TW202147340A - Dismantling method of heat exchanger - Google Patents

Abstract

An object of the present invention is to provide a dismantling method of a heat exchanger, the dismantling method of the heat exchanger being superior in workability and enabling an exposure dose to be further reduced and a tube plate to be easily reused as a metal material. Provided by the present invention is a dismantling method of a heat exchanger, the heat exchanger being for use in a nuclear power facility and comprising: a heat transfer tube; a tube plate securing the heat transfer tube; and a cylindrical body housing the heat transfer tube and the tube plate, wherein the heat transfer tube comprises: an arc-shaped portion; and straight tube portions each extending from one of both ends of the arc-shaped portion such that the straight tube portions are parallel with respect to a central axis of the body, and penetrate the tube plate from a front face to a rear face thereof, wherein the straight tube portions are welded to the tube plate at the rear face side of the tube plate, and the dismantling method comprises: removing the arc-shaped portion of the heat transfer tube; removing a welded portion at which the straight tube portions are welded to the tube plate by slicing the tube plate, the slicing being parallel to a surface of the tube plate; and extracting the straight tube portions after the arc-shaped portion-removing and the welded portion-removing.

Description

How to disassemble a heat exchanger

The present invention relates to a dismantling method of a heat exchanger.

In terms of equipment renewal and decommissioning of nuclear facilities, aging tanks, heat exchangers and other machinery will be removed. These machines will have radioactive substances attached to them. The reduction of radioactive waste can be achieved by removing the part to which the radioactive material is attached, and reusing the part to which the radioactive material does not adhere or the part that can be decontaminated with a small amount of radioactive material to be reused as metal raw materials.

In the case of a heat exchanger, radioactive substances may adhere to the inside of the heat transfer tubes and the water chambers fixed to the tube sheet. On the other hand, in the tube sheet, the radioactive material adheres only to the surface and can be easily removed. In this case, the tube sheet can be reused as long as the heat transfer tube is removed.

In the method of removing the heat transfer tube, after removing the arc portion of the heat transfer tube, the connection between the straight portion of the heat transfer tube and the tube sheet is cut off, and the straight portion of the heat transfer tube is removed from the heat exchanger along its extending direction. The dismantling method of the heat exchanger from which the trunk part is extracted is known (see Japanese Patent Laid-Open No. 2014-59149).

In the heat exchanger described in the aforementioned publication, the heat transfer tubes have an arc portion and a straight portion extending from both ends of the arc portion, are inserted and supported by a plurality of tube support plates, and are fixed to the trunk portion via the tube plates. . In the dismantling method of the heat exchanger described in the aforementioned publication, the heat transfer tube is removed in the following procedure. First, the circular arc portion of the heat transfer tube and the end portion on the tube sheet side fixed to the linear portion of the tube sheet are cut. Therefore, only the linear portion of the heat transfer tube that is cut and remains is inserted and supported straight by the tube support plate, and is in a state of being movable along the axial direction of the trunk portion of the heat exchanger. Then, the straight portion is extracted from the trunk portion along the extending direction (the aforementioned axial direction) from the side where the circular arc portion of the heat transfer tube is removed while maintaining the straight shape. [Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2014-59149

[Problems to be Solved by Invention]

In the dismantling method of the heat exchanger described in the aforementioned publication, the end portion on the tube sheet side of the linear portion of the heat transfer tube fixed to the tube sheet is cut. Usually, a heat exchanger has a plurality of heat transfer tubes, so it is necessary to cut off individual heat transfer tubes, which is easy to consume time, and it is difficult to sufficiently reduce the amount of explosion during operation.

In addition, in the dismantling method of the heat exchanger described in the aforementioned publication, the heat transfer tubes remain in the tube sheet. In the case of reusing the tube sheet, the tube sheet is melted and processed in a melting furnace to produce a product. However, when the tube sheet is reused with the heat transfer tube remaining on the tube sheet, radioactive substances adhere to the heat transfer tube. In the case of the inner surface of the tube, it becomes a contaminated reused product. When the material of the tube sheet and the heat transfer tube is different, the material will be doped when the material is directly melted, and the quality of the reused product may be lowered.

The present invention is based on the above-mentioned circumstances, and aims to provide a dismantling method for a heat exchanger, which is excellent in workability, can further reduce the amount of explosions, and can easily reuse the tube sheet as a metal material. [Technical means to solve problems]

A dismantling method of a heat exchanger according to an aspect of the present invention includes a heat transfer tube, a tube sheet to which the heat transfer tube is fixed, and a cylindrical trunk portion that accommodates the heat transfer tube and the tube sheet, and is installed in a nuclear facility. The dismantling method of the heat exchanger used, the heat transfer tube has a circular arc portion and two ends of the circular arc portion respectively extend in parallel with respect to the central axis of the trunk portion and pass the tube sheet from the surface to the back. The straight pipe portion is welded to the tube sheet on the back side of the tube sheet, and the dismantling method includes a procedure of removing the arc portion of the heat transfer tube, and placing the tube sheet parallel to the surface thereof. A procedure of slicing and removing the welded portion of the straight pipe portion to the tube sheet, and a procedure of extracting the straight pipe portion after the arc portion removing procedure and the welding portion removing procedure.

In this heat exchanger dismantling method, the tube sheet is sliced in parallel to remove the welded portion of the straight tube portion to the tube sheet. Therefore, regardless of the number of the heat transfer tubes, all the straight pipe portions can be made movable by one cut. In addition, in the dismantling method of the heat exchanger, the straight pipe portion is drawn out after the above-mentioned welding part removal process, so that the straight pipe portion in the tube sheet is drawn out at the same time. For this reason, the tube sheet from which the straight tube portion has been extracted can be directly reused as a metal material. Therefore, the dismantling method of the heat exchanger of the present invention is excellent in workability, can further reduce the amount of explosion, and can easily reuse the tube sheet as a metal material.

In the extraction process, it is preferable to perform extraction from the back side of the tube sheet. The straight tube portion extending from the tube sheet to the arc portion side is generally relatively long. In this way, the straight pipe portion is pulled out from the back side of the tube sheet in the above-described extraction process, so that the straight pipe portion is supported by the tube sheet to the end, so that the long straight pipe portion can be stably pulled out.

Preferably, the straight pipe portion is enlarged in diameter at the penetrating portion of the tube sheet to be in close contact with the tube sheet, and further includes a procedure for processing the enlarged diameter portion of the straight pipe portion after the welding portion removal procedure. In the case where the heat transfer tube is strongly adhered to the tube sheet by pipe expansion processing during construction or the like, it may not be possible to easily extract the straight tube portion only by removing the welded portion. In this way, when the diameter of the straight pipe portion is enlarged at the penetrating portion of the tube sheet and is in close contact with the tube sheet, since the procedure of processing the enlarged diameter portion of the straight pipe portion is provided after the welding portion removal procedure, the straight pipe portion can be easily removed. The tube is pulled out.

Preferably, the above-mentioned diameter-expanding portion processing procedure is performed by cutting the pipe wall of the above-mentioned straight pipe portion. In this way, the process of expanding the diameter portion is performed by cutting the pipe wall of the straight pipe portion, so that the close contact portion between the tube sheet and the heat transfer pipe can be surely removed, so that the straight pipe portion can be pulled out more easily.

Preferably, the above-mentioned diameter-expanding portion processing procedure is performed through relaxation of the adhesion force between the straight pipe portion and the tube sheet. In this way, the enlarged diameter portion processing procedure is performed through relaxation of the adhesion force between the straight pipe portion and the tube sheet, so that the enlarged diameter portion can be removed together with the extraction of the straight pipe portion, thereby improving workability.

In terms of the method for alleviating the adhesion force, it is preferable to employ a method of cutting a part of the pipe wall of the straight pipe portion in the plate thickness direction of the pipe sheet. In this way, the method of cutting a part of the pipe wall of the straight pipe portion in the plate thickness direction of the tube sheet is used as the method for alleviating the adhesion force, so that the straight pipe portion can be easily drawn out with a relatively small amount of cutting. Therefore, the amount of dust adhering to the radioactive material generated at the time of excision is suppressed, so that the amount of blasting can be further reduced.

It is preferable to use the method of heating and cooling at least the said tube sheet from the viewpoint of the relaxation method of the said adhesive force. In this way, the straight pipe portion can be drawn out without cutting the heat transfer pipe by using the method of heating and cooling at least the above-mentioned tube sheet in the method of reducing the adhesion force. [Inventive effect]

As described above, the dismantling method of the heat exchanger of the present invention is excellent in workability, can further reduce the amount of explosion, and can easily reuse the tube sheet as a metal material.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

The dismantling method of the heat exchanger shown in FIG. 1 is a dismantling method of a heat exchanger used in a nuclear facility, and includes a circular arc portion removal procedure S1, a welded portion removal procedure S2, a diameter expansion portion processing procedure S3, and an extraction procedure. S4.

＜Heat exchanger＞ In FIG. 2, the structure of the heat exchanger 1 disassembled by this heat exchanger disassembly method is shown. The heat exchanger 1 includes a plurality of heat transfer tubes 10 , a tube sheet 20 to which the heat transfer tubes 10 are fixed, and a cylindrical body portion 30 that accommodates the heat transfer tubes 10 and the tube sheet 20 .

(heat transfer tube) The heat transfer pipe 10 has a circular arc portion 11 and a straight pipe portion 12 extending parallel to the central axis of the trunk portion 30 from both ends of the circular arc portion 11 , respectively. Aspects of the plurality of heat transfer tubes 10 , as shown in FIG. 2 , are controlled by the wedge-shaped barrier metal member 13 , the tube support plate 14 to control the position within the torso portion 30 . The heat transfer tube 10 is not fixed to the wedge-shaped barrier metal member 13 and the tube support plate 14, but is held so that the heat transfer tube 10 can move.

(tube sheet) The tube plate 20 is a plate for fixing the end portion of the straight tube portion 12 on the opposite side to the arc portion 11 . The tube sheet 20 is arranged so that its surface is orthogonal to the central axis of the trunk portion 30 at the lower end portion of the trunk portion 30 , and the trunk portion 30 is divided into upper and lower regions.

As for the straight pipe portion 12, as shown in FIG. 3, the tube sheet 20 is penetrated from the front surface 20a toward the back surface 20b. The straight pipe portion 12 is welded to the tube sheet 20 on the back side of the tube sheet 20 (welded portion 21 in FIG. 3 ). In addition, the straight pipe portion 12 has an enlarged diameter portion 12 a whose diameter is enlarged at the penetration portion of the tube sheet 20 , and is closely adhered to the tube sheet 20 through the enlarged diameter portion 12 a.

(torso) The trunk portion 30 is divided into upper and lower sections by the tube sheet 20 , and a water chamber 31 to which the cooling material is supplied and discharged is provided at the lower portion thereof. Moreover, the trunk part 30 is comprised so that the to-be-cooled material (for example, water) can be supplied to the upper part partitioned by the tube sheet 20 so that the heat transfer tube 10 may be immersed.

(action) In the heat exchanger 1 , the high-temperature primary coolant heated in the nuclear reactor is supplied to the water chamber 31 . This primary cooling material flows through the inside of the heat transfer tube 10 , returns to the water chamber 31 , and is discharged from the water chamber 31 .

At this time, the periphery of the heat transfer tube 10 is filled with the material to be cooled so as to exchange heat with the material to be cooled. Therefore, the temperature of the discharged primary cooling material decreases. The primary cooling material having this low temperature is heated again in the nuclear reactor and supplied to the water chamber 31 .

On the other hand, the material to be cooled heated by the heat exchange is taken out from the heat exchanger 1, and the heat energy is used.

Since the heat exchanger 1 is used in this way in a nuclear facility, radioactive substances may pass through the heat transfer tube 10 and the inside of the water chamber 31 . Therefore, the radioactive material is mainly contained in the inside of the heat transfer tube 10 and the water chamber 31, and is not contained in other parts or is highly likely to be contained in a trace amount.

Hereinafter, each procedure of the dismantling method of the heat exchanger will be described based on this.

<Arc part removal program> In the arc portion removal step S1, the arc portion 11 of the heat transfer tube 10 is removed.

Specifically, it is based on the following procedure. First, the head of the heat exchanger 1 is cut and removed with a cutter or the like. At this time, as shown in FIG. 4 , the heat transfer tube 10 remains without cutting. As long as the heat transfer tube 10 is not broken, the possibility of exposure of the radioactive material to the outside is low, and therefore it is not necessary to seal the cut portion.

Next, the arc portion 11 is removed. When the circular arc portion 11 is removed, the inside of the heat transfer tube 10 is exposed, so that the radioactive material may be discharged to the outside. Therefore, this circular arc part 11 is carried out in the dismantling chamber which can prevent the leakage of radioactive substances. In addition, since the subsequent procedure is performed in a state where the inside of the heat transfer tube 10 is exposed, it is performed in the dismantling chamber until the dismantling is completed.

The removal of the circular arc portion 11 can be performed by, for example, a well-known method. For example, the portion surrounding the arc portion 11 surrounding the trunk portion 30 is removed, and the arc portion 11 is exposed, and is then cut and recovered by a cutter such as a cutter or a laser. Since the collected circular arc portion 11 has radioactive substances attached thereto, it is discarded as radioactive substances.

Through this, as shown in FIG. 5 , the heat exchanger 1 is disassembled until only a plurality of straight pipe portions 12 stand on the tube sheet 20 .

<Welding part removal procedure> In the welded portion removal step S2, the tube sheet 20 is sliced parallel to the surface thereof to remove the welded portion 21 of the straight pipe portion 12 to the tube sheet 20.

Specifically, for example, at the cutting position C in FIG. 3 , cutting is performed with, for example, a saw blade type cutting machine.

The cutting position C is not particularly limited. When reusing the removed portion of the tube sheet including the welded portion 21 removed by slicing, it is preferable to reduce the frictional resistance when the straight tube portion 12 is penetrated when the cutting position C is close to the surface side of the tube sheet 20 .

On the other hand, when the tube sheet removed portion is not reused, it is preferable that the amount of the reused tube sheet 20 can be secured when the cutting position C is close to the back side of the tube sheet 20 .

In addition, through this slicing, the tube sheet removal portion is integrally removed together with the water chamber 31, and as shown in FIG. "Tube sheet") and straight pipe portion 12.

<Processing program for enlarged diameter> The enlarged diameter portion 12a of the straight pipe portion 12 is processed in the enlarged diameter portion processing procedure S3 and after the welded portion removal procedure S2.

Although the straight pipe portion 12 can be pulled out without processing the enlarged diameter portion 12a, the heat transfer pipe 10 is strongly adhered to the tube sheet due to the pipe expanding process during construction, as in the straight pipe portion 12 shown in FIG. 3 . In the case of 20, there is a possibility that the extraction of the straight pipe portion 12 cannot be easily performed by only removing the welded portion 21. When the straight pipe portion 12 is in close contact with the tube sheet 20 by expanding the diameter of the penetrating portion of the pipe sheet 20 in this way, after the welding part removal procedure S2, a procedure for processing the enlarged diameter portion 12a of the straight pipe portion 12 is provided, The straight pipe portion 12 can be easily drawn out.

As a method of processing the enlarged diameter portion 12a, a method by cutting, a method by relaxation of the adhesion force, and the like can be exemplified.

(by cutting method) In the method of permeation cutting, the diameter-expanding part processing program S3 is performed through cutting of the pipe wall of the straight pipe portion 12 .

Specifically, the enlarged diameter portion 12 a is cut off from the back side of the tube sheet 20 by a cutter such as the drill D shown in FIG. 7 . As for the drill D, a diameter equal to or slightly larger than the outer diameter of the enlarged diameter portion 12a is used so that the enlarged diameter portion 12a can be cut off. In Fig. 7, although the drill D is used, other grinding machines such as a reamer can also function similarly. In addition, it is not necessary to cut the entire diameter-enlarged portion 12a, and the straight pipe portion 12 may be easily pulled out of the range. In this case, the straight pipe portion 12 remaining in the tube sheet 20 is extracted from the tube sheet 20 in the extraction step S4.

By performing the process S3 of the enlarged diameter portion by cutting the pipe wall of the straight pipe portion 12 in this way, the close contact portion between the tube sheet 20 and the heat transfer pipe 10 can be surely removed, so that the straight pipe portion 12 can be drawn out more easily.

(Method of relaxation through close contact) In this method, the diameter-expanding part processing procedure S3 is performed through relaxation of the adhesion force between the straight pipe portion 12 and the tube sheet 20 . In this method, after relaxing the adhesion force between the straight pipe portion 12 and the tube sheet 20 , the enlarged diameter portion 12 a can be removed simultaneously with the extraction of the straight pipe portion 12 in the extraction procedure S4 described later. For this reason, workability is improved.

In terms of the method of alleviating the aforementioned adhesion force, it is preferable to adopt a method of cutting a part of the pipe wall of the straight pipe portion 12 in the plate thickness direction of the pipe plate 20 .

Specifically, as shown in FIG. 8 , a part of the pipe wall of the straight pipe portion 12 is cut away in the plate thickness direction of the tube sheet 20 so that the cross section is C-shaped. That is, after cutting, the tube wall of the straight tube portion 12 has a gap S extending in the thickness direction of the tube sheet 20 in a part of the tube wall. By deforming the enlarged diameter portion 12a so as to narrow the gap S, the diameter of the enlarged diameter portion 12a can be reduced. Accordingly, the adhesion force between the straight pipe portion 12 and the tube sheet 20 can be relaxed.

This gap S can be formed by, for example, a known slot machine. In addition, when performing the slotting process, although only the pipe wall of the straight pipe portion 12 may be cut off, it is preferable that a part of the tube sheet 20 is also cut off as shown in FIG. 8 . A part of the tube sheet 20 is also cut together so that the gap S can be surely provided in a part of the tube wall of the straight tube portion 12 .

In this way, the method of cutting a part of the pipe wall of the straight pipe portion 12 in the plate thickness direction of the tube sheet 20 is used as the method for alleviating the aforementioned adhesion force, so that the straight pipe portion 12 can be easily drawn out with a relatively small cutting amount. Therefore, the amount of dust adhering to the radioactive material generated at the time of excision is suppressed, so that the amount of blasting can be further reduced.

In addition, it is preferable to use the method which heats and cools at least the tube sheet 20 from the viewpoint of the relaxation method of other said adhesive force.

In this method, only the tube sheet 20 or the tube sheet 20 and the enlarged diameter portion 12a are heated and cooled to obtain relaxation of the adhesion force by using the difference diagram of the thermal expansion rate. In this case, it is preferable to rapidly heat and cool, and it is particularly preferable to rapidly cool. Performing rapid cooling makes it easy to progress the relaxation of the adhesion force. In addition, heating and cooling may be performed a plurality of times.

In this way, the straight pipe portion 12 can be drawn out without cutting the heat transfer pipe 10 by using the method of heating and cooling at least the tube sheet 20 in the aforementioned method of reducing the adhesion force.

<Extraction program> In the extraction process S4, the straight pipe part 12 is extracted after the arc part removal process S1, the welded part removal process S2, and the diameter-expanded part processing process S3.

Specifically, the plurality of straight pipe portions 12 are pulled out from the tube sheet 20 one at a time. The straight tube portion 12 is supported by the tube sheet 20 and the tube support plate 14, and its posture is maintained in a direction perpendicular to the tube sheet 20, so that it can be pulled out relatively easily.

Here, the tube sheet 20 supports the straight tube portion 12 to such an extent that the straight tube portion 12 does not move in the direction perpendicular to the central axis, but the tube support plate 14 does not fix the straight tube portion 12 to such an extent that it does not move. In addition, the straight pipe portion 12 is generally relatively long. When the straight pipe portion 12 is pulled out from the surface side, first, the straight pipe portion 12 is detached from the tube sheet 20 . In this way, the straight pipe portion 12 is drawn out only through the pipe support plate 14, but the pipe support plate 14 does not fix the straight pipe portion 12 to such an extent that it does not move in the direction perpendicular to the central axis, so it is difficult to maintain the straight pipe portion. 12, the straight pipe portion 12 is easily stuck on the pipe support plate 14.

For this reason, it is preferable to extract|extract from the back surface side of the tube sheet 20 in extraction process S4. In this way, the straight pipe portion 12 is pulled out from the back side of the tube sheet 20 in the pull-out step S4 so that the straight pipe portion 12 is supported by the tube sheet 20 to the end, and the long straight pipe portion 12 can be stably pulled out.

Since the collected straight pipe portion 12 has radioactive substances attached thereto, it is discarded as radioactive substances. On the other hand, the tube sheet 20 after the straight tube portion 12 has been drawn out can be easily removed physically even if the radioactive material adheres, so that it can be directly reused as a metal material.

＜Other＞ In the case of reusing the tube sheet removed portion, it is preferable that the dismantling method of the heat exchanger includes a procedure of removing the penetrating portion of the straight pipe portion 12 from the tube sheet removed portion. The removal of the penetrating portion of the straight pipe portion 12 from the tube sheet removal portion can be performed by the same method as that of the enlarged diameter portion processing procedure S3.

＜Advantages＞ In this heat exchanger dismantling method, the tube sheet 20 is sliced in parallel to remove the welded portion 21 of the straight tube portion 12 to the tube sheet 20 . For this reason, regardless of the number of the heat transfer tubes 10 , all the straight pipe portions 12 can be made movable by one cut. In addition, in this heat exchanger dismantling method, the straight pipe portion 12 is drawn out after the welding part removal step S2, so the straight pipe portion 12 in the tube sheet 20 is also drawn out at the same time. For this reason, the tube sheet 20 from which the straight tube portion 12 has been extracted can be directly reused as a metal material. Therefore, the dismantling method of the heat exchanger is excellent in workability, and the tube sheet 20 can be easily reused as a metal material.

[Other Embodiments] In addition, this invention is not limited to the said embodiment.

In the above-mentioned embodiment, although the case where the diameter-enlarged part processing program is provided was described, this process is not an essential process, and can be omitted, for example, when a heat transfer tube having no diameter-enlarged part is used.

In the foregoing embodiment, although the case where the arc removal process and the welding part removal process are performed in this order has been described, these processes may be performed in the reverse order, that is, the arc part removal process is performed after the welding part removal process. . In addition, when performing in the reverse order, the extraction process is performed after the arc part removal process, that is, at the end. [industrial availability]

The dismantling method of the heat exchanger of the present invention is excellent in workability and can further reduce the amount of explosions, and at the same time, it is easy to reuse the tube sheet as a metal material.

1: heat exchanger 10: Heat transfer tube 11: Arc part 12: Straight pipe 12a: Expansion part 13: Wedge-shaped blocking metal piece 14: Tube support plate 20: Tube Sheet 20a: Surface 20b: Back 21: Welding part 30: Torso 31: Water Room C: Cut off position D: drill S: Clearance

[ Fig. 1] Fig. 1 is a flowchart illustrating a method for disassembling a heat exchanger according to an embodiment of the present invention. [ Fig. 2] Fig. 2 is a schematic cross-sectional view showing the heat exchanger disassembled by the dismantling method of the heat exchanger of Fig. 1 . [ Fig. 3] Fig. 3 is a schematic enlarged cross-sectional view of part III of Fig. 2 . [ Fig. 4] Fig. 4 is a schematic diagram illustrating a state in which the head portion of the heat exchanger is removed. [ Fig. 5] Fig. 5 is a schematic diagram showing a state in which the circular arc portion of the heat exchanger is removed. [ Fig. 6] Fig. 6 is a schematic diagram illustrating a state in which the tube sheet of the heat exchanger is sliced. [ Fig. 7] Fig. 7 is a schematic cross-sectional view illustrating an example of a method of processing an enlarged diameter portion by cutting. [ Fig. 8] Fig. 8 is a schematic plan view illustrating an example of a method of processing the enlarged diameter portion through relaxation of the adhesion force.

Claims (7)

A dismantling method of a heat exchanger, the heat exchanger comprising a heat transfer tube, a tube sheet for fixing the heat transfer tube, and a cylindrical trunk portion for accommodating the heat transfer tube and the tube sheet, and used in a nuclear facility, The heat transfer tube has a circular arc portion and a straight pipe portion extending parallel to the central axis of the trunk portion from both ends of the circular arc portion and penetrating the tube sheet from the front surface to the back surface. The back side of the tube sheet is welded to the aforementioned tube sheet, The aforementioned dismantling method includes: The procedure of removing the arc portion of the aforementioned heat transfer tube, a process of slicing the tube sheet parallel to the surface to remove the welded portion of the straight tube portion to the tube sheet, and The process of extracting the straight pipe part after the above-mentioned arc part removal process and the above-mentioned welding part removal process. The dismantling method of a heat exchanger according to claim 1, wherein, in the extraction step, the straight pipe portion is extracted from the back side of the tube sheet. The dismantling method of a heat exchanger as claimed in claim 1 or 2, wherein, The straight pipe portion is enlarged in diameter at the penetrating portion of the tube sheet, and is in close contact with the tube sheet, It further includes a program for processing the diameter-enlarged portion of the straight pipe portion after the welding portion processing program. The dismantling method of a heat exchanger according to claim 3, wherein the processing procedure of the enlarged diameter portion is performed by cutting the pipe wall of the straight pipe portion. The dismantling method of a heat exchanger according to claim 3, wherein the diameter-expanding portion processing procedure is performed through relaxation of the adhesion force between the straight pipe portion and the tube sheet. The dismantling method of a heat exchanger according to claim 5, wherein the method of reducing the adhesion force is a method of cutting a part of the tube wall of the straight tube portion in the plate thickness direction of the tube sheet. The dismantling method of a heat exchanger according to claim 5, wherein the method of reducing the adhesion force is a method of heating and cooling at least the tube sheet.

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