Segmented tenon-and-mortise type drill rod joint and preparation method thereof

Abstract

The invention provides a segmented tenon-and-mortise type drill rod joint and a preparation method thereof. The segmented tenon-and-mortise type drill rod joint structurally comprises a three-section tenon-and-mortise structure, a limiting hole structure located in the center area of the tenon-and-mortise structure and an inclined fixing hole structure penetrating through the tenon-and-mortise structure. Wherein the mortise and tenon joint structure consists of an inverted trapezoidal tenon structure with a fillet and a mortise structure corresponding to the inverted trapezoidal tenon structure; a transition layer and a multi-layer gradient AlCoCrFeNi-based high-entropy alloy coating are sequentially distributed on the outer surface of a tenon of the mortise and tenon structure, the inner surface of a corresponding mortise, the surface of a limiting hole structure and the surface of a fixing hole structure in the outward direction of a base body. According to the method, the service life of the drill rod joint is prolonged while the transmission efficiency is improved by optimally designing the segmented tenon-and-mortise structure of the drill rod joint, and the wear resistance and corrosion resistance of the drill rod structure are effectively enhanced and the stress concentration phenomenon is reduced while the binding force between the coating and a matrix is improved by preparing the multi-gradient composite coating on the surface of the tenon-and-mortise structure of the drill rod joint. And finally, the operation stability of the drill rod combination in the drilling fluid environment is enhanced.

Description

Technical Field

[0001] This invention belongs to the field of scientific drilling technology, specifically relating to a segmented tenon-and-mortise drill pipe joint and its preparation method. Background Technology

[0002] Drill pipe joints are an important component of drill pipe, primarily used to connect the drill pipe body, and typically consist of internal and external threaded joints. As one of the most stress-exposed components during drilling, it needs to withstand bending moments, stresses, and the corrosive effects of drilling fluids in multiple directions. The threads, as a key structural element of the drill pipe joint, primarily serve to transmit torque, bear loads, prevent drilling fluid leakage, and seal drilling mud.

[0003] In actual drilling operations, when the drill pipe passes through curved sections and areas with large doglegs in the wellbore, the drill pipe joint bears greater stress than the drill pipe body, making it prone to stress concentration. This can cause fatigue cracks to initiate on the threads of the drill pipe joint during transmission, and the cracks can propagate and eventually lead to fracture. Simultaneously, insufficient lubrication, excessive torque, and severe wear on the joint surface can cause metal adhesion and tearing, resulting in jamming. Furthermore, impacts, collisions, and mud particle erosion can cause pitting or deformation of the threads, leading to sealing failure and leakage. All of these common problems can cause drill pipe joint failure, preventing drilling operations and impacting project progress.

[0004] Therefore, existing technologies mostly employ nitriding, shot peening, or single-gradient coating treatments to improve surface hardness, wear resistance, and fatigue strength. However, nitriding or shot peening can only improve surface hardness, with limited improvement in corrosion resistance, and the processes are complex and costly; while conventional joint surface coatings cannot meet the different working conditions faced by different areas, making it difficult to achieve the operational requirements under complex working conditions.

[0005] Therefore, in order to extend the service life of drill pipe joints, it is an urgent technical problem to be solved by those skilled in the art to develop a new type of drill pipe joint that can still stably achieve the drill pipe connection function under working conditions of high wear, high torque, high impact and high corrosion. Summary of the Invention

[0006] The purpose of this invention is to provide a segmented tenon-and-mortise drill pipe joint. The three-segment tenon-and-mortise structure design adapts to the gradient stress conditions in different areas of the joint, and the differentiated gradient high-entropy alloy coating meets the construction performance requirements. Thus, while ensuring transmission efficiency, it increases the wear and corrosion resistance of the drill pipe joint, reduces stress concentration, and effectively extends the service life of the drill string assembly, thereby reducing exploration and mining costs.

[0007] To achieve the above objectives, the present invention provides a segmented tenon-and-mortise drill pipe joint.

[0008] The structure includes a first section, a second section, and a third section that are equidistantly distributed along the direction from the drill pipe body to the end of the drill pipe joint, forming a three-section mortise and tenon structure; a limiting hole structure located in the central area of ​​the mortise and tenon structure; and an oblique fixing hole structure that penetrates the mortise and tenon structure; wherein the mortise and tenon structure consists of an inverted trapezoidal tenon structure with rounded corners and a corresponding mortise structure;

[0009] On the outer surface of the tenon, the corresponding inner surface of the mortise, the surface of the limiting hole structure, and the surface of the fixing hole structure of the three-section mortise and tenon structure, a transition layer and a multi-layer gradient AlCoCrFeNi-based high-entropy alloy coating are sequentially distributed along the direction outward from the substrate.

[0010] The outer surfaces of the tenon structures and / or the inner surfaces of the corresponding mortise structures in the first, second, and third sections are respectively coated with Al content, Si content, and Mo content increasing sequentially. x CoCrFeNi, AlCoCrFeNiSi x AlCoCrFeNiMo x Multi-gradient composite coating;

[0011] A multi-gradient composite coating of AlCoCrFeNi / x-MoS2, AlCoCrFeNi / x-TiC, and AlCoCrFeNi / x-CeO2 with increasing MoS2, TiC, and CeO2 content is applied to the surfaces of the limiting hole structure and / or fixing hole structure in the first, second, and third sections, respectively.

[0012] In a preferred embodiment, the drill pipe joint body is frustum-shaped, and its inclination angle with the drill pipe body is 5~15°.

[0013] In a preferred embodiment, along the direction from the drill pipe body to the drill pipe joint end, the length and / or height of the inverted trapezoidal tenon structure in the three-section mortise and tenon structure increases sequentially; more preferably, the increase in length of adjacent tenon structures is less than 5 cm and / or the increase in height is less than 3 cm.

[0014] In a preferred embodiment, the three-section mortise and tenon structure is divided into sections according to axial position, and each section has 3 to 6 tenons.

[0015] In a preferred embodiment, the rounded corners are located at the two corners where the bottom of the inverted trapezoidal tenon connects to the main body of the drill pipe joint, forming arc-shaped rounded corners, and the difference between the two rounded corners does not exceed 5°, with the angle range of the two rounded corners being between 10° and 20°.

[0016] In a preferred embodiment, the limiting hole structure is square and located at the center of each inverted trapezoidal tenon structure. Its inclination direction is consistent with that of the tenon structure. The tenon and the corresponding mortise are limited by inserting a pin. More preferably, the length of the pin is no more than 3 cm.

[0017] In a preferred embodiment, the fixing hole structure is an oblique hole, and each tenon structure has two fixing holes that pass through and connect to the inverted trapezoidal tenon. The two fixing holes are symmetrically distributed according to the center of the limiting hole, and the line connecting the centers of each hole is parallel to the long side of the top of the inverted trapezoidal tenon. More preferably, the inclined direction of the fixing hole is at an angle of 15~25° to the top of the inverted trapezoidal tenon, the center position of the fixing hole is referenced to the center of the limiting hole, the distance is not more than 8 cm, and the hole diameter is not more than 4 cm.

[0018] In a preferred embodiment, the transition layer consists of two layers. For the outer surface of the tenon in the mortise and tenon structure, the first transition layer near the drill pipe joint substrate is a Ni-Al system with an atomic ratio of 1:1, and the second transition layer is a NiCrAlY system with an atomic ratio of 1:1:1:1. The thickness of a single transition layer is 80~180 μm, and the total thickness of the transition layer is 160~360 μm.

[0019] For the inner surface of the mortise, the surface of the limiting hole structure and the surface of the fixing hole structure, the first transition layer near the drill pipe joint substrate is a Si or Cr system with a thickness of 5~20 μm; the second transition layer is a NiCr system or a CrN system with an atomic ratio of 1:1 with a thickness of 5~20 μm; the total thickness of the first and second transition layers is 10~40 μm.

[0020] In a preferred embodiment, on the transition layer of the outer surface of the tenon structure, the Al content of the first section of the tenon structure is successively increased, with the increase not exceeding 15%. x CoCrFeNi multi-gradient composite coating; the second section's tenon structure is coated with AlCoCrFeNiSi, where the Si content increases sequentially, with the increase not exceeding 20%. x Multi-gradient composite coating; the third segment's tenon structure is coated with AlCoCrFeNiMo, where the Mo content increases sequentially, with the increase not exceeding 25%. x Multi-gradient composite coating; and the total thickness of the multi-layer gradient AlCoCrFeNi-based high-entropy alloy coating on the outer surface of each tenon structure is 450~600 μm, with 3~5 coating layers.

[0021] In a preferred embodiment, on the transition layer corresponding to the inner surface of the mortise structure, the Al content of the first segment of the mortise structure is successively increased, with the increase not exceeding 10%. xCoCrFeNi multi-gradient composite coating; the second section features an AlCoCrFeNiSi coating with progressively increasing Si content, with the increase not exceeding 15%. x Multi-gradient composite coating; the third segment features an AlCoCrFeNiMo coating with progressively increasing Mo content, with the increase not exceeding 20%. x Multi-gradient composite coating; and the total thickness of the multi-layer gradient AlCoCrFeNi-based high-entropy alloy coating on the inner surface of each mortise structure is 20~50 μm, with 3~5 coating layers.

[0022] In a preferred embodiment, in the Al x In the CoCrFeNi multi-gradient composite coating, the initial Al content is 1-3%, and the Al content increases by 2-3% in each gradient layer; in the AlCoCrFeNiSi... x In the multi-gradient composite coating, the initial Si content is 1-3%, and the Si content increases by 2-3% in each gradient layer; in the AlCoCrFeNiMo... x In multi-gradient composite coatings, the initial Mo content is 1-3%, and the Mo content increases by 2-3% in each gradient layer.

[0023] In a preferred embodiment, on the transition layer of the limiting hole structure surface and / or the fixing hole structure surface, the first segment of the limiting hole structure is coated with an AlCoCrFeNi / x-MoS2 multi-gradient composite coating with progressively increasing MoS2 content, the increase not exceeding 8%; the second segment of the limiting hole structure is coated with an AlCoCrFeNi / x-TiC multi-gradient composite coating with progressively increasing TiC content, the increase not exceeding 10%; and the third segment of the limiting hole structure is coated with an AlCoCrFeNi / x-CeO2 multi-gradient composite coating with progressively increasing CeO2 content, the increase not exceeding 9%. The total thickness of the multi-layer gradient AlCoCrFeNi-based high-entropy alloy coating on the surface of each segment of the limiting hole structure is 18~48 μm, and the number of coating layers is 3~5.

[0024] In a preferred embodiment, in the AlCoCrFeNi / x-MoS2 multi-gradient composite coating, the initial content of MoS2 is 1~2%, and the increase in MoS2 content per gradient layer is 1~3%; in the AlCoCrFeNi / x-TiC multi-gradient composite coating, the initial content of TiC is 1~2%, and the increase in TiC content per gradient layer is 1~3%; in the AlCoCrFeNi / x-CeO2 multi-gradient composite coating, the initial content of CeO2 is 1~2%, and the increase in CeO2 content per gradient layer is 1~3%.

[0025] Another objective of this invention is to provide a method for preparing a segmented tenon-and-mortise drill pipe joint, specifically comprising the following steps:

[0026] Drill pipe joint outer shape processing: The drill pipe joint is shaped and processed by CNC machining, and the following are made in sequence: frustum, three-section tenon and mortise structure distributed along the direction from the drill pipe body to the end of the joint, limiting hole structure located in the central area of ​​the tenon and mortise structure, and oblique fixing hole structure penetrating the tenon and mortise structure. The outer surface and inner hole of the tenon and mortise structure are pre-treated.

[0027] Coating powder preparation: The coating powder required for the AlCoCrFeNi-based high-entropy alloy coating was prepared using a powder preparation process;

[0028] Preparation of transition layers and high-entropy alloy coatings: Two transition layers composed of Ni-Al and NiCrAlY systems are prepared on the outer surface of the tenon using a surface coating process. On the corresponding inner surface of the mortise, the surface of the limiting hole structure, and the surface of the fixing hole structure, Si or Cr systems are prepared as the first transition layer and NiCr or CrN systems are prepared as the second transition layer. On the two transition layers, corresponding multilayer gradient AlCoCrFeNi-based high-entropy alloy coatings are prepared respectively.

[0029] Post-coating treatment: The formed AlCoCrFeNi-based high-entropy alloy coating is polished and sealed.

[0030] Joint assembly: The drill pipe joint after coating treatment is assembled. The assembly process is as follows: First, the tenon structure of the drill pipe joint is inserted into the mortise groove of the corresponding mortise structure. Then, it is rotated counterclockwise around the axis to screw the tenon into the mortise. Finally, the pins are inserted into the oblique fixing holes and limiting holes to complete the fixation.

[0031] In a preferred embodiment, in the machining step of the drill pipe joint, the purpose of the pretreatment is to remove impurities and oxide layers from the outer surface and inner hole of the tenon structure, and to improve the surface roughness to facilitate coating deposition. Therefore, conventional methods known to those skilled in the art can be used, including surface cleaning, removal of surface oxide layers, and surface roughening treatment. The surface roughness Ra value after the pretreatment is 5~15 μm.

[0032] In a preferred embodiment, in the coating powder preparation step, the powder preparation can be carried out using conventional processes known to those skilled in the art, such as using atomizing equipment and / or ball milling equipment to prepare the coating powder required for the AlCoCrFeNi-based high-entropy alloy coating.

[0033] In a preferred embodiment, in the transition layer and high-entropy alloy coating preparation steps, the surface coating process includes thermal spraying technology and / or magnetron sputtering technology. Preferably, the outer surface of the tenon is prepared using supersonic flame spraying technology, and the inner surface of the mortise, the inner surface of the limiting hole structure, and the inner surface of the fixing hole structure are prepared using magnetron sputtering technology.

[0034] More preferably, the process parameters for the supersonic flame spraying of the transition layer include: spraying distance 200-250 mm, oxygen flow rate 170-220 L / min, nitrogen flow rate 18-23 L / min, powder feed rate 37-43 g / min, air flow rate 280-330 L / min, and hydrogen flow rate 550-600 L / min; the process parameters for the supersonic flame spraying of the high-entropy alloy coating include: spraying distance 200-250 mm, oxygen flow rate 170-220 L / min, nitrogen flow rate 18-23 L / min, powder feed rate 37-43 g / min, air flow rate 280-330 L / min, hydrogen flow rate 550-600 L / min, repeated spraying 30 times, followed by stacking, cooling, and solidification to form a single-layer AlCoCrFeNi-based high-entropy alloy coating; the process parameters for the magnetron sputtering preparation of the transition layer and / or the high-entropy alloy coating include: working gas pressure 2-5... Pa, vacuum degree 5×10 -5 ~ 8×10 -1 Pa, power 180~300 W, argon flow rate 50~100 sccm;

[0035] The most preferred method is to prepare a single-layer coating with a thickness of 150~200 μm by supersonic flame spraying of high-entropy alloy coatings; and to prepare a single-layer coating with a thickness of no more than 20 μm by magnetron sputtering of high-entropy alloy coatings.

[0036] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0037] 1. Structurally, this invention completely abandons the traditional threaded connection of drill pipe joints, innovatively adopting a three-section inverted trapezoidal tenon and mortise structure, combined with a dual fixing design of limiting holes and fixing holes, fundamentally improving the stress concentration problem. By gradually increasing the length and height of the three sections of the tenon and mortise structure along the direction from the drill pipe body to the joint end, and with a 10-20° rounded corner at the bottom of the tenon, it adapts to the stress differences in different areas of the drill pipe joint. This allows the short tenon near the pipe body end to quickly transmit high torque and bending moment, while the long tenon at the end increases the sealing area of ​​the drilling fluid. The rounded corner structure further disperses stress, effectively preventing the initiation and propagation of fatigue cracks at the thread root. Simultaneously, the dual fixing structure achieves reliable circumferential and longitudinal limiting through pins, significantly reducing the risk of disengagement and seizing caused by drilling vibration. Both factors together improve the connection stability and failure resistance of the drill pipe joint.

[0038] 2. Regarding surface properties, this invention, targeting the different functional requirements of the three-section mortise and tenon structure, specifically designs a differentiated AlCoCrFeNi-based high-entropy alloy multi-gradient coating system, synergistically achieving improved wear resistance, corrosion resistance, and fracture resistance. Specifically, this includes:

[0039] Firstly, the tenon and mortise structure in the first section near the drill pipe body bears significant stress, and the low-Al content Al... x The CoCrFeNi high-entropy alloy coating exhibits good toughness and plasticity, effectively improving its adhesion to the transition layer. With increasing Al content, the coating's strength and toughness increase sequentially, with the Al content in the intermediate layer... x The CoCrFeNi high-entropy alloy coating exhibits high toughness and strength; Al element plays a role in improving mechanical properties and promoting the formation of Al2O3 passivation film, with the outermost Al layer... x The CoCrFeNi high-entropy alloy coating exhibits high wear resistance and corrosion resistance. MoS2, as a typical solid lubricating phase, forms a lubricating film at the friction interface, effectively reducing the coefficient of friction. Therefore, the AlCoCrFeNi / x-MoS2 coating with a low MoS2 content in the bottom layer of the first limiting hole and fixing hole has high strength, the middle layer AlCoCrFeNi / x-MoS2 coating has high toughness, and the outermost layer AlCoCrFeNi / x-MoS2 coating has good friction reduction and wear resistance.

[0040] Secondly, although the second mortise and tenon structure bears less stress, its wear resistance and corrosion resistance gradually improve. The AlCoCrFeNiSi high-entropy alloy coating with lower Si content has better adhesion. As the silicon content increases, the coating strength and toughness increase sequentially, with the middle AlCoCrFeNiSi layer exhibiting higher toughness and strength. Si plays a role in forming SiO2 and silicide lubricating layers, and the outermost high-Si content AlCoCrFeNiSi high-entropy alloy coating exhibits better wear resistance. TiC, as a typical ceramic particle, significantly affects coating performance due to variations in its content. High-entropy alloy coatings with different TiC content gradients were sequentially prepared on the inner surfaces of the second-section limiting hole and fixing hole structures. When the TiC content of the bottom layer is low, the AlCoCrFeNi / x-TiC coating exhibits better plasticity. As the TiC content increases, the AlCoCrFeNi / x-TiC coating exhibits better strength, and the outermost AlCoCrFeNi / x-TiC coating exhibits higher wear resistance.

[0041] Finally, the third mortise and tenon structure located at the end of the drill pipe joint primarily serves to seal the drilling fluid. Mo, as a typical corrosion-resistant element, exhibits high adhesion in the bottom AlCoCrFeNiMo high-entropy alloy coating when its content is low; as the Mo content increases, the middle AlCoCrFeNiMo high-entropy alloy coating shows better toughness; and the outermost AlCoCrFeNiMo high-entropy alloy coating possesses high corrosion resistance while also reducing the friction coefficient. High-entropy alloy coatings with different CeO2 contents were sequentially prepared on the surfaces of the third-section limiting hole and fixing hole structures. CeO2, as a typical rare-earth oxide reinforcing phase, significantly improves coating performance through its unique "active element effect" and "nanopinion effect." Specifically, the bottom AlCoCrFeNi / x-CeO2 coating exhibits good adhesion when the CeO2 content is low; as the CeO2 content increases, the AlCoCrFeNi / x-CeO2 coating shows better toughness; and the outermost AlCoCrFeNi / x-CeO2 coating exhibits high corrosion resistance. By significantly reducing wear, corrosion, and stress concentration in drill pipe joints, the service life of drill pipe joints can be extended.

[0042] 3. Regarding the preparation method, the two transition layer structures of this invention are prepared using different advanced surface technologies. The Ni-Al, Si, and Cr transition layers all exhibit high adhesion to the substrate, while the NiCrAlY, NiCr, and CrN transition layers exhibit high adhesion to the composite coating. This specific two-layer transition layer design reduces coating peeling during transmission (vibration, impact, etc.) of the drill pipe joint. Furthermore, the preparation method of the integral drill pipe joint is simple and reasonable, effectively improving the mechanical properties of the drill pipe joint while controlling processing costs and facilitating production.

[0043] 4. In terms of application effects, compared with traditional threaded joints, the segmented tenon-and-mortise drill pipe joint prepared by this invention has a wider range of applications and can be used in various harsh working conditions. At the same time, due to its excellent fracture resistance, wear resistance, and corrosion resistance, it can effectively avoid frequent joint replacement, significantly reduce operating costs, and improve exploration and mining efficiency. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0045] Figure 1This is a side view of the tenon structure of the segmented tenon-and-mortise drill pipe joint of the present invention;

[0046] Figure 2 The left image shows the main view of the tenon structure of the segmented tenon-tenon drill pipe joint of the present invention, and the rounded corners of the tenon structure (A and B in the right image).

[0047] Figure 3 This is a schematic diagram of the mortise structure corresponding to the tenon structure of the segmented tenon-and-mortise drill pipe joint of the present invention.

[0048] Figure 4 This is a cross-sectional view of the mortise structure corresponding to the tenon structure of the segmented tenon-and-mortise drill pipe joint of the present invention.

[0049] Figure 5 This is a side view of the mortise structure corresponding to the tenon structure of the segmented tenon-and-mortise drill pipe joint of the present invention.

[0050] Figure 6 This is a schematic diagram of the composite coating on the outer surface of the first mortise and tenon structure of the segmented mortise and tenon drill pipe joint of the present invention.

[0051] Figure 7 Al in Embodiment 1 of the present invention x CoCrFeNi high-entropy alloy coating friction coefficient;

[0052] Explanation of key figure labels:

[0053] 1- A trapezoidal tenon with rounded corners; 2- A limiting hole structure; 3- A fixing hole structure; 4- The substrate; 5- A Ni-Al or Si transition layer; 6- A NiCrAlY or NiCr transition layer; 7- Al 1% CoCrFeNi,8-Al 3% CoCrFeNi,9-Al 5% CoCrFeNi. Detailed Implementation

[0054] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. However, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0055] This invention provides a segmented tenon-and-mortise drill pipe joint and its preparation method, which solves the problems of severe surface wear and severe drilling fluid and mud corrosion in the prior art.

[0056] Unless otherwise specified, the technical means used in this invention are conventional means well known to those skilled in the art. All raw materials, reagents, instruments, and equipment used in this invention can be purchased commercially or prepared using existing methods. All coating powders used were purchased from Beijing Yanbang New Materials Technology Co., Ltd.

[0057] The tribological properties of AlCoCrFeNi-based high-entropy alloy coatings were tested using a reciprocating friction and wear testing machine. The reciprocating frequency was set to 10 Hz, the wear track length to 5 mm, the time to 30 min, and the load to 6 N. GCr15 bearing steel balls with a diameter of 6 mm were selected for the grinding balls.

[0058] Electrochemical tests were performed using an electrochemical workstation. The coated sample served as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum electrode as the counter electrode. The sample for electrochemical testing was encapsulated in epoxy resin and connected with copper wires, with approximately 1.0 cm exposed. 2 The area of ​​the sample was immersed in the drilling fluid. Electrochemical tests were conducted at room temperature (approximately 25 °C), including open-circuit potential testing, electrochemical impedance spectroscopy (EIS) testing, and potentiodynamic polarization testing. First, the electrochemical test sample was immersed in the drilling fluid for 10 minutes. Then, the open-circuit potential was measured over a time period of 1800 s. Next, the impedance spectrum was measured with an initial frequency of 100,000 Hz, a termination frequency of 0.01 Hz, and an AC amplitude of 10 mV. Resistance and capacitance parameters were obtained by fitting an analog circuit R(QR(QR)). Finally, the potentiodynamic polarization curve was measured with an initial potential of -0.5 V, a termination potential of 1.0 V, a potential interval of 0.5 mV, and a scan rate of 1 mV / s. The corrosion potential (E) was calculated using the Tafel curve extrapolation method. corr ) and corrosion current density (i corr ).

[0059] Example 1

[0060] A method for manufacturing a segmented tenon-and-mortise drill pipe joint includes:

[0061] (I) Machining of segmented tenon and mortise drill pipe joint: The truncated cone is milled using a CNC machine tool. Then, according to the pre-set program language, rough milling and then fine milling are performed from the drill pipe body to the end face of the drill pipe joint. The tenon structure is processed sequentially along the inclined direction of the drill pipe joint. Then, the limiting hole structure is machined on the upper surface of the tenon and mortise structure using a lathe. Finally, the inclined fixing hole structure is machined using a milling machine drill bit. The overall machining of the segmented tenon and mortise drill pipe joint is completed. The outer surface and inner hole of the tenon and mortise structure are pre-treated. The surface roughness Ra value after pre-treatment is 10 μm, which is beneficial to the subsequent deposition of the corresponding coating.

[0062] The specific structural parameters are as follows: a three-section mortise and tenon structure is distributed equidistantly along the direction from the drill pipe body to the end of the drill pipe joint, with 5 tenons in each section; the length of the inverted trapezoidal tenon structure of the first, second, and third sections increases by 4 cm and the height increases by 2 cm respectively, with the larger bottom radius being 15° and the smaller one being 12°, and the inner diameter of the inclined fixing hole being 3 cm, forming a 20° angle with the top of the inverted trapezoidal tenon.

[0063] (ii) Preparation of AlCoCrFeNi-based high-entropy alloy coating powder: The corresponding coating powder was prepared by vacuum atomization equipment and mechanical ball mill equipment, respectively.

[0064] (III) Preparation of transition layer and high-entropy alloy coating: For non-extremely narrow areas such as the outer surface of the tenon, thermal spraying technology (supersonic flame spraying) is used to prepare the coating. At the same time, for the AlCoCrFeNi-based high-entropy alloy coating, repeated spraying is used to achieve thickness stacking, ensuring the coating density and gradient composition. For areas that are difficult to penetrate with thermal spraying, such as the inner surface of the mortise, the inner surface of the limiting hole structure, and the inner wall of the oblique fixing hole, magnetron sputtering technology is used to prepare the coating, ensuring that all areas requiring coating are completely covered.

[0065] The process parameters for supersonic flame spraying of the transition layer include a spraying distance of 230 mm, oxygen flow rate of 190 L / min, nitrogen flow rate of 20 L / min, powder feed rate of 43 g / min, air flow rate of 300 L / min, and hydrogen flow rate of 580 L / min. The corresponding process parameters for the high-entropy alloy coating include a spraying distance of 200 mm, oxygen flow rate of 170 L / min, nitrogen flow rate of 18 L / min, powder feed rate of 37 g / min, air flow rate of 280 L / min, and hydrogen flow rate of 550 L / min. The coating is sprayed repeatedly 30 times, stacked, cooled, and solidified to form an AlCoCrFeNi-based high-entropy alloy coating. The process parameters for magnetron sputtering preparation of the transition layer are a working gas pressure of 2.3 Pa and a vacuum degree of 5 × 10⁻⁶. -5 The operating pressure is 2.7 Pa, power is 220 W, and argon flow rate is 50 sccm. The corresponding high-entropy alloy coating process parameters include: working pressure 2.7 Pa, vacuum degree 5 × 10⁻⁶. -5 Pa, power 180 W, argon flow rate 60 sccm.

[0066] On the outer surface of the tenon in the three-section mortise and tenon structure, the first transition layer Ni-Al system has a thickness of 100 μm, and the second transition layer NiCrAlY system has a thickness of 100 μm; on the corresponding inner surface of the mortise, the surface of the limiting hole structure and the surface of the fixing hole structure, the first transition layer Si system has a thickness of 10 μm, and the second transition layer NiCr system has a thickness of 20 μm.

[0067] On the second transition layer between the outer surface of the three-section tenon structure and the corresponding inner surface of the mortise structure, the first section (such as...) Figure 1 (Leftmost mortise and tenon structure) Al x CoCrFeNi coating: Al content 1%, 3%, 5%; second stage (e.g.) Figure 1 (Torch and mortise structure in the middle section) AlCoCrFeNiSi x Coating: Si content 1%, 3%, 5%; Third stage (e.g.) Figure 1 (Rightmost mortise and tenon structure) AlCoCrFeNiMo x Coating: Mo content 1%, 3%, 5%; the thickness of a single layer of high-entropy alloy coating on each segment of the outer surface of the tenon structure is 150 μm; the total thickness is 450 μm; the thickness of a single layer of high-entropy alloy coating on each segment of the inner surface of the corresponding mortise structure is 10 μm; the total thickness is 30 μm.

[0068] On the second transition layer of the three-segment limiting hole structure surface and the fixed hole structure surface, the first segment has a MoS2 content of 1%, 3%, and 5%, the second segment has a TiC content of 1%, 3%, and 5%, and the third segment has a CeO2 content of 1%, 3%, and 5%. The thickness of each high-entropy alloy single-layer coating on the limiting hole structure surface and the fixed hole structure surface is 6 μm; the total thickness is 18 μm.

[0069] (iv) Grinding and polishing the AlCoCrFeNi-based high-entropy alloy coating sample obtained in step three.

[0070] (v) Joint assembly: The drill pipe joint after coating treatment is assembled. The assembly process is as follows: First, the tenon structure of the drill pipe joint is inserted into the mortise groove of the corresponding mortise structure. Then, it is rotated counterclockwise around the axis to screw the tenon into the mortise. Finally, the pins are inserted into the oblique fixing hole and the limiting hole to complete the fixation.

[0071] The prepared drill pipe joint tenon and mortise structure coating was subjected to the following tests, with three sets of parallel tests for each test. The results are as follows:

[0072] Test 1: Tribological properties

[0073] The drill pipe joint with the AlCoCrFeNi-based coating deposited in Example 1 was placed in a friction and wear testing machine for friction and wear experiments. The experimental results showed that the friction and wear volume was 0.27~0.43 mm. 3 between.

[0074] Test 2: Corrosion Resistance

[0075] The drill pipe joint with the AlCoCrFeNi-based coating deposited in Example 1 was placed in an electrochemical workstation for corrosion performance testing. The results showed that the corrosion potential was between -0.75 V and -0.62 V.

[0076] Example 2

[0077] The preparation method is the same as in Example 1, except that:

[0078] On the second transition layer between the outer surface of the three-section tenon structure and the inner surface of the corresponding mortise structure, the first section Al x CoCrFeNi coating: Al content 2%, 4%, 6%; second stage AlCoCrFeNiSi x Coating: Si content 2%, 4%, 6%; Third stage AlCoCrFeNiMo x Coatings: Mo content 2%, 4%, 6%; the thickness of the transition layer and coating is consistent with that in Example 1.

[0079] On the second transition layer of the three-segment limiting hole structure surface and the fixed hole structure surface, the first segment has a MoS2 content of 2%, 4%, and 6%, the second segment has a TiC content of 2%, 4%, and 6%, and the third segment has a CeO2 content of 2%, 4%, and 6%. The thickness of the transition layer and the coating is consistent with that in Example 1.

[0080] The prepared drill pipe joint tenon and mortise structure coating was subjected to the following tests, with three sets of parallel tests for each test. The results are as follows:

[0081] Test 1: Tribological properties

[0082] The drill pipe joint with the AlCoCrFeNi-based coating deposited in Example 2 was placed in a friction and wear testing machine for friction and wear experiments. The experimental results showed that the friction and wear volume was 0.1~0.25 mm. 3 between.

[0083] Test 2: Corrosion Resistance

[0084] The drill pipe joint with the AlCoCrFeNi-based coating deposited in Example 2 was placed in an electrochemical workstation for corrosion performance testing. The results showed that the corrosion potential was between -0.68 V and -0.57 V.

[0085] Example 3:

[0086] The preparation method is the same as in Example 1, except that:

[0087] On the second transition layer between the outer surface of the three-section mortise and tenon structure and the outer surface of the inverted trapezoidal tenon structure, the first section Al xCoCrFeNi coating: Al content 3%, 5%, 8%; second stage AlCoCrFeNiSi x Coating: Si content 3%, 5%, 8%; Third stage AlCoCrFeNiMo x Coatings: Mo content 3%, 5%, 8%; the thickness of the transition layer and coating is consistent with that in Example 1.

[0088] On the second transition layer of the three-segment limiting hole structure surface and the fixed hole structure surface, the first segment has a MoS2 content of 3%, 5%, and 8%, the second segment has a TiC content of 3%, 5%, and 8%, and the third segment has a CeO2 content of 3%, 5%, and 8%. The thickness of the transition layer and the coating is consistent with that in Example 1.

[0089] The prepared drill pipe joint tenon and mortise structure coating was subjected to the following tests, with three sets of parallel tests for each test. The results are as follows:

[0090] Test 1: Tribological properties

[0091] The drill pipe joint with the AlCoCrFeNi-based coating deposited in Example 3 was placed in a friction and wear testing machine for friction and wear experiments. The experimental results showed that the wear volume was 0.05~0.18 mm. 3 between.

[0092] Test 2: Corrosion Resistance

[0093] The drill pipe joint with the AlCoCrFeNi-based coating deposited in Example 3 was placed in an electrochemical workstation for corrosion performance testing. The results showed that the corrosion potential was between -0.55 V and -0.35 V.

[0094] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A segmented tenon-and-mortise drill pipe joint, characterized in that, The structure includes a first section, a second section, and a third section that are equidistantly distributed along the direction from the drill pipe body to the end of the drill pipe joint, forming a three-section mortise and tenon structure; a limiting hole structure located in the central area of ​​the mortise and tenon structure; and an oblique fixing hole structure that penetrates the mortise and tenon structure; wherein the mortise and tenon structure consists of an inverted trapezoidal tenon structure with rounded corners and a corresponding mortise structure; On the outer surface of the tenon, the corresponding inner surface of the mortise, the surface of the limiting hole structure, and the surface of the fixing hole structure of the three-section mortise and tenon structure, a transition layer and a multi-layer gradient AlCoCrFeNi-based high-entropy alloy coating are sequentially distributed along the direction outward from the substrate. The outer surfaces of the tenon structures and / or the inner surfaces of the corresponding mortise structures in the first, second, and third sections are respectively coated with Al content, Si content, and Mo content increasing sequentially. x CoCrFeNi, AlCoCrFeNiSi x AlCoCrFeNiMo x Multi-gradient composite coating; A multi-gradient composite coating of AlCoCrFeNi / x-MoS2, AlCoCrFeNi / x-TiC, and AlCoCrFeNi / x-CeO2 with increasing MoS2, TiC, and CeO2 content is applied to the surfaces of the limiting hole structure and / or fixing hole structure in the first, second, and third sections, respectively.

2. The segmented tenon-and-mortise drill pipe joint as described in claim 1, characterized in that, Along the direction from the drill pipe body to the end of the drill pipe joint, the length and / or height of the inverted trapezoidal tenon structure in the three-section mortise and tenon structure increase sequentially.

3. The segmented tenon-and-mortise drill pipe joint as described in claim 1, characterized in that, The rounded corners are located at the two corners where the bottom of the inverted trapezoidal tenon connects to the main body of the drill pipe joint. They are arc-shaped rounded corners, and the difference between the rounded corners on both sides does not exceed 5°. The angle range of the rounded corners on both sides is between 10° and 20°.

4. The segmented tenon-and-mortise drill pipe joint as described in claim 1, characterized in that, The limiting hole structure is square and located at the center of each inverted trapezoidal tenon structure. Its inclination direction is consistent with that of the tenon structure. The tenon and the corresponding mortise are limited by inserting a pin.

5. The segmented tenon-and-mortise drill pipe joint as described in claim 1, characterized in that, The fixing hole structure is an oblique hole. Each tenon and mortise structure has two fixing holes that pass through and connect to the inverted trapezoidal tenon. The two fixing holes are symmetrically distributed according to the center of the limiting hole, and the line connecting the centers of each hole is parallel to the long side of the top of the inverted trapezoidal tenon.

6. The segmented tenon-and-mortise drill pipe joint as described in claim 1, characterized in that, The transition layer consists of two layers. For the outer surface of the tenon in the mortise and tenon structure, the first transition layer near the drill pipe joint substrate is a Ni-Al system, and the second transition layer is a NiCrAlY system. For the inner surface of the mortise, the surface of the limiting hole structure, and the surface of the fixing hole structure, the first transition layer near the drill pipe joint substrate is a Si or Cr system, and the second transition layer is a NiCr or CrN system.

7. The segmented tenon-and-mortise drill pipe joint as described in claim 1, characterized in that, On the transition layer of the outer surface of the tenon structure, the Al content of the first section of the tenon structure increases sequentially, with the increase not exceeding 15%. x CoCrFeNi multi-gradient composite coating; the second section's tenon structure is coated with AlCoCrFeNiSi, where the Si content increases sequentially, with the increase not exceeding 20%. x Multi-gradient composite coating; the third segment's tenon structure is coated with AlCoCrFeNiMo, where the Mo content increases sequentially, with the increase not exceeding 25%. x Multi-gradient composite coating; and the total thickness of the multi-layer gradient AlCoCrFeNi-based high-entropy alloy coating on the outer surface of each tenon structure is 450~600 μm, with 3~5 coating layers.

8. The segmented tenon-and-mortise drill pipe joint as described in claim 1, characterized in that, On the transition layer corresponding to the inner surface of the mortise structure, the Al content of the first segment of the mortise structure increases sequentially, with the increase not exceeding 10%. x CoCrFeNi multi-gradient composite coating; the second section features an AlCoCrFeNiSi coating with progressively increasing Si content, with the increase not exceeding 15%. x Multi-gradient composite coating; the third segment features an AlCoCrFeNiMo coating with progressively increasing Mo content, with the increase not exceeding 20%. x Multi-gradient composite coating; and the total thickness of the multi-layer gradient AlCoCrFeNi-based high-entropy alloy coating on the inner surface of each mortise structure is 20~50 μm, with 3~5 coating layers.

9. The segmented tenon-and-mortise drill pipe joint as described in claim 1, characterized in that, On the transition layer of the surface of the limiting hole structure and / or the surface of the fixing hole structure, the first segment of the limiting hole structure is coated with an AlCoCrFeNi / x-MoS2 multi-gradient composite coating with progressively increasing MoS2 content, the increase not exceeding 8%; the second segment of the limiting hole structure is coated with an AlCoCrFeNi / x-TiC multi-gradient composite coating with progressively increasing TiC content, the increase not exceeding 10%; the third segment of the limiting hole structure is coated with an AlCoCrFeNi / x-CeO2 multi-gradient composite coating with progressively increasing CeO2 content, the increase not exceeding 9%; and the total thickness of the multi-layer gradient AlCoCrFeNi-based high-entropy alloy coating on the surface of each segment of the limiting hole structure is 18~48 μm, and the number of coating layers is 3~5.

10. The segmented tenon-and-mortise drill pipe joint as described in any one of claims 1-9, characterized in that, Includes the following steps: Drill pipe joint outer shape processing: The drill pipe joint is shaped and processed by CNC machining, and the following are made in sequence: frustum, three-section tenon and mortise structure distributed along the direction from the drill pipe body to the end of the joint, limiting hole structure located in the central area of ​​the tenon and mortise structure, and oblique fixing hole structure penetrating the tenon and mortise structure. The outer surface and inner hole of the tenon and mortise structure are pre-treated. Coating powder preparation: The coating powder required for the AlCoCrFeNi-based high-entropy alloy coating was prepared using a powder preparation process; Preparation of transition layers and high-entropy alloy coatings: Two transition layers composed of Ni-Al and NiCrAlY systems are prepared on the outer surface of the tenon structure using a surface coating process. Si or Cr systems are prepared as the first transition layer and NiCr or CrN systems are prepared as the second transition layer on the inner surface of the corresponding mortise, the surface of the limiting hole structure, and the surface of the fixing hole structure. On the two transition layers, corresponding multilayer gradient AlCoCrFeNi-based high-entropy alloy coatings are prepared respectively. Post-coating treatment: The formed AlCoCrFeNi-based high-entropy alloy coating is polished and sealed. Joint assembly: The drill pipe joint after coating treatment is assembled. The assembly process is as follows: First, the tenon structure of the drill pipe joint is inserted into the mortise groove of the corresponding mortise structure. Then, it is rotated counterclockwise around the axis to screw the tenon into the mortise. Finally, the pins are inserted into the oblique fixing holes and limiting holes to complete the fixation.

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