CZ38680U1 - A viscous preparation to pickle carbon steels, stainless steels and aluminium alloys - Google Patents

Description

Viscous pickling agent for carbon steels, stainless steels and aluminum alloys

Technical area

The field of technology relates to a viscous (gel) pickling and cleaning agent for carbon steel, stainless steel and aluminum alloys, acting in the form of chemical substances, i.e. in the form of a viscous solution forming a gel, with the thixotropic physical properties of visco-elastic substances, which is a condition for easy use on vertical surfaces and other surfaces of products, for pickling welds or entire surfaces of products (especially vertical ones, etc.).

State of the art

Pickling of steel using gel (or paste) techniques refers to a treatment used to remove dirt, rust and scale from the surface of the material. During hot working processes, a layer of oxide (referred to as “scale”, due to the flaky nature of its appearance) forms on the surface of the metal, especially at welds etc. Carbon steels, stainless steels and aluminium alloys are often treated with a gel (or paste) preparation based on hydrochloric acid etc. Before pickling, the steels and aluminium alloys must be cleaned of grease, oils and other contaminants to ensure that everything works effectively. Common methods include degreasing with solvents or alkaline solutions. After pickling, the steels/aluminium alloys are rinsed with pressurized water to remove any remaining acid, including subsequent drying. Pickling as such has a significant impact on the mechanical properties of both carbon and stainless steels, including aluminium alloys. This is essential, for example, for steels requiring high stress resistance or so-called deformation tolerance. Pickling not only prepares the surface for passivation, but also removes oxides, chips, rust or other residues from previous production phases. During the production process, the surface of aluminum alloys, carbon and stainless steels is contaminated with grease, oil, etc., or initial corrosion (aluminum oxides, iron oxides, depending on the material). These impurities must be removed.

Standard working process of chemical oxidation technique - pickling with gel or paste:

- pickling by applying gel to smaller parts, especially in places of welds, etc.;

- pickling by gel spray (newer technology, e.g. Graco RS Gel Coat spray gun) of larger and larger parts, especially in places where there are welded seams, but also on the entire surface of large parts, which leads to lower costs due to the handling of these large parts (described below). This is always followed by rinsing with pressurized water and thorough drying of the material.

While pickling (cleaning) removes the damaged layer, passivation involves the formation of a new layer on the metal surface. The chemical reaction of pickling with a gel involves the dissolution of oxides, during the action time - approx. from 10 min. to 2 hours, depending on the ambient temperature, which facilitates the separation of oxides, etc. from the metal surface.

The next phase is neutralization - with high-pressure water jets that remove the gel from the metal surface. The chemical solution is incorporated into a viscous gel that allows it to perform its function over time, slowing down the evaporation of its components and creating a physical barrier. The above-mentioned properties, typical of the use of gel, extend the pickling time, inevitably also affect the delivery time of the treated products and, in particular, the production costs when using hazardous acids - high disposal costs due to hazardous liquid waste (including the purchase price of the pickling agent).

As a result, the process must be carried out in large and safe spaces, ensuring the containment of all residues and the neutralized solution (water + gel) must be collected to be subsequently purified in suitable tanks. The collected waste must be disposed of by an external company.

Pickling of metals in general:

Pickling of metals is a process in which oxidation layers are removed with acids, which

- 1 CZ 38680 U1 remove impurities from the surface of e.g. steels, aluminum alloys, etc. Impurities can be in the form of rust, scale, dirt, etc., which can appear on the surface of steels during processing or heat treatment.

These impurities (rust, scale, etc.) are removed from the steel surface using a pickling gel or paste. This process not only increases the aesthetic quality, but above all protects the steel or aluminum alloys against further damage.

Currently, at least 80% of pickled materials are pickled with inorganic acids, most of which are in hydrochloric acid, less in sulfuric acid, and relatively insignificantly in phosphoric acid (or other acids) or in a mixture of other acids.

These are, for example, the following acids, currently generally used:

• sulfuric acid (H2SO4);

• hydrochloric acid (HCl);

• nitric acid (HNO3);

• hydrofluoric acid (HF).

Pickling with nitric, phosphoric, hydrofluoric acid, etc.:

This is an older technique that involves applying a gel preparation (paste) to the steel surface containing nitric acid, hydrofluoric acid, etc., to remove free iron and improve corrosion resistance. However, this pickling method has unavoidable problems due to the hazardous nature of nitric acid, etc. In addition, it often requires special handling, produces toxic fumes, and can take a long time to process. Nitric acid is highly toxic and dangerous to handle, and its use and disposal are strictly regulated. It is a dangerous oxidizing caustic that damages the skin and mucous membranes, its fumes are also dangerous, and its disposal is economically expensive.

In general, the purpose of pickling is to restore the appearance and corrosion-resistant properties of metals after the manufacturing process (i.e., removal of iron contamination, etc.). Gel pickling is also intended to prepare these materials for subsequent treatments such as passivation and anodizing.

Not only does pickling prepare the surface for the passivation process, but it also removes oxides, chips, rust or other residues from previous manufacturing stages.

Pickling is regulated, for example, by the European standard:

Technical standard ČSN EN 4707 (318243):2020 - Aerospace - Pickling of aluminium and aluminium alloys without hexavalent chromium. Other standards apply to steels, etc.

[Literature 1]

Pickling steel in harsh conditions

Mika Maanonen - Steel Pickling in Challenging Conditions

Helsinki Metropolitan University of Applied Sciences

Materials Technology and Surface Engineering - Thesis

Source: https://www.theseus.fi/bitstream/handle/10024/70713/Steel_Pickling _in_Challenging_Conditions 2014 Thesis Mika Maanonen.pdf?sequence= 1 (par. 7.3.) Citric acid was tested with concentrations of 3.5%, 6.5% and 9.5%: the 6.5% concentration was tested in ten-step intervals between 10 °C and 60 °C; and the 3.5% and 9.5% concentrations were tested at 30 °C and 50 °C. Approximately 1 ml/l of ethanol was added to reduce the surface tension. No inhibitor was used. The effectiveness of citric acid clearly increased with increasing temperature. Higher concentrations had better effectiveness, but the differences between the tested concentrations remained relatively small, as shown in Fig. 10. Higher temperatures and a wider range of concentrations could be tested to gain a better insight into pickling. The effect of additives and mixing could test the potential of citric acid. Comparison of acid pickling inhibitor

- 2 CZ 38680 U1 lemon.

Conclusions and recommendations

Based on the information gathered and the tests performed, citric acid appears to be a good option for pickling steel in conditions with limited equipment. Citric acid - the solution can be heated above 60 °C, the effectiveness is the same as hydrochloric acid. At lower temperatures, citric acid requires more time compared to hydrochloric or phosphoric acid, but it is the best choice in terms of price, transport, safety and a promising substance. It is also readily available, as it is used in the food industry and other industries. Literature and tests have shown that acid consumption and base metal losses are significantly reduced even with minimal inhibition and can be recommended for all. Since commercial inhibitor products usually also contain wetting agents, iron oxide is removed more quickly, or alternatively lower temperatures can be used for the same effectiveness.

The benefits of using inhibition during pickling are clear, but chemicals should be selected on a case-by-case basis to ensure the correct action is taken. Pickling is usually the best choice for complex parts such as pipes and machined parts that need to be pickled. For example, the special nozzles required for blasting and water jetting are expensive and may not be sufficient to achieve the good results that pickling gives. Pickling also ensures a uniform surface quality and there is no risk of contamination from the blasting media. Depending on the application, it may also be impossible to achieve the desired surface quality with abrasive blasting, wire brushing and water cleaning. Alternative methods may be more cost-effective when used to clean simple products such as sheet metal and wire. Continuous cleaning lines are used.

The pickling tests performed as expected and provided good data on acids. The inhibitor tests were successful and showed the importance of choosing the right inhibitor. The data on the effect of rinse water temperature on acid residues was useful to avoid unnecessary heating. Further research should focus on inhibition and acid residues to ensure a more optimal cleaning process. Also, more acids, a wider temperature range and the effects of additives on effectiveness could be tested to recommend different conditions.

[Literature 2]

Corrosion resistance of low-alloy steel S355MC in raw Glycerol Mariána Palcutová, Žaneta Gerhátová, Patrik Šulhánek and Petr Gogola Faculty of Materials Science and Technology, Slovak University of Technology, J. Bottu 25, 91724 Trnava, Slovakia

Technologies 2023, 11(3), 69; https://doi.org/10.3390/technologies11030069

Submission received: March 27, 2023 // Revised: May 5, 2023 // Accepted: May 16, 2023

Source: https7/www.mdpLcom/2227-7080/H3/69

Abstract

Corrosion is the degradation of materials in an oxidizing environment. In aqueous solutions, it is initiated by the surface reaction of a metallic material with the surrounding electrolyte. The corrosion rate of metals can be significantly reduced by the presence of organic compounds. Crude glycerol is an organic by-product of biodiesel, soap and fatty acid production. It is produced in significant quantities by transesterification. Crude glycerol contains several impurities and has low economic value. Its disposal in the environment is undesirable and potential applications need to be explored. In the present short communication, steel corrosion in crude glycerol was investigated for the first time. The corrosion behavior of low-alloy structural steel S355MC in untreated crude glycerol was studied by electrochemical methods. The results were compared with the use of tap water. The open circuit potential (OCP) of S355MC in crude glycerol was more negative compared to the tap water potential (OAP). The OCP was stable over time, indicating rapid passivation of the steel substrate. The corrosion resistance was further investigated by electrode polarization. A wide passivation region was found on the polarization curve of S355MC in crude glycerol. In addition, the corrosion rate was 2.2 times lower compared to tap water.

- 3 CZ 38680 U1

The surface exposed to water was significantly degraded by red rose. On the contrary, the surface of S355MC after exposure to crude glycerol was less affected by corrosion and covered with a protective layer. The results show the significant activity of crude glycerol, which could be utilized in various 5 technologies.

Conclusions

In the present communication, the corrosion behavior of S355MC structural steel in crude glycerol was investigated by electrochemical methods. The results were compared with those using 10% tap water. Glycerol reduced the corrosion rate of the steel. The corrosion rate of S355MC steel in glycerol was 2.06 x 10 mm/year. This value was approximately 2.2 times lower compared to drinking water. The surface of the steel exposed to the glycerol solution was covered with a layer of corrosion products. This study suggests that crude glycerol can reduce the corrosion of structural steel in aqueous solutions. The inhibitory effect is probably related to the adsorption of glycerol on the metal surface.

The essence of the technical solution

The essence of the technical solution is a pickling viscous (gel) preparation that contains:

- citric acid (Citric acid);

- ammonium bifluoride (ABF);

- glycerol (Glycerin);

- a thixotropic substance;

- the balance up to 100% by weight of this pickling gel preparation consists of water.

According to the table of examples, the optimal composition was selected from column 3.

Raw material (g/1000 g water) 1 2 3 Citric acid (monohydrate) 38 grams 49 grams 60g Ammonium bifluoride (etching) 1.3 grams 1.5 grams 1.8 grams Glycerol (synergist) 0.9g 1.08 grams 1.2 grams Aerosil (thixotropic substance) 2.1 grams 2.8 grams 3.2 grams Water (filtered) up to 1000 g up to 1000 g up to 1000 g

For pickling in the form of a gel preparation, for example, hydrochloric acid, sulfuric acid, etc. are currently used, which are dangerous acids. This completely avoids the gel pickling procedure, these dangerous acids.

In this case, it's about finding a safer and, above all, cheaper alternative:

- Pickling with dangerous acids is replaced by citric acid (the basic active ingredient) - a safe natural substance. Citric acid is also a so-called green corrosion inhibitor.

- Highly hazardous etching chemicals are replaced with milder ammonium bifluoride (ABF).

- Furthermore, the technology of the product is supplemented with another green corrosion inhibitor, glycerol, i.e. an inhibitory-corrosion substance that creates crosslinking - protection of metal surfaces through polymerization.

- Glycerol - a green corrosion inhibitor that affects the mechanical, barrier and thermal properties of bio-stress polymers - it is about crosslinking metal surfaces.

- Thixotropic gel-forming substance. It is a white crystalline powder, a dispersible amorphous pure substance. It is not considered a harmful substance, it is used in pharmacy or cosmetics, it is considered orally and dermally safe, it has no mutagenic effects.

- Pickling with the product can be carried out with sufficient efficiency even at a normal temperature of around 20 °C.

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Pickling with citric acid, ABF and glycerol in the form of a gel does not require special handling and does not create significant toxic fumes that can harm production personnel (when applied with a brush to metals or sprayed with a special pressure gun) or the environment (as with gels with nitric acid, etc.). From an ecological point of view, passivation with citric acid, ABF and glycerol is a much better and at the same time cheaper choice than, for example, nitric acid.

The pickling process with citric acid in gel form is, compared to, for example, nitric acid:

- increased worker safety (one of the most important health protection items);

- more cost-effective - cheaper, due to lower material handling risks;

- reduction in the cost of purchasing raw materials - cheaper raw materials;

- reduction of waste disposal costs (one of the highest items for hazardous acids).

Forms of pickling with a gel preparation - or types of pickling, which are used to remove mainly unwanted oxide layers from stainless steel surfaces, decarburize and further eliminate impurities:

- staining with a brush or roller (smaller and larger areas);

- spray pickling - a newer method (large areas).

Pickling gel, a newer form of application by spraying - acts in the form of chemicals (it is a viscous solution), changing the color of welds, etc. of carbon steel, stainless steel and aluminum alloys, i.e. by removing weld scale, tarnish, oxides and also damaged metal layers not only in the weld area, but also on the other surfaces of larger areas of the given material.

This means that it is a newer spraying method, which is particularly suitable for oversized parts (they do not fit in the pickling immersion bath), when for this purpose, for example, the Graco RS Gel Coat spray gun is used - for larger and larger parts.

This means that pickling with a gel preparation takes place not only on welds, but also on large flat vertical parts or welds with complex shapes, since colored chromium oxides are released during welding.

General information about the ingredients in the pickling gel:

1. Citric acid is non-toxic (it is also used in the food industry) and biodegradable. In addition, it simplifies compliance with environmental regulations and, in particular, protects the health and safety of employees. The effect of this corrosion inhibitor is more pronounced where (during pickling) the surface of the material is irregularly oxidized and where the clean surface is exposed to pickling baths. Not only does citric acid effectively remove aluminum oxides from aluminum alloys and Fe oxides from carbon and stainless steels, but it is also needed in lower concentrations, in a pickling solution diluted in given proportions, which is economically significantly different in terms of the volume of funds (against dangerous acids) and in the volume by weight, in this preparation.

2. We also specialized in the effects of biodegradable glycerol, a green corrosion inhibitor, on improving the efficiency of the pickling process. Its function is esterification - which is a reaction to crosslink the surface of materials on a molecular basis - this leads to polymerization, which can distribute metal ions through polymer networks. This is about crosslinking surfaces and thus protecting metals, see more detailed description below. Glycerol adsorbs on the surface of steel and acts as a corrosion inhibitor.

3. Ammonium bifluoride (ABF) is a less toxic colorless salt (white crystalline solid) and when added to water, ABF becomes a less aggressive version of hydrofluoric acid. Ammonium bifluoride (NH4HF2) is a versatile chemical widely used in metalworking, glass etching and industrial cleaning. Due to its nature, it is very common in truck wash soaps and other cleaning products. Ammonium bifluoride (ABF) replaces the traditional but dangerous material - hydrofluoric acid, which is very aggressive (causes e.g. severe burns) and releases pollutants into the air (especially when inhaled). Using ammonium bifluoride is safer for use, storage and transportation and reduces costs by about 15%, is

- 5 CZ 38680 U1 non-flammable - not subject to ADR during transport. ABF is extremely soluble in cold water. ABF is also recently used in passivation and simultaneous anodizing of aluminum.

3.1. Surfaces with the help of ammonium bifluoride increase their resistance and longevity of steel. It is also used in production - cleaning of semiconductors, in anodizing, etc.:

- metal surface treatment - to remove iron stains (in the pickling process);

- building protection (as part of cleaning products);

- boiler and rust cleaning - removal of silica in boilers and evaporators;

- ammonium bifluoride successfully replaces wood preservatives.

4. Disposal of the used mixture is much easier and especially cheaper (against dangerous acids). This also applies to the purchase of chemicals and especially to the protection of employee health.

5. We also focused on ensuring a more optimal process and, in particular, use at a lower ambient temperature range (approx. 20 °C), which is economically advantageous from an energy point of view compared to higher temperatures.

Technical specifications of fabrics:

1. Citric acid:

Pickling based on citric acid and other substances used is safer, e.g. against nitric acid, sulfuric acid, etc.

1.1. It is environmentally friendly: citric acid is minimally toxic and is biodegradable, making it less harmful to the environment compared to, for example, nitric acid, etc.

1.2. Citric acid is a good chelating agent, which means that it can bind to metal ions and form soluble complexes, it can both pickle and passivate multiple types of alloys, i.e. it can pickle multiple types of carbon and stainless steel alloys, including aluminum alloys.

1.3. Citric acid effectively removes aluminum oxides from aluminum alloys. But also oxides: FeO iron oxide is porous and thus etches more stable oxides - iron oxide FeiOs and iron oxide FesO4, from carbon and stainless steels, while it is needed in lower concentrations than when using, for example, nitric acid, sulfuric acid or hydrofluoric acid.

1.4. Since this acid is used as a food additive and is on the GRAS (Generally Recognized as Safe) list, it is also suitable for use in food and beverage processing.

1.5. Citric acid is safe with negligible toxicity and does not have hazardous fumes, which reduces risks to worker safety (e.g. against nitric acid).

1.6. Effective cleaning - citric acid effectively chelates iron (a chemical process in which organic compounds bind to metal cations - a microencapsulation process), pickles and cleans the surface without leaving any residue on the surface.

1.7. Some other pickling hazardous substances remove nickel and chromium from steel alloys, as well as removing iron, which thins the metal layer (see scientific knowledge). The use of citric acid minimizes this potential for harmful removal of some of the metal.

1.8. Based on the above, the preparation is non-flammable (does not fall under the ADR regime).

In addition to these few advantages mentioned above, citric acid is a modern solution for pickling and passivation of carbon steel, stainless steel and aluminum alloys. It is safer, easier to handle (compared to nitric acid, for example), more environmentally friendly and generally less demanding to use. This emerging technical solution - citric acid together with glycerol, etc., combines safe formulations that offer users a new generation of technical, economic, reliable and ecological solutions.

2. Ammonium bifluoride (ABF), with very low content in the pickling agent:

2.1. Ammonium Bifluoride (ABF) - a etchant, is a less toxic colorless salt (white crystalline solid) and when added to water, ABF becomes a less aggressive version of hydrofluoric acid. Ammonium bifluoride products are often considered a safer alternative to acid.

- 6 CZ 38680 U1 hydrofluoric acid. Therefore, ABF is very common, for example, in truck wash soaps and other cleaning agents. ABF is extremely soluble in cold water.

2.2. It is used in cleaning, etching and also for anodizing metals - creating anodic coatings in an aqueous solution, which is a little-known matter, which is also used, for example, as a passivating agent.

• Glass processing: Used in the field of metal processing, glass (etching).

• Food processing: Used in sterilization and disinfection equipment, cleaning of beer dispensing equipment.

• Oil and Gas: Used in acidizing oil and natural gas wells.

• Nuclear chemistry: Used in the separation of uranium from other elements.

• Sugar industry: Used in controlling sugar loss due to bacteria.

• Wood preservatives: Used in preserving wood.

• Industrial cleaning: Used to remove dirt, rust and difficult-to-remove residue from various surfaces.

3. Glycerol (glycerin):

3.1. Glycerol is a potential bio-based material that provides prominent biocompatible yet biodegradable polymers for various applications through direct polymerization.

3.2. We specialized in the effects of this green corrosion inhibitor, in improving the efficiency of the gel pickling process and especially in the form - esterification, which is a reaction, to crosslink the surface of materials on a molecular basis, thereby causing polymerization, which can distribute metal ions through polymer networks. It is also anodization with glycerol, the so-called mechanism of formation of glycerol anodic layers, especially for aluminum, see. professional literature) and at the same time the coordinator of atoms into the network structure, plays a key role in the polymer field, as the glycerol molecule reacts with exposed carboxyl groups - i.e. it creates reinforced molecular coatings on steels.

3.3. Glycerol can reduce corrosion of e.g. structural steels in aqueous solutions. The inhibitory effect is related to the so-called adsorption of glycerol on surfaces (adsorption is the so-called accumulation of particles of atoms, molecules), or at the phase interface, by the effect of interfacial attractive forces.

4. White crystalline powder, based on silica:

4.1. The thixotropic substance colloidal silicate creates a viscous preparation (gel). It is a white crystalline powder based on silicon dioxide. It is a highly dispersed amorphous pure substance, which is produced by high-temperature hydrolysis of silicon chloride. It is not considered a harmful substance. When used in pharmacy or cosmetics, it is considered to be orally and dermally safe, has no mutagenic effects. It does not irritate the eyes and may cause skin irritation only in particularly sensitive individuals. It does not show carcinogenic effects.

4.2. The thixotropic property used is a physical phenomenon of viscoelastic substances that are semi-solid at rest. The physical properties of thixotropic materials consist in the change in the viscosity of these substances depending on time and the force acting on them. Materials with thixotropic properties have the ability to lose their viscosity and become less dense or fluid with increased mechanical action. When the force stops, they gradually regain their original viscosity (density). With the time of application of tension, e.g. painting with a brush - the viscosity decreases (paints and varnishes are easier to spread after a longer brush action and do not run off after the application is finished), then we speak of a thixotropic substance.

4.3. It has excellent thixotropic properties and, above all, is environmentally friendly.

Thixotropic properties can be advantageous in applications, especially on inclined and vertical objects, where it is desirable that the material is easy to apply, but at the same time it should maintain its structure or strength after the respective material (brush or roller application, or application with special spraying equipment, e.g. spray gun for applying gel coatings, Graco RS - Gel Coat.

Function of the gel pickling agent against metal corrosion:

Pickling/cleaning of welds, surfaces, etc. is a chemical process used in this case on carbon steels, stainless steels and aluminum alloys, which removes oxidation layers, scale,

- 7 CZ 38680 UI impurities and coatings that may appear on the surface of these materials during processing or heat treatment.

Citric acid pickling is currently a modern technology that is also highly effective in passivating stainless steels, aluminum alloys and other metals. On the other hand, the use of nitric acid, sulfuric acid, etc. has several well-known disadvantages and is probably in use due to the so-called industrial inertia. Some manufacturers believe that citric acid pickling is not suitable, for example, for industries with strict hygiene or corrosion requirements, for the resistance of products for industries such as food processing, medical devices, etc.

In fact, citric acid pickling meets or exceeds industry standards for cleanliness and corrosion protection. Citric acid is suitable as an advanced technology because it leaves no harmful residue and is a biodegradable material.

Unlike nitric acid, which slightly removes nickel and cobalt from the surface along with free iron, citric acid only removes free metals, for which there is scientific evidence.

That is, glycerin and citric acid are green corrosion inhibitors that include protection of metals in the form of coatings, including crosslinking of surfaces by polymerization.

• Glycerol influences mechanical, barrier and thermal properties in the form of bio-stress polymers.

• Efficient use of glycerol is essential to prevent environmental pollution.

• Glycerol is an emerging additive for today's polymer industry.

Citric acid and glycerin, together with the weaker chemical ABF - are currently, in my opinion, generally a very cost-effective method for pickling, passivation, anodizing metals, including descaling by the so-called circulation method, which is easily proven by basic indicators - the price of purchasing raw materials, disposal of raw materials and low hazard to employees.

Comparison table of preparations based on: nitric acid and citric acid.

Nitric acid (Acidum nitricum) Citric acid Manipulation Very dangerous. Safer to use. Air/emissions Toxic fumes are produced. Small toxic fumes. Flexibility Risk to the user. Time, temperature and concentration must be carefully monitored. Low risk to user, equipment or product in case of prolonged application or high concentration. Danger Toxic and corrosive gases. Special disposal required. Hazardous at high temperature. Very low toxic gas emissions. Easier disposal. Low high temperature hazard. Processing time 20 minutes to several hours. 5 minutes - up to several hours. Temperatures High temperature is required for most applications. Room for many applications. Effect on the device Degradation of stainless steel or polymer equipment. Low degradation only after a long time. Cost High costs for raw material purchase and disposal. High maintenance costs. Low raw material and disposal costs. Low maintenance costs. Environment Ecologically harmful. Eco-friendly.

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Technical data of the product and physical properties:

The product is non-flammable in viscous form (gel) (does not fall under the ADR regime).

Material effects - has no known effect on rubber or plastic.

The product causes slight damage to zinc and galvanized steel.

HDPE plastic or stainless steel should be used to store this product.

Some manufacturers worry that the citric acid pickling layer is less durable than that achieved with nitric acid, etc. However, citric acid not only increases corrosion resistance, but also prevents contamination of iron by foreign particles on the surface of stainless steels, etc. This makes it ideal for long-term durability in harsh environments, from marine facilities to chemical processing plants.

The pickling process with citric acid in gel form is, compared to, for example, nitric acid: - overall more cost-effective - cheaper, due to lower risks of material handling; - reduced costs for purchasing raw materials;

- reduction of waste disposal costs;

- increased safety for workers during handling.

Its less non-toxic nature and furthermore simplifies compliance with environmental regulations and especially protects employee health and safety.

Character of the gel pickling preparation:

This colorless gel preparation also removes traces of oil and grease not only on welds, but also on the surface of various types of carbon, stainless steels and also aluminum alloys, after which the preparation removes free iron ions from the molecular layers. This creates a positive change that leads to better resistance, while not creating a negative impact on the function of the pickled part, especially - welded seams in steels, etc.

Using a professional product:

Preparation intended for pickling metals:

For welded seams, surfaces, etc. of carbon steel, stainless steel and aluminum alloys, where oxidation layers, scale, dirt and coatings that may appear on the surface of carbon steel and aluminum during processing or heat treatment are removed. Ambient (surrounding) temperature may be adequate depending on the end use (Ambient temperature: ambient temperature within the range of 15 °C ± 22 °C). It is always recommended to time test the products before using the product. Always mix thoroughly before use.

Forms of use of gel pickling agent on carbon steel, stainless steel and aluminum alloys:

- applying the product with a brush;

- applying the product with a roller;

- application of the product with a special spraying device for large products (e.g. spray guns for applying gel coatings, Graco RS - Gel Coat), in the case of very large objects that cannot be placed in a tank, or those with particularly complex shapes where immersion would not reach all parts.

Procedure for applying pickling gel to carbon steels, stainless steels and aluminum alloys:

• Mix the product thoroughly before use. Do not dilute the product.

• To ensure the best results, the treated parts should be thoroughly cleaned of coarse dirt, oils and the surface should be wiped dry before using the product.

• All equipment, applicators, etc. should be clean and dry before use. Only polypropylene, polyethylene or other durable HDPE plastic containers, or stainless steel, should be used to hold or store this product.

• The product is applied with a brush, etc. (at an ambient temperature of 15 to 22°C), which is intended for

- 9 CZ 38680 U1 use without dilution, when for aluminum alloys it is necessary to shorten the reaction time compared to steels. For more aggressive cleaning, a longer time for the product to take effect is used.

• Time, temperature and product concentration should be tested before use in production.

• The product can also be applied by roller to larger flat surfaces. Coverage is approximately 23 ^m2 per 5 liters. Wait approximately 5 to 60 minutes during the test, depending on the material, and then rinse the product completely from the surface with pressurized water. Repeat the process if necessary to obtain the desired results.

• The recommended temperature for the gel to work is 15 to 22°C. The surface must be tested for specific use by applying a sample of the gel - and ensure a suitable working time: - the shortest time period for aluminum alloys, - the medium time period for carbon steel, - the longer time period for stainless steel.

• The product must remain moist during the pickling of the treated area. When using, it is not advisable to treat the material in direct sunlight or in other environments with high temperatures, this will prevent premature drying of the product from the surface of the product.

• The pickling procedure is followed by rinsing with pressurized water. The recommended pressure is 18 MPa.

• Drying is the final stage of the metal parts process, it is necessary to prevent possible corrosion by removing any moisture from the surface of the materials.

Notice:

- Although the pickling gel preparation is safe, it may cause irritation to the body surface, eyes, etc. Before using this preparation, it is necessary to use eye protection, reinforced rubber gloves and a rubber apron, including protective clothing. Other important warnings can be found in the Safety Data Sheet.

- The product contains a small amount of ammonium bifluoride (ABF) - may be harmful if swallowed or inhaled. It has negative effects on mucous membrane and upper respiratory tract tissues, as well as eyes and skin.

- Do not use the product on electrical wiring, etc., or on a product that is connected to an electrical current without first turning off all electricity, as the substance is conductive. - Do not allow it to act on materials without a prior time test. Damage to these materials may occur if exposed for too long.

Storage and disposal of the product:

The product should be stored at temperatures between 8°C and 26°C, in stainless steel or approved plastic containers - HDPE.

Warranty period: 18 months from the date of manufacture

Disposal - according to regulations.

Overview of pickling, passivation and gel preparations, a comprehensive coordinated product line:

1. Pickling agent for carbon, stainless steel and aluminum alloys (pickling solution):

The product is diluted 1:4 with water for aluminum alloys, with water (water supply lines).

The product is diluted 1:3 with water for carbon steels, with water (water supply lines).

The product is diluted 1:2 with water for stainless steel, with water (water supply lines).

The proportions can be adjusted by one part water (depending on the surface contamination) according to tests.

Pickling of carbon steels, stainless steels and aluminium alloys. This is a chemical cleaning or pickling process which is used to remove surface layers of oxides etc. (including the polymer function of metals). Pickling of the above metals results in etching of the surface and consequently in the chemical removal of corrosion, scale and impurities from the surface of these alloys. It is advisable to carry out time and temperature testing of the material at approx. 20 °C, or higher, to achieve a better result the procedure is repeated.

2. Preparation: Passivation, anodizing and polymerization of metals, for steels and aluminum alloys (passivation, anodizing and polymerization solution):

The product is diluted 1:3 with water for aluminum alloys (water supply lines).

The product is diluted 1:2 with water for carbon steels (water lines).

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The product is diluted 1:1 with water for stainless steel, with water (water supply lines).

The proportions can be adjusted by one part water (depending on the surface contamination) according to tests.

Passivation, simultaneous anodization and polymerization of carbon steels, stainless steels and aluminum alloys, the purpose of which is to create a protective film that effectively extends the life of the products.

Anodizing (or anodizing) is often synonymous with aluminum, which is new information for many experts, according to new scientific findings. Stainless steel is also able to benefit from the anodizing transformation process (or anodizing) based on the product.

Passivation and anodizing of carbon and stainless steels with the product not only optimizes their appearance, but also significantly improves resistance to corrosion and wear.

Passivation and anodizing of aluminum alloys with a preparation (anodic oxidation) is an electrochemical process in which a uniformly compact layer of aluminum oxide is formed on the aluminum surface.

Polymerization function - or polymer reaction (crosslinking of metal surfaces), which is divided into several phases (the resulting chain mechanism), is another function of the product. It is advisable to perform time and temperature testing of the material at approx. 20 °C, or higher, to achieve a better result, the procedure is repeated.

Use of cleaning, descaling, etc.

2.1. Product: Cleaning, descaling, passivation, anodization and polymerization of pressure boilers and piping systems made of carbon and stainless steel by circulation (not intended for aluminum alloys).

The product is diluted 1:2 with water for carbon steels (water lines).

The product is diluted 1:1 with water for stainless steel, with water (water supply lines).

This is a product that has dual use, according to point 2 and simultaneously according to point 2.1.

Anti-corrosion cleaning of rust and descaling, removal of scale - mineral deposits, sludge and biofilms. At the same time, passivation/anodization/polymerization of internal parts of piping systems and pressure boilers made of carbon and stainless steel is carried out (this applies to already installed piping systems and pressure boilers), which do not need to be dismantled with this treatment method, which significantly reduces costs.

Applications for carbon and stainless steels using the circulation method (circulation pump), on already installed piping systems and in pressure boilers (not intended for aluminum alloys).

The product provides protection against corrosion (before subsequent perforation of the pipe - surface and crevice corrosion, spot - pitting, etc.). Visual inspection by dismantling one element before and after cleaning is suitable, for boilers visual inspection or by camera system.

3. Pickling gel: For carbon steel, stainless steel and aluminum alloys (viscous gel): Do not dilute the product.

A preparation for pickling welds and large parts (including polymerization). It concerns changes in color, especially of welds and their surroundings, on small and large or complex welds, as well as the removal of various abrasions after contact with non-precious materials and other iron contamination.

Application method: brush, roller or special gel gun. Use for oversized products, or for large parts of product surfaces. The gel preparation can be painted (roller can also be used), and spraying is also possible (e.g. with a spray gun for applying gel coatings, Graco RS - Gel Coat).

To achieve a better result, the effect time is extended from 5 to 120 min., depending on the material - the lowest time for aluminum materials. The highest time for stainless steel (according to time tests). Depending on the type of material, weld and ambient temperature, it is left to act, then the surface must be rinsed with pressurized water and dried properly. It is advisable to perform time and temperature testing of the material at approx. 20 °C, or higher, to achieve a better result, the procedure is repeated.

Examples of implementing a technical solution

It is a viscous (gel) pickling agent (acting in the form of chemicals) for carbon steel, stainless steel and aluminum alloys, especially welds, etc., where this pickling removes oxidation layers, stains, etc.

- 11 CZ 38680 U1

Composition: citric acid is very soluble in water (59.2 g/100 ml at 20 °C), as are other substances - ammonium bifluoride (etching agent), glycerol (synergist), colloidal silicate (thixotropic substance - gel-forming).

This preparation is presented in three examples of technical solutions.

Example 1

Preparation with subsequent composition of a pickling agent with a cleaning effect for the treatment of carbon steels, stainless steels and aluminum alloys, i.e. various technological equipment and parts made of the aforementioned alloys. All of the listed substances (chemicals) have a liquid/solid form and are soluble in cold water. The substances listed below were mixed at temperatures ranging from 19 to 23 °C. The raw materials (chemicals) listed in the table of examples were dissolved at laboratory temperature in water, forming a pickling viscous solution. The tested samples are considered 100% and were diluted with water (filtered, with a 3-stage pre-filtration system for chlorine and chlorine derivatives, lead, heavy metals, organic compounds and other deposits) to the required concentrations.

The pickling agent is prepared by dissolving complexing agents:

- citric acid (monohydrate) - 38 g/1000 g;

- ammonium bifluoride (etching agent) - 1.3 g/1000 g;

- glycerol (synergist) - 0.9 g/1000 g;

- colloidal silicate (thixotropic substance) - 2.1 g/1000 g, in filtered water, see table of examples below.

The balance of up to 100% of the weight of this passivation preparation is water. The result of this process is a clear, homogeneous solution.

Example 2

Preparation with subsequent composition of a pickling agent with a cleaning effect for the treatment of carbon steels, stainless steels and aluminum alloys, i.e. various technological equipment and parts made of the aforementioned alloys. All of the listed substances (chemicals) have a liquid/solid form and are soluble in cold water. The substances listed below were mixed at temperatures ranging from 19 to 23 °C. The raw materials (chemicals) listed in the table of examples were dissolved at laboratory temperature in water, forming a pickling viscous solution. The tested samples are considered 100% and were diluted with water (filtered, with a 3-stage pre-filtration system for chlorine and chlorine derivatives, lead, heavy metals, organic compounds and other deposits) to the required concentrations.

The pickling agent is prepared by dissolving complexing agents:

- citric acid (monohydrate) - 49 g/1000 g;

- ammonium bifluoride (etching agent) - 1.5 g/1000 g;

- glycerol (synergist) - 1.08 g/1000 g;

- colloidal silicate (thixotropic substance) - 2.8 g/1000 g, in filtered water, see table of examples below.

The balance of up to 100% of the weight of this passivation preparation is water. The result of this process is a clear, homogeneous solution.

Example 3

Preparation with subsequent composition of a pickling agent with a cleaning effect for the treatment of carbon steels, stainless steels and aluminum alloys, i.e. various technological equipment and parts made of the aforementioned alloys. All of the listed substances (chemicals) have a liquid/solid form and are soluble in cold water. The substances listed below were mixed at temperatures ranging from 19 to 23 °C. The raw materials (chemicals) listed in the table of examples were dissolved at laboratory temperature in water, forming a pickling viscous solution. The tested samples are considered to be 100% and were diluted with water (filtered, with a 3-stage pre-filtration system for chlorine and chlorine derivatives, lead,

- 12 CZ 38680 U1 heavy metals, organic compounds and other deposits) to the required concentrations.

The pickling agent is prepared by dissolving complexing agents:

- citric acid (monohydrate) - 60 g/1000 g;

- ammonium bifluoride (etching agent) - 1.8 g/1000 g;

- glycerol (synergist) - 1.2 g/1000 g;

- colloidal silicate (thixotropic substance) - 3.2 g/1000 G, in filtered water, see table of examples below.

The balance up to 100% by weight of this passivation preparation is water. The result of this process 10 is a clear homogeneous solution.

According to the table of examples, the optimal composition was selected from column 3.

Raw material (g/1000 g water) 1 2 3 Citric acid (monohydrate) 38 grams 49 grams 60g Ammonium bifluoride (etching) 1.3 grams 1.5 grams 1.8 grams Glycerol (synergist) 0.9g 1.08 grams 1.2 grams Aerosil (thixotropic substance) 2.1 grams 2.8 grams 3.2 grams Water (filtered) up to 1000 g up to 1000 g up to 1000 g

Industrial applicability

Pickling with a gel preparation is carried out:

- on welds (brush application);

- on large flat vertical parts that cannot be completely immersed (roller, gun application);

- can also be applied to welds with complex shapes, as colored oxides are released during welding (application with a spray gun);

- it is then applied to large flat vertical parts with a special spraying device (e.g. Graco RS - Gel Coat spray gun).

Claims (2)

1. A viscous preparation for pickling carbon steels, stainless steels and aluminum alloys, characterized in that it contains citric acid in an amount of from 0.5% to 48% by weight of the preparation, ammonium bifluoride in an amount of from 0.4% to 16.9% by weight of the preparation, glycerol in an amount of from 0.3% to 28% by weight of the composition, the thixotropic substance colloidal silicate in an amount of from 0.2% to 11.6% by weight of the composition, the balance up to 100% by weight of this composition consists of water. 2. The viscous preparation according to claim 1, characterized in that it is in the form of a viscous solution.