Pickling passivation process for stainless steel pipes and pipe fittings

Abstract

The invention discloses a pickling and passivating process for stainless steel pipes and pipe fittings, which belongs to the technical field of pickling and passivating and comprises the following steps: removing oil stains on the stainless steel pipes and pipe fittings by using a degreasing agent; washing and cleaning the surface of the stainless steel pipe fitting; removing welding spots and high-temperature oxides on the surface of the stainless steel pipe fitting by using a pickling solution; removing a grey film and impurities on the surface of the stainless steel pipe fitting by using a release agent; forming a net-shaped chemical conversion film and a precipitation type adsorption film on the surface of the stainless steel pipe fitting by using a passivating agent; neutralizing and washing the stainless steel pipe fitting; forming a nano composite oxide film by using a dehydrating agent; and hot pure water washing is conducted on the stainless steel pipe fitting through heated pure water, and the final stainless steel pipe fitting is obtained. The method solves the problems that in the traditional pickling process, nitric acid, sulfuric acid and hydrochloric acid are used, acid mist is easily generated in the pickling process, the environment is polluted, waste liquid treatment is complex, and environmental protection requirements are not met.

Description

Technical Field

[0001] The invention relates to the technical field of pickling and passivation, in particular to a pickling and passivation process for stainless steel pipe fittings. Background Art

[0002] Stainless steel has been widely used in industry and construction due to its excellent corrosion resistance and aesthetics. However, even stainless steel may face the risk of corrosion in certain environments and conditions. Therefore, how to further improve the corrosion resistance of stainless steel has become the focus of attention of technical workers and industrial professionals. Against this background, the stainless steel pickling and passivation process came into being. The pickling and passivation process is a chemical treatment method that significantly improves the corrosion resistance, surface quality and wear resistance of stainless steel through the two steps of pickling and passivation. Pickling refers to the use of acid to corrode a layer of stainless steel surface about 10μm thick, remove the oxide layer, rust, welding slag and other contaminants on the surface of stainless steel, and make the surface of stainless steel tend to a uniform balance. Passivation is the rapid oxidation of the stainless steel surface after pickling to form a uniform and dense oxide film. This film is mainly composed of chromium oxide, which can effectively prevent corrosive media such as water and salt from contacting the stainless steel matrix, thereby improving the corrosion resistance of the material.

[0003] Although the stainless steel pickling and passivation process has significant advantages in improving the performance of stainless steel, it also has some disadvantages that cannot be ignored: the traditional pickling process uses strong acids such as nitric acid, sulfuric acid, and hydrochloric acid. These strong acids are prone to produce acid mist during the pickling process, which pollutes the environment, and the waste liquid treatment is complicated and does not meet environmental protection requirements; during the pickling process, a chemical reaction occurs between the metallic iron and the acid and hydrogen is produced, resulting in the loss of metallic iron; the pickling and passivation process needs to be adjusted according to the type of stainless steel alloy being treated, the temperature and type of the acid, which increases the complexity and cost of the process. Summary of the invention

[0004] The purpose of the present invention is to provide a pickling and passivation process for stainless steel pipes and fittings, which solves the problems existing in the traditional pickling process. The traditional process uses strong acids such as nitric acid, sulfuric acid, and hydrochloric acid. These strong acids are prone to produce acid mist during the pickling process, which pollutes the environment, and the waste liquid treatment is complicated and does not meet environmental protection requirements; during the pickling process, a chemical reaction occurs between the metallic iron and the acid and hydrogen is produced, resulting in the loss of the metallic iron; the pickling and passivation process needs to be adjusted according to the type of stainless steel alloy being treated, the temperature and type of the acid solution, which increases the complexity and cost of the process.

[0005] To achieve the above object, the present invention provides the following technical solutions: A pickling and passivation process for stainless steel pipe fittings comprises the following steps: Step 11, using a degreasing agent to remove oil stains from the stainless steel pipe fittings to obtain degreased stainless steel pipe fittings; Step 12, washing and cleaning the surface of the stainless steel pipe fittings to obtain cleaned stainless steel pipe fittings; Step 13, using a pickling solution to remove welding spots and high-temperature oxides on the surface of the stainless steel pipe fittings to obtain pickled stainless steel pipe fittings; Step 14, using a demolding agent to remove the gray film and impurities on the surface of the stainless steel pipe fittings to obtain demolded stainless steel pipe fittings; Step 15, using a passivating agent to form a network-type chemical conversion film and a precipitation adsorption film on the surface of the stainless steel pipe fittings to obtain passivated stainless steel pipe fittings; The passivating agent is prepared by mixing the passivating solutions of the film-forming agent, the corrosion inhibitor, the synergist, etc.; Step 16, neutralizing and washing the stainless steel pipes and fittings to obtain neutralized and washed stainless steel pipes and fittings; Step 17, using a dehydrating agent to combine and fill with a mesh-type chemical conversion film and a precipitation adsorption film formed on the surface of the stainless steel to form a coordination compound, and forming a layer of a nano-composite oxide film with excellent hydrophobicity on the surface of the stainless steel pipe fittings to obtain a dehydrated stainless steel pipe fittings; Step 18, using heated pure water to perform hot pure water washing on the stainless steel pipe fittings to obtain the final stainless steel pipe fittings.

[0006] Furthermore, the degreasing agent is prepared by mixing 1-5% by mass of tetrasodium ethylenediaminetetraacetate, 1-10% by mass of alkyl polyglycoside, 5-20% by mass of modified sodium silicate, 1-10% by mass of special polyether, 10-30% by mass of carbonate, and 60-75% by mass of water.

[0007] Further, the pickling solution is a mixture of 10-30% nitric acid, 1-5% ammonium bifluoride, 2-5% ammonium persulfate, 1-2% thiourea, 1-3% polyethylene glycol, and 60-75% deionized water by mass fraction; When the acidity is 3-4PT, add 12-14% pickling solution, and when the acidity is 5-6PT, add 5-8.5% pickling solution.

[0008] Further, the demolding agent is a mixture of 1-5% sulfuric acid, 1-5% sodium persulfate, 5-20% polyethylene glycol, 1-5% nitric acid, 1-5% tetrasodium ethylenediaminetetraacetate, and 65-76% deionized water by mass fraction; When the acidity is 3-4PT, add 10-20% of the release agent, and when the acidity is 4-5PT, add 5-10% of the release agent.

[0009] Further, a demolding agent is used to remove gray film and impurities on the surface of the stainless steel pipe fittings to obtain demolded stainless steel pipe fittings, including: Mix the release agent evenly according to the preset ratio; Place the pickled stainless steel pipes and fittings in the stripping tank; Use a stripping agent to remove the gray film and impurities on the surface of stainless steel pipes and fittings by spraying or immersing.

[0010] Furthermore, the passivating agent is prepared by mixing 5-30% of citric acid, 1-10% of nitric acid, 1-10% of phytic acid, 1-5% of formic acid, and 65-75% of deionized water by mass fraction.

[0011] Furthermore, a passivating agent is used to form a network-type chemical conversion film and a precipitation adsorption film on the surface of the stainless steel pipe fittings to obtain the passivated stainless steel pipe fittings, including: The passivating agents are mixed evenly in a certain proportion to form a passivating solution; Soak the stainless steel pipes and fittings in the passivation solution; During the immersion process, the chemical additives in the passivation solution will react chemically with the surface of the stainless steel pipes and fittings to form a network-like chemical conversion film and a precipitation adsorption film.

[0012] Further, the neutralization water washing ratio method: Use a composite neutralizer containing ingredients such as sodium carbonate and sodium hydroxide; Calculate the required amount of neutralizer based on the concentration and volume of the pickling solution and the effective ingredient content of the composite neutralizer; Slowly add the neutralizer to the pickling solution and keep stirring while monitoring the pH value. Stop adding when it reaches the neutral range.

[0013] Furthermore, the dehydrating agent is prepared by mixing 30-40% of ethylene glycol, 20-30% of isopropanol, 10-20% of toluene, 5-10% of silicone oil, and 20-35% of deionized water by mass fraction.

[0014] Further, the stainless steel pipes and fittings are washed with hot pure water to obtain the final stainless steel pipes and fittings, including: The pure water with TDS value of 0-9 produced by the pure water machine is heated to 60-70℃ through air circulation to obtain heated pure water; The stainless steel pipes and fittings are rinsed with heated pure water to obtain the final stainless steel pipes and fittings.

[0015] Furthermore, compared with the prior art, the present invention has the following beneficial effects: Precise control of heavy metal emissions and migration can significantly reduce environmental pollution; reduce the chance of heavy metals entering the food chain and ecosystem, thereby reducing the potential threat of heavy metals to human health; through precise control of heavy metals, it is possible to promote the green and sustainable development of industrial production and achieve a win-win situation of economic and environmental benefits; the passivation liquid can form a dense chemical passivation film on the metal surface, effectively preventing the metal from contacting with corrosive media, thereby improving the corrosion resistance of the metal; passivated metal parts can remain rust-free and discolored for a long time, thereby extending their service life; due to the protective effect of the passivation film, metal parts are not easily damaged during use, reducing the frequency of repairs and replacements, thereby reducing maintenance costs; the formula of the passivation liquid does not contain toxic substances such as sodium nitrite and heavy metals, and is harmless to the human body and the environment during use, meeting environmental protection requirements; the automation process can significantly improve production efficiency, reduce manual intervention and waiting time, and make the production process smoother and more efficient; the automation process can achieve precise control of production parameters, thereby ensuring the stability and consistency of the quality of stainless steel pipes and fittings; through automated production, it is possible to reduce dependence on labor, reduce labor costs, and improve the competitiveness of enterprises. DETAILED DESCRIPTION

[0016] The technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0017] In an embodiment of the present invention, a pickling and passivation process for stainless steel pipe fittings includes the following steps: Step 11, using a degreasing agent to remove oil stains from the stainless steel pipe fittings to obtain degreased stainless steel pipe fittings; Step 12, washing and cleaning the surface of the stainless steel pipe fittings to obtain cleaned stainless steel pipe fittings; Step 13, using a pickling solution to remove welding spots and high-temperature oxides on the surface of the stainless steel pipe fittings to obtain pickled stainless steel pipe fittings; Step 14, using a demolding agent to remove the gray film and impurities on the surface of the stainless steel pipe fittings to obtain demolded stainless steel pipe fittings; Step 15, using a passivating agent to form a network-type chemical conversion film and a precipitation adsorption film on the surface of the stainless steel pipe fittings to obtain passivated stainless steel pipe fittings; The passivating agent is prepared by mixing the passivating solutions of the film-forming agent, the corrosion inhibitor, the synergist, etc.; Step 16, neutralizing and washing the stainless steel pipes and fittings to obtain neutralized and washed stainless steel pipes and fittings; Step 17, using a dehydrating agent to combine and fill with a mesh-type chemical conversion film and a precipitation adsorption film formed on the surface of the stainless steel to form a coordination compound, and forming a layer of a nano-composite oxide film with excellent hydrophobicity on the surface of the stainless steel pipe fittings to obtain a dehydrated stainless steel pipe fittings; Step 18, using heated pure water to perform hot pure water washing on the stainless steel pipe fittings to obtain the final stainless steel pipe fittings.

[0018] In the embodiment of the present invention, the steps of the pickling and passivation process of stainless steel pipes and fittings are mainly to remove impurities such as oil stains, welding spots, high-temperature oxides, gray films, impurities, etc. on the surface of stainless steel pipes and fittings, and at the same time form a layer of chemical conversion film and precipitation adsorption film on the surface to improve the corrosion resistance and wear resistance of stainless steel pipes and fittings and extend their service life; specifically, the degreasing agent is used to remove oil stains, water washing is used to clean the surface, the pickling solution is used to remove welding spots and high-temperature oxides, the stripping agent is used to remove gray films and impurities, the passivating agent is used to form a chemical conversion film and a precipitation adsorption film, the neutralization water washing is used for neutralization treatment, the dehydrating agent is used to form a mesh-type chemical conversion film and a precipitation adsorption film, and the pure water washing is used for final cleaning; a layer of nano-composite oxide film with excellent hydrophobicity will be formed on the surface of the stainless steel pipes and fittings, which improves its corrosion resistance and wear resistance and makes it more durable; the entire process is complete and can effectively improve the quality and performance of stainless steel pipes and fittings.

[0019] Optionally, the degreasing agent is prepared by mixing 1-5% by mass of tetrasodium ethylenediaminetetraacetate, 1-10% by mass of alkyl polyglycoside, 5-20% by mass of modified sodium silicate, 1-10% by mass of special polyether, 10-30% by mass of carbonate, and 60-75% by mass of water.

[0020] In the embodiments of the present invention, tetrasodium ethylenediaminetetraacetic acid has good degreasing and cleaning effects, can effectively remove oil stains on the surface of stainless steel pipes and fittings, and improve the cleaning effect; alkyl glycoside has good surfactant properties, which can make the degreasing agent more easily combine with and remove oil stains; modified sodium silicate has the effect of removing dirt and increasing the dispersibility of oil stains, which can improve the cleaning effect of the degreasing agent; special polyether has good cleaning and dispersing properties, which can help to effectively disperse and remove dirt; carbonate can adjust the pH value of the degreasing agent to enhance the cleaning effect; the degreasing agent can effectively remove oil stains on the surface of stainless steel pipes and fittings, and ensure the cleanliness of the pipe fittings surface; at the same time, the formula ratio of the degreasing agent has been accurately calculated, which can reduce the impact on the environment while ensuring the cleaning effect, and meet environmental protection requirements. Overall, this degreasing agent plays an important role in the pickling and passivation process of stainless steel pipes and fittings, improving the efficiency of the process and the quality of stainless steel pipes and fittings.

[0021] Optionally, the pickling solution is a mixture of 10-30% nitric acid, 1-5% ammonium bifluoride, 2-5% ammonium persulfate, 1-2% thiourea, 1-3% polyethylene glycol, and 60-75% deionized water by mass fraction; When the acidity is 3-4PT, add 12-14% pickling solution, and when the acidity is 5-6PT, add 5-8.5% pickling solution.

[0022] In an embodiment of the present invention, components of the pickling solution include nitric acid, ammonium bifluoride, ammonium persulfate, thiourea, polyethylene glycol and deionized water. In addition, it is necessary to add a corresponding proportion of pickling solution according to the specific situation at different acidities; nitric acid, as a strong oxidant, can effectively remove oxides and other impurities on the surface of stainless steel pipes and fittings, and play a role in cleaning and decontamination; ammonium bifluoride, with strong corrosiveness, can dissolve oxides and dirt on the metal surface, which helps to further clean and remove pollutants on the surface of stainless steel pipes and fittings; ammonium persulfate, with oxidizing properties under acidic conditions, can remove organic matter and some insoluble substances on the metal surface; thiourea, with certain cleaning and degreasing effects, helps to disperse and remove some insoluble substances; polyethylene glycol, with good dispersibility and permeability, can enhance the cleaning effect of the pickling solution and form a protective film on the surface. The proportion of pickling solution added at different acidities also helps to adjust the concentration of the pickling solution and improve the cleaning effect, and the acidity can be adjusted according to actual conditions to ensure the best pickling effect; the formula of the pickling solution has been carefully designed to effectively remove oxides and pollutants on the surface of stainless steel pipes and fittings, ensure the cleanliness and finish of the pipe surface, and improve the corrosion resistance and aesthetics of the pipe fittings.

[0023] Optionally, the demolding agent is a mixture of 1-5% sulfuric acid, 1-5% sodium persulfate, 5-20% polyethylene glycol, 1-5% nitric acid, 1-5% tetrasodium ethylenediaminetetraacetate, and 65-76% deionized water by mass fraction; When the acidity is 3-4PT, add 10-20% of the release agent, and when the acidity is 4-5PT, add 5-10% of the release agent.

[0024] In an embodiment of the present invention, the components of the demolding agent include sulfuric acid, sodium persulfate, polyethylene glycol, nitric acid, tetrasodium ethylenediaminetetraacetic acid and deionized water; under different acidities, the demolding agent needs to be supplemented in corresponding proportions according to the specific situation; sulfuric acid has the function of removing surface oxides and impurities, and helps to clean the surface of stainless steel pipes and fittings; sodium persulfate has oxidizing properties, which can help remove insoluble organic matter and dirt, and improve the demolding effect; polyethylene glycol has good dispersibility and lubricity, and is helpful for surface cleaning and demolding; nitric acid, as an oxidant, can further remove organic matter and dirt, and improve the cleaning effect. Cleaning effect; Tetrasodium EDTA has a chelating effect, which can help remove dirt and impurities on the metal surface; the ratio of the stripping agent added at different acidities can adjust the concentration of the stripping agent and improve the cleaning effect, and the acidity can be adjusted according to actual conditions to ensure the best stripping effect; the formula of the stripping agent has been carefully designed to effectively clean the surface of stainless steel pipes and fittings, remove oxides and contaminants, and improve the smoothness and appearance quality of the pipes. At the same time, the ingredients in the stripping agent also help reduce friction during the stripping process, protect the surface of the pipe fittings from damage, and ensure the quality of stainless steel pipe fittings.

[0025] Optionally, a demolding agent is used to remove gray film and impurities on the surface of the stainless steel pipe fittings to obtain demolded stainless steel pipe fittings, including: Mix the release agent evenly according to the preset ratio; Place the pickled stainless steel pipes and fittings in the stripping tank; Use a stripping agent to remove the gray film and impurities on the surface of stainless steel pipes and fittings by spraying or immersing.

[0026] In an embodiment of the present invention, the demolding agent is mixed evenly according to a preset ratio to ensure that the various components are fully mixed, thereby improving the effect and stability of the demolding agent; the pickled stainless steel pipes and fittings are placed in a demolding tank so that the demolding agent can fully cover the surface of the pipes and fittings to ensure the demolding effect; the demolding agent is used by spraying or immersion, so that the demolding agent can be evenly attached to the surface of the pipes and fittings, effectively removing the gray film and impurities; the components in the demolding agent will react with the gray film and impurities on the surface of the stainless steel pipes and fittings, disperse and remove them, thereby achieving a cleaning effect on the surface of the pipes and fittings; the surface of the stainless steel pipes and fittings after demolding will become smooth, the gray film and impurities are removed, and the appearance quality and glossiness are improved; the components in the demolding agent also help to protect the surface of the pipes and fittings, prevent re-contamination and oxidation, and extend the service life of the pipes and fittings; using a demolding agent to remove gray film and impurities is a very important step in the pickling and passivation process of stainless steel pipes and fittings, which can effectively improve the quality and appearance of stainless steel pipes and fittings and ensure that the surface of the pipes and fittings is clean and smooth.

[0027] Optionally, the passivating agent is prepared by mixing 5-30% of citric acid, 1-10% of nitric acid, 1-10% of phytic acid, 1-5% of formic acid, and 65-75% of deionized water in mass fraction.

[0028] In the embodiment of the present invention, citric acid is an organic acid that can react chemically with the metal surface to form a protective film, thereby improving the corrosion resistance and wear resistance of stainless steel pipes and fittings; nitric acid, which has oxidizing properties, can help remove oxides and dirt on the metal surface and promote the formation of a passivation film; phytic acid, which has a chelating effect, can react with metal ions to form a stable protective film, thereby improving the corrosion resistance of stainless steel pipes and fittings; formic acid, which has a decontamination and cleaning effect, can help remove dirt and impurities on the metal surface and promote the passivation effect; deionized water, as a carrier, plays a role in diluting Release and dissolution effects ensure the uniform distribution and stability of the passivator; through the combination of the above ingredients, the passivator can form a protective passivation film on the surface of stainless steel pipes and fittings, improve their corrosion resistance and wear resistance, and extend their service life; the passivated stainless steel pipes and fittings have better corrosion resistance, can operate stably for a long time in harsh environments, and improve the quality and reliability of stainless steel pipes and fittings; the passivator plays an important role in the pickling and passivation process of stainless steel pipes and fittings, which can effectively protect the surface of the pipes, extend their service life, and improve the performance and quality of stainless steel pipes and fittings.

[0029] Optionally, a passivating agent is used to form a network-type chemical conversion film and a precipitation adsorption film on the surface of the stainless steel pipe fittings to obtain the passivated stainless steel pipe fittings, including: The passivating agents are mixed evenly in a certain proportion to form a passivating solution; Soak the stainless steel pipes and fittings in the passivation solution; During the immersion process, the chemical additives in the passivation solution will react chemically with the surface of the stainless steel pipes and fittings to form a network-like chemical conversion film and a precipitation adsorption film.

[0030] In the embodiment of the present invention, the passivator is mixed evenly in a certain proportion to ensure that the various components are fully mixed, thereby improving the effect and stability of the passivator; the stainless steel pipe fittings are immersed in the passivation solution so that the passivator can fully cover the surface of the stainless steel pipe fittings and promote the chemical reaction; during the immersion process, the chemical additives in the passivation solution will react chemically with the surface of the stainless steel pipe fittings to form a layer of mesh-type chemical conversion film and precipitation adsorption film; the film layer can effectively protect the surface of the stainless steel pipe fittings and improve its corrosion resistance and wear resistance; the mesh-type film formed by the chemical reaction can effectively prevent The corrosion of oxygen, water and other corrosive substances on the surface of stainless steel can extend the service life of stainless steel pipes and fittings; the formation of precipitation film can absorb impurities and dirt on the surface, making the surface of stainless steel pipes and fittings smoother and cleaner, and improving the appearance quality; the chemical conversion film and adsorption film formed on the surface of stainless steel pipes and fittings after passivation can effectively protect the surface of the pipes, improve their corrosion resistance and wear resistance, extend the service life, and also improve the appearance quality, making stainless steel pipes and fittings more beautiful; it can improve the quality and reliability of stainless steel pipes and fittings, and is suitable for applications requiring high corrosion resistance and aesthetics.

[0031] Optionally, the neutralization water washing ratio method is: Use a composite neutralizer containing ingredients such as sodium carbonate and sodium hydroxide; Calculate the required amount of neutralizer based on the concentration and volume of the pickling solution and the effective ingredient content of the composite neutralizer; Slowly add the neutralizer to the pickling solution and keep stirring while monitoring the pH value. Stop adding when it reaches the neutral range.

[0032] In the embodiment of the present invention, the composite neutralizer generally contains sodium carbonate, sodium hydroxide and other ingredients, which can neutralize the acidic substances in the pickling solution and adjust its pH value to a neutral range; the required amount of the neutralizer is calculated according to the concentration and volume of the pickling solution and the effective ingredient content of the composite neutralizer to ensure that the acidic substances can be completely neutralized; the neutralizer is slowly added to the pickling solution and continuously stirred to fully mix the neutralizer with the pickling solution to ensure that the neutralization reaction is uniform; in the process of adding the neutralizer, the pH value of the pickling solution is monitored, and the addition of the neutralizer is stopped when the pH value reaches the neutral range. and a neutralizing agent to ensure that the pickling solution is completely neutralized; the neutralization water washing ratio method can effectively neutralize the acidic substances in the pickling solution and adjust its pH value to a neutral range; the acidic substances can be prevented from corroding the environment and equipment, while also reducing the impact on subsequent processing procedures; the neutralized pickling solution becomes neutral, easier to handle and dispose of, and is beneficial to environmental protection and safe production; the neutralization water washing ratio method plays a key role in the pickling and passivation process of stainless steel pipes and fittings, which can ensure the safe handling of the pickling solution after neutralization, protect the environment, and is also beneficial to the subsequent process.

[0033] Optionally, the dehydrating agent is prepared by mixing 30-40% of ethylene glycol, 20-30% of isopropanol, 10-20% of toluene, 5-10% of silicone oil, and 20-35% of deionized water by mass fraction.

[0034] In the embodiment of the present invention, ethylene glycol is a solvent with good solubility and volatility, which can help remove moisture and accelerate the drying process; isopropyl alcohol has strong hydrophilicity and volatility, which helps absorb moisture and evaporate quickly, thereby improving the dehydration effect; toluene, as an organic solvent, can help remove moisture and accelerate the drying process, and also has good solubility; silicone oil has good water resistance and lubricity, which can form a protective film to prevent the reabsorption of moisture and keep the surface of stainless steel pipes and fittings dry; deionized water, as a carrier, is used to dilute and adjust the concentration of the dehydrating agent to ensure dehydration. The dehydrating agent can effectively remove moisture from the surface of stainless steel pipes and fittings, accelerate the drying process, and avoid corrosion and influence of moisture on the surface of pipes and fittings; the surface of stainless steel pipes and fittings after dehydration is dry and clean, preventing the formation of water spots and water marks, and improving the appearance quality of stainless steel pipes and fittings; the dehydrating agent plays an important role in the pickling and passivation process of stainless steel pipes and fittings, which can effectively remove moisture, accelerate the drying process, protect the surface of pipes and fittings, and improve the quality and appearance of stainless steel pipes and fittings; at the same time, the ingredients in the dehydrating agent also help prevent the surface of pipes from getting damp again and extend the service life of pipes.

[0035] Optionally, the stainless steel pipes and fittings are washed with hot pure water to obtain the final stainless steel pipes and fittings, including: The pure water with TDS value of 0-9 produced by the pure water machine is heated to 60-70℃ through air circulation to obtain heated pure water; The stainless steel pipes and fittings are rinsed with heated pure water to obtain the final stainless steel pipes and fittings.

[0036] In the embodiment of the present invention, pure water heated to 60-70°C by air circulation can increase the water temperature, increase the solubility and cleaning power of water, and help remove residual chemicals and impurities on the surface of stainless steel pipes and fittings; using heated pure water to rinse stainless steel pipes and fittings can effectively clean the surface of the pipes and fittings, remove residual degreasing agents, pickling agents, passivating agents and other chemicals, and ensure that the surface of the pipes and fittings is clean and residue-free; hot pure water washing can make the surface of stainless steel pipes and fittings smoother, remove water stains and water marks, and improve the appearance quality of stainless steel pipes and fittings; hot pure water washing can also help remove the surface of stainless steel pipes and fittings. The oxide film can improve its corrosion resistance and appearance quality; through hot pure water washing, the residual chemicals and impurities on the surface of stainless steel pipes and fittings can be completely removed to ensure that the surface of the pipes is clean, smooth and free of residual substances; it can improve the quality and appearance of stainless steel pipes and fittings, and meet the high-demand industrial standards and customer needs; hot pure water washing, as the last step in the pickling and passivation process of stainless steel pipes and fittings, plays a vital role, which can ensure the cleanliness and smoothness of the surface of the pipes and fittings, and improve the quality and reliability of stainless steel pipes and fittings; at the same time, it also helps to extend the service life of stainless steel pipes and fittings and maintain their good appearance.

[0037] In this application, temperature has an important influence on the pickling effect and equipment life. The automation system can monitor the acid temperature in real time through a temperature sensor, and automatically adjust the temperature through a heating or cooling device to keep it within a set range. For example, electric heating or steam heating is used, and the heating power is accurately controlled through a PID control algorithm to achieve stable temperature control; The acid concentration directly affects the pickling effect. The automation system can monitor the acid concentration in real time through an online concentration sensor and automatically add acid or water as needed to maintain the stability of the acid concentration. For example, an automatic acid adding device can be used to automatically adjust the acid addition amount according to the concentration feedback signal to ensure that the acid concentration always meets the process requirements. The acid level in the pickling equipment needs to be kept within a certain range to ensure the normal operation of the equipment and the pickling effect. The automation system can monitor the acid level in real time through the level sensor and control the level through automatic filling or draining devices; for example, when the liquid level is lower than the set value, the filling pump is automatically turned on for filling; when the liquid level is higher than the set value, the drain valve is automatically opened for draining.

[0038] Example 1

[0039] Degreasing: Use a degreasing agent composed of 3% tetrasodium ethylenediaminetetraacetic acid, 5% alkyl glycoside, 15% modified sodium silicate, 3% special polyether, 20% carbonate, and 54% water to remove oil stains; Water washing and cleaning: Rinse the surface of the pipe with clean water; Pickling: Use a pickling solution composed of 20% nitric acid, 3% ammonium bifluoride, 4% ammonium persulfate, 1.5% thiourea, 2% polyethylene glycol, and 70% deionized water to remove weld spots and high-temperature oxides. When the acidity is 4PT, add 13% pickling solution; Demolding: Use a demolding agent composed of 3% sulfuric acid, 3% sodium persulfate, 15% polyethylene glycol, 3% nitric acid, 3% tetrasodium ethylenediaminetetraacetic acid, and 73% deionized water to remove gray film and impurities by spraying. When the acidity is 3.5PT, add 15% demolding agent; Passivation: Soak the pipe fittings in a passivation solution composed of 15% citric acid, 5% nitric acid, 5% phytic acid, 3% formic acid, and 72% deionized water to form a network-like chemical conversion film and a precipitation-type adsorption film; Neutralization water washing: Use a composite neutralizer to adjust the pickling solution to neutrality; Dehydration: Use a dehydrating agent composed of 35% ethylene glycol, 25% isopropanol, 15% toluene, 8% silicone oil, and 17% deionized water to form a network-like chemical conversion film and a precipitation-type adsorption film; Hot pure water washing: Rinse the pipe fittings with pure water heated to 65°C to obtain the final product.

[0040] Experimental results: The surface of the pipe fittings is smooth, free of impurities such as oil stains, welding spots, oxides, gray film, etc.; the passivation film is uniform, and the corrosion resistance and wear resistance are significantly improved; after washing with hot pure water, there are no water stains or water marks on the surface of the pipe fittings, and the appearance quality is excellent.

[0041] Example 2

[0042] Adjust the formulation of pickling solution and stripping agent; Pickling solution: Increase the proportion of nitric acid to 25%, reduce the proportion of ammonium bifluoride to 2%, and keep the other ingredients unchanged; Demolding agent: Increase the proportion of sulfuric acid to 4%, reduce sodium persulfate to 2%, and keep the other ingredients unchanged.

[0043] Experimental results: The surface cleanliness of the pipe is higher, and the removal of welding spots and oxides is more thorough; after stripping, the surface of the pipe is smoother, and the removal effect of gray film and impurities is better; the formation of the passivation film and the corrosion resistance are comparable to those in Example 1.

[0044] Example 3

[0045] Adjust the formula of passivating agent and dehydrating agent; Passivator: Increase the proportion of citric acid to 20%, reduce phytic acid to 3%, and keep the other ingredients unchanged; Dehydrating agent: Increase the proportion of ethylene glycol to 40%, reduce isopropyl alcohol to 20%, and keep the other ingredients unchanged.

[0046] Experimental results: The passivation film is denser, and the corrosion resistance and wear resistance are further improved; after dehydration, the surface of the pipe dries faster and remains dry for a long time; the appearance quality is excellent, without defects such as watermarks and water marks.

[0047] Comparative Example The traditional pickling and passivation process uses concentrated nitric acid as the pickling solution, without adding corrosion inhibitors and synergists; no film stripping treatment is performed, and water is directly rinsed; a simple passivating agent is used, and no film-forming agent, corrosion inhibitor, etc. are added; no neutralization water washing and dehydration treatment is performed; and the final product is obtained after rinsing with pure water at room temperature.

[0048] Experimental results comparison table:

[0049] Experimental results analysis: The corrosion rates of Examples 1, 2, and 3 are all much lower than those of the comparative example, indicating that the pickling and passivation process of the present invention can significantly improve the corrosion resistance of stainless steel pipes and fittings; The surface roughness of Examples 1, 2, and 3 are all low, and the thickness of the passivation film is large, indicating that the process of the present invention can improve the surface quality of the pipe fittings and form a dense passivation film; The salt spray test results show that the process of the present invention can significantly improve the salt spray corrosion resistance of pipe fittings; Since the comparative example uses traditional technology without adding corrosion inhibitors, synergists, etc., it leads to high corrosion rate, large surface roughness, thin and uneven passivation film, and poor appearance quality.

[0050] In the description of the specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0051] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the invention or exceed the scope defined by the claims, they shall all fall within the protection scope of the present invention.

Claims

1. A pickling and passivation process for stainless steel pipes and fittings, characterized in that: The following steps are involved: Step 11, using a degreasing agent to remove oil stains from the stainless steel pipe fittings to obtain degreased stainless steel pipe fittings; the degreasing agent is a mixture of 1-5% by mass of tetrasodium ethylenediaminetetraacetic acid, 1-10% by mass of alkyl polyglycoside, 5-20% by mass of modified sodium silicate, 1-10% by mass of special polyether, 10-30% by mass of carbonate, and 60-75% by mass of water; Step 12, washing and cleaning the surface of the stainless steel pipe fittings to obtain cleaned stainless steel pipe fittings; Step 13, using a pickling solution to remove welding spots and high-temperature oxides on the surface of the stainless steel pipe fittings to obtain pickled stainless steel pipe fittings; the pickling solution is a mixture of 10-30% nitric acid, 1-5% ammonium bifluoride, 2-5% ammonium persulfate, 1-2% thiourea, 1-3% polyethylene glycol, and 60-75% deionized water by mass fraction; 12-14% of the pickling solution is added when the acidity is 3-4PT, and 5-8.5% of the pickling solution is added when the acidity is 5-6PT; Step 14, using a demolding agent to remove the gray film and impurities on the surface of the stainless steel pipe fittings to obtain demolded stainless steel pipe fittings; Step 15, using a passivating agent to form a network-type chemical conversion film and a precipitation adsorption film on the surface of the stainless steel pipe fittings to obtain passivated stainless steel pipe fittings; the passivating agent is prepared by mixing a passivating solution of a film-forming agent, a corrosion inhibitor, and a synergist; Step 16, neutralizing and washing the stainless steel pipes and fittings to obtain neutralized and washed stainless steel pipes and fittings; Step 17, using a dehydrating agent to combine and fill with a mesh-type chemical conversion film and a precipitation adsorption film formed on the surface of the stainless steel to form a coordination compound, and forming a layer of a nano-composite oxide film with excellent hydrophobicity on the surface of the stainless steel pipe fittings to obtain a dehydrated stainless steel pipe fittings; Step 18, using heated pure water to perform hot pure water washing on the stainless steel pipe fittings to obtain the final stainless steel pipe fittings.

2. A pickling and passivation process for stainless steel pipes and fittings according to claim 1, characterized in that: The demolding agent is prepared by mixing 1-5% sulfuric acid, 1-5% sodium persulfate, 5-20% polyethylene glycol, 1-5% nitric acid, 1-5% tetrasodium ethylenediaminetetraacetate, and 65-76% deionized water by mass fraction; When the acidity is 3-4PT, add 10-20% of the release agent, and when the acidity is 4-5PT, add 5-10% of the release agent.

3. A pickling and passivation process for stainless steel pipes and fittings according to claim 2, characterized in that: Use a demolding agent to remove the gray film and impurities on the surface of stainless steel pipes and fittings to obtain demolded stainless steel pipes and fittings, including: Mix the release agent evenly according to the preset ratio; Place the pickled stainless steel pipes and fittings in the stripping tank; Use a stripping agent to remove the gray film and impurities on the surface of stainless steel pipes and fittings by spraying or immersing.

4. A pickling and passivation process for stainless steel pipes and fittings according to claim 3, characterized in that: The passivating agent is prepared by mixing 5-30% of citric acid, 1-10% of nitric acid, 1-10% of phytic acid, 1-5% of formic acid and 65-75% of deionized water in terms of mass fraction.

5. A pickling and passivation process for stainless steel pipes and fittings according to claim 4, characterized in that: Use a passivating agent to form a network-type chemical conversion film and a precipitation adsorption film on the surface of stainless steel pipes and fittings to obtain passivated stainless steel pipes and fittings, including: The passivating agents are mixed evenly in a certain proportion to form a passivating solution; Soak the stainless steel pipes and fittings in the passivation solution; During the soaking process, the chemical additives in the passivation solution will react chemically with the surface of the stainless steel pipes and fittings to form a network-like chemical conversion film and a precipitation adsorption film.

6. A pickling and passivation process for stainless steel pipes and fittings according to claim 5, characterized in that: The neutralization and water washing ratio method: Use a composite neutralizer containing sodium carbonate and sodium hydroxide; Calculate the required amount of neutralizer based on the concentration and volume of the pickling solution and the effective ingredient content of the composite neutralizer; Slowly add the neutralizer to the pickling solution and keep stirring while monitoring the pH value. Stop adding when it reaches the neutral range.

7. A pickling and passivation process for stainless steel pipes and fittings according to claim 6, characterized in that: The dehydrating agent is prepared by mixing 30-40% of ethylene glycol, 20-30% of isopropanol, 10-20% of toluene, 5-10% of silicone oil and 20-35% of deionized water in terms of mass fraction.

8. A pickling and passivation process for stainless steel pipes and fittings according to claim 7, characterized in that: Use heated pure water to wash the stainless steel pipes and fittings with hot pure water to obtain the final stainless steel pipes and fittings, including: The pure water with TDS value of 0-9 produced by the pure water machine is heated to 60-70℃ through air circulation to obtain heated pure water; The stainless steel pipes and fittings are rinsed with heated pure water to obtain the final stainless steel pipes and fittings.

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