High collapse-resistant, corrosion-resistant oil and gas well casing for sour environments and method of making same

Abstract

The application discloses a high-collapse-resistant and corrosion-resistant oil and gas well casing for an acid environment and a preparation method thereof, relates to the technical field of metal material processing and steel pipe manufacturing, and solves the problems that the existing oil and gas well casing cannot simultaneously consider cost, strength and corrosion resistance, and is limited by the size precision of a hot rolling process, so that the collapse resistance of the oil and gas well casing cannot meet the requirements of deep harsh corrosion environments. The oil and gas well casing comprises the following components: C: 0.25% to 0.30%, Si: 0.17% to 0.35%, Mn: 0.40% to 0.65%, P: 0.015% or less, S: 0.003% or less, Cr: 0.40% to 0.60%, Mo: 0.75% to 0.90%, V: 0.05% to 0.08%, Ni: 0.20% or less, Cu: 0.10% or less, Nb: 0.015% to 0.035%, Al: 0.010% to 0.040%, and B: 0.001% to 0.002%.

Description

Technical Field

[0001] This application relates to the fields of metal material processing and steel pipe manufacturing technology, and more specifically, to a high-strength, anti-collapse, and corrosion-resistant oil and gas well casing for acidic environments and its preparation method. Background Technology

[0002] As oil extraction extends to deeper and more complex geological environments, the amount of corrosive media (such as H2S and CO2) in wells is increasing, placing extreme demands on the corrosion resistance and crush resistance of oil and gas well casing. However, traditional casing materials face severe challenges: while Super 13Cr is corrosion-resistant, it is expensive; L80-13Cr has a lower cost, but its strength and crush resistance are insufficient for deep wells. Studies show that for casings of the same strength and specifications, wall thickness variations significantly weaken their crush resistance. Hot-rolled seamless pipes under the current API-5CT standard generally suffer from low dimensional accuracy, uneven wall thickness, and difficulties in pipe diameter determination, directly leading to insufficient crush resistance. Summary of the Invention

[0003] The main objective of this application is to provide a high-strength, corrosion-resistant oil and gas well casing for acidic environments and its preparation method, in order to solve the problems faced by existing oil and gas well casings, such as the inability to balance cost, strength and corrosion resistance, and the insufficient dimensional accuracy due to hot rolling process, which makes it difficult for their crush resistance performance to meet the requirements of deep and harsh corrosive environments.

[0004] The specific technical solution is as follows:

[0005] In a first aspect, embodiments of this application provide a high-resistance to crushing and corrosion-resistant oil and gas well casing for acidic environments, the chemical composition of which, by mass percentage, is:

[0006] C: 0.25%~0.30%, Si: 0.17%~0.35%, Mn: 0.40%~0.65%, P≤0.015%, S≤0.003%, Cr: 0.40%~0.60%, Mo: 0.75%~0.90%, V: 0.05%~0.08%, Ni≤0.20%, Cu≤0.10%, Nb: 0.015%~0.035%, Al: 0.010%~0.040%, B: 0.001%~0.002%, with the balance being Fe and unavoidable impurities. The sum of the mass percentages of the above components is 100%.

[0007] Secondly, embodiments of this application provide a method for preparing the highly resistant to crushing and corrosion of oil and gas well casing for acidic environments as described in the first aspect, comprising the following steps:

[0008] S1, Smelting and Continuous Casting: The steel billet is obtained by primary smelting in an electric arc furnace, followed by refining in a refining furnace and vacuum degassing in a VD furnace.

[0009] S2, Hot rolling: The steel billet is hot rolled into a hot-rolled seamless steel pipe;

[0010] S3, Softening and Pretreatment: The hot-rolled seamless steel pipe is subjected to softening annealing treatment, followed by straightening, pickling, phosphating and saponification treatments to obtain a pretreated pipe blank;

[0011] S4, Cold drawing: The pretreated tube blank is cold drawn to obtain a cold-drawn precision seamless steel tube;

[0012] S5, Quenching and finishing: The cold-drawn precision seamless steel pipe is straightened, then quenched and tempered, and then straightened again.

[0013] S6, Inspection and Warehousing: Ultrasonic non-destructive testing, hydrostatic testing, and finished product inspection are carried out on the heat-treated and finished steel pipes. Qualified products are packaged and put into warehousing.

[0014] In some embodiments of this application, in step S2, the specific process of hot rolling forming is as follows: after heating the steel billet, it is pierced to form a rough tube, and then the rough tube is rolled into a blank tube using a three-roll continuous rolling mill, and then the blank tube is sized using a sizing mill to obtain the hot-rolled seamless steel pipe of the preset size.

[0015] In some embodiments of this application, the wall thickness accuracy of the hot-rolled seamless steel pipe after the hot rolling forming process is ≤ ±10% × wall thickness.

[0016] In some embodiments of this application, in step S3, the specific process of the softening annealing treatment is as follows: under a protective atmosphere, the hot-rolled seamless steel pipe is heated to 680~750℃, held for 1~3 hours, and then cooled in the furnace; after the softening annealing treatment, the Brinell hardness value of the hot-rolled seamless steel pipe is ≤190.

[0017] In some embodiments of this application, in step S3, the phosphating treatment is to form a phosphating film on the surface of the steel pipe, and the saponification treatment is to adsorb a layer of saponified lubricant on the phosphating film to form a lubricating layer.

[0018] In some embodiments of this application, in step S4, the cold drawing process is a multi-pass cold drawing, with the deformation amount of each pass controlled between 15% and 30%; the pre-treated tube blank is cold-drawn into the cold-drawn precision seamless steel tube using a 600-ton hydraulic cold drawing machine.

[0019] In some embodiments of this application, in step S5, the specific process of the quenching and tempering heat treatment is as follows: the quenching temperature is 890℃±10℃, the holding time is 45 minutes, and then rapid cooling is performed by water quenching or oil quenching; the tempering temperature is 630℃±10℃, the holding time is 90 minutes, and then air cooling or water cooling is performed.

[0020] In some embodiments of this application, the room temperature yield strength of the acidic environment high crush resistance and corrosion resistance oil and gas well casing is 758~965MPa, tensile strength ≥862MPa, elongation after fracture ≥18%, and V-notch impact energy ≥100J at -10℃.

[0021] In some embodiments of this application, the outer diameter tolerance of the acidic environment high-resistance to crushing and corrosion-resistant oil and gas well casing is ≤ ±0.5% × outer diameter, and the wall thickness tolerance is ≤ ±4% × wall thickness.

[0022] Compared with the prior art, this application has at least the following beneficial effects:

[0023] This application employs a medium-carbon micro-alloying path, a high hardenability design, and a high-purity smelting chemical composition design, resulting in steel with both high purity and excellent strength and toughness. Simultaneously, the production process of "hot-rolled seamless steel pipe + softening annealing + cold-drawn precision steel pipe + quenching and tempering" significantly improves dimensional accuracy, ensures uniformity of steel pipe wall thickness, and enhances the casing's resistance to crushing. Furthermore, it allows for further improvement of the cold-drawing die and optimization of the cold-drawing production process, employing a single-stage cold-drawing process to ensure success on the first attempt, avoiding double cold drawing, reducing production costs, and enhancing product competitiveness. This application utilizes a complete and fully controlled manufacturing process, enabling the stable production of high-performance precision seamless oil and gas well casing that combines high purity, high dimensional accuracy, and excellent strength and toughness, thereby solving the core material bottleneck in deep and ultra-deep well exploitation. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 A schematic diagram of the process flow for the preparation method of a high-strength and corrosion-resistant oil and gas well casing for acidic environments provided in this application;

[0026] Figure 2 Metallographic diagram of the high-strength, corrosion-resistant oil and gas well casing for acidic environments prepared in Example 1 of this application. Detailed Implementation

[0027] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0028] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The terms "comprising" and "having," and any variations thereof, in the embodiments and drawings of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or devices.

[0029] In existing technologies, traditional oil and gas well casing materials cannot simultaneously achieve cost, strength, and corrosion resistance. Meanwhile, in industrial fields such as hydraulic cylinders and bearings, precision seamless steel pipes produced through a "hot rolling + cold drawing" process have achieved precise control over dimensions, surface finish, and performance. However, directly applying this process to oil and gas well casing production is prone to mismanagement, leading to a series of problems: First, insufficient purity; high gas and inclusion content in the molten steel creates internal defects, affecting pressure resistance and fatigue life. Second, uneven microstructure and properties; coarse grains in the hot-rolled billet, if not properly softened before cold drawing, will lead to work hardening and drawing cracks. Third, poor surface quality; inadequate surface pretreatment (such as phosphating and saponification) can cause lubrication failure, scratching the inner wall and introducing significant residual stress. Fourth, substandard overall performance; if the final heat treatment is merely stress-relieving annealing, its strength and toughness cannot reach the level of high-end tempered steel. Therefore, oil and gas well casing with high resistance to crushing and corrosion in acidic environments must meet the high performance requirements of high purity, high dimensional accuracy, and excellent strength and toughness.

[0030] Based on the above requirements, this application provides the following technical solution.

[0031] This application provides a high-resistance to crushing and corrosion in oil and gas well casing for acidic environments. The chemical composition of this oil and gas well casing, by mass percentage, is as follows: C: 0.25%–0.30%, Si: 0.17%–0.35%, Mn: 0.40%–0.65%, P≤0.015%, S≤0.003%, Cr: 0.40%–0.60%, Mo: 0.75%–0.90%, V: 0.05%–0.08%, Ni≤0.20%, Cu≤0.10%, Nb: 0.015%–0.035%, Al: 0.010%–0.040%, B: 0.001%–0.002%, with the balance being Fe and unavoidable impurities. The sum of the mass percentages of all the above components is 100%.

[0032] By applying the technical solution of this application, while ensuring strength, fine-grained strengthening and precipitation strengthening are achieved through medium-carbon design combined with microalloying of elements such as vanadium, niobium, and boron, thus balancing strength and toughness. Simultaneously, the reasonable proportion of elements such as chromium, molybdenum, and boron significantly improves hardenability, aiming to obtain a metallographic structure dominated by bainite or tempered martensite, thereby achieving a balance between high strength and high toughness. Furthermore, high-purity smelting is employed, with strict control over the content of harmful elements such as P and S, ensuring that the steel possesses excellent low-temperature toughness and resistance to crack propagation. Although the carbon content in this application is slightly higher than that of conventional pipeline steel, by controlling the content of other elements and carbon equivalent, acceptable weldability can be maintained while meeting strength requirements, making it suitable for on-site welding needs in pipeline engineering.

[0033] The following explains the reasons for the chemical composition of the high-resistance to crushing and corrosion of oil and gas well casing in acidic environments as specified above. Here, the "%" indicating the content (concentration) of chemical composition means "mass %".

[0034] C: 0.25%~0.30%

[0035] Carbon (C) is a core element ensuring the strength and hardenability of oil and gas well casing steel. This application adopts a medium carbon content range to provide significant solid solution strengthening and carbide formation capabilities to meet the strength requirements of high-grade steels. The lower limit of 0.25% ensures that the oil and gas well casing steel has sufficient C content to provide the necessary solid solution strengthening effect and form sufficient alloy carbides (such as carbides formed with Cr, Mo, and V), thus laying the foundation for achieving the yield strength and tensile strength required for high-grade steels (such as X70 and above). Below this lower limit, the strength may not meet the requirements. Furthermore, the negative effects of excessively high C content are strictly controlled. Excessive C significantly reduces the toughness and weldability of the steel, drastically increases the susceptibility to cold cracking during welding, and causes the carbon equivalent to exceed the limit. The upper limit of 0.30% strikes a balance between ensuring strength and not severely impairing toughness and weldability.

[0036] Si: 0.17%~0.35%

[0037] Silicon (Si) primarily functions as a deoxidizer to remove oxygen from molten steel, improving its cleanliness. Simultaneously, Si provides a degree of solid solution strengthening. A minimum content of 0.17% ensures adequate deoxidation, guaranteeing sufficient Si for deoxidation during smelting, generating SiO2 which floats to the surface and is removed, thereby reducing the oxygen content in the steel, improving its cleanliness, and preventing porosity and oxide inclusions due to insufficient deoxidation. However, excessive Si content reduces the steel's plasticity and toughness, promotes temper brittleness, and increases the risk of surface cracking (such as internal folding) during rolling due to reduced heat permeability. To prevent the adverse effects of excessive Si content, an upper limit of 0.35% is set to prevent damage to the steel's plasticity, toughness, and surface quality.

[0038] Mn: 0.40%~0.65%

[0039] Manganese (Mn) is an austenite stabilizing element that enhances strength through solid solution strengthening and also improves hardenability. This application controls the Mn content at a low level primarily to ensure basic properties while avoiding the grain coarsening tendency and temper brittleness risks associated with high Mn content, thus maintaining excellent low-temperature toughness. A lower limit of 0.40% provides necessary solid solution strengthening and helps improve hardenability. Simultaneously, Mn can combine with sulfur (S) to form MnS, mitigating the hot brittleness hazard of S to some extent. Furthermore, excessively high Mn content increases the steel's grain coarsening tendency and temper brittleness sensitivity, adversely affecting low-temperature impact toughness and crack tip opening displacement (CTOD) values. Therefore, the upper limit of its content is set at 0.65% to avoid the negative effects of high Mn content.

[0040] P≤0.015%

[0041] Phosphorus (P) is a harmful element that readily segregates at grain boundaries. It exhibits a strong tendency to segregate at grain boundaries in steel, and even trace amounts can significantly increase the ductile-brittle transition temperature, worsen low-temperature toughness, and increase the cold cracking susceptibility of the weld heat-affected zone, exacerbating cold brittleness. This application strictly limits the P content to an upper limit of 0.015%, which is a key measure to ensure high toughness and excellent weldability of oil and gas well casing steel, especially the low-temperature toughness of the weld heat-affected zone.

[0042] S≤0.003%

[0043] Sulfur (S) forms sulfide inclusions (such as MnS), severely impairing the toughness and plasticity of steel, fracturing the matrix, and reducing resistance to hydrogen-induced cracking. It acts as a crack initiation point, drastically deteriorating the steel's transverse toughness, ductility, and resistance to hydrogen-induced cracking. This application strictly limits the S content to an upper limit of 0.003%, controlling it at an extremely low level, which is a prerequisite for obtaining high-purity steel and ensuring excellent resistance to crack propagation.

[0044] Cr: 0.40%~0.60%

[0045] Chromium (Cr) is a carbide-forming element that effectively improves the hardenability, strength, and hardness of steel. It combines with carbon to form fine, dispersed carbides, which helps refine the grain size and improve tempering stability. A lower limit of 0.40% ensures that Cr effectively improves the hardenability of steel and contributes to strength and grain refinement by forming fine chromium carbides. However, excessively high Cr levels can raise the brittle-brittle transition temperature of steel, negatively impacting low-temperature toughness. It also increases the carbon equivalent, negatively affecting weldability and potentially stabilizing certain undesirable phases. Therefore, its upper limit is set at 0.60%.

[0046] Mo: 0.75%~0.90%

[0047] Molybdenum (Mo) is a strong carbide-forming element, its core role being to significantly improve the hardenability of steel and strongly suppress temper brittleness caused by other elements. Simultaneously, Mo refines grains and works synergistically with microalloying elements V and Nb to enhance precipitation strengthening. As a key element for improving hardenability, suppressing temper brittleness, and inducing secondary hardening, sufficient Mo content is crucial for ensuring a microstructure dominated by lower bainite with high strength and high toughness; therefore, its lower limit is set at 0.75%. Furthermore, as a valuable element, excessive addition of Mo is uneconomical, and excessively high Mo content may promote the formation of high-temperature ferrite and increase susceptibility to weld reheat cracking; therefore, its upper limit is set at 0.90%.

[0048] V: 0.05%~0.08%

[0049] Vanadium (V) is a strong carbonitride forming element. In steel, it forms fine, dispersed V(C,N) precipitates, resulting in significant precipitation strengthening and effectively improving strength. Simultaneously, these precipitates pin grain boundaries, increasing the grain coarsening temperature. To ensure sufficient V to form V(C,N) precipitates in steel, effectively improving strength through precipitation strengthening and refining grains, its content is set at a lower limit of 0.05%. However, strict control of the V content is necessary to prevent a significant decrease in toughness due to excessive or coarse precipitates. Furthermore, excessively high V content can cause strong secondary hardening during tempering, potentially reducing toughness to unacceptable levels. Therefore, its content is set at an upper limit of 0.08%.

[0050] Ni≤0.20%

[0051] Nickel (Ni) can dissolve in ferrite to improve strength, but more importantly, it can significantly improve the low-temperature toughness of steel and lower the ductile-brittle transition temperature. Its content is set at an upper limit of 0.20%, primarily for cost control, and to prevent the subtle negative impact of excessive Ni on weldability (such as increased hot cracking tendency) while ensuring a certain level of low-temperature toughness. Its role in improving toughness is mainly achieved through other core mechanisms (such as grain refinement strengthening).

[0052] Cu≤0.10%

[0053] Copper (Cu) can improve the atmospheric corrosion resistance of oil and gas well casing steel and produce a certain degree of solid solution strengthening. However, the melting point of Cu is lower than the hot working temperature of steel. Excessive Cu will cause "copper embrittlement" due to surface enrichment during hot working, leading to cracks on the hot-rolled surface. Therefore, its content is strictly limited to an upper limit of 0.10%.

[0054] Nb: 0.015%~0.035%

[0055] Niobium (Nb) is a key microalloying element. At higher temperatures, it precipitates Nb(C,N), strongly inhibiting austenite recrystallization and grain growth, thus simultaneously improving the strength and toughness of steel through a "grain refinement strengthening" mechanism. A minimum content of 0.015% ensures that Nb effectively inhibits austenite grain growth, simultaneously enhancing strength and toughness through this grain refinement strengthening mechanism—a core design element for achieving a high-strength, high-toughness combination. Conversely, excessive Nb forms coarse Nb(C,N) particles. While its precipitation strengthening effect becomes saturated, it also acts as a crack initiation point, impairing toughness and the performance of the weld heat-affected zone. Therefore, its maximum content is set at 0.035%.

[0056] Al: 0.010%~0.040%

[0057] Aluminum (Al) is the primary deoxidizer. It combines with oxygen to form Al₂O₃, which floats to the slag, thus purifying the molten steel. Furthermore, Al refines austenite grains, contributing to improved toughness. A lower limit of 0.010% ensures sufficient Al for deoxidation, allowing fine Al₂O₃ or aluminate inclusions to float and maintain steel cleanliness. However, excessive Al promotes the formation of large, clustered Al₂O₃ inclusions. These hard and brittle inclusions severely degrade the fatigue properties and toughness of the steel; therefore, its upper limit is 0.040%. This 0.010%–0.040% content range ensures effective deoxidation and grain control while preventing the formation of large inclusions.

[0058] B: 0.001%~0.002%

[0059] Boron (B) is an extremely effective hardenability element. It preferentially segregates at austenite grain boundaries, reducing the nucleation rate of high-temperature transformation structures such as ferrite, thereby significantly improving the hardenability of steel and enabling the formation of bainitic or martensitic structures even at lower cooling rates. However, its effect is insufficient if its content is too low, so a lower limit of 0.001% is set. But the content window for B is very narrow; excessive B easily forms brittle borides. These compounds not only negate B's hardenability-enhancing effect, but they themselves often exhibit a network distribution at grain boundaries, drastically increasing the brittleness of the steel. Therefore, an upper limit of its content is set at 0.002%.

[0060] The chemical composition of the oil and gas well casing of this application has a balance of Fe and unavoidable impurities. Here, impurities refer to elements mixed in by the ore and waste used as raw materials during steel manufacturing, or elements mixed in from the environment during the manufacturing process.

[0061] Meanwhile, the chemical composition design of the acidic environment-resistant, high-crush-resistance, and corrosion-resistant oil and gas well casing in this application achieves the goals of low cost, high purity, high strength, high toughness, and excellent comprehensive performance through the precise coordination and synergistic effect of various elements. Its synergistic effect is mainly reflected in the following aspects:

[0062] First, the synergistic achievement of high strength and high toughness:

[0063] The “C–B” system forms the core of this application's hardenability assurance system. 0.25%–0.30% carbon (C) acts as the primary strengthening element, providing significant solid solution strengthening and ensuring sufficient carbide formation, which is fundamental to strength. 0.001%–0.002% boron (B) is an extremely strong hardenability element. Through grain boundary segregation, it significantly inhibits the nucleation of ferrite and pearlite, thus ensuring a high-strength, high-toughness microstructure dominated by bainite or low-carbon martensite, even at relatively low cooling rates. Furthermore, 0.40%–0.60% chromium (Cr) and 0.75%–0.90% molybdenum (Mo) further enhance hardenability and form a strong synergy with the “C–B” system. Mo also effectively suppresses temper brittleness that may be caused by elements such as Cr and P, ensuring high toughness levels at high strength.

[0064] The core microalloying and microstructure refinement system of this application is the “V–Nb–Mo” system. V (0.05%–0.08%) and Nb (0.015%–0.035%), as strong carbonitride forming elements, play a crucial role in rolling and heat treatment. Nb precipitates at higher austenitizing temperatures, strongly inhibiting austenite grain growth and simultaneously improving strength and toughness through a “grain refinement strengthening” mechanism, which is the core of achieving high toughness. Meanwhile, V carbonitrides precipitate at slightly lower temperatures, providing a significant “precipitation strengthening” effect. Furthermore, Mo, synergistically with V and Nb, improves the precipitation stability of microalloyed carbonitrides and refines the final microstructure. V, Nb, and Mo together construct a dual strengthening mechanism of “grain refinement strengthening + precipitation strengthening,” significantly improving strength without significantly compromising toughness.

[0065] Second, the synergistic protection of weldability and heat-affected zone performance:

[0066] In this application, although the carbon content is not low, the overall carbon equivalent is controlled by maintaining Mn at a relatively low level of 0.40%–0.65% and limiting the content of elements such as Cu (≤0.10%) and Ni (≤0.20%), thereby reducing the susceptibility to cold cracking in welding. Furthermore, the addition of B, Cr, and Mo ensures the performance of the base metal, although they will redissolve during the welding thermal cycle. Through strict process control (such as controlling the heat input energy and preheating temperature), a fine bainitic structure can be formed in the heat-affected zone during subsequent cooling, thus avoiding the formation of martensite, which is sensitive to cold cracking, and ensuring the performance of the welded joint. This achieves a balance between carbon equivalent control and hardenability elements.

[0067] Strict control of P ≤ 0.015% and S ≤ 0.003% significantly reduces the amount of grain boundary segregation and sulfide inclusions. This not only improves the low-temperature toughness of the base metal but also directly enhances the toughness of the weld heat-affected zone and reduces its embrittlement tendency. Simultaneously, Al content of 0.010%–0.040% acts as a deoxidizer, synergistically with Si, ensuring the cleanliness of the molten steel and reducing oxide inclusions, thus laying the foundation for excellent weldability and matrix toughness.

[0068] Third, synergistic optimization of overall performance:

[0069] Elements such as Si, Mn, Cu, and Ni provide certain solid solution strengthening as a strength supplement. Among them, the addition of Ni, while strengthening, also has the unique ability to reduce the ductile-brittle transition temperature, which, together with the microstructure refinement mechanism, further ensures the low-temperature toughness of the steel pipe, achieving a balance between solid solution strengthening and toughness.

[0070] Cr, Mo, and V carbides exhibit high structural stability during tempering, effectively inhibiting structural recovery and recrystallization, thus improving the tempering stability of oil and gas well casing steel. This allows the steel pipe to maintain high strength and hardness during subsequent processing or service at certain temperatures, and provides strong resistance to softening.

[0071] This acidic environment-resistant, high-crush-resistance, and corrosion-resistant oil and gas well casing utilizes a "C-B-Cr-Mo" alloy to achieve deep hardenability, ensuring a high-strength, high-toughness bainitic / martensite matrix. Simultaneously, "Nb-V-Mo" microalloying and precipitation strengthening are employed to precisely enhance the strength-toughness balance. Furthermore, extremely low P and S content and high-purity smelting processes provide a fundamental guarantee for excellent low-temperature toughness and weldability. This application employs a multi-element, multi-mechanism synergistic design, enabling this oil and gas well casing to meet the stringent requirements of high-performance pipelines, especially high-steel grade pipelines used in harsh environments.

[0072] Furthermore, the oil and gas well casing strictly limits the levels of sulfides (Class A), alumina (Class B), silicates (Class C), spherical oxides (Class D), and single-particle oxides (DS), with a total inclusion index (A+B+C+D+DS) ≤ 6, ensuring material purity. Further, the gaseous element control of the oil and gas well casing in this application is as follows: nitrogen (N≤80ppm), oxygen (O≤30ppm), and hydrogen (H≤2ppm), reducing the risk of porosity and brittleness.

[0073] This application also provides a method for preparing the aforementioned high-resistance to crushing and corrosion-resistant oil and gas well casing for acidic environments. The method employs a process route of smelting and continuous casting → hot rolling → softening and pretreatment → cold drawing → tempering and finishing → inspection and warehousing, significantly improving dimensional accuracy, ensuring uniformity of steel pipe wall thickness, and enhancing the casing's resistance to crushing. Specifically, as... Figure 1 As shown, the preparation method includes the following steps:

[0074] S1, Smelting and Continuous Casting: The steel billet is obtained by primary smelting in an electric arc furnace, followed by refining in a refining furnace and vacuum degassing in a VD furnace.

[0075] S2, Hot rolling: Hot rolling of steel billets into hot-rolled seamless steel pipes.

[0076] S3, Softening and Pretreatment: Hot-rolled seamless steel pipes are softened and annealed, and then straightened, pickled, phosphated and saponified in sequence to obtain pretreated pipe blanks.

[0077] S4, Cold drawing: The pre-treated tube blank is cold drawn to obtain a cold-drawn precision seamless steel tube.

[0078] S5, Quenching and Finishing: The cold-drawn precision seamless steel pipe is straightened, then quenched and tempered, and then straightened again.

[0079] S6, Inspection and Warehousing: Ultrasonic non-destructive testing, hydrostatic testing, and finished product inspection are carried out on the heat-treated and finished steel pipes. Qualified products are packaged and put into warehousing.

[0080] In step S1, a smelting method involving an electric arc furnace, refining furnace, and VD furnace with vacuum degassing is employed to precisely control the chemical composition and inclusions of the high-resistance to crushing and corrosion-resistant oil and gas well casing in an acidic environment, ensuring compliance with design requirements. Furthermore, during the arc-shaped continuous casting of the steel billet, the billet drawing speed and cooling rate are strictly controlled according to the operating procedures to prevent loosening of the billet's central structure and shrinkage cracks.

[0081] In one embodiment of this application, the specific process of hot rolling in step S2 is as follows: after heating the steel billet, it is pierced to form a rough tube, then the rough tube is rolled into a blank tube using a three-roll continuous rolling mill, and then the blank tube is sized using a sizing mill to obtain a hot-rolled seamless steel pipe of a preset size. The three-roll continuous rolling mill mentioned in this application can preferably be a PQF type continuous rolling mill provided by SMS Group, realizing steel billet piercing → three-roll continuous rolling → sizing by a sizing mill. The wall thickness accuracy of the hot-rolled seamless steel pipe after hot rolling is ≤ ±10% × wall thickness, and the ultrasonic testing meets the requirements of API-5CT version 10 standard, with no surface defects.

[0082] In one embodiment of this application, the specific process of softening annealing in step S3 is as follows: Under a protective atmosphere, the hot-rolled seamless steel pipe is heated to 680~750℃, held at that temperature for 1~3 hours, and then cooled in the furnace. After softening annealing, the hot-rolled seamless steel pipe has a Brinell hardness value ≤190. The bending caused by annealing is then straightened to restore and ensure dimensional accuracy and shape tolerances, optimize mechanical properties and performance, and create conditions for subsequent manufacturing processes.

[0083] In one embodiment of this application, pickling, phosphating, and saponification treatments are performed separately in a pickling tank, a phosphating tank, and a saponification tank. Pickling removes iron oxide scale, phosphating forms a phosphating film on the steel pipe surface, and saponification adsorbs a saponified lubricant onto the phosphating film, forming a lubricating layer. Subsequently, cold drawing significantly improves the dimensional accuracy of the hot-rolled seamless steel pipe. Furthermore, the pre-treated billet in this application is cold-drawn into a cold-drawn precision seamless steel pipe using a 600-ton hydraulic cold drawing machine, ensuring that the dimensions fully meet design requirements.

[0084] In one embodiment of this application, the specific process of the quenching and tempering heat treatment in step S5 is as follows: quenching temperature is 890℃±10℃, holding time is 45 minutes, followed by rapid cooling by water quenching or oil quenching; tempering temperature is 630℃±10℃, holding time is 90 minutes, followed by air cooling or water cooling. Thus, through quenching at 890℃ for 45 minutes and tempering at 630℃ for 90 minutes, the performance is ensured to fully meet the requirements.

[0085] In one embodiment of this application, the room temperature yield strength of the high-strength, crush-resistant, and corrosion-resistant oil and gas well casing for acidic environments is 758~965MPa, tensile strength ≥862MPa, elongation after fracture ≥18%, and V-notch impact energy ≥100J at -10℃. Furthermore, its outer diameter tolerance is ≤±0.5%×outer diameter, and its wall thickness tolerance is ≤±4%×wall thickness.

[0086] This application adopts a process flow of steelmaking (using electric arc furnace, refining furnace, or VD furnace vacuum degassing) → arc-shaped continuous casting billet → hot-rolled seamless steel pipe → steel pipe softening annealing → straightening → pickling, phosphating, saponification → cold-drawn precision seamless steel pipe → straightening → tempering heat treatment → straightening → ultrasonic flaw detection → hydrostatic test → finished product inspection → packaging and warehousing. This process improves dimensional accuracy and solves a series of problems caused by directly transplanting the existing "hot rolling + cold drawing" process to oil and gas well casing production.

[0087] In summary, this application discloses a high-strength, corrosion-resistant oil and gas well casing for acidic environments and its manufacturing method. It employs a medium-carbon micro-alloying path, a high-hardenability design, and a high-purity smelting chemical composition design, resulting in steel with both high purity and excellent strength and toughness. Simultaneously, the production process of "hot-rolled seamless steel pipe + softening annealing + cold-drawn precision steel pipe + quenching and tempering" significantly improves dimensional accuracy, ensures uniform steel pipe wall thickness, and enhances the casing's resistance to collapse. Furthermore, the cold-drawing die can be further improved, and the cold-drawing production process optimized, employing a single-stage cold-drawing process to ensure success on the first attempt, avoiding double cold drawing, reducing production costs, and improving product competitiveness. This application utilizes a complete and fully controlled manufacturing process, enabling the stable production of high-performance precision seamless oil and gas well casing that combines high purity, high dimensional accuracy, and excellent strength and toughness, thereby solving the core material bottleneck in deep and ultra-deep well development.

[0088] The beneficial effects of this application are further illustrated below with reference to typical but non-limiting embodiments.

[0089] Example 1

[0090] By manufacturing Specifications for oil and gas well casing. This application contains the specifications for oil and gas well casing.

[0091] The acid-environment-resistant and corrosion-resistant oil and gas well casing manufactured in this embodiment contains the following components by weight percentage:

[0092] C: 0.28%, Si: 0.28%, Mn: 0.53%, P: 0.011%, S: 0.001%, Cr: 0.53%, Mo: 0.83%, V: 0.07%, Ni: 0.20%, Cu: 0.01%, Nb: 0.022%, Al: 0.025%, B: 0.0015%, with the balance being Fe and unavoidable impurities. The sum of the mass percentages of the above components is 100%.

[0093] The above-mentioned oil and gas well casing shall be prepared according to the following method:

[0094] In S1, during the initial smelting in the electric arc furnace, 80% high-quality scrap steel and 20% direct reduced iron (DRI) are used as raw materials to control residual elements. The steel is melted by electric current, dephosphorized by oxygen blowing, and tapped when the temperature reaches 1580℃. Next, the molten steel is heated to 1580±5℃ in the LF furnace, followed by white slag formation and deep deoxidation with the addition of aluminum blocks. Microalloying elements are precisely added according to the formula. The temperature of the molten steel is precisely adjusted to the superheat range required for continuous casting through electric arc heating, completing the refining furnace refining. Vacuum degassing is then performed in the VD furnace, maintained at a high vacuum (≤67Pa) for at least 18 minutes. Finally, protective casting is used, with the superheat strictly controlled at 20~25℃, combined with electromagnetic stirring to obtain… 350mm continuous casting round billet.

[0095] S2, the billet is heated to 1250℃ in a walking beam furnace and pierced at around 1150℃ to form a rough tube. Then, the rough tube is rolled into a blank tube using a PQF continuous rolling mill, and finally sized using a sizing mill to obtain... Hot-rolled seamless steel pipes.

[0096] S3. Under a protective atmosphere, the hot-rolled seamless steel pipe is heated to 680°C, held at that temperature for 90 minutes, and then cooled in the furnace. Afterwards, it is straightened according to the standard procedure, and then subjected to pickling, phosphating, and saponification treatments in pickling, phosphating, and saponification tanks respectively to prepare the surface for cold drawing.

[0097] S4 involves a single cold drawing process on a 600-ton hydraulic cold drawing machine, with the deformation controlled at 12% to 15%, to produce cold-drawn precision seamless steel pipes.

[0098] S5 involves straightening the cold-drawn precision seamless steel pipe. Afterwards, it is quenched at 890℃ for 45 minutes, followed by high-temperature tempering at 630℃ for 90 minutes. Finally, a large-scale high-precision straightening machine is used for fine straightening to ensure that the straightness of this large-diameter steel pipe meets high standards.

[0099] S6. Perform ultrasonic flaw detection, hydrostatic testing and finished product inspection according to standards, and package qualified products into warehouse.

[0100] Example 2

[0101] By manufacturing Specifications for oil and gas well casing. This application contains the specifications for oil and gas well casing.

[0102] The acid-environment-resistant and corrosion-resistant oil and gas well casing manufactured in this embodiment contains the following components by weight percentage:

[0103] C: 0.28%, Si: 0.27%, Mn: 0.53%, P: 0.012%, S: 0.001%, Cr: 0.53%, Mo: 0.85%, V: 0.06%, Ni: 0.02%, Cu: 0.01%, Nb: 0.021%, Al: 0.025%, B: 0.0015%, with the balance being Fe and unavoidable impurities. The sum of the mass percentages of the above components is 100%.

[0104] The above-mentioned oil and gas well casing shall be prepared according to the following method:

[0105] In S1, during the initial smelting in the electric arc furnace, 80% high-quality scrap steel and 20% direct reduced iron (DRI) are used as raw materials to control residual elements. The steel is melted by electric current, dephosphorized by oxygen blowing, and tapped when the temperature reaches 1580℃. Next, the molten steel is heated to 1580±5℃ in the LF furnace, followed by white slag formation and deep deoxidation with the addition of aluminum blocks. Microalloying elements are precisely added according to the formula. The temperature of the molten steel is precisely adjusted to the superheat range required for continuous casting through electric arc heating, completing the refining furnace refining. Vacuum degassing is then performed in the VD furnace, maintained at a high vacuum (≤67Pa) for at least 18 minutes. Finally, protective casting is used, with the superheat strictly controlled at 20~25℃, combined with electromagnetic stirring to obtain… 310mm continuous casting round billet.

[0106] S2, the billet is heated to 1250℃ in a walking beam furnace and pierced at around 1150℃ to form a rough tube. Then, the rough tube is rolled into a blank tube using a PQF continuous rolling mill, and finally sized using a sizing mill to obtain... Hot-rolled seamless steel pipes.

[0107] S3. Under a protective atmosphere, the hot-rolled seamless steel pipe is heated to 680°C, held at that temperature for 90 minutes, and then cooled in the furnace. Afterwards, it is straightened according to the standard procedure, and then subjected to pickling, phosphating, and saponification treatments in pickling, phosphating, and saponification tanks respectively to prepare the surface for cold drawing.

[0108] S4 involves a single cold drawing process on a 600-ton hydraulic cold drawing machine, with the deformation controlled at 13% to 15%, to produce cold-drawn precision seamless steel pipes.

[0109] S5 involves straightening the cold-drawn precision seamless steel pipe. Afterwards, it is quenched at 890℃ for 45 minutes, followed by high-temperature tempering at 630℃ for 90 minutes. Finally, a large-scale high-precision straightening machine is used for fine straightening to ensure that the straightness of this large-diameter steel pipe meets high standards.

[0110] S6. Perform ultrasonic flaw detection, hydrostatic testing and finished product inspection according to standards, and package qualified products into warehouse.

[0111] Example 3

[0112] By manufacturing Specifications for oil and gas well casing. This application contains the specifications for oil and gas well casing.

[0113] The acid-environment-resistant and corrosion-resistant oil and gas well casing manufactured in this embodiment contains the following components by weight percentage:

[0114] C: 0.27%, Si: 0.29%, Mn: 0.52%, P: 0.012%, S: 0.001%, Cr: 0.53%, Mo: 0.84%, V: 0.06%, Ni: 0.02%, Cu: 0.01%, Nb: 0.022%, Al: 0.026%, B: 0.0015%, with the balance being Fe and unavoidable impurities. The sum of the mass percentages of the above components is 100%.

[0115] The above-mentioned oil and gas well casing shall be prepared according to the following method:

[0116] In S1, during the initial smelting in the electric arc furnace, 80% high-quality scrap steel and 20% direct reduced iron (DRI) are used as raw materials to control residual elements. The steel is melted by electric current, dephosphorized by oxygen blowing, and tapped when the temperature reaches 1580℃. Next, the molten steel is heated to 1580±5℃ in the LF furnace, followed by white slag formation and deep deoxidation with the addition of aluminum blocks. Microalloying elements are precisely added according to the formula. The temperature of the molten steel is precisely adjusted to the superheat range required for continuous casting through electric arc heating, completing the refining furnace refining. Vacuum degassing is then performed in the VD furnace, maintained at a high vacuum (≤67Pa) for at least 18 minutes. Finally, protective casting is used, with the superheat strictly controlled at 20~25℃, combined with electromagnetic stirring to obtain… 250mm continuous casting round billet.

[0117] S2: The billet is heated to 1240±20℃ in a walking beam furnace and held for about 1.5 hours. It is then pierced at approximately 1150℃ to form a rough tube. The rough tube is then rolled into a blank tube using a PQF continuous rolling mill, and finally sized using a sizing mill to obtain... Hot-rolled seamless steel pipes.

[0118] S3. Under a protective atmosphere, the hot-rolled seamless steel pipe is heated to 680°C, held at that temperature for 90 minutes, and then cooled in the furnace. Afterwards, it is straightened according to the standard procedure, and then subjected to pickling, phosphating, and saponification treatments in pickling, phosphating, and saponification tanks respectively to prepare the surface for cold drawing.

[0119] S4 involves a single cold drawing process on a 600-ton hydraulic cold drawing machine, with the deformation controlled at 12% to 15%, to produce cold-drawn precision seamless steel pipes.

[0120] S5 involves straightening the cold-drawn precision seamless steel pipe. Afterwards, it is quenched at 890℃ for 45 minutes, followed by high-temperature tempering at 630℃ for 90 minutes. Finally, a large-scale high-precision straightening machine is used for fine straightening to ensure that the straightness of this large-diameter steel pipe meets high standards.

[0121] S6. Perform ultrasonic flaw detection, hydrostatic testing and finished product inspection according to standards, and package qualified products into warehouse.

[0122] Example 4

[0123] By manufacturing Specifications for oil and gas well casing. This application contains the specifications for oil and gas well casing.

[0124] The acid-environment-resistant and corrosion-resistant oil and gas well casing manufactured in this embodiment contains the following components by weight percentage:

[0125] C: 0.26%, Si: 0.30%, Mn: 0.55%, P: 0.010%, S: 0.001%, Cr: 0.55%, Mo: 0.85%, V: 0.065%, Ni: 0.03%, Cu: 0.02%, Nb: 0.025%, Al: 0.028%, B: 0.0016%, with the balance being Fe and unavoidable impurities. The sum of the mass percentages of the above components is 100%.

[0126] The above-mentioned oil and gas well casing shall be prepared according to the following method:

[0127] In S1, during the initial smelting in the electric arc furnace, 80% high-quality scrap steel and 20% direct reduced iron (DRI) are used as raw materials to control residual elements. The steel is melted by electric current, dephosphorized by oxygen blowing, and tapped when the temperature reaches 1580℃. Then, in the LF furnace, the molten steel is heated to 1575±5℃, followed by white slag formation and deep deoxidation with the addition of aluminum blocks. Microalloying elements are precisely added according to the formula. The temperature of the molten steel is precisely adjusted to the superheat range required for continuous casting through electric arc heating, completing the refining furnace refining. Vacuum degassing is then performed in the VD furnace, maintained at a high vacuum (≤67Pa) for at least 15 minutes. Finally, protective casting is used, with the superheat strictly controlled at 20~25℃, combined with electromagnetic stirring to obtain… 250mm continuous casting round billet.

[0128] S2: The billet is heated to 1230~1250℃ in a walking beam furnace, held for about 100 minutes, and then pierced at 11300~1150℃ to form a rough tube. The rough tube is then rolled into a blank tube using a PQF continuous rolling mill, and finally sized using a sizing mill to obtain... Hot-rolled seamless steel pipes.

[0129] S3. Under a protective atmosphere, the hot-rolled seamless steel pipe is heated to 680°C, held at that temperature for 90 minutes, and then cooled in the furnace. Afterwards, it is straightened according to the standard procedure, and then subjected to pickling, phosphating, and saponification treatments in pickling, phosphating, and saponification tanks respectively to prepare the surface for cold drawing.

[0130] S4 is cold-drawn in one pass on a 600-ton hydraulic cold drawing machine, with deformation controlled within 12%~15%. The dimensions of the steel pipe after cold drawing are precisely controlled within... .

[0131] S5 involves straightening the cold-drawn precision seamless steel pipe. Afterwards, it is quenched at 890℃ for 45 minutes, followed by high-temperature tempering at 630℃ for 90 minutes. Finally, a large-scale high-precision straightening machine is used for fine straightening to ensure that the straightness of this large-diameter steel pipe meets high standards.

[0132] S6. Perform ultrasonic flaw detection, hydrostatic testing and finished product inspection according to standards, and package qualified products into warehouse.

[0133] Product Inspection and Testing

[0134] The performance of the oil and gas well casings prepared in Examples 1–4 was tested using conventional methods in the art, and the results are as follows:

[0135] Table 1

[0136] ;

[0137] As can be seen from the data in Table 1:

[0138] The room temperature yield strength of the oil and gas well casings prepared in Examples 1 - 4 ranges from 815 to 830 MPa, far exceeding that of conventional high-strength steels (such as Q690D), reaching the level of ultra-high-strength steel; the tensile strength ranges from 905 to 914 MPa, with a very high strength level. The calculated values of the yield ratio are between 89.6% and 90.8% (for example: Example 1: 828 / 905 ≈ 91.5%). This value is relatively high, indicating that the reserve of the ability for strain hardening after the material yields is small. A higher allowable stress can be used in the design, and the structural efficiency is high.

[0139] The elongation after fracture of the oil and gas well casings prepared in Examples 1 - 4 are all ≥ 23%. At such a high strength level, maintaining an elongation of more than 23% indicates that the material combines high strength and good plasticity, can withstand a certain amount of plastic deformation without brittle fracture, and has good processing formability. The impact energy at -10°C ranges from 156 - 165 J, with a relatively high value, far higher than the requirements of most engineering standards for high-strength steels, indicating that the material has extremely excellent anti-brittle fracture ability at low temperatures, and the ductile-brittle transition temperature is extremely low, making it suitable for harsh environments such as polar regions and deep seas.

[0140] In addition, the grain sizes of the oil and gas well casings prepared in Examples 1 - 4 are all grade 10, which is a very fine grain size, such as Figure 2 the oil and gas well casing prepared in Example 1 as shown. Grade 10 grain size is the fundamental reason for the material to obtain high strength and high impact toughness. The hardness ranges from 25.8 to 27.1, and the hardness values of the four examples are highly consistent. This hardness value is matched with the provided tensile strength, further confirming the reliability of the strength test results. The uniform hardness also indicates that the heat treatment process is well controlled and the structure is uniform.

[0141] The finished product size accuracy of the oil and gas well casings prepared in Examples 1 - 4 was detected and the acid-resistant SSC experiment was carried out. Among them, the results of the acid-resistant SSC experiment are all qualified; the physical and chemical properties and size accuracy of the products fully meet the design requirements.

[0142] In summary, the oil and gas well casings prepared in Examples 1 - 4 all belong to ultra-high-strength steels with extremely excellent comprehensive properties. Such materials are very suitable for fields with extremely high requirements for weight, strength, and safety.

[0143] It should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit it. This application uses the above embodiments to illustrate the detailed process equipment and process flow of this application, but this application is not limited to the above detailed process equipment and process flow, that is, it does not mean that this application must rely on the above detailed process equipment and process flow to be implemented. Those skilled in the art should understand that any improvements to this application, equivalent substitutions of the raw materials of this application's products, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of this application.

Claims

1. A high-resistance to crushing and corrosion-resistant oil and gas well casing for acidic environments, characterized in that, Its chemical composition, by mass percentage, is as follows: C: 0.25%~0.30%, Si: 0.17%~0.35%, Mn: 0.40%~0.65%, P≤0.015%, S≤0.003%, Cr: 0.40%~0.60%, Mo: 0.75%~0.90%, V: 0.05%~0.08%, Ni≤0.20%, Cu≤0.10%, Nb: 0.015%~0.035%, Al: 0.010%~0.040%, B: 0.001%~0.002%, with the balance being Fe and unavoidable impurities. The sum of the mass percentages of the above components is 100%. The acidic environment-resistant, high-crush-resistance, and corrosion-resistant oil and gas well casing is obtained by the following preparation method: Includes the following steps: S1, Smelting and Continuous Casting: The steel billet is obtained by primary smelting in an electric arc furnace, followed by refining in a refining furnace and vacuum degassing in a VD furnace. S2, Hot rolling: The steel billet is hot rolled into a hot-rolled seamless steel pipe; S3, Softening and Pretreatment: The hot-rolled seamless steel pipe is subjected to softening annealing treatment, followed by straightening, pickling, phosphating and saponification treatments to obtain a pretreated pipe blank; S4, Cold drawing: The pretreated tube blank is cold drawn to obtain a cold-drawn precision seamless steel tube; S5, Quenching and finishing: The cold-drawn precision seamless steel pipe is straightened, then quenched and tempered, and then straightened again. S6, Inspection and Warehousing: Ultrasonic non-destructive testing, hydrostatic testing and finished product inspection are carried out on the steel pipes after quenching and finishing. Qualified products are packaged and put into warehousing. The high-strength, anti-crushing, and anti-corrosion oil and gas well casing for acidic environments has a room temperature yield strength of 758~965MPa, a tensile strength of ≥862MPa, an elongation after fracture of ≥18%, and a V-notch impact energy of ≥100J at -10℃.

2. A method for preparing a high-resistance to crushing and corrosion-resistant oil and gas well casing for acidic environments as described in claim 1, characterized in that, Includes the following steps: S1, Smelting and Continuous Casting: The steel billet is obtained by primary smelting in an electric arc furnace, followed by refining in a refining furnace and vacuum degassing in a VD furnace. S2, Hot rolling: The steel billet is hot rolled into a hot-rolled seamless steel pipe; S3, Softening and Pretreatment: The hot-rolled seamless steel pipe is subjected to softening annealing treatment, followed by straightening, pickling, phosphating and saponification treatments to obtain a pretreated pipe blank; S4, Cold drawing: The pretreated tube blank is cold drawn to obtain a cold-drawn precision seamless steel tube; S5, Quenching and finishing: The cold-drawn precision seamless steel pipe is straightened, then quenched and tempered, and then straightened again. S6, Inspection and Warehousing: Ultrasonic non-destructive testing, hydrostatic testing and finished product inspection are carried out on the steel pipes after quenching and finishing. Qualified products are packaged and put into warehousing. The high-strength, anti-crushing, and anti-corrosion oil and gas well casing for acidic environments has a room temperature yield strength of 758~965MPa, a tensile strength of ≥862MPa, an elongation after fracture of ≥18%, and a V-notch impact energy of ≥100J at -10℃.

3. The preparation method according to claim 2, characterized in that, In step S2, the specific process of hot rolling forming is as follows: after heating the steel billet, it is pierced to form a rough tube, and then the rough tube is rolled into a blank tube using a three-roll continuous rolling mill. Then, the blank tube is sized using a sizing mill to obtain the hot-rolled seamless steel pipe of the preset size.

4. The preparation method according to claim 3, characterized in that, The wall thickness accuracy of the hot-rolled seamless steel pipe after the hot rolling forming process is ≤ ±10% × wall thickness.

5. The preparation method according to claim 2, characterized in that, In step S3, the specific process of the softening annealing treatment is as follows: under a protective atmosphere, the hot-rolled seamless steel pipe is heated to 680~750℃, held for 1~3 hours, and then cooled in the furnace; after the softening annealing treatment, the Brinell hardness value of the hot-rolled seamless steel pipe is ≤190.

6. The preparation method according to claim 2, characterized in that, In step S3, the phosphating treatment forms a phosphating film on the surface of the steel pipe, and the saponification treatment adsorbs a layer of saponified lubricant onto the phosphating film to form a lubricating layer.

7. The preparation method according to claim 2, characterized in that, In step S4, the pre-treated tube blank is cold-drawn into the cold-drawn precision seamless steel tube using a 600-ton hydraulic cold drawing machine.

8. The preparation method according to claim 2, characterized in that, In step S5, the specific process of the quenching and tempering heat treatment is as follows: the quenching temperature is 890℃±10℃, the holding time is 45 minutes, and then rapid cooling is performed by water quenching or oil quenching; the tempering temperature is 630℃±10℃, the holding time is 90 minutes, and then air cooling or water cooling is performed.

9. The preparation method according to claim 2, characterized in that, The outer diameter tolerance of the high-resistance to crushing and corrosion of oil and gas well casing for acidic environments is ≤ ±0.5% × outer diameter, and the wall thickness tolerance is ≤ ±4% × wall thickness.

Images