Method for manufacturing a control rod drive mechanism pressure shell

Abstract

This invention provides a method for manufacturing a pressure-resistant housing for a control rod drive mechanism, comprising: S1, rough machining of the SA508 Gr.3 pressure-resistant housing; S2, overall preheating of the SA508 Gr.3 pressure-resistant housing, maintaining the preheating temperature of the inner wall of the SA508 Gr.3 pressure-resistant housing at 150°C to 200°C; S3, circumferentially overlaying welding of the inner wall of the SA508 Gr.3 pressure-resistant housing, and providing nickel-based alloy welding wire and shielding gas to the welding position; S4, during the circumferential overlaying welding process, introducing low-temperature dry argon gas into the solidified weld bead located behind the weld pool along the welding direction, maintaining the local surface temperature of the solidified weld bead at 60°C to 100°C before the next overlaying welding; S5, after the overlaying welding is completed, heat-insulating the SA508 Gr.3 pressure-resistant housing, allowing it to naturally and slowly cool to below 80°C; S6, after the overlaying welding of the SA508 Gr.3 pressure-resistant housing... Gr.3 pressure shells undergo low-temperature isothermal stress relief treatment at 510℃ to 540℃. Preheating temperature and interpass temperature are controlled separately, effectively solving the problem of easy cracking defects in the nickel-based alloy overlay welded to the inner wall of SA508 Gr.3.

Description

Technical Field

[0001] This invention relates to the field of nuclear power equipment manufacturing and welding technology, specifically to a method for manufacturing a pressure-resistant shell for a control rod drive mechanism. Background Technology

[0002] Traditional control rod drive mechanisms utilize a thick-walled 304LN steel shell with an external magnetic ring and a thick ductile iron yoke, resulting in complex component structures, heavy overall weight, and difficulties in assembly, hoisting, and transportation. SA508 Gr.3 is a commonly used low-alloy tempered steel for nuclear power pressure vessels. While possessing excellent strength, toughness, and pressure-bearing capacity, it lacks resistance to uniform corrosion and stress corrosion in the primary coolant environment. In engineering practice, an Inconel 690 nickel-based alloy isolation and corrosion-resistant layer is typically welded onto the inner wall of the SA508 Gr.3 shell to isolate the substrate from the coolant and ensure the long-term integrity of the equipment. Using SA508 Gr.3 to manufacture the pressure shell allows for a significant reduction in wall thickness while maintaining mechanical properties, achieving structural lightweighting.

[0003] Currently, hot-wire TIG automatic welding is commonly used for nickel-based cladding on the inner wall of the SA508 Gr.3 casing. A Chinese patent with publication number CN108568580A discloses a welding equipment and process for cladding nickel-based alloys. Specifically, it employs an alternating mixture of cold metal transfer and pulse transfer, along with an oscillating welding process, to clad nickel-based 690 alloy onto low-alloy steel forgings. Adjusting the oscillation width, oscillation speed, and edge dwell time to match the welding speed and wire feed speed ensures a stable welding process and uniform weld formation, guaranteeing welding quality and improving welding efficiency.

[0004] However, SA508 Gr.3 is a quenched and tempered low-alloy steel with a high hardening tendency, making it prone to hydrogen-induced cold cracking in the fusion line region during welding. Inconel 690 nickel-based alloys are highly sensitive to hot cracking, and prolonged high-temperature thermal cycling can easily induce grain boundary liquefaction cracks. Existing surfacing processes have several shortcomings: conventional processes lack systematic and coordinated design for preheating and interpass temperature matching. If the preheating temperature is too low, the low-alloy steel substrate is prone to cold cracking; if the interpass temperature is too high, the nickel-based surfacing layer remains in the high-temperature range for a long time, increasing the risk of hot cracking. At the same time, for slender pressure shells with a large length-to-diameter ratio, ordinary slender rod hot wire TIG welding torches rely on rear cantilever support, which cannot provide radial restraint over long distances, easily causing uneven heating of the tube during the surfacing process and affecting the surfacing quality. Furthermore, if traditional high-temperature stress-relieving heat treatment is used after welding, the heat treatment temperature is close to the original tempering temperature of SA508 Gr.3, which can easily cause a decrease in the strength of the base material. If effective stress relief treatment is not carried out, the residual stress level at the dissimilar metal interface is high, and there is a risk of weld layer peeling under operating conditions. Summary of the Invention

[0005] In view of the deficiencies in the prior art, the purpose of this invention is to provide a method for manufacturing a pressure-resistant housing for a control rod drive mechanism.

[0006] A method for manufacturing a pressure-resistant housing for a control rod drive mechanism according to the present invention includes: S1. Rough machining of SA508 Gr.3 pressure shell; S2. Preheat the SA508 Gr.3 pressure shell as a whole, so that the preheating temperature of the inner wall of the SA508 Gr.3 pressure shell is maintained at 150°C to 200°C. S3. Circumferential welding is performed on the inner wall of the SA508 Gr.3 pressure shell, and nickel-based alloy welding wire and protective gas are provided to the welding position; S4. During the circumferential welding process, low-temperature dry argon gas is introduced into the solidified weld bead located behind the weld pool along the welding direction to keep the local surface temperature of the solidified weld bead between 60°C and 100°C before the next welding pass. S5. After the welding is completed, the SA508 Gr.3 pressure shell is kept warm to allow it to cool down naturally and slowly to below 80°C. S6. Perform low-temperature isothermal stress relief treatment at 510°C to 540°C on the SA508 Gr.3 pressure shell after overlay welding.

[0007] Preferably, in step S3, an inner wall support ring is provided on the inner wall of the SA508 Gr.3 pressure shell, and the slender rod hot wire TIG welding gun and the off-axis wire feeding mechanism are passed through the inner wall support ring. The slender rod hot wire TIG welding torch includes a main shielding gas nozzle, which introduces shielding gas into the weld pool, and the off-axis wire feeding mechanism supplies nickel-based alloy welding wire to the welding position. A tail gas shield is installed behind the main shielding gas nozzle of the welding torch along the welding travel direction. The tail gas shield is fitted along the contour of the inner wall of the SA508 Gr.3 pressure shell. The low-temperature dry argon gas in step S4 is introduced into the solidified weld bead through the tail gas shield.

[0008] Preferably, the inner wall support ring is made of graphite-modified polyimide, and the inner wall support ring includes an outer flange and a perforated body connected to the inner side of the outer flange; The outer diameter of the outer flange is adapted to the inner diameter of the SA508 Gr.3 pressure shell, and the perforated body is provided with a through hole for the slender rod hot wire TIG welding gun and the off-axis wire feeding mechanism to pass through. The slender rod hot wire TIG welding torch is equipped with a water-cooled circulation channel, and the off-axis wire feeding mechanism includes a wire feeding nozzle located on one side of the end of the slender rod hot wire TIG welding torch.

[0009] Preferably, in step S3, the protective gas is a mixture of 30% Ar and 70% He by volume.

[0010] Preferably, in steps S2 and S5, a heating and insulation component disposed on the outer wall of the SA508 Gr.3 pressure shell is used to preheat and insulate the SA508 Gr.3 pressure shell as a whole. The heating and insulation component includes a ceramic heating block and insulation cotton. The ceramic heating block is disposed on the outer wall of the SA508 Gr.3 pressure-resistant shell, and the insulation cotton is wrapped around the outside of the ceramic heating block.

[0011] Preferably, in step S3, the inner wall of the SA508 Gr.3 pressure shell is circumferentially welded to form at least three weld overlay layers, and the total thickness of the weld overlay layers is not less than 6 mm.

[0012] Preferably, the welding current of the first layer of weld overlay is 165A, the voltage is 14V, the welding speed is 14cm / min, and the wire feed speed is 1000mm / min; The welding current for the remaining weld overlay layers is 180A, the voltage is 17V, the welding speed is 17cm / min, and the wire feed speed is 1200mm / min.

[0013] Preferably, in step S6, the heat preservation time of the low-temperature isothermal stress relief treatment is determined according to the principle that the effective thickness of the SA508 Gr.3 pressure shell is maintained for 1 hour for every 25 mm.

[0014] Preferably, after step S6, the method further includes: After the low-temperature isothermal stress relief treatment, the weld overlay layer is subjected to liquid penetration testing and ultrasonic testing. The weld overlay layer on the inner wall of the SA508 Gr.3 pressure shell is machined to retain an effective weld overlay layer with a thickness of 5 mm; A coil groove and a lower magnetic shielding ring groove are machined on the outer wall of the SA508 Gr.3 pressure-resistant shell. The bottom of the coil groove is rounded. A coil is wound in the coil groove. An upper magnetic shielding ring, a middle magnetic shielding ring, a lower magnetic shielding ring, and a magnetic guide ring are installed on the outer wall of the SA508 Gr.3 pressure-resistant shell.

[0015] Preferably, the upper magnetic shielding ring, the middle magnetic shielding ring, the lower magnetic shielding ring, and the magnetic conductive ring each include two half-rings; The upper magnetic shielding ring, the middle magnetic shielding ring, and the two half rings of the lower magnetic shielding ring are locked and installed on the outer wall of the SA508 Gr.3 pressure shell by means of clamps; The two half-rings of the magnetic guide ring are locked and installed on the step of the magnetic shielding ring by means of clamps; The upper magnetic shielding ring is axially limited by a nut, and the lower magnetic shielding ring is installed in the groove of the lower magnetic shielding ring.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention provides an inner wall support ring on the inner wall of the SA508 Gr.3 pressure shell. The inner wall support ring serves to guide and stabilize the slender rod hot wire TIG welding gun and the off-axis wire feeding mechanism, thereby effectively achieving continuous and stable overlay welding on the inner wall of the SA508 Gr.3 pressure shell. 2. This invention employs a dual defect constraint process for dissimilar metal overlay welding, providing a protective gas to the welding position and introducing low-temperature dry argon gas into the solidified weld bead behind the weld pool. This controls the local surface temperature of the solidified weld bead before the next overlay welding pass, i.e., controls the interpass temperature. The local temperature control does not affect the overall temperature of the SA508 Gr.3 pressure shell, i.e., the preheating temperature. The separate control of the preheating temperature and interpass temperature effectively solves the problem of easy cracking defects in the nickel-based alloy overlay welding of the inner wall of SA508 Gr.3. 3. This invention employs low-temperature isothermal stress relief treatment, controlling the temperature below the tempering temperature range of SA508 Gr.3, thus avoiding the problem of strength reduction after conventional heat treatment of SA508 Gr.3.

[0017] 4. This invention uses an SA508 Gr.3 pressure-resistant housing with a grooved coil winding on the outer wall, combined with an external magnetic ring and a magnetic isolation ring to achieve a closed-loop magnetic circuit. The structure is highly integrated, effectively reducing the overall weight of the equipment and facilitating assembly, hoisting and transportation of the whole machine. Attached Figure Description

[0018] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram illustrating the structure of the SA508 Gr.3 pressure-resistant shell, which is the main feature of this invention. Figure 2 This is a schematic diagram illustrating the structure of the inner wall support ring, which is the main feature of this invention. Figure 3 This is a schematic diagram illustrating the structure of the present invention, which mainly uses a slender rod hot wire TIG welding gun 3 to perform circumferential welding on the inner wall of the SA508 Gr.3 pressure shell. Figure 4 This is a schematic diagram illustrating the structure of the tail protection gas shield, which is the main feature of this invention. Figure 5 This is a schematic diagram illustrating the structure of the coil groove and the lower magnetic shielding ring groove of the present invention. Figure 6This is a schematic diagram illustrating the winding of the SA508 Gr.3 pressure-resistant shell, which is the main feature of this invention.

[0019] The figure shows: 1. SA508 Gr.3 pressure-resistant shell; 11. Coil groove; 111. Coil; 12. Lower magnetic shielding ring groove; 121. Upper magnetic shielding ring; 122. Middle magnetic shielding ring; 123. Lower magnetic shielding ring; 124. Magnetic guide ring; 125. Nut; 2. Inner wall support ring; 3. Slender rod hot wire TIG welding torch; 31. Main protective gas nozzle of welding torch; 32. Tail protective gas cover; 4. Off-shaft wire feeding mechanism. Detailed Implementation

[0020] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0021] like Figures 1 to 6 As shown, a method for manufacturing a pressure-resistant housing for a control rod drive mechanism according to the present invention includes: S1. Roughly machine the SA508 Gr.3 pressure shell 1.

[0022] S2. The heating and insulation components installed on the outer wall of the SA508 Gr.3 pressure shell 1 are used to preheat the SA508 Gr.3 pressure shell 1 as a whole, so that the preheating temperature of the inner wall of the SA508 Gr.3 pressure shell 1 is maintained at 150℃ to 200℃.

[0023] S3. An inner wall support ring 2 is installed on the inner wall of the SA508 Gr.3 pressure shell 1, and a slender rod hot wire TIG welding torch 3 and a bypass wire feeding mechanism 4 are inserted through the inner wall support ring 2. The slender rod hot wire TIG welding torch 3 is used to perform circumferential welding on the inner wall of the SA508 Gr.3 pressure shell 1. The main shielding gas nozzle 31 of the welding torch introduces shielding gas into the weld pool, and the bypass wire feeding mechanism 4 supplies nickel-based alloy welding wire to the welding position.

[0024] S4. A tail protective gas cover 32 is installed behind the main protective gas nozzle 31 of the welding torch along the welding travel direction. The tail protective gas cover 32 is fitted along the inner wall contour of the SA508 Gr.3 pressure shell 1 and low temperature dry argon gas is introduced into the solidified weld behind the weld pool to keep the local surface temperature of the solidified weld between 60°C and 100°C before the next weld overlay.

[0025] S5. After the welding is completed, maintain the insulation of the outer wall of the SA508 Gr.3 pressure shell 1 by the heating and insulation components, so that the SA508 Gr.3 pressure shell 1 can be naturally and slowly cooled to below 80°C.

[0026] S6. Perform low-temperature isothermal stress relief treatment at 510℃ to 540℃ on the SA508 Gr.3 pressure shell 1 after overlay welding.

[0027] The present invention provides an inner wall support ring 2 on the inner wall of the SA508 Gr.3 pressure shell 1. The inner wall support ring 2 serves to guide and stabilize the slender rod hot wire TIG welding gun 3 and the off-axis wire feeding mechanism 4, effectively realizing continuous and stable overlay welding on the inner wall of the SA508 Gr.3 pressure shell 1.

[0028] Furthermore, a dual-defect constraint process for dissimilar metal cladding is employed. A tail shielding gas cover 32 is installed behind the main shielding gas nozzle 31 of the welding torch along the welding travel direction. The tail shielding gas cover 32 is fitted along the contour of the inner wall of the SA508 Gr.3 pressure shell 1 and introduces low-temperature dry argon gas into the solidified weld bead behind the weld pool. This controls the local surface temperature of the solidified weld bead before the next cladding pass, i.e., controls the interpass temperature. Local temperature control does not affect the overall temperature of the SA508 Gr.3 pressure shell 1, i.e., the preheating temperature. The separate control of preheating temperature and interpass temperature effectively solves the problem of easy cracking defects in the cladding of nickel-based alloys on the inner wall of SA508 Gr.3.

[0029] Low-temperature isothermal stress relief treatment is adopted, and the temperature is controlled below the tempering temperature range of SA508 Gr.3, thus avoiding the problem of strength reduction after conventional heat treatment of SA508 Gr.3.

[0030] In one feasible implementation, the method further includes the following after step S6: S7. After low-temperature isothermal stress relief treatment, liquid penetration testing and ultrasonic testing are performed on the weld overlay.

[0031] S8, the weld overlay layer on the inner wall of SA508 Gr.3 pressure shell 1 is machined to retain an effective weld overlay layer with a thickness of 5mm.

[0032] S9, a coil groove 11 and a lower magnetic shielding ring groove 12 are machined on the outer wall of the SA508 Gr.3 pressure-resistant shell 1. The bottom of the coil groove 11 is rounded. A coil 111 is wound in the coil groove 11. An upper magnetic shielding ring 121, a middle magnetic shielding ring 122, a lower magnetic shielding ring 123 and a magnetic guide ring 124 are installed on the outer wall of the SA508 Gr.3 pressure-resistant shell 1.

[0033] The coil is wound in groove 11 by machining the outer wall of the SA508 Gr.3 pressure-resistant housing. Combined with the external magnetic guide ring and magnetic isolation ring structure, the magnetic circuit is closed-loop. The structure is highly integrated, which effectively reduces the overall weight of the equipment and facilitates the assembly, hoisting and transportation of the whole machine.

[0034] In one feasible implementation, the welding gun structure and tooling in the manufacturing method of the pressure-resistant housing of the control rod drive mechanism provided by the present invention can also be used in other surfacing welding materials. The surfacing welding materials can be at least one of ERNiCrFe-7A, ER308L, and ER309L, and the corresponding surfacing welding process is different.

[0035] According to the present invention, a method for manufacturing a pressure-resistant housing for a control rod drive mechanism is provided as Example 1, comprising: S11. The grade of the pressure shell used is SA508 Gr.3. The inner and outer diameters of the SA508 Gr.3 pressure shell 1 are rough machined to the required dimensions, with the inner diameter ranging from φ100mm to φ500mm.

[0036] S21. The heating and insulation assembly includes a ceramic heating block and insulation cotton. The ceramic heating block is placed on the outer wall of the SA508 Gr.3 pressure shell 1, and the insulation cotton covers the outside of the ceramic heating block. The ceramic heating block placed on the outer wall of the SA508 Gr.3 pressure shell 1 is used to preheat the entire SA508 Gr.3 pressure shell 1, so that the preheating temperature of the inner wall of the SA508 Gr.3 pressure shell 1 is maintained between 150°C and 200°C.

[0037] S31. An inner wall support ring 2 is provided on the inner wall of the SA508 Gr.3 pressure shell 1. The inner wall support ring 2 is made of heat insulation material, such as graphite modified polyimide, and has an operating temperature of -200℃ to 280℃, which can cover the welding conditions.

[0038] The inner wall support ring 2 includes an outer flange and a perforated body connected to the inner side of the outer flange. The outer diameter of the outer flange is adapted to the inner diameter of the SA508 Gr.3 pressure shell 1. The perforated body has through holes for the slender rod hot wire TIG welding torch 3 and the off-axis wire feeding mechanism 4 to pass through, facilitating their insertion and guiding and stabilizing them, ensuring stable arc length and uniform weld layer thickness. Compared to ordinary slender rod hot wire TIG welding torches that rely on rear cantilever support and cannot be radially limited over long distances, resulting in instability during the welding process, this structure effectively ensures the stability of the slender rod hot wire TIG welding torch 3 and the off-axis wire feeding mechanism 4 during the welding process, effectively improving welding efficiency and quality.

[0039] The slender rod hot wire TIG welding torch 3 is equipped with a water-cooled circulation channel, and the off-axis wire feeding mechanism 4 includes a wire feeding nozzle located on one side of the end of the slender rod hot wire TIG welding torch 3, which works in conjunction with the slender rod hot wire TIG welding torch 3 to perform continuous welding.

[0040] A slender-rod hot-wire TIG welding torch 3 is used to perform circumferential welding on the inner wall of the SA508 Gr.3 pressure shell 1. The main shielding gas nozzle 31 of the torch supplies shielding gas to the weld pool, and the off-axis wire feeding mechanism 4 supplies nickel-based alloy welding wire to the welding position. The circumferential welding of the inner wall of the SA508 Gr.3 pressure shell 1 using the slender-rod hot-wire TIG welding torch 3 forms at least three weld overlay layers, with a total thickness of not less than 6 mm. The purpose of the weld overlay on the inner wall of the SA508 Gr.3 is for corrosion resistance.

[0041] S41. A tail gas shield 32 is installed behind the main shielding gas nozzle 31 of the welding torch along the welding travel direction. The tail gas shield 32 is fitted along the contour of the inner wall of the SA508 Gr.3 pressure shell 1 and low-temperature dry argon gas is introduced into the solidified weld behind the weld pool. The distance between the outlet of the tail gas shield 32 and the inner wall of the SA508 Gr.3 pressure shell 1 is 2mm to 5mm. The outlet of the tail gas shield 32 is located 3mm to 5mm behind the tail end of the weld pool along the welding travel direction, covering a weld length range of 20mm to 30mm.

[0042] The tail protective gas hood 32 continuously introduces dry argon gas at a temperature of 5°C to 35°C and a flow rate of 15L / min to 35L / min into the solidified weld bead. The dew point of the dry argon gas is not higher than -55°C.

[0043] The tail gas shield 32 moves at a speed of 12 cm / min to 18 cm / min, which is consistent with the welding speed.

[0044] The first temperature measuring point is set at 5mm to 15mm from the end of the weld pool along the welding direction. The local surface temperature of the first temperature measuring point before the next welding pass is measured to be 60℃ to 100℃ by inserting thermocouples or infrared thermometers. A second temperature measuring point is set in the base material area to be welded outside the area covered by the tail protective gas cover 32, and the temperature of the second temperature measuring point is maintained between 150°C and 200°C.

[0045] This maintains the local surface temperature of the solidified weld bead at 60°C to 100°C before the next weld pass; at this time, the preheating temperature of the inner wall of the SA508 Gr.3 pressure shell 1 remains unaffected, remaining at 150°C to 200°C. The tail gas shield 32 locally cools the solidified weld bead without changing the preheating temperature of the base material area to be welded.

[0046] A dual-defect constraint process using dissimilar metal overlay welding is employed. The thick-walled, high-mass substrate of the cylinder is preheated as a whole by ceramic heating blocks on the outer wall of the SA508 Gr.3 pressure shell 1, maintaining a stable temperature of 150℃ to 200℃ to prevent cold cracking at the fusion line. The thin nickel-based weld bead on the inner surface is cooled locally by blowing low-temperature dry argon gas through a tail protective gas hood 32. This tail protective gas hood is arc-shaped and fits snugly against the inner wall of the pressure shell, effectively achieving tail protection and weld cooling, rapidly reducing the weld temperature to below 100℃ to prevent nickel-based hot cracking and intergranular sensitization. This process simultaneously addresses the control of cold cracking in low-alloy steel and hot cracking in nickel-based alloys. Existing processes generally suffer from interpass temperatures exceeding the preheating temperature, resulting in a high upper limit.

[0047] S51. After the welding is completed, wrap the outer wall of the SA508 Gr.3 pressure shell 1 with insulation cotton to keep it warm and allow the SA508 Gr.3 pressure shell 1 to cool down naturally and slowly to below 80°C. Forced air cooling is prohibited to reduce residual stress.

[0048] S61. The SA508 Gr.3 pressure shell 1 after welding is not subjected to the traditional overall high-temperature stress-relieving heat treatment, but instead undergoes a low-temperature isothermal stress-relieving treatment at 510℃ to 540℃. The holding time is determined according to 1 hour for every 25mm of effective thickness of the SA508 Gr.3 pressure shell 1. This temperature is lower than the tempering temperature range of SA508 Gr.3 to avoid a decrease in the strength of the pressure shell after tempering.

[0049] S71. Perform liquid penetration testing on the weld overlay according to NB / T47013.5-2015, and accept it as a Class 1 weld. Perform ultrasonic testing on the weld overlay according to NB / T47013.3-2015, and accept it as a Class 1 weld.

[0050] S81, the weld overlay on the inner wall of the SA508 Gr.3 pressure shell 1 is machined to the final size, retaining an effective weld overlay with a thickness of 5mm.

[0051] S91, a coil groove 11 and a lower magnetic shielding ring groove 12 are machined on the outer wall of the SA508 Gr.3 pressure-resistant shell 1. The bottom of the coil groove 11 is rounded. A coil 111 is wound in the coil groove 11. An upper magnetic shielding ring 121, a middle magnetic shielding ring 122, a lower magnetic shielding ring 123 and a magnetic guide ring 124 are installed on the outer wall of the SA508 Gr.3 pressure-resistant shell 1.

[0052] The upper magnetic shielding ring 121, the middle magnetic shielding ring 122, and the lower magnetic shielding ring 123 are made of non-magnetic stainless steel or nickel-based alloy, while the magnetic ring 124 is made of electrical pure iron or carbon steel or stainless steel with good magnetic permeability.

[0053] The upper magnetic shielding ring 121, the middle magnetic shielding ring 122, the lower magnetic shielding ring 123, and the magnetic guiding ring 124 each include two half-rings; the two half-rings of the upper magnetic shielding ring 121, the middle magnetic shielding ring 122, and the lower magnetic shielding ring 123 are locked and installed on the outer wall of the SA508 Gr.3 pressure shell 1 by clamping or mechanical assembly; the two half-rings of the magnetic guiding ring 124 are locked and installed on the step of the magnetic shielding ring by clamping or mechanical assembly; thus realizing a closed-loop magnetic circuit.

[0054] The upper magnetic shielding ring 121 is axially limited by the nut 125, and the lower magnetic shielding ring 123 is installed in the groove 12 of the lower magnetic shielding ring, which plays the role of axial limiting support.

[0055] According to the present invention, a method for manufacturing a pressure-resistant housing for a control rod drive mechanism, which is more specific than Embodiment 1, is provided as Embodiment 2, comprising: S12. Taking a pressure shell for a certain project as an example, the grade of the pressure shell used is SA508 Gr.3. The inner and outer diameters of the SA508 Gr.3 pressure shell 1 are roughly machined to the required dimensions, with an inner diameter of φ135mm and a wall thickness of 25mm with allowance.

[0056] S22. The heating and insulation assembly includes a ceramic heating block and insulation cotton. The ceramic heating block is placed on the outer wall of the SA508 Gr.3 pressure shell 1, and the insulation cotton covers the outside of the ceramic heating block. The ceramic heating block placed on the outer wall of the SA508 Gr.3 pressure shell 1 is used to preheat the entire SA508 Gr.3 pressure shell 1, so that the preheating temperature of the inner wall of the SA508 Gr.3 pressure shell 1 is maintained between 150°C and 200°C.

[0057] S32. An inner wall support ring 2 is provided on the inner wall of the SA508 Gr.3 pressure shell 1. The inner wall support ring 2 is made of heat insulation material, such as graphite modified polyimide, and has an operating temperature of -200℃ to 280℃, which can cover the welding conditions.

[0058] The inner wall support ring 2 includes an outer flange and a perforated body connected to the inner side of the outer flange. The outer diameter of the outer flange is adapted to the inner diameter of the SA508 Gr.3 pressure shell 1. The perforated body has through holes for the slender rod hot wire TIG welding torch 3 and the off-axis wire feeding mechanism 4 to pass through, facilitating their insertion and guiding and stabilizing them, ensuring stable arc length and uniform weld layer thickness. Compared to ordinary slender rod hot wire TIG welding torches that rely on rear cantilever support and cannot be radially limited over long distances, resulting in instability during the welding process, this structure effectively ensures the stability of the slender rod hot wire TIG welding torch 3 and the off-axis wire feeding mechanism 4 during the welding process, effectively improving welding efficiency and quality.

[0059] The slender rod hot wire TIG welding torch 3 is equipped with a water-cooled circulation channel. The off-axis wire feeding mechanism 4 includes a wire feeding nozzle located on one side of the end of the slender rod hot wire TIG welding torch 3, which works in conjunction with the slender rod hot wire TIG welding torch 3 to perform continuous welding. A positioner is used in conjunction with a dedicated slender rod hot wire TIG welding torch to achieve uniform speed surfacing in a flat welding position.

[0060] A slender-rod hot-wire TIG welding torch 3 is used to perform circumferential welding on the inner wall of the SA508 Gr.3 pressure shell 1. The main shielding gas nozzle 31 of the welding torch supplies shielding gas to the weld pool, and the off-axis wire feeding mechanism 4 supplies nickel-based alloy welding wire to the welding position. The nickel-based alloy welding wire is grade ERNiCrFe-7A, with a specification of φ1.6mm, and has 4 layers of welding, with a layer thickness of ≥8mm.

[0061] The welding current for the first weld overlay is 165A, the voltage is 14V, the welding speed is 14cm / min, and the wire feed speed is 1000mm / min. For the remaining weld overlays, the welding current is 180A, the voltage is 17V, the welding speed is 17cm / min, and the wire feed speed is 1200mm / min. The shielding gas supplied to the weld pool by the main shielding gas nozzle 31 of the welding torch is a mixture of 30% Ar and 70% He by volume. The gas flow rate for the first weld overlay is 15L / min, and the gas flow rate for the remaining weld overlays is 13L / min. Smaller parameters are used for the first layer to reduce the base metal dilution rate and lower the risk of root pass cracking defects; the parameters for the remaining weld overlays are slightly larger.

[0062] Furthermore, the welding process should begin with welding the inner wall of the smaller diameter on the right side, followed by welding the inclined surface and the inner wall of the larger diameter on the left side. The intersection of the inclined surface and the larger and smaller diameters should be chamfered for a smooth transition.

[0063] S42. A tail gas shield 32 is installed behind the main shielding gas nozzle 31 of the welding torch along the welding travel direction. The tail gas shield 32 is fitted along the contour of the inner wall of the SA508 Gr.3 pressure shell 1 and low-temperature dry argon gas is introduced into the solidified weld behind the weld pool. The distance between the outlet of the tail gas shield 32 and the inner wall of the SA508 Gr.3 pressure shell 1 is 4mm. The outlet of the tail gas shield 32 is located 3mm behind the tail end of the weld pool along the welding travel direction, covering a weld length of 25mm.

[0064] The tail protective gas cover 32 continuously introduces dry argon gas with a temperature of 5°C to 35°C and a flow rate of 25L / min into the solidified weld bead. The dew point of the dry argon gas is not higher than -55°C.

[0065] The tail protection air shield 32 moves at a speed of 14 cm / min to 17 cm / min.

[0066] Since the length of the covered weld is 25mm, the blowing time for the weld is 8.8s to 10.7s.

[0067] A first temperature measuring point is set 10 mm from the end of the weld pool along the welding direction on the surface of the weld bead. The local surface temperature of the first temperature measuring point before the next weld is measured to be 60℃ to 100℃ by an insertion thermocouple. A second temperature measuring point is set in the base material area to be welded outside the area covered by the tail protective gas cover 32, and the temperature of the second temperature measuring point is maintained between 150°C and 200°C.

[0068] This maintains the local surface temperature of the solidified weld bead at 60°C to 100°C before the next weld pass; at this time, the preheating temperature of the inner wall of the SA508 Gr.3 pressure shell 1 remains unaffected, remaining at 150°C to 200°C. The tail gas shield 32 locally cools the solidified weld bead without changing the preheating temperature of the base material area to be welded.

[0069] A dual-defect constraint process using dissimilar metal overlay welding is employed. The thick-walled, high-mass substrate of the cylinder is preheated as a whole by ceramic heating blocks on the outer wall of the SA508 Gr.3 pressure shell 1, maintaining a stable temperature of 150℃ to 200℃ to prevent cold cracking at the fusion line. The thin nickel-based weld bead on the inner surface is cooled locally by blowing low-temperature dry argon gas through a tail protective gas hood 32. This tail protective gas hood is arc-shaped and fits snugly against the inner wall of the pressure shell, effectively achieving tail protection and weld cooling, rapidly reducing the weld temperature to below 100℃ to prevent nickel-based hot cracking and intergranular sensitization. This process simultaneously addresses the control of cold cracking in low-alloy steel and hot cracking in nickel-based alloys. Existing processes generally suffer from interpass temperatures exceeding the preheating temperature, resulting in a high upper limit.

[0070] S52. After the welding is completed, wrap the outer wall of the SA508 Gr.3 pressure shell 1 with insulation cotton to keep it warm and allow the SA508 Gr.3 pressure shell 1 to cool down naturally and slowly to below 80°C. Forced air cooling is prohibited to reduce residual stress.

[0071] S62. Instead of using the traditional overall high-temperature stress-relieving heat treatment, the SA508 Gr.3 pressure shell 1 after welding is subjected to a low-temperature isothermal stress-relieving treatment at 510℃ to 540℃ for 1 hour. This temperature is lower than the tempering temperature range of SA508 Gr.3 to avoid a decrease in the strength of the pressure shell after tempering.

[0072] S72. Liquid penetration testing of the weld overlay shall be performed according to NB / T 47013.5-2015. Acceptance shall be based on Class 1 weld, and the inspection result shall be qualified. Ultrasonic testing of the weld overlay shall be performed according to NB / T 47013.3-2015. Acceptance shall be based on Class 1 weld, and the inspection result shall be qualified.

[0073] S82, the weld overlay on the inner wall of the SA508 Gr.3 pressure shell 1 is machined to the final size, retaining an effective weld overlay with a thickness of 5mm.

[0074] S92, a coil groove 11 is machined on the outer wall of the SA508 Gr.3 pressure-resistant shell 1. The bottom of the coil groove 11 is rounded, with a rounding radius R=5mm. The lower magnetic shielding ring groove 12 is machined, with a groove depth of 4mm and a width of 70mm.

[0075] A coil 111 is wound in the coil groove 11, and an upper magnetic shielding ring 121, a middle magnetic shielding ring 122, a lower magnetic shielding ring 123 and a magnetic guide ring 124 are installed on the outer wall of the SA508 Gr.3 pressure-resistant housing 1.

[0076] The upper magnetic shielding ring 121, the middle magnetic shielding ring 122, and the lower magnetic shielding ring 123 are made of 304LN, and the magnetic conducting ring 124 is made of 10# steel.

[0077] The upper magnetic shielding ring 121, the middle magnetic shielding ring 122, the lower magnetic shielding ring 123, and the magnetic guiding ring 124 each include two half-rings; the two half-rings of the upper magnetic shielding ring 121, the middle magnetic shielding ring 122, and the lower magnetic shielding ring 123 are locked and installed on the outer wall of the SA508 Gr.3 pressure-resistant shell 1 by clamping; the two half-rings of the magnetic guiding ring 124 are locked and installed on the step of the magnetic shielding ring by clamping or mechanical assembly; thus realizing a closed-loop magnetic circuit.

[0078] The upper magnetic shielding ring 121 is axially limited by the nut 125, and the lower magnetic shielding ring 123 is installed in the groove 12 of the lower magnetic shielding ring, which plays the role of axial limiting support.

[0079] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0080] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for manufacturing a pressure-resistant housing for a control rod drive mechanism, characterized in that, include: S1. Rough machining of SA508 Gr.3 pressure shell (1); S2. Preheat the SA508 Gr.3 pressure shell (1) as a whole, so that the preheating temperature of the inner wall of the SA508 Gr.3 pressure shell (1) is maintained at 150°C to 200°C; S3. Circumferential welding is performed on the inner wall of the SA508 Gr.3 pressure shell (1), and nickel-based alloy welding wire and protective gas are provided to the welding position; S4. During the circumferential welding process, low-temperature dry argon gas is introduced into the solidified weld bead located behind the weld pool along the welding direction to keep the local surface temperature of the solidified weld bead between 60°C and 100°C before the next welding pass. S5. After the welding is completed, the SA508 Gr.3 pressure shell (1) is kept warm so that the SA508 Gr.3 pressure shell (1) can be naturally and slowly cooled to below 80°C. S6. Perform low-temperature isothermal stress relief treatment at 510°C to 540°C on the SA508 Gr.3 pressure shell (1) after overlay welding.

2. The method for manufacturing the pressure-resistant housing of the control rod drive mechanism as described in claim 1, characterized in that, In step S3, an inner wall support ring (2) is provided on the inner wall of the SA508 Gr.3 pressure shell (1), and a slender rod hot wire TIG welding gun (3) and a lateral wire feeding mechanism (4) are passed through the inner wall support ring (2). The slender rod hot wire TIG welding torch (3) includes a main shielding gas nozzle (31), which introduces shielding gas into the weld pool, and the off-axis wire feeding mechanism (4) supplies nickel-based alloy welding wire to the welding position. A tail gas shield (32) is provided behind the main shielding gas nozzle (31) of the welding torch along the welding travel direction. The tail gas shield (32) is fitted along the inner wall contour of the SA508 Gr.3 pressure shell (1). The low-temperature dry argon gas in step S4 is introduced into the solidified weld bead through the tail gas shield (32).

3. The method for manufacturing the pressure-resistant housing of the control rod drive mechanism as described in claim 2, characterized in that, The inner wall support ring (2) is made of graphite-modified polyimide, and the inner wall support ring (2) includes an outer flange and a perforated body connected to the inner side of the outer flange; The outer diameter of the outer flange is adapted to the inner diameter of the SA508 Gr.3 pressure shell (1), and the perforated body is provided with a through hole for the slender rod hot wire TIG welding gun (3) and the off-axis wire feeding mechanism (4) to pass through. The slender rod hot wire TIG welding torch (3) is provided with a water-cooled circulation channel, and the off-axis wire feeding mechanism (4) includes a wire feeding nozzle located on one side of the end of the slender rod hot wire TIG welding torch (3).

4. The method for manufacturing the pressure-resistant housing of the control rod drive mechanism as described in claim 1, characterized in that, In step S3, the protective gas is a mixture of 30% Ar and 70% He by volume.

5. The method for manufacturing the pressure-resistant housing of the control rod drive mechanism as described in claim 1, characterized in that, In steps S2 and S5, a heating and heat preservation assembly disposed on the outer wall of the SA508 Gr.3 pressure shell (1) is used to preheat and heat preservation the SA508 Gr.3 pressure shell (1) as a whole. The heating and heat preservation assembly includes a ceramic heating block and heat preservation cotton. The ceramic heating block is disposed on the outer wall of the SA508 Gr.3 pressure-resistant shell (1), and the heat insulation cotton is wrapped around the outside of the ceramic heating block.

6. The method for manufacturing the pressure-resistant housing of the control rod drive mechanism as described in claim 1, characterized in that, In step S3, the inner wall of the SA508 Gr.3 pressure shell (1) is circumferentially welded to form at least three weld overlay layers, and the total thickness of the weld overlay layers is not less than 6 mm.

7. The method for manufacturing the pressure-resistant housing of the control rod drive mechanism as described in claim 6, characterized in that, The welding current for the first layer of weld overlay is 165A, the voltage is 14V, the welding speed is 14cm / min, and the wire feed speed is 1000mm / min. The welding current for the remaining weld overlay layers is 180A, the voltage is 17V, the welding speed is 17cm / min, and the wire feed speed is 1200mm / min.

8. The method for manufacturing the pressure-resistant housing of the control rod drive mechanism as described in claim 1, characterized in that, In step S6, the heat preservation time of the low temperature constant temperature stress relief treatment is determined according to the effective thickness of the SA508 Gr.3 pressure shell (1) for 25 mm heat preservation for 1 hour.

9. The method for manufacturing the pressure-resistant housing of the control rod drive mechanism as described in claim 1, characterized in that, The process after step S6 also includes: After the low-temperature isothermal stress relief treatment, the weld overlay layer is subjected to liquid penetration testing and ultrasonic testing. The weld overlay layer on the inner wall of the SA508 Gr.3 pressure shell (1) is machined to retain an effective weld overlay layer with a thickness of 5 mm; A coil groove (11) and a lower magnetic shielding ring groove (12) are machined on the outer wall of the SA508 Gr.3 pressure-resistant shell (1). The bottom of the coil groove (11) is rounded. A coil (111) is wound in the coil groove (11). An upper magnetic shielding ring (121), a middle magnetic shielding ring (122), a lower magnetic shielding ring (123), and a magnetic guide ring (124) are installed on the outer wall of the SA508 Gr.3 pressure-resistant shell (1).

10. The method for manufacturing the pressure-resistant housing of the control rod drive mechanism as described in claim 9, characterized in that, The upper magnetic shielding ring (121), the middle magnetic shielding ring (122), the lower magnetic shielding ring (123), and the magnetic guiding ring (124) each include two half-rings; The upper magnetic shielding ring (121), the middle magnetic shielding ring (122), and the two half rings of the lower magnetic shielding ring (123) are locked and installed on the outer wall of the SA508 Gr.3 pressure shell (1) by means of clamps; The two half-rings of the magnetic guide ring (124) are locked and installed on the step of the magnetic shielding ring by means of clamps; The upper magnetic shielding ring (121) is axially limited by a nut (125), and the lower magnetic shielding ring (123) is installed in the groove (12) of the lower magnetic shielding ring.

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