Screw connection structure for steel pipe and sheath pipe for burying water collection / drainage pipe using the same

Abstract

To provide a screw connecting structure for a steel pipe and a sheath pipe for burying a water collecting and draining pipe using the same, capable of preventing infiltration of underground water from a connecting part, when connecting mutual steel pipes by a male screw and a female screw.SOLUTION: In a screw connection structure 3 for a steel pipe for connecting steel pipes 2 to each other by a male screw 4 and a female screw 6, an annular rubber ring 5 for water cut-off is disposed at a base end side internal corner portion 41 of the male screw 4, and an inclined pressing surface 7 having an inner diameter gradually increased toward a tip is formed at an inner external corner portion 61 in contact with the annular rubber ring 5 at the tip of the female screw 6.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a threaded connection structure for steel pipes that can waterproof the connection portion between steel pipes, and a sheath pipe for burying a collection and drainage pipe using the same. [Background technology]

[0002] In weak ground such as sand or mud, when a large earthquake occurs, disasters such as landslides and other sediment-related disasters, and building collapses due to liquefaction, etc. Meanwhile, the area around the Japanese archipelago is an environment where there is no escape from the occurrence of a large-scale earthquake, as it is located on the boundary between four plates: the Pacific Plate, the Philippine Sea Plate, the Eurasian Plate, and the North American Plate.

[0003] Therefore, construction methods are being developed that can prevent disasters such as landslides and liquefaction even when an earthquake occurs.

[0004] The groundwater level lowering method is a construction method to prevent such disasters. It involves burying porous, permeable collection and drainage pipes in a predetermined section of the ground beneath the construction site, either horizontally or at a gentle slope. The buried collection and drainage pipes collect and drain underground rainwater and spring water, lowering the groundwater level in the target ground and preventing landslides and liquefaction.

[0005] Japanese Patent Application Laid-Open Publication No. 2017-223050 proposes a drain pipe made of a three-dimensional network structure as a drainage pipe used in the groundwater level lowering method, and a manufacturing method thereof (Patent Document 1).

[0006] Furthermore, Patent Publication No. 2020-33714 proposes a method for laying such collection and drainage pipes by forming a horizontal tunnel penetrating horizontally between a starting shaft and a reaching shaft, connecting multiple composite pipes each consisting of a sheath pipe with a drain pipe inside, and pushing them from the starting shaft toward the reaching shaft while laying the composite pipes over the entire length of the cross-shaft, and then pushing only the sheath pipe from inside the cross-shaft toward the reaching shaft and removing it, thereby laying the drain pipe underground (Patent Document 2).

[0007] Furthermore, Japanese Patent Application Laid-Open Publication No. 2020-180527 proposes an excavator capable of inserting and extracting a sheath pipe from an adit (Patent Document 3). By using an excavator capable of extracting a sheath pipe as described in Patent Document 3, it is possible to push the sheath pipe into an adit, insert a collection and drainage pipe into the sheath pipe, and extract the sheath pipe from a single vertical shaft. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-223050 [Patent Document 2] Japanese Patent Publication No. 2020-33714 [Patent Document 3] Japanese Patent Publication No. 2020-180527 Summary of the Invention [Problem to be solved by the invention]

[0009] However, if groundwater seeps into the inside of a sheath pipe buried underground, it will hinder the insertion of a collection and drainage pipe into the sheath pipe. To address this, a conventional method is to seal the gaps between the threads by wrapping sealing tape around the threads that connect the male and female threads of the sheath pipes and screwing them together to stop water leakage.

[0010] However, because sealing tape cannot adequately adapt to the shape of the threads, it often breaks or clumps when screwed in, resulting in an ineffective watertight seal. Therefore, when installing deep underground, the groundwater pressure is high, and when the sheath pipe is pushed into the adit, friction between the sheath pipe and the ground applies large tensile and compressive forces to the joint, so even with sealing tape, groundwater can seep into the pipe, leading to a water leak.

[0011] The present invention has been made to solve the above-mentioned problems, and aims to provide a threaded connection structure for steel pipes that can prevent groundwater from seeping in through the connection when steel pipes are connected together using male and female threads, and a sheath pipe for burying collection and drainage pipes using the same. [Means for solving the problem]

[0012] The threaded connection structure for steel pipes according to the present invention is a threaded connection structure for steel pipes that connects steel pipes together using male and female threads in order to solve the problem of improving the watertight performance of the threaded connection portion, and a watertight annular rubber ring is placed in the recessed corner portion on the base end side of the male thread, and an inclined pressing surface whose inner diameter gradually increases toward the tip is formed in the inner recessed corner portion that contacts the annular rubber ring at the tip of the female thread.

[0013] In addition, as one aspect of the present invention, in order to solve the problem of compressing the annular rubber ring without damaging it and pressing it against the corner of the inside corner portion on the base end side of the male screw, the inclination angle of the inclined pressing surface may be formed at 45 degrees with respect to the tip end surface of the female screw.

[0014] Furthermore, as one aspect of the present invention, in order to solve the problem of stably positioning the annular rubber ring, a concave ring retaining groove for retaining the annular rubber ring may be formed in the base end inside corner portion.

[0015] In one aspect of the present invention, in order to solve the problem of stably disposing the annular rubber ring, the ring holding groove may be formed in an end face of the base end side inside corner portion.

[0016] Furthermore, as one aspect of the present invention, in order to solve the problem of stably positioning the annular rubber ring and making it easy to compress by the inclined pressing surface of the female screw, the groove width of the ring retaining groove may be formed narrower than the wire diameter of the annular rubber ring.

[0017] Furthermore, as one aspect of the present invention, in order to solve the problem of forming a space that causes the annular rubber ring to bulge when pressed, thereby preventing damage to the annular rubber ring, the base end inside corner portion of the male screw is configured as a threadless portion whose outer diameter is approximately the same as the root of the thread, and the inner surface of the tip of the female screw is configured as a threadless portion whose inner diameter is approximately the same as the root of the thread, and a space is formed between the outer diameter of the base end inside corner portion of the male screw and the inner diameter of the threadless portion of the tip of the female screw, which is pressed by the inclined pressing surface to cause the annular rubber ring to bulge.

[0018] Furthermore, as one aspect of the present invention, in order to solve the problem of preventing the male screw and the female screw from being damaged by the load applied to the screw connection portion, the male screw and the female screw may be formed as square threads.

[0019] The sheath pipe for burying a collection and drainage pipe according to the present invention is made up of a plurality of steel pipes connected by any of the above-described threaded connection structures for steel pipes in order to solve the problem of preventing groundwater from seeping in when the pipe is buried underground. [Effects of the Invention]

[0020] According to the present invention, when steel pipes are connected to each other using male and female threads, it is possible to prevent groundwater from seeping in through the connection portion. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a partially cutaway cross-sectional view showing one embodiment of a steel pipe constituting a sheath pipe for burying a drainage pipe according to the present invention. [Figure 2] 1 is an enlarged cross-sectional end view showing a state in which an annular rubber ring is disposed on a male thread in the threaded connection structure for steel pipes of the present embodiment. FIG. [Figure 3] FIG. 2 is an enlarged cross-sectional end view showing a female thread in the threaded connection structure for steel pipes of the present embodiment. [Figure 4] 1 is an enlarged cross-sectional end view showing a state in which a male thread and a female thread in a threaded connection structure for steel pipes according to the present embodiment are threaded together via an annular rubber ring. FIG. [Figure 5] 1 is a photographic image showing a state in which steel pipes equipped with a threaded connection structure for steel pipes according to the present invention are connected to each other in Example 1. [Figure 6] 10 is a photographic image showing a state in which a water pressure test of a connecting portion is being carried out in this Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of a threaded connection structure for steel pipes and a sheath pipe for burying a drainage pipe using the same according to the present invention will be described with reference to the drawings.

[0023] The sheath pipe 1 for burying collection and drainage pipes is a circular pipe used to bury collection and drainage pipes underground, and is pushed into an underground adit or the like, and after inserting a collection and drainage pipe inside, is pulled out from the ground while leaving the collection and drainage pipe underground. The sheath pipe 1 for burying collection and drainage pipes of this embodiment is constructed by connecting multiple steel pipes 2 with a steel pipe thread connection structure 3. Each component will be described in detail below.

[0024] As shown in FIG. 1, the steel pipe 2 is a circular pipe that is connected to other steel pipes 2 to form a sheath pipe 1 for burying collection and drainage pipes. In this embodiment, the steel pipe 2 is a circular steel pipe having a length of approximately 1000 mm, an outer diameter of 355.6 mm, and a wall thickness of 7.9 mm.

[0025] The dimensions of the steel pipe 2, such as its length and outer diameter, are not particularly limited and may be selected appropriately depending on the inner diameter and depth of the horizontal tunnel into which it will be pushed, the outer diameter of the drainage pipe to be buried underground, etc.

[0026] As shown in Figures 2 to 4, the threaded connection structure 3 for steel pipes is a threaded structure for detachably connecting steel pipes 2 to each other, and in this embodiment, it is composed of a male thread 4, an annular rubber ring 5 placed in a base end side inside corner portion 41 of the male thread 4, a female thread 6 that screws into the male thread 4, and an inclined pressing surface 7 formed in an inside outside corner portion 61 of the female thread 6.

[0027] The male screw 4 is a male screw for connecting steel pipes 2 together, and in this embodiment, the threads are formed using a high-strength square screw to prevent damage from tensile and compressive forces caused by friction between the steel pipe 2 and the ground.

[0028] This male thread 4 is formed within a predetermined range from the tip on the outer peripheral surface of one end of the steel pipe 2. Specifically, the threaded portion extends from about 10 mm to about 40 mm from the tip, and the ranges of 0 mm to about 10 mm and about 40 mm to about 50 mm before and after that are configured as non-threaded portions.

[0029] The non-threaded portion is formed with an outer diameter of 345.6 mm, which is approximately the same diameter as the root diameter of the threads. As a result, the base end side of male thread 4 forms a base end inside corner 41 by outer circumferential surface 411, which is the non-threaded portion, and end face 412 formed perpendicularly from outer circumferential surface 411. A concave ring retaining groove 42 that retains annular rubber ring 5 is formed in this base end inside corner 41.

[0030] The ring holding groove 42 is a concave groove for stably holding the annular rubber ring 5 in the base-end inside corner portion 41, and in this embodiment, is formed from the corner of the base-end inside corner portion 41 to the perpendicularly formed end face 412. Specifically, the groove width of the ring holding groove 42 is approximately 3 mm, which is narrower than the wire diameter (approximately 4 mm) of the annular rubber ring 5, and the depth is approximately 0.75 mm.

[0031] The location where the ring retaining groove 42 is formed is not limited to the position and shape of this embodiment, and may be formed on the outer peripheral surface 411 near the base end inside corner 41 or in a different groove shape as long as the desired watertight effect is obtained. Also, the thread is not limited to a square thread, and may be appropriately selected from triangular threads, trapezoidal threads, round threads, etc., taking into consideration strength, etc. Furthermore, the dimensions of the male thread 4 described above are examples and may be changed as appropriate.

[0032] The annular rubber ring 5 is a watertight rubber ring formed into an annular shape from a rubber material, and as shown in Figure 2, is placed in advance at the base-end inside corner 41 of the male thread 4 before being threaded onto the female thread 6. In this embodiment, the annular rubber ring 5 is formed from a rubber wire with a wire diameter of approximately 4 mm into a ring with an inner diameter of approximately 290 mm. The inner diameter of the annular rubber ring 5 is approximately 0.8 times the outer diameter of the base-end inside corner 41 of the male thread 4.

[0033] The dimensions of the wire diameter and inner diameter of the annular rubber ring 5 are not particularly limited, and may be selected appropriately depending on the shape of the male thread 4, the gap between the male thread 4 and the female thread 6, and the like.

[0034] The female thread 6 is a thread that can be threaded into the male thread 4 formed on the inner surface of one end of the steel pipe 2. In this embodiment, as shown in FIG. 3, the female thread 6 is formed within a predetermined range from one end of the steel pipe 2, just like the male thread 4 that it threads into, and the thread is formed by a square thread.

[0035] Specifically, the female screw 6 has threads formed in a range of about 10 mm to about 40 mm from the tip, similar to the male screw 4, with the ranges of 0 mm to about 10 mm and about 40 mm to about 50 mm before and after that being configured as non-threaded sections. The non-threaded section on the base end side is formed with an inner diameter of 345.7 mm, which is approximately the same diameter as the diameter of the threads.

[0036] On the other hand, the non-threaded portion on the tip side is formed with an inner diameter of 350.3 mm, which is approximately the same diameter as the root diameter of the thread. As a result, as shown in Figure 4, a space approximately 3 mm wide, narrower than the wire diameter (4 mm) of the annular rubber ring 5, is formed between the inner diameter of the non-threaded portion on the tip side of the female thread 6 and the outer diameter of the base-end inside corner portion 41 of the male thread 4 that is threaded into it. As will be described later, this space functions as an escape route for the annular rubber ring 5, which is pressed by the tip of the female thread 6 and bulges out laterally.

[0037] At the tip of the female screw 6, an inclined pressing surface 7 is formed at an inner corner portion 61 that comes into contact with the annular rubber ring 5. The inner corner portion 61 is formed by an inner peripheral surface 611 that is a portion without threads and a tip surface 612 of the female screw 4.

[0038] The inclined pressing surface 7 applies pressure to the annular rubber ring 5 placed in the base-end inside corner 41 of the male thread 4 to be threaded therewith without damaging it, and is formed as an inclined surface so that the inner diameter gradually increases toward the tip. The inclined pressing surface 7 in this embodiment is formed at an inclination angle of 45 degrees with respect to the tip surface 612 of the female thread 6 and has a width of approximately 1.4 mm so that pressure can be applied to the annular rubber ring 5 toward the corner of the base-end inside corner 41.

[0039] The angle of inclination of the inclined pressing surface 7 is not particularly limited, but is preferably set within a range of about 30 degrees to 60 degrees relative to the tip surface 612 of the female screw 6.

[0040] Next, the operation of each component of the threaded connection structure for steel pipes 3 of this embodiment and the sheath pipe for burying drainage pipes 1 using the same will be described.

[0041] The sheath pipe 1 for burying collection and drainage pipes is inserted into the ground using an excavator or the like. In this embodiment, the excavator is used to push the steel pipe 2 into an adit formed at a depth for collecting and draining groundwater. Then, other steel pipes 2 are connected and pushed in. By repeating this process of pushing and connecting steel pipes 2, the sheath pipe 1 for burying collection and drainage pipes is constructed underground.

[0042] At this time, the steel pipes 2 are connected to each other by screwing together the male thread 4 and the female thread 6 of the threaded connection structure 3 for steel pipes.

[0043] 2, the ring retaining groove 42 retains a portion of the annular rubber ring 5 by fitting it thereinto. Therefore, the annular rubber ring 5 is kept stably disposed in the inside corner portion 41 on the base end side of the male thread 4.

[0044] As the female screw 6 is threaded, the inclined pressing surface 7 at the tip applies pressure to the annular rubber ring 5. As shown in Figure 4, the inclined pressing surface 7 is formed so that the inner diameter gradually increases toward the tip, so that the annular rubber ring 5 can be compressed toward the corner of the base-end inside corner portion 41 of the male screw 4 without being damaged.

[0045] At this time, the annular rubber ring 5 is elastically deformed by being pressed by the inclined pressing surface 7, and comes into close contact with the inclined pressing surface 7, the ring retaining groove 42, the outer surface 411 of the male screw 4, and the inner surface 611 of the female screw 6, thereby filling the gap between the male screw 4 and the female screw 6 and enhancing the waterproofing effect of the connecting portion.

[0046] The space formed by the difference between the inner diameter of the ring retaining groove 42 and the tip of the female thread 6 and the outer diameter of the base end inside corner portion 41 of the male thread 4 provides an escape route for the annular rubber ring 5, which bulges axially due to elastic deformation, and prevents the annular rubber ring 5 from breaking when fastened.

[0047] After the sheath pipe 1 for burying a collection and drainage pipe is inserted into the adit, the collection and drainage pipe is inserted. In the sheath pipe 1 for burying a collection and drainage pipe of this embodiment, each connecting portion is watertight by the steel pipe thread connecting structure 3, so the collection and drainage pipe can be inserted smoothly without water leakage.

[0048] After the collection and drainage pipes are inserted, the sheath pipe 1 for burying collection and drainage pipes is pulled out of the adit using an excavator or the like and removed. Each steel pipe 2 constituting the sheath pipe 1 for burying collection and drainage pipes is removed from the other steel pipes 2 by loosening the screws. Each removed steel pipe 2 is reused as a sheath pipe 1 for burying collection and drainage pipes.

[0049] According to the threaded connection structure for steel pipes 3 of this embodiment and the sheath pipe for burying a drainage pipe using the same, the following effects can be achieved. 1. When the annular rubber ring 5 is pressed by the inclined pressing surface 7, it comes into close contact with the inclined pressing surface 7, the ring retaining groove 42, the outer surface 411 of the male thread 4, and the inner surface 611 of the female thread 6, filling the gap between the male thread 4 and the female thread 6 and improving the water-stopping effect at the connecting portion. 2. The inner diameter of the inclined pressing surface 7 gradually increases toward the tip, so that the inclined pressing surface 7 can be pressed toward the corner of the base end inside corner portion 41 to hold the annular rubber ring 5 without damaging it. 3. The ring holding groove 42 allows the annular rubber ring 5 to be stably positioned. 4. The male and female threads are formed as square threads, which are resistant to tension and compression and prevent damage to the threads. The steel pipe 2 used as the sheath pipe 1 for burying drainage pipes can also be reused. [Example]

[0050] In this Example 1, a steel pipe equipped with a threaded connection structure for steel pipes according to the present invention was produced, and a water pressure resistance test of the connection portion was carried out.

[0051] Figure 5 shows the state in which the two steel pipes prepared in Example 1 were connected. Then, as shown in Figure 6, a cylindrical sealed space was created on the outer periphery of the connecting portion of the two steel pipes, and water pressure was applied to the sealed space to check whether water had entered through the connecting portion.

[0052] Even when a water pressure of 2M (mega) Pa (pascals) (equivalent to the water pressure at a depth of approximately 200m) was applied to the enclosed space for five minutes, no water was seen.

[0053] Therefore, it was confirmed that the threaded connection structure for steel pipes according to the present invention has high water-stopping properties.

[0054] The threaded connection structure for steel pipes and the sheath pipe for buried collection and drainage pipes using the same according to the present invention are not limited to the above-described embodiment and can be modified as appropriate. For example, a single steel pipe is formed with a male thread at one end and a female thread at the other end, but it is also possible to form male or female threads at both ends and connect them to the female or male thread of another steel pipe. [Explanation of symbols]

[0055] 1. Sheath pipe for buried drainage pipes 2 Steel pipe 3. Steel pipe screw connection structure 4 male threads 5 Annular rubber ring 6 female thread 7 Inclined pressing surface 41 Base end inside corner 42 Ring retaining groove 61 Inside corner 411 Outer surface 412 End face 611 Inner surface 612 Tip surface

Claims

1. A threaded connection structure for steel pipes that connects steel pipes together using male and female threads, A waterproof annular rubber ring is disposed at the inside corner of the base end of the male screw, The threaded connection structure for steel pipes, wherein an inclined pressing surface whose inner diameter gradually increases toward the tip is formed at the inner corner portion where the tip of the female thread contacts the annular rubber ring.

2. 2. A threaded connection structure for steel pipes according to claim 1, wherein the inclined pressing surface has an inclination angle of 45 degrees relative to the tip end surface of the female thread.

3. 2. The threaded connection structure for steel pipes according to claim 1, wherein a concave ring-retaining groove for retaining the annular rubber ring is formed in the base-end inside corner portion.

4. The connecting screw structure according to claim 3 , wherein the ring holding groove is formed on an end face of the base end side inside corner portion.

5. 4. The threaded connection structure for steel pipes according to claim 3, wherein the groove width of the ring holding groove is formed narrower than the wire diameter of the annular rubber ring.

6. 2. The threaded connection structure for steel pipes according to claim 1, wherein the base-end inside corner portion of the male thread is configured as a threadless portion having an outer diameter approximately the same as the thread roots, and the inner circumferential surface of the tip of the female thread is configured as a threadless portion having an inner diameter approximately the same as the thread roots, and a space is formed between the outer diameter of the base-end inside corner portion of the male thread and the inner diameter of the threadless portion of the tip of the female thread into which the annular rubber ring bulges when pressed by the inclined pressing surface.

7. 2. The threaded connection structure for steel pipes according to claim 1, wherein the male thread and the female thread are square threads.

8. A sheath pipe for burying a collection and drainage pipe, comprising a plurality of steel pipes connected by the threaded connection structure for steel pipes according to any one of claims 1 to 7.

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