Large-size thick-wall high-strength drill pipe and its preparation method

Abstract

The application relates to a large-size thick-wall high-strength feeding drill rod and a preparation method thereof. The drill rod comprises an elongated drill rod female joint with a lifting clamp groove, a thick-wall slip clamp holding section, a drill rod pipe body, and a drill rod male joint. The end of the drill rod pipe body is provided with a thickened end. The drill rod pipe body is connected with the thick-wall slip clamp holding section, the drill rod male joint, and the elongated drill rod female joint with a lifting clamp groove through a welding mode. The yield strength of the drill rod pipe body and the thick-wall slip clamp holding section is 150-180 ksi. The yield strength of the drill rod male joint and the elongated drill rod female joint with a lifting clamp groove is 135 ksi-145 ksi. After the two ends of the drill rod pipe body are thickened, the thickened ends are respectively welded with the thick-wall slip clamp holding section and the drill rod male joint. Then, the elongated drill rod female joint with a lifting clamp groove is welded at the other end of the thick-wall slip clamp holding section. Finally, overall quenching and tempering heat treatment is carried out. The large-size thick-wall high-strength feeding drill rod manufactured through the application has high tensile strength and high lifting clamp lifting strength, and is suitable for drilling applications in super-deep wells and ocean deepwater wells.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of drill pipe manufacturing, in particular to a large-specification thick-wall high-strength running-in drill pipe and a preparation method thereof. BACKGROUND

[0002] In land ultra-deep and ocean ultra-deep water drilling operations, a running-in drill pipe is needed to lower the casing into the hole. With the increase of drilling depth, the problem of overlength and overweight of the pipe string becomes increasingly prominent, and the weight of the casing string may exceed 900 tons. If the tripping operation under complex working conditions is considered, in order to ensure safety, the drill pipe needs to have higher tensile allowance, and the conventional drill pipe for drilling obviously cannot meet this requirement, so it is urgent to develop a large-specification, thick-wall, high-strength drill pipe to improve its carrying capacity.

[0003] At present, the thick-wall drill pipe with a 6-5 / 8 inch outer diameter, a wall thickness of 19.05 mm and a V150 steel grade has been applied to casing running operations. In order to further improve the carrying capacity of the running-in drill pipe, it has become a focus of drill pipe research and development to develop a thick-wall drill pipe with larger size, thicker wall thickness and higher steel grade. However, with the increase of the outer diameter and wall thickness of the drill pipe body, the size of the weld neck also increases accordingly, which will cause two problems:

[0004] Firstly, in order to meet the lifting capacity of the elevator, the outer diameter of the drill pipe joint needs to be further increased passively. For example, the outer diameter of the weld neck of the 6-5 / 8 inch, 20.65 mm thick-wall, 165 ksi high-strength running-in drill pipe is designed to be 185 mm, and the outer diameter of the drill pipe joint needs to reach more than 230 mm to provide sufficient lifting capacity. However, such a large joint outer diameter will bring many problems in the process of production and manufacturing and drilling use.

[0005] Secondly, after the size of the weld neck increases, the wall thickness of the weld neck may reach or exceed 40 mm. At this time, if the weld area is subjected to quenching and tempering heat treatment by medium-frequency induction heating, it is difficult to achieve uniform heating or quenching and cooling of the inner and outer walls, resulting in significant differences in the microstructure and performance of the inner and outer walls. In addition, due to the influence of the quenching temperature gradient, the welded area inevitably has a heat-affected zone, and the microstructure of the heat-affected zone is a low-strength dual-phase structure, which leads to low strength, poor toughness and poor fatigue performance of the welded area. Therefore, the welded area will become a weak link of the entire drill string in terms of tensile lifting capacity, and may fail due to fracture in complex accidents.

[0006] Therefore, for a large-specification, thick-wall, high-strength drill pipe, two difficult problems need to be solved: firstly, how to achieve a good match between the tensile capacity of the pipe body and the lifting capacity of the elevator through reasonable structure and strength design; and secondly, how to effectively avoid the problems of microstructure and performance differences between the inner and outer walls and low strength of the dual-phase zone caused by the existing weld heat treatment process in the production and manufacturing process. SUMMARY

[0007] To solve the above problems, the application provides a large-specification thick-wall high-strength running-in drill pipe and a preparation method thereof.

[0008] In a first aspect, the application provides a large-specification thick-wall high-strength running-in drill pipe, which adopts the following technical scheme:

[0009] The large-specification thick-wall high-strength running-in drill pipe comprises an elongated drill pipe female joint with a lifting clamp groove, a thick-wall slip clamp holding section, a drill pipe body, and a drill pipe male joint. The end of the drill pipe body is provided with a thickened end. The drill pipe body is connected to the thick-wall slip clamp holding section, the drill pipe male joint, and the elongated drill pipe female joint with a lifting clamp groove through welding.

[0010] The yield strength of the drill pipe body and the thick-wall slip clamp holding section is 150-180 ksi, and the yield strength of the drill pipe male joint and the elongated drill pipe female joint with a lifting clamp groove is 135 ksi-145 ksi.

[0011] The inner and outer diameters of the thick-wall slip clamp holding section are the same as the inner and outer diameters of the thickened end of the drill pipe body and the inner and outer diameters of the welding neck of the elongated drill pipe female joint with a lifting clamp groove.

[0012] The outer diameter of the drill pipe female joint at the lifting clamp groove is smaller than the outer diameter of the welding neck.

[0013] The inner and outer diameters of the drill pipe female joint at the lifting clamp groove satisfy the following relationship with the inner and outer diameters of the drill pipe body:

[0014] Further, the outer diameter of the drill pipe body is 149.2 mm-177.8 mm, and the wall thickness is 12.7 mm-38.1 mm.

[0015] Further, the length of the thick-wall slip clamp holding section is 800-1200 mm.

[0016] Further, the length of the elongated drill pipe female joint with a lifting clamp groove is 800-1200 mm, and the length of the lifting clamp groove is >400 mm.

[0017] In a second aspect, the application provides a preparation method of a large-specification thick-wall high-strength running-in drill pipe, which comprises the following steps: thickening the two ends of the drill pipe body, respectively welding the thickened ends to the thick-wall slip clamp holding section and the drill pipe male joint, and then welding the drill pipe female joint to the other end of the thick-wall slip clamp holding section. After the above welding is completed, the whole is subjected to quenching and tempering heat treatment.

[0018] Further, the specific steps are as follows:

[0019] S1, thickening and pretreatment of the drill pipe body end: the drill pipe body end is heated to 1000-1500℃ in stages, end upsetting thickening treatment is performed, after thickening forming, the inner and outer surface quality is checked, then when the temperature of the thickened end region is reduced to below 700℃, induction heating normalizing heat treatment is performed, then air cooling to room temperature, end inner and outer diameter size finishing is performed;

[0020] S2, drill pipe joint forming and pretreatment: the drill pipe male joint adopts hot-rolled annealed thick-walled pipe rough machining size shape or solid bar material die forging forming after annealed rough machining size shape; the lengthened type drill pipe female joint with a lifting slot adopts hot-rolled annealed thick-walled pipe rough machining size shape or solid bar material die forging forming after annealed rough machining size shape; the drill pipe male joint and the lengthened type drill pipe female joint with a lifting slot are precisely machined in terms of the neck size;

[0021] S3, drill pipe body and thick-walled slip clamping section, male / female joint friction welding and post-welding treatment: the thickened ends of the drill pipe body are first welded with the drill pipe male joint and the thick-walled slip clamping section respectively, then the lengthened type drill pipe female joint with a lifting slot is welded at the other end of the thick-walled slip clamping section, inner flash is immediately cut off by an inner punch after each welding; the outer flash is annealed, then the outer flash is turned; the inner and outer surfaces of the welding area are ground to be smooth and flat by using a grinding wheel or a grinding belt;

[0022] S4, overall heat treatment of the drill pipe: the welded drill pipe is subjected to stepwise continuous heating furnace heat treatment, the quenching temperature is 860-920℃, the holding time is 60-90min; the quenching cooling is performed by inner spraying and outer spraying water; the tempering temperature is 570-620℃, the holding time is 90-150min, after the furnace is discharged, the pipe body is hot straightened when the temperature is above 300℃, then air cooling to room temperature; the drill pipe is subjected to non-destructive testing;

[0023] S5, local heat treatment of the joint part: the male joint and the female joint at both ends are subjected to local induction heating tempering heat treatment, the tempering temperature is 600-660℃, the holding time is 240-480s, then air cooling to room temperature, the pipe body, the welding zone, the thickened end and the joint mechanical properties are sampled and analyzed according to the requirements;

[0024] S6, joint thread and drill pipe size finishing: the required lifting slot outer diameter and length are machined on the machining equipment, and the threads and shoulder faces of the male joint and the female joint are machined, and the drill pipe is obtained.

[0025] Further, the lengthened type drill pipe female joint with a lifting slot needs to be processed into a structure with a cylindrical shape at both ends and a conical shape in the middle during rough machining in S2.

[0026] In summary, the present application has the following beneficial effects:

[0027] 1. The present application can effectively increase the contact area between the elevator shoulder and the elevator by setting a smaller outer diameter of the elevator groove near the shoulder of the female joint elevator groove, without increasing the outer diameter of the joint, thereby increasing the lifting capacity of the elevator;

[0028] 2. The present application adopts the whole process of heating furnace to perform quenching and tempering heat treatment on the drill pipe, which can realize uniform heating of the inner and outer walls of the weld area and quenching cooling, and avoid the low-strength duplex zone generated by traditional medium-frequency induction quenching heating. The weld area and the pipe body and joint are all tempered sorbite structure with excellent comprehensive performance. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 It is a schematic diagram of an intermediate blank of a large-specification thick-walled high-strength drill pipe according to an embodiment of the present application;

[0030] Figure 2 It is a schematic diagram of a finished product of a large-specification thick-walled high-strength drill pipe according to an embodiment of the present application;

[0031] Figure 3 It is a schematic diagram of a finished product of a drill pipe in a comparative example of the present application;

[0032] Figure 4 It is a metallographic structure diagram (500 times) of the weld area of a large-specification thick-walled high-strength drill pipe according to an embodiment of the present application;

[0033] Figure 5 It is a duplex structure diagram (500 times) of the heat-affected zone in the heat treatment process of a drill pipe in a comparative example of the present application.

[0034] Reference signs: 1, female joint; 2, elevator groove; 3, thick-wall slip clamp section; 4, drill pipe body; 5, male joint; 6, weld (thick-wall slip clamp section-female joint); 7, weld (drill pipe body-thick-wall slip clamp section); 8, weld (drill pipe body-male joint). DETAILED DESCRIPTION

[0035] In order to more clearly illustrate the present application, the present application will be further described below in combination with preferred embodiments. It should be clear that the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0036] EMBODIMENT

[0037] A large-size thick-wall high-strength drill rod, which is a 168.3mm outer diameter, 22.23mm wall thickness, 165ksi steel grade wall thickness drill rod, comprises a lengthened type drill rod box joint with a hook slot, a thick-wall slip clamp section, a drill rod pipe body, and a drill rod pin joint, and the end of the drill rod pipe body is provided with a thickened end;

[0038] The drill rod pipe body raw material is a thick-wall seamless pipe with an outer diameter of 168.3mm, a wall thickness of 22.23mm, and a length of 7m-8m; the thick-wall slip clamp section raw material is a thick-wall seamless pipe with an outer diameter of 185mm and a wall thickness of 38.50mm, which is cut to a length of 1000mm; and the drill rod joint raw material is a hot-rolled annealed thick-wall pipe with an outer diameter of 225mm and a wall thickness of 65mm, the pin joint is cut to a length of 500mm, and the box joint is cut to a length of 1000mm.

[0039] The drill rod is prepared by the following method:

[0040] S1, thickening and pretreatment of the end of the drill rod pipe body: the end of the drill rod pipe body is gradually heated to 1000-1500℃, and two passes of thickening are performed, the thickening form is inner and outer thickening, the thickened outer diameter is 191-193mm, and the thickened inner diameter is 98-100mm. When the temperature of the thickened end region decreases to below 700℃, the thickened end is subjected to induction heating normalizing heat treatment, and then air-cooled to room temperature, the end inner and outer diameter size is precisely machined, the outer diameter is machined to 185mm, and the inner diameter is machined to 108mm;

[0041] S2, rough machining and pretreatment of the drill rod joint: the raw pipe of the saw-cut length joint is first roughly machined into a joint blank, wherein the inner diameter and the outer diameter are both reserved with a subsequent machining allowance of more than 1mm on one side, and the pin joint and the box joint are first machined into a tapered surface and reserved with a machining allowance at the threaded part; the box joint adopts a tapered surface transition between the welding neck and the outer diameter of the large wrench, so that it can smoothly travel on the conveying roller during subsequent overall heat treatment;

[0042] The drill rod pin joint and the box joint welding neck size are precisely machined to an outer diameter of 185mm and an inner diameter of 108mm, which is the same as the precise machining size of the pipe body thickened end, and the same as the inner and outer diameters of the thick-wall slip clamp section;

[0043] S3. Friction welding of drill pipe body, thick-walled slip clamping section, male / female joint, and post-weld treatment: First, weld the male joint and thick-walled slip clamping section to the thickened ends of the drill pipe body. Then, weld the extended female joint with lifting slot to the other end of the thick-walled slip clamping section. The welding shortening should be at least 10mm to ensure the extrusion of interface impurities and effective welding on both sides. Immediately after each weld, use an internal punch to cut the inner flash; anneal the outer flash, then machine it; grind the inner and outer surfaces of the welding area with a grinding wheel or belt until smooth and flat. The finished drill pipe intermediate blank is as follows: Figure 1 As shown;

[0044] S4. Overall heat treatment of the drill pipe: After welding, the drill pipe is sequentially sent to a quenching and tempering furnace for heat treatment. The furnace type is a walking beam furnace. The quenching temperature is 860℃-920℃, and the holding time is 60-90min. The quenching cooling is achieved by internal spraying and external water spraying. After quenching, the temperature of the tube body, the thickened end, and the thick-walled slip support section are all below 90℃. The tempering temperature is 570℃-620℃, and the holding time is 90-150min. After exiting the furnace, hot straightening is performed when the tube body temperature is above 300℃, and then air-cooled to room temperature. Non-destructive testing is then performed on the drill pipe.

[0045] S5. Localized heat treatment of the joint area: The male and female joints at both ends undergo induction heating and tempering heat treatment. The heating range includes the large clamps and threaded areas of the male and female joints, as well as the lifting groove area of ​​the female joint. The tempering temperature is 600℃-660℃, and the holding time is 240s-480s, followed by air cooling to room temperature. Samples are taken as required to analyze the mechanical properties of the pipe body, weld area, thickened end, and joint.

[0046] S6. Finishing of connector threads and drill pipe dimensions: On machining equipment, the male and female connectors are precision machined, with the inner and outer diameters machined to the target dimensions. The required outer diameter and length of the hanger groove are machined, and the connector threads and shoulder surface are machined. The final drill pipe product is as follows: Figure 2 As shown.

[0047] Comparative Example

[0048] A drill pipe, which is a thick-walled drill pipe with an outer diameter of 168.3 mm, a wall thickness of 22.23 mm, and made of 165 ksi steel grade.

[0049] It includes a drill pipe body, a male connector, a female connector, and a thick-walled slip clamping section. The drill pipe body is provided with a thickened end. The drill pipe body is connected to the thick-walled slip clamping section by welding. The two ends of the thick-walled slip clamping section are respectively connected to a female connector and a male connector.

[0050] The thick-walled seamless pipe with an outer diameter of 168.3 mm, a wall thickness of 22.23 mm and a length of 7 m-8 m is used as the raw material of the drill pipe body; the thick-walled seamless pipe with an outer diameter of 185 mm and a wall thickness of 38.50 mm in a quenched and tempered state is used as the raw material of the thick-walled slip clamping section, and the steel grade is not less than 150 ksi, and the length of the cut raw material is 1000 mm; the hot-rolled annealed thick-walled pipe with an outer diameter of 225 mm and a wall thickness of 95 mm is used as the raw material of the drill pipe joint, the length of the cut male joint is 500 mm, and the length of the cut female joint is 1000 mm.

[0051] Specifically, the method is prepared by the following method:

[0052] S1, thickening the end of the drill pipe body: gradually heating the end of the drill pipe body to 1000-1500℃, and performing two passes of thickening, the thickening form is internal and external thickening, the thickening outer diameter is 191-193 mm, and the thickening inner diameter is 98-100 mm;

[0053] S2, heat treatment of the drill pipe body: the drill pipe body is sequentially sent into a quenching and tempering furnace for heat treatment, the furnace form is a step-by-step heating furnace, the quenching temperature is 860-920℃, and the holding time is 60-90 min; the quenching cooling adopts internal spraying and external water spraying, the temperature of the pipe body and the thickened end after quenching is lower than 90℃; the tempering temperature is 570-620℃, the holding time is 90-150 min, and the pipe body is hot straightened when the temperature is higher than 300℃ after being taken out of the furnace, and then air-cooled to room temperature. The internal and external diameters of the end are precisely processed, the outer diameter is processed to 185 mm, the inner diameter is processed to 108 mm, and the drill pipe is non-destructively detected;

[0054] S3, drill pipe joint processing: the cut raw material pipe of the male and female joints is first roughly processed into a joint blank, and a certain amount of finishing allowance is reserved for the internal and external diameters and the threaded area to be processed, and then the quenched and tempered heat treatment is performed: the quenching temperature is 880-940℃, the holding time is 120-240 min, and the water cooling is to room temperature; the tempering temperature is 600-660℃, the holding time is 120-240 min, and then the internal and external diameters, threads, shoulder surfaces are precisely processed;

[0055] S4, welding of the thick-walled slip clamping section to the drill pipe body and post-welding heat treatment: the thick-walled slip clamping section is friction welded to one side of the thickened end of the drill pipe body, the welding shortening amount is ensured to be more than 10 mm, and the inner flash is punched after the welding is completed; the outer flash is annealed and then turned; then the welding area is quenched and tempered by using medium-frequency induction heating: the quenching temperature is 880-920℃, the holding time is 180-360 s, the quenching cooling adopts external PAG quenching liquid and internal compressed air, the tempering temperature is 620-660℃, the holding time is 180-360 s, and then air-cooled to room temperature, and the inner and outer surfaces of the welding area are ground to be smooth and flat by using a grinding wheel or a grinding belt;

[0056] S5, welding male and female joints and post-weld heat treatment: welding a lengthened drill pipe female joint at the other end of the thick-wall slip clamp section, welding a male joint at the other thickened end of the pipe body, the welding shrinkage is ensured to be more than 10 mm, and after the welding is completed, the inner flash is punched; the outer flash is annealed and then turned; then the welding area is quenched and tempered by using medium-frequency induction heating, the quenching temperature is 880-920 °C, the holding time is 180-360 s, the quenching cooling is performed by using outer PAG quenching liquid and inner compressed air spraying, the tempering temperature is 620-660 °C, the holding time is 180-360 s, and then air cooling is performed to room temperature, the inner and outer surfaces of the welding area are ground to be smooth and flat by using a grinding wheel or a grinding belt, and the mechanical properties of the pipe body, the welding area, the thickened end and the joint are sampled and analyzed according to requirements. The final drill pipe product is shown in FIGS. 1-3. Figure 3

[0057] For the drill pipes prepared in the above examples and the comparative example, the mechanical property samples and the metallographic analysis samples of the welding areas are sampled according to the API 5DP standard requirements, the tensile property test, the impact property test and the metallographic structure analysis are performed, and the test results are shown in the following table. (Note: 1, when calculating the allowable suspended weight of the slip clamp section, the friction coefficient is 0.08, the slip clamp length is 22 in, and the slip clamp back angle is 14°; 2, when calculating the lifting capacity of the elevator, the elevator strength is selected to be 130 ksi.)

[0058] Performance indicators Examples Comparative examples Tensile strength / MPa 1257 913 Yield strength / MPa 1180 779 Impact energy at -20°C / J 65 62 Tensile load of the tube / t 1184 1184 Allowance of the suspended weight of the clamp segment / t 1562 1420 Tensile load at the elevator slot / t 1498 1498 Tensile load of the friction weld / t 2131 1407 Lifting capacity of the joint elevator / t 1207 976 Overall tensile capacity of the drill pipe / t 1184 976

[0059] As can be seen from the comparison of the mechanical properties of the welding areas in the above table, the strength of the welding area in the example is greatly improved, the yield strength is increased by about 50% compared with the comparative example, and reaches the same steel grade of 165 ksi as the pipe body;

[0060] In addition, for the drill pipes obtained in the example and the comparative example, the carrying capacity of each part is calculated based on the material strength and size, and as can be seen from the table, the lifting capacity of the joint of the drill pipe obtained in the comparative example is only 976 tons, which is lower than the 1184 t of the pipe body, and becomes the short board of the tensile capacity of the drill pipe; the lifting capacity of the joint of the drill pipe obtained in the example is 1207 tons, which is higher than the 1184 tons of the pipe body, so that the overall tensile capacity of the drill pipe is determined by the pipe body, which meets the design principle of the drill pipe; and the carrying capacity of the welding seam is greatly improved, which avoids the possibility of fracture failure of the welding seam under overload.

[0061] The comparison results of the metallographic structures can be referred to FIGS. 4-6. Figure 4 and FIGS. 7-9. Figure 5 ​It can be seen that, in the comparative example, because the welding zone is heat treated by using a conventional induction heating method, a heat affected zone inevitably exists at the edge of the heating zone, the heating temperature of which is between the Ac1 line and the Ac3 line, thus resulting in a dual-phase structure of ferrite and sorbite after heat treatment. In the example, because the whole heat treatment method is used, the final welding zone obtains a uniform and fine tempered sorbite structure, and the strength and toughness thereof will be better than the dual-phase structure.

[0062] The above are all modifications or obvious technical inspirations made by those skilled in the art after reading the specification, which do not contribute to the creativity of the embodiments, but as long as they are within the scope of the claims of the present application, they should be protected by the Patent Law.

Claims

1. A large-size, thick-walled, high-strength feed drill pipe, characterized in that, It includes an extended drill pipe female connector with a lifting slot, a thick-walled slip clamping section, a drill pipe body, and a drill pipe male connector. The drill pipe body is provided with a thickened end. The drill pipe body is connected to the thick-walled slip clamping section, the drill pipe male connector, and the extended drill pipe female connector with a lifting slot by welding. The yield strength of the drill pipe body and the thick-walled slip clamping section is 150-180 ksi, and the yield strength of the drill pipe male connector and the extended drill pipe female connector with lifting slot is 135-145 ksi. The inner and outer diameters of the thick-walled slip clamping section are the same as the inner and outer diameters of the thickened end weld neck of the drill pipe body, and are also the same as the inner and outer diameters of the weld neck of the extended drill pipe female joint with lifting slot. The outer diameter of the drill pipe female joint hanger groove is smaller than the outer diameter of the weld neck; The inner and outer diameters of the drill pipe female connector hanger groove must satisfy the following relationship with the inner and outer diameters of the drill pipe body:

2. The large-size, thick-walled, high-strength feed drill pipe according to claim 1, characterized in that, The outer diameter of the drill pipe is 149.2mm-177.8mm, and the wall thickness is 12.7mm-38.1mm.

3. The large-size, thick-walled, high-strength feed drill pipe according to claim 1, characterized in that, The length of the thick-walled clamping section is 800-1200mm.

4. The large-size, thick-walled, high-strength feed drill pipe according to claim 1, characterized in that, The length of the extended drill pipe female connector with lifting slot is 800-1200mm, and the length of the lifting slot is >400mm.

5. The method for preparing large-size, thick-walled, high-strength feed drill pipe according to any one of claims 1-4, characterized in that, Includes the following steps: After thickening both ends of the drill pipe body, it is welded to the thick-walled slip clamping section and the drill pipe male connector respectively. Then, the drill pipe female connector is welded to the other end of the thick-walled slip clamping section. After the above welding is completed, the whole body is quenched and tempered.

6. The method for preparing large-size, thick-walled, high-strength feed drill pipe according to claim 5, characterized in that, The specific steps are as follows: S1. Thickening and pretreatment of drill pipe end: The end of the drill pipe is heated to 1000-1500℃ in stages for end upsetting and thickening. After thickening and forming, the quality of the inner and outer surfaces is checked. Then, when the temperature of the thickened end area drops to below 700℃, induction heating normalizing heat treatment is performed. Then, it is air-cooled to room temperature and the inner and outer diameters of the end are precision machined. S2. Drill pipe joint forming and pretreatment: The drill pipe male joint is made from hot-rolled annealed thick-walled tube with rough-machined dimensions or solid bar stock with die forging and then annealed with rough-machined dimensions; the extended drill pipe female joint with lifting slot is made from hot-rolled annealed thick-walled tube with rough-machined dimensions or solid bar stock with die forging and then annealed with rough-machined dimensions; the weld neck dimensions of the drill pipe male joint and the extended drill pipe female joint with lifting slot are precision machined; S3. Friction welding of drill pipe body and thick-walled slip clamping section, male / female joint and post-weld treatment: First, weld the drill pipe male joint and thick-walled slip clamping section to the thickened ends of the drill pipe body respectively. Then, weld the extended drill pipe female joint with lifting chuck groove to the other end of the thick-walled slip clamping section. Immediately after each welding, use an internal punch to cut and weld the inner flash. Anneal the outer flash and then turn the outer flash. Use a grinding wheel or abrasive belt to grind the inner and outer surfaces of the welding area until smooth and flat. S4. Overall heat treatment of the drill pipe: The welded drill pipe is subjected to heat treatment in a walking beam continuous heating furnace. The quenching temperature is 860℃-920℃, and the holding time is 60-90min. The quenching cooling is achieved by internal spraying and external water spraying. The tempering temperature is 570℃-620℃, and the holding time is 90-150min. After exiting the furnace, the drill pipe is hot-straightened when the pipe temperature is above 300℃, and then air-cooled to room temperature. The drill pipe is then subjected to non-destructive testing. S5. Local heat treatment of joints: Local induction heating and tempering heat treatment is performed on the male and female joints at both ends. The tempering temperature is 600℃-660℃ and the holding time is 240s-480s. Then, the joints are air-cooled to room temperature. Samples are taken and analyzed according to the requirements to determine the mechanical properties of the pipe body, weld area, thickened end and joint. S6. Precision machining of connector threads and drill rod dimensions: On a machining equipment, the required outer diameter and length of the hanger groove are machined, and the threads and shoulder surfaces of the male and female connectors are machined.

7. The method for preparing large-size, thick-walled, high-strength feed drill pipe according to claim 6, characterized in that, The extended drill pipe female connector with lifting slot in S2 needs to be machined into a cylindrical shape at both ends and a conical shape in the middle during rough machining.

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