Ultrahigh-strength corrosion-resistant drill rod and preparation method thereof

Abstract

The invention discloses an ultrahigh-strength corrosion-resistant drill rod and a preparation method thereof, and relates to the technical field of design and manufacturing of drilling tools. The drill rod comprises, by mass, 0.23%-0.29% of C, 0.20%-0.35% of Si, 0.40%-0.60% of Mn, smaller than or equal to 0.012% of P, smaller than or equal to 0.003% of S, 2.20%-2.50% of Cr, 0.80%-0.95% of Ni, 0.75%-0.87% of Mo, 0.20%-0.35% of Cu, 0.06%-0.11% of V, 0.030%-0.045% of Ti, 0.003%-0.009% of RE, 0.010%-0.020% of Al, 0.009%-0.018% of Ca, smaller than or equal to 0.0015% of O, smaller than or equal to 0.00015% of H, smaller than or equal to 0.005% of N and the balance Fe and other inevitable impurities. Wherein RE is a rare earth element. The drill rod has excellent comprehensive performance such as strength, plasticity, low-temperature toughness and corrosion resistance, can meet the requirements of deep and ultra-deep low-temperature and complex oil and gas field development on high-strength, high-low-temperature toughness and corrosion-resistant drill rods, and remarkably improves the safety and reliability and prolongs the service life of the drill rod.

Description

Technical Field

[0001] This invention relates to the field of drill tool design and manufacturing technology, and in particular to an ultra-high strength corrosion-resistant drill pipe and its preparation method. Background Technology

[0002] Drill pipe is a crucial tool in oil and gas development, and its corrosion has been a long-standing problem. Under the influence of dissolved oxygen, CO2, H2S, dissolved salts, and various acids in the downhole media and drilling mud, corrosion is almost unavoidable. While appropriate internal coating materials can typically be used to address corrosion on the inner surface of the drill pipe, there is currently no mature solution for corrosion on the outer surface. External wall corrosion has become a key factor in the obsolescence of high-strength drill pipes, and oilfields urgently require measures to reduce corrosion at the material level. Moreover, the higher the strength of the drill pipe, the greater the impact of corrosion on operational safety. Corrosion reduces the effective wall thickness of the drill pipe, causes stress concentration, and often induces stress corrosion and corrosion fatigue. Drill pipes with corrosion defects require higher safety toughness. From a materials perspective, significantly increasing the content of alloying elements such as Cr would greatly benefit CO2 corrosion resistance, but it would significantly increase costs. Furthermore, high-strength steel drill pipes are difficult to prevent H2S stress corrosion. In the development of deep, ultra-deep, and extra-deep oil and gas wells, the original design required V150 steel grade drill pipes for strength. However, due to concerns about fracture accidents, S135 steel grade drill pipes were often used instead, hindering the development of ultra-deep and extra-deep wells. Currently used S135 drill pipes, while lacking sulfide stress corrosion resistance, possess some hydrogen-induced delayed fracture (HFC) resistance, failing to fracture after 120 hours according to the NACE A method and D solution HFC test. If appropriate composition design and processing techniques are employed, V150 and higher grade drill pipes can achieve the same resistance to HFCs after 120 hours of HFC test (i.e., quasi-sulfur-resistant drill pipes). This would provide sufficient time for engineering safety measures to prevent drilling accidents in ultra-deep and extra-deep well drilling processes encountering H2S environments. To meet the needs of ultra-deep and extra-deep oil and gas development in corrosive environments, there is an urgent need to develop economical, high-strength, and high-toughness drill pipes with certain corrosion resistance.

[0003] Unlike ordinary drill pipes (yield strength range of 137–207 MPa), sulfur-resistant or quasi-sulfur-resistant drill pipes have a narrower yield strength range (103 MPa), requiring stricter material uniformity and correspondingly more demanding processing techniques. The strength requirements for 150 ksi grade quasi-sulfur-resistant drill pipes are a yield strength of 1034–1138 MPa and a tensile strength ≥1103 MPa; while for 165 ksi grade quasi-sulfur-resistant drill pipes, the requirements are a yield strength of 1138–1241 MPa and a tensile strength ≥1207 MPa.

[0004] This invention addresses the above-mentioned situation by proposing an ultra-high strength corrosion-resistant drill pipe with a strength of V150 or higher and its preparation method, in order to meet the demand for ultra-high strength corrosion-resistant drill pipes in the development of oil and gas fields under harsh conditions such as ultra-deep and extra-deep low temperatures. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide an ultra-high strength corrosion-resistant drill pipe and its preparation method. The drill pipe has high strength, good low-temperature toughness and corrosion resistance, and is suitable for the development of oil and gas fields under harsh working conditions such as ultra-deep and extra-deep low temperature, so as to solve the problems of unreasonable strength and toughness matching, insufficient low-temperature toughness and severe corrosion of existing high-strength drill pipes.

[0006] The technical solution of the present invention is as follows: In a first aspect, an ultra-high strength corrosion-resistant drill pipe is provided, wherein the ultra-high strength corrosion-resistant drill pipe comprises the following chemical components by mass percentage: C 0.23%~0.29%, Si 0.20%~0.35%, Mn 0.40%~0.60%, P≤0.012%, S≤0.003%, Cr 2.20%~2.50%, Ni 0.80%~0.95%, Mo 0.75%~0.87%, Cu 0.20%~0.35%, V 0.06%~0.11%, Ti 0.030%~0.045%, RE 0.003%~0.009%, Al 0.010%~0.020%, Ca 0.009%~0.018%, O≤0.0015%, H≤0.00015%, N≤0.005%, balance Fe and other unavoidable impurities; RE represents rare earth elements.

[0007] In the preferred embodiment, the chemical composition of the ultra-high strength corrosion-resistant drill pipe, by mass percentage, satisfies at least one of the following conditions: Mo / P > 60, Al / N ≥ 2, Ca / S ≥ 3, and (Ca+Re) / S ≥ 4.

[0008] In a preferred embodiment, the rare earth element is Ce.

[0009] According to the preferred technical solution, the ultra-high strength corrosion-resistant drill pipe comprises the following chemical components by weight percentage: C 0.23%~0.25%, Si 0.20%~0.35%, Mn 0.40%~0.49%, P≤0.012%, S≤0.002%, Cr 2.20%~2.35%, Ni 0.80%~0.87%, Mo 0.75%~0.79%, V 0.06%~0.08%, Ti 0.030%~0.035%, RE 0.003%~0.005%, Al 0.010%~0.015%, Ca 0.009%~0.014%, O≤0.0015%, H≤0.00015%, N≤0.0046%, with the balance being Fe and other unavoidable impurities.

[0010] According to the preferred technical solution, the ultra-high strength corrosion-resistant drill pipe comprises the following chemical components by weight percentage: C 0.26%~0.29%, Si 0.24%~0.31%, Mn 0.51%~0.60%, P≤0.010%, S≤0.0019%, Cr 2.39%~2.50%, Ni 0.90%~0.95%, Mo 0.82%~0.87%, V 0.09%~0.11%, Ti 0.038%~0.045%, RE 0.007%~0.009%, Al 0.016%~0.020%, Ca 0.015%~0.018%, O≤0.0012%, H≤0.00012%, N≤0.0043%, with the balance being Fe and other unavoidable impurities.

[0011] Secondly, a method for preparing ultra-high strength corrosion-resistant drill pipe as described in the first aspect is provided, comprising the following steps: According to the chemical composition of the ultra-high strength corrosion-resistant drill pipe described in the first aspect, after batching, smelting, and continuous casting, a continuously cast billet is obtained; After hot piercing, hot continuous rolling and controlled rolling are performed on the continuously cast bar billet, a tube billet is obtained; After thickening the tube ends, heat treating the entire tube body, hot straightening, and stress-relieving tempering, the tube blank is used to obtain the drill pipe body; After friction welding and heat treatment of the drill pipe body and drill pipe joint, and secondary heat treatment of the welded parts, the ultra-high strength corrosion-resistant drill pipe is obtained.

[0012] The preferred technical solution, which involves batching, smelting, and continuously casting the ultra-high strength corrosion-resistant drill pipe according to the chemical composition described in the first aspect, specifically includes the following steps to obtain a continuously cast billet: The raw materials are prepared by mixing the chemical composition of the ultra-high strength corrosion-resistant drill pipe described in the first aspect; The raw materials are smelted in an oxygen-blown converter, refined outside the ladle, and degassed under vacuum to obtain molten steel; The molten steel is cast into a continuously cast bar billet.

[0013] In the preferred technical solution, the steps of obtaining a tube blank after hot piercing, hot continuous rolling, and controlled rolling of the continuously cast bar billet specifically include: The continuously cast billet is heated to 1220℃~1250℃ in an annular heating furnace and held for 90~120min. It is then hot-pierced at 1180℃~1230℃, hot-rolled at 900℃~1170℃, with the rolling ratio controlled at ≥5 and the final rolling temperature controlled at 900℃. After controlled rolling and sizing, it is air-cooled.

[0014] The preferred technical solution, which involves thickening the tube ends, heat treating the entire tube body, hot straightening, and stress-relieving tempering of the tube blank to obtain the drill pipe body, specifically includes the following steps: Pipe end thickening: The pipe end of the pipe blank is heated to 1050℃~1150℃, and upsetting is performed 1~3 times using the inner and outer diameter mold and the pipe end temperature gradient to obtain the inner and outer thickening dimensions and shape of the pipe end, forming the first pre-drilled rod pipe body; Normalizing heat treatment: The first pre-drilled rod tube body is heated to 910℃~930℃ in a controlled atmosphere furnace and held for 40~60min, then air-cooled; then tempered at 680℃~710℃ for 90~120min, and water-cooled after tempering to obtain the second pre-drilled rod tube body. Heat treatment: The second pre-drilled rod tube body is heated to 880℃~900℃ in a controlled atmosphere furnace and held for 40~60min. It is then water-quenched inside and outside with a cooling rate ≥25℃ / s. Then it is tempered at 570℃~600℃ for 90~120min and water-cooled after tempering to obtain the third pre-drilled rod tube body. Hot straightening and stress-relief tempering: The third pre-drilled pipe body is heated to 550℃~580℃ for hot straightening, and then stress-relief tempering is performed at 550℃~580℃ for 90~120 minutes. After tempering, it is air-cooled to obtain the drill pipe body.

[0015] The preferred technical solution, which involves friction welding and heat treatment of the drill pipe body and drill pipe joint, followed by secondary heat treatment of the welded area to obtain the ultra-high strength corrosion-resistant drill pipe, specifically includes the following steps: Friction welding and heat treatment: The inertial friction welding method is adopted, and the rotation speed, back pressure and upsetting pressure are controlled to weld the drill pipe body to the drill pipe joint. When the instantaneous temperature after friction welding upsetting is 920℃~950℃, the inner and outer surfaces of the weld area are sprayed with a mixture of water and compressed air for quenching. Then, the medium frequency induction heating is carried out to 670℃~700℃ for tempering for 5 minutes. After tempering, the flash and burrs inside and outside the weld area are processed. Secondary heat treatment of the welded area: The weld area is heated to 900℃~920℃ using medium frequency induction heating. A mixture of water and compressed air is sprayed onto the inner and outer surfaces of the weld area for quenching. Then, the area is tempered to 650℃~680℃ for 5 minutes using medium frequency induction heating.

[0016] Beneficial Effects: This invention provides an ultra-high strength corrosion-resistant drill pipe with excellent comprehensive properties such as strength, plasticity, low-temperature toughness, and corrosion resistance. The minimum yield strength is specified to reach steel grades of 150 kSi and 165 kSi, respectively. The room temperature yield strength of the pipe body is 1086–1201 MPa, the tensile strength is 1180–1291 MPa, the elongation is 21–24%, and the longitudinal Charpy V-notch impact toughness of the pipe body at -40℃ is 131–168 J. The weld bearing capacity is greater than that of the pipe body. The transverse Charpy V-notch impact toughness of the drill pipe weld at -40℃ is 82–96 J. It is also suitable for applications at temperatures of 150℃–200℃ and a mineralization of 20×10⁻⁶. 4 mg / L, Cl - 10~13×10 4 mg / L, H2S 0.003~12.4×10 4 mg / m 3 Under conditions of 0.5%–3% CO2 and 0.5%–1.0% oxygen, the uniform corrosion rate is <2.0 mm / a (compared to 3.5 mm / a for ordinary drill pipes). It does not fracture after 120 hours of hydrogen-induced delayed fracture testing using the NACE A method in D solution (compared to less than 50 hours for ordinary drill pipes). This meets the requirements for high-strength, high-low temperature toughness, and corrosion resistance drill pipes in deep and ultra-deep cryogenic and complex oil and gas field development, significantly improving the safety, reliability, and service life of drill pipes. Detailed Implementation

[0017] This invention provides an ultra-high strength corrosion-resistant drill pipe and its preparation method. To make the purpose, technical solution and effects of this invention clearer and more explicit, the invention is further described in detail below.

[0018] This invention provides an ultra-high strength corrosion-resistant drill pipe, wherein, by mass percentage, the ultra-high strength corrosion-resistant drill pipe comprises the following chemical components: C 0.23%~0.29%, Si 0.20%~0.35%, Mn 0.40%~0.60%, P≤0.012%, S≤0.003%, Cr 2.20%~2.50%, Ni 0.80%~0.95%, Mo 0.75%~0.87%, Cu 0.20%~0.35%, V 0.06%~0.11%, Ti 0.030%~0.045%, RE 0.003%~0.009%, Al 0.010%~0.020%, Ca 0.009%~0.018%, O≤0.0015%, H≤0.00015%, N≤0.005%, balance Fe and other unavoidable impurities; RE represents rare earth elements.

[0019] Specifically, to ensure that drill pipes meet multiple requirements such as strength, plasticity, toughness, corrosion resistance, and processability, their chemical composition must be rationally designed. In terms of composition design, this invention employs medium-low carbon (C), controlled Mn, alloying with Cr, Ni, Mo, and Cu, and micro-alloying with V and Ti. Rare earth (RE) elements are added, and harmful elements such as P, S, O, H, and N are controlled in the steel. Al and Si are fully deoxidized killed steel, and the molten steel is treated with Ca. Through the individual effects of C and alloying elements, especially their synergistic effects, the hardenability of the steel is improved (C-Cr-Mo-Ni), purification (P, S, O, H, N control), grain refinement (V-Ti-Al), inclusion modification (Ca-Re), improved weld heat-affected zone performance (V-Ti-Al), and improved corrosion resistance (Cr-Mo-Ni-Cu). This lays the foundation for drill pipes to achieve high strength, good plasticity, low-temperature toughness, corrosion resistance, and weldability. The drill pipe of this invention specifies minimum yield strengths of 150 kSi and 165 kSi steel grades, respectively. The room temperature yield strength of the pipe body is 1086–1201 MPa, tensile strength is 1180–1291 MPa, elongation is 21–24%, and the longitudinal Charpy V-notch impact toughness of the pipe body at -40℃ is 131–168 J. The weld bearing capacity is greater than that of the pipe body. The transverse Charpy V-notch impact toughness of the drill pipe weld at -40℃ is 82–96 J. This is achieved at temperatures of 150℃–200℃ and a mineralization of 20×10⁻⁶. 4 mg / L, Cl - 10~13×10 4 mg / L, H2S 0.003~12.4×10 4 mg / m 3Under conditions of 0.5%–3% CO2 and 0.5%–1.0% oxygen, the uniform corrosion rate is <2.0 mm / a (compared to 3.5 mm / a for ordinary drill pipes). It does not fracture after 120 hours of hydrogen-induced delayed fracture testing using the NACE A method in D solution (compared to less than 50 hours for ordinary drill pipes). This meets the requirements for high-strength, high-low temperature toughness, and corrosion resistance drill pipes in deep and ultra-deep cryogenic and complex oil and gas field development, significantly improving the safety, reliability, and service life of drill pipes.

[0020] The roles and content ranges of each element are as follows: C (Carbon): The most important strengthening element, ensuring the formation of a strong lath martensitic matrix after quenching, and providing secondary hardening through the precipitation of carbides during tempering. Too low a content is detrimental to hardenability and strength, while too high a content is detrimental to ductility, toughness, and weldability. Considering all factors, it is advisable to control the content within the range of 0.23% to 0.29%.

[0021] Silicon (Si) is the main deoxidizing element and also produces solid solution strengthening, improving tempering resistance. Too low a content affects the deoxidation effect, while too high a content will cause a decrease in plasticity and toughness. Considering all factors, it is advisable to control it within the range of 0.20% to 0.35%.

[0022] Manganese (Mn) is mainly used to improve the hardenability of steel, thereby increasing its strength, and also aids in deoxidation and sulfur fixation. However, it has a significant tendency to segregate and needs to be properly controlled. Considering all factors, it is advisable to control it within the range of 0.40% to 0.60%.

[0023] Cr (chromium): a core element for enhancing corrosion resistance. It promotes the formation of a dense, stable, Cr-rich passivation film (Cr2O3) on the surface, significantly improving resistance to uniform corrosion and chloride ion pitting. It also improves hardenability and strength. However, excessively high content increases costs. Considering all factors, it is advisable to control it within the range of 2.20% to 2.50%.

[0024] Ni (Ni): A key element for strengthening and toughening. It significantly improves the low-temperature toughness and fracture toughness of the matrix and lowers the brittle transition temperature. Synergistically with Cr, it further improves corrosion resistance, especially resistance to stress corrosion cracking in acidic or H₂S-containing environments. However, excessively high content increases costs. Considering all factors, it is advisable to control it within the range of 0.80% to 0.95%.

[0025] Mo (Mo): A powerful strengthening and corrosion-resistant element. A strong solid solution strengthener, it significantly improves resistance to high-temperature tempering (secondary hardening) and inhibits temper brittleness. It greatly enhances the stability of the passivation film, especially its resistance to chloride ion pitting and crevice corrosion. However, excessively high content increases costs. Considering all factors, it is advisable to control it within the range of 0.75% to 0.87%.

[0026] Cu (copper): It mainly produces a significant precipitation strengthening effect through the precipitation of Cu-rich phase (ε-Cu) during aging, while also improving the steel's resistance to atmospheric and acid corrosion. Considering all factors, it is advisable to control it within the range of 0.20% to 0.35%.

[0027] Vanadium (V): In steel, V primarily enhances overall performance through precipitation strengthening, grain refinement and toughening, and hardenability regulation. V combines with carbon and nitrogen to form fine VC, VN, or V(C,N) nanoprecipitates. These particles can precipitate in both austenite and ferrite, effectively hindering dislocation movement and increasing steel strength. During high-temperature tempering, V carbonitrides inhibit softening and improve tempering stability. V inhibits austenite grain growth, especially in the weld heat-affected zone (HAZ), where V carbonitrides pin grain boundaries, reducing coarse-grained regions and refining the final microstructure, thus improving the strength and toughness of the HAZ. V not only improves strength by refining grains but also significantly improves low-temperature impact toughness. V also enhances hardenability; when synergistically combined with elements such as Mn and Cr, V can further optimize hardenability. V carbides exhibit high-temperature stability, effectively resisting softening in the high-temperature environment of deep wells. The synergistic effect of V with microalloying elements such as Ti can further unleash its potential. However, excessive V may increase brittleness and cost due to the formation of coarse carbonitrides. Considering all factors, it is advisable to control it within the range of 0.06% to 0.11%.

[0028] Titanium (Ti): In steel, Ti enhances overall performance primarily through precipitation strengthening, grain refinement and toughening, and microstructure regulation. Ti combines with C and N to form fine TiC, TiN, or composite carbonitrides (such as Ti4C2S2). These nanoscale precipitates effectively hinder dislocation movement, significantly increasing steel strength. TiN preferentially precipitates in the high-temperature austenite region, inhibiting grain growth and refining the original austenite grains, thereby improving steel strength and toughness. The fine-grained structure also improves low-temperature impact toughness and fatigue resistance. The addition of Ti forms a dense passivation film (such as TiO2), enhancing the steel's corrosion resistance in corrosive environments containing H2S and CO2. Ti combines with N to form high-melting-point TiN particles (stable to approximately 1400℃), which pin austenite grain boundaries during the high-temperature thermal cycling of welding, effectively preventing grain coarsening. The refined austenite grains transform into an even finer microstructure upon cooling, thus improving the strength and toughness of the heat-affected zone. TiN particles can act as nucleation sites for phase transformation, promoting the formation of phase transformation structures and significantly improving the low-temperature impact toughness of the heat-affected zone. However, excessive Ti may lead to the precipitation of coarse TiN phases, causing brittleness and increasing costs. Considering all factors, it is advisable to control the content within the range of 0.030% to 0.045%.

[0029] Rare earth elements (RE): can purify molten steel and improve inclusion morphology: RE (such as Ce) can combine with impurities such as S and O to form high-melting-point compounds such as RE2O3 and RE2S3, reducing harmful inclusions (such as MnS) and improving the purity of steel; rare earth elements can change the morphology of sulfides (from elongated to spherical), improving the transverse impact toughness of steel. They also refine grains and improve strength and toughness: RE can inhibit austenite grain growth, refine the microstructure, and improve the strength and toughness of steel. Furthermore, they improve corrosion resistance: RE can form a dense oxide film on the steel surface, improving corrosion resistance. However, excessive content may lead to inclusion aggregation and increase costs. Considering all factors, it is advisable to control the content within the range of 0.003% to 0.009%.

[0030] Al (aluminum): Deoxidation and purification of molten steel: Al is a strong deoxidizer, preferentially combining with O in molten steel to form Al2O3, reducing oxide inclusions and improving steel purity. Grain refinement and improved strength and toughness: Al combines with N to form AlN, which pins austenite grain boundaries during hot rolling or welding, inhibiting grain growth and refining the final microstructure (ferrite / bainite). Grain refinement can simultaneously improve the strength and toughness of steel and lower the ductile-brittle transition temperature. Improved weldability: Appropriate amounts of Al can reduce grain coarsening in the weld heat-affected zone and improve weld toughness. However, excessive content will form excessive Al2O3 hard inclusions, affecting the fatigue performance of steel. If coarse AlN is formed, it may promote embrittlement of the weld heat-affected zone. Considering all factors, it is advisable to control the content within the range of 0.010% to 0.020%.

[0031] Ca (Calcium): Inclusion modification and improved toughness: Ca can combine with S and O in steel to form CaS, CaO, or composite calcium aluminate (CaO·Al2O3), transforming brittle MnS inclusions into spherical or spindle-shaped structures, reducing anisotropy, and improving transverse impact toughness. Improved corrosion resistance: Ca treatment can optimize the oxide film structure on the steel surface, improving corrosion resistance in corrosive environments containing H2S, CO2, etc., and reducing pitting corrosion and stress corrosion cracking (SCC). Improved continuous casting processability: Ca can prevent Al2O3 from forming nodules at the continuous casting nozzle, improving the surface quality of the continuously cast billet. However, excessive addition may lead to liquid calcium aluminate inclusions, affecting purity. Considering all factors, it is advisable to control it within the range of 0.009% to 0.018%.

[0032] P (phosphorus): A harmful element that mainly affects the ductility, toughness, and corrosion resistance of steel. P should ideally be controlled to ≤0.012%.

[0033] Sulfur (S): A harmful element that mainly affects the ductility, toughness, and corrosion resistance of steel. It is advisable to control S to ≤0.003%.

[0034] O (O): A harmful element that mainly affects the ductility, toughness, and corrosion resistance of steel. O should be controlled to ≤0.0015%.

[0035] H (hydrogen): A harmful element that mainly affects the ductility, toughness, and corrosion resistance of steel. H should ideally be controlled to ≤0.00015%.

[0036] Nitrogen (N): A harmful element that primarily affects the ductility, toughness, and corrosion resistance of steel. It is advisable to control N to ≤0.005%.

[0037] In some embodiments, the chemical composition of the ultra-high strength corrosion-resistant drill pipe, by mass percentage, satisfies at least one of the following conditions: Mo / P > 60, Al / N ≥ 2, Ca / S ≥ 3, and (Ca+Re) / S ≥ 4.

[0038] In this embodiment, Mo / P > 60 to control the adverse effect of P segregation on toughness; Al / N ≥ 2 to eliminate the adverse effect of N on toughness and strain aging properties; Ca / S ≥ 3 and (Ca+Re) / S ≥ 4 to control the effect of inclusion shape control modification treatment and improve the ductility, toughness and corrosion resistance of steel.

[0039] In some implementations, RE can be Ce (cerium).

[0040] In some embodiments, the ultra-high strength corrosion-resistant drill pipe comprises the following chemical components by weight percentage: C 0.23%~0.25%, Si 0.20%~0.35%, Mn 0.40%~0.49%, P≤0.012%, S≤0.002%, Cr 2.20%~2.35%, Ni 0.80%~0.87%, Mo 0.75%~0.79%, V 0.06%~0.08%, Ti 0.030%~0.035%, RE 0.003%~0.005%, Al 0.010%~0.015%, Ca 0.009%~0.014%, O≤0.0015%, H≤0.00015%, N≤0.0046%, with the balance being Fe and other unavoidable impurities.

[0041] In this embodiment, the specified minimum yield strength level of the ultra-high strength corrosion-resistant drill pipe can reach 150 ksi, with a room temperature yield strength of 1086–1097 MPa, tensile strength of 1180–1192 MPa, elongation of 24%, and a longitudinal Charpy V-notch impact toughness of 161–168 J at -40℃. The weld bearing capacity is greater than that of the pipe body; the transverse Charpy V-notch impact toughness of the drill pipe weld at -40℃ is 91–96 J. It operates at temperatures of 150℃–200℃ and a mineralization of 20×10⁻⁶. 4 mg / L, Cl - 10~13×10 4 mg / L, H2S 0.003~12.4×10 4 mg / m 3Under conditions of 0.5%–3% CO2 and 0.5%–1.0% oxygen, the uniform corrosion rate is <2.0 mm / a, and no fracture occurs after 150 hours of hydrogen-induced delayed fracture test in D solution according to NACE A method.

[0042] In some embodiments, the ultra-high strength corrosion-resistant drill pipe comprises the following chemical components by weight percentage: C 0.26%~0.29%, Si 0.24%~0.31%, Mn 0.51%~0.60%, P≤0.010%, S≤0.0019%, Cr 2.39%~2.50%, Ni 0.90%~0.95%, Mo 0.82%~0.87%, V 0.09%~0.11%, Ti 0.038%~0.045%, RE 0.007%~0.009%, Al 0.016%~0.020%, Ca 0.015%~0.018%, O≤0.0012%, H≤0.00012%, N≤0.0043%, with the balance being Fe and other unavoidable impurities.

[0043] In this embodiment, the specified minimum yield strength level of the ultra-high strength corrosion-resistant drill pipe can reach 165 ksi, with a room temperature yield strength of 1190–1201 MPa, tensile strength of 1280–1291 MPa, elongation of 21%, and a longitudinal Charpy V-notch impact toughness of 131–138 J at -40℃. The weld bearing capacity is greater than that of the pipe body; the transverse Charpy V-notch impact toughness of the drill pipe weld at -40℃ is 82–87 J. It is also suitable for temperatures of 150℃–200℃ and a mineralization of 20×10⁻⁶. 4 mg / L, Cl - 10~13×10 4 mg / L, H2S 0.003~12.4×10 4 mg / m 3 Under conditions of 0.5%–3% CO2 and 0.5%–1.0% oxygen, the uniform corrosion rate is <2.0 mm / a, and no fracture occurs after 120 hours of hydrogen-induced delayed fracture test in D solution according to NACE A method.

[0044] This invention also provides a method for preparing the ultra-high strength corrosion-resistant drill pipe as described above, comprising the following steps: S1. Based on the chemical composition of the ultra-high strength corrosion-resistant drill pipe as described above, the raw materials are prepared, smelted, and continuously cast to obtain a continuously cast billet. S2. After hot piercing, hot continuous rolling and controlled rolling of the continuously cast bar billet, a tube billet is obtained; S3. After thickening the tube ends, heat treating the entire tube body, hot straightening, and stress-relieving tempering, the tube blank is obtained as a drill pipe body. S4. After friction welding and heat treatment of the drill pipe body and drill pipe joint, and secondary heat treatment of the welded parts, the ultra-high strength corrosion-resistant drill pipe is obtained.

[0045] Specifically, this invention develops a matching preparation process for the chemical composition with the above-mentioned proportions. This process mainly involves steelmaking (including ladle refining and vacuum degassing), continuous casting (electromagnetic stirring and light reduction), hot piercing and hot continuous rolling in the austenitic region and controlled rolling, pipe end thickening, full pipe heat treatment, hot straightening, stress-relieving tempering, friction welding and post-weld heat treatment, etc., to obtain a fine and uniform tempered sorbite microstructure in the material, thereby achieving a reasonable match between the material's strength, plasticity, low-temperature toughness, corrosion resistance, etc.

[0046] In step S1, in some embodiments, the step of obtaining a continuously cast billet after batching, smelting, and continuously casting according to the chemical composition of the ultra-high strength corrosion-resistant drill pipe as described above specifically includes: The raw materials are prepared by mixing the ingredients according to the chemical composition of the ultra-high strength corrosion-resistant drill pipe as described above. The raw materials are smelted in an oxygen-blown converter, refined outside the ladle, and degassed under vacuum to obtain molten steel (containing the above-mentioned chemical components and having high purity). The molten steel is cast into a continuous casting billet (feeding Si-Ca wire and rare earth wire, and using electromagnetic stirring and light reduction technology during continuous casting to control the center segregation of the continuous casting billet).

[0047] In step S2, in some embodiments, the step of obtaining a tube blank after hot piercing, hot continuous rolling, and controlled rolling of the continuously cast bar billet specifically includes: The continuously cast billet is heated to 1220℃~1250℃ in an annular heating furnace and held for 90~120min. It is then hot-pierced at 1180℃~1230℃, hot-rolled at 900℃~1170℃, with the rolling ratio controlled at ≥5 and the final rolling temperature controlled at 900℃. After controlled rolling and sizing, it is air-cooled.

[0048] In this step, controlling the rolling ratio to be ≥5 and the final rolling temperature to be 900℃ is to obtain a finer and more uniform microstructure.

[0049] In step S3, in some embodiments, the steps of thickening the tube ends, heat treating the entire tube body, hot straightening, and stress-relieving tempering the tube blank to obtain the drill pipe body specifically include: Pipe end thickening: The pipe end of the pipe blank is heated to 1050℃~1150℃, and upsetting is performed 1~3 times using the inner and outer diameter mold and the pipe end temperature gradient to obtain the inner and outer thickening dimensions and shape of the pipe end, forming the first pre-drilled rod pipe body; Normalizing heat treatment: The first pre-drilled rod tube body is heated to 910℃~930℃ in a controlled atmosphere furnace and held for 40~60min, then air-cooled; then tempered at 680℃~710℃ for 90~120min, and water-cooled after tempering to obtain the second pre-drilled rod tube body. Heat treatment: The second pre-drilled rod tube body is heated to 880℃~900℃ in a controlled atmosphere furnace and held for 40~60min. It is then water-quenched inside and outside with a cooling rate ≥25℃ / s. Then it is tempered at 570℃~600℃ for 90~120min and water-cooled after tempering to obtain the third pre-drilled rod tube body. Hot straightening and stress-relief tempering: The third pre-drilled pipe body is heated to 550℃~580℃ for hot straightening, and then stress-relief tempering is performed at 550℃~580℃ for 90~120 minutes. After tempering, it is air-cooled to obtain the drill pipe body.

[0050] In this step, a protective atmosphere heating is used to prevent decarburization. The heat treatment process of normalizing followed by high-temperature tempering and quenching followed by high-temperature tempering eliminates the non-martensitic structure formed during pipe end thickening. Recrystallization refines the grains and microstructure of the pipe ends and body. Internal and external water-spray quenching with a cooling rate ≥25℃ / s ensures that almost all martensite is obtained after quenching, and fine, uniform tempered sorbite is obtained after tempering. Water cooling after tempering avoids potential temper brittleness. Hot straightening reduces work hardening and residual stress during the straightening process. Stress-relief tempering effectively eliminates or reduces residual stress generated during hot straightening. Reduced residual stress significantly improves the corrosion resistance of the drill pipe, thereby increasing its fatigue life.

[0051] In step S4, in some embodiments, the steps of friction welding and heat treatment of the drill pipe body and drill pipe joint, and secondary heat treatment of the welded parts to obtain the ultra-high strength corrosion-resistant drill pipe specifically include: Friction welding and heat treatment: The inertial friction welding method is adopted, and the rotation speed, back pressure and upsetting pressure are controlled to weld the drill pipe body to the drill pipe joint. When the instantaneous temperature after friction welding upsetting is 920℃~950℃, the inner and outer surfaces of the weld area are sprayed with a mixture of water and compressed air for quenching. Then, the medium frequency induction heating is carried out to 670℃~700℃ for tempering for 5 minutes. After tempering, the flash and burrs inside and outside the weld area are processed. Secondary heat treatment of the welded area: The weld area is heated to 900℃~920℃ using medium frequency induction heating. A mixture of water and compressed air is sprayed onto the inner and outer surfaces of the weld area for quenching. Then, the area is tempered to 650℃~680℃ for 5 minutes using medium frequency induction heating.

[0052] In this step, the residual heat from friction welding is used for weld heat treatment, which organically combines phase transformation strengthening and deformation strengthening, significantly improving the overall performance of the weld. Utilizing the residual heat from friction welding for heat treatment also saves energy. Medium-frequency induction heating and high-temperature tempering are beneficial for removing burrs and flash from both inside and outside the weld zone.

[0053] In some embodiments, the preparation method further includes, after step S4, applying a protective coating to the inner surface of the drill pipe to improve its corrosion resistance and corrosion fatigue resistance.

[0054] In summary, this invention employs low to medium C content, controlled Mn content, Cr, Ni, Mo, and Cu alloying, V and Ti micro-alloying, and the addition of rare earth (RE) elements to control harmful elements such as P, S, O, H, and N in the steel. It utilizes fully deoxidized Al and Si killed steel and treats the molten steel with Ca. Through the individual and especially synergistic effects of C and alloying elements, the hardenability of the steel is improved (C-Cr-Mo-Ni), purification (P, S, O, H, N control), grain refinement (V-Ti-Al), inclusion modification (Ca-Re), improved weld heat-affected zone performance (V-Ti-Al), and improved corrosion resistance (Cr-Mo-Ni-Cu). This lays the foundation for achieving high strength, good plasticity, low-temperature toughness, corrosion resistance, and weldability in drill pipes. Based on this, the present invention develops a matching preparation process for the aforementioned proportions of chemical composition. This process primarily involves steelmaking (including ladle refining and vacuum degassing), continuous casting (electromagnetic stirring and light reduction), hot piercing and hot continuous rolling in the austenitic region, controlled rolling, pipe end thickening, full-body heat treatment, hot straightening, stress-relieving tempering, friction welding, and post-weld heat treatment. These processes enable the material to obtain a fine and uniform tempered sorbite microstructure, achieving a reasonable balance of strength, plasticity, low-temperature toughness, and corrosion resistance. The preparation method provided by this invention includes improving purity and uniformity, reducing segregation, controlling inclusion morphology, controlled rolling, reasonable heat treatment microstructure regulation, and residual stress control, enabling the drill pipe to achieve high strength while possessing good plasticity, low-temperature toughness, and corrosion resistance. Utilizing the aforementioned unique composition design and manufacturing process, the drill pipe achieves minimum yield strengths of 150ksi and 165ksi steel grades, respectively. The pipe body exhibits a room temperature yield strength of 1086–1201 MPa, a tensile strength of 1180–1291 MPa, an elongation of 21–24%, and a longitudinal Charpy V-notch impact toughness of 131–168 J at -40℃. The weld seam has a greater load-bearing capacity than the pipe body. The transverse Charpy V-notch impact toughness of the drill pipe weld at -40℃ is 82–96 J. This is achieved at temperatures between 150℃ and 200℃ and a mineralization of 20×10⁻⁶. 4 mg / L, Cl - 10~13×10 4 mg / L, H2S 0.003~12.4×104 mg / m 3 Under conditions of 0.5%–3% CO2 and 0.5%–1.0% oxygen, the uniform corrosion rate is <2.0 mm / a (compared to 3.5 mm / a for ordinary drill pipes). It does not fracture after 120 hours of hydrogen-induced delayed fracture testing using the NACE A method in D solution (compared to less than 50 hours for ordinary drill pipes). This meets the requirements for high-strength, high-low temperature toughness, and corrosion resistance drill pipes in deep and ultra-deep cryogenic and complex oil and gas field development, significantly improving the safety, reliability, and service life of drill pipes.

[0055] The present invention will be further described below through specific embodiments.

[0056] Example Embodiments 1-6 of the present invention provide an ultra-high strength corrosion-resistant drill pipe, the chemical composition of which is shown in Table 1 by mass percentage, with the balance being Fe and unavoidable impurities.

[0057] Table 1. Chemical composition of ultra-high strength corrosion-resistant drill pipes in Examples 1-6

[0058] The methods for preparing ultra-high strength corrosion-resistant drill pipes in Examples 1-6 include the following steps: (1) Steelmaking: Batching, oxygen blowing converter steelmaking, ladle refining and vacuum degassing to obtain molten steel containing the chemical composition of Table 1.

[0059] (2) Continuous casting: The molten steel is cast into a rod-shaped continuous casting billet, and Si-Ca wire and rare earth (Ce) wire are fed. Electromagnetic stirring and light reduction technology are used in the continuous casting process to control the segregation in the continuous casting billet.

[0060] (3) Piercing, hot rolling and controlled rolling: The continuously cast billet is heated to 1230℃ in an annular heating furnace and held for 120 min. It is then hot-pierced at 1180℃~1230℃ and hot-rolled at 900℃~1170℃. The rolling ratio is controlled to be ≥5 and the final rolling temperature is controlled to be 900℃. After controlled rolling and sizing, it is air-cooled.

[0061] (4) Thickening of pipe end: The pipe end is heated to 1100℃, and three upsetting processes are carried out using the inner and outer diameter molds and the pipe end temperature gradient to obtain the inner and outer thickening dimensions and shape of the pipe end, forming a drill pipe body without overall heat treatment.

[0062] (5) Heat treatment of the entire tube, hot straightening and stress-relieving tempering: Normalizing heat treatment: Heating is carried out in a controlled atmosphere furnace. The quenching temperature is controlled at 920℃ and the holding time is 40min. Air cooling is performed. The tempering temperature is 700℃ and the tempering time is 60min. The microstructure is fine and uniform pearlite + ferrite. Water cooling is performed after tempering.

[0063] Heat treatment: The drill pipe body is heated to 890℃ and held for 60 min in a controlled atmosphere furnace, then water-quenched inside and out with a cooling rate of ≥25℃ / s; then tempered at 570℃~600℃ (adjusted according to different steel grades, see Table 2 for details) for 120 min, and then water-cooled after tempering. The metallographic structure is tempered sorbite with a grain size of 9~10.

[0064] Hot straightening and stress-relief tempering: Heat the drill pipe body to 550℃~580℃ for hot straightening, and then stress-relief tempering at 550℃~580℃ for 120 minutes. After tempering, air cool (the hot straightening temperature and stress-relief tempering temperature are adjusted according to different steel grades, see Table 2 for details).

[0065] (6) Friction welding and heat treatment of drill pipe body and drill pipe joint: Select a suitable drill pipe joint, adopt inertial friction welding method, and reasonably control the rotation speed, back pressure and upsetting pressure to make the drill pipe body and drill pipe joint firmly welded together. Immediately after friction welding upsetting (920℃~950℃), spray water and compressed air mixture on the inner and outer surfaces of the weld area for quenching, and then heat to 680℃ for 5 minutes for tempering. The weld structure is tempered sorbite, and the heat-affected zone is a mixture of tempered sorbite, pearlite and ferrite. Then, process the flash and burrs inside and outside the weld area.

[0066] (7) Secondary heat treatment of the welded area: The weld area is heated to 910°C by medium frequency induction heating, and water and compressed air mixture is sprayed on the inner and outer surfaces of the weld area for quenching. Then, the weld area is heated to 660°C by medium frequency induction heating for 5 minutes for tempering.

[0067] (8) Inner coating: Whether to apply it depends on the needs.

[0068] Table 2. Heat treatment process and performance of ultra-high strength corrosion-resistant drill pipes in Examples 1-6

[0069] Note: 150ksi grade drill pipe has an outer diameter of 5 7 / 8 in (149.22 mm) and a wall thickness of 9.17 mm; 165ksi grade drill pipe has an outer diameter of 5 7 / 8 in (149.22 mm) and a wall thickness of 11.50 mm.

[0070] In summary, the ultra-high strength corrosion-resistant drill pipe of this invention possesses excellent comprehensive performance (see Table 2 for details). The mechanical properties of the pipe body are as follows: room temperature yield strength 1086–1201 MPa, tensile strength 1180–1291 MPa, elongation 21–24%, longitudinal Charpy V-notch impact toughness 131–168 J at -40℃; the weld bearing capacity is greater than that of the pipe body; the transverse Charpy V-notch impact toughness of the drill pipe weld at -40℃ is 82–96 J. At temperatures of 150℃–200℃ and a mineralization of 20×10⁻⁶, the pipe exhibits superior performance. 4 mg / L, Cl - 10~13×10 4 mg / L, H2S 0.003~12.4×10 4 mg / m 3 Under conditions of 0.5%–3% CO2 and 0.5%–1.0% oxygen, the uniform corrosion rate is <2.0 mm / a, and no fracture occurs after 120 hours of hydrogen-induced delayed fracture testing in D solution using the NACE A method. This achieves a reasonable balance of strength, plasticity, low-temperature toughness, and corrosion resistance. It can meet the requirements of high-strength, high-low-temperature toughness, and corrosion-resistant drill pipes for deep and ultra-deep cryogenic and complex oil and gas field development, significantly improving the safety, reliability, and service life of drill pipes. Specifically: 150ksi grade drill pipe: room temperature yield strength 1086~1097MPa, tensile strength 1180~1192MPa, elongation 24%, longitudinal Charpy V-notch impact toughness of the pipe body at -40℃ 161~168J; weld bearing capacity is greater than that of the pipe body; transverse Charpy V-notch impact toughness of the drill pipe weld at -40℃ 91~96J. At temperatures of 150℃~200℃ and a mineralization of 20×10⁻⁶... 4 mg / L, Cl - 10~13×10 4 mg / L, H2S 0.003~12.4×10 4 mg / m 3 Under conditions of 0.5%–3% CO2 and 0.5%–1.0% oxygen, the uniform corrosion rate is <2.0 mm / a, and no fracture occurs after 150 hours of hydrogen-induced delayed fracture test in D solution according to NACE A method.

[0071] 165ksi grade drill pipe: room temperature yield strength 1190~1201MPa, tensile strength 1280~1291MPa, elongation 21%, longitudinal Charpy V-notch impact toughness of the pipe body at -40℃ 131~138J; weld bearing capacity is greater than that of the pipe body; transverse Charpy V-notch impact toughness of the drill pipe weld at -40℃ 82~87J. At temperatures of 150℃~200℃ and a mineralization of 20×10⁻⁶... 4 mg / L, Cl - 10~13×10 4mg / L, H2S 0.003~12.4×10 4 mg / m 3 Under conditions of 0.5%–3% CO2 and 0.5%–1.0% oxygen, the uniform corrosion rate is <2.0 mm / a, and no fracture occurs after 120 hours of hydrogen-induced delayed fracture test in D solution according to NACE A method.

[0072] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A high-strength, corrosion-resistant drill pipe, characterized in that, The ultra-high strength corrosion-resistant drill pipe comprises the following chemical components by weight percentage: C 0.23%~0.29%, Si 0.20%~0.35%, Mn 0.40%~0.60%, P≤0.012%, S≤0.003%, Cr 2.20%~2.50%, Ni 0.80%~0.95%, Mo 0.75%~0.87%, Cu 0.20%~0.35%, V 0.06%~0.11%, Ti 0.030%~0.045%, RE 0.003%~0.009%, Al 0.010%~0.020%, Ca 0.009%~0.018%, O≤0.0015%, H≤0.00015%, N≤0.005%, balance Fe and other unavoidable impurities; RE represents rare earth elements.

2. The ultra-high strength corrosion-resistant drill pipe according to claim 1, characterized in that, The chemical composition of the ultra-high strength corrosion-resistant drill pipe, by mass percentage, satisfies at least one of the following conditions: Mo / P > 60, Al / N ≥ 2, Ca / S ≥ 3, and (Ca+Re) / S ≥ 4.

3. The ultra-high strength corrosion-resistant drill pipe according to claim 1, characterized in that, The rare earth element is Ce.

4. The ultra-high strength corrosion-resistant drill pipe according to claim 1, characterized in that, The ultra-high strength corrosion-resistant drill pipe comprises the following chemical components by weight percentage: C 0.23%~0.25%, Si 0.20%~0.35%, Mn 0.40%~0.49%, P≤0.012%, S≤0.002%, Cr 2.20%~2.35%, Ni 0.80%~0.87%, Mo 0.75%~0.79%, V 0.06%~0.08%, Ti 0.030%~0.035%, RE 0.003%~0.005%, Al 0.010%~0.015%, Ca 0.009%~0.014%, O≤0.0015%, H≤0.00015%, N≤0.0046%, with the balance being Fe and other unavoidable impurities.

5. The ultra-high strength corrosion-resistant drill pipe according to claim 1, characterized in that, The ultra-high strength corrosion-resistant drill pipe comprises the following chemical components by weight percentage: C 0.26%~0.29%, Si 0.24%~0.31%, Mn 0.51%~0.60%, P≤0.010%, S≤0.0019%, Cr 2.39%~2.50%, Ni 0.90%~0.95%, Mo 0.82%~0.87%, V 0.09%~0.11%, Ti 0.038%~0.045%, RE 0.007%~0.009%, Al 0.016%~0.020%, Ca 0.015%~0.018%, O≤0.0012%, H≤0.00012%, N≤0.0043%, with the balance being Fe and other unavoidable impurities.

6. A method for preparing an ultra-high strength corrosion-resistant drill pipe as described in any one of claims 1 to 5, characterized in that, Includes the following steps: After the chemical composition of the ultra-high strength corrosion-resistant drill pipe according to any one of claims 1 to 5 is prepared, smelted, and continuously cast, a continuously cast billet is obtained; After hot piercing, hot continuous rolling and controlled rolling are performed on the continuously cast bar billet, a tube billet is obtained; After thickening the tube ends, heat treating the entire tube body, hot straightening, and stress-relieving tempering, the tube blank is used to obtain the drill pipe body; After friction welding and heat treatment of the drill pipe body and drill pipe joint, and secondary heat treatment of the welded parts, the ultra-high strength corrosion-resistant drill pipe is obtained.

7. The preparation method according to claim 6, characterized in that, The specific steps for obtaining a continuously cast billet after batching, smelting, and continuously casting the chemical composition of the ultra-high strength corrosion-resistant drill pipe according to any one of claims 1 to 5 include: The raw materials are prepared by mixing the chemical composition of the ultra-high strength corrosion-resistant drill pipe according to any one of claims 1 to 5; The raw materials are smelted in an oxygen-blown converter, refined outside the ladle, and degassed under vacuum to obtain molten steel; The molten steel is cast into a continuously cast bar billet.

8. The preparation method according to claim 6, characterized in that, The steps of obtaining a tube blank by hot piercing, hot continuous rolling and controlled rolling of the continuously cast bar billet specifically include: The continuously cast billet is heated to 1220℃~1250℃ in an annular heating furnace and held for 90~120min. It is then hot-pierced at 1180℃~1230℃, hot-rolled at 900℃~1170℃, with the rolling ratio controlled at ≥5 and the final rolling temperature controlled at 900℃. After controlled rolling and sizing, it is air-cooled.

9. The preparation method according to claim 6, characterized in that, The specific steps for obtaining the drill pipe body after thickening the pipe ends, heat treating the entire pipe body, hot straightening, and stress-relieving tempering of the pipe blank include: Pipe end thickening: The pipe end of the pipe blank is heated to 1050℃~1150℃, and upsetting is performed 1~3 times using the inner and outer diameter mold and the pipe end temperature gradient to obtain the inner and outer thickening dimensions and shape of the pipe end, forming the first pre-drilled rod pipe body; Normalizing heat treatment: The first pre-drilled rod tube body is heated to 910℃~930℃ in a controlled atmosphere furnace and held for 40~60min, then air-cooled; then tempered at 680℃~710℃ for 90~120min, and water-cooled after tempering to obtain the second pre-drilled rod tube body. Heat treatment: The second pre-drilled rod tube body is heated to 880℃~900℃ in a controlled atmosphere furnace and held for 40~60min. It is then water-quenched inside and outside with a cooling rate ≥25℃ / s. Then it is tempered at 570℃~600℃ for 90~120min and water-cooled after tempering to obtain the third pre-drilled rod tube body. Hot straightening and stress-relief tempering: The third pre-drilled pipe body is heated to 550℃~580℃ for hot straightening, and then stress-relief tempering is performed at 550℃~580℃ for 90~120 minutes. After tempering, it is air-cooled to obtain the drill pipe body.

10. The preparation method according to claim 6, characterized in that, The specific steps for obtaining the ultra-high strength corrosion-resistant drill pipe after friction welding and heat treatment of the drill pipe body and drill pipe joint, and secondary heat treatment of the welded parts include: Friction welding and heat treatment: The inertial friction welding method is adopted, and the rotation speed, back pressure and upsetting pressure are controlled to weld the drill pipe body to the drill pipe joint. When the instantaneous temperature after friction welding upsetting is 920℃~950℃, the inner and outer surfaces of the weld area are sprayed with a mixture of water and compressed air for quenching. Then, the medium frequency induction heating is carried out to 670℃~700℃ for tempering for 5 minutes. After tempering, the flash and burrs inside and outside the weld area are processed. Secondary heat treatment of the welded area: The weld area is heated to 900℃~920℃ using medium frequency induction heating. A mixture of water and compressed air is sprayed onto the inner and outer surfaces of the weld area for quenching. Then, the area is tempered to 650℃~680℃ for 5 minutes using medium frequency induction heating.

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