Threaded joint for steel pipes and pipe assembly

Abstract

Provided are a threaded joint for a steel pipe and a pipe assembly capable of being fastened quickly and properly. The threaded joint includes a steel pipe (20m), a steel pipe (20f), and a pipe joint (50) for connecting the steel pipes (20m, 20f) to each other. The pipe body (21m, 21f) of the steel pipes (20m, 20f) respectively includes a ring-shaped mark groove (23m, 23f) formed on the outer periphery of the pipe body (21m, 21f).

Description

[0001] This application is a divisional application of the PCT application PCT / JP2020 / 009003 filed by the applicant Nippon Steel Corporation on March 3, 2020, which entered the national phase on July 29, 2021, with application number 202080011492.8 and invention name “Threaded joint for steel pipes”. Technical Field

[0002] The present disclosure relates to a threaded joint for steel pipes, and more particularly to a combination-type threaded joint for connecting two steel pipes to each other. Background Art

[0003] For example, steel pipes known as oil country tubular goods are used in the exploration and production of oil and natural gas wells (hereinafter collectively referred to as "oil wells"), the development of unconventional resources such as oil sands and shale gas, the recovery and storage of carbon dioxide (CCS (Carbon Dioxide Capture and Storage)), geothermal power generation, and hot springs. Threaded joints are used to connect these steel pipes.

[0004] This type of threaded joint for steel pipes is roughly divided into a combination type and an integral type. In the case of the combination type, one of the pair of pipes to be connected is a steel pipe, and the other pipe is a pipe joint. In this case, external threads are formed on the outer periphery of both ends of the steel pipe, and internal threads are formed on the inner periphery of both ends of the pipe joint. In addition, the external threads of the steel pipe are screwed into the internal threads of the pipe joint, thereby tightening and connecting the two. In the case of the integral type, both of the pair of pipes to be connected are steel pipes, and no additional pipe joint is used. In this case, external threads are formed on the outer periphery of one end of the steel pipe, and internal threads are formed on the inner periphery of the other end. In addition, the external threads of one steel pipe are screwed into the internal threads of the other steel pipe, thereby tightening and connecting the two.

[0005] Typically, the fitting portion of a pipe end with an external thread includes an element that inserts into the internal thread, and is therefore called a "pin." On the other hand, the fitting portion of a pipe end with an internal thread includes an element that receives the external thread, and is therefore called a "box." These pins and boxes are the ends of the pipe and, therefore, are both tubular.

[0006] Oil wells, while using oil well tubing to reinforce the pit walls to prevent them from collapsing during excavation, have resulted in a multi-layered structure. In recent years, oil wells have become increasingly deep and deepwater. To efficiently develop oil wells in this environment, oil well tubing is often connected using threaded joints, where the inner and outer diameters of the joint are approximately the same as, or slightly larger than, those of the steel pipe. Using such threaded joints minimizes the gaps between the multi-layered oil well tubing, enabling efficient development of oil wells without significantly increasing the wellbore diameter, even at greater depths. Within these constraints, threaded joints must exhibit excellent sealing performance against both internal fluid pressure (hereinafter referred to as "internal pressure") and external fluid pressure (hereinafter referred to as "external pressure"). Furthermore, when used in deep oil wells, for example, thermal expansion of the oil well tubing imposes significant tensile and compressive loads on the threaded joints. In such an environment, threaded joints are also required to have excellent sealing performance.

[0007] Threaded joints that ensure sealing performance are known to utilize metal-to-metal contact (hereinafter referred to as "metal seals"). Metal seals refer to a structure in which, when the diameter of the pin's sealing surface is slightly larger than that of the box's sealing surface, the pin's sealing surface contracts while the box's sealing surface expands when the threaded joint is tightened. The elastic restoring force of the respective sealing surfaces as they return to their original diameters generates contact pressure on the sealing surfaces, resulting in a tight fit around the entire circumference and achieving sealing performance. Furthermore, threaded joints that ensure sealing performance are also known to utilize structures that either do not utilize metal seals or utilize sealing performance in the threaded portion in combination with metal seals. Specifically, in a region of the threaded portion exceeding a predetermined length in the tightened state, a viscous lubricant, known as a coating, is present in this gap. The interference of the thread diameters of the pin and box creates contact pressure on the threaded surfaces (hereinafter referred to as "thread seals"). There is also known a threaded joint having sealing performance against internal pressure and external pressure by providing such a thread seal.

[0008] This specification cites the following prior art documents.

[0009] Patent Document 1: WO2018 / 180218A1

[0010] Patent Document 2: WO2018 / 052141A1

[0011] Patent Document 3: US5233742A

[0012] Patent Document 4: WO2001 / 086185A1

[0013] Patent Document 5: WO2008 / 029957A1

[0014] Patent Document 6: WO2005 / 040657A1

[0015] Patent Document 7: US4641410A Summary of the Invention

[0016] An object of the present disclosure is to provide a threaded joint for steel pipes that can be fastened quickly and appropriately.

[0017] The threaded joint for steel pipes disclosed herein includes a first steel pipe, a second steel pipe, and a pipe joint for connecting the first and second steel pipes. The first steel pipe includes a first pipe body and a tubular first pin. The first pin is formed continuously with the first pipe body and is formed at the top end of the first steel pipe. The second steel pipe includes a second pipe body and a tubular second pin. The second pin is formed continuously with the second pipe body and is formed at the top end of the second steel pipe. The pipe joint includes a tubular first female buckle and a tubular second female buckle. The first female buckle is inserted into and fastened to the first female buckle. The second female buckle is formed on the opposite side of the first female buckle and is inserted into and fastened to the second female buckle. The first and second female buckles each include an external thread formed on the outer circumference of the pin. The first and second female buckles each include an internal thread corresponding to the external thread and formed on the inner circumference of the female buckle. The external and internal threads are trapezoidal and tapered threads. When tightened, at least a portion of the external and internal threads form a threaded seal. The external thread comprises an external thread crest, an external thread groove bottom, an external thread flank formed closer to the pin's tip, and an external thread load flank formed farther from the pin's tip. The external thread flank comprises a first external thread flank segment and a second external thread flank segment. The first external thread flank segment is formed farther from the steel pipe axis and has an flank angle of -10 to 15 degrees. The second external thread flank segment is formed closer to the pipe axis and has an flank angle of 20 to 60 degrees. The second external thread flank segment has a height of 20 to 60% of the height of the external thread. The internal thread comprises an internal thread crest opposite the external thread groove bottom, an internal thread groove bottom opposite the external thread crest, an internal thread flank opposite the external thread crest, and an internal thread load flank opposite the external thread load flank. The internal thread flank surface comprises a first internal thread flank segment and a second internal thread flank segment. The first internal thread flank segment is formed farther from the pipe axis and has an flank angle identical to that of the first external thread flank segment. The second internal thread flank segment is formed closer to the pipe axis and has an flank angle identical to that of the second external thread flank segment. The first pin further comprises a first pin shoulder surface formed at the top end of the first pin. The second pin further comprises a second pin shoulder surface formed at the top end of the second pin and in contact with the first pin shoulder surface when tightened. The first pipe body comprises a first annular marking groove formed on the outer circumference of the first pipe body. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a longitudinal sectional view of the threaded joint for steel pipes according to the embodiment, taken along the pipe axis direction.

[0019] Figure 2 are respectively expressed Figure 1Enlarged longitudinal sectional view of the shape of the external thread and the internal thread.

[0020] Figure 3 is Figure 1 Enlarged longitudinal sectional view of the shape of the external thread and the internal thread. DETAILED DESCRIPTION

[0021] The threaded joint for steel pipes of the present embodiment includes a first steel pipe, a second steel pipe, and a pipe joint for connecting the first steel pipe and the second steel pipe to each other. The first steel pipe includes a first pipe body and a tubular first pin. The first pin is formed continuously with the first pipe body and is formed at a top end portion of the first steel pipe. The second steel pipe includes a second pipe body and a tubular second pin. The second pin is formed continuously with the second pipe body and is formed at a top end portion of the second steel pipe. The pipe joint includes a tubular first box and a tubular second box. The first box is for the first pin to be inserted and fastened with the first pin. The second box is formed at an opposite side of the first box and is for the second pin to be inserted and fastened with the second pin. The first pin and the second pin each include an external thread formed at an outer periphery of the pin. The first box and the second box each include an internal thread corresponding to the external thread and formed at an inner periphery of the box. The external thread and the internal thread are trapezoidal threads and are tapered threads. At least a part of the external thread and the internal thread constitutes a thread seal in a fastened state. The external thread includes an external thread crest, an external thread root, an external thread stabbing flank formed at a side closer to a top end of the pin, and an external thread load flank formed at a side farther from the top end of the pin. The external thread stabbing flank has a first external thread stabbing flank section formed at a side farther from a pipe axis of the steel pipe and having a stabbing flank angle of -10 degrees to 15 degrees, and a second external thread stabbing flank section formed at a side closer to the pipe axis and having a stabbing flank angle of 20 degrees to 60 degrees. The second external thread stabbing flank section has a height of 20 to 60% of a height of the external thread. The internal thread includes an internal thread crest opposite to the external thread root, an internal thread root opposite to the external thread crest, an internal thread stabbing flank opposite to the external thread stabbing flank, and an internal thread load flank opposite to the external thread load flank. The internal thread stabbing flank has a first internal thread stabbing flank section formed at a side farther from the pipe axis and having a stabbing flank angle identical to that of the first external thread stabbing flank section, and a second internal thread stabbing flank section formed at a side closer to the pipe axis and having a stabbing flank angle identical to that of the second external thread stabbing flank section. The first pin further includes a first pin shoulder surface formed at a top end of the first pin. The second pin further includes a second pin shoulder surface formed at a top end of the second pin and contacting the first pin shoulder surface in the fastened state. The first pipe body includes a first mark groove formed at an outer periphery of the first pipe body in a ring shape.

[0022] According to this embodiment, the first steel pipe and the second steel pipe can be fastened to the pipe joint quickly and appropriately.

[0023] The second tube body may include an annular second marking groove formed on the outer circumference of the second tube body. The first marking groove may have a width narrower than a width of the second marking groove.

[0024] In this case, the first steel pipe can be appropriately fastened to the pipe joint more easily, and the second steel pipe can be quickly fastened to the pipe joint.

[0025] The first box snap may further include a tubular first recess. The first recess is formed at the open end of the first box snap and has an inner circumferential surface that faces the outer circumferential surface of the first tube body and is spaced apart from the outer circumferential surface. The second box snap may further include a tubular second recess. The second recess is formed at the open end of the second box snap and has an inner circumferential surface that faces the outer circumferential surface of the second tube body and is spaced apart from the outer circumferential surface.

[0026] In this case, the paint does not overflow from the open end of the pipe joint and reach the marking groove.

[0027] The thread diameter interference amount of the portion constituting the thread seal between the external thread of the second pin and the internal thread of the second box may be smaller than the thread diameter interference amount of the portion constituting the thread seal between the external thread of the first pin and the internal thread of the first box.

[0028] In this case, the amount of rotation of the first pin due to the co-rotation during the screwing process of the second steel pipe can be suppressed.

[0029] Alternatively, the external thread of the first pin and the internal thread of the first box may include a complete thread and an incomplete thread formed between the first pipe body and the complete thread. Alternatively, the first pin and the first box may be bonded together along all or part of the incomplete thread when tightened.

[0030] In this case, the amount of rotation of the first pin due to the co-rotation during the screwing process of the second steel pipe can be suppressed.

[0031] It is also possible that the steel pipe has an outer diameter exceeding 16 inches.

[0032] The pipe assembly of this embodiment includes a first steel pipe and a pipe joint for connecting the first steel pipe and a second steel pipe to each other. The first steel pipe includes a first pipe body and a tubular first pin. The first pin is formed continuously with the first pipe body and is formed at the top end of the first steel pipe. The pipe joint includes a tubular first female buckle and a tubular second female buckle. The first female buckle is inserted into the first male buckle and is fastened to the first male buckle. The second female buckle is formed on the opposite side of the first female buckle and is inserted into the second male buckle of the second steel pipe and is fastened to the second male buckle. The first male buckle includes an external thread formed on the outer periphery of the male buckle. The first female buckle includes an internal thread corresponding to the external thread and formed on the inner periphery of the female buckle. The external thread and the internal thread are trapezoidal threads and tapered threads. In the fastened state, at least parts of the external thread and the internal thread constitute a thread seal. The external thread comprises a top surface, a bottom surface of the external thread groove, a flank surface formed closer to the pin tip, and a load-bearing flank surface formed farther from the pin tip. The flank surface comprises a first flank segment, formed farther from the pipe axis, and having a flank angle of -10 to 15 degrees. The second flank segment, formed closer to the pipe axis, has a flank angle of 20 to 60 degrees. The second flank segment has a height of 20 to 60% of the external thread height. The internal thread comprises a top surface opposite the bottom surface of the external thread groove, a bottom surface opposite the top surface, a flank surface opposite the flank surface, and a load-bearing flank surface opposite the load-bearing flank surface. The internal thread flank surface comprises a first internal thread flank segment and a second internal thread flank segment. The first internal thread flank segment is formed farther from the pipe axis and has an flank angle identical to that of the first external thread flank segment. The second internal thread flank segment is formed closer to the pipe axis and has an flank angle identical to that of the second external thread flank segment. The first pin further includes a first pin shoulder surface formed at the top end of the first pin. The first pipe body includes an annular first marking groove formed on the outer circumference of the first pipe body. The open end of the first box is positioned within the width of the first marking groove.

[0033] Hereinafter, an embodiment of a threaded joint for steel pipes will be described with reference to the accompanying drawings. The same or corresponding parts in the drawings are denoted by the same reference numerals, and the same description will not be repeated.

[0034] Reference Figure 1The threaded joint 10 is a combination type, comprising a steel pipe 20m, a steel pipe 20f, and a pipe joint 50 for connecting the steel pipes 20m and 20f to each other. The steel pipes 20m and 20f are not particularly limited, but may have an outer diameter exceeding 16 inches. The steel pipe 20m comprises a pipe body 21m and a tubular pin 30m. The pin 30m is formed continuously with the pipe body 21m and is formed at the top end 22m of the steel pipe 20m. The steel pipe 20f comprises a pipe body 21f and a tubular pin 30f. The pin 30f is formed continuously with the pipe body 21f and is formed at the top end 22f of the steel pipe 20f. The pipe joint 50 comprises a tubular female buckle 40m and a tubular female buckle 40f. The female buckle 40m is inserted into the male buckle 30m and is fastened to the male buckle 30m. A box 40f is formed on the opposite side of the box 40m, into which the pin 30f is inserted and fastened. The pins 30m and 30f include external threads 31m and 31f formed on their outer circumferences, respectively. The boxes 40m and 40f include internal threads 41m and 41f formed on their inner circumferences, corresponding to the external threads 31m and 31f. The external threads 31m and 31f and the internal threads 41m and 41f are trapezoidal and tapered.

[0035] The pin 30m is pre-fastened to the box 40m at the factory and is therefore called the "mill end." The pin 30f is fastened to the box 40f in the oil well and is therefore called the "field end."

[0036] The external threads 31m and 31f are formed in a spiral shape on the outer circumference of the pins 30m and 30f, with the diameter of the spiral decreasing as it approaches the top end of the pins 30m and 30f (the pin shoulder surfaces 24m and 24f). The internal threads 41m and 41f are formed in a spiral shape on the inner circumference of the boxes 40m and 40f, with the diameter of the spiral increasing as it approaches the open ends 51m and 51f of the boxes 40m and 40f. The preferred taper ratio of the tapered thread is 6.0 to 18.0%. The taper ratio is designed to obtain an appropriate thread length based on the relationship with the wall thickness of the steel pipes 20m and 20f. The taper ratio can be constant, but it is preferred that the taper ratio of the external threads 31m and 31f decreases as it moves away from the top end of the pins 30m and 30f.

[0037] In the fastened state, at least a part of the external thread 31m, 31f and the internal thread 41m, 41f constitutes a thread seal. The part of the external thread 31m, 31f and the internal thread 41m, 41f constituting the thread seal has a length of 3 times or more the wall thickness of the steel pipe 20m, 20f in the pipe axis direction. The external thread 31m, 31f and the internal thread 41m, 41f constituting the thread seal are full threads. The longer the length of the thread seal, the more excellent the sealing performance. On the other hand, if the length of the thread seal is too long, there is a possibility that galling occurs at the time of fastening in addition to the cost and effort of thread cutting. The length of the thread seal is preferably 8 times or less the wall thickness. The threaded joint 10 has such a thread seal, but does not have a metal seal. However, it is also possible that a Teflon (registered trademark) seal ring is used in combination with the thread seal. The gap between the thread seal surfaces is filled with paint. The sealing performance is improved by the paint filling.

[0038] The part of the external thread 31m of the pin 30m and the internal thread 41m of the box 40m constituting the thread seal (hereinafter referred to as "thread seal part") has a thread diameter interference smaller than that of the part of the external thread 31f of the pin 30f and the internal thread 41f of the box 40f constituting the thread seal (thread seal part). The thread diameter interference refers to the difference between the outer diameter of the thread seal part of the pin 30m, 30f and the inner diameter of the thread seal part of the box 40m, 40f corresponding to the thread seal part. In the thread seal part, the outer diameter of the external thread 31m, 31f of the pin 30m, 30f is larger than the inner diameter of the internal thread 41m, 41f of the box 40m, 40f corresponding to the part. That is, in the entire region of the thread seal part, the thread diameter interference is a positive value.

[0039] The pin 30m further includes a pin shoulder surface 24m formed at the top end of the pin 30m. The pin 30f further includes a pin shoulder surface 24f formed at the top end of the pin 30f, which is in contact with the pin shoulder surface 24m in the fastened state. The threaded joint 10 has a so-called Pin to Pin configuration. In the threaded joint 10 of the present embodiment, usually first the pin 30m of the factory end is fastened to the box 40m. Thereafter, in the oil well, the pin 30f of the well site end is fastened to the box 40f. As a result, the pin shoulder surface 24f of the pin 30f is in contact with the pin shoulder surface 24m of the pin 30m.

[0040] The pipe body 21m includes an annular marking groove 23m. Marking groove 23m is formed on the outer circumference of the pipe body 21m. The pipe body 21f also includes an annular marking groove 23f. Marking groove 23f is formed on the outer circumference of the pipe body 21f. Marking groove 23m has a width wm that is narrower than the width wf of marking groove 23f (wm < wf). Marking grooves 23m and 23f are formed by cutting the pipe bodies 21m and 21f with a tool while rotating the steel pipes 20m and 20f on a lathe. Thus, marking grooves 23m and 23f extend circumferentially and surround the pipe bodies 21m and 21f.

[0041] More specifically, at the wellsite, the marking groove 23f is located at a distance of ±α (e.g., α = 0.75 mm) centered on the open end 51f of the female snap 40f. The width wf of the marking groove 23f is 2α (e.g., 1.5 mm). Meanwhile, at the factory, the marking groove 23m is located at a distance of +(α - β) from the open end 51m of the female snap 40m, further from the tip and -α from the tip. Here, β ≤ 3 / 4α (e.g., 0.5 mm). The width wm of the marking groove 23m is 2α - β (e.g., 1.0 mm). Therefore, the open end 51m of the female snap 40m is positioned within the width wm of the marking groove 23m.

[0042] The box snap 40m also includes a tubular recessed portion 52m. This recessed portion 52m is formed at the open end of the box snap 40m and has an inner circumferential surface that faces the outer circumferential surface of the tube body 21m and is spaced apart from the outer circumferential surface. The box snap 40f also includes a tubular recessed portion 52f. This recessed portion 52f is formed at the open end of the box snap 40f and has an inner circumferential surface that faces the outer circumferential surface of the tube body 21f and is spaced apart from the outer circumferential surface. Each recessed portion 52m, 52f has a length of at least 5 mm in the tube axial direction, for example, 15 mm.

[0043] Reference Figure 2 and Figure 3 The external threads 31m and 31f (hereinafter collectively referred to as "31") include an external thread crest surface 32, an external thread groove bottom surface 33, an external thread piercing flank surface 34, and an external thread load flank surface 35. The external thread piercing flank surface 34 is formed closer to the tip of the pin 30m and 30f. The external thread load flank surface 35 is formed farther from the tip of the pin 30m and 30f.

[0044] The external thread flank 34 has two external thread flank segments 341 and 342. External thread flank segment 341 is formed on the side farther from the pipe axis X of the steel pipe 20 and has an flank angle α1. External thread flank segment 342 is formed on the side closer to the pipe axis X and has an flank angle α2. Flank angles α1 and α2 are the angles at which the external thread flank 34 (external thread flank segments 341 and 342) are inclined relative to a plane Y perpendicular to the pipe axis X. When the flank 34 is overhanging, flank angle α1 is negative. Flank angle α2 is greater than flank angle α1 (α2>α1). Flank angle α1 is between -10 and 15 degrees. The upper limit of flank angle α1 is preferably 14 degrees, more preferably 13 degrees, and even more preferably 12 degrees. The smaller α1 is, the higher the compression resistance. The lower limit of flank angle α1 is preferably 0 degrees, more preferably 8 degrees. On the other hand, the larger α1 is, the easier the cutting process is when forming the threaded portion. The inserted tooth side angle α1 is, for example, about 10 degrees. The inserted tooth side angle α2 is 20 to 60 degrees. The upper limit of the inserted tooth side angle α2 is preferably 50 degrees, more preferably 40 degrees, and further preferably 32 degrees. The smaller α2 is, the higher the compression resistance. The lower limit of the inserted tooth side angle α2 is preferably 23 degrees, more preferably 26 degrees, and further preferably 28 degrees. The larger α2 is, the less likely it is to cause cross-threading. The inserted tooth side angle α2 is, for example, about 30 degrees. Therefore, the external thread inserted tooth side surface 34 is recessed approximately in the middle.

[0045] The height of the external thread flank section 342 (the length from the external thread groove bottom surface 33 to the boundary between the external thread flank sections 341 and 342 ) is 25 to 60% of the height of the external thread, for example, 35%.

[0046] Internal threads 41m and 41f (hereinafter collectively referred to as "41") include an internal thread top surface 42, an internal thread groove bottom surface 43, an internal thread piercing flank surface 44, and an internal thread load flank surface 45. The internal thread top surface 42 faces the external thread groove bottom surface 33. The internal thread groove bottom surface 43 faces the external thread top surface 32. The internal thread piercing flank surface 44 faces the external thread piercing flank surface 34. The internal thread load flank surface 45 faces the external thread load flank surface 35.

[0047] The internal thread insert tooth side surface 44 has two internal thread insert tooth side segments 441 and 442. The internal thread insert tooth side segment 441 is formed on the side farther from the pipe axis X and has an insert tooth side angle α1 that is the same as the insert tooth side angle α1 of the external thread insert tooth side segment 341. The internal thread insert tooth side segment 442 is formed on the side closer to the pipe axis X and has an insert tooth side angle α2 that is the same as the insert tooth side angle α2 of the external thread insert tooth side segment 342. Therefore, the internal thread insert tooth side surface 44 bulges approximately in the middle. The insert tooth side angles α1 and α2 of the external thread insert tooth side segments 341 and 342 and the insert tooth side angles α1 and α2 of the internal thread insert tooth side segments 441 and 442 do not need to be completely the same, as long as they are substantially the same. In other words, there is a case where the insert tooth side angles α1 and α2 have errors caused by cutting.

[0048] Preferably, the internal thread flank section 442 has the same height as the external thread flank section 342. This prevents the gap between the thread surfaces of the pin and box from increasing beyond its necessary size, enabling the thread seal structure to achieve excellent sealing performance. The heights of the external thread flank section 342 and the internal thread flank section 442 do not need to be exactly the same, as long as they are substantially the same. In other words, there may be variations in these heights due to machining.

[0049] External thread 31 also includes external thread rounded surfaces 36 to 39. External thread rounded surface 36 is formed at the angle between external thread top surface 32 and external thread stabbing flank surface 34. External thread rounded surface 37 is formed at the angle between external thread top surface 32 and external thread load flank surface 35. External thread rounded surface 38 is formed at the angle between external thread groove bottom surface 33 and external thread stabbing flank surface 34. External thread rounded surface 39 is formed at the angle between external thread groove bottom surface 33 and external thread load flank surface 35.

[0050] Internal thread 41 includes internal thread rounded surfaces 46 to 49. Internal thread rounded surface 46 is formed at the angle between internal thread top surface 42 and internal thread piercing flank surface 44. Internal thread rounded surface 47 is formed at the angle between internal thread top surface 42 and internal thread load flank surface 45. Internal thread rounded surface 48 is formed at the angle between internal thread groove bottom surface 43 and internal thread piercing flank surface 44. Internal thread rounded surface 49 is formed at the angle between internal thread groove bottom surface 43 and internal thread load flank surface 45.

[0051] The rounded surfaces 36 to 39 and 46 to 49 are so-called R-surfaces (round chamfered surfaces) and have a predetermined curvature radius of 0.1 to 1.2 mm, preferably 0.3 to 0.8 mm.

[0052] The external thread load flank 35 has a load flank angle β. The load flank angle β is the angle at which the external thread load flank 35 is inclined relative to a plane Y perpendicular to the pipe axis X. When the load flank 35 is overhanging, the load flank angle β is negative. The load flank angle β is -10 to 3 degrees, preferably -5 to -1 degrees, for example, approximately -3 degrees. The internal thread load flank 45 has a load flank angle β that is the same as the load flank angle β of the external thread load flank 35. The load flank angle β of the external thread load flank 35 and the load flank angle β of the internal thread load flank 45 do not have to be exactly the same, as long as they are substantially the same. In other words, there is a case where the load flank angle β has an error caused by cutting.

[0053] The external thread top surface 32 , the external thread groove bottom surface 33 , the internal thread top surface 42 , and the internal thread groove bottom surface 43 are formed parallel to the pipe axis X. Specifically, a line extending from the surfaces 32 , 33 , 42 , and 43 in a longitudinal section including the pipe axis X is parallel to the pipe axis X.

[0054] like Figure 3 As shown, the male thread flank surface 34 and the female thread flank surface 44 have a gap of 60 to 120 μm between them in the tightened state. Furthermore, the male thread top surface 32 and the female thread groove bottom surface 43 have a gap of 0 to 50 μm between them in the tightened state. The male thread groove bottom surface 33 and the female thread top surface 42 also have a gap of 0 to 50 μm between them in the tightened state.

[0055] Hereinafter, an example of a method for manufacturing the threaded joint 10 , that is, a method for fastening two steel pipes 20 m and 20 f using the pipe joint 50 will be described.

[0056] At the factory, the pin 30m at the factory end of the steel pipe 20m is screwed into the box 40m. The pin 30m is screwed in such a way that the open end 51m of the box 40m fits within the width wm of the marking groove 23m. This secures the steel pipe 20m at the factory end to the pipe joint 50. The steel pipe 20m at the factory end and the pipe joint 50 constitute a pipe assembly, which is then transported from the factory to the oil well.

[0057] Next, in the oil well, the pin 30f at the wellsite end of the steel pipe 20f is screwed into the box 40f. At this point, the pipe joint 50 is not held, and the pin 30f is screwed in while holding both the steel pipe 20m and the steel pipe 20f. Furthermore, the pin 30f is screwed in so that the open end 51f of the box 40f fits within the width wf of the marking groove 23f. This secures the steel pipe 20f at the wellsite end to the pipe joint 50. In this way, the two steel pipes 20m and 20f are connected to each other using the pipe joint 50, resulting in the production of the threaded joint 10.

[0058] When screwing a pin 30m at the factory end of a steel pipe 20m into a box 40m, the torque gradually increases as the screwing progresses, but there is no sudden increase in torque. Therefore, unlike screwing at the well site (described later), it is difficult to determine the proper tightening position based on the torque changes. However, the threaded joint 10, with its marking groove 23m, allows the factory end to visually confirm the positional relationship between the marking groove 23m and the open end 51m of the box 40m, allowing the steel pipe 20m to be tightened to the pipe joint 50 in the desired position.

[0059] When the steel pipe 20f is screwed in at the well site, the pin shoulder surface 24f of the pin 30f contacts the pin shoulder surface 24m at the factory. At this point, the tightening torque increases dramatically. Therefore, by screwing in the steel pipe 20f while monitoring this torque change, the steel pipe 20f can be tightened to the pipe joint 50 with the appropriate torque. However, to ensure this, it is necessary to monitor the torque increase after each tightening operation.

[0060] In contrast, if marking grooves 23f are also pre-formed in the steel pipe 20f, the positional relationship between the open end 51f of the box snap 40f and the marking grooves 23f can be visually confirmed after the steel pipe 20f is tightened to a predetermined, appropriate torque. This allows the steel pipe 20f to be quickly and appropriately tightened to the pipe joint 50, even without strictly monitoring torque changes as described above.

[0061] Whether the steel pipe 20f can be properly tightened depends primarily on whether the previously tightened steel pipe 20m was properly tightened. Therefore, if the groove width wm of the marking groove 23m at the factory end is previously narrowed compared to the groove width wf of the marking groove 23f at the well site end, the tightening of the steel pipe 20m at the factory end can be more strictly managed.

[0062] As a result of the above, tightening can be performed without strictly monitoring the tightening torque at an oil well site. Therefore, there is no need for equipment for monitoring the tightening torque, and the operation is easy and the efficiency is improved.

[0063] Furthermore, recessed portions 52m and 52f are formed in the open ends of the boxes 40m and 40f. Therefore, even if paint seeps out from the gaps between the threaded sealing surfaces, it accumulates in the gaps between the recessed portions 52m and 52f and the pipe bodies 21m and 21f. Consequently, paint does not overflow from the open ends 51m and 51f of the pipe joint 50 and reach the marking grooves 23m and 23f. As a result, the positional relationship between the marking grooves 23m and 23f and the open ends 51m and 51f can be visually checked at all times.

[0064] Furthermore, the thread diameter interference at the wellsite end is smaller than that at the factory end. Therefore, the contact surface pressure between the pin 30f and the box 40f during the screwing process of the steel pipe 20f, until the pin shoulder surface 24f contacts the pin shoulder surface 24m, is smaller than the contact surface pressure between the pin 30m and the box 40m. Consequently, the rotation at the factory end caused by co-rotation during tightening at the wellsite end can be reduced to zero or below the permissible limit. "Co-rotation" refers to the phenomenon whereby, when the steel pipe 20f at the wellsite end is rotated to screw the pin 30f into the box 40f, the pipe joint 50 rotates along with the steel pipe 20f, that is, rotates relative to the steel pipe 20m at the factory end. To prevent seizure, the thread diameter interference at the factory end is preferably below a predetermined value. To improve the sealing performance of the thread seal, the thread diameter interference at the wellsite end is preferably above a predetermined value.

[0065] Furthermore, the factory-side pin 30m and box 40m include zones Z1 to Z3, sequentially from the pin 30m's tip. The factory-side external thread 31m of the pin 30m and the internal thread 41m of the box 40m may include both a complete thread and an incomplete thread formed between the pipe body 21m and the complete thread. The complete thread is formed in zone Z2. The incomplete thread is formed in zones Z1 and Z3. The factory-side pin 30m and box 40m may also be bonded together in the incomplete thread in zone Z3 when tightened. Specifically, the pin 30m and box 40m may be bonded together in all or part of the incomplete thread in zone Z3. Furthermore, the pin 30m and box 40m may be bonded together in the part of the complete thread adjacent to the incomplete thread. When the factory-side pin 30m and box 40m are bonded together, the factory-side rotation caused by co-rotation during the screwing of the steel pipe 20f at the wellsite can be reduced to zero or below the permissible amount.

[0066] During factory-side tightening, adhesive is pre-applied to area Z3, where the pin 30m and box 40m are to be bonded, and paint is pre-applied to area Z2. This prevents seizures and ensures thread sealing performance. Adhesive can be applied to the entire area Z3 or to a portion of it. Alternatively, adhesive can be applied to a portion of area Z2 adjacent to area Z3, allowing it to overflow. Furthermore, adhesive can be applied only to the external thread 31m, only to the internal thread 41m, or to both.

[0067] As mentioned above, although embodiment was described, this invention is not limited to the said embodiment, Various changes are possible as long as they do not deviate from the summary.

[0068] Description of Reference Numerals

[0069] 10. Threaded joint; 20m, 20f, steel pipe; 21m, 21f, pipe body; 23m, 23f, marking groove; 24m, 24f, shoulder surface of pin; 30m, 30f, pin; 31, 31m, 31f, external thread; 32, top surface of external thread tooth; 33, bottom surface of external thread groove; 34, side surface of external thread insertion tooth; 341, 342, side section of external thread insertion tooth; 35, load side surface of external thread tooth; 40m, 40f, box; 41, 41m, 41f, internal thread; 42, top surface of internal thread tooth; 43, bottom surface of internal thread groove; 44, side surface of internal thread insertion tooth; 441, 442, side section of internal thread insertion tooth; 45, load side surface of internal thread tooth; 50, pipe joint; 51m, 51f, open end; 52m, 52f, recess.

Claims

1. A threaded joint, wherein: The threaded joint includes: No. 1 steel pipe; a second steel pipe; and a pipe joint for connecting the first steel pipe and the second steel pipe to each other, The first steel pipe comprises: a first tube body; and A tubular first male buckle is formed continuously with the first pipe body and is formed at the top end of the first steel pipe. The second steel pipe comprises: a second tube body; and A tubular second male buckle is formed continuously with the second pipe body and is formed at the top end of the second steel pipe. The pipe joint comprises: a tubular first female buckle into which the first male buckle is inserted and fastened with the first male buckle; and A tubular second female buckle is formed on the opposite side of the first female buckle, for the second male buckle to be inserted and fastened with the second male buckle. The first male buckle and the second male buckle each include an external thread formed on an outer circumference of the male buckle, The first female buckle and the second female buckle each include an internal thread corresponding to the external thread and formed on the inner circumference of the female buckle, The external thread and the internal thread are trapezoidal threads and tapered threads, In the tightened state, at least a portion of the external thread and the internal thread forms a thread seal. The external thread comprises: Top surface of external thread; Bottom surface of external thread groove; an external thread insertion flank formed on a side closer to the top end of the pin; and The load-bearing flank of the external thread is formed on the side farther from the top of the pin. The external thread insert tooth side has: a first external thread flank section, formed on a side farther from the pipe axis of the steel pipe, having an flank angle of -10 to 15 degrees; and The second external thread insert flank section is formed on the side closer to the pipe axis and has an insert flank angle of 20 to 60 degrees. The second external thread insert flank section has a height of 20 to 60% of the height of the external thread. The internal thread comprises: an internal thread top surface, which is opposite to the external thread groove bottom surface; a bottom surface of the internal thread groove, which is opposite to the top surface of the external thread; an internal thread insertion tooth side surface, which is opposite to the external thread insertion tooth side surface; and The internal thread load flank is opposite to the external thread load flank. The internal thread insert tooth side has: a first internal thread tangent flank section, formed on a side farther from the pipe axis and having an tangent flank angle identical to that of the first external thread tangent flank section; and The second internal thread flank section is formed on a side closer to the pipe axis and has an immersion flank angle that is the same as that of the second external thread flank section. The first male buckle further includes a first male buckle shoulder surface formed at the top end of the first male buckle. The second male buckle further includes a second male buckle shoulder surface formed at the top end of the second male buckle and in contact with the first male buckle shoulder surface in a tightened state. The first pipe body includes an annular first marking groove formed on the outer periphery of the first pipe body. The external thread of the first pin and the internal thread of the first box include a complete thread and an incomplete thread formed between the first pipe body and the complete thread. The first male thread and the first female thread are bonded to the entire or a portion of the incomplete thread in a tightened state.

2. The threaded joint according to claim 1, wherein The first and second steel pipes have outer diameters exceeding 16 inches.

3. A pipe assembly, wherein: The tube assembly includes: First steel pipe; and a pipe joint for connecting the first steel pipe and the second steel pipe to each other, The first steel pipe comprises: a first tube body; and A tubular first male buckle is formed continuously with the first pipe body and is formed at the top end of the first steel pipe. The pipe joint comprises: a tubular first female buckle into which the first male buckle is inserted and fastened with the first male buckle; and A tubular second female buckle is formed on the opposite side of the first female buckle, into which the second male buckle of the second steel pipe is inserted and fastened. The first pin includes an external thread formed on an outer circumference of the pin, The first female buckle includes an internal thread corresponding to the external thread and formed on the inner periphery of the female buckle, The external thread and the internal thread are trapezoidal threads and tapered threads, In the tightened state, at least a portion of the external thread and the internal thread forms a thread seal. The external thread comprises: Top surface of external thread; Bottom surface of external thread groove; an external thread insertion flank formed on a side closer to the top end of the pin; and The load-bearing flank of the external thread is formed on the side farther from the top of the pin. The external thread insert tooth side has: a first external thread flank section, formed on a side farther from the pipe axis of the steel pipe, having an flank angle of -10 to 15 degrees; and The second external thread insert flank section is formed on the side closer to the pipe axis and has an insert flank angle of 20 to 60 degrees. The second external thread insert flank section has a height of 20 to 60% of the height of the external thread. The internal thread comprises: an internal thread top surface, which is opposite to the external thread groove bottom surface; a bottom surface of the internal thread groove, which is opposite to the top surface of the external thread; an internal thread insertion tooth side surface, which is opposite to the external thread insertion tooth side surface; and The internal thread load flank is opposite to the external thread load flank. The internal thread insert tooth side has: a first internal thread tangent flank section, formed on a side farther from the pipe axis and having an tangent flank angle identical to that of the first external thread tangent flank section; and The second internal thread flank section is formed on a side closer to the pipe axis and has an immersion flank angle that is the same as that of the second external thread flank section. The first male buckle further includes a first male buckle shoulder surface formed at the top end of the first male buckle. The first pipe body includes an annular first marking groove formed on the outer periphery of the first pipe body. The opening end of the first female buckle is positioned within the width of the first marking groove. The external thread of the first pin and the internal thread of the first box include a complete thread and an incomplete thread formed between the first pipe body and the complete thread. The first male thread and the first female thread are bonded to the entire or a portion of the incomplete thread in a tightened state.

4. The tube assembly according to claim 3, wherein: The first steel pipe has an outer diameter exceeding 16 inches.

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