High-corrosion-resistance stainless steel composite pipe and preparation method thereof

Abstract

The invention relates to the technical field of stainless steel pipes, in particular to a high-corrosion-resistance stainless steel composite pipe and a preparation method thereof.The preparation method of the stainless steel composite pipe comprises the following steps that Inconel 625 alloy is rolled, welded and cleaned, and an outer pipe is obtained; stainless steel is rolled, welded, cleaned and subjected to sand blasting, and an inner pipe is obtained; after the casing pipe is assembled, the space between the inner pipe and the outer pipe is filled with bonding powder, and a composite pipe blank is obtained; drawing and reducing to obtain a stainless steel composite pipe; the bonding powder comprises tin powder, nickel powder, molybdenum powder, copper powder and nano titanium carbide powder; the method has the advantage that the corrosion resistance and the mechanical property of the stainless steel composite pipe are improved.

Description

Technical Field

[0001] This application relates to the technical field of stainless steel pipes, and in particular to a high corrosion-resistant stainless steel composite pipe and its preparation method. Background Technology

[0002] Currently, with the continuous development of industrial production, higher requirements are being placed on the corrosion resistance of pipeline materials. While traditional single-material stainless steel pipes possess a certain degree of corrosion resistance, they perform poorly in extreme environments or highly corrosive media. In recent years, stainless steel composite pipes have attracted attention due to their use of different materials for their inner and outer layers, combining the advantages of each while exhibiting high corrosion resistance and mechanical properties, demonstrating superior overall performance. This is especially true in fields such as chemical, petroleum, power, and marine engineering, where extremely high corrosion resistance of pipelines is required.

[0003] Currently, the production process of stainless steel composite pipes is complex and costly, and their corrosion resistance still needs improvement. Current solutions mainly involve adjusting the material ratio of the inner and outer layers and optimizing the welding process, but these methods often lead to reduced production efficiency and increased costs. Summary of the Invention

[0004] To improve the corrosion resistance and mechanical properties of stainless steel composite pipes, this application provides a highly corrosion-resistant stainless steel composite pipe and its preparation method.

[0005] In a first aspect, this application provides a method for preparing a highly corrosion-resistant stainless steel composite pipe, employing the following technical solution: A method for preparing a highly corrosion-resistant stainless steel composite pipe includes the following steps: S1. After rolling Inconel 625 alloy, weld it to obtain an outer tube blank. Then, perform alkaline washing, water washing, acid washing, and water washing on its inner and outer surfaces to obtain the outer tube. S2. After the stainless steel is rolled and welded, an inner tube blank is obtained. Then, its inner and outer surfaces are subjected to alkaline washing, water washing, acid washing, water washing, sandblasting, acid washing, and water washing to obtain the inner tube. S3. The inner tube and the outer tube are assembled into a blank by sleeve, and then the bonding powder is filled between the inner tube and the outer tube to obtain a composite tube blank; The binder powder includes tin powder, nickel powder, molybdenum powder, copper powder, and nano-titanium carbide powder; S4. Water is injected into the composite tube blank, and the two ends of the composite tube blank are sealed and welded. Then, the tube blank is drawn to reduce its diameter. The drawing speed is controlled at 0.5-1.2 m / min and the drawing temperature is 450-550℃. After the drawing is completed, the sealed parts at both ends of the composite tube blank are cut off to drain the water. Then, the composite tube blank is left to stand at 400-500℃ in a nitrogen atmosphere for 4-6 hours to cool naturally, thus obtaining a high corrosion-resistant stainless steel composite tube.

[0006] By adopting the above technical solution, this application uses stainless steel pipe as the inner tube, which enables the stainless steel composite pipe to have excellent strength. The outer tube is made of Inconel 625 alloy, which is a solid solution strengthened nickel-based wrought high-temperature alloy with molybdenum and niobium as the main strengthening elements. It has excellent corrosion resistance and oxidation resistance, good tensile and fatigue properties from low temperature to 980℃, and extremely strong corrosion resistance. It can meet the requirements of stainless steel composite pipes in fields such as chemical, petroleum, power, and marine engineering where the corrosion resistance of pipelines is extremely high.

[0007] In the manufacturing process, the water-swelling method of the inner lining is creatively combined with the powder interface strengthening technology. The traditional water-swelling method relies solely on mechanical force for bonding, while this invention achieves diffusion metallurgical bonding by adding active binder powder to the interface at the drawing temperature (450-550℃), resulting in a strength far exceeding that of pure mechanical composites. Furthermore, the drawing process operates at a temperature much lower than that of conventional cladding or hot isostatic pressing processes (typically >1000℃), which is beneficial for energy conservation and consumption reduction, and lower production costs. It also prevents the inner and outer tube substrates (especially the stainless steel inner tube) from developing coarse grains and degrading performance due to overheating. Additionally, it reduces internal stress caused by differences in thermal expansion coefficients, thereby improving the dimensional stability of the product.

[0008] In the raw materials of the binder powder, tin serves as the basic binder phase, melting at relatively low temperatures to effectively wet and fill the interface. Nickel is infinitely miscible with the inner and outer tube matrices, acting as a diffusion bridging and solid solution strengthening phase to promote a strong metallurgical bond. Copper, as a highly ductile phase, effectively buffers and releases interfacial stress, improving interfacial toughness and fatigue resistance. Molybdenum, as a strong carbide-forming element, dissolves in the matrix, significantly improving the strength and pitting resistance of the interfacial region, especially in chloride-containing environments. Nano-titanium carbide, as a nanoscale reinforcing phase, has extremely high hardness and can refine grains and disperse strengthening, pinning grain boundaries and preventing grain growth, greatly improving the strength, wear resistance, and high-temperature stability of the interface. The synergistic effects of the various raw materials in the binder powder greatly enhance the metallurgical bond between the inner and outer tubes, resulting in excellent mechanical properties of the stainless steel composite pipe. Furthermore, the post-processing step of letting the material stand in a nitrogen atmosphere at 400-500℃ for 4-6 hours after drawing is a crucial diffusion annealing / stress relief annealing process. This process allows the interfacial elements to fully diffuse, forming a wider and stronger diffusion layer; it also eliminates the internal stress generated during drawing, stabilizes the microstructure, and prevents stress corrosion cracking during future use; and the nitrogen protection prevents the interface from being oxidized during the high-temperature flexible stage.

[0009] Preferably, in step S3, when the inner tube and the outer tube are assembled by sleeve, the distance between the inner tube and the outer tube is 1-3 mm.

[0010] By adopting the above technical solution, the spacing is set at 1-3mm, which has strong operability in actual production. If the spacing is too small, the powder filling will be uneven, which will easily lead to defects; if the spacing is too large, the powder layer will be too thick, which will easily cause uneven deformation and cracking during drawing. This range ensures that the powder layer is uniform and dense, which is the key process window for achieving a high-quality composite interface, making the process of this application repeatable and stable for industrial production.

[0011] Preferably, the wall thickness ratio of the inner tube to the outer tube is (7-10):1.

[0012] By adopting the above technical solution, the wall thickness ratio of the inner tube and the outer tube is determined to be (7-10):1. The composite tube uses high-strength stainless steel as the pressure-bearing body and high corrosion-resistant nickel-based alloy as the key protective layer. This ratio balances cost (less expensive outer material is used) and performance (ensuring sufficient thickness of the corrosion-resistant layer).

[0013] Preferably, the weight parts of each raw material in the binder powder are as follows: 60-80 parts tin powder, 15-25 parts nickel powder, 7-13 parts molybdenum powder, 8-12 parts copper powder and 0.2-1.2 parts nano titanium carbide powder.

[0014] By adopting the above technical solutions and optimizing the proportions of various raw materials, the overall performance of stainless steel composite pipes can be made more stable during production, with a high yield rate that can basically reach 98% or more.

[0015] Preferably, the binder powder further includes 1-3 parts by weight of titanium powder.

[0016] By adopting the above technical solution, titanium (Ti), being a highly reactive element, can preferentially react with impurities such as oxygen and nitrogen on the powder and matrix surface, purifying the interface and thus significantly improving the quality and success rate of metallurgical bonding. Simultaneously, titanium can also undergo solid solution strengthening and form titanium carbide with carbon, further enhancing its strength.

[0017] Preferably, the binder powder further includes 1-2.5 parts by weight of silicon powder.

[0018] By adopting the above technical solution, the addition of silicon can form intermetallic compounds with nickel, tin, etc., refine the interface structure, reduce the melt viscosity, improve fluidity, and make the bonding denser. This can reflect the fine control of the interface microstructure and further improve the mechanical properties of stainless steel composite pipes.

[0019] Preferably, the preparation method of the binder powder is as follows: The raw materials, excluding nano-titanium carbide powder, are mixed and ground to an average particle size of 5-50 μm. Then, nano-titanium carbide powder is added and mixed evenly to obtain a binder powder.

[0020] By adopting the above technical solution, the components of the binder powder can be mixed evenly. Finally, the nano-titanium carbide powder is added and mixed, which can prevent the nanoparticles from agglomerating severely or their structure from being destroyed during long-term grinding. Furthermore, by exploring the particle size, it was found that the smaller the particle size, the better the mechanical properties of the stainless steel composite pipe. The analysis shows that the smaller the particle size is beneficial to its uniformity and also to the dispersion of the nano-titanium carbide powder.

[0021] Secondly, this application provides a highly corrosion-resistant stainless steel composite pipe, which adopts the following technical solution: A high corrosion-resistant stainless steel composite pipe, wherein the stainless steel composite pipe is prepared by the same method for preparing high corrosion-resistant stainless steel composite pipe.

[0022] By adopting the above technical solution, the stainless steel composite pipe prepared by the method of this application has a low cost for mass production and a high production efficiency, with a production qualification rate of 98% or higher.

[0023] In summary, this application includes at least one of the following beneficial technical effects: 1. This application uses stainless steel pipe as the inner tube, which enables the stainless steel composite pipe to have excellent strength. The outer tube is made of Inconel 625 alloy, which has excellent corrosion resistance and oxidation resistance. It has good tensile and fatigue properties from low temperature to 980℃, and has extremely strong corrosion resistance. It can meet the requirements of stainless steel composite pipes in fields such as chemical, petroleum, power, and marine engineering where the corrosion resistance of pipelines is extremely high.

[0024] In the preparation process, the water swelling method of the inner lining is creatively combined with the powder interface strengthening technology. The traditional water swelling method relies only on mechanical force for bonding, while the present invention achieves diffusion metallurgical bonding by adding active binder powder to the interface at the drawing temperature (450-550℃), with a strength far higher than that of pure mechanical composite.

[0025] In the raw materials of the binder powder, tin serves as the basic binder phase, melting at relatively low temperatures to effectively wet and fill the interface. Nickel is infinitely miscible with the inner and outer tube matrices, acting as a diffusion bridging and solid solution strengthening phase to promote a strong metallurgical bond. Copper, as a highly ductile phase, effectively buffers and releases interfacial stress, improving interfacial toughness and fatigue resistance. Molybdenum, as a strong carbide-forming element, dissolves in the matrix, significantly improving the strength and pitting resistance of the interfacial region, especially in chloride-containing environments. Nano-titanium carbide, as a nanoscale reinforcing phase, has extremely high hardness and can refine grains and disperse strengthening, pinning grain boundaries and preventing grain growth, greatly improving the strength, wear resistance, and high-temperature stability of the interface. The synergistic effects of the various raw materials in the binder powder greatly enhance the metallurgical bond between the inner and outer tubes, resulting in excellent mechanical properties of the stainless steel composite pipe. Furthermore, the post-processing step of letting the material stand in a nitrogen atmosphere at 400-500℃ for 4-6 hours after drawing is a crucial diffusion annealing / stress relief annealing process. This process allows the interfacial elements to fully diffuse, forming a wider and stronger diffusion layer; it also eliminates the internal stress generated during drawing, stabilizes the microstructure, and prevents stress corrosion cracking during future use; and the nitrogen protection prevents the interface from being oxidized during the high-temperature flexible stage.

[0026] 2. The corrosion rates of the stainless steel composite pipes prepared in this application are all 0.024 mm / a and below, while their yield strengths are all 686 MPa and above, and their interfacial bonding strengths are all between 440-462 MPa; indicating that the stainless steel composite pipes prepared in this application have both excellent corrosion resistance and mechanical properties. Detailed Implementation

[0027] The following provides a more detailed description of this application in conjunction with specific details.

[0028] raw material The raw materials used in this application are all commercially available products of industrial grade. Example

[0029] Example 1 A highly corrosion-resistant stainless steel composite pipe is prepared by the following method: S1. After rolling the Inconel 625 alloy, weld it by argon arc welding to obtain the outer tube blank. Then, perform alkaline washing on its inner and outer surfaces. The alkaline washing solution is 6wt% NaOH solution, the alkaline washing temperature is 50℃, and the alkaline washing time is 5min. After rinsing with clean water, perform acid washing. The acid washing solution is 10wt% sulfuric acid solution, the acid washing temperature is 45℃, and the acid washing time is 20min. Then rinse with clean water to obtain the outer tube. S2. After rolling 254SMO stainless steel, it is welded by argon arc welding to obtain an inner tube blank. Then, its inner and outer surfaces are alkaline washed with an 8wt% NaOH solution at a temperature of 50℃ for 5 minutes. After rinsing with clean water, it is acid-washed with a 10wt% sulfuric acid solution at a temperature of 50℃ for 20 minutes. Then, it is washed with clean water and sandblasted with a sandblasting grade of Sa2.5. The acid washing and water washing are repeated to obtain the inner tube. The wall thickness ratio of the inner tube to the outer tube is 8:1, and the total thickness of the inner tube and the outer tube is 10mm. S3. Perform the casing assembly, with a gap of 2mm between the inner and outer tubes. Then, vibrate and fill the space between the inner and outer tubes with bonding powder to obtain the composite tube blank. S4. Fill the composite tube blank with water, then seal both ends of the composite tube blank, and then draw to reduce the diameter. At the same time, check the water pressure inside the composite tube blank, control the drawing speed to be 0.8m / min, and the drawing temperature to be 500℃. After drawing, cut off the sealed parts at both ends of the composite tube blank to drain the water. Then, let the composite tube blank stand at 450℃ in a nitrogen atmosphere for 5 hours and let it cool naturally to obtain a high corrosion resistant stainless steel composite tube.

[0030] The raw materials and their quantities for the binder powder are shown in Table 1, and its preparation method is as follows: Tin powder, nickel powder, molybdenum powder, copper powder and titanium powder are mixed and ground until the average particle size is 5μm. Then, they are mixed evenly with nano-titanium carbide powder to obtain a binder powder. The average particle size of the nano-titanium carbide powder is 50nm.

[0031] Table 1. Raw materials and dosage (kg) of the binder powder in Example 1

[0032] Example 2 A highly corrosion-resistant stainless steel composite pipe differs from Example 1 in that its bonding powder also includes 2 kg of silicon powder, while the remaining steps are the same as in Example 1.

[0033] Example 3 A highly corrosion-resistant stainless steel composite pipe differs from Example 2 in that the grinding particle size of its bonding powder is 20 μm, while the remaining steps are the same as in Example 2.

[0034] Example 4 A highly corrosion-resistant stainless steel composite pipe differs from Example 2 in that the grinding particle size of its bonding powder is 50 μm, while the remaining steps are the same as in Example 2.

[0035] Example 5 A high corrosion-resistant stainless steel composite pipe differs from Example 2 in that titanium powder is replaced with an equal mass of tin powder in its bonding powder, while the remaining steps are the same as in Example 2.

[0036] Comparative Example 1 A highly corrosion-resistant stainless steel composite pipe differs from Example 1 in that nickel powder is replaced with an equal mass of tin powder in its bonding powder, while the remaining steps are the same as in Example 1.

[0037] Comparative Example 2 A high corrosion-resistant stainless steel composite pipe differs from Example 1 in that the nano-titanium carbide powder in its bonding powder is replaced with an equal mass of tin powder, while the remaining steps are the same as in Example 1.

[0038] Performance testing Detection methods / test methods Stainless steel composite pipes were prepared according to the preparation methods of Examples 1-5 and Comparative Examples 1-2, and then tested according to the following testing methods. The test results are shown in Table 2.

[0039] Corrosion rate: The test shall be conducted in accordance with the test method in GB / T 4334 "Corrosion of metals and alloys - Test method for intergranular corrosion of stainless steel". Yield strength: Tested according to the test method in GB / T 228.1-2021 "Metallic materials, tensile testing - Part 1: Test at room temperature"; Interfacial bonding strength: determined using a universal testing machine.

[0040] Table 2. Detection results of Examples 1-5 and Comparative Examples 1-2

[0041] As can be seen from the test data in Table 2, the corrosion rates of the stainless steel composite pipes prepared in this application are all 0.024 mm / a and below, while their yield strengths can all reach 686 MPa and above, and their interfacial bonding strengths are all between 440-462 MPa; indicating that the stainless steel composite pipes prepared in this application have both excellent corrosion resistance and mechanical properties.

[0042] As can be seen from Examples 1-5, this application uses a stainless steel pipe as the inner tube, which enables the stainless steel composite pipe to have excellent strength. The outer tube is made of Inconel 625 alloy, a solid solution strengthened nickel-based wrought high-temperature alloy with molybdenum and niobium as the main strengthening elements. It has excellent corrosion resistance and oxidation resistance, good tensile and fatigue properties from low temperatures to 980℃, and extremely strong corrosion resistance, meeting the requirements for stainless steel composite pipes in fields such as chemical, petroleum, power, and marine engineering where pipeline corrosion resistance is extremely high. In the manufacturing process, the inner lining water expansion method is creatively combined with powder interface strengthening technology. Traditional water expansion methods rely solely on mechanical force for bonding, while this invention achieves diffusion metallurgical bonding at the drawing temperature (450-550℃) by adding active binder powder to the interface, resulting in strength far exceeding that of purely mechanical composites.

[0043] In conjunction with Example 1 and Comparative Examples 1-2, in the raw materials of the binder powder, tin serves as the basic binder phase, melting at a relatively low temperature and effectively wetting and filling the interface. Nickel is infinitely miscible with the inner and outer tube substrates, acting as a diffusion bridging and solid solution strengthening phase, promoting a strong metallurgical bond. Nano-titanium carbide, as a nanoscale reinforcing phase, possesses extremely high hardness and can refine grains and provide dispersion strengthening, pinning grain boundaries, preventing grain growth, and greatly improving the interface strength, wear resistance, and high-temperature stability.

[0044] Combining Examples 1-2 and Example 5, titanium (Ti) is a highly reactive element that preferentially reacts with impurities such as oxygen and nitrogen on the powder and matrix surface, purifying the interface and thus significantly improving the quality and success rate of metallurgical bonding. Simultaneously, titanium can also achieve solid solution strengthening and form titanium carbide with carbon, further enhancing its strength. The addition of silicon can form intermetallic compounds with nickel, tin, etc., refining the intermetallic structure, reducing melt viscosity, improving fluidity, and making the bonding denser. This demonstrates precise control over the intermetallic microstructure, further improving the mechanical properties of the stainless steel composite pipe. Combining Examples 3-4, controlling the particle size of the binder powder ensures uniform mixing of its components. Finally, adding nano-titanium carbide powder prevents severe agglomeration or structural damage of nanoparticles during prolonged grinding. Furthermore, investigations into particle size revealed that smaller particle sizes result in better mechanical properties of the stainless steel composite pipe. Analysis suggests that smaller particle sizes promote uniformity and facilitate the dispersion of nano-titanium carbide powder.

[0045] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A method of making a high corrosion resistant stainless steel composite pipe, characterized by: It comprises the following steps: S1, after rolling, welding, Inconel 625 alloy tube blank, and then the inner and outer surface of the tube blank is alkaline washing, water washing, pickling, water washing, sand blasting, pickling, water washing, to get the outer tube; S2, after rolling, welding, stainless steel tube blank, and then the inner and outer surface of the tube blank is alkaline washing, water washing, pickling, water washing, sand blasting, pickling, water washing, to get the inner tube; S3, the inner tube and the outer tube are sleeved and assembled, and then the inner tube and the outer tube are filled with adhesive powder to obtain a composite tube blank; The adhesive powder comprises tin powder, nickel powder, molybdenum powder, copper powder and nano titanium carbide powder; S4, water injection in the composite tube blank, the both ends of the composite tube blank are sealed and welded, then drawing is carried out, the drawing speed is controlled to be 0.5-1.2m / min, the drawing temperature is 450-550℃, after drawing, the both ends of the composite tube blank are cut off for drainage, then the composite tube blank is placed at 400-500℃ under nitrogen atmosphere for 4-6h, and natural cooling is carried out, to obtain a high corrosion resistant stainless steel composite tube.

2. The method for preparing a high corrosion-resistant stainless steel composite pipe according to claim 1, characterized in that: In S3, when the inner tube and the outer tube are sleeved and assembled, the distance between the inner tube and the outer tube is 1-3mm.

3. The method for preparing a high corrosion-resistant stainless steel composite pipe according to claim 1, characterized in that: The wall thickness ratio of the inner tube to the outer tube is (7-10):

1.

4. The method for preparing a high corrosion-resistant stainless steel composite pipe according to claim 1, characterized in that: The weight parts of each raw material of the adhesive powder are as follows: tin powder 60-80 parts, nickel powder 15-25 parts, molybdenum powder 7-13 parts, copper powder 8-12 parts and nano titanium carbide powder 0.2-1.2 parts.

5. The method for preparing a high corrosion-resistant stainless steel composite pipe according to claim 4, characterized in that: The adhesive powder further comprises 1-3 parts by weight of titanium powder.

6. The method for preparing a high corrosion-resistant stainless steel composite pipe according to claim 5, characterized in that: The adhesive powder further comprises 1-2.5 parts by weight of silicon powder.

7. The method for preparing a high corrosion-resistant stainless steel composite pipe according to claim 1, characterized in that: The preparation method of the adhesive powder is as follows: Mix and grind the raw materials except the nano titanium carbide powder to an average particle size of 5-50μm, then add the nano titanium carbide powder and mix uniformly to obtain the adhesive powder.

8. A highly corrosion resistant stainless steel composite pipe characterized by: The stainless steel composite tube is prepared by the preparation method of the high corrosion resistant stainless steel composite tube according to any one of claims 1-7.

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