JP2014224579A - Pipe gasket - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gasket of a shape that can be used safely for a long period of time under high radiation dose characteristic of nuclear facilities, and to thereby provide facilities capable of keeping insulation of a flange part for connecting a stainless pipe to a carbon steel pipe in a high temperature environment and ensure sound transport of a fluid inside th pipe without leakage.SOLUTION: A pipe gasket provided between flanges on pipe end surfaces when pipes having the flanges formed on the end surfaces are coupled to each other, comprising: a central hole that is provided at a position opposed to a cavity on an inner surface of each pipe and through which a fluid inside a pipe passes; an abutment surface located around the central hole and abutting on the flange; a non-abutment surface that is located around the abutment surface and that does not abut on the flange; and means constituted by a plurality of bolt holes formed on the non-abutment surface for inhibiting occurrence of a crack to the non-abutment surface at a distant position from the central hole among the non-abutment surface from the central hole to an outer edge of the gasket via the bolt holes.

Description

  The present invention relates to a piping gasket, and more particularly, to a piping gasket suitable for insulating a dissimilar metal connection portion of a piping flange under a high temperature and a high radiation dose in a nuclear facility or the like.

  A phenomenon in which a metal having a lower potential corrodes when contacting with a metal having a different potential in an environment having moisture or the like is called galvanic corrosion. It is known that the same phenomenon occurs in piping, and when dissimilar metals having a large potential difference are connected, it is necessary to electrically insulate them from each other in order to prevent galvanic corrosion. For example, it corresponds to the case where a stainless steel pipe and a carbon steel pipe are connected.

  There are various methods for insulation, but the easiest way to do this is to install an insulating gasket made of non-metallic materials such as rubber, resin, inorganic and organic fibers on the flange connecting the stainless steel pipe and carbon steel pipe. The method of pinching is known. In particular, in a high temperature environment, a fluororesin-based gasket containing polytetrafluoroethylene (PTFE) having high heat resistance is used.

  When used in nuclear facilities, high radiation resistance is required for polymer materials such as rubber and resin because they are exposed to radiation exposure. This is because a leakage event from the flange must not occur. However, unlike steel pipes, polymer materials have the disadvantage of poor radiation resistance.

  More specifically, it is known that a polymer material such as rubber or resin is excited when radiation acts on the molecule, and the bond is broken and decomposed. When radiation acts on rubber or resin, hydrogen radicals or hydrocarbon radicals are generated. This radical is highly reactive, the radicals bond together (recombination), the radical pulls out the element to form another radical (drawing reaction), or the radical is added next to the double bond (addition) Reaction), the radicals are bonded to each other and the molecular chain is broken (disproportionation reaction).

  A recombination or addition reaction results in an increase in molecular weight called cross-linking, whereas a disproportionation reaction results in a decrease in molecular weight called decay. Whether to give priority to disintegration or cross-linking depends on the molecular structure and physical state of the polymer, for example, the ease of movement of the molecule. However, since the elasticity of both collapse and cross-linking is reduced, resistance to impact and deformation is reduced, or changes in physical properties such as brittleness are caused, so there are problems such as cracking and cracking when used as a gasket. There are concerns that arise.

  Among the polymer materials, polytetrafluoroethylene (PTFE) has extremely excellent physical properties such as heat resistance, chemical resistance, non-adhesiveness, low friction, and high electrical insulation. On the other hand, PTFE is also a typical material that causes radiolysis. Radiolysis refers to a phenomenon in which the main chain in a molecular chain is cleaved by the action of radiation and the molecular weight decreases. Polytetrafluoroethylene (PTFE) is usually used with a molecular weight of several million or more, but when it becomes less than one million, mechanical properties such as strength and elongation are drastically lowered and cannot be used. For this reason, polytetrafluoroethylene (PTFE) has a drawback that radiation dose is small, and even when the number of molecular chain breaks is small, the deterioration due to radiation appears extremely large. Even in an environment where decomposition is relatively difficult to proceed, such as at room temperature or in an inert gas, when the radiation acts, the main chain is easily cleaved, resulting in a decrease in molecular weight and brittleness. For these reasons, when a fluororesin-based gasket containing polytetrafluoroethylene (PTFE) is used in a radiation environment, there is a concern that defects such as cracking and cracking may occur.

  If cracks and cracks occur in the gasket and propagate to the inside of the pipe, there is a concern about leakage of fluid in the pipe. In addition, if the fluid in the pipe penetrates into the gasket along the cracks and cracks, and the insulation between the stainless steel pipe and the carbon steel pipe cannot be maintained, galvanic corrosion will occur, resulting in pipe thinning and rust generation. There is a concern that it may cause deformation of the piping. There is a concern that pressure resistance is impaired by cracks and cracks in the gasket and further progressing due to vibrations and shocks such as mechanical loads and earthquakes.

  Furthermore, when the gasket strength decreases and the thickness shrinks, tension is applied in the longitudinal direction of the pipe, which may cause deformation of the pipe and a decrease in strength. When the gasket becomes extremely brittle, there is a concern that the fine powder will progress from a portion where a slight impact and a crack have occurred and fall off. If gasket debris or piping rust is mixed in the piping, there is a concern that the flow in the piping may be hindered or the fluid may be contaminated. Moreover, there is a concern that gasket debris or piping rust may fall into the plant and cause other equipment or instruments to malfunction. There is also a concern that cracks may occur when gaskets are replaced during regular inspections and some of them may fall off.

  As a polytetrafluoroethylene (PTFE) gasket, for example, as described in Patent Document 1, it is disclosed to improve radiation resistance by improving additives and manufacturing methods. In addition, for polymer materials such as rubber and resin themselves, improvement of material composition relating to radiation resistance has already been studied.

JP 2002-36376 A

  However, gaskets used in nuclear facilities must be used for a long period of time under conditions exposed to high radiation doses, and sufficient improvements can be obtained only by improvement of polymer materials with additives and manufacturing methods. Not in. Furthermore, it has not been known what a highly reliable gasket shape is.

  From the above, the object of the present invention is to provide a gasket shape that can be used safely for a long time under a high radiation dose peculiar to nuclear facilities, thereby connecting a stainless steel pipe and a carbon steel pipe even in a high temperature environment. An object of the present invention is to provide a facility that can maintain sound insulation of a flange portion and can be transported soundly without leaking fluid inside a pipe.

  The present invention includes a plurality of means for solving the above problems. For example, a pipe gasket provided between the flanges of the pipe end faces when connecting pipes having flanges formed on the end faces. The gasket is provided at a position opposed to the cavity on the inner surface of the pipe, and has a central hole through which the fluid in the pipe passes, an abutting surface positioned around the central hole and abutting against the flange. It consists of a non-contact surface that is located around the contact surface and does not contact the flange, and a plurality of bolt holes formed in the non-contact surface, and reaches the outer edge of the gasket from the central hole via the bolt hole. Among the non-contact surfaces in the direction, there is provided means for suppressing cracks that occur on the non-contact surface located far from the central hole.

  According to the present invention, the occurrence of cracks and cracks in the gasket can be suppressed, and leakage of fluid from the flange portion can be prevented. As a result, the fluid in the pipe can be safely transported for a long time even under a high radiation dose. Furthermore, the fluid in the piping can be safely transported even in a high temperature environment.

  Specifically, since it is possible to maintain the insulation of the flange for a long period of time, galvanic corrosion that occurs by connecting stainless steel piping and carbon steel piping can be suppressed, and pipe thinning, deformation, or strength Does not cause a drop in

  If cracking and cracking of the gasket are suppressed, an event in which a part or lump of the gasket falls or scatters in the power plant during the service period can be suppressed. At the same time, during the inspection period, it is possible to suppress an event that gasket fragments are mixed into the pipe at the time of flange inspection or gasket inspection.

  Furthermore, it is possible to suppress an event in which pressure resistance is impaired due to the development of cracks and cracks due to mechanical external loads, impacts, vibrations, earthquakes, and the like.

  Moreover, it has the gasket diameter of a diameter equivalent to a flange. Thereby, the centering work becomes easy.

The figure which shows Example 1 of the planar shape of the gasket pinched | interposed into the flange. The figure showing the gasket shape which shows the modification of FIG. The figure showing the gasket shape which shows the modification of FIG. The figure showing the gasket shape which shows the modification of FIG. The figure showing the gasket shape which shows the modification of FIG. The figure showing the gasket shape which shows the modification of FIG. The figure which shows Example 2 of the planar shape of the gasket pinched | interposed into the flange. The figure which shows the relationship between the diameter of a flange and a gasket, and a crack. The figure which shows the prior art example of the planar shape of the gasket pinched | interposed into the flange.

  Hereinafter, examples of the present invention will be described in detail, but prior to that, knowledge obtained by the present inventors before reaching the present invention will be described.

  The inventors of the present invention have made an insulating gasket containing a polymer material such as rubber or resin, particularly a fluororesin polymer material such as polytetrafluoroethylene (PTFE), in a high temperature environment and a high radiation irradiation environment. Various durability tests were conducted. As a result, as a first finding, when a conventional disc-shaped gasket was applied to a flat seat flange, an event was observed in which the gasket became brittle and cracked by irradiation.

  The outline of the gasket sandwiched between the flanges and the planar shape thereof will be described with reference to FIG. In the lower part of FIG. 9, a flange 108 is attached to the end of the hollow pipe 111 by welding or the like. Here, the upper flange 108A is welded to the end of the upper pipe 111A, and the lower flange 108B is welded to the end of the lower pipe 111B. The flange surfaces of the upper and lower flanges 108 </ b> A and 108 </ b> B are opposed to each other with the gasket 101 interposed therebetween, and the bolt 109 is inserted into the bolt hole 103 provided in the periphery of the flange 108 and the gasket 101 and fastened by the nut 110.

  As shown in the plan view of the gasket in FIG. 9, the conventional gasket 101 has a disk shape, and when this is functionally divided, a central hole 107 through which the fluid in the pipe passes and a central hole 107 are formed. Formed on the non-contact surface 102 and the non-contact surface 102 of the flange positioned around the flange that contacts the upper and lower flanges, the non-contact surface 102 of the flange positioned around the contact surface 100 and not contacted with the upper and lower flanges And a bolt hole 103 formed at a position where the bolt 109 is inserted. In FIG. 9, 105 is the gasket inner periphery, 104 is the gasket outer periphery, and 106 is the gasket radius.

  As a result of various durability tests on the gasket 101 which is normally formed as described above and is used by being attached to the flange 108, a portion where a crack occurs is generated on the non-contact surface 102. Cracks occur most frequently at a point D1 having the smallest distance from the outer side of the bolt hole 103 of the non-contact surface 102 to the outer periphery 104 of the gasket, and then the inner surface of the non-contact surface 102 from the inner side of the bolt hole 103 to the contact surface. It turned out that a crack generate | occur | produces in the location D2 with the shortest distance to the outer periphery of 100. From this observation result, it is considered that a crack first occurs at the location D1, and the crack progresses to the location D2 after a further time has elapsed.

  As a means for avoiding this, it is conceivable to process a gasket having a conventional disk shape into a shape that does not cause cracking. Therefore, the inventors obtained the following second knowledge related to the configuration of the present invention as a result of carrying out the durability test on gaskets of various shapes in the same manner.

  One basic idea of the second knowledge related to the configuration of the present invention is to leave a portion where cracking is expected from the beginning as a cavity if cracking occurs after long-term use. . The idea is that no cracks will occur in the cavity.

  Another basic way of thinking of the second knowledge related to the configuration of the present invention is that if a crack occurs after a long period of use, it will take time from the beginning until the crack progresses. is there. The idea is that if the outer peripheral portion of the non-contact surface 102 is made larger (longer), the time until the crack reaches and reaches the outer peripheral portion can be increased.

  In short, the present invention is based on the first knowledge, “pipe gasket provided between the flanges of the pipe end faces when pipes having flanges formed on the end faces are connected, and the gasket is a cavity on the pipe inner face. A central hole through which the fluid in the pipe passes, a contact surface that is positioned around the central hole and that contacts the flange, and a flange that is positioned around the contact surface and contacts the flange. It is composed of a non-contact surface that does not contact and a plurality of bolt holes formed in the non-contact surface, and the center of the non-contact surface in the direction from the central hole to the outer edge of the gasket via the bolt hole Is provided with a means for suppressing cracks occurring in the non-contact surface located far from the hole portion.

  Further, as specific implementation examples, some means based on the second knowledge are proposed as Example 1 and Example 2.

  Example 1 is based on the idea that no cracks will occur in the cavity, and the part where cracks are expected from the beginning is made hollow. The outline of the gasket sandwiched between the flanges and the planar shape of the gasket of the present invention will be described with reference to FIG.

  In the lower drawing of FIG. 1, a flange 108 is attached to the end of the hollow pipe 111 by welding or the like. Here, the upper flange 108A is welded to the end of the upper pipe 111A, and the lower flange 108B is welded to the end of the lower pipe 111B. The flange surfaces of the upper and lower flanges 108 </ b> A and 108 </ b> B are opposed to each other with the gasket 101 interposed therebetween, and the bolt 109 is inserted into the bolt hole 103 provided in the periphery of the flange 108 and the gasket 101 and fastened by the nut 110. This mounting structure is the same as the conventional example of FIG.

  On the other hand, in the gasket structure in FIG. 1, the bolt hole diameter is 0.5 mm or more at the point D1 where the crack is most generated, that is, the point where the distance from the outer side of the bolt hole 103 to the outer periphery 104 of the gasket 101 is the smallest. The following notch 112 is processed. Thereby, cracking of the gasket 101 can be suppressed, and furthermore, the centering operation can be facilitated by passing the bolt 109 through the bolt hole 103 and matching the gasket outer diameter with the flange outer diameter. In the cutout structure of FIG. 1, this is a space where a crack should originally occur in this portion, and since there is no structure itself that causes a crack, there should be no crack.

  In order to confirm and verify the state of cracking of the entire gasket when the structure shown in FIG. 1 is used, a gasket 101 having the shape shown in FIG. 1 is sandwiched between flanges 108, and a radiation irradiation test and an accelerated test using heat are performed. Details of the test conditions are shown below.

[Radiation irradiation test]
In the irradiation test, γ rays emitted from a Co60 radiation source were irradiated under the condition of 3 kGy. The dose rate is 100 Gy / h.

[Accelerated test by heat]
An acceleration test was performed in a forced air circulation type thermostatic chamber by a method according to JIS standard K7212. The heat deterioration temperature was 190 ° C., and heating was performed for 105 hours. This condition is the same as that when the gasket 108 is used at 60 ° C. for 5 years from the activation energy obtained by the Arrhenius plot of the durability time when the gasket 108 is deteriorated at various heating temperatures.

[Pressure resistance test]
In accordance with the nuclear power equipment standard maintenance standard for power generation (leak test of IA-3000 series), it was kept at room temperature and withstand pressure test pressure of 1.3 MPa for 10 minutes or more, and the presence or absence of leakage was confirmed. As a confirmation method, the waste was brought into contact with the flange surface, and leakage was visually confirmed.

[Energization test]
In order to evaluate the insulation of the gasket, the surface resistivity was measured. In the measurement, the applied voltage was 500 V, the measurement time was 1 minute, and the gasket surface was measured at two locations (front and back). The evaluation criteria were compared with an untreated resistance value that was not subjected to an accelerated test by irradiation and heat, and the presence or absence of electrical conductivity was evaluated with the same or higher.

  A gasket 101 having the shape shown in FIG. 1 was sandwiched between the flanges 108 under the above conditions, and a radiation irradiation test and a thermal acceleration test were performed. As a result, it was confirmed that the gasket having the shape shown in FIG. 1 passed the pressure resistance test and the energization test, and there was no problem. In addition, cracks and cracks occurred in the conventional gasket shape, but in the shape of FIG. Furthermore, it was confirmed that the centering operation for aligning the center of the piping and the center of the gasket was easy.

  In addition, about the shape of the notch 112, the some shape described below is employable. FIG. 2 to FIG. 6 show a gasket shape showing a modification of FIG.

  In the gasket 101 having the notch shape shown in FIG. 2, the portion where the crack is most generated, that is, the portion where the distance from the outer side of the bolt hole 103 to the outer periphery 104 of the gasket is the smallest is the interval of the diameter of the bolt hole 103. It is largely removed, and the corners on the outer peripheral side that have been removed are rounded. It looks like a fan feather. Thereby, unnecessary corners can be removed, and dropout that occurs when an external force or impact is applied to the apex of the corners can be suppressed. Moreover, the centering operation | work which aligns the center of piping and the center of a gasket can be performed easily.

  In the gasket 101 having the notch shape shown in FIG. 3, while maintaining the characteristics of FIG. 2, the gasket 101 is perpendicular to the straight line connecting the gasket center and the bolt hole 103, and between the tangents on the outer periphery of the contact surface 100. The gasket portion of one or more non-contact surfaces 102 including the bolt hole 103 in parallel with the tangent line was removed, and the remaining gasket outer peripheral portion was rounded. That is, the structure is shown in which the portion 102X of the non-contact surface 102 shown by the dotted line in FIG. Accordingly, centering work is facilitated by the outer periphery of at least two gaskets, and cracking can be suppressed by removing the gasket part where cracking occurs.

  As in Example 1, gaskets having the shapes shown in FIGS. 2 and 3 were sandwiched between flanges, and a radiation irradiation test and an accelerated test using heat were performed. As a result, the gaskets having the shapes shown in FIGS. 2 and 3 passed the pressure resistance test and the energization test, and it was confirmed that there was no problem. Further, cracks and cracks were generated in the conventional gasket shape, but in the shapes of FIGS. 2 and 3, neither cracks nor cracks were generated, and it was confirmed that the gaskets were sound. Furthermore, it was confirmed that the centering operation for aligning the center of the piping and the center of the gasket was easy.

  In the gasket 101 having the notch shape shown in FIGS. 4, 5, and 6, at least two non-contact surfaces 102 between adjacent bolt holes 103 are left, and other non-contact surfaces 102 are formed. It was removed along the contact surface 100 and the corners on the outer peripheral side of the remaining gasket were rounded. Accordingly, centering work is facilitated by the outer periphery of at least two gaskets, and cracking can be suppressed by removing the gasket part where cracking occurs.

  The cutout shape shown in FIGS. 4, 5, and 6 has at least one pair of non-contact surfaces that face the center of the gasket. Accordingly, centering work is facilitated by the outer periphery of at least two gaskets, and cracking can be suppressed by removing the gasket part where cracking occurs.

  Similar to FIGS. 1, 2, and 3, gaskets having the shapes shown in FIGS. 4, 5, and 6 were sandwiched between flanges, and a radiation irradiation test and a thermal acceleration test were performed. As a result, it was confirmed that the gaskets having the shapes shown in FIGS. 4, 5, and 6 passed the pressure resistance test and the energization test and there was no problem. Further, cracks and cracks were generated in the conventional gasket shape, but in the shapes of FIGS. 4, 5, and 6, no cracks or cracks were generated, and it was confirmed that the gaskets were sound. Furthermore, it was confirmed that the centering operation for aligning the center of the piping and the center of the gasket was easy.

  In Example 2, if a crack occurs after a long period of use, an attempt is made to earn time from the beginning until the crack progresses. Here, the outer peripheral portion of the non-contact surface 102 is made larger (longer), and the time until the crack progresses and reaches the outer peripheral portion is lengthened. Specifically, the gasket 101 has a diameter r2 larger than the diameter r1 of the flange 108 as shown in FIG.

  FIG. 8 shows the relationship between the distance (mm) from the outside of the bolt hole 103 to the outside of the gasket and the value (%) obtained by dividing the distance from the outside of the bolt hole 103 to the outside of the gasket by the radius of the gasket. The table below summarizes the occurrence of cracks and cracks at each time. According to this test result, for example, it is desirable that the location where cracking occurs most, that is, the distance from the outside of the bolt hole to the outer periphery of the gasket be in the range of 20% to 62% of the radius of the gasket. If it is less than 20%, it is not preferable because cracks are easily generated in the above-mentioned places. On the other hand, if it is larger than 62%, the gasket protruding from the flange is not preferred because a tensile stress is applied downward by its own weight and a crack occurs along the outer periphery of the flange.

  As a result of the test under the above conditions, it was confirmed that the gasket 108 in the shape of FIG. 7 passed the pressure test and the current test, and there was no problem. In addition, cracks and cracks occurred in the conventional gasket shape, but in the shape of FIG. Furthermore, it was confirmed that the centering operation for aligning the center of the piping and the center of the gasket was easy.

  In the above-described embodiment of the present invention, as an example, a gasket having four bolt holes in JIS10K as shown in FIG. 1 is described. However, the present invention is applied to all JIS and ANSI standard flanges. It can be applied to insulating gaskets for compliant flanges.

100: flange contact surface 101: gasket 102: flange non-contact surface 103: bolt hole 104: gasket outer periphery 105: gasket inner periphery 106: gasket radius 107: gasket central hole 108: flange 109: bolt 110 : Nut 111: Piping 112: Notch

Claims (9)

A piping gasket provided between the flanges of the pipe end faces when connecting pipes having flanges formed on the end faces,
The gasket is provided at a position opposed to the hollow portion on the inner surface of the pipe, and has a central hole portion through which the fluid in the pipe passes, an abutting surface located around the central hole portion and in contact with the flange, and A non-contact surface that is located around the contact surface and does not contact the flange, and a plurality of bolt holes formed in the non-contact surface,
Of the non-contact surfaces in the direction from the central hole portion to the outer edge of the gasket via the bolt holes, cracks generated on the non-contact surface located far from the central hole portion are suppressed. A piping gasket characterized by comprising means. The piping gasket according to claim 1,
The means for suppressing the crack is a notch provided in the non-contact surface located far from the central hole portion of the non-contact surface in a direction reaching the outer edge of the gasket via the bolt hole. Piping gasket characterized by being a part. The piping gasket according to claim 1,
The gasket for piping according to claim 1, wherein the means for suppressing the crack is formed such that an outer edge of the non-contact surface exceeds the diameter of the flange. The piping gasket according to claim 2,
By applying a notch process of 0.5 mm or more and a bolt hole diameter or less in advance to at least one place where the distance from the outer periphery of the bolt hole to the outer edge of the gasket is the smallest, due to thermal expansion A gasket for piping characterized by the effect of preventing the growth of cracks. A piping gasket according to claim 3, wherein
A piping gasket characterized in that the distance from the outside of the bolt hole to the outer edge of the gasket is in the range of 20% to 62% of the radius of the gasket. The piping gasket according to claim 2,
At least one place is removed at an interval of the diameter of the bolt hole in parallel with a notch provided in the gasket outer peripheral direction from the bolt hole center, and the remaining corners on the outer peripheral side of the gasket are rounded. Gasket for piping. The piping gasket according to claim 2,
Removing one or more non-contact surface gasket parts including bolt holes in a direction perpendicular to the straight line connecting the gasket center and the bolt hole and parallel to the contact surface outer circumference; and A gasket for piping, wherein the outer periphery of the remaining gasket is rounded. The piping gasket according to claim 2,
It is characterized in that at least two non-contact surfaces between adjacent bolt holes are left, other non-contact surfaces are removed along the contact surface, and the remaining corners on the outer peripheral side of the gasket are rounded. Piping gasket. The piping gasket according to claim 2,
A gasket for piping characterized by at least one pair of non-contact surfaces facing the center of the gasket.

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