Paste for stainless steel after welding

The risk of corrosion on stainless steel most often appears after welding work or after finishing processing of the part mechanically (emery tools, sandblasting, etc.). The essence of the damage received by the metal is the disruption of the chromium oxide layer, as a result of which the iron is “bare” and becomes unprotected. Therefore, every impact on stainless steel must be “neutralized” by passivation and chemical etching.

Treatment of stainless steel seams

Stainless steels are actively used in industry for the manufacture of containers and pipelines for aggressive liquids. In everyday life, kitchen utensils and beautiful heated towel rails are made from this metal. The mirror surface has an attractive appearance, and the product can serve for a very long time. But to achieve such an effect on the finished structure, it is necessary to properly process the stainless steel welds. If this is not done, the weld areas will turn yellow and black, or they may even rust. Why is this happening? What mechanical and chemical processing methods are there?

Reasons for processing

In the manufacture of various stainless steel structures, methods of welding metals with an electric arc in an environment of inert gases are used. To do this, use a tungsten non-consumable electrode and a supply of pure argon to protect the weld pool from interaction with the environment. You can also create a seam using semi-automatic machines, where an arc burns between the tip of the wire and the product. A mixture of argon and carbon dioxide is supplied from the burner nozzle. The wire is pushed by a special mechanism, the speed of which is adjusted depending on the thickness of the metal and the current strength.

Although the seams are strong and even, they have an unattractive appearance and therefore need to be processed. The junction itself may have a bluish-mirrored hue. The peri-suture zone is often yellow. With a scaly pattern, black marks may be visible in the grooves. And over time, such places even rust.

All this happens due to overheating in the welding zone. High temperatures from an electric arc promote burnout of alloying elements and deplete this area. As a result, it changes color and becomes more vulnerable to external influences. The film formed on the surface has little resistance to an aggressive environment, therefore, when it comes into contact with working fluids at chemical plants, it becomes a weak point and becomes covered with corrosion.

Heated towel rails sometimes rust at the welding points due to the presence of a small electrical voltage in the pipes, which interacts with the material of the product and continues to weaken the weld. This also happens due to the wrong choice of stainless steel for a specific type of product. For example, instead of grade 304, which is rich in chromium, manufacturers use stainless steel 201, which is cheaper, but whose composition replaces chromium with manganese. It is difficult to distinguish them visually, but with prolonged work in contact with liquids, this will appear as red spots. Therefore, the correct choice of steel grade and subsequent processing of stainless steel is the key to a long, attractive appearance of the product.

Mechanical grinding

The good corrosion properties of stainless steel contribute to its extensive use in environments where liquids are used. Such products last longer than mild steel. And the shine and mirror appearance of the surface allow you to install structures in prominent places, improving the overall design of the room or facade. External railings and ramps, parking racks, and various heated towel rails are made from stainless steel. Despite contact with water and welding work on the products, all these elements retain their beautiful appearance. This is achieved through several types of processing.

One of them is mechanical grinding, which removes the top oxide layer on the weld, which is the weak point of the structure, and also eliminates color transitions and irregularities in the weld joint. This process occurs in the following sequence:

Using a grinder and a thick grinding wheel, the waves of the metal seam and its convexities protruding beyond the general plane of the surface are erased. This way you can quickly smooth out the seam, but the grinder leaves behind rough grooves from the abrasive and overheated areas with dark spots.
To remove these defects more carefully, you can use petal wheels for an angle grinder. The process will take a little longer, and more consumables will be spent for a large volume of work, but the risks will remain smaller.
Next, a grinding machine called Rebir is used. It has a straight shape, an electric motor and a handle to hold it. Petal circles (KSL) are put on the end, but their arrangement differs from the circles on the grinder. Thanks to the wide structure of the sandpaper pieces, it is possible to apply more pressure to the workpiece and cover a wide area. KSLs come in different calibers depending on the amount of abrasive used. To process stainless steel after welding, first use “40” and then “zero”. This eliminates all grooves from previous tools. The coating becomes monochromatic and matte.

Work should be carried out in a respirator, since dust from the abrasive and particles of removed metal float in the air. The grinder must also protect his eyes, for which he wears clear glasses. Stainless steel heats up from friction with grinding wheels, so the worker must wear gloves to avoid burns. As an analogue of manual grinding, sandblasting units are used, where sand granules are supplied under air pressure, removing the top oxide from the metal. This is used in enterprises with a large turnover of products. It is not advisable to install such equipment at home.

Polishing

The next stage of stainless steel processing is polishing the welding area, and the entire product, to give the final shine. This further cleans the surface, making it smooth and solid, which prevents the influence of aggressive liquids from the outside.

First, the welding seams are processed with a disk containing vulcanite. This is a rubber-like material, the circle of which is mounted on a drill. Using vulcanite it is possible to give the seam the desired depth and shape, “sawing it down” to create a concave structure. The material is gentle on steel. After this, polishing paste is applied to the already sanded surface. It may have a diamond composition. Regular GOI paste will do. A felt circle is placed on the drill and longitudinal movements are made over the entire surface. To thoroughly polish the welding areas, small circles are used, which are convenient for reaching areas in corner joints. Work is carried out until a mirror surface is obtained and there are no matte spots.

Etching with ready-made acid mixtures

Not every manufacturer has a special area for etching with concentrated acids. Therefore, many people use ready-made gels, sprays, pastes, concentrates, which can contain up to 4 different acids. To apply them to the surface, acid-resistant brushes and special sprayers are used. If you intend to process welds, then it is best to use a paste of thick consistency - its etching activity manifests itself already at a temperature of +10°C.

Before processing begins, the product is cleaned of rust, grease, and dirt. To do this, you can apply a special cleaning composition to the surface, which must be left for 30 minutes. If gels or pastes are used, they must be applied to the seams with a coverage of 20 cm on both sides. The duration of action of the composition is 20-90 minutes (in accordance with the instructions for use). After washing, a passivator is applied to the product, forming a stable film of chromium oxide. The passivator holding time is 30-60 minutes.

Acids and gels

To remove all color transitions after welding and eliminate the oxide layer that promotes corrosion, stainless steel is etched. This refers to the acidic type of material treatment. You can use sulfuric or hydrochloric acid. Analogs, such as fluoride or nitrogen, are also suitable. They are available in the form of gels and pastes. There are also special aerosols. The procedure goes like this:

After welding, scale and debris are removed from the surface. A metal brush is used for this.
The product is allowed to cool to a temperature of 50 degrees.
The composition is applied from above or the structure is immersed in a container with an acidic agent.
After 30 minutes, wash off the acid with plenty of water.

It is important for the worker to wear a respirator, since there will be a large amount of vapor in the air that is dangerous to the respiratory system. It is also necessary to protect the skin on your hands by wearing rubber gloves. If acid comes into contact with an open area of skin, rinse the area quickly and thoroughly with plenty of water.

Another processing method is electrochemical etching. To do this, use a container with acid. Two wires emanate from the current source, which are placed into the liquid through a resistance. The product is attached to the “plus”, which consists of a lead plate. The “minus” of the lead plate drops freely into the acid. Closing the voltage in the composition promotes the separation of oxides from the surface of the stainless steel, but prevents oversaturation of hydrogen. The procedure lasts up to 8 minutes.

Thanks to a variety of methods for processing stainless steel, you can achieve a beautiful appearance at the welding site. This is a painstaking process that requires diligence and perseverance, but thanks to such measures, a mirror-like surface is created that will not rust in the future due to the weak oxide layer.

Bath materials

Choosing the right material for making etching baths is a difficult task for chemists and materials scientists.

ceramic coated
glass covered brick
wood, lead-coated concrete
rubber derivatives
Certain grades of stainless steel for acid baths.

The content of nitrogenous acid with impurities of hydrofluoric or hydrochloric acid allows the use of the same materials. The only exceptions are lead as a coating, ceramics with a high silicon content, due to their interaction. It is quite possible to use steel in alkali baths, monitoring the progress and intensity of electrolysis in close proximity to the material. Under certain conditions and acid content, its temperature, and nature, it is possible to use stainless steel grades for pickling tanks. Such, for example, as 8Х18Н8М or 10Х20Н25М4.

From the information provided in this review, we can conclude that the processing mode, the chemical composition of the bath, the need for additional mechanical processing, and the use of electrolysis should be determined based on specific initial conditions (steel grade, state of the oxide film, technological capabilities) and regulated in the context of the expected final result .

How to treat stainless steel seams after welding

There are many products that are made from stainless steel, and most of them use welding. And although this method of fastening metal parts has advantages, it also has a disadvantage - the anti-corrosion properties of the material are reduced because of it. And to know how to fix this, it’s worth learning more about processing stainless steel after welding. This will be discussed further.

Grinding

Grinding is the main method of processing a stainless steel weld. For this, you will need a grinder and grinding wheels with different degrees of grain size, since all processing is done sequentially in several passes.

The process will be like this:

First, all deposits are removed with the hardest material. If there are no strong deposits, you can immediately move on to finer-grained materials.
The part to be sanded is limited with aluminum adhesive tape. It is attached to the surface in several layers to make the border more noticeable.
The un-glued surface is processed carefully; there is no need to apply pressure to the tool.
The tape is removed, the treated part is sealed with it to limit another one, for cleaning the next zone.

After each sanding, the surface is washed with water and wiped dry. This continues until all the circles, down to the finest grain, have been used. Usually three circles are enough, with a grit of 180, then 320 and 600. Everything ends with a felt circle, then the polishing procedure begins.

During the processing of seams after welding stainless steel, dust will fly, so eyes and respiratory organs must be protected.

Sanding sheets are sometimes used for sanding. But here, too, you need to select the grain size on the rough parts. Lathes with special grinding wheels can also be used for processing. These can be installed even on the simplest models that are installed in home workshops.

Polishing

Many people choose stainless steel not only because of its properties, but also because of its appearance. After all, it has a characteristic metallic shine that does not disappear over the years even without regular care.

But after welding, cloudy, noticeable seams appear at the fastening points, and the shine disappears. To return it, and thereby further strengthen the material by leveling its surface, polishing is used. She may be:

manual;
machine;
ultrasonic.

To polish a stainless steel seam after welding at home, you will need to carry out several treatments. First, the seam is cleaned with a disk containing vulcanite; it can be put directly on the drill. It is a soft material, similar to rubber, so it will not leave scratches, but it will be able to influence the joint and file it down to the smoothest possible state.

Afterwards, polishing paste is applied to the treated surface. In order for it to be distributed correctly, the seam must be treated with another circle, a felt one, which is also put on the drill. Make longitudinal movements along the entire seam so that the paste is distributed evenly. The size of the circle is selected depending on the size and type of the product, since without small circles the corners cannot be processed.

The polishing of the seams is carried out until the stainless steel, after welding, returns to its mirror-like appearance and the matte spots disappear.

Etching

The oxide layer and color stains can be removed by using a stainless steel acid after welding. The process that uses acids is called pickling, and usually sulfuric or hydrochloric acid is purchased for this. But you can also use analogues, for example, nitric acid.

You can also use alkali for etching. Then, for proper processing, after welding, the stainless steel part is placed in molten caustic soda. It removes the oxide film well without destroying the steel structure itself.

To make them convenient to use, means for etching stainless steel seams after welding are available in the form of special pastes or gels, as well as aerosols (for large parts). These materials are used according to the following algorithm:

Use a wire brush to remove all scale after welding.
The seam must cool to 50 °C.
The part is coated with a paste for processing stainless steel welds or placed in a container with an acidic composition, if it is liquid.
Afterwards everything is washed with plenty of water. If a paste is used, the procedure lasts from 10 minutes to an hour.

Depending on the manufacturer of the etching composition, additional steps may be added to this algorithm, so study the instructions for use.

Sometimes etching requires first treatment with a sulfuric acid solution, and then with a mixture of nitric acid.

It is important not to forget that when metal comes into contact with acids, vapors that are dangerous to the respiratory system and mucous membranes will begin to be released.

Therefore, you need to wear a respirator and it is advisable to wear special glasses. To protect your hands, it is recommended to wear rubber gloves. But if the acid or a composition with it does get on the skin, you need to urgently start rinsing the area with water, the more, the better. And then see a doctor.

Sometimes cleaning stainless steel welds is done by electrochemical etching. To do this, two wires are drawn from the current source, which must be placed directly into the acid. A stainless steel part is connected to the plus, the minus is simply placed in a container with acid. Due to the closure, oxides are quickly separated from the surface, and hydrogen supersaturation does not occur. The entire procedure takes no more than 10 minutes.

Acid etching

The maximum effect of etching stainless steel with acids is achieved by sequential interaction of the stainless steel surface in baths with two types of acids - sulfuric and nitric. The sequence of stages is as follows

Degreasing, removal of large snags, scale
Pickling in a sulfuric acid bath (concentration 10-12%) or sulfuric acid bath (8% sulfuric acid, 4% hydrochloric acid). In this case, corrosion of scale and roughness on the surface occurs. The ideal temperature for the process is between 60 and 80 degrees Celsius. Monitoring this parameter is important for process control. The duration of treatment depends on the steel grade, the presence of a controlled ratio, and the concentration of acids. If the bath is depleted, pitting corrosion may occur. For example, steel with 18% Cr, 8% Ni requires 23 to 45 minutes of pickling in a sulfuric acid bath. Reducing the processing time by half can be achieved if this operation is carried out in a controlled atmosphere.
Rinsing with plenty of running water
Immersion of the workpiece in a bath filled with a solution of nitric acid and hydrofluoric acid (10 - 20, 1-2 weight percent, respectively). At a bath temperature of 60–70 degrees, the treatment time is 7–15 minutes.
Repeated rinsing with large volumes of water

The presented method is basic and has many variations. Etching in one nitrate bath with an admixture of hydrofluoric acid increases the etching time to 30 minutes. Sodium fluoride can act as a substitute for hydrofluoric acid. Increasing the concentration of hydrofluoric acid to 10% allows the process to be carried out at low temperatures, avoiding preliminary immersion in sulfuric acid.

Reducing the etching time in sulfuric acid can be achieved by adding no more than 5% sodium chloride. This move gives the desired effect in 15 minutes, but at the same temperature, about 80 degrees Celsius.

Be careful: if it is necessary to carry out the procedure in a room with insufficient aspiration, replace the components of the second stage of etching. Acids produce harmful fumes when etching. A solution of ferrous sulfate (7%) and hydrofluoric acid (2%) is proposed as a replacement.

To correctly select the acid etching method, you need to know and take into account the state of the oxide film on the surface of stainless steel.
Appearance can tell you about the composition of the film. The green color of the scale indicates a high content of chromium oxides. Accordingly, the action of acidic environments will be difficult and will require more time. Intermediate mechanical cleaning between two baths is recommended if descaling is difficult.

Heat treatment

Heat treatment of a stainless steel seam after welding can be different, because this process has several varieties:

Annealing involves heating the metal and slowly cooling it.
Hardening, in which stainless steel is heated to maximum and then cooled sharply.
Normalization is similar to annealing, but cooling occurs not in an oven, but in the open air.

When heat treating, proper heating is of great importance. It needs to be monitored carefully, since overheating makes the structure of the material grainy, and this is a defect and cannot be corrected.

Heat treatment is difficult to carry out at home, since it is difficult to heat steel to the required temperature without the necessary equipment. It is also not possible to do chrome plating at home, as it requires tools, skills and the right consumables.

Thanks to so many methods for processing stainless steel welds, there should definitely be no problems with cleaning. And even though this is a long process that requires care and precision, the result will easily exceed any expectations. And its quality can be assessed for years.

Electrolyte preparation

After making sure that all the necessary varnish has been removed, we proceed to preparing the working solution. During this time the protective layer will have time to dry completely. As a substance in which steel products are etched, a solution of table salt is most often used at home. To prepare it, you need to dissolve the crystals in clean water in a ratio of two tablespoons of salt per 0.5 liter of liquid.

Instead of sodium chloride, you can use another quite accessible chemical called copper sulfate. It is not difficult to purchase at any hardware or garden store.

Chemistry for pickling and passivation of stainless steel

The high resistance of stainless steel to corrosion is achieved due to the formation of a chemically resistant layer of chromium oxides. To use stainless steel outdoors, in highly corrosive environments or for contact with chemicals, such a layer must evenly and completely cover the entire metal surface.

During the manufacture of stainless steel elements, the metal surface is subject to various deformations and damage due to thermal and mechanical treatment at all stages. Oxide layers on welds, dirt particles and other traces such as free iron can penetrate deep into the surface of the material during manufacturing processes. A protective layer cannot form in these areas, making stainless steel highly susceptible to rapid corrosion.

However, the process of etching stainless steel removes and dissolves oxides located on the surface of stainless steel, including those created during the welding process or secondary heating, as well as corrosive particles and slag deposits. After etching, a chemically clean metal surface is achieved, on which an optimal protective passive layer can be formed. For complete stainless steel pickling technology, FORSTEX offers a wide range of products for metal processing under different operating conditions.

Pickling baths

Dip pickling of stainless steel is suitable for small to medium-sized parts. The products are completely immersed in a bath of etching solution. Pickling and passivation of stainless steel is carried out over the entire surface of the metal. Means for pickling stainless steel using this method are divided into two basic types:

Formulations based on nitric acid, which are particularly quick and easy to use;
Solutions that do not contain nitric acid, which are safer, more productive and easier to dispose of.

All products are offered for purchase in concentrated form or as ready-to-use solutions.

Convenient etching using spray gels

Pickling and passivation of stainless steel in a bath by immersion is not always possible, for example in cases where large and very large surfaces are required. When working with large-sized products, more convenient etching compositions in the form of gel sprays are used. Etching gel sprays are also used to treat the surface of stainless steel products that need to be treated externally only, as well as those that cannot be transported and must be treated on site.

Etching gel sprays are applied by spraying onto the surface to be treated. Gels are liquid and can be sprayed onto large surfaces of workpieces. Due to their high viscosity, they literally stick to the metal surface and thus produce an etching effect.

In addition to standard products for a wide range of materials, FORSTEX offers the following types of etching gels:

Gel spray with soft etching effect;
Gel with reduced release of nitrogen oxides;
Gels with indicators;
Colored etching gels for optimal surface finish visibility.

Alkaline etching methods

The following methods are distinguished:

Aging in soda. The sodium nitrate content should range from 20-40%, heated to a temperature of 460-500 degrees Celsius. Etching in such an environment lasts for 15 minutes. Some austenitic grades of stainless steel are prohibited from being heated above 450 degrees. This can lead to intergranular corrosion. This is followed by a rinsing step in a large amount of water, followed by a 5-minute immersion in a sulfuric acid bath and up to 10 minutes in a nitrate bath.
Known in England since the first half of the 19th century, the etching method is combined with passing an electric current through the part being etched. At a current density of 11 A/m2, 15 seconds is sufficient. This reaction rate is associated with the electrolysis process. The release of sodium and hydrogen at the cathode contributes to the reduction of oxides. The reduced metal is deposited on the surface. This type of etching allows you to obtain degreased metal, characterized by purity and uniformity. This method uses soda. Variations are possible with the composition and addition of calcium chloride. This method is used for etching flat, rod blanks, and drawn products.
Treatment with sodium hydrides is based on reduction by exposing the metal to sodium and hydrogen. The presence of sodium hydride is achieved by the interaction of hydrogen and sodium, which is in a molten state. A cylinder without a bottom plane is placed in molten caustic soda. The top plane has a hole. Sodium is poured into this hole, it reacts on the surface of the bath. A stream of hydrogen is passed through a spot of sodium on caustic soda. A hydride is formed and diffuses throughout the bath. Achieving the required concentration of 1-2% sodium hydride occurs within controlled threshold values. In the absence of an air separation product, dissociated ammonia is used. The parts are heated in such a bath to 400 degrees Celsius. Stainless steels show good pickling results with this technique and duration of 4-17 minutes. After etching, it is recommended to thoroughly rinse the parts. If necessary, carry out additional treatment in a nitrate bath. Given the high cost of this method, its obvious advantage is the fact that the metal does not interact with the etchant. Metal losses are minimal. Lower process temperatures reduce coolant costs and reduce operational safety.

There are certain rules that must be followed for any of the presented methods. Among them, priority is the treatment of the metal surface before etching, removal of the oxide film, and degreasing. The etching process is no less important.

Pickling pastes: passivation of stainless steel welds

Etching pastes are very viscous, i.e. not current pickling agents. They are mainly used for cleaning and etching welds, removing oxides, slag and scale from the heat-affected zone. Application is carried out using a special acid-resistant brush. The etching paste is then thoroughly washed off with water to avoid further chemical reactions. We offer our customers a wide range of FORSTEX etching pastes for various types of stainless steels and types of welds.

Etching pastes are available for purchase in packages with a capacity of 1 kg or 3 kg.
All stainless steel processing products comply with the international standard ASTM380, ASTM A967, ASTM G48, ASTM B117 and other standards establishing specifications for cleaning, descaling and passivation of stainless steel products

Electrochemical cleaning, pickling, passivation, polishing of stainless steel welds

One of the types of processing of seams after welding on non-ferrous metals is the electrochemical method of etching and passivation.

This procedure involves exposing the heat-affected zone to electric current and specially developed electrolytes for cleaning, etching, passivation and polishing.

When removing tarnish from steel seams, we in no way spoil the surface of the metal itself, this means that if you use “mirror” (polished) steel, then after processing you will not see dull, dull spots in the heat-affected area that may remain when using nitrogen-containing etching pastes. Also, nothing happens to both matte and polished surfaces. Moreover, after processing steel using this technology, the alloying (passive) layer is completely restored, which during further operation protects the steel surface from corrosion.

presents to you our own, first in Russia and the CIS, unique equipment for electrochemical processing of steel - weld cleaning installations Steelguard 685 and SteelGuard 425. We also offer to purchase European-made installations from the Nitty-Gritty company.

Etching and passivation

The electrochemical pickling and passivation units we offer represent a complete line of devices for cleaning welds. Thanks to technological innovation - inverter technology

, which is implemented in installations for stripping welding seams, all our devices make it possible to control the required current strength.

Thanks to this, you can now work on any type of surface without fear of damaging the metal when touching a bare electrode, which previously left an irreparable mark and spoiled the surface of stainless steel. This was the main problem with the technology that used the transformer system

Another problem was the performance, which was 2.5 times lower than inverter technology.

What is the difference?

The difference is this: if a short circuit occurs, the inverter cuts off the current in 1/1000th of a second, which ultimately avoids various damages. In addition, all weld seam cleaners in the SteelGuard series perform both pickling and passivation restoration at the same time.

Polishing

Polishing welds is a fairly complex operation because it must be done with great care. This is especially true for steel that is treated with a special coating, for example, Super Mirror and BA, commonly known as mirror stainless steel.

There are two reasons

, because of which the process of polishing welds is so important:

When polishing, the process of unifying the surface of stainless steel occurs;
Polishing stainless steel improves and also promotes the passivation process of the steel.

Using SteelGuard installations you can save time and at the same time achieve maximum results due to the fact that when pickling and polishing welds, all the necessary processes occur in one stage. There is no need to use abrasive paper or paste.

Neutralization

Neutralization is a necessary stage of the work, since it cancels the effect of the agent that was used to pickle the welds. It is important to neutralize this effect to avoid the possible appearance of efflorescence (salt deposits).

This procedure is performed using a unique Inox Fit product, which was developed by Nitty-Gritty. It is applied directly after pickling and polishing of welds, affecting the entire treated surface, while guaranteeing a perfect surface cleanliness.

This was made possible due to the higher surface tension compared to water.

No pitting corrosion

If a transformer is used, it becomes impossible to control short circuits that occur during metal processing.

When working with stainless steel, an unpleasant phenomenon is sure to arise - pitting (pitting) corrosion.

It consists of microcracks, microscopic depressions that interfere with the process of proper and complete passivation, thereby reducing the strength of the steel.

Thanks to the inverter technology used, which is installed on all devices presented, all equipment is controlled by a high-precision microprocessor, which detects and reduces the possibility of short circuits.

This makes it possible to carry out proper passivation of stainless steel. This also applies to those products that will be used in various extreme environments such as marine environments, pharmaceutical, food, chemical and other industries.

Treatment of stainless steel seams after welding

#1 nadar

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#2 e233

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#3 HUMBLE

How is the weld seam treated after argon welding, for example, railings made of stainless steel pipes to give it a civilized appearance? The abrasive method will not work in this case as it will leave scratches. Polishing is also not suitable, there are unpolished places left, and you can’t get anywhere.

The pickling paste is used to restore stainless steel surfaces damaged during welding, casting, cutting and blowing. The paste removes welding oxides, chromium-depleted metal layers, micro-slag particles and other components that can cause local corrosion.

Compared to classic etching pastes, the blue paste emits 70% less nitrogen fumes when used. Thanks to its flowing consistency and blue color visible on the metal surface, the paste ensures high performance and economical use.

This paste can be used for etching standard steel grades 304 (08Х18Н10), 321 (08Х18Н10Т) and 316 (03Х17Н14М3). The paste is applied to the metal that has cooled to room temperature (10 - 30°C). Etching time - 90 min at 10°C; 45min at 20°C; and 20 min at 30°C. https://z-master.su/p. cts_id=58000008

Welding of all types of metal in SAMARA -

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#4 blazen79

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#5 HUMBLE

How is the weld seam treated after argon welding, for example, railings made of stainless steel pipes to give it a civilized appearance? The abrasive method will not work in this case as it will leave scratches. Polishing is also not suitable, there are unpolished places left, and you can’t get anywhere.

Welding of all types of metal in SAMARA -

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#6 blazen79

Attached images

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#7 MIHA75

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City: N. Tagil

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#8 HUMBLE

Welding of all types of metal in SAMARA -

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#9 HUMBLE

Welding of all types of metal in SAMARA -

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#10 HUMBLE

Just don’t rub with “black” brushes)) Attached images Attached image: rust_1.jpg

Welding of all types of metal in SAMARA -

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#11 copich

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How is the weld seam treated after argon welding, for example, railings made of stainless steel pipes to give it a civilized appearance? The abrasive method will not work in this case as it will leave scratches. Polishing is also not suitable, there are unpolished places left, and you can’t get anywhere.

There is a special tool, like a tape machine. For example here: https://www.gtool.ru/. /shlif/finitube

I scored it in Yandex and got it. I know that this tool is used to polish and clean heated towel rails. And you can get close and the result is quick and cheap.

Start respecting yourself and then they will respect you too.

work on equipment that will bring you joy and then work will be a pleasure!

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#12 nadar

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#13 HUMBLE

>All these tape machines are made on the basis of a grinder. A logical question arises: “Maybe there is such an attachment for a simple grinder. >

After all, the price of these tape machines is too high.

Maybe there is such a tool at a budget price, for example, made in China or Korea?

I haven’t found it yet, but I wanted to.

Welding of all types of metal in SAMARA -

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#14 nadar

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#15 Vasser

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#16 copich

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Hello everyone, have you tried phosphoric acid?

With acid there are disposal problems. If you have an installation with a recovery function, then you can use it. There are installations like https://www.techallia. pro-184353.html The principle is based on a weak solution of phosphoric acid. The accelerator of the process is electric current. Depending on the type of current, the result is either polishing or simply cleaning (i.e. for matte and polished surfaces). But all the same, if you use it serially, you have to think about what to do with the waste solution. or pour it into the sewer. But just like with powders, we turn a blind eye to this. But there is a huge advantage in contrast to powders and mechanical stripping. This garbage creates an additional protective layer that does not allow the metal to be corroded and you can also apply markings using a template. It turns out to be very beautiful crap (i.e. markings). This marking can only be removed mechanically (grinding or polishing), not like paint, you can’t just scratch it off.

All these tape machines are made on the basis of a grinder. A logical question arises: “Maybe there is such an attachment for a simple grinder. “After all, the price of these tape machines is too high. Maybe there is such a tool at a budget price, for example, made in China or Korea?

Start respecting yourself and then they will respect you too.

work on equipment that will bring you joy and then work will be a pleasure!

Stainless steel pickling

Pickling stainless steel is an important process that ensures the removal of the top layer of material and restoration of the original state. The bottom line is that after certain work is carried out, defects in the form of welds, oxides and scales can form on the surface of the stainless steel, which can significantly spoil the appearance of the material, as well as worsen the operational and aesthetic properties. A distinctive feature of steel is the presence of an oxide-chrome film, the purpose of which is to protect the top layer. It is because of this that the above defects arise, which are difficult to interact with reagents. If such troubles occur, you can correct the situation by using a special procedure - etching stainless steel.

Etching with ready-made pastes

Modern industry offers a variety of stainless steel pickling pastes . Their main purpose is local processing of welds, the consequences of changes in the uniformity of surface coloring under the influence of temperature. The principle of working with such pastes is simple and can be used even in small workshops.

Apply the paste in a thick layer up to 2 cm, using a brush
Exposure 60-90 minutes
Water jet rinsing

Stainless steel pickling procedure

Chemical and electrochemical treatment or etching is considered one of the best ways to clean the top layer of stainless steel. This procedure perfectly cleans the steel surface from welds, eliminates various types of deformations, and also helps strengthen the structure of the alloy after heat treatment. In addition to cleaning properties, the procedure ensures the restoration of the passive layer of steel, which is necessary to protect the alloy from structural destruction at elevated temperatures.

The essence of cleaning 12x18n10t steel is the chemical interaction of the top layer with a concentrated acid solution. Typically, hydrochloric or sulfuric acid is used, after which a mixture of molten alkali is used. The acid cleaning process has two stages: first of all, the metal is treated with a basic acid composition, and finally the alloy is kept in a bath with a solution of nitric acid.

When processing stainless steel, you should strictly follow the stages of the technological process. The container with the solution in which the alloy is placed should process only the upper layers of the metal, further eliminating existing damage. It is not recommended to allow changes in the macrostructure of stainless steel, as iron may lose its original properties.

Alkaline etching

Treating the surface of stainless steel with molten caustic soda is called alkaline etching. It should be noted that during this process the oxide film is destroyed, while the chemicals do not react with the metal. An increase in temperature promotes corrosion of the oxide film, improving the quality of the treated surface. Rapid cooling in liquid also helps to improve the treated surface.

It is almost impossible to achieve 100% results with this type of processing. Residual films from chromium oxides, nickel and iron oxides are possible on the metal. Among the recommendations for final finishing of such defects is a short-term treatment in a nitrate bath.

Application of etching

The etching process is widely used in production during the cleaning of the upper layers of steel from welds, scale, oxides and rust. It is used when searching for internal defects by removing the top layer of the workpiece or to study the structure of the metal.

This procedure cleans the material, thereby increasing the adhesion of the top layer. This is necessary for the successful connection of a metal workpiece with another surface, after which a paint, enamel, galvanic layer or other protective coating is applied.

This type of processing not only ensures quick cleaning of the workpiece, but also creates a specified pattern on the top layer of metal. Using etching, you can cut out a channel of any thickness or create a complex image. Processing of large workpieces and rolled products is also possible. You can easily adjust the processing depth down to microns, making it possible to process surfaces with complex areas and small grooves. The procedure is used to carry out analysis that determines the formation of intercrystalline corrosion in stainless steel.

In addition, this process is widely used during the processing of carbon, low-alloy and high-alloy steels, non-ferrous metals and titanium. This technology is indispensable when processing small metal parts, watch gears. It is used to manufacture semiconductor chips and printed circuit boards in electronics. This processing method ensures the formation of a conductive channel on the microcircuits. In aircraft manufacturing, etching plays an important role, since through this process the thickness of metal sheets is reduced, thereby reducing the weight of the aircraft. This operation also plays a big role in applying drawings and inscriptions. Etching produces a relief image created by destroying a metal surface according to specific patterns. In everyday life, the operation helps clean the pipeline.

Metal etching

Pickling is the process of cleaning and processing a metal workpiece. Chemical, acidic, alkaline, electrochemical - there are many ways to perform this technological operation. Where is metal etching used, why is it used in industry, what are the processing methods using this technology, all these issues are discussed in detail in the article below.

What is etching

This is a technology for removing the top layer from the surface of a metal part. The technology is used to clean workpieces from scale, rust, oxides and remove the top layer of metal. Using this method, the top layer is removed to search for internal defects and study the macrostructure of the material.

Using etching, they clean the part and increase surface adhesion. This is done for the subsequent connection of the metal surface with another workpiece, before applying paint, enamel, galvanic coating and other protective coatings.

The method allows you not only to quickly clean the part, but also to create the desired pattern on the metal surface. Using this method, the finest channels and complex images are cut out on a metal surface.

You can clean large parts or rolled products.

The processing depth is adjustable with an accuracy of several microns, which makes it possible to produce complex parts with small grooves and other complex elements.

Application of etching in industry

For cleaning parts made of carbon, low-alloy and high-alloy steel, titanium and aluminum from oxide film.
To improve adhesion before applying galvanic and other types of protective coatings.
To prepare steel surfaces for hot-dip galvanizing.
To conduct macroanalysis to detect the formation of intergranular corrosion in stainless steels.
This technology is used to process small metal parts, such as watch gears.
Copper processing is used to make semiconductor chips and printed circuit boards in electronics.
This method applies a conductive pattern to the microcircuit.
For quick cleaning of hot rolled metal products, heat-treated parts, from oxides.
In the aircraft industry, this technology is used to reduce the thickness of aluminum sheets to reduce the weight of the aircraft.
In the manufacture of metal inscriptions and drawings.
Etching produces relief images drawn by removing a layer of metal according to a specific stencil.

Types of etching

The main types of metal processing used in industry:

electrolytic - there are cathode and anodic;
chemical;
plasma.

Electrolytic etching

Electrolytic or galvanic metal processing is used to quickly clean parts, apply engravings and produce grooves. Metal parts are immersed in an acid or salt electrolyte. The part becomes a cathode - a negative electrode or an anode - a positive electrode. Therefore, two types of electrolytic etching are classified - cathodic and anodic.

Cathodic etching. The method is used to remove scale from the surface of carbon steel products after hot rolling or oil quenching. In cathodic etching, the material for the anode is lead, and the electrolyte is a solution of hydrochloric, sulfuric acid or an alkali metal salt. During the electrolysis process, hydrogen gas is actively released at the cathode, which interacts with iron and removes scale. During the cathode method, the metal surface is actively saturated with hydrogen, which increases the fragility of the workpiece. Therefore, the cathode method is not used for thin-walled products.
Anodic electrochemical cleaning. This is the most common method in mechanical engineering. The process involves mechanically tearing off the oxide film on the anode with oxygen and mixing metal molecules with the electrolyte. An electrolyte is a solution of acids or salts of the metal being processed. Lead, copper and other metals are used as the cathode. During anodic treatment, the surface of the product becomes clean, with slight roughness, and the metal dissolves in the electrolyte. With this method, there is a risk of reducing the thickness of the workpiece and over-etching.

Chemical etching

The chemical treatment method is used to clean the surface of a part from oxide film, scale and rust for workpieces made of the following materials:

ferrous metals;
stainless and heat-resistant steels;
titanium and its alloys;
aluminum

For etching, sulfuric, hydrochloric or nitric acid is used. The workpiece is immersed in an acid or alkaline solution, molten salt and kept for the required time interval. The required cleaning time can range from 1 to 120 minutes.

The cleaning process occurs due to the release of hydrogen when the acid interacts with the metal. Acid molecules penetrate through pores and cracks under the oxide film. There they interact with the metal surface and hydrogen is released. The released gas tears off the oxide film and cleans the part.

Simultaneously with the oxides, the metal being treated dissolves in the acid. To prevent this process, corrosion inhibitors are used.

Plasma etching

With the ion-plasma method, cleaning and removal of the surface layer occurs by bombarding the part with ions of inert gases that do not react chemically with the molecules of the material being processed. Allows you to make high-precision notches and grooves with an accuracy of up to 10 nm. The technology is used in microelectronics.

The plasma-chemical method involves excitation of plasma in a chemically active medium, which causes the formation of ions and radicals. Active particles falling on a metal surface cause a chemical reaction. In this case, light compounds are formed, which are removed from the surrounding air by vacuum pumps.

The method is based on chemical reactions that occur when using reactive gases, such as oxygen, which are highly reactive. These gases actively interact in the gas discharge plasma. Unlike plasma treatment in inert gases, with this cleaning method, the active gas reacts only with certain molecules.

The disadvantage of this method is the lateral expansion of the grooves.

Etchants

Pickling of carbon steels is carried out in an 8-20% solution of sulfuric or 10-20% hydrochloric acid. With the obligatory addition of corrosion inhibitors (KS, ChM, UNIKOL) to eliminate the fragility of the material and reduce the possibility of over-etching.

Products made of stainless or heat-resistant steel are processed using a solution consisting of: 12% hydrochloric, 12% sulfuric, 1% nitric acid. If required, processing is done in several stages. The first is that scale is loosened in 20% hydrochloric acid. The second stage is immersion in a 20-40% nitric acid solution to completely remove surface contaminants.

The thick layer of scale that forms on stainless steel is removed during its production by 75-85% molten caustic soda with 20-25% sodium nitrate. After which, complete removal of oxides is carried out in 15-20% nitric acid.

Processing of aluminum and alloys based on it involves removing the refractory oxide film from the surface of the workpiece. For this purpose, alkaline or acidic solutions are used. Usually 10-20% alkali is used, at a temperature of 50-80 ºС, the etching procedure takes less than 2 minutes. The addition of sodium chloride and sodium fluoride to the alkali makes this process more uniform.

The purification of titanium and its alloys, carried out after heat treatment, is carried out in several stages. At the first stage, scale is loosened in concentrated caustic soda.

Then the scale is removed in a solution of sulfuric, nitric or hydrofluoric acid.

To remove the remaining pickling sludge, use hydrochloric or nitric acid with the addition of a small amount of hydrofluoric acid.

When processing copper and its alloys, etchants from hydrogen peroxide, chromic acid and the following salts are used:

copper chloride;
ferric chloride;
ammonium persulfate.

This information material describes in detail the pickling process used in metallurgical plants. The method allows you to quickly clean the metal surface from oxides, scale, rust and other contaminants. Thanks to etching, it is possible to apply various designs to metal, create complex microcircuits and make microscopic channels of the desired shape.

Acid etching

Degreasing, removal of large snags, scale
Pickling in a sulfuric acid bath (concentration 10-12%) or sulfuric acid bath (8% sulfuric acid, 4% hydrochloric acid). In this case, corrosion of scale and roughness on the surface occurs. The ideal temperature for the process is between 60 and 80 degrees Celsius. Monitoring this parameter is important for process control. The duration of treatment depends on the steel grade, the presence of a controlled ratio, and the concentration of acids. If the bath is depleted, pitting corrosion may occur. For example, steel with 18% Cr, 8% Ni requires 23 to 45 minutes of pickling in a sulfuric acid bath. Reducing the processing time by half can be achieved if this operation is carried out in a controlled atmosphere.
Rinsing with plenty of running water
Immersion of the workpiece in a bath filled with a solution of nitric acid and hydrofluoric acid (10 - 20, 1-2 weight percent, respectively). At a bath temperature of 60–70 degrees, the treatment time is 7–15 minutes.
Repeated rinsing with large volumes of water

The presented method is basic and has many variations. Etching in one nitrate bath with an admixture of hydrofluoric acid increases the etching time to 30 minutes.

Sodium fluoride can act as a substitute for hydrofluoric acid.

Increasing the concentration of hydrofluoric acid to 10% allows the process to be carried out at low temperatures, avoiding preliminary immersion in sulfuric acid.

Be careful: if it is necessary to carry out the procedure in a room with insufficient aspiration, replace the components of the second stage of etching. Acids produce harmful fumes when etching. A solution of ferrous sulfate (7%) and hydrofluoric acid (2%) is proposed as a replacement.

To correctly select the acid etching method, you need to know and take into account the state of the oxide film on the surface of stainless steel. Appearance can tell you about the composition of the film. The green color of the scale indicates a high content of chromium oxides. Accordingly, the action of acidic environments will be difficult and will require more time.

Intermediate mechanical cleaning between two baths is recommended if descaling is difficult.

Etching with ready-made pastes

Apply the paste in a thick layer up to 2 cm, using a brush
Exposure 60-90 minutes
Water jet rinsing

The use of pastes is advisable for processing welding seams of stainless steel grades. The treated seam is able to resist corrosion even in the damp conditions of a car wash.

Alkaline etching

Treating the surface of stainless steel with molten caustic soda is called alkaline etching.

It should be noted that during this process the oxide film is destroyed, while the chemicals do not react with the metal.

An increase in temperature promotes corrosion of the oxide film, improving the quality of the treated surface. Rapid cooling in liquid also helps to improve the treated surface.

Alkaline etching methods

The following methods are distinguished:

Aging in soda. sodium nitrate should fluctuate between 20-40%, heated to a temperature of 460-500 degrees Celsius. Etching in such an environment lasts for 15 minutes. Some austenitic grades of stainless steel are prohibited from being heated above 450 degrees. This can lead to intergranular corrosion. This is followed by a rinsing step in a large amount of water, followed by a 5-minute immersion in a sulfuric acid bath and up to 10 minutes in a nitrate bath.
Known in England since the first half of the 19th century, the etching method is combined with passing an electric current through the part being etched. At a current density of 11 A/m2, 15 seconds is sufficient. This reaction rate is associated with the electrolysis process. The release of sodium and hydrogen at the cathode contributes to the reduction of oxides. The reduced metal is deposited on the surface. This type of etching allows you to obtain degreased metal, characterized by purity and uniformity. This method uses soda. Variations are possible with the composition and addition of calcium chloride. This method is used for etching flat, rod blanks, and drawn products.
Treatment with sodium hydrides is based on reduction by exposing the metal to sodium and hydrogen. The presence of sodium hydride is achieved by the interaction of hydrogen and sodium, which is in a molten state. A cylinder without a bottom plane is placed in molten caustic soda. The top plane has a hole. Sodium is poured into this hole, it reacts on the surface of the bath. A stream of hydrogen is passed through a spot of sodium on caustic soda. A hydride is formed and diffuses throughout the bath. Achieving the required concentration of 1-2% sodium hydride occurs within controlled threshold values. In the absence of an air separation product, dissociated ammonia is used. The parts are heated in such a bath to 400 degrees Celsius. Stainless steels show good pickling results with this technique and duration of 4-17 minutes. After etching, it is recommended to thoroughly rinse the parts. If necessary, carry out additional treatment in a nitrate bath. Given the high cost of this method, its obvious advantage is the fact that the metal does not interact with the etchant. Metal losses are minimal. Lower process temperatures reduce coolant costs and reduce operational safety.

Etching methods

The following types of processing are used at home and at production sites:

Acid cleaning;
Electrolytic cleaning;
Cleaning with pastes.

Acid etching

The best results when processing stainless steel are obtained by keeping the top layer of stainless steel for a long time in a container of acids made from sulfur and nitrogen. How this process happens:

The initial stage is considered to be degreasing the top layer of steel, followed by cleaning of burrs and burns;
Next, etching occurs in sulfuric acid baths. During the process, the acid composition eats away surface roughness, scale and burrs. The best temperature during corrosion is 60-80 degrees Celsius. It is important to control this parameter during the process. The duration of etching depends on the acid concentration (10-12%) and the marking of the steel. It is worth being more careful, since depletion of the acid bath leads to the formation of pitting corrosion on the metal surface. For example, steel containing chromium (18%) and nickel (8%) will require 20-40 minutes of treatment in a sulfuric acid bath. It is possible to reduce the time of this procedure several times. To do this, you need to control the atmospheric level.
The next step is to wash the workpiece in a large amount of liquid.
Next, you should immerse the workpiece in a bath filled with nitrate solution. The procedure takes from 5 to 15 minutes, taking into account the bath temperature of 50-70 degrees Celsius.
The final stage is repeated rinsing with running water.

The etching method described is considered standard and includes several processing options. For example, holding in a container with a nitrogen solution, which is enriched with hydrofluoric acid elements, increases the procedure to half an hour. If you raise the concentration level of the fluoride impurity to 15%, you will be able to carry out the processing process at a low temperature, while avoiding the preliminary lowering of the workpiece into acid. Another available treatment option is steel cleaning using phosphoric acid. To complete the procedure, you should follow the following steps:

Degrease the steel workpiece using any available means;
Rinse the part in running water and dry;
Fill the treatment bath with orthophosphoric acid in a proportion of 150 mg per liter of water;
Place the alloy in a container and wait for an hour;
Remove and rinse the cleaned part in running water.

You can reduce the processing time in a sulfuric acid bath by adding sodium chloride at a rate of 5%. Thanks to this, the process takes 15 minutes, but you should adhere to the appropriate temperature regime (80 degrees).

It is important to remember that in a room with poor aspiration, the composition for the second stage of treatment should be replaced. The problem is the release of harmful vapors from the acid, so it is better to replace the solution using 8% ferrous sulfate and 3% hydrofluoric solution.

The oxide film located on the top layer of stainless steel can help in determining the etching method. The advantage is that the external state indicates the composition of the film layer. If the color of the scale is green, this indicates a high level of chromium in the composition. As a result, the interaction between the steel and the acid bath may be more difficult, resulting in longer processing times.

Electrolytic etching

The essence of electrolytic cleaning is the uneven anodic treatment of various structural elements, as well as the selective coloring of the metal due to the appearance of films. A distinctive feature of this processing is the presence of external current sources.

Electrolytic processing is most effective when determining the macrostructure of metals, alloys that have undergone deformation, as well as high-alloy steels that are characterized by high chemical resistance. Electrolytic processing has three etching variations:

Cleaning by anodic dissolution;
Anodic film sedum;
Cathodic film cleaning.

The most common method of electroetching is considered to be anodic dissolution, due to which a relief on the surface is formed as a result of individual grain boundaries or phases.

Etching with ready-made pastes

At the moment, the modern market is provided with a huge assortment of different pastes for pickling stainless steel. The main task of the paste is to change the unevenness of the painted surface as a result of high temperature changes, as well as to clean welds. The process of using etching paste is quite simple and can be used even at home. After welding, stainless steel can be easily cleaned with a thick paste, because its effectiveness begins to manifest itself at a temperature of 80 degrees. Before etching, the metal surface must be cleaned of corrosion and other defects.

The paste etching process consists of the following steps:

Processing the top layer of the workpiece with a layer of paste up to several centimeters;
Exposure for one and a half hours;
Rinsing under running water.

Etching paste is ideal for processing welds on stainless steel grades. Once properly treated, the surface is able to withstand corrosive attacks in the most adverse conditions.

Stainless steel pickling: indications, etching methods and materials

Stainless steel often requires surface treatment to achieve the desired aesthetic or performance properties. Treatment with shot blasting and sandblasting devices is limited due to the high probability of hardening.

Modern production uses etching of stainless steel, after preliminary thermal or mechanical treatment. The complexity of this process, compared to conventional black, low-alloy steels, is explained by the presence of a chromium oxide film that acts as a protective barrier.

It is this that forms hard scale that does not interact well with reagents. Technological influences may cause color changes on the surface. These include welding, soldering, and other operations involving high temperatures. Iridescent tarnish can be removed by etching.

For different chemical compositions of stainless steel, individual pickling methods and compositions have been developed, taking into account the influence of the steel elements, to achieve maximum results.

The predominant methods of etching stainless steels are alkaline and acid, which can be intensified by electrolysis or proceed without it.

Immersion treatment with high concentration acids

The procedure is carried out in specialized areas, since it is associated with the release of saturated acid vapors that are hazardous to health. The technology includes several stages.

Dissolving scale by immersing the welded assembly in a bath with a solution of sulfuric (6-8% by volume) and hydrochloric (2-4%) acids. The mixture is heated to 60-80 degrees and left for half an hour. Electrolytic submersible etching helps to destroy the oxide film faster: current is passed through the bath, and the product is connected to the positive or negative pole
Intensive rinsing in water.
Immersion in a container where nitric (weight fraction -10-20%) and hydrofluoric (1-2%) acids are mixed.
Rinse with plenty of water.

Treatment with ready-mixed acids

Preparations for etching welds are produced in the form of pastes, sprays, gels, concentrates containing from 2 to 4 acidic components. It is most convenient to use thick paste-like mixtures.

They are laid in a thicker layer, are better retained on vertical surfaces, and their activity manifests itself already at +10°C. The most effective pastes are SAROX TS-K 2000, Avesta BlueOne, Stain Clean (ESAB).

Etching is performed in this order:

Removing dirt, rust, degreasing the product with any detergent. The cleansing agent is applied for 30 minutes.
Etching.
Cover the seams with etching gel or paste, covering 20 cm to the left and right, spray the spray over the entire surface of the product. The exposure time ranges from 10 to 90 minutes - it depends on the concentration of the drug, the chemical composition of the steel, the thickness of the scale, and the ambient temperature.
Passivation.
A substance is applied that creates a stable layer of chromium oxide on the surface of the stainless steel. Exposure time – 30-60 minutes.

Equipment

Etching requires special tools and equipment.

Brushes, plastic spatulas - they must be acid resistant.
Sprayers - they are used to process large-sized products.
Metal baths for immersion degreasing and pickling. Their design includes steam coils for heating the solution and ventilation casings for removing harmful fumes generated during etching. The inside of the bath is covered with an acid-resistant lining.
Containers for washing. They are made without lining and ventilation, cold washing baths - without steam pipes.

In mass production, rotary pickling installations are used.

Performs etching of stainless steel after welding strictly according to the technology and in accordance with the technical requirements of the drawing. The work is carried out by qualified specialists using modern equipment, the quality of the products meets the standards laid down in the international standard ISO 9001.

Oddly enough, but even on high-quality, good stainless steel, traces of rust may appear over time. This usually happens in a so-called “aggressive environment”, with high humidity and temperature. To prevent this from happening, the steel should not come into contact with dust and metal shavings.

During subsequent processing, do not expose the product to the harmful and destructive effects of alkali and acids. After welding, a thin oxide layer is formed on the surface of the product. It weakens the connection's resistance to corrosion. Corrosion is divided into electrochemical and chemical.

Electrochemical is the breakdown of metal in electrolytes.
Chemical is the destruction of metal from environmental influences.

Processing methods for stainless steel after welding

To do this, you will need a special protective suit and mask. As a rule, sulfuric, hydrochloric, hydrofluoric or nitric acids are used for etching in the form of gels, pastes, aerosols, and sprays. For etching seams, it is better to use pastes with a very thick consistency. The paste must be applied with a brush in a very even layer.

The first method is acid etching.

Corrosion of scale using hydrochloric and sulfuric acid. Strict control of solution saturation and temperature must be observed.
Washing with water.
Immersion in a bath with a mixture of hydrofluoric and nitric acid.
Thorough rinsing.

The process of etching stainless steel with acids.

Acid vapors form in the air; this requires a serious approach to protecting the skin and respiratory organs. This process has many different variations with the concentration of the composition, time and sequence of actions.

Electrolytic etching is one of the acid etching methods. An electric current, either direct or alternating, is passed into the bath; it produces a mechanical effect. The methods described above are very complex and require large financial investments.

When to passivate

For new equipment, a lot depends on its origin.

High quality equipment is often immersed in nitric acid as one of the last steps in production and may only require a good cleaning to remove oil residues before first use. Manufacturers of less expensive equipment may skip the final immersion after running-in, welding, and polishing in order to save money.

Even if you know the source of your new equipment, I would lean toward both the thorough cleaning and passivation steps.

Thorough cleaning is required to remove oils, polishes and other contaminants that could ruin your beer.

But the extra step of passivation after cleaning is not a big price to pay compared to fairly expensive stainless steel equipment that can last you a lifetime.

You should also consider passivating your stainless steel at any time if you think you have damaged the protective chrome layer.

This includes stubborn stains that require excessive cleaning, any scratches, dents on stainless steel, exposure to regular steel, steel or iron pads, or exposure to bleach cleaners.

Also, if you use it for brewing often, it might not be a bad idea to passivate it every year or two just as a preventative measure.

Lastly, if you get rust or corrosion, it's important to fix it immediately. A mild abrasive such as Bar Keeper's Friend will help you remove rust and will also passivate the area to prevent further damage.