Abstract:
Provided is a flange joining structure having excellent earthquake resistance, for which the joining operation can be performed simply and easily, similar to conventional practice. A flange joining structure provided with a first member having a first annular flange part, a second member having a second annular flange part, and a seal body placed between the first member and the second member, these components being connected and joined together by a bolt and a nut. The seal body has an annular base part formed from a metal plate and an elastic seal part provided integrally to the annular base part, the elastic seal part being provided so as to cover the annular base part, and the elastic seal part of the seal body sealing the space between the first annular flange part and the second annular flange part.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is the U.S. national stage of application No. PCT/JP2014/060538, filed on Apr. 11, 2014. Priority under 35 U.S.C. §119(a) and 35 U.S.C. §365(b) is claimed from Japanese Application No. 2013-115055, filed May 31, 2013, the disclosure of which is also incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a flange joining structure used for connecting between fluid pipes such as a water pipe, a gas pipe, and plant piping, between such a fluid pipe and a device (such as an air valve, a fire plug, or a repair valve, for example) coupled to the pipe, between these devices, or the like, and to a seal body used in the flange joining structure. 
       BACKGROUND ART 
       [0003]    Various flange joining structures used for connection between fluid pipes have been proposed (see, for example, Patent Literatures 1 and 2), and various seal bodies for sealing have also been proposed (see, for example, Patent Literature 3). For example, in the flange joining structure disclosed in Patent Literature 1, a seal body, disposed between a flange portion of a first member (for example, a pipe member) and a flange portion of a second member (for example, a pipe member), includes a hard ring and a ring-shaped packing that is disposed on an inner circumference portion of the hard ring and, the hard ring is thinner than the hard ring. In the flange joining structure, when the first and the second members are joined to each other (fixed to each other through fastening with a bolt, a nut, and the like, for example) with the seal body sandwiched between the flange portions of the first and the second members, the hard ring has one surface in contact with an end surface of the flange portion of the first member and the other surface in contact with an end surface of the flange portion of the second member. Thus, the ring-shaped packing can be prevented from being excessively compressed, and thus compression exceeding an elastic limit can be prevented. 
         [0004]    In the flange joining structure disclosed in Patent Literature 2, a seal body, disposed between a flange portion of a first member (for example, a pipe member) and a flange portion of a second member (for example, a pipe member), includes a ring-shaped packing main body and a plurality of compression limiting pieces that are embedded in the packing main body at an interval along a circumference direction. In the flange joining structure, when the first and the second members are joined to each other with the seal body sandwiched between the flange portions of the first and the second members, the plurality of compression limiting pieces limit the movement of the first and the second members toward each other, whereby the ring-shaped packing can be prevented from being excessively compressed. 
         [0005]    The seal body disclosed in Patent Literature 3 is disposed between a first member (for example, a cylinder) and a second member (for example, a cylinder head), and includes a sealing annular body formed of an elastic material such as rubber and a ring-shaped reinforcement body that reinforces the sealing annular body. The ring-shaped reinforcement body is integrally provided to the sealing annular body by molding. The seal body has the ring-shaped reinforcement body increasing the rigidity of the sealing annular body, and thus prevents the sealing annular body from deforming (deforming at the time of replacing, deformation due to performance degradation, or the like). 
       CITATION LIST 
     Patent Literature 
       [0006]    PTL1: Japanese Unexamined Patent Application Publication No. H7-332557 
         [0007]    PTL2: Japanese Unexamined Patent Application Publication No. H9-292071 
         [0008]    PTL3: Japanese Unexamined Utility Model Application Publication No. S51-85155 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0009]    The flange joining structure is applied to a piping structure illustrated in  FIG. 26  for example. In the piping structure illustrated in  FIG. 26 , a T shaped pipe  102 , defining a T shaped flow path, includes three connection pipe portions  104 ,  106 , and  108 . The connection pipe portion  104  is connected to a pipe member  110  extending toward an upstream side for example. The connection pipe portion  106  is connected to a pipe member  114  extending toward a downstream side for example. The connection pipe portion  108  is connected to an air valve  118  via a repair valve  116  for example. The flange joining structure described above is applied to these connections. For example, the connection pipe portion  104  of the T shaped pipe  102  is connected to the pipe member  110  as follows. More specifically, a joining bolt is inserted through a through hole of a flange portion  120 , a seal body  124 , and a flange portion  122  with the seal body  124  disposed between the flange portions  120  and  122  of the connection pipe portion  104  and the pipe member  110 . Then, a nut is screwed onto a male screw portion of a bolt protruding beyond the through hole, whereby the flange portion  120  of the T shaped pipe  102  and the flange portion  122  of the pipe member  110  are joined to each other with the seal body  124  disposed in between. 
         [0010]    However, in the flange joining structures in Patent Literatures 1 and 2, the through holes through which the joining bolt is inserted are formed in a packing (packing main body) providing a sealing function. Thus, when large bending stress is applied to the flange joining structure by an earthquake or the like, the packing (packing main body) might move with respect to the bolt, to be damaged. When the packing (packing main body) is damaged, a sealing performance (airtightness) might be degraded. The problem regarding the sealing performance is likely to occur in a joining structure between the connection pipe portion  108  of the T shaped pipe  102  and the repair valve  116 , and in a joining structure between the repair valve  116  and the air valve  118 . 
         [0011]    When the seal body disclosed in Patent Literature 3 is used in the flange joining structure, the sealing annular body (that functions as the packing) is not fixed, and is likely to move and deform upon receiving the large bending stress due to an earthquake, and might even be damaged when the movement and deformation are large, and thus the same problem occurs. 
         [0012]    An object of the present invention is to provide a highly earthquake proof flange joining structure with which a joining operation can be simply and easily performed as in the conventional case. 
         [0013]    Another object of the present invention is to provide a highly earthquake proof seal body. 
       Solution to Problem 
       [0014]    A flange joining structure according to the present invention includes a first member including a first annular flange portion, a second member including a second annular flange portion, and a seal body disposed between the first annular flange portion of the first member and the second annular flange portion of the second member. A bolt is inserted through a through hole in each of the first annular flange portion, the second annular flange portion, and the seal body. A nut is screwed onto a male screw portion of the bolt so that the first annular flange portion and the second annular flange portion are joined to each other. The seal body includes: an annular base portion formed of a metallic plate, and an elastic sealing unit integrally formed on the annular base portion. A plurality of the through holes are provided on the annular base portion at an interval along a circumference direction. The elastic sealing unit is provided to cover the annular base portion. The elastic sealing unit of the seal body provides sealing between the first annular flange portion of the first member and the second annular flange portion of the second member. 
         [0015]    In the flange joining structure according to the present invention, the elastic sealing unit of the seal body may be integrally provided to cover an area extending from one surface of an inner circumference portion of the annular base portion to another side via the inner circumference surface. 
         [0016]    In the flange joining structure according to the present invention, a first protrusion that comes into contact with the first annular flange portion of the first member may be provided on one surface side of the annular base portion of the seal body, and a second protrusion that comes into contact with the second annular flange portion of the second member may be provided on another surface side. 
         [0017]    In the flange joining structure according to the present invention, a plurality of the first protrusions of the seal body may be provided on the one surface side of the annular base portion at an interval along the circumference direction, and a plurality of the second protrusions of the seal body may be provided on the other surface side of the annular base portion at an interval along the circumference direction. 
         [0018]    In the flange joining structure according to the present invention, the annular base portion may be formed of first and second metallic plates, the first protrusions of the annular base portion may be formed by bending a plurality of portions of the first metallic plate in the circumference direction, the second protrusions of the annular protrusion may be formed by bending a plurality of portions of the second metallic plate in the circumference direction, and the annular base portion may be formed by stacking the first metallic plate and the second metallic plate with the first protrusions on the one surface side of the seal body and the second protrusions on the other surface side of the seal body. 
         [0019]    In the flange joining structure according to the present invention, roughening to form a rough surface and/or drilling for forming a through hole may be performed on the inner circumference portion of the annular base portion of the seal body. 
         [0020]    A seal body according to the present invention is disposed between a first annular flange portion of a first member and a second annular flange portion of a second member. The seal body includes an annular base portion formed of a metallic plate, and an elastic sealing unit integrally provided to the annular base portion. A plurality of through holes through which bolts are inserted are provided on the annular base portion at an interval along a circumference direction. The elastic sealing unit is provided to cover the annular base portion. The elastic sealing unit provides sealing between the first annular flange portion of the first member and the second annular flange portion of the second member. 
       Advantageous Effects of Invention 
       [0021]    In the flange joining structure according to the present invention, the seal body, disposed between the first annular flange portion of the first member and the second annular flange portion of the second member includes: an annular base portion formed of a metallic plate; and an elastic sealing unit integrally formed on the annular base portion, and a plurality of the through holes are provided on the annular base portion. Thus, the annular base portion can be surely held between the first and the second annular flange portions with a bolt and a nut, whereby the movement of the elastic sealing unit can be prevented, and a damage caused by the movement can be prevented. The elastic sealing unit is integrally provided to the annular base portion, whereby the elastic sealing unit can be prevented from moving and being damaged. 
         [0022]    In the flange joining structure according to the present invention, the elastic sealing unit of the seal body is integrally provided to cover an area extending from one surface of an inner circumference portion of the annular base portion to another side via the inner circumference surface. Thus, a large contact area between the elastic sealing unit and the annular base portion can be achieved, whereby the elastic sealing unit can be more rigidly integrated to the annular base portion. 
         [0023]    In the flange joining structure according to the present invention, a first protrusion that comes into contact with the first annular flange portion of the first member is provided on one surface side of the annular base portion of the seal body, and a second protrusion that comes into contact with the second annular flange portion of the second member is provided on another surface side. Thus, the first protrusion comes into contact with the first annular flange portion of the first member, whereby the elastic sealing unit can be prevented from excessively deforming on the one surface side of the seal body. Furthermore, the second protrusion comes into contact with the second flange portion of the second member, whereby the elastic sealing unit can be prevented from excessively deforming on the other surface side of the seal body. 
         [0024]    In the flange joining structure according to the present invention, a plurality of the first protrusions of the seal body are provided on the one surface side of the annular base portion in an annular form, and a plurality of the second protrusions of the seal body are provided on the other surface side of the annular base portion in an annular form. Thus, the first protrusion can stably act on the first annular flange portion of the first member to prevent the elastic sealing unit from excessively deforming on the one surface side of the seal body. The second protrusion can stablely act on the second annular flange portion of the second member to prevent the elastic sealing unit from excessively deforming on the other surface side of the seal body. 
         [0025]    In the flange joining structure according to the present invention, a plurality of the first protrusions of the seal body are provided on the one surface side of the annular base portion at an interval along the circumference direction, and a plurality of the second protrusions of the seal body are provided on the other surface side of the annular base portion at an interval along the circumference direction. Also with this configuration, the plurality of first protrusions can stably act on the first annular flange of the first member to prevent the elastic sealing unit from excessively deforming on the one surface side of the seal body. The plurality of second protrusions can act on the second annular flange of the second member to prevent the elastic sealing unit from excessively deforming on the other surface side of the seal body. 
         [0026]    In the flange joining structure according to the present invention, the first protrusions of the annular base portion are formed by bending a plurality of portions of the first metallic plate in the circumference direction, the second protrusions of the annular protrusion are formed by bending a plurality of portions of the second metallic plate in the circumference direction. Thus, the first protrusion and the second protrusion can be easily manufactured by pressing for example. The annular base portion is formed by stacking with which the first protrusions are provided on the one surface side of the seal body and the second protrusions are provided on the other surface side of the seal body, and thus can be easily manufactured. 
         [0027]    In the flange joining structure according to the present invention, roughening to form a rough surface and/or drilling for forming a through hole is performed on the inner circumference portion of the annular base portion of the seal body. Thus, a large contact area between the elastic sealing unit and the annular base portion can be achieved, whereby the elastic sealing unit can be more rigidly integrated to the annular base portion. 
         [0028]    The seal body according to the present invention has the basic structure that is the same as that of the seal body in the flange joining structure according to the present invention, the annular base portion can be surely fixed between the first and the second annular flange portions with a bolt and a nut, whereby the elastic sealing unit can be prevented from moving and from being damaged by the movement. Furthermore, the elastic sealing unit can be integrally provided to the annular base portion. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0029]      FIG. 1  is a front view illustrating a seal body of a first mode used in a flange joining structure according to the present invention. 
           [0030]      FIG. 2  is a cross-sectional view taken along a line II-II in  FIG. 1 . 
           [0031]      FIG. 3  is a cross-sectional view illustrating the flange joining structure according to a first embodiment using the seal body illustrated in  FIG. 1 . 
           [0032]      FIG. 4  is a cross-sectional view illustrating a seal body of a second mode. 
           [0033]      FIG. 5  is a cross-sectional view illustrating a part of a seal body of a third mode. 
           [0034]      FIG. 6  is a front view illustrating a seal body of a fourth mode. 
           [0035]      FIG. 7  is a cross-sectional view taken along a line VI-VI in  FIG. 6 . 
           [0036]      FIG. 8  is an exploded view illustrating a flange joining structure according to a second embodiment employing a seal body of a fifth mode, in an exploded state. 
           [0037]      FIG. 9  is a cross-sectional view illustrating a part of the seal body of the fifth mode. 
           [0038]      FIG. 10  is a cross-sectional view illustrating a part of a seal body of a sixth mode. 
           [0039]      FIG. 11  is a cross-sectional view illustrating a part of a seal body of a seventh mode. 
           [0040]      FIG. 12  is a cross-sectional view illustrating a part of a seal body of an eighth mode. 
           [0041]      FIG. 13  is a cross-sectional view taken along a line XII-XII in  FIG. 12 . 
           [0042]      FIG. 14  is a cross-sectional view illustrating a part of a seal body of a ninth mode. 
           [0043]      FIG. 15  is a perspective view of a metallic plate in the seal body illustrated in  FIG. 14 . 
           [0044]      FIG. 16A  is a cross-sectional view of a seal body in which one of metallic plates forming an annular base portion is bent, and  FIG. 16B  is a cross-sectional view of the seal body in which the other one of the metallic plates forming the annular base portion is bent. 
           [0045]      FIG. 17  is a perspective view of a metallic plate in the seal body illustrated in  FIG. 16 . 
           [0046]      FIG. 18  is a front view illustrating another mode of a metallic plate. 
           [0047]      FIG. 19  is a cross-sectional view taken along a line XVII-XVII in  FIG. 18 . 
           [0048]      FIG. 20  is a cross-sectional view taken along a line XVIII-XVIII in  FIG. 18 . 
           [0049]      FIG. 21  is a cross-sectional view illustrating a part of a seal body of a twelfth mode. 
           [0050]      FIG. 22  is a front view of the seal body illustrated in  FIG. 21 . 
           [0051]      FIG. 23  is a partial cross-sectional view illustrating the inside of the seal body illustrated in  FIG. 21 . 
           [0052]      FIG. 24  is a cross-sectional view illustrating a part of a seal body of a thirteenth mode. 
           [0053]      FIG. 25A  is a front view of the seal body illustrated in  FIG. 24 , and  FIG. 25B  is an enlarged front view of a protrusion of the seal body. 
           [0054]      FIG. 26  is s simplified view illustrating an example of a piping structure to which a conventional flange joining structure is applied. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0055]    Various embodiments of a flange joining structure and a seal body used in the same according to the present invention are described below with reference to the attached drawings. 
         [0056]    First of all, a seal body of a first mode used in the flange joining structure is described with reference to  FIGS. 1 and 2 . An illustrated seal body  2  includes an annular base portion  4  and an annular elastic sealing unit  6  integrally provided to an inner circumference portion of the annular base portion  4 . The annular base portion  4  is formed of a metallic plate such as stainless steel for example. In the annular base portion  4 , a plurality of (four in this mode) through holes  8  are formed at a substantially equal interval along a circumference direction. The inner circumference portion of the annular base portion  4  is an inner circumference surface proximate portion in the inner circumference surface of the annular base portion  4  and a surface adjacent to the inner circumference surface (upper and lower surfaces in  FIG. 2 ). 
         [0057]    The elastic sealing unit  6  is formed of synthetic rubber and the like for example, and is provided to cover the inner circumference portion of the annular base portion  4 . As illustrated in  FIG. 2 , an outer circumference portion of the elastic sealing unit  6  protrudes radially outer. A first sealing unit  10  on one side covers one surface (upper surface in  FIG. 2 ) of the inner circumference portion of the annular base portion  4  and a second sealing unit  12  on the other side covers the other surface (lower surface in  FIG. 2 ) of the inner circumference portion of the annular base portion  4 . A connecting section  14 , connecting between the first and the second sealing units  10  and  12 , covers the inner circumference surface of the annular protrusion  4 . 
         [0058]    The elastic sealing unit may be provided as illustrated in  FIG. 4 . An elastic sealing unit  6 ′ of a seal body  2 ′ illustrated in  FIG. 4  includes no connecting section covering the inner circumference surface of the annular base portion  4 . The first sealing unit  10  of the elastic sealing unit  6 ′ at least partially covers the one surface (upper surface in  FIG. 4 ) of the inner circumference portion of the annular base portion  4 . The second sealing unit  12  at least partially covers the other surface (lower surface in  FIG. 4 ) of the inner circumference portion of the annular base portion  4 . The advantageous effects that are substantially the same as those obtained by the seal body  2  illustrated in  FIGS. 1 and 2  can also be obtained with the seal body  2 ′. 
         [0059]    The seal body  2  can be formed as follows. The annular base portion  4  is set in a fixed mold (not illustrated), clamping is performed with a movable mold (not illustrated) moved with respect to the fixed mold, and then synthetic rubber for example is injected into a molding space defined by the fixed mold and the movable mold. Through this vulcanized molding, the elastic sealing unit  6  illustrated in the figure can be integrally formed on the inner circumference portion of the annular base portion  4 . 
         [0060]    As illustrated in  FIG. 3 , the seal body  2  is installed between a first annular flange portion  18  of a first member  16  and a second annular flange portion  22  of a second member  20 . A plurality of (four in this mode) of through holes  24 , corresponding to the plurality of through holes  8  formed in the annular base portion  4  of the seal body  2 , are provided to the first annular flange portion  18  of the first member  16 . A plurality of (four in this mode) of through holes  26 , corresponding to the plurality of through holes  8  of the seal body  2 , are also provided to the second annular flange portion  22  of the second member  20 . 
         [0061]    For example, the joined connection between the first member  16  and the second member  20  is achieved as follows. The seal body  2  is disposed between the first annular flange portion  18  of the first member  16  and the second annular flange portion  22  of the second member  20 . In this state, a male screw portion  30  of a joining bolt  28  is inserted through the through hole  24  of the first annular flange portion  18 , the through hole  8  of the annular base portion  4  of the seal body  2 , and the through hole  26  of the second annular flange portion  22 . Then, a nut  32  is screwed onto and fastened to the male screw portion  30  of the bolt  28  protruding from the second annular flange portion  22 . Thus, the desired joined connection between the first member  16  and the second member  20  can be achieved. A higher earthquake-proof effect can be achieved by using a lock nut (product name: hardlock nut) manufactured and sold by HARDLOCK INDUSTRY CO., LTD., for example as the nut  32 . 
         [0062]    In the joined state, the elastic sealing unit  6  of the seal body  2  is disposed in a compressed state between an end surface (what is known as a gasket seat) of the first annular flange portion  18  of the first member  16  and an end surface (what is known as a gasket seat) of the second annular flange portion  22  of the second member  20 . Thus, the elasticity of the elastic sealing unit  6  ensures the sealing between the first annular flange portion  18  and the second annular flange portion  22 . The male screw portion  30  of the joining bolt  28  extends through the through hole  8  of the annular base portion  4  of the seal body  2 . Thus, the movement of the annular base portion  4  is inhibited by the male screw portion  30 , whereby relative movement of the seal body  2  with respect to the elastic sealing unit  6  can be prevented. Thus, even when the first and the second members  16  and  20  are relatively shifted from each other by a certain amount by an earthquake and the like, the elastic sealing unit  6  of the seal body  2  is prevented from moving. As a result, the elastic sealing unit  6  can be prevented from being damaged, and the sealing performance provided by the elastic sealing unit  6  can be maintained. 
         [0063]    The first member  16  and the second member  20  are a fluid pipe such as a water pipe, a gas pipe, and plant piping as a pipe member, and are a device connected to the fluid pipe such as an air valve, a fire plug, and a repair valve. The seal body  2  can be used in the flange joining structure for achieving the joined connection between the members as described above. 
         [0064]    Next, a seal body of a third mode will be described with reference to  FIG. 5 . In the third mode, the configuration described below is employed to make the elastic sealing unit  6  more rigidly integrated. The configurations in the following mode that are substantially the same as that in the modes described above are denoted with the same reference numerals, and the description thereof will be omitted. 
         [0065]    This seal body  2 A illustrated in  FIG. 5  has a surface partially provided with rough surface areas  42 ,  44 , and  46  including minute recesses and protrusions, with roughening performed on an inner circumference portion of an annular base portion  4 A. In this mode, the rough surface area  42  is provided to one surface of the inner circumference portion of the annular base portion  4  to which the first sealing unit  10  of the elastic sealing unit  6  is provided. The rough surface area  44  is provided to the other surface of the inner circumference portion of the annular base portion  4  to which the second sealing unit  12  of the elastic sealing unit  6  is provided. The rough surface area  46  is provided to the inner circumference surface of the annular base portion  4 . The rough surface areas  42 ,  44 , and  46  can be formed through roughening such as shot blasting and sand blasting. The other configurations of the third mode are the same as the counterparts in the first mode described above. 
         [0066]    With the rough surface areas  42 ,  44 , and  46 , a large contact area between the annular base portion  4 A and the elastic sealing unit  6  can be achieved, whereby the annular base portion  4 A and the elastic sealing unit  6  can be more rigidly integrated with each other. 
         [0067]    The rough surface areas  42 ,  44 , and  46  may not necessarily to be provided to all of the one, the other, and the inner circumference surfaces of the inner circumference portion of the annular base portion  4 A as in this mode. The advantageous effect that is the same as that described above can also be obtained by providing the three areas to any one or two of the areas. 
         [0068]    Next, a seal body according to a fourth mode is described with reference to  FIGS. 6 and 7 . In the fourth mode, the following improvement is made so that an elastic sealing unit  6 B is more rigidly integrated. 
         [0069]    The seal body  2 B of the fourth mode illustrated in  FIGS. 6 and 7  includes a plurality of (four in this mode) communication holes  48  arranged at an interval on an inner circumference portion of an annular base portion  4 B. The communication holes  48  are formed from one surface to the other surface of the annular base portion  4 B. The communication holes  48  can be formed by drilling. The number of communication holes  48  may be set as appropriate, and may six or eight for example. 
         [0070]    When the communication holes  48  are formed as described above, the synthetic rubber partially flows into the communication holes  48 , while the vulcanized molding of the elastic sealing unit  6 B is in process, to be integrated with the annular base portion  4 B. Thus, the annular base portion  4 B and the elastic sealing unit  6 B can be more rigidly integrated with each other. The rough surface areas (the areas denoted with  42 ,  44 , and  46  in  FIG. 5 ) may be provided to the inner circumference portion of the annular base portion  4 B on which the communication holes  48  are formed, so that the annular base portion  4 B and the elastic sealing unit  6 B can be even more rigidly integrated with each other. 
         [0071]    In the fourth mode, the eight through holes  8  are arranged at an interval along a circumference direction of the annular base portion  4 B. For example, the seal body  2 B including the eight through holes  8  can be used for achieving the joined connection between the first and the second members having the first and the second annular flange portions each including eight through holes, and between the first and the second members having the first and the second annular flange portions each including four through holes. The through holes  8  thus formed in various ways (for four-points fastening, six-points fastening, eight-points fastening, or the like for example) can be used for achieving the fastened connection between the first and the second members of various types, whereby the seal body  2 B can be more commonly used. 
         [0072]    Next, a second embodiment of a flange joining structure including a seal body of a fifth mode is described with reference to  FIG. 8 . In the second embodiment, an annular base portion  4 C of a seal body  2 C has a protrusion for preventing an elastic sealing unit  6 C from excessively deforming. 
         [0073]    In  FIG. 8 , the seal body  2 C of the fifth mode includes the annular base portion  4 C and the elastic sealing unit  6 C provided to the inner circumference portion of the annular base portion  4 C. The annular base portion  4 C includes the plurality of (four for example) through holes  8  provided at an interval along the circumference direction. The plurality of (four for example) communication holes  48  may be provided on the inner circumference portion (where the elastic sealing unit  6 C is provided) at an interval along the circumference direction. The communication holes  48  and the configuration related thereto are substantially the same as that in the fourth mode illustrated in  FIGS. 6 and 7 . With the communication holes  48 , the advantageous effect that the elastic sealing unit  6 C is more rigidly integrated with the annular base portion  4 C can be obtained as described above. 
         [0074]    In this mode, a first ring-shaped member  52  is provided at a portion of one surface side of the annular base portion  4 C more on a radially outer side than a portion where the communication hole  48  is provided. The first ring-shaped member  52  functions as a first protrusion that prevents the elastic sealing unit  6 C from excessively deforming on the one surface side of the annular base portion  4 C as described later. A second ring-shaped member  54  is provided at a portion of the other side of the annular base portion  4 C more on a radially outer side than the portion where the communication hole  48  is provided. The second ring-shaped member  54  functions as a second protrusion that prevents the elastic sealing unit  6 C from excessively deforming on the other side of the annular base portion  4 C as described later. The first and the second ring-shaped members  52  and  54  may be formed of a hard material such as stainless steel, hard plastic, and the like for example. 
         [0075]    In this mode, as illustrated in  FIG. 8 , the elastic sealing unit  6 C is provided to cover the first and the second ring-shaped members  52  and  54  (more specifically, the inner circumference surface and the upper surface thereof). A pair of first annular sealing protrusions  56  are formed on one surface (upper surface in  FIG. 8 ) of the elastic sealing unit  6 C while being apart from each other in the radial direction. A pair of second annular sealing protrusions  58  are formed on the other surface (lower surface in  FIG. 8 ) while being apart from each other in the radial direction. Alternatively, three or more first annular sealing protrusion  56  and three or more second annular sealing protrusions  58  may be provided to achieve higher sealing performance. The other configurations of the flange joining structure of the second embodiment are the same as the counterparts in the first embodiment described above. 
         [0076]    In the flange joining structure of the second embodiment, the seal body  2 C is manufactured as follows. The first ring-shaped member  52  (first protrusion) is fixed on a predetermined position of the one surface of the annular base portion  4 C through fixing adhesion with adhesive, welding, or the like. The second ring-shaped member  54  (second protrusion) is fixed on a predetermined position of the other surface through fixing adhesion with adhesive, welding, or the like. The annular base portion  4 C (having the first and the second ring-shaped members  52  and  54  fixed thereon) is set in a fixed mold (not illustrated), clamping is performed with a movable mold (not illustrated) moved with respect to the fixed mold, and then synthetic rubber for example is injected into a molding space defined by the fixed mold and the movable mold. Through this vulcanized molding, the elastic sealing unit  6 C as illustrated in the figure can be integrally formed on the inner circumference portion of the annular base portion  4 C. 
         [0077]    Through the vulcanized molding, the annular base portion  4 C and the elastic sealing unit  6 C can be rigidly integrated with each other with the synthetic rubber partially flowing into the communication holes  48  of the annular base portion  4 C during the molding, as in the fourth mode. The first and the second ring-shaped members  52  and  54  are covered with the synthetic rubber. Thus, the first and the second ring-shaped members  52  and  54  do not come into direct contact with the end surfaces (i.e., the gasket seats  60  and  62 ) of the first and the second annular flange portions  18  and  22  of the first and the second members  16  and  20  when fixed connection is achieved as described later. 
         [0078]    The joined connection between the first member  16  and the second member  20  is achieved in a manner that is the same as that described above. As can be seen in  FIG. 8 , in the joined connection state, the first ring-shaped member  52  is in contact with the end surface (gasket seat  60 ) of the first annular flange portion  18  via a synthetic rubber layer  64 . Thus, a constant elastic deformation amount of the elastic sealing unit  6 C is achieved and excessive elastic deformation is prevented, on the one surface side of the annular base portion  4 C. The second ring-shaped member  54  is in contact with the end surface (gasket seat  62 ) of the second annular flange portion  22  via a synthetic rubber layer  66 . Thus, a constant elastic deformation amount of the elastic sealing unit  6 C is achieved and excessive elastic deformation is prevented, also on the other surface side of the annular base portion  4 C. 
         [0079]    In this joined connection state, elasticity of the pair of first annular sealing protrusions  56  acts on the end surface (the gasket surface  60 ) of the first annular flange portion  18  on the one surface side of the seal body  2 C. Thus, the sealing between the first annular flange portion  18  and the seal body  6 C can be ensured. Furthermore, elasticity of the pair of second annular sealing protrusions  58  acts on the end surface (the gasket surface  62 ) of the second annular flange portion  22  on the other surface side of the seal body  2 C. Thus, the sealing between the second annular flange portion  22  and the seal body  6 C can be ensured. 
         [0080]    When the fasting is performed between the joining bolt and the nut (that are not illustrated) with the seal body  6 C disposed between the first annular flange portion  18  and the second annular flange portion  22 , conventionally, non-uniform crushing of the seal body  6 C over the portions due to insufficient fastening (for example, non-uniform clamping over a plurality of fastening portions), has resulted in the inclined end surface (gasket surface  60 ) of the first annular flange portion  18  and/or the inclined end surface (gasket surface  62 ) of the second annular flange portion  22  causing water stop failure. To address this, the first and the second ring-shaped members  52  and  54  are provided. More specifically, the fastening is performed until the gasket surfaces  60  and  62  of the first and the second members  18  and  22  come into contact with the first and the second ring-shaped members  52  and  54  via the synthetic rubber layers  64  and  66 . Thus, the plurality of fastening portions can have a uniform size without the need for a special torque managing at the time of fastening. All things considered, the fastening can be extremely easily prevented from being insufficient at the time of manufacturing, and an attempt to improve the manufacturing operability can be facilitated. 
         [0081]    The first and the second protrusions need not to be formed in the ring shape from the first and the second ring-shaped members  52  and  54  as in this mode, and may be formed as a plurality of short column members or arc-shaped members that are disposed at an interval along the circumference direction, and adjacent to the through holes  8  where the fastening force is applied in particular. 
         [0082]      FIG. 9  illustrates a seal body of a sixth mode. The basic configuration of a seal body  2 G of the sixth mode illustrated in  FIG. 9  is substantially the same as that in the fifth mode illustrated in  FIG. 8 . The first ring-shaped member  52  is provided to the one surface of the annular base portion  4 G, the second ring-shaped member  54  is provided to the other surface thereof. The first ring-shaped member  52  functions as the first protrusion that maintains the constant elastic deformation amount on the one surface side of the elastic sealing unit  6 G. The second ring-shaped member  54  functions as the second protrusion that maintains the constant elastic deformation amount on the other surface side of the elastic sealing unit  6 G. The first and the second ring-shaped member  52  and  54  can be attached to the annular base portion  4 G in a manner that is the same as that in the fifth mode described above. 
         [0083]    In this mode, an upper surface of the first ring-shaped member  52  is exposed to the outside. The one surface side of the elastic sealing unit  6 G protrudes beyond the upper surface of the first ring-shaped member  52  toward the one surface side. In the joined connection state, the upper surface of the first ring-shaped member  52  is in direct contact with the end surface (gasket seat  60 ) of the first flange portion  18 . Furthermore, an upper surface of the second ring-shaped member  54  is also exposed to the outside. The other surface side of the elastic sealing unit  6 G protrudes beyond the upper surface of the second ring-shaped member  54  toward the other surface side. In the joined connection state, the upper surface of the second ring-shaped member  54  is in direct contact with the end surface (gasket seat  62 ) of the second flange portion  22  (see  FIG. 8  for the first and the second members  16  and  20 ). 
         [0084]    In the seal body  2 G of this sixth mode, as in that in the fifth mode, the annular base portion  4 G and the elastic sealing unit  6 G can be integrally formed with the synthetic rubber flowing in in the vulcanized molding as described above. In the sixth mode, the communication holes of the annular base portion  4 G are omitted. Thus, the elastic sealing unit  6 G is integrally provided to an area covering the one, the inner circumference, and the other surfaces of the inner circumference portion of the annular base portion  4 G. 
         [0085]    When the seal body  2 G of the sixth mode is used, because the basic configuration is substantially the same as that in the fourth mode, the same advantageous effect as that in the case where the fourth mode is employed can be obtained. Because the pair of first annular sealing protrusions  56  and the pair of second annular sealing protrusions  58  are supported by the annular base portion  4 G, the sealing between the first and the second flange portions  18  and  22  can be stably ensured, as in the fourth mode. 
         [0086]      FIG. 10  illustrates a seal body of a seventh mode. In the seventh mode, a seal body obtained by modifying the annular base portion in the first mode is used. In the seal body  2 D illustrated in  FIG. 10 , washer members  70  and  71  are provided that have a predetermined thickness and correspond to the through holes  8  provided to the annular base portion  4 D. The washer members  70  and  71  are provided to have insertion holes  72  and  73  thereof aligned with the through holes  8  of the annular base portion  4 D, and are fixed to the annular base portion  4 D through fixing adhesion with adhesive, welding, or the like. The washer members  70  and  71  need not to be fixed as described above. Alternatively, joining bolts (not illustrated) may be inserted through the insertion holes  72  and  73  of the washer members  70  and  71  and the through holes  8  of the annular base portion  4 D, so that the one washer member  70  is provided to the one surface side of the annular base portion  4 D and the other washer member  71  is provided to the other surface side thereof. 
         [0087]    In the seal body  2 D, as illustrated in  FIG. 10 , the elastic sealing unit  6  has a one side portion protruding beyond the washer member  70  toward the one surface side, and the other side portion protruding beyond the other washer member  71  toward the other surface side. In a state where the first annular flange portion  18  of the first member  16  and the second flange portion  22  of the second member  20  are fastened to each other with the elastic sealing unit  6  of the seal body  2 D disposed in between, the elastic sealing unit  6  is disposed between the end surface (gasket seat  60 ) of the first annular flange portion  18  and the end surface (gasket seat  62 ) of the second annular flange portion  22  to provide the sealing therebetween. 
         [0088]    The washer member  70  comes into contact with a recessed step portion  74  of the first annular flange portion  18 . Thus, a constant distance between the annular base portion  4 D and the end surface (gasket seat  60 ) of the first annular flange portion  18 , in other words, a constant elastic deformation amount of the elastic sealing unit  6  on one surface side of the annular base portion  4 D is achieved, whereby the excessive elastic deformation on the one surface side can be prevented. The other washer member  71  comes into contact with a recessed step portion  75  of the second annular flange portion  22 . Thus, a constant distance between the annular base portion  4 D and the end surface (gasket seat  62 ) of the second annular flange portion  22 , in other words, a constant elastic deformation amount of the elastic sealing unit  6  on the other surface side of the annular base portion  4 D is achieved, whereby the excessive elastic deformation on the other surface side can be prevented. 
         [0089]    As described above, the one washer member  70  functions as the first protrusion that comes into contact with the first annular flange portion  18  (more specifically, the recessed step portion  74  thereof), and the other washer member  71  functions as the second protrusion that comes into contact with the second annular flange portion  22  (more specifically, the recessed step portion  75  thereof). Also with this configuration, the advantageous effect that is the same as the case where the first and the second ring-shaped members  52  and  54  in the fifth mode illustrated in  FIG. 8  are provided can be obtained. 
         [0090]      FIG. 11  illustrates a seal body of an eighth mode. In the eighth mode, a short sleeve member  79  is used instead of the washer members  70  and  71  in the seventh mode in  FIG. 10 . In a seal body  2 E illustrated in  FIG. 11 , the short sleeve member  76  having a desired length is inserted in the through hole  8  of the annular base portion  4 E and is fixed to the annular base portion  4 E through fixing adhesion with adhesive, welding, or the like. 
         [0091]    When the seal body  2 E is used, as can be seen in  FIG. 11 , a joining bolt (not illustrated) is inserted through a sleeve hole  79  for the short sleeve member  76  of the seal body  2 E. The short sleeve member  76  has one end portion  77  protruding beyond the annular base portion  4 E toward one side (upper side in  FIG. 11 ) and the other end portion  78  protruding beyond the annular base portion  4 E toward the other side (lower side in  FIG. 11 ). The coupling connection can be achieved as desired as in the above described case also when this seal body  2 E is used. 
         [0092]    In this joined connection state, the elastic sealing unit  6  of the seal body  2 E is disposed between the end surface (gasket seat  60 ) of the first annular flange portion  18  and the end surface (gasket seat  62 ) of the second annular flange portion  22  to provide the sealing therebetween. The one end portion  77  of the short sleeve member  76  comes into contact with the recessed step portion  74  of the first annular flange portion  18 , to achieve a constant elastic deformation amount of the elastic sealing unit  6  on the one surface side of the annular base portion  4 E. The other end portion  78  of the short sleeve member  76  comes into contact with the recessed step portion  75  of the second annular flange portion  22 , to achieve a constant elastic deformation amount of the elastic sealing unit  6  on the other surface side of the annular base portion  4 E. All things considered, the advantageous effect that is the same as that in the seventh mode illustrated in  FIG. 10  can be achieved. 
         [0093]    As described above, in this mode, the one end portion  77  of the short sleeve member  76  functions as the first protrusion that comes into contact with the first annular flange portion  18  (more specifically, the recessed step portion  74  thereof), and the other end portion  78  of the short sleeve member  76  functions as the second protrusion that comes into contact with the second annular flange portion  22  (mode specifically, the recessed step portion  75  thereof). 
         [0094]    Next, a seal body of a ninth mode is described with reference to  FIGS. 12 and 13 . In the ninth mode, deformation processing is executed on an annular base portion  4 F of the seal body  2 F, whereby the first and the second protrusions are integrally formed. 
         [0095]    In the seal body  2 F of the ninth mode illustrated in  FIGS. 12 and 13 , the plurality of (eight in this mode) through holes  8  are provided on the annular base portion  4 F at an interval along the circumference direction. The first protrusions respectively related to four alternating holes of the eight through holes  8  are provided, and the second protrusions related to the four remaining holes of the through holes  8  are provided. 
         [0096]    For example, the annular base portion  4 F can be manufactured as follows. More specifically, the eight through holes  8  are formed on an annular metallic plate at an interval along the circumference direction. Then, first protruding portions  82  (as the first protrusions) protruding toward one surface side (upper side in  FIG. 13 ) are formed by performing, for example, pressing in a predetermined direction (toward the upper side in  FIG. 13 ) at portions of the alternating holes of the through holes  8 . Subsequently, second protruding portions  84  (as the second protrusions) protruding toward the other surface side (lower side in  FIG. 12 ) are formed by performing, for example, pressing in a direction opposite to the predetermined direction (toward the lower side in  FIG. 13 ) at portions of the remaining holes of the through holes  8 . Then, the elastic sealing unit  6  is integrally provided to the inner circumference portion of the annular base portion  4 F described above, in the manner described above, whereby the seal body  2 F illustrated in  FIGS. 12 and 13  can be manufactured. 
         [0097]    When the seal body  2 F is used, in the joined connection state, the first protruding portion  82  of the annular base portion  4 F comes into contact with the first flange portion  18  (see  FIG. 10  (recessed step portion  74 )). Thus, a constant elastic deformation amount is achieved on the one surface side of the elastic sealing unit  6 . The second protruding portion  84  thereof comes into contact with the second flange portion  22  (see  FIG. 10  (recessed step portion  76 )). Thus, a constant elastic deformation amount is achieved on the other surface side of the elastic sealing unit  6 . All things considered, the advantageous effect that is the same as that in the seventh mode can be achieved with the seal body  2 F described above. 
         [0098]    Next, a seal body of a tenth mode is described with reference to  FIGS. 14 and 15 . In the tenth mode, an annular base portion  4 H of a seal body  2 H is formed of a pair of metallic plates, and the first and the second protrusions are formed by the deformation processing. 
         [0099]    In the seal body  2 H of the tenth mode illustrated in  FIGS. 14 and 15 , the annular base portion  4 H is formed of a pair of ring-shaped metallic plates, that is, first and second metallic plates  86  and  88 . The first and second metallic plates  86  and  88  have substantially the same configuration. The first metallic plate  86  (second metallic plate  88 ) is described below. 
         [0100]    The first metallic plate  86  (second metallic plate  88 ) is formed of stainless steel for example, and has the plurality of (four in this mode) through holes  8  provided on the outer circumference side thereof at an interval along the circumference direction. Joining bolts (not illustrated) are inserted through the through holes  8 . A plurality of (four in this mode) communication holes  90  and protrusions  92  are provided on an inner circumference side of the first metallic plate  86  (second metallic plate  88 ) at an interval along the circumference direction. The plurality of through holes  8 , the plurality of communication holes  90 , and the protrusions  92  need not to be aligned in the radial direction as in this mode, and may be provided to form a zigzag pattern in the circumference direction. The numbers of the through holes  8 , the communication holes  90 , and the protrusions  92  need not to be the same as in this mode. For example, the numbers of the communication hole  90  and the protrusions  92  may be larger than the number of through holes. For example, the communication hole  90  and the protrusions  92  may be provided on both sides of the through holes  8 . 
         [0101]    For example, the first metallic plate  86  (second metallic plate  88 ) can be easily manufactured as follows. First of all, the metallic plate  86  ( 88 ) having a disk shape has a center portion punched by pressing (first pressing) to be in a ring shape. The through holes  8  can be formed by punching out a circular shape while the first pressing is in process (or in second pressing after the first pressing), and at the same time, a tongue piece (a portion to be the protrusion  92 ) is formed by punching out a rectangular U shape. Then, the tongue piece is bent toward the inner side in the diameter direction for example, through plastic deformation by pressing, whereby the protrusions  92  are formed. 
         [0102]    In the first metallic plate  86  (second metallic plate  88 ) formed as described above, the protrusion  92 , obtained by bending the tongue piece, functions as the first protrusion (second protrusion) and an opening obtained by bending the tongue piece functions as the communication hole  90 , as can be seen in  FIGS. 14 and 15 . 
         [0103]    The seal body  2 H is manufactured as follows. The first and the second metallic plates  86  and  88  are stacked as desired so that the protrusions  92  are positioned on both sides, and fixing or temporary connecting is performed through fixing adhesion with adhesive, welding, and the like for example as appropriate. In the stacked state, as illustrated in  FIG. 14 , the protrusion  92  of the first metallic plate  86  is positioned on one surface side of the seal body  2 H to function as the first protrusion. The protrusion  92  of the second metallic plate  88  is positioned on the other surface side of the seal body  2 H to function as the second protrusion. The through holes  8  as well as the communication holes  90  of the first and the second metallic plates  86  and  88  are aligned with each other. 
         [0104]    The annular base portion  4 H (the first and the second metallic plates  86  and  88 ) is set in a fixed mold (not illustrated), clamping is performed with a movable mold (not illustrated) moved with respect to the fixed mold, and then synthetic rubber for example is injected into a molding space defined by the fixed mold and the movable mold. Through this vulcanized molding, the elastic sealing unit  6 H illustrated in the figure can be integrally formed at the inner circumference portion of the annular base portion  4 H. 
         [0105]    Through the vulcanized molding, the annular base portion  4 H and the elastic sealing unit  6 H can be rigidly integrated with each other with the synthetic rubber partially flowing into the communication holes  90  of the annular base portion  4 H in the molding, as in the fourth mode. The upper surfaces of the protrusions  92  of the first and the second metallic plates  86  and  88  are covered with the synthetic rubber. Thus, the protrusions  92  (first and second protrusions) do not come into direct contact with the end surfaces (see FIG.  10  (i.e., the gasket seats  60  and  62 )) of the first and the second annular flange portions  18  and  22  of the first and the second members  16  and  20 , when the fixed connection is achieved. 
         [0106]    As can be seen in  FIG. 14 , in a joined connection state using the seal body  2 H, the protrusion  92  (first protrusion) of the first metallic plate  86  is in contact with the end surface (see  FIG. 10  (gasket seat  60 )) of the first annular flange portion  18  of the first member  16  via a synthetic rubber layer  94 . Thus, the excessive elastic deformation of the elastic sealing unit  6 H can be prevented on the one surface side of the annular base portion  4 H. The protrusion  92  of the second metallic plate  88  is in contact with the end surface (see  FIG. 10  (gasket seat  62 )) of the second annular flange portion  22  of the second member  20  via a synthetic rubber layer  96 . Thus, the excessive elastic deformation of the elastic sealing unit  6 H can be prevented on the other surface side of the annular base portion  4 H. A first annular sealing protrusion  97  that provides sealing with respect to the end surface (see  FIG. 10  (gasket surface  60 )) of the first annular flange portion  18  is provided on the one surface side of the elastic sealing unit  6 H. A second annular sealing portion  98  that provides sealing with respect to the end surface (see  FIG. 10  (gasket surface  62 )) of the second annular flange portion  22  is provided on the other surface side of the elastic sealing unit  6 H. Thus, the sealing can be ensured between the seal body  6 H and the first and the second annular flange portion  18  and  22  (see  FIG. 10 ) of the first and the second members  16  and  20  as in the case described above. Furthermore, the protrusions  92  are formed on the first and the second metallic plates  86  and  88  by deformation processing (bending), and thus can be easily formed without requiring an additional member. 
         [0107]    A seal body of an eleventh mode is described with reference to  FIGS. 16 and 17 . In this seal body  2 K illustrated in  FIG. 16 , an annular base portion  4 K of the seal body  2 K is formed from a pair of ring-shaped metallic plates, that is, a first metallic plate  130  and a second metallic plate  132 , and protrusions (the first and the second protrusions  134  and  136 ) are formed by partially bending the first and the second metallic plates  130  and  132 , as in the case of the seal body  2 H of the tenth mode. In the seal body  2 K illustrated in  FIG. 17 , the plurality of (four in this mode) through holes  8  are provided on the annular base portion  4 K at an interval along the circumference direction. The first protrusions  134  respectively related to the two alternating holes of the four through holes  8 , and the second protrusions  136  respectively related to the remaining two holes of the through holes  8  are provided. 
         [0108]    For example, the annular base portion  4 K can be manufactured as follows. More specifically, the four through holes  8  are formed on the annular first metallic plate  130  at an interval along the circumference direction. Tongue pieces (to be bent to be the first protrusion  134 ) and the communication holes  90  are alternately formed along the circumference direction, on the radially inner side of the through holes  8 . 
         [0109]    Similarly, the four through holes  8  are formed on the annular second metallic plate  132  at an interval along the circumference direction. Tongue pieces (to be bent to be the second protrusion  136 ) and the communication holes  90  are alternately formed along the circumference direction, on the radially inner side of the through holes  8 . 
         [0110]    The tongue piece of the first metallic plate  130  and the communication hole  90  of the second metallic plate  132  and the communication hole  90  of the first metallic plate  130  and the tongue piece of the second metallic plate  132  are disposed to be overlapped one another. Pressing is performed in such a manner that the tongue piece of the first metallic plate  130  is bent toward the communication hole  90  of the second metallic plate  132  to clamp the second metallic plate  132 . Processing is performed in such a manner that the tongue piece of the second metallic plate  132  is bent toward the communication hole  90  of the first metallic plate  130  to clamp the first metallic plate  130 . Thus, the first metallic plate  130  and the second metallic plate  132  are integrally formed with the tongue piece of the first metallic plate  130  wrapped around the second metallic plate  132  and the tongue piece of the second metallic plate  132  wrapped around the first metallic plate  130 . 
         [0111]    As can be seen in  FIGS. 16 and 17 , in the first metallic plate  130  (second metallic plate  132 ) thus formed, the tongue piece is bent to function as the first protrusion  134  (second protrusion  136 ), and an opening formed by bending the tongue piece toward the first metallic plate  130  (second metallic plate  132 ) functions as the communication hole  90 . 
         [0112]    The seal body  2 K is manufactured as follows. The annular base portion  4 K (the first metallic plate  130  and the second metallic plate  132 ) is set in a fixed mold (not illustrated), clamping is performed with a movable mold (not illustrated) moved with respect to the fixed mold, and then synthetic rubber for example is injected into a molding space. Through this vulcanized molding, the elastic sealing unit  6 K illustrated in the figure can be integrally formed on the inner circumference portion of the annular base portion  4 K. 
         [0113]    As described above, the first metallic plate  130  and the second metallic plate  132  need not to be temporarily connected in advance for manufacturing the seal body  2 K, whereby a lower manufacturing cost can be achieved. 
         [0114]    Other embodiments of a metallic plate (forming the annular base portion) are described with reference to  FIGS. 18 to 20 . In this modification, an annular base portion  4 J of a seal body is formed from a single metallic plate, and the first and the second protrusions are formed by deformation processing as in the tenth embodiment. 
         [0115]    In  FIGS. 18 to 20 , the annular base portion  4 J of the seal body is formed from a single metallic plate, that is, a metallic plate  99 . The metallic plate  99  is formed of stainless steel as in the tenth mode, and has the plurality of (four in this mode) through holes  8  at an outer circumference portion thereof at an interval along the circumference direction. Joining bolts (not illustrated) are inserted through the through holes  8 . In this mode, the communication holes  90  and protrusions  92 A and  92 B are formed on both sides of each of the plurality of through holes  8 . The protrusion  92 A on the downstream side of the through hole  8  in a clockwise direction in  FIG. 18  is bent toward the one surface side of the metallic plate  99  (annular base portion  4 J) to function as the first protrusion as illustrated in  FIG. 19 . The protrusions  92 B on the upstream side of the through hole  8  in the clockwise direction is bent toward the other surface side of the metallic plate  99  (annular base portion  4 J) to function as the second protrusion as illustrated in  FIG. 20 . 
         [0116]    The communication holes  90  as well as the protrusions (the first and the second protrusions  92 A and  92 B) need not to be provided on both sides of each of the through holes  8  as in this mode. The plurality of through holes  8 , the plurality of communication holes  90 , and the protrusions (the first and the second protrusions  92 A and  92 B) may be provided to form a zigzag pattern in the circumference direction. Alternatively, the plurality of communication holes  90  and the protrusions (the first and the second protrusions  92 A and  92 B) may be provided to match the plurality of through holes  8  in the radial direction (here, the number of the communication holes  90  is the same as the number of the through holes  8 , but the number of the first protrusions  92  and the number of the second protrusions  92 B are half the number of the through holes  8  because the first and the second protrusions  92 A and  92 B are alternately arranged). 
         [0117]    For example, the metallic plate  99  can be manufactured easily as follows as in the case of the tenth mode. First of all, the metallic plate  89  having a disk shape has a center portion punched by pressing (first pressing) to be in a ring shape. The through holes  8  can be formed by punching out a circular shape while the first pressing is in process (or in second pressing after the first pressing), and at the same time, a tongue pieces (a portion to be the protrusions  92 A and  92 B) are formed by punching out a rectangular U shape. Then, the tongue pieces are plastically deformed as desired, whereby the protrusions (first protrusions  92 A and  92 B) are formed. 
         [0118]    More specifically, the tongue piece on the downstream side of the through hole  8  in the clockwise direction in  FIG. 18  is bent toward the radially inner side toward the one surface side of the metallic plate  99  (annular base portion  4 J) so that the first protrusion  92 A is formed as illustrated in  FIG. 19 . The communication hole  90 , corresponding to the first protrusion  92 A, is formed by the bending. The tongue piece on the upstream side of the through hole  8  in the clockwise direction is bent toward the radially inner side toward the other surface side of the metallic plate  99  (annular base portion  4 J) so that the second protrusion  92 B is formed as illustrated in  FIG. 20 . The communication hole  90 , corresponding to the second protrusion  92 B, is formed by the bending. 
         [0119]    The annular base portion  4 J formed of the metallic plate  99  is used in the vulcanized molding in the substantially same manner as that in the tenth mode, whereby an elastic sealing unit (not illustrated) is integrally formed on the inner circumference portion of the annular base portion  4 J so that the seal body is formed. 
         [0120]    In the above described mode, a plurality of portions of the metallic plate  99  are punched to form the tongue piece, and the protrusions (first protrusions  92 A and the second protrusions  92 B) are formed by bending the tongue pieces as desired. However, the shape is not limited to this. For example, a tongue piece including a plurality of tongue sections may be formed by punching out other shapes such as an E shape or a shape with recesses and protrusions. Then, the plurality of tongue sections of the tongue piece may be bent toward any of the one and the other sides of the metallic plate  99  (annular base portion  4 J) or both so that the protrusions (the first and the second protrusions  92 A and  92 B) are formed. 
         [0121]    In the embodiment described above, the tongue pieces of the metallic plate  99  are bent toward the radially inner side to form the protrusions (the first and the second protrusions  92 A and  92 B). However, this should not be construed in a limiting sense, and the protrusions (the first and the second protrusions  92 A and  92 B) may be formed by bending the tongue pieces toward the radially outer side or laterally in the circumference direction. 
         [0122]      FIGS. 21 to 23  illustrate a seal body of a twelfth mode. An annular base portion  4 L of this seal body  2 L of the twelfth mode illustrated in  FIG. 21  is formed of a single ring-shaped metallic plate. As illustrated in  FIGS. 22 and 23 , the annular base portion  4 L of the seal body  2 L is entirely covered with synthetic rubber. 
         [0123]    In  FIG. 21 , the seal body  2 L of the twelfth mode includes the annular base portion  4 L, an elastic sealing unit  6 L provided to cover the entire annular base portion  4 L, the first ring-shaped member  52  provided on one surface of the annular base portion  4 L, and the second ring-shaped member  54  provided on the other surface of the annular base portion  4 L. The plurality of (four for example) through holes  8  are provided on the annular base portion  4 L at an interval along the circumference direction. 
         [0124]    As in the case of the seal body  2 G of the sixth mode, the first ring-shaped member  52  functions as the first protrusion that prevents the elastic sealing unit  6 L from excessively deforming on the one surface side of the annular base portion  4 L. The second ring-shaped member  54  functions as the second protrusion that prevents the elastic sealing unit  6 L from excessively deforming on the other surface side of the annular base portion  4 L. 
         [0125]    In this mode, the elastic sealing unit  6 L are provided to entirely cover the first ring-shaped member  52 , the second ring-shaped member  54 , and the annular base portion  4 L as illustrated in  FIG. 21 . The pair of first annular sealing protrusions  56  are provided on one surface (upper surface in  FIG. 21 ) of the elastic sealing unit  6 L at an interval in the radial direction. The pair of second annular sealing protrusions  58  are provided on the other surface (lower surface in  FIG. 21 ) of the elastic sealing unit  6 L at an interval in the radial direction. 
         [0126]    When the first and the second annular sealing protrusions  56  and  58  are provided, in the joined connection state of the first member  16  and the second member  20 , the first and the second annular sealing protrusions  56  and  58  come into contact with the end surface (see  FIG. 10  (gasket seat  60 )) of the first annular flange portion  18  of the first member  16  or the end surface (see  FIG. 10  (gasket seat  62 )) of the second annular flange portion  22  of the second member  20 . Thus, high pressure is applied to the first and the second annular sealing protrusions  56  and  58 . Accordingly, the first annular sealing protrusion  56  comes into closer contact with the end surface (see  FIG. 10  (gasket seat  60 )) of the first annular flange portion  18  of the first member  16 , and the second annular sealing protrusion  58  comes into closer contact with the end surface (see  FIG. 10  (gasket seat  62 )) of the second annular flange portion  22  of the second member  20 . Furthermore, the first and the second annular sealing protrusions  56  and  58  are largely deformed to offset the assembly error of the seal body  2 L, whereby high sealing performance and water pressure resistance can be achieved. 
         [0127]    The same effect can be achieved also in the seal body (embodiments illustrated in  FIGS. 8, 9, 14, and 16  for example) provided with the first and the second annular sealing protrusions. 
         [0128]    The seal body  2 L is manufactured as follows. The first ring-shaped member  52  (first protrusion) and the second ring-shaped member  54  (second protrusion) are respectively fixed to predetermined positions on one and the other surfaces of the annular base portion  4 L through the fixing adhesion with adhesive, welding, or the like. The annular base portion  4 L (to which the first ring-shaped member  52  and the second ring-shaped member  54  are fixed) is set in a fixed mold (not illustrated), clamping is performed with a movable mold (not illustrated) moved with respect to the fixed mold, and then synthetic rubber for example is injected into a molding space. Through this vulcanized molding, the elastic sealing unit  6 L illustrated in the figure can be integrally formed on the inner circumference portion of the annular base portion  4 L. 
         [0129]    The seal body  2 L is waterproofed and insulated with the elastic sealing unit  6 L entirely covering the first ring-shaped member  52 , the second ring-shaped member  54 , and the annular base portion  4 L. Thus, the annular base portion  4 L can be prevented from corroding due to rust and electrolytic corrosion attributable to current flowing in the ground. Thus, iron cheaper than stainless steel can be used as a material for forming the annular base portion  4 L to achieve cost reduction. 
         [0130]    When the stainless steel is used as the material for forming the annular base portion  4 L, there is no risk of rusting even when the elastic sealing unit  6 L is damaged, whereby higher durability can be achieved. 
         [0131]    As illustrated in  FIGS. 22 and 23 , with a flange  140  provided to the seal body  2 L, for example, the joining bolt  28  and the through hole  8  can be finely adjusted by using the flange  140  when the seal body  2 L is disposed between laterally installed pipes, that is, as illustrated in  FIG. 26 , between a pipe member  110  and a connection pipe member  104 , between a connection pipe member  106  and a pipe member  114 , between a pipe member  110  and an unillustrated upstream side pipe member, between the pipe member  114  and an unillustrated downstream pipe member, or the like. Thus, the installability of the seal body  2 L can be improved. 
         [0132]      FIGS. 24 and 25  illustrate a seal body of a thirteenth mode. An annular base portion  4 M of this seal body  2 M of the thirteenth mode illustrated in  FIG. 24  is formed of a single ring-shaped metallic plate. A protrusion  150  is formed by bending the metallic plate. As illustrated in  FIG. 25A , the annular base portion  4 M is entirely covered with synthetic rubber. 
         [0133]    The seal body  2 M of the thirteenth mode illustrated in  FIG. 25A  includes the annular base portion  4 M and an elastic sealing unit  6 M provided to cover the entire annular base portion  4 M. The plurality of (four in this mode) through holes  8  are provided on the annular base portion  4 M at an interval along the circumference direction. The plurality of (eight in this mode) protrusions  150  are provided at an interval along the circumference direction. 
         [0134]    The annular base portion  4 M can be manufactured as follows. More specifically, the four through holes  8  are formed at an interval along the circumference direction of the annular base portion  4 M. The tongue pieces (to be bent to be the protrusions  150 ) are formed by punching out, in the annular base portion  4 M, the rectangular U shape in radially inner and outer directions from portions where the protrusions  150  are formed at an interval along the circumference direction that are more on the radially inner side than the through holes  8 . As illustrated in  FIG. 25B , the tongue piece has a substantially trapezoidal shape with a width W 1  of a distal end portion smaller than a width W 2  of a base end portion. The pressing can be facilitated by forming the tapered tongue piece in a substantially trapezoidal shape. The tongue pieces are plastically deformed in opposite directions with the tongue piece, formed on the radially inner side by the pressing, plastically deformed toward the radially outer side, and the tongue piece, formed on the radially outer side by the pressing, plastically deformed toward the radially inner side, to be formed as the protrusions  150 . 
         [0135]    With the protrusion  150  provided to the annular base portion  4 M, the communication holes  152  are provided on radially inner and outer sides of the protrusion  150 . Thus, the synthetic rubber, for vulcanized molding of the elastic sealing unit  6 M, partially flows into the communication holes  152  to be integrated with the annular base portion  4 M. Thus, the annular base portion  4 M and the elastic sealing unit  6 M can be rigidly integrated with each other. 
         [0136]    As illustrated in  FIG. 25A , with the flange  140  provided to the seal body  2 M, for example, the joining bolt  28  and the through hole  8  can be finely adjusted by using the flange  140  when the seal body  2 M is disposed between laterally installed pipes as illustrated in  FIG. 26 , that is, between the pipe member  110  and the connection pipe member  104 , between the connection pipe member  106  and the pipe member  114 , between the pipe member  110  and an unillustrated upstream side pipe member, between the pipe member  114  and an unillustrated downstream pipe member, or the like. Thus, the installability of the seal body  2 M can be improved. 
         [0137]    In the embodiments described above, the pressing can be facilitated by employing punching with which a tapered tongue piece is obtained as illustrated in  FIG. 25B  when punching out a rectangular U shape in the annular base portion. In the embodiment illustrated in  FIG. 25B , the tongue piece has a substantially trapezoidal shape. Burr and the like, generated by drilling and punching on the annular base portion, might damage the elastic sealing unit, and thus processing such as chamfering for removing the burrs and the like is preferably executed. 
         [0138]    The present invention is not limited to the various embodiments of the flange joining structure and the various modes of the seal body used therein according to the present invention, and can be changed or modified in various ways without departing from the scope of the present invention. 
       INDUSTRIAL APPLICABILITY 
       [0139]    The present invention can be applied to a flange joining structure used for connecting between fluid pipes such as a water pipe, a gas pipe, and plant piping, between such a fluid pipe and a device (such as an air valve, a fire plug, or a repair valve, for example) connected to the pipe, between these devices, or the like, and to a seal body used in the flange joining structure. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           2 ,  2 A,  2 B,  2 C,  2 D,  2 E,  2 F,  2 G,  2 H,  2 K,  2 L,  2 M Seal body 
           4 ,  4 A,  4 B,  4 C,  4 D,  4 E,  4 F,  4 G,  4 H,  4 J,  4 K,  4 L,  4 M Annular base portion 
           6 ,  6 B,  6 C,  6 G,  6 H,  6 K,  6 L,  6 M Elastic sealing unit 
           8  Through hole 
           16  First member 
           20  Second member 
           28  Joining bolt 
           32  Nut 
           48 ,  92  Communication hole 
           52  First ring-shaped member (first protrusion) 
           54  Second ring-shaped member (second protrusion) 
           60 ,  62  Gasket seat 
           70 ,  71  Washer member 
           74 ,  76  Recessed step portion 
           77  Short sleeve member 
           86  First metallic plate 
           88  Second metallic plate 
           92  Protrusion 
           92 A First protrusion 
           92 B Second protrusion 
           99  Metallic plate