A method for preventing overheating expansion welding of tube sheets and heat exchanger tubes, and a tube sheet heat exchanger.

Abstract

This invention provides a method for preventing overheating and expansion during welding of tube sheets and heat exchanger tubes, and a tube sheet heat exchanger, relating to the field of heat exchanger manufacturing technology. The method includes: planning a welding sequence based on multiple tube sheet joints to be welded on the tube sheet, ensuring that consecutive tube sheet joints are not spatially adjacent; welding is performed according to the welding sequence, while simultaneously using heat-conducting fixtures to contact the tube sheet joints and dissipate heat; after welding a predetermined number of tube sheet joints, the weld temperature is detected and compared with a preset temperature threshold: if the weld temperature is less than or equal to the preset temperature threshold, welding continues with the next set of tube sheet joints; if the weld temperature is greater than the preset temperature threshold, welding is paused and the weld is cooled until the weld temperature drops below or equal to the preset temperature threshold. Through a synergistic mechanism of path dispersion, active heat conduction, and closed-loop temperature control, the method overcomes the problems of weld overheating oxidation, microstructure deterioration, and poor process stability caused by differences in thermal conductivity between dissimilar metals and heat accumulation during batch welding.

Description

Technical Field

[0001] This invention relates to the field of heat exchanger manufacturing technology, and in particular to a method for preventing overheating expansion welding of tube sheets and heat exchange tubes, and a tube sheet heat exchanger. Background Technology

[0002] In the field of heat exchanger manufacturing, the connection quality between tube sheets and heat exchange tubes directly determines the sealing performance and service life of the equipment. This is especially true when using dissimilar metal connections between carbon steel tube sheets and stainless steel heat exchange tubes, which presents significant thermal management challenges.

[0003] Because stainless steel has a significantly lower thermal conductivity than carbon steel and a larger coefficient of linear expansion, heat tends to accumulate in the weld area during welding and cannot dissipate quickly. In mass-produced large heat exchangers, thousands of weld joints are densely distributed on the tube sheet. If traditional continuous welding is used, significant heat accumulation is easily generated. This heat accumulation leads to a sustained increase in local temperature on the tube sheet, causing subsequent welds to remain at high temperatures for extended periods. This results in severe weld oxidation (appearing dark blue or black), grain coarsening, decreased corrosion resistance, and even thermal cracking.

[0004] Therefore, it is necessary to improve the existing tube sheet heat exchanger overheat expansion welding technology to overcome the shortcomings of the existing technology. Summary of the Invention

[0005] To overcome the problems existing in related technologies, the purpose of this invention is to provide a method for preventing overheating expansion welding of tube sheets and heat exchange tubes. This method for preventing overheating expansion welding of tube sheets and heat exchange tubes overcomes the problems of weld overheating oxidation, microstructure deterioration and poor process stability caused by the difference in thermal conductivity of dissimilar metals and the accumulation of heat in batch welding in the prior art through a synergistic mechanism of path dispersion, active heat conduction and closed-loop temperature control.

[0006] A method for preventing overheating expansion during welding of a tube sheet and heat exchanger tubes, comprising:

[0007] The welding sequence is planned according to the multiple tube sheet joints to be welded on the tube sheet, so that the tube sheet joints that are consecutive in the welding sequence are not adjacent in spatial position.

[0008] Welding is performed according to the welding sequence described above, while using heat-conducting tooling to contact the tube sheet joints to dissipate heat.

[0009] After completing the welding of a predetermined number of tube sheet joints, the weld temperature is measured and compared with a preset temperature threshold.

[0010] If the weld temperature is less than or equal to the preset temperature threshold, then continue welding the next set of tube sheet joints;

[0011] If the weld temperature is higher than the preset temperature threshold, welding is paused and the weld is cooled until the weld temperature drops below or equal to the preset temperature threshold.

[0012] Furthermore, the heat-conducting tooling is a heat-conducting rod made of copper, and the outer contour of the heat-conducting rod is adapted to the inner hole shape of the heat exchange tube.

[0013] The step of using a heat-conducting tool to contact the tube sheet joint to conduct heat away specifically includes:

[0014] Before welding, the heat-conducting rod is inserted into the heat exchange tube at the joint of the tube sheet to be welded, so that the outer wall of the heat-conducting rod is in contact with the inner wall of the heat exchange tube, thus establishing a radial heat conduction path from the root of the weld to the inside of the heat-conducting rod.

[0015] Compared to conventional methods that only use gas protection or low thermal conductivity pads on the back, this invention further specifies that the heat-conducting fixture is a copper heat-conducting rod that is attached to the inner wall of the heat exchange tube. Stainless steel has extremely low thermal conductivity (only about 1 / 3 that of carbon steel), causing heat to easily accumulate at the weld root and inside the tube wall. This solution introduces copper, a high thermal conductivity medium (thermal conductivity approximately 20 times that of stainless steel), and forcibly establishes a direct contact interface between the weld root, the inner wall of the heat exchange tube, and the copper heat-conducting rod. This allows the high-temperature heat generated during welding to be preferentially conducted to the copper rod inside the tube, rather than diffused to the surrounding tube wall, thereby greatly improving the cooling rate of the weld area, effectively inhibiting the growth of austenitic stainless steel grains and the precipitation of carbides, and ensuring the forming quality of the weld root.

[0016] Furthermore, the preset temperature threshold is set to any value between 70°C and 90°C;

[0017] The step of pausing welding and cooling specifically includes:

[0018] The arc initiation action is forcibly stopped, and the welding remains stopped until the detected weld temperature value is lower than or equal to the preset temperature threshold.

[0019] Stainless steel exhibits a sensitization temperature range of 450℃-850℃, and at high temperatures, it readily reacts with oxygen to form unsightly oxide scale. This invention, with its 70℃-90℃ temperature range, ensures that the enthalpy of the base metal has dropped to near ambient levels before the next weld arc is initiated. Even with additional welding heat input, the high-temperature dwell time after the peak temperature can be compressed to an extremely short range. This directly blocks the possibility of sensitization, fundamentally preventing the formation of chromium-depleted zones, resulting in a final weld with an ideal golden or silvery-white color, rather than the deep blue or black of overheated oxidation, significantly improving the corrosion resistance of the joint.

[0020] Furthermore, the predetermined quantity is set to be between 15 and 25;

[0021] After each predetermined number of tube sheet joints is welded, the weld temperature is checked, specifically including:

[0022] After each predetermined number of tube sheet joint welding operations are completed, temperature data of the current weld area is immediately collected using a temperature measuring device.

[0023] Compared to the traditional, rudimentary management approach of relying on experience to determine when to measure temperature or measuring only after all welding is complete, this invention establishes a testing cycle of 15 to 25 tube sheet joints. Excessive testing (e.g., testing after each weld) severely reduces production efficiency, while excessively long testing intervals (e.g., testing after 100 welds) can lead to heat accumulation exceeding a critical value before it is detected. The 15-25 cycle is based on the golden ratio of heat accumulation and heat dissipation balance. Within this range, with the aid of heat-conducting fixtures, the overall temperature rise of the tube sheet remains in a controllable linear growth phase, not yet entering an exponentially uncontrollable zone. While ensuring the continuity of the production cycle, it accurately captures the inflection point of heat accumulation, achieving the optimal balance between production efficiency and quality monitoring, ensuring neither delays in the project schedule nor overlooking any overheating risks.

[0024] Furthermore, the step of pausing welding and cooling until the weld temperature drops below or equal to the preset temperature threshold specifically includes:

[0025] Determine a cooling strategy, which is selected from natural cooling and air cooling;

[0026] After the welding operation is stopped, the cooling strategy shall be immediately implemented for the current inspection area;

[0027] The cooling process is maintained, and the weld temperature is continuously monitored. Cooling is terminated and welding is resumed only when the real-time temperature data drops below or equal to the preset temperature threshold.

[0028] Passive waiting is often inefficient and results in an unpredictable state. A closed-loop feedback system continuously monitors the temperature until it falls back to a threshold. If the temperature exceeds the limit (input signal), the system immediately cuts off the heat source (suspends welding) and introduces a negative heat source (air cooling) until the deviation is eliminated (temperature reaches the target). This transforms the previously uncontrollable heat dissipation process into a controllable step, eliminating the subjectivity of human judgment (such as relying on touch to test the temperature), ensuring that every re-welding is performed under compliant thermal conditions, and guaranteeing the consistency of batch welding quality.

[0029] Furthermore, the step of planning the welding sequence specifically includes:

[0030] Based on the array arrangement of the tube sheet joints to be welded, set the interval step size for skip welding or the partition rotation strategy.

[0031] Develop a welding path that ensures that, in time sequence, there is at least one other tube sheet joint to be welded between two consecutive welding operations targeting tube sheet joints to be welded.

[0032] The heat-affected zone (HAZ) of a weld has a certain physical radius. If the welds are only separated in time but still adjacent in space (e.g., welding the second weld after the first one), the residual heat field of the previous weld will directly superimpose into the molten pool of the subsequent weld. Forcing spatial non-adjacency utilizes the unwelded cold metal as a natural thermal insulation wall, blocking the direct conduction and superposition of heat fields. This disperses the originally concentrated thermal stress field into a uniformly distributed micro-stress field, not only reducing the risk of localized overheating but also significantly reducing the overall deformation of the tube sheet after welding and improving the flatness of the tube sheet.

[0033] Furthermore, in planning the welding sequence based on multiple tube sheet joints to be welded on the tube sheet, so that tube sheet joints that are consecutive in welding sequence are not adjacent in spatial position, the method also includes:

[0034] The tube sheet joint to be welded is processed into a V-shaped bevel, and the angle of one side of the V-shaped bevel is controlled to be 25° to 35°.

[0035] Assemble the tube sheet and heat exchange tubes, and control the root gap of the V-groove to be 3.0 mm to 4.5 mm.

[0036] Compared to conventional bevel designs, this invention optimizes the 25°-35° V-groove and 3.0-4.5mm root gap to suit the process characteristics of using heat-conducting tooling. An excessively large bevel results in a large filler volume and high heat input, while a too-small bevel easily leads to incomplete fusion. A gap that is too small cannot form an effective weld pool, while a gap that is too large easily leads to burn-through. The smaller angle (around 30°) reduces the filler volume of the weld metal, thereby lowering the total heat input; while the wider gap (3.0-4.5mm) is for use with a copper backing, allowing the arc to penetrate deeper and using the backing to support the weld pool. This reduces heat input while achieving deep penetration welding at low heat input.

[0037] Furthermore, the welding is performed using filler wire tungsten inert gas welding;

[0038] The welding current for the filler wire tungsten inert gas welding is 75A to 125A, the welding voltage is 13V to 17V, and the shielding gas flow rate is 10L / min to 16L / min.

[0039] Compared to high-current welding processes that prioritize speed, this invention limits the current range to a medium-low range of 75A-125A, along with specific voltage and flow parameters. If the current is too high, the input heat exceeds the thermal conductivity limit of the copper rod, causing the fixture to malfunction or even melt; if the current is too low, a molten pool cannot be formed. This parameter window represents the optimal energy efficiency range that matches the heat absorption rate of the copper heat-conducting rod, ensuring that the input arc heat is just enough to melt the base material, while excess heat is promptly dissipated, preventing lateral heat accumulation within the stainless steel tube wall.

[0040] Furthermore, before welding is performed according to the welding sequence, and heat is dissipated by using a heat-conducting tool to contact the tube sheet joints:

[0041] The clean zone is defined as the area extending 20mm to 50mm to both sides along the pipe axis, starting from the bevel position of the pipe-to-plate joint to be welded.

[0042] Mechanical polishing is performed on the inner wall of the heat exchange tube, the outer wall of the heat exchange tube, and the surface of the tube sheet holes in the clean zone to remove the oxide film. Acetone is then used to wipe the polished surface to remove any oil residue until the surface in the clean zone shows a metallic luster.

[0043] Compared to conventional methods that only remove surface stains, this solution includes cleaning the inner walls of the heat exchange tubes and removing oil stains with acetone. Conventional cleaning often neglects the inner walls. The oxide film or oil stains on the inner walls are poor conductors of heat, significantly increasing the contact thermal resistance between the copper heat exchange rod and the tube wall, leading to the failure of the heat dissipation fixture; the hydrogen produced by the decomposition of oil stains at high temperatures can cause porosity. This step effectively ensures welding quality and heat dissipation, guaranteeing that the heat dissipation fixture can achieve the expected heat dissipation effect.

[0044] A tube sheet heat exchanger includes a tube sheet and heat exchange tubes, wherein the connection between the tube sheet and the heat exchange tubes is formed by welding using the overheat-resistant expansion welding method described above.

[0045] The beneficial effects of this invention are as follows:

[0046] This invention provides a method for preventing overheating expansion welding of tube sheets and heat exchanger tubes. This method, through planned welding sequence, mandates that consecutive tube sheet joints welded in sequence are not spatially adjacent. This dispersion strategy prevents the accumulation of continuous heat sources in localized areas, avoiding the rapid formation of localized hotspots. Simultaneously, a heat-conducting tool is used to contact the tube sheet joints to dissipate heat. This structure utilizes the heat-conducting tool as a heat flow shortcut, compensating for the poor thermal conductivity of heat exchanger tubes (especially stainless steel), rapidly absorbing and dissipating the instantaneous high heat generated during welding from the joints, significantly reducing the peak weld temperature and shortening the high-temperature dwell time. After welding a predetermined number of tube sheet joints, the weld temperature is detected and compared with a preset temperature threshold. When the weld temperature exceeds the preset threshold, welding is forcibly paused and cooled, eliminating the risk of unlimited heat accumulation from continuous operation and ensuring that each welding operation starts on a safe thermal baseline. By combining spatial heat dissipation, physical auxiliary heat dissipation, and temporal rhythm control, the overheating problem in dissimilar metal welding is effectively solved, and the weld formation quality and corrosion resistance are greatly improved. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the method for preventing overheating expansion welding of tube sheet and heat exchange tube provided in this application;

[0048] Figure 2 This is a flowchart of the method for preventing overheating expansion welding of tube sheet and heat exchange tube provided in the embodiments of this application;

[0049] Figure 3 This is a schematic diagram of the welding sequence provided in this application. Detailed Implementation

[0050] Preferred embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While preferred embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0051] Example 1

[0052] like Figures 1 to 3 As shown, this embodiment provides a method for preventing overheating expansion welding of a tube sheet and heat exchange tubes. The method includes:

[0053] The welding sequence is planned according to the multiple tube sheet joints to be welded on the tube sheet, so that the tube sheet joints that are consecutive in the welding sequence are not adjacent in spatial position.

[0054] Welding is performed according to the welding sequence described above, while using heat-conducting tooling to contact the tube sheet joints to dissipate heat.

[0055] After completing the welding of a predetermined number of tube sheet joints, the weld temperature is measured and compared with a preset temperature threshold.

[0056] If the weld temperature is less than or equal to the preset temperature threshold, then continue welding the next set of tube sheet joints;

[0057] If the weld temperature is higher than the preset temperature threshold, welding is paused and the weld is cooled until the weld temperature drops below or equal to the preset temperature threshold.

[0058] More specifically, before the welding operation begins, the positions of all points to be welded are obtained based on the array arrangement of the tube sheet joints to be welded on the tube sheet (e.g., equilateral triangle arrangement, square arrangement, or concentric circle arrangement).

[0059] Based on this coordinate information, a non-continuous welding path is developed. The core principle of this path planning is to require that two welding operations that are immediately followed in time (e.g., the Nth and N+1th welding operations) must have corresponding tube sheet joints that are not adjacent in physical space.

[0060] In specific planning, a zoned rotation strategy can be adopted, dividing the tube sheet into several sector-shaped or grid-like areas. After welding one point in area A, immediately jump to the more distant area B to weld the next point, using the physical distance between areas as a thermal barrier. Alternatively, a large-step jump strategy can be used. In a concentric circle arrangement, instead of welding one hole at a time clockwise, welding is performed every X holes (e.g., every 5 or 10 holes), completing one circle before filling the gaps in the middle. Computer algorithms can also be used to generate random or optimized maximum distance paths based on the tube sheet hole coordinates, ensuring that after a heat field is generated in one second, the heat source moves away from the area in the next second, giving the previous area sufficient natural cooling time.

[0061] When performing welding according to the above-described sequence, a physical heat dissipation mechanism must be introduced simultaneously. In this embodiment, a heat-conducting fixture is used to maintain physical contact with the current tube sheet joint.

[0062] The core indicator of this heat-conducting fixture is that the thermal conductivity of the material is significantly higher than that of the heat exchange tube itself. For example, copper or oxygen-free copper can be selected to absorb heat quickly using their extremely high thermal conductivity; aluminum alloy can also be selected to achieve a balance between cost and thermal conductivity; under certain special high-cleanliness requirements, even heat-conducting rods filled with graphite copper composite materials or internal phase change materials (such as heat pipe principle) can be used.

[0063] The fixture can be an insert type, designed as a rod or plug, directly inserted into the heat exchange tube. Its outer wall adheres to the inner wall of the tube, directly absorbing heat from the center of the heat source (the root of the weld). If the tube diameter is too small for insertion, it can be designed as a heat dissipation module covering the tube sheet surface, contacting the metal around the tube sheet holes, thus increasing the surface area to accelerate heat dissipation. Regardless of the material or shape, the working mechanism is to establish a heat flow shortcut that is faster than the heat transfer through the tube wall itself. When the electric arc generates heat, this heat preferentially flows to the heat-conducting fixture with lower thermal resistance, and is absorbed by the fixture's own heat capacity or conducted to the external environment, thereby reducing the residence time of the weld metal in the high-temperature zone.

[0064] During the welding process, welding should not be continued blindly. Instead, a predetermined number of units should be set as inspection points. This number is not arbitrary but is predetermined based on the thickness, material, and heat dissipation conditions of the tube sheet. For example, for thinner tube sheets with lower heat capacity, the predetermined number can be set to be smaller (e.g., 10 units per group); for thicker tube sheets with faster heat dissipation, the predetermined number can be larger (e.g., 30 units per group).

[0065] After welding the predetermined number of joints in succession, it is necessary to stop and use temperature measuring equipment (such as infrared thermometer, surface thermocouple or thermal imager) to detect the weld temperature (usually referring to interpass temperature) of the area that has just been welded or the next group of areas to be welded.

[0066] Dynamic process interventions are implemented based on the test results. The measured temperature is compared with a preset threshold.

[0067] Scenario 1 (Good Thermal Condition): If the detected temperature does not exceed (is less than or equal to) the preset threshold, it means that the current macroscopic skip welding and microscopic heat dissipation measures are effective and the heat has not accumulated to a dangerous level. Welding of the next set of tube sheet joints can continue.

[0068] Scenario 2 (Thermal Risk Warning): If the detected temperature exceeds the preset threshold, it indicates that the rate of heat input exceeds the rate of heat dissipation, and the tube sheet is locally overheated (e.g., at temperatures that could cause sensitization or oxidation of stainless steel). In this case, a forced pause command must be executed.

[0069] During the pause, natural cooling (waiting) can be used, or active air cooling (using compressed air or a blower) can be used to accelerate cooling. The pause is not indefinite or for a fixed time, but is based on the temperature dropping. Only when the temperature data detected again drops back to within the preset threshold range can the pause be lifted and welding operations resume.

[0070] Through the iterative process of the above four steps, this embodiment transforms the welding process, which originally relied on worker experience, into a standardized manufacturing process driven by space planning, physical heat dissipation, and data decision-making. This ensures that the welding quality of each tube sheet joint is within a controlled and safe range, regardless of the production batch size.

[0071] Example 2

[0072] like Figures 1 to 3 As shown, this embodiment provides a method for preventing overheating expansion welding of tube sheet and heat exchange tube. This embodiment is a further elaboration based on embodiment 1. Furthermore, in this embodiment, the heat-conducting tooling of the method for preventing overheating expansion welding of tube sheet and heat exchange tube is a heat-conducting rod made of copper, and the outer contour of the heat-conducting rod is adapted to the inner hole shape of the heat exchange tube.

[0073] The step of using a heat-conducting tool to contact the tube sheet joint to conduct heat away specifically includes:

[0074] Before welding, the heat-conducting rod is inserted into the heat exchange tube at the joint of the tube sheet to be welded, so that the outer wall of the heat-conducting rod is in contact with the inner wall of the heat exchange tube, thus establishing a radial heat conduction path from the root of the weld to the inside of the heat-conducting rod.

[0075] The preset temperature threshold is set to any value between 70°C and 90°C.

[0076] The step of pausing welding and cooling specifically includes:

[0077] The arc initiation action is forcibly stopped, and the welding remains stopped until the detected weld temperature value is lower than or equal to the preset temperature threshold.

[0078] The predetermined quantity is set to be between 15 and 25;

[0079] After each predetermined number of tube sheet joints is welded, the weld temperature is checked, specifically including:

[0080] After each predetermined number of tube sheet joint welding operations are completed, temperature data of the current weld area is immediately collected using a temperature measuring device.

[0081] The step of pausing welding and cooling until the weld temperature drops below or equal to the preset temperature threshold specifically includes:

[0082] Determine a cooling strategy, which is selected from natural cooling and air cooling;

[0083] After the welding operation is stopped, the cooling strategy shall be immediately implemented for the current inspection area;

[0084] The cooling process is maintained, and the weld temperature is continuously monitored. Cooling is terminated and welding is resumed only when the real-time temperature data drops below or equal to the preset temperature threshold.

[0085] The welding is performed using filler wire tungsten inert gas welding;

[0086] The welding current for the filler wire tungsten inert gas welding is 75A to 125A, the welding voltage is 13V to 17V, and the shielding gas flow rate is 10L / min to 16L / min.

[0087] More specifically, the method for preventing overheating and expansion during welding of the tube sheet and heat exchange tubes in this embodiment includes the following steps:

[0088] Before welding, the tube sheet joint to be welded is first subjected to standardized beveling and cleaning.

[0089] The tubesheet joints are machined into V-grooves, with the angle on one side controlled at 30°. The root gap between the assembled tubesheet and heat exchanger tubes is strictly controlled between 3.5mm and 4.0mm. This gap design is intended to accommodate the subsequent insertion of heat-conducting fixtures, allowing for deep arc penetration and good double-sided forming.

[0090] A cleaning zone was defined as a 30mm area extending to both sides from the end face of the tube sheet joint. Operators used mechanical polishing to remove the oxide scale from this area, followed by repeated wiping of the inner wall of the heat exchange tubes and the bevel surface with a lint-free cloth dampened with acetone until no black oil residue remained and a metallic luster was exposed. This step not only prevents porosity but also reduces the contact thermal resistance between the inner wall of the tubes and the heat-conducting fixture.

[0091] In this embodiment, a solid heat-conducting rod made of T2 copper (high-purity copper) is selected as the heat-conducting tooling.

[0092] The outer diameter of the copper heat-conducting rod is precision machined to form a slight interference fit or transition fit with the inner diameter of the heat exchange tube (for example, a gap of less than 0.05 mm).

[0093] Before igniting the arc at each tube sheet joint, the operator inserts a copper heat-conducting rod into the heat exchange tube, ensuring that its outer wall is tightly attached to the inner wall of the heat exchange tube, thus establishing a radial heat flow shortcut from the root of the weld directly into the interior of the copper rod.

[0094] The welding parameters used were filler wire tungsten inert gas (TIG) welding, with a welding current of 100A, an arc voltage of 15V, and a shielding gas flow rate of 14L / min. This combination of parameters represents a medium heat input, ensuring penetration while avoiding overheating.

[0095] Based on the spatial location of the tube sheet holes, a skip welding sequence that maximizes spatial spacing is determined. For example, a strategy of welding one hole every five holes in concentric circles is adopted to ensure that any two consecutively welded tube sheet joints are physically separated by at least five unwelded holes, thus using physical distance to prevent the superposition of heat-affected zones.

[0096] The welding process strictly follows a closed-loop logic of counting, temperature measurement, and decision-making:

[0097] The welding cycle was set to one inspection node after every 20 tube sheet joints were continuously welded. A preset temperature threshold of 80℃ was set. This is the critical safety line to ensure that the stainless steel welds do not undergo severe oxidation. After welding 20 tube sheet joints consecutively, an infrared thermometer was immediately used to check the interpass temperature of the just-completed area.

[0098] If the measured temperature T ≤ 80℃: the current heat dissipation measures are deemed effective and heat accumulation is controllable. The heat-conducting rod should be immediately removed and cleaned, and the welding of the next group of 20 joints should continue.

[0099] If the measured temperature T > 80℃: a risk of heat accumulation is identified, and welding is forcibly suspended. At this time, forced air cooling is not used; instead, natural cooling (utilizing the natural heat dissipation of the workshop environment) is maintained until the measured temperature drops below 80℃ before welding operations can resume.

[0100] After batch welding using the method described in this embodiment, inspection revealed that 100% of the weld surfaces exhibited a golden or silvery-white color, with no dark blue or black overheat oxidation. The first-pass yield rate for PT (penetrating penetration testing) exceeded 99.5%, with no cracks or porosity detected. The specimens successfully passed a 5.4 MPa pressure test, maintaining the pressure for 30 minutes without leakage, demonstrating the superior reliability of this process in ensuring both sealing and strength.

[0101] Example 3

[0102] like Figures 1 to 3 As shown, this embodiment provides a method for preventing overheating expansion welding of tube sheet and heat exchange tube. This embodiment is a further elaboration based on embodiment 1. This embodiment is applicable to production scenarios with high welding efficiency requirements, large tube sheet wall thickness, or large filling volume. Furthermore, the preset temperature threshold of the method for preventing overheating expansion welding of tube sheet and heat exchange tube in this embodiment is set to any value between 70°C and 90°C.

[0103] The step of pausing welding and cooling specifically includes:

[0104] The arc initiation action is forcibly stopped, and the welding remains stopped until the detected weld temperature value is lower than or equal to the preset temperature threshold.

[0105] The predetermined quantity is set to be between 15 and 25;

[0106] After each predetermined number of tube sheet joints is welded, the weld temperature is checked, specifically including:

[0107] After each predetermined number of tube sheet joint welding operations are completed, temperature data of the current weld area is immediately collected using a temperature measuring device.

[0108] The step of pausing welding and cooling until the weld temperature drops below or equal to the preset temperature threshold specifically includes:

[0109] Determine a cooling strategy, which is selected from natural cooling and air cooling;

[0110] After the welding operation is stopped, the cooling strategy shall be immediately implemented for the current inspection area;

[0111] The cooling process is maintained, and the weld temperature is continuously monitored. Cooling is terminated and welding is resumed only when the real-time temperature data drops below or equal to the preset temperature threshold.

[0112] Planning the welding sequence based on multiple tube sheet joints to be welded on a tube sheet, ensuring that tube sheet joints that are sequentially welded are not adjacent in spatial position, also includes:

[0113] The tube sheet joint to be welded is processed into a V-shaped bevel, and the angle of one side of the V-shaped bevel is controlled to be 25° to 35°.

[0114] Assemble the tube sheet and heat exchange tubes, and control the root gap of the V-groove to be 3.0 mm to 4.5 mm.

[0115] The welding is performed using filler wire tungsten inert gas welding;

[0116] The welding current for the filler wire tungsten inert gas welding is 75A to 125A, the welding voltage is 13V to 17V, and the shielding gas flow rate is 10L / min to 16L / min.

[0117] More specifically, the method for preventing overheating and expansion during welding of the tube sheet and heat exchange tubes in this embodiment includes the following steps:

[0118] To meet the welding requirements of thick-walled tube sheets, this embodiment processes the tube sheet joint to be welded into a wide-opening V-groove, controlling the angle on one side to be 35°, and setting the root gap after assembly to 4.5mm. Although this large gap design increases the amount of weld metal filling and total heat input, combined with the supporting effect of the heat-conducting fixture, it can ensure complete root penetration in thick plate welding.

[0119] Considering that high heat input can lead to an expansion of the heat-affected zone, the cleaning zone is defined as extending 50mm to both sides from the bevel. The inner walls of the heat exchange tubes and the surface of the tube sheet within this zone are thoroughly polished and wiped with acetone to ensure that there are no oil or impurities within the high-temperature diffusion range, preventing porosity defects caused by high-temperature hydrogen evolution.

[0120] It uses a copper heat-conducting rod that is precisely fitted to the inner bore of the heat exchange tube. Under high heat input, it plays a role in heat dissipation.

[0121] The welding current for filler wire tungsten inert gas (TIG) welding was set to 125A, the welding voltage to 17V, and the shielding gas flow rate to 16L / min. Under these parameters, the heat input per unit time was significantly higher than in Example 2, posing a more severe challenge to the heat dissipation system.

[0122] Strictly implement the spatial non-adjacent skip welding strategy to disperse high-intensity heat flow by utilizing physical distance.

[0123] To balance production efficiency and quality control, this embodiment sets the inspection node to be every 25 tube sheet joints to be welded. This allows for longer continuous operation times, making the heat accumulation effect more significant.

[0124] Considering that high-current welding inevitably leads to a high overall temperature rise, the preset temperature threshold was set at 90℃. Although this temperature is higher than the optimal value of 80℃, it is still within the allowable range for stainless steel to resist intergranular corrosion, and falls within the acceptable boundary under the efficiency-first strategy.

[0125] Because this embodiment uses high current and long cycle time (25 units / group), the heat accumulation rate is fast. Relying solely on natural cooling may lead to excessive downtime and affect the production schedule. Therefore, this embodiment adopts an active cooling strategy:

[0126] After welding 25 joints, the weld temperature was checked.

[0127] If T ≤ 90℃, proceed to the next group.

[0128] If T > 90℃, immediately suspend welding and start the forced air cooling process.

[0129] Use industrial clean compressed air or a high-power axial flow fan to directionally purge the hot areas of the tube sheet.

[0130] With air cooling, temperature changes are continuously monitored. Once the temperature drops to 90°C or below, purging is immediately stopped and welding operations resume. This rapid stop and rapid cooling mode significantly shortens non-productive time.

[0131] Example 4

[0132] like Figures 1 to 3As shown, this embodiment provides a method for preventing overheating expansion welding of tube sheets and heat exchanger tubes. This embodiment further elaborates on Embodiment 1 and is applicable to tube sheet welding scenarios with extremely high heat sensitivity, thin wall thickness, or extremely stringent requirements for corrosion resistance (such as nuclear-grade equipment or high-pressure hydrogenation units). Furthermore, the steps for planning the welding sequence in the method for preventing overheating expansion welding of tube sheets and heat exchanger tubes in this embodiment specifically include:

[0133] Based on the array arrangement of the tube sheet joints to be welded, set the interval step size for skip welding or the partition rotation strategy.

[0134] Develop a welding path that ensures that, in time sequence, there is at least one other tube sheet joint to be welded between two consecutive welding operations targeting tube sheet joints to be welded.

[0135] Planning the welding sequence based on multiple tube sheet joints to be welded on a tube sheet, ensuring that tube sheet joints that are sequentially welded are not adjacent in spatial position, also includes:

[0136] The tube sheet joint to be welded is processed into a V-shaped bevel, and the angle of one side of the V-shaped bevel is controlled to be 25° to 35°.

[0137] Assemble the tube sheet and heat exchange tubes, and control the root gap of the V-groove to be 3.0 mm to 4.5 mm.

[0138] Before welding is performed according to the welding sequence, and heat is dissipated by using a heat-conducting fixture to contact the tube sheet joints:

[0139] The clean zone is defined as the area extending 20mm to 50mm to both sides along the pipe axis, starting from the bevel position of the pipe-to-plate joint to be welded.

[0140] Mechanical polishing is performed on the inner wall of the heat exchange tube, the outer wall of the heat exchange tube, and the surface of the tube sheet holes in the clean zone to remove the oxide film. Acetone is then used to wipe the polished surface to remove any oil residue until the surface in the clean zone shows a metallic luster.

[0141] More specifically, the method for preventing overheating and expansion during welding of the tube sheet and heat exchange tubes in this embodiment includes the following steps:

[0142] In this embodiment, based on the array arrangement of the tube sheet joints to be welded, the interval step size for skip welding or the zone rotation strategy is set, and the layout is carried out using digital means:

[0143] The positional information of thousands of tube sheet joints to be welded on the tube sheet is digitized to construct a two-dimensional spatial coordinate model. ;

[0144] The path generation algorithm is configured with the constraint of "minimum thermal isolation distance". The algorithm mandates that if the first... The joint coordinates for the second weld are: Then the first Joint coordinates of the second weld Must meet (For example, setting) (200mm).

[0145] The generated welding paths are macroscopically distributed in a starry sky pattern, ensuring that the heat source is always surrounded by a vast area of ​​cold metal, completely blocking the superposition of thermal fields from the physical level.

[0146] To achieve precise control, this embodiment employs the most stringent pre-weld preparation standards. The V-groove angle is controlled at 25° on each side, and the root gap is controlled at 3.0 mm. This narrow and deep groove design significantly reduces the amount of weld metal filling, thereby minimizing the total heat input.

[0147] The cleaning zone is set to extend 50mm along the tube axis. In particular, the inner wall of the heat exchange tube is deeply polished and wiped with acetone to ensure that the micro-roughness of the contact surface between the copper heat-conducting rod and the tube wall is minimized and free of oil film, reducing the contact thermal resistance to the physical limit to meet the rapid heat dissipation requirements under low current.

[0148] The heat-conducting fixture uses a high-precision copper heat-conducting rod, which has a stricter tolerance to fit the inner diameter of the tube, ensuring a tight fit after insertion.

[0149] The welding parameters were set as follows: 75A welding current, 13V welding voltage, and 10L / min shielding gas flow rate for filler wire tungsten inert gas welding. This was just enough to maintain root melting with a gap of 3.0mm. Excess heat was instantly absorbed by the copper rod, with almost no excess heat diffusion.

[0150] To capture minute fluctuations in heat accumulation, this embodiment sets the detection node to perform a temperature measurement every 15 tube sheet joints to be welded. This high-frequency interruption mechanism ensures that the heat accumulation effect is contained in its early stages.

[0151] The safety threshold is set at 70°C. This is an extremely conservative temperature line to ensure that the weld metal remains at a low temperature, far from the sensitization range, throughout the entire multi-layer, multi-pass welding process.

[0152] If the measured temperature exceeds 70°C, immediately stop the process and allow natural cooling to bring the temperature down to near ambient temperature before re-welding. Due to the extremely low heat input per cycle (75A), the natural cooling time is usually very short and will not significantly affect the overall project schedule.

[0153] Example 5

[0154] like Figures 1 to 3 As shown, this embodiment provides a method for preventing overheating and expansion welding of tube sheets and heat exchanger tubes, as well as a tube sheet heat exchanger. This embodiment further elaborates on the above embodiments, and the specific steps are as follows:

[0155] Specific skip soldering paths are determined based on the array arrangement of the tube sheet holes. (Reference) Figure 3 The local layout shown employs a strategy of skip-hole soldering and layered staggered placement. The specific execution sequence is as follows:

[0156] In a specific row of the tube sheet, the first hole is welded first (marked as ① in the figure); the next hole is skipped and the third hole is welded directly (marked as ② in the figure); the next hole is skipped again and the fifth hole is welded (marked as ③ in the figure). This process continues until the bottom layer of spacing welding is completed. Then, the holes in the next layer (marked as ④, ⑤, and ⑥ in the figure) are welded according to the same spacing logic. This sequence ensures that any two spatially adjacent solder joints are separated by as many other solder joint operations as possible on the time axis, thereby maximizing the cooling time between adjacent solder joints.

[0157] After establishing the above order, according to Figure 2 The control flow diagram executes specific welding operations, and the entire process constitutes an adaptive closed-loop system:

[0158] S1. Start batch welding:

[0159] The entire welding task is broken down into several batches. In this embodiment, each batch consists of 20 consecutively welded tube sheet joints.

[0160] S2. Install the heat-conducting fixture:

[0161] For each specific weld joint on the current batch path, before welding, a specially made high thermal conductivity copper gasket is inserted into the stainless steel heat exchange tube, ensuring that the outer wall of the gasket fits tightly against the inner wall of the tube. This gasket acts as a micro-heat dissipation unit, responsible for dissipating heat from the root of the weld the instant the arc is generated.

[0162] S3, Perform welding:

[0163] With the help of the copper backing, the filler wire tungsten inert gas welding of the current weld point is completed. Then the backing is removed and the machine moves to the next point in the sequence until all 20 weld points in the current batch are completed.

[0164] S4. Measurement Feedback:

[0165] After the current batch is completed, work must be stopped immediately and the interpass temperature (T) of the weld area must be measured using temperature measuring equipment.

[0166] S5, Temperature Control Decision:

[0167] The measured temperature T was compared with the critical threshold of 80℃.

[0168] Branch 1 (continued): If T ≤ 80℃, it indicates that macroscopic skip welding and microscopic heat dissipation are effective, and the heat accumulation is within a safe range. Directly proceed to the next batch of welding cycles.

[0169] Branch 2 (Pause): If T > 80℃, it indicates that the heat accumulation exceeds the limit, and a pause and cooling process is initiated. Welding remains stopped, and natural cooling or auxiliary air cooling is used until the temperature monitoring shows that T has dropped to 80℃ or below. Only then can the pause be ended and the next batch of welding resume.

[0170] The tube sheet heat exchanger produced by the above process has a golden yellow or silver-white color at the tube sheet joint weld, and the first-pass yield of PT flaw detection is ≥99.5%, which effectively solves the problem of heat accumulation and overheating in dissimilar metal welding.

[0171] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of this application. Any specific values ​​in all examples shown and discussed herein should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0172] Furthermore, it should be noted that the use of terms such as "first" and "second" is merely for ease of distinction, and unless otherwise stated, these terms have no special meaning and therefore should not be construed as limiting the scope of protection of this application.

[0173] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preventing overheating expansion during welding of a tube sheet and heat exchange tubes, characterized in that, include: The welding sequence is planned according to the multiple tube sheet joints to be welded on the tube sheet, so that the tube sheet joints that are consecutive in the welding sequence are not adjacent in spatial position. Welding is performed according to the welding sequence described above, while using heat-conducting tooling to contact the tube sheet joints to dissipate heat. After completing the welding of a predetermined number of tube sheet joints, the weld temperature is measured and compared with a preset temperature threshold. If the weld temperature is less than or equal to the preset temperature threshold, then continue welding the next set of tube sheet joints; If the weld temperature is greater than the preset temperature threshold, welding is suspended and the weld is cooled until the weld temperature drops to below or equal to the preset temperature threshold. The heat-conducting tooling is a heat-conducting rod made of copper, and the outer contour of the heat-conducting rod is adapted to the inner hole shape of the heat exchange tube. The step of using a heat-conducting tool to contact the tube sheet joint to conduct heat away specifically includes: Before welding, the heat-conducting rod is inserted into the heat exchange tube at the joint of the tube sheet to be welded, so that the outer wall of the heat-conducting rod is in contact with the inner wall of the heat exchange tube, thus establishing a radial heat conduction path from the root of the weld to the inside of the heat-conducting rod. The predetermined quantity is set to be between 15 and 25; After each predetermined number of tube sheet joints is welded, the weld temperature is checked, specifically including: After each predetermined number of tube sheet joint welding operations are completed, temperature data of the current weld area is immediately collected using a temperature measuring device. The steps for planning the welding sequence specifically include: Based on the array arrangement of the tube sheet joints to be welded, set the interval step size for skip welding or the partition rotation strategy. Develop a welding path that ensures that there is at least one other tube sheet joint to be welded between two welding operations that are performed immediately in time. Planning the welding sequence based on multiple tube sheet joints to be welded on a tube sheet, ensuring that tube sheet joints that are sequentially welded are not adjacent in spatial position, also includes: The tube sheet joint to be welded is processed into a V-shaped bevel, and the angle of one side of the V-shaped bevel is controlled to be 25° to 35°. Assemble the tube sheet and heat exchange tubes, and control the root gap of the V-groove to be 3.0 mm to 4.5 mm.

2. The method for preventing overheating and expansion welding of tube sheets and heat exchange tubes according to claim 1, characterized in that, The preset temperature threshold is set to any value between 70°C and 90°C. The step of pausing welding and cooling specifically includes: The arc initiation action is forcibly stopped, and the welding remains stopped until the detected weld temperature value is lower than or equal to the preset temperature threshold.

3. The method for preventing overheating and expansion welding of tube sheets and heat exchange tubes according to claim 1, characterized in that, The step of pausing welding and cooling until the weld temperature drops below or equal to the preset temperature threshold specifically includes: Determine a cooling strategy, which is selected from natural cooling and air cooling; After the welding operation is stopped, the cooling strategy shall be immediately implemented for the current inspection area; The cooling process is maintained, and the weld temperature is continuously monitored. Cooling is terminated and welding is resumed only when the real-time temperature data drops below or equal to the preset temperature threshold.

4. The method for preventing overheating and expansion welding of tube sheets and heat exchange tubes according to claim 1, characterized in that, The welding is performed using filler wire tungsten inert gas welding; The welding current for the filler wire tungsten inert gas welding is 75A to 125A, the welding voltage is 13V to 17V, and the shielding gas flow rate is 10L / min to 16L / min.

5. The method for preventing overheating and expansion welding of tube sheets and heat exchange tubes according to claim 1, characterized in that, Before welding is performed according to the welding sequence, and heat is dissipated by using a heat-conducting tool to contact the tube sheet joints: The clean zone is defined as the area extending 20mm to 50mm to both sides along the pipe axis, starting from the bevel position of the pipe joint to be welded. Mechanical polishing is performed on the inner wall of the heat exchange tube, the outer wall of the heat exchange tube, and the surface of the tube sheet holes in the clean zone to remove the oxide film. Acetone is then used to wipe the polished surface to remove any oil residue until the surface in the clean zone shows a metallic luster.

6. A tube sheet heat exchanger, characterized in that, The tube sheet heat exchanger includes a tube sheet and heat exchange tubes, and the connection between the tube sheet and the heat exchange tubes is formed by welding the tube sheet and the heat exchange tubes using the anti-overheating expansion welding method as described in any one of claims 1 to 5.

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