed in the process and production plants and the connected systems. The process according to the invention is characterized in particular by treating said process and production plants by means of an aqueous cleaning solution containing a reducing agent and at least one complex binder, removing the changes from the treated surfaces and bringing them into solution, and subsequently removing them from the system together with the cleaning solution be removed.

The present invention further relates to the use of an aqueous cleaning solution containing a reducing agent and at least one Kornpiexbildner for removing Rougingbeiägen on surfaces, especially on media wetted surfaces, stainless steels selected from Gruppeer group of chromium / nickel and chromium / nickel / molybdenum steels in the neutral pH range , in particular in a pH range from about pH 4.5 to about pH 9.0, in particular from about pH 6.0 to about pH 8.0, in particular from about pH 6.5 to about pH 7.5. Said Rougingbeläge usually have a layer thickness between 0.1 .mu.m and 10 .mu.m, in particular between 0.4 .mu.m and 0.8 .mu.m.

In a specific embodiment of the use according to the invention and described herein, said rouging coating is composed of iron oxide and / or iron hydroxide layers containing Cr and / or Ni and / or Mo embedded therein, wherein said oxidic iron compounds are oxidized iron, in particular Fe (II), Fe (II!) And / or Fe (Ii) ZFe (IIi) oxides or hydroxides with constituents of Cr ₁ Ni and / or Mo.

In a further specific embodiment of the use according to the invention and described herein, the steels to be cleaned are those of quality classes AiSI 304 (* 1.4301), AISI 304L (1.4307, 1.4306), AISI 316 (1.4401), AISI 316L (1.4404, 1.4435 ), AIS! 316 Ti (1.4571) and AIS! 904L (1.4539). [* 1.xxxx = according to DIN 10027-2], wherein said steels may be cold-rolled, ground, pickled or electropolished steels, in particular steels having a surface roughness of Ra <3.0 μm. In a further specific embodiment of the use according to the invention and described herein, the steels to be cleaned are those whose surfaces are exposed to ultrapure water or media-carrying ultrapure water or ultrapure water, wherein said ultrapure water is a. (.. Ph Eur) purified water (Aqua Purifϊcata (AP)) with a conductivity of <4.3 .mu.S at 2O ⁰ C and <4.7 .mu.S at 25 ⁰ C (USP 25) is; b. highly purified water (Aqua valde purifϊcata) with a conductivity of <2.1 μS at 25 ⁰ C acts; c. Water for injections (Aqua ad iniectabilia) with a conductivity of <1, 1 μS at 20 ⁰ C (Ph. Eur.) Or <1, 3 μS at 25 ° C (USP 25); and said purest (water) vapor has a conductivity of <5.0 μS.

In a further specific embodiment of the use according to the invention and described herein, the cleaning solution contains at least 2 different complexing agents as well as optionally an additional substance which has both grain-complexing and reducing properties, e.g. Oxalic acid or one of its salts.

Another object of the present invention therefore relates to an aqueous cleaning solution for use in a method for removing Rougingbetägen on media-contacting surfaces of stainless steels selected from the group of chromium / nickel and / or chromium / nickel / molybdenum steels, especially steels of the above grades , in the neutral pH range, characterized in that said cleaning solution contains a reducing agent and at least 2 different Compiexbüdner, and optionally an additional substance which has both complexing and also reducing properties, such as Oxalic acid or one of its salts.

In a specific embodiment, the reducing agent used is a salt-like reducing oxygen compound, in particular a reducing oxygen compound selected from the group consisting of sulfur, nitrogen and phosphorus oxygen compounds, in particular a reducing sulfur-oxygen compound, such as, for example. Dithionite or disulfite.

In a further embodiment of the invention, an acid is selected as the complexing agent from the group of phosphonic acids, phosphonocarboxylic acids, hydroxyacids, iminosuccinic acids, acetic acids and citric acids or one of them Salts used, in particular a phosphonic acid selected from the group of hydroxyalkane and Alkylenphosphonsäuren, in particular a 1-hydroxyethane-1, 1-diphosphonic acid (HEDP), a Aminotri (methylenephosphonic acid) (ATMP), a Hexarnethylendiaminotetra (methylphosphonic) (HDTMP) a Diethyientriaminα penta (methylenephosphonic acid) (DTPMP) or one of its salts, or a 2-phosphonobutane-1,2,4-tricarboxylic acid or one of its salts.

In a further specific embodiment, the complexing agent employed is an iminosuccinylic acid or one of its salts, but in particular an iminodisuccmic acid or one of its salts.

The concentration of reducing agent and complexing agent in the cleaning solution to be used according to the invention is in each case in a range from 0.1% by weight to 1% by weight, in particular in a range from 0.2% by weight to 0.8% by weight. ,

A further specific embodiment of the present invention provides the use according to the invention as described herein of an aqueous cleaning solution comprising a reducing agent and at least one complexing agent for avoiding contamination of production or process products which are operated in ultrapure water or media-carrying ultrapure water or with ultrapure (water) steam - And production facilities are made, in particular of contaminants, which are caused by itself from the changed surface detaching particles or constituents, in particular by oxidic Eisenverbtndungs containing particles or constituents, in the context of a process that is characterized in that said surfaces said Process and Praduktionsanlagen mitteis a reducing agent and at least one KomplexbiJdner containing aqueous cleaning solution treated, the changes of the treated surfaces dissolve, dissolve them and remove them from the system along with the cleaning solution.

In the following, certain of the terms used in the context of the present invention will be explained in more detail.

In the context of the present invention, it is good for the use of the singular forms "a", "an" and "the", "the", "that" that also includes multiple-figure aspects, unless a different interpretation is required from the overall context Thus, for example, if reference is made to "a compound,""a reducing agent,""acompiler," etc., this will preclude the use of two or more compounds, two or more reducing agents, two or more complexing agents, etc.

The term "media" in the context of the present invention in the broadest sense ultrapure water and prepared using ultrapure water reaction, nutrient and / or other media-carrying aqueous solutions are understood as in process and Produktäonsanlagen that in the production and Further processing of pharmaceutical agents, pharmaceutical pharmaceutical forms, biotechnologically produced drugs, food, etc., can be used.

For the purposes of the present invention, "ultrapure water" means highly purified waters which have a conductivity in the range of <1.0 μS and <5.0 μS, measured at a temperature between 20 ^° C. and 25 ^° C. . (. Ph. Eur): ultrapure water to be understood a purified water (Aqua purificata (AP)) with a conductivity of <4.3 .mu.S at 20 ⁰ C or <4.7 .mu.S at 25 ° C (USP 25); b highly purified water (Aqua valde purificata) with a conductivity of <2.1 μS at 25 ° C, c. Water for injections (Aqua ad iniectabiüa) with a conductivity of <1, 1 μS at 20 ⁰ C (Ph. Eur. ) or <1.3 μS at 25 ^° C. (USP 25).

The term "pure steam ¹ " or "steam" refers to water vapor which is used inter alia for sterilization purposes, produced by distilling treated drinking water having a conductivity of <5.0 μS at 25 ^° C. or of Aqua Purificata (AP) with a conductivity of <2.1 μS at 25 ° C or <4.7 μS at 25 ° C (USP 25) or highly purified water (Aqua valde purificata) with a conductivity of <2.1 μS at 25 ^D C or WFI (Water for Injection) with a conductivity of <1, 1 μS at 20 ⁰ C (Ph. Eur.) Or <1, 3 μS at 25 ⁰ C (USP 25), and a conductivity of <5.0 μS having.

In the context of the present invention, in the most general embodiment, "structural changes" are intended to mean any structural change of stainless metallic surfaces, but especially surfaces of stainless steels, in particular stainless steels selected from the group of chromium / nickel and / or chromium / nickel / molybdenum steels, in particular steels grades AISF 304 (M.4301), aS! 304L (1.4307, 1.4306), AISl 316 (1.4401), AIS! 318L (1.4404, 1.4435), AISI 316 Ti (1.4571) and AISI 904L (1.4539). ^[* 1.xxxx = according to DiN 10027-2] be understood, the on Changes in the passive layer of said surfaces are based, which can build new iron oxide-rich layers on the metallic surface, which, in contrast to an intact passive layer is usually associated with changes in color.

In particular, these are cold-rolled, ground, pickled or electropolished steels of the quality grades with a surface roughness of Ra <3.0 μm.

Stainless steels of this steel grade, but in particular CrNi or CrNiMo steels of the quality classes AISI 304 ( ^* 1.4301), AiSI 304L (1.4307, 1.4306), AISI 316 (1.4401), AISI 316L (1.4404, 1.4435), AISI 316 Ti (1.4571) and AISI 904L (1.4539). [ ^* 1.xxxx = according to DIN 10027-2] are primarily used in: apparatus construction for the chemical industry and textile finishing, the food processing industry as well as transport and storage containers for aggressive media, pulp mills, devices for photo development, etc. in one More specifically, in connection with stainless Cr / Ni steels and / or CrNiMo steels, the term "surface changes" is to be understood to mean structural changes in the chromium oxide-rich passive layer of the metallic surface, which are based on the fact that the Cr / Fe ratio is unfavorable to the chromium oxide. Reduced share, whereby the iron can build a new additional iron oxide-rich layer.

In contrast to an intact passive layer, this new iron oxide-rich surface is usually visually recognizable by color changes. The color spectrum ranges from yellow, orange, red, beige, brown, gray to black, but in some cases only after mechanical wiping. In the context of the present invention, "oxidic iron" or "oxidic iron compounds" are to be understood as meaning iron (III) oxides, iron (III) oxides and iron (II) oxides, such as, for example, Fe ₂ O ₃ . Fe ₃ O ₄ , FeO and iron hydroxides or iron (III) oxide hydrates. The latter are a group of substances that can be derived from the iron ([II] oxide and have a different hydration. Examples which its steep at this Fe ₂ O ₃ 3H ₂ O ₁ 2Fe ₂ O ₃ 3H ₂ O, Fe ₂ O ₃ 2H ₂ O and Fe ₂ O ₃ H ₂ O.

The surface changes occurring on said stainless metallic materials are primarily precipitates of oxidic iron compounds, which may occur in the form of fine red-brown particles of iron oxide or iron hydroxide, or in the form of adherent deposits or deposits, the in said particles, deposits or deposits existing oxidische Elsen in the rain! is present as sparingly soluble trivalent Fe (IIi). In contrast to the particulate surface changes present in a powdery consistency, which are easily removed mechanically, for example by wiping, the aforementioned coverings and deposits are permanently adhering surface changes that can no longer be removed mechanically. These newly created surface layers can have a color spectrum from Geib, blue, red, brown to black.

The surface changes mentioned above include, in particular, the deposits and deposits on stainless metallic surfaces, in particular on surfaces of stainless steels, such as, for example, CrNi or CrNiMo steels, in particular on stainless surfaces made of CrNiMo steels of the quality class of the quality grades, which contain the oxidic iron compounds known under the heading "rouging" AiSi 304 (* 1.4301), AiSI 304L (1.4307, 1.4306), AISI 316 (1, 4401), AlSl 316L (1.4404, 1.4435), AIS! 316 Ti (1.4571) and AlSl 904L (1.4539). [ ^* 1.xxxx = according to DIN 10027-2], as can be found in production and process plants and systems, which are operated with ultrapure water or pure steam and are used in particular in the pharmaceutical and food processing industry.

The term "rouging", "rouging coating", "rouging deposit" is used interchangeably herein by "rouging" is to be understood a special form of oxide deposits, as occur on Edelstahioberffächen, in particular surfaces of austenitic stainless steel alloys in hot WFI plant systems or in steam systems, and typically constructed of iron oxide. Iron hydroxide-dominated layers, which typically contain Cr, Ni and Mo or their oxides embedded. These porous and particle-forming iron oxide-rich rouging layers, which generally have a layer thickness between 0.1 and 10 μm and have the character of a surface corrosion, take the place of the originally present chromium oxide-rich, dense and solid passive layers. Only the thinner coverings can be described as rouge contamination, whereas the more massive coverings, which are also to be observed, are more likely to correspond to rust contamination and represent secondary phenomena independent of the actual roughening phenomenon.

The Rougingbelag forming substances are primarily iron oxides (FeO, Fe ₂ O ₃ ) or iron hydroxides, such as Fe (OH) ₂ or Fe (OH). ₃ The emergence of typical "rouging" on stainless steel surfaces is closely linked and therefore dependent on the materials used and the thermodynamic conditions that are exposed to these materials. "Rouging" occurs almost exclusively on surfaces of stainless chromium / nickel steels, particularly stainless steels Chromium / nickel / molybdenum steels, in particular of stainless chromium / nickel / molybdenum steels of the grade AISi 304 ( ^* 1.4301), AiSI 304L (1.4307, 1.4306), AISI 316 (1.4401), AIS! 318L (1.4404, 1.4435), A! S! 316 Ti (1.4571) and AiSI 904L (1.4539). [* 1.xxxx - according to DIN 10027-2], and under conditions that favor local depassivation of the chromium oxide protective layer on said surfaces.

This includes, for example, the presence of ultrapure water and / or steam at a temperature of> 70 ° C and a pH value of <7.

Particularly stubborn and difficult to remove deposits occur when using the following water and Dampfquafitäten: a. purified water (Aqua Purificata (AP)) with a conductivity of <4.3 μS at 2O ⁰ C (Ph. Eur.) or <4.7 μS at 25 ^D C (USP 25); b. highly purified water (Aqua valde purificata) with a conductivity of <2.1 μS at 25 ° C; c. Water for injections (Aqua ad iniectabifia) with a conductivity <1, 1 μS at 20 ⁰ C (Ph. Eur.) Or <1, 3 μS at 25 ° C (USP 25); d. Ultrapure (water) vapor, produced by distillation of treated drinking water with a conductivity of <5.0 μS at 25 ⁰ C or of ultrapure water according to a) - α).

In particular, compounds which have a redox potential which is sufficiently high to reductively dissolve the surface changes, but in particular a redox potential sufficient to convert the Fe (II) which has been oxidically bound in the surface changes into soluble Fe (II), are used as "reducing agents" In a specific embodiment of the present invention compounds are used as reducing agents which have a redox potential in the range from -0.4 E7V to -2.0 EW, in particular from -0.5 E7V to -1.5 EW, in particular from -0.6 EW to -1.2 EW, in particular -0.7 EW to -1.0 EW, based on the Normalwassersfoffelektrode measured in a concentration of 1 mol / liter and at a temperature of 25 ° C. All individual numerical values which fall within the abovementioned range from -0.4 E7V to -2.0 E7V, but which are not specifically mentioned here, are likewise to be the subject of the present invention.

In a specific embodiment of the process according to the invention, a salt-like reducing oxygen compound, in particular a salt-like reducing inorganic oxygen compound, in particular a compound selected from the group of sulfur, nitrogen and phosphorus oxygen compounds as reduction center! be used in the cleaning solution. Examples of such inorganic reducing sulfur oxygen compounds are, in particular, sulfite, bisulfite, and dithionite, and their salts, in particular their sodium salts.

Commercially available compounds which are known per se and which are capable of complexing iron ions, in particular iron (H) ions, in solution and, moreover, are inert towards the effect of the reducing agent present in the cleaning solution or else are sufficient as "complexing agents" have high Kurzzeitstabilttät against said reducing agent, so that they can perform their function as Kompiexbildner for the necessary period for the cleaning.

Examples of such complexing agents which can be used in a specific embodiment of the process according to the invention are acids selected from the group consisting of the phosphonic acids, hydroxyacids, carboxylic acids, iminosuccinylic acids, acetic acids and citric acids or one of their salts.

The present invention is based on the surprising finding that it is possible by the combined use of acting as a reducing agent or as Kompiexbifdner compounds in an aqueous Reϊnigungsiösung complete removal of surface changes on stainless metallic materials. These surface changes are, in particular, oxidized iron compounds which form on metallic surfaces, in particular on metallic surfaces of red-free materials. These stainless materials are, for example, stainless steels, in particular stainless steels with a Cr-Ni steel grade, in particular a Cr-Ni-Mo steel grade, which have good corrosion resistance due to the molybdenum content and improved mechanical properties at high temperatures Relationship to other steel grades without molybdenum. According to the invention, reducing agents, in particular inorganic reducing agents, can be used in the cleaning agents which can be used to remove these surface changes. used in neutral aqueous solution have a great ability to disintegrate against oxidic iron compounds, especially against oxidic iron compounds from sparingly soluble trivalent trivalent Fe (ili).

In the context of the present invention, it is generally possible to use compounds as reducing agents which are capable of the polyvalent insoluble oxidic metals present in the above-described surface changes, but in particular oxide trivalent Fe (Hf), in more readily soluble forms such as, for example, B. Fe (II), as far as such compounds can be used in the respective case in compliance with water regulations. Said reduction center! In particular, they have a redox potential which lies in a range between about -0.4 E ° / V to -2.0 E ⁰ A /, in particular from -0.5 E ⁰ A / to -1.5 E ⁰ A /, in particular from -0.6 EW to -1.2 E7V, in particular from -0.7 EW to -1.0 E7V, measured in relation to the normal hydrogen electrode in a concentration of 1 moi / liter and at a temperature of 25 ° C.

In a specific embodiment of the present invention, inorganic reducing agents are used! but especially salt-like, reducing inorganic oxygen compound including, but not limited to, reducing oxygen compound selected from the group of sulfur, nitrogen and phosphorus oxygen compounds for use. Examples of inorganic reducing nitrogen oxygen compounds are, in particular, nitrite. Hydrazine can also be used as a reducing agent.

In a further specific embodiment of the present invention, the reducing agents used are in particular reducing sulfur oxygen compounds, such as e.g. Dithionite and / or disulfite and / or sulfite and / or bisulfite and / or thiosulfate. The predominantly Fe (1H) -containing deposits / deposits are converted with the reduction of Fe (III) into the more easily complexable Fe (Ij) and thus dissolved and / or converted into colorless crusts, which are more easily blasted off than the original deposits / deposits.

It has been found in the context of the present invention that in particular dithionite and disulfite (pyrosulfite) or mixtures of these compounds in neutral aqueous Solution over a large digestibility against oxidic

Have iron compounds.

Dithionitic solutions and dissolution solutions or mixtures of these solutions are thus similarly effective as mixtures of hydrochloric acid and inhibitors or other inorganic or organic acids. Due to the pH neutral

Application and their reducing character are the inventive center! However, also applicable for the treatment of stainless steels without restriction, BeSäge of oxidic iron compounds are thus by the inventive means gently from Metallioberflächen stainless

Steel, as they are B. in process and production facilities including lines or

Container surfaces are present, removed, bringing their life and their

Function can be increased significantly.

In particular, this also applies to the surfaces of non-metallic constituents of said process and production equipment, e.g. Valves, seals, etc, which are also deposits of oxidic due to carryover

May have iron compounds.

Furthermore, the risks during transport and use of the inventive cleaning solution or its components are significantly lower than when using hydrochloric acid and / or other inorganic or organic

Acids. The final result of the reaction with the oxidic iron compounds

Sulfate is toxicologically and ecologically unproblematic. As technical chemicals are dithionite and pyrosulfite, i.a. as sodium dithionite or as sodium disulfite

(Sodium pyrosuifite), inexpensive to purchase and therefore economical in the

Application.

As possible substitutes for the reducing sulfur oxygen compounds

Dithionate and disulfite in carrying out the inventive method are also salts of reducing acidic nitrogen oxygen compounds, eg. B.

Nitrite, or reducing acidic phosphorus oxygen compounds, e.g. As phosphites or hypophosphites to call. Hydrazine can also be used as a reducing agent.

In a particular embodiment of the present invention thus comes

Dithionite or disuifite or a combination of dithionite and disuifite as the inorganic reducing agent in the cleaning solution for use.

It has also been found that the effect of the reducing agent, ie in particular the dithionite / disulfite, in the sense of removal of the iron oxide Covering / deposits is improved when the Reinigungsiösuπg addition, one or more complexing agents are added.

The invention further relates to the use of certain known per se

Complexing agents capable of forming complexes with higher valent metal ions, but especially with Fe (Ui) and in particular Fe (II).

The Kompiexbilder applicable in the context of the present invention should also be inert to the reducing effect of the reducing agent present in the treatment solution under the prevailing conditions there or have a Kurzzeitstabifität against said reducing agents, which is sufficient to the full functionality of said reducing agent said time To guarantee compiled biologists.

It may therefore be advantageous for the complexing agent to be delayed in time

Adding reducing agent to the cleaning solution at a time when some of the oxide-bonded metals has already been removed by the reducing agent from the surface changes and converted into a suitable form for the complexing agent. in a particular embodiment of the present invention is therefore the

Komplexbüdner the cleaning solution mixed with a time delay, after the

Treatment has already begun, but in particular at least 10 minutes, preferably at least 20 minutes, preferably at least 30 minutes and up to 1 hour after the start of treatment.

Alternatively, the complexing agent may also be consumed or consumed by the

Effect of Reduktionsmittete is impaired in its effect, be replaced by the addition of fresh complex in the course of the cleaning process.

Examples of such complexing agents which can be used in a specific embodiment of the process according to the invention are acids selected from the group of phosphonic acids, hydroxy acids, carboxylic acids,

Iminosuccinylsäuren, acetic acids and citric acids or one of their salts.

As Kompiebxbiidner, for use in the Erfrndungsgemässen

In particular, compounds which contain phosphonic acid groups, if appropriate in salt form, such as, for example,

Hydroxyalkaπphosphonsäure or one of its salts, but especially 1-

Hydroxyethane-1,1-diphosphinic acid (HEDP) or an alkylenephosphonic acid, but in particular aminotri (methylenephosphonic acid) (ATMP), H-oxamethylenediamino-tetra (methylphenyl acid) (HDTMP) or diethylenetriaminopenta (methylenephosphite) phosphonic acid) (DTPMP) and / or compounds which contain succinylic acid groups, optionally in salt form, such as, for example, fminosuccinic acid, but in particular iminodisuccinic acid.

The known complexing agents phosphonic acid type have in their

Use for the removal of deposits and deposits on stainless surfaces in pharmaceutical, food and biotechnoiogischen plants the advantage that they are toxic harmless.

Further examples of compounds used in the context of the present invention as

Granulizers may be employed, but are not limited to compounds of the hydroxy (poly! Y) carboxylic acid type, in particular

Hydroxypolycarboxylic acids with 2-4 Carbσxylgruppen such. Citric acid, tartaric acid or apidic acid or one of their salts.

It is also possible to use compounds of the acetic acid type, but in particular di-, tri- or tetraacetic acids, but especially one of N, N-diacetic acid

(ISDA), ethylenediaminetetraacetic acid (EDTA), propylenediaminetetraacetic acid (PDTA),

Nitrilotriacetic acid (NTA) or one of its salts.

In a further specific embodiment, said

Kompfexbildner thus to a carboxylic acid, in particular an amino carboxylic acid or a phosphonocarboxylic acid, in particular a phosphonotricarboxylic, in particular a phosphonobutanetricarboxylic acid such. a 2-

Phosphonobutane, 2,4-t-carboxylic acid or one of its salts.

Furthermore, in the process according to the invention, sodium citrate or

Ethanoidigiycin be used as a complexing agent.

The salts which can be used in the cleaning solutions described above are primarily the alkali metal salts of those mentioned therein

Acids, in particular their lithium, sodium, potassium, rubidium and

Cesium salts, but especially their sodium and potassium salts.

The presence of the complexing agents prevents the reaction of the oxidic iron with the reducing agent to lead to the formation of crusts. It was found that the complexing agents significantly improve the stripping process of the constituents of the oxidic iron from the stainless metal surface.

Preferably, therefore, in the context of the present invention, a

Cleaning solution used, which contain a combination of reducing agent and at least one, but especially two or more Compiexbüdner belonging to different classes of substances and optionally a buffer. In a further embodiment according to the invention, said aqueous pure solution may additionally comprise further constituents selected from the group of buffer salts, wetting agents, stabilizers and / or further reducing agents which may be dissolved, emuligated or incorporated as suspended solids. The process according to the invention is carried out in a pH range from about 4.Q to about 10.0, in particular from about 4.5 to about 9.5, in particular from about 6.0 to about 8.0, in particular from about 6.5 to about 7.5.

In order to keep the pH of the cleaning solution in the desired range constant, the cleaning solution is usually also added buffer, in particular buffers based on harmless Saize of weak mineral acids. Suitable buffer systems for setting a desired pH can be taken from relevant chemical reference works. For the setting of a neutral pH, in particular the system bicarbonate / carbonic acid is well suited. However, other buffer systems can also be used. It has also been found that the effect of an aqueous cleaning solution containing a reducing agent, i. in particular dithioite or disulfite or a combination of dithionite and disulfite, and at least one, but especially at least two, complexing agents, i. in particular compounds of the phosphonate and / or succinate type, in the sense of a gentle removal of the iron oxide deposits / deposits of stainless metallic surfaces is improved, when the cleaning solution also carboxylic acids and / or salts thereof are added, such. Oxalic acid and / or salts thereof. The additional use of such carboxylic acids and / or their salts enhances the removal of oxidic iron compounds on the stainless surfaces to be treated, in that these carboxylic acids and / or carbonates can exhibit both complexing and reducing effects.

The chemical components required for carrying out the process according to the invention can be introduced into the aqueous cleaning solution in any suitable form, ie as separate or premixed solids, as solutions and concentrates or as pastes or gels. The preparation of the cleaning solution can be carried out prior to its snaking contacts with the deposits to be treated, but the cleaning solution can also be prepared in situ in the equipment to be treated, eg in a production container or in a piping system, by adding the individual components at different times. This alternative must be taken into account when a two-stage process is provided, wherein in a first stage, the reduction stage, a treatment of the surface changes with a reducing agent containing the first cleaning solution i and in a subsequent second stage, a Kompiexierungsstufe, a treatment with a second cleaning solution II is carried out, which contains at least one Komplexbϊldner, which is able to enter into a soluble complex with divalent iron ions. Alternatively, the Kompiexbildner also be added directly or with a time lag in situ the cleaning solution I.

The reducing agent and the complexing agent can, as indicated, be added to the cleaning solution in advance or in situ, these in each case in a concentration range from 0.025% by weight to 25% by weight, in particular in a concentration range of 0.05% by weight. % to 15 wt .-%, in particular in a concentration range of 0.1 wt .-% to 10 wt .-%, in particular in a Konzentratioπsbereich of 0.2 wt .-% to 5 wt .-%, in particular in a Koπzentrationsbereich from 0.25 wt .-% to 1 wt .-%, in particular in a concentration range of 0.25 wt .-% to 0.5 wt .-%, in particular in a Konzentratäonsbereich from 0.5 wt .-% to 1.5 wt. % in the cleaning solution.

It has been found that particularly good cleaning performance can be achieved if reducing agent and complexer in the cleaning solution in a concentration ratio of 6% reducing agent / 10% complexing agent, in particular in a concentration ratio of 5% reduction center! / 8% Komplexbüdner, in particular in a Konzentrationsverhit of 3% reducing agent / 5% Komplexbifdner, especially in a concentration ratio of 1.5% reducing agent / 2.5% complexing agent, especially in a concentration ratio of 0.6% reduction center! / 1% complexing agent, in particular in a concentration ratio of 0.5% reducing agent / 0.8% complexing agent, in particular in a concentration ratio of 0.3% reducing agent / 0.5% complexing agent, in particular in a concentration ratio of 0.15% reducing agent / 0.25% complexing agent, in particular in a concentration ratio of 0.1% Reducing agent / 0.2% complexing agent present.

In a specific embodiment of the present invention, a cleaning solution is used which has a reducing agent such as dithionite or disulfite or a combination of dithionite or disulfite or one of its salts and at least contains one, but preferably at least two kσmplexbüdende substances, such as phosphonic acid and / or a compound containing Succinylsäuregruppen, or one of its salts. In cleaning solutions containing at least two kompiexbüdende substances, these are preferably chemically different substances.

In a further specific embodiment of the present invention, a cleaning solution is used which comprises dithionite or disulphite or a combination of dithionite or disulphite or one of its salts as inorganic reducing agent! and a phosphonic acid and a compound containing succinylic acid groups, or one of their salts, as a complexing agent.

In a further specific embodiment, the cleaning solution consists of dithionite or one of its salts and a combination of phosphonic acid and iminosuccinic acid, or one of its salts, and optionally a buffer. In a further specific embodiment, the cleaning solution consists of dithionite or one of its salts and a combination of phosphonic acid and iminosuccinic acid, or one of its salts, and oxalic acid or one of its salts, and optionally a buffer.

In particular, the phosphonic acid mentioned above is a phosphonobufanetricarboxylic acid or one of its salts, and iminosuccinic acid is an iminodisuccinylic acid or one of its salts.

In a further specific embodiment, the reducing agent and the complexing agent are present in a concentration ratio of 0.7% reducing agent / 1.0% complexing agent, in particular in a concentration ratio of 0.3% reducing agent / 0.5% of complexing agent, if the cleaning solution contains only one complexing agent or in a concentration ratio of 3% reducing agent / 8% of complexing agent, in particular 0.5% reducing agent / 1.5% Kompfexbildπer, in particular 0.6% reducing agent / 1.1% Komplexbüdner, in particular 0.25% reducing agent / 0.75% Komplexbiidner, in particular in a concentration ratio of 0.3% reducing agent / 0.6% complexing agent, if the cleaning solution contains two different complexing agents.

In a further specific embodiment, the cleaning solution may additionally contain between 0.01% and 0.5%, in particular between 0.04% and 0.2%, in particular between 0.05% and 0.1%, of a compound which has both complexing and reducing properties. The treatment of oxidic Eϊsenverbindungen containing deposits and deposits on stainless metallic surfaces, in particular on surfaces of stainless steels, preferably takes place in a temperature range of about 20 ^p C to about 98 ° C, in particular in a temperature range from about 40 ⁰ C to about 90 ⁰ C. , in particular in a temperature range of about 5O ⁰ C to about 80 ⁰ C, in particular in a temperature range of about 6O ⁰ C to about 85 ° C, in particular in a temperature range of about 70 ⁰ C to about 8O ⁰ C, and at a pH Value of about 4.0 to about 10.0, in particular from about 4.5 to about 9.5, in particular from about 6.0 to about 8.0, in particular from about 6.5 to about 7.5. in a specific embodiment, the inventive method is designed so that the stainless metallic surfaces, in particular the surfaces of stainless steels, depending on the strength and extent of the deposits, for a period of about 30 minutes to 12 hours, in particular for a period of 60 minutes 8 hours, in particular for a period of 1.5 to 6 hours, in particular for a period of 2 to 5 hours, in particular for a period of 3 to 4 hours, in particular for a period of 1, 5 to 2 hours in contact with the aqueous cleaning solution stay.

All individual numerical values that fall within the above defined ranges, but are not specifically mentioned here, are likewise to be the subject of the present invention.

In a further specific embodiment of the process according to the invention, the stainless metallic surfaces to be cleaned are located in process and / or production plants, in particular in process and / or production plants, which contribute ultrapure water and / or ultrapure steam, in particular hot ultrapure water and / or pure steam Temperatures of more than 60 ⁰ C, operated. To purify said process and production equipment, the containers and devices to be cleaned are filled with the cleaning solution according to the invention and the pH is adjusted within a range from pH 4.0 to pH 8.0, in particular in a range from pH 6.0 to pH 8.0. One then iässt the cleaning solution at a temperature of 50 ⁰ C to 95 ⁰ C, in particular from 6O ⁰ C to 9O ⁰ C _1, in particular from 70 ⁰ C to 85 ° C for a period of 1.0 h to 5 h, in particular 1, 5 hours to 3.0 hours on the surfaces to be cleaned. The cleaning solution can be used, for example, by using the stirring or flow in the containers. or by using external circulation pumps are moved through the system, with slow Riessgeschwindigkeiten are preferred.

All individual numerical values that fall within the above-defined ranges, but are not specifically mentioned here, should also be the subject of the present invention.

By periodically taking samples from the cleaning solution, it is possible to check, with the aid of methods known per se, whether the reducing agent is still present in an effective concentration. For example, by using a

Methylene blue solution can be easily checked for sufficient amounts

Reducing agent present in the cleaning solution. If this is the case, it results in a clearly visible discoloration of the methylene blue solution. On the other hand, is the concentration of reduction center! suboptimal, the methylene blue is not decolorized and it may be necessary to add reducing agent.

The endpoint of a purification process may be determined by means of iron impact measurements (e.g., coiorimetric). If the iron content in the cleaning solution reaches a stable value after a certain exposure time, the cleaning process can be ended.

First, the cleaning solution is removed and the cleaned containers and

Devices then rinsed with.

Repassivation of the stainless steel surfaces can (such as HNO _3; <20 ppm Cl ^"or Wasserstoffperxoid) by means of an aqueous solution containing an oxidizing agent, in particular an oxygen-donating acid, soft capable the stainless steel build protective passive layer and optionally at least one

Complexing agent and / or using oxygen-containing ultrapure water, in particular of oxygen-containing ultrapure water having a conductivity of 0.5 .mu.S / cm and at a temperature of 10 ⁰ C - 20 ⁰ C, in particular from 12 ° C to 15 ° C, preferably at 14 ° C are performed.

Since the ultrapure water used contains the natural load of dissolved O 2 according to the preparation, the necessary chromium oxide-rich passive layer can be built up.

Finally, a free rinse using ultrapure water in

Durchspühlverfahren until the conductivity of the effluent water an acceptable

Has achieved value. This value is preferably <0.7 μS / cm.

If the coverings / deposits of items, eg. B. individual pieces of pipe or

Fittings to be removed, which are taken from the plant or device can, the process of the invention can also be carried out so as to put the disassembled parts to be liberated by the Befägen / deposits in a bath of a cleaning solution according to the invention.

Particularly good cleaning results can also be obtained by spraying (via, for example, spray balls, C (leaning) i (n) P (Iace) sprayers), which is preferably felt under an inert atmosphere and also constituents! of the present invention. Inert reaction conditions can be achieved by gassing the systems to be cleaned with inert gases, e.g. Nitrogen or noble gases, hersteiien.

Also included in the present invention is a cleaning solution for use in the process of the invention having the composition disclosed hereinbefore.

EXAMPLES

Examples describing the effects of the process according to the invention on the example of deposits / deposits of oxidic iron compounds (rouging) on the surface of stainless steels are described in more detail below,

Step Example! 1 :

Substances used or _± agents: Muscle plates are used by

Tubes made of stainless steel (AiSi 316L), which are made of a pharmaceutical

Piping system for the distribution of hot ultrapure water (WFI) come and are treated with a strong oxidic iron layer (rouging).

The oxidic iron layer (rouging) in this example consists predominantly chemically of sparingly soluble Fe (! I [) compounds.

To remove the rouging from the surface of the sample add a freshly prepared 3% solution of solid sodium dithionite in water, which additionally contains 5% 2

Phosphonobutane 1,2,4-tricarboxylic acid sodium salt (PBTC-Na4), 3% tetrasodium iminodisuccinate and 1% of a sodium bicarbonate / carbonic acid buffer is used.

Experimental Procedure: A sample platelet size of 4 x 5 crn is placed in 500 ml of the above dithionite solution. The solution (pH value (beginning) approx.

8) is stirred at 60 - 8O ⁰ C for 4 h at low speed. After the reaction time, 10 mL of the solution are removed and analyzed for their iron content.

Result: The oxidic iron layer (rouging) has been greatly reduced. There is only a weak residual coating left. The iron content of the solution is after 4 h

Reaction time 4.2 mg / L iron. The pH changes slightly during the reaction: pH

(End) about 7,

A further improvement of the result can be achieved by adding about 0.5% potassium oxalate to the abovementioned difhionite solution.

Comparison with the procedure used hitherto: A reaction solution containing 15%

Contains phosphoric acid and 2% citric acid and has a pH of <1, under otherwise identical experimental conditions (such as reaction time and temperature) shows no significant change in the surface coating. The iron content of

Solution is after 4 h exposure time 0.7 mg / L iron. Example 2:

Substances / agents used: Short tube sections of

Stainless steel tubes (AiSl 316L), which are made of a pharmaceutical grade

Piping system for the distribution of hot ultrapure water (WFi) come and are subjected to a strong oxidic iron layer (rouging).

The oxidic iron layer (rouging) in this example consists predominantly chemically of sparingly soluble Fe (Ili) bonds.

Experimental procedure: To remove the Rouging of the metal surface is a freshly prepared 0.5% solution of solid Natriurπdithionϊt in water, the additional

1% 2-phosphonobutane, 2,4-tricarboxylic acid sodium salt (PBTC-Na4), 0.5%

Tetrasodiumimiπodisuccinate, 0.1% potassium oxalate and 0.2% of a sodium bicarbonate / carbonic acid buffer.

Experimental procedure: A pipe section with a width of 5 cm and a

Diameter of 7 cm is placed in 250 ml of the above dithionite solution. The solution (pH (beginning) about 7.5) at 7O ⁰ C for 5 h at low

Speed stirred. After the reaction time, 10 mL of the solution are removed and analyzed for their iron content.

Result: The oxidic iron layer (rouging) has been greatly reduced. There is only a faint residual heat in the form of a black abrasion (Fe (!! / Hi) -

Connections). The iron content of the solution after 5 h exposure time 21, 4 mg / L iron. The pH changes slightly during the reaction: pH (end) ca. 8.5.

Example 3:

Substances / agents used: A 300 liter stainless steel batch tank (AISI 316L) is used, which is used in pharmaceutical production and is treated with an oxidic iron layer (rouging). These

Layer is abradable with a white wipe and discolored after the

Wiping off the surface strongly red.

The oxidic iron layer (rouging) in this example consists predominantly chemically of sparingly soluble Fe (III) compounds,

Experimental Procedure: To remove rouging from the container surface, add a freshly prepared 0.25% solution of solid sodium dithionite in water, the additionally 0.5% 2-phosphonobutane, 2,4-tricarboxylic acid sodium salt (PBTC-Na4), _r 0.25% tetrasodium iminodisuccinate, 0.05% potassium oxalate uncf contains 0.1% of a sodium bicarbonate / carbonic acid buffer. Experimental procedure: The batch tank is completely filled with 300 liters of the above dithionite solution. The solution (pH (beginning) approx. 7.5) is allowed to act at 75 ° C. for 1.5 h. The cleaning solution is circulated via a circulation pump. After the reaction time, 10 mL of the solution are removed and analyzed for their iron content. The container is then rinsed with water and a wipe sample is performed with a white wipe.

Result: The oxidic iron layer (rouging) is completely removed. The iron content of the solution after the contact time is 0.65 mg / L iron. The pH changes slightly during the reaction: pH (end) ca. 7.0. The wipe remains completely white after wiping the container surface.

The presence of an effective Dithionitkonzentratioπ can be easily checked by the decolorization of a Methylenblauiösung, is too little dithionite in the solution, the methylene blue is not decolorized. Thus, methylene blue is suitable for tracking the cleaning process (derouging process) in which one tests a pumped subset at regular intervals.

The endpoint of a cleaning process (derouging process) can be determined by means of iron content measurements (e.g., colorimetric). If the iron content in the cleaning solution reaches a stable value after a certain exposure time, the cleaning process can be ended.

Example 4:

Substances / agents used: A 750 liter stainless steel batch tank (AlSl 316L) with CIP spraying equipment used in pharmaceutical production and with an oxidic iron layer is used

(Rouging) is applied. This layer is abradable with a white wipe and discolored after wiping the top coat red.

The oxidic iron layer (rouging) continues in this example! chemically predominantly from sparingly soluble Fe (lil) compounds together.

To remove the rouging from the container surface is a freshly prepared

0.25% solution of solid sodium dithionite in water, which additionally contains 0.5% 2-

Phosphonobutane 1, 2,4-tricarboxylic acid sodium salt (PBTC-Na4), 0.25% Tetrasodium inodisuccinate, 0.05% potassium oxalate, 0.1% oxalic acid and 0.1% of a sodium bicarbonate / Kohjensäurepuffers used. Experimental procedure: The batch tank and the circulating pump pipelines required for the CIP spraying unit are completely purged with gaseous nitrogen. 150 liters of the above-mentioned dithionite solution are poured into the inertized feed tank. The solution (pH (start) approx. 7.5) is circulated over the circulation pump and the pipe lines at 75 ° C for 45 minutes. The container wall is permanently wetted with the dithiological solution via the C! P spray ball. During the entire cleaning time, the preparation tank remains inert with nitrogen. After the cleaning time, 10 ml of the solution are removed and analyzed for their iron content. The container is then rinsed with water and a wipe sample is performed with a white wipe.

Result: The oxidic iron layer (rouging) is completely removed. The iron content of the solution after the exposure time is 1.23 mg / L iron. The pH changes slightly during the reaction; pH (end) approx. 7.0. The wipe remains completely white after wiping the container surface.

Claims

claims

1. Use of an aqueous cleaning solution containing a reducing agent and at least one Komplexbüdner for removing Rougingbelägen on media wetted surfaces stainless steel selected from the group of chromium / nickel and chromium / nickel / molybdenum steels in the neutral pH range.

2. Use according to claim 1, characterized in that the cleaning solution has a pH of about pH 6.0 to about pH 8.0.

3. Use according to claim 1 or 2, characterized in that said Rougingbelag is composed of layers of oxidic iron compounds containing Cr and / or Ni and / or Mo embedded,

4. Use according to claim 3, characterized in that said oxide-containing iron compounds are oxide-bound Fe (HI) with constituents of Cr, Ni and / or Mo.

5. Use according to claim 3 or 4 _r characterized in that the RougingbeSag has a layer thickness between 0.1 microns - 10 microns.

6. Use according to one of claims 1 to 5, characterized in that said steels are those of the quality classes AiSI 304 <* 1.4301), AiSI 304L (1.4307, 1.4306), AISI 316 (1.4401), AISI 316L (1.4404, 1.4435), AIS! 316 Ti (1.4571) and AISI 904L (1.4539). [* 1.xxxx = according to DIN 10027-2].

7. Use according to one of claims 1 to 6, characterized in that said steels are cold-rolled, ground, pickled or electropolished steels having a surface roughness of Ra <3.0 μm. is. δ. Use according to any one of Claims 1 to 7, characterized in that said wetted surfaces are those which are exposed to ultrapure water and / or ultrapure (water) vapor and / or surfaces which are exposed to media based on rice water.

9. Use according to claim 8, characterized in that it is in said ultrapure water to a. (.. Ph Eur) purified water (Aqua purificata (AP)) with a conductivity of <4.3 .mu.S at 2O ⁰ C and <4.7 .mu.S at 25 ⁰ C (USP 25) is; b. highly purified water (Aqua vaide purificata) with a conductivity of <2.1 μS at 25 ° C; c. Water for injections (Aqua ad iniectabilia) with a conductivity of <1, 1 μS at 20 ⁰ C (Ph. Eur.) Or <1, 3 μS at 25 ⁰ C (USP 25).

10. Use according to claim 8, characterized in that said ultrapure (water) vapor has a conductivity of <5.0 μS.

11. Use according to any one of claims 1 to 10, characterized in that said cleaning solution contains at least 2 different complexing agents.

12. Use according to any one of claims 1 to 11, characterized in that said cleaning solution additionally contains a substance having both complexing and reducing properties.

13. Use according to any one of claims 1 to 12, characterized in that a salt-like reducing oxygen compound is used as the reducing agent, in particular a reducing oxygen compound selected from the group of sulfur, nitrogen and phosphorus oxygen compounds.

14. Use according to claim 13, characterized in that said reducing sulfur oxygen compound is dithionite or disulfite

15. Use according to any one of claims 1 to 14, characterized in that the complexing agent used is an acid selected from the group of phosphonic acids, phosphonocarboxylic acids, hydroxyacids, iminosuccinyl acids, acetic acids and citric acids or one of their safes, in particular a phosphonic acid selected from A group of hydroxyalkanoic and alkylenephosphonic acids, in particular a 1-hydroxyethane-1,1-diphosphonic acid (HEDP), an aminotri (methylenephosphonic acid) (ATMP), a hexamethylenediaminotetra (methylphosphonic acid) (HDTMP), a diethylenetriaminopenta (methylphosphonic acid) (DTPMP) or one of its salts, or a 2-phosphonobutane-1,2,4-tricarboxylic acid or one of its salts.

16. Use according to claim 15, characterized in that said acid is an iminosuccinic acid or one of its salts.

17. Use according to claim 16, characterized in that said iminosuccinic acid is an iminodisuccinylic acid or one of its salts

18. Use according to one of claims 1 to 17, characterized in that the reducing agent and the complexing agent in the Behaπdluπgsiösung each in a concentration range of 0.1 Gβw .-% to 1 wt .-%, in particular in a concentration range of 0.2 wt % to 0.8% by weight

19. Aqueous cleaning solution containing a reducing agent and a Kompiexbildner for removing Rougingbelägen on media-contacting surfaces of stainless steels selected from the group of chromium / nickel and chromium / nickel / Molybdäπ steels in the neutral pH range, characterized in that said cleaning solution is a reducing agent and at least contains different complexing agents

20. Cleaning solution according to claim 19, characterized in that it contains dlthionite or disulfite or a combination of dithionite or disulfite or one of its salts as inorganic reducing agent and a phosphonic acid and a compound containing Succinylsäuregruppen, or one of their salts, as Komplexbiidner.

21. Cleaning solution according to claim 20, characterized in that it contains dithionite or one of its salts and a combination of phosphonic acid and iminosuccinic acid, or one of its salts, and optionally a buffer.

22. Cleaning solution according to one of claims 19 to 21, characterized in that it additionally contains oxalic acid

23. A cleaning solution according to any one of claims 19 to 22, characterized in that said phosphonic acid is a phosphonotricarboxylic acid, in particular a 2-phosphonobutane, 2,4-tricarboxylic acid or one of its salts.

24. Cleaning solution according to one of claims 21 to 23, characterized in that said immosuccinic acid is an iminodisuccinylic acid or one of its salts.

25. Cleaning solution according to one of claims 19 to 24, characterized in that the reducing agent and the two complexing agents in a concentration ratio 0.6% reducing agent / 1.1% Komplexbiidner, in particular in a concentration ratio of 0.3% reducing agent / 0.6% Komplexbiidner present.

26. Use of a cleaning solution according to one of claims 19 to 25 according to one of claims 1 to 19.

27. A method for complete removal of rouging-based surface changes on stainless metallic materials, in particular media-wetted stainless metallic materials, in particular on materials of stainless chromium / nickel steels and / or chrome / nickel / (vlo! Ybdän Stähfen, characterized in that said surfaces are treated with one of the cleaning solutions defined in claims 1 to 25.

28. A method for the complete removal of rouging based Oberfiächenveränderungen on stainless metallic materials, in particular on media-wetted stainless metallic materials, in particular on materials of stainless chromium / nickel steels and / or ChroπWNickek / molybdenum steels and anschüessendeπ Repasstvierung said surfaces, characterized in that said surfaces treated with one of the defined in claims 1 to 25 cleaning solutions and said deposits completely removed and anschießend with an aqueous solution containing an oxidizing agent and / or with oxygenated ultrapure water spühit so that the protective stainless steel passive layer is built up.

29. The method according to any one of claims 27 or 28, characterized in that the method is carried out in a spray process under an inert atmosphere.