A welding process for reducing the display of j-type welds of a reactor pressure vessel and application

Abstract

The present application relates to a kind of welding process and application for reducing the PT display of reactor pressure vessel J type weld, the welding adopts stick arc welding, nickel-based 690 welding material, including root pass welding, filling pass welding, cover pass welding;The welding process of the present application is first from the selection of welding material specification, the optimization of welding parameter, further combined with the optimization of arc backfill mode, arc pit polishing, weld arrangement, welding piece cooling etc., further improve the welding operation condition, so that the welding quality is changed from the experience control of welder to the control by solidification process, improve the welding quality, improve weld crack, reduce PT display, compared with prior art, it can shorten 50% manufacturing cycle, welding material consumption reduces 20%, weld surface PT display reduces 85%, wherein linear display (arc pit crack) reduces more than 95%.Applied to reactor pressure vessel, can greatly improve the reliability of container.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of welding, and particularly relates to a welding process for reducing PT display of a J-shaped weld of a reactor pressure vessel and application. BACKGROUND

[0002] The reactor pressure vessel is one of main equipments of a reactor coolant system, and is a second important barrier for safety protection of a nuclear island core radioactivity. At present, a control rod drive mechanism penetrating piece is designed on a top cover of each type of reactor pressure vessel, which is used as a channel for nuclear reaction fuel to enter and exit the vessel, a channel for detecting instruments in a nuclear reaction process, and a channel for reaction heat to enter and exit. The control rod drive mechanism penetrating piece and the top cover are connected in a welding manner. Since the top cover of the reactor pressure vessel is a spherical head, a welding bevel of the top cover and the control rod drive mechanism penetrating piece is an irregular J-shaped bevel. Based on a service condition of the equipment, a nickel-based welding material with better corrosion resistance needs to be used for welding of the weld. However, while good corrosion resistance is obtained, the welding difficulty is also increased. Due to the characteristics of the nickel-based material, micro cracks are easily generated in the welding process. The root cause of reducing PT display is to reduce the micro cracks in the welding process through PT detection in engineering application.

[0003] At present, in the manufacturing of such products, a welding method is mostly arc welding with a welding rod. However, a large amount of PT display is generated in the welding process. According to the functional requirements of the products, the weld is not allowed to have any PT display. The welding requirement of the weld is very high, and therefore it is inevitable to return to repair to meet the product use. SUMMARY

[0004] In order to solve at least one technical problem in the prior art, the present application aims to provide a welding process for reducing PT display of a J-shaped weld of a reactor pressure vessel.

[0005] One of the purposes of the present application is to provide a welding process for reducing PT display of a J-shaped weld of a reactor pressure vessel. The welding adopts arc welding with a welding rod, and a nickel-based 690 welding material, and includes the following steps.

[0006] 1) Root pass welding: a welding rod with a specification of φ2.4 is used, and a welding current is 62A-68A;

[0007] 2) Filling pass welding: a welding rod with a specification of φ2.4 or 3.2 is used. For the welding rod with the specification of φ2.4, the welding current is 62A-68A; and for the welding rod with the specification of φ3.2, the welding current is 90A-98A;

[0008] 3) Cover face welding; φ2.4 or 3.2 specification electrode is adopted, wherein for φ2.4 specification electrode, welding current is 62A-68A; for φ3.2 specification electrode, welding current is 90A-98A.

[0009] Nickel-based 690 alloy has unique physical, mechanical and corrosion resistance, and has good high temperature and low temperature mechanical properties, and is one of the most corrosion-resistant metals in the atmosphere, and is selected as the welding material of the reactor pressure vessel, and has good reliability, but the weldability of the nickel-based alloy is sensitive to impurity elements such as S, P, Pb, Zr, B and Bi, which are practically insoluble in Ni, and will form low-melting eutectic when the weld solidifies, and has high hot crack sensitivity. When the welding parameter is set improperly and the heat input is too high, it will have an adverse effect. Therefore, the change of the welding parameter must be strictly controlled during the welding process of the nickel-based alloy. Through a large number of tests, the optimal welding parameter is determined as follows: φ2.4 specification, 62A-68A; φ3.2 specification, 90A-98A, which avoids the formation of coarse grains, reduces the formation of intermetallic compounds between grain boundaries and promotes the formation of liquid cracks, thereby reducing the tendency of hot cracking and reducing the PT display of J-shaped welds.

[0010] Preferably, in steps 1), 2) and 3) above, when each welding arc is received, 2 turns are adopted, and the arc is raised upward after 2 seconds, so that the arc pit is smooth and the depth is consistent.

[0011] Further preferably, after each welding is completed, the arc receiving area is polished, and the polishing depth is 1.2mm-1.8mm, which can completely eliminate the existence of arc pit cracks in the weld.

[0012] Preferably, in step 3), the weld size is determined at any time during welding by using a detection tool, so as to assist the welder in arranging the welding bead, accurately control the welding amount, and avoid the problems of insufficient welding or excessive welding, thereby effectively guiding the production process to be done once and done well.

[0013] Preferably, in steps 1), 2) and 3), during welding, the pipe wall side and the groove side are welded respectively, and then pushed to the center of the weld respectively, and the last welding is set in the middle of the weld, so as to better reduce the cumulative stress.

[0014] Preferably, in steps 1), 2) and 3), during welding, the welding part is also connected with a cooling anti-deformation tool, which improves the cooling effect, avoids overheating of the weld, reduces thermal stress, and is beneficial to reduce hot cracking and welding defects.

[0015] The second purpose of the present application also provides a welded joint welded by using the above welding process.

[0016] The third purpose of the present application also provides a reactor pressure vessel comprising the above welded joint.

[0017] Compared with the prior art, the present application has the following beneficial effects:

[0018] The present application optimizes the welding process of the J-shaped weld of the reactor pressure vessel, first from the selection of welding material specifications and the optimization of welding parameters, and further combines the arc recovery backfill mode to optimize the arc recovery of the welder, so that the arc pit is uniform and the crack depth is consistent, which can accurately guide the arc pit polishing, thereby completely eliminating the existence of arc pit cracks in the weld. Compared with the previous process, the original process has a large number of linear displays after every 3 layers of PT inspection after welding, and the method of the present application is basically eliminated after polishing, greatly improving the quality of the weld. Further combined with weld arrangement, welding part cooling and other optimizations, further improve the welding operation conditions, so that the welding quality is changed from the experience control of the welder to the control by the solidification process, which improves the welding quality, improves the weld crack, reduces the PT display, and compared with the existing process, the manufacturing cycle can be shortened by 50%, the welding material consumption is reduced by 20%, and the weld surface PT display is reduced by 85%, of which the linear display (arc pit crack) is reduced by more than 95%. Applied to the reactor pressure vessel, the reliability of the container can be greatly improved. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is a schematic diagram of the J-shaped weld joint;

[0020] Figure 2 It is a residual stress distribution test result of the J-shaped weld joint;

[0021] Figure 3 It is a schematic diagram of detecting the weld size by using the detection tool of the embodiment of the present application;

[0022] Figure 4 It is a schematic diagram of the weld arrangement during welding in the embodiment of the present application;

[0023] Figure 5 It is a schematic diagram of the cooling anti-deformation tool of the embodiment of the present application;

[0024] Figure 6 It is a schematic diagram of the welding process of the embodiment of the present application. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application and the drawings. Obviously, the described embodiments are only part of the embodiments of the present application, not all embodiments.

[0026] Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0027] The reagents, materials and equipment used in the embodiments of the present application are commercially available unless otherwise specified. The test methods are conventional test methods in the art unless otherwise specified.

[0028] The reactor pressure vessel head is a spherical head, and the welding groove of the control rod drive mechanism penetrating piece is an irregular J-shaped groove. The welding joint schematic diagram is shown in Figure 1 The structure is a self-constrained welding joint, and the constraint stress can only be released in the filler metal. Therefore, the weld metal is subjected to the action of welding residual stress, Figure 2 The J-shaped weld joint residual stress distribution test results are shown in the table. In the joint structure, the penetrating piece material is NC30Fe, the head material is 16MND5, the head inner wall is cladded with an austenitic stainless steel cladding layer, and the J-shaped weld groove is cladded with a nickel-based material isolation layer. In the table, the positive value represents residual tensile stress, and the negative value represents residual compressive stress. According to the residual stress test results, the weld surface of the J-shaped weld is the maximum residual stress area and is prone to PT display.

[0029] The embodiments of the present application provide a welding process for reducing PT display of a J-shaped weld of a reactor pressure vessel, which adopts stick arc welding, nickel-based 690 welding material, and includes the following steps:

[0030] 1) Root pass welding: φ2.4 specification welding rod is used, and the welding current is 62A-68A;

[0031] 2) Filler pass welding: φ2.4 or 3.2 specification welding rod is used, wherein for the φ2.4 specification welding rod, the welding current is 62A-68A; and for the φ3.2 specification welding rod, the welding current is 90A-98A;

[0032] 3) Cover pass welding: φ2.4 or 3.2 specification welding rod is used, wherein for the φ2.4 specification welding rod, the welding current is 62A-68A; and for the φ3.2 specification welding rod, the welding current is 90A-98A.

[0033] Nickel-based 690 alloy has unique physical, mechanical and corrosion resistance, and has good high and low temperature mechanical properties, and is one of the most corrosion resistant metals in the atmosphere. Selecting it as the welding material of the reactor pressure vessel has good reliability, but the weldability of nickel-based alloy is sensitive to impurity elements such as S, P, Pb, Zr, B and Bi. These elements are practically insoluble in Ni, and when the weld solidifies, low-melting eutectic will be formed, which has high hot crack sensitivity. When the welding parameter is set improperly and the heat input is too high, it will have an adverse effect. Annealing and grain growth occur to a certain extent in the heat-affected zone. High heat input may cause excessive segregation, precipitation of carbides or other harmful metallurgical phenomena, which may cause hot cracking or reduce corrosion resistance. Moreover, the nickel-based alloy weld metal is not as easy to wet and spread as steel weld metal. Even increasing the welding current cannot improve the fluidity of the weld metal, but has a harmful effect. Similarly, the penetration of nickel-based corrosion-resistant alloy is shallow, and increasing the welding current cannot increase the penetration, but has a harmful effect. Therefore, the welding parameters must be strictly controlled during the welding process of nickel-based alloy. Through a large number of tests, the optimal welding parameters are determined as follows: φ2.4 specification, 62A-68A; φ3.2 specification, 90A-98A. The scheme of the present application selects nickel-based 690 as the welding material, and then controls the process parameters to avoid the formation of coarse grains, reduce the formation of intermetallic compounds between grain boundaries and promote the formation of liquid cracking, thereby reducing the hot crack tendency and reducing the PT display of J-type weld.

[0034] In some embodiments, during each welding of steps 1), 2) and 3) above, the arc is collected by rotating 2 turns and lifting up after 2 seconds, which can make the arc pit smooth and consistent in depth.

[0035] Collecting arc refers to the operation of filling the arc pit at the end of a weld. If the arc is extinguished immediately at the end of welding, a very deep arc pit will appear at the end of the weld, which not only reduces the strength of the weld at the end, but also easily produces arc pit cracks; quickly breaking the arc, the gas in the molten pool cannot escape in time, resulting in porosity defects. In order to prevent these defects, a reasonable arc collection method must be used to ensure that the arc pit at the end of the weld is filled.

[0036] Nickel-based alloy has high hot crack sensitivity. In the engineering application environment, common materials such as grease, oil, paint, marker pen, lubricant, cutting coolant, etc. contain elements such as S, P, Pb, Sn, Zn, Bi, Sb and As. These elements are extremely easy to form low-melting eutectic with Ni, thereby increasing the hot crack sensitivity of nickel-based corrosion-resistant alloy. Especially in the arc collection area, cracks are concentrated.

[0037] The application optimizes the arc collecting mode based on the circle drawing arc collecting method, can make the backfilling arc pit smooth and consistent in depth, provides quantitative data for polishing operation of the arc collecting position in actual production, can accurately eliminate the arc collecting cracks in the welding process, and finally guarantees the product quality.

[0038] As in an embodiment, 16MnD5+ nickel-based alloy is respectively used for surfacing, the arc pit is not backfilled, the crack depth is 3.2-3.5mm, the arc pit is backfilled by using the arc collecting method of the application, and the crack depth is about 1.2mm.

[0039] In another embodiment, nickel-based alloy+ nickel-based alloy is used for surfacing, the arc pit is not backfilled, the crack depth is 3.6-4mm, the arc pit is backfilled by using the arc collecting method of the application, and the crack depth is 2-2.5mm.

[0040] The above embodiments show that, whether the materials are different or the same, after the arc pit is backfilled by using the arc collecting method of the application, the crack propagation depth is obviously shallower than that of the arc pit not backfilled, and the depth is more consistent, the arc pit crack depth can be measured to guide the welder to correctly collect the arc and accurately polish the arc pit, and the existence of the arc pit crack in the weld is completely eliminated. Compared with the previous process, the original process has a large number of linear displays after every 3 layers of PT inspection after welding, the linear display is basically eliminated by using the arc collecting method of the application, and the quality of the weld is greatly improved.

[0041] In some embodiments, the arc collecting area is polished after each welding is completed, the polishing depth is 1.2mm-1.8mm, and the arc collecting crack in the welding process can be accurately eliminated.

[0042] The PT display is mainly caused by the microcracks of the welding arc pit, the microcracks can be removed by polishing during the welding process, and in the existing process, the microcrack depth is difficult to control due to the lack of corresponding guidance in the welding operation process control. Based on a large number of researches on the arc pit microcracks, the optimal welding parameters are determined through a large number of tests, that is, φ2.4 specification 62A-68A and φ3.2 specification 90A-98A. First, the welding parameters are controlled to avoid the generation of coarse grains, reduce the carbides between the grain boundaries and promote the formation of intermetallic compounds of liquidized cracks, so as to reduce the tendency of hot cracks. For the arc collecting arc pit, the arc pit is filled according to the optimized arc collecting method described above under the welding parameters, the measured arc pit crack depth is about 1.2mm, and the welder is guided to polish the arc pit to a depth of about 1.2mm-1.8mm after the arc collecting in the welding process, and the PT display of the arc pit crack is basically eliminated.

[0043] In some embodiments, in step 3), the size of the welding bead is determined by the detection tool during welding, thereby assisting the welder in arranging the welding bead and accurately controlling the welding amount, avoiding the problems of insufficient or excessive welding, and effectively guiding the production process to be done correctly and well at one time.

[0044] According to the product structure, the groove and post-weld shape of the J-shaped welding seam are irregular spatial curved surfaces, and the size of the welding seam cannot be measured by conventional detection means during welding. Therefore, the welder cannot accurately determine whether the welding amount is sufficient when performing welding operations, and can only determine the welding filling amount based on his own experience, which may result in insufficient or excessive welding, and excessive welding is the main situation. Excessive welding means increasing the number of welding beads, and the more welding, the greater the thermal stress and residual stress, which is not conducive to the welding quality. The scheme of the present application designs matching detection tools for different pipe hole shapes to assist the welder in arranging the welding bead, accurately controls the welding amount, and avoids the problems of insufficient or excessive welding. The detection tool can take the pipe end face as a reference, loft the theoretical shape according to the shape of the welding seam in different quadrants of the groove, and set the process polishing allowance based on the theoretical shape to ensure that the final shape requirements are met and excellent welding bead quality is obtained.

[0045] Figure 2 A schematic diagram of detecting the size of the cover surface welding bead by using a detection tool in an embodiment is shown.

[0046] In some embodiments, in steps 1), 2), and 3), during welding, the pipe wall side and the groove side are welded respectively, and then pushed to the center of the welding seam, and the last welding seam is set in the middle of the welding seam to better reduce the cumulative stress.

[0047] When the welding bead arrangement and welding sequence are unreasonable, the stress level of each region will be increased. When a reasonable welding bead arrangement and welding sequence are adopted, the stress of each region will be at a reasonable level. As known, the welding process is a process of repeated thermal cycles, and the corresponding melting-solidification-shrinkage is also a process of repeated cycles, which will produce the effect of stress and strain accumulation and superposition, thereby making the first welded region bear the maximum stress. In order to reduce this adverse process, we control the deformation by reducing the number of cycles. According to the structural analysis, the welding operation of the pipe wall side and the groove side needs corresponding space to ensure the welding quality, and the pipe wall side and the groove side are regions with relatively large stress, respectively. Whether welding from the pipe wall side to the groove side or welding from the groove side to the pipe wall side, the thermal cycle process cannot be reduced. Therefore, referring to Figure 3In this application, the welding operation is divided into two parts: first, welding is performed separately on the pipe wall side and the bevel side; then, the welding is advanced towards the center of the weld, with the final weld placed in the middle of the weld. This reduces the number of thermal cycles for the pipe wall side and the bevel side welds by half, thereby reducing accumulated stress.

[0048] In some embodiments, during steps 1), 2), and 3), a cooling and anti-deformation fixture is connected below the workpiece during welding. By improving the cooling effect, the weld is prevented from overheating, thereby reducing thermal stress and helping to reduce hot cracks and welding defects.

[0049] Due to structural reasons, the filler amount of the J-shaped weld varies significantly in different areas, inevitably causing welding deformation. If left uncontrolled, this can adversely affect the smooth movement of the control rod drive mechanism. Therefore, this invention utilizes a cooling and anti-deformation fixture to remove the heat generated during welding, thereby controlling deformation.

[0050] like Figure 4 As shown, in one embodiment of the present invention, a water-cooled anti-deformation fixture is installed below the welded part. Its bottom is designed with a water inlet channel, which is connected to an external water pipe via a pipeline. Water flows into the interior of the fixture cavity and out through small holes distributed around the inner wall of the fixture. This increases the contact area between the water flow and the welded workpiece, improving the cooling effect; it also reduces the water flow pressure, lowering the fixture's sealing pressure and preventing water leakage from affecting the weld; and the inlet and outlet water pipes both enter and exit from the bottom of the workpiece, freeing up space at the top of the workpiece and facilitating welding operations.

[0051] An embodiment of this application also provides a welded joint formed by the above-described welding process.

[0052] One embodiment of this application also provides a reactor pressure vessel, including a welded joint formed by the above-described welding process.

[0053] Example 1

[0054] See Figure 5 A J-type weld joint for a reactor pressure vessel is provided, which is welded using shielded metal arc welding with nickel-based 690 welding material. The welding process includes the following steps:

[0055] Phase 1: Pipe assembly; Prepare the top cover and through pipes, assemble them, and clean them after assembly;

[0056] Phase 2: Pre-welding preparation; including installing water-cooled anti-deformation fixtures, determining weld boundaries, and cleaning and protecting the weld bead before welding; the anti-deformation fixtures are designed with a water inlet channel at the bottom, which is connected to an external water pipe via a pipeline. Water flows into the interior of the fixture cavity and flows out from small holes distributed around the inner wall of the fixture.

[0057] Stage 3: root welding and inspection; root welding is performed by using a 2.4 specification welding rod and a current of 62A-68A; during each welding, 2 circles are turned, and after 2 seconds, the arc is lifted upward to fill back; after each welding, the arc area is polished to a depth of 1.2mm-1.8mm; after welding, PT inspection is performed;

[0058] Stage 4: filling welding and inspection; a 2.4 specification (pipe wall) is used, and a current of 62A-68A is used; a 3.2 specification is used, and a current of 90A-98A is used; during each welding, 2 circles are turned, and after 2 seconds, the arc is lifted upward to fill back; after each welding, the arc area is polished to a depth of 1.2mm-1.8mm;

[0059] PT inspection is performed every three layers of welding

[0060] Stage 5: cover (cover) welding and post-weld polishing and forming;

[0061] Cover welding uses a 2.4 specification (pipe wall) and a current of 62A-68A; a 3.2 specification is used, and a current of 90A-98A is used; during each welding, 2 circles are turned, and after 2 seconds, the arc is lifted upward to fill back; after each welding, the arc area is polished to a depth of 1.2mm-1.8mm; during cover welding, a detection tool is used at any time to determine the size of the welding bead, and it is ensured that the shape meets the requirements.

[0062] Stage 6: final welding polishing and forming.

[0063] The welding method of Example 1 has been used to complete the welding of one reactor pressure vessel (107 pipes), and the post-welding inspection results completely meet the requirements, and the number of PT displays after welding is greatly reduced.

[0064] The present application provides a welding process for reducing the PT display of the J-shaped weld of the reactor pressure vessel by comprehensively and systematically analyzing the factors affecting the welding quality of the J-shaped weld and formulating countermeasures. By using the welding process of the present application, the operation conditions of the welder are greatly improved, the manufacturing cycle is shortened by 50%, the welding material consumption is reduced by 20%, the PT display on the welding surface is reduced by 85%, and the linear display (crack pit) is reduced by more than 95%, and the welding quality is greatly improved.

[0065] The present application is a welding process for reducing the display of J-shaped welds PT of a reactor pressure vessel, which makes systematic test verification from the aspects of the selection of welding material specifications, the optimization of welding parameters and the rationalization of welding pass arrangement for the welding of J-shaped welds of a reactor pressure vessel, determines the optimal welding parameters, the most reasonable welding pass arrangement and the welding material specifications that can simultaneously consider welding quality and production efficiency, changes the control of welding quality by experience of welders into the control by solidification process, and greatly improves the welding quality. Through a large number of tests, a nickel-based alloy electrode arc welding stopping method is determined as follows: after filling the crater, the stopping is lifted upward after 2 seconds of 2 turns. The depth of the stopping crack when the nickel-based electrode is welded in this way is determined, so that the grinding depth of the stopping area is 1.2mm-1.8mm. The removal amount of the stopping crack in the welding process can be quantitatively determined, and the grinding range and grinding depth in the welding process are guided and supported by data, which changes the existing uncontrollable into quantitative determination; and a detection tool is used to assist the welder in arranging the welding pass and accurately control the welding amount, avoiding the problems of insufficient welding or excessive welding, effectively guiding the production process to do it right and do it well at one time; meanwhile, a deformation prevention tool is used to improve the cooling effect, avoid the influence of tool pipeline on the operation of the welder, and avoid the influence of cooling water leakage on the weld quality, so as to improve the overall welding quality.

[0066] The technical features of the above-mentioned embodiments can be combined arbitrarily, and in order to make the description simple, all possible combinations of the technical features in the above-mentioned embodiments are not described, however, as long as the combination of the technical features does not exist contradictory, it should be considered as the scope of the present application.

[0067] The above-mentioned embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as the limitation of the scope of the patent. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which belong to the protection scope of the present application. Therefore, the protection scope of the present application patent should be subject to the appended claims.

Claims

1. A welding process to reduce the appearance of J-groove welds in a reactor pressure vessel, characterized in that, The welding adopts shielded metal arc welding, nickel-based 690 welding material, and comprises the following steps: 1) root pass welding: adopting a welding rod with a diameter of 2.4, and a welding current of 62A-68A; 2) filling pass welding: adopting a welding rod with a diameter of 2.4 or 3.2, wherein for the welding rod with a diameter of 2.4, the welding current is 62A-68A; and for the welding rod with a diameter of 3.2, the welding current is 90A-98A; 3) cover pass welding: adopting a welding rod with a diameter of 2.4 or 3.2, wherein for the welding rod with a diameter of 2.4, the welding current is 62A-68A; and for the welding rod with a diameter of 3.2, the welding current is 90A-98A; and a detection tool is used to determine the size of the welding pass during welding; In the above steps 1), 2) and 3), a circle-arc collection method is adopted, and the arc collection mode comprises: adopting a rotation of 2 circles when each welding pass is collected, and the arc is collected upward after 2 seconds; After each welding pass is completed, the arc collection area is polished, and the polishing depth is 1.2mm-1.8mm; During welding, the welding of the pipe wall side and the groove side is respectively carried out first, then the welding is respectively pushed to the center of the weld, and the last welding pass is set in the middle of the weld; and during welding, the welding piece is also connected with a cooling anti-deformation tool.

2. A welded joint, characterized by The welding process is welded by using the welding process as claimed in claim 1.

3. A reactor pressure vessel characterized by, The welded joint comprises the welded joint as claimed in claim 2.

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