Method of processing a nickel-based alloy pressure shell

Abstract

The application provides a nickel-based alloy pressure shell processing method and relates to the technical field of reactor pressure shell processing. The method comprises the following steps: S1, pretreating an austenitic stainless steel stroke sleeve and processing a preset bevel at the connecting end of the stroke sleeve; S2, depositing a nickel-based alloy at the preset bevel to form a nickel-based alloy deposited layer; S3, processing the deposited layer to form a first half-Ω bevel; S4, processing a nickel-based alloy sealing shell and processing a matched second half-Ω bevel at the connecting end of the sealing shell; S5, assembling and positioning the stroke sleeve and the sealing shell; and S6, performing Ω weld sealing welding along the butt joint of the two bevels to complete the processing. The nickel-based alloy is directly deposited on the stroke sleeve by automatic argon arc welding, the half-Ω bevel is processed by using the deposited layer, and Ω weld welding is performed, so that the technical problem of sealing welding of dissimilar metals between the nickel-based alloy sealing shell and the austenitic stainless steel stroke sleeve is solved from the process.

Description

Technical Field

[0001] This invention relates to the field of pressure shell processing technology, and more specifically, to a method for processing a nickel-based alloy pressure shell. Background Technology

[0002] The control rod drive mechanism is installed on the top cover of the reactor pressure vessel, and its pressure shell component is part of the pressure boundary of the reactor coolant system. Its function is to drive the control rod assemblies up and down within the reactor core according to commands, maintain the control rod assemblies at the commanded height, and release the control rod assemblies upon power failure, allowing them to quickly insert into the reactor core under gravity. This enables tasks such as reactor startup, power regulation, normal shutdown, and accident shutdown. The pressure shell of the control rod drive mechanism is part of the primary circuit pressure boundary and typically includes a sealing shell and a travel sleeve.

[0003] Currently, the sealing shell and travel sleeve of the control rod drive mechanism are generally connected by threads and sealed by an Ω-weld. This Ω-weld is typically 2–3 mm thick and 6.5–8 mm wide. After welding, liquid penetration testing and a 27.3 MPa hydrostatic test are required, making the welding process quite challenging. In terms of materials, the sealing shell is generally machined from a single piece of nickel-based alloy, while the travel sleeve is made of austenitic stainless steel. Connecting the two requires pre-welding a nickel-based alloy ring to the travel sleeve side, then machining the nickel-based alloy ring into a half-Ω bevel to achieve the threaded connection and Ω-weld seal between the sealing shell and the travel sleeve. This existing process has significant drawbacks: the butt welding of the travel sleeve and the nickel-based alloy ring is dissimilar metal welding, and the significant differences in thermal conductivity and coefficient of thermal expansion between nickel-based alloys and stainless steel make them highly susceptible to DDC cracks, leading to a certain scrap rate.

[0004] Patent document CN114141395A discloses a sealing shell device and a control rod drive mechanism, including a sealing shell body and a magnetic shielding ring assembly. The sealing shell body includes a shell made of martensitic stainless steel and austenitic stainless steel section and a 690 alloy section welded to both ends of the shell. This patent document ensures that the shell and the travel sleeve are welded to the same metal by making the first connecting end of the sealing shell body made of austenitic stainless steel and welding the first connecting end to the travel sleeve. The disadvantages of this patent document are: high manufacturing complexity and low efficiency. It requires processing the martensitic stainless steel shell first, then completing the dissimilar metal welding at both ends, and subsequently requiring inspection and verification of multiple welds. Compared with solutions using a single material or simplified processes, the process is cumbersome and the processing cycle is long. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for processing and welding nickel-based alloy pressure shells.

[0006] A method for processing a nickel-based alloy pressure shell according to the present invention includes the following steps: S1: Pre-treat the austenitic stainless steel travel sleeve and process a pre-set bevel at the connection end of the travel sleeve; S2: A nickel-based alloy is pre-deposited at the preset bevel using a welding process to form a nickel-based alloy weld overlay layer; S3: Process the nickel-based alloy weld overlay to form a first half-Ω bevel; S4: The sealing shell made of nickel-based alloy is processed, and a second half-Ω bevel matching the first half-Ω bevel is processed at the connection end between the shell and the travel sleeve. S5: Assemble and position the finished travel sleeve and sealing shell; S6: Perform Ω-seam sealing welding along the joint between the first half Ω bevel and the second half Ω bevel to complete the pressure shell processing.

[0007] Preferably, in step S1, the pretreatment includes: rough machining the travel sleeve using a stainless steel forging, the machining contents including at least the outer circle, the inner blind hole and the preset bevel, the preset bevel being a conical bevel.

[0008] Preferably, after the stroke sleeve is rough-machined and formed, it undergoes a dimensional stabilization heat treatment at a temperature of 410±10℃ and a holding time of 4h.

[0009] Preferably, in step S2, the travel sleeve is preheated before welding, with a preheating temperature of 120℃~150℃ and a preheating holding time of ≥1h.

[0010] Preferably, the welding process uses automatic argon arc welding, the interpass temperature during the welding process is ≤150℃, and the number of welding layers is 5 to 8. During the welding process, a variable speed drive mechanism is used to rotate the travel sleeve to achieve uniform welding at the flat welding position; The first layer of welding uses low-parameter welding to reduce the dilution of the weld seam by the base material of the bushing.

[0011] Preferably, the small-parameter surfacing welding parameters are: current 165A, voltage 13.5V, welding speed 13cm / min, wire feed speed 1000mm / min, and shielding gas is a mixture of 30%Ar and 70%He with a gas flow rate of 15L / min. The uniform speed surfacing welding parameters are: current 175A, voltage 14.5V, welding speed 15cm / min, wire feed speed 1100mm / min, shielding gas is a mixture of 30%Ar and 70%He, gas flow rate 15L / min.

[0012] Preferably, after the welding is completed in step S2, the step of slow cooling treatment of the welded parts of the travel sleeve is further included. The slow cooling treatment method is: cooling in a heat treatment furnace to ≤80°C and then air cooling, or cooling in a heat insulation medium to room temperature. Between steps S2 and S3, there is also a step of detecting internal defects in the nickel-based alloy weld overlay, wherein the detection method is ultrasonic testing.

[0013] Preferably, in step S3, the finishing process of the travel sleeve includes: first, machining the outer circle of the travel sleeve to form a positioning reference surface, then finishing the inner hole with the positioning reference surface as a reference, and then finishing the outer circle a second time, correcting the coaxiality of the inner and outer circles during the machining process; Simultaneously, the first half-Ω bevel is formed on the nickel-based alloy weld overlay, and an external thread is machined at the end of the travel sleeve connection.

[0014] Preferably, in step S4, the sealing shell is integrally formed by machining a nickel-based alloy forging, and the machining content includes at least an outer circle, an inner through hole, an internal thread that matches the external thread of the travel sleeve, and the second half-Ω bevel; In step S5, the travel sleeve and the sealing shell are assembled and positioned by engaging the external and internal threads.

[0015] Preferably, in step S6, the Ω weld is welded using manual argon arc welding or automatic welding; After welding is completed, the Ω weld shall be subjected to at least one liquid penetration test, and the test standard shall be that no defects are shown. After the liquid permeability test, a water pressure test is also performed. The water pressure test pressure is ≥27MPa and the pressure holding time is ≥30min. After the water pressure test, the liquid permeability test is performed again.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention solves the technical problem of dissimilar metal sealing welding between nickel-based alloy sealing shell and austenitic stainless steel travel sleeve by using automatic argon arc welding to directly deposit nickel-based alloy on the travel sleeve and using the deposited layer to process a half Ω bevel for Ω weld welding. 2. This invention replaces the process of butt welding the travel sleeve and the nickel-based alloy ring in the original process, thereby fundamentally avoiding the problem of DDC cracks caused by material differences in butt welding of dissimilar metals and reducing the product scrap rate. 3. This invention improves manufacturing efficiency by processing the semi-Ω bevel and welding it to the sealing shell, making the Ω weld seam reliable in sealing performance. It can successfully pass the 27.3MPa water pressure test and liquid penetration test, meeting the high-pressure sealing and safe use requirements of the pressure-resistant shell. Attached Figure Description

[0017] 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 travel sleeve with a tapered bevel, which is the main feature of this invention. Figure 2 This is a schematic diagram illustrating the structure of the weld overlay on the travel sleeve, which is the main feature of this invention. Figure 3 This is a schematic diagram illustrating the structure of the half-Ω bevel of the weld overlay layer of the sleeve, which is the main feature of this invention. Figure 4 This is a schematic diagram illustrating the structure of the semi-Ω bevel of the sealing shell, which is the main feature of this invention. Figure 5 This is a schematic diagram illustrating the structure of the pressure-resistant shell assembly, which is the main feature of this invention.

[0018] Figure label: Stroke sleeve 1, sealing shell 2, tapered bevel 3, weld overlay 4, first half Ω bevel 51, second half Ω bevel 52, external thread 6, internal thread 7, Ω weld 8. Detailed Implementation

[0019] 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.

[0020] Example 1 Taking the pressure hull of Hualong One as an example, the pressure hull consists of a travel sleeve 1 and a sealing shell 2. The travel sleeve 1 and the sealing shell 2 are connected by threads and Ω-sealed welding. The base material of the travel sleeve 1 is 022Cr19Ni10N (an austenitic stainless steel), and the base material of the sealing shell 2 is Inconel-690 (a nickel-based alloy). The manufacturing process of the pressure hull is as follows: The first step is to rough machine the integrated travel sleeve 1 using an austenitic stainless steel forging. The outer circle and inner blind hole of the travel sleeve 1 are machined into the austenitic stainless steel forging. Simultaneously, a pre-set bevel is machined on the outer circumference of the travel sleeve 1. In this embodiment, the pre-set bevel is specifically a tapered bevel 3. See the attached diagram for details of the travel sleeve 1 with the tapered bevel 3. Figure 1 .

[0021] The second step involves performing a dimensional stabilization heat treatment on the rough-machined travel sleeve 1 at a temperature of 410±10℃ for 4 hours. The inner blind hole has a large machining volume and is prone to generating machining stress. The purpose of this dimensional stabilization heat treatment is primarily to eliminate the machining stress generated after machining the inner blind hole of the travel sleeve 1.

[0022] The third step is to place the roughly machined stroke sleeve 1 into a heat treatment furnace for preheating treatment, with the preheating temperature controlled at 120℃-150℃. In specific operation, it is necessary to ensure that the stroke sleeve 1 is fully preheated. It can be placed in a heat treatment furnace with a furnace temperature of 120~150℃ and the preheating holding time is ≥1h to ensure that the stroke sleeve 1 is fully preheated.

[0023] The fourth step involves automatic argon arc welding on the conical bevel 3 of the travel sleeve 1. During the welding process, the interpass temperature is controlled to be ≤150℃, and the number of welding layers is 5 to 8. After welding, a nickel-based alloy welding layer 4 is formed, with a thickness ≥15mm and a width ≥35mm. A schematic diagram of the welding process is attached. Figure 2 .

[0024] The first layer of welding uses low-parameter welding to reduce the dilution of the weld seam by the base material of the travel sleeve 1. During welding, a variable-speed drive mechanism rotates the travel sleeve 1 to achieve uniform welding at the flat welding position, ensuring the uniform thickness of the weld layer 4. In this embodiment, the variable-speed drive mechanism specifically uses a variable-speed machine. The nickel-based welding wire used in this step is ERNiCrFe-7A, with a specification of φ1.6mm. The low-parameter welding parameters are: current 165A, voltage 13.5V, welding speed 13cm / min, wire feed speed 1000mm / min, and a shielding gas mixture containing 30%Ar and 70%He, with a flow rate of 15L / min. The uniform-speed welding parameters are: current 175A, voltage 14.5V, welding speed 15cm / min, wire feed speed 1100mm / min, and a shielding gas mixture containing 30%Ar and 70%He, with a flow rate of 15L / min.

[0025] The fifth step is to perform a slow cooling treatment on the welded parts of the travel sleeve after the welding is completed. There are two slow cooling treatment methods: one is to put it in a heat treatment furnace to slow cooling to ≤80℃ and then air cooling; the other is to put it in a heat insulation medium to slow cooling to room temperature. Mica powder can be used as the heat insulation medium.

[0026] The sixth step is to perform internal defect detection on the weld overlay 4 of the travel sleeve 1. The detection method is ultrasonic testing (UT testing) to ensure that the weld overlay 4 has no internal defects.

[0027] Step 7: Precision machining of the integrated travel sleeve 1: First, machine the outer circle of the travel sleeve 1. A positioning reference surface is then machined on the outer circle of the travel sleeve 1. Using this positioning reference surface as a reference, the inner deep hole of the travel sleeve 1 is precision machined. Then, the outer circle of the travel sleeve 1 is precision machined again. During the machining process, the coaxiality of the inner and outer circles of the travel sleeve 1 needs to be corrected in real time. Simultaneously, a first half-Ω bevel 51 is machined on the weld overlay layer 4 of the travel sleeve 1, and an external thread 6 is machined at the end of the travel sleeve 1 that connects to the sealing shell 2. Other key structures, such as the positioning surface, are also machined. For details on the first half-Ω bevel 51 on the weld overlay layer 4 of the travel sleeve 1, see [link to details]. Figure 3 .

[0028] Step 8: Machining the integrated sealing shell through-hole part using a nickel-based alloy forging: Machining the outer circle and inner through hole of the sealing shell 2 onto the nickel-based alloy forging; machining the internal thread 7 at the end where the sealing shell 2 connects to the travel sleeve 1; and simultaneously machining the second half-Ω bevel 52 at this end, matching the first half-Ω bevel 51 of the travel sleeve 1. Details of the second half-Ω bevel 52 of the sealing shell 2 can be found in [link to documentation]. Figure 4 .

[0029] Step 9: Insert the finished travel sleeve 1 into the finished sealing shell 2, so that the external thread 6 of the travel sleeve 1 and the internal thread 7 of the sealing shell 2 are precisely engaged, thereby achieving the assembly and positioning of the travel sleeve 1 and the sealing shell 2.

[0030] Step 10: Use nickel-based alloy welding wire to perform Ω-weld 8 sealing welding on the joint between the integrated sealing shell through-piece and the integrated travel sleeve 1. See the attached diagram for a detailed welding schematic. Figure 5 The Ω weld 8 can be welded manually using TIG welding or automatically using TIG welding. In this embodiment, manual TIG welding is used for the Ω weld 8. The TIG welding is divided into two layers, each layer being a single-pass welding process. The nickel-based welding wire used is ERNiCrFe-7A, with a specification of φ1.6mm. The welding parameters are: current 60-100A, voltage 8-12V, and welding speed 5-15cm / min. During the first layer of welding, a special device or tooling covering five-sixths of the circumferential weld should be used to achieve back protection during welding, and a gap of about 4mm should be left at the end of the weld. During the second layer of welding, a subcutaneous vent needle is first inserted into the 4mm gap left during the last weld of the first pass to achieve back protection in this area. After retracting the subcutaneous vent needle, two welds are used to fill the reserved 4mm gap.

[0031] Step 11: Perform a liquid penetration test on the completed Ω weld 8. The test standard is that no defects are allowed to be displayed.

[0032] Step 12: Perform a hydrostatic test on Ω weld 8 to verify its sealing performance. The hydrostatic test pressure should be ≥27MPa and the holding time should be ≥30min. In this embodiment, the selected hydrostatic test pressure is 27.3MPa and the holding time is 30min.

[0033] Step 13: After the hydrostatic test is completed, liquid penetration test is performed on Ω weld 8 again. The inspection standard is still that no defects are allowed.

[0034] In this embodiment, the test results of steps eleven, twelve, and thirteen are as follows: the liquid penetration test of Ω weld 8 after welding and after the hydrostatic test is qualified. After maintaining the pressure at 27.3 MPa for 30 minutes, there is no leakage in Ω weld 8 and no visible abnormal deformation, so the hydrostatic test is qualified.

[0035] The innovation of this invention lies in: 1. For the first time, a tapered bevel 3 is reserved on the travel sleeve 1 and used for the welding of the weld overlay layer 4, proposing a new pre-welding structure of the travel sleeve 1 with a tapered bevel 3; 2. For the first time, an automatic argon arc welding method is used to pre-deposit a nickel-based alloy to form a weld overlay layer 4 on the travel sleeve 1, and the first half-Ω bevel 51 is directly machined on the weld overlay layer 4. A new method for machining the Ω bevel on the weld overlay layer is proposed, which effectively improves manufacturing efficiency. 3. For the first time, a weld overlay layer 4 is used to replace the nickel-based alloy weld ring structure, resulting in a new structure of pre-welded layer 4 for the travel sleeve 1, which effectively avoids the problem of DDC cracks easily generated when dissimilar metals are joined between the travel sleeve 1 and the nickel-based alloy weld ring; 4. For the first time, the first half-Ω bevel 51 processed on the weld overlay layer 4 and the second half-Ω bevel 52 of the sealing shell 2 were used to weld the Ω weld 8. The Ω weld 8 passed the hydrostatic test and the liquid penetration test, which solved the problem of sealing the dissimilar metals of the travel sleeve 1 and the sealing shell 2.

[0036] 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.

[0037] 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 processing a nickel-based alloy pressure shell, characterized in that, Includes the following steps: S1: Pre-treat the austenitic stainless steel travel sleeve (1) and process a pre-set bevel at the connection end of the travel sleeve (1); S2: A nickel-based alloy is pre-stacked at the preset bevel using a welding process to form a nickel-based alloy weld overlay (4). S3: The nickel-based alloy weld overlay (4) is processed to form a first half-Ω bevel (51). S4: The sealing shell (2) made of nickel-based alloy is processed, and a second half-Ω bevel (52) matching the first half-Ω bevel (51) is processed at the connection end of the shell (2) with the stroke sleeve (1). S5: Assemble and position the completed stroke sleeve (1) and sealing shell (2); S6: Perform Ω weld (8) sealing welding along the joint between the first half Ω bevel (51) and the second half Ω bevel (52) to complete the pressure shell processing.

2. The method for processing nickel-based alloy pressure shells as described in claim 1, characterized in that, In step S1, the pretreatment includes: using stainless steel forgings to rough process the stroke sleeve (1), the processing content includes at least the outer circle, the inner blind hole and the preset bevel, the preset bevel is a conical bevel (3).

3. The method for processing nickel-based alloy pressure-resistant shells as described in claim 2, characterized in that, After the stroke sleeve (1) is roughly machined and formed, it undergoes a dimensional stabilization heat treatment. The temperature of the dimensional stabilization heat treatment is 410±10℃, and the holding time is 4h.

4. The method for processing a nickel-based alloy pressure shell as described in claim 1, characterized in that, In step S2, the travel sleeve (1) is preheated before welding. The preheating temperature is 120℃~150℃ and the preheating time is ≥1h.

5. The method for processing a nickel-based alloy pressure shell as described in claim 4, characterized in that, The welding process uses automatic argon arc welding, with an interpass temperature ≤150℃ and 5 to 8 welding layers. During the welding process, a variable speed drive mechanism is used to drive the stroke sleeve (1) to rotate, so as to achieve uniform welding at the flat welding position; The first layer of welding uses small-parameter welding to reduce the dilution of the weld by the base material of the travel sleeve (1).

6. The method for processing a nickel-based alloy pressure shell as described in claim 5, characterized in that, The welding parameters for the small-parameter welding are: current 165A, voltage 13.5V, welding speed 13cm / min, wire feed speed 1000mm / min, and shielding gas is a mixture of 30%Ar and 70%He with a flow rate of 15L / min. The uniform speed surfacing welding parameters are: current 175A, voltage 14.5V, welding speed 15cm / min, wire feed speed 1100mm / min, shielding gas is a mixture of 30%Ar and 70%He, gas flow rate 15L / min.

7. The method for processing nickel-based alloy pressure shells as described in claim 1, characterized in that, After the welding is completed in step S2, the weld overlay of the travel sleeve (1) is also subjected to slow cooling treatment. The slow cooling treatment is: placed in a heat treatment furnace to cool to ≤80°C and then air-cooled, or placed in a heat insulation medium to cool to room temperature. Between steps S2 and S3, an internal defect detection is performed on the nickel-based alloy weld overlay (4), wherein the internal defect detection is ultrasonic detection.

8. The method for processing a nickel-based alloy pressure shell as described in claim 1, characterized in that, In step S3, the finishing process of the stroke sleeve (1) includes: first, machining the outer circle of the stroke sleeve (1) to form a positioning reference surface, then finishing the inner hole with the positioning reference surface as the reference, and then finishing the outer circle a second time, correcting the coaxiality of the inner and outer circles during the machining process; Meanwhile, the first half-Ω bevel (51) is formed on the nickel-based alloy weld overlay (4), and an external thread (6) is formed at the connecting end of the stroke sleeve (1).

9. The method for processing a nickel-based alloy pressure shell as described in claim 1, characterized in that, In step S4, the sealing shell (2) is integrally formed by nickel-based alloy forging. The processing includes at least the outer circle, the inner through hole, the inner thread (7) matching the outer thread (6) of the stroke sleeve (1), and the second half Ω bevel (52). In step S5, the travel sleeve (1) and the sealing shell (2) are assembled and positioned by engaging the external thread (6) and the internal thread (7).

10. The method for processing a nickel-based alloy pressure shell as described in claim 1, characterized in that, In step S6, the Ω weld (8) is welded using manual argon arc welding or automatic welding; After welding is completed, the Ω weld (8) shall be subjected to at least one liquid penetration test, and the test standard shall be that no defects are shown. After the liquid permeability test, a water pressure test is also performed. The water pressure test pressure is ≥27MPa and the pressure holding time is ≥30min. After the water pressure test, the liquid permeability test is performed again.

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