High-strength sulfur-resistant drill rod as well as preparation method and application thereof

Abstract

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

Description

Technical Field

[0001] The present invention belongs to the technical field of oil drill pipes resistant to hydrogen sulfide corrosion, and specifically relates to a high-strength sulfur-resistant drill pipe and a preparation method and application thereof. Background Art

[0002] Acidic oil and gas account for a large proportion of my country's oil and gas resources, mainly distributed in oil and gas fields such as Southwest, Tarim, Daqing, Changqing, Dagang, and North China. In a hydrogen sulfide environment, steel materials are prone to sulfide stress corrosion damage under the synergistic effect of corrosive media and working stress, which often leads to serious 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, not only are higher requirements placed on the strength and toughness of drill pipes, but also on the resistance to hydrogen sulfide corrosion, especially hydrogen sulfide stress corrosion resistance. However, the strength and toughness of the material and the resistance to sulfide stress corrosion often show a phenomenon of one growing while the other shrinks, which makes the design and manufacture of high-strength sulfur-resistant drill pipes very difficult.

[0003] At present, the steel grade of sulfur-resistant drill pipe that can pass the NACE TM 0177A test and is widely used is 105ksi. Although there are patents and literature reports on sulfur-resistant drill pipes with steel grades of 120ksi and 125ksi or even higher, they have not yet been widely used in industry. Moreover, the chemical composition range of the drill pipes in these patents is too wide, the process has obvious personalized characteristics, the industrial production cost is high, and some component designs and preparation processes are not reasonable, which brings difficulties to the quality control and promotion of their products. In view of the above situation, the present invention proposes a steel grade design and preparation method for sulfur-resistant drill pipe to meet the demand for sulfur-resistant drill pipe in the development of sour oil and gas fields. Summary of the invention

[0004] In order to solve the deficiencies of the prior art, the present invention provides a high-strength sulfur-resistant drill pipe and a preparation method and application thereof. The high-strength sulfur-resistant drill pipe provided by the present invention has a yield strength of 105ksi to 125ksi and has sufficient toughness and resistance to hydrogen sulfide stress corrosion. According to NACE TM 0177A method A solution loading and 720h test, no cracks or fractures are generated, which can meet the requirements for the safe use of sulfur-resistant drill pipes in the development of acidic deep oil and gas fields.

[0005] In order to ensure that the multiple requirements of the strength, toughness and hydrogen sulfide stress corrosion resistance of the anti-sulfur drill pipe are met, the present invention has made innovations in chemical composition and manufacturing.

[0006] In terms of composition, the present invention adopts medium-low C, controls Mn, adds Cr, Ni, Mo, Cu, Nb, Ti microalloying, adds rare earth (Re) elements, controls harmful elements such as P, S, O, H, N in the steel, adopts Al, Si fully deoxidized killed steel, and performs Ca treatment on the molten steel. 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 not conducive to toughness and corrosion resistance. It is advisable to control C within the range of 0.26% to 0.29%.

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

[0009] Mn: It is mainly used to improve the hardenability of steel, thereby improving the strength of steel, but it has a greater tendency to segregate and is easy to form MnS inclusions with S, which is unfavorable to the toughness and corrosion resistance of steel, so it must be strictly controlled. It is best to control it within the range of 0.58% to 0.72%.

[0010] Cr: Mainly used to improve the hardenability of steel, thereby improving the strength and tempering stability of steel. It is advisable to control it within the range of 1.25% to 1.35%. Ni: Mainly used to improve the hardenability of steel, thereby improving the strength and toughness of steel, and at the same time can improve the hot brittleness that may be caused by the addition of Cu. It is advisable to control it within the range of 1.05 to 1.20%.

[0011] Mo: Mainly used to improve the hardenability of steel, thereby improving the strength and tempering stability of steel, but too high a content will increase the cost. It is advisable to control it within the range of 0.42% to 0.58%.

[0012] Cu: Mainly used to improve the corrosion resistance of steel, and can also improve the hardenability and strength of steel, but too high a content will also cause Cu brittleness. It is best to control it within the range of 0.15-0.25%.

[0013] Nb: Added into steel, it forms NbC and NbN with C and N in steel, which has the function of hindering the growth of austenite grains, refining grains, and improving strength and toughness. It is better to control it within the range of 0.07% to 0.10%.

[0014] Ti: It is added to steel to form TiC and TiN with C and N in steel, which has the effect of hindering the growth of austenite grains, refining grains, and improving strength and toughness. It is better to control it within the range of 0.015% to 0.035%. Using Nb and Ti composite microalloying can achieve better strengthening and toughening effects than single microalloying elements.

[0015] Ca: It can improve the properties and morphology of inclusions, thereby improving the toughness and corrosion resistance of steel. It is best to control it within the range of 0.006% to 0.012%.

[0016] Re: It has multiple functions of purifying molten steel, refining grains, modifying inclusions, and alloying. It is best to control it within the range of 0.012% to 0.015%.

[0017] Al: It is an important deoxidizer. It forms oxides with oxygen to deoxidize, and forms nitrides with nitrogen to partially eliminate the adverse effects of N. It also refines grains and improves strength and toughness. It is best to control it within the range of 0.009% to 0.015%.

[0018] P: Harmful element, mainly affecting the plasticity, toughness and corrosion resistance of steel. It is advisable to control P ≤ 0.012%.

[0019] S: Harmful element, mainly affecting the plasticity, toughness and corrosion resistance of steel. It is advisable to control S ≤ 0.002%.

[0020] O: Harmful element, mainly affects the plasticity, toughness and corrosion resistance of steel. It is advisable to control O≤0.002%.

[0021] H: Harmful element, mainly affects the plasticity, toughness and corrosion resistance of steel. It is advisable to control H≤0.00015%.

[0022] N: Harmful element, mainly affects the plasticity, toughness and corrosion resistance of steel. It is advisable to control N ≤ 0.0025%.

[0023] At the same time, control Mo / P≥25 or W / P≥50 to control the adverse effects of P segregation on corrosion resistance and toughness; control Al / N≥2 to eliminate the adverse effects of N on toughness and corrosion resistance; control (Ca+Re) / S≥3 to control the effect of inclusion modification treatment and improve the toughness and corrosion resistance of steel.

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

[0025] The sulfur-resistant drill pipe components include 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: 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; the balance is Fe and other inevitable impurities.

[0026] In terms of drill pipe preparation technology, drill pipe products are mainly prepared through pure static steel smelting, continuous casting, perforation, hot rolling, sizing, straightening, pipe end thickening, heat treatment, friction welding drill pipe joints, weld heat treatment, non-destructive testing, internal coating (when necessary) and other processes. Through reasonable process parameters and control, the drill pipe can obtain a fine and uniform microstructure, thereby achieving a reasonable match of strength, plasticity and toughness and resistance to hydrogen sulfide corrosion.

[0027] Preparation 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 rod-shaped continuous casting billets. During the continuous casting process, electromagnetic stirring and light pressure reduction technology are used to control the segregation in the continuous casting billets.

[0030] 3) Piercing and hot rolling: The continuous casting billet is heated in a ring-shaped heating furnace at a temperature of 1200°C to 1250°C for 90 to 120 minutes, preferably 120 minutes, hot-pierced at 1170°C to 1220°C, hot-rolled at 980°C to 1190°C, sizing, straightening, cooling, double tube sawing, and then non-destructive testing.

[0031] 4) Initial heat treatment: adopt the heat treatment process of protective atmosphere furnace heating (to prevent decarburization), quenching and high temperature tempering. The quenching heating temperature is controlled at 890℃~910℃, the holding time is 45 minutes, the internal and external water spray quenching, 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℃, the tempering time is 90 minutes, in order to obtain fine and uniform tempered troostite, the grain size is 8~9, and water cooling is performed after tempering to avoid possible temper brittleness; then sizing and hot straightening are carried out, the straightening temperature is controlled at 620℃~650℃, preferably 620℃, and then water cooling is carried out; after non-destructive inspection, sawing is carried out to the appropriate size.

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

[0033] 6) Full tube quenching and tempering heat treatment: adopt controlled atmosphere furnace heating, quenching heating temperature is controlled at 880℃~900℃, holding time is 40~60 minutes, internal and external water spray quenching, cooling rate is 20℃ / s~30℃ / s, ensure that basically all martensitic structures are obtained after quenching; tempering temperature is controlled at 600℃~670℃, tempering time is 90~120 minutes, in order to obtain fine and uniform tempered troostite, grain size is 9~10, water cooling is carried out after tempering to avoid possible temper brittleness; then non-destructive and dimensional inspection is carried out.

[0034] 7) Friction welding and heat treatment of drill pipe body and drill pipe joint: Inertia friction welding method is used to reasonably control the rotation speed, back pressure and upsetting pressure to make the drill pipe body and drill pipe joint firmly welded together. At the moment after friction welding upsetting (900℃~930℃), PAG quenching liquid is sprayed on the outer surface of the welding area and compressed air is sprayed on the inner surface for quenching, and then medium frequency induction heating is heated to 680℃~700℃ for tempering. The weld structure is tempered troostite, and the heat affected zone is a mixed structure of tempered troostite, pearlite and ferrite. Then the flash and burrs inside and outside the welding area are processed. This heat treatment method organically combines phase change and deformation, which can significantly improve the comprehensive performance of the weld. Medium frequency induction heating and high temperature tempering are conducive to the removal of flash and burrs inside and outside the welding area.

[0035] 8) Secondary heat treatment of welding parts: Use medium frequency induction heating method to heat the welding area to 870℃~890℃, spray PAG quenching liquid on the outer surface of the welding area and compressed air on the inner surface for quenching, and then use medium frequency induction heating to 670℃~690℃ for tempering. Then carry out non-destructive testing.

[0036] 9) With or without inner coating.

[0037] The invention also provides the application of high-strength sulfur-resistant drill pipe, which is suitable for making sulfur-resistant drilling tools for acidic oil and gas fields, and is particularly suitable for making drilling engineering tools for deep acidic oil and gas fields.

[0038] The high-strength sulfur-resistant drill pipe provided by the present invention is applied to deep acidic oil and gas fields and has the comprehensive advantages of high strength, good toughness, excellent hydrogen sulfide corrosion resistance and the like.

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

[0040] The sulfur-resistant drill pipe material of the present invention has excellent comprehensive performance after being properly prepared. The yield strength of the pipe body can reach the requirements of 95ksi to 125ksi, preferably 95ksi, 105ksi, 120ksi, and 125ksi, that is, 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 load-bearing capacity of the weld is higher than the pipe body requirement; the -20 Charpy impact toughness of the pipe body and the weld is ≥100J and 42J. It can meet the requirements of NACE TM 0177A method A solution loading for 720 hours without fracture. DETAILED DESCRIPTION

[0041] The principles and features of the present invention are described below. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0042] Example

[0043] The chemical composition of the sulfur-resistant drill pipes provided in the embodiments of the present invention 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) are shown in Table 1, wherein O≤0.002%, H≤0.00015%, N≤0.0025% not listed, and the remainder is Fe and unavoidable impurities.

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

[0045]

[0046]

[0047] The embodiment of the present invention also provides a method for preparing a sulfur-resistant drill pipe with a yield strength level of 95 ksi, 100 ksi, 120 ksi, and 125 ksi, comprising the following steps:

[0048] 1) Steelmaking: batching, electric 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 furnace 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 rod-shaped continuous casting billets. During the continuous casting process, electromagnetic stirring and light pressure reduction technology are used to control the segregation in the continuous casting billets.

[0050] 3) Piercing and hot rolling: The continuous casting billet is heated in a ring-shaped heating furnace with a heating furnace temperature of 1200℃~1250℃ and a heating time of 120 minutes. It is hot-pierced at 1170℃~1220℃, hot-rolled at 980℃~1190℃, sizing, straightening, sizing and hot straightening temperature of 620℃, cooled, double tube sawing, and then non-destructive testing is performed.

[0051] 4) Initial heat treatment: adopt the heat treatment process of protective atmosphere furnace heating (to prevent decarburization), quenching + high temperature tempering. Quenching heating temperature is 900±10℃, holding time is 45 minutes, internal and external water spray quenching, cooling rate is 20℃ / s~30℃ / s; tempering temperature is 700±10℃, tempering time is 90 minutes, the organization is tempered troostite, grain size is 8~9, water cooling after tempering; then sizing and hot straightening are carried out, sizing and hot straightening temperature is 620℃, then water cooling; after non-destructive inspection, sawing to the appropriate size.

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

[0053] 6) Full tube quenching and tempering heat treatment: heated in a controlled atmosphere furnace, quenching heating temperature of 890±10℃, holding time of 40 to 60 minutes, internal and external water spray quenching, cooling rate of 20℃ / s to 30℃ / s, quenching structure of martensite; tempering temperature of 600℃ to 690℃, tempering time of 90 to 120 minutes (tempering temperature and tempering time are adjusted according to different steel grades, see Table 2 for details), the structure is tempered troostite, grain size of 9 to 10, water cooling after tempering; then non-destructive and dimensional inspection are carried out.

[0054] 7) Friction welding and heat treatment of drill pipe body and drill pipe joint: Use inertia friction welding method, control the rotation speed, back pressure and upsetting pressure, so that the prepared drill pipe body and the selected anti-sulfur drill pipe joint are firmly welded together. At the moment after friction welding upsetting (900℃~930℃), spray PAG quenching liquid on the outer surface of the welding area and compressed air on the inner surface for quenching, and then heat to 690±10℃ for 6 minutes by medium frequency induction heating for tempering. The weld structure is tempered troostite, and the heat affected zone is a mixed structure of tempered troostite, pearlite and ferrite. Grain size 8~9. Then process the flash and burrs inside and outside the welding area.

[0055] 8) Secondary heat treatment of welding parts: Use medium frequency induction heating method to heat the welding area to 880±10℃ for 3 minutes, spray PAG quenching liquid on the outer surface of the welding area and compressed air on the inner surface for quenching, and then use medium frequency induction heating to 680±10℃ for 8 minutes for tempering. The weld structure is fine and uniform tempered troostite, and the heat affected zone is a mixed structure of tempered troostite, pearlite and ferrite. The grain size is 9-10. Then carry out non-destructive testing.

[0056] 9) Inner coating.

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

[0058] Table 2 Heat treatment process and performance of sulfur-resistant drill pipe in Example

[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 principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A high-strength sulfur-resistant drill pipe, It is characterized in that The components of the drill pipe include, 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, and the balance is Fe and other inevitable impurities.

2. The high-strength sulfur-resistant drill pipe according to claim 1, Features: In terms of mass percentage, it also includes: Nb: 0.07% to 0.10%, Ti: 0.015% to 0.035%, Re: 0.012% to 0.015%, Ca: 0.006% to 0.012%, (Ca+Re) / S≥9, and the balance is Fe and other unavoidable impurities; And / or: the yield strength level is 95ksi~125ksi, the room temperature yield strength is greater than 655~862MPa, the tensile strength is greater than 758~931MPa, and the elongation is ≥15~17%; the weld bearing capacity is higher than the pipe body; the -20℃ Charpy impact toughness of the pipe body and the weld is ≥100J and 42J respectively; no fracture occurs when loading in solution A for 720 hours according to NACE TM 0177A method.

3. A method for preparing the high-strength sulfur-resistant drill pipe according to claim 1 or 2, It is characterized in that The following steps are involved: Step 1), preparing the steel according to the proportions described in claim 1 or 2, and then making steel; Step 2), continuous casting; Step 3), perforation and hot rolling; Step 4), initial heat treatment; Step 5), thickening the pipe end; Step 6), the whole tube body is subjected to quenching and tempering heat treatment; Step 7), friction welding and heat treatment of drill pipe body and drill pipe joint; Step 8), secondary heat treatment of welding parts; Step 9), with or without inner coating.

4. The method for preparing the high-strength sulfur-resistant drill pipe according to claim 3, It is characterized in that The specific steps of piercing and hot rolling in step 3) are as follows: the continuous casting billet obtained in step 2) is heated in a ring heating furnace with a heating furnace temperature of 1200°C to 1250°C and a heating time of 90 to 120 minutes, hot pierced at 1170°C to 1220°C, and hot rolled at 980°C to 1190°C.

5. The method for preparing the high-strength sulfur-resistant drill pipe according to claim 3, It is characterized in that The specific steps of the initial heat treatment of step 4) are as follows: a heat treatment process of heating in a protective atmosphere furnace, quenching and high-temperature tempering is adopted, wherein the quenching heating temperature is controlled at 890°C to 910°C, the holding time is 45 minutes, the internal and external water spray quenching, and the cooling rate is 20°C / s to 30°C / s; the tempering temperature is controlled at 690°C to 710°C, 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°C to 650°C, and then water cooling is performed.

6. The method for preparing the high-strength sulfur-resistant drill pipe according to claim 3, It is characterized in that The specific steps of the tube end thickening in step 5) are as follows: the tube end is heated to 1100°C to 1200°C, and upsetting is performed 3 to 5 times using inner and outer diameter dies and a temperature gradient of the tube end to obtain the inner and outer thickened size and shape of the tube end.

7. The method for preparing the high-strength sulfur-resistant drill pipe according to claim 3, It is characterized in that The specific steps of the tempering heat treatment of the whole tube body in step 6) are as follows: heating in a controlled atmosphere furnace, the quenching heating temperature is controlled at 880°C to 900°C, the holding time is 40 to 60 minutes, internal and external water spray quenching, and the cooling rate is 20°C / s to 30°C / s; the tempering temperature is controlled at 600°C to 670°C, the tempering time is 90 to 120 minutes, and water cooling is performed after tempering.

8. The method for preparing the high-strength sulfur-resistant drill pipe according to claim 3, It is characterized in that The specific steps of friction welding and heat treatment of the drill pipe body and the drill pipe joint in step 7) are as follows: adopt the inertia friction welding method, control the rotation speed, back pressure and upsetting pressure, so that the drill pipe body and the drill pipe joint are firmly welded, when the instantaneous temperature after friction welding upsetting is 900°C to 930°C, spray PAG quenching liquid on the outer surface of the welding area and compressed air on the inner surface for quenching, then medium frequency induction heating to 680°C to 700°C for tempering, and then process the flash and burrs inside and outside the welding area.

9. The method for preparing the high-strength sulfur-resistant drill pipe according to claim 3, It is characterized in that The specific steps of the secondary heat treatment of the welding part in step 8) are as follows: the welding area is heated to 870°C~890°C by medium frequency induction heating method, PAG quenching liquid is sprayed on the outer surface of the welding area and compressed air is sprayed on the inner surface for quenching, and then medium frequency induction heating is performed to 670°C~690°C for tempering.

10. An application of the high-strength sulfur-resistant drill pipe according to claim 1 or 2, Features: Used to make drilling engineering tools for deep acidic oil and gas fields.

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