Method for improving annealing straightness and outer diameter of nuclear zirconium alloy cladding tube

Abstract

The present application relates to the technical field of pipe annealing, and discloses a method for improving straightness and outer diameter of nuclear zirconium alloy cladding pipe after annealing, which comprises the following steps: step one, installing an elastic constraint structure on the inner wall of an annealing tool; step two, arranging the pipe to be annealed into the annealing tool with the elastic constraint structure through a specific arrangement method; step three, annealing the arranged annealing tool in a vacuum annealing furnace; and step four, removing the pipe to be annealed from the annealing tool after annealing. The elastic constraint structure in the present application overcomes the shortcomings of rigid constraint between the pipes and between the pipes and the tool in the existing annealing tool. The thermal expansion between the pipes is absorbed by the elastic constraint structure during the annealing process, and the local outer diameter size change caused by the rigid contact between the pipes and the tool is reduced. The straightness and outer diameter size change after annealing in the present application are obviously improved compared with the existing annealing method.

Description

Technical Field

[0001] This invention relates to the field of pipe annealing technology, and in particular to a method for improving the straightness and outer diameter of nuclear-grade zirconium alloy clad pipes during annealing. Background Technology

[0002] To meet the harsh operating conditions within nuclear reactors, nuclear-grade zirconium alloy cladding tubes are typically formed using a multi-pass cold rolling process on a cold rolling mill. This forming method is characterized by large deformation per pass (approximately 60-80%) and high production efficiency. However, this large deformation generates significant stress; therefore, annealing is performed after each rolling pass to relieve stress and achieve a uniform microstructure, facilitating subsequent processing and ensuring good material properties.

[0003] In reality, zirconium alloy tubing undergoes stress release during annealing, and the straightness and local outer diameter of the tubing deteriorate due to thermal expansion and compression between the tubing sections. This is particularly true for clad tubing with small outer diameters (≤15mm). Poor straightness after annealing can affect subsequent straightening processes, leading to insufficient straightness or hydride content, ultimately significantly impacting the safety of the clad tubing in-pile service. Furthermore, variations in the local outer diameter of the clad tubing can cause non-destructive testing to fail to meet technical specifications, thus affecting the yield and economic efficiency of clad tubing production. Currently, rigid annealing fixtures or metal sleeves are commonly used for annealing shelled pipes. Rigid annealing fixtures, lacking elastic constraints, are prone to causing deterioration in the outer diameter and straightness of the pipes after annealing. Metal sleeve annealing, due to the limited number of shelled pipes loaded inside the sleeve, results in a smaller change in the outer diameter. However, since there are no constraints between the pipes, the straightness is often poor. Furthermore, annealing a batch of material requires preparing multiple sleeves, which is inconvenient for loading and unloading, has a long loading time, a small loading capacity, and poor economic efficiency.

[0004] Therefore, in the field of zirconium alloy clad tube annealing, there is an urgent need for a new method for annealing zirconium alloy clad tubes that is convenient for material loading and unloading, economical, and easy to maintain with tooling. At the same time, it can also improve the straightness and outer diameter of the clad tubes after annealing. Summary of the Invention

[0005] To address at least one of the problems existing in the above-mentioned background art, the present invention provides a method for improving the straightness and outer diameter of nuclear zirconium alloy cladding tubing after annealing.

[0006] The present invention provides a method for improving the straightness and outer diameter of nuclear-grade zirconium alloy cladding tubing after annealing, comprising the following four steps:

[0007] Step 1: Install the elastic constraint structure onto the inner wall of the annealing fixture;

[0008] Step 2: Apply material to the tube to be annealed using a specific material application method, and then apply the material to the annealing fixture with an elastic constraint structure.

[0009] Step 3: Anneal the fabric in a vacuum annealing furnace;

[0010] Step 4: After annealing, remove the tube to be annealed from the annealing fixture.

[0011] Furthermore, in the aforementioned method for improving the straightness and outer diameter of annealed zirconium alloy cladding tubing for nuclear applications, the elastic constraint structure in step one uses heat-resistant stainless steel mesh. The entire mesh is woven and then pressed into a wave-shaped structure, resulting in a clean surface, smooth and complete waves, without deformation or steel filings, and without any uneven or missing weaves. The annealing fixture is made of heat-resistant stainless steel and includes a bottom bracket and a material boat. When the elastic constraint structure is installed on the inner wall of the annealing fixture, the stainless steel mesh must be tightly fitted to the sides and bottom plate of the material boat, and there should be no protrusions larger than the first preset dimension.

[0012] Furthermore, in the above-mentioned method for improving the straightness and outer diameter of the annealed zirconium alloy cladding tube for nuclear applications, the specific material distribution method in step two is a combination of a pad tube and a tube to be annealed. The pad tube is distributed at the bottom and top, and the tube to be annealed is placed in the middle of the pad tube. The pad tube and the tube to be annealed are of the same material and specifications. The pad tube is longer than the tube to be annealed. The pad tube should be in a recrystallized state, and the straightness should be ≤0.5 / 1000mm.

[0013] Furthermore, in the above-mentioned method for improving the straightness and outer diameter of annealed zirconium alloy cladding tubing for nuclear applications, step three involves annealing in a vacuum annealing furnace, including: an external feeding trolley delivering the annealing fixture to the cooling chamber; an internal material car drive device delivering the annealing fixture to the heating chamber for vacuum or argon heating; transferring the annealing fixture into the cooling chamber for vacuum or argon cooling; and an external feeding trolley pulling the annealing fixture out onto an external fixture platform.

[0014] Furthermore, in the above-mentioned method for improving the straightness and outer diameter of nuclear-grade zirconium alloy cladding tubing during annealing, the annealing conditions in the vacuum annealing furnace are: the ultimate vacuum in the heating and cooling chambers is ≤8.0×10⁻⁶. -4 Pa, the working vacuum of the heating and cooling chambers is ≤5.0×10 Pa. -3 Pa, maximum heating temperature 900℃, temperature control accuracy ≤±1℃, temperature uniformity ≤±5℃, uniform temperature zone ≥10m.

[0015] Furthermore, the above-mentioned method for improving the straightness and outer diameter of the annealed zirconium alloy cladding tube for nuclear applications also includes: periodically identifying changes in the straightness and outer diameter of the cladding tube, and correcting or replacing the cladding tube when the straightness is poor or the outer diameter is deformed to a value greater than a second preset dimension.

[0016] Furthermore, in the above-mentioned method for improving the straightness and outer diameter of the annealed zirconium alloy cladding tube for nuclear use, the bottom bracket is a square tube structure made of heat-resistant stainless steel. During assembly, the crossbeams and longitudinal beams of the bottom bracket are assembled together, and the crossbeams and longitudinal beams of the bottom bracket are welded together using argon arc welding.

[0017] Furthermore, in the above-mentioned method for improving the straightness and outer diameter of the annealed zirconium alloy cladding tube for nuclear applications, the boat is formed by stamping, has a hexagonal cross-section, and an open design at the top.

[0018] Furthermore, in the above-mentioned method for improving the straightness and outer diameter of the annealed zirconium alloy cladding tube for nuclear applications, the material boat is installed on the bottom bracket.

[0019] The beneficial effects of this invention are as follows: the annealing fixture of this invention facilitates cleaning inside the annealing furnace, and the material boat can be hoisted as a whole, which has the advantage of strong maintainability; this invention not only improves the straightness and size of the tubes after annealing and reduces the consumption of auxiliary materials, but also overcomes the disadvantage of rigid constraints between tubes and between tubes and fixtures in existing annealing fixtures with elastic constraint structure. During the annealing process, the thermal expansion between tubes is absorbed by the elastic constraint structure, which reduces the local outer diameter changes caused by rigid contact between tubes and fixtures. It also has the advantages of convenient material loading and unloading and neat material stacking. It has good compatibility with tubes of different specifications, and the stainless steel mesh and pads used can be reused multiple times, reducing the consumption of auxiliary materials. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 A schematic flowchart of a method for improving the straightness and outer diameter of a nuclear-grade zirconium alloy clad tube during annealing, provided in an embodiment of the present invention;

[0022] Figure 2 A schematic diagram of the annealing fixture and elastic constraint structure in a method for improving the straightness and outer diameter of nuclear-grade zirconium alloy cladding tubing provided in an embodiment of the present invention. Figure 1 ;

[0023] Figure 3 This invention provides a schematic diagram of the fabric arrangement structure in a method for improving the straightness and outer diameter of annealed zirconium alloy cladding tubing for nuclear applications, as illustrated in an embodiment of the invention. Figure 2 ;

[0024] Figure 4 A schematic diagram of the annealing fixture structure in a method for improving the straightness and outer diameter of nuclear-grade zirconium alloy cladding tubing provided in an embodiment of the present invention. Figure 3 . Detailed Implementation

[0025] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0027] Figure 1 This is a schematic flowchart illustrating a method for improving the straightness and outer diameter of a nuclear-grade zirconium alloy clad tube during annealing, as provided in an embodiment of the present invention.

[0028] This invention provides a method for improving the straightness and outer diameter of annealed zirconium alloy cladding tubing for nuclear applications, combined with... Figure 1 It includes the following four steps, S101 to S104:

[0029] S101: Install the elastically constrained structure onto the inner wall of the annealing fixture.

[0030] S102: The tube to be annealed is laid with material using a specific material laying method, and the material is laid into the annealing fixture with an elastic constraint structure.

[0031] S103: Anneal the fabric in a vacuum annealing furnace;

[0032] S104: After annealing, remove the tube to be annealed from the annealing fixture.

[0033] Figure 2 A schematic diagram of the annealing fixture and elastic constraint structure in a method for improving the straightness and outer diameter of nuclear-grade zirconium alloy cladding tubing provided in an embodiment of the present invention. Figure 1 .

[0034] Furthermore, in the above-mentioned method for improving the straightness and outer diameter of the annealed zirconium alloy cladding tube for nuclear use, the elastic constraint structure 4 in step S101 adopts heat-resistant stainless steel mesh. After the whole mesh is woven, it is pressed into a wave-shaped structure with a clean surface, smooth and complete waves, no deformation or steel chips, and no wavy or missing weave.

[0035] Specifically, in this embodiment of the invention, the elastic constraint type 4 structure overcomes the shortcomings of the existing annealing fixtures where there are rigid constraints between pipes and between pipes and fixtures. During the annealing process, the thermal expansion between pipes is absorbed by the elastic constraint structure, which reduces the local outer diameter changes caused by the rigid contact between pipes and fixtures.

[0036] It should be understood that the present invention has the advantages of convenient material loading and unloading, neat material stacking, good compatibility with different specifications of pipes, and the stainless steel mesh and gaskets used can be reused multiple times, reducing the consumption of auxiliary materials and improving economy.

[0037] Furthermore, in the above-mentioned method for improving the straightness and outer diameter of annealed zirconium alloy cladding tubing for nuclear applications, the annealing fixture in step S101 is made of heat-resistant stainless steel and includes: a bottom bracket 1 and a material boat 5; the elastic constraint structure into which the tube pair to be annealed is placed flat on the inner wall of the annealing fixture is to place the elastic constraint structure into which the tube pair to be annealed is placed flat on the inner wall of the material boat 5; and the stainless steel mesh is tightly fitted to the side and bottom plate of the material boat 5, and there shall be no protrusions larger than the first preset size.

[0038] Specifically, in this embodiment of the invention, the requirement that there must be no protrusions larger than the first preset size means that there must be no obvious protrusions visible to the naked eye.

[0039] Figure 3 This invention provides a schematic diagram of the fabric arrangement structure in a method for improving the straightness and outer diameter of annealed zirconium alloy cladding tubing for nuclear applications, as illustrated in an embodiment of the invention. Figure 2 .

[0040] Furthermore, in the above-mentioned method for improving the straightness and outer diameter of the nuclear zirconium alloy cladding tube after annealing, the specific material distribution method in S102 is a combination of pad tube 6 and tube 7 to be annealed. Pad tubes 6 and 8 are distributed at the bottom and top, and tube 7 to be annealed is placed in the middle of pad tubes 6 and 8. Pad tubes 6 and 8 are of the same material and specifications as tube 7 to be annealed. Pad tubes 6 and 8 are longer than tube 7 to be annealed. The pad tubes should be in a recrystallized state, and the straightness should be ≤0.5 / 1000mm.

[0041] Specifically, in this embodiment of the invention, the pads 6 and 8 are longer than the tube 7 to be annealed, or the pads 6 and 8 are slightly longer than the tube 7 to be annealed. When laying the material, the pads 6 are neatly stacked from the bottom layer to the top layer covering the pads 8. The pads 8 are used to adsorb the impurity gases released during the annealing process, and the tubes 7 to be annealed are neatly stacked in the middle.

[0042] Figure 4 A schematic diagram of the annealing fixture and elastic constraint structure in a method for improving the straightness and outer diameter of nuclear-grade zirconium alloy cladding tubing provided in an embodiment of the present invention. Figure 3 .

[0043] Furthermore, combined Figure 4 In the above-mentioned method for improving the straightness and outer diameter of the annealed zirconium alloy cladding tube for nuclear use, the bottom bracket 1 is a square tube structure made of heat-resistant stainless steel. During assembly, the crossbeam 2 and longitudinal beam 3 of the bottom bracket are assembled together, and the crossbeam and longitudinal beam of the bottom bracket are welded together using argon arc welding.

[0044] Furthermore, in the above-mentioned method for improving the straightness and outer diameter of the annealed zirconium alloy cladding tube for nuclear applications, the boat is formed by stamping, has a hexagonal cross-section, and an open design at the top.

[0045] Specifically, in this embodiment of the invention, the material boat 5 is formed by stamping and has a hexagonal cross-section. To facilitate furnace loading and internal cleaning, the top is designed with an open top.

[0046] Furthermore, in the above-mentioned method for improving the straightness and outer diameter of the annealed zirconium alloy cladding tube for nuclear applications, the material boat is installed on the bottom bracket.

[0047] Specifically, in this embodiment of the invention, the entire material boat 5 is hoisted onto the bottom stainless steel bracket 1.

[0048] Furthermore, in the above-mentioned method for improving the straightness and outer diameter of annealed zirconium alloy cladding tubing for nuclear applications, step S104 involves annealing in a vacuum annealing furnace, including: an external feeding trolley delivering the annealing fixture to the cooling chamber; an internal feeding trolley driving device delivering the annealing fixture to the heating chamber for vacuum or argon heating; transferring the annealing fixture into the cooling chamber for vacuum furnace cooling or argon cooling; and an external feeding trolley pulling the annealing fixture out onto the external fixture platform.

[0049] Specifically, in this embodiment of the invention, the process of the external feeding trolley delivering the annealing fixture to the cooling chamber, the internal material trolley driving device delivering the annealing fixture to the heating chamber for vacuum or argon heating, the transfer of the annealing fixture to the cooling chamber for vacuum cooling or argon cooling, and the external feeding trolley pulling the annealing fixture out onto the external fixture platform are all controlled by the electrical control system.

[0050] Furthermore, in the above-mentioned method for improving the straightness and outer diameter of nuclear-grade zirconium alloy cladding tubing during annealing, the annealing conditions in the vacuum annealing furnace are: the ultimate vacuum in the heating and cooling chambers is ≤8.0×10⁻⁶. -4 Pa, the working vacuum of the heating and cooling chambers is ≤5.0×10 Pa. -3Pa, maximum heating temperature 900℃, temperature control accuracy ≤±1℃, temperature uniformity ≤±5℃, uniform temperature zone ≥10m.

[0051] Furthermore, the above-mentioned method for improving the straightness and outer diameter of the annealed zirconium alloy cladding tube for nuclear applications also includes: periodically identifying changes in the straightness and outer diameter of the cladding tube, and correcting or replacing the cladding tube when the straightness is poor or the outer diameter is deformed to a value greater than a second preset dimension.

[0052] Specifically, in this embodiment of the invention, the straightness and outer diameter changes of the pad tube are periodically identified. For example, the straightness and outer diameter changes of the pad tube are identified every 5 to 6 furnaces. When the straightness is poor or the outer diameter is deformed beyond the second preset size, the pad tube is corrected or replaced. When the straightness is poor or the outer diameter is obviously deformed to the naked eye, it should be corrected or replaced.

[0053] The following describes a method for improving the straightness and outer diameter of nuclear-grade zirconium alloy clad tubing during annealing, using a specific embodiment.

[0054] Step 1: Install the elastic constraint structure onto the inner wall of the annealing fixture, including: installing the elastic constraint structure 4 onto the inner wall of the material boat 5 of the annealing fixture. The elastic constraint structure is a stainless steel mesh, and the stainless steel mesh 4 must be flush and fitted against the inner wall of the material boat 5. The bottom bracket 1 of the annealing fixture is a square tube structure made of heat-resistant stainless steel. During assembly, the crossbeam 2 and longitudinal beam 3 of the bracket are assembled together and welded together using argon arc welding. Finally, stress-relief annealing is performed. After assembly, all dimensional tolerances of the bottom bracket should meet the design requirements. The material boat 5 of the annealing fixture is formed by stamping, and its cross-section is hexagonal. To facilitate furnace loading and internal cleaning, the top adopts an open design. The entire material boat 5 of the annealing fixture is hoisted onto the bottom bracket 1, ensuring that the positioning pins are installed in place.

[0055] Step Two: The tube to be annealed is laid out using a specific laying method into the annealing fixture that houses the elastic constraint structure. This includes using φ10.1mm cold-rolled zirconium alloy clad tubes, according to… Figure 3 The loading diagram shows the material being laid. During the laying process, the pad tubes 6 are neatly stacked from the bottom layer to the top layer, and a layer of pad tubes 8 is placed on top to absorb the impurity gases released during the annealing process. The tubes to be annealed are neatly stacked in the middle.

[0056] Step 3: Anneal the annealing fixture after fabrication in a vacuum annealing furnace, including: the external feeding trolley transports the annealing fixture to the cooling chamber; the internal feeding trolley drive device transports the annealing fixture to the heating chamber for vacuum or argon heating; the annealing fixture is transferred to the cooling chamber for vacuum furnace cooling or argon cooling; and the external feeding trolley pulls the annealing fixture out onto the external fixture platform. The cold-state ultimate vacuum of the vacuum annealing furnace in the heating and cooling chambers is ≤7.0×10⁻⁶.-4 Pa, the working vacuum of the heating and cooling chambers is ≤4.0×10 Pa. -3 Pa, maximum heating temperature 900℃, temperature control accuracy ≤±1℃, temperature uniformity ≤±5℃, uniform temperature zone is 10m.

[0057] Step 4: After annealing, remove the tube to be annealed from the annealing fixture.

[0058] The straightness and outer diameter changes of the annealed clad pipes were measured using the above embodiments. The straightness was tested one by one on a Grade 0 marble platform, and the outer diameter changes were measured by ultrasonic full-length testing. The results are shown in Table 1.

[0059] Table 1. Statistics on changes in straightness and outer diameter after annealing.

[0060]

[0061] As can be seen from the table above, the percentage of clad pipes annealed using the present invention with a straightness better than 0.7 / 1000mm after annealing has reached over 90%, and the deviation of the outer diameter along the entire length is less than 0.02mm. The straightness and outer diameter changes after annealing are significantly improved compared with existing annealing methods.

[0062] Those skilled in the art will understand that although some embodiments described herein include certain features included in other embodiments but not others, combinations of features from different embodiments are meant to be within the scope of the invention and form different embodiments.

[0063] Those skilled in the art will understand that the descriptions of the various embodiments have different focuses, and for parts not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0064] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for improving the straightness and outer diameter of annealed zirconium alloy clad tubing for nuclear applications, characterized in that, It includes the following four steps: Step 1: Install the elastic constraint structure onto the inner wall of the annealing fixture; Step 2: Apply material to the tube to be annealed using a specific material application method, and then apply the material to the annealing fixture with an elastic constraint structure. Step 3: Anneal the fabric in a vacuum annealing furnace; Step 4: After annealing, remove the tube to be annealed from the annealing fixture; The elastic constraint structure in steps one and two uses heat-resistant stainless steel mesh. The specific fabric application method in step two is a combination of pad tube and tube to be annealed, with the pad tube distributed at the bottom and top, and the tube to be annealed placed in the middle of the pad tube.

2. The method for improving the straightness and outer diameter of annealed zirconium alloy cladding tubing for nuclear applications according to claim 1, characterized in that, The heat-resistant stainless steel mesh is woven as a whole and then pressed into a wave-shaped structure. The surface is clean, the waves are smooth and complete, and there is no deformation or steel shavings. There are no irregular or missing weaves. The annealing fixture is made of heat-resistant stainless steel and includes a bottom bracket and a material boat. The elastic constraint structure is installed on the inner wall of the annealing fixture. The stainless steel mesh must be tightly fitted to the side and bottom plate of the material boat, and there must be no protrusions larger than the first preset size.

3. The method for improving the straightness and outer diameter of annealed zirconium alloy cladding tubing for nuclear applications according to claim 1, characterized in that, The spacer tube and the tube to be annealed are of the same material and specifications. The spacer tube is longer than the tube to be annealed. The spacer tube should be in a recrystallized state and the straightness should be ≤0.5 / 1000mm.

4. The method for improving the straightness and outer diameter of annealed zirconium alloy cladding tubing for nuclear applications according to claim 1, characterized in that, Step 3 involves annealing in a vacuum annealing furnace, including: the external feeding trolley delivering the annealing fixture to the cooling chamber; the internal material car drive device delivering the annealing fixture to the heating chamber for vacuum or argon heating; transferring the annealing fixture into the cooling chamber for vacuum or argon cooling; and the external feeding trolley pulling the annealing fixture out onto the external fixture platform.

5. The method for improving the straightness and outer diameter of nuclear-grade zirconium alloy cladding tubing after annealing, as described in claim 1, is characterized in that... The annealing conditions in a vacuum annealing furnace are: the ultimate vacuum in the heating and cooling chambers at cold state ≤ 8.0 × 10⁻⁶. -4 Pa, the working vacuum of the heating and cooling chambers is ≤5.0×10 Pa. -3 Pa, maximum heating temperature 900 ℃, temperature control accuracy ≤±1 ℃, temperature uniformity ≤±5 ℃, uniform temperature zone ≥10 m.

6. The method for improving the straightness and outer diameter of annealed zirconium alloy cladding tubing for nuclear applications according to claim 1, characterized in that, The method further includes: periodically identifying changes in the straightness and outer diameter of the pad tube, and correcting or replacing the pad tube when the straightness is poor or the outer diameter is deformed to a size greater than the second preset size.

7. The method for improving the straightness and outer diameter of annealed zirconium alloy cladding tubing for nuclear applications according to claim 2, characterized in that, The bottom bracket is a square tube structure made of heat-resistant stainless steel. During assembly, the crossbeams and longitudinal beams of the bottom bracket are assembled together and welded together using argon arc welding.

8. The method for improving the straightness and outer diameter of annealed zirconium alloy cladding tubing for nuclear applications according to claim 2, characterized in that, The material boat is formed by stamping, with a hexagonal cross-section and an open top design.

9. The method for improving the straightness and outer diameter of annealed zirconium alloy cladding tubing for nuclear applications according to claim 2, characterized in that, The material boat is installed on the bottom bracket.

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