Bimetallic composite pipe and method of making same

Abstract

The application provides a bimetal composite pipe and a preparation method thereof. The preparation method comprises the following steps: preparing a pipe blank: taking a square pipe as an outer square pipe and taking a round pipe as an inner round pipe; assembling: sleeving the outer square pipe on the outer periphery of the inner round pipe, inserting a mandrel into the inner round pipe, and inserting an air extraction pipe into a gap between the R angle of the outer square pipe and the inner round pipe to obtain an assembled pipe; pre-heading: performing pre-heading treatment on the assembled pipe to obtain an inner-outer pipe blank with the mandrel; and periodic pipe rolling: performing periodic pipe rolling on the inner-outer pipe blank to obtain a composite pipe blank. The preparation method of the technical scheme can solve the problem that the inner and outer pipes of the existing bimetal composite pipe are prone to movement.

Description

Technical Field

[0001] This invention relates to the field of composite tube manufacturing technology, and more specifically, to a bimetallic composite tube and its manufacturing method. Background Technology

[0002] Corrosion is a persistent and serious problem in the use of steel pipes. Pipes inevitably encounter corrosive media containing H2S, CO2, and Cl ions, which are highly corrosive, causing not only huge economic losses but also often catastrophic consequences for the environment and personnel safety. Generally, inexpensive carbon or low-alloy steel pipes have poor corrosion resistance, while materials with good corrosion resistance, such as stainless steel and nickel-based alloys, are expensive. To save on the use of these expensive materials, bimetallic composite pipes have been developed. Bimetallic composite pipes typically consist of an outer base pipe for strength and a corrosion-resistant inner lining pipe. In terms of corrosion resistance, bimetallic composite pipes are essentially no different from corrosion-resistant alloy pipes, but they are superior in strength to carbon steel pipes and general alloy pipes. Their price is about half that of corrosion-resistant alloy pipes, and their service life is far longer than that of carbon steel pipes. Bimetallic composite pipes combine strength, corrosion resistance, wear resistance, high pressure resistance, and economy, and are widely used in oil and gas extraction and transportation, marine engineering, power industry, and water supply projects. They cover a wide range of specifications. In recent years, due to the deteriorating service environment (high temperature, high pressure, high corrosion, etc.) and cost considerations, the application of bimetallic composite pipes in various industries has been increasing.

[0003] In the prior art known to the inventor, the inner and outer tubes of the bimetallic composite tube are both round tubes. During assembly, there is a gap between the outer circumference of the inner tube and the inner circumference of the outer tube. In order to facilitate the outer tube to be fitted onto the outer circumference of the inner tube, the gap between the inner and outer tubes is generally large. Therefore, the inner and outer tubes are prone to movement. Summary of the Invention

[0004] The main objective of this invention is to provide a bimetallic composite tube and its preparation method, which can solve the problem of easy cross-flow between the inner and outer tubes of existing bimetallic composite tubes, ensure the integrity of the composite interface, and effectively improve the quality of the composite tube.

[0005] To achieve the above objectives, according to one aspect of the present invention, a method for preparing a bimetallic composite tube is provided, comprising the following steps: preparing a tube blank: taking a square tube as the outer square tube and a round tube as the inner round tube; assembling: fitting the outer square tube around the outer circumference of the inner round tube, inserting a mandrel into the inner round tube, and inserting a suction tube into the gap between the radius (R) of the outer square tube and the inner round tube to obtain an assembled tube; pre-heading: performing pre-heading treatment on the assembled tube to obtain an inner and outer tube blank with a mandrel; periodic rolling: performing periodic rolling on the inner and outer tube blanks to obtain a composite tube blank.

[0006] Furthermore, the outer diameter of the inner circular tube is 5mm to 10mm smaller than the inscribed circle diameter of the outer square tube.

[0007] Furthermore, the outer square tube has a side length of A, a side concavity / convexity of ≤0.2%A, an outer corner radius of 1.5 to 3 times the wall thickness, and a side perpendicularity of 90°±0.3°. The outer diameter of the round tube is 5mm to 10mm smaller than the minimum inner diameter of the square tube.

[0008] Furthermore, in the assembly process, the outer square tube and the inner round tube of the assembly tube are axially offset by a distance of 2mm to 5mm.

[0009] Furthermore, the pre-heading step includes the following steps: placing the assembly tube on the heading machine, pressing down the first and second heading modules of the heading machine, then raising the first and second heading modules, rotating the assembly tube by 90°, and pressing down the first and second heading modules again to obtain the inner and outer tube preforms, and performing vacuuming and sealing treatment from the vacuum tube.

[0010] Furthermore, in the pre-heading step, the hole shape of both the first and second heading modules consists of three diagonal lines. The sum of the widths of the first and second heading modules is 300mm, and the sum of the widths of the first and second heading modules is also 300mm. The width of the first heading module's first section ranges from 218mm to 235mm, and its angle with the horizontal line is 16.8° to 28°. The width of the second heading module's second section ranges from 65mm to 82mm, and its angle with the horizontal line is... The width of the third segment of the first leading module ranges from 28mm to 145mm, and the angle with the horizontal line is from 46° to 52°. The width of the first segment of the second leading module ranges from 218mm to 235mm, and the angle with the horizontal line is from 16.8° to 28°. The width of the second segment of the second leading module ranges from 65mm to 82mm, and the angle with the horizontal line is from 6° to 10°. The width of the third segment of the second leading module ranges from 4mm to 32mm, and the angle with the horizontal line is from 78° to 83°.

[0011] Furthermore, the outer diameter of the composite tube blank obtained by periodic rolling is 150mm to 600mm, the angle between the first end of the composite tube blank and the horizontal line is 46° to 52°, the angle between the second end of the composite tube blank and the horizontal line is 78° to 83°, and the ratio of the wall thickness of the outer square tube to the wall thickness of the inner round tube of the composite tube blank is 1:1.25 to 6:1.

[0012] Further, the steps of cyclic tube rolling include: using a cyclic tube rolling mill to cyclically roll inner and outer tube preforms to obtain composite tube preforms; setting the roll profile of the cyclic tube rolling mill to φ150mm~φ600mm, the roll profile including forging section, finishing section, final rolling section and air rolling section; determining the curve equations of the forging section, finishing section, final rolling section and air rolling section; the forging section is the envelope curve; the starting angle of the forging section is 27°~30°, the included angle is 74°~84°, and the curve unfolding length is 200mm~600mm; controlling the roll speed of the cyclic tube rolling mill to 46rpm~72rpm and the air pressure to 3bar~4bar.

[0013] Furthermore, after the periodic rolling step, a heating step is also included: preheating the composite tube blank at a temperature less than or equal to 620°C, and homogenizing the composite tube blank at a temperature of 1210°C to 1240°C, with the sum of the preheating time and homogenization time being 2.5h to 16h.

[0014] Furthermore, after the heating step, there is also a piercing step: the heated composite tube blank is pierced with a piercing machine to obtain a capillary tube. The outer square tube and the inner round tube of the capillary tube are flush. The total diameter reduction rate of the piercing machine is 16% to 18%, the ellipticity is 1.02, and the diameter expansion rate is 5% to 20%.

[0015] Furthermore, after the end-piercing step, there is also a rolling step: rolling the tube to obtain a composite rough tube.

[0016] Furthermore, after the rolling step, a reheating step is also included: the composite rough tube is reheated in a walking beam furnace, with the furnace temperature below 450℃, the solution strengthening heating temperature of the walking beam furnace being 1000℃±10℃, and the holding time being 0.5h~4h.

[0017] Furthermore, after the reheating step, a sizing step is also included: the reheated composite rough tube is sizing using a sizing machine and a cooling water ring on the sizing machine to obtain a composite tube; the composite tube is then cooled by a cooling water ring assembly to obtain a bimetallic composite tube. The temperature of the composite rough tube entering the sizing machine is 940℃~980℃, and the temperature of the composite rough tube exiting the sizing machine is 680℃~720℃. When the composite rough tube enters the cooling water ring assembly, the temperature of the cooling water in the cooling water ring assembly is 670℃~710℃, and when the composite rough tube exits the cooling water ring assembly, the temperature of the cooling water in the cooling water ring assembly is 380℃~420℃.

[0018] To achieve the above objectives, according to another aspect of the present invention, a bimetallic composite tube is provided, which is prepared using the above-described preparation method.

[0019] By applying the technical solution of this invention, a combination of an outer square tube and an inner round tube is used. After the outer square tube is fitted onto the outer circumference of the inner round tube, the inner walls of the inner round tube and the outer square tube have a nearly tangent portion. In this portion, the gap between the inner round tube and the outer square tube is small, and the inner round tube can contact the outer square tube by moving a short distance radially. Friction can be generated between the two, which can reduce the distance of the inner round tube relative to the outer square tube to a certain extent. When the minimum gap between the inner round tube and the outer square tube is very small, the movement between the inner round tube and the outer square tube can also be prevented. Attached Figure Description

[0020] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0021] Figure 1 A flowchart illustrating the preparation method of an embodiment of the present invention is shown;

[0022] Figure 2 This figure shows a longitudinal cross-sectional view of an embodiment of the present invention after the outer square tube is fitted around the outer periphery of the thin-walled inner circular tube;

[0023] Figure 3 A longitudinal cross-sectional view of the outer circular tube of the comparative embodiment of the present invention is shown after it is fitted around the outer periphery of the thick-walled inner circular tube.

[0024] Figure 4 A cross-sectional view of the inner and outer tube preforms according to an embodiment of the present invention is shown;

[0025] Figure 5 A cross-sectional view of a composite tube blank according to an embodiment of the present invention is shown;

[0026] Figure 6 The heading cross-section of the inner and outer tube preforms according to an embodiment of the present invention is shown;

[0027] Figure 7 A schematic diagram illustrating the flush-end perforation steps of an embodiment of the present invention is shown;

[0028] Figure 8 The figure illustrates a schematic diagram of the periodic tube ligation steps according to an embodiment of the present invention;

[0029] Figure 9 A schematic diagram of the continuous rolling mill according to an embodiment of the present invention is shown.

[0030] The above figures include the following reference numerals:

[0031] 1. Square tube; 2. Round tube; 3. Heading module; 4. End-cutting; 5. Continuous rolling mill. Detailed Implementation

[0032] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0033] It should be noted that, among the prior art known to the inventor, there are five commonly used methods for preparing bimetallic composite tubes: mechanical rolling, explosive bonding, drawing bonding, hydraulic bonding, and explosive bonding + hot rolling bonding.

[0034] Mechanical spinning utilizes the mechanical properties of two different materials: the elastic deformation range of the outer base tube (carbon steel pipe) and the low yield strength of the inner liner tube (stainless steel pipe). Under the extrusion of the spiral feed of the rolling machine, the inner liner tube undergoes continuous localized plastic deformation, while the outer base tube remains within its elastic deformation range. When the external force is removed, the outer base tube elastically contracts, while the inner liner tube, having undergone plastic deformation, cannot shrink. This results in a strong embedding of the outer surface of the inner liner tube into the inner surface of the outer base tube, forming a composite structure.

[0035] The explosive composite method involves placing the assembled inner and outer tubes in a water tank, placing a cluster of explosives on the axis of the inner liner tube, and using the explosive force generated instantaneously to cause a sudden increase in water pressure in the tank. This sudden increase in water pressure pushes the inner liner tube outward in the diameter direction. Under the action of water pressure, the outward-expanding inner liner tube expands onto the inner surface of the outer base tube and continues to expand along with the outer base tube until the pressure disappears. Meanwhile, the outer base tube contracts inward in the axial direction, ultimately forming a composite shape.

[0036] The hydraulic composite method involves completely sealing the assembled inner and outer tubes within a closed long cylinder, then injecting liquid into the cylinder and gradually increasing the pressure inside. This causes the inner liner tube to gradually expand outward in the diametrical direction and contract inward in the axial direction. Through continuous and gradual pressure application, the inner liner tube eventually reaches plastic deformation, while the outer base tube remains within the elastic deformation range. When the pressure gauge indicates that the inner and outer tubes have reached plastic deformation and the outer base tube is within the elastic deformation range, the pressure is released, completing the composite process.

[0037] The drawing composite method involves drawing the assembled inner and outer tubes along the axis of the inner liner tube using a tapered die (typically 1:25 or 1:50) with a fixed maximum outer diameter. Through the extrusion and expansion of the drawing die, the inner liner tube is diametrically bonded to the inner surface of the outer base tube, and further expansion brings the outer base tube into an elastic deformation range. When the external force is removed, the inner liner tube undergoes plastic deformation and cannot shrink, while the outer base tube undergoes elastic deformation and tends to shrink. However, constrained by the inner liner tube, the inner surface of the outer base tube is strongly embedded in the outer surface of the inner liner tube, thus forming the composite shape.

[0038] The explosive bonding + hot rolling bonding method involves feeding bimetallic composite hollow billets produced by explosive bonding process one by one into an annular heating furnace for heating. The heated bimetallic composite hollow billets are then conveyed via roller conveyor to the center line of the piercing mill, where they are pierced into tubes by the action of the piercing mill rolls and mandrel. The tubes are then moved to the borax station, where the inner wall is first purged with nitrogen, followed by borax spraying and continuous rolling. After borax spraying protection, the tubes are quickly moved to the center line of the continuous rolling mill, where a prepared mandrel is inserted, and the tubes are rolled into rough tubes. The rough tubes are then conveyed via roller conveyor to the tension reduction center line, where they are gradually reduced in diameter by the tension reduction mill to form bimetallic composite seamless steel pipes.

[0039] The above five manufacturing processes for bimetallic composite pipes all involve the composite forming of pre-formed stainless steel and carbon steel pipes. The resulting composite pipes exhibit poor roundness, uneven wall thickness, and low bonding strength. Bimetallic composite pipes manufactured using explosive bonding, mechanical rolling, drawing bonding, and hydraulic bonding methods have gaps between the outer base pipe and the inner liner pipe, resulting in low production efficiency, small deformation, poor interlayer bonding, and a limited range of applicable specifications. The explosive bonding + hot rolling bonding method suffers from low production efficiency, high production cost, long production cycle, and a limited range of applicable specifications. Furthermore, the explosive bonding and explosive bonding + hot rolling bonding methods require the use of explosives, posing certain environmental pollution and safety hazards. The common drawbacks of these five manufacturing processes—low production efficiency, high production cost, and limited applicable specifications—limit the promotion and application of bimetallic composite pipes.

[0040] The purpose of this invention is to overcome the aforementioned shortcomings of existing technologies and provide a method for preparing bimetallic composite tubes. Compared with the five existing methods for preparing bimetallic composite tubes, this invention has significant advantages. This invention overcomes the deficiencies of traditional composite tube production methods, achieving full coverage of composite tube specifications and featuring a wide range of product specifications. This invention also overcomes the deficiencies of traditional composite tube production methods, achieving large deformation rolling of composite tubes and mutual penetration of double-layer metal elements, significantly improving interlayer bonding strength and composite quality. This invention fully utilizes the advantages of "outer square tube and inner round tube"—low cost, low energy consumption, and high yield—reducing costs from both process and raw material perspectives. Furthermore, the effective combination of end-piercing technology, rolling technology, controlled rolling and cooling, and online solution treatment technology ensures excellent performance of the bimetallic composite tubes under this process, significantly improving production efficiency, effectively reducing manufacturing costs, and simultaneously achieving full coverage of bimetallic composite tube production specifications.

[0041] See also Figures 1 to 9As shown, this invention provides a method for preparing a bimetallic composite tube, comprising the following steps: preparing the tube blank: taking a square tube as the outer square tube and a round tube as the inner round tube; assembling: fitting the outer square tube around the outer circumference of the inner round tube, inserting a mandrel into the inner round tube, and inserting a suction tube into the gap between the radius (R) of the outer square tube and the inner round tube to obtain an assembled tube; pre-heading: performing pre-heading treatment on the assembled tube to obtain an inner and outer tube blank with a mandrel; periodic rolling: performing periodic rolling on the inner and outer tube blanks to obtain a composite tube blank.

[0042] In this embodiment, a combination of an outer square tube and an inner round tube is used. After the outer square tube is fitted onto the outer circumference of the inner round tube, the inner walls of the inner round tube and the outer square tube have a nearly tangent portion. In this portion, the gap between the inner round tube and the outer square tube is small. The inner round tube can contact the outer square tube by moving a short distance radially, and friction can be generated between them. This can reduce the distance of the inner round tube relative to the outer square tube to a certain extent. When the minimum gap between the inner round tube and the outer square tube is very small, the movement between the inner round tube and the outer square tube can also be prevented.

[0043] The combination of the outer square tube and the inner round tube is beneficial in two ways: firstly, it facilitates the assembly of both; secondly, it facilitates the assembly of the exhaust pipe and the discharge of gas from the gap between the outer square tube and the inner round tube, thus ensuring the quality of the composite tube blank and significantly improving the interlayer bonding strength of the composite tube.

[0044] Specifically, based on the required model of the bimetallic composite pipe, select the appropriate outer square tube and inner round tube. Grind both the inner and outer surfaces of the outer square tube and the inner round tube to remove surface oxide scale and impurities, ensuring the smoothness of both and preventing assembly issues caused by unground surfaces. The metal of the outer square tube is of boiler tube grade, high-efficiency chemical tube grade, oil casing tube grade, or pipeline tube grade, etc., while the metal of the inner round tube is of austenitic stainless steel grade, martensitic stainless steel grade, ferritic stainless steel grade, or duplex stainless steel grade, as well as copper-based alloys, nickel-based alloys, Hastelloy, titanium, and titanium alloys, and other new high-corrosion-resistant alloy materials.

[0045] See also Figures 1 to 3 As shown, in one embodiment of the present invention, the outer diameter of the inner circular tube is 5mm to 10mm smaller than the inner circle diameter of the outer square tube.

[0046] See also Figures 1 to 3 As shown, in one embodiment of the present invention, the outer square tube has a side length of A, a side concavity / convexity of ≤0.2%A, an outer corner radius of 1.5 to 3 times the wall thickness, and a side perpendicularity of 90°±0.3°. The outer diameter of the round tube is 5mm to 10mm smaller than the minimum inner diameter of the square tube.

[0047] See also Figures 1 to 3 As shown, in one embodiment of the present invention, during the assembly step, the outer square tube and the inner round tube of the assembly tube are axially offset by a distance of 2mm to 5mm to ensure that the bonding surfaces are tightly joined during rolling and that the ends of the inner and outer steel tubes are flush.

[0048] In one embodiment, the outer square tube has a side length of 192–676 mm and a wall thickness of 36–88 mm, while the inner round tube has an outer diameter of 115–490 mm and a wall thickness of 13.5–90 mm.

[0049] See also Figures 1 to 4 As shown, in one embodiment of the present invention, the pre-heading step includes: placing the assembly tube on the heading machine, pressing down the first heading module and the second heading module of the heading machine, then raising the first heading module and the second heading module, rotating the assembly tube by 90°, pressing down the first heading module and the second heading module again to obtain the inner and outer tube preforms, and performing vacuuming and sealing treatment from the vacuum tube.

[0050] See also Figures 1 to 4 As shown, in one embodiment of the present invention, in the pre-heading step, the hole shape of both the first heading module and the second heading module consists of three oblique lines. The sum of the widths of the first and second sections of the hole shape of the first heading module is 300mm, and the sum of the widths of the first and second sections of the hole shape of the second heading module is 300mm. The width of the first section of the first heading module ranges from 218mm to 235mm, and the angle between it and the horizontal line is 16.8° to 28°. The width of the second section of the first heading module ranges from 65mm to 82mm, and the angle between it and the horizontal line is 16.8° to 28°. The included angle of the line is 6° to 10°. The width of the third segment of the first starting module ranges from 28mm to 145mm, and the included angle with the horizontal line is 46° to 52°. The width of the first segment of the second starting module ranges from 218mm to 235mm, and the included angle with the horizontal line is 16.8° to 28°. The width of the second segment of the second starting module ranges from 65mm to 82mm, and the included angle with the horizontal line is 6° to 10°. The width of the third segment of the second starting module ranges from 4mm to 32mm, and the included angle with the horizontal line is 78° to 83°.

[0051] Specifically, the first heading module is the left heading module of the heading machine, and the second heading module is the right heading module of the heading machine.

[0052] See also Figures 1 to 6As shown, in one embodiment of the present invention, the outer diameter of the composite tube blank obtained by periodic rolling is 150mm to 600mm, the angle between the first end of the composite tube blank and the horizontal line is 46° to 52°, the angle between the second end of the composite tube blank and the horizontal line is 78° to 83°, and the ratio of the wall thickness of the outer square tube to the wall thickness of the inner round tube of the composite tube blank is 1:1.25 to 6:1, so as to ensure the cladding of the inner and outer metal layers at the end, which facilitates the subsequent periodic rolling and forging into a composite tube.

[0053] Specifically, the first end of the composite tube blank is the left end, corresponding to the first heading module, and the second end of the composite tube blank is the right end, corresponding to the second heading module.

[0054] See also Figures 1 to 8 As shown, in one embodiment of the present invention, the step of periodic tube rolling includes: using a periodic tube rolling mill to periodically roll inner and outer tube blanks to obtain a composite tube blank; setting the pass shape of the periodic tube rolling mill to φ150mm~φ600mm, the pass shape including a forging section, a finishing section, a final rolling section and an air rolling section; determining the curve equations of the forging section, the finishing section, the final rolling section and the air rolling section; the forging section being the envelope; the starting angle of the forging section being 27°~30°, the included angle being 74°~84°, and the curve unfolding length being 200mm~600mm; and controlling the roll speed of the periodic tube rolling mill to 46rpm~72rpm and the air pressure to 3bar~4bar.

[0055] In this embodiment, the Pilger head can be completely bent through the die design of the cyclic rolling tube, improving material utilization by 20%. Since the first end of the inner and outer tube preforms has a slope of 28mm to 145mm, cyclic headless rolling can be achieved.

[0056] In one embodiment of the present invention, after the periodic rolling step, a heating step is further included: preheating the composite tube blank at a temperature less than or equal to 620°C, homogenizing the composite tube blank at a temperature of 1210°C to 1240°C, and the sum of the preheating time and the homogenizing time being 2.5h to 16h.

[0057] In this embodiment, preheating refers to the temperature of the preheating section when the composite tube blank enters the annular furnace, and homogenization refers to the temperature of the composite tube blank in the homogenization section within the annular furnace. Heating the composite tube blank using an annular furnace is prone to heating defects and delamination due to the high alloying elements in the stainless steel layer and the relatively large size of some composite tube blanks. Therefore, this embodiment employs an appropriate heating temperature and heating rate.

[0058] See also Figures 1 to 7As shown, in one embodiment of the present invention, after the heating step, a piercing step is further included: the heated composite tube blank is pierced using a piercing machine to obtain a capillary tube, the outer square tube and the inner round tube of the capillary tube are flush, the total diameter reduction rate of the piercing machine is 16% to 18%, the ellipticity is ≥0.98 and the diameter expansion rate is 5% to 20%.

[0059] Setting a larger total diameter reduction ratio is beneficial for the first and second bite of the composite tube blank; setting a smaller ellipticity can reduce harmful additional deformation of the tube along the circumferential direction and avoid perforation and delamination defects in the tube.

[0060] In one embodiment, the ellipticity is 1.02 to 1.03.

[0061] Specifically, the piercing mill is a conical piercing mill. The outer diameter of the tube is 158mm to 630mm, and the wall thickness is 14mm to 110mm. Considering the characteristics of piercing hollow composite tube blanks, a piercing process with a flat-head mandrel and a negative mandrel extension is designed, where the mandrel extension is -10mm to -20mm, and the mandrel nose is located on the outlet side of the deformation zone. The ratio of the mandrel nose diameter to the mandrel diameter is 0.52 to 0.75, which is 10mm to 20mm smaller than the inner diameter of the composite tube blank.

[0062] In one embodiment of the present invention, after the end-piercing step, a rolling step is further included: rolling the tube to obtain a composite rough tube.

[0063] In this embodiment, rolling is achieved through a continuous rolling mill, a high-efficiency mill for producing seamless steel pipes. It involves placing a pierced tube onto a long mandrel and rolling it through multiple continuously arranged stands, thus achieving a high degree of mechanization and automation. Since periodic rolling mills are well-suited for producing large-diameter steel pipes, the pierced tube is placed on a mandrel and rolled by cyclic rolls. The periodic rolling process features a forging-rolling combination deformation method, a large rolling ratio, and excellent comprehensive mechanical properties. Therefore, in conjunction with the periodic rolling process, the continuous rolling mill pass is designed to be φ158mm and φ293mm, and the periodic rolling mill pass is designed to be φ150mm~φ600mm, preferably φ520mm. Rolling parameters such as roll gap and rotational speed are calculated to rationally control the dimensions of the resulting composite rough tube, ensuring the quality of the incoming material before sizing.

[0064] Specifically, the continuous rolling mill is designed with high-strength, high-toughness, and high-heat-dissipation continuous rolling rolls. The weight percentage of each chemical element in the material is as follows: C 0.60~0.80, Si 0.80~1.00, Mn 0.3~0.5, Cu 0.05~0.15, Ni 0.1~0.2, Cr 4.8~5.8, Mo 0.4~0.7, W 0.2~0.3, V 0.3~0.5, B 0.0025~0.0035, Al 0.08~0.15, Co 0.08~0.15, N 0.012~0.018, with the balance being Fe and unavoidable impurities. The continuous rolling mill consists of six stands. The nominal diameter of the continuous rolling rolls is 700-720 mm, the roll width is 220-240 mm, the eccentricity is 0-3.88 mm, the connecting arc radius is 15-50 mm, the first arc radius is 323-431 mm, the roll throat radius is 117-128 mm, the connecting angle is 8°-16.5°, the first pass arc angle is 30-32 mm, the roll gap is 14-16 mm, and the roll throat depth is 39.5-45 mm.

[0065] In one embodiment of the present invention, after the rolling step, a reheating step is further included: the composite rough tube is reheated by a walking beam furnace, the furnace temperature is below 450°C, the solid solution strengthening heating temperature of the walking beam furnace is 1000°C ± 10°C, and the holding time is 0.5h to 4h.

[0066] See also Figures 1 to 8 As shown, in one embodiment of the present invention, after the reheating step, a sizing step is further included: the reheated composite rough tube is sizing using a sizing machine and a cooling water ring on the sizing machine to obtain a composite tube; the composite tube is then cooled by a cooling water ring assembly to obtain a bimetallic composite tube. The temperature of the composite rough tube entering the sizing machine is 940℃~980℃, and the temperature of the composite rough tube exiting the sizing machine is 680℃~720℃. When the composite rough tube enters the cooling water ring assembly, the temperature of the cooling water in the cooling water ring assembly is 670℃~710℃, and when the composite rough tube exits the cooling water ring assembly, the temperature of the cooling water in the cooling water ring assembly is 380℃~420℃.

[0067] In this embodiment, the sizing mill includes multiple round tube rolling mill units, which are arranged along the conveying direction of the composite rough tube, enabling integration with other processes to achieve continuous production of bimetallic composite tubes. The sizing mill stand is equipped with a cooling water ring assembly to rapidly cool the composite rough tube; that is, after sizing, the composite rough tube is rapidly cooled using a square cooling water ring assembly. The angle between the water ring nozzles of the square cooling water ring assembly and the vertical line is 10° to 15°. The total reduction rate of the sizing mill is less than 28%, the reduction rate per stand is less than 3%, and the ellipticity of the die is less than 1.04.

[0068] In one embodiment of the present invention, after the reheating step and before the sizing step, a high-pressure water descaling step is included: using high-pressure water to descal the reheated composite rough pipe.

[0069] In one embodiment of the present invention, the sizing step is followed by a cooling bed cutting step, a head and tail cutting step, a straightening step, a manual inspection step, a non-destructive testing step, a physical and chemical testing step, a manual re-inspection step, and a packaging and warehousing step.

[0070] In this embodiment, the seven steps following the sizing step are all conventional steps in the preparation of bimetallic composite steel pipes, ensuring that the quality and performance of the bimetallic composite pipes meet the requirements.

[0071] This invention provides a bimetallic composite tube, which is prepared using the above-described method.

[0072] In this embodiment, the bimetallic composite tube is prepared using all the above-described preparation methods and has all the technical effects of the bimetallic composite tube described above, which will not be repeated here.

[0073] Example 1

[0074] Preparation of small-diameter bimetallic composite pipes

[0075] The manufactured specifications are 73mm×5.51mm, with the outer square tube being 26CrMo with specifications of 73mm×4.51mm and the inner round tube being LC2205 stainless steel with specifications of 63.98mm×1mm. The performance meets the technical requirements of Q125 steel grade for oil pipes.

[0076] Step SA1: Prepare the tube blank, using the tube blank preparation steps described above;

[0077] Outer square tube: side length A is 192mm, wall thickness T is 36mm, edge concavity / convexity ≤0.2% A, outer corner radius R and wall thickness T satisfy R=1.5×T, edge perpendicularity does not exceed 90°±0.3°.

[0078] Inner round tube: outer diameter is 115mm, wall thickness is 13.5mm, the outer diameter of the round tube is 5mm smaller than the minimum inner diameter of the square tube.

[0079] Step SA2: Assembly, using the assembly steps described above;

[0080] The outer square tube and the inner round tube of the assembly tube are axially offset by 2mm.

[0081] Step SA3: Pre-heading, using the pre-heading steps described above;

[0082] The first segment of the first leading module has a width of 230mm and an angle of 16.8° with the horizontal line. The second segment of the first leading module has a width of 70mm and an angle of 6° with the horizontal line. The third segment of the first leading module has a width of 30.2mm and an angle of 50° with the horizontal line. The first segment of the second leading module has a width of 230mm and an angle of 16.8° with the horizontal line. The second segment of the second leading module has a width of 70mm and an angle of 6° with the horizontal line. The third segment of the second leading module has a width of 6.35mm and an angle of 80° with the horizontal line.

[0083] Step SA4: Periodic rolling, using the periodic rolling steps described above;

[0084] The roll pass of the periodic tube rolling mill is set to Φ150mm, the starting angle of the forging and rolling section is 27°, the included angle is 74°, and the curve unfolding length is 300mm. The roll speed of the periodic tube rolling mill is controlled at 72rpm and the air pressure is 3bar. The first end of the inner and outer tube preforms has a 30mm slope.

[0085] The composite tube blank obtained from the periodic rolling process has an outer diameter of 150 mm and a wall thickness of 36 mm. The angle between the first end of the composite tube blank and the horizontal line is 50°, and the angle between the second end of the composite tube blank and the horizontal line is 80°. The outer square tube is made of the same metal grade as oil casing pipe, and the inner round tube is made of duplex stainless steel. The ratio of the wall thickness of the outer square tube to the wall thickness of the inner round tube in the composite tube blank is 3.5:1.

[0086] Step SA5: Heating, using the heating steps described above;

[0087] The preheating temperature is less than or equal to 620℃, and the composite tube blank is homogenized at a temperature of 1210℃~1240℃. The sum of the preheating time and the homogenization time is 2.5h.

[0088] Step SA6: Flush punching, using the flush punching steps described above;

[0089] The total diameter reduction rate of the piercing mill is 16%, the ellipticity is 1.02, and the diameter expansion rate is 5%. The outer diameter of the capillary tube obtained by flush piercing is 158 mm and the wall thickness is 14 mm. In the flat-head and negative-head protrusion piercing processes, the mandrel protrusion is -10 mm, the mandrel nose is on the outlet side of the deformation zone, and the ratio of the mandrel nose diameter to the mandrel diameter is 0.59, which is 10 mm smaller than the inner diameter of the composite tube blank.

[0090] Step SA7: Rolling, using the rolling steps described above;

[0091] The continuous rolling mill's pass is designed to be φ158mm, and the periodic rolling mill's pass is designed to be φ520mm. The continuous rolling rolls feature high strength, toughness, and high heat dissipation. The weight percentage of each chemical element in the material is as follows: C 0.60~0.80, Si 0.80~1.00, Mn 0.3~0.5, Cu 0.05~0.15, Ni 0.1~0.2, Cr 4.8~5.8, Mo 0.4~0.7, W 0.2~0.3, V 0.3~0.5, B 0.0025~0.0035, Al 0.08~0.15, Co 0.08~0.15, N 0.012~0.018, with the balance being Fe and unavoidable impurities.

[0092] Step SA8: Reheat, using the reheating steps described above;

[0093] Step SA9: Sizing, using the sizing steps described above;

[0094] Step SA10: Straightening and cutting off the head and tail;

[0095] The ends of the sized bimetallic composite pipe are cut off using a gang saw, and the cut ends of the bimetallic composite pipe are straightened using a six-roll straightener to ensure that the curvature is no more than 1.2 mm / m.

[0096] Step SA11: Initial manual inspection;

[0097] The surface quality and dimensional accuracy of the straightened bimetallic composite tube are inspected.

[0098] Step SA12: Heat treatment;

[0099] The quenching and tempering treatment involved a quenching temperature of 940℃~970℃ and a holding time of 18 min, followed by a tempering temperature of 640~660℃ and a holding time of 36 min. This resulted in a high-strength, high-toughness tempered sorbite structure in the 26CrMo layer.

[0100] Step SA13: Non-destructive testing;

[0101] Cracks, folds, scars, and delamination are not allowed on the inner and outer surfaces of bimetallic composite pipes. L2-level ultrasonic testing is performed according to GB / T5777 standards to automatically detect and remove longitudinal and / or transverse defects around the entire circumference of the bimetallic composite pipe, ensuring the internal quality of the composite pipe.

[0102] Step SA14: Physicochemical testing;

[0103] The performance of the bimetallic composite pipe was sampled and tested, and the test results are shown in Table 1.

[0104] Table 1 Mechanical properties of bimetallic composite pipes

[0105]

[0106] Step SA15: Manual re-inspection;

[0107] There are no visible defects such as cracks, scratches, indentations, or rust on the inner surface of the bimetallic composite pipe.

[0108] Step SA16: Packaging and warehousing;

[0109] After printing and weighing, the bimetallic composite pipes are packaged and stored.

[0110] Example 2

[0111] Preparation of medium-diameter bimetallic composite pipes;

[0112] The manufactured specifications are 245mm×12mm, with the outer square tube being Q345B with a specification of 245mm×10mm and the inner round tube being LC2205 stainless steel with a specification of 225mm×2mm. The performance meets the technical requirements of X70 grade pipeline pipe.

[0113] Step SA1: Prepare the tube blank, using the tube blank preparation steps described above;

[0114] Outer square tube: side length A is 346mm, wall thickness T is 62mm, edge concavity / convexity ≤0.2% A, outer corner radius R and wall thickness T satisfy R=1.5×T, edge perpendicularity does not exceed 90°±0.3°.

[0115] Inner round tube: outer diameter is 212mm, wall thickness is 21mm, the outer diameter of the round tube is 10mm smaller than the minimum inner diameter of the square tube.

[0116] Step SA2: Assembly, using the assembly steps described above;

[0117] The outer square tube and the inner round tube of the assembly tube are axially offset by 3mm.

[0118] Step SA3: Pre-heading, using the pre-heading steps described above;

[0119] The first segment of the first leading module has a width of 218mm and an angle of 28° with the horizontal line. The second segment of the first leading module has a width of 82mm and an angle of 10° with the horizontal line. The third segment of the first leading module has a width of 50.3mm and an angle of 50° with the horizontal line. The first segment of the second leading module has a width of 218mm and an angle of 28° with the horizontal line. The second segment of the second leading module has a width of 82mm and an angle of 10° with the horizontal line. The third segment of the second leading module has a width of 10.6mm and an angle of 80° with the horizontal line.

[0120] Step SA4: Periodic rolling, using the periodic rolling steps described above;

[0121] The roll pass of the periodic tube rolling mill is set to Φ280mm, the starting angle of the forging and rolling section is 27°, the included angle is 75°, and the curve unfolding length is 350mm. The roll speed of the periodic tube rolling mill is controlled at 62rpm and the air pressure is 3.2bar. The first end of the inner and outer tube preforms has a 50.3mm slope.

[0122] The composite tube blank obtained from the periodic rolling process has an outer diameter of 280 mm and a wall thickness of 60 mm. The angle between the first end of the composite tube blank and the horizontal line is 50°, and the angle between the second end of the composite tube blank and the horizontal line is 80°. The ratio of the wall thickness of the outer square tube to the inner round tube of the composite tube blank is 4:1.

[0123] Step SA5: Heating, using the heating steps described above;

[0124] The preheating temperature is less than or equal to 620℃, and the composite tube blank is homogenized at a temperature of 1210℃~1240℃. The sum of the preheating time and the homogenization time is 4 hours.

[0125] Step SA6: Flush punching, using the flush punching steps described above;

[0126] The total diameter reduction rate of the piercing mill is 16%, the ellipticity is 1.02, and the diameter expansion rate is 20%. The outer diameter of the capillary tube obtained by flush piercing is 336 mm and the wall thickness is 23 mm. In the flat-head and negative-head protrusion piercing processes, the mandrel protrusion is -15 mm, the mandrel nose is on the outlet side of the deformation zone, and the ratio of the mandrel nose diameter to the mandrel diameter is 0.54, which is 15 mm smaller than the inner diameter of the composite tube blank.

[0127] Step SA7: Rolling, using the rolling steps described above;

[0128] The continuous rolling mill's pass profile is designed to be φ293mm, while the periodic rolling mill's pass profile is designed to be φ520mm.

[0129] Step SA8: Reheat, using the reheating steps described above;

[0130] The holding time in the walking beam furnace is 35 minutes.

[0131] Step SA9: Sizing, using the sizing steps described above;

[0132] Step SA10: Straightening and cutting off the head and tail;

[0133] The ends of the sized bimetallic composite pipe are cut off using a gang saw, and the cut ends of the bimetallic composite pipe are straightened using a six-roll straightener to ensure that the curvature is no more than 1.2 mm / m.

[0134] Step SA11: Initial manual inspection;

[0135] The surface quality and dimensional accuracy of the straightened bimetallic composite tube are inspected.

[0136] Step SA12: Non-destructive testing;

[0137] Cracks, folds, scars, and delamination are not allowed on the inner and outer surfaces of bimetallic composite pipes. According to the requirements of GB / T5777-2019 "Automatic Ultrasonic Testing of Longitudinal and / or Transverse Defects in Seamless and Welded (Except Submerged Arc Welded) Steel Pipes", L2 level ultrasonic testing is carried out to automatically detect longitudinal and / or transverse defects in the entire circumference of the bimetallic composite pipe and remove them to ensure the internal quality of the composite pipe.

[0138] Step SA13: Physicochemical testing;

[0139] The performance of the bimetallic composite pipe was sampled and tested, and the test results are shown in Table 1.

[0140] Table 1 Mechanical properties of bimetallic composite pipes

[0141]

[0142] Step SA14: Manual re-inspection;

[0143] There are no visible defects such as cracks, scratches, indentations, or rust on the inner surface of the bimetallic composite pipe.

[0144] Step SA15: Packaging and warehousing;

[0145] After printing and weighing, the bimetallic composite pipes are packaged and stored.

[0146] Example 3

[0147] Preparation of large-diameter bimetallic composite pipes

[0148] The manufactured specifications are 508mm×75mm, with the outer square tube being 508mm×40mm (20G) and the inner round tube being 428mm×35mm (TP304L). The performance meets the technical requirements of 20G high-pressure boiler tubes.

[0149] Step SA1: Prepare the tube blank, using the tube blank preparation steps described above;

[0150] Outer square tube: side length A is 676mm, wall thickness T is 88mm, edge concavity ≤ 0.2% A, outer corner radius R and wall thickness T satisfy R = 3 × T, edge perpendicularity does not exceed 90° ± 0.3°.

[0151] Inner round tube: outer diameter is 490mm, wall thickness is 90mm, the outer diameter of the round tube is 10mm smaller than the minimum inner diameter of the square tube.

[0152] Step SA2: Assembly, using the assembly steps described above;

[0153] The outer square tube and the inner round tube of the assembly tube are axially offset by 5mm.

[0154] Step SA3: Pre-heading, using the pre-heading steps described above;

[0155] The first segment of the first leading module has a width of 235mm and an angle of 28° with the horizontal line. The second segment of the first leading module has a width of 65mm and an angle of 10° with the horizontal line. The third segment of the first leading module has a width of 125.9mm and an angle of 50° with the horizontal line. The first segment of the second leading module has a width of 235mm and an angle of 28° with the horizontal line. The second segment of the second leading module has a width of 65mm and an angle of 10° with the horizontal line. The third segment of the second leading module has a width of 26.5mm and an angle of 80° with the horizontal line.

[0156] Step SA4: Periodic rolling, using the periodic rolling steps described above;

[0157] The roll pass of the periodic tube rolling mill is set to Φ600mm, the starting angle of the forging and rolling section is 30°, the included angle is 84°, and the curve unfolding length is 600mm. The roll speed of the periodic tube rolling mill is controlled at 46rpm and the air pressure is 4bar. The first end of the inner and outer tube preforms has a 125.9mm slope.

[0158] The composite tube blank obtained from the periodic rolling process has an outer diameter of 600 mm and a wall thickness of 150 mm. The first end of the composite tube blank makes an angle of 50° with the horizontal line, and the second end makes an angle of 80° with the horizontal line. The ratio of the wall thickness of the outer square tube to the inner round tube of the composite tube blank is 1:1.03.

[0159] Step SA5: Heating, using the heating steps described above;

[0160] The preheating temperature is less than or equal to 620℃, and the composite tube blank is homogenized at a temperature of 1210℃~1240℃. The sum of the preheating time and the homogenization time is 16h.

[0161] Step SA6: Flush punching, using the flush punching steps described above;

[0162] The total diameter reduction rate of the piercing mill is 16%, the ellipticity is 1.02, and the diameter expansion rate is 5%. The outer diameter of the capillary tube obtained by flush piercing is 630 mm and the wall thickness is 110 mm. In the flat-head and negative-head protrusion piercing processes, the mandrel protrusion is -20 mm, the mandrel nose is on the outlet side of the deformation zone, and the ratio of the mandrel nose diameter to the mandrel diameter is 0.74, which is 20 mm smaller than the inner diameter of the composite tube blank.

[0163] Step SA7: Rolling, using the rolling steps described above;

[0164] The roll pass of the periodic tube rolling mill is designed to be φ520mm. The continuous rolling rolls feature high strength, toughness, and high heat dissipation. The weight percentage of each chemical element in the material is as follows: C 0.60~0.80, Si 0.80~1.00, Mn 0.3~0.5, Cu 0.05~0.15, Ni 0.1~0.2, Cr 4.8~5.8, Mo 0.4~0.7, W 0.2~0.3, V 0.3~0.5, B 0.0025~0.0035, Al 0.08~0.15, Co 0.08~0.15, N 0.012~0.018, with the balance being Fe and unavoidable impurities.

[0165] Step SA8: Straightening and cutting off the head and tail;

[0166] The ends of the sized bimetallic composite pipe are cut off using a gang saw, and the cut ends of the bimetallic composite pipe are straightened using a six-roll straightener to ensure that the curvature is no more than 1.2 mm / m.

[0167] Step SA9: Initial manual inspection;

[0168] The surface quality and dimensional accuracy of the straightened bimetallic composite tube are inspected.

[0169] Step SA10: Heat treatment;

[0170] Solution treatment + normalizing: Solution temperature: 1060℃~1070℃, holding time: 80min; Normalizing temperature: 910℃~930℃, holding time: 100min.

[0171] Step SA11: Non-destructive testing;

[0172] Cracks, folds, scars, and delamination are not allowed on the inner and outer surfaces of bimetallic composite pipes. L2-level ultrasonic testing is performed according to GB / T5777 standards to automatically detect and remove longitudinal and / or transverse defects around the entire circumference of the bimetallic composite pipe, ensuring the internal quality of the composite pipe.

[0173] Step SA12: Physicochemical testing;

[0174] The performance of the bimetallic composite pipe was sampled and tested, and the test results are shown in Table 1.

[0175] Table 1 Mechanical properties of bimetallic composite pipes

[0176]

[0177] Step SA13: Manual re-inspection;

[0178] There are no visible defects such as cracks, scratches, indentations, or rust on the inner surface of the bimetallic composite pipe.

[0179] Step SA14: Packaging and warehousing;

[0180] After printing and weighing, the bimetallic composite pipes are packaged and stored.

[0181] As can be seen from the above description, the above embodiments of the present invention achieve the following technical effects: using the combination of an outer square tube and an inner round tube, after the outer square tube is sleeved on the outer periphery of the inner round tube, the inner walls of the inner round tube and the outer square tube have a nearly tangent portion. In this portion, the gap between the inner round tube and the outer square tube is small, and the inner round tube can contact the outer square tube by moving a short distance radially. Friction can be generated between the two, which can reduce the distance of the inner round tube relative to the outer square tube to a certain extent. When the minimum gap between the inner round tube and the outer square tube is very small, the movement between the inner round tube and the outer square tube can also be avoided.

[0182] Obviously, the embodiments described above are merely some, not all, embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0183] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0184] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a bimetallic composite tube, characterized in that, Includes the following steps: Prepare the tube blanks: take square tubes as the outer square tubes and round tubes as the inner round tubes; Assembly: The outer square tube is fitted around the outer circumference of the inner round tube, the mandrel is inserted into the inner round tube, and the suction tube is inserted into the gap between the R-angle of the outer square tube and the inner round tube to obtain the assembly tube; Pre-heading: The assembly tube is pre-headed to obtain an inner and outer tube preform with a mandrel; Periodic tube rolling: The inner and outer tube blanks are periodically rolled to obtain a composite tube blank; The pre-heading step includes: placing the assembly tube on the heading machine, pressing down the first and second heading modules of the heading machine, then raising the first and second heading modules, rotating the assembly tube by 90°, and pressing down the first and second heading modules again to obtain the inner and outer tube preforms, and performing vacuuming and sealing from the extraction tube.

2. The method for preparing the bimetallic composite tube according to claim 1, characterized in that, The outer diameter of the inner circular tube is 5mm to 10mm smaller than the inner circle diameter of the outer square tube.

3. The method for preparing the bimetallic composite tube according to claim 1, characterized in that, The outer square tube has a side length of A, a side concavity / convexity of ≤0.2%A, an outer corner radius of 1.5 to 3 times the wall thickness, and a side perpendicularity of 90°±0.3°. The outer diameter of the round tube is 5mm to 10mm smaller than the minimum inner diameter of the square tube.

4. The method for preparing the bimetallic composite tube according to claim 1, characterized in that, In the assembly step, the outer square tube and the inner round tube of the assembly tube are axially offset by a distance of 2mm to 5mm.

5. The method for preparing the bimetallic composite tube according to claim 1, characterized in that, In the pre-heading step, the hole shape of both the first and second heading modules consists of three diagonal lines. The sum of the widths of the first and second heading modules is 300mm, and the sum of the widths of the first and second heading modules is also 300mm. The width of the first heading module's first section ranges from 218mm to 235mm, and its angle with the horizontal line is 16.8° to 28°. The width of the second heading module's second section ranges from 65mm to 82mm, and its angle with the horizontal line is... The first heading module has a width range of 28mm to 145mm and an angle of 46° to 52° with the horizontal line. The second heading module has a width range of 218mm to 235mm and an angle of 16.8° to 28° with the horizontal line. The second heading module has a width range of 65mm to 82mm and an angle of 6° to 10° with the horizontal line. The second heading module has a width range of 4mm to 32mm and an angle of 78° to 83° with the horizontal line.

6. The method for preparing the bimetallic composite tube according to claim 1, characterized in that, The outer diameter of the composite tube blank obtained by the periodic rolling is 150mm~600mm, the angle between the first end of the composite tube blank and the horizontal line is 46°~52°, the angle between the second end of the composite tube blank and the horizontal line is 78°~83°, and the ratio of the wall thickness of the outer square tube to the wall thickness of the inner round tube of the composite tube blank is 1:1.25~6:

1.

7. The method for preparing the bimetallic composite tube according to claim 6, characterized in that, The steps of the cyclic tube rolling process include: using a cyclic tube rolling mill to cyclically roll the inner and outer tube preforms to obtain a composite tube preform; setting the pass shape of the cyclic tube rolling mill to φ150mm~φ600mm, the pass shape including a forging section, a finishing section, a final rolling section, and an air rolling section; determining the curve equations of the forging section, the finishing section, the final rolling section, and the air rolling section; the forging section being an envelope curve; the starting angle of the forging section being 27°~30°, the included angle being 74°~84°, and the curve unfolding length being 200mm~600mm; and controlling the roll speed of the cyclic tube rolling mill to 46rpm~72rpm and the air pressure to 3bar~4bar.

8. The method for preparing the bimetallic composite tube according to claim 1, characterized in that, Following the cyclic rolling step, the process further includes a heating step: preheating the composite tube blank at a temperature less than or equal to 620°C, homogenizing the composite tube blank at a temperature of 1210°C to 1240°C, and the sum of the preheating time and the homogenizing time being 2.5h to 16h.

9. The method for preparing the bimetallic composite tube according to claim 8, characterized in that, Following the heating step, the process further includes a piercing step: using a piercing machine to pierce the heated composite tube blank to obtain a capillary tube. The outer square tube and inner round tube sections of the capillary tube are flush. The total diameter reduction rate of the piercing machine is 16%~18%, the ellipticity is 1.02, and the diameter expansion rate is 5%~20%.

10. The method for preparing the bimetallic composite tube according to claim 9, characterized in that, Following the step of end-to-end perforation, a rolling step is also included: rolling the tube to obtain a composite rough tube.

11. The method for preparing the bimetallic composite tube according to claim 10, characterized in that, Following the rolling step, a reheating step is also included: the composite rough tube is reheated in a walking beam furnace, with the furnace temperature below 450°C, the solution strengthening heating temperature of the walking beam furnace being 1000°C ± 10°C, and the holding time being 0.5h to 4h.

12. The method for preparing the bimetallic composite tube according to claim 11, characterized in that, Following the reheating step, a sizing step is also included: the reheated composite rough tube is sizing using a sizing machine and a cooling water ring on the sizing machine to obtain a composite tube; the composite tube is then cooled using a cooling water ring assembly to obtain a bimetallic composite tube. The temperature of the composite rough tube entering the sizing machine is 940℃~980℃, and the temperature of the composite rough tube exiting the sizing machine is 680℃~720℃. When the composite rough tube enters the cooling water ring assembly, the temperature of the cooling water in the cooling water ring assembly is 670℃~710℃, and when the composite rough tube exits the cooling water ring assembly, the temperature of the cooling water in the cooling water ring assembly is 380℃~420℃.

13. A bimetallic composite pipe, characterized in that, It is prepared using the preparation method as described in any one of claims 1 to 12.

Images