Method for synchronous expanded connection and resistance brazing of tube plate joints of pressure vessel

Abstract

The invention discloses a synchronous expanded connection and resistance brazing method for tube plate joints of a pressure vessel, which belongs to the technical field of heat exchanger brazing and comprises the following steps of: S1, drilling tube holes in tube plates; s2, the inner wall of the pipe hole is cleaned; s3, the inner wall of the pipe hole is evenly coated with self-fluxing flux brazing filler metal, and after the self-fluxing flux brazing filler metal is dried, dustproof treatment is conducted on the pipe plate through plastic cloth; s4, the heat exchange pipe is cleaned; s5, enabling the heat exchange tube to penetrate into the tube hole from the tube pass side of the tube plate; and S6, the mechanical tube expander is inserted into the inner hole of the heat exchange tube, and the tube plate and the mechanical tube expander are electrified while the tube is expanded by adopting a method of simultaneously performing expanded connection and resistance brazing, so that the self-brazing flux brazing filler metal realizes synchronous expanded connection brazing between the heat exchange tube and the tube hole under the effects of tube expansion pressure and resistance heat. The mechanical pipe expander and the external power source are adopted for achieving synchronous operation of expanded connection and brazing, the operation efficiency is high, and the sealing performance is good.

Description

Technical Field

[0001] The invention belongs to the technical field of heat exchanger brazing, and in particular relates to a method for synchronous expansion and resistance brazing of a tube sheet joint of a pressure vessel. Background Art

[0002] Heat exchangers are widely used in petrochemical, electric power, environmental protection and other industrial fields. Heat exchangers are energy-saving equipment that realizes heat transfer between materials between two or more fluids at different temperatures, so that heat is transferred from a higher temperature fluid to a lower temperature fluid, so that the fluid temperature reaches the specified index of the process to meet the needs of process conditions. It is also one of the main equipment for improving energy utilization. In the production process of heat exchangers, multiple heat exchange tubes need to be connected to the tube sheet of the heat exchanger.

[0003] Regarding the connection methods between the heat exchanger tube sheet and the heat exchange tube, there are currently mainly furnace brazing, flame brazing, expansion and synchronous expansion friction brazing. Among them, furnace brazing has better sealing, but the tolerance requirements for the tube holes on the tube sheet are relatively strict; the cost of the heat treatment furnace used for flame brazing is relatively high, resulting in high cost investment, and flame brazing is affected by manual operation and has unstable quality; the expansion connection method has high requirements for the roughness of the fitting surface; the synchronous expansion friction brazing method cannot achieve the expansion of the entire connection surface between the heat exchange tube and the tube sheet, and the friction heat generated can only maintain the melting of low-melting point brazing, which is only suitable for welding conditions using low-melting point brazing. Summary of the invention

[0004] In order to solve the problem existing in the connection method between the tube sheet and the heat exchange tube in the heat exchanger, the present invention provides a method for simultaneous expansion and resistance brazing of the tube sheet joint of a pressure vessel.

[0005] A method for simultaneous expansion and resistance brazing of a tube-sheet joint of a pressure vessel comprises the following steps: Step S1, drilling tube holes on the tube sheet; Step S2, cleaning the inner wall of the tube hole; Step S3, evenly apply the self-soldering flux on the inner wall of the tube hole, and after the self-soldering flux is dried, use plastic cloth to perform dust prevention treatment on the tube sheet; Step S4, cleaning the heat exchange tube; Step S5, inserting the heat exchange tube into the tube hole from the tube side of the tube sheet; Step S6, inserting a mechanical expander into the inner hole of the heat exchange tube, adopting a method of simultaneously carrying out expansion and resistance brazing, while expanding the tube, energizing the tube sheet and the mechanical expander, so that the self-brazing agent brazing material can achieve synchronous expansion and brazing between the heat exchange tube and the tube hole under the action of expansion pressure and resistance heat.

[0006] Preferably, in step S1, the roughness of the pore wall is controlled within the range of 3.2-6.3 μm, and the lower deviation of the pore diameter tolerance is -0.05 mm and the upper deviation is +0.1 mm.

[0007] Preferably, in step S1, the spiral knife marks on the inner wall of the tube hole are retained when drilling the tube hole.

[0008] Preferably, in step S2, a dust-free cloth dipped in alcohol is used to remove oil stains, dust and impurities on the inner wall of the tube hole.

[0009] Preferably, in step S4, a dust-free cloth dipped in alcohol is used to remove oil stains, dust and impurities on the heat exchange tube.

[0010] Preferably, the mechanical tube expander comprises a coaxially arranged expansion rod and an insulating keel, wherein the insulating keel is a cylindrical structure, and a plurality of expansion bead hole grooves are evenly arranged on the wall surface of the insulating keel along the circumferential direction, and an expansion bead is arranged in each expansion bead hole groove; The expansion rod is located inside the insulating keel and all the expansion beads surround the expansion rod; The outer wall surface of the expansion rod and the outer wall surface of the expansion bead are both conical structures, and the conical structure of the outer wall surface of the expansion rod is arranged in the opposite direction to the conical structure of the outer wall surface of the expansion bead; The big end of the expansion rod is connected to the tube expander.

[0011] Preferably, the length of the expansion bead along the axial direction of the expansion rod is greater than the thickness of the tube sheet.

[0012] Preferably, after all the expansion beads are attached to the expansion rod, the outer envelope surface surrounding all the expansion beads and being tangent to all the expansion beads is a cylindrical surface.

[0013] Preferably, at least three expansion hole grooves are arranged on the insulating keel.

[0014] Preferably, step S6 includes the following sub-steps: Step S61, inserting a mechanical tube expander into the inner hole of the heat exchange tube so that the expansion joint position between the tube hole and the heat exchanger is aligned with each expansion bead; Step S62, connecting the big end of the expansion rod to the tube expander; Step S63, connecting an external power supply between the expansion rod and the tube sheet; Step S64, starting the tube expander and the external power supply; The tube expander controls the expansion rod to rotate and feed forward at the same time. As the expansion rod rotates, the expansion bead revolves around the expansion rod on the inner wall of the heat exchange tube, and expands outward along the expansion bead hole groove as the expansion rod moves forward, thus realizing the rolling expansion process of the inner wall of the heat exchange tube. The external power supply is started, so that the expansion rod, expansion bead, heat exchange tube and tube sheet form a closed power circuit, and the resistance heat generated by the power is used to melt the self-brazing agent and brazing material; The brazing agent brazing material realizes synchronous expansion brazing between the heat exchange tube and the tube hole under the action of tube expansion pressure and resistance heat.

[0015] The beneficial effects of the present invention are: (1) The present invention uses a mechanical tube expander and an external power supply to achieve simultaneous expansion and brazing operations, which has high operating efficiency and good sealing performance and is suitable for heat exchangers of various sizes. In addition, when the expansion is performed in a heated state, the yield strength of the heat exchange tube is lower than that at room temperature, and plastic deformation is more likely to occur. A smaller torque can be used, and expansion is easier.

[0016] (2) Compared with the single brazing process, the present invention has lower requirements on the tolerance of the tube hole. For brazing, if the gap between the heat exchange tube and the tube hole is too large, it will lead to poor brazing. However, the present invention can ensure the fit between the heat exchange tube and the tube hole through expansion.

[0017] (3) The brazing in the present invention does not need to be performed inside a heat treatment furnace, so the cost investment is low, it is not affected by manual operation, and the quality is stable.

[0018] (4) Compared with the single expansion joint, the present invention has a lower requirement for the roughness of the tube hole. In order to ensure the sealing performance, the roughness of the contact surface is between 1.6 and 3.2 μm during the single expansion joint. The higher the roughness requirement of the contact surface, the better the sealing performance. However, due to the presence of brazing, the sealing performance of the present invention is very good, and there is no need to additionally control the roughness of the contact surface. In addition, the roughness of the tube hole is within the range of 3.2 to 6.3 μm, which is beneficial to the retention of the brazing agent and the brazing material. On the other hand, after expansion, the heat exchange tube will be partially embedded in the texture of the tube hole, further improving the joint strength.

[0019] (5) Compared with synchronous expansion friction brazing, the mechanical tube expander in the present invention performs synchronous expansion resistance welding on the entire connection surface between the heat exchange tube and the tube hole, thereby improving the joint strength.

[0020] (6) Compared with synchronous expansion friction brazing, the present invention has a wider application range. The resistance heat generated during the brazing process of the present invention is higher than the friction heat, so the melting point range of the applicable self-brazing flux brazing material is wider. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings in the specification, which constitute a part of the present application, are used to provide further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0022] Figure 1 It is a schematic diagram of the matching between the tube hole and the heat exchange tube before expansion welding; Figure 2 It is a schematic diagram of expansion welding of tube holes and heat exchange tubes using the method of the present invention; Figure 3 It is a schematic diagram of the state of the tube hole and the heat exchange tube after expansion welding by the method of the present invention; Figure 4 It is a structural schematic diagram of the mechanical tube expander in the present invention; Figure 5 yes Figure 4 AA section view; in: 1-tube sheet, 2-tube hole, 3-heat exchange tube, 4-expansion rod, 5-insulation keel, 6-expansion bead hole groove, 7-expansion bead, 8-external envelope surface, 9-external power supply, 10-self-brazing flux brazing material. DETAILED DESCRIPTION

[0023] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0024] A method for simultaneous expansion and resistance brazing of a tube-sheet joint of a pressure vessel comprises the following steps: Step S1, drilling a tube hole 2 on a tube sheet 1; Specifically, in step S1, the roughness of the wall of the tube hole 2 is controlled within the range of 3.2-6.3 μm, and the lower deviation of the diameter tolerance of the tube hole 2 is -0.05 mm and the upper deviation is +0.1 mm.

[0025] Specifically, in the step S1 , the spiral cuts on the inner wall of the tube hole 2 are retained when drilling the tube hole 2 , so as to facilitate the retention of the self-brazing agent brazing material 10 .

[0026] Step S2, cleaning the inner wall of the tube hole 2; Specifically, in step S2, a dust-free cloth dipped in alcohol is used to remove oil stains, dust and impurities on the inner wall of the tube hole 2.

[0027] Step S3, evenly apply the self-soldering flux 10 on the inner wall of the tube hole 2, and after the self-soldering flux 10 is dried, use plastic cloth to perform dust prevention on the tube sheet 1; specifically, use a tube brush to evenly apply the self-soldering flux 10 on the inner wall of the tube hole 2, which can increase the welding area of ​​the inner wall of the tube hole 2 and make the welding more firm; then leave it for more than 4 hours to fully dry and firmly adhere to the inner wall of the tube hole 2, and then use plastic cloth to perform dust prevention on the tube sheet 1 to prevent the tube hole 2 from being contaminated due to waiting; Step S4, cleaning the heat exchange tube 3; Specifically, in step S4, a dust-free cloth dipped in alcohol is used to remove oil stains, dust and impurities on the heat exchange tube 3.

[0028] Step S5, such as Figure 1As shown, the heat exchange tube 3 is inserted into the tube hole 2 from the tube side of the tube sheet 1, and care is taken to avoid scratching the fitting surface between the outer wall of the heat exchange tube 3 and the inner surface of the tube hole 2 during insertion; Step S6, inserting the mechanical expander into the inner hole of the heat exchange tube 3, adopting the method of simultaneously carrying out expansion and resistance brazing, while expanding the tube, energizing the tube sheet 1 and the mechanical expander, so that the self-brazing agent brazing material 10 can realize synchronous expansion and brazing between the heat exchange tube 3 and the tube hole 2 under the action of the expansion pressure and resistance heat.

[0029] Specifically, Figure 4-Figure 5 As shown, the mechanical tube expander comprises a coaxially arranged expansion rod 4 and an insulating keel 5, wherein the insulating keel 5 is a cylindrical structure, and a plurality of expansion bead hole grooves 6 are evenly arranged on the wall surface of the insulating keel 5 along the circumferential direction, and an expansion bead 7 is arranged in each expansion bead hole groove 6; the size of the expansion bead hole groove 6 is set so that the expansion bead 7 can bulge outward under the squeezing of the expansion rod 4, but will not completely fall out of the expansion bead hole groove 6; The expansion rod 4 is located inside the insulating keel 5 and all the expansion beads 7 surround the expansion rod 4; under the squeezing of the expansion rod 4, the expansion beads 7 can protrude radially outward to achieve expansion and compression of the heat exchange tube 3; The outer wall surfaces of the expansion rod 4 and the expansion bead 7 are both conical structures, and the conical structure of the outer wall surface of the expansion rod 4 is set in the opposite direction to the conical structure of the outer wall surface of the expansion bead 7, that is, if the big end of the expansion rod 4 faces upward, the big end of the expansion bead 7 faces downward; the taper of the outer wall surface of the expansion bead 7 is 2~2.5°.

[0030] The big end of the expansion rod 4 is connected to a tube expander, wherein the tube expander controls the rotation of the expansion rod 4 around its own axis and the forward and backward movement along the axis. The tube expander is a prior art, and its specific implementation structure is not described here.

[0031] Specifically, the length of the expansion bead 7 along the axial direction of the expansion rod 4 is greater than the thickness of the tube sheet 1 , that is, the length of the expansion bead 7 along the axial direction of the expansion rod 4 is greater than the axial length of the tube hole 2 .

[0032] Specifically, after all the expansion beads 7 are attached to the expansion rod 4, the outer envelope surface 8 surrounding all the expansion beads 7 and tangent to all the expansion beads 7 is a cylindrical structure, so as to achieve uniform expansion of the connection between the heat exchange tube 3 and the tube hole 2. In the present application, the size of the expansion beads 7, the expansion bead hole groove 6, and the expansion rod 4 is matched and set, and during the expansion bead 7 extending outward, the maximum value of the difference between the radius of the outer envelope surface 8 and the radius of the outer wall of the insulating keel 5 is 70 wires, that is, the length range of the expansion bead 7 protruding in the radial direction of the insulating keel 5 is 0 to 70 wires.

[0033] Specifically, at least three expansion hole grooves 6 are arranged on the insulating keel 5 .

[0034] Specifically, step S6 includes the following sub-steps: Step S61, inserting a mechanical tube expander into the inner hole of the heat exchange tube 3, so that the expansion position between the tube hole 2 and the heat exchanger 3 is aligned with each expansion bead 7; Step S62, connecting the big end of the expansion rod 4 to the tube expander; Step S63, connecting an external power source 9 between the expansion rod 4 and the tube sheet 1, as follows Figure 2 As shown; Step S64, starting the tube expander and the external power supply 9; The tube expander controls the expansion rod 4 to rotate and feed forward at the same time. As the expansion rod 4 rotates, the expansion bead 7 revolves around the expansion rod 4 on the inner wall of the heat exchange tube 3, and expands outward along the expansion bead hole groove 6 as the expansion rod 4 moves forward, thereby realizing the rolling expansion process of the inner wall of the heat exchange tube 3. The external power supply 9 is started, so that the expansion rod 4, the expansion bead 7, the heat exchange tube 3, and the tube sheet 1 form a closed power circuit, and the resistance heat generated by the power is used to melt the self-brazing agent 10; The brazing material 10 of the self-brazing agent realizes synchronous expansion brazing between the heat exchange tube 3 and the tube hole 2 under the action of the expansion pressure and the resistance heat. The state of the tube hole 2 and the heat exchange tube 3 after expansion brazing by the method of the present invention is as follows: Figure 3 shown.

[0035] In the present invention, a mechanical tube expander and an external power supply 9 are used to realize the simultaneous operation of expansion and brazing, which has high operation efficiency and good sealing performance, and is suitable for heat exchangers of various sizes. In addition, when the expansion is performed in a heated state, the yield strength of the heat exchange tube 3 is lower than that at room temperature, and plastic deformation is more likely to occur. A smaller torque can be used, and expansion is easier. Compared with the single brazing process, the present invention has lower tolerance requirements for the tube hole 2. For brazing, if the gap between the heat exchange tube 3 and the tube hole 2 is too large, it will lead to poor brazing. However, the present invention can ensure the fit between the heat exchange tube 3 and the tube hole 2 by expansion. The brazing in the present invention does not require a heat treatment furnace. It is carried out internally, with low cost investment, is not affected by manual operation, and has stable quality. Compared with the single expansion connection, the present invention has lower requirements on the roughness of the tube hole 2. In order to ensure the sealing performance, the roughness of the contact surface is between 1.6 and 3.2 μm during the single expansion connection. The higher the roughness requirement of the contact surface, the better the sealing performance. Due to the presence of brazing, the sealing performance of the present invention is very good, and there is no need to additionally control the roughness of the contact surface. Moreover, the roughness of the tube hole 2 is within the range of 3.2 to 6.3 μm, which is beneficial to the retention of the self-brazing agent brazing material 10 on the one hand, and on the other hand, the heat exchange tube 3 will be partially embedded in the texture of the tube hole 2 after expansion, further improving the joint strength.

[0036] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not a limitation of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the protection scope of the present invention.

Claims

1. A method for simultaneous expansion and resistance brazing of a tube-sheet joint of a pressure vessel, characterized in that: The following steps are involved: Step S1, drilling a tube hole (2) on a tube sheet (1); Step S2, cleaning the inner wall of the tube hole (2); Step S3, evenly applying the self-soldering agent brazing material (10) on the inner wall of the tube hole (2), and after the self-soldering agent brazing material (10) is dried, using plastic cloth to perform dust prevention treatment on the tube sheet (1); Step S4, cleaning the heat exchange tube (3); Step S5, inserting the heat exchange tube (3) into the tube hole (2) from the tube side of the tube sheet (1); Step S6, inserting a mechanical tube expander into the inner hole of the heat exchange tube (3), adopting a method of simultaneously carrying out expansion and resistance brazing, energizing the tube sheet (1) and the mechanical tube expander while expanding the tube, so that the self-brazing agent brazing material (10) can achieve synchronous expansion and brazing between the heat exchange tube (3) and the tube hole (2) under the action of the expansion pressure and resistance heat.

2. The method for simultaneous expansion and resistance brazing of a tube-sheet joint of a pressure vessel according to claim 1, characterized in that: In the step S1, the roughness of the wall of the tube hole (2) is controlled within the range of 3.2-6.3 μm, and the lower deviation of the diameter tolerance of the tube hole (2) is -0.05 mm and the upper deviation is +0.1 mm.

3. The method for simultaneous expansion and resistance brazing of a tube-sheet joint of a pressure vessel according to claim 1, characterized in that: In the step S1, the spiral cuts on the inner wall of the pipe hole (2) are retained when drilling the pipe hole (2).

4. The method for simultaneous expansion and resistance brazing of a tube-sheet joint of a pressure vessel according to claim 1, characterized in that: In step S2, a dust-free cloth dipped in alcohol is used to remove oil stains, dust and impurities on the inner wall of the tube hole (2).

5. The method for simultaneous expansion and resistance brazing of a tube-sheet joint of a pressure vessel according to claim 1, characterized in that: In step S4, a dust-free cloth dipped in alcohol is used to remove oil stains, dust and impurities on the heat exchange tube (3).

6. The method for simultaneous expansion and resistance brazing of a tube-sheet joint of a pressure vessel according to claim 1, characterized in that: The mechanical tube expander comprises a coaxially arranged expansion rod (4) and an insulating keel (5); the insulating keel (5) is in a cylindrical structure; a plurality of expansion bead hole grooves (6) are evenly arranged on the wall surface of the insulating keel (5) along the circumferential direction; and an expansion bead (7) is arranged in each expansion bead hole groove (6); The expansion rod (4) is located inside the insulating keel (5) and all the expansion beads (7) surround the expansion rod (4); The outer wall surface of the expansion rod (4) and the outer wall surface of the expansion bead (7) are both conical structures, and the conical structure of the outer wall surface of the expansion rod (4) and the conical structure of the outer wall surface of the expansion bead (7) are arranged in the opposite direction; The large end of the expansion rod (4) is connected to a tube expander.

7. The method for simultaneous expansion and resistance brazing of a tube-sheet joint of a pressure vessel according to claim 6, characterized in that: The length of the expansion bead (7) along the axial direction of the expansion rod (4) is greater than the thickness of the tube sheet (1).

8. The method for simultaneous expansion and resistance brazing of a tube-sheet joint of a pressure vessel according to claim 7, characterized in that: After all the expansion beads (7) are attached to the expansion rod (4), the outer envelope surface (8) surrounding all the expansion beads (7) and being tangent to all the expansion beads (7) is a cylindrical surface.

9. The method for simultaneous expansion and resistance brazing of a tube-sheet joint of a pressure vessel according to claim 6, characterized in that: At least three expansion hole grooves (6) are arranged on the insulating keel (5).

10. The method for simultaneous expansion and resistance brazing of a tube-sheet joint of a pressure vessel according to any one of claims 6 to 9, characterized in that: The step S6 comprises the following sub-steps: Step S61, inserting a mechanical tube expander into the inner hole of the heat exchange tube (3), so that the expansion position between the tube hole (2) and the heat exchanger (3) is aligned with each expansion bead (7); Step S62, connecting the large end of the expansion rod (4) to the tube expander; Step S63, connecting an external power source (9) between the expansion rod (4) and the tube sheet (1); Step S64, starting the tube expander and the external power supply (9); The tube expander controls the expansion rod (4) to rotate and feed forward at the same time, and the expansion bead (7) performs a revolution around the expansion rod (4) on the inner wall of the heat exchange tube (3) as the expansion rod (4) rotates, and expands outward along the expansion bead hole groove (6) as the expansion rod (4) moves forward, thereby realizing a rolling expansion connection process for the inner wall of the heat exchange tube (3); The external power supply (9) is activated, so that the expansion rod (4), the expansion bead (7), the heat exchange tube (3) and the tube sheet (1) form a closed power circuit, and the resistance heat generated by the power supply realizes the melting of the brazing agent brazing material (10); The self-brazing agent brazing material (10) realizes synchronous expansion brazing between the heat exchange tube (3) and the tube hole (2) under the action of tube expansion pressure and resistance heat.

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