Seamless steel tube for petroleum casing and manufacturing method thereof

Abstract

The invention relates to a seamless steel tube for a petroleum casing and a manufacturing method of the seamless steel tube. The seamless steel tube comprises the following chemical components: 0.37%-0.43% of C, 0.61%-0.75% of Si, 3.50%-5.75% of Mn, less than or equal to 0.015% of P, less than or equal to 0.001% of S, 0.005%-0.050% of Al and 0.005%-0.050% of Mg. And the balance Fe and impurities. A high-carbon alloy design breaking through conventional thinking is adopted, alloy elements such as Cr, Mo, V, Ti and Nb are replaced with carbon, the basic strength and hardenability of the material are guaranteed, and the problems of large internal stress and uniform distribution of high-carbon steel are emphatically solved; a dispersed nucleation particle is introduced as a core, an electric pulse homogenization treatment process is adopted, carbide distribution and structure distribution are homogenized, the situation that the SSC resistance of different parts in the steel is large in difference is fundamentally improved, local hydrogen-induced stress concentration is reduced, and the SSC resistance is improved.

Description

Technical Field

[0001] The invention relates to the technical field of seamless steel pipe manufacturing, in particular to a seamless steel pipe for petroleum casing and a manufacturing method thereof. Background Art

[0002] 655MPa steel grade oil casing is the product with the largest market demand. Its main use is as a carrier for oil and natural gas extraction. As oil and natural gas are mined in more demanding areas, the presence of hydrogen sulfide in the environmental medium is a common phenomenon. An important problem faced is the stress corrosion of oil casing caused by wet hydrogen sulfide.

[0003] The Chinese patent application with publication number CN102719752A discloses "a seamless steel pipe with excellent hydrogen sulfide stress corrosion resistance and a manufacturing method thereof". The chemical composition of the steel pipe by weight percentage is C: 0.19%~0.24%, Si≤0.30%, Mn: 0.20%~0.50%, Cr: 0.90%~1.30%, Mo: 0.60%~0.80%, V: 0.10%~0.15%, Ti: 0.01%~0.03%, P≤0.012%, S≤0.005%, H≤0.00015%, N≤0.0050%, O≤0.0040%, As+Sn+Pb+Sb+Bi≤0.0080%, Ca: 0.0010%~0.0030%. The seamless steel pipe with the above composition is subjected to a double quenching and tempering heat treatment to solve the SSC corrosion problem of the 110ksi high-strength steel pipe. However, the composition design of the seamless steel pipe contains more precious metal elements such as Cr, Mo, V, and Ti, resulting in a high manufacturing cost. According to its composition and heat treatment process, it is not possible to economically obtain a 655MPa grade SSC-resistant seamless steel pipe product.

[0004] The Chinese patent application with publication number CN103469080A discloses "a method for manufacturing 80ksi steel grade oil well pipe". The chemical composition (Wt%) of the seamless steel pipe is C: 0.15% to 0.19%, Si: 0.20% to 0.30%, Mn: 1.20% to 1.40%, P≤0.015%, S≤0.003%, Cr: 0.60% to 0.90%, Nb: 0.01% to 0.03%, Ti: 0.04% to 0.06%, Cu: 0.08% to 0.12%, and a certain amount of RE element is added; the seamless steel pipe with this composition is subjected to a tempering heat treatment process to obtain a product with excellent SSC resistance. However, the seamless steel pipe also contains precious metal elements such as Cr, Nb, Ti, Cu, and RE, and the manufacturing cost is also high. After the steel pipe is hot-rolled, a tempering heat treatment process must be added, and the manufacturing cycle and delivery cycle are both long, which is not conducive to the market competitiveness of the product.

[0005] The Chinese invention patent with announcement number CN106319371B discloses a "90ksi steel grade oil well pipe with excellent SSC resistance and its manufacturing method". The composition of the seamless steel pipe is C: 0.18% to 0.22%, Mn: 0.30% to 0.45%, P≤0.015%, S≤0.003%, Mo: 0.18% to 0.20%, Cr: 1.60% to 1.80%, V: 0.04% to 0.06%, Ti: 0.07% to 0.09%, Cu: 0.05% to 0.17%, and a certain amount of RE element is added. The seamless steel pipe with this composition is subjected to a tempering heat treatment process to obtain a product with excellent SSC resistance. The seamless steel pipe also contains precious metal elements such as Cr, V, Ti, Cu, and RE, and the manufacturing cost is also high. After the steel pipe is hot-rolled, a tempering heat treatment process must be added. The manufacturing cycle and delivery cycle are both long, which is not conducive to the market competitiveness of the product.

[0006] The Chinese patent application with publication number CN114540715A discloses "an acid corrosion resistant steel, its preparation method and corrosion resistant pipe". The chemical composition of the acid corrosion resistant steel includes, by weight percentage: C 0.05-0.15%, Si≤0.3%, Mn≤0.6%, Cr 0.8-1.2%, Mo 0.6-0.9%, V≤0.3%, Nb 0.01-0.05%, Al≤0.05%, S≤0.005%, P≤0.01%, Cu 0.7-2%, the weight percentage of Ni and Cu satisfies 0.5≤Ni / Cu≤1, and the balance is iron and unavoidable impurities. Based on the characteristics of low carbon content, the acid corrosion resistant steel is endowed with higher SSC resistance. However, the carbon content of the seamless steel pipe is too low, and it is easy to cause sticking when threading the oil well pipe, resulting in poor quality of the make-up and make-up, and it is easy to cause stress concentration at the threaded connection of the oil well pipe, thereby reducing the SSC resistance of this position.

[0007] The Chinese patent application with publication number CN110331249A discloses "a method for smelting oil casing steel 26CrMoVTiB", including converter smelting, LF furnace refining, vacuum treatment, continuous casting, and slow cooling of the ingot off the line, with the slow cooling time being ≥72h. Chemical composition and its mass percentage: C: 0.25-0.27%, Si: 0.22-0.28%, Mn: 0.45-0.55%, P≤0.010%, S≤0.0015%, TAl: 0.015-0.035%, Cu≤0.10%, Ni≤0.10%, Cr: 0.45-0.55%, Mo: 0.78-0.82%, V: 0.09-0.11%, Ti: 0.025-0.035%, Nb: 0.02-0.04%, B: 0.0022-0.0030%, Ca: 0.0010-0.0020%, O≤15ppm, N≤70ppm, H≤2ppm, the balance is Fe and unavoidable impurities. The composition of its seamless steel pipe is designed to contain more precious metal elements such as Cr, Mo, V, Ti, etc., which leads to high manufacturing cost. During the manufacturing process, the ingot needs to be slowly cooled off the line, and the slow cooling time is ≥72h. The production cycle is long, the production efficiency is low, and the product is not competitive in the market.

[0008] The above public documents all adopt the traditional design concept of "low carbon + alloy + heat treatment" to manufacture 655MPa grade oil casing products. The component design cost is high, the manufacturing process is complicated, and the efficiency is low, which cannot meet the economical and SSC-resistant production requirements of 655MPa grade oil casing. Summary of the invention

[0009] The invention provides a seamless steel pipe for oil casing and a manufacturing method thereof. A high-carbon alloy design scheme that breaks through conventional thinking is adopted to manufacture a 655MPa-grade SSC-resistant seamless steel pipe for oil casing. Carbon is used to replace alloy elements such as Cr, Mo, V, Ti, and Nb to ensure the basic strength and hardenability of the material, and the problem of large internal stress and uniform distribution of high-carbon steel is focused on solving the problem. By introducing dispersed nucleation particles as the core and adopting an electric pulse homogenization treatment process, carbide distribution and tissue distribution are uniformed, and the situation of large differences in anti-SSC performance between different parts inside the steel is fundamentally improved, local hydrogen-induced stress concentration is reduced, and the anti-SSC ability is improved.

[0010] In order to achieve the above object, the present invention adopts the following technical solutions:

[0011] A seamless steel pipe for petroleum casing, wherein the chemical composition of the steel is, by mass percentage, C: 0.37%-0.43%, Si: 0.61%-0.75%, Mn: 3.50%-5.75%, P≤0.015%, S≤0.001%, Al: 0.005%-0.050%, Mg: 0.005%-0.050%; wherein O:S≤1, Ca:Mg≤0.7; the remainder is Fe and unavoidable impurities.

[0012] The finished product properties of seamless steel pipe are: tensile strength R m It is 655-719MPa, the SSC threshold value is 90%-95%, the SSC stress value is 622-671MPa, the grain size is 5-14μm, the cementite size is 0.6-1.9μm, and the inclusion size is 3.7-5.0μm.

[0013] A method for manufacturing a seamless steel pipe for petroleum casing comprises the following steps:

[0014] 1) The holding temperature during smelting of molten steel is 1650-1780°C. After alloying, the molten steel is stirred evenly, top slag is added, and after the top slag is melted, Mg alloy is added for deoxidation. After 10-25 minutes, Al is added for deep deoxidation. After another 10 minutes, Ca wire is added for further modification. After holding for 10 minutes, steel is tapped. The molten steel after vacuum degassing is cast into a billet by protective casting.

[0015] 2) After heating, perforating and rolling, the steel billet is converted into a seamless steel pipe;

[0016] 3) The seamless steel pipe is subjected to electric pulse homogenization treatment; the pulse magnetic field discharge voltage is 80-120V, the pulse magnetic field action time period is 0.5-2s, and the pulse magnetic field cooling rate is controlled within the range of 5-50°C / s;

[0017] 4) Temper the seamless steel pipe; the tempering temperature is 570~650℃.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1) A high-carbon alloy design scheme that breaks through conventional thinking is adopted to manufacture 655MPa grade seamless steel pipe for SSC-resistant petroleum casing; carbon is used to replace alloy elements such as Cr, Mo, V, Ti, and Nb to ensure the basic strength and hardenability of the material, and the main technical problem is transferred to how to solve the problem of large internal stress and uniform distribution of high-carbon steel; after a large number of experimental studies, it is found that under normal circumstances, the reason why the carbon content in steel increases and the SSC resistance is not high is mainly the presence of coarse twins and coarse cementite in the phase transformation structure; the present invention introduces dispersed nucleation particles as the core, adopts an electric pulse homogenization process, and evenly distributes carbides and tissues, fundamentally improving the situation where the SSC resistance between different parts of the steel is greatly different, reducing local hydrogen-induced stress concentration, and improving the SSC resistance;

[0020] 2) The product meets the requirements of 655MPa grade oil casing for SSC resistance and is highly economical; the SSC stress resistance threshold value (critical stress value for resisting hydrogen sulfide stress corrosion) of the manufactured 655MPa grade oil casing seamless steel pipe is increased by 5% to 10%, saving strategic precious metal materials such as Cr, Mo, V, Nb, Cu, etc., reducing production costs and greatly improving product competitiveness. DETAILED DESCRIPTION

[0021] The invention discloses a seamless steel pipe for petroleum casing, wherein the chemical composition of the steel is C: 0.37%-0.43%, Si: 0.61%-0.75%, Mn: 3.50%-5.75%, P≤0.015%, S≤0.001%, Al: 0.005%-0.050%, Mg: 0.005%-0.050% by mass percentage; wherein O:S≤1, Ca:Mg≤0.7; and the balance is Fe and unavoidable impurities.

[0022] The finished product properties of seamless steel pipe are: tensile strength R m It is 655-719MPa, the SSC threshold value is 90%-95%, the SSC stress value is 622-671MPa, the grain size is 5-14μm, the cementite size is 0.6-1.9μm, and the inclusion size is 3.7-5.0μm.

[0023] A method for manufacturing a seamless steel pipe for petroleum casing comprises the following steps:

[0024] 1) The holding temperature during smelting of molten steel is 1650-1780°C. After alloying, the molten steel is stirred evenly, top slag is added, and after the top slag is melted, Mg alloy is added for deoxidation. After 10-25 minutes, Al is added for deep deoxidation. After another 10 minutes, Ca wire is added for further modification. After holding for 10 minutes, steel is tapped. The molten steel after vacuum degassing is cast into a billet by protective casting.

[0025] 2) After heating, perforating and rolling, the steel billet is converted into a seamless steel pipe;

[0026] 3) The seamless steel pipe is subjected to electric pulse homogenization treatment; the pulse magnetic field discharge voltage is 80-120V, the pulse magnetic field action time period is 0.5-2s, and the pulse magnetic field cooling rate is controlled within the range of 5-50°C / s;

[0027] 4) Temper the seamless steel pipe; the tempering temperature is 570~650℃.

[0028] The chemical composition of the seamless steel pipe for petroleum casing described in the present invention does not contain precious metal elements such as Cr, Mo, V, and Nb. During the steel smelting process, deoxidation is carried out by adding Mg, Al, and Ca in combination, and the order of addition is mainly controlled, that is, Mg is added first, then Al is added, and after the Mg-Al compound is added, Ca is fed. By controlling the order of adding Mg and Al, a large amount of fine granular MgO-Al 2 O 3 The specific process is as follows: the holding temperature during smelting of molten steel is 1650-1780℃, the molten steel is alloyed and stirred evenly, top slag is added, Mg alloy is added after the top slag is melted for deoxidation, Al is added for deep deoxidation after 10-25 minutes, Mg-Al alloy is used to modify inclusions in the later stage of deoxidation, Ca wire is added for further modification after 10 minutes, and steel is tapped after 10 minutes of holding. Protective casting is used during casting to reduce the S and O content in steel.

[0029] After casting, the billet is heated, perforated, rolled and treated with electric pulse homogenization to obtain the finished seamless steel pipe. Among them, the electric pulse homogenization treatment of the seamless steel pipe uses a pulsed magnetic field to reduce the austenite grain size, which has a significant refining effect on the steel pipe structure, making the inclusions inside the austenite grains in the steel pipe more evenly dispersed. During the electric pulse homogenization treatment, the pulse magnetic field discharge voltage is controlled in the range of 80 to 120V. The higher the discharge voltage, the greater the pulse magnetic field intensity and the smaller the average grain size. In addition, the pulse magnetic field action time and cooling rate are controlled, and the pulse magnetic field cooling rate is adjusted in the range of 5 to 50℃ / s, and the pulse magnetic field action time period is controlled to be 0.5 to 2s; through the electric pulse homogenization treatment, the grain size of the seamless steel pipe and the carbides in the steel are effectively reduced.

[0030] Finally, the seamless steel pipe is subjected to a soaking treatment (tempering treatment) at 570 to 650°C.

[0031] In order to more intuitively embody the present invention, the embodiments of the present invention are further described in conjunction with examples. The following examples are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any technical solution that can be obviously obtained by a person skilled in the art within the technical scope disclosed in the present invention, including simple changes or equivalent replacements, is within the protection scope of the present invention.

[0032] [Example]

[0033] This embodiment includes Embodiment 1 to Embodiment 8, and the seamless steel pipe production process is as follows:

[0034] The molten iron is subjected to converter-LF furnace-VD-continuous casting to obtain a steel billet having the following composition ranges: C: 0.37%-0.43%, Si: 0.61%-0.75%, Mn: 3.50%-5.75%, P≤0.015%, S≤0.001%, Al: 0.005%-0.050%, Mg: 0.005%-0.050%. O: S≤1, Ca: Mg≤0.7. The chemical composition of each example steel is shown in Table 1.

[0035] During the steel smelting process, deoxidation is carried out by adding Mg, Al and Ca in a composite manner, and the order of addition is Mg first, then Al. After the Mg-Al composite is added, Ca is fed. Specifically, the refining and insulation temperature of the molten steel is 1650-1780°C. After alloying, the molten steel is stirred evenly, and top slag is added. After the top slag is melted, Mg alloy is added for deoxidation. After 10-25 minutes, Al is added for deep deoxidation. In the later stage of deoxidation, Mg-Al alloy is used to modify the inclusions; after another 10 minutes, Ca wire is added for further modification, and finally the steel is tapped after 10 minutes of insulation. The vacuum degassed molten steel is cast into round billets by protective casting.

[0036] The billet is heated, perforated and rolled to obtain a seamless steel pipe. The specifications of the seamless steel pipe are The seamless steel pipe is subjected to electric pulse homogenization treatment, wherein the pulse magnetic field discharge voltage is controlled within the range of 80 to 120 V, the pulse magnetic field action time period is 0.5 to 2 s, and the pulse magnetic field cooling rate is controlled within the range of 5 to 50 °C / s.

[0037] Finally, the seamless steel pipe is tempered; the tempering temperature is 570-650°C.

[0038] The main manufacturing process parameters of the seamless steel pipes of each embodiment are shown in Table 2, and the properties of the finished seamless steel pipes are shown in Table 3.

[0039] Table 1 Chemical composition of steel

[0040]

[0041] Table 2 Manufacturing process parameters of seamless steel pipe

[0042]

[0043] Table 3 Properties of finished seamless steel pipes

[0044]

[0045] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A seamless steel pipe for petroleum casing, characterized in that: The chemical composition of the steel is as follows by mass percentage: C: 0.37% ~ 0.43%, Si: 0.61% ~ 0.75%, Mn: 3.50% ~ 5.75%, P ≤ 0.015%, S ≤ 0.001%, Al: 0.005% ~ 0.050%, Mg: 0.005% ~ 0.050%; among which O: S ≤ 1, Ca: Mg ≤ 0.7; the balance is Fe and unavoidable impurities.

2. A seamless steel pipe for petroleum casing according to claim 1, characterized in that: The finished product properties of seamless steel pipe are: tensile strength R m It is 655-719MPa, the SSC threshold value is 90%-95%, the SSC stress value is 622-671MPa, the grain size is 5-14μm, the cementite size is 0.6-1.9μm, and the inclusion size is 3.7-5.0μm.

3. A method for manufacturing a seamless steel pipe for petroleum casing as claimed in claim 1 or 2, characterized in that: The steps include: 1) The holding temperature during smelting of molten steel is 1650-1780°C. After alloying, the molten steel is stirred evenly, top slag is added, and after the top slag is melted, Mg alloy is added for deoxidation. After 10-25 minutes, Al is added for deep deoxidation. After another 10 minutes, Ca wire is added for further modification. After holding for 10 minutes, steel is tapped. The molten steel after vacuum degassing is cast into a billet by protective casting. 2) After heating, perforating and rolling, the steel billet is converted into a seamless steel pipe; 3) The seamless steel pipe is subjected to electric pulse homogenization treatment; the pulse magnetic field discharge voltage is 80-120V, the pulse magnetic field action time period is 0.5-2s, and the pulse magnetic field cooling rate is controlled within the range of 5-50°C / s; 4) Temper the seamless steel pipe; the tempering temperature is 570~650℃.

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