Flange fastening section and cooling system of flange fastening section

In a flange fastening section that includes a flange of a pipe for forming a connection of the pipe to another pipe by connection of the flange to a flange of the another pipe, the flange has a groove in the face to be connected to the flange of the another pipe for forming the connection. A gasket including expanded graphite is at least partly accommodated in the groove, and at least one O-ring is at least partly accommodated in the groove and at the peripheral surface of the gasket. The O-ring has a cavity through which working fluid may flow, an inlet piping into which the working fluid may flow and an outlet piping out of which the working fluid may flow.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims benefit of priority under 35 USC §119 to Japanese Patent Application No. 2009-290502, filed on Dec. 22, 2009, the entire contents of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a flange fastening section for connecting pipings and a cooling system of the flange fastening section used especially in a thermal power station such as a chemical plant and an electric plant.

2. Related Art

The flange fastening section is provided for connecting two pipings in the chemical plant, a nuclear power station, the thermal power station, a gas turbine and the like. A spiral gasket is accommodated along a circumferential groove in the flange in order to prevent leak of fluid from the flange fastening section and to improve sealing performance.

A problem of the conventional spiral gasket is described with reference to the drawings.

A spiral gasket102is accommodated in a flange groove120as illustrated inFIG. 12Bin many cases in a flange fastening section112for connecting steam pipings113in a main steam system and a reheat steam system of the thermal power station up to a steam temperature of about 600° C. as illustrated inFIG. 12A. Heat from the steam fluid is transmitted in a direction indicated by an arrow118.

The spiral gasket102has a structure obtained by rolling a filler material and a hoop material together, and expanded graphite and a superalloy material made of nonferrous metal are generally used as materials of the filler material and the hoop material, respectively.

Metallic O-ring101, C-ring and the like are used as illustrated inFIG. 12Cin the gas turbine and the like in addition to the spiral gasket102. In this case also, the heat from the steam fluid is transmitted in the direction indicated by the arrow118.

In this case, the sealing performance of the spiral gasket102depends on the expanded graphite mainly used as the filler material, and the sealing performance is hardly maintained with other materials.

However, recently, in order to prevent global warming, it is globally attempted to reduce emission of carbon dioxide (CO2), which largely affects the warming. In a thermal power plant and the like also, a high-temperature steam turbine system has been developed in order to reduce the carbon dioxide emission, and the high-temperature system up to a steam temperature of about 750° C. has been discussed.

However, since steam oxidation of the expanded graphite used as the filler material is started at approximately 650° C. or higher, there is a problem that the graphite is burned down at about 750° C., so that this cannot be conventionally used.

There is also a problem that materials of the hoop material of the spiral gasket102and the O-ring capable of being used up to such a high-temperature range are limited to an extremely narrow range in terms of strength. Further, even when the materials may be used, it is significantly difficult to obtain the hoop material of the spiral gasket102and the O-ring by cutting work from such materials. Further, there is also a problem that plastic deformation such as creep deformation occurs when using a metal material in the high-temperature range and a sealing surface pressure gradually decreases.

The document, which discloses the technology regarding the conventional flange fastening section, is as follows.Patent Document 1: Japanese Laid-Open Patent Application Publication No. 2007-127178

As described above, conventionally, the expanded graphite cannot be used as the filler material of the gasket embedded in the flange fastening section when realizing the high temperature in the chemical plant and the thermal and nuclear power stations, the materials for the hoop material and the O-ring are limited and the plastic deformation occurs, thereby a problem that the sealing surface pressure decreases arises.

SUMMARY OF THE INVENTION

An object of the present invention is to provide the flange fastening section and the cooling system of the flange fastening section, which may solve such a problem.

According to the present invention, there is provided a flange fastening section, comprising, a gasket including expanded graphite capable of being accommodated in a groove of a flange for connecting a plurality of pipings; and at least one O-ring arranged on an outer periphery of the gasket, wherein the O-ring has a cavity through which working fluid may flow, an inlet piping into which the working fluid may flow and an outlet piping out of which the working fluid may flow.

In this case, the O-ring may be arranged on an inner periphery of the gasket or on the inner periphery and the outer periphery thereof. Also, the O-ring and the gasket may be arranged in a joined state or so as to be adjacent to each other without being joined to each other.

According to the present invention, there is provided a cooling system of a flange fastening section, comprising, the above-mentioned flange fastening section, a first piping connected to the inlet piping for supplying the working fluid to the O-ring; and a second piping connected to the outlet piping for discharging the working fluid flowing out of the O-ring, wherein a pressure in the first piping is higher than a pressure in the second piping, and the working fluid is water whose temperature is lower than a temperature of fluid flowing through the piping.

According to the present invention, there is provided a cooling system of a flange fastening section, comprising, the above-mentioned flange fastening section; a first piping connected to the inlet piping for supplying the working fluid to the O-ring; a second piping connected to the outlet piping for discharging the working fluid flowing out of the O-ring; a first feed-water system piping connected to the first piping through an input adjusting valve; and a second feed-water system piping connected to the second piping through an output adjusting valve, wherein a pressure in the first piping is higher than a pressure in the second piping, and the working fluid is water of which temperature is lower than a temperature of fluid flowing through the piping.

According to the present invention, there is provided a cooling system of a flange fastening section, comprising, the above-mentioned flange fastening section; a first piping connected to the inlet piping for supplying the working fluid to the O-ring; a second piping connected to the outlet piping for discharging the working fluid flowing out of the O-ring; a third piping connected to the first piping through an input adjusting valve; a fourth piping connected to the second piping through an output adjusting valve; and a turbine connected to the third piping, wherein a pressure in the first piping is higher than a pressure in the second piping, and the working fluid is water of which temperature is lower than a temperature of fluid flowing through the piping.

According to the flange fastening section and the cooling system of the flange fastening section of the present invention, by cooling the gasket and the O-ring exposed to a severe temperature condition to turn down the temperature, the existing material may be used as the gasket and the O-ring, thereby realizing the high temperature.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(Configuration of First Embodiment)

A configuration of a flange fastening section according to a first embodiment of the present invention is described with reference toFIGS. 1A and 1B.

As illustrated inFIG. 1A, an O-ring1is arranged on an outer side of a spiral gasket2so as to be joined or adjacent thereto. The O-ring1has a cavity through which working fluid may flow, and one or a plurality of working fluid inlet pipings3and one or a plurality of working fluid outlet pipings4are connected thereto. Herein, a configuration in which one working fluid inlet piping3and one working fluid outlet piping4are connected to one O-ring1is illustrated inFIG. 1A.

FIG. 1Bis an enlarged view of a vertical cross-sectional surface of a part A1enclosed by a circle inFIG. 1A.

Meanwhile, a configuration in which the O-ring1and the spiral gasket2are joined to each other at a joint section5by welding and the like is illustrated inFIG. 1B. However, it does not limit the configuration, and a configuration in which the O-ring1and the spiral gasket2are not joined to each other and arranged so as to be independently adjacent to each other is also possible.

A state in which the O-ring1and the spiral gasket2are accommodated in the flange in such a flange fastening section is illustrated inFIG. 2. Holes20for fastening bolts are arranged on an outer peripheral portion of a flange19for connecting two steam pipings, and a piping inner portion21which communicates with a steam piping is located on a central portion.

A ring-shaped groove exists between the outer peripheral portion of the flange19and the piping inner portion21, and the above-described O-ring1and the spiral gasket2are accommodated therein.

The working fluid of which temperature is lower than that of the fluid flowing through the steam piping flows into the O-ring1from the working fluid inlet piping3and flows out of the working fluid outlet piping4, thereby cooling the spiral gasket2and the O-ring1.

Meanwhile, in the configuration illustrated inFIGS. 1A,1B and2, one O-ring1is arranged on the outer side of the spiral gasket2. However, the number is not limited to this, and a plurality of O-rings1may be arranged on the outer side of the spiral gasket2.

(Configuration of Second Embodiment)

The configuration of the flange fastening section according to a second embodiment of the present invention is described with reference toFIGS. 3A and 3B.

As illustrated inFIG. 3A, the O-ring1is arranged on an inner side of the spiral gasket2so as to be joined or adjacent thereto. The O-ring1has a cavity through which the working fluid may flow, and one or a plurality of working fluid inlet pipings3and one or a plurality of working fluid outlet pipings4are connected thereto.

A configuration in which one working fluid inlet piping3and one working fluid outlet piping4are connected to one O-ring1is illustrated inFIG. 3A.

FIG. 3Bis an enlarged view of a vertical cross-sectional surface of a part A2enclosed by a circle inFIG. 3A. An example in which the O-ring1and the spiral gasket2are joined to each other at the joint section5by welding and the like is illustrated inFIG. 3B. However, it is not limited to this configuration, and a configuration in which the O-ring1and the spiral gasket2are not joined to each other and arranged so as to be separately adjacent to each other is also possible.

The working fluid flows into the O-ring1from the working fluid inlet piping3and flows out of the working fluid outlet piping4, thereby cooling the spiral gasket2and the O-ring1.

In the configuration illustrated inFIG. 3, one O-ring1is arranged on the inner side of the spiral gasket2. However, the number is not limited to this, and a plurality of O-rings1may be arranged on the inner side of the spiral gasket2.

(Configuration of Third Embodiment)

A configuration of the flange fastening section according to a third embodiment of the present invention is described with reference toFIG. 4.

As illustrated inFIG. 4A, the O-rings1are arranged on the inner side and the outer side of the spiral gasket2so as to be joined or adjacent thereto.

The O-ring1has the cavity through which the working fluid may flow, and one or a plurality of working fluid inlet pipings3and one or a plurality of working fluid outlet pipings4are connected thereto.

A configuration in which one O-ring1is arranged on each of the inner and outer sides of the spiral gasket2and one working fluid inlet piping3and one working fluid outlet piping4are connected to the O-rings1is illustrated inFIG. 4A.

FIG. 4Bis an enlarged view of a vertical cross-sectional surface of a part A3enclosed by a circle inFIG. 4A. An example in which the O-rings1and the spiral gasket2are joined to each other at the joint section5by welding and the like is illustrated inFIG. 4B. However, it is not limited to the example, and a configuration in which the O-ring1and the spiral gasket2are not joined to each other and are separately arranged so as to be adjacent to each other is also possible.

The working fluid flows into the O-ring1from the working fluid inlet piping3and flows out of the working fluid outlet piping4, thereby more efficiently cooling the spiral gasket2through the O-rings1arranged on the inner and outer sides thereof.

Meanwhile, in the configuration illustrated inFIG. 4, one O-ring1is arranged on each of the inner side and the outer side of the spiral gasket2. However, the number is not limited to this, and a plurality of O-rings1may be arranged on the inner side of the spiral gasket2and a plurality of O-rings1may be arranged on the outer side of the spiral gasket2.

(Configuration of Fourth Embodiment)

A configuration of the flange fastening section according to a fourth embodiment of the present invention is described with reference toFIGS. 5A and 5B.

As illustrated inFIG. 5A, one or a plurality of working fluid inlet pipings3and one or a plurality of working fluid outlet pipings4are connected to one or a plurality of O-rings1. The O-ring1has the cavity through which the working fluid may flow. A configuration in which one working fluid inlet piping3and one working fluid outlet piping4are connected to two O-rings1is illustrated inFIG. 5A.

FIG. 5Bis an enlarged view of a vertical cross-sectional surface of a part A4enclosed by a circle inFIG. 5A. The working fluid flows into the O-ring1from the working fluid inlet piping3and flows out of the working fluid outlet piping4, thereby cooling the O-ring1.

A configuration in which the two O-rings1are coupled to each other by the working fluid piping3by welding and the like is illustrated inFIGS. 5A and 5B. However, it is not limited to the configuration and a configuration with one O-ring1is also possible. Alternatively, a configuration in which a plurality of O-rings1are not joined to each other and are arranged so as to be separately adjacent to each other is also possible.

A configuration of the flange fastening section according to a fifth embodiment is described with reference toFIGS. 6A and 6B.

As illustrated inFIG. 6A, the O-ring1is arranged on the inner side of the spiral gasket2so as to be joined or adjacent thereto.

The O-ring1has the cavity through which the working fluid may flow and one or a plurality of working fluid inlet pipings3and one or a plurality of working fluid outlet pipings4are connected thereto.

FIG. 6Bis an enlarged view of a vertical cross-sectional surface of a part A5enclosed by a circle inFIG. 6A. A plurality of openings6are formed on a surface of the O-ring1in a scattering manner. The opening6is desirably formed on a side closer to the spiral gasket2in the vertical cross-sectional surface of the O-ring1as illustrated inFIG. 6B. More specifically, as will be described later with reference toFIG. 9B, the opening6is desirably formed in an area, which faces a space enclosed by a sheet portion at which a flange groove and the O-ring1come into contact with each other and the spiral gasket2.

When the working fluid flows into the O-ring1from the working fluid inlet piping3and flows out of the working fluid outlet piping4, the working fluid leaks from the opening6arranged on the side closer to the spiral gasket2, thereby directly cooling the spiral gasket2more efficiently.

A configuration in which the O-ring1and the spiral gasket2are not joined to each other and are arranged so as to be independently and separately adjacent to each other is illustrated inFIGS. 6A and 6B. However, a configuration in which the O-ring1and the spiral gasket2are joined at the joint section by welding and the like is also possible.

It is also possible that a plurality of O-rings1are arranged on the inner side or the outer side of the spiral gasket2. In this case, the opening6may be formed on the side closer to the spiral gasket2in at least one O-ring1arranged on a position the closest to the spiral gasket2out of a plurality of O-rings1.

Alternatively, the opening6may be formed also in a case in which one or a plurality of O-rings1are arranged on the inner side of the spiral gasket2and further one or a plurality of O-rings1are arranged on the outer side of the spiral gasket2as in the above-described third embodiment. In this case, the opening6may be formed on the side closer to the spiral gasket2in at least one of the O-rings1arranged on positions the closest to the spiral gasket2out of one or a plurality of O-rings1arranged on each of the inner and outer sides of the spiral gasket2.

A configuration of a cooling system of the flange fastening section according to a sixth embodiment of the present invention is described with reference toFIG. 10. In the cooling system according to the sixth embodiment, the flange fastening section according to any one of the above-described first to fourth embodiments is used.

A configuration of the cooling system of the flange fastening section according to the sixth embodiment is illustrated inFIG. 10to describe the cooling system according to this embodiment.

Herein, water is used as the working fluid. The working fluid inlet piping3is branched from a high-pressure feed-water system piping10connected to a high-pressure heater (HP-htr). The branched working fluid inlet piping3passes through an inlet adjusting valve14to reach the flange fastening section12through the working fluid inlet piping3. The flange fastening section12is a connecting section of two steam pipings13, and steam, which is the working fluid flowing through the steam piping13, heats the flange fastening section12.

The water guided into the flange fastening section12cools the O-ring1and the spiral gasket2or the O-ring1by the above-described configuration provided on the flange fastening section according to any one of the above-described first to fourth embodiments. The water after a certain heat exchange flows out of the flange fastening section12and passes through an outlet adjusting valve15through the working fluid outlet piping4to reach a low-pressure feed-water system piping11in which pressure is lower than that on an upstream side. The low-pressure feed-water system piping11is connected to a low-pressure feed-water heater (LP-htr).

Meanwhile, due to high heat exchanger effectiveness and manageability of the water, not the steam but the water is used in this case as the working fluid.

The cooling system of the flange fastening section according to a seventh embodiment of the present invention is described with reference toFIG. 11. The seventh embodiment is the system to cool the flange fastening section according to any one of the above-described first to fifth embodiments and uses the steam as the working fluid.

Herein, the flange fastening section of a reheat steam lead piping arranged before a combination reheat valve (CRV) of a hot reheat piping is described as an example of the flange fastening section12.

The working fluid inlet piping3is branched from a main steam piping18connected to a high-pressure turbine16. Meanwhile, the steam is herein used as the working fluid.

The branched working fluid inlet piping3passes through the inlet adjusting valve14to reach the flange fastening section12through the working fluid inlet piping3. The flange fastening section12corresponds to a connecting section of the reheat steam piping19and the steam, which flows through the reheat steam piping19, heats the flange fastening section12.

The steam of which temperature is lower than that of the working fluid in the steam piping13, which is guided into the flange fastening section12, cools the O-ring1and the spiral gasket2by the above-described configuration of the flange fastening section according to any one of the above-described first to fifth embodiments. The steam after the certain heat exchange flows out of the flange fastening section12and passes through the working fluid outlet piping4, the outlet adjusting valve15and low-pressure feed-water system piping11to flow out to a condenser not illustrated in which pressure is lower than that on the upstream side. The low-pressure feed-water system piping11is connected to a low-pressure feed-water heater (LP-htr).

(Function and Effect of First Embodiment)

A function and an effect obtained by the flange fastening section according to the first embodiment are described in detail with reference toFIGS. 7A and 7B.

A state in which the working fluid flows through the flange fastening section according to the first embodiment is illustrated inFIG. 7A.FIG. 7Bis an enlarged view of a vertical cross-sectional surface of a part A6enclosed by a circle inFIG. 7A, which illustrates a state in which the O-ring1and the spiral gasket2are cooled by a heat exchange effect by the working fluid.

The working fluid of which temperature is lower than that of the working fluid in the steam piping fastened by the flange fastening section delivered from outside the flange fastening section flows into the O-ring1from the working fluid inlet piping3from a right side inFIG. 7A. The working fluid, which flows by being divided to an upper side and a lower side in the drawing in the O-ring1, joins together to flow out of the flange fastening section from the working fluid outlet piping4.

A state in which a pressure of the working fluid, which flows into the O-ring1from the working fluid inlet piping3, acts in a direction perpendicular to a surface of the O-ring1by the Archimedes' principle is illustrated inFIG. 7B. The flange groove20is cooled at the sheet portion at which the flange groove20and the O-ring1come into contact with each other, and the spiral gasket2is cooled in a direction indicated by an arrow8.

Since the working fluid flows in from outside the flange fastening section and flows out of the same, the flange groove20, which comes into contact with the O-ring1at the flange fastening section, acts as a kind of heat exchanger, and the spiral gasket2loaded on the flange groove20is cooled. According to this, expanded graphite being a hoop material composing the spiral gasket2may be cooled to 650° C. at which steam oxidation occurs or lower, so that original stable sealing performance of the expanded graphite may be maintained.

(Function and Effect of Second and Third Embodiments)

The description of functions and effects of the second and third embodiments of the present invention is similar to that of the function and the effect of the first embodiment described with reference toFIGS. 7A and 7B.

With reference toFIG. 7A, in the flange fastening section according to the second embodiment, since the O-ring1is arranged on the inner side of the spiral gasket2, a cooling effect is transmitted from the O-ring1on the inner side to the spiral gasket2on the outer side in the flange fastening section.

Further, in the flange fastening section according to the third embodiment, since the O-ring1is arranged on each of the inner side and the outer side of the spiral gasket2, the cooling effect is transmitted from the O-ring1on the inner side of the flange to the spiral gasket2on the outer side thereof, and further transmitted from the O-ring1on the outer side to the spiral gasket2on the inner side thereof. According to this, the effect of cooling the spiral gasket may be further improved.

(Function and Effect of Fourth Embodiment)

A function and an effect of the fourth embodiment of the present invention are described with reference toFIGS. 8A and 8B.

A state in which the working fluid is allowed to flow through the flange fastening section according to the fourth embodiment is illustrated inFIG. 8A.FIG. 8Bis an enlarged view of a vertical cross-sectional surface of a part A7enclosed by a circle inFIG. 8Aand illustrates a state in which the cooling effect is transmitted by the heat exchange effect of the working fluid.

InFIG. 8A, the working fluid acting as refrigerant of which temperature is lower than that of the working fluid in the steam piping fastened by the flange fastening section delivered from a right side in the drawing of the flange fastening section flows into the O-ring1from the working fluid inlet piping3. The working fluid divided into an upper side and a lower side in the drawing at a crossroad at which the O-ring1and the working fluid inlet piping3are connected to each other flows around the O-ring1and joins together again at a crossroad at which the O-ring1and the working fluid outlet piping4are connected to each other to flow out of the flange fastening section from the working fluid outlet piping4.

InFIG. 8B, the pressure of the working fluid, which flows into the O-ring1from the working fluid inlet piping3, acts in the direction perpendicular to the surface of the O-ring1by the Archimedes' principle. The flange groove20and the O-ring1itself, which come into contact with each other at the sheet portion of the O-ring1, are cooled in the direction indicated by the arrow8.

Since the working fluid flows into the flange fastening section from outside and flows out of the same, the flange groove20acts as a kind of heat exchanger, and the flange groove20and the O-ring1itself loaded on the flange groove20remain cooled. According to this, since plastic deformation due to a high temperature does not occur in the O-ring1, original stable sealing performance may be maintained and a selection range of a material of the O-ring1body may be extended.

(Function and Effect of Fifth Embodiment)

A function and an effect of the fifth embodiment of the present invention are described with reference toFIGS. 9A and 9B.

A state of the inner portion of the flange fastening section according to the fifth embodiment in which the spiral gasket2and the O-ring1are cooled in the direction indicated by the arrow8by the heat exchange effect of the working fluid is illustrated inFIG. 9A. In this case, the sheet portion at which the O-ring1and the flange groove20come into contact with each other is illustrated inFIG. 9Bin an enlarged manner.

As illustrated inFIG. 9B, the pressure of the working fluid, which flows into the O-ring1as indicated by an arrow7from the working fluid inlet piping3, acts in the direction perpendicular to the surface of the O-ring1by the Archimedes' principle to cool the flange groove20, which comes into contact with the sheet portion of the O-ring1and further the spiral gasket2.

As illustrated inFIG. 9A, a plurality of openings6are formed on the surface of the O-ring1. In the O-ring1, the opening6is desirably formed in the area, which faces the space enclosed by the sheet portion, at which this comes into contact with the flange groove20and the spiral gasket2.

The steam leaks from the opening6of the O-ring1. A precondition in this case is that the working fluid of which pressure is higher and temperature is lower than those of the steam flowing through the steam piping fastened by the flange fastening section flows through the O-ring1.

The pressure and the temperature in a space X enclosed by the sheet portion of the O-ring1at which the flange groove20and the O-ring1come into contact with each other and the spiral gasket2and the pressure and the temperature in the O-ring1are substantially the same in a stagnating state due to the steam leaked from the opening6.

A case in which the sheet portion of the O-ring1at which the flange groove20and the O-ring1come into contact with each other is broken by some reasons is considered. The pressure in the steam piping fastened by the flange fastening section is lower than the pressure in the above-described space X. As indicated as the flow direction7of the working fluid inFIG. 9B, inner leak occurs from a right side to a left side in the drawing. According to this, the working fluid of which temperature is high in the steam piping flowing on the left side in the drawing does not come into contact with the spiral gasket, so that a case in which the spiral gasket2is exposed to the high temperature may be prevented.

(Function and Effect of Sixth Embodiment)

A function and an effect of the cooling system of the flange fastening section according to the sixth embodiment are described with reference toFIG. 10. In this embodiment, the flange fastening section according to any one of the above-described first to fourth embodiments is used as described above.

The working fluid inlet piping3is branched from the high-pressure feed-water system piping10connected to the high-pressure heater (HP-htr) and passes through the inlet adjusting valve14to reach the flange fastening section12through the working fluid inlet piping3. The water as the working fluid is guided into the flange fastening section12through this route to cool the O-ring1and the spiral gasket2. After the heat exchange, the water as the working fluid flows out of the flange fastening section12and passes through the outlet adjusting valve15through the working fluid outlet piping4, and flows out to the low-pressure feed-water system piping11. The low-pressure feed-water system piping11is connected to the low-pressure feed-water heater (LP-htr).

According to this, the expanded graphite being the hoop material composing the spiral gasket2may be cooled to 650° C. at which the steam oxidation occurs or lower, so that the stable sealing performance of the expanded graphite may be maintained.

Function and Effect of Seventh Embodiment

A function and an effect of the cooling system of the flange fastening section according to the seventh embodiment of the present invention are described with reference toFIG. 11. In this embodiment, the flange fastening section according to any one of the above-described first to fifth embodiments is used as described above.

The working fluid inlet piping3is branched from the main steam piping18connected to the high-pressure turbine16and passes through the inlet adjusting valve14to reach the flange fastening section12through the working fluid inlet piping3. The steam as the working fluid is guided into the flange fastening section12through this route to cool the O-ring1and the spiral gasket2. After the heat exchange, the steam as the working fluid flows out of the flange fastening section12and passes through the working fluid outlet piping4, the outlet adjusting valve15and the low-pressure feed-water system piping11, and flows out to the condenser not illustrated. The low-pressure feed-water system piping11is connected to the low-pressure feed-water heater (LP-htr).

Especially, when using the flange fastening section according to the above-described fifth embodiment, although the opening6is formed on the O-ring1as illustrated inFIG. 9B, since the steam is used as the working fluid, steam explosion does not occur at the time of internal leak of the working fluid flowing out of the opening6as described above.

In this manner, the expanded graphite being the hoop material composing the spiral gasket2may be cooled to 650° C. or lower at which the steam oxidation occurs or lower, so that the stable sealing performance of the expanded graphite may be maintained.

Each of the above-described embodiments is merely an example and does not intend to limit the present invention, and may be modified within the technical scope of the present invention.