Pulse laser welding method for dense nickel-based high-temperature heat exchange tube

Abstract

The invention provides a pulse laser welding method for a dense nickel-based high-temperature heat exchange tube, which comprises the following steps: S1, by adjusting the machining dimensional tolerance and controlling the outer diameter of the heat exchange tube and the size of a tube hole in a tube plate, when the heat exchange tube is assembled in the tube hole, the radial assembly gap between the heat exchange tube and the tube hole is within a preset range; s2, the axial assembly protruding amount of the heat exchange tubes on the front face of the tube plate is controlled to be gradually increased from the outer ring to the inner ring; s3, pulse laser welding is adopted for welding, a preset welding path is planned, and welding of all heat exchange tubes and tube plate welding seams is completed in sequence according to the preset welding path; and S4, technological parameters of pulse laser welding are set and controlled, and welding operation is completed based on the technological parameters. According to the method, through control over the assembly clearance of the pipe and the pipe plate, control over the axial assembly protrusion gradient of the pipe and control over the welding penetration, after welding of the pipe and the pipe plate is completed, the flatness of the pipe plate is effectively controlled within 0.02 mm, and after a welding seam is subjected to 1000-DEG C high-temperature circulation, the air pressure test detection result meets the requirement.

Description

Technical Field

[0001] This invention relates to the field of laser welding technology, specifically to a pulsed laser welding method for dense nickel-based high-temperature heat exchange tubes. More particularly, it relates to a pulsed laser welding method that ensures leak-free weld seams in dense nickel-based high-temperature heat exchange tubes after undergoing a 1000°C high-temperature thermal cycle. Background Technology

[0002] In engineering applications, there are scenarios where 900 GH4169 nickel-based alloy heat exchange tubes need to be welded onto a circular ring with an outer diameter of 284 mm and an inner diameter of 194 mm. Each heat exchange tube has a diameter of 4.5 mm, a length of 100.5 mm, and a wall thickness of 0.5 mm. Both ends need to be welded to two vertically parallel GH4169 nickel-based alloy tube sheets, each 6 mm thick. After welding the heat exchange tubes to the tube sheets, a pressure test of 0.2–0.3 MPa is required on the weld. After passing the pressure test, the component undergoes a 1000℃ high-temperature heat cycle. Following this high-temperature heat cycle, another pressure test of 0.2–0.3 MPa is required on the weld. The core requirement is that no leakage occurs at the weld between the tubes and the tube sheets after the high-temperature heat cycle.

[0003] In the field of tube-to-tubesheet welding, a common method to improve welding quality is to perform tube expansion before welding to reduce the assembly gap between the heat exchange tubes and the tubesheet. However, in the above-mentioned engineering scenario, on the one hand, both the heat exchange tubes and the tubesheet are made of GH4169 nickel-based alloy, and the properties of the homogeneous materials are consistent, making it difficult to achieve the goal of reducing the gap through tube expansion; on the other hand, the heat exchange tubes used in this scenario are designed with a quincunx-shaped inner core to increase the heat exchange area, and the irregular inner core structure does not meet the conditions for tube expansion.

[0004] The main problems with existing technologies are that conventional tube expansion-assisted welding methods are not feasible for welding densely arranged nickel-based alloy heat exchange tubes to tube sheets. Furthermore, there is a lack of suitable welding methods that can simultaneously ensure welding quality, control welding deformation, and prevent leakage of the weld after cycling at 1000℃. Specifically, there is a lack of clearly defined suitable welding methods, reasonable tube-to-tube sheet fit clearance, reasonable tube protrusion control, scientific welding paths, and optimized welding process parameters.

[0005] Patent document CN114178389A discloses a hydraulic expansion joint and expansion method for heat exchanger tube ends, including a hydraulic expansion joint with an inner hole having an ultra-high pressure water channel. A high-pressure water inlet is provided at the tail end of the hydraulic expansion joint, through which the ultra-high pressure water channel of the hydraulic expansion joint is connected to an ultra-high pressure water source. The front half of the hydraulic expansion joint is the expansion joint body, and a groove is provided on the outer surface of the expansion joint body. This groove is connected to the ultra-high pressure water channel of the hydraulic expansion joint, and an inner expansion sleeve is provided within this groove. The inner expansion sleeve is injection-molded together with the expansion joint body. The two bonding sections A on both sides of the inner expansion sleeve are injection-molded together with the expansion joint body to form a seal. The middle expansion joint working section B of the inner expansion sleeve is separated from the expansion joint body after injection. The middle expansion joint working section B of the inner expansion sleeve is provided with a high-pressure water outlet. When ultra-high pressure water enters, it causes expansion and deformation, which is the expansion joint working section. An outer expansion sleeve is provided on the outer layer of the inner expansion sleeve, which is injection-molded together with the expansion joint body and the inner expansion sleeve. The outer expansion sleeve has greater strength and higher hardness than the inner expansion sleeve.

[0006] The hydraulic expansion method in the prior art document CN114178389A cannot solve the technical problems faced by this invention. The reason is that its technical solution relies entirely on the principle of tube expansion, which is exactly the problem that this invention needs to avoid. The expansion effect on homogeneous materials (such as GH4169 nickel-based alloy) is almost zero, and it cannot adapt to the plum blossom-shaped irregular inner core structure, and does not meet the conditions for tube expansion. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a pulsed laser welding method for dense nickel-based high-temperature heat exchange tubes.

[0008] A pulsed laser welding method for dense nickel-based high-temperature heat exchange tubes according to the present invention includes the following steps: S1: By adjusting the machining dimensional tolerance, the outer diameter of the heat exchange tube and the size of the tube hole on the tube sheet are controlled, so that when the heat exchange tube is assembled into the tube hole, the radial assembly gap between the heat exchange tube and the tube hole is within the preset range. S2: Control the axial assembly dimensions of the heat exchange tubes on the tube sheet. Set the axial assembly parameters between the heat exchange tube ends and the front of the tube sheet in a manner that gradually increases the assembly protrusion from the outer ring to the inner ring. S3: Welding is performed using pulsed laser welding. A preset welding path is planned, and all heat exchange tubes and tube sheet welds are completed sequentially according to the preset welding path. S4: Set and control the process parameters for pulsed laser welding, and complete the welding operation based on the process parameters.

[0009] Preferably, in S1, the preset range of the radial assembly gap between the heat exchange tube and the tube hole is 0.008 to 0.012 mm.

[0010] Preferably, in S2, the axial assembly parameters are as follows: multiple heat exchange tubes are distributed in three regions radially from the outside to the inside along the tube sheet end face. The ends of the heat exchange tubes in the outermost region are flush with the tube sheet end face. The ends of the heat exchange tubes in the middle region protrude from the tube sheet end face by a preset first dimension. The ends of the heat exchange tubes in the innermost region protrude from the tube sheet end face by a preset second dimension, and the preset second dimension is greater than the preset first dimension.

[0011] Preferably, the heat exchange tube is arranged in 10 rings from the outside to the inside, wherein the outermost three rings are the outermost ring area, the middle four rings are the middle ring area, and the innermost three rings are the innermost ring area. The preset first dimension is 0.005mm, and the preset second dimension is 0.01mm.

[0012] Preferably, in S3, the preset welding path is as follows: starting welding from the outermost heat exchange tube, after the current weld is completed, the welding torch is moved step by step to the position of the next weld at preset intervals and welded, until all welds are completed.

[0013] Preferably, the stepwise movement at the preset interval angle is as follows: after welding the first weld, move clockwise 180° to weld the second weld; after welding the second weld, move clockwise 90° to weld the third weld; after welding the third weld, move clockwise 180° to weld the fourth weld; move clockwise 90° and move radially inward one full circle; and so on. For each subsequent circle of heat exchange tubes, the welding torch is moved according to the above interval angle pattern for welding until the welding is completed.

[0014] Preferably, in S3, the weld penetration depth of the heat exchange tube and tube sheet is controlled within the range of 0.8 to 1 mm during the welding process.

[0015] Preferably, in S4, the process parameters of the pulsed laser welding are: frequency 10-13Hz, welding speed 4-6mm / s, pulse width 4-5ms, focal length 135-140mm, and welding angle 380-400°.

[0016] Preferably, in S4, the welding operation includes: for the weld seam corresponding to each heat exchange tube, pulsed laser spot welding is performed first, and then pulsed laser full welding is performed. Specifically, spot welding is performed by spot welding one weld point every 90° in the circumferential direction of the heat exchange tube. The spot welding process parameters are: frequency 13Hz, pulse width 5ms, focal length 136mm.

[0017] Preferably, it also includes S5: inspecting the weld after welding and the weld after cycling at 1000℃. The inspection includes liquid penetration testing and air pressure testing. The air pressure testing parameters are: test pressure 0.2~0.3MPa, pressure holding time 30 minutes. The test is considered qualified if there is no pressure drop during the pressure holding process and no bubbles emerge when the component is immersed in water.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. By gradient control of the axial protrusion of the tube, this invention can effectively control the flatness of the back side of the tube sheet within ±0.01mm after the front side of the tube sheet is welded, thus ensuring the smooth implementation of the back side welding. 2. This invention controls the assembly gap between the tube and the tube sheet by processing dimensional tolerances, selects reasonable welding methods and process control, and the obtained welds meet the requirements after being subjected to a gas pressure test at 1000℃ high temperature cycling. 3. This invention employs a reasonable welding path planning that starts from the outermost ring, welds the first weld, moves clockwise 180° to weld the second weld, then moves clockwise 90° to weld the third weld, and continues clockwise 180° to weld the fourth weld. After completing the welding of a total of 1800 welds on the front and back of the tube sheet, the welding deformation of the tube sheet can be effectively controlled, and the flatness of the front and back of the tube sheet can be kept within 0.02mm, thus ensuring the overall precision of the component. Attached Figure Description

[0019] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram illustrating the welding path planning of the pulsed laser welding method, which is the main feature of this invention.

[0020] Figure label: Heat exchange tube 1; tube sheet 2. Detailed Implementation

[0021] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0022] For welding of dense nickel-based high-temperature heat exchanger tubes that require no leakage after undergoing a 1000℃ high-temperature thermal cycle, this embodiment adopts the following pulsed laser welding method, and the specific steps are as follows: Example 1 Step S1: By adjusting the machining dimensional tolerances, the outer diameter of the heat exchange tube and the size of the tube hole on the tube sheet are controlled, so that when the heat exchange tube is assembled into the tube hole, the radial assembly gap between the heat exchange tube and the tube hole is within a preset range. In this embodiment, the preset range is 0.008~0.012mm.

[0023] Step S2: Control the axial assembly dimensions of the heat exchange tubes on the tube sheet. Multiple heat exchange tubes are welded to different radial positions on the tube sheet. The axial assembly parameters between the heat exchange tube ends and the front of the tube sheet are set according to the principle that the height of the heat exchange tubes protruding from the tube sheet gradually increases from the outer ring to the inner ring. Specifically, the axial assembly parameters are as follows: multiple heat exchange tubes are distributed in three regions radially from the outside to the inside of the tube sheet end face. The heat exchange tube ends in the outermost ring region are flush with the tube sheet end face. The heat exchange tube ends in the middle ring region protrude from the tube sheet end face by a preset first dimension. The heat exchange tube ends in the innermost ring region protrude from the tube sheet end face by a preset second dimension, and the preset second dimension is greater than the preset first dimension. In this embodiment, a total of 10 rings of heat exchange tubes are arranged from the outside to the inside, where the outermost three rings are the outermost ring region, the middle four rings are the middle ring region, and the innermost three rings are the innermost ring region. The preset first dimension is 0.005 mm, and the preset second dimension is 0.01 mm.

[0024] Step S3: Welding is performed using pulsed laser welding. A preset welding path is planned, and all heat exchanger tubes and tube sheet welds are completed sequentially according to the preset welding path. During the welding process, the weld penetration of the heat exchanger tubes and tube sheet is controlled within the range of 0.8–1 mm. In this embodiment, the preset welding path is as follows: Figure 1 As shown, the welding sequence of the weld is in Figure 1 The welding path, indicated by circled numbers, is as follows: Welding begins with the outermost heat exchange tubes. After completing the current weld, the welding torch is moved step-by-step at preset intervals to the next weld position and welded, until all welds are completed. Specifically, the preset intervals are as follows: after welding the first weld, the torch moves 180° clockwise to weld the second weld. After welding the second weld, it moves 90° clockwise to weld the third weld. After welding the third weld, it moves 180° clockwise to weld the fourth weld. Then, it moves 90° clockwise and radially inwards for one full circle to begin welding the next circle. Each subsequent circle of heat exchange tubes is welded using the same interval pattern until all heat exchange tubes and tube sheet welds are completed. In this embodiment, pulsed laser welding with a laser power of 3KW is used.

[0025] Step S4: Set and control the process parameters for pulsed laser welding, and complete the welding operation based on the process parameters. In this embodiment, the process parameters for pulsed laser welding are: frequency 10-13Hz, welding speed 4-6mm / s, pulse width 4-5ms, focal length 135-140mm, and welding angle 380-400°. The welding operation includes: for each heat exchanger tube, pulsed laser spot welding is performed first, followed by pulsed laser full welding. Specifically, spot welding involves spot welding one weld point every 90° along the circumference of the heat exchanger tube. The spot welding process parameters are: frequency 13Hz, pulse width 5ms, and focal length 136mm. The pulsed laser full welding process parameters are: frequency 13Hz, welding speed 6mm / s, pulse width 5ms, focal length 136mm, and welding angle 400°.

[0026] Step S5: The completed weld is subjected to a 1000℃ high-temperature cycle. The weld is inspected before and after the high-temperature cycle, including liquid penetration testing and a pressure test. The pressure test parameters are: test pressure 0.2–0.3 MPa, holding time 30 minutes; no pressure drop during the holding time and no bubbles emerging when the component is immersed in water indicate a passing test. In this embodiment, liquid penetration testing was performed on the weld before and after the 1000℃ high-temperature cycle, and the results met the requirements. The pressure test used a test pressure of 0.26 MPa, a holding time of 30 minutes, and no pressure drop; the component was immersed in water, and no bubbles emerged, indicating a passing test result.

[0027] The laser welding method of this invention optimizes pulsed laser welding process parameters, resulting in well-formed, spatter-free welds and reducing subsequent repair processes such as grinding, thus lowering processing costs. By precisely controlling assembly gaps and optimizing the welding process and path, the welds pass 0.2–0.3 MPa pressure tests and continue to meet the same pressure test requirements after undergoing a 1000°C high-temperature thermal cycle, ensuring excellent high-temperature stability and sealing performance, meeting core engineering requirements. By employing pulsed laser welding and controlling the weld penetration depth to 0.8–1 mm, both weld connection strength and heat exchanger tube wall thickness protection are balanced, avoiding weak connections due to insufficient penetration or leakage risks caused by excessive penetration through thin-walled heat exchanger tubes.

[0028] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application 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. Therefore, they should not be construed as limitations on this application.

[0029] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A pulsed laser welding method for dense nickel-based high-temperature heat exchange tubes, characterized in that, Includes the following steps: S1: By adjusting the machining dimensional tolerance, the outer diameter of the heat exchange tube and the size of the tube hole on the tube sheet are controlled, so that when the heat exchange tube is assembled into the tube hole, the radial assembly gap between the heat exchange tube and the tube hole is within the preset range. S2: Control the axial assembly dimensions of the heat exchange tubes on the tube sheet. The heat exchange tubes are welded to different radial positions on the tube sheet. The axial assembly parameters between the heat exchange tube ends and the front of the tube sheet are set in a way that the height of the heat exchange tubes protruding from the tube sheet gradually increases from the outer ring to the inner ring of the tube sheet. S3: Welding is performed using pulsed laser welding. A preset welding path is planned, and all heat exchange tubes and tube sheet welds are completed sequentially according to the preset welding path. S4: Set and control the process parameters for pulsed laser welding, and complete the welding operation based on the process parameters.

2. The pulsed laser welding method for dense nickel-based high-temperature heat exchange tubes as described in claim 1, characterized in that, In S1, the preset range of the radial assembly clearance between the heat exchange tube and the tube hole is 0.008 to 0.012 mm.

3. The pulsed laser welding method for dense nickel-based high-temperature heat exchange tubes as described in claim 1, characterized in that, In S2, the axial assembly parameters are as follows: multiple heat exchange tubes are distributed in three regions radially from the outside to the inside along the tube sheet end face. The ends of the heat exchange tubes in the outermost region are flush with the tube sheet end face. The ends of the heat exchange tubes in the middle region protrude from the tube sheet end face by a preset first dimension. The ends of the heat exchange tubes in the innermost region protrude from the tube sheet end face by a preset second dimension, and the preset second dimension is greater than the preset first dimension.

4. The pulsed laser welding method for dense nickel-based high-temperature heat exchange tubes as described in claim 3, characterized in that, The heat exchange tube is arranged in 10 rings from the outside to the inside, with the outermost three rings being the outermost ring area, the middle four rings being the middle ring area, and the innermost three rings being the innermost ring area. The preset first dimension is 0.005mm, and the preset second dimension is 0.01mm.

5. The pulsed laser welding method for dense nickel-based high-temperature heat exchange tubes as described in claim 4, characterized in that, In S3, the preset welding path is as follows: starting welding from the outermost heat exchange tube, after the current weld is completed, the welding gun is moved step by step to the position of the next weld at preset intervals and angles and welded until all welds are completed.

6. The pulsed laser welding method for dense nickel-based high-temperature heat exchange tubes as described in claim 5, characterized in that, The stepwise movement at the preset interval angle is as follows: after welding the first weld, move the torch 180° clockwise to weld the second weld. After welding the second weld, move the torch 90° clockwise to weld the third weld. After welding the third weld, move the torch 180° clockwise to weld the fourth weld. Move the torch 90° clockwise and then move it radially inward for one full circle. For each subsequent circle of heat exchange tubes, the welding torch is moved according to the above interval angle pattern until the welding is completed.

7. The pulsed laser welding method for dense nickel-based high-temperature heat exchange tubes as described in claim 1, characterized in that, In S3, the penetration depth of the weld between the heat exchange tube and the tube sheet is controlled within the range of 0.8 to 1 mm during the welding process.

8. The pulsed laser welding method for dense nickel-based high-temperature heat exchange tubes as described in claim 1, characterized in that, In S4, the process parameters for pulsed laser welding are: frequency 10-13Hz, welding speed 4-6mm / s, pulse width 4-5ms, focal length 135-140mm, and welding angle 380-400°.

9. The pulsed laser welding method for dense nickel-based high-temperature heat exchange tubes as described in claim 1, characterized in that, In S4, the welding operation includes: for the weld seam corresponding to each heat exchange tube, pulsed laser spot welding is performed first, followed by pulsed laser full welding. Specifically, spot welding is performed by spot welding one weld point every 90° in the circumferential direction of the heat exchange tube. The spot welding process parameters are: frequency 13Hz, pulse width 5ms, and focal length 136mm.

10. The pulsed laser welding method for dense nickel-based high-temperature heat exchange tubes as described in claim 1, characterized in that, It also includes S5: inspecting the weld seam after welding and the weld seam after cycling at 1000℃. The inspection includes liquid penetration test and air pressure test. The air pressure test parameters are: test pressure 0.2~0.3MPa, pressure holding time 30 minutes. The test is considered qualified if there is no pressure drop during the pressure holding process and no bubbles emerge when the component is immersed in water.

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