High-strength tubing and casing resistant to hydrogen sulfide corrosion, and manufacturing method therefor

Abstract

A tubing and casing resistant to H2S corrosion, and a manufacturing method therefor. In addition to Fe and inevitable impurities, the tubing and casing comprises the following chemical elements in percentage by mass: C: 0.12-0.2%, Si: 0.1-0.5%, Mn: 0.6-0.9%, Cr: 0.3-0.5%, Mo: 1.1-1.5%, V: 0.05-0.1%, Nb: 0.05-0.1%, W: 0.05-0.18%, Al: 0.01-0.05%, Ce: 0.0005-0.0018%, and B: 0.0015-0.005%.

Description

A high-strength oil casing resistant to hydrogen sulfide corrosion and a manufacturing method thereof Technical Field

[0001] The present invention relates to a steel material and a manufacturing method thereof, in particular to an oil casing and a manufacturing method thereof. Background Art

[0002] In practical applications, oil casing is a type of steel pipe widely used in oil and gas development. Since oil and gas reservoirs often contain H2S, and H2S-containing oil and gas are buried deep, typically between 5,000 and 9,000 meters, with the increasing development of sulfur-containing oil and gas wells and the continuous increase in oil and gas drilling depths, it is expected that oil casing will not only resist hydrogen sulfide corrosion but also possess higher strength.

[0003] Several seamless pipe developments have been made in the prior art:

[0004] For example, Japanese patent document No. JP2004332059A, published on November 25, 2004, and entitled “Low Alloy Steel”, proposes improving hydrogen sulfide stress corrosion resistance by reducing amorphous inclusions.

[0005] For example, Japanese patent document JP2005350754A, published on December 22, 2005, and entitled "LOW ALLOY STEEL FOR OIL WELL TUBE HAVING EXCELLENT SULFIDE STRESS CRACKING RESISTANCE," proposes a technology for controlling dislocation density and hydrogen diffusion coefficient to improve the hydrogen sulfide stress corrosion resistance of 125ksi steel-grade sulfur-resistant pipes.

[0006] However, as the depth of oil and gas drilling continues to increase, in order to meet the requirements of casing tensile strength and internal pressure resistance in the development of deep highly acidic oil and gas fields, it is expected to further improve the strength and sulfur resistance of oil casing. Summary of the Invention

[0007] One of the purposes of the present invention is to provide a high-strength oil casing and tubing resistant to H2S corrosion, which can obtain an oil casing and tubing having both ultra-high strength and excellent H2S stress corrosion resistance through reasonable chemical element composition design.

[0008] To achieve the above object, the present invention provides a high-strength oil casing resistant to H2S corrosion, which, in addition to Fe and inevitable impurities, also contains the following chemical elements in percentage by mass:

[0009] C: 0.12~0.2%, Si: 0.1~0.5%, Mn: 0.6%~0.9%, Cr: 0.30~0.50%, Mo: 1.1~1.5%, V: 0.05~0.1% , Nb: 0.05~0.1%, W: 0.05~0.18%, Al: 0.01~0.05%, Ce: 0.0005~0.0018%; B: 0.0015~0.005%.

[0010] The present invention also provides a high-strength oil casing and tubing resistant to H2S corrosion, which comprises the following chemical elements in percentage by mass:

[0011] C: 0.12~0.2%, Si: 0.1~0.5%, Mn: 0.6%~0.9%, Cr: 0.30~0.50%, Mo: 1.1~1.5%, V: 0.05~0.1%, Nb: 0.05~0.1%, W: 0.05~0.18%, Al: 0.01~0.05%, Ce: 0.0005~0.0018%; B: 0.0015~0.005%; the balance is Fe and unavoidable impurities.

[0012] There are many factors that affect the material's resistance to hydrogen sulfide stress corrosion. After quenching and tempering heat treatment, substructures of martensite laths, martensite lath bundles, and martensite lath blocks will form in the steel. Among them, a primary austenite grain is divided into multiple lath bundles, each lath bundle is composed of several lath blocks, and each lath block is composed of several laths. The grain boundary orientation differences between these organizations are significantly different. The interface with an orientation difference of ≥15° between the lath-block boundary is called a high-angle interface, while the interface with an orientation difference of <15° between the lath-block boundary and the lath boundary is called a low-angle interface.

[0013] Through research, the inventors discovered that crack propagation in sulfur-resistant steel pipes in hydrogen sulfide environments is also affected by grain boundaries. Cracks deflect when passing through martensite lath interfaces with an orientation difference of 15° or greater, consuming a certain amount of energy and hindering crack propagation. Furthermore, high-angle grain boundaries increase the resistance to crack propagation and consume more energy, thus hindering crack expansion. Therefore, the inventors believe that smaller the effective grain size of the steel pipe and larger the grain boundary area, greater the energy consumed by deformation and unstable crack propagation within a given area, thereby improving sulfur resistance.

[0014] Based on this, the present invention combines composition design, uses alloy elements to refine the grains in the recrystallization zone, and optimizes manufacturing process conditions (for example, controlled cooling of hot-rolled tubes after rolling to refine the grains, and a low-temperature austenitization process to suppress grain coarsening, etc.), to ensure that the obtained oil casing has a smaller effective grain size.

[0015] Specifically, the design principles of the chemical elements in the H2S corrosion resistant high-strength oil casing of the present invention are as follows:

[0016] C: In the H2S corrosion resistant high-strength oil casing of the present invention, C is an important element to ensure strength and hardenability. When the C content in the steel is less than 0.12%, it is difficult to achieve the strength of 120ksi steel grade. When the C content in the steel is too high, quenching cracks are likely to occur, and the coarse carbides M at the grain boundaries will increase. 23 Therefore, in the high-strength oil casing resistant to H2S corrosion of the present invention, the mass percentage of the C element is controlled between 0.12% and 0.2%.

[0017] Si: In the high-strength, H2S-resistant oil casing and tubing described herein, Si is introduced into the steel by the addition of a deoxidizer. A Si content exceeding 0.5% significantly increases the steel's tendency to become cold brittle; a content below 0.1% reduces the deoxidizing effect. Therefore, in the high-strength, H2S-resistant oil casing and tubing described herein, the mass percentage of Si is controlled between 0.1% and 0.5%.

[0018] Mn: In the high-strength, H2S-resistant oil casing and tubing described herein, Mn has the beneficial effect of expanding the austenite phase and increasing hardenability. However, excessive Mn content can easily segregate during solidification, leading to component segregation in the steel and affecting its sulfur resistance. Furthermore, to ensure deoxidation and increase hardenability, the steel pipe requires a certain Mn content. Therefore, in the high-strength, H2S-resistant oil casing and tubing described herein, the mass percentage of Mn is controlled between 0.6% and 0.9%.

[0019] Cr: In the H2S corrosion resistant high strength oil casing of the present invention, Cr is an element that improves strength and hardenability, which can effectively improve the corrosion resistance of steel. However, it should be noted that the Cr content in the steel should not be too high, as too high a Cr content will cause coarse Cr to precipitate at the grain boundaries during tempering. 23 C6 carbides are detrimental to hydrogen sulfide stress corrosion resistance. Furthermore, the use of online controlled cooling processes can easily cause cracking in the inner wall of the steel pipe, leading to pipe defects. Therefore, in the high-strength H2S corrosion-resistant oil casing described in the present invention, the mass percentage of Cr is controlled between 0.30 and 0.50%.

[0020] Mo: In the high-strength, H2S-resistant oil casing and tubing described herein, Mo improves strength, tempering stability, and hardenability, while also enhancing the material's corrosion resistance. High Mo content leads to the precipitation of coarse carbides, which is detrimental to hydrogen sulfide stress corrosion resistance. Low Mo content makes it difficult to achieve a 120 ksi steel strength grade during high-temperature tempering. Therefore, in the high-strength, H2S-resistant oil casing and tubing described herein, the mass percentage of Mo is controlled between 1.1% and 1.5%.

[0021] V: In the high-strength, H2S-resistant oil casing and tubing described herein, V is an effective grain refiner and precipitation-strengthening element. It improves resistance to high-temperature tempering, reduces dislocation density during high-temperature tempering, and enhances resistance to hydrogen sulfide stress corrosion. However, it's important to note that the V content in the steel should not be too high. Excessive V content can lead to poor strength uniformity and reduced stress corrosion resistance due to the varying precipitation strengthening effects of various V compounds during the precipitation process. Therefore, in the H2S-resistant oil casing and tubing described herein, the mass percentage of V is controlled between 0.05% and 0.1%.

[0022] Nb: In the high-strength, H2S-resistant oil casing and tubing described herein, Nb is an effective grain-refining element. The Nb precipitates formed in the austenite region refine the grains, positively impacting both the steel's strength, toughness, and sulfur resistance. Therefore, the mass percentage of Nb in the H2S-resistant oil casing and tubing described herein is controlled between 0.05% and 0.1%.

[0023] W: In the high-strength, H2S-resistant oil casing and tubing described herein, W exists in the steel as a solid solution and as precipitation. The precipitated phase is evenly dispersed throughout the steel, exhibiting excellent precipitation strengthening effects, improving resistance to high-temperature tempering and enhancing the material's strength. However, excessively high W content can lead to coarsening of the precipitated phase, forming hydrogen-induced cracking sensitive sites. Excessively low W content can lead to insufficient strengthening, making it difficult to achieve a strength level of 125 ksi. Therefore, in the H2S-resistant oil casing and tubing described herein, the mass percentage of W is controlled between 0.05% and 0.18%.

[0024] Al: In the high-strength, H2S-resistant oil casing and tubing described herein, Al is an essential element for deoxidizing the steel. However, the Al content in the steel should not be too high. Exceeding 0.05% Al can negatively impact the casting process. Therefore, in the H2S-resistant oil casing and tubing described herein, the mass percentage of Al is controlled between 0.01% and 0.05%.

[0025] Ce: In the high-strength, H2S-resistant oil casing and tubing described herein, Ce contributes to purifying molten steel, modifying inclusions, and precipitation strengthening. In this invention, Ce is added via the crystallizer, eliminating rare earth burnout. Therefore, the mass percentage of Ce in the H2S-resistant oil casing and tubing is controlled between 0.0005% and 0.0018%.

[0026] B: In the high-strength H2S corrosion-resistant oil casing described in the present invention, element B can significantly improve the hardenability of the steel. At the same time, element B can aggregate at grain boundaries and inhibit hydrogen penetration. In steels with low C content, element B can solve the problem of poor hardenability caused by the reduced C content. However, when the B content is less than 0.0015%, the effect of improving the hardenability of the steel and inhibiting hydrogen penetration is not significant; when the B content is higher than 0.005%, BN brittle phases are easily formed, thereby reducing the toughness of the steel. Therefore, in the H2S corrosion-resistant oil casing described in the present invention, the mass percentage of the B content control element is controlled between 0.0015-0.005%.

[0027] Preferably, among the inevitable impurities in the H2S corrosion resistant high-strength oil casing of the present invention: S≤0.002%, P≤0.01%, N≤0.008%, O≤0.002%.

[0028] In the above technical solution of the present invention, P, S, N, and O are all harmful impurity elements. In order to obtain steel with better performance and higher quality, the content of P, S, N, and O should be reduced as much as possible if the technology permits.

[0029] Preferably, the average effective grain size of the H2S corrosion resistant high-strength oil casing of the present invention is ≤2.6 μm, preferably 2.0-2.6 μm.

[0030] Preferably, the microstructure of the H2S corrosion resistant high-strength oil casing of the present invention is tempered troostite, and the matrix (continuous phase) is tempered troostite.

[0031] Preferably, the performance of the high-strength oil casing resistant to H2S corrosion of the present invention meets the following requirements: yield strength ≥ 827 MPa, impact energy at 0°C ≥ 120 J, and H2S stress corrosion resistance meets the following requirements: K 1SCC Value ≥28MPa*m 1 / 2 And according to NACE TM0177 standard A method using D solution, when loaded with 85% of the nominal yield strength, the steel pipe does not break after 720 hours.

[0032] K 1SCCIt is the critical value of the material's resistance to stress corrosion cracking (SCC). In the present invention, it is the resistance to hydrogen sulfide stress cracking, reflecting the ability of the oil casing to resist crack propagation under specific environmental and loading conditions. 1SCC The higher the value, the less likely the steel pipe is to suffer from stress corrosion cracking in an H2S environment.

[0033] Another object of the present invention is to provide a method for manufacturing the above-mentioned high-strength oil casing and tubing resistant to H2S corrosion, which has a simple process and low production cost.

[0034] In order to achieve the above object, the present invention proposes a method for manufacturing the above-mentioned high-strength oil casing and tubing resistant to H2S corrosion, comprising the following steps performed in sequence:

[0035] (1) Smelting and continuous casting to obtain tube blanks;

[0036] (2) heating, perforating, and rolling to obtain a steel pipe;

[0037] (3) Cooling after rolling;

[0038] (4) First quenching and tempering heat treatment: quenching temperature is Ac3+30℃ to Ac3+40℃, holding time is 60-80min; tempering temperature is 680-715℃, holding time is 80-120min;

[0039] (5) Second quenching and tempering heat treatment: quenching temperature is Ac3+10℃ to Ac3+20℃, holding time is 60-80min; tempering temperature is 680-715℃, holding time is 80-120min;

[0040] (6) Thermal straightening.

[0041] Where, Ac3=910-203[C] 1 / 2 +44.7[Si]+104[V]+31.5[Mo]+13.1[W]. When calculating, substitute the element symbols C, Si, V, Mo, and W in the formula for the values ​​before the percentage sign representing the mass percentage of the corresponding element in the steel. The unit of Ac3 is °C. For example, if the mass percentage of C in the steel is 0.12%, substitute 0.12 for the calculation.

[0042] In the present invention, Ac3 is the final temperature at which the steel transforms into austenite when heated.

[0043] Preferably, in step (1) of the above method, the superheat of the molten steel during the continuous casting process is 25° C. to 35° C., and the continuous casting speed is 1.6 to 2.0 m / min.

[0044] Preferably, in step (2) of the above method, the tube blank is heated to an soaking temperature of 1200-1260°C.

[0045] Preferably, in step (2) of the above method, the perforation temperature is 1150-1230°C.

[0046] Preferably, in step (2) of the above method, the finishing rolling temperature is 880-930°C.

[0047] Preferably, in step (3) of the above method, the steel pipe is water-cooled online at a cooling rate of 10 to 20°C / s, cooled to 620-670°C, and then air-cooled to room temperature.

[0048] Preferably, in step (6) of the above method, the heat straightening temperature is 500-550°C.

[0049] The high-strength oil casing and tubing resistant to H2S corrosion and the manufacturing method thereof of the present invention have the following advantages and beneficial effects:

[0050] The high-strength H2S corrosion-resistant oil casing of the present invention can produce oil well pipes with fine effective grains, high strength and good H2S stress corrosion resistance by controlling the reasonable ratio of alloy elements, rare earth modification treatment and grain refinement process measures.

[0051] The high-strength oil casing resistant to H2S corrosion of the present invention has an average effective grain size of less than 2.6 μm, a yield strength of ≥827 MPa, an impact energy of ≥120 J at 0°C, and an H2S stress corrosion resistance that meets K 1SCC Value ≥28MPa*m 1 / 2 And according to NACE TM0177 standard A method using D solution, when loaded with 85% of the nominal yield strength, the oil casing will not break after 720 hours.

[0052] The high-strength oil casing and tubing resistant to H2S corrosion of the present invention can be used for the exploitation of oil and natural gas containing hydrogen sulfide in ultra-deep wells exceeding 9,000 meters. DETAILED DESCRIPTION

[0053] The high-strength oil casing and tubing resistant to H2S corrosion and the manufacturing method thereof according to the present invention will be further explained and illustrated below in conjunction with specific embodiments. However, such explanation and illustration do not constitute an undue limitation to the technical solution of the present invention.

[0054] Examples 1-6 and Comparative Examples 1-8

[0055] The H2S corrosion resistant high-strength oil casings of Examples 1-6 and the comparative oil casings of Comparative Examples 1-8 were all prepared by sequentially performing the following steps:

[0056] (1) Smelting, LF furnace refining, VD furnace vacuum treatment, and continuous casting to obtain a tube billet. The tube billet composition is shown in Table 1. During the continuous casting process, rare earth wire is fed into the crystallizer, and the superheat temperature of the molten steel is controlled at 25°C to 35°C. The continuous casting speed is controlled at 1.6 to 2.0 m / min.

[0057] (2) Heating: The tube billet is heated to an even temperature of 1200-1260°C in a ring furnace.

[0058] (3) Piercing: The piercing temperature of the tube blank is controlled to be 1150-1230°C to obtain the steel tube.

[0059] (4) Rolling (hot rolling): The final rolling temperature is controlled at 880-930°C to obtain the rolled steel pipe.

[0060] (5) Post-rolling cooling: Use water spray cooling equipment to perform online water cooling on the rolled steel pipe, control the online water cooling cooling rate to 10-20℃ / s, cool to 620-670℃, and then air cool to room temperature to make pipe (i.e. the outer diameter of the steel pipe is 244.48mm and the wall thickness is 11.99mm).

[0061] (6) First quenching and tempering heat treatment: quenching temperature is Ac3+30℃ to Ac3+40℃, holding time is 60~80min; tempering temperature is 680~715℃, holding time is 80~120min.

[0062] (7) Second quenching and tempering heat treatment: quenching temperature is Ac3+10℃ to Ac3+20℃, holding time is 60~80min; tempering temperature is 680~715℃, holding time is 80~120min.

[0063] In the above steps (6) and (7), Ac3 = 910 - 203 [C] 1 / 2 +44.7[Si]+104[V]+31.5[Mo]+13.1[W]. When calculating, the element symbols C, Si, V, Mo and W in the formula are substituted into the values ​​before the percentage sign of the mass percentage of the corresponding elements in the steel pipe.

[0064] (8) Hot straightening: The hot straightening temperature is 500-550℃, and the composition content of the finished oil casing is the same as that of the tube blank.

[0065] It should be noted that the chemical composition and related process design of the high-strength H2S corrosion-resistant oil casing and tubing of Examples 1-6 of the present invention meet the design specifications of the present invention. However, the chemical composition of the comparative oil casing and tubing of Comparative Examples 1-6 does not meet the design specifications of the present invention, and the process parameters of Comparative Examples 7 and 8 do not meet the design specifications of the present invention.

[0066] Table 1 lists the mass percentages (wt%, with the remainder being Fe and other unavoidable impurities except P, O, N, and S) of the high-strength oil casing and tubing resistant to H2S corrosion of Examples 1-6 and the comparative oil casing and tubing of Comparative Examples 1-8, as well as the corresponding calculated Ac3 values ​​(°C).

[0067] Table 1.

[0068] Note: Ac3 in Table 1 is Ac3 = 910-203[C] 1 / 2 +44.7[Si]+104[V]+31.5[Mo]+13.1[W]. When calculating, the element symbols C, Si, V, Mo and W in the formula are substituted into the values ​​before the percentage sign of the mass percentage of the corresponding elements in the steel pipe.

[0069] Table 2-1 and Table 2-2 list the specific process parameters of the H2S corrosion resistant high strength oil casing of Example 1-6 and the comparative oil casing of Comparative Example 1-8 in the above process steps.

[0070] Table 2-1.

[0071] Note: The water cooling rate and water cooling final cooling temperature of Comparative Example 7 in Table 2-1 are both "-", indicating that this step was not performed and only air cooling was used.

[0072] Table 2-2.

[0073] The H2S corrosion resistant high strength oil casing pipes of Examples 1-6 and the comparative pipes of Comparative Examples 1-8 were sampled and tested, and the test results are listed in Table 3. The relevant test process is as follows:

[0074] (1) Microstructure: The H2S corrosion resistant high strength oil casing of Examples 1-6 was sampled and observed by EBSD (electron backscatter diffraction). The microstructure (continuous phase) was found to be tempered bainite. In addition, the average effective grain size is listed in Table 3.

[0075] Effective grains refer to grains that are closely related to the mechanical properties of the material (such as strength and plasticity), and are obtained by statistically analyzing the distribution of high-angle grain boundaries (grain boundaries with orientation difference ≥15°). In the present invention, the average effective grain size is determined by analysis using Oxford Instruments' HKL Channel 5 software.

[0076] (2) Tensile test: The room temperature tensile property test is measured according to GB / T 228.1-2000.

[0077] (3) Impact test: The 0℃ impact energy test is carried out in accordance with GB / T 229-2007 "Metallic Materials Charpy Pendulum Impact Test Method".

[0078] (4) Anti-sulfur performance test: The anti-sulfur performance of the present invention includes K 1SCC The fracture conditions of oil casing and tubing under specific conditions are measured according to Method D and Method A in NACE TM0177-2016 respectively.

[0079] Table 3 lists the test results of the H2S corrosion resistant high strength oil casing pipes of Examples 1-6 and the comparative pipes of Comparative Examples 1-8.

[0080] Table 3.

[0081] As can be seen from Table 3, the yield strength of the high-strength oil casing resistant to H2S corrosion of Examples 1-6 of the present invention is greater than 827 MPa, the impact energy at 0°C is greater than 120 J, and the H2S stress corrosion resistance meets the K 1SCC The values ​​are all greater than 28MPa*m 1 / 2 The average effective grain size is less than 2.6μm and the oil casing does not break after 720h when loaded with 85% nominal yield strength using D solution according to NACE TM0177 standard A method.

[0082] It can be seen that by adopting the technical solution described in the present invention, an oil casing with both ultra-high strength and H2S stress corrosion resistance can be obtained.

[0083] Comparative Examples 1 to 6 do not meet the design specifications of the present invention due to their chemical element composition or process parameters, so that some of their properties do not meet the requirements of the present invention.

[0084] The Ce content in the steel pipes of Comparative Examples 1 and 2 does not meet the requirements of the present invention. The Ce content in Comparative Example 1 is low, resulting in grain size that does not meet the requirements. The steel pipe is broken after testing according to NACE TM0177 standard A method, and the K 1SCC It does not meet the requirements of the present invention.

[0085] The W and Cr contents in the steel pipe of Comparative Example 3 are lower than the requirements of the present invention, and the strength of the steel pipe does not meet the requirements of 120 ksi steel grade. Moreover, the steel pipe breaks after testing according to NACE TM0177 standard A method, and the K 1SCC It does not meet the requirements of the present invention.

[0086] The W and Cr contents in the steel pipe of Comparative Example 4 are higher than the requirements of the present invention. The steel pipe is broken after testing according to the A method of NACE TM0177 standard, and the K1SCC It does not meet the requirements of the present invention.

[0087] The Mo and Nb contents in the steel pipe of Comparative Example 5 are lower than the requirements of the present invention, and the sulfur resistance is unqualified.

[0088] The Mo and Nb contents in the steel pipe of Comparative Example 6 are higher than the limits of the present invention, and the toughness and sulfur resistance of the steel pipe are unqualified.

[0089] In the preparation process of Comparative Example 7, the air cooling process after hot-rolling of the pipe was not adopted, the effective grain size of the steel pipe was large, and the impact resistance and sulfur resistance were unqualified.

[0090] The austenitizing temperature of the steel pipe of Comparative Example 8 does not meet the requirements of the present invention, the effective grain size is large, and the sulfur resistance is unqualified.

[0091] It should be noted that the combination of the various technical features in this case is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All technical features recorded in this case can be freely combined or combined in any way unless there is a contradiction between them.

[0092] It should also be noted that the embodiments listed above are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made therefrom that can be directly derived from or easily conceived by those skilled in the art based on the disclosure of the present invention are intended to fall within the scope of protection of the present invention.

Claims

1. An oil casing pipe resistant to H2S corrosion, characterized in that, In addition to containing Fe and inevitable impurities, the casing pipe contains the following chemical elements by mass percentage: C: 0.12 - 0.2%, Si: 0.1 - 0.5%, Mn: 0.6% - 0.9%, Cr: 0.30 - 0.50%, Mo: 1.1 - 1.5%, V: 0.05 - 0.1%, Nb: 0.05 - 0.1%, W: 0.05 - 0.18%, Al: 0.01 - 0.05%, Ce: 0.0005 - 0.0018%. B：0.0015～0.005％。 2. The casing pipe as claimed in claim 1, wherein The casing pipe contains the following chemical elements by mass percentage: C: 0.12 - 0.2%, Si: 0.1 - 0.5%, Mn: 0.6% - 0.9%, Cr: 0.30 - 0.50%, Mo: 1.1 - 1.5%, V: 0.05 - 0.1%, Nb: 0.05 - 0.1%, W: 0.05 - 0.18%, Al: 0.01 - 0.05%, Ce: 0.0005 - 0.0018%. B: 0.0015 - 0.005%; the balance is Fe and inevitable impurities.

3. The oil casing according to claim 1 or 2, characterized in that, Among the inevitable impurities: S ≤ 0.002%, P ≤ 0.01%, N ≤ 0.008%, O ≤ 0.002%.

4. The oil casing according to claim 1 or 2, characterized in that, The average effective grain size of the casing pipe ≤ 2.6 μm.

5. The oil casing according to claim 1 or 2, characterized in that, The microstructure of the casing pipe is tempered sorbite.

6. The casing and tubing according to claim 1 or 2, characterized in that, The properties of the casing and tubing meet the requirements: yield strength ≥ 827 MPa, impact energy at 0°C ≥ 120 J, and the anti-H2S stress corrosion performance meets the K 1SCC value ≥ 28 MPa*m 1 / 2 .

7. A method for manufacturing an oil casing pipe according to any one of claims 1-6, characterized in that, The method includes the following steps carried out in sequence: (1) Smelting and continuous casting to obtain a billet; (2) Heating, piercing, and rolling to obtain a steel pipe; (3) Cooling after rolling; (4) First quenching and tempering heat treatment: the quenching temperature is Ac3 + 30°C to Ac3 + 40°C, and the holding time is 60 - 80 min; the tempering temperature is 680 - 715°C, and the holding time is 80 - 120 min; (5) Second quenching and tempering heat treatment: the quenching temperature is Ac3 + 10°C to Ac3 + 20°C, and the holding time is 60 - 80 min; the tempering temperature is 680 - 715°C, and the holding time is 80 - 120 min; (6) Hot straightening, where Ac3 = 910 - 203[C] 1 / 2 + 44.7[Si] + 104[V] + 31.5[Mo] + 13.1[W], in °C. When calculating, the elemental symbols C, Si, V, Mo, and W in the formula are respectively substituted with the numerical values before the percentage sign of the mass percentage content of the corresponding elements in the casing pipe.

8. The method according to claim 7, wherein In step (1), during continuous casting, the superheat of the molten steel is 25°C - 35°C, and the continuous casting speed is 1.6 - 2.0 m / min.

9. The method according to claim 7, wherein In step (2), the billet is heated to the soaking temperature of 1200 - 1260°C.

10. The method according to claim 7, characterized in that, In step (2), the piercing temperature is 1150 - 1230°C.

11. The method according to claim 7, wherein In step (2), the final rolling temperature is 880 - 930°C.

12. The method according to claim 7, characterized in that In step (3), the steel pipe is water-cooled online, and the cooling rate of the online water-cooling is 10 - 20°C / s, cooled to 620 - 670°C, and then air-cooled to room temperature.

13. The method according to claim 7, characterized in that, In step (6), the hot straightening temperature is 500 - 550°C.

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