Temperature control induction heating system for nuclear power main pump shell inner wall surfacing and heating method of temperature control induction heating system

Abstract

The invention relates to a temperature control induction heating system for surfacing of the inner wall of a nuclear power main pump shell. The system is formed by splicing a top induction heating tool, a bottom induction heating tool and a plurality of side induction heating tools through a stainless steel connecting frame, and an intelligent temperature control system. The intelligent temperature control system is composed of a distributed temperature measurement sensor, a central control unit and a man-machine interaction terminal. The heating method comprises the steps of tool assembly, preheating, dynamic interlayer temperature control in the surfacing process, programmed postweld heat treatment and data recording and dismounting. The device has the advantages that the device is adaptive to the special-shaped curved surface of the pump shell through modular design, the power of each tool is dynamically and independently adjusted, the problems of uneven temperature and low efficiency of a traditional heating mode are solved, and the surfacing quality and the process traceability are remarkably improved.

Description

Technical Field

[0001] This invention relates to a temperature-controlled induction heating system and heating method for welding the inner wall of a nuclear power plant main pump casing, belonging to the field of nuclear power equipment manufacturing. Background Technology

[0002] The function of the reactor coolant pump (main pump) is to force the coolant to circulate, thereby transferring the heat energy generated in the reactor to the steam generator to produce steam, which drives the turbine to do work.

[0003] The pump casing is part of the main system's pressure-bearing boundary. Its wall thickness should be able to withstand various loads transmitted through pipes under accident conditions. This means that in addition to considering the design conditions, it should also consider various loads under accident conditions, such as the maximum working pressure, transient temperature changes, seismic loads, and pipe rupture. The pump casing is integrally forged from low-alloy steel, with ultra-low carbon stainless steel, nickel-based materials, etc., welded to the inner surface. The welding process requires preheating of the welded areas on the inner wall before welding and hydrogen removal and heat treatment after welding. Before welding, the base material of the pump casing should be heated to a temperature of 150℃~200℃; the hydrogen removal temperature after welding needs to meet the requirement of heating the base material to 250℃~400℃. Uniform temperature is required during heating and heat preservation, with a temperature difference between the outer and inner walls ≤40℃. Post-weld heat treatment at 595℃-620℃ requires uniform temperature during heating, with a temperature difference between the outer and inner walls controllable to ≤50℃, and heat preservation ensuring that all parts of the workpiece meet the 595℃-620℃ requirement.

[0004] For example, the pump casing of the main pump in the Hualong One nuclear reactor is a core component of the nuclear island. Its inner wall needs to be overlaid with 308L / 309L stainless steel to ensure radiation and corrosion resistance. Preheating before welding and interpass temperature control directly affect the welding quality. Traditional flame heating and ceramic resistance heating suffer from uneven temperature, low efficiency, and inability to precisely control temperature. Conventional induction heating fixtures are difficult to adapt to the structural characteristics of the pump casing's ultra-thick wall and irregular curved surface, and lack intelligent closed-loop temperature control capabilities, thus failing to meet the stringent welding quality requirements of the Hualong One RCC-M standard.

[0005] Currently, the two most commonly used processes in production are external wall flame heating and internal wall ceramic resistance element heating.

[0006] Flame heating: Flame heating uses the heat generated by the combustion of combustible gases (such as propane, natural gas, acetylene, etc.) to heat the workpiece through direct radiation and convection. Multiple torches or specially designed heating frames are typically used, moving or stationary around the workpiece for heating.

[0007] shortcoming: Poor temperature uniformity: It relies on manual operation and is prone to local overheating or insufficient heating.

[0008] Low temperature control accuracy: Due to factors such as flame stability and gas pressure, it is difficult to achieve precise constant temperature control.

[0009] Safety hazards: Open flame operations pose a risk of fire and explosion, and strict fire prevention and ventilation measures are required.

[0010] Environmental impact: Combustion products may pollute the workshop environment, which is detrimental to nuclear-grade components with high cleanliness requirements.

[0011] Ceramic plate heating (resistance heating): Ceramic heating is a type of resistance heating that converts electrical energy into heat energy. A ceramic heating element with a resistance wire is attached or fixed to the surface of the workpiece, and programmed heating and heat preservation are achieved through linkage with a temperature control system via a temperature sensor (such as a thermocouple).

[0012] Disadvantages: Uneven surface contact: The ceramic sheet is a rigid / semi-rigid block, which has poor fit with curved surfaces (cylinder, end cap, pipe), resulting in gaps. This leads to a sharp drop in local heat transfer efficiency and the formation of "cold spots"; while areas with tight fit are prone to "hot spots".

[0013] Fixed power density: The power of a single block is not adjustable, making it impossible to perform zoned temperature control for thick walls, corners, and variable cross sections, and making it difficult to meet the ±15℃ or even ±10℃ uniform temperature zone requirements of nuclear power.

[0014] Large circumferential / axial temperature difference: The radial temperature difference of thick-walled parts is more difficult to control, which can easily cause additional thermal stress, which, combined with residual stress, increases the risk of cracking.

[0015] Insufficient temperature control accuracy and stability make it difficult to meet the requirements for nuclear power plant recording. Thermal inertia and slow response: The ceramic sheet heats up / cools down slowly, and the PID control is prone to overshoot, especially in the heat preservation section, where the temperature fluctuates greatly and is difficult to stabilize within the process window.

[0016] Therefore, there is an urgent need for a new heating device that is efficient, environmentally friendly, and has good processability in production. Summary of the Invention

[0017] To overcome the shortcomings of existing technologies and solve the problems of low efficiency, poor processability, and uneven heating temperature in the heating processes of pre-welding, heat preservation during welding, hydrogen removal after welding, and heat treatment of the inner wall of the coolant pump casing in nuclear power plants, this invention provides a temperature-controlled induction heating system and its heating method for welding the inner wall of the main pump casing in nuclear power plants. The technical solution of this invention is as follows: A temperature-controlled induction heating system for welding the inner wall of a nuclear power plant main pump casing includes: The modular induction heating unit includes a top induction heating fixture (1), a bottom induction heating fixture (2), and several side induction heating fixtures installed between the top induction heating fixture (1) and the bottom induction heating fixture (2). The top induction heating fixture (1), the bottom induction heating fixture (2), and the side induction heating fixtures are detachably spliced ​​together by a stainless steel connecting frame (12) for fitting and wrapping around the outer wall of the pump casing. The intelligent temperature control unit includes: The distributed temperature measurement network includes several temperature sensors (13) deployed on the outer wall of the pump casing to collect temperature data of different areas of the outer wall of the pump casing in real time. The central control unit has an input end connected to all temperature sensors (13) and an output end connected to the power modules of the top induction heating fixture (1), the bottom induction heating fixture (2) and the side induction heating fixture; the central control unit has a built-in process parameter database, which stores the temperature-time control curves corresponding to preheating before welding, interlayer insulation and post-weld heat treatment. The human-machine interface terminal is communicatively connected to the central control unit and is used to set and display the temperature-time process curve and real-time temperature field information, and automatically store process data to generate process records. The central control unit dynamically adjusts the output power of each induction heating fixture based on the temperature-time control curve retrieved from the process parameter database and the real-time feedback data from the temperature sensor (13), so as to achieve closed-loop control of the entire pump casing heating process.

[0018] The top induction heating fixture (1), bottom induction heating fixture (2) and side induction heating fixture have the same structure, all including a fiberglass frame (9), an induction heating cable (10) and an insulation layer (11). The induction heating cable (10) is wound on the fiberglass frame (9). The induction heating cable (10) is used to pass a medium frequency induction current to generate eddy current heat inside the pump casing. The insulation layer (11) is composited on the inner side of the fiberglass frame (9).

[0019] When the central control unit is in operation, it performs temperature field prediction and power optimization decisions, wherein: The temperature field prediction is based on the geometry of the pump casing, the thermal properties of the material, the layout of each induction heating fixture and the current power parameters, and integrates the real-time temperature feedback data of the temperature sensor (13) to dynamically calculate the predicted temperature field distribution of the inner and outer walls of the pump casing. The power optimization decision compares the predicted temperature field distribution with the target temperature field required by the preset process, and calculates the power adjustment amount for each induction heating tool by solving a preset optimization objective function, so as to make the actual temperature field close to the target temperature field.

[0020] The coiling density of the induction heating cable (10) on each fiberglass frame (9) is non-uniformly distributed.

[0021] The stainless steel connecting frame (12) is used to detachably connect the top induction heating fixture (1), the bottom induction heating fixture (2) and the side induction heating fixture together to form a stable overall structure and ensure that each fixture fits tightly against the complex curved surface of the pump casing; the heat insulation material (11) is filled between the top induction heating fixture (1), the bottom induction heating fixture (2) and the side induction heating fixture and the outer wall of the pump casing to reduce radial heat loss.

[0022] The control objectives of the central control unit are: during the preheating and interlayer insulation stages, control the temperature difference between the inner and outer walls of the pump casing to ≤40℃; during the post-weld heat treatment heating stage, control the temperature difference to ≤50℃; and during any insulation stage, control the temperature fluctuation within the working area to be within ±5℃.

[0023] The number of side induction heating fixtures is six, and they are arranged in a ring around each other in sequence. Specifically, they include a first side induction heating fixture (3), a second side induction heating fixture (4), a third side induction heating fixture (5), a fourth side induction heating fixture (6), a fifth side induction heating fixture (7), and a sixth side induction heating fixture (8).

[0024] A heating method using the temperature-controlled induction heating system for welding the inner wall of the main pump casing of a nuclear power plant includes the following steps: S1. Tooling placement and assembly: First, place the bottom induction heating tooling (2) in the heating station; hoist the pump casing to the station and make it fit with the bottom tooling; then hoist the top induction heating tooling (1) to the top of the pump casing; then hoist each side induction heating tooling in sequence; finally, use the stainless steel connecting frame (12) to fix the top induction heating tooling, bottom induction heating tooling and side induction heating tooling into an integral wrapping structure; S2. Preheating: The preheating temperature curve is preset through the human-machine interface; the central control unit is started. The intelligent temperature control unit dynamically adjusts the power of each tool according to the real-time feedback of the temperature sensor (13) so that the temperature field of the pump casing is uniformly raised to 150℃–200℃. S3. Welding and Dynamic Interlayer Temperature Control: Welding of the inner wall begins after the preheating temperature is reached; during the welding process, the central control unit continuously monitors the interlayer temperature and performs pulsed power adjustment on the top induction heating fixture, bottom induction heating fixture and side induction heating fixture to maintain the stability of the interlayer temperature and avoid heat input fluctuations. S4. Post-weld heat treatment: After the welding is completed, the heat treatment program is started through the human-machine interface; the central control unit automatically controls the top induction heating fixture, the bottom induction heating fixture and the side induction heating fixture to raise the temperature so that the pump casing reaches the post-weld heat treatment temperature of 595℃–620℃ and is kept at that temperature. S5. Cooling, disassembly and data archiving: After the heat treatment is completed, the intelligent temperature control unit stops heating; after the pump casing cools down, each induction heating fixture and connecting frame is disassembled in sections (12); the temperature data of the entire heating process is automatically recorded by the intelligent temperature control unit and a traceable process report is generated.

[0025] The temperature sensors (13) in the distributed temperature measurement network are positioned at locations corresponding to the geometric changes and thickness transition zones of the outer wall of the pump casing, in order to monitor the temperature gradient.

[0026] The advantages of this invention are: 1. The modular and splicable induction heating fixture design allows for rapid assembly via a stainless steel connecting frame. It perfectly fits the irregular curved surface and ultra-thick wall structure of the main pump casing of nuclear power plants such as Hualong One, solving the problems of poor adaptability and difficult hoisting of traditional integral fixtures, and significantly improving the versatility of the fixture and the efficiency of on-site operation.

[0027] 2. Through real-time feedback from a distributed temperature measurement network, combined with a temperature field prediction model and power optimization decisions, millisecond-level dynamic adjustment of the power of eight independent tooling units was achieved. This solution can control the temperature difference between the inner and outer walls during the preheating and interlayer insulation stages to ≤40℃, and the temperature difference during the post-weld heat treatment heating stage to ≤50℃, with an overall temperature control accuracy of ±5℃, thereby achieving uniformity and stability in weld overlay quality.

[0028] 3. The non-uniform induction cable winding design based on wall thickness distribution (density increases with wall thickness) is adopted, combined with the medium frequency induction heating principle, so that eddy current heat is directly generated inside the pump casing metal, realizing efficient and uniform heat penetration from the outer wall to the inner wall, and without open flame or pollution, making it safe and environmentally friendly.

[0029] 4. It can preset, store, and automatically execute process curves, display temperature field cloud maps in real time, and automatically generate electronic process reports containing all key parameters. This meets the stringent quality control and full traceability requirements of the nuclear power industry for the manufacturing process.

[0030] 5. The system integrates multiple heating processes such as preheating before welding, interlayer insulation, and post-weld heat treatment into a single system for automatic completion, reducing the traditional steps of multiple disassembly and reassembly. This not only significantly reduces labor intensity and human error, but also significantly improves the consistency and pass rate of the weld overlay quality through continuous and stable intelligent temperature control. Attached Figure Description

[0031] Figure 1 This is an exploded view of the main structure of the present invention.

[0032] Figure 2 yes Figure 1 A schematic diagram of the structure of the induction heating fixture on the middle side. Detailed Implementation

[0033] The present invention will be further described below with reference to specific embodiments, and the advantages and features of the present invention will become clearer as a result. However, these embodiments are merely exemplary and do not constitute any limitation on the scope of the present invention. Those skilled in the art should understand that modifications or substitutions can be made to the details and form of the technical solutions of the present invention without departing from the spirit and scope of the present invention, but all such modifications and substitutions fall within the protection scope of the present invention.

[0034] See Figure 1 and Figure 2 This invention relates to a temperature-controlled induction heating system for welding the inner wall of a nuclear power plant main pump casing, comprising: The modular induction heating unit includes a top induction heating fixture 1, a bottom induction heating fixture 2, and several side induction heating fixtures installed between the top and bottom induction heating fixtures 1 and 2. The top, bottom, and side induction heating fixtures are detachably assembled together by a stainless steel connecting frame 12 for fitting and wrapping around the outer wall of the pump casing. By designing the induction heating unit as a modular structure composed of top, bottom, and several side fixtures, and using a stainless steel connecting frame for detachable assembly, the entire heating fixture can be flexibly combined and adjusted to closely fit the complex irregular curved surface of the nuclear power main pump casing, achieving effective wrapping and uniform heating of ultra-thick-walled, irregularly shaped workpieces that are difficult to adapt to with traditional integral induction heaters.

[0035] The detachable and modular design allows the bulky heating fixture to be disassembled and assembled on-site, avoiding the difficulties of hoisting a large, monolithic fixture and the need for extremely high alignment precision. This not only significantly reduces the difficulty and risk of on-site installation but also makes the disassembly, cleaning, maintenance, and storage of the fixture after use much more convenient, greatly improving the operability and efficiency of the entire heating process. The intelligent temperature control unit includes: The distributed temperature measurement network includes several temperature sensors 13 deployed on the outer wall of the pump casing, which are used to collect temperature data of different areas of the outer wall of the pump casing in real time. The central control unit has its input end connected to all temperature sensors 13, and its output end connected to the power modules of the top induction heating fixture 1, the bottom induction heating fixture 2, and the side induction heating fixture. The central control unit has a built-in process parameter database, which stores the temperature-time control curves corresponding to preheating before welding, interlayer insulation, and post-weld heat treatment. The human-machine interface terminal P is communicatively connected to the central control unit and is used to set and display the temperature-time process curve and real-time temperature field information, and automatically store process data to generate process records. The central control unit dynamically adjusts the output power of each induction heating fixture based on the temperature-time control curve retrieved from the process parameter database and the real-time feedback data from the temperature sensor 13, so as to achieve closed-loop control of the entire pump casing heating process.

[0036] The distributed temperature measurement network provides comprehensive, real-time external wall temperature field data. Based on this, the central control unit dynamically calculates and adjusts the output power of each independent tooling. This closed-loop control mode based on real-time feedback can actively compensate for heat loss or accumulation caused by the complex pump casing structure and uneven heat capacity, thereby precisely constraining the heating process within the preset temperature-time process curve range. This ensures the temperature uniformity and stability of each stage of preheating, interlayer insulation, and post-weld heat treatment, fundamentally meeting the stringent quality requirements of nuclear power welding.

[0037] The integrated human-machine interface terminal and process parameter database transform complex heating processes into standardized, callable, and monitorable procedures. Operators no longer need to rely on experience to manually adjust the temperature; they can easily set up, start, and monitor the fully automated heating process through the interface, significantly reducing operational difficulty and the risk of human error. Simultaneously, it automatically stores temperature data throughout the entire process and generates detailed process records, establishing a complete electronic quality archive for each product.

[0038] The top induction heating fixture 1, the bottom induction heating fixture 2, and the side induction heating fixture have the same structure, all including a fiberglass frame 9, an induction heating cable 10, and an insulation layer 11. The induction heating cable 10 is wound on the fiberglass frame 9. The induction heating cable 10 is used to pass a medium-frequency induction current to generate eddy current heat inside the pump casing. The insulation layer 11 is laminated on the inner side of the fiberglass frame 9.

[0039] The top, bottom, and side induction heating fixtures are composed of a fiberglass frame 9, induction heating cables 10, and an insulation layer 11. The fiberglass frame of the top induction heating fixture is circular, the bottom induction heating fixture is conical, and the side induction heating fixture is rectangular. This simplifies the manufacturing process and reduces the types of spare parts and inventory costs. In terms of use and maintenance, damage or replacement of individual components does not require customization and can be quickly replaced, greatly improving the maintainability and overall service life of the equipment, which is the foundation for the efficient operation of the modular system.

[0040] The fiberglass frame 9 serves as an insulating skeleton, ensuring electrical safety and providing a stable coiling base for the cable; the induction heating cable 10 is directly fed with medium-frequency current, efficiently generating eddy current heat inside the pump casing, resulting in high energy utilization; the inner composite insulation layer 11 effectively reduces heat radiation loss from the tooling to the environment, directing heat more concentratedly to the pump casing, thereby improving heating efficiency and creating stable thermal boundary conditions for subsequent precise temperature control.

[0041] When the central control unit is in operation, it performs temperature field prediction and power optimization decisions, wherein: The temperature field prediction is based on the pump casing geometry, material thermal properties, layout of each induction heating fixture, and current power parameters, and integrates real-time temperature feedback data from the temperature sensor 13 to dynamically calculate the predicted temperature field distribution on the inner and outer walls of the pump casing. The power optimization decision compares the predicted temperature field distribution with the target temperature field required by the preset process, and calculates the power adjustment amount for each induction heating fixture by solving a preset optimization objective function, so that the actual temperature field is close to the target temperature field. This central control unit realizes a fundamental shift from passive control based on local temperature point feedback to active intelligent control based on global temperature field prediction and optimization, overcoming the control lag and overshoot problems caused by large and complex components with large thermal inertia and uneven heat transfer, and providing a guarantee for achieving high-precision temperature control of ±5℃ and strict temperature difference limits.

[0042] The induction heating cable 10 is wound with a non-uniform density on each fiberglass frame 9. This winding density distribution is designed based on the wall thickness of different regions of the pump casing, resulting in higher cable winding densities in areas with thicker pump casing walls to ensure uniform heat penetration along the thickness direction. This induction heating cable layout abandons the traditional practice of uniformly winding induction coils, creatively customizing the winding density based on the wall thickness distribution data of the pump casing's three-dimensional model. In areas with thicker walls and higher thermal resistance, increasing the cable density enhances the electromagnetic field strength and heat flux density in that local area, thereby actively and precisely compensating for the heat transfer attenuation to the inner wall caused by the increased wall thickness. This allows heat to penetrate synchronously and uniformly to the entire inner wall surface of the pump casing, laying the physical foundation for obtaining a uniform temperature field.

[0043] The stainless steel connecting frame 12 is used to detachably connect the top induction heating fixture 1, the bottom induction heating fixture 2, and the side induction heating fixture together, forming a stable overall structure and ensuring that each fixture fits tightly against the complex curved surface of the pump casing. The insulation material 11 is filled between the top induction heating fixture 1, the bottom induction heating fixture 2, and the side induction heating fixture and the outer wall of the pump casing to reduce radial heat loss. The detachable stainless steel connecting frame 12, as a rigid mechanical skeleton, firmly connects the separate top, bottom, and side fixtures into a stable overall structure. This effectively prevents displacement or deformation of the modules during heating, hoisting, or welding vibrations, ensuring that the entire heating assembly fits tightly and stably against the complex irregular curved surface of the pump casing as a whole.

[0044] The control objectives of the central control unit are: during the preheating and interlayer insulation stages, control the temperature difference between the inner and outer walls of the pump casing to ≤40℃; during the post-weld heat treatment heating stage, control the temperature difference to ≤50℃; and during any insulation stage, control the temperature fluctuation within the working area to be within ±5℃.

[0045] The system comprises six side-mounted induction heating fixtures arranged sequentially around each other, specifically including a first side-mounted induction heating fixture 3, a second side-mounted induction heating fixture 4, a third side-mounted induction heating fixture 5, a fourth side-mounted induction heating fixture 6, a fifth side-mounted induction heating fixture 7, and a sixth side-mounted induction heating fixture 8. By dividing the side area into six independently controllable heating fixtures, a physical basis is provided for highly flexible and precise zoned temperature control. This allows the system to independently compensate or adjust the power for each local area, taking into account the complex curved surface structure, wall thickness variations, and heat capacity differences on the pump casing side. This effectively eliminates cold or hot spots in large-area heating, ensuring the uniformity of the temperature field across the entire side.

[0046] The present invention also relates to a heating method using the temperature-controlled induction heating system for welding the inner wall of the main pump casing of a nuclear power plant, comprising the following steps: S1. Tooling Positioning and Assembly: First, place the bottom induction heating tooling 2 in the heating station; hoist the pump casing to the station and make it fit with the bottom tooling; then hoist the top induction heating tooling 1 to the top of the pump casing; then hoist each side induction heating tooling in sequence; finally, use the stainless steel connecting frame 12 to fix and connect the top induction heating tooling, bottom induction heating tooling and side induction heating tooling into an integral wrapping structure; Specifically, a modular installation logic is adopted from bottom to top and from the center outwards. First, the bottom induction heating fixture 2 is positioned, and then the pump casing is hoisted into place and fitted to it to ensure foundation stability. Then, the top induction heating fixture 1 is installed to form axial constraint. Finally, the six side induction heating fixtures are installed in sequence, and all modules are rigidly connected into a heating shell that fits tightly with the shape of the pump casing using a stainless steel frame 12. S2. Preheating: The preheating temperature curve is preset through the human-machine interface; the central control unit is started, which dynamically adjusts the power of each tooling according to the real-time feedback of the temperature sensor 13, so that the temperature field of the pump casing inner wall is uniformly raised to 150℃–200℃. Specifically, the operator calls or sets the preheating program (150-200℃) through the human-machine interface. After startup, the central control unit no longer performs simple on / off control, but dynamically adjusts the differentiated power commands for the eight independent tooling units based on real-time data from multiple temperature sensors 13, driving the system to quickly and uniformly bring the temperature of the pump casing inner wall to the target range. S3. Welding and Dynamic Interlayer Temperature Control: Welding of the inner wall begins after the preheating temperature is reached; during the welding process, the central control unit continuously monitors the interlayer temperature and performs pulsed power adjustment on the top induction heating fixture, bottom induction heating fixture and side induction heating fixture to maintain the stability of the interlayer temperature and avoid heat input fluctuations. Specifically, after the welding operation begins, the working mode switches from heating up to precise temperature maintenance. The central control unit continuously monitors the interlayer temperature, and once it detects that the temperature deviates from the set range due to welding heat input or ambient heat dissipation, it immediately issues a short, rapid pulse power command to the tooling in the corresponding area for fine-tuning. S4. Post-weld heat treatment: After the welding is completed, the heat treatment program is started through the human-machine interface; the central control unit automatically controls the top induction heating fixture, bottom induction heating fixture and side induction heating fixture to raise the temperature so that the pump casing reaches the post-weld heat treatment temperature of 595℃–620℃ and is kept at that temperature; during this process, the global temperature field is continuously optimized to ensure that the temperature difference between the inner and outer walls can be strictly controlled in the high-temperature section and uniform heat preservation can be achieved.

[0047] S5. Cooling, disassembly and data archiving: After heat treatment, the intelligent temperature control unit stops heating; after the pump casing cools down, each induction heating fixture and connecting frame 12 is disassembled in sections; the temperature data of the entire heating process is automatically recorded by the intelligent temperature control unit and a traceable process report is generated, which is convenient for maintenance and use in the next workpiece.

[0048] The temperature sensors 13 in the distributed temperature measurement network are positioned at locations corresponding to geometric changes and thickness transition zones on the outer wall of the pump casing, in order to achieve focused monitoring of the temperature gradient.

[0049] Based on the above steps, the following advantages are achieved: 1. The complex pump casing heating process is solidified into five clear, standardized steps, guided by a human-machine interface. From assembly and preheating to heat treatment, the entire process is automatically executed by a central controller according to a predetermined program, significantly reducing human intervention points and the risk of operational errors, resulting in more stable and repeatable process quality.

[0050] 2. Uninterrupted closed-loop control with different objectives is achieved in the three major stages of preheating, welding, and heat treatment. In particular, the dynamic interlayer temperature control introduced in the welding stage can respond to the interference of welding thermal cycle in real time, which is impossible with traditional heating methods, and fundamentally ensures the uniformity and reliability of the weld layer quality.

[0051] 3. It provides a complete chain of evidence from equipment parameters to process results, fully meeting the stringent traceability and process verification requirements of the nuclear power industry for manufacturing processes, and providing support for product certification and lifelong quality records.

[0052] 4. The modular assembly design enables rapid tooling placement and disassembly, reducing the time spent on large dedicated workstations. Simultaneously, integrating preheating, interlayer insulation, and post-weld heat treatment into a single continuous heating process avoids the interruptions of traditional methods, such as multiple heating equipment changes or long waiting times, significantly improving overall production efficiency.

[0053] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A temperature-controlled induction heating system for welding the inner wall of a nuclear power plant main pump casing, characterized in that, include: The modular induction heating unit includes a top induction heating fixture (1), a bottom induction heating fixture (2), and several side induction heating fixtures installed between the top induction heating fixture (1) and the bottom induction heating fixture (2). The top induction heating fixture (1), the bottom induction heating fixture (2), and the side induction heating fixtures are detachably spliced ​​together by a stainless steel connecting frame (12) for fitting and wrapping around the outer wall of the pump casing. The intelligent temperature control unit includes: The distributed temperature measurement network includes several temperature sensors (13) deployed on the outer wall of the pump casing to collect temperature data of different areas of the outer wall of the pump casing in real time. The central control unit has an input end connected to all temperature sensors (13) and an output end connected to the power modules of the top induction heating fixture (1), the bottom induction heating fixture (2) and the side induction heating fixture; the central control unit has a built-in process parameter database, which stores the temperature-time control curves corresponding to preheating before welding, interlayer insulation and post-weld heat treatment. The human-machine interface terminal is communicatively connected to the central control unit and is used to set and display the temperature-time process curve and real-time temperature field information, and automatically store process data to generate process records. The central control unit dynamically adjusts the output power of each induction heating fixture based on the temperature-time control curve retrieved from the process parameter database and the real-time feedback data from the temperature sensor (13), so as to achieve closed-loop control of the entire pump casing heating process.

2. The temperature-controlled induction heating system for welding the inner wall of the main pump casing of a nuclear power plant according to claim 1, characterized in that, The top induction heating fixture (1), bottom induction heating fixture (2) and side induction heating fixture have the same structure, all including a fiberglass frame (9), an induction heating cable (10) and an insulation layer (11). The induction heating cable (10) is wound on the fiberglass frame (9). The induction heating cable (10) is used to pass a medium frequency induction current to generate eddy current heat inside the pump casing. The insulation layer (11) is composited on the inner side of the fiberglass frame (9).

3. The temperature-controlled induction heating system for welding the inner wall of the main pump casing of a nuclear power plant according to claim 1 or 2, characterized in that, When the central control unit is in operation, it performs temperature field prediction and power optimization decisions, wherein: The temperature field prediction is based on the geometry of the pump casing, the thermal properties of the material, the layout of each induction heating fixture and the current power parameters, and integrates the real-time temperature feedback data of the temperature sensor (13) to dynamically calculate the predicted temperature field distribution of the inner and outer walls of the pump casing. The power optimization decision compares the predicted temperature field distribution with the target temperature field required by the preset process, and calculates the power adjustment amount for each induction heating tool by solving a preset optimization objective function, so as to make the actual temperature field close to the target temperature field.

4. The temperature-controlled induction heating system for welding the inner wall of the main pump casing of a nuclear power plant according to claim 1 or 2, characterized in that, The coiling density of the induction heating cable (10) on each fiberglass frame (9) is non-uniformly distributed.

5. The temperature-controlled induction heating system for welding the inner wall of the main pump casing of a nuclear power plant according to claim 4, characterized in that, The stainless steel connecting frame (12) is used to detachably connect the top induction heating fixture (1), the bottom induction heating fixture (2) and the side induction heating fixture together to form a stable overall structure and ensure that each fixture fits tightly against the complex curved surface of the pump casing; the heat insulation material (11) is filled between the top induction heating fixture (1), the bottom induction heating fixture (2) and the side induction heating fixture and the outer wall of the pump casing to reduce radial heat loss.

6. The temperature-controlled induction heating system for welding the inner wall of the main pump casing of a nuclear power plant according to claim 5, characterized in that, The control objectives of the central control unit are: during the preheating and interlayer insulation stages, control the temperature difference between the inner and outer walls of the pump casing to ≤40℃; during the post-weld heat treatment heating stage, control the temperature difference to ≤50℃; and during any insulation stage, control the temperature fluctuation within the working area to be within ±5℃.

7. The temperature-controlled induction heating system for welding the inner wall of the main pump casing of a nuclear power plant according to claim 6, characterized in that, The number of side induction heating fixtures is six, and they are arranged in a ring around each other in sequence, specifically including the first side induction heating fixture (3), the second side induction heating fixture (4), the third side induction heating fixture (5), the fourth side induction heating fixture (6), the fifth side induction heating fixture (7) and the sixth side induction heating fixture (8).

8. A heating method using the temperature-controlled induction heating system for welding the inner wall of the main pump casing of a nuclear power plant as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Tooling placement and assembly: First, place the bottom induction heating tooling (2) in the heating station; hoist the pump casing to the station and make it fit with the bottom tooling; then hoist the top induction heating tooling (1) to the top of the pump casing; then hoist each side induction heating tooling in sequence; finally, use the stainless steel connecting frame (12) to fix the top induction heating tooling, bottom induction heating tooling and side induction heating tooling into an integral wrapping structure; S2. Preheating: The preheating temperature curve is preset through the human-machine interface; the central control unit is started. The intelligent temperature control unit dynamically adjusts the power of each tool according to the real-time feedback of the temperature sensor (13) so that the temperature field of the inner wall of the pump casing rises uniformly to 150℃–200℃. S3. Welding and Dynamic Interlayer Temperature Control: Welding of the inner wall begins after the preheating temperature is reached; during the welding process, the central control unit continuously monitors the interlayer temperature and performs pulsed power adjustment on the top induction heating fixture, the bottom induction heating fixture and the side induction heating fixture to maintain the stability of the interlayer temperature and avoid heat input fluctuations. S4. Post-weld heat treatment: After the welding is completed, the heat treatment program is started through the human-machine interface; the central control unit automatically controls the top induction heating fixture, the bottom induction heating fixture and the side induction heating fixture to raise the temperature so that the pump casing reaches the post-weld heat treatment temperature of 595℃–620℃ and is kept at that temperature. S5. Cooling, disassembly and data archiving: After the heat treatment is completed, the intelligent temperature control unit stops heating; after the pump casing cools down, each induction heating fixture and connecting frame is disassembled in sections (12); the temperature data of the entire heating process is automatically recorded by the intelligent temperature control unit and a traceable process report is generated.

9. The temperature-controlled induction heating system for welding the inner wall of the main pump casing of a nuclear power plant according to claim 8, characterized in that, The temperature sensors (13) in the distributed temperature measurement network are positioned at locations corresponding to the geometric changes and thickness transition zones of the outer wall of the pump casing, in order to monitor the temperature gradient.

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