JP2003314692A - Pressure container and purging method for pressure container seal portion - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pressure container capable of easily purging water remaining in a seal portion between a container body and each flange of a top cover. <P>SOLUTION: This pressure container is composed of the container body 2 formed with a shell plate flange 3 having a sheet surface at an upper end, the top cover 6 made from a end plate flange 5 having an upper end plate 4 and a sheet surface at a lower end, and an inner O-ring 14 and an outer O-ring 15 respectively stored in annular grooves doubly formed on the sheet surface of the end plate flange 5. Both sheet surfaces are sealed by the both O-rings. Two through holes 8, 19 opening so as to be opposite to a part between both O-rings 14, 15 on the sheet surface of the end plate flange 5 and penetrating the flange 3 from the sheet surface of the shell plate flange 3 to achieve the outer surface are provided to be symmetric about an axis of the pressure container, and a gas blowing means 35 is provided on a port positioned on a flange 3 lower surface in regard to one through hole 19. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure vessel having a high temperature and high pressure fluid such as a nuclear power pressure vessel, and more particularly to a pressure vessel having a structure suitable for purging fluid that has entered a seal portion of the pressure vessel. The present invention relates to a container and a purging method thereof.

[0002]

2. Description of the Related Art A conventional seal structure for a flange joint of a pressure vessel 1 will be described with reference to FIGS. Figure 11
As shown in FIG. 1, the pressure vessel 1 includes a container body 2 having an annular body plate flange 3 formed at an upper end thereof, and an upper lid 6 composed of an upper mirror 4 and an annular lens plate flange 5 formed at a lower end of the upper mirror 4.
It consists of and. The container body 2 and the upper lid 6 are assembled by bolting with an O-ring interposed between the upper surface of the body plate flange 3 and the lower surface of the end plate flange 5.
Generally, a pair of the body plate flange 3 and the end plate flange 5 is called a main flange.

The pressure vessel 1 has a
The structure is such that the upper lid 6 can be opened and closed. The operation of opening and closing the upper lid 6 is performed by removing and attaching the stat bolts 7, nuts, washers and the like for tightening the body plate flange 2 and the end plate flange 5.

As shown in FIG. 12, the sealing structure of the body plate flange 2 and the end plate flange 5 has a seat surface 19 of the body plate flange 2 and a seat surface 2 of the end plate flange 4 which face each other.
4 and an inner O-ring 14 and an outer O-ring 15 that are housed in annular grooves 16 and 17 that are double formed in the seat surface 24. By tightening the stat bolt 7, the seat surface 19 of the body plate flange 2 and the end plate flange 4
The seat surface 24 which is the bottom surface of the inner and outer grooves 16 and 17 on the side of the body plate flange 2 and the end plate flange 4 side when the inner O ring 14 and the outer O ring 15 are compressed. By contacting 25 and 27, the sealing function between the main plate flange 2 and the end plate flange 2 is ensured.

Further, the seat surface 19 of the body plate flange 2 and the seat surface 24 of the end plate flange 4 are provided with paddings 12 and 13 of a corrosion-resistant metal material so that the sealing function soundness can be ensured. . Further, the seal of the main flange has the double O-ring structure of the inner O-ring 14 and the outer O-ring 15 as described above, and even if the primary seal (the inner O-ring 14) and the secondary seal (the outer O-ring 15) are used. ) Is designed to ensure the integrity of the sealing function even if the internal pressure of the pressure vessel is applied between

A through hole reaching from the sealing surface 19 on the upper surface to the lower surface is provided at one location of the body plate flange 2.
The through hole is located between the inner O-ring 14 and the outer O-ring 15, and is provided in succession to the leak detecting hole 8A formed downward from the sealing surface 19 and the leak detecting hole 8A in the body flange 2. The leak detection holes 8B and 8C are formed. When fluid flows between the seat surfaces of the inner O-ring 14 and the outer O-ring 15, these detection holes 8A to 8A are provided.
Fluid flows through C. Then, the fluid flows from the leakage detection nozzle 9 provided at the outlet of the leakage detection hole 8C on the lower surface of the body plate flange 2 to the leakage detection pipe 10 attached to the detection nozzle 9, and the fluid is released with the valve 11 open. It is possible to confirm the possibility that the fluid has flowed into the main flange after dropping.

[0007]

The conventional seal structure described above has the following problems. That is, the upper lid 6 of the pressure vessel 1, in particular, the upper lid 6 of the reactor pressure vessel is repeatedly opened and closed each time a periodical inspection for nuclear fuel exchange and in-reactor inspection is performed. After the work of closing the upper lid 6, a pressure resistance test is performed in order to confirm the soundness of the reactor pressure vessel including the confirmation of the soundness of the sealing function of each seat surface (19, 24) of the main flange. Prior to the execution of this closing work, the leak detection pipe 10 is blown with air to remove the fluid accumulated in the leak detection pipe 10.

However, when fluid (water) enters the seat surface between the inner O-ring 14 and the outer O-ring 15 due to the following factors (1) to (3) during the closing operation,
During this pressure resistance test, water that has entered between both O-rings due to displacement of the leak detection tube 10 or displacement of the main flange is discharged to the outside from the leak detection tube 10 via the leak detection holes 8A to 8C and the leak detection nozzle 9. Will be done.

Factor (1): Inflow of water condensed on the seat surface and the O-ring groove. During the work of closing the upper lid 6, condensation may occur on the seat surface and the O-ring groove depending on atmospheric conditions, and this condensed water flows in.

Factor (2): Inflow of condensed water on the inner surface of the upper lid 6. At the time of periodic inspection, the upper lid 6 is stored in a temporary storage place and moved to the position of the body plate flange 2 when closing the upper lid 6, but during this time, the inner surface of the upper lid 6 may be condensed, and this condensed water It flows along the inner surface of the upper lid 6 and flows into the seat surface.

Factor (3): Inflow of water from a pipe installed on the upper lid 6. Nozzles and spray pipes connected to the nozzles are installed in the central portion of the upper lid 6. However, similarly to the cause, there is a possibility that dew condensation may occur in the spray pipes when the upper lid 6 is closed. It flows along the inner surface of the upper lid 6 and flows into the seat surface.

In the main flange seal structure according to the above-mentioned prior art, when there is a possibility that accumulated water and leak water exist on the seat surface between the inner and outer O-rings, consideration should be given to discharge of these water, that is, the flange seal. No consideration was given to discharging accumulated water and leaked water in a short time, which would affect the confirmation of functional integrity.

As shown in FIG. 13, water entering between the inner O-ring 14 and the outer O-ring 15 (the accumulated water 2
9) exists at a position 180 ° opposite to the leakage detection hole 8A provided at one location of the body plate flange 3, the accumulated water 29 passes between the O-rings 14 and 15 around the flange. The water flows in the direction (water flow directions 30 and 31) and reaches the leak detection hole 8A. However, the accumulated water 2
Since the distance between the position of 9 and the leak detection hole 8A is long,
It takes a long time for the accumulated water 29 to reach the leak detection holes 8A, and the leak detection holes 8A to 8B, 8
C. It also takes some time to drop from the leak detecting tube 10 through the leak detecting nozzle 9.

Further, the leak detecting hole 8A is provided on the end plate flange 5.
The seat surface 24 is covered with water, and it is difficult for the water flowing through the groove 16 or 17 of the O-ring to flow into the leak detection hole 8A. This is also a factor that prolongs the time until dropping.

On the other hand, while maintaining the water pressure during the pressure resistance test, the inside O
Even when a leak occurs between the ring 14 and the seat surface 19, the leak water is dropped from the leak detection tube 10 through the path from the leak detection hole 8A to the leak detection nozzle 9 as in the above. However, in this case, the water pressure holding time is limited, and if it takes a long time to drip from the leak detection tube 10, the leak water cannot be detected within the water pressure holding time. Further, even if leaked water is detected, it cannot be determined whether it is the water 29 accumulated in the closing work or the leaked water in the pressure resistance test. For example, if the leaked water is mistakenly determined to be stagnant water, it will be recognized as a leak after the plant is started, and a large amount of backtracking work will occur, including opening and closing of the pressure vessel. Also,
On the contrary, if the accumulated water is mistakenly determined to be leaked water, the opening and closing work of the pressure vessel, which is not necessary originally, is performed.
Both of these are backtracking operations, which have a great impact on the subsequent steps. Therefore, if dripping water from the leak detection pipe 10 is observed, a great deal of labor is required.

The present invention has been made in view of the above circumstances, and is a pressure container capable of easily purging accumulated water generated in the seal portion between the flanges of the container body and the upper lid, and a method of purging the pressure container seal portion. To provide.

[0017]

In order to achieve the above object, a first pressure vessel of the present invention comprises a vessel body having a body plate flange having an annular seat surface at its upper end, a top mirror and An upper lid made of an end plate flange having an annular seat surface at the lower end of the upper mirror, and an inner O-ring and an outer O-ring respectively housed in an annular groove double formed on the seat surface of the end plate flange. In addition, both seat surfaces are aligned and the body plate flange and the end plate flange are fastened to seal both seat surfaces with both O-rings, and the seat surface of the end plate flange is located between the inner and outer O-rings. Two through-holes, which are opposed to each other and extend from the seat surface of the body plate flange to the outer surface through the body plate flange, are provided symmetrically with respect to the central axis of the pressure vessel, and one of the through holes is located on the lower surface of the body plate flange. Characterized in that a gas blowing means for blowing gas from the mouth that.

The second pressure vessel of the present invention is obtained by further adding two through holes and a gas blow to the first pressure vessel, that is, the inner O-ring of the seat surface of the end plate flange. Four through-holes are provided at equal intervals so as to be opposed to a portion existing between the outer O-ring and penetrate the body plate flange from the seat surface of the body plate flange to reach the outer surface. On the other hand, it is characterized in that the gas blow means is provided at the mouth located on the outer surface of the body plate flange.

Further, the third pressure vessel of the present invention is the first pressure vessel.
Like the pressure vessel of, a vessel body having a body plate flange,
An upper lid having an end plate flange, and an inner O-ring and an outer O-ring that are housed in a groove in the seat surface of the end plate flange doubly and seal both seat surfaces with both O-rings. On the side, there are two through-holes that are open to face the part of the seat surface that is between the O-rings and that penetrates the body plate flange from the seat surface to the outer surface and is symmetrical with respect to the center axis of the pressure vessel. Installed in
On the other hand, on the end plate flange side, one through-hole is formed in the portion of the seat surface existing between the O-rings and penetrates the end plate flange from the seat surface of the end plate flange to reach the outer surface. It is characterized in that the gas blowing means is provided at a position equidistant from the two provided through holes, and a gas blow means is provided at a port located on the outer surface of the flange with respect to the through hole provided in the end plate flange.

In each of the first to third pressure vessels, an annular shape that connects the ports of the through holes located on the seat surface of the body plate flange so as to face the portion of the seat surface of the end plate flange that is located between both O-rings. It is preferable to form the groove on the sheet surface.

In order to achieve the above object, the method of purging the seal portion of the pressure vessel of the present invention uses an inner O-ring by a gas blowing means immediately before raising the water pressure in the water pressure test of the first pressure vessel. Gas purging is performed between both seat surfaces located between the outer O-rings.

The gas blown out from the gas blowing means is
From one through-hole to which the gas blowing means is attached, the fluid (water) that bisects and flows between both seat surfaces located between both O-rings at this time is removed, and the other one is removed. It is released to the outside through the through hole. Therefore, no water is retained on the seal surface, and the soundness of the seal surface can be surely confirmed before the pressure resistance test.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION <First Embodiment> A pressure vessel according to a first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a sectional view showing the structure of a pressure vessel according to the present invention, FIGS.
5 is a view showing a detailed structure of the pressure vessel seal portion.

As shown in FIG. 1, the pressure vessel 1 has a vessel body 2 having an annular body plate flange 3 formed on the upper end thereof, an upper mirror 4 as a lid of the vessel body 2 and a lower end of the upper mirror 4. The upper lid 6 is composed of an annular end plate flange 5 and a double O-ring provided between the upper surface of the body plate flange 3 and the lower surface of the end plate flange 5, and further from the upper surface to the lower surface of the body plate flange 3. It has two through holes 8 and 19 penetrating therethrough. These through holes will be described in detail later. Pressure vessel 1
The body flange 3 and the end plate flange are bolted so that the upper lid 6 can be opened and closed to inspect the inside. The operation of opening and closing the upper lid 6 is performed by removing and attaching the stat bolts 7, nuts, washers and the like for tightening the body plate flange 2 and the end plate flange 5.

As shown in FIG. 2, the seal structure of the body plate flange 2 and the end plate flange 5 has a seat surface 18 of the body plate flange 2 and a seat surface 24 of the end plate flange 4 which face each other.
And an inner O-ring 14 and an outer O-ring 15 which are housed in annular grooves 16 and 17 formed in the seat surface 24 so as to be double inside and outside. By tightening the stat bolt 7, the seat surface 18 of the body plate flange 2 and the seat surface 24 of the end plate flange 4 come into contact with each other, and the inner O-ring 14 and the outer O-ring 15 are compressed, so that the seat on the body plate flange 2 side is seated. By contacting the surface 18 with the bottom surfaces 25 and 27 of the inner and outer grooves 16 and 17 on the end plate flange 4 side, a sealing function between the body plate flange 2 and the end plate flange is ensured.

Further, the seat surface 18 of the body plate flange 2 and the seat surface 24 of the end plate flange 4 are provided with paddings 12 and 13 of a corrosion-resistant metal material, so that the sealing function soundness can be ensured. . Furthermore, both flanges 2, 4
The seal between the inner O-ring 14 and the outer O-ring 15
It has a double O-ring structure, even if the primary seal (inner O-ring 14) and the secondary seal (outer O-ring 1)
Even if the internal pressure of the pressure vessel acts between the above and 5), the soundness of the sealing function can be secured.

One of the two through holes formed in the body plate flange 2 is a through hole 19 for blowing a purge gas, for example, an air blow, and is a seat surface 24 of the end plate flange 5.
Of the blow holes 19A, which are open to the seal surface 19 and extend downward, so as to face the portion between the inner O-ring 14 and the outer O-ring 15, and blow holes formed successively following the blow holes 19A. 19B and 19C. As shown in FIG. 1, a blow nozzle 20, a blow pipe 21, and a valve 2 are provided in the blow hole 19 opening on the lower surface of the end plate flange 5.
2. The connecting flange 23 and the connecting pipe 34 are sequentially connected.

The other through hole 8 of the two through holes is the leak detecting hole 8 described in the section of the prior art, and is formed at a position 180 degrees away from the blow hole 19 as shown in FIG. The blow hole 1 so that it is located between the inner and outer O-rings 14 and 15 on the seat surface 18 of the body plate flange 2.
An annular leak detection groove 36 is provided so as to connect the opening of 9A and the leak detection hole 8A. Further, the sheet surface 12 of the end plate flange where the opening of the leak detection hole 8A faces
As shown in FIGS. 3 and 4, a leakage detection groove 37 that communicates the inner O-ring groove 16 and the outer O-ring groove 17 is provided in the portion.

The operation and effect of providing the pair of blow holes 19 and the leak detection hole 8 as described above are as follows. First, if the condition of the seal portion of the pressure vessel before the pressure resistance test is checked, that is, if water is retained on the body plate flange sheet surface 18 for some reason, the leakage detection groove 36 easily retains the water, and By performing the air blow through the blow hole 19, the water accumulated in the directions 32 and 33 of the blow fluid can be discharged from the leak detection hole 8, so that no water remains on the sealing surface, and the discharged water is further discharged. Since the leak detection nozzle 9 flows to the leak detection tube 10 and the fluid drops while the valve 11 is open, the soundness of the seal portion before the pressure resistance test can be surely confirmed.

Secondly, when the possibility of leaking from the seat surface 18 near the inner O-ring 14 is generated while the water pressure is being held during the pressure resistance test, the leak water leaks into the leak detecting groove 3
Since it can reach the leak detection hole 8 in a short time after 6 and can be performed, the leak water can be detected within the water pressure holding time, and the soundness of the sealing surface can be surely judged within the water pressure holding time. Become.

Further, as described above, since the fluid existing on the seat surface 18 can be removed in a short time, the adverse effect of the presence of the fluid on the flange sealing surface is eliminated and the quality of the flange sealing surface can be maintained.

In the first embodiment, the leak detection groove 3
Although the case where 6 is provided is shown, the leak detection groove 36 is not always necessary.
Need not be provided. If the leak detection groove 36 is provided,
Leaked water leak detection groove 36 compared to the case without
It can be effectively discharged by air blow.

<Second Embodiment> FIG. 6 is a view showing a pressure vessel provided with three blow holes 19 which are opened in a seat surface 18 of a body flange 3. In addition to the pair of blow holes 19 (first blow hole 19) and the leak detection hole 8 shown in FIG. 5, the second blow hole 19 and the leak detection hole 8 are located at an intermediate position between the first blow hole 19 and the leak detection hole 8 on the flange circumference. , The third blow hole 19 is provided. Compared with the example shown in FIG. 5, the purge gas flows through only one flow passage, and water does not stay in the other flow passage. In this case, first, the purge gas is blown from the first blow hole 19, and after stopping it, the purge gas is blown from the second and third blow holes 19. As a result, the average stroke of the purge gas is shortened, and the fluid accumulated in the seal portion can be discharged more quickly. The blow from the first blow hole 19 and the second and third blows may be repeated if necessary.

<Third Embodiment> A pressure vessel according to a third embodiment will be described with reference to FIGS. FIG. 8 is an overall configuration diagram of the pressure vessel, and FIGS. 9 and 10 are diagrams showing a detailed structure of the pressure vessel sealing portion. The pressure vessel 1 according to the present embodiment is provided with a pair of blow holes 19 and a leak detection hole 8 in the body plate flange 2, and one blow hole 38 in the end plate flange 4. The pair of blow holes 19 and the leak detection hole 8 in the body plate flange 2 are the same as those in the first embodiment. On the other hand, the blow hole 38 passes between the blow hole 38 </ b> A extending laterally from the side surface of the end plate flange 4 and the blow hole 38 and downwardly extending to pass through the O-ring grooves 16 and 17 to pass through the body plate flange 2.
And a blow hole 38B that opens to the seat surface 18 of. The blow hole 38 is formed on the circumference of the flange by the blow hole 1
It is provided at an intermediate position between 9 and the leak detection hole 8.

When the water flowing into the seat surface 18 is purged using the blow hole 38, the blow hole 19 provided with the body plate flange 2 serves as a drainage mechanism for draining the water accumulated in the seat surface 18 to the outside. , To use. A blow nozzle 40, a blow pipe 41, and a blow valve 42 are provided as components for supplying the blow fluid to the blow hole 38.

According to the pressure vessel of this embodiment, since the drainage mechanism is added, there is an effect that the time required for draining the water accumulated on the seat surface 18 can be further shortened. In addition,
Similar to the first embodiment, it is of course possible to obtain the effects of confirming the soundness of the seal portion before the pressure resistance test, determining the soundness of the seal surface within the water pressure holding time, and maintaining the quality of the seat surface. .

That is, according to the embodiment of the present invention,
Even if fluid (water) flows into the flange sheet surface, water can be removed in a short time, so the status of the sealing surface can be checked before the pressure resistance test and the sealing function of the sealing surface can be sound within the water pressure holding time. Can be surely determined.

As a result, it is possible to shorten the period for opening and closing the pressure vessel (returning work is eliminated,
There is no impact on the subsequent process. ), The process of periodic inspection can be shortened. In addition, because the periodic inspection process can be shortened and unscheduled O-ring replacement work will not occur due to the absence of backtracking work, it is possible to reduce the radiation dose to workers especially in the reactor pressure vessel. Can be achieved. Further, these effects improve the utilization efficiency of the plant. Further, the influence of the presence of fluid on the flange seal surface is eliminated, and the quality of the flange seal surface can be maintained and improved.

[0039]

As described above, according to the present invention, it is possible to easily purge the accumulated water generated in the seal portion between the pressure vessel and the flange of the pressure vessel seal portion.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a pressure vessel according to a first embodiment of the present invention.

FIG. 2 is a detailed view of a “II” part in FIG.

3 is a sectional view taken along line III-III in FIG.

4 is a sectional view taken along line IV-IV of FIG.

5 is a sectional view taken along line VV of FIG.

FIG. 6 shows a pressure vessel according to a second embodiment of the present invention.
It is a figure which shows the example which provided the some blow hole.

FIG. 7 is a detailed view of section VII of FIG.

FIG. 8 is a sectional view showing a seal structure of a pressure vessel according to a third embodiment of the present invention.

FIG. 9 is a detailed view of an IX part in FIG.

10 is a sectional view taken along line XX of FIG.

FIG. 11 is a cross-sectional view of a seal structure for a flange joint of a pressure vessel according to the related art.

FIG. 12 is a detailed view of a section XII in FIG.

13 is a sectional view taken along line XIII-XIII in FIG.

[Explanation of symbols]

1 pressure vessel 2 Body plate flange 3 container body 4 upper mirror 5 End plate flange 6 Upper lid 7 Stud bolt 8, 8A, 8B, 8C Leakage detection hole 9 Leakage detection nozzle 10 Leakage detection tube 14 Inner O-ring 15 Outer O-ring 16 Inner O-ring groove 17 Outer O-ring groove 18 Seat surface (body plate flange side) 19, 19A, 19B, 19C Blow hole 21 blow piping 24 Seat surface (end plate flange side) 36, 37 Leakage detection groove

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G21D 1/00 G21C 13/00 C F term (reference) 3J040 AA17 BA02 EA16 FA05 HA15 HA30 3J046 AA07 AA11 BA01 BC16 DA05

Claims (5)

[Claims] 1. A container body having a body plate flange having an annular seat surface at an upper end, an upper mirror as a lid of the container body, and an end plate flange having an annular seat surface at a lower end of the upper mirror. It is composed of an upper lid and an inner O-ring and an outer O-ring which are respectively housed in an annular groove formed on the seat surface of the end plate flange, and the body plate flange and end plate flange are fastened by matching both seat surfaces. In a pressure vessel that seals both seat surfaces with both O-rings,
The sheet surface of the end plate flange is opened so as to face a portion existing between the inner O-ring and the outer O-ring, and penetrates the body plate flange from the seat surface of the body plate flange to reach the outer surface 2
Two through holes are provided symmetrically with respect to the central axis of the pressure vessel,
A pressure vessel characterized in that one of the through holes is provided with gas blowing means for blowing gas from an opening located on the lower surface of the body plate flange. 2. A container body having an upper end formed with a body plate flange having an annular seat surface, an upper mirror as a lid of the container body, and an end plate flange having an annular seat surface at the lower end of the upper mirror. It is composed of an upper lid and an inner O-ring and an outer O-ring which are respectively housed in an annular groove formed on the seat surface of the end plate flange, and the body plate flange and end plate flange are fastened by matching both seat surfaces. In a pressure vessel that seals both seat surfaces with both O-rings,
The sheet surface of the end plate flange is opened so as to face a portion existing between the inner O-ring and the outer O-ring, and penetrates the body plate flange from the seat surface of the body plate flange to reach the outer surface.
A pressure vessel, wherein one through hole is provided at equal intervals, and three out of four through holes are provided with gas blowing means for blowing gas from a port located on the outer surface of the body plate flange. 3. A container body having a body plate flange having an annular seat surface at an upper end, an upper mirror as a lid of the container body, and an end plate flange having an annular seat surface at a lower end of the upper mirror. It is composed of an upper lid and an inner O-ring and an outer O-ring which are respectively housed in an annular groove formed on the seat surface of the end plate flange, and the body plate flange and end plate flange are fastened by matching both seat surfaces. In a pressure vessel that seals both seat surfaces with both O-rings,
The sheet surface of the end plate flange is opened so as to face a portion existing between the inner O-ring and the outer O-ring, and penetrates the body plate flange from the seat surface of the body plate flange to reach the outer surface 2
Two through holes are provided symmetrically with respect to the central axis of the pressure vessel,
The body plate flange is provided with one through hole which is opened in a portion of the sheet surface of the end plate flange between the inner O ring and the outer O ring and penetrates the end plate flange from the seat surface of the end plate flange to reach the outer surface. A pressure vessel characterized in that it is provided at positions equidistant from the two through-holes, and gas-blowing means for blowing gas from a port located on the outer surface of the end plate flange is provided in the through-hole provided in the end plate flange. 4. An annular groove, which faces a portion of the seat surface of the end plate flange between the inner O-ring and the outer O-ring, and which connects the mouths of the through holes located on the seat surface of the body plate flange. The pressure vessel according to claim 1, wherein the pressure vessel is formed on the sheet surface. 5. Immediately before raising the water pressure in the water pressure test of the pressure vessel according to claim 1, a pressure vessel seal portion for gas purging between both seat surfaces located between the inner O-ring and the outer O-ring by the gas blowing means. Purge method.