Pipe joining method

Abstract

To provide a piping connection method capable of improving safety by suppressing occurrence of leakage or rupture.SOLUTION: A piping connection method includes, as shown from (1) to (4), the steps of: (1) forming a protrusion 131 on each connection surface 130 of two piping, and a passage groove 132 enclosing the protrusion 131, and passable by chemical polishing liquid; (2) superposing each connection surface 130 of two piping; (3) introducing chemical polishing liquid into the passage groove 132 of the piping; (4) subjecting each connection surface 130 of two piping to ultrasonic junction by an ultrasonic vibrator.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a pipe joining method. [Background technology]

[0002] Many pipes run through structures such as power plants and factories. Two pipes are connected by overlapping and joining their ends.

[0003] FIG. 8 is a diagram showing an example of a conventional pipe joining method. In one example of a conventional pipe joining method shown in Fig. 8, first, the flange 20A of the first pipe 10A and the flange 20B of the second pipe 10B are overlapped. Then, the flange 20A of the first pipe 10A and the flange 20B of the second pipe 10B are fastened and fixed using bolts 30 and nuts 40. Furthermore, a plurality of bolts 30 and nuts 40 are provided along the circumferential direction of the flanges 20A and 20B.

[0004] In one example of a conventional pipe joining method, an O-ring 50 is used as a seal member. To fit this O-ring 50, a seal groove 60 is formed in the flange 20A of the first pipe 10A and the flange 20B of the second pipe 10B. Then, by tightening the bolt 30 and the nut 40, the joining surfaces of the flange 20A of the first pipe 10A and the flange 20B of the second pipe 10B are brought closer to each other. As a result, the O-ring 50 installed in the seal groove 60 strongly contacts the inner surface of the seal groove 60, realizing a seal between the first pipe 10A and the second pipe 10B.

[0005] FIG. 9 is a diagram showing another example of a conventional pipe joining method. In the pipe joining method shown in FIG. 9, end faces of a first pipe 90A and a second pipe 90B are overlapped with each other, and the end faces of the pipes 90A and 90B are joined with a weld metal 80.

[0006] Another example of a conventional pipe joining method is an ultrasonic joining method in which two members are brought into strong contact with each other and ultrasonic waves are introduced from the outside to relatively vibrate the two contacting surfaces in an in-plane direction (see Patent Document 1). In the ultrasonic joining method, the vibrations cause plastic deformation in a surface coating such as an oxide coating, and a new surface appears directly below the coating. The new surfaces bond metallically to each other to join the pipes. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2007-253164 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the case of fastening using bolts and nuts, if the bolts 30 loosen during operation of the device, as shown in Fig. 8, the tightening of the flanges 20A, 20B weakens, and the O-ring 50 no longer makes strong contact with the inner surface of the seal groove 60. This may cause leakage due to a path 70 formed between the two flanges 20A, 20B. Furthermore, if the O-ring 50 deteriorates over time due to creep or the like, a path 70 will similarly form between the two flanges 20A, 20B, causing leakage.

[0009] Furthermore, in the pipe joining method shown in FIG. 8, if the tightening force of the multiple bolts 30 and nuts 40 becomes uneven, the surface pressure of the two flanges 20A, 20B becomes uneven, and leaks occur at points where the surface pressure is weak.

[0010] 9, an unwelded portion K1 was generated at the interface between the pipes 90A and 90B, which are the base materials, and the weld metal 80. Furthermore, tensile stress P1 was generated in the metal of the welded portion due to the influence of heat input during welding. Therefore, in the joining method using welding, there was a possibility that a crack would be generated starting from the unwelded portion K1 and a break would occur due to vibration being applied to the pipes 90A and 90B during operation of the equipment.

[0011] In addition, the ultrasonic bonding method requires plastic deformation of the surface coating by ultrasonic vibration and subsequent metal bonding between the newly formed surfaces, and thus has been used for relatively soft metals such as copper, aluminum, and their alloys. However, for piping in power plants and factories such as nuclear power plants, steel materials such as carbon steel and low alloy steel, which have a higher yield stress and are harder than copper and aluminum, are used. And, for members such as piping made of these steel materials, even if the joining surfaces are strongly contacted and ultrasonic waves are introduced, the surface coating is not easily plastically deformed and a new surface does not appear. Therefore, it was difficult to reliably join two pipes with the conventional ultrasonic bonding method shown in Patent Document 1.

[0012] In consideration of the above problems, an object of the present invention is to provide a pipe joining method capable of suppressing the occurrence of leakage and breakage and improving safety. [Means for solving the problem]

[0013] In order to solve the above problems and achieve the object, a pipe joining method includes the following steps (1) to (4). (1) A process for forming a convex portion on the joint surface of two pipes and a flow channel surrounding the convex portion, through which the chemical polishing liquid can pass. (2) The process of overlapping the joint surfaces of two pipes. (3) A process of introducing a chemical polishing solution into the flow channel of the piping. (4) A process in which the joint surfaces of two pipes are ultrasonically joined using an ultrasonic vibrator. Effect of the Invention

[0014] According to the pipe joining method having the above-mentioned configuration, the occurrence of leakage and breakage can be suppressed, and safety can be improved. [Brief description of the drawings]

[0015] [Figure 1] FIG. 2 is a schematic diagram showing a pipe joining method according to the first embodiment. [Diagram 2] 1 is a front view showing a joint surface of a pipe in a pipe joining method according to a first embodiment. FIG. [Diagram 3] 3 is an explanatory view showing, in an enlarged scale, a state in which the joining surfaces of two pipes are brought into contact with each other in the pipe joining method according to the first embodiment; FIG. [Figure 4] FIG. 13 is a diagram showing the relationship between the gap width at the joint surfaces of two pipes and the penetration length of a chemical polishing liquid. [Diagram 5] 5A to 5C are diagrams showing modified examples of a protrusion in the pipe connecting method according to the first embodiment. [Figure 6] FIG. 4 is a schematic diagram showing a pipe joining method according to a second embodiment. [Figure 7] FIG. 11 is a front view showing a joint surface of a pipe in a pipe joining method according to a second embodiment. [Figure 8] FIG. 11 is a cross-sectional view showing a conventional pipe joining method. [Figure 9] FIG. 13 is a schematic diagram showing a conventional pipe joining method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the pipe joining method will be described with reference to Figures 1 to 7. In addition, the same reference numerals are used to designate common members in each figure.

[0017] 1. First embodiment 1-1.Example of pipe connection method First, an example of a structure in which a pipe connecting method according to a first embodiment (hereinafter referred to as "this example") is installed will be described with reference to FIG. FIG. 1 is a schematic diagram showing an example of a structure.

[0018] The pipe joining method of this embodiment is applied to, for example, pipes connected to a reactor pressure vessel of a nuclear power plant. The pipes pass through the reactor coolant and are provided with an isolation valve. By directly connecting the isolation valve to the reactor pressure vessel, even if a pipe such as a main steam pipe breaks, the loss of reactor coolant in the reactor pressure vessel can be avoided by closing the isolation valve.

[0019] As shown in Fig. 1, the pipe joining method of this embodiment is a method for joining a first pipe 110A and a second pipe 110B. A flange 120A is provided at an end portion of the first pipe 110A, which is a joining portion, and a flange 120B is provided at an end portion of the second pipe 110B, which is a joining portion. The flanges 120A and 120B protrude in a direction perpendicular to the axial direction of the pipes 110A and 110B. The flange 120A of the first pipe 110A and the flange 120B of the second pipe 110B are fixed by a plurality of jigs 160 such as vices with their joining surfaces 130, which are the surfaces facing each other, in contact with each other.

[0020] The jig 160 has a pressing bolt 162 that contacts the flanges 120A, 120B, and a nut 161 that screws into the pressing bolt 162. Then, by tightening the nut 161, the pressing bolt 162 presses the flanges 120A, 120B in a direction in which they come into contact with each other. In addition, an ultrasonic vibrator 230 used for ultrasonic bonding comes into contact with the flanges 120A, 120B.

[0021] FIG. 2 is a front view showing the joining surface 130 of the flanges 120A, 120B. 2, the flanges 120A and 120B are formed in a substantially disk shape so as to surround the cylindrical holes 111 of the pipes 110A and 110B. Note that the shape of the flanges 120A and 120B is not limited to a disk shape, and may be various other shapes such as a square or a hexagon.

[0022] A labyrinth structure 133 consisting of a plurality of convex portions 131 and a plurality of flow path grooves 132 is formed on a joint surface 130 of the flanges 120A, 120B. The plurality of convex portions 131 protrude from the joint surface 130. As a result, a plurality of flow path grooves 132 are formed between the plurality of convex portions 131. The plurality of convex portions 131 are formed on concentric circles of the cylindrical hole 111. Similarly to the convex portions 131, the plurality of flow path grooves 132 are also formed on concentric circles of the cylindrical hole 111.

[0023] A communication groove 132b is formed in the protrusion 131 to communicate with the two flow grooves 132, 132 sandwiching the protrusion 131. Therefore, the multiple flow grooves 132 are all communicated with each other via the communication groove 132b. Note that the communication groove 132b is not formed in the innermost protrusion 131a arranged at the innermost portion in the radial direction of the joint surface 130 of the multiple protrusions 131 and the outermost protrusion 131b arranged at the outermost portion.

[0024] The innermost convex portion 131a is formed continuously in the circumferential direction of the cylindrical hole 111 of the pipes 110A and 110B and surrounds the cylindrical hole 111. This makes it possible for the innermost convex portion 131a to prevent the fluid passing through the cylindrical hole 111 of the pipes 110A and 110B from leaking out of the pipes 110A and 110B via the flow path groove 132.

[0025] During the pipe joining operation, an introduction hole 180 communicating with the flow path groove 132 is formed in the outermost convex portion 131b. The introduction hole 180 is a through hole penetrating the outermost convex portion 131b in the radial direction, and is formed in the side surface of the flanges 120A and 120B. An introduction pipe 190 is connected to this introduction hole 180. Then, the chemical polishing liquid M1 (see FIG. 3) is introduced into the flow path groove 132 through the introduction pipe 190 and the introduction hole 180. As described above, by not providing the communication groove 132b in the outermost convex portion 131b, it is possible to prevent the liquid introduced into the flow path groove 132 during the pipe joining operation from leaking out to the outside.

[0026] Furthermore, the multiple protrusions 131 formed on the joint surface 130 of the flange 120A of the first pipe 110A and the multiple protrusions 131 formed on the joint surface 130 of the flange 120B of the second pipe 110B are formed in the same positions and shapes. This allows the protrusions 131 formed on each joint surface 130 to face each other and be close to each other when the joint surfaces 130 of the flanges 120A and 120B are overlapped.

[0027] In this embodiment, the protrusions 131 and the flow channel grooves 132 are formed on concentric circles, but the present invention is not limited to this. For example, the protrusions 131 and the flow channel grooves 132 may be formed radially along the radial direction of the joining surface 130, or may have various other shapes.

[0028] 1-2. Piping joining method Next, a pipe joining method will be described with reference to FIGS. First, as shown in Fig. 1, the joint surface 130 of the flange 120A of the first pipe 110A and the joint surface 130 of the flange 120B of the second pipe 110B are overlapped. Then, the flanges 120A, 120B are fixed using a plurality of jigs 160. In addition, a contact plate 170 is installed between the flanges 120A, 120B and the pressing bolts 162 of the jigs 160. This allows the load from the plurality of jigs 160 to be applied to the flanges 120A, 120B so as to be uniformly distributed.

[0029] Furthermore, when the joining surfaces 130 of the two flanges 120A, 120B are brought into contact with each other, the positions are adjusted so that the convex portions 131 of the labyrinth structures 133 formed on the joining surfaces 130 come into contact with each other.

[0030] 2, after the two flanges 120A, 120B are fixed to a jig 160, an introduction hole 180 is formed in the side surface of the flanges 120A, 120B, i.e., in the outermost convex portion 131b. Further, a thread is formed in the introduction hole 180 to connect an introduction pipe 190.

[0031] The operation of forming the introduction holes 180 may be performed before the flanges 120A, 120B are fixed by the jig 160. The positions and number of the introduction holes 180 can be set arbitrarily.

[0032] Next, an introduction pipe 190 is connected to the introduction hole 180. Then, the chemical polishing liquid M1 is introduced into the flow channel 132 of the labyrinth structure 133 via the introduction pipe 190, and the insides of the plurality of flow channels 132 are filled with the chemical polishing liquid M1.

[0033] The chemical polishing liquid M1 may be introduced from at least one of the multiple introduction pipes 190, and the chemical polishing liquid M1 may be discharged to the outside from at least one of the multiple introduction pipes 190. Then, even after the flow channel 132 is filled with the chemical polishing liquid M1, the introduction and discharge of the chemical polishing liquid M1 from the introduction pipe 190 is continued. This allows the chemical polishing liquid M1 to circulate within the flow channel 132 of the labyrinth structure 133.

[0034] The chemical polishing liquid M1 may be, for example, hydrogen peroxide solution heated from room temperature to about 50°C.

[0035] FIG. 3 is an explanatory diagram showing an enlarged view of the state where joint surfaces 130 of two pipes 110A and 110B are in contact with each other. It is difficult to form the joining surface 130 into a completely smooth surface. Therefore, even if the joining surfaces 130 of the two flanges 120A and 120B are brought into contact with each other, a gap 220 of, for example, about 0.1 mm to 0.5 mm is formed between the two joining surfaces 130, 130 as shown in FIG. 3. Therefore, the chemical polishing liquid M1 introduced into the flow groove 132 of the labyrinth structure 133 is also introduced into the gap 220 formed between the two joining surfaces 130, 130 by capillary action. As a result, not only the side portion of the convex portion 131 on the flow groove 132 side, but also the opposing surfaces of the two joining surfaces 130, 130 can be wetted with the chemical polishing liquid M1.

[0036] By introducing the chemical polishing liquid M1, the oxide film 136 formed on the surface of the joining surface 130 is removed by the chemical polishing liquid M1. This allows the metal surfaces of the protrusions 131 formed on the two flanges 120A, 120B to come into strong contact with each other. When minute plastic deformation occurs on the metal surface, it makes it easier for new metal surface 137 present directly below the metal surface film to appear on the surface.

[0037] Furthermore, by removing the oxide film 136 with the chemical polishing solution M1, the surface roughness of the metal after removal is reduced compared to before removal. This makes it possible to increase the contact area of ​​the convex portions 131 of the labyrinth structure 133 when the convex portions 131 of the joining surfaces 130 of the flanges 120A, 120B are brought into contact with each other after chemical polishing. As a result, strong contact of the metal surfaces occurs over the entire contact surface, and the appearance of new metal surfaces 137 due to the occurrence of plastic deformation also occurs over the entire expanded contact surface.

[0038] FIG. 4 is a diagram showing the relationship between the width H1 of the gap 220 and the penetration length of the chemical polishing liquid M1 into the gap 220. As shown in FIG. 4, even when the width H1 of gap 220 is relatively large at 0.5 mm, chemical polishing liquid M1 penetrates about 3 cm into gap 220. As a result, even when joint surfaces 130 of two pipes 110A, 110B are in contact with each other, chemical polishing liquid M1 can be spread throughout convex portion 131 of labyrinth structure 133, and oxide film 136 can be removed reliably.

[0039] The chemical polishing liquid M1 permeates the protrusion 131 disposed between the innermost protrusion 131a and the outermost protrusion 131b from both radial sides due to the two flow channel grooves 132, 132. Therefore, the thickness of the protrusion 131 disposed between the innermost protrusion 131a and the outermost protrusion 131b, i.e., the length in the radial direction, may be set to twice the thickness of the innermost protrusion 131a or the outermost protrusion 131b. This makes it possible to increase the contact area of ​​the bonding surface 130 and to increase the bonding strength between the two flanges 120A, 120B.

[0040] Furthermore, an innermost convex portion 131a and an outermost convex portion 131b are formed on the bonding surface 130, and the chemical polishing liquid M1 seeps out from the gap 220 onto the inner surface on the innermost periphery side and the outer surface on the outermost periphery side of the flanges 120A, 120B. This allows the chemical polishing liquid M1 to block the intrusion of outside air into the bonding surface 130, and prevents the oxide film 136 from being formed again on the bonding surface 130.

[0041] Next, after a predetermined time has elapsed since the introduction of the chemical polishing liquid M1, as shown in FIG. 1, an ultrasonic vibrator 230 is brought into contact with the flanges 120A, 120B via the contact plate 170. Then, the ultrasonic vibrator 230 is driven to apply ultrasonic vibrations to the flanges 120A, 120B. The application of ultrasonic vibrations increases the wettability of the metal surface in the gap 220 formed between the convex portions 131 of the joining surfaces 130. This makes it easier for the chemical polishing liquid M1 to permeate between the convex portions 131 of the two joining surfaces 130, 130.

[0042] After a predetermined time has elapsed since driving the ultrasonic vibrator 230, the introduction of the chemical polishing liquid M1 is stopped, and the driving of the ultrasonic vibrator 230 is also stopped. When the introduction of the chemical polishing liquid M1 is stopped, the chemical polishing liquid M1 is not discharged from the flow channel 132 of the labyrinth structure 133, and the introduction pipe 190 is kept connected to the introduction hole 180.

[0043] Next, jig 160 is tightened further to bring joint surfaces 130 of two pipes 110A, 110B closer to each other. By tightening further, the surface pressure of two joint surfaces 130 increases, and chemical polishing liquid M1 present on the surface of protrusion 131 is discharged into flow channel 132.

[0044] FIG. 5 is a diagram showing a modified example of the convex portion of the labyrinth structure. The convex portion 135 of the labyrinth structure shown in Fig. 5 is formed in a mountain shape. That is, the center of one surface of the convex portion 135 facing the convex portion 135 of the other joint surface 130 bulges toward the convex portion 135 of the other joint surface 130. According to the convex portion 135 shown in Fig. 5, the force applied to the center of one surface of the convex portion 135 during the retightening operation is stronger than that applied to other portions. This allows the chemical polishing liquid M1 to be smoothly discharged from one surface of the convex portion 135 to the flow channel 132 side.

[0045] When the tightening of the jig 160, that is, the discharge of the chemical polishing liquid M1 present on the surface of the protrusion 131, is completed, the driving of the ultrasonic vibrator 230 is resumed. At this point, the flow channel 132 is filled with the chemical polishing liquid M1. Therefore, the chemical polishing liquid M1 filling the flow channel 132 acts as an airtight material, and it is possible to prevent air from entering the surface of the protrusion 131.

[0046] When ultrasonic vibration is applied to the protrusions 131 provided on the joining surfaces 130 of the two flanges 120A, 120B in contact with each other, plastic deformation occurs on the metal surfaces of the protrusions 131. This causes new surfaces 137 directly below the oxide film 136 to appear on the surface. As a result, the new surfaces 137 can be brought into contact with each other, and the pipes 110A, 110B can be reliably ultrasonically joined together even if the pipes 110A, 110B are made of a steel material such as carbon steel or low alloy steel, which has a higher yield stress and is harder than copper or aluminum.

[0047] After completing the ultrasonic bonding of flanges 120A, 120B of pipes 110A, 110B, negative pressure is applied to inlet pipe 190 to drain the chemical polishing liquid M1 remaining in flow channel 132. Then, inlet pipe 190 is removed from inlet hole 180, and inlet hole 180 is blocked. By performing the above-mentioned steps, first pipe 110A and second pipe 110B are bonded together.

[0048] In addition, since the joining surfaces 130 of the flanges 210A and 120B are ultrasonically joined, no load is applied to the introduction hole 180. Therefore, the sealing member that blocks the introduction hole 180 will not be damaged during operation of the device.

[0049] In this way, according to the pipe joining method of this embodiment, by introducing the chemical polishing liquid M1 into the labyrinth structure 133 formed on the joining surface 130 before ultrasonic joining, the oxide film 136 can be removed and a new surface 137 can be made to appear on the surface of the joining surface 130. This makes it possible to perform ultrasonic joining on pipes made of steel materials such as carbon steel and low alloy steel, which have a higher yield stress and are harder than copper and aluminum, such as pipes used in nuclear power plants. As a result, the pipes can be joined reliably, the occurrence of leakage and breakage can be suppressed, and safety can be improved.

[0050] 2. Second embodiment Next, a pipe joining method according to a second embodiment will be described with reference to FIGS. 6 is a schematic diagram showing a pipe joining method according to a second embodiment. It is a front view showing a joining surface of a pipe in the pipe joining method according to the second embodiment. Note that the same reference numerals are used for the parts common to the pipe joining method according to the first embodiment, and the duplicated explanation will be omitted.

[0051] 6, a fitting protrusion 251 is formed on the joint surface 130 of the first pipe 110A. A fitting recess 250 into which the fitting protrusion 251 fits is formed on the joint surface 130 of the second pipe 110B. The fitting protrusion 251 is formed on the radial center side of the joint surface 130 so as to surround the cylindrical hole 111. The fitting protrusion 251 protrudes from the joint surface 130 toward the joint surface 130 of the second pipe 110B.

[0052] 6 and 7, the fitting recess 250 is formed so as to surround the cylindrical hole 111 on the radial center side of the joint surface 130. The fitting recess 250 is formed in a tapered shape that is inclined from the joint surface 130 toward the end of the cylindrical hole 111.

[0053] As shown in Fig. 7, among the multiple protrusions 131 constituting the labyrinth structure 133 formed on the joint surface 130 of the second pipe 110B, the innermost protrusion 131a is disposed radially outward of the fitting recess 250. That is, the innermost protrusion 131a is formed radially outward of the arrow B shown in Fig. 6. Here, the tightening force of the jig 160 is applied to the region indicated by the dashed line C on the joint surface 130. Therefore, even if the protrusion 131 is not provided radially inward of the arrow B, the ultrasonic bonding is not affected.

[0054] By fitting the fitting protrusion 251 into the fitting recess 250, the joint surface 130 of the flange 120A of the first pipe 110A and the joint surface 130 of the flange 120B of the second pipe 110B can be easily positioned. This allows the surfaces of the protrusions 131 formed on the joint surfaces 130 to be reliably in contact with each other.

[0055] Other configurations are the same as those of the pipe joining method according to the first embodiment, and therefore the description thereof will be omitted. The pipe joining method having such a configuration can also obtain the same effects as those of the pipe joining method according to the first embodiment described above.

[0056] The above describes the embodiment of the pipe connecting method, including its effects. However, the pipe connecting method is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the invention described in the claims.

[0057] In the above-mentioned embodiment, the labyrinth structure 133 is formed with a plurality of convex portions 131 and flow grooves 132, but the present invention is not limited to this. For example, the convex portion 131 may have at least the innermost convex portion 131a, and at least one flow groove 132 may be formed so as to surround the innermost convex portion 131a in order to allow the chemical polishing liquid M1 to permeate the innermost convex portion 131a. In addition, by forming a plurality of convex portions 131 as in the above-mentioned embodiment, the joining area of ​​the two pipes 110A and 110B can be increased, and the joining strength can be increased. This allows the two pipes 110A and 110B to be joined firmly.

[0058] In this specification, words such as "parallel" and "orthogonal" are used, but these do not mean only "parallel" and "orthogonal" in the strict sense, but also include "parallel" and "orthogonal" and may also mean a "nearly parallel" or "nearly orthogonal" state within a range in which the functions can be exerted. [Explanation of symbols]

[0059] 110A, 110B...piping, 111...tubular hole, 120A, 120B...flange, 130...joint surface, 131, 135...convex portion, 131a...innermost convex portion, 131b...outermost convex portion, 132...flow path groove, 132b...communicating groove, 133...labyrinth structure, 136...oxide coating, 137...new surface, 160...jig, 180...introduction hole, 190...introduction pipe, 220...gap, 230...ultrasonic transducer, 250...fitting recess, 251...fitting protrusion, H1...spacing, K1...unwelded portion, M1...chemical polishing liquid, P1...tensile stress

Claims

1. forming a convex portion on the joint surface of the two pipes and a flow channel surrounding the convex portion and through which the chemical polishing liquid can pass; overlapping the joint surfaces of the two pipes; introducing a chemical polishing liquid into the flow channel of the piping; ultrasonically bonding the joining surfaces of the two pipes by an ultrasonic vibrator; A pipe joining method comprising:

2. The protrusions and the flow channel are formed in a plurality on the joining surface. The pipe joining method according to claim 1.

3. the protrusion has an innermost protrusion disposed on an innermost periphery of the joining surface, The innermost protrusion is formed continuously in a circumferential direction of the cylindrical hole of the pipe and surrounds the cylindrical hole. The pipe joining method according to claim 1.

4. A fitting protrusion is formed on the joint surface of one of the two pipes, The other of the two pipes has a mating recess formed on the joint surface thereof, the mating recess being fitted into the mating protrusion. The pipe joining method according to claim 3.

5. The fitting recess is formed to surround the periphery of the cylindrical hole, The innermost protrusion is formed outside the fitting recess. The pipe joining method according to claim 4.

6. The central portion of the protrusion bulges toward the protrusion of the pipe to be joined. The pipe joining method according to claim 1.

7. an outermost protrusion disposed on the outermost periphery of the joint surface among the plurality of protrusions has an introduction hole formed therein and communicating with the flow channel; The chemical polishing liquid is introduced into the flow channel through the introduction hole. The pipe joining method according to claim 2.

8. The step of ultrasonic bonding using the ultrasonic vibrator is carried out in a state where the flow channel is filled with the chemical polishing liquid. The pipe joining method according to claim 1.

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