Retaining structure for pipe joint

Abstract

To provide a retaining structure of an insertion-type pipe joint in which an outer pipe body and an inner pipe body are connected in a retained state by a stop ring, such that the stop ring is reliably and easily brought into a locked state or unlocked state without using any special locking member or tool.SOLUTION: A stop ring (3) is made of an elastic wire material, and includes: a C-shaped ring portion (30) that connects an outer pipe body (1) and an inner pipe body (2) in a retained state; a pair of projecting portions (31a), (31b) that project outward from each of open end edges of the C-shaped ring portion toward the outside of the outer pipe body (1), and that are movable within through notches (14) that open to an insertion opening (10a) of the outer pipe body (1); arc-shaped portions (32a), (32b) that extend in a reverse direction along an outer peripheral surface of the outer pipe body (1) from leading ends of the projecting portions; and a bent portion (33b) that is bent inward from the extension ends of the arc-shaped portions. A tip end of the bent portion (33b) can be engaged in a locked state with an engaging portion (12b) of the outer pipe body (1) by the elastic force of the arc-shaped portions (32a), (32b).SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a retaining structure for a pipe joint, and more particularly to a retaining structure for a plug-in type pipe joint in which one pipe body is inserted into the other pipe body and held in a retained state. [Background technology]

[0002] For example, a pipe fitting for connecting two pipes includes a plug-in type in which a pipe connected to one pipe is inserted into a pipe connected to the other pipe to hold them in place.

[0003] One known example of the above-mentioned plug-in type pipe joint is one in which annular grooves are formed circumferentially on the inner surface of the outer pipe body located on the outside and the outer surface of the inner pipe body located on the inside, opening toward the opposing surfaces, and when the open ends of the annular grooves are aligned, a stop ring engages across both annular grooves to prevent them from coming loose, thereby holding the outer pipe body and inner pipe body in a non-dislodging state.

[0004] In the case of a conventional C-shaped elastic ring used as the stop ring, the outer and inner pipes cannot be disassembled because it is difficult to remove the C-shaped elastic ring that is engaged so as to straddle both annular grooves in the elastic return state. As a result, if there is a problem with either the outer or inner pipe, it is not possible to separate the two and replace or repair one, which results in the problem that the entire pipe fitting and the piping connected to it must be replaced. In contrast, in the stop ring disclosed in Patent Document 1, in which the extension operating portions are extended outward from the C-shaped ring portion from each of the open end edges of the C-shaped elastic ring, the ring portion can be reduced in diameter by elastically deforming both extension operating portions in a direction that brings them closer to each other.Therefore, if the reduced-diameter ring portion is accommodated in the annular groove of the inner tube, the two can be separated by removing the inner tube from the outer tube. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Utility Model Application Publication No. 1-156390 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the stop ring of the above shape, if the extension operating portion is not exposed to the outside from the outer tube, a special tool is required to operate the extension operating portion, and the operation of reducing the diameter of the ring portion is troublesome and difficult. Also, if the extension operating portion is exposed to the outside from a notch provided in the outer tube, the exposed portion can be operated with fingers, making the operation of reducing the diameter of the ring portion easy, but a dedicated locking member must be separately provided to prevent the inconvenience of the ring portion being accidentally reduced in diameter by tampering, etc., which increases the number of parts and makes assembly difficult.

[0007] The present invention has been made in consideration of the above-mentioned problems, and has as its object to provide a stopper structure for a plug-in type pipe joint that can be connected in a state where an inner pipe body is inserted into an outer pipe body and where the two are prevented from coming out by a stop ring interposed between the two, and when the connection of the outer pipe body and the inner pipe body is complete, the two can be locked in a stopper state without the need for a separate locking member, and when removal is required, the engagement by the stop ring can be easily released and the two can be separated without the use of special tools, etc. [Means for solving the problem]

[0008] The technical means for solving the above problem is as follows: "A plug-in type pipe joint is a pipe joint in which one pipe is inserted into the other pipe to connect them, and a stop ring made of elastic wire is interposed between the inner circumferential surface of the outer pipe located on the outside and the outer circumferential surface of the inner pipe located on the inside to prevent the pipe joint from coming off. An inward-facing annular groove that opens inward is formed on the inner peripheral surface of the outer tube body over the entire circumferential area, An outwardly facing annular groove that opens outward is formed on the outer peripheral surface of the inner pipe body over the entire circumferential direction, The outer tube is cut out in an axial direction from an insertion opening for inserting the inner tube to the inward annular groove to form a through-notch of a predetermined width, the stop ring comprises a C-shaped ring portion having a wire diameter smaller than the depth of the outward annular groove portion, and elastically returning to engage with the inward annular groove and the outward annular groove when they are aligned, a pair of protruding portions protruding from each open end edge of the C-shaped ring portion to the outside of the outer tube body through the through-notch portion, arc-shaped portions extending from the tips of both protruding portions in opposite directions along the outer peripheral surface of the outer tube body and elastically deformable in directions away from the outer peripheral surface of the outer tube body, and a bent portion bent from the extended ends of the arc-shaped portions toward the outer peripheral surface of the outer tube body, When the C-shaped ring portion engages with the inward annular groove and the outward annular groove, an engaging portion is formed on the outer peripheral surface of the outer tube body to which the tip of the bent portion corresponds, with which the tip of the bent portion can engage by the elastic restoring force of the arc-shaped portion.

[0009] The above technical means operates as follows. The C-shaped ring portion of the stop ring, made of elastic wire, is fitted onto the inner tube while expanding its diameter slightly, and then, with the C-shaped ring portion positioned in line with the outward-facing annular groove, the protruding portions are resiliently pinched together with the fingers to reduce the diameter of the C-shaped ring portion. Because the wire diameter of the elastic wire is set smaller than the depth of the outward-facing annular groove, the C-shaped ring portion in its reduced diameter state can be accommodated in the outward-facing annular groove without protruding outward. By maintaining this state and moving the pair of protruding portions axially while protruding outward from the through-cutouts in the outer tube, the inner tube can be inserted into the insertion opening of the outer tube.

[0010] The protruding portion is formed to a length that protrudes outward from the through-cutout portion of the outer tube, and the through-cutout portion is formed in the axial direction up to the range that reaches the inward-facing annular groove. Therefore, if the protruding portion moves within the through-cutout portion and is released when it reaches the inward-facing annular groove, the stop ring will elastically return to its original position and the C-shaped ring portion will engage so as to straddle both the inward-facing annular groove and the outward-facing annular groove, and the outer tube and inner tube will be connected in a non-disconnected state by the stop ring. At this time, the tips of the bent portions provided at the extension ends of the arc-shaped portions that extend in opposite directions along the outer surface of the outer tube from the tip of the protruding portion will elastically engage with the engaging portions provided on the outer surface of the outer tube, thereby maintaining the stop ring in a locked state.

[0011] To remove the stop ring, the arc-shaped portion is forcibly elastically deformed in a direction away from the outer surface of the outer tube, thereby disengaging the tip of the bent portion from the engaging portion and releasing the locked state. Then, the pair of protruding portions are brought close together again to reduce the diameter of the C-ring portion and accommodate it in the outward-facing annular groove of the inner tube, and the pair of protruding portions are moved within the through-cut portion toward the insertion opening, allowing the inner tube to be removed from the outer tube and separated from the outer tube.

[0012] In the above-described pipe joint retaining structure, preferably, "the engaging portions are provided at positions symmetrical with respect to the through-notch portion." Since the stop ring has engagement portions at positions on the outer surface of the outer tube symmetrically with respect to the cutout, the stop ring can be symmetrical with respect to the center line passing between the protruding portions, making it possible to attach the stop ring to the inner tube without worrying about its orientation relative to the outer tube, facilitating the attachment process.

[0013] In the above-mentioned pipe joint slip-out prevention structure, if "the engaging portion is provided in a diameter direction perpendicular to the diameter of the outer pipe body passing through the center line of the through-cutout portion" or "the engaging portion is a through hole through which the tip of the bent portion can be inserted and which passes through the inward annular groove," then the engaging portion on the outer pipe body can be easily processed.

[0014] In the above-mentioned pipe joint retaining structure, preferably, "the open end of the inner pipe body is formed with a small-diameter cylindrical portion that can be tightly inserted into the insertion opening of the outer pipe body, the outward annular groove is formed in the small diameter cylindrical portion, When the small diameter cylindrical portion of the inner tube is inserted into the insertion port of the outer tube until the open end face on the insertion port side abuts against the outer step portion of the base end of the small diameter cylindrical portion, the inward facing annular groove is formed on the inner peripheral surface of the outer tube that corresponds to the outward facing annular groove. The pair of protruding portions of the stop ring are elastically deformed in a direction that brings them closer to each other, and the C-shaped ring portion is accommodated in the outward-facing annular groove formed in the small-diameter cylindrical portion of the inner tube. Then, while moving the protruding portions along the through-notch, the small-diameter cylindrical portion is inserted into the insertion opening of the outer tube. When the open end face of the outer tube facing the insertion opening abuts the outer step at the base end of the small-diameter cylindrical portion, the insertion of the inner tube into the outer tube is complete. At the same time, the C-shaped ring portions hold the two in place, preventing them from slipping out. This makes the connection process easy and straightforward. [Effects of the Invention]

[0015] The present invention has the following unique effects due to the above-described configuration. The inner and outer tubes are connected in a non-disconnecting manner by the C-shaped ring portion of the stop ring, and at the same time, the tip of the bent portion of the stop ring can be elastically engaged with an engaging portion provided on the outer surface of the outer tube to create a locked state. This makes it possible to maintain the connection state of the pipe joint for a long period of time without providing a separate locking member to keep the stop ring in the locked state.

[0016] By elastically deforming the arc-shaped portion in a direction away from the outer surface of the outer tube, the engagement between the tip of the bent portion and the engagement portion can be released, making it possible to easily release the locked state of the stop ring without using special tools, etc. After unlocking, by bringing the protruding portions closer to each other and elastically reducing the diameter of the C-shaped ring portion so that it is accommodated in the outward-facing annular groove of the inner tube, the inner tube can be easily removed from the outer tube, allowing the outer and inner tubes to be separated for repair or maintenance. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a cross-sectional view showing a state in which an outer pipe body and an inner pipe body are connected in a non-detachable state by a stop ring employed in a pipe joint non-detachment structure according to a first embodiment of the present invention. FIG. [Figure 2] 1 is a cross-sectional view showing an inner pipe body fitted with a stop ring employed in a pipe joint retaining structure according to a first embodiment of the present invention, and an outer pipe body before connection. [Figure 3] 1 is a perspective view showing an inner pipe body fitted with a stop ring employed in a pipe joint retaining structure according to a first embodiment of the present invention, and an outer pipe body before connection. FIG. [Figure 4] 1 is a cross-sectional view showing a state in which a stop ring employed in a pipe joint retaining structure according to a first embodiment of the present invention is elastically deformed. [Figure 5] 10 is a cross-sectional view showing a state in which an outer pipe body and an inner pipe body are connected in a non-detachable state by a stop ring employed in a pipe joint non-detachable structure according to a second embodiment of the present invention. FIG. [Figure 6] 10 is a cross-sectional view showing a state in which an outer pipe body and an inner pipe body are connected in a non-detachable state by a stop ring employed in a pipe joint non-detachable structure according to a third embodiment of the present invention. FIG. [Figure 7] 10 is a plan view of an outer tube showing a modified example of the through-notch portion of the retaining structure of the pipe joint according to the embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, the best mode for carrying out the present invention will be described with reference to the accompanying drawings. FIG. 1 is a cross-sectional view showing a state in which an outer pipe body (1) and an inner pipe body (2) that constitute a pipe joint are connected in a non-detachable state using a stop ring (3) of the first embodiment, FIG. 2 is a cross-sectional view showing a state before the inner pipe body (2) fitted with the stop ring (3) is inserted into the outer pipe body (1), and FIG. 3 is a perspective view thereof.

[0019] As shown in Figure 2, a large-diameter cylindrical portion 10 is formed on the insertion opening 10a side of the outer pipe 1, and a small-diameter cylindrical portion 20 is formed at the open end of the inner pipe 2, as shown in Figures 2 and 3, so that it can be tightly inserted into the large-diameter cylindrical portion 10 of the outer pipe 1. Two outward-facing, first and second annular grooves 21 and 22 that open outward are formed in the small-diameter cylindrical portion 20 over the entire circumferential area.

[0020] When the small-diameter cylindrical portion (20) of the inner pipe (2) is inserted into the large-diameter cylindrical portion (10) through the insertion opening (10a) of the outer pipe (1) and the open end face (13) of the insertion opening (10a) abuts against the outer step portion (23) at the base end of the small-diameter cylindrical portion (20), an inward-facing annular groove (11) is formed on the inner surface of the large-diameter cylindrical portion (10) corresponding to the first outward-facing annular groove (21), and the large-diameter cylindrical portion (10) is cut out in the range from the open end face (13) to the inward-facing annular groove (11), forming a through-notch (14) of a predetermined width.

[0021] In addition, a pair of through holes (12a) (12b) are drilled through the large-diameter cylindrical portion (10) of the outer tube body (1) in a diameter direction perpendicular to the diameter of the outer tube body (1) passing through the center line of the through cutout portion (14) so ​​as to open into the inward annular groove (11). It should be noted that the various dimensions are set so that when the small diameter cylindrical portion (20) is inserted into the large diameter cylindrical portion (10) to connect the outer pipe body (1) and the inner pipe body (2), the outer surfaces of the outer pipe body (1) and the inner pipe body (2) are at the same height.

[0022] The stop ring (3) is made entirely of an elastic wire having a wire diameter smaller than the depth of the first outward annular groove portion (21). The stop ring (3) is composed of a C-shaped ring portion (30) having an inner diameter slightly smaller than the outer diameter of the small-diameter cylindrical portion (20), a pair of protruding portions (31a) (31b) protruding outward from each of the open end edges of the C-shaped ring portion (30) along the diameter of the C-shaped ring portion (30), arc-shaped portions (32a) (32b) extending in opposite directions concentrically with the C-shaped ring portion (30) from the respective tips of the protruding portions (31a) (31b), and bent portions (33a) (33b) bent inward from the extended ends of the arc-shaped portions (32a) (32b).

[0023] When the C-shaped ring portion (30) is aligned with the first outward annular groove portion (21) of the small-diameter cylindrical portion (20) of the inner pipe body (2), in a free state, its inner peripheral side fits into the first outward annular groove portion (21) and its outer peripheral side protrudes outward from the open end of the first outward annular groove portion (21). The protruding portions 31a, 31b are set to a length that protrudes a predetermined distance outward from the outer pipe 1 from the through-notch 14 when the small-diameter cylindrical portion 20 of the inner pipe 2 is inserted into the large-diameter cylindrical portion 10 of the outer pipe 1, and the arc-shaped portions 32a, 32b are set to a length that substantially matches the length of the arc of a quadrant concentric with the outer pipe 1. As a result, the bent portions 32a, 32b are positioned in the radial direction of the C-shaped ring portion 30 and are set to a length that allows them to be inserted into the through-holes 12a, 12b in a free state.

[0024] First, the structure for connecting the outer pipe body 1 and the inner pipe body 2 using the stop ring 3 will be described. Before inserting into the outer tube (1), the C-shaped ring portion (30) of the stop ring (3) is aligned with the first outward annular groove (21) of the small-diameter cylindrical portion (20) of the inner tube (2), and a rubber O-ring (4) serving as an airtight sealing member is accommodated in the second outward annular groove (22) so that it protrudes slightly outward.

[0025] In this state, to insert the small-diameter cylindrical portion 20 of the inner tubular body 2 into the large-diameter cylindrical portion 10 through the insertion opening 10a of the outer tubular body 1, the pair of protruding portions 31a, 31b of the stop ring 3 are brought closer together with fingers, as shown in Fig. 4. Because the stop ring 3 is made of an elastic material, when the protruding portions 31a, 31b are elastically deformed so as to bring them closer together, the C-shaped ring portion 30 is elastically deformed in a radially contracting direction accordingly. Because the wire diameter of the stop ring 3 is set smaller than the depth of the first outward annular groove 21, by contracting the diameter of the C-shaped ring portion 30, it can be accommodated entirely within the first outward annular groove 21. In this manner, while the C-shaped ring portion (30) of the stop ring (3) is elastically deformed in the direction of reducing the diameter so as not to protrude from the first outward annular groove (21), the small diameter cylindrical portion (20) of the inner pipe body (2) is inserted into the large diameter cylindrical portion (10) through the insertion opening (10a) of the outer pipe body (1).

[0026] At this time, the posture of the outer tube body (1) relative to the inner tube body (2) is set so that the through-cutout portions (14) correspond to the protruding portions (31a) and (31b), and the pair of protruding portions (31a) and (31b) are elastically deformed with fingers in the direction of approaching each other while being moved within the through-cutout portions (14), whereby the small-diameter cylindrical portion (20) can be inserted through the insertion opening (10a) of the outer tube body (1). The width of the through-cutout portion (14) is set to a width that allows the pair of protruding portions (31a) and (31b) to be inserted simultaneously in a free state, and during the process of inserting the small-diameter cylindrical portion (20), the tip ends of the bent portions (33a) and (33b) are separated from the outer surface of the outer tube body (1).

[0027] The airtight O-ring (4) in the second outward annular groove (22) is inserted into the outer tube body (1) before the stop ring (3), and the part protruding from the second outward annular groove (22) advances deeper while being pressed and deformed by the inner peripheral surface of the large-diameter cylindrical portion (10) of the outer tube body (1), thereby ensuring airtightness between the outer tube body (1) and the inner tube body (2).

[0028] When the open end surface 13 of the outer pipe 1 abuts against the outer cut-off portion 23 of the inner pipe 2, insertion of the inner pipe 2 is prevented. At the same time, the first outward annular groove 21 corresponds to the inward annular groove 11, causing the C-shaped ring portion 30 of the stop ring 3 to elastically return and engage across the inward annular groove 11 and the first outward annular groove 21. This prevents the outer pipe 1 and the inner pipe 2 from slipping out. At this time, the elastic return force of the arc-shaped portions 32a and 32b causes the tip ends of the bent portions 33a and 33b to be inserted into a pair of through-holes 12a and 12b penetrating the large-diameter cylindrical portion 10 of the outer pipe 1, preventing accidental removal. Therefore, the stop ring (3) is locked without the need for a special locking member, and the outer tube body (1) and the inner tube body (2) can be held connected in a non-detachable state for a long period of time.

[0029] Next, a procedure for removing the connected outer pipe body (1) and inner pipe body (2) will be described. When it becomes necessary to separate the outer and inner tubes (1, 2) due to a malfunction at the connection between the outer and inner tubes (1, 2) or a defect in one of them, the arc-shaped portions (32a, 32b) can be elastically deformed with fingers in a direction away from the outer surface of the outer tube (1), and the tip ends of the bent portions (33a, 33b) can be forcibly pulled out of the through holes (12a, 12b) as shown in Figure 4, thereby releasing the locked state of the stop ring (3).

[0030] Thereafter, in the same manner as when inserting the inner pipe (2) into the outer pipe (1), the protruding portions (31a) and (31b) are brought close to each other to reduce the diameter of the C-shaped ring portion (30) and accommodate it in the first outward annular groove (21) of the inner pipe (2), and the pair of protruding portions (31a) and (31b) are moved within the through-cut portion (14) toward the insertion opening (10a), whereby the inner pipe (2) can be removed from the outer pipe (1), and the two can be separated. Therefore, if a malfunction or defect occurs in the outer pipe body (1) or the inner pipe body (2), there is no need to discard the entire pipe joint, and either one can be repaired or replaced, making it easy to use.

[0031] In the above embodiment, the through holes 12a, 12b are configured to penetrate predetermined locations of the outer tube body 1 in the diametrical direction, which makes it easy to process the outer tube body 1, but the positions of the through holes 12a, 12b can be freely changed by changing the length of the arc-shaped portions 32a, 32b of the stop ring 3. For example, the length of the arc-shaped portions 32a and 32b of the stop ring 3 may be shorter than the length of the arc of the quadrant as shown in FIG. 5, or longer as shown in FIG. 6, but it is desirable to form them symmetrically with respect to the center line of the C-shaped ring portion 30 that passes between the protruding portions 31a and 31b.

[0032] By making the shape of the stop ring (3) symmetrical, the through holes (12a) and (12b) formed in the outer tube body (1) can be provided at positions symmetrical with respect to the center line of the outer tube body (1). This makes it easy to process the outer tube body (1), and also makes it easy to assemble the stop ring (3) since there is no need to consider the orientation of the outer tube body (1) when attaching it to the small-diameter cylindrical portion (20) of the inner tube body (2).

[0033] In the above embodiment, the engaging portions that engage the tip ends of the bent portions 33a, 33b at the extended ends of the arc-shaped portions 32a, 32b in a locked state are through holes 12a, 12b that pass through the outer pipe 1. However, as shown in FIG. 6, these may be holes 15a, 15b that do not pass through the outer pipe 1. As shown in FIG. 6, when the arc-shaped portions 32a and 32b are set long, they are easily elastically deformed, and therefore the tip ends of the bent portions 33a and 33b can be fitted into the holes 15a and 15b with a strong elastic restoring force, and there is no inconvenience of them accidentally falling out of the holes 15a and 15b.

[0034] 7 shows a modified example of the through-cut portion 14 provided in the outer tube 1, which is formed in a generally trapezoidal shape, narrower on the insertion opening 10a side and wider on the inner side. With this shape, the protruding portions 31a, 31b, which are elastically deformed to approach each other, will not accidentally fall out of the narrow opening portion 14a of the through-cut portion 14 when they return to their original elastic state at the inner wide portion 14b after passing through the narrow opening portion 14a. Therefore, even if the bent portions 33a, 33b of the stop ring 3 in the locked state accidentally fall off from the through holes 12a, 12b or the holes 15a, 15a, the protruding portions 31a, 31b will not come off from the narrow opening portion 14a, so the connection between the outer tube body 1 and the inner tube body 2 is maintained and there is no inconvenience of them accidentally separating. [Explanation of symbols]

[0035] (1) · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · (2) Inner tube (3) Stop ring (10a) Insertion port (11) Inward circular groove (12a)(12b)...Through hole (engaging part) (14) Through-cut portion (21) First outward annular groove (outward annular groove) (30) C-ring part (31a)(31b) Protruding part (32a)(32b) Arc-shaped portion (33a)(33b)...Bending section

Claims

1. A plug-in type pipe joint is one in which one pipe is inserted into the other pipe to connect them, and a stop ring made of an elastic wire is interposed between the inner peripheral surface of the outer pipe located on the outside and the outer peripheral surface of the inner pipe located on the inside to prevent the pipe joint from coming off. An inward-facing annular groove that opens inward is formed on the inner peripheral surface of the outer tube body over the entire circumferential area, An outwardly facing annular groove that opens outward is formed on the outer peripheral surface of the inner pipe body over the entire circumferential direction, The outer tube is cut out in an axial direction from an insertion opening for inserting the inner tube to the inward annular groove to form a through-notch of a predetermined width, the stop ring comprises a C-shaped ring portion having a wire diameter smaller than the depth of the outward annular groove portion, and elastically returning to engage with the inward annular groove and the outward annular groove when they are aligned, a pair of protruding portions protruding from each open end edge of the C-shaped ring portion to the outside of the outer tube body through the through-notch portion, arc-shaped portions extending from the tips of both protruding portions in opposite directions along the outer peripheral surface of the outer tube body and elastically deformable in directions away from the outer peripheral surface of the outer tube body, and a bent portion bent from the extended ends of the arc-shaped portions toward the outer peripheral surface of the outer tube body, When the C-ring portion engages with the inward annular groove and the outward annular groove, an engaging portion is formed on the outer peripheral surface of the outer tube body to which the tip of the bent portion corresponds, with which the tip of the bent portion can engage by the elastic restoring force of the arc-shaped portion.

2. 2. The pipe joint retaining structure according to claim 1, wherein the engaging portions are provided at positions symmetrical with respect to the through-notch.

3. 3. The pipe joint retaining structure according to claim 2, wherein the engaging portion is provided in a diameter direction perpendicular to a diameter of the outer pipe body that passes through a center line of the through cutout portion.

4. 4. The pipe fitting retaining structure according to claim 2, wherein the engaging portion is a through hole through which the tip of the bent portion can be inserted and which passes through the inward annular groove.

5. 3. The pipe joint retaining structure according to claim 1, wherein the open end of the inner pipe is formed with a small-diameter cylindrical portion that can be tightly inserted into the insertion opening of the outer pipe, the outward annular groove is formed in the small diameter cylindrical portion, When the small-diameter cylindrical portion of the inner pipe body is inserted into the insertion port of the outer pipe body until the open end face on the insertion port side abuts the outer step portion of the base end of the small-diameter cylindrical portion, the inward-facing annular groove is formed on the inner peripheral surface of the outer pipe body that corresponds to the outward-facing annular groove.

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