Internal thread joint

Abstract

The internal thread joint comprises an API round thread body, the API round thread body comprises a first internal thread section, a conical surface section and a second internal thread section, and the first internal thread section, the conical surface section and the second internal thread section are sequentially arranged from the end of the API round thread body to the bottom of the API round thread body; according to the structure, the thread forms of the threads are cut in the positions where the API round thread body is evenly stressed and small, the influence on the connection strength of the threads is not large, stress concentration of the threads is relieved, machining is convenient, operation is easy, meanwhile, due to the fact that the thread forms are reduced, the thread screwing-on speed can be increased, and the probability of wrong screwing can also be reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of oil casing threaded connection, and in particular relates to an internal threaded joint. Background Art

[0002] At present, after the API threads commonly used in oil fields are engaged, the weak part of the fatigue strength of the internal threads is at the root of the first engagement thread near the center surface of the coupling, such as Figure 1 Arrow position shown.

[0003] from Figure 2 It can also be seen from the stress distribution of the internal thread that the red part is the part with the greatest stress (due to the end effect, the end is not considered for the time being), followed by yellow, followed by green and blue. It can be seen that when meshing, the stress is greater in 1 to 5 buckles from the end face, the stress is more average in 6 to 10 buckles, the stress is smaller, and the stress is greater in 11 to 13 buckles. When meshing, the stress is greater in 1 to 5 buckles from the end face, the stress is more average in 6 to 10 buckles, the stress is smaller, and the stress is greater in 11 to 13 buckles.

[0004] The stress concentration of the joint is affected by the local shape of the thread. The notch effect is generally described by the stress concentration coefficient. Under the complex underground action, once the small end of the internal thread has cracks and reaches the fatigue crack threshold, fatigue fracture will occur, causing huge economic losses to the oil field. Therefore, the structural design of the internal thread affects the stress concentration of the joint, which in turn affects the production efficiency of the oil field. Summary of the invention

[0005] The purpose of the present invention is to provide an internal thread joint, which solves the defect that the existing internal thread structure causes a large stress concentration in the joint; the present invention reduces the stress concentration degree of the joint through the structural design of the internal thread, improves the ability of the joint to resist low-cycle fatigue, and realizes high-efficiency and low-cost operation.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] The present invention provides an internal thread joint, comprising an API round thread body, wherein the API round thread body comprises a first internal thread segment, a conical surface segment and a second internal thread segment, wherein the first internal thread segment, the conical surface segment and the second internal thread segment are arranged in sequence from the end to the bottom of the API round thread body.

[0008] Preferably, the conical surface segment is disposed from the eighth opening to the tenth thread from the end of the internal thread of the API round thread body.

[0009] Preferably, the taper of the conical surface segment is 1:16.

[0010] Preferably, the taper of the conical surface segment is 1:12.

[0011] Preferably, the vertical distance between the conical surface of the conical surface segment and the tooth bottom conical surface of the first internal thread segment is greater than or equal to zero, and less than or equal to half of the thread profile height.

[0012] Preferably, the width of the conical surface segment is greater than or equal to 3 times the pitch - 1 mm, and less than or equal to 3 times the pitch + 1 mm.

[0013] Preferably, the conical surface segment is placed from the eighth to the tenth thread from the end of the internal thread of the API round thread body;

[0014] The vertical distance between the conical surface of the conical surface segment and the conical surface of the tooth bottom of the first internal thread segment is greater than or equal to zero, and less than or equal to half of the thread profile height;

[0015] The width of the conical surface segment is greater than or equal to 3 times the pitch - 1 mm, and less than or equal to 3 times the pitch + 1 mm.

[0016] Preferably, the taper of the conical surface segment is 1:16.

[0017] Preferably, the taper of the conical surface segment is 1:12.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention provides an internal thread joint, which has a structure in which several thread profiles are cut at positions where the API round thread body is subjected to uniform and small forces, which has little effect on the connection strength of the thread and relieves the stress concentration of the thread. The processing is convenient and the operation is simple. At the same time, due to the reduction of the thread profile, the thread threading speed can be accelerated and the probability of wrong threading can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is the weak point of fatigue strength of internal thread corresponding to traditional API round thread;

[0021] Figure 2 This is the stress distribution diagram of the internal thread corresponding to the traditional API round thread;

[0022] Figure 3 It is a schematic diagram of the structure of an internal thread joint involved in the present invention;

[0023] Figure 4 It is a partial enlarged diagram of the conical surface of the internal thread joint involved in the present invention;

[0024] Figure 5 The present invention relates to a thread engagement plane figure of an internal thread joint;

[0025] Figure 6 It is an internal thread joint of Ф88.6 thickened oil pipe to reduce stress concentration;

[0026] Figure 7 It is the location of cracks in traditional API round threads;

[0027] Figure 8 It is the boundary load condition of the traditional API round thread;

[0028] Fig. 9 It is the boundary load condition of the internal thread joint involved in the present invention;

[0029] Fig.10 It is the calculation result of the traditional API round thread;

[0030] Fig.11 It is the maximum equivalent stress of traditional API round thread;

[0031] Fig.12 is the calculation result of the internal thread joint involved in the present invention;

[0032] Fig.13 is the maximum equivalent stress of the internal thread joint involved in the present invention;

[0033] Among them, 1 is the conical surface segment; 2 is the bottom conical surface of the first internal thread segment; 3 is the original thread profile; 4 is the API round thread body; 5 is the external thread. DETAILED DESCRIPTION

[0034] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present application. However, it should be clear to those skilled in the art that the present application may also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present application.

[0035] It should be understood that when used in the present specification and the appended claims, the term "comprising" indicates the presence of described features, wholes, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or combinations thereof.

[0036] It should also be understood that the term “and / or” used in the specification and appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0037] As used in the specification and appended claims of this application, the term "if" can be interpreted as "when" or "uponce" or "in response to determining" or "in response to detecting", depending on the context. Similarly, the phrase "if it is determined" or "if [described condition or event] is detected" can be interpreted as meaning "uponce it is determined" or "in response to determining" or "uponce [described condition or event] is detected" or "in response to detecting [described condition or event]", depending on the context.

[0038] In addition, in the description of the present application specification and the appended claims, the terms "first", "second", "third", etc. are only used to distinguish the descriptions and cannot be understood as indicating or implying relative importance.

[0039] References to "one embodiment" or "some embodiments" etc. described in the specification of this application mean that one or more embodiments of the present application include specific features, structures or characteristics described in conjunction with the embodiment. Therefore, the statements "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. that appear in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0040] Example 1

[0041] An internal thread joint provided in this embodiment includes an API round thread body, wherein the API round thread body includes a first internal thread segment, a conical surface segment, and a second internal thread segment, wherein the first internal thread segment, the conical surface segment, and the second internal thread segment are arranged in sequence from the end to the bottom of the API round thread body.

[0042] Example 2

[0043] Based on Example 1, the conical surface segment is placed from the eighth to the tenth thread from the end of the internal thread of the API round thread body.

[0044] Example 3

[0045] On the basis of Example 1, the original API round thread is processed, and the 8th to 10th threads from the end of the internal thread are turned from the bottom of the thread into a conical surface, and the taper thereof maintains the original taper of the thread, that is, the taper of the conical surface segment is 1:16 or 1:12; see Figure 3 and Figure 4 .

[0046] Example 4

[0047] Based on Example 1, the vertical distance between the conical surface of the conical surface segment and the bottom conical surface of the first internal thread segment is greater than or equal to zero and less than or equal to half of the thread profile height, so as to reduce the overall stress concentration of the internal thread.

[0048] Example 5

[0049] On the basis of Example 1, the width of the conical surface segment is 3 times the pitch (P) ± 1 mm, which reduces the number of internal thread teeth and reduces the overall stress concentration of the internal thread without reducing the connection strength of the thread.

[0050] The designed internal thread meshes with the API external thread. Figure 5 .

[0051] Example 6

[0052] Take the thickened oil pipe with an outer diameter of 88.9mm as an example. The thread is 8 threads per inch, and its pitch in API is 3.175mm. The distance between the conical surface segment and the bottom cone surface of the first internal thread segment is 0mm, and the width of the conical surface segment is 10mm. Figure 6 .

[0053] Example 7

[0054] Based on Example 6, the stress intensity factor of the internal threaded joint described in the present application was determined.

[0055] There are three main methods for determining stress intensity factors: analytical method, numerical calculation method and direct measurement method. Among them, analytical method is only applicable to simple problem calculations, and most problems need to be solved by numerical methods. With the rapid development of computer hardware and software, calculations using numerical methods have become feasible. Many numerical methods have been attempted to be used for fracture parameter calculations, such as finite difference method, boundary element method and meshless method. However, due to the lack of support from commercial software, there are relatively few industrial application examples of these numerical methods. Over the past half century, the finite element method has been successfully applied in many industrial sectors due to its high efficiency and low cost. There are now many powerful software available. This application uses finite element software for calculations. Compared with the threads of the same specification of API, the same crack is found at the same position, with a crack length of 5 mm. The crack tip area is the circular area of ​​0.5 mm in the figure, and the expansion direction extends to both ends of the crack, such as Figure 7 shown.

[0056] When calculating, the boundary conditions of the two are the same. The center of the coupling is fixed in the X direction, the outer diameter of the coupling is fixed in the Y direction, and the end is subjected to a tensile load of 100 MPa. Figure 8 And as shown in FIG9.

[0057] The model uses the traditional contour integration algorithm in the finite element. The crack tip is calculated using CPS6 (six-node quadratic plane stress triangle element), and the rest is calculated using CPS8 (eight-node bidirectional quadratic plane stress quadrilateral element). The results are shown in Figure 10 to Figure 13 :

[0058] This crack is perpendicular to the tensile stress and belongs to Type I crack (opening type), which is also the most dangerous and common crack. The results of comparing the maximum equivalent stress and stress intensity factor (calculated using four-circumference channels) are shown in the following table:

[0059] Table 1 Comparison of calculation results between API thread and an internal thread joint

[0060]

[0061] It can be seen from Table 1 that the stress intensity factor, J integral (J integral is generally used to describe the degree of singularity of the stress-strain field at the crack tip of an elastic-plastic plane crack body) and maximum equivalent stress of an internal thread joint are all lower than those of the API thread, especially the maximum equivalent stress is reduced by 20%. This structure improves the prevention capability of the joint low-cycle fatigue accidents and realizes high-efficiency and low-cost operation.

[0062] This structure cuts three thread profiles at the position where the internal thread is subjected to uniform and small force, which has little effect on the connection strength of the thread and relieves the stress concentration of the thread. It is easy to process and simple to operate. Due to the reduction of the thread profile, the thread threading speed can be accelerated and the chance of wrong threading can be reduced.

[0063] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. An internal threaded joint, characterized in that: It comprises an API round thread body, wherein the API round thread body comprises a first internal thread segment, a conical surface segment and a second internal thread segment, wherein the first internal thread segment, the conical surface segment and the second internal thread segment are arranged in sequence from the end to the bottom of the API round thread body.

2. An internal threaded joint according to claim 1, characterized in that: The conical surface segment is placed from the eighth to the tenth thread from the end of the internal thread of the API circular thread body.

3. An internal thread joint according to claim 1, characterized in that: The taper of the conical surface segment is 1:

16.

4. An internal thread joint according to claim 1, characterized in that: The taper of the conical surface segment is 1:

12.

5. An internal thread joint according to claim 1, characterized in that: The vertical distance between the conical surface of the conical surface segment and the tooth bottom conical surface of the first internal thread segment is greater than or equal to zero, and less than or equal to half of the thread profile height.

6. An internal thread joint according to claim 1, characterized in that: The width of the conical surface segment is greater than or equal to 3 times the pitch - 1 mm, and less than or equal to 3 times the pitch + 1 mm.

7. An internal thread joint according to claim 1, characterized in that: The conical surface segment is placed from the eighth to the tenth turn from the end of the internal thread of the API circular thread body; The vertical distance between the conical surface of the conical surface segment and the conical surface of the tooth bottom of the first internal thread segment is greater than or equal to zero, and less than or equal to half of the thread profile height; The width of the conical surface segment is greater than or equal to 3 times the pitch - 1 mm, and less than or equal to 3 times the pitch + 1 mm.

8. An internal thread joint according to claim 7, characterized in that: The taper of the conical surface segment is 1:

16.

9. An internal thread joint according to claim 7, characterized in that: The taper of the conical surface segment is 1:12.

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