Durable double-sided composite stainless steel connecting pipe and preparation method thereof

Abstract

The invention belongs to the technical field of stainless steel composite connecting pipe production, and discloses a durable double-sided composite stainless steel connecting pipe and a preparation method thereof in order to solve the problems of low interface bonding strength, intergranular corrosion and the like caused by carbon element migration of an existing composite connecting pipe. The durable double-sided composite stainless steel connecting pipe is obtained by assembling a stainless steel pipe, a low-carbon steel pipe and a stainless steel connecting pipe with threads; the inner surface and the outer surface of the low-carbon steel pipe are coated with barrier slurry, and raw materials of the barrier slurry comprise modified core-shell nanoparticles and epoxy-polyimide hybrid resin. The preparation method comprises the processes of core-shell particle modification, gradient curing, thermocompression bonding and thread synergistic strengthening. The barrier slurry improves the interface bonding strength and corrosion resistance through double mechanisms of chemical bonding and physical barrier.

Description

Technical Field

[0001] The present application relates to the technical field of stainless steel composite pipe production, and in particular to a durable double-sided composite stainless steel pipe and a preparation method thereof. Background Art

[0002] Stainless steel pipes, as core components of industrial piping systems, are widely used in fields such as petrochemicals, nuclear power, pharmaceuticals, and marine engineering. Their performance directly impacts the safety and reliability of the systems. Traditional single-material stainless steel pipes, such as 304 and 316L, offer excellent corrosion resistance and mechanical strength, but they suffer from limitations such as high cost and heavy weight. To reduce costs and optimize overall performance, composite pipes have become a research hotspot. A typical composite structure achieves a balance between corrosion resistance, mechanical properties, and cost-effectiveness through a design that includes an inner stainless steel layer for corrosion resistance, a middle carbon steel layer for load-bearing, and an outer stainless steel layer for reinforcement.

[0003] The existing preparation processes of composite nozzles mostly use mechanical composite technologies such as cold drawing and rolling, or welding composite technology to achieve interlayer connection through physical bonding. There is a risk of carbon elements migrating into the stainless steel, causing changes in the hardness of the stainless steel, a decrease in interfacial bonding strength, and intergranular corrosion, resulting in insufficient durability of the composite nozzles. Summary of the Invention

[0004] In response to the shortcomings of the existing technology, the present application provides a durable double-sided composite stainless steel pipe and a preparation method thereof. The durable double-sided composite stainless steel pipe is assembled from a stainless steel pipe, a low-carbon steel pipe, and a threaded stainless steel pipe. The inner and outer surfaces of the low-carbon steel pipe are coated with a barrier slurry, the raw materials of which include modified core-shell nanoparticles (alumina core and silica shell, treated with an aminosilane coupling agent) and an epoxy-polyimide hybrid resin; the preparation method includes core-shell particle modification, gradient curing, hot pressing bonding, and thread synergistic strengthening processes. The barrier slurry improves the interfacial bonding strength and corrosion resistance through the dual mechanisms of chemical bonding and physical barrier.

[0005] To achieve the above objectives, this application adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a method for preparing a durable double-sided composite stainless steel pipe, comprising the following steps:

[0007] Core-shell nanoparticles with aluminum oxide as the core and silicon dioxide as the shell are prepared and modified with an amino-containing silane coupling agent to obtain modified core-shell nanoparticles; modified epoxy resin is blended with carboxyl-terminated polyimide to form an epoxy-polyimide hybrid resin; the modified core-shell nanoparticles and the epoxy-polyimide hybrid resin are mixed to obtain a barrier slurry;

[0008] Activating the inner and outer surfaces of the low-carbon steel pipe to obtain an activated low-carbon steel pipe; coating the barrier slurry on the surface of the activated low-carbon steel pipe and treating it with a gradient curing process to obtain a barrier-modified low-carbon steel pipe;

[0009] The stainless steel pipe, the barrier modified low carbon steel pipe and the stainless steel pipe with threads on both ends of the outer surface are assembled in sequence; and hot pressing and bonding treatment is performed to obtain a double-sided composite pipe;

[0010] The threads of the double-sided composite pipe are subjected to heat activation treatment and electrochemical surface modification treatment to obtain the durable double-sided composite stainless steel pipe.

[0011] In a feasible implementation scenario, the barrier slurry also includes a boron-containing compound and a curing agent; the barrier slurry includes 18-23wt% modified core-shell nanoparticles, 65-70wt% epoxy-polyimide hybrid resin, 7-8wt% boron-containing compound and 5wt% curing agent; the boron-containing compound is zinc borate; the curing agent is dicyandiamide; the amino-containing silane coupling agent is one of KH-550 and KH-792.

[0012] In a feasible implementation scenario, the method for preparing the modified core-shell nanoparticles includes:

[0013] Alumina nanoparticles with a particle size of 30-80 nm are ultrasonically dispersed in anhydrous ethanol at a solid-liquid ratio of 1:200, stirred, and ethyl orthosilicate is added dropwise at a rate of 1 drop / s, with a mass ratio of ethyl orthosilicate to alumina nanoparticles being 1:1. The stirring reaction is continued for 2 hours, centrifuged, washed, and dried to obtain the core-shell nanoparticles;

[0014] The core-shell nanoparticles are dispersed in a 6 wt % ethanol solution of an amino-containing silane coupling agent, reacted at 75° C. for 6 h, centrifuged at 6000-8000 rpm, and dried to obtain the modified core-shell nanoparticles.

[0015] The alumina core can act as a rigid physical barrier, and its high-density crystal structure can effectively block the migration of carbon elements in low-carbon steel. Silica acts as a shell, and its surface is rich in silanol Si-OH. Chromium hydroxyl groups Cr-OH and iron oxide compounds exist on the surface of low-carbon steel and stainless steel. Under high temperature conditions during the gradient solidification process, silanol and chromium hydroxyl groups form stable Si-O-Cr covalent bonds by removing water molecules, and form Si-O-Fe with iron oxide compounds, closing the grain boundaries to block carbon element migration and enhancing the interface bonding strength.

[0016] The modified core-shell nanoparticles are evenly distributed in the barrier slurry, which improves the tensile strength of the barrier slurry after curing; and the silica shell has low electrical conductivity, which isolates the carbon steel-stainless steel galvanic couple, blocks galvanic corrosion, and improves corrosion resistance; the silane coupling agent with amino group introduces amino group on the surface of the core-shell nanoparticles, undergoes a ring-opening reaction with the epoxy group of epoxy-polyimide, forms a covalent bond, and enhances the interfacial bonding strength between the modified core-shell nanoparticles and the epoxy-polyimide hybrid resin.

[0017] In a feasible implementation scenario, the preparation method of the epoxy-polyimide hybrid resin includes:

[0018] Epoxy resin E51 and ethanolamine were mixed at a mass ratio of 10:1 to obtain a mixed system, 0.5% by mass of triphenylphosphine was added to the mixed system, and the mixture was reacted at 60° C. for 1 hour to obtain the modified epoxy resin;

[0019] The steps of: uniformly mixing pyromellitic dianhydride and N-methylpyrrolidone, adding 4,4'-diaminodiphenyl ether, maintaining the reaction at 35° C. with stirring for 4 hours, and then adding trimellitic anhydride, wherein the mass ratio of the pyromellitic dianhydride, N-methylpyrrolidone, 4,4'-diaminodiphenyl ether and trimellitic anhydride is 10:50:35:3.5, continuing the reaction for 1 hour, and then rotary evaporation to obtain a polyimide precursor; heating the polyimide precursor at 250° C. for 2 hours, dissolving it with m-cresol, precipitating it in methanol, and centrifuging and drying it to obtain the carboxyl-terminated polyimide;

[0020] The modified epoxy resin and the carboxyl-terminated polyimide were blended at a mass ratio of (2-4):1, and stirred at 60° C. for 2 hours to obtain the epoxy-polyimide hybrid resin.

[0021] The epoxy-polyimide hybrid resin is composed of a modified epoxy resin containing hydroxyl groups and a carboxyl-terminated polyimide. The modified epoxy resin introduces hydroxyl groups into the epoxy resin E51 through ethanolamine. The hydroxyl groups react and cross-link with dicyandiamide during the gradient curing process, thereby improving the toughness and interfacial strength of the barrier slurry after curing. The amino groups introduced by the silane coupling agent on the surface of the core-shell nanoparticles can undergo a ring-opening reaction with the epoxy groups of the epoxy-polyimide hybrid resin to form -OCN- covalent bonds. The introduction of high-temperature resistant polyimide chain segments improves the heat resistance of the barrier slurry after curing. Trimellitic anhydride is used as a capping agent to introduce carboxylic acid groups at the end of the polyimide chain. The carboxylic acid forms Cr-OOC-R or Fe-OOC-R with the chromium ions and iron ions on the stainless steel surface, thereby enhancing the bonding strength between the barrier slurry and the stainless steel after curing.

[0022] In a feasible implementation, the activation treatment includes sandblasting the inner and outer surfaces of the low-carbon steel pipe to a roughness of Ra=2 μm, and then performing plasma treatment.

[0023] In a feasible implementation scenario, the parameters of the gradient curing process are: first stage: temperature 80-100°C, curing time 1-2h; second stage: temperature 120-180°C, curing time 1.5-2.5h; third stage: temperature 220-250°C, curing time 0.5-1.5h.

[0024] The cross-linking density of the barrier paste is optimized through a gradient curing process. By increasing the temperature in stages, dicyandiamide decomposes at high temperatures to produce amino groups -NH2, which react with epoxy groups to form ester bonds, completing cross-linking and curing. The gradient curing process gradually activates dicyandiamide and reduces the internal stress of the barrier paste after curing.

[0025] In a feasible implementation, the temperature of the hot-pressing bonding is 200-240° C., the pressure is 20 MPa, and the holding time is 1 hour; and the hot-pressing bonding is performed in an inert gas atmosphere.

[0026] Boron ions in zinc borate release boron ions and zinc ions at a high temperature of more than 200°C in the third stage of gradient curing. An iron oxide layer is formed on the surface of the carbon steel, which contains active sites such as ferrous ions, ferric ions and hydroxyl groups. Boron ions and ferric ions form a Fe-OBO-Zn structure through oxygen, and zinc ions and ferric ions form a spinel ZnFe2O4 structure with high chemical stability. FeBO3 and ZnFe2O4 are cross-linked through Fe-OB and Fe-O-Zn bonds to form a FeBO3-ZnFe2O4 composite passivation layer at the interface, which inhibits the penetration of corrosive media. The modified core-shell nanoparticles, epoxy-polyimide hybrid resin and zinc borate form a dense barrier layer, which blocks the diffusion of carbon elements while enhancing the interfacial bonding strength.

[0027] In a feasible implementation scenario, the laser scanning wavelength of the thermal activation treatment is 980nm, and the scanning is performed until the temperature of the threaded area reaches 180°C; the electrolyte used in the electrochemical surface modification treatment contains 12wt% phosphoric acid and 6wt% molybdate, the voltage is 20V, and the power-on time is 3min.

[0028] The threaded area is subjected to thermal activation treatment, and the high temperature causes micro-melting on the surface of the threaded area to seal processing defects, reduce stress concentration, and thus improve fatigue life; the electrolyte of the subsequent electrochemical surface modification treatment contains phosphoric acid and sodium molybdate, which forms a Cr-Mo-PO4 composite passivation film on the thread surface, thereby improving the fatigue life of the threaded area.

[0029] In a feasible implementation scenario, the wall thickness of the stainless steel pipe is 1-2 mm; the carbon content of the low-carbon steel pipe is less than 0.25%, and the wall thickness is 2-3 times that of the stainless steel pipe; the wall thickness of the stainless steel pipe with threads on the outer surfaces of both ends is 3-5 mm.

[0030] In a second aspect, the present application provides a durable double-sided composite stainless steel pipe.

[0031] Beneficial technical effects:

[0032] The present application provides a durable double-sided composite stainless steel pipe and a preparation method thereof. The barrier slurry is coated on the active surface. The modified core-shell nanoparticles in the barrier slurry have aluminum oxide as the core and silicon dioxide as the shell. The modified core-shell nanoparticles are modified by a silane coupling agent with an amino group. An amino group is introduced on the surface of the silicon dioxide shell layer. The amino group undergoes a ring-opening reaction with the epoxy group of the epoxy-polyimide hybrid resin to form a covalent bond, thereby enhancing the interfacial bonding strength between the modified core-shell nanoparticles and the epoxy-polyimide hybrid resin. The surface of the silicon dioxide shell is rich in silicon hydroxyl Si-OH, which can covalently bond with the chromium hydroxyl Cr-OH and iron oxide compounds on the surface of the stainless steel to seal the grain boundaries. Blocking the migration of carbon elements; the modified epoxy resin in the epoxy-polyimide hybrid resin is obtained by introducing hydroxyl groups into the epoxy resin E51 by ethanolamine. The hydroxyl groups react with dicyandiamide to cross-link during the curing process, which can improve the toughness and interface strength of the barrier slurry after curing; the carboxyl groups at the ends of the polyimide segments in the epoxy-polyimide hybrid resin form Cr-OOC-R or Fe-OOC-R with the chromium ions and iron ions on the surface of stainless steel, enhancing the bonding strength between the barrier slurry and stainless steel, thereby blocking the migration of carbon elements without significantly reducing the interface bonding strength between carbon steel and stainless steel, thereby ensuring the mechanical properties of the stainless steel pipe. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic diagram of the preparation method of the durable double-sided composite stainless steel pipe of this application. DETAILED DESCRIPTION

[0034] In order to make the technical problems, technical solutions, and beneficial effects to be solved by this application more clearly understood, the present application is further described in detail below with reference to the following examples. However, this should not be construed as limiting the scope of this application to the following examples. Without departing from the above-mentioned method concepts of this application, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this application.

[0035] In this application, the terms used in this application are for the purpose of describing specific embodiments only and are not intended to be limiting of the application.

[0036] As used in this application, the singular forms "for," "or," "an," "any," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0037] In addition, the terms “first” and “second”, if used, are only used for descriptive purposes and should not be understood as indicating or implying relative importance.

[0038] The following will describe in detail a durable double-sided composite stainless steel pipe and its preparation method provided by the present application in combination with different embodiments.

[0039] The particle size of the aluminum oxide nanoparticles used in the embodiment is 30-80 nm.

[0040] Example 1

[0041] like Figure 1 As shown, a method for preparing a durable double-sided composite stainless steel pipe includes the following steps:

[0042] 1. Alumina nanoparticles were ultrasonically dispersed in anhydrous ethanol at a solid-liquid ratio of 1:200, magnetically stirred at 450 rpm, and ethyl orthosilicate was added dropwise at a rate of 1 drop / s. The mass ratio of ethyl orthosilicate to alumina nanoparticles was 1:1. The reaction was continued with stirring for 2 hours. During the reaction, the pH of the system was adjusted to 9 with ammonia water. The mixture was centrifuged, washed, and dried to obtain core-shell nanoparticles. The core-shell nanoparticles were dispersed in an ethanol solution containing 6 wt% KH-550 at a solid-liquid ratio of 1:5, reacted at 75°C for 6 hours, centrifuged at 8000 rpm, and dried at 80°C to obtain modified core-shell nanoparticles.

[0043] 2. Epoxy resin E51 and ethanolamine were mixed in a mass ratio of 10:1 to obtain a mixed system, 0.5% of the mass of the mixed system was added with triphenylphosphine, and the mixture was reacted at 60°C for 1 hour to obtain the modified epoxy resin; pyromellitic dianhydride and N-methylpyrrolidone were evenly mixed, 4,4'-diaminodiphenyl ether was added, and the mixture was stirred at 35°C for 4 hours before adding trimellitic anhydride. The mass ratio of pyromellitic dianhydride, N-methylpyrrolidone, 4,4'-diaminodiphenyl ether and trimellitic anhydride was 10:50:35:3.5. The reaction was continued for 1 hour and then rotary evaporated to obtain a polyimide precursor; the polyimide precursor was heated at 220°C for 2 hours, dissolved with m-cresol, precipitated in methanol, and centrifuged and dried to obtain a carboxyl-terminated polyimide; the modified epoxy resin and the carboxyl-terminated polyimide were blended in a mass ratio of 4:1 to obtain an epoxy-polyimide hybrid resin; the modified core-shell nanoparticles, epoxy-polyimide hybrid resin, zinc borate and dicyandiamide were mixed in a mass ratio of 18:70:7:5 and ultrasonically dispersed at a power of 300 W for 30 minutes to obtain a barrier slurry;

[0044] 3. Activate the inner and outer surfaces of a 20# mild steel pipe with a wall thickness of 2mm. First, sandblast the inner and outer surfaces using 120-mesh quartz sand at a pressure of 0.6 MPa to a roughness of Ra = 2.0 μm. Then, perform plasma treatment with an O2 / Ar gas mixture with a volume ratio of 4:1 at a power of 150W, a mixed gas flow rate of 20 sccm, and a treatment time of 10 minutes. This results in an activated mild steel pipe.

[0045] 4. Use the dip coating method to coat the surface of the activated low-carbon steel pipe. Immerse the activated low-carbon steel pipe in the barrier slurry and pull it up at a speed of 5 mm / s. After taking it out, perform gradient curing treatment: the first stage: temperature 80°C, curing time 1 hour; the second stage: temperature 120°C, curing time 1.5 hours; the third stage: temperature 220°C, curing time 0.5 hours, to obtain a barrier-modified low-carbon steel pipe;

[0046] 5. Assemble a 1mm thick 304 stainless steel pipe, a barrier-modified low-carbon steel pipe, and a 3mm thick 316L stainless steel pipe with threads on both ends from the inside out. Hot press bonding is performed in an inert gas atmosphere at a temperature of 200°C, a pressure of 20 MPa, and a holding time of 1 hour to obtain a double-sided composite pipe.

[0047] 6. Thermal activation is performed in the threaded area using a laser scan with a wavelength of 980 nm and a power density of 10 kW / cm 2 , scanning speed 0.2m / s, scanning until the temperature of the threaded area reaches 180℃; immersing the heat-activated threaded area in an electrolyte containing 12wt% phosphoric acid and 6wt% molybdate for electrochemical surface modification, passing a voltage of 20V for 3min, and obtaining a durable double-sided composite stainless steel pipe.

[0048] Example 2

[0049] like Figure 1 As shown, a method for preparing a durable double-sided composite stainless steel pipe includes the following steps:

[0050] 1. Alumina nanoparticles were ultrasonically dispersed in anhydrous ethanol at a solid-liquid ratio of 1:200. TEOS was added dropwise at a rate of 1 drop / s with a magnetic stirring at 450 rpm. The mass ratio of TESO to alumina nanoparticles was 1:1. The mixture was stirred for 2 h. During the reaction, the pH of the system was adjusted to 9 with ammonia water. The mixture was centrifuged, washed, and dried to obtain core-shell nanoparticles. The core-shell nanoparticles were then dispersed in a methanol / water solution containing 6 wt% KH-792 at a solid-liquid ratio of 1:5 (methanol / water = 9:1 (volume ratio)). The mixture was reacted at 75°C for 6 h, centrifuged at 8000 rpm, and dried at 80°C to obtain modified core-shell nanoparticles.

[0051] 2. Epoxy resin E51 and ethanolamine were mixed in a mass ratio of 10:1 to obtain a mixed system, 0.5% of the mass of the mixed system was added with triphenylphosphine, and the mixture was reacted at 60°C for 1 hour to obtain the modified epoxy resin; pyromellitic dianhydride and N-methylpyrrolidone were evenly mixed, 4,4'-diaminodiphenyl ether was added, and the mixture was stirred at 35°C for 4 hours before adding trimellitic anhydride. The mass ratio of pyromellitic dianhydride, N-methylpyrrolidone, 4,4'-diaminodiphenyl ether and trimellitic anhydride was 10:50:35:3.5. The reaction was continued for 1 hour and then rotary evaporated to obtain a polyimide precursor; the polyimide precursor was heated at 250°C for 2 hours, dissolved with m-cresol, precipitated in methanol, and centrifuged and dried to obtain a carboxyl-terminated polyimide; the modified epoxy resin and the carboxyl-terminated polyimide were blended in a mass ratio of 3:1 to obtain an epoxy-polyimide hybrid resin; the modified core-shell nanoparticles, epoxy-polyimide hybrid resin, zinc borate and dicyandiamide were mixed in a mass ratio of 20:68:7:5, and ultrasonically dispersed at a power of 300 W for 30 minutes to obtain a barrier slurry;

[0052] 3. Activate the inner and outer surfaces of a 3mm-thick 20# mild steel pipe by sandblasting the inner and outer surfaces with 120-mesh quartz sand at a pressure of 0.6 MPa to a roughness of Ra = 2.0 μm. Then, perform plasma treatment with an O2 / Ar gas mixture with a volume ratio of 4:1 at a power of 150 W and a mixed gas flow rate of 20 sccm for 10 minutes. This results in an activated mild steel pipe.

[0053] 4. Use the dip coating method to coat the surface of the activated low-carbon steel pipe. Immerse the activated low-carbon steel pipe in the barrier slurry and pull it up at a speed of 5 mm / s. After taking it out, perform gradient curing treatment: the first stage: temperature 90°C, curing time 1.5 hours; the second stage: temperature 150°C, curing time 2 hours; the third stage: temperature 230°C, curing time 1 hour, to obtain a barrier-modified low-carbon steel pipe;

[0054] 5. Assemble a 1mm thick 304 stainless steel pipe, a barrier-modified low-carbon steel pipe, and a 3mm thick 316L stainless steel pipe with threads on both ends from the inside out. Hot press bonding is performed in an inert gas atmosphere at a temperature of 220°C, a pressure of 20 MPa, and a holding time of 1 hour to obtain a double-sided composite pipe.

[0055] 6. Thermal activation is performed in the threaded area using a laser scan with a wavelength of 980 nm and a power density of 10 kW / cm 2 , scanning speed 0.2m / s, scanning until the temperature of the threaded area reaches 180℃; immersing the heat-activated threaded area in an electrolyte containing 12wt% phosphoric acid and 6wt% molybdate for electrochemical surface modification, passing a voltage of 20V for 3min, and obtaining a durable double-sided composite stainless steel pipe.

[0056] Example 3

[0057] like Figure 1 As shown, a method for preparing a durable double-sided composite stainless steel pipe includes the following steps:

[0058] 1. Alumina nanoparticles were ultrasonically dispersed in anhydrous ethanol at a solid-liquid ratio of 1:200, magnetically stirred at 450 rpm, and tetraethyl orthosilicate was added dropwise at a rate of 1 drop / s. The mass ratio of tetraethyl orthosilicate to alumina nanoparticles was 1:1. The reaction was continued with stirring for 2 hours. During the reaction, the pH of the system was adjusted to 9 with ammonia water. The reaction was centrifuged, washed, and dried to obtain core-shell nanoparticles. The core-shell nanoparticles were dispersed in an ethanol solution containing 8 wt% KH-550 at a solid-liquid ratio of 1:5, reacted at 75°C for 6 hours, centrifuged at 6000 rpm, and dried at 80°C to obtain modified core-shell nanoparticles.

[0059] 2. Epoxy resin E51 and ethanolamine were mixed in a mass ratio of 10:1 to obtain a mixed system, 0.5% of the mass of the mixed system was added with triphenylphosphine, and the mixture was reacted at 60°C for 1 hour to obtain the modified epoxy resin; pyromellitic dianhydride and N-methylpyrrolidone were evenly mixed, 4,4'-diaminodiphenyl ether was added, and the mixture was stirred at 35°C for 4 hours before adding trimellitic anhydride. The mass ratio of pyromellitic dianhydride, N-methylpyrrolidone, 4,4'-diaminodiphenyl ether and trimellitic anhydride was 10:50:35:3.5. The reaction was continued for 1 hour and then rotary evaporated to obtain a polyimide precursor; the polyimide precursor was heated at 250°C for 2 hours, dissolved with m-cresol, precipitated in methanol, and centrifuged and dried to obtain a carboxyl-terminated polyimide; the modified epoxy resin and the carboxyl-terminated polyimide were blended in a mass ratio of 2:1 to obtain an epoxy-polyimide hybrid resin; the modified core-shell nanoparticles, epoxy-polyimide hybrid resin, zinc borate and dicyandiamide were mixed in a mass ratio of 23:65:8:5, and ultrasonically dispersed at a power of 300 W for 30 minutes to obtain a barrier slurry;

[0060] 3. Activate the inner and outer surfaces of a 4mm-thick 20# mild steel pipe by sandblasting the inner and outer surfaces with 120-mesh quartz sand at a pressure of 0.6 MPa to a roughness of Ra = 2.0 μm. Then, perform plasma treatment with an O2 / Ar gas mixture with a volume ratio of 4:1 at a power of 150 W and a mixed gas flow rate of 20 sccm for 10 minutes. This results in an activated mild steel pipe.

[0061] 4. Use the dip coating method to coat the surface of the activated low-carbon steel pipe. Immerse the activated low-carbon steel pipe in the barrier slurry and pull it up at a speed of 5 mm / s. After taking it out, perform gradient curing treatment: the first stage: temperature 100°C, curing time 2h; the second stage: temperature 180°C, curing time 2.5h; the third stage: temperature 250°C, curing time 1.5h, to obtain a barrier-modified low-carbon steel pipe;

[0062] 5. Assemble a 2mm thick 304 stainless steel pipe, a barrier-modified low-carbon steel pipe, and a 5mm thick 316L stainless steel pipe with threads on both ends from the inside out. Hot press bonding is performed in an inert gas atmosphere at a temperature of 240°C, a pressure of 20 MPa, and a holding time of 1 hour to obtain a double-sided composite pipe.

[0063] 6. Thermal activation is performed in the threaded area using a laser scan with a wavelength of 980 nm and a power density of 10 kW / cm 2 , scanning speed 0.2m / s, scanning until the temperature of the threaded area reaches 180℃; immersing the heat-activated threaded area in an electrolyte containing 12wt% phosphoric acid and 6wt% molybdate for electrochemical surface modification, passing a voltage of 20V for 3min, and obtaining a durable double-sided composite stainless steel pipe.

[0064] Comparative Example 1

[0065] A durable double-sided composite stainless steel pipe is prepared by the same method and parameters as in Example 3, except that the coating of the barrier slurry is omitted, and the activated low-carbon steel pipe is directly assembled with the 304 stainless steel pipe and the 316L stainless steel pipe and then hot-pressed and bonded.

[0066] Comparative Example 2

[0067] A durable double-sided composite stainless steel pipe is prepared using the same method and parameters as in Example 3, except that the core-shell nanoparticles are replaced by alumina nanoparticles not coated with silica, and no silane coupling modification is performed.

[0068] Comparative Example 3

[0069] A durable double-sided composite stainless steel pipe is prepared using the same method and parameters as in Example 3, except that the threaded area is subjected to only conventional polishing, without the use of laser thermal activation and electrochemical surface modification.

[0070] The performance of the durable double-sided composite stainless steel pipe prepared in Examples 1-3 and Comparative Examples 1-3 was tested. The results are shown in Table 1:

[0071] Corrosion resistance: The durable double-sided composite stainless steel pipe prepared in this application was subjected to a salt spray test using a 5% sodium chloride solution at 35±2°C to obtain the corrosion area after 500 hours. The smaller the corrosion area, the stronger the corrosion resistance.

[0072] Interface bonding strength: the durable double-sided composite stainless steel adapter prepared in the application was subjected to tensile shear test to obtain the bonding strength.

[0073] Thread fatigue life: the durable double-sided composite stainless steel adapter prepared in the application was subjected to cycle test to complete the "tightening-loosening" cycle action, and the cycle number was recorded. Every 100 times was checked, and the failure was considered when the visible crack appeared on the thread. The more the failure cycle number was, the longer the thread fatigue life was.

[0074] Electrochemical performance: the durable double-sided composite stainless steel adapter prepared in the application was tested by linear polarization resistance method to obtain the polarization resistance. The greater the polarization resistance was, the stronger the electrochemical corrosion resistance was.

[0075] Table 1 Performance test results of the durable double-sided composite stainless steel adapters prepared in examples 1-3 and comparative examples 1-3

[0076]

[0077] As shown in Table 1, the 500h corrosion area of examples 1-3 was 0.3%-0.8%, the interface bonding strength was 85-105MPa, the thread failure cycle number was 12000-18000 times, and the polarization resistance was 1.2x10 5 -4.8x10 5 The 500h corrosion area of comparative examples 1-3 was 5.2%-9.1%, the interface bonding strength was 38-50MPa, the thread failure cycle number was 1800-5200 times, and the polarization resistance was 9.5x10 3 -3.2x10 4 The corrosion resistance, fatigue life, interface bonding strength and electrochemical performance of examples 1-3 were all better than those of comparative examples 1-3.

[0078] Comparative example 1 was compared with example 3, and the coating of barrier slurry was omitted, and the activated low-carbon steel pipe was directly assembled with 304 stainless steel pipe and 316L stainless steel adapter and then heat-pressed and bonded. The barrier coating layer formed by cross-linking of modified core-shell nanoparticles and epoxy-polyimide hybrid resin was not formed, and the pinning effect of nanoparticles and the covalent bonding of epoxy-polyimide hybrid resin with low-carbon steel pipe, stainless steel pipe and stainless steel adapter were lacked, and the interface bonding strength was only 50MPa. Since there was no barrier slurry, the carbon element of the activated low-carbon steel pipe migrated to the stainless steel, and intergranular corrosion occurred. The low-carbon steel and the stainless steel formed a galvanic couple, and the polarization resistance was significantly lower than that of example 3, and the corrosion resistance was significantly decreased.

[0079] Comparative Example 2, compared to Example 3, replaced the core-shell nanoparticles with unsilica-coated alumina nanoparticles, and no silane coupling modification was performed. The hydroxyl groups on the alumina particle surface were not silanized, making them prone to agglomeration. This resulted in an uneven barrier layer and reduced corrosion resistance. Due to the lack of silanol and amino groups on the alumina particle surface, it was unable to form covalent bonds with the stainless steel Cr2O3 layer and the epoxy-polyimide hybrid resin, resulting in a bonding strength of only 42 MPa. Furthermore, alumina has a higher electrical conductivity than silica, so galvanic corrosion between carbon steel and stainless steel was not blocked, significantly reducing polarization resistance.

[0080] In Comparative Example 3, the threaded area was only subjected to conventional polishing treatment, and laser thermal activation and electrochemical surface modification were not used, resulting in no generation of a Cr-Mo-PO4 composite passivation film in the threaded area and poor corrosion resistance of the threaded area; the polishing treatment was unable to eliminate surface microcracks, and stress concentration resulted in only 1,800 failure cycles, which was significantly lower than that in Example 3.

[0081] The above results show and describe the basic principles and main features of this application as well as the advantages of this application.

[0082] Those skilled in the art should understand that the present application is not limited to the above-described embodiments. The above-described embodiments and descriptions are merely illustrative of the principles of the present application. Various changes and improvements may be made to the present application without departing from the spirit and scope of the present application. Such changes and improvements are intended to fall within the scope of the present application. The scope of protection claimed in the present application is defined by the equivalents of the appended claims.

Claims

1. A method for preparing a durable double-sided composite stainless steel pipe, characterized in that: The following steps are involved: Core-shell nanoparticles with aluminum oxide as the core and silicon dioxide as the shell are prepared and modified with an amino-containing silane coupling agent to obtain modified core-shell nanoparticles; modified epoxy resin is blended with carboxyl-terminated polyimide to form an epoxy-polyimide hybrid resin; the modified core-shell nanoparticles and the epoxy-polyimide hybrid resin are mixed to obtain a barrier slurry; Activating the inner and outer surfaces of the low-carbon steel pipe to obtain an activated low-carbon steel pipe; coating the barrier slurry on the surface of the activated low-carbon steel pipe and treating it with a gradient curing process to obtain a barrier-modified low-carbon steel pipe; The stainless steel pipe, the barrier modified low carbon steel pipe and the stainless steel pipe with threads on both ends of the outer surface are assembled in sequence; and hot pressing and bonding treatment is performed to obtain a double-sided composite pipe; The threads of the double-sided composite pipe are subjected to heat activation treatment and electrochemical surface modification treatment to obtain the durable double-sided composite stainless steel pipe.

2. The method for preparing a durable double-sided composite stainless steel pipe according to claim 1, characterized in that: The barrier slurry also includes a boron-containing compound and a curing agent; the barrier slurry includes 18-23wt% modified core-shell nanoparticles, 65-70wt% epoxy-polyimide hybrid resin, 7-8wt% boron-containing compound and 5wt% curing agent; the boron-containing compound is zinc borate; the curing agent is dicyandiamide; the amino-containing silane coupling agent is one of KH-550 and KH-792.

3. The method for preparing a durable double-sided composite stainless steel pipe according to claim 1, characterized in that: The preparation method of the modified core-shell nanoparticles comprises: Alumina nanoparticles with a particle size of 30-80 nm are ultrasonically dispersed in anhydrous ethanol at a solid-liquid ratio of 1:200, stirred, and ethyl orthosilicate is added dropwise at a rate of 1 drop / s, with a mass ratio of ethyl orthosilicate to alumina nanoparticles being 1:

1. The stirring reaction is continued for 2 hours, centrifuged, washed, and dried to obtain the core-shell nanoparticles; The core-shell nanoparticles are dispersed in a 6 wt % ethanol solution of an amino-containing silane coupling agent, reacted at 75° C. for 6 h, centrifuged at 6000-8000 rpm, and dried to obtain the modified core-shell nanoparticles.

4. The method for preparing a durable double-sided composite stainless steel pipe according to claim 1, characterized in that: The preparation method of the epoxy-polyimide hybrid resin comprises: Epoxy resin E51 and ethanolamine were mixed at a mass ratio of 10:1 to obtain a mixed system, 0.5% by mass of triphenylphosphine was added to the mixed system, and the mixture was reacted at 60° C. for 1 hour to obtain the modified epoxy resin; The steps of: uniformly mixing pyromellitic dianhydride and N-methylpyrrolidone, adding 4,4'-diaminodiphenyl ether, maintaining the reaction at 35° C. with stirring for 4 hours, and then adding trimellitic anhydride, wherein the mass ratio of the pyromellitic dianhydride, N-methylpyrrolidone, 4,4'-diaminodiphenyl ether and trimellitic anhydride is 10:50:35:3.5, continuing the reaction for 1 hour, and then rotary evaporation to obtain a polyimide precursor; heating the polyimide precursor at 250° C. for 2 hours, dissolving it with m-cresol, precipitating it in methanol, and centrifuging and drying it to obtain the carboxyl-terminated polyimide; The modified epoxy resin and the carboxyl-terminated polyimide were blended at a mass ratio of (2-4):1, and stirred at 60° C. for 2 hours to obtain the epoxy-polyimide hybrid resin.

5. The method for preparing a durable double-sided composite stainless steel pipe according to claim 1, characterized in that: The activation treatment includes sandblasting the inner and outer surfaces of the low-carbon steel pipe to a roughness of Ra=2 μm, and then performing plasma treatment.

6. The method for preparing a durable double-sided composite stainless steel pipe according to claim 1, characterized in that: The parameters of the gradient curing process are: first stage: temperature 80-100°C, curing time 1-2h; second stage: temperature 120-180°C, curing time 1.5-2.5h; third stage: temperature 220-250°C, curing time 0.5-1.5h.

7. The method for preparing a durable double-sided composite stainless steel pipe according to claim 1, characterized in that: The temperature of the hot-press bonding is 200-240° C., the pressure is 20 MPa, and the holding time is 1 hour; the hot-press bonding is performed in an inert gas atmosphere.

8. The method for preparing a durable double-sided composite stainless steel pipe according to claim 1, characterized in that: The laser scanning wavelength of the thermal activation treatment is 980nm, and the scanning is performed until the temperature of the threaded area reaches 180°C; the electrolyte used in the electrochemical surface modification treatment contains 12wt% phosphoric acid and 6wt% molybdate, the voltage is 20V, and the power-on time is 3min.

9. The method for preparing a durable double-sided composite stainless steel pipe according to claim 1, characterized in that: The wall thickness of the stainless steel pipe is 1-2 mm; the carbon content of the low-carbon steel pipe is less than 0.25%, and the wall thickness is 2-3 times that of the stainless steel pipe; the wall thickness of the stainless steel pipe with threads on the outer surfaces of both ends is 3-5 mm.

10. A durable double-sided composite stainless steel pipe is prepared according to the preparation method according to any one of claims 1 to 9.

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