Integral ultrahigh-strength feeding drill rod and preparation method thereof

Abstract

The invention relates to the technical field of oil and gas drill manufacturing, in particular to an integral type ultrahigh-strength feeding drill rod and a preparation method thereof.The integral type ultrahigh-strength feeding drill rod is characterized in that in the aspect of chemical component design, medium carbon, Mn-Cr-Ni-Mo alloying and V-Nb composite microalloying are adopted, rare earth elements are added, the content of Si and the content of Al are controlled, and the overall strength of the feeding drill rod is improved; harmful elements and harmful gases such as P, S, O, H and N in steel are strictly controlled, Al-Si is adopted for full deoxidation, and Ca treatment is conducted on molten steel. Meanwhile, through the independent effect and the synergistic effect of carbon and alloy elements, the hardenability, purification, grain refinement, inclusion modification and the like of the steel are improved, and a foundation is laid for the feeding drill rod to obtain the comprehensive performance such as high strength, good plasticity and low-temperature toughness. The feeding drill rod with the chemical components in the mass percentage can meet the requirements of deep and ultra-deep low temperature and complex oil and gas field development working conditions for the high-strength and high-low-temperature toughness improving capability feeding drill rod, and has high safety and reliability and excellent geometric dimension precision.

Description

Technical Field

[0001] This invention relates to the field of oil and gas drilling technology, and in particular to an integral ultra-high strength feed drill pipe and its preparation method. Background Technology

[0002] In drilling and completion engineering, there are three types of drill pipe: drilling pipe, weighted drill pipe, and delivery drill pipe. Drill pipe and weighted drill pipe have complete standard systems, but delivery drill pipe also has technical standards. In recent years, delivery drill pipe has become one of the most important tubing components in ultra-deep wells, extra-deep wells, and offshore deepwater wells. Its main function is to safely deliver large-sized and heavy tailpipe tubing (casing) to the bottom of the well; therefore, it possesses high or ultra-high strength as well as good ductility and toughness.

[0003] For conventional drilling pipes, the drill pipe body and drill pipe joint have different geometric dimensions and chemical compositions. They are usually manufactured separately and then joined together by welding (such as friction butt welding) to form a complete drill pipe. Feed drill pipes can also be produced by welding or as a single unit. If produced by welding, the presence of weld seams raises concerns about the safety and reliability of the feed drill pipe. Integral feed drill pipes are weld-free and safe and reliable. However, due to the significant difference in dimensions, especially the effective wall thickness, between the drill pipe body and drill pipe joint, special attention must be paid to composition design. If only the drill pipe body is considered in the composition design, the hardenability of the drill pipe joint is often insufficient. From a process performance perspective, the material should be suitable for water quenching as much as possible, avoiding oil quenching or quenching with other media (such as polymers).

[0004] Currently, the feed drill pipe is in the research, development, testing, and trial stage. Patents CN120946250A and CN120701257A disclose an integral and welded feed drill pipe and its preparation method, but do not disclose its chemical composition. It is well known that the chemical composition, processing technology, microstructure, comprehensive mechanical properties, and service performance of a material are inherently related. Without a defined material composition, the processing technology lacks specificity and it is difficult to obtain the desired mechanical and service performance.

[0005] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide an integral ultra-high strength feed drill pipe and its manufacturing method, which aims to solve the problems of insufficient strength and poor plasticity and toughness of existing feed drill pipes.

[0007] The technical solution of the present invention is as follows: An integral ultra-high strength feed drill pipe, wherein the chemical composition of the integral ultra-high strength feed drill pipe, by mass percentage, comprises: The composition is as follows: C 0.31%–0.35%, Si 0.31%–0.45%, Mn 1.01%–1.13%, P≤0.012%, S≤0.003%, Cr 0.95%–1.05%, Ni 1.01%–1.14%, Mo 0.62%–0.74%, V 0.03%–0.05%, Nb 0.01%–0.03%, RE 0.006%–0.009%, Al 0.031%–0.045%, Ca 0.009%–0.018%, N≤0.005%, O≤0.002%, H≤0.00015%, with the balance being Fe and other unavoidable impurities; RE represents rare earth elements.

[0008] The integral ultra-high strength feed drill pipe, wherein the chemical composition of the integral ultra-high strength feed drill pipe, by mass percentage, includes: C 0.31%~0.33%, Si 0.36%~0.45%, Mn 1.01%~1.07%, P≤0.012%, S≤0.003%, Cr0.95%~0.99%, Ni 1.01%~1.06%, Mo 0.62%~0.67%, V 0.03%~0.05%, Nb 0.01%~0.03%, RE 0.006%~0.008%, Al 0.031%~0.037%, Ca 0.009%~0.018%, N≤0.0045%, O≤0.0018%, H≤0.00013%, with the balance being Fe and other unavoidable impurities.

[0009] The integral ultra-high strength feed drill pipe, wherein the chemical composition of the integral ultra-high strength feed drill pipe, by mass percentage, includes: C 0.33%~0.35%, Si 0.31%~0.37%, Mn 1.06%~1.13%, P≤0.011%, S≤0.002%, Cr 1.01%~1.05%, Ni 1.09%~1.14%, Mo 0.69%~0.74%, V 0.03%~0.05%, Nb 0.01%~0.03%, RE 0.007%~0.009%, Al 0.039%~0.045%, Ca 0.011%~0.016%, N≤0.0044%, O≤0.0016%, H≤0.00012%, with the balance being Fe and other unavoidable impurities.

[0010] The integral ultra-high strength feed drill pipe, wherein the rare earth element is one or more of Ce, La, and Ce-La alloy.

[0011] A method for manufacturing an integral ultra-high strength feed drill pipe includes the following steps: Based on the chemical composition mass percentage of the integral ultra-high strength feed drill pipe, the raw materials are batched, smelted and continuously cast in sequence to obtain a continuously cast billet; The continuously cast bar billet is subjected to hot piercing, controlled rolling and cooling and first tempering heat treatment in sequence to obtain a tube blank; The tube blank is subjected to die forging and a second tempering heat treatment in sequence to obtain a tube blank; The tube blank is subjected to overall quenching and tempering heat treatment, hot straightening and non-destructive testing in sequence, and after threading at both ends, it is fed into the drill pipe.

[0012] The method for preparing the integral ultra-high strength feed drill pipe includes the following steps: batching, smelting, and continuous casting are performed sequentially according to the mass percentage of the chemical composition of the integral ultra-high strength feed drill pipe to obtain a continuously cast billet. After the chemical composition of the integral ultra-high strength feed drill pipe is prepared according to the mass percentage, the steel liquid is obtained after oxygen blowing converter smelting, ladle refining, vacuum degassing, and feeding with Si-Ca wire. The molten steel is used for casting, the superheat is controlled to be ≤25℃, and rare earth wire is fed during the casting process to obtain the continuously cast billet.

[0013] The method for preparing the integral ultra-high strength feed drill pipe includes the following steps: the hot piercing temperature is 1190℃-1240℃; the controlled rolling and cooling involves hot continuous rolling at 950℃-1200℃, controlling the rolling ratio to ≥3, controlling the final rolling temperature to 930℃-960℃, followed by water cooling at a controlled cooling rate to ≥25℃; the temperature of the first tempering heat treatment is 690℃-710℃, and the time of the first tempering heat treatment is 60min-90min.

[0014] The method for preparing the integral ultra-high strength feed drill pipe includes the following steps: sequentially performing die forging and a second tempering heat treatment on the blank to obtain the tube blank: The tube blank is heated to 950℃-1150℃, and then forged and hot-formed using inner and outer diameter dies. The forging ratio is controlled to be ≥3, and the final forging temperature is controlled to be 930℃-960℃. After final forging and sizing, the tube blank is water-cooled, and the cooling rate is controlled to be ≥25℃ / s. After die forging, the tube blank is subjected to a second tempering heat treatment at 690℃-710℃ for 60min-90min and then water-cooled to obtain the tube blank.

[0015] The method for preparing the integral ultra-high strength feed drill pipe, wherein the integral quenching and tempering heat treatment includes: The tube blank is heated to 900℃-920℃ and held for 60min-90min, then water-quenched inside and outside with a cooling rate ≥25℃ / s; then tempered at 550℃-580℃ for 90min-120min and then water-cooled.

[0016] In the method for preparing the integral ultra-high strength feed drill pipe, the temperature of the hot straightening is 500℃-530℃.

[0017] Beneficial Effects: This invention provides an integral ultra-high strength feed drill pipe and its preparation method. The chemical composition of the integral ultra-high strength feed drill pipe, by mass percentage, includes: C 0.31%–0.35%, Si 0.31%–0.45%, Mn 1.01%–1.13%, P≤0.012%, S≤0.003%, Cr 0.95%–1.05%, Ni 1.01%–1.14%, Mo 0.62%–0.74%, V 0.03%–0.05%, Nb 0.01%–0.03%, RE 0.006%–0.009%, Al The composition is as follows: 0.031%–0.045% Ca, 0.009%–0.018% N ≤ 0.005%, O ≤ 0.002%, H ≤ 0.00015%, with the balance being Fe and other unavoidable impurities; RE represents rare earth elements. In terms of chemical composition design, this invention employs medium carbon (C), Mn-Cr-Ni-Mo alloying, and V-Nb composite microalloying, with the addition of rare earth (RE) elements, control of Si and Al content, strict control of harmful elements and gases such as P, S, O, H, and N in the steel, Al-Si full deoxidation, and Ca treatment of the molten steel. Simultaneously, through the individual and synergistic effects of carbon and alloying elements, the hardenability of steel is improved (C-Cr-Mo-Ni-Mn-Si), purification (P, S, O, H, N control), grain refinement (V-Nb-Al), and inclusion modification (Ca-RE), laying the foundation for the drill pipe to achieve comprehensive properties such as high strength, good plasticity, and low-temperature toughness. Drill pipes with this chemical composition at this mass percentage can meet the requirements of deep and ultra-deep cryogenic and complex oil and gas field development conditions for drill pipes with high strength and high low-temperature toughness, and possess high safety and reliability (integral seamless construction) and excellent dimensional accuracy (die forging). Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the process flow for a method of preparing an integral ultra-high strength feed drill pipe according to the present invention. Detailed Implementation

[0019] This invention provides an integral ultra-high strength feed drill pipe and its manufacturing method. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0020] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined as herein.

[0021] For shallower wells, the tailpipe is installed directly into the casing using drill pipe, and the axial tensile load on the string is within the capacity of standard drill pipe and tools. As well depth and water depth increase, it is often necessary to run ultra-heavy tailpipe strings. At this point, the demand for ultra-high strength drill pipe is very urgent, which is also a pressing need for deep earth engineering and deep well projects.

[0022] The performance of the drill pipe directly determines the success or failure of casing running operations. If the strength and toughness of the drill pipe do not meet the requirements, it will bring safety hazards to the tailpipe running and cementing operations, namely, the drill pipe may break and cause the tailpipe to fall into the well.

[0023] Based on the analysis of the service conditions of the drill pipe, the performance requirements for the drill pipe are: to have a large load-bearing capacity in order to send large-sized and heavy tailpipe strings (casings) to the bottom of the well, which requires the use of high-strength or ultra-high-strength thick-walled pipes; and to have good plasticity and toughness (including low-temperature toughness) to prevent sudden brittle fracture during operation (including low-temperature environments, -40℃).

[0024] Based on this, the present invention provides an integral ultra-high strength feed drill pipe, wherein the chemical composition of the integral ultra-high strength feed drill pipe, by mass percentage, comprises: The composition is as follows: C 0.31%–0.35%, Si 0.31%–0.45%, Mn 1.01%–1.13%, P≤0.012%, S≤0.003%, Cr 0.95%–1.05%, Ni 1.01%–1.14%, Mo 0.62%–0.74%, V 0.03%–0.05%, Nb 0.01%–0.03%, RE 0.006%–0.009%, Al 0.031%–0.045%, Ca 0.009%–0.018%, N≤0.005%, O≤0.002%, H≤0.00015%, with the balance being Fe and other unavoidable impurities; RE represents rare earth elements.

[0025] In this embodiment, the chemical composition design employs medium carbon (C), Mn-Cr-Ni-Mo alloying, and V-Nb composite microalloying, along with the addition of rare earth (RE) elements and control of Si and Al content. Strict control is maintained over harmful elements and gases such as P, S, O, H, and N in the steel. Al-Si full deoxidation is used, and the molten steel undergoes Ca treatment. Simultaneously, through the individual and synergistic effects of carbon and alloying elements, the hardenability of the steel is improved (C-Cr-Mo-Ni-Mn-Si), purification (P, S, O, H, N control), grain refinement (V-Nb-Al), and inclusion modification (Ca-RE), laying the foundation for high strength, good plasticity, and low-temperature toughness in the drill pipe. The drill pipe with this chemical composition at this mass percentage can meet the requirements of high-strength, high-low-temperature toughness drill pipes for deep and ultra-deep cryogenic and complex oil and gas field development conditions, exhibiting high safety and reliability (integral, weld-free design) and excellent dimensional accuracy (die forging).

[0026] Specifically, the integral ultra-high strength feed drill pipe is designed according to the concept of "high hardenability, high tempering stability, ultra-fine grains, ultra-high cleanliness and excellent strength and toughness matching" to ensure that it meets multiple requirements such as strength, plasticity, toughness and process performance of the feed drill pipe. Under the specified chemical composition and mass percentage, drill pipes with minimum yield strengths of 150ksi and 165ksi grades can be manufactured. The 150ksi grade drill pipe has a room temperature yield strength of 1034–1072 MPa, tensile strength ≥1103 MPa, elongation ≥15%, and longitudinal Charpy V-notch impact toughness ≥70J at -40℃. The 165ksi grade drill pipe has a room temperature yield strength of 1034–1072 MPa, tensile strength ≥1103 MPa, elongation ≥13%, lifting capacity ≥7123–12312 kN (outer diameter D168.28 mm, wall thickness 13.26–22.23 mm), and longitudinal Charpy V-notch impact toughness ≥60J at -40℃. These specifications can meet the requirements for high-strength, high-low temperature toughness drill pipes in deep and ultra-deep cryogenic and complex oil and gas field development conditions. Meanwhile, the chemical composition of this feed pipe is also suitable for integrally weighted drill pipes and their preparation and application.

[0027] In this embodiment, the roles and content ranges of each element in the integral ultra-high strength drill pipe are as follows: C: The mass percentage of C should be controlled within the range of 0.31% to 0.35%. As the main strengthening element, too low a content is not conducive to improving hardenability and strength, while too high a content is not conducive to plasticity and toughness.

[0028] Si: The mass percentage of Si should be controlled within the range of 0.31% to 0.45%. As the main deoxidizing element, too low a content will affect the deoxidation effect; it is also a solid solution strengthening element, but too high a content will cause a decrease in plasticity and toughness.

[0029] Mn: The mass percentage of Mn is controlled within the range of 1.01% to 1.13%, mainly to improve the hardenability of steel, thereby increasing its strength. However, it has a relatively large tendency to segregate and needs to be properly controlled.

[0030] Cr: The mass percentage of Cr is controlled within the range of 0.95% to 1.05%. It is mainly used to improve the hardenability of steel, thereby improving the strength and tempering stability of steel. At the same time, it can improve the corrosion resistance of steel. However, too high a content will increase the cost.

[0031] Ni: The mass percentage of Ni is controlled within the range of 1.01% to 1.14%. It is mainly used to improve the hardenability of steel, thereby improving the strength and low-temperature toughness of steel. At the same time, it can improve the corrosion resistance of steel. It can also achieve better results in synergy with Cr and Mo. However, excessive content will increase the cost.

[0032] Mo: The mass percentage of Mo is controlled within the range of 0.62% to 0.74%. It is mainly used to improve the hardenability of steel, thereby improving the strength and tempering stability of the steel. Mo can inhibit temper brittleness. It works synergistically with microalloying elements such as V and Nb to form carbides such as Mo2C, which enhances the precipitation strengthening effect. Mo can inhibit austenite grain growth, refine the microstructure, and improve the high-temperature strength of steel. At the same time, it can improve the corrosion resistance of steel, but too high a content will increase the cost.

[0033] V (Volume): By controlling the mass percentage of V within the range of 0.03% to 0.05%, V in steel mainly enhances its 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 improving the strength of the steel. During high-temperature tempering, V carbonitrides can inhibit softening and improve the tempering stability of the steel. V can inhibit austenite grain growth. V not only improves strength by refining grains but also significantly improves low-temperature impact toughness. V can also improve the hardenability of steel, and when it works synergistically with elements such as Mn and Cr, V can further optimize hardenability. V carbides have high-temperature stability and can effectively resist softening in the high-temperature environment of deep wells. The synergistic effect of V with microalloying elements such as Nb can further unleash its potential. However, excessive V may increase brittleness and cost due to the formation of coarse carbonitrides.

[0034] Nb: When Nb is added to steel at a mass percentage controlled within the range of 0.01% to 0.03%, it forms Nb(C,N) with the C and N in the steel. This Nb inhibits austenite grain growth and refines the grains, thereby improving strength and toughness. However, excessive content will increase the carbide content, leading to brittleness and increasing costs.

[0035] V-Nb composite microalloying has a better strengthening and toughening effect than adding V or Nb alone.

[0036] 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 also 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, RE can 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.

[0037] Ca: By controlling the mass percentage of Ca within the range of 0.009% to 0.018%, inclusion modification and improved toughness are achieved: Ca can combine with S and O in steel to form CaS, CaO, or composite calcium aluminates (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.

[0038] Al: The mass percentage of Al is controlled within the range of 0.031% to 0.045%. 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, 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. However, excessive content will form excessive Al2O3 hard inclusions, affecting the fatigue properties of the steel.

[0039] P: A harmful element that mainly affects the ductility, toughness, and corrosion resistance of steel. P should be controlled to ≤0.012%.

[0040] S: A harmful element that mainly affects the ductility, toughness, and corrosion resistance of steel. S should ideally be controlled to ≤0.003%.

[0041] O: A harmful element that mainly affects the ductility, toughness, and corrosion resistance of steel. O should be controlled to ≤0.002%. H: A harmful element that mainly affects the ductility, toughness, and corrosion resistance of steel. H should ideally be controlled to ≤0.00015%.

[0042] 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%.

[0043] In some implementations, the ratio of the mass percentage of Mo to the mass percentage of P (Mo / P) is controlled to be greater than 50 to control the adverse effect of P segregation on toughness; the ratio of the mass percentage of Al to the mass percentage of N (Al / N) is controlled to be greater than 6 to eliminate the adverse effect of N on toughness and strain aging properties; the ratio of the mass percentage of Ca to the mass percentage of S (Ca / S) is controlled to be greater than 3 and the ratio of the total mass percentage of Ca and RE to the mass percentage of S ((Ca+RE) / S) is controlled to be greater than 5 to control the effect of inclusion shape control modification treatment and improve the ductility, toughness and corrosion resistance of steel.

[0044] In a preferred embodiment, the chemical composition of the integral ultra-high strength feed drill pipe, by mass percentage, includes: C 0.31%–0.33%, Si 0.36%–0.45%, Mn 1.01%–1.07%, P≤0.012%, S≤0.003%, Cr 0.95%–0.99%, Ni 1.01%–1.06%, Mo 0.62%–0.67%, V 0.03%–0.05%, Nb 0.01%–0.03%, RE 0.006%–0.008%, Al 0.031%–0.037%, Ca 0.009%–0.018%, N≤0.0045%, O≤0.0018%, H≤0.00013%, with the balance being Fe and other unavoidable impurities. The chemical composition of the integral ultra-high strength feed drill pipe, at this mass percentage, allows the specified minimum yield strength level of the feed drill pipe to reach 150 ksi, room temperature yield strength of 1105–1116 MPa, tensile strength of 1188–1200 MPa, elongation of 21–22%, and longitudinal Charpy V-notch impact toughness of 112–123 J at -40℃.

[0045] In a preferred embodiment, the chemical composition of the integral ultra-high strength feed drill pipe, by mass percentage, includes: C 0.33%–0.35%, Si 0.31%–0.37%, Mn 1.06%–1.13%, P≤0.011%, S≤0.002%, Cr 1.01%–1.05%, Ni 1.09%–1.14%, Mo 0.69%–0.74%, V 0.03%–0.05%, Nb 0.01%–0.03%, RE 0.007%–0.009%, Al 0.039%–0.045%, Ca 0.011%–0.016%, N≤0.0044%, O≤0.0016%, H≤0.00012%, with the balance being Fe and other unavoidable impurities. The chemical composition of the integral ultra-high strength feed drill pipe, at this mass percentage, allows the specified minimum yield strength level of the feed drill pipe to reach 165 ksi, room temperature yield strength of 1201–1216 MPa, tensile strength of 1291–1308 MPa, elongation of 18–19%, and longitudinal Charpy V-notch impact toughness of 102–109 J at -40℃.

[0046] In some embodiments, the rare earth element may be one or more of Ce, La, and Ce-La alloys. The rare earth element can purify molten steel, improve inclusion morphology, refine grains, increase strength and toughness, and enhance corrosion resistance.

[0047] In a preferred embodiment, the rare earth element (RE) is Ce. Ce can combine with impurities such as S and O to form high-melting-point compounds such as Ce2O3 and Ce2S3, reducing harmful inclusions (such as MnS), improving the purity of steel, and changing the morphology of sulfides (from elongated to spherical), thereby improving the transverse impact toughness of steel. At the same time, Ce can inhibit austenite grain growth, refine the microstructure, and improve the strength and toughness of steel. Furthermore, Ce can form a dense oxide film on the steel surface, improving corrosion resistance.

[0048] In addition, this invention provides a matching preparation process for the chemical composition of the integral ultra-high strength feed drill pipe. It mainly involves steelmaking (including ladle refining, vacuum degassing, and feeding Si-Ca wire), continuous casting (feeding rare earth wire, electromagnetic stirring, and light reduction), hot continuous rolling in the austenitic region, controlled rolling and cooling, rolling residual heat treatment, die forging, forging residual heat treatment, integral quenching and tempering heat treatment, hot straightening, and thread machining. This process enables the material to obtain a fine and uniform tempered sorbite microstructure, thereby achieving a reasonable match between the material's strength, plasticity, and low-temperature toughness.

[0049] Based on this, the present invention provides a method for manufacturing an integral ultra-high strength feed drill pipe, comprising the following steps: Step S10: According to the chemical composition mass percentage of the integral ultra-high strength feed drill pipe, batching, smelting and continuous casting are carried out in sequence to obtain a continuously cast billet; Step S20: The continuously cast billet is subjected to hot piercing, controlled rolling and cooling and first tempering heat treatment in sequence to obtain a tube blank; Step S30: The tube blank is subjected to die forging and a second tempering heat treatment in sequence to obtain a tube blank; Step S40: The tube blank is subjected to overall quenching and tempering heat treatment, hot straightening and non-destructive testing in sequence. After threading at both ends, it is fed into the drill pipe.

[0050] In this embodiment, the drill pipe produced by this method based on the above-mentioned mass percentages exhibits excellent comprehensive properties such as strength, plasticity, and low-temperature toughness. The minimum yield strength of the drill pipe is specified to reach 150ksi and 165ksi steel grades, respectively; the room temperature yield strength is 1105-1216MPa; the tensile strength is 1188-1308MPa; the elongation is 18-22%; the lifting capacity is 7749-13167kN (outer diameter D168.28, wall thickness 13.26-22.23mm); and the longitudinal Charpy V-notch impact toughness at -40℃ is 102-123J. Furthermore, the geometric dimension control accuracy of the drill pipe can be controlled to ±3%t. The preparation method provided by this invention includes improving purity and uniformity, reducing segregation, controlling inclusion morphology, controlled rolling and cooling, heat treatment using residual heat from rolling (first tempering heat treatment), heat treatment using residual heat from die forging and forging (second tempering heat treatment), reasonable control of heat treatment microstructure, and control of residual stress, so that the drill pipe can obtain high strength while possessing good plasticity and low-temperature toughness. This can meet the demand for high-strength, high-low-temperature toughness, and significantly improved performance drill pipes in deep and ultra-deep cryogenic and complex oil and gas field development conditions.

[0051] Specifically, based on the chemical composition mass percentage of the integral ultra-high strength drill pipe, a unique manufacturing process is adopted to achieve the minimum specified yield strength of the drill pipe reaching 150ksi and 165ksi steel grades, respectively. The 150ksi steel grade drill pipe has a room temperature yield strength of 1034-1072MPa, tensile strength ≥1103MPa, elongation ≥15%, and longitudinal Charpy V-notch impact toughness ≥70J at -40℃. The 165ksi steel grade drill pipe has a room temperature yield strength of 1034-1072MPa, tensile strength ≥1103MPa, elongation ≥13%, lifting capacity ≥7123-12312kN (outer diameter D168.28, wall thickness 13.26-22.23mm), and longitudinal Charpy V-notch impact toughness ≥60J at -40℃.

[0052] In some embodiments, step S10, which involves sequentially batching, smelting, and continuously casting the integral ultra-high strength drill pipe according to its chemical composition mass percentage to obtain a continuously cast billet, includes: Step S11: After batching the materials according to the chemical composition mass percentage of the integral ultra-high strength feed drill pipe, the steel liquid is obtained after oxygen blowing converter smelting, ladle refining, vacuum degassing, and feeding with Si-Ca wire. Step S12: Use the molten steel for casting, control the superheat to ≤25℃, and feed rare earth wire during the casting process to obtain the continuous casting billet.

[0053] In some embodiments, during step S12, when feeding rare earth wire during the casting process, electromagnetic stirring and light reduction techniques are used to control the center segregation of the continuously cast billet.

[0054] In some embodiments, the hot piercing temperature is 1190℃-1240℃; the controlled rolling and cooling is carried out by hot continuous rolling at 950℃-1200℃, controlling the rolling ratio ≥3, controlling the final rolling temperature at 930℃-960℃, and water cooling after controlled rolling, controlling the cooling rate ≥25℃; the temperature of the first tempering heat treatment is 690℃-710℃, and the time of the first tempering heat treatment is 60min-90min.

[0055] Specifically, in step S20, the step of sequentially performing hot piercing, controlled rolling and cooling, and first tempering heat treatment on the continuously cast billet to obtain a rough tube blank includes: heating the continuously cast billet to 1230℃~1260℃ in an annular heating furnace and holding it at that temperature for 90~120min; hot piercing at 1190℃~1240℃; hot continuous rolling at 950℃~1200℃, controlling the rolling ratio ≥3; controlling the final rolling temperature at 950℃; water cooling after controlled rolling, controlling the cooling rate ≥25℃ / s; and then tempering at 690℃~710℃ for 60~90min, followed by water cooling to obtain the rough tube blank.

[0056] In this embodiment, in step S20, controlling the rolling ratio ≥3 and the final rolling temperature 950℃ can obtain a finer and more uniform microstructure; controlling the cooling rate ≥25℃ / s can obtain a fully martensitic quenched structure, so that a fine and uniform tempered sorbite structure can be obtained after tempering; using a higher tempering temperature can reduce tempering time and improve production efficiency, and water cooling after tempering can avoid temper brittleness. Preferably, step S20 utilizes the residual heat of rolling for the first tempering heat treatment, which can save energy.

[0057] In some embodiments, step S30, which involves sequentially performing die forging and a second tempering heat treatment on the tube blank to obtain the tube blank, includes: Step S31: Heat the tube blank to 950℃-1150℃, perform die forging and hot forming using inner and outer diameter dies, control the forging ratio ≥3, control the final forging temperature to 930℃-960℃, and water cool after final forging and sizing, controlling the cooling rate ≥25℃ / s. Step S32: After die forging, the tube blank is subjected to a second tempering heat treatment at 690℃-710℃ for 60min-90min and then water-cooled to obtain the tube blank.

[0058] In a preferred embodiment, the final forging temperature of step S31 is 950°C.

[0059] Specifically, in step S30, controlling the forging ratio ≥3 and the final forging temperature 950℃ is to obtain a finer and more uniform microstructure; controlling the cooling rate ≥25℃ / s is to obtain a fully martensitic quenched structure so that a fine and uniform tempered sorbite structure can be obtained after tempering; using a higher tempering temperature reduces tempering time and improves production efficiency, and water cooling after tempering avoids potential temper brittleness. Using inner and outer diameter dies for forging and hot forming allows for good control of the drill pipe's geometric dimensional accuracy. Utilizing the residual heat from forging for the second tempering heat treatment saves energy.

[0060] In some embodiments, the overall quenching and tempering heat treatment includes: heating the tube blank to 900℃-920℃, holding it at that temperature for 60min-90min, then quenching it internally and externally with water spraying at a cooling rate ≥25℃ / s; followed by tempering at 550℃-580℃ for 90min-120min and then water cooling. Under this overall quenching and tempering heat treatment, the drill pipe microstructure of the tube blank is fine and uniform tempered sorbite.

[0061] In this embodiment, the overall quenching and tempering heat treatment is performed under a protective atmosphere to prevent decarburization. The overall quenching and tempering heat treatment process, involving quenching followed by high-temperature tempering, refines the grain size and microstructure of the billet through recrystallization. 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 prevents temper brittleness.

[0062] In some embodiments, the temperature for hot straightening is 500℃-530℃. Using hot straightening can reduce work hardening and residual stress during the straightening process, significantly improving the safety and reliability of the drill pipe.

[0063] In some embodiments, the non-destructive testing includes performing 100% ultrasonic testing on the hot-straightened tube blank to ensure that all indicators meet the requirements.

[0064] In some embodiments, the thread processing includes: machining API standard or non-API standard internal and external threads at both ends of the tube blank after non-destructive testing, and performing magnetic particle inspection on the threads.

[0065] In summary, this invention is designed based on the principles of "high hardenability, high tempering stability, ultra-fine grains, ultra-high purity, and excellent strength and toughness." It employs medium-carbon (C), Mn-Cr-Ni-Mo alloying, V-Nb composite micro-alloying, and the addition of rare earth (RE) elements. Si and Al are controlled, and harmful elements and gases such as P, S, O, H, and N in the steel are strictly controlled. Al and Si are completely deoxidized, and the molten steel is treated with Ca. Through the individual and especially synergistic effects of C and alloying elements, the hardenability (C-Cr-Mo-Ni-Mn-Si), purity (P, S, O, H, N control), grain refinement (V-Nb-Al), and inclusion modification (Ca-Re) of the steel are improved, laying the foundation for achieving high strength, good plasticity, and low-temperature toughness in the drill pipe. Based on this, a matching preparation process is developed for the chemical composition with the aforementioned proportions. This mainly involves steelmaking (including ladle refining, vacuum degassing, and feeding Si-Ca wire), continuous casting (feeding rare earth wire, electromagnetic stirring, and light reduction), hot continuous rolling in the austenitic region, controlled rolling and cooling, rolling residual heat treatment, die forging, forging residual heat treatment, overall quenching and tempering heat treatment, hot straightening, and thread machining. This process enables the material to obtain a fine and uniform tempered sorbite microstructure, achieving a reasonable balance of strength, plasticity, and low-temperature toughness. The preparation method provided by this invention includes improving purity and uniformity, reducing segregation, controlling inclusion morphology, controlled rolling and cooling, rolling residual heat treatment, die forging and forging residual heat treatment, overall heat treatment, reasonable heat treatment microstructure control, and residual stress control. This allows the drill pipe to achieve high strength while possessing good plasticity, low-temperature toughness, and significant lifting capacity. Employing the aforementioned unique manufacturing process, the minimum yield strength of the drill pipe reaches 150ksi and 165ksi steel grades, respectively; room temperature yield strength is 1105–1216 MPa; tensile strength is 1188–1308 MPa; elongation is 18–22%; lifting capacity reaches ≥7749–13167 kN (outer diameter D168.28 mm, wall thickness 13.26–22.23 mm); and longitudinal Charpy V-notch impact toughness at -40℃ is 102–123 J. The geometric dimensional control accuracy of the drill pipe can be improved from the usual ±12.5%t to ±3%t. This meets the requirements for high-strength, high-low temperature toughness drill pipes in deep and ultra-deep cryogenic and complex oil and gas field development conditions, significantly improving the safety and reliability of the drill pipe. With mold replacement, this invention is also applicable to integrally weighted drill pipes and their manufacturing and application.

[0066] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention.

[0067] Example 1 This embodiment provides a variety of integral ultra-high strength feed drill pipes with different mass percentages, the chemical composition of which is shown in Table 1, with the balance being Fe and unavoidable impurities.

[0068] Table 1 Chemical composition (wt%) of integral ultra-high strength feed drill pipe

[0069] This embodiment also provides a method for preparing an integral ultra-high strength feed drill pipe, including the following steps: 1) Steelmaking: Batching, oxygen-blown converter steelmaking, ladle refining, vacuum degassing, and feeding Si-Ca wire to obtain the chemical composition shown in Table 1.

[0070] 2) Continuous casting: The molten steel is cast into continuous casting billets, and the superheat is controlled to be ≤25℃. Rare earth wire is fed during the continuous casting process, and electromagnetic stirring and light reduction technology are used to control the center segregation of the continuous casting billet.

[0071] 3) Piercing, controlled rolling and cooling, and residual heat treatment of rolling to obtain the billet: The continuously cast billet is heated to 1240℃ in an annular heating furnace and held for 120 min. It is then hot-pierced at 1190℃~1240℃, hot-rolled at 950℃~1200℃, with the rolling ratio controlled at ≥3 and the final rolling temperature controlled at 950℃. After controlled rolling, it is water-cooled with a cooling rate controlled at ≥25℃ / s. Then it is tempered at 700℃ for 60 min and water-cooled after tempering.

[0072] 4) Perform die forging and residual heat treatment on the tube blank to obtain the tube blank: heat the tube blank to 950℃~1150℃, forge and hot form using inner and outer diameter dies, forge ratio ≥3, control the final forging temperature to 950℃, water cool after final forging and sizing, control the cooling rate to ≥25℃ / s, then temper at 700℃ for 60min, and water cool after tempering.

[0073] 5) The tube blank undergoes overall quenching and tempering heat treatment, hot straightening, non-destructive testing, and threading at both ends to obtain the drill pipe: The above-mentioned tube blank was heated to 910℃ and held for 60–90 min in a controlled atmosphere furnace (the holding time was adjusted according to the wall thickness, as shown in Table 2). It was then subjected to internal and external water quenching at a cooling rate ≥25℃ / s. Next, it was tempered at 550℃–580℃ for 90–120 min, followed by water cooling. (The tempering temperature and time were adjusted according to the steel grade and wall thickness, as shown in Table 2). The microstructure of the drill pipe was fine and uniform tempered sorbite.

[0074] The tube blank is heated to 500℃~530℃ for hot straightening. (The straightening temperature is adjusted according to the steel grade, as shown in Table 2).

[0075] The tube blank is subjected to 100% ultrasonic testing to ensure that all indicators meet the requirements.

[0076] Finally, API standard or non-API standard internal and external threads are machined at both ends of the tube blank, and the threads are inspected by magnetic particle testing.

[0077] The integral ultra-high strength drill pipe material of this embodiment, after undergoing the above-described preparation process, exhibits excellent comprehensive properties (as shown in Table 2). The minimum specified yield strength of the drill pipe reaches 150ksi and 165ksi steel grades, respectively; room temperature yield strength is 1105–1216 MPa; tensile strength is 1188–1308 MPa; elongation is 18–22%; lifting capacity reaches 7749–13167 kN (outer diameter D168.28, wall thickness 13.26–22.23 mm); and longitudinal Charpy V-notch impact toughness at -40℃ is 102–123 J. The geometric dimensional control accuracy of the drill pipe can be improved from the usual ±12.5%t to ±3%t. A reasonable match is achieved between strength, plasticity, lifting capacity, low-temperature toughness, and geometric dimensional accuracy. Among these: 150ksi grade steel feed drill pipe: room temperature yield strength 1105~1116MPa, tensile strength 1188~1200MPa, elongation 21~22%, longitudinal Charpy V-notch impact toughness 112~123J at -40℃. Lifting capacity reaches 7749~12127kN (outer diameter D168.28, wall thickness 13.26~22.23mm).

[0078] 165ksi grade steel feed pipe: room temperature yield strength 1201~1216MPa, tensile strength 1291~1308MPa, elongation 18~19%, longitudinal Charpy V-notch impact toughness 102~109J at -40℃. Lifting capacity reaches 8450~13167kN (outer diameter D168.28, wall thickness 13.26~22.23mm).

[0079] Table 2. Overall tempering heat treatment process and performance of integral ultra-high strength feed drill pipe

[0080] In summary, the present invention provides an integral ultra-high strength feed drill pipe and its preparation method. The chemical composition of the integral ultra-high strength feed drill pipe, by mass percentage, includes: C 0.31%–0.35%, Si 0.31%–0.45%, Mn 1.01%–1.13%, P≤0.012%, S≤0.003%, Cr 0.95%–1.05%, Ni 1.01%–1.14%, Mo 0.62%–0.74%, V 0.03%–0.05%, Nb 0.01%–0.03%, RE 0.006%–0.009%, Al 0.031%–0.045%, Ca The composition is 0.009%–0.018%, N≤0.005%, O≤0.002%, H≤0.00015%, with the balance being Fe and other unavoidable impurities; RE represents rare earth elements. In terms of chemical composition design, this invention employs medium carbon (C), Mn-Cr-Ni-Mo alloying, and V-Nb composite microalloying, with the addition of rare earth (RE) elements, and controls the Si and Al content. It strictly controls harmful elements and gases such as P, S, O, H, and N in the steel, uses Al-Si full deoxidation, and performs Ca treatment on the molten steel. Simultaneously, through the individual and synergistic effects of carbon and alloying elements, it improves the hardenability of the steel (C-Cr-Mo-Ni-Mn-Si), purification (P, S, O, H, N control), grain refinement (V-Nb-Al), and modification of inclusions (Ca-RE), laying the foundation for obtaining high strength, good plasticity, and low-temperature toughness in drill pipes. The drill pipe with the chemical composition at this mass percentage can meet the requirements of high strength and high and low temperature toughness for drill pipes used in deep and ultra-deep cryogenic and complex oil and gas field development conditions. It has high safety and reliability (integral seamless) and excellent geometric accuracy (forged).

[0081] 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 one-piece ultra-high strength feed drill pipe, characterized in that, The chemical composition of the integral ultra-high strength feed drill pipe, by mass percentage, includes: The composition is as follows: C 0.31%–0.35%, Si 0.31%–0.45%, Mn 1.01%–1.13%, P≤0.012%, S≤0.003%, Cr 0.95%–1.05%, Ni 1.01%–1.14%, Mo 0.62%–0.74%, V 0.03%–0.05%, Nb 0.01%–0.03%, RE 0.006%–0.009%, Al 0.031%–0.045%, Ca 0.009%–0.018%, N≤0.005%, O≤0.002%, H≤0.00015%, with the balance being Fe and other unavoidable impurities; RE represents rare earth elements.

2. The integral ultra-high strength feed drill pipe according to claim 1, characterized in that, The chemical composition of the integral ultra-high strength feed drill pipe, by mass percentage, includes: C 0.31%~0.33%, Si 0.36%~0.45%, Mn 1.01%~1.07%, P≤0.012%, S≤0.003%, Cr0.95%~0.99%, Ni 1.01%~1.06%, Mo 0.62%~0.67%, V 0.03%~0.05%, Nb 0.01%~0.03%, RE 0.006%~0.008%, Al 0.031%~0.037%, Ca 0.009%~0.018%, N≤0.0045%, O≤0.0018%, H≤0.00013%, with the balance being Fe and other unavoidable impurities.

3. The integral ultra-high strength feed drill pipe according to claim 1, characterized in that, The chemical composition of the integral ultra-high strength feed drill pipe, by mass percentage, includes: C 0.33%~0.35%, Si 0.31%~0.37%, Mn 1.06%~1.13%, P≤0.011%, S≤0.002%, Cr 1.01%~1.05%, Ni 1.09%~1.14%, Mo 0.69%~0.74%, V 0.03%~0.05%, Nb 0.01%~0.03%, RE 0.007%~0.009%, Al 0.039%~0.045%, Ca 0.011%~0.016%, N≤0.0044%, O≤0.0016%, H≤0.00012%, with the balance being Fe and other unavoidable impurities.

4. The integral ultra-high strength feed drill pipe according to claim 1, characterized in that, The rare earth element is one or more of Ce, La, and Ce-La alloys.

5. A method for manufacturing an integral ultra-high strength feed drill pipe, characterized in that, Including the following steps: The chemical composition of the integral ultra-high strength feed drill pipe according to any one of claims 1-4 is sequentially batched, smelted, and continuously cast to obtain a continuously cast billet; The continuously cast bar billet is subjected to hot piercing, controlled rolling and cooling and first tempering heat treatment in sequence to obtain a tube blank; The tube blank is subjected to die forging and a second tempering heat treatment in sequence to obtain a tube blank; The tube blank is subjected to overall quenching and tempering heat treatment, hot straightening and non-destructive testing in sequence, and after threading at both ends, it is fed into the drill pipe.

6. The method for preparing the integral ultra-high strength feed drill pipe according to claim 5, characterized in that, The steps of batching, smelting, and continuously casting the integral ultra-high strength drill pipe according to its chemical composition by mass percentage to obtain a continuously cast billet include: After the chemical composition of the integral ultra-high strength feed drill pipe is prepared according to the mass percentage, the steel liquid is obtained after oxygen blowing converter smelting, ladle refining, vacuum degassing, and feeding with Si-Ca wire. The molten steel is used for casting, the superheat is controlled to be ≤25℃, and rare earth wire is fed during the casting process to obtain the continuously cast billet.

7. The method for preparing the integral ultra-high strength feed drill pipe according to claim 5, characterized in that, The temperature for hot piercing is 1190℃-1240℃; the controlled rolling and cooling is carried out by hot continuous rolling at 950℃-1200℃, controlling the rolling ratio ≥3, controlling the final rolling temperature at 930℃-960℃, and water cooling after controlled rolling, controlling the cooling rate ≥25℃; the temperature for the first tempering heat treatment is 690℃-710℃, and the time for the first tempering heat treatment is 60min-90min.

8. The method for preparing the integral ultra-high strength feed drill pipe according to claim 5, characterized in that, The step of sequentially performing die forging and second tempering heat treatment on the tube blank to obtain the tube blank includes: The tube blank is heated to 950℃-1150℃, and then forged and hot-formed using inner and outer diameter dies. The forging ratio is controlled to be ≥3, and the final forging temperature is controlled to be 930℃-960℃. After final forging and sizing, the tube blank is water-cooled, and the cooling rate is controlled to be ≥25℃ / s. After die forging, the tube blank is subjected to a second tempering heat treatment at 690℃-710℃ for 60min-90min and then water-cooled to obtain the tube blank.

9. The method for preparing the integral ultra-high strength feed drill pipe according to claim 5, characterized in that, The overall quenching and tempering heat treatment includes: The tube blank is heated to 900℃-920℃ and held for 60min-90min, then water-quenched inside and outside with a cooling rate ≥25℃ / s; then tempered at 550℃-580℃ for 90min-120min and then water-cooled.

10. The method for preparing the integral ultra-high strength feed drill pipe according to claim 5, characterized in that, The temperature for thermal straightening is 500℃-530℃.

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