How to dismantle a heat exchanger

Abstract

In the method for dismantling heat exchangers, it is possible to properly dismantle the heat exchanger while reducing the amount of waste. [Solution] A method for dismantling a heat exchanger in which a plurality of heat transfer tubes, each having a curved portion and a pair of straight portions continuous with each end of the curved portion, are arranged inside a shell, and at least a portion of the pair of straight portions is inserted into and supported by a tube sheet, comprising the steps of: removing the curved portion of the heat transfer tube; cutting the tube sheet radially at an axial position of the tube sheet according to the repair history of the heat transfer tube; and pulling out the remaining straight portions from the tube sheet.

Description

Technical Field

[0001] The present disclosure relates to a method for disassembling a heat exchanger.

Background Art

[0002] A nuclear power plant includes a nuclear reactor, a steam generator, a steam turbine, a generator, etc. In the steam generator, a tube sheet is disposed at the lower part of the shell, and a plurality of tube support plates are arranged vertically spaced above the tube sheet, and a plurality of heat transfer tubes forming an inverted U-shape are arranged inside the tube bundle outer cylinder. The heat transfer tubes are supported by a plurality of tube support plates at the intermediate part and supported by the tube sheet at each end. Further, the shell is provided with an inlet side water chamber mirror and an outlet side water chamber mirror at the lower end. One end of the heat transfer tube communicates with the inlet side water chamber, and the other end communicates with the outlet side water chamber.

[0003] In a nuclear power plant, aging equipment is disassembled and removed, and new equipment is introduced for renewal. In the steam generator, radioactive substances adhere to some parts. Therefore, when disassembling and removing the steam generator, it is necessary to separate and disassemble the members without radioactive substances attached and the members with radioactive substances attached. As a method for disassembling a heat exchanger, for example, there is one described in Patent Document 1 below.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The method for dismantling a heat exchanger described in Patent Document 1 involves removing the curved portion of the heat transfer tube, then slicing the tube sheet radially to remove the welded portion of the straight section of the heat transfer tube from the tube sheet, and finally pulling out the straight section from the tube sheet. However, if the heat transfer tube deteriorates due to long-term use, there is a risk of primary cooling water leakage. Therefore, leakage of primary cooling water is prevented by sealing the deteriorated or potentially deteriorated end of the heat transfer tube with a stopper plug. The heat exchanger to be dismantled may have heat transfer tubes with plugs attached. Since the stopper plug is attached to the straight section inserted into the tube sheet, if the tube sheet is sliced ​​radially, the stopper plug remains, and even if the welded portion of the straight section is removed, it becomes difficult to pull out the straight section from the tube sheet.

[0006] This disclosure aims to solve the aforementioned problems and to provide a method for dismantling a heat exchanger that enables proper dismantling of the heat exchanger and reduces the amount of waste. [Means for solving the problem]

[0007] A method for dismantling a heat exchanger according to the present disclosure to achieve the above objective, wherein a plurality of heat transfer tubes having curved portions and a pair of straight portions continuous to each end of the curved portions are arranged inside a shell, and at least a portion of the pair of straight portions is inserted into and supported by a tube sheet, the method for dismantling a heat exchanger comprises the steps of: removing the curved portions of the heat transfer tubes; cutting the tube sheet radially at an axial position of the tube sheet according to the repair history of the heat transfer tubes; and pulling out the straight portions remaining on the tube sheet from the tube sheet. [Effects of the Invention]

[0008] According to the method for dismantling a heat exchanger described herein, the heat exchanger can be properly dismantled, and the amount of waste can be reduced. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic diagram showing the internal configuration of a steam generator. [Figure 2]Figure 2 is a cross-sectional view showing the lower structure of the steam generator. [Figure 3] Figure 3 is a flowchart illustrating the method for dismantling a heat exchanger. [Figure 4] Figure 4 is a cross-sectional view showing a tube sheet with heat transfer tubes installed. [Figure 5] Figure 5 is a plan view showing a tube sheet with heat transfer tubes installed. [Figure 6] Figure 6 is a cross-sectional view of the tube sheet showing the disassembled state of the heat exchanger. [Figure 7] Figure 7 is a cross-sectional view showing the disassembled state of the tube sheet on the inlet side water chamber. [Figure 8] Figure 8 is a cross-sectional view showing the disassembled state of the tube sheet on the outlet side water chamber. [Modes for carrying out the invention]

[0010] Preferred embodiments of the present disclosure will be described in detail below with reference to the drawings. However, these embodiments do not limit the present disclosure, and where there are multiple embodiments, they may be combinations of these embodiments. Furthermore, the components in the embodiments include those readily conceivable by those skilled in the art, those that are substantially identical, and those that are equivalent.

[0011] <Steam Generator> Figure 1 is a schematic diagram showing the internal configuration of a steam generator.

[0012] As shown in Figure 1, the steam generator 100 is a heat exchanger used in a nuclear power plant. The steam generator 100 performs heat exchange between the primary coolant, which has become hot in the reactor, and the secondary coolant supplied to the steam turbine. By performing heat exchange between the primary and secondary coolant, the steam generator 100 generates steam by heating the secondary coolant with the primary coolant.

[0013] The steam generator 100 is arranged along the vertical direction. The steam generator 100 has a body 102. The body 102 is hollow cylindrical in shape. A heat transfer tube group 104 is provided inside the body 102. The heat transfer tube group 104 consists of a plurality of heat transfer tubes 105 that are inverted U-shaped. The heat transfer tubes 105 are arranged such that the curved portion at the top, which is inverted U-shaped, is convex upwards. The lower end of the heat transfer tube 105 is supported by a tube sheet 106, and the middle part is supported by the body 102 via a plurality of tube support plates 108. The tube support plates 108 have a large number of through holes, and the heat transfer tubes 105 are inserted through the through holes. The tube support plates 108 are arranged along the vertical direction at predetermined intervals (preferably at equal intervals).

[0014] The shell section 102 has a water chamber 110 at its lower end. The water chamber 110 is bowl-shaped and its interior is divided into an inlet-side water chamber 114 and an outlet-side water chamber 116 by a partition plate 112. One end of a heat transfer tube 105 is connected to the inlet-side water chamber 114, and the other end of a heat transfer tube 105 is connected to the outlet-side water chamber 116. Furthermore, the inlet-side water chamber 114 has an inlet-side pipe support 115 that leads to the outside of the shell section 102, and the outlet-side water chamber 116 has an outlet-side pipe support 117 that leads to the outside of the shell section 102. The inlet-side pipe support 115 is connected to a primary cooling water pipe (not shown) from a pressurized water reactor, and the outlet-side pipe support 117 is connected to a primary cooling water pipe (not shown) that sends the heat-exchanged primary cooling water to the pressurized water reactor.

[0015] The cylinder part 102 has a steam-water separator 118 for separating feed water into steam and hot water and a moisture separator 120 for removing the moisture of the separated steam to make it in a state close to dry steam disposed in its upper half. A water supply pipe 122 for supplying secondary cooling water from the outside into the cylinder part 102 is inserted between the steam-water separator 118 and the heat transfer tube group 104 in the cylinder part 102. A steam discharge port 124 is formed at the upper end of the cylinder part 102. In the lower half of the cylinder part 102, a water supply path 128 is formed for flowing down the secondary cooling water supplied from the water supply pipe 122 into the inside of the cylinder part 102 between the cylinder part 102 and the tube group outer cylinder 126, turning it back by the tube sheet 106, and raising it along the heat transfer tube group 104. Note that the steam discharge port 124 is connected to a secondary cooling water pipe (not shown) for sending steam to a steam turbine, and the water supply pipe 122 is connected to a secondary cooling water pipe (not shown) for supplying the secondary cooling water in which the steam used in the steam turbine is cooled by a condenser (not shown).

[0016] The cylinder part 102 is provided with hand holes 132 and 134 for communicating the inside and the outside. The hand holes 132 and 134 are provided, for example, on the side surfaces of the upper and lower halves of the cylinder part 102. In the present embodiment, they are provided at positions above the lowermost tube support plate 108 and above the uppermost tube support plate 108. The hand holes 132 and 134 are also provided so as to penetrate the tube group outer cylinder 126 and are configured to enable access from the outside of the cylinder part 102 toward the tube support plate 108. Note that the hand holes 132 and 134 are closed with lids when the steam generator 100 is in use. The hand holes 132 and 134 are provided on both sides of the cylinder part 102 so as to pass through the center of the reverse U-shape of the heat transfer tube 105 and face each other.

[0017] <Tube support plate> Figure 2 is a cross-sectional view showing the lower structure of the steam generator.

[0018] As shown in FIG. 2, a tube sheet 106 is disposed at the lower part inside the body 102. The tube sheet 106 has a disk shape with a predetermined thickness. A plurality of through holes 141 are provided in the tube sheet 106 along the axial direction (thickness direction). The plurality of through holes 141 are provided, for example, in a staggered pattern. The plurality of heat transfer tubes 105 form an inverted U shape. That is, the heat transfer tube 105 has a curved portion 105a, a straight portion 105b continuous with one end of the curved portion 105a, and a straight portion 105c continuous with the other end of the curved portion 105a. The heat transfer tube 105 is inserted through each through hole 141 of the tube sheet 106 with the straight portion 105b and the straight portion 105c, and is fixed, for example, by tube expanding and welding.

[0019] A water chamber 110 is provided at the lower end of the body 102, and the water chamber 110 is partitioned into an inlet side water chamber 114 and an outlet side water chamber 116 by a partition plate 112. The inlet side water chamber 114 communicates with the straight portion 105b of the heat transfer tube 105 passing through the tube sheet 106, and the outlet side water chamber 116 communicates with the straight portion 105c of the heat transfer tube 105 passing through the tube sheet 106.

[0020] In the steam generator 100, high-temperature primary cooling water heated in a pressurized water reactor is supplied from the inlet side header 115 to the inlet side water chamber 114. The high-temperature primary cooling water supplied to the inlet side water chamber 114 is introduced into each heat transfer tube 105 from a plurality of straight portions 105b opening to the lower surface 106a of the tube sheet 106. The high-temperature primary cooling water flows through the straight portion 105b, the curved portion 105a, and the straight portion 105c of the heat transfer tube 105. At this time, the high-temperature primary cooling water exchanges heat with the secondary cooling water supplied inside the body 102. That is, the heat of the high-temperature primary cooling water is transferred to the secondary cooling water, so that the primary cooling water is cooled and the secondary cooling water is heated.

[0021] The cooled primary cooling water is discharged from the straight portion 105c opening to the lower surface 106b of the tube sheet 106 to the outlet side header 117. The primary cooling water discharged to the outlet side header 117 is discharged from the outlet side header 117 to the outside and returned to the pressurized water reactor.

[0022] In the steam generator 100, primary cooling water containing radioactive material flows through the inlet water chamber 114, heat transfer tubes 105, and outlet water chamber 116. As a result, radioactive material adheres to the lower end of the shell 102 where the inlet water chamber 114 and outlet water chamber 116 are located, the heat transfer tubes 105, and the underside of the tube sheet 106. When the steam generator 100 is dismantled, components that do not have radioactive material attached can be reused. On the other hand, components that do have radioactive material attached cannot be reused and are treated as waste.

[0023] In other words, when dismantling the steam generator 100, it is necessary to separate the components that do not have radioactive material attached from the components that do. Specifically, when dismantling the steam generator 100, it is necessary to separate the multiple heat transfer tubes 105 with radioactive material attached to their lower surfaces 106a, 106b from the tube sheet 106. At this time, it is preferable to minimize the portion of the tube sheet 106 that is treated as waste.

[0024] <How to dismantle a heat exchanger> Figure 3 is a flowchart showing the method for dismantling the heat exchanger, Figure 4 is a cross-sectional view showing the tube sheet with the heat transfer tubes installed, Figure 5 is a plan view showing the tube sheet with the heat transfer tubes installed, Figure 6 is a cross-sectional view of the tube sheet showing the dismantled state of the heat exchanger, Figure 7 is a cross-sectional view showing the dismantled state of the tube sheet on the inlet side water chamber, and Figure 8 is a cross-sectional view showing the dismantled state of the tube sheet on the outlet side water chamber.

[0025] The method for dismantling the heat exchanger in this embodiment includes the steps of: removing the curved portion 105a of the heat transfer tube 105; cutting the tube sheet 106 radially at an axial position of the tube sheet 106 corresponding to the repair history of the heat transfer tube 105; and pulling out the straight portions 105b and 105c remaining on the tube sheet 106.

[0026] Specifically, the method for dismantling the heat exchanger in this embodiment involves cutting the tube sheet 106 in the axial direction, and then cutting the divided tube sheets 106A and 106B radially at positions in the axial direction corresponding to the repair history of the heat transfer tubes 105.

[0027] The method for disassembling the heat exchanger of this embodiment will be described in detail below.

[0028] As shown in Figures 1 and 3, in step S11, the upper part of the steam generator 100 is removed by cutting it with a cutting device (not shown). Specifically, the upper part of the shell 102, the steam-water separator 118, the moisture separator 120, the feedwater pipe 122, and the upper part of the outer tube assembly 126 are cut and removed from the steam generator 100. This process exposes multiple heat transfer tubes 105. Then, the heat transfer tubes 105 and the tube sheet 106 are separated from the shell 102.

[0029] As shown in Figures 3 and 5, in step S12, the curved portion 105a is cut and removed from the heat transfer tube 105 supported by the tube sheet 106. That is, for multiple heat transfer tubes 105, the boundary between the curved portion 105a and the straight portions 105b, 105c, or the exposed portion from the tube sheet 106 in the straight portions 105b, 105c, is cut at cutting position L1. When the curved portion 105a of the heat transfer tube 105 is cut, the inside of the heat transfer tube 105 is exposed, and there is a risk that primary cooling water containing radioactive material may leak out. For this reason, it is preferable to perform the cutting of the curved portion 105a inside a dismantling room (not shown). Furthermore, it is preferable to perform the processing after the cutting of the curved portion 105a inside the dismantling room as well. The cut curved portion 105a has radioactive material attached to it and is therefore disposed of as radioactive waste.

[0030] As shown in Figures 3, 4, and 5, in step S13, the tube sheet 106 is cut along the axial direction (thickness direction). Of the multiple heat transfer tubes 105, any heat transfer tubes 105 that are deteriorated or likely to deteriorate have their ends sealed with stopper plugs 142 to prevent leakage of primary cooling water. The straight section 105b of the heat transfer tube 105 that penetrates the tube sheet 106 communicates with the inlet water chamber 114, and the straight section 105c that penetrates the tube sheet 106 communicates with the outlet water chamber 116. The stopper plug 142 is attached, for example, to the straight section 105b of the heat transfer tube 105 that communicates with the inlet water chamber 114.

[0031] Therefore, the tube sheet 106 is cut axially at the boundary between one straight section 105b and the other straight section 105c of the heat transfer tube 105. That is, the tube sheet 106 is cut axially at cutting position L2 at the boundary between the inlet side water chamber 114 and the outlet side water chamber 116 (the position where the partition plate 112 is provided). Cutting position L2 passes through the center position O of the tube sheet 106. By cutting the tube sheet 106 along the axial direction, the tube sheet 106 is divided into two parts.

[0032] When cutting the tube sheet 106 along the axial direction, the cutting position L2 was defined as the boundary position between the straight section 105b and the straight section 105c, that is, the boundary position between the inlet water chamber 114 and the outlet water chamber 116, but it is not limited to this position. The heat transfer tube 105 (straight section 105b) with the stopper plug 142 attached is stored in the repair history. Also, the stopper plug 142 may be attached to the straight section 105c of the heat transfer tube 105 that communicates with the outlet water chamber 116. Therefore, the cutting position L2 may be defined as the boundary position between the heat transfer tube 105 (straight sections 105b, 105c) with the stopper plug 142 attached and the heat transfer tube 105 (straight sections 105b, 105c) without the stopper plug 142 attached. In this case, the cutting position L2 is not limited to a position passing through the center position O of the tube sheet 106. Alternatively, the tube sheet 106 may be divided into three or more pieces by cutting it along its axial direction.

[0033] As shown in Figures 3 and 6, in step S14, the tube sheet 106 is cut radially (into slices) at predetermined positions in the axial direction of the tube sheet 106 according to the repair history of the heat transfer tube 105. By cutting the tube sheet 106 axially, it is divided into one semicircular section tube sheet 106A and the other semicircular section tube sheet 106B. The straight sections 105b and 105c of the heat transfer tube 105 are inserted into the through holes 141 of the tube sheet 106, and the ends extend to the lower surfaces 106a and 106b, where they are fixed by welding to form connection sections 143a and 143b. In addition, a stopper plug 142 is attached to the straight section 105b of some of the heat transfer tubes 105 in one of the section tube sheets 106A.

[0034] Therefore, after cutting the tube sheet 106 axially at cutting position L2, the divided tube sheets 106A and 106B are cut radially at axial positions corresponding to the repair history of the heat transfer tube 105. Specifically, the divided tube sheet 106A is cut radially at cutting position L3, which is a thickness t1 away from the bottom surface 106a. On the other hand, the divided tube sheet 106B is cut radially at cutting position L4, which is a thickness t2 (t1>t2) away from the bottom surface 106a.

[0035] In the divided tube sheet 106A, there are stopper plugs 142 on the straight sections 105b of some of the heat transfer tubes 105. In this case, it is difficult to pull out the heat transfer tubes 105 from the divided tube sheet 106A unless both the connection section 143a and the stopper plugs 142 are removed. Therefore, the cutting position L3 is set to be the area above the stopper plugs 142 in the divided tube sheet 106A. On the other hand, in the divided tube sheet 106B, there are no stopper plugs 142 on the straight sections 105b of the heat transfer tubes 105. In this case, the heat transfer tubes 105 can be pulled out from the divided tube sheet 106B by removing only the connection section 143b. Therefore, the cutting position L4 is set to be the area above the connection section 143b in the divided tube sheet 106B.

[0036] As shown in Figures 6 and 7, the divided tube sheet 106A is cut radially at cutting position L3, dividing it into an upper divided tube sheet 106A-1 and a lower divided tube sheet 106A-2. The upper divided tube sheet 106A-1 side has an upper divided tube sheet 106A-1 that is free of radioactive material and a straight section 105b-1 of multiple heat transfer tubes 105. The upper divided tube sheet 106A-1 and the straight section 105b-1 can be reused. On the other hand, the lower divided tube sheet 106A-2 side has a lower divided tube sheet 106A-2 that is covered with radioactive material and a straight section 105b-2 of multiple heat transfer tubes 105. The lower divided tube sheet 106A-2 and the straight section 105b-2 are treated as radioactive waste.

[0037] Furthermore, as shown in Figures 6 and 8, the divided tube sheet 106B is cut radially at cutting position L4, dividing it into an upper divided tube sheet 106B-1 and a lower divided tube sheet 106B-2. The upper divided tube sheet 106B-1 side has an upper divided tube sheet 106B-1 that is free of radioactive material and a straight section 105c-1 of multiple heat transfer tubes 105. The upper divided tube sheet 106B-1 and the straight section 105c-1 can be reused. On the other hand, the lower divided tube sheet 106B-2 side has a lower divided tube sheet 106B-2 that is covered with radioactive material and a straight section 105c-2 of multiple heat transfer tubes 105. The lower divided tube sheet 106B-2 and the straight section 105c-2 are treated as radioactive waste. In this case, because the thickness of the lower split tube sheet 106B-2 is thin, the amount of tube sheet 106 that becomes radioactive waste can be reduced.

[0038] As shown in Figures 3, 7, and 8, in step S15, the straight sections 105b-1 and 105c-1 of the heat transfer tube 105 mounted on the upper split tube sheets 106A-1 and 106B-1 are treated to enlarge their diameter. That is, the straight sections 105b-1 and 105c-1 are enlarged to fix them to the through holes 141 in the upper split tube sheets 106A-1 and 106B-1. Therefore, by removing the enlarged portions of the straight sections 105b-1 and 105c-1, it becomes possible to pull the straight sections 105b-1 and 105c-1 out of the upper split tube sheets 106A-1 and 106B-1.

[0039] As a process for removing the enlarged diameter portion of the straight sections 105b-1 and 105c-1, one method is to cut the enlarged diameter portion with a cutting tool, but this method is not limited to this method, and other existing methods may also be used.

[0040] As shown in Figures 3, 7, and 8, step S16 involves the extraction of the heat transfer tube 105. Specifically, multiple straight sections 105b-1 and 105c-1 are extracted from the upper split tube sheets 106A-1 and 106B-1.

[0041] In the embodiment described above, the tube sheet 106 was cut axially, and then the divided tube sheets 106A and 106B were cut radially at positions in the axial direction corresponding to the repair history of the heat transfer tubes 105. However, the dismantling method is not limited to this. For example, the tube sheet 106 may be cut radially at positions in the axial direction corresponding to the repair history of the heat transfer tubes 105 without cutting the tube sheet 106 axially.

[0042] [Effects of this embodiment] The method for dismantling a heat exchanger according to the first embodiment includes the steps of removing the curved portion 105a of the heat transfer tube 105, cutting the tube sheet 106 radially at an axial position of the tube sheet 106 according to the repair history of the heat transfer tube 105, and pulling out the straight portions 105b and 105c remaining on the tube sheet 106.

[0043] According to the first embodiment of the method for dismantling a heat exchanger, the tube sheet 106 is cut radially at a position corresponding to the repair history of the heat transfer tubes 105. Therefore, for example, even if there is a stopper plug 142 in the straight section 105b of the heat transfer tube 105, the tube sheet 106 is cut in such a way that the stopper plug 142 is removed, allowing the heat exchanger to be properly dismantled. Furthermore, if there is no stopper plug 142 in the straight section 105c of the heat transfer tube 105, the tube sheet 106 can be thinly cut and removed, thereby reducing the amount of radioactive waste.

[0044] The method for dismantling a heat exchanger according to the second embodiment is the method for dismantling a heat exchanger according to the first embodiment, further comprising: a connection portion 143 provided between the ends of the straight sections 105b and 105c of the heat transfer tube 105 and the end face of the tube sheet 106; a stopper plug 142 installed inside the straight section 105b; and the tube sheet 106 being cut radially to remove the connection portion 143 and the stopper plug 142 from the tube sheet 106. By cutting the tube sheet 106 so that the connection portion 143 and the stopper plug 142 are removed, the straight sections 105b and 105c can be easily pulled out from the tube sheet 106.

[0045] The third embodiment of the heat exchanger dismantling method is the first or second embodiment of the heat exchanger dismantling method, further comprising cutting the tube sheet 106 axially, and then cutting the divided tube sheets 106A and 106B radially at axial positions corresponding to the repair history of the heat transfer tubes 105. This makes it possible to set a cutting position along the radial direction for each divided tube sheet 106A and 106B, thereby reducing radioactive waste. In addition, it is not necessary to cut the disc-shaped tube sheet 106 into sections, and the radial cutting work can be simplified.

[0046] A method for dismantling a heat exchanger according to a fourth embodiment is a method for dismantling a heat exchanger according to a third embodiment, further comprising cutting the tube sheet 106 axially at the boundary position between one straight section 105b continuous with the end of the curved section 105a and the other straight section 105c continuous with the end of the curved section 105a. This allows for, for example, the dismantling of the tube sheet into a divided tube sheet 106A with a stopper plug 142 and a divided tube sheet 106B without a stopper plug 142.

[0047] The fifth embodiment of the method for dismantling a heat exchanger is the method for dismantling a heat exchanger according to the third or fourth embodiment, further comprising cutting the tube sheet 106 axially at the center position O of the tube sheet 106. This simplifies the cutting work of the tube sheet 106.

[0048] The sixth embodiment of the method for dismantling a heat exchanger is a method for dismantling a heat exchanger according to any one of the first to fifth embodiments, further comprising dividing the tube sheet 106 into two or more parts by cutting the tube sheet 106 in the axial direction. This makes it possible to subdivide the heavy tube sheet 106 and improve the handling of the tube sheet 106. [Explanation of Symbols]

[0049] 100 Steam Generator 102 Torso 104 Heat transfer tube group 105 Heat transfer tube 106 Tube plate 108 Pipe support plate 110 Water room 112 Partition Plate 114 Water chamber on the entrance side 115 Inlet side pipe stand 116 Outlet side water chamber 117 Outlet side nozzle 141 Through hole 142 Stop plug 143a, 143b Connection section

Claims

1. In a method for dismantling a heat exchanger in which a plurality of heat transfer tubes, each having a curved portion and a pair of straight portions continuous with each end of the curved portion, are arranged inside a shell, and at least a portion of the pair of straight portions is inserted into and supported by a tube sheet, The steps include removing the curved portion of the heat transfer tube, The steps include: cutting the tube sheet radially at a position in the axial direction of the tube sheet corresponding to the repair history of the heat transfer tube; The steps include: pulling out the straight portion remaining on the tube sheet from the tube sheet; A method for dismantling a heat exchanger having [a specific feature / feature].

2. The heat transfer tube has a connection portion between the end of the straight section and the end face of the tube sheet, a stopper plug is installed inside the straight section, and the tube sheet is cut radially so as to remove the connection portion and the stopper plug from the tube sheet. A method for dismantling a heat exchanger as described in claim 1.

3. After cutting the tube sheet in the axial direction, the divided tube sheet is cut radially at positions in the axial direction corresponding to the repair history of the heat transfer tube. A method for dismantling a heat exchanger as described in claim 1.

4. The tube sheet is cut axially at the boundary between one straight section continuous with the end of the curved section and the other straight section continuous with the end of the curved section. The method for dismantling a heat exchanger as described in claim 3.

5. The tube sheet is cut axially at the center of the tube sheet. The method for dismantling a heat exchanger as described in claim 3.

6. The tube sheet is divided into two or more parts by cutting it in the axial direction. The method for dismantling a heat exchanger as described in claim 3.

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