Low-temperature-resistant heat-resistant high-toughness pipe and preparation method thereof

Abstract

The invention relates to the technical field of material metallurgy, and particularly discloses a low-temperature-resistant heat-resistant high-toughness pipe and a preparation method thereof, the low-temperature-resistant heat-resistant high-toughness pipe comprises the following components in percentage by weight: 0.08% < = C < = 0.12%, 0.15% < = Si < = 0.35%, 2.0% < = Mn < = 3.0%, 0.50% < = Cr < = 0.70%, 0.35% < = W < = 0.45%, 0.05% < = V < = 0.07%, 0.08% < = Ni < = 0.12%, 0.01% < = Al < = 0.04%, 0.006% < = N, 0.01% < = P < = 0.01%, 0.002% < = S, and the balance of Fe and impurities. The components are matched with one another according to a specific proportion, the strength, toughness, low temperature resistance and heat resistance of steel are remarkably improved, the technical problem that an existing metal pipe cannot meet the balance requirement of low-temperature toughness at the temperature of 60 DEG C below zero and heat resistance at the temperature of 350 DEG C at the same time is solved, and the metal pipe can be widely applied to thermal recovery of oil and gas reservoirs in high and cold zones.

Description

Technical Field

[0001] The present invention relates to the technical field of material metallurgy, and in particular to a low-temperature-resistant, heat-resistant, high-strength and tough pipe and a preparation method thereof. Background Art

[0002] As global economic consumption of oil and gas resources continues to grow, oil and gas exploration and production are gradually expanding into challenging regions such as high altitudes, deep earth, and the deep sea. The Arctic region holds 13% of the world's unproven oil and gas reserves (approximately 90 billion barrels of oil equivalent), and deep-sea and permafrost regions are becoming key areas for future oil and gas reserve growth. However, oil and gas production in extreme environments faces the daunting challenge of extremely low temperatures. Oil well pipes operating in these environments must not only withstand high loads of hundreds or even thousands of atmospheres of pressure, but also avoid brittle fracture at low temperatures. Furthermore, heavy oil thermal recovery requires pipes with excellent heat resistance, resulting in extremely demanding service conditions.

[0003] Currently, common metal pipes and polymer pipes on the market all have certain defects in low-temperature environments. Traditional oil well pipes are prone to brittle fracture below -40°C, leading to wellbore failure and making it difficult to meet the needs of polar operations. Ordinary carbon steel is prone to brittle transition at low temperatures, with a sharp drop in toughness and extremely easy to crack under pressure. Although some polymer pipes have a certain degree of low-temperature resistance, they lack strength and rigidity and cannot withstand high pressure. In recent years, researchers have modified metal pipes through alloying, heat treatment, and other methods, but it is still difficult to simultaneously meet the requirements of balancing low-temperature toughness at -60°C and heat resistance at 350°C. In addition, low-temperature pipes produced by existing technologies also have problems such as high production costs, complex processes, and low production efficiency, which limit their large-scale promotion and application. Therefore, developing a pipe that can maintain excellent strength and toughness in extreme low-temperature environments while also having good heat resistance, simple preparation processes, and controllable costs has important practical significance and broad market prospects. Summary of the Invention

[0004] In view of the fact that existing metal pipes are difficult to simultaneously meet the balancing requirements of -60°C low-temperature toughness and 350°C heat resistance, as well as the problems of high production cost and low production efficiency, the present invention provides a low-temperature and heat-resistant high-strength and toughness pipe and its preparation method.

[0005] To solve the above technical problems, the technical solutions provided by the embodiments of the present invention are:

[0006] A low-temperature and heat-resistant high-strength and tough pipe, whose components in weight percentage are: 0.08%≤C≤0.12%, 0.15%≤Si≤0.35%, 2.0%≤Mn≤3.0%, 0.50%≤Cr≤0.70%, 0.35%≤W≤0.45%, 0.05%≤V≤0.07%, 0.08%≤Ni≤0.12%, 0.01%≤Al≤0.04%, N≤0.006%, P≤0.01%, S≤0.002%, and the balance is Fe and unavoidable impurities.

[0007] Compared with the prior art, the design ideas of the chemical composition of the low-temperature-resistant, heat-resistant and high-strength and tough pipe provided by the present invention are as follows:

[0008] (1) C easily forms a large amount of carbides with alloying elements such as Cr, W, and V, which reduces impact toughness. In order to reduce the precipitation of large-particle carbides and avoid reducing the hardenability of steel, the present invention controls the C content to 0.08% to 0.12%. Mn is a weak carbide-forming element and plays a strengthening role mainly by solid solution in ferrite. However, if the Mn content is too high, segregation will be serious, which will reduce impact toughness. Therefore, the present invention controls the Mn content to 2.0% to 3.0%.

[0009] (2) Ni is an austenite-forming element, which can expand the austenite phase area and increase the proportion of retained austenite after quenching, thereby improving the low-temperature impact toughness of steel; Al can refine the grains and form dispersed AlN, further improving the low-temperature toughness; Ni and Al can synergistically significantly improve the low-temperature impact toughness of the material;

[0010] (3) Cr and W can improve the heat resistance of the material. However, Cr and W are strong carbide-forming elements, which increase the brittleness of the material and deteriorate the machinability. Therefore, the present invention controls the Cr content to 0.5% to 0.7% and the W content to 0.35% to 0.45%. Si can further enhance the oxidation resistance of Cr and improve the high-temperature performance of the pipe.

[0011] (4) Adding a small amount of V element is conducive to the dispersion and precipitation of carbides, hindering dislocation movement and improving strength and hardness; at the same time, these carbonitrides can also refine the grains and improve low-temperature impact toughness.

[0012] The aforementioned components, combined in specific proportions, significantly improve the steel's strength, toughness, low-temperature resistance, and heat resistance, resolving the technical challenge of existing metal pipes in simultaneously meeting the required balance between -60°C low-temperature toughness and 350°C heat resistance. The pipes of this invention boast a grain size of 10-12, room-temperature yield strength >1062 MPa, room-temperature tensile strength >1138 MPa, elongation >20%, -60°C impact toughness >100 J, 350°C yield strength >965 MPa, and 350°C tensile strength >1035 MPa. They are widely used in thermal recovery of oil and gas reservoirs in high-altitude cold regions and hold promising market prospects.

[0013] Furthermore, the metallographic structure of the low-temperature-resistant, heat-resistant and high-strength and tough pipe is tempered bainite, and the grain size is 10 to 12 levels.

[0014] The present invention also provides a method for preparing the above-mentioned low-temperature resistant, heat-resistant, high-strength and tough pipe, comprising the following steps:

[0015] A continuous casting round billet having the same chemical composition as the low-temperature-resistant and heat-resistant high-strength and toughness pipe is heated in an annular furnace, punched to form a rough pipe, the rough pipe is rolled to obtain a rough pipe, the rough pipe is subjected to slight tension reduction and air cooling to obtain a seamless steel pipe;

[0016] The seamless steel pipe is subjected to heat treatment to obtain a low-temperature resistant, heat-resistant and high-strength and tough pipe.

[0017] The preparation method of the low-temperature and heat-resistant high-strength and toughness pipe provided by the present invention has a simple preparation process and is easy to implement in production.

[0018] Furthermore, the continuous casting round billet is made by subjecting steelmaking raw materials to electric arc furnace melting, ladle refining, VD vacuum refining and continuous casting processes.

[0019] Furthermore, in the continuous casting process, the weight percentage of the components of the mold powder is:

[0020] CaO 35%~45%, SiO2 30%~40%, Al2O3 5%~10%, MnO 10%~15%, F - <

[0021] 5%, Li2O+Na2O 3%~5%, MgO≤2%, Fe2O3≤1%, and the balance are inevitable impurities; wherein, 1≤(CaO / SiO2)≤1.2; the viscosity of the crystallizer protection slag is 0.1Pa·s~0.3Pa·s, and the basicity is 1.0~1.2.

[0022] The preferred protective slag can quickly form a uniform liquid slag layer during the continuous casting process, tightly covering the surface of the molten steel, isolating the air, and preventing the molten steel from being oxidized at high temperatures, thereby improving the high-temperature oxidation resistance of the pipe; at the same time, the protective slag has low surface tension and can form a uniform slag film between the ingot and the crystallizer wall, effectively improving the lubrication conditions between the ingot and the crystallizer, reducing friction, and reducing defects such as cracks and depressions on the surface of the ingot, thereby improving the surface quality of the pipe and the uniformity of the internal structure.

[0023] Furthermore, in the continuous casting process, the water content of the crystallizer is 0.8L / kg to 1.2L / kg, and the water content of the secondary cooling zone is 0.3L / kg to 0.5L / kg.

[0024] Controlling the mold water content within a range of 0.8L / kg to 1.2L / kg ensures sufficient cooling intensity, allowing the molten steel to quickly form a shell of sufficient thickness and strength within the mold, preventing dangerous situations such as breakout during subsequent traction. It also prevents excessive thermal stress in the shell caused by excessive cooling, which could lead to surface cracking. Controlling the secondary cooling zone water content within a range of 0.3L / kg to 0.5L / kg refines the grain size, reduces internal defects such as shrinkage cavities and porosity, and improves the internal structure of the ingot. The coordination of the secondary cooling zone water content with the mold water content precisely regulates the solidification process of the ingot, ensuring a uniform drop in surface temperature, reducing surface temperature gradients, and effectively avoiding defects such as surface depressions and transverse cracks. This provides high-quality ingot for subsequent processing into high-performance pipes, ensuring the pipes' low-temperature resistance, heat resistance, and mechanical properties.

[0025] Furthermore, in the continuous casting process, electromagnetic stirring is adopted at the end of solidification of the continuous casting round billet, the frequency of the electromagnetic stirring is 3Hz to 8Hz, and the current is 200A to 400A.

[0026] The electromagnetic force generated by this frequency and current range effectively stirs the molten steel at the end of solidification, breaking up growing dendrites and transforming them into fine equiaxed nuclei. This refines the grain structure of the ingot, laying the foundation for achieving excellent mechanical properties in the pipe. It also significantly reduces component segregation within the ingot, improves central porosity and shrinkage defects, and enhances the strength and toughness of the pipe.

[0027] Furthermore, after the continuous casting process is completed, the continuously cast round billet is placed in a slow cooling pit for slow cooling, with a cooling rate of ≤10°C / h.

[0028] The optimal cooling rate can reduce the internal stress of the casting and avoid the generation of cracks.

[0029] Furthermore, the heating temperature of the annular furnace is 1150°C to 1200°C, the perforation temperature is 1100°C to 1150°C, the rolling temperature is 950°C to 1050°C, and the micro-tension reducing temperature is 750°C to 850°C.

[0030] Controlling the temperature of the annular heating furnace to 1150℃~1200℃ can ensure that the carbides are fully dissolved and evenly distributed in the matrix, avoiding Mn segregation; during the perforation process, the temperature is maintained at 1100℃~1150℃, which can not only ensure that the material has good plasticity for easy forming, but also prevent excessive temperature from causing overoxidation on the pipe surface and affecting the surface quality; entering the continuous rolling process, the temperature is controlled at 950℃~1050℃. Within this temperature range, the original austenite grains can be refined and the comprehensive mechanical properties of the pipe can be improved; controlling the micro-tension reducing temperature at 750℃~850℃ and maintaining the final rolling temperature below the recrystallization temperature can promote strain accumulation, further refine the grains, and ultimately significantly improve the strength and toughness of the pipe.

[0031] Furthermore, the heat treatment process includes the following steps: heating the seamless steel pipe to 820℃~860℃ and keeping it warm, and then quenching it with water; then heating the seamless steel pipe to 520℃~580℃ and keeping it warm, and then air cooling it; then heating the seamless steel pipe to 520℃~580℃ again and keeping it warm, and then air cooling it.

[0032] Furthermore, in the heat treatment process, the holding time of the seamless steel pipe at 820°C to 860°C is 3min to 5min; the cooling rate of quenching is 140°C / s to 160°C / s; and the holding time at 520°C to 580°C is 10min to 15min.

[0033] After being kept at 820℃~860℃, the austenite inside the steel pipe is fully homogenized, and then quickly water quenched to quickly transform the austenite into martensite structure, effectively refine the grains, increase the grain boundary area, effectively hinder the diffusion of atoms at high temperature, and improve heat resistance, strength and toughness; then tempered twice at 520℃~580℃, on the one hand, it can ensure the full decomposition of martensite and the full transformation of retained austenite, and completely eliminate the quenching stress; on the other hand, it can also ensure that the tempered carbides are fully globalized and finely dispersed, without aggregation and coarsening.

[0034] Through the synergistic effect of quenching and tempering, the pipe not only has high strength to withstand the pressure under complex working conditions of oil wells, but also has good toughness and heat resistance, and can resist brittle fracture in low-temperature environments, thereby meeting the stringent requirements of pipes in mining operations for low-temperature resistance, heat resistance and high strength and toughness, and effectively ensuring the safety and efficiency of oil well mining operations.

[0035] The beneficial effects of adopting the above technical solution are:

[0036] The pipe prepared by the present invention can serve stably in complex underground environments such as high temperature and high pressure, and has low-temperature resistance, high strength and toughness, and good heat resistance. The room temperature yield strength is >1062MPa, the tensile strength is >1138MPa, the elongation is >20%, the -60℃ impact toughness is >100J, the 350℃ yield strength is >965MPa, and the tensile strength is >1035MPa. It can be widely used in thermal recovery of oil and gas reservoirs in high-altitude and cold areas, and has broad market prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is the metallographic structure diagram of the low-temperature-resistant, heat-resistant, high-strength and tough pipe prepared in Example 1 of the present invention;

[0038] Figure 2 This is the metallographic structure diagram of the low-temperature-resistant, heat-resistant, high-strength and tough pipe prepared in Example 2 of the present invention;

[0039] Figure 3 This is the metallographic structure diagram of the low-temperature, heat-resistant, high-strength and tough pipe prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0041] In order to better illustrate the present invention, further examples are given below.

[0042] The components of the mold powder used in the following examples are as follows: CaO 35% to 45%, SiO2 30% to 40%, Al2O3 5% to 10%, MnO 10% to 15%, F - <5%, Li2O+Na2O3%~5%, MgO≤2%, Fe2O3≤1%, and the remainder are inevitable impurities; among which, 1≤(CaO / SiO2)≤1.2; the viscosity of the crystallizer protective slag is 0.1Pa·s~0.3Pa·s, and the basicity is 1.0~1.2.

[0043] Example 1

[0044] An embodiment of the present invention provides a low-temperature and heat-resistant high-strength and tough oil well pipe, the weight percentage of which is as follows:

[0045] C 0.08%, Si 0.15%, Mn 2.0%, Cr 0.5%, W 0.35%, V 0.05%, Ni 0.08%, Al 0.01%, N 0.004%, S 0.001%, P 0.008%, and the balance is Fe and inevitable impurities.

[0046] The preparation steps of the above-mentioned low-temperature-resistant, heat-resistant, high-strength and tough oil well pipe are as follows:

[0047] S1, the steelmaking raw materials are subjected to 100t electric arc furnace melting, ladle refining, VD vacuum refining, and continuous casting processes to produce a continuously cast round billet with a diameter of 200mm having the same chemical composition as the above-mentioned pipe;

[0048] S2, the continuously cast round billet is heated in an annular furnace, punched to form a rough tube, the rough tube is rolled by a three-roller continuous rolling mill to obtain a rough tube, the rough tube is removed by a three-stand tube-removing machine, slightly tension-reduced, and air-cooled to produce a seamless steel pipe;

[0049] S3, heating the seamless steel pipe to 840°C and keeping it warm for 4 minutes, and then quenching it with water at a cooling rate of 150°C / s; then heating the seamless steel pipe to 550°C and keeping it warm for 12 minutes, and then air-cooling it to room temperature; finally, heating the seamless steel pipe to 550°C again and keeping it warm for 12 minutes, and then air-cooling it to room temperature to obtain a 140KSI steel grade low-temperature and heat-resistant high-strength and tough oil well pipe with an outer diameter of 139.7 mm and a wall thickness of 12.7 mm.

[0050] Among them, in the continuous casting process, the water content of the crystallizer is 1.0L / kg, and the water content of the secondary cooling zone is 0.4L / kg; electromagnetic stirring is used at the solidification end of the continuous casting round billet, the frequency of the electromagnetic stirring is 6Hz, and the current is 320A; after the continuous casting process is completed, the continuous casting round billet is placed in a slow cooling pit for slow cooling, and the cooling rate is ≤10℃ / h.

[0051] The temperature of the ring furnace heating is 1180℃, the temperature of the piercing is 1130℃, the temperature of the rolling is 1000℃, and the temperature of the micro-tension reducing is 800℃.

[0052] The low temperature and heat resistant high strength and toughness oil well pipe prepared by this embodiment is mainly composed of tempered troostite, with fine grains and a grain size of 10 to 12. Figure 1 shown.

[0053] Example 2

[0054] An embodiment of the present invention provides a low-temperature and heat-resistant high-strength and tough oil well pipe, the weight percentage of which is as follows:

[0055] C 0.1%, Si 0.25%, Mn 2.6%, Cr 0.65%, W 0.41%, V 0.06%, Ni 0.1%, Al 0.03%, N 0.003%, S 0.0013%, P 0.0085%, and the balance is Fe and inevitable impurities.

[0056] The preparation steps of the above-mentioned low-temperature-resistant, heat-resistant, high-strength and tough oil well pipe are as follows:

[0057] S1, the steelmaking raw materials are subjected to 100t electric arc furnace melting, ladle refining, VD vacuum refining, and continuous casting processes to produce a continuously cast round billet with a diameter of 200mm having the same chemical composition as the above-mentioned pipe;

[0058] S2, the continuous casting round billet is heated in an annular furnace, punched to form a rough tube, the rough tube is rolled by a three-roller continuous rolling mill to obtain a rough tube, the rough tube is removed by a three-stand tube-removing machine, slightly tension-reduced, and air-cooled to produce a seamless steel pipe;

[0059] S3, heating the seamless steel pipe to 820°C and keeping it warm for 5 minutes, and then quenching it with water at a cooling rate of 140°C / s; then heating the seamless steel pipe to 580°C and keeping it warm for 10 minutes, and then air-cooling it to room temperature; finally, heating the seamless steel pipe to 580°C again and keeping it warm for 10 minutes, and then air-cooling it to room temperature to obtain a 140KSI steel grade low-temperature and heat-resistant high-strength and tough oil well pipe with an outer diameter of 139.7 mm and a wall thickness of 12.7 mm.

[0060] Among them, in the continuous casting process, the water content of the crystallizer is 1.2L / kg, and the water content of the secondary cooling zone is 0.3L / kg; electromagnetic stirring is used at the solidification end of the continuous casting round billet, the frequency of the electromagnetic stirring is 3Hz, and the current is 400A; after the continuous casting process is completed, the continuous casting round billet is placed in a slow cooling pit for slow cooling, and the cooling rate is ≤10℃ / h.

[0061] The temperature of the ring furnace heating is 1150℃, the temperature of the piercing is 1100℃, the temperature of the rolling is 950℃, and the temperature of the micro-tension reducing is 750℃.

[0062] The low temperature and heat resistant high strength and toughness oil well pipe prepared by this embodiment is mainly composed of tempered troostite, with fine grains and a grain size of 10 to 12. Figure 2 shown.

[0063] Example 3

[0064] An embodiment of the present invention provides a low-temperature and heat-resistant high-strength and tough oil well pipe, the weight percentage of which is as follows:

[0065] C 0.12%, Si 0.35%, Mn 3.0%, Cr 0.7%, W 0.45%, V 0.07%, Ni 0.12%, Al 0.04%, N 0.005%, S 0.0015%, P 0.009%, and the balance is Fe and inevitable impurities.

[0066] The steps for preparing the above-mentioned low-temperature-resistant, heat-resistant, high-strength and tough oil well pipe are as follows:

[0067] S1, the steelmaking raw materials are subjected to 100t electric arc furnace melting, ladle refining, VD vacuum refining, and continuous casting processes to produce a continuously cast round billet with a diameter of 200mm having the same chemical composition as the above-mentioned pipe;

[0068] S2, the continuously cast round billet is heated in an annular furnace, punched to form a rough tube, the rough tube is rolled by a three-roller continuous rolling mill to obtain a rough tube, the rough tube is removed by a three-stand tube-removing machine, slightly tension-reduced, and air-cooled to produce a seamless steel pipe;

[0069] S3, heating the seamless steel pipe to 860°C and keeping it warm for 3 minutes, and then quenching it with water at a cooling rate of 160°C / s; then heating the seamless steel pipe to 520°C and keeping it warm for 15 minutes, and then air-cooling it to room temperature; finally, heating the seamless steel pipe to 520°C again and keeping it warm for 15 minutes, and then air-cooling it to room temperature to obtain a 140KSI steel grade low-temperature and heat-resistant high-strength and tough oil well pipe with an outer diameter of 139.7 mm and a wall thickness of 12.7 mm.

[0070] Among them, in the continuous casting process, the water content of the crystallizer is 0.8L / kg, and the water content of the secondary cooling zone is 0.5L / kg; electromagnetic stirring is used at the solidification end of the continuous casting round billet, the frequency of the electromagnetic stirring is 8Hz, and the current is 200A; after the continuous casting process is completed, the continuous casting round billet is placed in a slow cooling pit for slow cooling, and the cooling rate is ≤10℃ / h.

[0071] The temperature of the ring furnace heating is 1200℃, the temperature of the piercing is 1150℃, the temperature of the rolling is 1050℃, and the temperature of the micro-tension reducing is 850℃.

[0072] The low temperature and heat resistant high strength and toughness oil well pipe prepared by this embodiment is mainly composed of tempered troostite, with fine grains and a grain size of 10 to 12. Figure 3 shown.

[0073] Performance Testing

[0074] According to the requirements of API Specification 5CT 11th Edition, samples of the low-temperature and heat-resistant, high-strength and tough oil well pipes prepared in Examples 1 to 3 were collected and analyzed for yield strength and tensile strength at room temperature, yield strength and tensile strength at 350°C, and transverse full-scale impact energy at -60°C. The results are shown in Table 1.

[0075] Table 1

[0076] Inspection items Number of samples Minimum Maximum average value Standard deviation Room temperature yield strength / MPa 38 1062 1118 1082.4 13.8 Room temperature tensile strength / MPa 38 1138 1193 1157.4 12.4 -60℃ Charpy impact energy / J 38 112 155 128.7 13.1 350℃ yield strength / MPa 38 965 1015 985.2 13.2 350℃ tensile strength / MPa 38 1035 1083 1050.1 12.8

[0077] The oil well pipes produced by the above method have a yield strength of 1062-1118 MPa, a tensile strength of 1138-1193 MPa, and a transverse full-scale Charpy impact energy of ≥100 J at -60°C. The average room temperature yield strength is 1082.4 MPa with a standard deviation of 13.8 MPa, and the average tensile strength is 1157.4 MPa with a standard deviation of 12.4 MPa. The average transverse full-scale Charpy impact energy at -60°C is 128.7 J with a standard deviation of 13.1 J. The yield strength at 350°C is 965-1015 MPa, and the tensile strength is 1035-1083 MPa. The average yield strength at 350°C is 985.2 MPa with a standard deviation of 13.2 MPa, and the average tensile strength at 350°C is 1050.1 MPa with a standard deviation of 12.8 MPa.

[0078] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A low-temperature and heat-resistant high-strength and tough pipe, characterized in that: The weight percentage of its components is: 0.08%≤C≤0.12%, 0.15%≤Si≤0.35%, 2.0%≤Mn≤3.0%, 0.50%≤Cr≤0.70%, 0.35%≤W≤0.45%, 0.05%≤V≤0.07%, 0.08%≤Ni≤0.12%, 0.01%≤Al≤0.04%, N≤0.006%, P≤0.01%, S≤0.002%, and the balance is Fe and unavoidable impurities.

2. The low-temperature and heat-resistant high-strength and tough pipe according to claim 1, characterized in that: Its metallographic structure is tempered troostite and the grain size is 10 to 12 levels.

3. A method for preparing a low-temperature-resistant, heat-resistant, high-strength and tough pipe according to claim 1 or 2, characterized in that: The steps include: A continuous casting round billet having the same chemical composition as the low-temperature-resistant and heat-resistant high-strength and toughness pipe is heated in an annular furnace, punched to form a rough pipe, the rough pipe is rolled to obtain a rough pipe, the rough pipe is subjected to slight tension reduction and air cooling to obtain a seamless steel pipe; The seamless steel pipe is subjected to heat treatment to obtain a low-temperature resistant, heat-resistant and high-strength and tough pipe.

4. The method for preparing a low-temperature-resistant, heat-resistant, high-strength and tough pipe according to claim 3, characterized in that: The continuous casting round billet is made by subjecting steelmaking raw materials to electric arc furnace melting, ladle refining, VD vacuum refining and continuous casting processes.

5. The method for preparing a low-temperature-resistant, heat-resistant, high-strength and tough pipe according to claim 4, characterized in that: In the continuous casting process, the weight percentage of the components of the mold powder is: CaO 35%~45%,SiO2 30%~40%,Al2O3 5%~10%,MnO 10%~15%,F - < 5%, Li2O+Na2O 3%~5%, MgO≤2%, Fe2O3≤1%, and the balance are inevitable impurities; wherein, 1≤(CaO / SiO2)≤1.2; the viscosity of the crystallizer protection slag is 0.1Pa·s~0.3Pa·s, and the basicity is 1.0~1.

2.

6. The method for preparing a low-temperature-resistant, heat-resistant, high-strength and tough pipe according to claim 5, characterized in that: During the continuous casting process, the water content of the crystallizer is 0.8L / kg to 1.2L / kg, and the water content of the secondary cooling zone is 0.3L / kg to 0.5L / kg.

7. The method for preparing a low-temperature-resistant, heat-resistant, high-strength and tough pipe according to claim 3, characterized in that: During the continuous casting process, electromagnetic stirring is used at the end of solidification of the continuous casting round billet, with a frequency of 3Hz to 8Hz and a current of 200A to 400A; and / or After the continuous casting process is completed, the continuously cast round billet is placed in a slow cooling pit for slow cooling, with a cooling rate of ≤10℃ / h.

8. The method for preparing a low-temperature-resistant, heat-resistant, high-strength and tough pipe according to claim 3, characterized in that: The heating temperature of the annular furnace is 1150° C. to 1200° C., the perforation temperature is 1100° C. to 1150° C., the rolling temperature is 950° C. to 1050° C., and the micro-tension reducing temperature is 750° C. to 850° C.

9. The method for preparing a low-temperature-resistant, heat-resistant, high-strength and tough pipe according to claim 3, characterized in that: The heat treatment process includes the following steps: heating the seamless steel pipe to 820℃~860℃ and keeping it warm, then quenching it with water; then heating the seamless steel pipe to 520℃~580℃ and keeping it warm, then air cooling it; Then heat the seamless steel pipe again to 520℃~580℃ and keep it warm before air cooling.

10. The method for preparing a low-temperature-resistant, heat-resistant, high-strength and tough pipe according to claim 9, characterized in that: In the heat treatment process, the holding time of the seamless steel pipe at 820℃~860℃ is 3min~5min; the cooling rate of quenching is 140℃ / s~160℃ / s; the holding time at 520℃~580℃ is 10min~15min.

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