A toothed connection structure for anti-galling of titanium alloy oil casing

Abstract

This invention relates to the field of petroleum engineering equipment and advanced materials processing technology, specifically to an anti-galling toothed connection structure suitable for titanium alloy oil casing, comprising interlocking female and male threads. Through parametric design of tooth width and groove dimensions, female and male thread angles and tooth heights, the galling phenomenon caused by high temperature and friction during processing is reduced, the risk of stress concentration is lowered, sealing and connection reliability are improved, thread engagement accuracy is guaranteed, and combined with surface treatment processes, the overall sealing and connection strength is enhanced. It is suitable for extreme environments such as deep wells, ultra-deep wells and offshore oil and gas extraction.

Description

Technical Field

[0001] This invention relates to the field of petroleum engineering equipment and advanced materials processing technology, specifically to an anti-sticking toothed connection structure suitable for titanium alloy oil casing. Background Technology

[0002] With the increasing depth of oil and gas exploration and extraction, higher requirements are being placed on the mechanical strength, sealing performance, and long-term corrosion resistance of oil casing materials and connection structures. Titanium alloys have become ideal materials for oil casings due to their low density, high strength, and excellent corrosion resistance; however, their low thermal conductivity (approximately 7.6 W / m·K) and high viscosity characteristics present the following problems during thread processing and assembly:

[0003] (1) Heat accumulation and sticking problem during processing: In high-temperature processing environment, local heat is not easy to dissipate, which can easily cause the surface temperature of the thread to be too high, resulting in sticking and affecting the reliability and service life of the connection.

[0004] (2) Tooth surface damage problem: The high viscosity of titanium alloys can easily lead to damage to the tooth surface during machining or assembly, thereby reducing thread accuracy and connection strength;

[0005] (3) Stress concentration problem: Since the elastic modulus of titanium alloy (110GPa) is only about 50% of that of steel, the traditional symmetrical tooth shape is prone to stress concentration due to the mismatch of elastic deformation when under load, which reduces the overall strength and fatigue life of the structure.

[0006] Chinese patent CN103527110A discloses a multi-stage sealing anti-sticking thread for titanium alloy oil casing, including an oil casing coupling and an oil casing end. It adopts a three-stage sealing (conical surface + cylindrical surface + negative angle shoulder) and API thread improvement, relying on variable taper thread and interference fit of the sealing surface. It requires the machining of multi-stage sealing structure and variable taper thread, making the process complex. Chinese patent CN112878927A discloses a joint structure for titanium alloy oil pipes, including a female end and a male end that are tightened together. The male end adopts a multi-stage sealing and complex shoulder structure, attempting to improve performance by increasing the number of sealing layers, but it brings new problems: the elastic modulus of titanium alloy is only 50% of that of steel (about 110 GPa), the complex shoulder structure is prone to stress concentration, and poor thermal matching; moreover, the multi-stage structure requires extremely high assembly accuracy (≤0.01mm), and micro-defects can easily cause inter-stage leakage, resulting in high process and inspection costs.

[0007] Therefore, a toothed connection structure with a simple structural design that can improve anti-gluing ability and avoid problems such as tooth surface damage and stress concentration is needed. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides an anti-galling toothed connection structure suitable for titanium alloy oil casing. By combining the elastic modulus, Poisson's ratio, and impact toughness of titanium alloy materials, the tooth parameters and surface treatment process are optimized to prepare an anti-galling toothed connection structure that solves the problems of galling, tooth surface damage, and stress concentration that occur in traditional thread processing. It is suitable for extreme working conditions such as deep wells, ultra-deep wells, and offshore oil and gas extraction.

[0009] The objective of this invention is achieved through the following technical solutions:

[0010] An anti-sticking toothed connection structure for titanium alloy oil casing, the toothed connection structure comprising interlocking female end threads and male end threads.

[0011] For threaded connections, the design distinguishes between the parameters of the female end (internal thread) and the male end (external thread) to ensure precise dimensional fit at both ends, while also considering requirements for anti-galling, wear resistance, and uniform stress distribution. The female end thread has a tooth width L. box The tooth width LC_box, the female end tooth height H_box, the bearing side angle CZ_box, the lead-in side angle DR_box, and the male end thread having a tooth width L pin The tooth groove width LC_pin, male tooth height H_pin, bearing side angle CZ_pin, and guide side angle DR_pin are designed as follows:

[0012] Female end thread: tooth width L box The tooth width at the female end is related to the number of teeth per inch and must be consistent with the tooth width L_pin at the male end. The tooth width is primarily based on the variation in outer diameter D, while also considering wall thickness T and effective tooth length. The design specifies L... box The value is 4.0–6.5 mm. For ease of parametric design, the following linear interpolation formula is given (when D is between its minimum and maximum values):

[0013]

[0014] The tooth groove width LC_box must be greater than or equal to L. box / 2, and considering that to ensure connection strength and smooth assembly during thread engagement, a certain tolerance ΔLC needs to be maintained between the tooth width of the female thread and the tooth width LC_pin of the male thread. Taking into account the elastic modulus of titanium alloy, ΔLC is controlled within 0.01–0.04 mm, and increases appropriately with the increase of the outer diameter D. The following formula is used for calculation:

[0015] ΔLC=0.01+(D-60.32) / 279.4×0.03

[0016] Therefore, the actual tooth groove width at the female end can be defined as:

[0017] LC_box = L box / 2+ΔLC

[0018] The tooth height H_box, taking into account the contact surface and load distribution, is generally taken as a function of LC_box and the Poisson's ratio of the titanium alloy, and is calculated using the following formula:

[0019] H_box = LC_box × (1-ν);

[0020] Male thread:

[0021] To ensure smooth thread engagement between the female and male ends, the male end tooth width L pin With the mother end L box Maintain consistency, that is

[0022] L pin＝ L box

[0023] The male end tooth groove width LC_pin should be less than or equal to L_pin / 2, and at the same time, to achieve the fit tolerance,

[0024] LC_pin = LC_box - ΔLC

[0025] To ensure there is an appropriate gap between the two.

[0026] For easy meshing and installation, the tooth height difference between the female and male ends must meet the following requirements:

[0027] 0mm≤(H_box-H_pin)≤0.1mm

[0028] Typically, H_pin can be taken to be close to H_box.

[0029] The angle CZ_pin on the male end bearing side is: CZ_pin = CZ_box;

[0030] The imported side angle DR_pin is: DR_pin = DR_box.

[0031] Furthermore, the outer diameter D of the titanium alloy oil casing is 60.32–339.72 mm;

[0032] Furthermore, the wall thickness T of the titanium alloy tube is 4–25 mm;

[0033] Furthermore, the elastic modulus E of the titanium alloy is 110 GPa, and the minimum yield strength σ of the titanium alloy is 500–1000 MPa.

[0034] Furthermore, the Poisson's ratio ν of the titanium alloy is 0.3 to 0.4, preferably 0.34; when ν = 0.34, then H_box ≈ LC_box × 0.66.

[0035] Furthermore, to ensure uniform stress distribution, the bearing side angle CZ_box of the female end thread is -10° to 10°, preferably 0° to 5°.

[0036] Furthermore, to improve engagement guidance performance, the inlet side angle DR_box is 10° to 40°, preferably 20°–30°.

[0037] The advantages and beneficial effects of this invention are:

[0038] (1) Improved anti-sticking performance: By reasonably controlling the tooth width and tooth groove size and optimizing the tolerance design, the sticking phenomenon caused by high temperature and friction during processing and assembly is effectively reduced, thus improving the reliability of threaded connection.

[0039] (2) Uniform stress distribution and reduced stress concentration risk: Through the optimized design of the thread angle and tooth height of the female and male ends, the stress is effectively distributed, reducing the risk of stress concentration, thereby enhancing the overall strength and fatigue life of the structure.

[0040] (3) Improved sealing and connection reliability: Ensure thread engagement accuracy and improve overall sealing and connection strength by combining surface treatment process;

[0041] Through in-depth synergistic optimization of tooth profile parameters and material properties, it exhibits significant advantages in anti-galling, uniform stress distribution, sealing performance, and environmental adaptability, providing reliable technical support for the application of titanium alloy oil casing in complex working conditions. It is especially suitable for extreme environments such as deep wells, ultra-deep wells, and offshore oil and gas extraction, giving full play to the advantages of titanium alloy materials. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the thread profile at the female end;

[0043] Figure 2 This is a schematic diagram of the male end thread profile;

[0044] Figure 3 This is a schematic diagram of the male and female threaded fit. Detailed Implementation

[0045] The present invention will be further described in detail below through specific embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0046] An anti-galling toothed connection structure suitable for titanium alloy oil casing includes a female end thread and a male end thread that mesh with each other, wherein the female end thread has a tooth width L. box ,

[0047] The tooth groove width LC_box, tooth height H_box, bearing side angle CZ_box, lead-in side angle DR_box, and the male end thread having a tooth width Lpin The tooth groove width LC_pin, tooth height H_pin, bearing side angle CZ_pin, and guide side angle DR_pin, and L box =L pin , CZ_box=CZ_pin, DR_box=DR_pin;

[0048] The tooth width L of the female end thread box Satisfying the formula:

[0049] The tooth groove width LC-box satisfies the formula: LC_box=L box / 2+ΔLC;

[0050] The tooth groove width LC-pin satisfies the formula: LC_pin≤L pin / 2, and LC_pin=LC_box-ΔLC;

[0051] The tooth height H_box satisfies the formula: H_box=LC_box×(1-ν);

[0052] ΔLC is the tolerance between the tooth groove width of the female end thread and the tooth groove width of the male end thread, satisfying the formula ΔLC=0.01+(D-60.32) / 279.4×0.03, where ν is the Poisson's ratio of the titanium alloy and D is the outer diameter of the titanium alloy pipe.

[0053] Preferably, the tooth heights of the female end thread and the male end thread satisfy: 0mm≤(H_box-H_pin)≤0.1mm, where H_pin is the male end tooth height.

[0054] Preferably, the bearing side angle is -10° to 10°.

[0055] Preferably, the angle of the inlet side is 10° to 40°.

[0056] Preferably, the Poisson's ratio is 0.30 to 0.40.

[0057] Preferably, the outer diameter of the titanium alloy oil casing is 60.32–339.72 mm.

[0058] Preferably, the wall thickness of the titanium alloy oil casing is 4–25 mm.

[0059] Preferably, the tooth width of the female end thread is 4.0–6.5 mm.

[0060] The toothed connection structure of the present invention will be described below with reference to embodiments.

[0061] Example 1

[0062] An anti-galling toothed connection structure suitable for titanium alloy oil casing includes interlocking female and male threads. The titanium alloy oil casing is the male end, with an outer diameter D = 150 mm, a wall thickness T = 10 mm, and a Poisson's ratio of 0.34.

[0063] Calculate the larger value L according to the formula. box :

[0064]

[0065] The calculation yields:

[0066] Mole: 150 – 60.32 = 89.68

[0067] Denominator: 339.72 – 60.32 = 279.40

[0068] The ratio is approximately 0.321.

[0069] Therefore: L box =4.0+0.321×2.5=4.0+0.785=4.802mm

[0070] Determination of ΔLC and LC_box: ΔLC = 0.01962 mm

[0071] Therefore: LC_box = 2.4206mm; H_box = 1.5976mm.

[0072] CZ_box = 10°, which can be finely adjusted within the range of -10° to 10° according to the actual force. DR_box = 20° (or between 10° and 40° depending on the installation requirements).

[0073] Male thread parameter L box =L pin = 4.802mm;

[0074] LC_pin=LC_box-ΔLC=2.4206-0.01962=2.4001mm;

[0075] To ensure that the difference between H_box and H_pin is within the range of 0 to 0.1 mm,

[0076] Select H_pin = H_box - 0.05mm = 1.5476mm.

[0077] CZ_box=CZ_pin, DR_box=DR_pin.

[0078] With the above parameter design, the threads of the female and male ends can effectively avoid the sticking phenomenon caused by factors such as temperature and friction during actual processing and assembly, while ensuring uniform force and good sealing performance at the connection.

[0079] Example 2

[0080] An anti-galling toothed connection structure suitable for titanium alloy oil casing includes a female end thread and a male end thread that mesh with each other. The titanium alloy oil casing is the male end, with an outer diameter D = 300 mm and a wall thickness T = 15 mm.

[0081] The same calculation method as in Example 1 is used:

[0082] L box =6.14 (relatively large, close to the upper limit of 6.5mm);

[0083] ΔLC = 0.036 mm, and ΔLC is appropriately increased (close to 0.04 mm) for larger pipe diameters;

[0084] Therefore: LC_box = 3.43mm; H_box = 2.2638mm.

[0085] CZ_box = 10°, which can be finely adjusted within the range of -10° to 10° according to the actual force. DR_box = 20° (or between 10° and 40° depending on the installation requirements).

[0086] Male thread parameter L box =L pin =6.14mm;

[0087] LC_pin=LC_box-ΔLC=3.43-0.036=3.364mm;

[0088] To ensure that the difference between H_box and H_pin is within the range of 0 to 0.1 mm,

[0089] Select H_pin = H_box - 0.05mm = 2.2138mm.

[0090] CZ_box=CZ_pin, DR_box=DR_pin.

[0091] Finite element simulation and actual machining verification were performed on the anti-gluing toothed connection structures of Examples 1 and 2 to test the tooth surface gluing performance, stress concentration risk, and sealing performance.

[0092] A composite load testing machine is used to apply internal pressure, external pressure, axial tensile load, and axial compressive load to the threaded structure and sealing structure to verify the sealing effect of the thread, or the casing is lowered into the corresponding high-pressure well to test the sealing effect of the casing.

[0093] For Example 1, a toothed connection structure with an outer diameter of 150mm and a wall thickness of 10mm, suitable for titanium alloy oil casing, was designed and developed. In a high-temperature, high-pressure downhole environment, a composite load evaluation test was conducted at a temperature of 180℃, a maximum internal pressure of 93MPa, and an external pressure of 90MPa. No leakage was observed during the test, demonstrating excellent casing sealing performance. The casing could complete more than 10 uncoupling cycles without sticking. In high carbon dioxide and hydrogen sulfide environments, no corrosive media flowed out, successfully sealing corrosive media such as hydrogen sulfide and carbon dioxide within the casing. The casing could complete more than 10 uncoupling cycles without sticking.

[0094] A composite load evaluation test was conducted on the anti-sticking toothed connection structure for titanium alloy oil casing, designed and developed in Example 2, with an outer diameter of 300mm and a wall thickness of 15mm. The test was conducted under internal pressure of 60MPa, external pressure of 30MPa, and a high temperature of 180℃. No leakage was observed during the test, demonstrating excellent casing sealing performance. The casing could complete more than three uncoupling cycles without sticking. In high carbon dioxide and hydrogen sulfide environments, no corrosive media flowed out, successfully sealing corrosive media such as hydrogen sulfide and carbon dioxide within the casing. The casing could complete more than three uncoupling cycles without sticking.

[0095] The results show that the parametric design method effectively reduces the risk of tooth surface sticking, while improving the stress condition and sealing performance of the overall connection structure, and increasing the service life of titanium alloy tubing under deep well and marine operating conditions.

[0096] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several modifications and improvements can be made without departing from the inventive concept, and these all fall within the protection scope of the present invention.

Claims

1. A toothed connection structure for anti-galling of titanium alloy oil casing, characterized in that, It includes a female end thread and a male end thread that mesh with each other, the female end thread having a tooth width L box The tooth width LC-box, tooth height H-box, bearing side angle CZ-box, and guide side angle DR-box, wherein the male end thread has a tooth width L pin Tooth spacer width LC-pin, tooth height H-pin, bearing side angle CZ-pin, guide side angle DR-pin, and L box =L pin , CZ-box=CZ-pin, DR-box=DR-pin; The tooth width L box Satisfying the formula: The tooth groove width LC-box satisfies the formula: LC_box=L box / 2+ΔLC; The tooth groove width LC-pin satisfies the formula: LC_pin≤L pin / 2, and LC_pin=LC_box-ΔLC; The tooth height H-box satisfies the formula: H_box=LC_box×(1-ν); ΔLC is the tolerance between the tooth width of the female thread and the tooth width of the male thread, which satisfies the formula: ΔLC=0.01+(D-60.32) / 279.4×0.03, ν is the Poisson's ratio of the titanium alloy, and D is the outer diameter of the titanium alloy tube.

2. The toothed connection structure according to claim 1, characterized in that, The tooth height of the female end thread and the tooth height of the male end thread satisfy the following condition: 0mm≤(H_box-H_pin)≤0.1mm.

3. The toothed connection structure according to claim 1, characterized in that, The angle of the bearing side is -10° to 10°.

4. The toothed connection structure according to claim 1, characterized in that, The angle of the inlet side is 10° to 40°.

5. The toothed connection structure according to claim 1, characterized in that, The Poisson's ratio is 0.30 to 0.

40.

6. The toothed connection structure according to claim 1, characterized in that, The outer diameter of the titanium alloy oil casing is 60.32–339.72 mm.

7. The toothed connection structure according to claim 1, characterized in that, The wall thickness of the titanium alloy oil casing is 4-25 mm.

8. The toothed connection structure according to claim 1, characterized in that, The tooth width of the female end thread is 4.0 to 6.5 mm.

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