JP7313891B2 - Expansion joints and corrosion protection methods for expansion joints - Google Patents

Description

The present invention relates to an expansion joint and a corrosion protection method that is also applicable to the maintenance of expansion joints.

Conventionally, expansion joints are used at the joints of ducts that transfer fluid such as exhaust gas discharged from combustion equipment such as thermal power plants, steel plants, and garbage incinerators for the purpose of absorbing thermal expansion and vibration of the duct itself.
FIG. 1 is a perspective view for showing an example of an expansion joint.
The expansion joint 10 shown in FIG. 1 is for elastically connecting a pair of ducts (not shown) through which a corrosive fluid flows. The pair of joint flanges 7a and 9a and the bellows 11 are configured in a cylindrical shape as shown in FIG. The bellows 11 has dimensions necessary to ensure that the distance between both ends of the expansion joint (connecting surfaces to the ductwork) is sufficiently longer than the distance between the ductwork to be connected. By attaching the expansion joint between the ducts with the bellows 11 loosened, it is possible to absorb thermal expansion, axial displacement, vibration, etc. of the duct system.

FIG. 2 is a vertical cross-sectional view of the expansion joint.
The expansion joint 10 is used, for example, in a power generation facility of a petrochemical plant, etc. Corrosive fluid flows through the pair of ducts 3 and 5, which are the pair of connected members. For this reason, in order to protect the bellows necessary for maintaining airtightness from wear due to heat and dust contained in the fluid, a complicated protective structure using heat insulating materials and baffles is provided. The expansion joint 10 is disposed between the upstream duct 3 and the downstream duct 5 and includes a pair of flanged joint bodies 7 and 9, a tubular bellows 11 connecting the pair of joint bodies 7 and 9, and a plurality of heat insulating materials 13, 15, 17, 19 and 21 arranged inside the bellows 11. A pair of coupling bodies 7,9 each consist of a tubular member to be connected to the corresponding duct 3,5. A joint flange portion 7 a is formed on the upstream side of the first joint main body 7 . On the other hand, a similar duct flange portion 3a is formed on the downstream side of the upstream duct 3, and the first joint body 7 is airtightly connected to the upstream duct 3 by connecting the joint flange portion 7a and the duct flange portion 3a with a fastening means 23 or the like. Similar joint flange portions 9a and duct flange portions 5a are also formed on the downstream side of the second joint body 9 and the upstream side of the downstream duct 5, and the second joint body 9 is airtightly connected to the downstream duct 5 by connecting these joint flange portions 9a and duct flange portions 5a with fastening means 23 or the like.

Annular metal frames 7b and 9b are erected by welding on the outer surfaces of the first and second joint bodies 7 and 9, respectively. The upstream end and downstream end of the bellows 11 are engaged with these frame portions 7b and 9b, respectively. Further, pressing plates 7c and 9c are provided outside the upstream and downstream ends of the bellows 11 engaged with the frame portions 7b and 9b. With the upstream and downstream ends of the bellows 11 sandwiched between the frame portions 7b, 9b and the pressing plates 7c, 9c, these frame portions and pressing plates are connected by fastening means 25. As shown in FIG. The bellows 11 is thus fixed between the pair of joint bodies 7 and 9 . A pair of pressing plates 7c and 9c are connected by shipping bolts 27 via L-shaped metal fittings 7d and 9d fixed by fastening means 25. As shown in FIG. The shipping bolt 27 is used to set the expansion joint to the installation size, and is removed after the connection between the ducts 3 and 5 is completed.

A heat insulating material 13 is arranged on the outermost side among a plurality of heat insulating materials provided inside the bellows 11, and a first elastic insulating material 15 and a second elastic insulating material 17 are arranged in order inside it. These heat insulating materials 13 , 15 , 17 are positioned inside the bellows 11 and outside the joint bodies 7 , 9 at the same time, and are surrounded by the pair of frame portions 7 b , 9 b and the bellows 11 .

An exposed heat insulating material 19 is arranged further inside the second elastic heat insulating material 17 , and a pair of fixed heat insulating materials 21 are arranged inside the exposed heat insulating material 19 . These heat insulating materials 19 and 21 are located inside the bellows 11 and inside the joint bodies 7 and 9 at the same time. Also, the pair of fixed heat insulating materials 21 are provided separately on the upstream side and the downstream side with a flow direction central portion of the expansion joint 10 left open. As a result, the exposed heat insulating material 19 is exposed to the flow path between the pair of fixed heat insulating materials 21, that is, at the central portion in the flow direction. A stud pin 29a is erected from each of the inner surfaces of the pair of joint bodies 7 and 9 toward the inner side, that is, toward the channel axis. These stud pins 29 a pass through the exposed heat insulating material 19 and the fixed heat insulating material 21 , and their tips protrude from the inner peripheral surface of the fixed heat insulating material 21 . On the other hand, stud bolts 29b are erected from the outer side surfaces of the pair of joint bodies 7 and 9 in the direction opposite to the flow path axis side, and fix the heat insulators 15 and 17 thereon. Further, a heat insulating material cover 31 is provided around each fixed heat insulating material 21, and each heat insulating material cover 31 is fixed by a nut screwed onto the tip of the stud pin 29a. A baffle 33 is attached to the heat insulating material cover 31 on the upstream side.

The basic configuration of the bellows 11 consists of three elements, starting from the side of the fluid flowing inside, for example, a polytetrafluoroethylene (PTFE) sealing layer, a reinforcing layer on the outside air side (the side farther from the fluid, i.e., radially outside) than the sealing layer, and a skin layer provided on the outside air side. The heat insulating materials described above can reduce the thermal influence on the bellows 11 and extend the life of the bellows 11 . Furthermore, by adopting such a structure, even when replacing the bellows material and heat insulating material, it is excellent in maintainability because it is sufficient to replace only the bellows material and heat insulating material while leaving the metal members such as the flange and frame as they are.

However, in an expansion joint using a heat insulating material, when acidic and high-temperature internal fluid such as combustion gas enters the bellows 11 side, the gas temperature is lowered to the acid dew point due to the heat insulating material in a portion near the bellows 11. Therefore, there is a problem that the internal fluid becomes acidic drain and corrodes metal members such as the frame parts 7b and 9b. Further, when the operation is stopped or the operation is performed at a low temperature, the same problem occurs when acidic drain or the like flows in from the surrounding duct.

As a method for preventing the corrosion of metal members due to such acid drainage, methods such as the use of corrosion-resistant steel and the coating with anticorrosion paint have been conventionally known. However, it is difficult to process special corrosion-resistant steel, and it is not practical to use large-sized ones because the cost is too high. Coating with anti-corrosion paint has the problem that it cannot follow the expansion and contraction of the metal in applications such as expansion joints where there is a large temperature difference between operation and stop, and cracks and peeling occur. A method for preventing corrosive substances from entering the gap between the flange and the bellows has also been proposed (Patent Document 1).

JP-A-63-225786

Accordingly, an object of the present invention is to provide an expansion joint that can effectively prevent corrosion of metal members due to drain or corrosive gas without adversely affecting cost and workability, and a corrosion prevention method that can be applied to maintenance thereof.

As a result of intensive research, the present inventor found that the above problems can be solved by providing a specific drain discharge structure in at least one portion of the seal layer, which is the lower side of the expansion joint where drain tends to accumulate, and completed the present invention.
That is, the present invention is as follows.
1. An expansion joint for elastically connecting a pair of ducts through which a corrosive fluid flows,
The expansion joint has a pair of flanges for connecting with the duct and a metal frame portion that holds the bellows and insulation,
The bellows has an airtight sealing layer,
A drain discharge structure is provided in at least one location of the seal layer, which is on the lower side when the expansion joint is installed, where drain tends to accumulate,
The drain discharge structure is a structure in which a drain pipe passing through the bellows is integrally connected to the seal layer,
The expansion joint is characterized in that the seal layer and the drain pipe are made of the same material.
2. 2. The expansion joint according to 1 above, wherein both the sealing layer and the drain pipe are made of polytetrafluoroethylene.
3. 3. The expansion joint according to 1 or 2 above, wherein the inner surface of the frame portion on the fluid side is provided with an anticorrosive layer comprising an anticorrosive undercoat, an anticorrosive tape, and an anticorrosive topcoat in this order.
4. A corrosion protection method for an expansion joint for elastically connecting a pair of ducts through which a corrosive fluid flows, comprising:
The expansion joint has a pair of flanges for connecting with the duct and a metal frame portion that holds the bellows and insulation,
The bellows has an airtight sealing layer,
A step of providing a drain discharge structure in at least one location of the seal layer, which is on the lower side when the expansion joint is installed, where drain tends to accumulate,
The drain discharge structure is a structure in which a drain pipe passing through the bellows is integrally connected to the seal layer,
The method for preventing corrosion of an expansion joint, wherein the seal layer and the drain pipe are made of the same material.
5. 1. A corrosion protection method for maintenance of an expansion joint in use or after use that expands and contracts between a pair of ducts through which a corrosive fluid flows, comprising:
The expansion joint has a pair of flanges for connecting with the duct and a metal frame portion that holds the bellows and insulation,
The bellows has an airtight sealing layer,
A step of providing a drain discharge structure in at least one location of the seal layer, which is on the lower side when the expansion joint is installed, where drain tends to accumulate,
The drain discharge structure is a structure in which a drain pipe passing through the bellows is integrally connected to the seal layer,
Further, the corrosion prevention method for an expansion joint applicable to maintenance is characterized in that the seal layer and the drain pipe are made of the same material.

The expansion joint of the present invention is for elastically connecting a pair of ducts through which a corrosive fluid flows, and includes a pair of flanges for connecting the ducts, a metal frame portion that holds a bellows and a heat insulating material, the bellows has an airtight seal layer, and a drain discharge structure is provided in at least one portion of the seal layer, which is a lower side when the expansion joint is installed, where drain tends to accumulate. Since the structure is integrally connected to the seal layer, and the seal layer and the drain pipe are made of the same material, the corrosion of the heat insulating material and the metal frame due to the drain can be efficiently prevented. Moreover, since the drain discharge structure is a simple structure in which the drain pipe passing through the bellows is integrally connected to the seal layer, there is no adverse effect on cost and workability.
In addition, according to the corrosion prevention method of the present invention, by providing a similar drain discharge structure in connection with maintenance of an existing expansion joint that has progressed to some degree of corrosion, it is possible to effectively prevent corrosion due to drain of internal fluid and corrosive gas in subsequent use.
As described above, according to the present invention, it is possible to provide an expansion joint that can satisfactorily prevent corrosion of metal members due to drain or corrosive gas without adversely affecting cost and workability, and a corrosion prevention method that can be applied to maintenance thereof.

It is a perspective view for showing an example of an expansion joint. FIG. 2 is a longitudinal sectional view of the expansion joint of FIG. 1; 1 is a longitudinal sectional view of one embodiment of an expansion joint of the present invention; FIG. FIG. 4 is an enlarged sectional view of the drain discharge structure A circled in FIG. 3; It is a partially enlarged view of the expansion joint for explaining the drain discharge structure. FIG. 4 is a longitudinal cross-sectional view of another embodiment of the expansion joint of the invention; FIG. 7 is a cross-sectional view of a frame anti-corrosion layer in the expansion joint of FIG. 6;

Hereinafter, embodiments of the present invention will be further described with reference to the drawings.
FIG. 3 is a longitudinal sectional view of one embodiment of the expansion joint of the present invention.

The expansion joint 1 shown in FIG. 3 has substantially the same construction as the expansion joint 1 shown in FIGS.

The expansion joint 1 shown in FIG. 3 is exemplified as being used for power generation equipment of a petrochemical plant, etc., like the expansion joint 10 shown in FIGS.
The expansion joint 1 is disposed between an upstream duct 3 and a downstream duct 5 and includes a pair of flanged joint bodies 7 and 9, a tubular bellows 11 connecting the pair of joint bodies 7 and 9, and a plurality of heat insulating materials 13, 15, 17, 19 and 21 arranged inside the bellows 11. A pair of coupling bodies 7,9 each consist of a tubular member to be connected to the corresponding duct 3,5. A joint flange portion 7 a is formed on the upstream side of the first joint main body 7 . On the other hand, a similar duct flange portion 3a is formed on the downstream side of the upstream duct 3, and the first joint body 7 is airtightly connected to the upstream duct 3 by connecting the joint flange portion 7a and the duct flange portion 3a with a fastening means 23 or the like. Similar joint flange portions 9a and duct flange portions 5a are also formed on the downstream side of the second joint body 9 and the upstream side of the downstream duct 5, and the second joint body 9 is airtightly connected to the downstream duct 5 by connecting these joint flange portions 9a and duct flange portions 5a with fastening means 23 or the like.

Annular metal frames 7b and 9b are erected by welding on the outer surfaces of the first and second joint bodies 7 and 9, respectively. The upstream end and downstream end of the bellows 11 are engaged with these frame portions 7b and 9b, respectively. Further, pressing plates 7c and 9c are provided outside the upstream and downstream ends of the bellows 11 engaged with the frame portions 7b and 9b. With the upstream and downstream ends of the bellows 11 sandwiched between the frame portions 7b, 9b and the pressing plates 7c, 9c, these frame portions and pressing plates are connected by fastening means 25. As shown in FIG. The bellows 11 is thus fixed between the pair of joint bodies 7 and 9 . A pair of pressing plates 7c and 9c are connected by shipping bolts 27 via L-shaped metal fittings 7d and 9d fixed by fastening means 25. As shown in FIG. The shipping bolt 27 is used to set the expansion joint to the installation size, and is removed after the connection between the ducts 3 and 5 is completed.

A heat insulating material 13 is arranged on the outermost side among a plurality of heat insulating materials provided inside the bellows 11, and a first elastic insulating material 15 and a second elastic insulating material 17 are arranged in order inside it. These heat insulating materials 13 , 15 , 17 are positioned inside the bellows 11 and outside the joint bodies 7 , 9 at the same time, and are surrounded by the pair of frame portions 7 b , 9 b and the bellows 11 .

An exposed heat insulating material 19 is arranged further inside the second elastic heat insulating material 17 , and a pair of fixed heat insulating materials 21 are arranged inside the exposed heat insulating material 19 . These heat insulating materials 19 and 21 are located inside the bellows 11 and inside the joint bodies 7 and 9 at the same time. Also, the pair of fixed heat insulating materials 21 are provided separately on the upstream side and the downstream side with a flow direction central portion of the expansion joint 1 left open. As a result, the exposed heat insulating material 19 is exposed to the flow path between the pair of fixed heat insulating materials 21, that is, at the central portion in the flow direction. A stud pin 29a is erected from each of the inner surfaces of the pair of joint bodies 7 and 9 toward the inner side, that is, toward the channel axis. These stud pins 29 a pass through the exposed heat insulating material 19 and the fixed heat insulating material 21 , and their tips protrude from the inner peripheral surface of the fixed heat insulating material 21 . On the other hand, stud bolts 29b are erected from the outer side surfaces of the pair of joint bodies 7 and 9 in the direction opposite to the flow path axis side, and fix the heat insulators 15 and 17 thereon. Further, a heat insulating material cover 31 is provided around each fixed heat insulating material 21, and each heat insulating material cover 31 is fixed by a nut screwed onto the tip of the stud pin 29a. A baffle 33 is attached to the heat insulating material cover 31 on the upstream side.

For the heat insulating materials 13, 15, 17, 19, and 21, any of known heat insulating materials can be used. Examples of heat resistant fibers include alumina fiber, mullite fiber, silica fiber, silica alumina fiber, zirconia fiber, alkaline earth metal silicate fiber, glass wool, glass fiber, rock wool, slag wool, silicon carbide fiber, carbon fiber, silica alumina magnesia fiber, silica alumina zirconia fiber, silica magnesia calcia fiber, basalt fiber, biosoluble inorganic fiber, and the like. Examples of organic fibers include aramid fibers and PBO (polyparaphenylenebenzobisoxazole) fibers. Furthermore, examples of metal fibers include boron fibers, titanium fibers, and steel fibers. One example is to provide a futon-like heat insulating layer in which ceramic cloth is wrapped around ceramic felt. Further, the blanket-like heat insulating layer can be further wrapped with a wire mesh such as a demister for reinforcement. These structures can be appropriately selected and combined according to usage conditions such as the temperature and atmosphere of the internal fluid and the presence or absence of particulate matter.

As described above, the expansion joint 1 shown in FIG. 3 is provided with a drain discharge structure A in at least one portion of the seal layer of the bellows 11, which tends to accumulate drain when installed.

4 and 5 are partially enlarged views of the expansion joint for explaining the drain discharge structure A. FIG.
FIG. 4 shows the structure near the bottom surface of the expansion joint, and the bellows 11 is configured by laminating a seal layer 11a and a reinforcing layer 11b in this order from the fluid side, and a drain pipe 82 passing through the bellows 11 is integrally connected to the inside of the bellows 11, that is, the seal layer 11a facing the fluid side. According to the expansion joint 1 of the present invention, the generated drainage is efficiently discharged to the outside of the expansion joint 1 by the drain pipe 82, and the metal frames 7b and 9b can be prevented from being corroded by the drainage. Moreover, since the drain discharge structure A has a simple structure in which the drain pipe 82 passing through the bellows 11 and the seal layer 11a are fused and integrated, there is no adverse effect on cost and workability.
Further, as shown in FIG. 5, this drain discharge structure A has a valve 822, and by opening and closing the valve 822, drain and corrosive gas can be efficiently discharged.
Here, as the material of the seal layer 11a in the bellows 11, fluororesins such as PTFE, FEP, PFA, and ETFE, and rubbers such as ethylene propylene rubber, butyl rubber, and chlorosulfonated polyethylene rubber can be appropriately selected. In particular, PTFE (polytetrafluoroethylene) is suitable in consideration of workability, corrosion resistance, and the like.
Also, the drain pipe 82 can be selected from the same material group as the seal layer 11a of the bellows 11, for example, and it is more preferable that the seal layer 11a and the drain pipe 82 are made of the same material. Therefore, when the sealing layer 11a is made of PTFE, the drain pipe 82 is also preferably made of PTFE.
As a method for connecting the drain pipe 82, a known method such as using an adhesive, heat-sealing by heating, threading the drain pipe 82 and screwing it with a nut, or the like can be appropriately used.
When both the seal layer 11a and the drain pipe 82 are made of PTFE and are made of the same material, the bellows-side end of the drain pipe 82 is hot-rolled into a flange shape to form a flange-shaped portion 821, which is inserted into the through-hole of the bellows 11 from the fluid side, and a PFA film is sandwiched between the fluid-side surface of the bellows and the ground surface of the flange-shaped portion 821 of the drain pipe 82 and thermally fused to connect them. It is possible to appropriately select a method of overlapping them in a circular shape, interposing PFA between them, and connecting them by thermal fusion.
Moreover, when the sealing layer 11a of the bellows 11 and the drain pipe 82 are made of different materials, they can be connected by a method using an adhesive suitable for the combination of materials.

In the expansion joint of the present invention, an anticorrosive layer may be provided on the fluid-side inner surfaces of the frame portions 7b and 9b, comprising an anticorrosive undercoat, an anticorrosive tape, and an anticorrosive topcoat in this order.

FIG. 6 is a longitudinal sectional view for explaining another embodiment of the expansion joint of the present invention provided with such an anticorrosion layer.
According to FIG. 6, the expansion joint 2 has substantially the same configuration as the expansion joint 1 shown in FIG. 3, but the inner surfaces of the frame portions 7b and 9b on the fluid side, preferably the entire inner surfaces, are provided with an anticorrosive layer 52 comprising an anticorrosive undercoat, an anticorrosive tape, and an anticorrosive topcoat in this order.

FIG. 7 is a cross-sectional view of the anti-corrosion layer 52 provided on the fluid-side inner surface of the frame portion 7b. An undercoat anticorrosion coating 522, an anticorrosion tape 524, and a top anticorrosion coating 526 are provided in this order in the direction from the frame portion 7b toward the fluid-side inner surface of the frame portion 7b. It is preferable that the surface of the frame portion 7b on which the anticorrosive layer 52 is to be provided is preliminarily subjected to two or more types of surface preparation.

The paint (undercoat anticorrosion paint) for forming the undercoat anticorrosion paint 522 is not particularly limited as long as it has heat resistance and adhesion to the metal frame portion. As the heat-resistant silicone resin, those known in the art can be appropriately selected and used. The rust preventive pigment can be appropriately selected from existing basic rust preventive pigments, nonconductive film-forming rust preventive pigments, reducing rust preventive pigments, and the like, and used. However, since heat resistance is required, inorganic rust preventive pigments are preferred, and those containing no lead or chromium are particularly preferred. In addition, since the coloring pigment and the extender pigment also require heat resistance, it is preferable to use an inorganic pigment.
The thickness of the undercoat anticorrosive coating 522 is, for example, 70 μm to 200 μm, preferably 100 μm to 150 μm.

As the material of the anti-corrosion tape 524, inorganic fiber woven fabric is preferable, and glass fiber woven fabric or alumina fiber woven fabric is more preferable from the viewpoint that it exhibits excellent followability to metal expansion and contraction and can satisfactorily prevent cracks and peeling.
The weight of such inorganic fiber woven fabric is preferably 50 to 400 g, more preferably 100 to 300 g, per 1 m ² .
The width of the anticorrosion tape 524 is, for example, 10 mm to 300 mm, preferably 50 mm to 200 mm.
The thickness of the anticorrosion tape 524 is, for example, 0.1 mm to 1.0 mm, preferably 0.3 mm to 0.7 mm.
The anti-corrosion tape 524 can be installed as a single layer or by stacking a plurality of layers and adhering them to the fluid-side inner surfaces of the frame portions 7b and 9b via the undercoat anti-corrosion coating 522 .

As the paint for forming the top anticorrosive coating 526 (top anticorrosive coating), the same paint as the undercoat anticorrosive coating 522 can be used.
The thickness of the overcoat anticorrosive coating 526 is, for example, 50 μm to 200 μm, preferably 70 μm to 120 μm.

The anti-corrosion layer 52 can be formed by applying an anti-corrosion undercoat paint to the base, adhering an anti-corrosion tape thereon, and then applying an anti-corrosion top coat coating on the anti-corrosion tape. As the coating method, a known method may be adopted, and there are no particular restrictions, but examples thereof include brush coating and spray coating.
The inorganic fiber woven fabric may be impregnated with the same paint as the undercoat anticorrosive paint and/or the topcoat anticorrosive paint before application, and this may be used as the anticorrosion tape. According to this embodiment, the adhesion between the undercoat anticorrosion coating 522, the anticorrosion tape 524, and the top anticorrosion coating 526 is improved, and heat resistance, workability, etc. can be further improved. In this embodiment, the impregnation amount of the undercoat anticorrosive paint and/or topcoat anticorrosive paint is preferably 400 to 1,200 g, more preferably 400 to 800 g, per 1 m ² of the anticorrosive tape.
In the above embodiment, the thickness of the anticorrosion layer 52 is, for example, 1,200 μm to 2,000 μm, preferably 1,200 μm to 1,600 μm.

According to the expansion joint 2 of the present invention, the inner surfaces of the metal members of the flange and frame, which are prone to corrosion, are protected by the anti-corrosion layer 52. Therefore, even if acidic drain or corrosive gas of the internal fluid is generated, these do not come into direct contact with the metal members, and corrosion of the metal members can be reduced. In addition, since the anticorrosion layer 52 exhibits excellent followability to the expansion and contraction of the metal due to the presence of the anticorrosion tape 524, cracks and peeling are unlikely to occur, and the anticorrosion effect is maintained for a long period of time. Furthermore, since the anticorrosion layer 52 has a simple structure consisting of the undercoat anticorrosion coating 522, the anticorrosion tape 524, and the top anticorrosion coating 526, it is excellent in terms of cost and workability.

ADVANTAGE OF THE INVENTION According to the present invention, it is possible to realize an expansion joint that can satisfactorily prevent corrosion of metal members due to drain or corrosive gas without adversely affecting cost and workability, and a corrosion prevention method that can be applied to maintenance thereof.

1, 2, 10 Expansion joint 3 Upstream duct 5 Downstream duct 7, 9 Joint bodies 7a, 9a Joint flanges 7b, 9b Frames 7c, 9c Holding plates 7d, 9d L-shaped fitting 11 Bellows 11a Seal layer 11b Reinforcing layers 13, 15, 17, 19, 21 Heat insulating material 27 Shipping bolt 29a Stud pin 29b Stud bolt 52 Anticorrosive layer 522 Undercoat Anti-corrosion coating 524 Anti-corrosion tape 526 Top coating anti-corrosion coating 82 Drain pipe 821 Flange shaped portion 822 Valve A Drain discharge structure

Claims (4)

An expansion joint for elastically connecting a pair of ducts through which a corrosive fluid flows,
The expansion joint has a pair of flanges for connecting with the duct and a metal frame portion that holds the bellows and insulation,
The bellows has an airtight sealing layer,
A drain discharge structure is provided in at least one location of the seal layer, which is on the lower side when the expansion joint is installed, where drain tends to accumulate,
The drain discharge structure includes a drain pipe passing through the bellows, a bellows-side end portion of the drain pipe is a flange-shaped portion, and a fluid-side surface of the bellows and a ground contact surface of the flange-shaped portion are integrally connected,
An expansion joint, wherein both the seal layer and the drain pipe are made of polytetrafluoroethylene . 2. The expansion joint according to claim 1 , wherein the inner surface of the frame portion on the fluid side is provided with an anticorrosive layer comprising an anticorrosive undercoat, an anticorrosive tape, and an anticorrosive topcoat in this order. A corrosion protection method for an expansion joint for elastically connecting a pair of ducts through which a corrosive fluid flows, comprising:
The expansion joint has a pair of flanges for connecting with the duct and a metal frame portion that holds the bellows and insulation,
The bellows has an airtight sealing layer,
A step of providing a drain discharge structure in at least one location of the seal layer, which is on the lower side when the expansion joint is installed, where drain tends to accumulate,
The drain discharge structure includes a drain pipe passing through the bellows, a bellows-side end portion of the drain pipe is a flange-shaped portion, and a fluid-side surface of the bellows and a ground contact surface of the flange-shaped portion are integrally connected,
A method for preventing corrosion of an expansion joint, wherein both the seal layer and the drain pipe are made of polytetrafluoroethylene . 1. A corrosion protection method for maintenance of an expansion joint in use or after use that expands and contracts between a pair of ducts through which a corrosive fluid flows, comprising:
The expansion joint has a pair of flanges for connecting with the duct and a metal frame portion that holds the bellows and insulation,
The bellows has an airtight sealing layer,
A step of providing a drain discharge structure in at least one location of the seal layer, which is on the lower side when the expansion joint is installed, where drain tends to accumulate,
The drain discharge structure includes a drain pipe passing through the bellows, a bellows-side end portion of the drain pipe is a flange-shaped portion, and a fluid-side surface of the bellows and a ground contact surface of the flange-shaped portion are integrally connected,
A corrosion prevention method for an expansion joint applicable to maintenance, characterized in that both the sealing layer and the drain pipe are made of polytetrafluoroethylene .

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