Method of welding a magnet cooling tube

Abstract

The application discloses a kind of welding methods of magnet cooling pipe, it is related to nuclear fusion device technical field, and welding method is suitable for welding the cooling pipe of longitudinal field magnet of tokamak fusion device, and include: prepare two to be welded cooling pipe;In the radial outer side area of two to be welded cooling pipe's to be welded end face towards each other, welding bevel is processed, and root face is reserved in the radial inner side area of to be welded end face;Two to be welded cooling pipe is fixed, so that the root face of two to be welded end face is attached and welding bevel forms welding groove;First, from the root of welding groove, using pulse self-fusion mode is carried out backing welding;Again, using pulse wire filling mode is carried out cover surface welding to welding groove.The welding method of magnet cooling pipe of the application can effectively control the internal weld reinforcement of to-be-welded cooling pipe, avoid the pipe opening of to-be-welded cooling pipe being blocked, and can improve the weld quality, effectively reduce the permeability of weld, and the mode of pulse welding can reduce welding heat input, reduce the possibility of to-be-welded cooling pipe deformation.

Description

Technical Field

[0001] This invention relates to the field of nuclear fusion device technology, and in particular to a welding method for magnet cooling tubes. Background Technology

[0002] The TF (longitudinal field) superconducting magnet is one of the key components of a tokamak nuclear fusion device, used to generate a strong magnetic field to confine high-temperature plasma. During operation, it needs to continuously remove heat through cooling tubes to prevent the superconducting coils from overheating and affecting magnetic field generation. Due to the compact structure of the fusion device, the cooling tubes are φ8×1.5mm in size. Austenitic stainless steel has excellent low-temperature resistance, corrosion resistance, and processing properties; therefore, the magnet cooling tubes are made of 316LN austenitic stainless steel. The cooling tubes are connected together by welding and distributed on the magnet surface. During operation, liquid helium is circulated inside the cooling tubes to cool the magnet.

[0003] Because the cooling pipe is small in size, with an outer diameter of 8mm and an inner diameter of only 5mm, the root weld metal during the welding process can easily block the inside of the pipe and cause large welding deformation, making the cooling pipe lose its normal working ability. There is room for improvement. Summary of the Invention

[0004] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a welding method for a magnet cooling tube. The welding method can effectively control the weld reinforcement inside the cooling tube to be welded, avoid clogging the tube opening, improve weld quality, effectively reduce weld permeability, and the pulse welding method can greatly reduce welding heat input and reduce the possibility of deformation of the cooling tube to be welded.

[0005] According to the welding method of the magnet cooling tube of the present invention, the welding method is applicable to welding the cooling tube of the longitudinal field magnet of the tokamak fusion device, and includes: preparing two cooling tubes to be welded; processing a welding bevel in the radially outer region of the two cooling tubes facing each other, and reserving a blunt edge in the radially inner region of the two end faces to be welded; fixing the two cooling tubes to be welded so that the blunt edges of the two end faces to be welded fit together and the welding bevel forms a welding groove; first performing root welding from the root of the welding groove using a pulsed self-fusion method; and then performing cover welding on the welding groove using a pulsed filler wire method.

[0006] According to the welding method of the magnet cooling tube of the present invention, by forming welding bevels and blunt edges on the welding end faces of the two cooling tubes to be welded respectively, after fixing the two cooling tubes to be welded, the root pass welding can be performed first from the root of the welding groove formed by the two welding bevels using a pulse self-fusion method to connect the blunt edge areas of the two welding end faces. This can effectively control the weld reinforcement inside the cooling tubes to be welded and avoid clogging the tube openings. Then, the welding grooves are covered by a pulse filler wire method to connect the welding bevel areas of the two welding end faces. This can improve the weld quality, effectively reduce the weld permeability, and the pulse welding method can greatly reduce the welding heat input and reduce the possibility of deformation of the cooling tubes to be welded.

[0007] According to the welding method of the magnet cooling tube of the present invention, the step of performing root welding from the root of the welding groove using a pulse self-fusion method includes: firstly, starting an arc from the bottom of the two end faces to be welded, welding along a first direction from the bottom of the end face to the top of the end face to be welded at the root of the welding groove; secondly, starting an arc from the bottom of the two end faces to be welded again, welding along a second direction from the bottom of the end face to the top of the end face to be welded at the root of the welding groove, wherein the second direction is opposite to the first direction.

[0008] According to the welding method of the magnet cooling tube of the present invention, the pulse base current for the first root welding using pulse self-fusion method from the root of the welding groove is I1, the peak current is I2, and the duty cycle is C1, and satisfies: 15A < I1 < 25A, 35A < I2 < 45A, 35% < C1 < 45%.

[0009] According to the welding method of the magnet cooling tube of the present invention, the step of performing cover welding on the welding groove using a pulse filler wire method includes: firstly, starting an arc from the bottom of the two end faces to be welded, welding along the first direction at the welding groove from the bottom of the end face to be welded to the top of the end face to be welded; and again starting an arc from the bottom of the two end faces to be welded, welding along the second direction at the welding groove from the bottom of the end face to the top of the end face to be welded.

[0010] According to the welding method of the magnet cooling tube of the present invention, the pulse base current of the welding groove for the cover welding using the pulse filler wire method is I3, the peak current is I4, and the duty cycle is C2, and satisfies: 15A < I3 < 25A, 35A < I4 < 45A, 30% < C2 < 40%.

[0011] According to the welding method of the magnet cooling tube of the present invention, the step of processing a welding bevel in the radially outer region of the two cooling tubes to be welded facing each other, and reserving a blunt edge in the radially inner region of the end faces to be welded includes: processing a sloped surface in the radially outer region of the end faces to be welded to form the welding bevel, wherein the angle between the sloped surface and the end face to be welded is α, and satisfies: 25°<α<35°; forming the blunt edge in the radially inner region of the end faces to be welded, and grinding the blunt edge.

[0012] According to the welding method of the magnet cooling tube of the present invention, the step of fixing the two cooling tubes to be welded so that the blunt edges of the two end faces to be welded fit together and the welding bevel forms a welding groove includes: fixing the two cooling tubes to be welded to a fixed tube frame respectively, and distributing the end faces to be welded of the two cooling tubes facing each other; and tightly fitting the end faces to be welded of the two cooling tubes so that the gap between the two end faces to be welded is not greater than 0.5 mm and the bend angle of the tube openings of the two cooling tubes to be welded is not greater than 1°.

[0013] The welding method for the magnet cooling tube according to the present invention further includes cleaning the outer side of the end face to be welded and the welding groove before fixing the two cooling tubes to be welded.

[0014] The welding method for the magnet cooling tube according to the present invention further includes: before welding, introducing a back protective gas for a first duration into the cooling tube to be welded, the first duration being t, and satisfying: 30s < t < 60s; after the gas is introduced, spot welding is performed on the two end faces of the cooling tubes to be welded, the spot welding position being located at the top of the cooling tubes to be welded.

[0015] The welding method for the magnet cooling tube according to the present invention further includes: performing non-destructive testing on the weld after welding, wherein the non-destructive testing methods include visual inspection, penetrant testing and radiographic testing.

[0016] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0017] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 The process flow of the welding method for the magnet cooling tube according to the present invention is as follows. Figure 1 ; Figure 2 The process flow of the welding method for the magnet cooling tube according to the present invention is as follows. Figure 2 ; Figure 3The process flow of the welding method for the magnet cooling tube according to the present invention is as follows. Figure 3 ; Figure 4 The process flow of the welding method for the magnet cooling tube according to the present invention is as follows. Figure 4 ; Figure 5 The process flow of the welding method for the magnet cooling tube according to the present invention is as follows. Figure 5 ; Figure 6 This is a schematic diagram of two cooling pipes to be welded according to the present invention. Figure 1 ; Figure 7 This is a schematic diagram of two cooling pipes to be welded according to the present invention. Figure 2 ; Figure 8 This is a schematic diagram of the cooling pipe to be welded according to the present invention.

[0018] Figure label: 1. Cooling pipe to be welded; 2. End face to be welded; 3. Welding bevel; 4. Blunt edge; 5. Welding groove; 6. Sloping surface; 7. Weld. Detailed Implementation

[0019] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0020] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, features defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0021] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0022] The following is for reference. Figures 1-8 The welding method for the magnet cooling tube according to the present invention can effectively control the weld reinforcement inside the cooling tube 1 to be welded, avoid clogging the tube opening of the cooling tube 1 to be welded, improve the weld quality, effectively reduce the weld permeability, and the pulse welding method can greatly reduce the welding heat input and reduce the possibility of deformation of the cooling tube 1 to be welded.

[0023] like Figure 1 As shown, the welding method for the magnet cooling tube according to the present invention is applicable to welding the cooling tube of the longitudinal field magnet of a tokamak fusion device, and includes: S10: Prepare two cooling pipes 1 to be welded.

[0024] Specifically, a tokamak fusion device is a toroidal device that uses magnetic confinement to achieve controlled nuclear fusion. The superconducting magnet system of a tokamak fusion device includes a longitudinal field magnet and a poloidal field magnet, which are used to generate a strong confinement magnetic field after being energized. It is equipped with a dedicated magnet cooling tube to maintain superconducting operation. The magnet cooling tube in this invention is used to cool the longitudinal field magnet. Due to industrial manufacturing limitations, the length of a single magnet cooling tube has an upper limit and cannot be adapted to the length and requirements of the longitudinal field magnet. Therefore, it is necessary to connect multiple magnet cooling tubes end to end in sequence to increase the overall length of the magnet cooling tube, so that the connected magnet cooling tube can be adapted to the length and requirements of the longitudinal field magnet.

[0025] Among them, due to the good low temperature resistance, corrosion resistance and processing performance of austenitic stainless steel, the material of magnet cooling tubes is usually 316LN austenitic stainless steel. Two adjacent magnet cooling tubes are connected together by welding process and distributed on the surface of the longitudinal field magnet. During the operation of the magnet cooling tubes, liquid helium is usually introduced into them to cool the longitudinal field magnet.

[0026] The welding method for magnet cooling tubes of the present invention is applicable to welding magnet cooling tubes of longitudinal field magnets in tokamak fusion devices. That is, the welding method of the present invention can be used to weld two adjacent magnet cooling tubes together to increase the length of the magnet cooling tubes. Before welding two magnet cooling tubes, two cooling tubes 1 to be welded need to be prepared. The two cooling tubes 1 to be welded are two magnet cooling tubes waiting to be welded together. That is, before welding two cooling tubes 1 to be welded, two magnet cooling tubes for cooling longitudinal field magnets that need to be welded together need to be prepared.

[0027] S20: Welding grooves 3 are machined in the radially outer region of the two end faces 2 of the cooling pipes 1 facing each other, and blunt edges 4 are reserved in the radially inner region of the end faces 2.

[0028] Specifically, the two cooling pipes 1 to be welded are connected end to end by welding. The two cooling pipes 1 to be welded are arranged opposite each other along the axial direction, and the two cooling pipes 1 to be welded are connected by welding one end face of each other. That is, the one end face of each cooling pipe 1 to be welded is the welding end face 2. The cooling pipe 1 to be welded is hollow and has a certain wall thickness. The welding end faces 2 of the two cooling pipes 1 to be welded are distributed opposite each other and are both constructed as annular. Welding grooves 3 are processed in the radially outer region of the welding end faces 2 of the two cooling pipes 1 to be welded. Welding grooves 3 are processed in the radially outer region of the welding end faces 2 to be welded. A blunt edge 4 is reserved in the radially inner region of the welding end faces 2 to be welded. Welding grooves 3 and blunt edges 4 are formed on the welding end faces 2 respectively, and the blunt edge 4 can be located inside the radial direction of the welding groove 3 on the welding end faces 2.

[0029] Thus, when welding two cooling pipes 1 to be welded together, the welding groove 3 and the blunt edge 4 of the two cooling pipes 1 to be welded together can be welded together to form a multi-layer weld. The heat input of each weld is small, the welding stress distribution is more uniform, and the welding deformation caused by local overheating is greatly reduced. The welding groove 3 is a groove of a specific geometric shape pre-processed on the end face 2 to be welded, which is used to allow the electric arc to penetrate deep into the root of the weld 7 to ensure full fusion and avoid welding defects such as root non-fusion. The blunt edge 4 is a straight edge reserved at the root of the welding groove 3 to prevent the root burn-through problem during the welding process.

[0030] S30: Fix the two cooling pipes 1 to be welded so that the blunt edges 4 of the two end faces 2 to be welded fit together and the welding bevel 3 forms a welding groove 5.

[0031] Specifically, fixing the two cooling tubes 1 to be welded can prevent any one of them from shifting or moving during the welding process, which could lead to welding failure or poor weld quality. When fixing the two cooling tubes 1, they need to be set and fixed according to their welding positions to facilitate subsequent welding steps. The welding end faces 2 of the two cooling tubes 1 can be set facing each other so that the blunt edges 4 of the two welding end faces 2 are in contact, so that the blunt edges 4 of the two cooling tubes 1 can be connected by welding. The welding bevel 3 of the two welding end faces 2 forms a welding groove 5. The welding groove 5 is used to provide the arc with operating space that reaches the root of the weld 7, and can also be used to accommodate filler metal.

[0032] S40: First, perform root welding using pulse self-fusion method from the root of welding groove 5.

[0033] Specifically, after fixing the two cooling pipes 1 to be welded, the two cooling pipes 1 can be welded. First, as follows... Figure 7 As shown, the root welding can be performed from the root of the welding groove 5 using pulse self-fusion. The root welding is the first root welding process in the multi-layer welding process. It is the core foundation process to ensure that the weld 7 achieves full penetration. It directly acts on the blunt edge 4 and the butt gap at the root of the welding groove 5 and is the basis for the subsequent cover welding. The core goal is to completely melt the blunt edge 4 at the root of the welding groove 5 to form a continuous and uniform root weld, achieve single-sided welding and double-sided forming, and avoid defects such as incomplete penetration and burn-through.

[0034] The pulsed self-melting method relies on the periodic energy output of the pulsed arc to melt the blunt edge 4 region of the cooling tube 1 to be welded, stably achieving single-sided welding and double-sided forming. It utilizes the periodically changing current output of the pulsed power supply to rapidly melt the blunt edge 4 at the root of the welding groove 3 during the peak current stage, forming a fully molten liquid pool. During the base current stage, the arc is kept stable, while a short cooling and solidification time is reserved for the molten pool. The total heat input of the molten pool is precisely controlled. No filler wire is used throughout the process, and the weld 7 is formed entirely by melting the metal of the cooling tube 1 to be welded, avoiding the contamination problems that may be caused by filler wire.

[0035] S50: Then, use the pulse filler wire method to perform cover welding on the welding groove 5.

[0036] Then, as Figure 7 As shown, the welding groove 5 can be covered by pulse filler welding. Cover welding is the last surface weld of the multi-layer welding process. It is the key link that determines the final appearance and surface quality of the weld 7. It is the core finishing process after the root welding is completed. The core goal is to completely fill the remaining welding groove 5 after the root welding to form a continuous and flat surface weld, so that the appearance indicators such as weld height and width meet the standard requirements.

[0037] The pulsed filler wire method and the pulsed self-fusion method complement each other and are the core welding process that takes into account both the penetration quality and the performance of the weld seam 7. The pulsed power supply outputs a periodically changing current. During the peak current stage, the cooling tube 1 to be welded and the simultaneously fed filler wire at the welding groove 3 are melted to form a liquid molten pool with penetration. During the base current stage, the arc is kept stable, while a short cooling time is reserved for the molten pool. The total heat input is precisely controlled to avoid overheating and deformation of the cooling tube 1 to be welded.

[0038] Among them, the welding wire can be ER316LMn welding wire, etc. ER316LMn is a special filler welding wire specifically adapted for welding austenitic stainless steel. When used with pulse welding, it can effectively reduce the magnetic permeability of the weld.

[0039] It should be noted that the pulse self-fusion method for root pass welding can effectively control the weld reinforcement inside the cooling tube 1 to be welded, and avoid clogging the tube opening of the cooling tube 1 to be welded. The pulse filler wire method for cover pass welding can improve the weld quality, effectively reduce the weld permeability, and the pulse welding method can greatly reduce the welding heat input and reduce the possibility of deformation of the cooling tube 1 to be welded.

[0040] According to the welding method of the magnet cooling tube of the present invention, by forming welding grooves 3 and blunt edges 4 on the welding end faces 2 of the two cooling tubes 1 to be welded respectively, after fixing the two cooling tubes 1 to be welded, the root welding can be performed first from the root of the welding groove 5 formed by the two welding grooves 3 using a pulse self-fusion method to connect the blunt edge 4 areas of the two welding end faces 2 to be welded. This can effectively control the weld reinforcement inside the cooling tube 1 to be welded and avoid clogging the tube opening of the cooling tube 1 to be welded. Then, the welding groove 5 is covered by a pulse filler welding method to connect the welding groove 3 areas of the two welding end faces 2 to be welded. This can improve the weld quality, effectively reduce the weld permeability, and the pulse welding method can greatly reduce the welding heat input and reduce the possibility of deformation of the cooling tube 1 to be welded.

[0041] In this invention, such as Figure 2 As shown, the root pass welding is performed first from the root of the welding groove 5 using a pulse self-fusion method, including: S41: Start from the bottom of the two end faces 2 to be welded, and weld along the first direction from the bottom of the end face 2 to the top of the end face 2 at the root of the welding groove 5.

[0042] It should be noted that in practice, when welding two cooling pipes 1 to be welded, they are usually joined together in a horizontal direction. This allows the two cooling pipes 1 to be distributed and connected in a horizontal direction, so that the end face 2 to be welded can be located in a vertical plane. That is, the bottom of the end face 2 to be welded is below the end face 2 to be welded in the vertical direction, and the top of the end face 2 to be welded is above the end face 2 to be welded in the vertical direction. Moreover, the welding groove 5 is defined by the welding bevel 3 of the two end faces 2 to be welded. That is, the welding groove 5 extends radially along the end face 2 to be welded, so that the root of the welding groove 5 is the inner end of the welding groove 5 radially along the end face 2 to be welded, that is, the root of the welding groove 5 is the end of the welding groove 5 facing the blunt edge 4.

[0043] Specifically, when performing root pass welding using pulse self-fusion at the root of the welding groove 5, the arc can be started from the bottom of the two end faces 2 to be welded, and welding can be performed along the first direction from the bottom of the end face 2 to the top of the end face 2 at the root of the welding groove 5. Welding can be performed at the root of the welding groove 5, and welding can be performed along the first direction from the bottom of the end face 2 to the top of the end face 2. The first direction can be clockwise or counterclockwise, and welding can be performed from bottom to top along the first direction. Welding can also be performed at the blunt edge 4 of half annular area of ​​the two end faces 2 to be welded. The welding position can be advanced from the low position to the high position, which can provide a deeper penetration to fully ensure the complete penetration of the root of the weld 7, avoid root non-fusion defects, and require less heat input, which helps to reduce the possibility of welding deformation of the cooling pipe 1 to be welded.

[0044] S42: Starting from the bottom of the two end faces 2 to be welded again, weld along the second direction from the bottom of the end face 2 to the top of the end face 2 at the root of the welding groove 5. The second direction is opposite to the first direction.

[0045] Then, starting from the bottom of the two end faces 2 to be welded again, welding can be performed along the second direction from the bottom of the end face 2 to the top of the end face 2 at the root of the welding groove 5. Welding can be performed at the root of the welding groove 5, and welding can be performed along the second direction from the bottom of the end face 2 to the top of the end face 2 to be welded. Welding can be performed from bottom to top along the second direction, and the second direction is opposite to the first direction. That is, when the first direction is clockwise, the second direction can be counterclockwise, or when the first direction is counterclockwise, the second direction can be clockwise. In this way, the blunt edge 4 of the other half of the annular area of ​​the two end faces 2 to be welded can be welded, and the blunt edge 4 area can be completely welded at the root of the welding groove 5, which can ensure the reliable connection of the two cooling pipes 1 to be welded at the blunt edge 4.

[0046] Furthermore, advancing the welding position from a low position to a high position can provide a deeper penetration, ensuring complete penetration of the root of weld 7, avoiding root incomplete fusion defects, and requiring less heat input, which helps reduce the possibility of welding deformation of the cooling pipe 1 to be welded.

[0047] In such Figure 8 In the illustrated embodiment, the first direction can be clockwise and the second direction can be counterclockwise.

[0048] In this invention, the pulse base current for the root welding of the welding groove 5 using the pulse self-fusion method is I1, the peak current is I2, and the duty cycle is C1, and the following conditions are met: 15A < I1 < 25A, 35A < I2 < 45A, 35% < C1 < 45%.

[0049] Specifically, the root pass is first welded from the bottom of the welding groove 5 using a pulsed self-fusion method. This method utilizes the periodically changing current output by the pulsed power supply to rapidly melt the blunt edge 4 at the root of the welding groove 3 during the peak current stage, forming a fully fused liquid pool. During the base current stage, the arc is kept stable, while a short cooling and solidification time is reserved for the molten pool, thus precisely controlling the total heat input of the molten pool.

[0050] The pulse base current can be set to I1, and the pulse base current can be between 15A and 25A. For example, the pulse base current can be 18A, 20A or 23A, etc. This can avoid the pulse base current being too small or too large. If the pulse base current is too small, it will lead to insufficient heat input and easy to cause non-fusion defects. If the pulse base current is too large, it will lead to higher average heat input and increase the total heat received by the cooling tube 1 to be welded.

[0051] The peak current can be set to I2, and the peak current can be between 35A and 45A, such as 38A, 40A or 43A. This can avoid the peak current being too small or too large. If the peak current is too small, it will lead to insufficient penetration depth and easy to cause incomplete penetration defects. If the peak current is too large, it will lead to excessive instantaneous heat input and excessive fluidity of the molten pool metal, which will easily cause problems such as surface collapse of weld 7 and uneven distribution of weld reinforcement.

[0052] Duty cycle refers to the proportion of the peak current duration within the pulse period to the entire pulse period. The duty cycle can be set to C1 and should be between 35% and 45%, such as 38%, 40%, or 43%. This avoids the duty cycle being too small or too large. If the duty cycle is too small, the peak current duration will be too short, which may lead to defects such as incomplete penetration or lack of fusion at the root. If the duty cycle is too large, the overall heat input will be too large, which may lead to severe welding deformation.

[0053] It should be noted that the pulse self-fusion type root pass welding of the present invention is a low-current pulse welding.

[0054] In this invention, such as Figure 3 As shown, the next step of welding the welding groove 5 using the pulse filler wire method for cover welding includes: S51: Start from the bottom of the two end faces 2 to be welded, and weld along the first direction from the bottom of the end face 2 to the top of the end face 2 at the welding groove 5.

[0055] Specifically, when using pulse filler wire method to perform cover welding on the welding groove 5, the arc can be started from the bottom of the two end faces 2 to be welded, and welding can be performed from the bottom to the top of the end face 2 to be welded along the first direction at the welding groove 5. Welding can be performed at the welding groove 5, and welding can be performed from the bottom to the top of the end face 2 to be welded along the first direction. Welding can be performed from bottom to top along the first direction. Welding can also be performed at the welding bevel 3 of half annular area of ​​the two end faces 2 to be welded. The welding position can be advanced from the low position to the high position, which can provide a deeper penetration to fully ensure the complete penetration of the root of the weld 7, avoid root non-fusion defects, and require less heat input, which helps to reduce the possibility of welding deformation of the cooling pipe 1 to be welded.

[0056] S52: Starting from the bottom of the two end faces 2 to be welded again, weld along the second direction from the bottom of the end face 2 to the top of the end face 2 at the welding groove 5.

[0057] Then, starting from the bottom of the two end faces 2 to be welded again, welding can be performed along the second direction at the welding groove 5 from the bottom to the top of the end face 2 to be welded. Welding can be performed at the root of the welding groove 5. Welding can be performed along the second direction from the bottom to the top of the end face 2 to be welded. Welding can be performed from bottom to top along the second direction. Welding can also be performed at the welding bevel 3 of the other half of the annular area of ​​the two end faces 2 to be welded. Welding can be performed completely at the root of the welding groove 5 at the welding bevel 3. This can ensure a reliable connection of the two cooling pipes 1 to be welded at the welding bevel 3. The welding position can be advanced from the low position to the high position, which can provide a deeper penetration to fully ensure the complete penetration of the root of the weld 7, avoid root non-fusion defects, and require less heat input, which helps to reduce the possibility of welding deformation of the cooling pipe 1 to be welded.

[0058] In this invention, the pulse base current for the welding groove 5 to be covered by the pulse filler wire method is I3, the peak current is I4, and the duty cycle is C2, and the following conditions are met: 15A < I3 < 25A, 35A < I4 < 45A, 30% < C2 < 40%.

[0059] Specifically, the welding groove 5 is then covered by a pulse filler wire method. The pulse power supply outputs a periodically changing current. During the peak current stage, the cooling tube 1 to be welded at the welding groove 3 and the simultaneously fed filler wire are melted to form a fully molten liquid pool. During the base current stage, the arc is kept stable, while a short cooling time is reserved for the molten pool. The total heat input is precisely controlled to avoid overheating and deformation of the cooling tube 1 to be welded.

[0060] The pulse base current can be set to I3, and the pulse base current can be between 15A and 25A. For example, the pulse base current can be 18A, 20A or 23A, etc. This can avoid the pulse base current being too small or too large. If the pulse base current is too small, it will lead to insufficient heat input and easy to cause non-fusion defects. If the pulse base current is too large, it will lead to higher average heat input and increase the total heat received by the cooling tube 1 to be welded.

[0061] The peak current can be set to I4, and the peak single current can be between 35A and 45A, such as 38A, 40A or 43A, etc. This can avoid the peak current being too small or too large. If the peak current is too small, it will lead to insufficient penetration depth and easy to have incomplete penetration defects. If the peak current is too large, it will lead to excessive instantaneous heat input, excessive fluidity of the molten pool metal, and easy to have problems such as surface collapse of weld 7 and uneven distribution of reinforcement height.

[0062] The duty cycle can be set to C2, and the duty cycle should be between 30% and 40%, such as 33%, 35% or 38%, etc. This can avoid the duty cycle being too small or too large. If the duty cycle is too small, the peak current duration will be too short, which will easily lead to defects such as incomplete penetration and lack of fusion at the root. If the duty cycle is too large, the overall heat input will be too large, which will easily lead to serious welding deformation.

[0063] It should be noted that the pulse filler wire type cover welding of the present invention is a low current pulse welding.

[0064] In this invention, such as Figure 4 As shown, the process of machining a welding bevel 3 in the radially outer region of the two cooling pipes 1 facing each other on their respective welding end faces 2, and reserving a blunt edge 4 in the radially inner region of the welding end faces 2 includes: S21: A sloped surface 6 is machined in the radially outer region of the end face 2 to form a welding groove 3. The angle between the sloped surface 6 and the end face 2 to be welded is α, and satisfies: 25°<α<35°.

[0065] Specifically, the end face 2 to be welded is annular. A sloped surface 6 is machined in the radially outer region of the end face 2 to form a welding groove 3. The sloped surface 6 is machined in the part of the end face 2 facing the outside of the cooling pipe 1 to be welded. The sloped surface 6 is inclined relative to the end face 2 to be welded and gradually approaches the cooling pipe 1 from the inside to the outside along the radial direction of the end face 2 to form a welding groove 3 at the sloped surface 6 of the end face 2 to be welded. Then, when the blunt edges 4 of the two cooling pipes 1 to be welded are put together, the two welding grooves 3 can jointly form an outwardly open welding groove 5.

[0066] For each cooling pipe 1 to be welded, the angle between the slope surface 6 and the end face 2 to be welded can be set to α, and α can be between 25° and 35°, such as α being 28°, 30° or 32°, etc. This can avoid the angle between the slope surface 6 and the end face 2 to be welded being too small or too large. If the angle is too small, the electric arc will have difficulty penetrating to the root of the weld 7, which will easily lead to defects such as incomplete penetration and incomplete fusion at the root. If the angle is too large, the amount of filler metal will be too large, and the surface of the weld 7 will easily have problems such as excessive excess height and uneven formation.

[0067] S22: A blunt edge 4 is formed in the radial inner region of the end face 2 to be welded, and the blunt edge 4 is ground.

[0068] Specifically, a sloped surface 6 is machined in the area of ​​the end face 2 facing outwards from the cooling pipe 1, so that a blunt edge 4 is formed in the area of ​​the end face 2 facing inwards from the cooling pipe 1. In other words, a part of the end face 2 is machined into a sloped surface 6, and another part forms a blunt edge 4. The blunt edge 4 is then ground. Grinding is a key pre-processing step to ensure welding quality. For example, the blunt edge 4 can be processed by an angle grinder to remove impurities such as oxide scale and oil stains from the surface of the blunt edge 4, so that the heat of the electric arc can be fully transferred to the root, achieving complete fusion at the root and avoiding incomplete penetration defects. Grinding can also eliminate the sharp edges at the blunt edge 4 and reduce stress concentration at the root of the weld 7.

[0069] For example, such as Figure 6 As shown, in practice, the outer diameter of the cooling tube 1 to be welded can be 8mm, and the inner diameter can be 5mm, meaning the wall thickness of the cooling tube 1 to be welded can be 1.5mm. This also means the radial length of the end face 2 to be welded is 1.5mm, allowing the depth L1 of the welding groove 5 to be 0.5mm and the height L2 of the blunt edge 4 to be 1mm, thus meeting the process requirements of pulse self-fusion root pass welding. It should be noted that the height of the blunt edge 4 cannot be too small to avoid burn-through at the root.

[0070] In this invention, such as Figure 5 As shown, fixing the two cooling pipes 1 to be welded so that the blunt edges 4 of the two end faces 2 to be welded fit together and the welding groove 3 forms a welding groove (5) includes: S31: Fix the two cooling pipes 1 to be welded to the fixed pipe rack respectively, and make the welding end faces 2 of the two cooling pipes 1 face each other.

[0071] Specifically, when fixing the two cooling pipes 1 to be welded, the two cooling pipes 1 to be welded can be fixed to the fixed pipe rack respectively. The fixed pipe rack is used to fix the cooling pipes 1 to be welded separately, so that the two cooling pipes 1 to be welded can be fixed at different positions on the fixed pipe rack, which can avoid interference and ensure reliable fixing of the two cooling pipes 1 to be welded. Moreover, by making the end faces 2 of the two cooling pipes 1 to be welded face to face, the two cooling pipes 1 to be welded can be arranged coaxially, so that there is no obvious misalignment on the inner wall of the two cooling pipes 1 to be welded. When conveying the medium, there will be no local eddy currents and sudden changes in resistance, which reduces the operating energy consumption of the magnet cooling pipe. Furthermore, the gap of the welding bevels 3 on both sides is uniform and consistent, and the arc can evenly cover the entire root circumference during the root welding, avoiding local incomplete penetration.

[0072] S32: The welding end faces 2 of the two cooling pipes 1 to be welded are tightly fitted together so that the gap between the two welding end faces 2 is no greater than 0.5mm and the bend angle of the pipe openings of the two cooling pipes 1 to be welded is no greater than 1°.

[0073] Specifically, by tightly fitting the welding end faces 2 of the two cooling pipes 1 to be welded, the blunt edges 4 of the two welding end faces 2 can be tightly fitted together, which can control the root gap within a reasonable range to meet the process requirements of self-fusion root welding, avoid burn-through problems caused by excessive gap, and ensure that the gap between the two welding end faces 2 is no greater than 0.5mm. For example, the gap between the two welding end faces 2 can be 0.2mm, 0.3mm or 0.4mm, etc., to avoid the gap between the two welding end faces 2 being too large, thereby preventing the arc heat from directly penetrating the root of the weld 7 and forming defects such as weld burn-through and weld beads.

[0074] Furthermore, the bend angle of the pipe opening refers to the angle formed by the assembly deviation of the axes of the two cooling pipes 1 to be welded. The bend angle of the pipe opening of the two cooling pipes 1 to be welded should not be greater than 1°. For example, the bend angle of the pipe opening of the two cooling pipes 1 to be welded can be 0.6°, 0.7° or 0.8°, etc. This can avoid the bend angle of the pipe opening of the two cooling pipes 1 to be welded being too large, thereby avoiding the gap of the local position of the entire welding bevel 3 being too large, and reducing the possibility of local root incomplete welding defects.

[0075] In this invention, such as Figure 1 As shown, the welding method for magnet cooling pipes also includes: S60: Before fixing the two cooling tubes 1 to be welded, clean the outer side of the end face 2 to be welded and the welding groove 5.

[0076] Specifically, the two cooling pipes 1 to be welded are connected by welding. The end faces 2 of the two cooling pipes 1 to be welded form a welding bevel 3 and a blunt edge 4 respectively. When welding the two cooling pipes 1 to be welded, the two cooling pipes 1 to be welded can be fixed first, then the blunt edges 4 of the two cooling pipes 1 to be welded can be connected by welding first, and then the welding bevel 3 of the two cooling pipes 1 to be welded can be connected by welding.

[0077] Before fixing the two cooling pipes 1 to be welded, it is necessary to clean the outer side of the end face 2 to be welded and the welding groove 5. Cleaning the end face 2 to be welded means cleaning the bevel surface 6 and the blunt edge 4 to thoroughly remove impurities such as oil, rust, and oxide scale from the surface of the end face 2 to prevent these substances from decomposing and generating a large amount of gas under the high temperature of the electric arc, thus avoiding the formation of dense pores inside the weld 7 from the source. Cleaning the outer side of the welding groove 5 means cleaning the area of ​​the outer wall of the cooling pipe 1 to be welded near the welding groove 5, which can remove the oxide layer and foreign impurities attached to the edge of the welding groove 3, and prevent these non-metallic substances from being mixed into the molten pool during the welding process and forming hidden slag inclusion defects.

[0078] It should be noted that acetone or alcohol can be used for cleaning, and can remove oil, rust and other dirt within 20mm of the edge of the welding groove 5.

[0079] In this invention, such as Figure 1 As shown, the welding method for magnet cooling pipes also includes: S71: Before welding, a back shielding gas for a first duration is introduced into the cooling pipe 1 to be welded. The first duration is t, and it satisfies: 30s < t < 60s.

[0080] Specifically, before welding, a back shielding gas is introduced into the cooling pipe 1 to be welded. The back shielding gas can be argon or the like. The back shielding gas can be used to completely replace the air in the cooling pipe 1 to prevent the oxygen and nitrogen in the air from reacting with the high-temperature molten pool metal, and to prevent the root of the weld 7 from being oxidized and nitrided. The gas introduction time is the first time, which can be set to t, and t should be between 30s and 60s. For example, the first time can be 40s, 45s or 50s, etc., to avoid the first time being too short or too long.

[0081] If the first welding time is too short, the original air in the cooling pipe 1 to be welded will not be completely discharged, resulting in a large amount of oxygen and nitrogen remaining in the root area of ​​weld 7. The high-temperature molten pool is directly oxidized when exposed to air, forming an oxidized blue and embrittled layer. If the first welding time is too long, it will lead to excessive consumption of inert protective gases such as argon. The gas consumption of a single weld 7 far exceeds the process requirements, and the material cost increases several times.

[0082] S72: After ventilation, spot weld the end faces 2 of the two cooling pipes 1 to be welded, and the spot weld position is located at the top of the cooling pipe 1.

[0083] Then, the two end faces 2 of the two cooling pipes 1 to be welded can be spot welded and fixed. For example, a cold welding machine can be used to spot weld and fix the cooling pipes 1 to be welded. Spot welding is used to completely fix the two aligned cooling pipes 1 to be welded, so as to avoid the coaxiality deviation caused by thermal deformation or external force during the subsequent all-position welding process, and to ensure that the pipe opening bend angle is always controlled within the allowable range. The spot welding position can be located at the top of the cooling pipe 1 to be welded. Since there is no obstruction of vision at the top position, the welder can accurately control the formation of the spot weld pool, avoiding the problems of spot welding failure and false welding caused by blind spots. The reliability of spot welding positioning is higher, and in practice, only one spot welding is required.

[0084] In this invention, such as Figure 1 As shown, the welding method for magnet cooling pipes also includes: S80: After welding is completed, non-destructive testing is performed on weld 7. Non-destructive testing methods include visual inspection, penetrant testing and radiographic testing.

[0085] Specifically, after welding is completed, non-destructive testing (NDT) can be performed on the weld 7 area. NDT is a method that accurately identifies defects such as porosity, slag inclusions, and incomplete penetration inside the weld 7 without damaging the weld 7 body, thus preventing unqualified magnetic cooling tubes from flowing into subsequent use stages. NDT methods include visual inspection, penetrant testing, and radiographic testing. Visual inspection is a non-destructive testing method that directly observes the surface forming quality of the weld 7 with the human eye or auxiliary optical tools. Penetrant testing is a non-destructive testing method that detects open-type defects on the surface of the weld 7 through the capillary action of colored penetrant. Radiographic testing is a conventional internal inspection method that uses X-rays or gamma rays to penetrate the weld 7 and collects images of the difference in radiation attenuation through film or digital imaging to identify internal defects in the weld 7.

[0086] In practice, the three detection methods can be combined according to the actual situation to ensure the reliability and accuracy of the weld seam detection results.

[0087] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0088] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A welding method for a magnet cooling pipe, characterized in that, The welding method is applicable to welding the cooling tubes of the longitudinal field magnet in a tokamak fusion device, and includes: Prepare two cooling pipes to be welded (1); Welding bevels (3) are machined in the radially outer regions of the two weldable end faces (2) of the two cooling pipes (1) facing each other, and blunt edges (4) are reserved in the radially inner regions of the weldable end faces (2). The two cooling pipes (1) to be welded are fixed so that the blunt edges (4) of the two end faces (2) to be welded fit together and the welding bevel (3) forms a welding groove (5). First, perform root welding using pulse self-fusion method from the root of the welding groove (5); Then, the welding groove (5) is covered by welding using the pulse filler method.

2. The welding method for the magnet cooling tube according to claim 1, characterized in that, The step of first performing root welding using a pulse self-fusion method from the root of the welding groove (5) includes: First, start the arc from the bottom of the two end faces (2) to be welded, and weld from the bottom of the end face (2) to the top of the end face (2) to the root of the welding groove (5) along the first direction; Starting again from the bottom of the two end faces (2) to be welded, an arc is formed along the second direction from the bottom of the end face (2) to the top of the end face (2) to be welded at the root of the welding groove (5), the second direction being opposite to the first direction.

3. The welding method for the magnet cooling tube according to claim 2, characterized in that, The pulse base current for the root welding of the welding groove (5) using pulse self-fusion method is I1, the peak current is I2, and the duty cycle is C1, and the following conditions are met: 15A < I1 < 25A, 35A < I2 < 45A, 35% < C1 < 45%.

4. The welding method for the magnet cooling tube according to claim 2, characterized in that... The step of performing a cover welding on the welding groove (5) using a pulse filler wire method includes: First, start the arc from the bottom of the two end faces (2) to be welded, and weld from the bottom of the end face (2) to the top of the end face (2) to be welded at the welding groove (5) along the first direction; Starting again from the bottom of the two end faces (2) to be welded, the welding is performed along the second direction at the welding groove (5) from the bottom of the end face (2) to the top of the end face (2).

5. The welding method for the magnet cooling tube according to claim 4, characterized in that, The pulse base current for the welding groove (5) to be covered by the pulse filler wire method is I3, the peak current is I4, and the duty cycle is C2, and the following conditions are met: 15A < I3 < 25A, 35A < I4 < 45A, 30% < C2 < 40%.

6. The welding method for the magnet cooling tube according to claim 1, characterized in that, The process of machining a welding bevel (3) in the radially outer region of the two welding end faces (2) of the two cooling pipes (1) facing each other, and reserving a blunt edge (4) in the radially inner region of the welding end faces (2) includes: A sloped surface (6) is machined in the radially outer region of the end face (2) to form the welding groove (3). The angle between the sloped surface (6) and the end face (2) to be welded is α, and satisfies: 25°<α<35°. The blunt edge (4) is formed in the radial inner region of the end face (2) to be welded, and the blunt edge (4) is ground.

7. The welding method for the magnet cooling tube according to claim 1, characterized in that, The step of fixing the two cooling pipes (1) to be welded so that the blunt edges (4) of the two end faces (2) to be welded fit together and the welding bevel (3) forms a welding groove (5) includes: The two cooling pipes (1) to be welded are fixed to the fixed pipe rack respectively, and the welding end faces (2) of the two cooling pipes (1) to be welded are arranged facing each other; The welding end faces (2) of the two cooling pipes (1) to be welded are tightly fitted together so that the gap between the two welding end faces (2) is no greater than 0.5 mm and the folding angle of the pipe openings of the two cooling pipes (1) to be welded is no greater than 1°.

8. The welding method for the magnet cooling tube according to claim 7, characterized in that, Also includes: Before fixing the two cooling tubes (1) to be welded, clean the outer side of the end face (2) to be welded and the welding groove (5).

9. The welding method for the magnet cooling tube according to claim 1, characterized in that, Also includes: Before welding, a back protective gas for a first duration is introduced into the cooling pipe (1) to be welded. The first duration is t, and it satisfies: 30s < t < 60s. After ventilation, spot welding is performed on the end faces (2) of the two cooling pipes (1) to be welded, and the spot welding position is located at the top of the cooling pipe (1).

10. The welding method for the magnet cooling tube according to claim 1, characterized in that, Also includes: After welding is completed, the weld (7) is subjected to non-destructive testing, including visual inspection, penetrant testing and radiographic testing.

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