Seal welding method for tube plate of outward-extending tube of nuclear power spent assembly

Abstract

The invention belongs to the technical field of welding, and particularly relates to a sealing welding method for a nuclear power spent assembly overhanging type pipe and pipe plate. Positioning expansion is carried out by adopting a mechanical method; automatic TIG helium arc welding is adopted for welding, helium and argon mixed gas serves as welding shielding gas, a cerium tungsten electrode serves as an electrode, and all-position rotary welding is conducted after arc starting. Spot welding is replaced by mechanical expansion, and almost no gap exists between the tube and the tube plate, so that the welding method is more stable; according to the method, the welding quality is stable (the minimum leakage drift diameter of the root is stable, and welding defects do not exist), the welding efficiency is high (the welding efficiency is two times that of conventional argon arc welding), and the method has important significance on nuclear power outward-extending pipe and pipe plate seal welding.

Description

Technical Field

[0001] The invention belongs to the technical field of welding, and in particular relates to a sealing welding method for an extended tube sheet of a nuclear power spent component. Background Art

[0002] As a clean energy with low carbon emissions, mature technology, safety and high efficiency, nuclear energy is gaining more and more attention in the face of global warming. Fast neutron reactors (abbreviated as "fast reactors") are the preferred reactor type for the world's fourth-generation advanced nuclear energy systems, with outstanding advantages such as improved uranium resource utilization, economic safety, and less radioactive waste. Stainless steel spent fuel assemblies are spent fuel retired from fast reactors, with strong radioactivity and wrapped in hard stainless steel. The safety and cost issues of their storage and the recycling and reuse of nuclear elements have become important factors restricting the development of nuclear power. Therefore, the "closed cycle" treatment method of stainless steel spent fuel assemblies has been adopted by the world's nuclear powers.

[0003] One side of the stainless steel spent fuel assembly has multiple protruding tube-tube sheet welded joints. In order to achieve the "closed circulation" of the stainless steel spent fuel assembly, the welding requirements for its joints include: 1) the minimum leakage channel size ≥ 1.33mm; 2) the weld should be free of cracks; 3) the tube sheet and the tube wall are completely fused; 4) the weld penetrates 0.4mm into the root of the joint; 5) the pores must not reduce the thickness of the fillet weld to below the required minimum leakage channel thickness.

[0004] At present, the welding joints of the extended tube and tube sheet of the stainless steel spent fuel assembly usually adopt the automatic argon arc process. In order to ensure the root penetration and the minimum leakage diameter size of the root to reach a certain size, two-layer welding is usually adopted. The first layer is self-melting without adding wire to ensure the root penetration, and the second layer is welded with wire to ensure the minimum leakage diameter size of the root.

[0005] However, in actual production, due to the difference in coaxiality between the welding gun and the workpiece, the fluctuation of the distance between the tungsten electrode and the side wall of the pipe mouth, the change in the state of the tungsten electrode tip, the pipe wall thickness, the fluctuation of the gap between the pipe and the tube sheet, and the shallow penetration of argon arc welding itself, it often leads to incomplete penetration of the root or the weld penetration of the root does not reach 0.4mm, unstable welding quality (the minimum leakage diameter size of the root is poorly stable, and there are many welding defects), and low welding efficiency. Summary of the invention

[0006] The purpose of the present invention is to provide a method for sealing the tube sheet of an extended tube of a nuclear power spent component. The method provided by the present invention not only has stable welding quality (the minimum leakage diameter size at the root is stable and there are no welding defects), but also has high welding efficiency, which is of great significance for sealing the tube sheet of an extended tube of a nuclear power spent component.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] The present invention provides a sealing welding method for an extended tube sheet of a nuclear power spent assembly, comprising the following steps:

[0009] Step 1) mechanically positioning the expansion;

[0010] Step 2) automatic TIG helium arc welding is used for welding, the welding shielding gas is a helium-argon mixed gas, the electrode is a cerium tungsten electrode, and full-position rotary welding is performed after arcing;

[0011] The parameters of the all-position rotary welding include: peak current of 90-110A, peak time of 50-100ms, base current of 40-60A, base time of 150-200ms, welding speed of 100-120mm / min, wire feeding speed of 0.3-0.4m / min, welding angle of 0-375°, and arc length of 1.5-2.2mm.

[0012] Preferably, the parameters of the all-position rotary welding also include: the distance between the cerium tungsten electrode and the tube wall is 1.5 to 1.8 mm;

[0013] When the welding angle is 0-5°, the arc length is 1.5-1.7mm.

[0014] When the welding angle is 5-345°, the arc length is 1.6-2mm.

[0015] When the welding angle is 345-360°, the arc length is 1.7-2.1mm.

[0016] When the welding angle is 360-375°, the arc length is 1.7-2.2 mm.

[0017] Preferably, the conditions for positioning expansion include: the extension length of the pipe mouth is 3.5-4 mm, the expansion length is 18-23 mm, and the expansion force is 6 Nm.

[0018] Preferably, the helium-argon mixed gas includes helium and argon, and the volume ratio of helium to argon is 3:1; the flow rate of the helium-argon mixed gas during welding is 13-15 L / min.

[0019] Preferably, the diameter of the cerium tungsten electrode is 3.2 mm, the tip angle is 30-35°, and the diameter of the tip platform is 0.3-0.5 mm.

[0020] Preferably, the conditions for arc starting include: the arc starting point is located in the 10:00-11:00 direction, the welding gun angle is 15°, the cerium tungsten electrode contacts the workpiece and is lifted 1.7mm, the arc starts after 10s of gas supply, the pre-melting current after arc starting is 80A, the welding gun stops in place for pre-melting for 0.5s before starting wire feeding, and waits for 1.2s after wire feeding to start the full-position rotary welding.

[0021] Preferably, the material of the tube sheet is SA-182F316L, with a wall thickness of 60 mm; the diameter of the tube sheet drilling hole is 20.2-20.3 mm, and the tube sheet hole bridge distance is 6.75 mm.

[0022] Preferably, the material of the tube is SA-213TP316I, the diameter is 20 mm, and the wall thickness is 1.8 to 2.2 mm.

[0023] Preferably, the material of the welding wire used for the all-position rotary welding is 316L, and the diameter is 0.9 mm.

[0024] Preferably, it also includes: when the welding angle in step 2) reaches 375°, the current begins to decay, and the decay is that the current decays to 5A within 8 seconds, and the timing starts from the moment when the current begins to decay, and the wire feeding is continued for 0.5 seconds; when the current is turned off, the gas supply is continued for 10 seconds.

[0025] The present invention provides a sealing welding method for an extended tube sheet of a nuclear power spent assembly, comprising the following steps:

[0026] Step 1) mechanical method is used for positioning expansion; Step 2) automatic TIG helium arc welding is used for welding, the welding shielding gas is a helium-argon mixed gas, the electrode is a cerium tungsten electrode, and full-position rotary welding is performed after arcing; the parameters of the full-position rotary welding include: peak current of 90-110A, peak time of 50-100ms, base current of 40-60A, base time of 150-200ms, welding speed of 100-120mm / min, wire feeding speed of 0.3-0.4m / min, welding angle of 0-375°, and arc length of 1.5-2.2mm. Because the positioning spot welding will cause a gap between the tube and the tube sheet, and it is difficult to ensure the consistency of the gap size, and the gap can easily lead to defects such as root incomplete fusion and incomplete penetration. The present invention adopts mechanical expansion instead of spot welding, and there is almost no gap between the tube and the tube sheet, so the welding method is more stable. The results of the embodiment show that: 40 macroscopic metallographic minimum leakage diameters: 1.6mm 4 pieces, 1.7mm 34 pieces, 1.8mm 2 pieces. At the same time, the present invention adopts a helium arc one-layer plus wire welding method, the helium arc has a large melting depth, and the one-layer plus wire welding not only ensures the root penetration, but also improves the welding efficiency by 1 times compared with argon arc welding, and effectively avoids the burning tube mouth defects caused by the accumulation of heat from continuous two layers of welding and the appearance of oxidation color on the inner wall of the root heat exchange tube. In summary, the method provided by the present invention not only has stable welding quality (the minimum leakage diameter size of the root is stable and there are no welding defects), but also has high welding efficiency (the welding efficiency is twice that of conventional argon arc welding), which is of great significance for the sealing welding of nuclear power extension tubes and tube sheets. The results of the embodiments show that the sealing welding method for the extended tube sheet of the nuclear power spent assembly provided by the present invention has a golden gas protection effect, the tube and the tube sheet are well fused, the weld width and the excess height are uniform as a whole, no cracks are found at the arc closing point, there is no burnt tube mouth defect, and no oxidation color is found on the inner wall of the tube mouth. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the weld structure in the present invention;

[0028] Figure 2 This is a physical picture of the welding joint in the present invention;

[0029] Figure 3 It is a schematic diagram of the minimum leakage path of welding in the present invention. DETAILED DESCRIPTION

[0030] The present invention provides a sealing welding method for an extended tube sheet of a nuclear power spent assembly, comprising the following steps:

[0031] Step 1) mechanically positioning the expansion;

[0032] Step 2) automatic TIG helium arc welding is used for welding, the welding shielding gas is a helium-argon mixed gas, the electrode is a cerium tungsten electrode, and full-position rotary welding is performed after arcing;

[0033] The parameters of the all-position rotary welding include: peak current of 90-110A, peak time of 50-100ms, base current of 40-60A, base time of 150-200ms, welding speed of 100-120mm / min, wire feeding speed of 0.3-0.4m / min, welding angle of 0-375°, and arc length of 1.5-2.2mm.

[0034] In the present invention, unless otherwise specified, all preparation raw materials / components are commercially available products well known to those skilled in the art.

[0035] The present invention adopts mechanical method to carry out positioning expansion. In the present invention, the material of the tube sheet is preferably stainless steel, specifically preferably SA-182F316L, and the wall thickness is preferably 60mm (such as Figure 1 The diameter of the tube sheet hole is preferably 20.2-20.3 mm, and the distance between the tube sheet hole bridges is preferably 6.75 mm. The material of the tube is preferably stainless steel, specifically SA-213TP316I, and the diameter is preferably 20 mm (such as Figure 1 The wall thickness is preferably 1.8 to 2.2 mm, and more preferably 2 mm (as shown in the figure). Figure 1 The present invention preferably pre-cleans the tube sheet or the tube. The pre-cleaning preferably includes: cleaning the tube holes of the tube sheet or the surface of the tube with a cleaning agent, and the cleaning agent is preferably alcohol or acetone. The present invention preferably removes oxides, oil stains and other harmful impurities on the tube holes of the tube sheet and the surface of the tube by pre-cleaning.

[0036] In the present invention, the positioning expansion conditions preferably include: the extension length of the tube mouth is preferably 3.5 to 4 mm (such as Figure 1 The expansion length is preferably 18-23 mm, and the expansion force is preferably 6 Nm. In the present invention, the extended tube-to-sheet welding is easy to burn the tube orifice, so the extended length of the tube orifice is often required to be greater than 4.5 mm. The method provided by the present invention has a lower limit of 3.5 mm for the extended length of the tube orifice, which greatly increases the process window and reduces the assembly accuracy requirements.

[0037] After mechanical positioning and expansion, the present invention adopts automatic TIG helium arc welding for welding, the welding shielding gas is a helium-argon mixed gas, the electrode is a cerium tungsten electrode, and full-position rotary welding is performed after arc starting; the parameters of the full-position rotary welding include: a peak current of 90 to 110A, a peak time of 50 to 100ms, specifically 100ms, a base current of 40 to 60A, a base time of 150 to 200ms, specifically 200ms, a welding speed of 100 to 120mm / min, a wire feeding speed of 0.3 to 0.4m / min, a welding angle of 0 to 375°, and an arc length of 1.5 to 2.2mm.

[0038] In the present invention, for argon arc welding, the current is constant, the arc length is constant, and the flow rate fluctuation of the welding shielding gas argon will not cause the fluctuation of the arc voltage, so the welding heat input is constant. However, for helium arc welding, the current is constant, the arc length is constant, and the flow rate fluctuation of the welding shielding gas helium will cause a significant fluctuation of the arc voltage, thereby affecting the welding heat input.

[0039] In the present invention, the material of the welding wire used for the all-position rotary welding is preferably 316L, and the diameter is preferably 0.9mm. The helium-argon mixed gas preferably includes helium and argon, and the volume ratio of helium and argon is preferably 3:1; the flow rate of the helium-argon mixed gas during welding is preferably 13-15L / min. The present invention uses helium and argon with a volume ratio of preferably 3:1 as welding shielding gas, and the welding penetration is large. Only one circle (one layer) of welding is required to meet the welding quality requirements, while ordinary argon arc welding requires two circles (two layers) of welding, and the welding quality is also unstable. The diameter of the cerium tungsten electrode The preferred diameter is 3.2 mm, the preferred angle is 30-35°, and the preferred diameter of the tip platform is 0.3-0.5 mm. The present invention can avoid excessive helium arc energy and long-term welding leading to burning of the tip of the cerium tungsten electrode by controlling the parameters of the diameter, the tip angle, and the tip platform diameter of the cerium tungsten electrode.

[0040] In the present invention, the conditions for arc starting preferably include: the arc starting point is preferably located at 10:00-11:00, the welding gun angle is preferably 15°, the cerium tungsten electrode is preferably lifted 1.7mm when contacting the workpiece, the arc is started 10s after gas supply, the pre-melting current after arc starting is preferably 80A, the welding gun stops in place and preferably pre-melts for 0.5s before starting wire feeding, and after wire feeding, it is preferably necessary to wait for 1.2s before starting the full-position rotary welding.

[0041] In the present invention, the parameters of the all-position rotary welding preferably also include: the distance between the cerium tungsten electrode and the tube wall is preferably 1.5-1.8 mm.

[0042] When the welding angle is 0-5°, the arc length is preferably 1.5-1.7 mm.

[0043] When the welding angle is 5-345°, the arc length is preferably 1.6-2 mm.

[0044] When the welding angle is 345-360°, the arc length is preferably 1.7-2.1 mm.

[0045] When the welding angle is 360-370°, the arc length is preferably 1.7-2.2 mm.

[0046] When the welding angle is 370-375°, the arc length is preferably 1.7-2.2 mm.

[0047] In the present invention, the sealing welding method for the extended tube and tube sheet of the nuclear power spent component also includes: when the welding angle of the all-position rotary welding reaches 375°, the current begins to decay, and the decay is preferably that the current decays to 5A within 8 seconds, and the timing starts from the moment when the current begins to decay, and preferably the wire feeding is continued for 0.5 seconds; when the current is turned off, the present invention preferably continues to supply gas for 10 seconds.

[0048] In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0049] Example 1

[0050] Figure 1 It is a schematic diagram of the weld structure in Example 1 of the present invention. This embodiment provides a method for sealing the tube sheet of an extended tube of a nuclear power spent assembly, wherein the tube sheet material is SA-182F316L, the wall thickness is 60 mm, the tube diameter is 20 mm, the wall thickness is 2 mm, the hole bridge distance is 6.75 mm, the material is SA-213TP316I, the tube sheet drilling diameter is 20.2 mm-20.3 mm, the welding wire material is 316L, the welding wire diameter is 0.9 mm, and automatic TIG helium arc welding is adopted.

[0051] Step 1) Use alcohol or acetone to remove oxides, oil stains and other harmful impurities on the stainless steel pipe holes and the surface of the stainless steel pipe.

[0052] Step 2) Use mechanical method to position and expand, the extension length of the pipe mouth is 3.5-4mm, the expansion length is 18-23mm, and the expansion force is 6Nm.

[0053] Step 3) The welding shielding gas is a helium-argon mixed gas, in which the volume percentage of helium is 75% and the volume percentage of argon is 25%. The flow rate of the helium-argon mixed gas during welding is 13-15 L / min.

[0054] Step 4) Use Cerium tungsten electrode, the tip angle of cerium tungsten electrode is 30-35°, and the platform diameter of cerium tungsten electrode is 0.3-0.5mm, so as to avoid the burning of the tungsten electrode tip due to high helium arc energy and long-term welding.

[0055] Step 5) The arc starting point is at 10:00-11:00, the welding gun angle is 15 degrees, the tungsten electrode contacts the workpiece and is lifted 1.7mm, the arc is started after 10s of gas supply, the pre-melting current after arc starting is 80A, the welding gun stops in place for pre-melting for 0.5s and then starts wire feeding, and then waits for another 1.2s before starting full-position rotary welding.

[0056] The welding parameters in step 6) are shown in Table 1.

[0057] Table 1 Welding parameters of all-position rotary welding

[0058]

[0059] Step 7. After welding to 375°, the current begins to decay gradually and decays to 5A within 8s. From the moment the current begins to decay, continue to feed the wire for 0.5s to ensure that there are no cracks at the end of the arc. Continue to feed gas for 10s after the current stops.

[0060] Observe the actual picture of the integral welded joint prepared in this embodiment. Figure 2 As shown: the gas protection effect is golden yellow, the tube and the tube sheet are well fused, the weld width and the excess height are uniform as a whole, no cracks are found at the arc closing point, there are no burnt tube mouth defects, and no oxidation color is found on the inner wall of the tube mouth.

[0061] After welding, the following tests are performed:

[0062] 1. Appearance inspection: The tube-tube sheet joints are inspected in accordance with the requirements of ASME Volume IX. The welds are well formed, without cracks or pores, and the heat exchange tubes have no obvious deformation.

[0063] 2. Metallographic inspection test method: ASTM E3-2017; ASTM E407-2015: (P&C)-2018-0002Rev.2;

[0064] 40 samples were taken at the 12H, 3H, 6H, and 9H positions perpendicular to the welding direction, and no welding defects were found. The minimum leakage diameters were: 4 pieces with 1.6mm, 34 pieces with 1.7mm, and 2 pieces with 1.8mm, all of which were larger than the minimum leakage diameter requirement of 1.33mm. Figure 3 is a schematic diagram of the minimum leakage diameter. Figure 3 The 3.98mm marked in the figure is the minimum leakage diameter.

[0065] 3. Intergranular corrosion method: GB / T4334-2008 "E" method; (P&C)-2018-0002Rev.2;

[0066] No corrosion cracks occurred in specimens 41# and 42#.

[0067] 4. Helium leak detection report

[0068] A total of 19 samples, single tube leakage rate <1×10 -8 Pa·m / s, in compliance with the single tube leakage rate <1×10 -7 Technical requirements for Pa·m / s.

[0069] 5. Penetration testing

[0070] Acceptance criteria: XPKLQ-MNJ-NDE-PTY / A, no defects were found within 5mm of the pipe mouth weld and the heat affected zones on both sides.

[0071] From the above examples, it can be seen that the present invention uses mechanical expansion instead of spot welding, and there is almost no gap between the tube and the tube sheet, so the welding method is more stable. The results of the examples show that: 40 macroscopic metallographic minimum leakage diameters: 1.6mm 4 pieces, 1.7mm 34 pieces, 1.8mm 2 pieces. At the same time, the present invention adopts a helium arc one-layer plus wire welding method, the helium arc has a large melting depth, and the one-layer plus wire welding not only ensures the root penetration, but also improves the welding efficiency by 1 times compared with argon arc welding, and effectively avoids the burning tube mouth defects caused by the accumulation of heat from continuous 2 layers of welding and the appearance of oxidation color on the inner wall of the root heat exchange tube. In summary, the method provided by the present invention not only has stable welding quality (the minimum leakage diameter size of the root is stable and there are no welding defects), but also has high welding efficiency (the welding efficiency is twice that of conventional argon arc welding), which is of great significance for the sealing welding of nuclear power extension tubes and tube sheets. The results of the embodiments show that the sealing welding method for the extended tube sheet of the nuclear power spent assembly provided by the present invention has a golden gas protection effect, the tube and the tube sheet are well fused, the weld width and the excess height are uniform as a whole, no cracks are found at the arc closing point, there is no burnt tube mouth defect, and no oxidation color is found on the inner wall of the tube mouth.

[0072] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for sealing and welding the tube sheet of an extended tube of a nuclear power spent component, characterized in that: The following steps are involved: Step 1) mechanically positioning the expansion; Step 2) automatic TIG helium arc welding is used for welding, the welding shielding gas is a helium-argon mixed gas, the electrode is a cerium tungsten electrode, and full-position rotary welding is performed after arcing; The parameters of the all-position rotary welding include: peak current of 90-110A, peak time of 50-100ms, base current of 40-60A, base time of 150-200ms, welding speed of 100-120mm / min, wire feeding speed of 0.3-0.4m / min, welding angle of 0-375°, and arc length of 1.5-2.2mm.

2. The sealing welding method for the extended tube sheet of a nuclear power spent assembly according to claim 1 is characterized in that: The parameters of the all-position rotary welding also include: the distance between the cerium tungsten electrode and the tube wall is 1.5 to 1.8 mm; When the welding angle is 0-5°, the arc length is 1.5-1.7mm. When the welding angle is 5-345°, the arc length is 1.6-2mm. When the welding angle is 345-360°, the arc length is 1.7-2.1mm. When the welding angle is 360-375°, the arc length is 1.7-2.2 mm.

3. The sealing welding method for the extended tube sheet of a nuclear power spent assembly according to claim 1 or 2, characterized in that: The conditions for positioning expansion include: the extension length of the pipe mouth is 3.5-4 mm, the expansion length is 18-23 mm, and the expansion force is 3-6 Nm.

4. The sealing welding method for the extended tube sheet of a nuclear power spent assembly according to claim 1 or 2, characterized in that: The helium-argon mixed gas includes helium and argon, and the volume ratio of the helium and argon is 3:1; the flow rate of the helium-argon mixed gas during welding is 13-15 L / min.

5. The sealing welding method for the extended tube sheet of a nuclear power spent assembly according to claim 1 or 2, characterized in that: The diameter of the cerium tungsten electrode is 3.2 mm, the tip angle is 30-35°, and the diameter of the tip platform is 0.3-0.5 mm.

6. The sealing welding method for the extended tube sheet of a nuclear power spent assembly according to claim 1 or 2, characterized in that: The arc starting conditions include: the arc starting point is located in the 10:00-11:00 direction, the welding gun angle is 15°, the cerium tungsten electrode contacts the workpiece and is lifted 1.7mm, the arc is started after 10s of gas supply, the pre-melting current after arc starting is 80A, the welding gun stops in place for pre-melting for 0.5s before starting wire feeding, and after wire feeding, wait for 1.2s to start the full-position rotary welding.

7. The sealing welding method for the extended tube sheet of a nuclear power spent assembly according to claim 1 is characterized in that: The material of the tube sheet is SA-182F316L, and the wall thickness is 60 mm; the diameter of the tube sheet drilling hole is 20.2-20.3 mm, and the distance between the tube sheet hole bridges is 6.75 mm.

8. The sealing welding method for the extended tube sheet of a nuclear power spent assembly according to claim 1 or 7, characterized in that: The material of the tube is SA-213TP316I, the diameter is 20 mm, and the wall thickness is 1.8-2.2 mm.

9. The sealing welding method for the extended tube sheet of a nuclear power spent assembly according to claim 1 or 2, characterized in that: The material of the welding wire used in the all-position rotary welding is 316L, and the diameter is 0.9 mm.

10. The sealing welding method for the extended tube sheet of a nuclear power spent assembly according to claim 1 or 2, characterized in that: Also includes: When the welding angle in step 2) reaches 375°, the current begins to decay, and the decay is that the current decays to 5A within 8 seconds. The timing starts from the moment when the current begins to decay, and the wire feeding is continued for 0.5 seconds; when the current is turned off, the gas supply is continued for 10 seconds.

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