High-strength sulfur-resistant drill pipe and preparation method and application thereof

Abstract

The application belongs to the technical field of anti-hydrogen sulfide corrosion oil drill pipe, and particularly relates to a high-strength anti-sulfur drill pipe and a preparation method and application thereof. The drill pipe comprises the following components in percentage by mass: C: 0.26%-0.29%, Si: 0.20%-0.40%, Mn: 0.58%-0.72%, P: 0.012% or less, S: 0.002% or less, Cr: 1.25%-1.35%, Ni: 1.05-1.20%, Mo: 0.42%-0.58%, Cu: 0.15-0.25%, Nb: 0.07%-0.10%, Ti: 0.015%-0.035%, Re: 0.012%-0.015%, Al: 0.009%-0.015%, Ca: 0.006%-0.012%, O: 0.002% or less, H: 0.00015% or less, and N: 0.0025% or less; Mo / P is controlled to be greater than or equal to 35, Al / N is controlled to be greater than or equal to 3, and (Ca+Re) / S is controlled to be greater than or equal to 9; the balance is Fe and other inevitable impurities. The yield strength of the drill pipe body can reach 95 ksi-125 ksi; and the -20 Charpy impact toughness of the body and the weld is greater than or equal to 100 J and 42 J, respectively.

Description

Technical Field

[0001] This invention belongs to the field of anti-hydrogen sulfide corrosion petroleum drill pipe technology, specifically relating to a high-strength anti-sulfur drill pipe, its preparation method, and its application. Background Technology

[0002] Acidic oil and gas constitute a significant proportion of my country's oil and gas resources, mainly distributed in the Southwest, Tarim, Daqing, Changqing, Dagang, and North China oil and gas fields. In hydrogen sulfide environments, steel materials are highly susceptible to sulfide stress corrosion damage under the combined effects of corrosive media and working stress, often leading to severe consequences. The higher the material strength, the greater the probability of sulfide stress corrosion damage. With the development of deep wells, ultra-deep wells, and highly acidic oil and gas fields, there are not only high requirements for the strength and toughness of drill pipes, but also for their resistance to hydrogen sulfide corrosion, especially hydrogen sulfide stress corrosion. However, the strength and toughness of materials often exhibit a trade-off with their resistance to sulfide stress corrosion, making the design and manufacture of high-strength, sulfur-resistant drill pipes extremely difficult.

[0003] Currently, the 105ksi grade of sulfur-resistant drill pipe steel, which can be tested using the NACE™ 0177A method and is widely used, is the most common grade. While there are patents and literature reports on sulfur-resistant drill pipes with grades of 120ksi, 125ksi, and even higher, they have not yet seen large-scale industrial application. Furthermore, the chemical composition range of these patented drill pipes is too broad, the manufacturing processes are highly customized, industrial production costs are high, and some component designs and preparation processes are not entirely reasonable, posing difficulties for product quality control and widespread use. This invention addresses these issues by proposing a steel grade design and preparation method for sulfur-resistant drill pipes to meet the needs of sulfur-resistant drill pipes in the development of acidic oil and gas fields. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a high-strength sulfur-resistant drill pipe, its preparation method, and its applications. The high-strength sulfur-resistant drill pipe provided by this invention has a yield strength of 105 ksi to 125 ksi and possesses sufficient toughness and resistance to hydrogen sulfide stress corrosion. Under NACE™ 0177A method, solution A loading and a 720-hour test showed no cracks or fractures, meeting the requirements for safe use of sulfur-resistant drill pipes in acidic deep oil and gas field development.

[0005] To ensure that the multiple requirements for strength, toughness, and resistance to hydrogen sulfide stress corrosion of drill pipes are met, this invention innovates in chemical composition and manufacturing.

[0006] In terms of composition, this invention uses medium-low carbon (C), controls Mn (Mn), adds Cr, Ni, Mo, Cu, Nb, and Ti for microalloying, and incorporates rare earth (Re) elements to control harmful elements such as P, S, O, H, and N in the steel. It uses fully deoxidized Al and Si killed steel and treats the molten steel with Ca. The main functions of each element are as follows:

[0007] C is the most important strengthening element. Too low a content is not conducive to improving strength, while too high a content is detrimental to toughness and corrosion resistance. It is advisable to control the C content within the range of 0.26% to 0.29%.

[0008] Si is a common element in steel and should be controlled within the range of 0.20% to 0.40%.

[0009] Mn: Primarily used to improve the hardenability of steel, thereby increasing its strength. However, it has a strong tendency to segregate and easily forms MnS inclusions with S, which are detrimental to the toughness and corrosion resistance of steel. Therefore, its content must be strictly controlled. It is advisable to control it within the range of 0.58% to 0.72%.

[0010] Cr: Primarily used to improve the hardenability of steel, thereby increasing its strength and tempering stability. It should be controlled within the range of 1.25% to 1.35%. Ni: Primarily used to improve the hardenability of steel, thereby increasing its strength and toughness, and can also mitigate the hot brittleness that may result from the addition of Cu. It should be controlled within the range of 1.05% to 1.20%.

[0011] Mo: Primarily used to improve the hardenability of steel, thereby increasing its strength and tempering stability; however, excessive content can increase costs. It is advisable to control it within the range of 0.42% to 0.58%.

[0012] Cu: Primarily used to improve the corrosion resistance of steel, while also enhancing its hardenability and strength. However, excessive content can cause Cu embrittlement. It is advisable to control the content within the range of 0.15–0.25%.

[0013] Nb: When added to steel, it forms NbC and NbN with the steel, which can inhibit the growth of austenite grains, refine the grains, and improve strength and toughness. It should be controlled within the range of 0.07% to 0.10%.

[0014] Ti: When added to steel, it forms TiC and TiN with C and N in the steel, which can inhibit austenite grain growth, refine grains, and improve strength and toughness. The content should be controlled within the range of 0.015% to 0.035%. Using Nb and Ti composite microalloying can achieve better strengthening and toughening effects than using a single microalloying element.

[0015] Ca can improve the properties and morphology of inclusions, thereby enhancing the toughness and corrosion resistance of steel. It should be controlled within the range of 0.006% to 0.012%.

[0016] Re: It has multiple functions, including purifying molten steel, refining grains, modifying inclusions, and alloying. Its concentration should be controlled within the range of 0.012% to 0.015%.

[0017] Al is an important deoxidizer. It forms oxides with oxygen to perform deoxidation, and forms nitrides with nitrogen to partially eliminate the adverse effects of nitrogen. It also refines grains and improves strength and toughness. Its concentration should be controlled within the range of 0.009% to 0.015%.

[0018] P: A harmful element that mainly affects the ductility, toughness, and corrosion resistance of steel. P should be controlled to ≤0.012%.

[0019] S: A harmful element that mainly affects the ductility, toughness, and corrosion resistance of steel. S should ideally be controlled to ≤0.002%.

[0020] O: A harmful element that primarily affects the ductility, toughness, and corrosion resistance of steel. O content should ideally be controlled to ≤0.002%.

[0021] H: A harmful element that mainly affects the ductility, toughness, and corrosion resistance of steel. H should ideally be controlled to ≤0.00015%.

[0022] Nitrogen (N): A harmful element that primarily affects the ductility, toughness, and corrosion resistance of steel. It is advisable to control N to ≤0.0025%.

[0023] Meanwhile, controlling Mo / P ≥ 25 or W / P ≥ 50 controls the adverse effects of P segregation on corrosion resistance and toughness; controlling Al / N ≥ 2 eliminates the adverse effects of N on toughness and corrosion resistance; controlling (Ca+Re) / S ≥ 3 controls the effect of inclusion modification treatment and improves the toughness and corrosion resistance of steel.

[0024] The technical solution provided by this invention is as follows:

[0025] The composition of sulfur-resistant drill pipe, by mass percentage, includes: C: 0.26%–0.29%, Si: 0.20%–0.40%, Mn: 0.58%–0.72%, P≤0.012%, S≤0.002%, Cr: 1.25%–1.35%, Ni: 1.05%–1.20%, Mo: 0.42%–0.58%, Cu: 15%–0.25%, Nb: 0.07%–0.1%. 0%, Ti: 0.015%~0.035%, Re: 0.012%~0.015%, Al: 0.009%~0.015%, Ca: 0.006%~0.012%, O≤0.002%, H≤0.00015%, N≤0.0025%; control Mo / P≥35, Al / N≥3, (Ca+Re) / S≥9; balance is Fe and other unavoidable impurities.

[0026] In terms of drill pipe manufacturing process, the main processes are pure static steel smelting, continuous casting, piercing, hot continuous rolling, sizing, straightening, pipe end thickening, heat treatment, friction welding of drill pipe joints, weld heat treatment, non-destructive testing, and internal coating (if necessary) to produce drill pipe products. Through reasonable process parameters and control, the drill pipe obtains a fine and uniform microstructure, thereby achieving a reasonable match between strength, ductility, toughness and resistance to hydrogen sulfide corrosion.

[0027] Manufacturing process of sulfur-resistant drill pipe:

[0028] 1) Steelmaking: Batching, electric furnace or oxygen-blown converter steelmaking, feeding rare earth (Re) wire, refining outside the furnace and vacuum degassing to obtain the above chemical composition, feeding Si-Ca wire to modify the inclusions in the steel.

[0029] 2) Continuous casting: The molten steel is cast into a bar-shaped continuous casting billet. Electromagnetic stirring and light reduction technology are used in the continuous casting process to control segregation in the continuous casting billet.

[0030] 3) Piercing and hot rolling: The continuously cast billet is heated in an annular heating furnace at a temperature of 1200℃~1250℃ for 90~120 minutes, preferably 120 minutes. Hot piercing is performed at 1170℃~1220℃, followed by hot rolling at 980℃~1190℃, sizing, straightening, cooling, and tube-doubled sawing. Then, non-destructive testing is carried out.

[0031] 4) Initial heat treatment: A protective atmosphere furnace heating process (to prevent decarburization), quenching, and high-temperature tempering are adopted. The quenching heating temperature is controlled at 890℃~910℃, the holding time is 45 minutes, and internal and external water spray quenching is performed. The cooling rate is 20℃ / s~30℃ / s to ensure that the martensite structure is basically obtained after quenching. The tempering temperature is controlled at 690℃~710℃, and the tempering time is 90 minutes to obtain fine and uniform tempered sorbite with a grain size of 8~9. After tempering, water cooling is performed to avoid possible temper brittleness. Then, sizing and hot straightening are performed. The straightening temperature is controlled at 620℃~650℃, preferably 620℃, followed by water cooling. After non-destructive testing, the material is sawn to the appropriate size.

[0032] 5) Thickening of pipe ends: Heat the pipe ends to 1100℃~1200℃, and use the inner and outer diameter molds and the temperature gradient of the pipe ends to perform 3 to 5 upsetting forgings to obtain the inner and outer thickening dimensions and shape of the pipe ends.

[0033] 6) Full tube heat treatment: Heating is carried out in a controlled atmosphere furnace. The quenching temperature is controlled at 880℃~900℃ and the holding time is 40~60 minutes. Water is sprayed inside and outside for quenching, and the cooling rate is 20℃ / s~30℃ / s to ensure that the martensite structure is basically obtained after quenching. The tempering temperature is controlled at 600℃~670℃ and the tempering time is 90~120 minutes to obtain fine and uniform tempered sorbite with a grain size of 9~10. Water cooling is performed after tempering to avoid possible temper brittleness. Then, non-destructive and dimensional inspections are carried out.

[0034] 7) Friction welding and heat treatment of drill pipe body and drill pipe joint: Inertial friction welding is used, with reasonable control of rotation speed, back pressure, and upsetting pressure to ensure a firm weld between the drill pipe body and drill pipe joint. Immediately after upsetting (900℃~930℃), PAG quenching liquid is sprayed onto the outer surface of the weld zone, and compressed air is sprayed onto the inner surface for quenching. Then, medium-frequency induction heating to 680℃~700℃ is used for tempering. The weld microstructure is tempered sorbite, and the heat-affected zone is a mixture of tempered sorbite, pearlite, and ferrite. Then, burrs and flash are removed from both inside and outside the weld zone. This heat treatment method organically combines phase transformation and deformation, significantly improving the overall performance of the weld. Medium-frequency induction heating and high-temperature tempering are beneficial for removing burrs and flash from both inside and outside the weld zone.

[0035] 8) Secondary heat treatment of welded areas: The weld area is heated to 870℃~890℃ using medium-frequency induction heating. PAG quenching liquid is sprayed on the outer surface of the weld area and compressed air is sprayed on the inner surface for quenching. Then, it is tempered by medium-frequency induction heating to 670℃~690℃. Then, non-destructive testing is performed.

[0036] 9) To apply or not to apply an inner coating.

[0037] The invention also provides applications for high-strength sulfur-resistant drill pipes, suitable for manufacturing sulfur-resistant drilling tools for acidic oil and gas fields, and especially suitable for manufacturing drilling engineering tools for deep acidic oil and gas fields.

[0038] The high-strength sulfur-resistant drill pipe provided by this invention is applicable to deep acidic oil and gas fields and has comprehensive advantages such as high strength, good toughness, and excellent resistance to hydrogen sulfide corrosion.

[0039] The present invention has the following beneficial effects:

[0040] The anti-sulfur drill pipe material of this invention, after appropriate preparation, exhibits excellent comprehensive performance. The yield strength of the pipe body can reach 95 kSi to 125 kSi, preferably 95 kSi, 105 kSi, 120 kSi, or 125 kSi, which corresponds to a room temperature yield strength greater than 655–862 MPa, a tensile strength greater than 758–931 MPa, and an elongation ≥15–17%. The weld seam achieves a load-bearing capacity higher than the pipe body requirements. The -20 Charpy impact toughness of the pipe body and weld seam is ≥100 J and 42 J, respectively. It meets the requirement of not fracturing after 720 hours of loading with solution A in the NACE™ 0177A method. Detailed Implementation

[0041] The principles and features of the present invention are described below. The embodiments given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0042] Example

[0043] The chemical compositions of the sulfur-resistant drill pipes with yield strength levels of 95 ksi (D95 in the table), 105 ksi (F105 in the table), 120 ksi (R120 in the table), and 125 ksi (Y125 in the table) provided in the embodiments of the present invention are shown in Table 1. Among them, O ≤ 0.002%, H ≤ 0.00015%, N ≤ 0.0025% (not listed), and the balance is Fe and unavoidable impurities.

[0044] Table 1 Chemical composition of sulfur-resistant drill pipe in the examples

[0045]

[0046]

[0047] This invention also provides a method for preparing sulfur-resistant drill pipes with yield strength levels of 95 ksi, 100 ksi, 120 ksi, and 125 ksi, comprising the following steps:

[0048] 1) Steelmaking: Batching, electric arc furnace steelmaking (Examples 1, 3, 5, 7, 9, 11, 13, 15, 17, 19; using sponge iron and high-quality scrap steel as raw materials) or oxygen-blown converter steelmaking (Examples 2, 4, 6, 8, 10, 12, 14, 16, 18, 20; using blast furnace iron and high-quality scrap steel as raw materials), feeding rare earth (Re) wire, refining outside the ladle and vacuum degassing to obtain the chemical composition shown in Table 1, feeding Si-Ca wire to modify the inclusions in the steel.

[0049] 2) Continuous casting: The molten steel is cast into a bar-shaped continuous casting billet. Electromagnetic stirring and light reduction technology are used in the continuous casting process to control segregation in the continuous casting billet.

[0050] 3) Piercing and hot rolling: The continuously cast billet is heated in an annular heating furnace at a temperature of 1200℃~1250℃ for 120 minutes. It is then hot-pierced at 1170℃~1220℃, hot-rolled at 980℃~1190℃, sizing, straightened, and the sizing and hot straightening temperature is 620℃. After cooling, the billet is cut into multiples and then non-destructive testing is performed.

[0051] 4) Initial heat treatment: A protective atmosphere furnace heating process (to prevent decarburization), quenching, and high-temperature tempering are adopted. The quenching heating temperature is 900±10℃, the holding time is 45 minutes, and water quenching is carried out inside and outside, with a cooling rate of 20℃ / s~30℃ / s; the tempering temperature is 700±10℃, the tempering time is 90 minutes, the microstructure is tempered sorbite, the grain size is 8~9, and it is water-cooled after tempering; then sizing and hot straightening are performed at a temperature of 620℃, followed by water cooling; after non-destructive testing, it is sawn to the appropriate size.

[0052] 5) Thickening of pipe ends: Heat the pipe ends to 1100℃~1200℃, and use the inner and outer diameter molds and the temperature gradient of the pipe ends to perform 3 to 5 upsetting forgings to obtain the inner and outer thickening dimensions and shape of the pipe ends.

[0053] 6) Full tube heat treatment: Heating is carried out in a controlled atmosphere furnace. The quenching temperature is 890±10℃, the holding time is 40~60 minutes, and the tube is quenched by internal and external water spraying. The cooling rate is 20℃ / s~30℃ / s, and the quenched microstructure is martensite. The tempering temperature is 600℃~690℃, and the tempering time is 90~120 minutes (the tempering temperature and tempering time are adjusted according to different steel grades, see Table 2 for details). The microstructure is tempered sorbite with a grain size of 9~10. The tube is water-cooled after tempering. Then, non-destructive and dimensional inspections are performed.

[0054] 7) Friction welding and heat treatment of drill pipe body and drill pipe joint: Inertial friction welding is used, controlling the rotation speed, back pressure, and upsetting pressure to firmly weld the prepared drill pipe body to the selected sulfur-resistant drill pipe joint. Immediately after friction welding upsetting (900℃~930℃), PAG quenching liquid is sprayed onto the outer surface of the weld area, and compressed air is sprayed onto the inner surface for quenching. Then, it is tempered by medium-frequency induction heating to 690±10℃ and held for 6 minutes. The weld microstructure is tempered sorbite, and the heat-affected zone is a mixture of tempered sorbite, pearlite, and ferrite. The grain size is 8~9. Finally, the burrs and flash inside and outside the weld area are removed.

[0055] 8) Secondary heat treatment of the welded area: The weld area is heated to 880±10℃ using medium-frequency induction heating and held for 3 minutes. PAG quenching liquid is sprayed onto the outer surface of the weld area, and compressed air is sprayed onto the inner surface for quenching. Then, it is tempered by medium-frequency induction heating to 680±10℃ and held for 8 minutes. The weld microstructure is fine and uniform tempered sorbite, and the heat-affected zone is a mixture of tempered sorbite, pearlite, and ferrite. The grain size is 9-10. Non-destructive testing is then performed.

[0056] 9) Inner coating.

[0057] The sulfur-resistant drill pipe material of this invention, after being prepared using the process provided by this invention, exhibits excellent comprehensive properties (see Table 2 for details). The mechanical properties of the pipe body are as follows: D95S and D95SS drill pipes: room temperature yield strength 714–733 MPa, tensile strength 825–841 MPa, elongation 26–29%, longitudinal Charpy V-notch impact toughness at -20℃ 133–146 J; F105S and F105SS drill pipes: room temperature yield strength 791–809 MPa, tensile strength 903–918 MPa, elongation 22–29%. 4%, longitudinal Charpy V-notch impact toughness at -20℃ 120~133J; R120S drill pipe room temperature yield strength 892~913MPa, tensile strength 993~1012MPa, elongation 20~21%, longitudinal Charpy V-notch impact toughness at -20℃ 116~126J; Y125S drill pipe room temperature yield strength 927~946MPa, tensile strength 1022~1043MPa, elongation 19~20%, longitudinal Charpy V-notch impact toughness at -20℃ 108~119J. The weld seam's load-bearing capacity is greater than that of the pipe body; the longitudinal Charpy V-notch impact toughness of the D95S and D95SS drill pipe weld seams at -20℃ is 79–93 J; the longitudinal Charpy V-notch impact toughness of the F105S and F105SS drill pipe weld seams at -20℃ is 78–86 J; the longitudinal Charpy V-notch impact toughness of the R120S drill pipe weld seams at -20℃ is 75–83 J; and the longitudinal Charpy V-notch impact toughness of the Y125S drill pipe weld seams at -20℃ is 62–74 J. A 720-hour hydrogen sulfide stress corrosion test was conducted using NACE™ 0177A method A solution, loading the pipe body with 85% and / or 95% SMYS and the weld seams with 60% SMYS. No cracks or fractures were observed.

[0058] Table 2. Heat treatment process and performance of sulfur-resistant drill pipes in the examples.

[0059]

[0060]

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-strength sulfur-resistant drill pipe, characterized in that, Includes the following steps: Step 1) Prepare the raw materials according to the ingredients, and then smelt the steel. Step 2), continuous casting; Step 3) Piercing and hot continuous rolling; Step 4) Initial heat treatment; Step 5) Thicken the pipe end; Step 6) Heat treatment of the entire tube body; Step 7) Friction welding and heat treatment of drill pipe body and drill pipe joint; Step 8) Secondary heat treatment of the welded area; Step 9): Apply or not apply the inner coating; The drill pipe comprises, by mass percentage: C: 0.26%–0.29%, Si: 0.20%–0.40%, Mn: 0.58%–0.72%, P≤0.012%, S≤0.002%, Cr: 1.25%–1.35%, Ni: 1.05%–1.20%, Mo: 0.42%–0.58%, Cu: 0.15%–0.25%, Al: 0.009%– 0.015%, O≤0.002%, H≤0.00015%, N≤0.0025%, Mo / P≥35, Al / N≥3, Nb: 0.07%~0.10%, Ti: 0.015%~0.035%, RE: 0.012%~0.015%, Ca: 0.006%~0.012%, (Ca+RE) / S≥9, balance being Fe and other unavoidable impurities; The specific steps of the initial heat treatment in step 4) are as follows: a heat treatment process of heating in a protective atmosphere furnace, quenching, and high-temperature tempering is adopted. The quenching heating temperature is controlled at 890℃~910℃, the holding time is 45 minutes, internal and external water spray quenching is performed, and the cooling rate is 20℃ / s~30℃ / s; the tempering temperature is controlled at 690℃~710℃, the tempering time is 90 minutes, and water cooling is performed after tempering; then sizing and hot straightening are performed, the straightening temperature is controlled at 620℃~650℃, and then water cooling is performed. The specific steps of the whole tube heat treatment in step 6) are as follows: heating is carried out in a controlled atmosphere furnace, the quenching temperature is controlled at 880℃~900℃, the holding time is 40~60 minutes, internal and external water spray quenching is carried out, and the cooling rate is 20℃ / s~30℃ / s; the tempering temperature is controlled at 600℃~670℃, the tempering time is 90~120 minutes, and water cooling is carried out after tempering; The specific steps for friction welding and heat treatment of the drill pipe body and drill pipe joint in step 7) are as follows: Inertial friction welding method is adopted, and the rotation speed, back pressure and upsetting pressure are controlled to make the drill pipe body and drill pipe joint firmly welded. When the instantaneous temperature after friction welding upsetting is 900℃~930℃, PAG quenching liquid is sprayed on the outer surface of the weld area and compressed air is sprayed on the inner surface for quenching. Then, medium frequency induction heating is carried out to 680℃~700℃ for tempering. Then, the flash and burrs inside and outside the weld area are processed. The specific steps for the secondary heat treatment of the welded area in step 8) are as follows: The weld area is heated to 870℃~890℃ using medium frequency induction heating method. PAG quenching liquid is sprayed on the outer surface of the weld area and compressed air is sprayed on the inner surface for quenching. Then, the weld area is tempered by medium frequency induction heating to 670℃~690℃.

2. The method for preparing high-strength sulfur-resistant drill pipe according to claim 1, characterized in that, The specific steps for piercing and hot rolling in step 3) are as follows: The continuously cast billet obtained in step 2) is heated in an annular heating furnace at a temperature of 1200℃~1250℃ for 90~120 minutes, and hot piercing is performed at 1170℃~1220℃, followed by hot rolling at 980℃~1190℃.

3. The method for preparing high-strength sulfur-resistant drill pipe according to claim 1, characterized in that, The specific steps for thickening the pipe end in step 5) are as follows: heat the pipe end to 1100℃~1200℃, and use the inner and outer diameter molds and the pipe end temperature gradient to perform 3 to 5 upsetting forgings to obtain the inner and outer thickening dimensions and pipe end shape.

4. A high-strength sulfur-resistant drill pipe, characterized in that: It is prepared according to any one of claims 1 to 3.

5. The high-strength sulfur-resistant drill pipe according to claim 4, characterized in that: The yield strength is 95ksi to 125ksi, the room temperature yield strength is greater than 655 to 862MPa, the tensile strength is greater than 758 to 931MPa, and the elongation is ≥15 to 17%. The weld has a higher load-bearing capacity than the pipe body. The Charpy impact toughness of the pipe body and the weld at -20℃ is ≥100J and 42J, respectively. No fracture occurs after loading in solution A for 720 hours according to the NACE™ 0177A method.

6. An application of the high-strength sulfur-resistant drill pipe according to claim 4 or 5, characterized in that: Used to manufacture drilling tools for deep, acidic oil and gas fields.

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