Method for manufacturing titanium-steel composite welded pipe

Abstract

The application discloses a preparation method, in particular to a preparation method for titanium-steel composite welded pipe, and belongs to the technical field of titanium composite steel pipe production and manufacturing process. The preparation method for titanium-steel composite welded pipe can effectively ensure the welding quality with significantly reduced operation difficulty. The preparation method comprises the following steps: precise blanking, precise forming and assembling, controllable welding and pressure shaping, and titanium covering layer assembling and welding. The titanium-steel composite welded pipe obtained through the above steps has mechanical properties and corrosion resistance reaching the specified requirements. In the process of precise blanking, the titanium covering layer within a specified width near the welding groove is removed. In the process of precise forming and assembling, the titanium-steel composite plate is rolled into a round pipe through the concave-convex die bending method, and then the precise butt joint is realized to complete the precise forming and assembling. In the process of controllable welding and pressure shaping, the steel base layer of the round pipe is welded first, and then the pressure shaping is performed on the inner weld.

Description

Technical Field

[0001] This invention relates to a preparation method, and more particularly to a preparation method for titanium-steel composite welded pipes, belonging to the technical field of titanium composite steel pipe manufacturing process. Background Technology

[0002] Titanium or titanium alloys exhibit excellent corrosion resistance in seawater and common acidic and alkaline media, making them frequently used in critical applications in chemical, energy, and marine engineering fields. However, titanium and titanium alloys are expensive, typically costing tens of times more than steel. To reduce costs, titanium alloys are often used in the form of titanium / steel composite plates. In this process, the titanium alloy acts as the composite layer in contact with the medium, providing corrosion resistance, while steel, with its superior mechanical properties, serves as the matrix material, providing the composite's mechanical properties.

[0003] The most promising application areas for titanium-steel composite plates are pipelines for oil and gas transmission, chemical solutions, or seawater transmission. As mentioned earlier, welded pipes made with a steel outer layer and titanium inner wall, constructed from titanium-steel composite plates, possess both pressure resistance and excellent corrosion resistance, preventing pipeline failure due to corrosion of the internal media during long-term service. However, although titanium-steel composite plates have been applied in various industries such as coking, chemicals, and marine engineering, their use is currently limited to the manufacture of large-diameter pipes and containers, and their widespread adoption in the huge markets of oil and gas pipelines and seawater pipelines is difficult. This is because the manufacture of titanium-steel composite welded pipes is difficult, and the most critical issue is welding.

[0004] The fabrication of welded pipes using composite plates involves welding the longitudinal weld plates. The challenge lies in the fact that if iron and titanium are mixed during welding, a brittle intermetallic compound phase is formed, leading to cracking during welding and hindering weld formation. Even a small amount of mixing will impair the joint's mechanical properties and corrosion resistance. Therefore, when welding steel, the titanium layer near the weld must be removed; otherwise, titanium will enter the weld, causing embrittlement. Furthermore, when welding the titanium layer, iron must be prevented from entering the weld, otherwise, the weld's corrosion resistance will be severely reduced.

[0005] Currently, industrial production typically employs a cover plate lap welding process for welding titanium-steel composite plates. Before pipe rolling, during the blanking stage of the titanium-steel composite plate, the titanium cladding near both sides is removed. After pipe rolling, the steel butt joint layer is welded. Then, a titanium strip is used as a cover plate, covering the steel weld seam, and lap welding is used to complete the welding of the titanium strip cover plate and the titanium layer of the composite plate. Cover plate welding has significant drawbacks: the cover plate forms a protrusion on the inner wall of the pipe, which reduces the cross-sectional area through which the medium passes, especially for the most commonly used small-diameter pipes, causing the pipe fittings to fail to meet industry standard application requirements. In particular, oil and gas transmission pipe fittings require ball testing for inspection; welded pipes prepared using cover plate lap welding are unlikely to pass this test.

[0006] For titanium-steel composite welded pipes requiring ball testing, butt welding is necessary. Various butt welding methods have been studied, such as the transition layer welding method. This involves first welding a steel or titanium butt layer, then welding, depositing, or cold-spraying V, Nb, Cu, or other Cu or nickel welding wires at the titanium-steel interface, and finally welding the titanium or steel butt layer again to avoid direct fusion of titanium and steel. However, this welding method uses expensive V and Nb, and cannot completely avoid a brittle layer. The transition layer welding operation is difficult, and improper or unstable processes can easily damage both the mechanical properties and corrosion resistance of the joint. The transition layer titanium-steel composite butt welding process has not yet been widely adopted. Other butt welding methods, including direct butt welding, flat plate butt welding, and bent plate butt welding, require careful beveling and precise control of the welding process to avoid burning through the titanium cladding while maximizing penetration. These methods are difficult to implement, and the weld quality is highly inconsistent. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a method for preparing titanium-steel composite welded pipes that significantly reduces the difficulty of operation and can effectively ensure welding quality.

[0008] The technical solution adopted to solve the above-mentioned technical problems is: a method for preparing titanium-steel composite welded pipes. This method, through several steps including precise material cutting, precision forming and assembly, steel substrate welding and weld shaping, and titanium cladding assembly and welding, yields titanium-steel composite welded pipes with qualified mechanical properties and corrosion resistance, capable of passing ball testing.

[0009] This involves precisely cutting the material while removing the titanium cladding within a specified width near the welding bevel.

[0010] During precision forming and assembly, the titanium-steel composite plate is rolled into a round tube using a die bending method to achieve precise alignment and complete the precision forming and assembly work.

[0011] When welding the steel substrate and shaping the weld seam, the steel substrate layer of the round pipe is welded first, and then the weld seam inside the pipe is remelted and shaped.

[0012] Furthermore, during precise material cutting, the titanium-steel composite plate is first cut into rough blanks of a specified width using laser cutting, water jet cutting, plasma cutting, or wire cutting. Then, milling or planing and finally grinding are used to obtain a precise blank with straight side surfaces and a plate width of W = 3.14D - δ + δ, where D is the outer diameter of the welded pipe, δ is the pipe wall thickness, and the tolerance of the plate width W is ±0.2mm.

[0013] The preferred method of the above scheme is to use laser cutting or waterjet cutting to obtain the raw slab blank, and to use milling for fine finishing and trimming.

[0014] Furthermore, when removing the titanium cladding, after finishing the edge trimming, a precision cutting machine is used with a diamond cutting disc to cut off the titanium cladding. Then, the titanium cladding is peeled off from the steel substrate to remove the titanium cladding near the weld bevel. The width w of the removed titanium cladding is 5-30±0.2mm on each side, and the cutting depth is the titanium cladding thickness δ-0.1-0.2mm.

[0015] The preferred method of the above scheme is that, during the precision forming and assembly of the die bending method, before bending, a steel needle is used to scribing a line with the side as the reference, and a positioning line is drawn every 5° corresponding to the cross-sectional circle of the tube. The parallelism between the positioning line and the side, and between the positioning lines, is ±0.2mm. During bending, the center of the bottom of the punch is aligned with the positioning line.

[0016] Furthermore, after the titanium-steel composite plate is formed by bending and rolling in a die, it is then joined and spot-welded in a pipe joining machine. The specific process is as follows:

[0017] First, use anhydrous ethanol or acetone to clean the oil stains on the surface near the weld. Then, transfer the rolled tube blank into the welding machine mold and use a hydraulic mechanism to weld the tube. During welding, the two sides of the weld are completely aligned with a gap of 0-0.5mm and the misalignment does not exceed 0.5mm. Next, spot welding is performed using the MIG welding method, with a spacing of 200±5mm between two adjacent weld points.

[0018] The preferred method of the above scheme is that, after spot welding, plasma filler wire welding is used to perform butt welding of the steel substrate layer inside the pipe. The welding parameters should ensure full penetration; the wire feeding parameters should ensure that the top of the weld is 0-3mm above the outer surface of the pipe; the covering material of the titanium cladding assembly is annealed TA1 or TA2 pure titanium strip. The width of the annealed TA1 or TA2 pure titanium strip is 3.14wD-2δ / Wk, where k is 0.1-0.5mm, the strip width tolerance is 0.2mm, and the thickness is 0.3-0.6mm.

[0019] Furthermore, after the steel substrate layer inside the pipe is welded, the weld bead bottom height is shaped using argon arc welding remelting. The specific process is as follows:

[0020] An argon arc welding torch driven by a linear guide slide module is used to remelt the excess weld height of the steel substrate layer inside the pipe, ensuring that the excess weld height after remelting is less than 0.5mm.

[0021] The preferred method of the above scheme is that, during the assembly of the titanium cladding layer inside the pipe, at least two layers of annealed TA1 or TA2 pure titanium strips are overlapped and arranged above the weld bead of the steel substrate layer inside the pipe. The sides of each overlapping layer of annealed TA1 or TA2 pure titanium strip are aligned with the existing titanium cladding layer inside the pipe. Then, copper strips are used to press each layer of annealed TA1 or TA2 pure titanium strips together, ensuring that the compacted thickness of each layer is greater than the thickness of the existing titanium cladding layer. Finally, each layer of annealed TA1 or TA2 pure titanium strip is spot-welded firmly to the existing titanium cladding layer on the corresponding side to complete the assembly of the titanium cladding layer inside the pipe.

[0022] The spot welding is carried out using an argon arc welding gun driven by a linear guide slide module. The spot welding sequence is as follows: first, spot weld the midpoint of the longitudinal direction of the weld; then, spot weld the 1 / 4 and 3 / 4 lengths of the longitudinal direction of the weld, as well as both ends; then, spot weld continuously at intervals not exceeding 300mm; finally, drive the argon arc welding gun to complete the welding of the entire weld.

[0023] Furthermore, the spot welding process parameters are 60–100A, spot welding time 0.3–0.8s, and shielding gas flow rate 5–10L / min; the full weld welding process parameters are: tungsten needle diameter 2.0–4.0mm, tungsten needle tip angle 30–45°, tungsten needle tip aligned with the side of the groove, tungsten needle tip height 1–3mm, welding current 150–250A, welding wire diameter 1.0–1.6mm, welding speed 2–5mm / s, wire feed speed 10–25mm / s, welding torch shielding gas flow rate 5–10L / min, and the drag shield protection range is at least 50mm in length directly behind the welding torch and 10mm in width on both sides of the weld, with a drag shield gas flow rate of 20–30L / min.

[0024] The beneficial effects of this invention are as follows: The technical solution provided in this application obtains a titanium-steel composite welded pipe with qualified mechanical properties and corrosion resistance through several steps, including precise blanking, precision forming and assembly, steel substrate welding and weld shaping, and titanium cladding assembly and welding. It can also pass ball inspection. Furthermore, while precisely blanking, the titanium cladding within a specified width near the welding bevel is removed. Then, during precision forming and assembly, a groove of a specified width for removing the titanium cladding is left. Finally, the titanium cladding is covered in the groove and welded. Thus, the preparation method of this application achieves independent welding of the steel substrate layer and the titanium cladding layer, and the titanium cladding layer inside the pipe is also achieved through butt welding of the titanium cladding layer. This solves the technical problem in the prior art where the lap joint reduces the flow area and makes it impossible to pass the ball inspection. Because the technical solution of this application first welds the steel substrate layer independently and then assembles and welds the titanium cladding layer inside the pipe, the welding of the two is carried out independently, which effectively avoids titanium from mixing into the steel weld and iron from mixing into the titanium weld. This not only significantly reduces the difficulty of operation, but also effectively ensures the welding quality and makes it easy to obtain a weld with stable welding quality. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the automatic in-pipe welding device involved in the preparation method of titanium-steel composite welded pipe of the present invention;

[0026] Figure 2 for Figure 1 Side sectional view.

[0027] The following are labeled in the diagram: 1. Titanium cladding layer; 2. Steel substrate layer; 3. Annealed TA1 or TA2 pure titanium strip; 4. Linear guide slide module; 5. Copper strip; 6. Argon arc welding gun; 7. Steel substrate layer weld bead. Detailed Implementation

[0028] like Figure 1 , Figure 2 This invention provides a method for preparing titanium-steel composite welded pipes that significantly reduces operational difficulty and effectively ensures welding quality. The method involves several steps: precise blanking, precision forming and assembly, steel substrate welding and weld shaping, and titanium cladding assembly and welding. These steps result in butt-welded titanium-steel composite welded pipes with satisfactory mechanical properties and corrosion resistance, capable of passing ball-passing inspection. Specifically, during precise blanking, the titanium cladding 1 within a specified width near the welding bevel is removed. During precision forming and assembly, the titanium-steel composite plate is rolled into a circular tube using a die bending method, achieving precise butt welding to complete the precision forming and assembly. During steel substrate welding and weld shaping, the circular tube steel substrate layer 2 is welded first, followed by remelting and shaping of the internal weld. The technical solution provided in this application obtains a butt-welded titanium-steel composite welded pipe with mechanical properties and corrosion resistance that meet the specified requirements through several steps, including precise blanking, precision forming and assembly, steel substrate welding and remelting shaping, and titanium cladding assembly and welding. At the same time as precise blanking, the titanium cladding within a specified width near the welding bevel is removed. Then, during precision forming and assembly, a groove of a specified width for removing the titanium cladding is left. Finally, the titanium cladding is covered in the groove and welded. Thus, the preparation method of this application achieves independent welding of the steel substrate layer and the titanium cladding layer, and the titanium cladding layer inside the pipe is also achieved through butt welding of the titanium cladding layer. This solves the technical problem in the prior art where the lap joint reduces the flow area and makes it impossible to pass the ball inspection. Because the technical solution of this application first welds the steel substrate layer independently and then assembles and welds the titanium cladding layer inside the pipe, the welding of the two is carried out independently, which effectively avoids titanium from mixing into the steel weld and iron from mixing into the titanium weld. This significantly reduces the difficulty of operation and effectively ensures the welding quality, making it easy to obtain a weld with stable welding quality.

[0029] Accordingly, considering the actual conditions of the production site, this application first uses laser cutting, waterjet cutting, plasma cutting, or wire cutting to cut the titanium-steel composite plate into rough blanks of a specified width during precise material cutting. Then, milling or planing and finally grinding are used to obtain a precise blank with straight side surfaces and a plate width of W = 3.14D - δ + δ, where D is the outer diameter of the welded pipe, δ is the pipe wall thickness, and the tolerance of the plate width W is ±0.2mm. The preferred method is to use laser cutting or waterjet cutting to obtain the rough blank, and milling for finishing and trimming. When removing the titanium cladding 1, after finishing the edge trimming, a diamond cutting disc is used as the cutting tool and a precision cutting machine is used to cut off the titanium cladding 1. Then, the titanium cladding 1 is peeled off from the steel substrate layer 2 to complete the removal of the titanium cladding 1 near the weld bevel. The width of the titanium cladding 1 to be removed is 5 to 30 ± 0.2 mm on each side, and the cutting depth is δ - 0.1 to 0.2 mm of the thickness of the titanium cladding 1.

[0030] Furthermore, in this application, when using the die bending method for precision forming and assembly, before bending, a steel needle is used to mark a positioning line every 5° corresponding to the cross-sectional circle of the pipe, with the side as the reference. The parallelism between the positioning line and the side, and between the positioning lines themselves, is ±0.2mm. During bending, the center of the bottom of the punch is aligned with the positioning line. After the titanium-steel composite plate is bent and rolled in the die, it is then joined and spot-welded in a pipe joining machine. The specific process is as follows: first, the oil stains on the surface near the weld are cleaned with anhydrous ethanol or acetone. The rolled pipe blank is then transferred into the joining machine mold, and the joining is performed using a hydraulic mechanism. During joining, the two sides of the weld are completely fitted together, with a gap between 0-0.5mm and a misalignment of no more than 0.5mm. Then, spot welding is performed using the MIG welding method, with a spacing of 200±5mm between two adjacent weld points. After spot welding, the inner steel substrate layer 2 is butt-welded using plasma filler wire welding. Welding parameters should ensure full penetration; wire feeding parameters should ensure the weld top protrudes 0-3mm above the outer surface of the pipe. The titanium cladding layer 1 uses annealed TA1 or TA2 pure titanium strip 3. The width of the annealed TA1 or TA2 pure titanium strip 3 is 3.14wD-2δ / Wk, where k is 0.1-0.5mm, the strip width tolerance is 0.2mm, and the thickness is 0.3-0.6mm. More specifically, after the inner steel substrate layer 2 is welded, the weld bead bottom excess height is shaped using argon arc welding remelting. Specifically, an argon arc welding gun driven by a linear guide slide module 4 is used to remelt the excess height portion of the weld bead in the inner steel substrate layer 2, ensuring the excess height of the weld bead after remelting is less than 0.5mm.

[0031] As a crucial step in the preparation method of this application, during the assembly of the titanium cladding layer 1 inside the pipe, at least two layers of annealed TA1 or TA2 pure titanium strips 3 are overlapped and arranged above the weld bead 7 of the steel substrate layer inside the pipe. The sides of each overlapping layer of annealed TA1 or TA2 pure titanium strips 3 are aligned with the existing titanium cladding layer inside the pipe. Then, copper strips 5 are used to press each layer of annealed TA1 or TA2 pure titanium strips 3 to achieve a compacted thickness of each layer of annealed TA1 or TA2 pure titanium strips 3. The thickness is greater than that of the existing titanium cladding 1. Then, each layer of annealed TA1 or TA2 pure titanium strip 3 is spot welded to the existing titanium cladding 1 on the corresponding side to complete the assembly of the titanium cladding inside the pipe. The spot welding is carried out by the argon arc welding gun 6 driven by the linear guide slide module 4. The spot welding sequence is as follows: first spot weld the midpoint of the longitudinal direction of the weld, then spot weld the 1 / 4 and 3 / 4 length of the longitudinal direction of the weld and both ends, then spot weld continuously at intervals not exceeding 300mm, and finally drive the argon arc welding gun 6 to complete the welding of the entire weld. Correspondingly, the spot welding process parameters are 60-100A, spot welding time is 0.3-0.8s, and shielding gas flow rate is 5-10L / min; the full weld welding process parameters are: tungsten needle diameter 2.0-4.0mm, tungsten needle tip angle 30-45°, tungsten needle tip aligned with the side of the groove, tungsten needle tip height 1-3mm, welding current 150-250A, welding wire diameter 1.0-1.6mm, welding speed 2-5mm / s, wire feed speed 10-25mm / s, welding torch shielding gas flow rate 5-10L / min, the drag shield protection range is at least 50mm in length directly behind the welding torch and 10mm in width on both sides of the weld, and the drag shield gas flow rate is 20-30L / min.

[0032] In summary, the principle of the preparation method in this application is as follows: through precise design of the titanium-steel composite plate and titanium strip cutting process, pipe rolling, and steel layer welding process, and utilizing the soft and easily deformable characteristics of pure titanium thin strips, multiple layers of titanium strips are used to fill the groove inside the pipe, providing conditions for the precise assembly and welding of the titanium strips and the titanium cladding weld bead on the inner wall of the welded pipe. The composite plate has high dimensional accuracy after cutting, and the dimensions of its welded pipe are precisely controllable. Using the side edge of the plate as a reference, precise cutting and removal of the titanium cladding for subsequent welding ensures precise control of the groove width. Precise positioning during pipe forming prevents weld skewing. After spot welding using the MIG / MAG method, plasma welding is used to weld the steel butt layer, ensuring full penetration and preventing defects such as deformation, misalignment, and incomplete penetration. Argon arc welding is used to remelt the back reinforcement of the steel butt weld bead to prevent excessive reinforcement from obstructing the titanium strip. Copper strips are used to press the titanium strips together, utilizing their rapid thermal conductivity to prevent the thin titanium strips from curling after being heated by the electric arc. The linear guide slide module and argon arc welding gun are small in size, enabling arc spot welding and general welding of small-diameter pipes. Argon arc welding is a precision welding process that ensures controllable weld depth, preventing burn-through to the steel butt joint layer while guaranteeing a weld depth of 80-90% of the titanium cladding thickness when it is 1-3mm. With proper inert gas protection, the titanium molten pool exhibits good fluidity, resulting in a smooth weld surface and minimal weld reinforcement. Using the method provided by this invention, titanium-steel composite welded pipes with no obvious protrusions on the inner wall, conforming dimensions and shape, and excellent mechanical and corrosion resistance can be obtained.

[0033] The technical solution of this application will be further described below through specific embodiments:

[0034] This invention provides a method for preparing titanium-steel composite welded pipes. The procedure for preparing the welded pipe includes the following steps:

[0035] (1) Material preparation: Plate cutting and finishing. Remove a certain width of titanium cladding near the bevel. Prepare thin titanium strips for butt welding. (2) Tube rolling: Roll the plate into a tube. (3) Seam joining and welding: Butt weld the longitudinal seams of the tube in the mold, spot weld and fix, and weld to complete the steel layer butt weld. (4) Finishing of the weld seam inside the tube: Remove the excess height on the back of the steel layer weld inside the tube. (5) Titanium layer butt welding: Place the titanium strip into the groove on the inner wall of the tube and butt its two sides with the titanium cladding of the plate to complete the titanium layer welding inside the tube.

[0036] In the procedure of the welded pipe preparation method, in step (1), the plate blanking method is laser cutting, water jet cutting, plasma cutting, or wire cutting, followed by milling, planing, and grinding to refine the side edges, making the side surface straight and ensuring its width W = 3.14(D-δ) + δ, where D is the outer diameter of the welded pipe, δ is the pipe wall thickness, and the tolerance is 0.2 mm. Preferably, the composite plate for pipe making is prepared by laser cutting or water jet cutting, followed by milling and finally grinding.

[0037] In the procedure of the welded pipe preparation method, in step (1), the width w of removing the titanium cladding near the bevel is 5-30 mm with a tolerance of 0.2 mm. The method for removing the titanium cladding is as follows: taking the side edge of the plate as a reference, the titanium cladding is cut with a precision cutting machine using a diamond cutting disc under water cooling. The cutting depth is the titanium cladding thickness minus 0.1-0.2 mm. After cutting, the titanium cladding is peeled off from the steel plate.

[0038] In the procedure of the welded pipe preparation method, in step (1), the titanium strip used for butt welding is annealed TA1 or TA2 pure titanium strip with a width of 3.14w(D-2δ) / Wk, where k is 0.1-0.5mm, tolerance is 0.2mm, and thickness is 0.3-0.6mm. Laser cutting is used.

[0039] In the procedure of the welded pipe preparation method, step (2) involves a pipe rolling method using a punch and die. Before bending, a steel needle is used to mark a positioning line every 5° corresponding to the cross-sectional circle of the pipe, with the side edge as the reference. The parallelism between the positioning line and the side edge, and between the positioning line and the positioning line, is 0.2mm. During bending, the center of the bottom of the punch is aligned with the positioning line.

[0040] In the procedure of the welded pipe preparation method, step (3) involves seaming the pipe in a seam-sealing machine. First, clean the oil stains on the surface near the seam using anhydrous ethanol or acetone. Transfer the pipe into the seam-sealing machine mold and use a hydraulic mechanism to seam the pipe. After seaming, the two sides of the seam are completely fitted together without any obvious gaps or misalignments. Spot welding is performed using the MIG / MAG method. One weld point is placed every 200 mm. After spot welding, the steel butt joint is welded using the plasma filler wire welding method. The welding parameters should ensure full penetration; the wire feeding parameters should ensure the weld top height, i.e., the weld height above the outer surface of the pipe is 0-3 mm.

[0041] In the procedure of the welded pipe preparation method, step (4) involves removing the excess height at the bottom of the weld bead in the inner steel layer by argon arc welding remelting. An argon arc welding gun driven by a linear guide slide module is used to remelt the excess height portion of the weld bead in the inner steel layer. The remelted weld bead has a remaining height of less than 0.5 mm.

[0042] In the procedure of the welded pipe preparation method, step (5) involves butt welding of the titanium layer inside the pipe by stacking multiple thin titanium strips into the groove on the inner wall of the pipe, with a total thickness greater than or equal to the thickness of the titanium cladding. The two sides of the strips are aligned with the two sides of the groove on the inner wall of the pipe, with a relatively equal gap between them. Then, copper strips are pressed onto the thin titanium strips to fix them. The width of the copper strips ensures that the distance between its sides and the weld seams on both sides is 5-10 mm. A linear guide slide module is placed above the copper strips, and the argon arc welding gun is moved using the module to spot weld and fix the multiple layers of thin titanium strips to the titanium cladding. The spot welding sequence is as follows: first, spot weld the midpoint of the longitudinal direction of the weld seam; then, spot weld at 1 / 4 and 3 / 4 of the longitudinal length of the weld seam; then, spot weld both ends; and then, spot weld continuously at intervals of 300 mm. Finally, the argon arc welding gun is moved using the module to complete the welding of the entire weld seam. The spot welding process parameters are 60-100A, spot welding time 0.3-0.8s, and shielding gas flow rate 5-10L / min. Full weld seam welding process parameters: tungsten needle diameter 2.0-4.0mm, tungsten needle tip angle 30-45°, tungsten needle tip aligned with the side of the groove, tungsten needle tip height 1-3mm, welding current 150-250A, welding wire diameter 1.0-1.6mm, welding speed 2-5mm / s, wire feed speed 10-25mm / s, welding torch shielding gas flow rate 5-10L / min, drag shield protection range is at least 50mm in length directly behind the welding torch and 10mm in width on both sides of the weld seam, drag shield gas flow rate 20-30L / min.

[0043] Example 1

[0044] The titanium-steel composite welded pipe preparation method proposed in this invention is used to prepare a titanium-steel composite pipe with an outer diameter of 273 mm and a wall thickness of 9.2 mm (where the steel layer is Q235 carbon steel with a thickness of 8 mm and the titanium cladding is TA1 pure titanium with a thickness of 1.2 mm). The method includes the following steps: (1) Material preparation: cutting and finishing of the plate. Remove a certain width of titanium cladding near the bevel. Prepare thin titanium strips for butt welding. (2) Pipe rolling: roll the plate into a pipe. (3) Seam joining and welding: butt weld the longitudinal seam of the pipe in the mold, spot weld and fix it, and weld to complete the butt weld of the steel layer. (4) Finishing of the weld seam inside the pipe: remove the excess height on the back of the weld seam of the steel layer inside the pipe. (5) Butt welding of titanium layer: put the titanium strip into the groove of the inner wall of the pipe and butt its two sides with the titanium cladding of the plate to complete the welding of the titanium layer inside the pipe.

[0045] In step (1), the plate material is cut by water jet cutting, and then the side edges are finished by milling and grinding to make the side surface flat. The width is calculated by the formula W = 3.14(D-δ) + δ, where D is the outer diameter of the welded pipe and δ is the pipe wall thickness, which is 835.82 mm; after inspection, the tolerance is 0.1 mm.

[0046] In step (1), the width w of the titanium cladding near the bevel is set to 20mm. The method for removing the titanium cladding is as follows: The position of the cutting machine guide rail is adjusted based on the side edge of the plate. The titanium cladding is cut using a precision cutting machine with diamond cutting discs under water cooling. The cutting depth is set to the titanium cladding thickness minus 1.9mm. After cutting, a hydraulic press is used to peel the titanium cladding off the steel plate. Inspection shows that the width of the removed titanium cladding is 20mm, with a tolerance of 0.2mm.

[0047] In step (1), the butt-welding titanium strip used is 0.5mm thick annealed TA1 pure titanium strip. The width is calculated using the formula 6.28w(D-2δ) / Wk, where k is 0.2mm, resulting in a value of 37.5mm. Laser cutting is employed. Inspection revealed a width tolerance of 0.05mm.

[0048] In step (2), the titanium-steel composite pipe is rolled using a die-bending method. Before bending, a positioning line is drawn every 5° with a steel needle, using the side as a reference. The parallelism between the positioning line and the side and the positioning line is 0.2mm. During bending, the center of the bottom of the punch is aligned with the positioning line.

[0049] In step (3), the pipe jointing machine is used for jointing. First, anhydrous ethanol is used to clean the oil stains on the surface near the joint. The pipe is transferred into the jointing machine mold, and the pipe is joined using a hydraulic mechanism. After jointing, the two sides of the joint are completely fitted together, with no obvious gaps or misalignments. Spot welding is performed using the MIG / MAG welding method. 1.2mm diameter carbon steel welding wire is used, and the welding current is 120A; one weld point is made every 200mm. After spot welding, the steel butt joint is welded using the plasma filler wire welding method. The welding process parameters are: welding current 195A, plasma gas 2.8L / min, travel speed 0.5m / min, and wire feed speed 3.0m / min. After welding, the weld is inspected to ensure that the back of the weld, i.e., the surface of the weld inside the pipe, is fully penetrated; the weld top has an additional height of about 2mm.

[0050] In step (4), the method for removing the excess height at the bottom of the weld bead in the inner steel layer of the pipe is argon arc welding remelting. An argon arc welding torch driven by a linear guide slide module is used to remelt the excess height portion of the weld bead in the inner steel layer of the pipe. The remelting current is 100A, the tungsten needle tip angle is 30°, the tungsten needle tip height is 2mm, and the welding torch travel speed is 3mm / s. Upon inspection, the excess height of the remelted weld bead is less than 0.5mm throughout the entire weld length.

[0051] In step (5), during the butt welding of the titanium layer inside the pipe, multiple thin titanium strips are stacked into the groove on the inner wall of the pipe. The total thickness of the titanium strips is equal to the thickness of the titanium cladding. The two sides of the strips are aligned with the two sides of the groove on the inner wall of the pipe, and the gaps on both sides are roughly the same. Then, copper strips are pressed onto the thin titanium strips to fix them. The copper strips are 25mm wide, ensuring that the distance between their sides and the weld seams on both sides is about 6-7mm. The linear guide slide module is placed above the copper strips, and the argon arc welding gun is moved using the module to spot weld and fix the multiple layers of thin titanium strips to the titanium cladding. The spot welding sequence is as follows: first, spot weld the midpoint of the longitudinal direction of the weld seam, then spot weld at 1 / 4 and 3 / 4 of the longitudinal length of the weld seam, then spot weld the two ends, and then spot weld continuously at intervals of 300mm. Then, the argon arc welding gun is moved using the module to complete the welding of the entire weld seam. The spot welding process parameters are 80A, spot welding time 0.5s, and shielding gas flow rate 7L / min. Full weld seam welding process parameters: tungsten needle diameter 3.0mm, tungsten needle tip angle 30°, tungsten needle tip aligned with the side of the groove, tungsten needle tip height controlled at 1-2mm, welding current 180A, welding wire diameter 1.2mm, welding speed 3mm / s, wire feed speed 18mm / s, welding torch shielding gas flow rate 7L / min, drag shield protection range is a 60mm length directly behind the welding torch and a 10mm width area on each side of the weld seam, drag shield gas flow rate 25L / min.

[0052] Through precise design of the titanium-steel composite plate and titanium strip cutting process, as well as the pipe rolling and steel layer welding process, and utilizing the soft and easily deformable characteristics of pure titanium strips, multi-layer titanium strips were used to fill the grooves inside the pipe, achieving precise alignment of the titanium strips with the titanium cladding on the inner wall of the welded pipe. Observation revealed that after the titanium strips were pressed by copper strips, their sides were tightly attached to the sides of the grooves, and their bottoms were tightly attached to the bottoms of the grooves, ensuring no obvious protrusions after welding. Process inspection results showed high dimensional accuracy of the composite plate and titanium strips after cutting, resulting in precise control of the welded pipe dimensions. Precise cutting using the side of the plate as a reference, and removal of the titanium cladding for subsequent pipe welding, ensured precise control of the groove width. Precise positioning during pipe forming prevented weld skewing. After spot welding using the MIG / MAG method, plasma welding was used to weld the steel butt layer, achieving full penetration in one pass and preventing defects such as deformation, misalignment, and incomplete penetration. Argon arc welding was used to remelt the back reinforcement of the steel butt weld to prevent excessive reinforcement from obstructing the titanium strips. The above measures ensured the dimensions of the groove and titanium strip, preventing the titanium strip width from exceeding the groove width, thus avoiding the formation of a protrusion after welding, and also preventing the titanium strip width from being too narrow, resulting in an excessive gap between its side and the groove side after clamping. Using copper strips to clamp the titanium strips, taking advantage of their rapid thermal conductivity, prevented the thin titanium strips from curling after being heated by the electric arc. The small size of the linear guide slide module and the argon arc welding gun enabled arc spot welding and welding inside small-diameter pipes. Utilizing the precision welding process of argon arc welding, the weld depth was ensured to be controllable, preventing burn-through to the steel butt joint layer. Inspection showed that all four layers of strip at the weld were melted, and the weld depth exceeded 80%. Due to the filler wire, an excess height of approximately 0.8-1mm was formed at the weld. A weld with no obvious protrusions on the inner wall of the pipe and conforming to the required dimensions and shape was obtained. Non-destructive testing showed that the steel layer weld had no defects such as incomplete penetration, porosity, or cracks, ensuring mechanical properties. The titanium butt weld did not exhibit defects such as undercut or burn-through, and its corrosion resistance was also guaranteed. High-performance titanium-steel composite welded pipes were obtained.

[0053] Example 2

[0054] The titanium-steel composite welded pipe preparation method proposed in this invention is used to prepare a titanium-steel composite pipe with an outer diameter of 273 mm and a wall thickness of 10 mm (where the steel layer is Q235 carbon steel with a thickness of 8 mm and the titanium cladding is TA1 pure titanium with a thickness of 2 mm). The method includes the following steps: (1) Material preparation: cutting and finishing of the plate. Remove a certain width of titanium cladding near the bevel. Prepare thin titanium strips for butt welding. (2) Pipe rolling: roll the plate into a pipe. (3) Seam joining and welding: butt weld the longitudinal seam of the pipe in the mold, spot weld and fix it, and weld to complete the butt weld of the steel layer. (4) Finishing of the weld seam inside the pipe: remove the excess height on the back of the weld seam inside the pipe. (5) Butt welding of titanium layer: put the titanium strip into the groove of the inner wall of the pipe and butt its two sides with the titanium cladding of the plate to complete the welding of the titanium layer inside the pipe.

[0055] In step (1), the plate material is cut by laser cutting, and then the side edges are finished by milling and grinding to make the side surface flat. The width is calculated by the formula W = 3.14(D-δ) + δ, where D is the outer diameter of the welded pipe and δ is the pipe wall thickness, which is 837.53 mm; after inspection, the tolerance is about 0.1 mm.

[0056] In step (1), the width w of the titanium cladding near the bevel is set to 25mm. The method for removing the titanium cladding is as follows: The position of the cutting machine guide rail is adjusted with the side edge of the plate as a reference. The titanium cladding is cut using a precision cutting machine with a diamond cutting disc under water cooling. The cutting depth is set to the titanium cladding thickness minus 1.1mm. After cutting, a hydraulic press is used to peel the titanium cladding off the steel plate. Inspection shows that the width of the removed titanium cladding is 25mm, with a tolerance of 0.15mm.

[0057] In step (1), the butt welding titanium strip used is 0.5mm thick annealed TA2 pure titanium strip. The width is calculated using the formula 6.28w(D-2δ) / Wk, where k is 0.23mm, resulting in a value of 47.5mm. Laser cutting is used. Inspection shows the width tolerance is 0.05mm. Three pure titanium strips are used.

[0058] In step (2), the titanium-steel composite pipe is rolled using a die-bending method. Before bending, a positioning line is drawn every 5° with a steel needle, using the side as a reference. The parallelism between the positioning line and the side and the positioning line is 0.2mm. During bending, the center of the bottom of the punch is aligned with the positioning line.

[0059] In step (3), the pipe joint is performed using a pipe jointing machine. First, acetone is used to clean the oil stains on the surface near the joint. The pipe is transferred into the jointing machine mold, and the pipe is joined using a hydraulic mechanism. After joining, the two sides of the joint are completely fitted together, with no obvious gaps or misalignments. Spot welding is performed using the MIG / MAG welding method. 1.2mm diameter carbon steel welding wire is used, and the welding current is 120A; one weld point is made every 200mm. After spot welding, the steel butt joint is welded using the plasma filler wire welding method. The welding process parameters are: welding current 190A, plasma gas 2.7L / min, travel speed 0.5m / min, and wire feed speed 2.8m / min. After welding, the weld is inspected to ensure that the back of the weld, i.e., the surface of the weld inside the pipe, is fully penetrated; the weld top reinforcement is about 1.8mm.

[0060] In step (4), the method for removing the excess height at the bottom of the weld bead in the inner steel layer of the pipe is argon arc welding remelting. An argon arc welding torch driven by a linear guide slide module is used to remelt the excess height portion of the weld bead in the inner steel layer of the pipe. The remelting current is 80A, the tungsten needle tip angle is 30°, the tungsten needle tip height is 2mm, and the welding torch travel speed is 3.5mm / s. Upon inspection, the excess height of the remelted weld bead is less than 0.5mm throughout the entire weld length.

[0061] In step (5), during the butt welding of the titanium layer inside the pipe, multiple thin titanium strips are stacked into the groove on the inner wall of the pipe. The total thickness of the titanium strips is equal to the thickness of the titanium cladding. The two sides of the strips are aligned with the two sides of the groove on the inner wall of the pipe, and the gaps on both sides are roughly the same. Then, copper strips are pressed onto the thin titanium strips to fix them. The copper strips are 30mm wide, ensuring that the distance between their sides and the weld seams on both sides is about 9-10mm. The linear guide slide module is placed above the copper strips. The module is used to move the argon arc welding gun to spot weld and fix the multiple thin titanium strips to the titanium cladding. The spot welding sequence is as follows: first, spot weld the midpoint of the longitudinal direction of the weld seam, then spot weld at 1 / 4 and 3 / 4 of the longitudinal length of the weld seam, then spot weld the two ends, and then spot weld continuously at intervals of 300mm. Then, the module is used to move the argon arc welding gun to complete the welding of the entire weld seam. The spot welding process parameters are 80A, spot welding time 0.6s, and shielding gas flow rate 7L / min. Full weld seam welding process parameters: tungsten needle diameter 3.0mm, tungsten needle tip angle 30°, tungsten needle tip aligned with the side of the groove, tungsten needle tip height controlled at 1-2mm, welding current 200A, welding wire diameter 1.2mm, welding speed 3.5mm / s, wire feed speed 17mm / s, welding torch shielding gas flow rate 9L / min, drag shield protection range is a 60mm length directly behind the welding torch and a 10mm width area on each side of the weld seam, drag shield gas flow rate 20L / min.

[0062] Through precise design of the titanium-steel composite plate and titanium strip cutting process, as well as the pipe rolling and steel layer welding process, and utilizing the soft and easily deformable characteristics of pure titanium strips, multi-layer titanium strips were used to fill the grooves inside the pipe, achieving precise alignment of the titanium strips with the titanium cladding on the inner wall of the welded pipe. Observation revealed that after the titanium strips were pressed by copper strips, their sides were tightly attached to the sides of the grooves, and their bottoms were tightly attached to the bottoms of the grooves, ensuring no obvious protrusions after welding. Process inspection results showed high dimensional accuracy of the composite plate and titanium strips after cutting, resulting in precise control of the welded pipe dimensions. Precise cutting using the side of the plate as a reference, and removal of the titanium cladding for subsequent pipe welding, ensured precise control of the groove width. Precise positioning during pipe forming prevented weld skewing. After spot welding using the MIG / MAG method, plasma welding was used to weld the steel butt layer, achieving full penetration in one pass and preventing defects such as deformation, misalignment, and incomplete penetration. Argon arc welding was used to remelt the back reinforcement of the steel butt weld to prevent excessive reinforcement from obstructing the titanium strips. The above measures ensured the dimensions of the groove and titanium strip, preventing the titanium strip width from exceeding the groove width, thus avoiding the formation of a protrusion after welding, and also preventing the titanium strip width from being too narrow, resulting in an excessive gap between its side and the groove side after clamping. Using copper strips to clamp the titanium strips, taking advantage of their rapid heat conduction, prevented the thin titanium strips from curling after being heated by the electric arc. The small size of the linear guide slide module and the argon arc welding gun enabled arc spot welding and welding inside small-diameter pipes. Utilizing the precision welding process of argon arc welding, the weld depth was ensured to be controllable, preventing burn-through to the steel butt joint layer. Inspection showed that all three layers of strip at the weld were melted, and the weld depth exceeded 80%. Due to the filler wire, an additional height of approximately 1mm was formed at the weld. A weld with no obvious protrusions on the inner wall of the pipe and conforming to the required dimensions and shape was obtained. Non-destructive testing showed that the steel layer weld had no defects such as incomplete penetration, porosity, or cracks, ensuring mechanical properties. The titanium butt weld did not exhibit defects such as undercut or burn-through, and its corrosion resistance was also guaranteed. High-performance titanium-steel composite welded pipes were obtained.

Claims

1. A method for preparing titanium-steel composite welded pipes, characterized in that: The aforementioned preparation method, through several steps including precise material cutting, precision forming and assembly, steel substrate welding and weld shaping, and titanium cladding assembly and welding, yields titanium-steel composite welded pipes with qualified mechanical properties and corrosion resistance, capable of passing ball testing. Among them, while accurately cutting the material, the titanium coating within the specified width near the welding groove is removed (1). During precision forming and assembly, the titanium-steel composite plate is rolled into a round tube using a die bending method to achieve precise alignment and complete the precision forming and assembly work. When welding the steel substrate and shaping the weld, first weld the round steel substrate layer (2), and then remelt and shape the weld inside the pipe. When removing the titanium cladding (1), after finishing the edge trimming, a diamond cutting disc is used as the cutting tool and a precision cutting machine is used to cut the titanium cladding (1). Then, the titanium cladding (1) is peeled off from the steel substrate layer (2) to complete the removal of the titanium cladding (1) near the weld bevel. The width w of the removed titanium cladding (1) is (5~30) ±0.2 mm on one side, and the cutting depth is the thickness of the titanium cladding (1) δ - (0.1~0.2) mm. After the steel substrate layer (2) inside the pipe is welded, the bottom height of the weld bead is shaped by argon arc welding remelting method. The specific process is as follows: An argon arc welding torch driven by a linear guide slide module (4) is used to remelt the excess weld height of the steel substrate layer (2) inside the pipe, ensuring that the excess weld height after remelting is less than 0.5 mm. When assembling the titanium cladding (1) inside the pipe, at least two layers of annealed TA1 or TA2 pure titanium strips (3) are overlapped and arranged above the weld bead (7) of the steel substrate layer inside the pipe. The two sides of each layer of annealed TA1 or TA2 pure titanium strips (3) are aligned with the existing titanium cladding inside the pipe. Then, copper strips (5) are used to press each layer of annealed TA1 or TA2 pure titanium strips (3) so that the compacted thickness of each layer of annealed TA1 or TA2 pure titanium strips (3) is greater than the thickness of the existing titanium cladding (1). Then, each layer of annealed TA1 or TA2 pure titanium strips (3) is spot welded firmly to the existing titanium cladding (1) on the corresponding side to complete the assembly of the titanium cladding inside the pipe. The spot welding is carried out by an argon arc welding gun (6) driven by a linear guide slide module (4). The spot welding sequence is as follows: first spot weld the midpoint of the longitudinal direction of the weld, then spot weld the 1 / 4 and 3 / 4 length of the longitudinal direction of the weld and both ends, then spot weld continuously at intervals not exceeding 300mm, and finally drive the argon arc welding gun (6) to complete the welding of the entire weld.

2. The method for preparing titanium-steel composite welded pipe according to claim 1, characterized in that: During precise material cutting, the titanium-steel composite plate is first cut into rough blanks of a specified width using laser cutting, water jet cutting, plasma cutting, or wire cutting. Then, milling or planing and finally grinding are used to obtain a precise blank with straight side surfaces and a plate width of W=3.14(D-δ)+δ, where D is the outer diameter of the welded pipe, δ is the pipe wall thickness, and the tolerance of the plate width W is ±0.2mm.

3. The method for preparing titanium-steel composite welded pipe according to claim 2, characterized in that: The raw slabs are obtained by laser cutting or waterjet cutting, and the finishing and trimming are done by milling.

4. The method for preparing titanium-steel composite welded pipe according to claim 1, 2 or 3, characterized in that: During precision forming and assembly using the die bending method, before bending, a steel needle is used to scribing a line with the side as a reference. A positioning line is drawn every 5° to the cross-sectional circle of the tube. The parallelism between the positioning line and the side, and between the positioning lines themselves, is ±0.2mm. During bending, the center of the bottom of the punch is aligned with the positioning line.

5. The method for preparing titanium-steel composite welded pipe according to claim 4, characterized in that: The titanium-steel composite plate is formed by bending and rolling in a die, and then joined and spot-welded in a pipe joining machine. The specific process is as follows: First, use anhydrous ethanol or acetone to clean the oil stains on the surface near the weld. Then, transfer the rolled tube blank into the welding machine mold and use a hydraulic mechanism to weld the tube. During welding, the two sides of the weld are completely aligned with a gap of 0-0.5mm and the misalignment does not exceed 0.5mm. Next, spot welding is performed using the MIG welding method, with a spacing of 200±5mm between two adjacent weld points.

6. The method for preparing titanium-steel composite welded pipe according to claim 5, characterized in that: After spot welding, the inner steel substrate layer (2) is butt welded using plasma filler wire welding. The welding parameters should ensure full penetration. The wire feeding parameters should ensure that the top of the weld is 0-3mm above the outer surface of the pipe. The covering material of the titanium cladding (1) assembly is annealed TA1 or TA2 pure titanium strip (3). The width of the annealed TA1 or TA2 pure titanium strip (3) is 3.14w(D-2δ) / Wk, where k is 0.1-0.5mm and the strip width tolerance is 0.2mm. The thickness is 0.3-0.6mm.

7. The method for preparing titanium-steel composite welded pipe according to claim 1, characterized in that: The tack welding process parameters for titanium cladding butt welds are 60–100 A, tack welding time 0.3–0.8 s, and shielding gas flow rate 5–10 L / min. The full weld welding process parameters are: tungsten needle diameter 2.0–4.0 mm, tungsten needle tip angle 30–45°, tungsten needle tip aligned with the side of the groove, tungsten needle tip height 1–3 mm, welding current 150–250 A, welding wire diameter 1.0–1.6 mm, welding speed 2–5 mm / s, wire feed speed 10–25 mm / s, shielding gas flow rate 5–10 L / min, and the shielding range is at least 50 mm in length directly behind the welding torch and 10 mm in width on both sides of the weld, with a shielding gas flow rate of 20–30 L / min.

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