A method for preventing and controlling defects of a nuclear-grade dissimilar metal overlay interface

Abstract

The application discloses a kind of prevention and control methods of nuclear grade dissimilar metal surfacing interface defect, including five steps;S1, mainly realize the surfacing of the whole stainless steel surfacing layer in the inner wall of lower head, and leave out the nickel-based isolation layer to be surfacing area;S2, mainly in main body carrying area is carried out main body nickel-based isolation layer surfacing operation, and reserve transition area not to be welded;S3, the support key is welded together with main body nickel-based isolation layer;S4, mainly first weld out support weld;Then, in transition area, first weld lap stainless steel surfacing layer side, then weld lap main body nickel-based isolation layer side, then the lap weld of two sides is connected together;Afterwards, according to step-by-step welding process realizes the fusion of the dissimilar interface of stainless steel surfacing layer and main body nickel-based isolation layer;S5, realize the detection of weld at transition area, ensure that the weld of transition area is defectless generation.The application can effectively avoid the generation of dissimilar metal surfacing interface defect, can improve component nondestructive testing qualified rate and operation safety.

Description

Technical Field

[0001] This invention belongs to the field of welding technology, specifically relating to a method for preventing and controlling defects at the interface of nuclear-grade dissimilar metal overlay welding. Background Technology

[0002] The lower head of the reactor pressure vessel is the core pressure-bearing equipment of the nuclear power plant. It operates in a high-temperature and high-pressure water environment, with the operating medium being primary loop water containing boric acid, hydrogen, and trace corrosive ions. It faces a long-term wet corrosion environment and is also subject to strong radioactive irradiation. Its inner wall needs to be overlaid with a stainless steel weld overlay (as a corrosion-resistant layer), and a nickel-based isolation layer is set in the support key area of ​​the lower head to solve the problems of transition between dissimilar materials, improve structural adaptability, and enhance corrosion resistance. The key structural element involves the composite welding of a stainless steel weld overlay, a nickel-based isolation layer, and a thick-walled support key in the lower head. The existing traditional manufacturing process involves first completing the overall stainless steel weld overlay on the inner wall of the lower head, then using shielded metal arc welding to fill the nickel-based isolation layer area, creating a continuous interface between the nickel-based isolation layer and the stainless steel weld overlay, and finally welding the support key onto the nickel-based isolation layer. While this process allows for overall component forming, due to unreasonable process layout, crude welding methods, and the stress superposition effect of the thick-walled support key welding, shallow defects are prevalent at the interface between the nickel-based isolation layer and the stainless steel weld overlay, severely restricting the yield rate of key nuclear power components. Currently, there is an urgent need to develop a method for controlling defects at the interface of nuclear-grade dissimilar metal weld overlays to effectively avoid their occurrence and improve the non-destructive testing yield and operational safety of components. Summary of the Invention

[0003] To address the aforementioned problems in the prior art, this invention provides a method for preventing and controlling defects at the interface of nuclear-grade dissimilar metal weld overlays. This method can effectively avoid the generation of defects at the interface of dissimilar metal weld overlays and improve the pass rate of non-destructive testing of components and operational safety.

[0004] The present invention adopts the following technical solution: A method for preventing defects at the interface of nuclear-grade dissimilar metal weld overlays includes the following steps: S1. The area to be welded on the inner wall of the lower head of the reactor pressure vessel is treated to ensure that the cleanliness of the surface to be welded meets the requirements of nuclear power plant welding. Then, the entire stainless steel weld overlay layer of the inner wall of the lower head is welded using the welding process, and the area to be welded for the nickel-based isolation layer is left blank. After that, the stainless steel weld overlay layer is visually inspected and / or non-destructively tested to confirm that the stainless steel weld overlay layer is qualified and free of defects. S2. Divide the area to be welded in the nickel-based isolation layer into a main bearing area and a transition area. Perform the main nickel-based isolation layer welding operation in the main bearing area to ensure that the main nickel-based isolation layer is well-formed and densely fused. During the welding process, leave the transition area between the main nickel-based isolation layer and the stainless steel welding layer unwelded. S3. Weld the support key to the main nickel-based insulating layer and complete the stress release; S4. Process the transition zone to ensure that the cleanliness of the edge of the stainless steel weld overlay meets the requirements for argon arc welding and the cleanliness of the edge of the main nickel-based isolation layer meets the requirements for argon arc welding; then, weld a support weld bead on the stainless steel weld overlay near the transition zone. Then, in the transition zone, first weld one side of the stainless steel overlay layer, then weld the other side of the main nickel-based isolation layer, and then connect the lap welds on both sides together; after that, according to this step-by-step welding process, the dissimilar interface between the stainless steel overlay layer and the main nickel-based isolation layer is fully fused. S5. Eliminate the excess height of the support weld and grind the weld surface in the transition zone; then, inspect the weld in the transition zone to ensure that there are no defects in the weld in the transition zone.

[0005] Furthermore, in step S1, the area to be welded on the inner wall of the reactor pressure vessel lower head is subjected to grinding, rust removal, degreasing, oxide scale removal, oil removal, and impurity removal.

[0006] Furthermore, in step S2, an automatic TIG welding machine is used to perform the main nickel-based isolation layer cladding operation in the main body bearing area. The welding current is controlled at 180A to 260A, the welding voltage is controlled at 9V to 15V, the welding speed is controlled at 8.03cm / min to 19.44cm / min, the preheating temperature is controlled at 150℃, the welding heat input is controlled at 0.30KJ / mm to 1.75KJ / mm, and the maximum interpass temperature is controlled at 225℃.

[0007] Furthermore, the thickness of the support key is ≥200mm.

[0008] Furthermore, the support key has a first bevel and a second bevel; In step S3, welding the support bond to the main nickel-based insulating layer includes the following steps: A1. First, perform root welding at the root of the bevel on one side of the first bevel. A2. Next, clean the root on one side of the second bevel and perform symmetrical welding of the root pass, referring to the root pass weld on the first bevel side. A3. Weld alternately on the first bevel and the second bevel until both bevels are fully welded.

[0009] Furthermore, step A3 includes the following steps: A31. First, weld 3 to 5 layers on one side of the first bevel; A32. Then weld 3 to 5 layers on one side of the second bevel; Perform alternating welding according to steps A31 to A32 until both bevels are fully welded.

[0010] Furthermore, in step S2, after the main nickel-based isolation layer is welded, the transition area between the main nickel-based isolation layer and the stainless steel weld layer is an annular groove.

[0011] Furthermore, the width of the annular groove is 4.0mm to 12.0mm; the bevel angle of the annular groove is 18° to 22°; and the radius of the root transition fillet of the annular groove is 1.0mm to 1.5mm.

[0012] Furthermore, in step S4, manual argon arc welding is used in the transition zone, with the welding current controlled at 100A to 180A, the welding voltage controlled at 12V to 18V, the welding heat input controlled at 0.87KJ / mm to 2.41KJ / mm, and the width of each weld bead controlled at 2.5mm to 4mm.

[0013] Furthermore, in step S5, non-destructive testing is performed on the weld in the transition zone; the non-destructive testing is one or more of penetrant testing, magnetic particle testing, ultrasonic testing, and radiographic testing.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention discloses a method for preventing and controlling defects at the interface of nuclear-grade dissimilar metal overlay welding. It overturns the traditional process logic by adopting a core concept of high-stress process pre-processing and dissimilar metal transition sealing post-processing. It prioritizes the welding of the thick-walled support key and the main nickel-based isolation layer, allowing most of the welding deformation, thermal stress, and residual stress to be fully released in the main nickel-based isolation layer area. Finally, the dissimilar metal overlay welding interface sealing welding in the transition zone is completed. This completely avoids the secondary thermal cycle and stress superposition effects on the sensitive interface of dissimilar metals during the welding of the thick-walled support key. It effectively avoids the generation of dissimilar metal overlay welding interface defects from the source of the process, and can improve the non-destructive testing pass rate and operational safety of components (such as the head below). Attached Figure Description

[0015] The technology of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments: Figure 1This is a schematic diagram showing the connection between the support key and the main nickel-based insulating layer on the inner wall of the lower head; Figure 2 yes Figure 1 A schematic diagram of the F-direction view at point F; Figure 3 This is a diagram showing the arrangement of the stainless steel weld overlay, transition zone, and main nickel-based insulating layer (Note: Figure 1 (Developed view of "stainless steel weld overlay, transition zone and main nickel-based isolation layer" from point K in the K direction) Figure 4 This is a schematic diagram showing that the support key has a first bevel and a second bevel; Figure 5 This is a schematic diagram showing the connection between the support key and the main nickel-based isolation layer (where "stainless steel weld overlay, transition zone and main nickel-based isolation layer" are unfolded views). Figure 6 It is a cross-sectional view (partial schematic diagram) of the thickness direction of the "stainless steel overlay, transition zone and main nickel-based isolation layer" (showing the support weld, first weld, second weld and third weld).

[0016] Figure label: 1-Lower head; F: Viewing angle in the F direction; K: Viewing angle in the K direction; 2- Stainless steel weld overlay; 3-Main nickel-based insulating layer; H-Thickness direction (from bottom to surface); 4-Transition zone; B-Annular groove; C-Bevel angle; D-Thickness direction line; E-Root transition fillet; 5-Support key; 51-First bevel; 52-Second bevel; G-Thickness; 6-Support weld bead; 71 - First weld pass; 72 - Second weld pass; 73 - Third weld pass. Detailed Implementation

[0017] The following will provide a clear and complete description of the concept, specific structure, and technical effects of the present invention in conjunction with embodiments and accompanying drawings, so as to fully understand the purpose, solution, and effects of the present invention. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The same reference numerals used throughout the accompanying drawings indicate the same or similar parts.

[0018] It should be noted that, unless otherwise specified, when a feature is referred to as "fixed" or "connected" to another feature, it can be directly fixed or connected to the other feature, or indirectly fixed or connected to the other feature. Furthermore, the descriptions of "up," "down," "left," and "right" used in this invention are only relative to the relative positional relationships of the various components of the invention in the accompanying drawings.

[0019] Reference Figures 1 to 6 A method for preventing defects at the interface of nuclear-grade dissimilar metal overlay welding includes the following steps: S1. The area to be welded on the inner wall of the lower head 1 of the reactor pressure vessel is treated to ensure that the cleanliness of the surface to be welded meets the requirements of nuclear power welding. Then, the "integral stainless steel weld overlay layer 2" on the inner wall of the lower head 1 is welded using the weld overlay process, and the area to be welded for the nickel-based isolation layer is left empty. Then, the stainless steel weld overlay layer 2 is visually inspected and / or non-destructively tested to confirm that the stainless steel weld overlay layer 2 is formed in a qualified manner and without defects. Then, the lower head 1 with the stainless steel weld overlay layer 2 is cooled to room temperature for use. S2. Divide the area to be welded of the nickel-based isolation layer into a main bearing area and a transition area 4. Perform a welding operation on the "main nickel-based isolation layer 3" in the main bearing area to ensure that the main nickel-based isolation layer 3 is well-formed and densely fused. During the welding process, leave the transition area 4 unwelded between the main nickel-based isolation layer 3 and the stainless steel weld overlay layer 2. S3. Weld the support key 5 to the main nickel-based isolation layer 3 and complete the stress release (wherein, in step S2, the transition area 4 is left unwelded, and the main nickel-based isolation layer 3 has room for deformation, which is beneficial to release stress when the support key 5 is welded to the main nickel-based isolation layer 3). S4. Process the transition zone 4 to ensure that the cleanliness of the edge of the stainless steel weld overlay 2 meets the requirements for argon arc welding and the cleanliness of the edge of the main nickel-based isolation layer 3 meets the requirements for argon arc welding; then, weld the support weld 6 at the position of the stainless steel weld overlay 2 near the transition zone 4. Then, within the transition zone 4, one side of the lapped stainless steel weld overlay 2 is first welded (e.g. Figure 6 The first weld bead 71), then weld over one side of the main nickel-based insulating layer 3 (e.g., Figure 6 The second weld bead 72), then connect the lap weld beads on both sides together (e.g. Figure 6 The third weld pass 73); then, following this step-by-step welding process (i.e., first weld pass 71 → second weld pass 72 → third weld pass 73), the dissimilar interface between the stainless steel weld overlay 2 and the main nickel-based isolation layer 3 is fully fused. S5. Eliminate the excess height of the support weld 6 and grind the weld surface at the transition zone 4; then, inspect the weld at the transition zone 4 to ensure that the weld at the transition zone 4 is free of defects.

[0020] In one embodiment, in step S1, the area to be welded on the inner wall of the reactor pressure vessel lower head 1 is subjected to grinding, rust removal, degreasing, oxide scale removal, oil removal, and impurity removal. Impurities include dust.

[0021] In one embodiment, in step S1, the stainless steel weld overlay 2 is formed by strip electrode submerged arc welding, and the welding equipment used is a strip electrode submerged arc welding machine.

[0022] In one embodiment, in step S2, an automated TIG welding machine is used to perform the "main body nickel-based isolation layer 3" cladding operation in the main body bearing area. The welding current, welding voltage, welding speed, welding heat input, and interpass temperature are strictly controlled to ensure that the main body nickel-based isolation layer is regularly formed and densely fused. Specifically, the welding current is controlled between 180A and 260A, the welding voltage between 9V and 15V, the welding speed between 8.03cm / min and 19.44cm / min, the preheating temperature between 150℃, the welding heat input between 0.30KJ / mm and 1.75KJ / mm, and the maximum interpass temperature between 225℃. The full English name for "TIG welding" is "Tungsten Inert Gas Welding"; the automated TIG welding machine is an existing welding equipment and will not be described in detail here.

[0023] Reference Figure 2 In one embodiment, the thickness G of the support key 5 is ≥ 200 mm (therefore, it is often referred to as: thick wall support key); in this embodiment, the thickness G of the support key 5 is 270 mm.

[0024] Reference Figure 4 and Figure 5 In one embodiment, the support key 5 has a first bevel 51 and a second bevel 52; In step S3, the support bond 5 is welded to the main nickel-based insulating layer 3, which includes the following steps: A1. First, perform root welding at the root of the bevel on one side of the first bevel 51, with a welding thickness of 10mm to 15mm. A2. Next, clean the root on one side of the second bevel 52, and make symmetrical welding for the root pass, referring to the root pass on one side of the first bevel 51. A3. Weld alternately on the first bevel 51 and the second bevel 52 until both bevels are fully welded.

[0025] Reference Figure 4 and Figure 5 In one embodiment, step A3 includes the following steps: A31. First, weld 3 to 5 layers on one side of the first bevel 51; A32. Then weld 3 to 5 layers on one side of the second bevel 52; Perform alternating welding according to steps A31 to A32 until both bevels are fully welded.

[0026] This invention utilizes this process (i.e., A1 step → A2 step → A3 step) to complete multi-layer and multi-pass welding of thick plates, which can effectively control the welding deformation of large-wall-thick support plates, and can fully release the welding thermal stress and shrinkage stress of thick plates, so that the structural stress of the thick plates tends to be stable after welding, and effectively avoid the interface between the subsequent main nickel-based isolation layer and the stainless steel weld overlay layer bearing superimposed stress.

[0027] In one embodiment, after the support key 5 is welded, the flatness of the upper and lower surfaces does not exceed 0.2 mm, the parallelism of the upper and lower surfaces does not exceed 0.2 mm, and the perpendicularity of the support key 5 does not exceed 0.2 mm.

[0028] Reference Figure 3 In one embodiment, in step S2, after the main nickel-based isolation layer 3 is welded, the transition region 4 between the main nickel-based isolation layer 3 and the stainless steel weld overlay layer 2 is an annular groove B.

[0029] Reference Figures 1 to 6 In one embodiment, the width of the annular groove B is 4.0 mm to 12.0 mm; preferably, the width of the annular groove B is 4 mm, 5 mm, or 6 mm; the bevel angle C of the annular groove B is 18° to 22° (bevel angle C refers to the angle between the inclined surface of the annular groove B and the thickness direction line D; the thickness direction H is combined with...). Figure 6 (For understanding); the radius of the root transition fillet E of the annular groove B is 1.0mm to 1.5mm.

[0030] In one embodiment, the height of the support weld 6 is ≤5mm.

[0031] Preferably, the material of the support weld 6 is stainless steel; the support weld 6 is welded into the stainless steel overlay 2 near the transition zone 4, the purpose of which is: First: Maintain the geometric stability of the boundary bevel of the stainless steel weld overlay 2 to prevent the filling weld in the subsequent transition zone 4 from melting down the edge of the boundary bevel of the stainless steel weld overlay 2, and ensure the accessibility of welding. Second: Eliminate stress concentration sources at the edge of the stainless steel weld overlay bevel, alleviate edge stress concentration of dissimilar metal joints under service thermal cycling, and prevent cracks from initiating at the edge of the stainless steel weld overlay bevel and propagating to the weld in the transition zone. Third: Define the welding boundary above the bevel of the stainless steel weld overlay to prevent the weld pool from overflowing and metal loss when welding the first weld pass 71 at the upper part of the bevel. This serves as a boundary constraint and process support.

[0032] In one embodiment, in step S4, manual TIG welding is used at the transition zone 4. During welding, the heat input is strictly controlled, and narrow weld beads are used for rapid forming to reduce the heat-affected zone and achieve full fusion of the dissimilar interface between the stainless steel weld overlay layer 2 and the main nickel-based isolation layer 3, thus completing the overall composite weld overlay structure. Specifically, manual TIG welding is used, with the welding current controlled at 100A–180A, the welding voltage controlled at 12V–18V, and the welding speed controlled at 5.5cm / min–7.4cm / min (Note: manual TIG welding is a relatively efficient and rapid operation while ensuring quality). The welding heat input is controlled at 0.87KJ / mm–2.41KJ / mm, and the width of each weld bead is controlled at 2.5mm–4mm. This invention limits the upper limit of heat input in manual TIG welding by using narrow weld beads for rapid forming, thereby reducing the heat-affected zone at the dissimilar metal weld overlay interface and lowering the risk of weld cracking.

[0033] In one embodiment, the weld material filling the transition zone 4 is a nickel-based material, which is the same as the material of the main nickel-based isolation layer 3.

[0034] In one embodiment, in step S5, non-destructive testing (NDT) is performed on the weld at the transition zone 4. The NDT is one or more of penetrant testing, magnetic particle testing, ultrasonic testing, and radiographic testing. Penetrant testing is also known as PT testing. In one embodiment, if no point or linear defects are found in the weld at the transition zone 4 after testing, it indicates that the weld meets the nuclear power equipment quality acceptance standards.

[0035] Combination Figures 1 to 6 In one embodiment, the present invention provides a method for preventing and controlling defects at the interface of nuclear-grade dissimilar metal overlays, which has the following advantages: (1) The new process can improve the pass rate of non-destructive testing of components (such as the end cap).

[0036] As a preliminary explanation: The lower head 1 of the reactor pressure vessel must withstand long-term high-temperature, high-pressure boron-containing water corrosion, neutron irradiation, and alternating loads from start-up and shutdown thermal cycles. It is a crucial core component of nuclear power equipment. During manufacturing, the welding and fixing of the thick-walled support key generates significant residual stress and intense thermal cycling. Traditional processes first perform a full-scale welding of the nickel-based isolation layer to create a continuous dissimilar interface between the stainless steel weld overlay and the nickel-based isolation layer. Subsequently, the thick-walled support key is welded to the nickel-based isolation layer. The high stress generated during the welding of the thick-walled support key directly acts on the fragile dissimilar metal interface area, which can easily induce interface microcracks and fatigue defects, leading to excessive defects in PT testing and severely restricting the production qualification rate of key nuclear power components.

[0037] This invention discloses a method for preventing and controlling defects at the interface of nuclear-grade dissimilar metal overlay welding. It overturns the traditional process logic by adopting a core concept of high-stress process pre-processing and dissimilar metal transition sealing post-processing. The welding of the thick-walled support key 5 and the "main nickel-based isolation layer 3" is completed first, so that most of the welding deformation, thermal stress, and residual stress are fully released in the main nickel-based isolation layer area. Finally, the dissimilar metal overlay welding interface sealing welding in the transition zone 4 is completed. This completely avoids the secondary thermal cycle and stress superposition effects on the sensitive interface of dissimilar metals during the welding of the thick-walled support key. It effectively avoids the generation of dissimilar metal overlay welding interface defects from the source of the process, and can improve the non-destructive testing pass rate and operational safety of components.

[0038] (2) The transition zone 4 forms an annular groove B, realizing a smooth gradient transition between dissimilar metals (combined with...) Figure 6 (The cross-section in the image shows the approximate trapezoidal shape of the annular groove B).

[0039] Preliminary explanation: Stainless steel weld overlay and nickel-based isolation layer have significant differences in linear expansion coefficient, elastic modulus and metallographic structure. Traditional stainless steel weld overlay and nickel-based isolation layer are in direct contact, resulting in severe performance abrupt changes and significant stress concentration effect. Under long-term thermal cycling, irradiation aging and severe accident IVR extreme high temperature molten material impact and large plastic deformation conditions, the interface between stainless steel weld overlay and nickel-based isolation layer is very prone to cracking and failure.

[0040] This invention innovatively designs the annular groove B, with a groove width of 4.0mm to 12.0mm, a bevel angle C of 18° to 22°, and a root transition fillet E radius of 1.0mm to 1.5mm. By limiting the width, bevel angle C, and root transition fillet E of the annular groove B, this invention eliminates the stress sharpness at the weld overlay interface and disperses concentrated stress at the interface. Simultaneously, relying on the annular groove B, a continuous metallographic structure and mechanical property gradient transition layer is formed between the stainless steel weld overlay layer 2 and the main nickel-based isolation layer 3, effectively buffering the interface stress caused by the difference in properties between dissimilar materials. Under normal operating conditions of the lower head, the interface of this invention can resist damage caused by long-term alternating stress and irradiation aging. The interface of this invention can effectively improve the deformation adaptability and structural integrity of the dissimilar metal interface, avoiding the risk of cracking and leakage at the dissimilar metal interface under large creep deformation conditions.

[0041] (3) Differentiated welding process for different zones, taking into account both welding efficiency and interface welding quality.

[0042] Preliminary explanation: Traditional processes use shielded metal arc welding (SMAW) to complete the "integral nickel-based isolation layer" cladding, which has problems such as unstable heat input, rough weld bead formation, large human error, and many defects such as slag inclusions and porosity. It cannot meet the high reliability welding requirements of nuclear power, and the welding quality in narrow junction areas is even more difficult to control.

[0043] This invention employs automated TIG welding to achieve surfacing in the main load-bearing area and manual argon arc welding to achieve surfacing in the transition zone 4, thereby realizing zoned differentiation of the welding process and enabling precise and high-quality welding. The surfacing in the main load-bearing area is done using automatic TIG welding, which has stable welding parameters, uniform heat input, and regular weld formation, effectively ensuring the uniformity of the microstructure and the consistency of the mechanical properties of the large-area nickel-based isolation layer; at the same time, automatic TIG welding can improve construction efficiency. For the narrow transition zone 4, manual argon arc welding with controllable heat input and fine forming is used for edge sealing and filling, and a specific and refined welding sequence is limited (i.e., first weld 71 → second weld 72 → third weld 73) to further optimize the interface stress distribution and strictly control welding defects. Before the overlay welding, it is preferable to weld a support weld 6 on the stainless steel overlay layer 2 near the transition zone 4. The support weld 6 can consolidate the stability of the boundary interface of the stainless steel overlay layer 2, which is conducive to achieving a smooth fusion transition between the nickel-based welding material and the dissimilar interface of stainless steel. After the support weld 6 is welded, the transition zone 4 is filled layer by layer. The welding sequence in step S4 of this invention can effectively avoid the problem of sudden stress increase caused by a large heat input during the one-time filling of the dissimilar metal overlay interface. This invention first stabilizes the boundary interface of the stainless steel overlay layer 2 through low-heat lap welding (note: the role of the supporting weld 6), weakening the sudden stress change at the interface caused by the performance difference between stainless steel and nickel-based materials. Then, this invention performs welding filling at the transition zone 4. During the welding filling process, by utilizing the approximately trapezoidal cross-sectional structure of the annular groove B and the step-by-step welding process (i.e., first weld 71 → second weld 72 → third weld 73), the stress can be released uniformly and slowly, avoiding local stress accumulation. The present invention uses manual argon arc welding at the transition zone 4. This welding method is suitable for the narrow welding space of the transition zone 4, avoiding the problems of large spatter, poor fusion and many surface defects of shielded metal arc welding, and ensuring full fusion of dissimilar metal overlay interfaces. This invention optimizes the stress distribution at the interface of dissimilar metal welds from both the welding method and the process sequence, significantly reducing the probability of PT defects and improving the pass rate of non-destructive testing and operational safety of components.

[0044] Other aspects of the method for preventing and controlling defects at the interface of nuclear-grade dissimilar metals as described in this invention can be found in the prior art and will not be repeated here.

[0045] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Therefore, any modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preventing and controlling defects at the interface of nuclear-grade dissimilar metal overlay welding, characterized in that, Includes the following steps: S1. The area to be welded on the inner wall of the lower head of the reactor pressure vessel is treated to ensure that the cleanliness of the surface to be welded meets the requirements of nuclear power plant welding. Then, the entire stainless steel weld overlay layer of the inner wall of the lower head is welded using the welding process, and the area to be welded for the nickel-based isolation layer is left blank. After that, the stainless steel weld overlay layer is visually inspected and / or non-destructively tested to confirm that the stainless steel weld overlay layer is qualified and free of defects. S2. Divide the area to be welded in the nickel-based isolation layer into a main bearing area and a transition area. Perform the main nickel-based isolation layer welding operation in the main bearing area to ensure that the main nickel-based isolation layer is well-formed and densely fused. During the welding process, leave the transition area between the main nickel-based isolation layer and the stainless steel welding layer unwelded. In step S2, after the main nickel-based isolation layer is welded, the transition area between the main nickel-based isolation layer and the stainless steel weld layer is an annular groove. The width of the annular groove is 4.0mm to 12.0mm; the bevel angle of the annular groove is 18° to 22°; and the radius of the root transition fillet of the annular groove is 1.0mm to 1.5mm. S3. Weld the support key to the main nickel-based insulating layer and complete the stress release; The thickness of the support key is ≥200mm; S4. Process the transition zone to ensure that the cleanliness of the edge of the stainless steel weld overlay meets the requirements for argon arc welding and the cleanliness of the edge of the main nickel-based isolation layer meets the requirements for argon arc welding; then, weld a support weld bead on the stainless steel weld overlay near the transition zone. Then, in the transition zone, first weld one side of the stainless steel overlay layer, then weld the other side of the main nickel-based isolation layer, and then connect the lap welds on both sides together; after that, according to this step-by-step welding process, the dissimilar interface between the stainless steel overlay layer and the main nickel-based isolation layer is fully fused. The weld material filling the transition zone is nickel-based, which is the same as the material of the main nickel-based isolation layer. S5. Eliminate the excess height of the support weld and grind the weld surface in the transition zone; then, inspect the weld in the transition zone to ensure that there are no defects in the weld in the transition zone.

2. The method for preventing and controlling defects at the interface of nuclear-grade dissimilar metal overlay welding according to claim 1, characterized in that, In step S1, the area to be welded on the inner wall of the lower head of the reactor pressure vessel is ground, derusted, degreased, and cleaned to remove oxide scale, oil, and impurities.

3. The method for preventing and controlling defects at the interface of nuclear-grade dissimilar metal overlay welding according to claim 1, characterized in that, In step S2, an automatic TIG welding machine is used to perform the main nickel-based isolation layer cladding operation in the main body bearing area. The welding current is controlled at 180A to 260A, the welding voltage is controlled at 9V to 15V, the welding speed is controlled at 8.03cm / min to 19.44cm / min, the preheating temperature is controlled at 150℃, the welding heat input is controlled at 0.30KJ / mm to 1.75KJ / mm, and the maximum interpass temperature is controlled at 225℃.

4. The method for preventing and controlling defects at the interface of nuclear-grade dissimilar metal overlay welding according to claim 1, characterized in that, The support key has a first bevel and a second bevel; In step S3, welding the support bond to the main nickel-based insulating layer includes the following steps: A1. First, perform root welding at the root of the bevel on one side of the first bevel. A2. Next, clean the root on one side of the second bevel and perform symmetrical welding of the root pass, referring to the root pass weld on the first bevel side. A3. Weld alternately on the first bevel and the second bevel until both bevels are fully welded.

5. The method for preventing and controlling defects at the interface of nuclear-grade dissimilar metal overlay welding according to claim 4, characterized in that, Step A3 includes the following steps: A31. First, weld 3 to 5 layers on one side of the first bevel; A32. Then weld 3 to 5 layers on one side of the second bevel; Perform alternating welding according to steps A31 to A32 until both bevels are fully welded.

6. A method for preventing and controlling defects at the interface of nuclear-grade dissimilar metal overlay welding according to any one of claims 1 to 5, characterized in that, In step S4, manual argon arc welding is used in the transition zone. The welding current is controlled between 100A and 180A, the welding voltage is controlled between 12V and 18V, the welding heat input is controlled between 0.87KJ / mm and 2.41KJ / mm, and the width of each weld bead is controlled between 2.5mm and 4mm.

7. The method for preventing and controlling defects at the interface of nuclear-grade dissimilar metal overlay welding according to claim 1, characterized in that, In step S5, non-destructive testing is performed on the weld in the transition zone; the non-destructive testing is one or more of penetrant testing, magnetic particle testing, ultrasonic testing, and radiographic testing.

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