Large-diameter thick-wall bimetal composite steel pipe and manufacturing method thereof

Abstract

The large-diameter thick-wall bimetal composite steel pipe comprises a hydraulic oil cylinder, the output end of the hydraulic oil cylinder is fixedly connected with a connecting rod, a baffle is arranged on the surface of the connecting rod, the right side of the baffle communicates with a base pipe, and the base pipe is located on the surface of the connecting rod; and a clamping device is arranged on the right side of the outer side of the base tube. The base pipe and the composite pipe are subjected to heat treatment and then composited, heat treatment is not needed after compositing, adverse effects on interlayer bonding strength caused by different expansion coefficients of different materials in the heat processing or heat treatment process are eliminated, traditional cold sizing / cold diameter expanding is replaced with hot diameter expanding, and the heat treatment efficiency is improved. In this way, the large-caliber thick-wall base pipe can be subjected to inner sizing machining without a large-power sizing / expanding unit, the size precision of the inner circle of the base pipe is improved, spiral grooves are machined in the inner surface of the base pipe at equal intervals, the inner surface is rough, the machining method is simple and reliable, time and labor are saved, and the bonding strength of the base pipe and a composite pipe is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of metal forming and processing, in particular to a large-diameter thick-wall bimetallic composite steel pipe and a manufacturing method thereof. Background Art

[0002] Amidst the current energy transition, compressed air energy storage (CAES) can effectively address the peak-shaving issues of traditional power grids and the curtailment of wind and solar power generation. Abandoned salt caverns are often used as compressed air storage. CAES utilizes redundant electricity from off-peak electricity, curtailed solar power, and wind power generation to drive compressors that compress and store air in underground salt caverns. During peak hours, the high-pressure air is released to drive turbine expanders for power generation, achieving peak-shaving and valley-filling for the power grid. Salt cavern gas storage facilities are connected to surface compressors and turboexpanders via large-diameter steel pipes to transport high-pressure compressed air. Due to the high salt and water content of salt cavern gas storage facilities, the compressed air is rich in Cl-, which increases the corrosion rate of ordinary carbon steel or alloy pipes. Although stainless steel pipes offer excellent corrosion resistance, with the increasing installed capacity of compressed air energy storage systems, the outer diameter of compressed air pipelines has reached φ965-φ1066mm, with wall thicknesses of 50-60mm. These large pipe diameters and thick walls, coupled with long transport distances, make stainless steel pipes several times more expensive than ordinary carbon steel or alloy pipes. The high material cost has made these projects prohibitive, and the industry urgently needs composite pipes that combine corrosion resistance with cost-effectiveness. In the prior art, bimetallic composite pipes are classified into inner-clad composite pipes (i.e., metallurgical composite pipes) and inner-lined composite pipes (i.e., mechanical composite pipes) based on the interface bonding method between the clad layer (composite pipe) and the base layer (substrate pipe). Inner-clad composite pipes refer to pipes in which the clad layer is composited onto a base pipe or substrate through processes such as hot rolling, surfacing welding, powder metallurgy, laser cladding, or explosive composite. The clad layer and the base layer achieve metallurgical bonding, resulting in high interface bonding strength. However, the process is complex, the production cost is high, and the production efficiency is low, making them unsuitable for long-distance pipeline steel pipes. Lined composite pipe refers to a composite pipe that achieves a mechanical interference fit with the base pipe through mechanical expansion, mechanical reduction (drawing), mechanical spinning, hydraulic expansion, and explosive expansion. This production process is relatively simple and has high production efficiency, but the interfacial bonding strength between the composite pipe and the base pipe is low, and the presence of gas between the layers can cause the composite pipe to become unstable or blister. In addition, the two metals have different thermal expansion coefficients, and the thermal expansion and contraction caused by temperature changes during subsequent hot processing or use will weaken the interfacial bonding strength.

[0003] According to the patents published on the China Patent Network, the patent name is: A method for manufacturing a metal composite seamless pipe, and the patent application number is: CN119303992A; the following improvements are adopted: (1) a strip-shaped boss is machined on the inner surface of the outer tube blank, and a groove is machined on the outer surface of the inner tube blank; (2) the inner tube and the outer tube are preliminarily mechanically composited by cold rolling or cold drawing after being sleeved; (3) metallurgical composite and further mechanical composite are achieved by medium frequency thermal expansion; (4) the desired finished product specifications are achieved by further cold rolling or cold drawing; Although the above method can improve the interface bonding strength, for large quantities of pipeline steel pipes, processing bosses on the outer layer pipe and grooves on the inner layer pipe is not only time-consuming and labor-intensive, but also wastes a lot of materials. Although the outer and inner layer pipes have undergone a series of complex mechanical composite processes such as diameter reduction and diameter expansion, they have not undergone heat treatment. The thermal expansion and contraction effects of the subsequent heat treatment process will weaken the interlayer interface bonding strength. Therefore, there is an urgent need for economical and efficient large-diameter thick-walled bimetallic composite pipes for salt cavern compressed air energy storage systems. Summary of the Invention

[0004] In order to solve the problems raised in the above background technology, the purpose of the present invention is to provide a large-diameter thick-walled bimetallic composite steel pipe and its manufacturing method, which has the advantages of low production cost, no waste of materials, and no need for heat treatment, solving the problems of time-consuming, labor-intensive, wasteful, and material-wasting, and requiring heat treatment.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solutions: a large-diameter thick-walled bimetallic composite steel pipe and a manufacturing method thereof, comprising a hydraulic cylinder, wherein the output end of the hydraulic cylinder is fixedly connected to a connecting rod, a baffle is provided on the surface of the connecting rod, and a base pipe is connected to the right side of the baffle. The base pipe is located on the surface of the connecting rod, a clamping device is provided on the right side of the outer side of the base pipe, a conical connecting block is provided on the right side of the inner cavity of the base pipe, and a composite pipe is connected to the right side of the conical connecting block.

[0006] As a preferred embodiment of the present invention, the base tube is manufactured by: Step 1: Heat the continuous casting billet to 1220℃~1300℃ in a ring heating furnace and keep it warm for 200~400min. The holding time increases by 50~55min for every 100mm increase in the diameter of the continuous casting billet. Step 2: The heated continuous casting billet is then pierced, secondarily cross-rolled, and sized using a two-roll cross-rolling mill to obtain a base tube blank. The rolling ratio is ensured to be greater than 3, the outer diameter deviation after sizing is less than ±0.8%, the wall thickness deviation is ±12.5%, the wall thickness unevenness is less than 20%, and the full-length straightness is less than 0.05%. Step 3: Select a high-precision expansion mandrel to ensure that the outer diameter deviation of the sizing section, flattening section, and straightening section of the mandrel is less than ±0.1mm. Use internal shot blasting to remove debris and oxide scale on the inner wall of the base tube capillary, and then evenly apply lubricant for hot expansion. Use a medium-frequency induction coil to heat the base tube capillary and then perform hot expansion. Due to the large wall thickness of the base tube capillary, the cold sizing or cold expansion method requires a high level of cold processing equipment capacity and a large equipment investment. Therefore, this solution prefers hot expansion. Step 4: The expansion ratio of the thermal expansion process is 1.03~1.05. The main purpose is to improve the inner diameter accuracy of the base tube capillary. After the thermal expansion process, the inner diameter deviation of the base tube capillary is less than ±0.2mm; Step 5: The heating temperature for the expansion process is determined based on the lower critical temperature Ac1 of the base tube material: T = (Ac1-50) ~ (Ac1-20), and is adjusted appropriately based on the wall thickness of the base tube capillary. Step 6: During the thermal expansion process, consider the effect of the different linear expansion of the core rod material and the base tube material at the expansion temperature (thermal expansion difference ∆D); Step 7: Heat treat the substrate capillary tube according to the qualified heat treatment process, and take samples of the heat-treated substrate tube for physical and chemical performance tests. The test results should meet the requirements of relevant standards and technical agreements; Step 8: Straighten the heat-treated substrate tube to a straightness of less than 1 mm / m and a straightness of less than 5 mm / m along the entire length of the substrate tube; Step 9: Shot blast the outer surface of the base tube to a level not lower than Sa2 specified in GB / T8923.1-2011; machine the inner surface with a 16-mesh or 18-mesh cubic boron nitride or diamond heavy-duty grinding wheel. The grinding wheel thickness is 10-30mm, and the edges of the grinding wheel are smoothed and rounded. Adjust the rotation speed of the base tube and the feed speed of the grinding wheel to machine equally spaced spiral grooves on the inner surface of the base tube. The groove depth is 0.10-0.15mm, the groove width is 10-30mm, the groove bottom angle is smoothly rounded, and the spacing between adjacent grooves is twice the groove width. The surface roughness after machining is Ra25-Ra50. Step 10: Use fully automatic ultrasonic and eddy current combined automatic testing equipment to perform 100% ultrasonic testing, eddy current testing and automatic thickness measurement on the base pipe. The acceptance level of ultrasonic testing is Level I specified in NB / T47013.3-2015, and the acceptance level of eddy current testing is Level B specified in GB / T7735-2004. The wall thickness of the base pipe is not allowed to be less than the minimum design wall thickness.

[0007] As a preferred embodiment of the present invention, the method for making the composite tube is: Step 1: First, the composite pipe is made of stainless steel cold-rolled seamless pipe or stainless steel straight seam welded pipe. The straight weld of the welded pipe should be polished and smoothed. The composite pipe is subjected to solid solution treatment according to the qualified heat treatment process to obtain pitting corrosion resistance and comprehensive mechanical properties. During the solid solution treatment, a supporting device is used to support and fix the inner surface of the composite pipe to prevent the composite pipe from losing roundness and deformation during the solid solution treatment process. Step 2: Then straighten the composite tube after solution treatment to make the straightness less than 1mm / m, the straightness of the entire length of the base tube less than 5mm / m, and the outer diameter deviation of the composite tube less than ±0.3mm; Step 3: Then the inner and outer surfaces of the composite tube are shot blasted, and dimensional inspection, ultrasonic inspection, eddy current inspection and automatic thickness measurement are carried out. The acceptance level of ultrasonic inspection is Level I specified in NB / T47013.3-2015, and the acceptance level of eddy current inspection is Level B specified in GB / T7735-2004. The wall thickness of the composite tube is 3~6mm, and the outer diameter of the composite tube is 4~6mm smaller than the inner diameter of the base tube.

[0008] As a preferred embodiment of the present invention, the composite method of the base tube and the composite tube is: Step 1: Process a 45° to 60° outer bevel on one end of the composite pipe, and evenly apply a layer of stainless steel pipe cold drawing lubricant on the inner surface of the composite pipe. The lubricant is based on refined mineral oil and contains functional additives that do not contain sulfur or chlorine. It can improve the lubrication performance, cooling performance and extreme pressure and anti-wear performance during the cold working of the composite pipe, and will not pollute the environment after cleaning; Step 2: Fix the base pipe on the composite pipe sleeve drawing device, and pass the connecting rod through the composite pipe. One end of the connecting rod is connected to the end of the composite pipe through a tapered connecting block, and the other end is connected to the hydraulic cylinder. Driven by the hydraulic cylinder, the connecting rod drags the composite pipe into the base pipe. When the composite pipe is flush with the base pipe, the tapered die is separated from the composite pipe. The sleeve drawing device can make the outer diameter of the composite pipe as close to the inner diameter of the base pipe as possible. Even if the base pipe and the composite pipe have dimensional deviations such as straightness and ovality, the composite pipe and the base pipe can be easily sleeved, and the phenomenon of instability caused by the small wall thickness of the composite pipe when the composite pipe is pushed into the base pipe is avoided. Step 3: Align the drawing starting ends of the composite tube and the base tube, with a radial gap of 2.0-3.0 mm between the composite tube and the base tube. Fix the composite tube and the base tube by spot welding at the drawing starting end. Select a suitable first tapered drawing inner die according to the inner diameter of the composite tube. The small end diameter of the first tapered drawing inner die is: d1 = Di composite - (6.0-10.0) mm, where Di composite is the inner diameter of the composite tube, that is, the small end diameter of the drawing inner die is 6.0-10.0 mm smaller than the inner diameter of the composite tube; the large end diameter of the first tapered drawing inner die is: d2 = Di base - 2*t composite + (0.6-1.0) mm, where Di base is the inner diameter of the base tube and t composite is the wall thickness of the composite tube. The cone angle of the tapered section (deformation section) of the first tapered drawing inner die is 8°-10°, and the length of the sizing section is 40-60 mm. Step 4: The connecting rod is connected to the first tapered drawing inner die. Under the action of the hydraulic cylinder, the connecting rod drives the first tapered drawing inner die to pass through the composite tube, causing the composite tube to undergo plastic deformation and adhere closely to the inner wall of the base tube. A wall reduction of 0.3 to 0.5 mm is generated, eliminating the radial gap between the composite tube and the base tube to obtain a composite tube. The composite tube has a smaller wall thickness. A smaller wall reduction is used during the composite process to prevent the composite tube from cracking due to excessive force. Step 5: Flush the two ends of the composite pipe and fix the composite pipe to the base pipe by spot welding at both ends. Shot blast the inner surface of the composite pipe to clean the lubricant and other impurities on the inner surface. Then, evenly apply a layer of stainless steel pipe cold drawing special lubricant on the inner surface of the pipe. Step 6: Select a suitable second tapered drawing inner die and perform a second drawing on the primary composite tube. The cone angle of the tapered section (deformation section) of the first tapered drawing inner die is 4° to 6°, and the length of the sizing section is 40 to 60 mm. The second drawing process reduces the wall thickness of the composite tube by 0.3 to 0.4 mm, causing plastic deformation of the composite tube, so that the metal on the outer surface of the composite tube is embedded in the spiral groove on the inner surface of the base tube, forming a secondary composite tube. Step 7: Seal the ends of the secondary composite steel pipes and then perform radiographic testing on the welds in accordance with NB / T47013.2-2015 "Non-destructive testing of pressure equipment - Part 2: Radiographic testing" or NB / T47013.11-2023 "Non-destructive testing of pressure equipment - Part 11: Radiographic digital imaging testing". The image quality level should reach AB level, and the acceptance quality level should be II. Clean the inner surface of the secondary composite pipe to obtain the final product. Step 8: Take samples from the product and conduct performance tests according to the provisions of Sections 6.6 and 6.7 of GB / T31940-2015 "Bimetallic Composite Corrosion-Resistant Steel Pipe for Fluid Transportation", and conduct bonding strength tests according to the requirements of b) in 6.8.2.2.

[0009] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention performs heat treatment on the base pipe and the composite pipe respectively before composite. No heat treatment is required after composite, thereby eliminating the adverse effect of different expansion coefficients of different materials on the interlayer bonding strength during heat processing or heat treatment. Hot expansion is used instead of traditional cold sizing / cold expansion. In this way, the large-diameter thick-walled base pipe can be internally sized without a high-power sizing / expansion unit, thereby improving the dimensional accuracy of the inner circle of the base pipe. Spiral grooves with equal spacing are machined on the inner surface of the base pipe, and the inner surface is relatively rough. The processing method is simple and reliable, saving time and labor, and is conducive to improving the bonding strength with the composite pipe. The composite pipe is pulled into the base pipe by a sleeve drawing device, and can be sleeved when the radial gap between the composite pipe and the base pipe is small. It is fast and efficient and can avoid This method eliminates the problem of jamming or unstable deformation of the composite tube when it is manually or mechanically pushed into the base tube. By utilizing the thick wall, good rigidity, and high yield strength of the base tube, as well as the low yield strength of the composite tube, the traditional cold drawing method is changed. During the drawing process, the composite tube is fixed, and the tapered drawing inner die is driven by the hydraulic cylinder and connecting rod to pass through the composite tube, causing the composite tube to undergo plastic deformation first, while the base tube has not yet reached the conditions for plastic deformation. In this way, the composite tube clings to the inner wall of the base tube after plastic deformation. This eliminates the need for the outer die used in traditional cold drawing methods, allowing composite tubes of larger diameters to be processed. In addition, during traditional cold drawing, the hydraulic clamping device clamps the outer surface of the base tube, and the clamping end must be cut off due to the deep claw grooves left, resulting in material waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a structural schematic diagram of the present invention.

[0011] In the figure: 1. Hydraulic cylinder; 2. Connecting rod; 3. Baffle; 4. Base pipe; 5. Clamping device; 6. Conical connecting block; 7. Composite pipe. DETAILED DESCRIPTION

[0012] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0013] Example 1 The present invention provides a large-diameter, thick-walled bimetallic composite steel pipe and a manufacturing method thereof, comprising a hydraulic cylinder 1, wherein the output end of the hydraulic cylinder 1 is fixedly connected to a connecting rod 2, a baffle 3 is provided on the surface of the connecting rod 2, a base pipe 4 is connected to the right side of the baffle 3, the base pipe 4 is located on the surface of the connecting rod 2, a clamping device 5 is provided on the right side of the outer side of the base pipe 4, a tapered connecting block 6 is provided on the right side of the inner cavity of the base pipe 4, and a composite pipe 7 is connected to the right side of the tapered connecting block 6.

[0014] The present invention is further configured as follows: the manufacturing method of the base tube 4 is: Step 1: Heat the continuous casting billet to 1220℃~1300℃ in a ring heating furnace and keep it warm for 200~400min. The holding time increases by 50~55min for every 100mm increase in the diameter of the continuous casting billet. Step 2: The heated continuous casting billet is then pierced, secondarily cross-rolled, and sized using a two-roll cross-rolling mill to obtain a base tube 4 capillary tube, ensuring that the rolling ratio is greater than 3, the outer diameter deviation after sizing is less than ±0.8%, the wall thickness deviation is ±12.5%, the wall thickness unevenness is less than 20%, and the full-length straightness is less than 0.05%; Step 3: Select a high-precision expansion mandrel to ensure that the outer diameter deviation of the sizing section, flattening section, and straightening section of the mandrel is less than ±0.1mm. Use internal shot blasting to remove debris and oxide scale on the inner wall of the base tube 4 capillary tube, and then evenly apply lubricant for hot expansion. Use a medium-frequency induction coil to heat the base tube 4 capillary tube and then perform hot expansion processing. Due to the large wall thickness of the base tube 4 capillary tube, the cold sizing or cold expansion method requires high capacity of the cold processing equipment and large equipment investment. Therefore, this solution prefers the hot expansion method; Step 4: The expansion ratio of the thermal expansion process is 1.03-1.05. The main purpose is to improve the inner diameter accuracy of the base tube 4 capillary tube. After the thermal expansion process, the inner diameter deviation of the base tube 4 capillary tube is less than ±0.2mm. Step 5: The heating temperature for the diameter expansion process is determined based on the lower critical temperature Ac1 of the substrate 4 material: T = (Ac1-50) ~ (Ac1-20), and is appropriately adjusted based on the wall thickness of the substrate 4 capillary tube; Step 6: During the thermal expansion process, the influence of the different linear expansion amounts of the core rod material and the base tube 4 material at the expansion processing temperature (thermal expansion difference ∆D) is considered; Step 7: Heat-treat the substrate tube 4 capillary according to the qualified heat treatment process, and take samples of the heat-treated substrate tube 4 for physical and chemical property tests. The test results should meet the requirements of relevant standards and technical agreements; Step 8: Straighten the heat-treated substrate tube 4 to a straightness of less than 1 mm / m and a straightness of less than 5 mm / m along the entire length of the substrate tube 4; Step 9: Shot blast the outer surface of the base tube 4 to a level not lower than Sa2 specified in GB / T8923.1-2011; machine the inner surface with a 16-mesh or 18-mesh cubic boron nitride or diamond heavy-duty grinding wheel. The grinding wheel has a thickness of 10-30 mm, and the edges of the grinding wheel are smoothed and rounded. The rotation speed of the base tube 4 and the feed speed of the grinding wheel are adjusted to form equally spaced spiral grooves on the inner surface of the base tube 4. The groove depth is 0.10-0.15 mm, the groove width is 10-30 mm, the groove bottom angle is smoothly rounded, and the spacing between adjacent grooves is twice the groove width. The surface roughness after machining is Ra25-Ra50. Step 10: Use fully automatic ultrasonic and eddy current combined automatic testing equipment to perform 100% ultrasonic testing, eddy current testing and automatic thickness measurement on the base pipe 4. The acceptance level of ultrasonic testing is Level I specified in NB / T47013.3-2015, and the acceptance level of eddy current testing is Level B specified in GB / T7735-2004. The wall thickness of the base pipe 4 is not allowed to be less than the minimum design wall thickness.

[0015] The present invention is further configured as follows: the manufacturing method of the composite tube 7 is: Step 1: First, the composite tube 7 is made of stainless steel cold-rolled seamless tube or stainless steel straight seam welded tube, and the straight weld of the welded tube should be polished and smoothed; the composite tube 7 is subjected to solid solution treatment according to a qualified heat treatment process to obtain pitting corrosion resistance and comprehensive mechanical properties. During the solid solution treatment, a supporting device is used to support and fix the inner surface of the composite tube 7 to prevent the composite tube 7 from losing roundness and deformation during the solid solution treatment process; Step 2: Then straighten the composite tube 7 after the solid solution treatment to make the straightness less than 1 mm / m, the straightness of the entire length of the base tube 4 less than 5 mm / m, and the outer diameter deviation of the composite tube 7 less than ±0.3 mm; Step 3: Then, the inner and outer surfaces of the composite tube 7 are shot blasted, and dimensional inspection, ultrasonic inspection, eddy current inspection, and automatic thickness measurement are performed. The acceptance level of the ultrasonic inspection is Class I specified in NB / T47013.3-2015, and the acceptance level of the eddy current inspection is Class B specified in GB / T7735-2004. The wall thickness of the composite tube 7 is 3-6 mm, and the outer diameter of the composite tube 7 is 4-6 mm smaller than the inner diameter of the base tube 4.

[0016] The present invention is further configured as follows: the composite method of the base tube 4 and the composite tube 7 is: Step 1: Process a 45° to 60° outer bevel at one end of the composite tube 7, and evenly apply a layer of stainless steel tube cold drawing lubricant on the inner surface of the composite tube 7. The lubricant is based on refined mineral oil and contains functional additives that do not contain sulfur or chlorine. It can improve the lubrication performance, cooling performance, and extreme pressure and anti-wear performance of the composite tube 7 during the cold working process, and will not pollute the environment after cleaning. Step 2: Fix the base pipe 4 on the composite pipe sleeve drawing device, and the connecting rod 2 passes through the composite pipe 7. One end of the connecting rod 2 is connected to the end of the composite pipe 7 through the tapered connecting block 6, and the other end is connected to the hydraulic cylinder 1. Driven by the hydraulic cylinder 1, the connecting rod 2 drags the composite pipe 7 into the base pipe 4. When the composite pipe 7 is flush with the base pipe 4, the tapered die is separated from the composite pipe 7. The sleeve drawing device can make the outer diameter of the composite pipe 7 as close to the inner diameter of the base pipe 4 as possible. Even if the base pipe and the composite pipe 7 have dimensional deviations such as straightness and ovality, the composite pipe 7 can be easily sleeved with the base pipe 4, and avoid the phenomenon of instability caused by the small wall thickness of the composite pipe 7 when the composite pipe 7 is pushed into the base pipe 4. Step 3: Align the composite tube 7 with the drawing starting end of the base tube 4, with a radial gap of 2.0-3.0 mm between the composite tube 7 and the base tube 4. Fix the composite tube 7 to the base tube 4 by spot welding at the drawing starting end. Select a suitable first tapered drawing inner die according to the inner diameter of the composite tube 7. The small end diameter of the first tapered drawing inner die is: d1 = Di composite - (6.0-10.0) mm, where Di composite is the inner diameter of the composite tube 7, that is, the small end diameter of the drawing inner die is 6.0-10.0 mm smaller than the inner diameter of the composite tube 7; the large end diameter of the first tapered drawing inner die is: d2 = Di base - 2*t composite + (0.6-1.0) mm, where Di base is the inner diameter of the base tube 4 and t composite is the wall thickness of the composite tube 7. The cone angle of the tapered section (deformation section) of the first tapered drawing inner die is 8°-10°, and the length of the sizing section is 40-60 mm. Step 4: The connecting rod 2 is connected to the first tapered drawing inner die. Under the action of the hydraulic cylinder 1, the connecting rod 2 drives the first tapered drawing inner die through the composite tube 7, causing the composite tube 7 to undergo plastic deformation and adhere closely to the inner wall of the base tube 4. A wall reduction of 0.3 to 0.5 mm is generated, eliminating the radial gap between the composite tube 7 and the base tube 4, thereby obtaining a composite tube. The composite tube 7 has a relatively small wall thickness. A relatively small wall reduction is used during the composite process to prevent the composite tube 7 from cracking due to excessive force. Step 5: Flush the two ends of the composite pipe, and fix the composite pipe 7 to the base pipe 4 at both ends by spot welding. Shot blast the inner surface of the composite pipe, clean the lubricant and other impurities on the inner surface, and then evenly apply a layer of stainless steel pipe cold drawing special lubricant on the inner surface of the pipe; Step 6: Select a suitable second tapered drawing inner die and perform a second drawing on the primary composite tube. The taper angle of the tapered section (deformation section) of the first tapered drawing inner die is 4° to 6°, and the length of the sizing section is 40 to 60 mm. The second drawing process reduces the wall thickness of the composite tube 7 by 0.3 to 0.4 mm, causing plastic deformation of the composite tube 7. The metal on the outer surface of the composite tube 7 is embedded in the spiral groove on the inner surface of the base tube 4, forming a secondary composite tube. Step 7: Seal the ends of the secondary composite steel pipes and then perform radiographic testing on the welds in accordance with NB / T47013.2-2015 "Non-destructive testing of pressure equipment - Part 2: Radiographic testing" or NB / T47013.11-2023 "Non-destructive testing of pressure equipment - Part 11: Radiographic digital imaging testing". The image quality level should reach AB level, and the acceptance quality level should be II. Clean the inner surface of the secondary composite pipe to obtain the final product. Step 8: Take samples from the product and conduct performance tests according to the provisions of Sections 6.6 and 6.7 of GB / T31940-2015 "Bimetallic Composite Corrosion-Resistant Steel Pipe for Fluid Transportation", and conduct bonding strength tests according to the requirements of b) in 6.8.2.2.

[0017] Example 2 The present invention provides a large-diameter, thick-walled bimetallic composite steel pipe and a manufacturing method thereof, comprising a hydraulic cylinder 1, wherein the output end of the hydraulic cylinder 1 is fixedly connected to a connecting rod 2, a baffle 3 is provided on the surface of the connecting rod 2, a base pipe 4 is connected to the right side of the baffle 3, the base pipe 4 is located on the surface of the connecting rod 2, a clamping device 5 is provided on the right side of the outer side of the base pipe 4, a tapered connecting block 6 is provided on the right side of the inner cavity of the base pipe 4, and a composite pipe 7 is connected to the right side of the tapered connecting block 6.

[0018] The present invention is further configured as follows: the manufacturing method of the base tube 4 is: Step 1: The base pipe 4 is made of L555Q steel, and the manufacturing standard is GB / T9711-2017 "Steel pipes for pipeline transportation systems in the petroleum and natural gas industry". 900mm continuous casting billets are smelted, and the chemical composition and non-metallic inclusions meet the requirements of L555Q in GB / T9711-2017 standard; Step 2: The continuous casting billet is heated to 1240℃~1250℃ in a ring heating furnace and kept warm for 300min; Step 3: The heated continuous casting billet is pierced, secondarily cross-rolled, and sized using a two-roll cross-rolling mill to obtain a φ980×56mm base tube and a 4-tube blank. The rolling ratio is 3.91, and the outer diameter deviation after sizing is less than ±0.8%, the wall thickness deviation is ±10%, the wall thickness unevenness is less than 15%, and the full-length straightness is less than 0.05%. Step 4: Use internal shot blasting to remove debris and oxide scale on the inner wall of the base tube 4 capillary tube, and then evenly apply lubricant for thermal expansion; Step 5: The lower critical temperature Ac1 of L555Q is 725°C. Considering the thick wall of the capillary tube of substrate tube 4, the medium frequency induction heating temperature is determined to be 700°C. Step 6: The core rod is made of 07Cr19Ni11Ti, which has a total expansion of 13.1 mm / m at 700°C. The total expansion of L555Q at 700°C is 10.3 mm / m. After thermal expansion, the inner diameter of the base tube 4 is 905 mm. The difference in expansion between the base tube 4 material and the core rod material at 700°C is ∆D = -2.5 mm. Step 7: Select a high-precision expansion mandrel with an outer diameter of 902.5 ± 0.1 mm at the sizing section. Use a medium-frequency induction coil to heat the substrate tube 4 capillary and then perform thermal expansion. The expansion ratio is 1.037. After thermal expansion, the substrate tube 4 has a specification of φ1016 × 55.2 mm, and the inner diameter deviation of the substrate tube 4 is less than ±0.2 mm. Step 8: Heat the substrate tube 4 to 930°C in a quenching furnace, keep it at this temperature for 60 minutes, then remove it from the furnace and cool it with water. Then, heat the substrate tube 4 to 650°C in a tempering furnace, keep it at this temperature for 60 minutes, then remove it from the furnace and cool it with air. Step 9: Straighten the heat-treated substrate tube 4 to a straightness of less than 1 mm / m and a straightness of less than 5 mm / m along the entire length of the substrate tube 4; Step 10: Shot blast the outer surface of the base tube 4 to a level not lower than Sa2 specified in GB / T8923.1-2011; machine the inner surface of the base tube 4 using a 16-mesh cubic boron nitride or diamond heavy-duty grinding wheel. The grinding wheel has a thickness of 16 mm, and the edges of the grinding wheel are smoothed and rounded. The rotation speed of the base tube 4 is adjusted to 6 rpm, and the feed speed of the grinding wheel is adjusted to 1.6 mm / s. Equally spaced spiral grooves are machined on the inner surface of the base tube 4. The groove depth is 0.10-0.15 mm, the groove width is 16 mm, the groove bottom angle is smoothly rounded, and the spacing between adjacent grooves is twice the groove width. The surface roughness after machining is Ra25-Ra50. The specifications of the base tube 4 after machining are φ1016×55 mm. Step 11: The fully automatic ultrasonic and eddy current combined automatic testing equipment performs 100% ultrasonic testing, eddy current testing, and automatic thickness measurement on the base pipe 4. The acceptance level of the ultrasonic testing is Level I specified in NB / T47013.3-2015, and the acceptance level of the eddy current testing is Level B specified in GB / T7735-2004. The wall thickness of the base pipe 4 is not allowed to be less than the minimum design wall thickness; Step 12: The longitudinal tensile properties of the base tube 4 are shown in Table 1: Table 1 Longitudinal tensile test of base pipe 4

[0019] The present invention is further configured as follows: the manufacturing method of the composite tube 7 is: Step 1: The material of the composite pipe 7 is 022Cr17Ni12Mo2, and the manufacturing standard is GB / T12771-2019 "Stainless Steel Welded Steel Pipe for Fluid Transportation". The composite pipe 7 adopts austenitic stainless steel straight seam welded pipe. The specification of the composite pipe 7 is: φ900×5mm. The outer diameter of the composite pipe 7 is 5.0mm smaller than the inner diameter of the base pipe 4. The straight weld of the welded pipe is polished and smooth. Step 2: Use a supporting device to support the inner wall of the composite tube 7, then perform a solid solution treatment, heat to 1060℃±5℃ and keep warm for 30min, and then put it into water for rapid cooling after taking it out of the furnace; Step 3: Straighten the composite tube 7 after solution treatment to ensure that the straightness is less than 1 mm / m, the straightness of the entire length is less than 3 mm / m, and the outer diameter deviation of the composite tube 7 is less than ±0.3 mm; Step 4: Shot blasting is performed on the inner and outer surfaces of the composite tube 7, and dimensional inspection, ultrasonic inspection, eddy current inspection, and automatic thickness measurement are performed. The acceptance level of the ultrasonic inspection is Class I specified in NB / T47013.3-2015, and the acceptance level of the eddy current inspection is Class B specified in GB / T7735-2004. Step 5: The longitudinal tensile properties of the composite tube 7 are shown in Table 2: Table 2 Test results

[0020] The present invention is further configured as follows: the composite method of the base tube 4 and the composite tube 7 is: Step 1: Process a 50° outer bevel at one end of the composite tube 7, evenly apply a layer of stainless steel tube cold drawing lubricant on the inner surface of the composite tube 7, fix the base tube on the composite tube sleeve drawing device, pass the connecting rod 2 through the composite tube 7, and connect one end of the connecting rod 2 to the bevel end of the composite tube 7 through the tapered connecting block 6. The other end of the connecting rod 2 is connected to the hydraulic cylinder 1. Driven by the hydraulic cylinder 1, the connecting rod 2 drags the composite tube 7 into the base tube 4. When the composite tube 7 is flush with the base tube 4, separate the tapered connecting block 6 from the composite tube 7. Step 2: Align the composite tube 7 with the drawing starting end of the base tube 4, with a radial gap of 3 mm between the composite tube 7 and the base tube 4. Fix the composite tube 7 to the base tube 4 by spot welding at the drawing starting end. The inner diameter of the composite tube 7 is Di composite = 890 mm. Select a suitable first tapered inner drawing die according to the inner diameter of the composite tube 7. The small end diameter of the first tapered inner drawing die is: d1 = Di composite - 8 = 890 - 8 = 882 mm, that is, the small end diameter of the drawing inner die is 8.0 mm smaller than the inner diameter of the composite tube 7; the large end diameter of the first tapered inner drawing die is: d2 = D base - 2*t composite + 0.6 = 906 - 2*5 + 0.6 = 896.6 mm, where Di base is the inner diameter of the base tube 4 = 906 mm, and t composite is the wall thickness of the composite tube 7 = 5 mm. The cone angle of the tapered section (deformation section) of the first tapered inner drawing die is 9°, and the length of the sizing section is 50 mm. Step 3: The tensile performance test data in Tables 1 and 2 show that the yield strength of the composite tube 7 is much lower than that of the base tube 4. By utilizing the fact that the composite tube 7 yields first, the composite tube 7 can be tightly fitted to the base tube 4 simply by the expansion effect of the inner mold. Step 4: Connecting rod 2 is connected to the first tapered inner drawing die. Under the action of hydraulic cylinder 1, connecting rod 2 drives the tapered inner drawing die through composite tube 7, causing composite tube 7 to undergo plastic deformation and adhere closely to the inner wall of base tube 4. A wall reduction of 0.3 mm is generated, eliminating the radial gap between composite tube 7 and base tube 4, and obtaining a primary composite tube. Step 5: Flush the two ends of the composite pipe, and fix the composite pipe 7 to the base pipe 4 at both ends by spot welding. Shot blast the inner surface of the composite pipe, clean the lubricant and other impurities on the inner surface, and then evenly apply a layer of stainless steel pipe cold drawing special lubricant on the inner surface of the pipe; Step 6: Select a suitable second tapered drawing inner die and perform a second drawing on the primary composite tube. The inner diameter of the primary composite tube is 896.6 mm. The small end diameter of the second tapered drawing inner die is 888 mm, and the large end diameter is 897.2 mm. The cone angle of the tapered section (deformation section) of the second tapered drawing inner die is 6°, and the length of the sizing section is 50 mm. The second drawing process reduces the wall thickness of the composite tube 7 by 0.3 mm, causing plastic deformation of the composite tube 7. The metal on the outer surface of the composite tube 7 is embedded in the spiral groove on the inner surface of the base tube 4, forming a secondary composite tube. The specification of the secondary composite tube is φ1016×59.4 mm. Step 7: seal the ends of the secondary composite steel pipes, and then perform radiographic testing on the welds in accordance with NB / T47013.2-2015 "Non-destructive testing of pressure equipment - Part 2: Radiographic testing" or NB / T47013.11-2023 "Non-destructive testing of pressure equipment - Part 11: Radiographic digital imaging testing". The image quality level should reach AB level, and the acceptance quality level is level II. Clean the inner surface of the secondary composite pipe to obtain the final product. The product specifications are as follows; Step 8: Samples were taken from the product and performance tests were conducted according to Sections 6.6 and 6.7 of GB / T31940-2015 "Bimetallic Composite Corrosion-Resistant Steel Pipes for Fluid Transportation". A bonding strength test was conducted according to the requirements of Section b) of 6.8.2.2. The measured bonding strength between the composite pipe 7 and the base pipe 4 was 23.2 MPa.

[0021] Comparative Example The remaining steps were the same as those in the example except that in the tenth step of manufacturing the base tube 4, shot blasting was performed on the inner surface instead of processing the spiral grooves. A bonding strength test was conducted according to the requirements of 6.8.2.2 b). The measured bonding strength between the composite tube 7 and the base tube 4 was 18.9 MPa. This shows that processing the spiral grooves on the inner surface of the base tube 4 can effectively improve the bonding strength by 22.7%.

[0022] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0023] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A large-diameter, thick-walled bimetallic composite steel pipe, comprising a hydraulic cylinder (1), characterized in that: The output end of the hydraulic cylinder (1) is fixedly connected to a connecting rod (2), a baffle (3) is provided on the surface of the connecting rod (2), the right side of the baffle (3) is connected to a base pipe (4), the base pipe (4) is located on the surface of the connecting rod (2), a clamping device (5) is provided on the right side of the outer side of the base pipe (4), a conical connecting block (6) is provided on the right side of the inner cavity of the base pipe (4), and the right side of the conical connecting block (6) is connected to a composite pipe (7).

2. The method for manufacturing a large-diameter, thick-walled bimetallic composite steel pipe according to claim 1, characterized in that: The manufacturing method of the base tube (4) is: Step 1: Heat the continuous casting billet to 1220℃~1300℃ in a ring heating furnace and keep it warm for 200~400min. The holding time increases by 50~55min for every 100mm increase in the diameter of the continuous casting billet. Step 2: Then, the heated continuous casting billet is perforated, secondarily cross-rolled and sized by a two-roll cross-rolling mill to obtain a base tube (4) rough tube, ensuring that the rolling ratio is greater than 3, the outer diameter deviation after sizing is less than ±0.8%, the wall thickness deviation is ±12.5%, the wall thickness unevenness is less than 20%, and the full-length straightness is less than 0.05%; Step 3: Select a high-precision expansion mandrel to make the outer diameter deviation of the sizing section, flattening section and straightening section of the mandrel less than ±0.1mm, use internal shot blasting to remove debris and oxide scale on the inner wall of the base tube (4) capillary tube, and evenly apply lubricant for hot expansion, use a medium-frequency induction coil to heat the base tube (4) capillary tube and then perform hot expansion processing. Because the wall thickness of the base tube (4) capillary tube is relatively large, the cold sizing or cold expansion method requires a high capacity of the cold processing equipment and a large equipment investment. Therefore, this scheme preferably uses the hot expansion method; Step 4: The expansion ratio of the thermal expansion process is 1.03-1.05, and the main purpose is to improve the inner diameter accuracy of the base tube (4) capillary tube. After the thermal expansion process, the inner diameter deviation of the base tube (4) capillary tube is less than ±0.2 mm; Step 5: The heating temperature for the diameter expansion process is determined according to the lower critical temperature Ac1 of the base tube (4) material: T = (Ac1-50) ~ (Ac1-20), and is appropriately adjusted according to the wall thickness of the base tube (4); Step 6: During the thermal expansion process, the influence of the different linear expansion amounts (thermal expansion difference ∆D) of the core rod material and the base tube (4) material at the expansion temperature is considered; Step 7: heat-treating the capillary tube of the base tube (4) according to the qualified heat treatment process, sampling the base tube (4) after the heat treatment and conducting physical and chemical property tests. The test results should meet the requirements of relevant standards and technical agreements; Step eight: straightening the heat-treated base tube (4) to a straightness of less than 1 mm / m and a straightness of less than 5 mm / m along the entire length of the base tube (4); Step 9: Shot blast the outer surface of the base tube (4), and the treatment grade shall not be lower than Sa2 grade specified in GB / T8923.1-2011; the inner surface shall be machined with a 16-mesh or 18-mesh cubic boron nitride or diamond heavy grinding wheel, the thickness of the grinding wheel is 10-30 mm, the edge of the grinding wheel is eliminated with sharp corners and smooth transition, the rotation speed of the base tube (4) and the feed speed of the grinding wheel are adjusted, and spiral grooves with equal spacing are machined on the inner surface of the base tube (4), the groove depth is 0.10-0.15 mm, the groove width is 10-30 mm, the groove bottom angle is smooth transition, the spacing between adjacent grooves is twice the groove width, and the surface roughness after machining is Ra25-Ra50; Step 10: Use the fully automatic ultrasonic and eddy current combined automatic testing equipment to perform 100% ultrasonic testing, eddy current testing and automatic thickness measurement on the base pipe (4). The acceptance level of the ultrasonic testing is Class I specified in NB / T47013.3-2015, and the acceptance level of the eddy current testing is Class B specified in GB / T7735-2004. The wall thickness of the base pipe (4) is not allowed to be less than the minimum design wall thickness.

3. The method for manufacturing a large-diameter, thick-walled bimetallic composite steel pipe according to claim 1, characterized in that: The manufacturing method of the composite tube (7) is as follows: Step 1: First, the composite pipe (7) is made of a stainless steel cold-rolled seamless pipe or a stainless steel straight seam welded pipe, and the straight weld of the welded pipe should be ground and smooth; the composite pipe (7) is subjected to a solid solution treatment according to a qualified heat treatment process to obtain pitting corrosion resistance and comprehensive mechanical properties. During the solid solution treatment, a supporting device is used to support and fix the inner surface of the composite pipe (7) to prevent the composite pipe (7) from losing its roundness and deformation during the solid solution treatment process; Step 2: Then straighten the solution treated composite tube (7) to make the straightness less than 1 mm / m, the straightness of the entire length of the base tube (4) less than 5 mm / m, and the outer diameter deviation of the composite tube (7) less than ±0.3 mm; Step 3: Then, the inner and outer surfaces of the composite tube (7) are shot blasted, and dimensional inspection, ultrasonic inspection, eddy current inspection and automatic thickness measurement are performed. The acceptance level of the ultrasonic inspection is Class I specified in NB / T47013.3-2015, and the acceptance level of the eddy current inspection is Class B specified in GB / T7735-2004. The wall thickness of the composite tube (7) is 3~6mm, and the outer diameter of the composite tube (7) is 4~6mm smaller than the inner diameter of the base tube (4).

4. The method for manufacturing a large-diameter, thick-walled bimetallic composite steel pipe according to claim 1, characterized in that: The composite method of the base tube (4) and the composite tube (7) is: Step 1: Processing an outer bevel of 45° to 60° at one end of the composite tube (7), and evenly applying a layer of stainless steel tube cold drawing special lubricant on the inner surface of the composite tube (7). The lubricant is based on refined mineral oil and is added with functional additives that do not contain sulfur or chlorine components. It can improve the lubrication performance, cooling performance and extreme pressure and anti-wear performance during the cold working process of the composite tube (7) and does not pollute the environment after cleaning; Step 2: Fix the base tube (4) on the composite tube sleeve drawing device, and the connecting rod (2) passes through the composite tube (7). One end of the connecting rod (2) is connected to the end of the composite tube (7) through the tapered connecting block (6), and the other end is connected to the hydraulic cylinder (1). Driven by the hydraulic cylinder (1), the connecting rod (2) drags the composite tube (7) into the base tube (4). When the composite tube (7) is flush with the base tube (4), the tapered die is separated from the composite tube (7). Through the sleeve drawing device, the outer diameter of the composite tube (7) can be made close to the inner diameter of the base tube (4) to the maximum extent. Even if the base tube and the composite tube (7) have dimensional deviations such as straightness and ovality, the composite tube (7) can be easily sleeved with the base tube (4), and the phenomenon of instability caused by the small wall thickness of the composite tube (7) when the composite tube (7) is pushed into the base tube (4) is avoided. Step 3: Align the composite tube (7) with the base tube (4) at the drawing starting end. The radial gap between the composite tube (7) and the base tube (4) is 2.0~3.0 mm. Fix the composite tube (7) and the base tube (4) by spot welding at the drawing starting end. Select a suitable first tapered drawing inner die according to the inner diameter of the composite tube (7). The small end diameter of the first tapered drawing inner die is: d1=Di composite-(6.0~10.0) mm, Di composite is the composite tube (7). The inner diameter of the tube (7), that is, the small end diameter of the drawing inner die is 6.0 to 10.0 mm smaller than the inner diameter of the composite tube (7); the large end diameter of the first tapered drawing inner die is: d2 = Di base - 2 * t complex + (0.6 to 1.0) mm, Di base is the inner diameter of the base tube (4), t complex is the wall thickness of the composite tube (7), the cone angle of the tapered section (deformation section) of the first tapered drawing inner die is 8° to 10°, and the length of the sizing section is 40 to 60 mm; Step 4: The connecting rod (2) is connected to the first tapered drawing inner die. Under the action of the hydraulic cylinder (1), the connecting rod (2) drives the first tapered drawing inner die through the composite tube (7), causing the composite tube (7) to undergo plastic deformation and adhere closely to the inner wall of the base tube (4). A wall reduction of 0.3 to 0.5 mm is generated, eliminating the radial gap between the composite tube (7) and the base tube (4), thereby obtaining a composite tube. The composite tube (7) has a smaller wall thickness. A smaller wall reduction is used during the composite process to prevent the composite tube (7) from cracking due to excessive force. Step 5: flush the two ends of the composite pipe, and fix the composite pipe (7) to the base pipe (4) at both ends by spot welding, shot blast the inner surface of the composite pipe, clean the lubricant and other impurities on the inner surface, and then evenly apply a layer of stainless steel pipe cold drawing special lubricant on the inner surface of the pipe; Step 6: Select a suitable second tapered drawing inner die and perform a second drawing on the primary composite tube. The cone angle of the tapered section (deformation section) of the first tapered drawing inner die is 4° to 6°, and the length of the sizing section is 40 to 60 mm. The second drawing process causes the wall reduction of the composite tube (7) to reach 0.3 to 0.4 mm, causing the composite tube (7) to undergo plastic deformation, so that the metal on the outer surface of the composite tube (7) is embedded in the spiral groove on the inner surface of the base tube (4), thereby forming a secondary composite tube. Step 7: Seal the ends of the secondary composite steel pipes and then perform radiographic testing on the welds in accordance with NB / T47013.2-2015 "Non-destructive testing of pressure equipment - Part 2: Radiographic testing" or NB / T47013.11-2023 "Non-destructive testing of pressure equipment - Part 11: Radiographic digital imaging testing". The image quality level should reach AB level, and the acceptance quality level should be II. Clean the inner surface of the secondary composite pipe to obtain the final product. Step 8: Take samples from the product and conduct performance tests according to the provisions of Sections 6.6 and 6.7 of GB / T31940-2015 "Bimetallic Composite Corrosion-Resistant Steel Pipe for Fluid Transportation", and conduct bonding strength tests according to the requirements of b) in 6.8.2.2.

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