A pin and box coupling

Abstract

The application discloses a partial round thread joint, which comprises a male end with external thread and a female end with internal thread which are connected by mutual adaptation and engagement, the tooth top between the load bearing surface and the guide surface of the external thread is a tooth top fillet, the tooth bottom between the load bearing surface and the guide surface of the external thread is a tooth bottom fillet, and the respective angle bisectors of the tooth top fillet and the tooth bottom fillet have a non-zero included angle A with the radial direction. The partial round thread joint is convenient to process and is not easy to be unbuckled, has high tensile resistance and high air tightness, and can be conveniently buckled and improve the buckling efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to a steel pipe joint, in particular to a threaded joint. BACKGROUND

[0002] In the field of drilling and developing subterranean resources such as oil and gas, it is often necessary to drill the formation with drill pipes, and then to use casing to isolate the formation from the fluid in the pipe, and then to transport the oil and gas through the tubing. Drill pipes, casings and tubing are often connected by threaded connections, and the steel pipes are connected one by one to be lowered to the bottom of the earth, which is several kilometers deep, and each pipe is about 10 meters long.

[0003] In the API 5B standard, it is agreed that the tubing joint should be able to withstand 4 make-up and break-out operations without thread galling, and the API 5C5 standard test procedure provides that the tubing should be able to withstand 10 make-up and 9 break-out operations without thread galling, and the casing should be able to withstand 3 make-up and 2 break-out operations without thread galling. However, the tubing and casing used in the oilfield site often have thread galling after 1 make-up and break-out operation due to the poor working conditions, environmental sand, operating pipe wrenches, over-torque and other reasons. In addition, after the pipe string is used for a period of time, it is often taken out and placed on the ground well site due to various reasons, and the inner and outer surfaces of the pipe are often severely corroded. The thread surface often cannot be used again due to thread galling, corrosion, bumping and other reasons of improper protection, and must be recovered, cleaned and processed with new threads before use.

[0004] The processing plant for recycling and processing may be less precise and less technically capable than the original manufacturing plant, and it is difficult to process high-performance gas seal premium threaded joints, and can only process conventional threaded joints specified in the API standard, such as plain-end pipe round threaded tubing NU, external upset round threaded tubing EU, short round threaded casing SC, long round threaded casing LC and buttress threaded casing BC. The external upset EU joint is a kind of joint in which the pipe end is heated and upset, and the threads are processed again. However, the upset end needs to be cut off after the threads are damaged, and the threads are processed again at this time, and the length of the upset end cannot meet the processing requirements, and can only be processed into NU joints without upset. However, the round threaded NU joint has poor anti-slip performance, and the joint tensile strength is only 60% to 80% of the pipe body. When the tensile force increases, the joint will be tripped.

[0005] The types of recycled pipes are diverse, some are high-alloy steels with high prices, some are low-alloy steels, and some are ordinary carbon steels; the corrosion degrees of these pipes are different, some are not corroded, some are slightly corroded, and some are severely corroded; the original threaded joints are different, some are pipe end upsets, some are gas seal premium threads, and some are plain-end pipes. However, the API ordinary thread has low performance and cannot meet the use requirements, and part of the recycled pipes still hope to be processed into higher performance joint products under the existing processing equipment conditions.

[0006] Based on this, in order to improve the performance of the threaded joint processed by the secondary recycled pipe, while considering the advantages and disadvantages of the existing round thread and the buttress thread, the present application designs a deflective round thread joint, which is convenient to process and is not easy to be unbuckled, and has high tensile resistance and high air tightness.

[0007] The deflective round thread joint can greatly facilitate the make-up and improve the make-up efficiency, and has excellent performance and very wide applicability, and can be effectively applied to harsh working conditions such as oil field exploitation, is convenient for subsequent repeated repair, and has good popularization prospect and application value. SUMMARY

[0008] One of the purposes of the present application is to provide a deflective round thread joint, which is convenient to process and is not easy to be unbuckled, and has high tensile resistance and high air tightness; the deflective round thread joint can greatly facilitate the make-up and improve the make-up efficiency.

[0009] The deflective round thread joint has excellent performance and very wide applicability, and can be effectively applied to harsh working conditions such as oil field exploitation, is convenient for subsequent repeated repair, and has good popularization prospect and application value.

[0010] In order to achieve the above purpose, the present application provides a deflective round thread joint, which comprises a male end with an external thread and a female end with an internal thread which are connected by mutual adaptation and engagement, the crest between the load bearing surface and the guide surface of the external thread is a crest fillet, the root between the load bearing surface and the guide surface of the external thread is a root fillet, and the respective angle bisectors of the crest fillet and the root fillet have a non-zero included angle A with the radial direction.

[0011] In the prior art, the round thread specified in the API oil casing standard is 10 teeth and 8 teeth per inch, and the buttress thread is 5 teeth per inch. The round thread is easy to process, and after being screwed, only the gaps at the crest and root fillets are present, and after being filled with thread grease, the sealing performance is good. However, when the round thread is made up, the radial interference is large, and the thread is easy to stick, and batch sticking is easy to occur in repeatedly used oil pipes; and the anti-unbuckling performance is poor, and the joint tensile resistance is only 60% to 80% of the pipe body, when the tensile force increases, the joint will be unbuckled, the pipe string will fall into the well, and production accidents will occur, so the round thread is difficult to use in deep wells and high pressure wells with more severe well conditions. The buttress thread has high tensile resistance, but the buttress thread has a gap of 0.05 to 0.20 mm in the axial tooth width except for the four fillets, and these gaps make the sealing performance of the buttress thread worse than that of the round thread.

[0012] Therefore, considering that the round thread and the buttress thread each has advantages and disadvantages, the application combines the advantages of the two, and a new buttress round thread joint is invented.

[0013] In the application, through reasonable design of the joint structure, the buttress round thread joint can obtain higher tensile resistance and higher air tightness; the buttress round thread joint can greatly facilitate the screwing of the male end and the female end, improve the screwing efficiency, and the male end and the female end are not easy to unscrew.

[0014] Further, in the buttress round thread joint, the included angle B between the load bearing surface and the guide surface satisfies: 50°≤B≤70°.

[0015] Further, in the buttress round thread joint, the included angle B between the load bearing surface and the guide surface satisfies: 50°≤B≤70°.

[0016] Further, in the buttress round thread joint, it satisfies:

[0017]

[0018] wherein H represents the radial distance between the virtual intersection point of the load bearing surface and the guide surface at the tooth top and the virtual intersection point of the load bearing surface and the guide surface at the tooth bottom, p represents the pitch, and γ represents the half cone angle, which is half of the thread taper.

[0019] Further, in the buttress round thread joint, it satisfies:

[0020]

[0021] wherein S cs represents the radial distance between the highest point of the tooth top rounding portion and the virtual intersection point of the load bearing surface and the guide surface at the tooth top, R cs is the rounding radius of the tooth top rounding portion, γ represents the half cone angle, which is half of the thread taper.

[0022] Further, in the buttress round thread joint, it satisfies:

[0023]

[0024] wherein S rs represents the radial distance between the lowest point of the tooth bottom rounding portion and the virtual intersection point of the load bearing surface and the guide surface at the tooth bottom, R rs is the rounding radius of the tooth bottom rounding portion, γ represents the half cone angle, which is half of the thread taper.

[0025] Further, in the pin round thread joint, the following conditions are met:

[0026]

[0027] wherein h s represents the radial distance between the lowest point of the root fillet and the virtual intersection point of the load face and the guide face at the root; rs represents the radial distance between the lowest point of the root fillet and the virtual intersection point of the load face and the guide face at the root; rs represents the radial distance between the lowest point of the root fillet and the virtual intersection point of the load face and the guide face at the root.

[0028] Further, in the pin round thread joint, when the pin end and the box end are connected, there is a gap between the crest fillet of the pin thread and the root fillet of the box thread, and there is a gap between the root fillet of the pin thread and the crest fillet of the box thread.

[0029] In the above technical solution of the present application, the pin round thread joint has a small gap at the crest fillet and the root fillet position after the pin thread of the pin end and the box thread of the box end are matched, and the gap is intentionally designed to be small. Because when the pin round thread joint is screwed tightly, the small gap can be filled with thread grease, thereby effectively improving the sealing performance of the joint.

[0030] Further, in the pin round thread joint, the pin end and the box end are both pipe fittings; or the box end is a coupling, and the pin end is a pipe fitting.

[0031] Further, in the pin round thread joint, the pipe fitting or the coupling satisfies the following conditions:

[0032] When the outer diameter is 60.32-114.30 mm, the tooth height is 1.20 mm, the pitch is 3.175 mm, and the number of teeth per inch is 8;

[0033] When the outer diameter is 127.00-219.08, the tooth height is 1.58 mm, the pitch is 4.23 mm, and the number of teeth per inch is 6;

[0034] When the outer diameter is 244.48-339.72, the tooth height is 2.00 mm, the pitch is 5.08 mm, and the number of teeth per inch is 5.

[0035] In the above technical solution of the present application, for different outer diameter steel pipes, the pin round thread joint is designed with three different thread numbers, and appropriate outer diameter, tooth height and pitch are selected to improve the applicability. As can be seen, the pin round thread joint has very wide applicability, and can be applied to large diameter steel pipes, and has good application prospect.

[0036] Therefore, in the present application, compared with the prior art, the pin round thread joint has the following advantages and beneficial effects:

[0037] Unlike the prior art, the present application starts from the joint structure design and provides a new pin round thread joint which is convenient to process and not easy to be unthreaded. The pin round thread joint not only has high tensile strength, but also has high air tightness. The pin round thread joint can greatly facilitate the make-up and improve the make-up efficiency.

[0038] The pin round thread joint has excellent performance and very wide applicability, and can be effectively applied to harsh working conditions such as oil field exploitation. After failure, it is convenient for subsequent repeated repair, and has good popularization prospect and application value. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The tooth profile of the pin round thread joint in one embodiment is schematically shown.

[0040] Figure 2 The tooth profile of the pin round thread joint in one embodiment is schematically shown.

[0041] Figure 3 The structure schematic diagram of the pin round thread joint in one embodiment is schematically shown.

[0042] Figure 4 The joint matching profile of the pin round thread joint in one embodiment is schematically shown.

[0043] Figure 5 The profile of the box end coupling of the pin round thread joint in one embodiment is schematically shown.

[0044] Figure 6 The profile of the pin end pipe fitting of the pin round thread joint in one embodiment is schematically shown. DETAILED DESCRIPTION

[0045] The bias round thread joint described in the present application will be further explained and described in the following with specific examples and the accompanying drawings, however, the explanation and description does not constitute undue limitation on the technical solution of the present application.

[0046] In the present application, the bias round thread joint described in the present application can include a male end with external thread and a female end with internal thread. Wherein, the male end and the female end of the bias round thread joint described in the present application can be connected with each other in a matching engagement, which has wide applicability, not only has higher tensile performance, but also has higher air tightness.

[0047] Figure 1 The tooth profile of the external thread of the male end of the bias round thread joint described in the present application in one embodiment is schematically shown.

[0048] As shown in Figure 1 In the present application, the crest of the bias round thread joint described in the present application between the load bearing surface a and the guide surface b of the external thread X of the male end is a crest fillet, and the root between the load bearing surface a and the guide surface b of the external thread is a root fillet. Wherein, the included angle between the load bearing surface a and the guide surface b can be set as an included angle B; the respective angle bisector c of the crest fillet and the root fillet both have a non-zero included angle A with the radial direction.

[0049] It should be noted that in the present application, the degree of the included angle B can be controlled to meet: 50°≤B≤70°, and the included angle α of the guide surface b of the external thread with the radial direction can be set as (B / 2+A), and the included angle β of the load bearing surface a of the external thread X with the radial direction can be set as (B / 2-A).

[0050] According to the test, the friction coefficient of the thread grease is about μ=0.1, and according to the friction angle formula arctanμ=5.71, then -5.71≤β≤5.71, and thus the degree of the included angle A can meet: B / 2-5.71≤A≤B / 2+5.71.

[0051] Referring to Figure 1 As can be seen, in the present embodiment, the crest fillet and the root fillet of the bias round thread joint described in the present application can both be 60°, that is, the included angle B between the load bearing surface a and the guide surface b can be 60°; accordingly, the included angle A of the respective angle bisector c of the crest fillet and the root fillet with the radial direction can both be preferably 30°; thus, the included angle α of the guide surface b of the external thread X with the radial direction can be 60°, and the included angle β of the load bearing surface a of the external thread X with the radial direction can be 0°.

[0052] It should be noted that in the present embodiment, the thread taper of the bias round thread joint described in the present application can be 1:16, and the half taper angle γ thereof meets tanγ=1 / 32.

[0053] Further reference is made to Figure 1 It can be seen that, in the present embodiment, the addendum corner is tangent to the load flank a and the guide flank b, whereby Rcs can be set as the corner radius of the addendum corner; correspondingly, the dedendum corner is also tangent to the load flank a and the guide flank b on both sides, whereby Rrs can be set as the corner radius of the dedendum corner.

[0054] Thus, for the external thread X of the partial round thread joint according to the present application, the following is satisfied:

[0055]

[0056] wherein H represents the radial distance between the virtual intersection of the load flank a and the guide flank b at the addendum and the virtual intersection of the load flank a and the guide flank b at the dedendum, p represents the pitch, and γ represents the half-cone angle, which is half of the thread taper.

[0057]

[0058] wherein S cs represents the radial distance between the highest point of the addendum corner and the virtual intersection of the load flank a and the guide flank b at the addendum, R cs is the corner radius of the addendum corner, and γ represents the half-cone angle, which is half of the thread taper.

[0059]

[0060] wherein S rs represents the radial distance between the lowest point of the dedendum corner and the virtual intersection of the load flank a and the guide flank b at the dedendum, R rs is the corner radius of the dedendum corner, and γ represents the half-cone angle, which is half of the thread taper.

[0061]

[0062] wherein h s represents the thread height, H represents the radial distance between the virtual intersection of the load flank a and the guide flank b at the addendum and the virtual intersection of the load flank a and the guide flank b at the dedendum, S rs represents the radial distance between the lowest point of the dedendum corner and the virtual intersection of the load flank a and the guide flank b at the dedendum, and S rs represents the radial distance between the lowest point of the dedendum corner and the virtual intersection of the load flank a and the guide flank b at the dedendum.

[0063] Figure 2 The tooth profile of the internal thread of the female end of the partial round thread joint according to the present application in one embodiment is schematically shown.

[0064] As Figure 2As shown, Figure 2 The female end internal thread Y can be connected with Figure 1 The male end external thread X and the female end internal thread Y are adapted to each other, thus, in fact, the structure of the female end internal thread Y is the same as that of the male end external thread X, and there is no substantial difference between them.

[0065] As described above for the male end external thread X, the same applies to Figure 2 The corner radius R of the tooth tip of the female end internal thread Y cn satisfies: R cs =R cn ; the corner radius R of the tooth root of the female end internal thread Y rn satisfies: R rs =R rn ; the radial distance S between the highest point of the tooth tip and the virtual intersection point of the load surface a and the guide surface b at the tooth tip of the female end internal thread Y cn satisfies: S cs =S cn ; the radial distance S between the lowest point of the tooth root and the virtual intersection point of the load surface a and the guide surface b at the tooth root of the female end internal thread Y rn satisfies: S rs =S rn ; the tooth height h of the female end internal thread Y n satisfies: h s =h n . In addition, in the partial circular thread joint of the present application, it also satisfies: R rs =R rn <R cs =R cn .

[0066] Figure 3 The structure of the internal and external thread of the partial circular thread joint of the present application is shown schematically.

[0067] As shown, Figure 3 in the present embodiment, the partial circular thread joint of the present application has small gaps at the tooth tip and tooth root corner positions after the external thread X and the internal thread Y are connected, and the gaps are intentionally designed to be small. This is because, when the partial circular thread joint of the present application is screwed tightly, the small gaps can be filled with thread grease, thereby effectively improving the sealing performance of the joint.

[0068] It should be noted that the male end and the female end of the partial circular thread joint of the present application can be selected as pipe fittings. Of course, in some embodiments, the female end of the partial circular thread joint can be selected as a coupling, and the male end can be selected as a pipe fitting.

[0069] In the present application, the outer diameter of the coupling or pipe fitting of the pin end and the box end can be preferably controlled between 114.3mm and 508mm. In the prior art, the casing box thread in the API standard is 8 teeth per inch, and the tooth height is 1.81mm. For large outer diameter casing, the pitch is too small, and belongs to fine thread. Large diameter casing is not only low in efficiency during processing, but also low in efficiency during make-up on the oilfield site, and the thread is easy to be damaged.

[0070] Therefore, in the present application, three different thread numbers are designed for different outer diameter steel pipes: (1) when the number of teeth per inch is 8 and the tooth height is 1.20mm, it is suitable for the coupling or pipe fitting with an outer diameter of 60.32mm to 114.30mm; (2) when the number of teeth per inch is 6 and the tooth height is 1.58mm, it is suitable for the coupling or pipe fitting with an outer diameter of 127.00mm to 219.08mm; (3) when the number of teeth per inch is 5 and the tooth height is 2.00mm, it is suitable for the coupling or pipe fitting with an outer diameter of 244.48mm to 339.72mm. The specific dimensions of the above three types of couplings or pipe fittings can be referred to Table 1 below.

[0071] Table 1.

[0072]

[0073] Figure 4 The coupling matching profile of the pin end and the box end of the pin and box coupling according to the present application is schematically shown.

[0074] As shown in Figure 4 , in the present embodiment, the pin and box coupling according to the present application can be composed of one coupling 1 as the box end and two pipe fittings 2 as the pin end. The pipe fittings 2 can be processed on both ends of the steel pipe with an outer diameter of 60.32mm to 339.72mm, and the pipe fittings 2 are all processed with external threads, and the coupling 1 is processed with internal threads on both ends.

[0075] In the present application, at a position with a certain length from both sides of the coupling 1 as the box end, a triangular stamp mark 25 can be provided, and the height of the triangular stamp mark 25 can be controlled between 6.35mm and 9.52mm. When the cross section of the coupling 1 covers between the bottom side and the vertex of the triangular stamp mark 25, the make-up is in place.

[0076] Figure 5 The cross section of the coupling 1 as the box end of the pin and box coupling according to the present application is schematically shown.

[0077] As shown in Figure 5As shown, in this embodiment, the coupling 1 of the female end of the off-round threaded connector of the present invention has internal threads 11 processed at both ends, and internal chamfers 12 are processed at both ends of the coupling 1. The internal chamfer 12 can preferably be selected as 65°. In order to prevent the threads at both ends from being connected by misaligned teeth, the thread processing position at both ends of the coupling 1 is adjusted just right, so that the middle thread of the coupling 1 can be smoothly transitioned.

[0078] Figure 6 A schematic cross-sectional view of the male end of the off-center threaded connector according to one embodiment of the present invention is shown.

[0079] like Figure 6 As shown, in this embodiment, the male end of the pipe fitting 2 of the off-center threaded connector of the present invention has an external thread machined on the pipe end. Except for the external thread, the rest is a straight section 24. The external thread can be composed of a complete thread 21 and an incomplete thread 22. Correspondingly, an external chamfer 23 is machined on the male end of the pipe fitting 2. The external chamfer 23 can preferably be selected as 60°.

[0080] The off-center threaded connector described in this invention can be repaired and reused after failure. Considering that the surface of the fitting 2 may have varying degrees of corrosion during the secondary repair, the surface of the fitting 2 needs to be machined and stripped. The stripping length should be greater than the position of the triangular steel stamp mark 25. The stripped outer diameter should be adjusted on-site according to the degree of corrosion of the fitting 2, and should be equal to or 1mm smaller than the actual outer diameter of the fitting 2. Because the actual outer diameter of the fitting 2 is usually slightly larger than the nominal outer diameter, if the pipe is new or only slightly corroded, the nominal outer diameter of the fitting 2 should be preferentially selected for the stripped outer diameter.

[0081] To further illustrate the feasibility of the off-round threaded connector described in this invention, specific embodiments are used for implementation description, and the dimensions of the off-round threaded connectors in the relevant embodiments are shown in Table 2 below.

[0082] Table 2.

[0083]

[0084]

[0085] As shown in Table 2, for tubing (60.32–114.30 mm) and casing (127.00 mm–339.72 mm) with different outer diameters, this invention designs off-round threads with three different tooth heights, pitches, and number of teeth. In Table 2, the coupling is the female end, and the casing or tubing is the male end.

[0086] Therefore, the thread of the pin-up round thread joint has the advantages of easy processing, high air tightness of the API round thread, and high tensile resistance of the pin-up round thread, and does not "trip" under high tensile resistance.

[0087] Meanwhile, in some preferred embodiments, the included angle B between the bearing surface and the guide surface can be set to 60° to obtain a large guide surface, which can make the make-up more convenient.

[0088] In addition, the pin-up round thread joint has higher processing efficiency and make-up efficiency, and the coarse thread is less likely to stick than the fine thread.

[0089] In summary, unlike the prior art, the present application provides a new pin-up round thread joint from the joint structure design, which is convenient to process and less likely to trip, has high tensile resistance and high air tightness, and can greatly facilitate the make-up and improve the make-up efficiency.

[0090] The pin-up round thread joint has excellent performance and wide applicability, can be effectively applied to harsh working conditions such as oil field exploitation, is convenient for subsequent repeated repair after failure, and has good popularization prospect and application value.

[0091] It should be noted that the combination of the technical features in the case is not limited to the combination mode or the combination mode described in the specific embodiments of the claims, and all the technical features described in the case can be freely combined or combined in any way, unless contradictory to each other.

[0092] It should also be noted that the above-mentioned embodiments are only specific embodiments of the present application. Obviously, the present application is not limited to the above-mentioned embodiments, and similar changes or modifications can be easily obtained from the disclosure of the present application, and should all belong to the protection scope of the present application.

Claims

1. A pin and box connection comprising a pin having external threads and a box having internal threads connected in mating engagement with each other, characterized in that, The crest between the load flank and the guide flank of the external thread is a crest round corner, the root between the load flank and the guide flank of the external thread is a root round corner, and the respective angular bisectors of the crest round corner and the root round corner have a non-zero included angle A with the radial direction; The bias round thread joint satisfies: where H represents a radial distance between a virtual intersection of the load face and the guide face at the addendum and a virtual intersection of the load face and the guide face at the dedendum, p where p represents the pitch, and γ represents the half-conical angle, which is half of the thread taper; where S cs represents the radial distance between the highest point of the addendum corner and the virtual intersection point of the load flank and the guide flank at the addendum, R cs is the rounding radius of the addendum corner, and γ represents the half-cone angle, which is half of the thread taper; where S rs represents the radial distance between the lowest point of the tooth root fillet and the virtual intersection of the load flank and the guide flank at the tooth root, R rs is the radius of the tooth root fillet, and γ represents the half-cone angle, which is half of the thread taper; wherein, h s represents the radial distance between the virtual intersection of the load and guide faces at the addendum and the virtual intersection of the load and guide faces at the dedendum, S rs represents the radial distance between the lowest point of the dedendum fillet and the virtual intersection of the load and guide faces at the dedendum, S rs represents the radial distance between the lowest point of the dedendum fillet and the virtual intersection of the load and guide faces at the dedendum.

2. A pin and box threaded connection as defined in claim 1 wherein, The included angle B between the load flank and the guide flank satisfies: 50°≤B≤70°.

3. A pin and box threaded connection as defined in claim 1 wherein, The included angle B between the load flank and the guide flank satisfies: B / 2-5.71≤A≤B / 2+5.

71.

4. A pin and box threaded connection as defined in claim 1 wherein, When the male end and the female end are engaged, the crest round corner of the external thread and the root round corner of the internal thread have a gap, and the root round corner of the external thread and the crest round corner of the internal thread have a gap.

5. A pin and box threaded connection as defined in claim 1 wherein, The male end and the female end are both pipe fittings; or the female end is a coupling, and the male end is a pipe fitting.

6. A pin and box threaded connection as defined in claim 1 wherein, The pipe fitting or the coupling satisfies: When the outer diameter is 60.32-114.30 mm, the tooth height is 1.20 mm, the pitch is 3.175 mm, and the number of teeth per inch is 8; When the outer diameter is 127.00-219.08 mm, the tooth height is 1.58 mm, the pitch is 4.23 mm, and the number of teeth per inch is 6; When the outer diameter is 244.48-339.72 mm, the tooth height is 2.00 mm, the pitch is 5.08 mm, and the number of teeth per inch is 5.

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