Pipe joint

Abstract

A pipe joint according to the present disclosure comprises: a cylindrical inner member with its inner peripheral surface serving as a contact surface that comes into contact with a transferred fluid; a cylindrical joint member that is fitted to the outer periphery of the inner member and has a male screw part on the outer periphery thereof; and a union nut that has, on the inner periphery thereof, a female screw part fastened to the male screw part, the inner member being connected to a fluid device having a first thin-walled part in contact with the transferred fluid. The inner member comprises an insulating annular second thin-walled part having a thickness that extends radially outward from the contact surface and is smaller than that of the first thin-walled part, the joint member being provided with a conductive part that comes into contact with the outer peripheral surface of the second thin-walled part.

Description

Pipe fittings

[0001] The present invention relates to a pipe joint.

[0002] A pipe fitting described in Patent Document 1 is known as a connection structure for connecting flow paths formed in fluid devices such as tubes and diaphragm pumps in manufacturing equipment in various technical fields, such as semiconductor manufacturing and medical / pharmaceutical manufacturing. The pipe fitting in Patent Document 1 includes an inner ring attached to the inner periphery of one end of the tube, a fitting body attached to the outer periphery of the one end of the tube, and a union nut attached to the outer periphery of the fitting body.

[0003] Japanese Patent Application Laid-Open No. 2018-168947

[0004] When an electrically charged transport fluid flows through a fluidic device connected by the pipe joint, the charge can cause dielectric breakdown such as pinholes in thin-walled portions of the fluidic device (such as the peripheral wall of a tube or the diaphragm membrane of a diaphragm pump). When such dielectric breakdown occurs, the entire fluidic device must be replaced, which poses a problem of taking a long time to complete.

[0005] The present disclosure aims to prevent dielectric breakdown from occurring in thin-walled portions of a fluid device connected to a pipe joint even when an electrically charged transfer fluid flows through the fluid device.

[0006] (1) The pipe fitting of the present disclosure comprises a cylindrical inner member whose inner peripheral surface is a contact surface that comes into contact with the transported fluid, a cylindrical coupling member that is fitted onto the outer periphery of the inner member and has a male threaded portion on its outer periphery, and a union nut that has a female threaded portion on its inner periphery and is tightened onto the male threaded portion, and the inner member is connected to a fluid device that has a first thin-walled portion that comes into contact with the transported fluid, and the inner member comprises an insulating annular second thin-walled portion that has a thickness extending radially outward from the contact surface and that is smaller than the thickness of the first thin-walled portion, and a conductive portion that is provided on the coupling member and comes into contact with the outer periphery of the second thin-walled portion.

[0007] According to the pipe fitting of the present disclosure, when an electrically charged transfer fluid flows through the inner member, the charge on the transfer fluid passes radially through the second thin-walled portion and is discharged to the conductive portion, making it more likely that a breakdown will occur in the second thin-walled portion. Furthermore, because the thickness of the second thin-walled portion is smaller than the thickness of the first thin-walled portion, a breakdown is more likely to occur in the second thin-walled portion of the inner member before a breakdown occurs in the first thin-walled portion due to the electrically charged transfer fluid flowing through the fluidic device. This makes it possible to prevent a breakdown from occurring in the first thin-walled portion of the fluidic device.

[0008] (2) In the pipe fitting of (1), the conductive portion preferably has an annular protrusion tapered radially inward, and the outer peripheral surface of the second thin-walled portion is recessed radially inward along the tapered shape of the annular protrusion. In this case, the radial thickness of the second thin-walled portion is locally smallest at a location corresponding to the protruding end of the annular protrusion, i.e., at a location where the outer peripheral surface of the second thin-walled portion is recessed most radially inward. This makes it easier for dielectric breakdown to occur at the location of the second thin-walled portion. As a result, dielectric breakdown can be further suppressed in the first thin-walled portion of the fluidic device.

[0009] (3) In the pipe fitting of (1) or (2), it is preferable that one of the conductive portion and the inner member has an engaging groove recessed in the axial direction, and the other of the conductive portion and the inner member has an engaging portion that engages with the engaging groove. In this case, the engaging portion engages with the engaging groove, thereby holding the conductive portion in contact with the outer peripheral surface of the second thin-walled portion.

[0010] (4) It is preferable that any of the pipe fittings described in (1) to (3) further includes a detection device that detects the occurrence of dielectric breakdown in the second thin-walled portion. In this case, the pipe fitting manager can quickly determine that dielectric breakdown has occurred in the second thin-walled portion of the inner member using the detection device, allowing the inner member to be replaced promptly. As a result, leakage of the transferred fluid from the location where dielectric breakdown has occurred in the second thin-walled portion can be reduced. In addition, since replacement of the fluid device is no longer necessary, the time required for the replacement work can be shortened accordingly.

[0011] (5) In the pipe fitting of (4), the detection device preferably includes a measuring instrument that measures the charge of the conductive portion. In this case, the detection device can directly detect that a breakdown has occurred in the second thin-walled portion based on the charge of the conductive portion measured by the measuring instrument. This allows a pipe fitting manager to accurately and quickly determine that a breakdown has occurred in the second thin-walled portion.

[0012] According to the present disclosure, even if an electrically charged transfer fluid flows into a fluid device connected to a pipe joint, it is possible to prevent dielectric breakdown from occurring in a thin-walled portion of the fluid device.

[0013] Fig. 1 is a cross-sectional view showing a pipe fitting according to a first embodiment. Fig. 2 is an enlarged cross-sectional view showing a main portion of the pipe fitting. Fig. 3 is an enlarged cross-sectional view showing a main portion of a pipe fitting according to a second embodiment. Fig. 4 is a cross-sectional view showing a pipe fitting according to a third embodiment. Fig. 5 is a cross-sectional view showing a pipe fitting according to a fourth embodiment.

[0014] Next, preferred embodiments of the present disclosure will be described with reference to the accompanying drawings. [First Embodiment] <Overall Configuration of Pipe Fitting> Fig. 1 is a cross-sectional view showing a pipe fitting 1 according to a first embodiment. The pipe fitting 1 is used, for example, in a piping path through which a chemical liquid used in semiconductor manufacturing equipment flows as a transfer fluid, to connect the flow paths of two fluid devices. In this embodiment, each of the two fluid devices is, for example, a tube 50 made of synthetic resin.

[0015] The tube 50 has a thin-walled portion (first thin-walled portion) 51 formed in a circular cross section. The thin-walled portion 51 in this embodiment is formed over the entire longitudinal length of the tube 50. A flow path 52 through which a transfer fluid flows is formed radially inward of the thin-walled portion 51 of the tube 50. The inner circumferential surface of the thin-walled portion 51 serves as a contact surface 53 that comes into contact with the transfer fluid. The pipe fitting 1 of this embodiment is used to connect the flow paths 52 of both tubes 50 to each other.

[0016] The pipe joint 1 includes a joint member 2, a pair of union nuts 3, and an inner member 4. Hereinafter, in this embodiment, the direction from the axial center of the pipe joint 1 toward both axial sides is referred to as the axial outer side, and the direction from both axial sides of the pipe joint 1 toward the axial center is referred to as the axial inner side.

[0017] The inner member 4 has a first ring 5 and a pair of second rings 6. The first ring 5 is disposed in the axial center of the pipe joint 1. The second rings 6 are disposed on both axially outer sides of the first ring 5. Both the first ring 5 and the second ring 6 are formed in a cylindrical shape. The inner diameter of the first ring 5 and the inner diameter of the second ring 6 are the same.

[0018] The first ring 5 is made of an insulating synthetic resin material. Examples of insulating synthetic resin materials include polyvinyl chloride (PVC), polypropylene (PP), polyethylene (PE), and fluororesin (perfluoroalkoxyalkane (PFA), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.). The first ring 5 of this embodiment is made of fluororesin because purity is required for the transfer fluid (chemical liquid) used in semiconductor manufacturing equipment. The second ring 6 is made of the same synthetic resin material as the first ring 5, for example.

[0019] The internal space of the first ring 5 is a flow path 5a through which the transfer fluid flows. The inner circumferential surface of the first ring 5 is a contact surface 5b that comes into contact with the transfer fluid. Similarly, the internal space of the second ring 6 is a flow path 6a through which the transfer fluid flows. The inner circumferential surface of the second ring 6 is a contact surface 6b that comes into contact with the transfer fluid. The flow path 5a of the first ring 5 and the flow paths 6a of the pair of second rings 6 are connected to each other.

[0020] A primary seal groove 5c is formed on the radially inner side of each of the two axially outer end portions of the first ring 5. The primary seal groove 5c is a tapered groove that is cut out so that its diameter gradually increases from the contact surface 6b, which is the axially inner end, toward the axially outer end. A secondary seal groove 5d is formed on the radially outer side of each of the two axially outer end portions of the first ring 5. The secondary seal groove 5d is a stepped groove formed on the outer periphery of each of the two axially outer end portions of the first ring 5.

[0021] The second ring 6 has a bulge portion 7 and a seal portion 8. The bulge portion 7 is formed on the axially outer side of the second ring 6, protruding radially outward in a mountain-like shape. The bulge portion 7 is press-fitted into one end of the tube 50, expanding the diameter of the end. This connects the second ring 6 to the one end of the tube 50. The seal portion 8 is formed on the axially inner side of the second ring 6. The seal portion 8 has a primary seal portion 8a and a secondary seal portion 8b.

[0022] The primary seal portion 8a is formed in an annular shape on the radially inner side of the seal portion 8. The outer peripheral surface of the primary seal portion 8a gradually expands in diameter from the axially inner end to the axially outer end. The primary seal portion 8a is press-fitted into the primary seal groove 5c of the first ring 5. The secondary seal portion 8b is formed in a cylindrical shape on the radially outer side of the primary seal portion 8a. The secondary seal portion 8b is press-fitted into the secondary seal groove 5d of the first ring 5.

[0023] The joint member 2 is formed into a cylindrical shape from a conductive material. Examples of conductive materials include metal and conductive resin. The joint member 2 of this embodiment is made of a carbon resin blended with a filler that is conductive and chemical-resistant. From the perspective of reducing the environmental impact, it is preferable to use a recyclable conductive resin (such as a fluororesin) for the joint member 2. From the perspective of reducing weight, it is preferable to use a conductive resin with a low specific gravity (such as polypropylene or polyethylene) for the joint member 2.

[0024] The coupling part 2 has a circular inner peripheral surface and is fitted onto the outer peripheral surface of the inner part 4 (first ring 5 and second ring 6). The coupling part 2 has a coupling body 21 and a pair of sockets 22. The coupling body 21 is formed in the axial center of the coupling part 2. The sockets 22 are formed on both axial outer sides of the coupling part 2.

[0025] The second ring 6, with the bulge 7 press-fitted onto one end of the tube 50, is fitted onto the inner periphery of the socket 22 of the coupling part 2. As a result, one end of the tube 50 is clamped between the bulge 7 of the second ring 6 and the socket 22 of the coupling part 2. A male thread 23 is formed on the outer periphery of each socket 22.

[0026] The union nut 3 is cylindrical and made of a synthetic resin material such as PVC, PP, PE, or a fluororesin (such as PFA or PTFE). The union nut 3 has a pressing portion 31 and a female thread portion 32. The pressing portion 31 is formed on the axially outer side of the union nut 3, protruding radially inward. The female thread portion 32 is formed on the inner periphery of the axially inner side of the union nut 3. The female thread portion 32 is screwed into the male thread portion 23 of the coupling member 2. As a result of this screwing, the axially inner end of the pressing portion 31 presses against the outer peripheral surface of the tube 50, which is bulging radially outward due to the bulging portion 7.

[0027] With the above configuration, when the female thread portion 32 of the union nut 3 is tightened onto the male thread portion 23 of the coupling member 2, the primary seal portion 8a and secondary seal portion 8b of the second ring 6 are press-fitted into the primary seal groove 5c and secondary seal groove 5d of the first ring 5, respectively. This ensures sealing performance at the connection between the first ring 5 and the second ring 6, as well as sealing performance between the outer circumferential surface of the second ring 6 and the inner circumferential surface of the coupling member 2. In addition, the pressing portion 31 of the union nut 3 prevents one end of the tube 50 from slipping out of the pipe coupling 1.

[0028] Regarding the shape of the joint member 2, it is sufficient that the socket portion 22 in which the male thread portion 23 is formed is formed cylindrically, and the joint body portion 21 may be formed cylindrically or polygonal tubularly.

[0029] <Discharge Structure> Figure 2 is an enlarged cross-sectional view showing a main part of the pipe fitting 1. The pipe fitting 1 is equipped with a discharge structure 10 that induces discharge of the electric charge on the transferred fluid when the transferred fluid is electrically charged. The discharge structure 10 is composed of a thin portion (second thin portion) 12 and a conductive portion 13. Details of the discharge structure 10 will be described below.

[0030] The first ring 5 has a fitting recess 11 and the thin-walled portion 12. The fitting recess 11 is formed in the axial center of the first ring 5 and opens on the outer circumferential surface of the axial center. The fitting recess 11 is formed in an annular shape around the entire circumference of the first ring 5.

[0031] The thin-walled portion 12 is formed in the axial center of the first ring 5, between the bottom surface 11a of the fitting recess 11 and the contact surface 5b of the first ring 5. The thin-walled portion 12 is formed in an annular shape over the entire circumference of the first ring 5. Hereinafter, the bottom surface 11a and the contact surface 5b will also be referred to as the outer peripheral surface 11a and the inner peripheral surface 5b of the thin-walled portion 12, respectively.

[0032] The thin-walled portion 12 is insulating as described above because it is part of the first ring 5. The thin-walled portion 12 has a thickness t2 extending radially outward from the inner circumferential surface 5b of the first ring 5. The thickness t2 of the thin-walled portion 12 is smaller than the radial thickness t1 (see FIG. 1 ) of the thin-walled portion 51 of the tube 50.

[0033] The joint member 2 is provided with the conductive portion 13. In this embodiment, the conductive portion 13 is provided integrally with the joint body 21. Specifically, the conductive portion 13 protrudes radially inward from the inner circumferential surface of the axial center of the joint body 21. The conductive portion 13 is formed in an annular shape around the entire circumference of the joint body 21 and is fitted into the fitting recess 11 of the first ring 5. The inner circumferential surface 13a of the conductive portion 13 is in surface contact with the outer circumferential surface 11a of the thin-walled portion 12. The conductive portion 13 is made of the same material as the joint member 2 and is conductive. The conductive portion 13 may be provided separately from the joint body 21.

[0034] The conductive part 13 has a pair of engagement grooves 13b. The engagement grooves 13b are recessed axially inward on both axial side surfaces of the conductive part 13. Each engagement groove 13b is formed in an annular shape around the entire circumference of the joint body 21.

[0035] The first ring 5 has a pair of engaging portions 5e. The engaging portions 5e protrude axially inward from both axial side surfaces of the fitting recess 11. Each engaging portion 5e is formed in an annular shape around the entire circumference of the joint body 21 and engages with a corresponding engaging groove 13b of the conductive portion 13. This keeps the conductive portion 13 fitted in the fitting recess 11.

[0036] With the above configuration, when the transfer fluid is electrically charged, the charge on the transfer fluid passes through the thin-walled portion 12 in the radial direction and is easily discharged to the conductive portion 13 when passing through the flow path 5a of the first ring 5. When the charge is discharged to the conductive portion 13, insulation breakdown such as pinholes is easily generated in the thin-walled portion 12.

[0037] 1, the pipe fitting 1 further includes a detection device 15 that detects the occurrence of dielectric breakdown in the thin-walled portion 12 of the inner member 4. The detection device 15 of this embodiment includes a measuring device 15a and a lead wire 15b. The measuring device 15a measures the charge discharged from the transport fluid to the conductive portion 13. For example, an oscilloscope or a resistance meter may be used as the measuring device 15a.

[0038] One end of the lead wire 15b is electrically connected to the measuring instrument 15a. The other end of the lead wire 15b is embedded in the joint body 21 and electrically connected to the joint body 21. The measuring instrument 15a detects the charge of the conductive portion 13 via the lead wire 15b and the joint body 21. The detection device 15 detects the occurrence of dielectric breakdown in the thin-walled portion 12 based on the charge measured by the measuring instrument 15a. Therefore, the detection device 15 of this embodiment measures the charge of the conductive portion 13, which is directly related to the dielectric breakdown of the thin-walled portion 12, and can therefore directly detect the occurrence of dielectric breakdown in the thin-walled portion 12.

[0039] When the detector 15 detects a breakdown in the thin-walled portion 12, a notification means (not shown) notifies the manager of the pipe fitting 1 that a breakdown has occurred in the thin-walled portion 12. The manager who receives this notification disassembles the pipe fitting 1 and replaces at least the first ring 5 having the thin-walled portion 12 where the breakdown has occurred with a new one.

[0040] The detection device 15 is not limited to the present embodiment, and may indirectly detect the occurrence of dielectric breakdown in the thin-walled portion 12 of the inner member 4. For example, the detection device 15 may have a pressure sensor, a flow rate sensor, or a weight sensor. These sensors measure changes in the pressure, flow rate, or weight of the transfer fluid flowing through the flow paths 5a, 6a of the inner member 4 when the transfer fluid leaks from the location where dielectric breakdown has occurred in the thin-walled portion 12. Therefore, the detection device 15 can indirectly detect the occurrence of dielectric breakdown in the thin-walled portion 12 by measuring the change in state of the transfer fluid associated with the dielectric breakdown of the thin-walled portion 12.

[0041] Furthermore, the detection device 15 may have a leakage sensor or a capacitance sensor that detects leakage of the transfer fluid from the location where dielectric breakdown has occurred in the thin-walled portion 12. In this case, the detection device 15 can also indirectly detect that dielectric breakdown has occurred in the thin-walled portion 12 by detecting leakage of the transfer fluid associated with dielectric breakdown in the thin-walled portion 12.

[0042] <Operation and Effect> According to the pipe fitting 1 of the first embodiment, when charged transfer fluid flows through the flow paths 5a, 6a of the inner member 4, the electric charge on the transfer fluid passes radially through the thin-walled portion 12 of the first ring 5 and is discharged to the conductive portion 13, making it easier for dielectric breakdown to occur in the thin-walled portion 12. Moreover, the thickness t2 of the thin-walled portion 12 of the first ring 5 is smaller than the thickness t1 of the thin-walled portion 51 of the tube 50. Therefore, dielectric breakdown is easier to occur in the thin-walled portion 12 of the first ring 5 before dielectric breakdown occurs in the thin-walled portion 51 due to the charged transfer fluid flowing through the flow path 52 of the tube 50. This makes it possible to suppress dielectric breakdown in the thin-walled portion 51 of the tube 50.

[0043] The engaging grooves 13b of the conductive portion 13 engage with the engaging portions 5e of the first ring 5, so that the conductive portion 13 is held in a fitted state in the fitting recess 11. As a result, the conductive portion 13 can be held in contact with the outer peripheral surface 11a of the thin portion 12 of the first ring 5.

[0044] The detector 15 detects that a breakdown has occurred in the thin-walled portion 12 of the inner member 4. This allows the manager of the pipe fitting 1 to quickly recognize that a breakdown has occurred in the thin-walled portion 12, allowing the inner member 4 to be replaced promptly. As a result, it is possible to reduce leakage of the transported fluid from the location where a breakdown has occurred in the thin-walled portion 12. In addition, since there is no need to replace the tube 50, which is a fluid device, the time required for the replacement work can be shortened accordingly.

[0045] The detection device 15 directly detects that a dielectric breakdown has occurred in the thin-walled portion 12 based on the charge of the conductive portion 13 measured by the measuring device 15a. This allows the manager of the pipe fitting 1 to accurately and quickly grasp that a dielectric breakdown has occurred in the thin-walled portion 12.

[0046] Second Embodiment Figure 3 is an enlarged cross-sectional view showing the main parts of a pipe fitting 1 according to a second embodiment. In this embodiment, the shapes of the thin-walled portion 12 and the conductive portion 13 of the discharge structure 10 differ from those of the first embodiment. The conductive portion 13 of this embodiment has an annular protrusion 13c that tapers radially inward from the inner circumferential surface 13a. The annular protrusion 13c of this embodiment is formed in a mountain-like cross section at the axial center of the inner circumferential surface 13a. The annular protrusion 13c is formed in an annular shape around the entire circumference of the conductive portion 13.

[0047] The outer peripheral surface 11 a of the thin-walled portion 12 is recessed radially inward along the tapered shape of the annular protrusion 13 c. In this embodiment, the outer peripheral surface 11 a of the thin-walled portion 12 is recessed in a V-shaped cross section over the entire circumference at the axial center. This allows the annular protrusion 13 c of the conductive portion 13 to be in surface contact with the outer peripheral surface 11 a of the thin-walled portion 12.

[0048] The thickness t2 of the thin-walled portion 12 is locally smallest at a location corresponding to the protruding end of the annular protrusion 13c, i.e., at a location 12a where the outer peripheral surface 11a of the thin-walled portion 12 is recessed most radially inward. Since the other configurations of this embodiment are the same as those of the first embodiment, the same reference numerals are used and their description will be omitted.

[0049] The pipe fitting 1 of this embodiment also achieves the same effects as the first embodiment. Furthermore, in this embodiment, the thickness t2 of the thin-walled portion 12 is locally smallest at the location 12a where the outer circumferential surface 11a of the thin-walled portion 12 is recessed most radially inward. This makes it easier for dielectric breakdown to occur at the location 12a of the thin-walled portion 12. As a result, dielectric breakdown in the thin-walled portion 51 of the tube 50 can be further suppressed.

[0050] [Third embodiment] Figure 4 is a cross-sectional view showing a pipe fitting 1 according to a third embodiment. In this embodiment, the connection structure between the first ring 5 and the second ring 6 of the inner member 4 differs from that of the first embodiment. In this embodiment, a primary seal groove 5f is formed over the entire radial length of each of the two axially outer end portions of the first ring 5. The primary seal groove 5f is a tapered groove that is cut out so that its diameter gradually decreases from its axially inner end toward the contact surface 6b, which is its axially outer end.

[0051] The seal portion 8 of the second ring 6 consists only of a primary seal portion 8c. The primary seal portion 8c is formed in an annular shape on the axially inner side of the seal portion 8. The inner circumferential surface of the primary seal portion 8c gradually reduces in diameter from the axially inner end to the axially outer end. The primary seal portion 8c is press-fitted into the primary seal groove 5f of the first ring 5. This ensures sealing performance at the connection between the first ring 5 and the second ring 6.

[0052] The other configurations of this embodiment are the same as those of the first embodiment, so the same reference numerals are used and the description thereof will be omitted. The pipe fitting 1 of this embodiment also achieves the same effects as those of the first embodiment.

[0053] [Fourth embodiment] Figure 5 is a cross-sectional view showing a pipe fitting 1 according to a fourth embodiment. In this embodiment, the configuration of the inner member 4 differs from that of the first embodiment. The inner member 4 of this embodiment is composed of only a first ring 5. The first ring 5 of this embodiment is formed longer axially outward than in the first embodiment. Both outer axial ends of the first ring 5 are press-fitted into one end of the tube 50, respectively, to expand the diameter of that end. In this way, the first ring 5 is connected to one end of the tube 50.

[0054] The other configurations of this embodiment are the same as those of the first embodiment, so the same reference numerals are used and the description thereof will be omitted. The pipe fitting 1 of this embodiment also achieves the same effects as those of the first embodiment.

[0055] [Others] The above-disclosed embodiments are illustrative in all respects and are not limiting. For example, in the above-described embodiments, the fluid device to which the inner member 4 is connected is not limited to the tube 50 as long as it has a thin-walled portion that contacts the transport fluid. For example, the fluid device may be a diaphragm pump having a thin-walled diaphragm membrane. In this case, the inner member 4 is connected to a tubular inlet or outlet pipe of the diaphragm pump. Furthermore, since dielectric breakdown occurs in the thin-walled portion 12 of the pipe fitting 1 before dielectric breakdown occurs in the diaphragm membrane, there is no need to replace the expensive diaphragm pump. Therefore, the replacement work can be performed in a short time and at low cost.

[0056] In the first to third embodiments described above, the thin-walled portion 12 of the discharge structure 10 is formed on the first ring 5, but it may also be formed on the second ring 6. In each of the above embodiments, the inner member 4 is provided with the engaging portion 5e and the conductive portion 13 is provided with the engaging groove 13b, but it is also possible for the conductive portion 13 to be provided with an engaging portion and the inner member 4 to be provided with an engaging groove. The pipe fitting 1 of the present disclosure can be applied not only to semiconductor manufacturing equipment, but also to the liquid crystal / organic EL field, the medical / pharmaceutical field, and the automotive-related field, etc.

[0057] REFERENCE SIGNS LIST 1 Pipe joint 2 Joint member 3 Union nut 4 Inner member 5b Contact surface 5e Engagement portion 11a Outer circumferential surface 12 Thin-walled portion (second thin-walled portion) 13 Conductive portion 13b Engagement groove 13c Annular protrusion 15 Detector 15a Measuring instrument 23 Male threaded portion 32 Female threaded portion 50 Tube (fluid device) 51 Thin-walled portion (first thin-walled portion) t1 Thickness of first thin-walled portion t2 Thickness of second thin-walled portion

Claims

1. A pipe fitting comprising: a cylindrical inner member whose inner surface is a contact surface that comes into contact with a transported fluid; a cylindrical coupling member that is fitted onto the outer periphery of the inner member and has a male threaded portion on its outer periphery; and a union nut that has a female threaded portion on its inner periphery and is screwed into the male threaded portion, wherein the inner member is connected to a fluid device having a first thin-walled portion that comes into contact with the transported fluid, wherein the inner member has an insulating annular second thin-walled portion that has a thickness extending radially outward from the contact surface and that is smaller than the thickness of the first thin-walled portion, and the pipe fitting comprises a conductive portion that is provided on the coupling member and comes into contact with the outer periphery of the second thin-walled portion.

2. A pipe fitting as set forth in claim 1, wherein the conductive portion has an annular protrusion tapered radially inward, and the outer circumferential surface of the second thin-walled portion is recessed radially inward along the tapered shape of the annular protrusion.

3. A pipe fitting as described in claim 1 or claim 2, wherein one of the conductive portion and the inner member has an engagement groove recessed in the axial direction, and the other of the conductive portion and the inner member has an engagement portion that engages with the engagement groove.

4. A pipe fitting as described in claim 1 or claim 2, further comprising a detection device for detecting the occurrence of dielectric breakdown in the second thin-walled portion.

5. The pipe joint according to claim 4, wherein the detection device has a measuring instrument for measuring the charge of the conductive portion.

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