X80qs thick wall seamless pipe line steel pipe and its preparation method

Abstract

The application provides an X80QS thick-wall seamless pipeline steel pipe and a preparation method thereof, and relates to the technical field of seamless pipeline steel pipe manufacturing. The thick-wall seamless pipeline steel pipe has the following chemical components and mass percentages: C 0.08-0.12%, Si 0.20-0.50%, Mn 1.00-1.40%, P≤0.010%, S≤0.003%, Cr 0.20-0.50%, Mo 0.20-0.50%, Ni 0.20-0.50%, V 0.05-0.20%, Nb 0.01-0.05%, Cu≤0.05%, Al≤0.040%, Ti≤0.040%, and the rest is iron and inevitable impurity elements; the crack sensitivity index CE Pcm of the steel pipe is ≤0.25%; and the wall thickness of the steel pipe is more than 40 mm. The preparation method solves the problem of uneven core structure of the thick-wall pipe.

Description

Technical Field

[0001] This invention relates to the field of seamless pipeline steel pipe manufacturing technology, and in particular to an X80QS thick-walled seamless pipeline steel pipe and its preparation method. Background Technology

[0002] Currently, fossil fuels such as oil and natural gas dominate global energy demand. With the development of the world economy and drastic changes in the international situation, the demand for fossil fuels is also growing rapidly. After over a century of exploitation, neutral oil and gas resources on land and at sea are facing depletion, thus the development of acidic oil and gas fields has gradually increased. Acidic oil and gas fields are characterized by the presence of certain amounts of acidic gases such as H2S and HCl in the oil or natural gas. These acidic gases can cause severe corrosion to pipelines, leading to leaks, ruptures, and other serious consequences. For seamless pipelines transporting oil and gas containing these acidic gases, the highest steel grade currently used is X70QS; there are no reports of X80QS steel grade applications.

[0003] Acid-resistant pipelines primarily withstand two corrosion modes: HIC (hydrogen-induced cracking) and SSCC (hydrogen sulfide stress corrosion). As the strength of the steel pipe increases, the material's sensitivity to acid corrosion also increases, multiplying the risk of cracking or even breakage. Steel pipes manufactured using traditional processes rarely meet corrosion resistance requirements.

[0004] In addition, because pipeline pipes require welding, the materials must have a low carbon equivalent (CE) rating. Pcm ≤0.25), which results in extremely poor hardenability of the material. For thick-walled tubes (wall thickness ≥25.4mm), poor hardenability will prevent the central structure from completely transforming into martensite during heat treatment, leading to problems such as uneven performance and reduced corrosion resistance.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The purpose of this invention is to provide X80QS thick-walled seamless pipeline steel pipe and its manufacturing method. Since the purity of steel has a significant impact on HIC and SSCC performance, this invention controls the sulfur content to below 0.003% and uses Ca treatment to spheroidize sulfide inclusions, thereby reducing stress concentration during corrosion. The manganese (Mn) content is controlled to below 1.4%, and Mn segregation is controlled through process control to obtain a good original microstructure. This is achieved through continuous casting + high-temperature diffusion (cast billet heat treatment) + a specific rolling process to control microstructure segregation in the steel. Simultaneously, the quenching and strengthening water-cooling heat treatment process in the tempering step (e.g., for 40-60mm wall thickness steel pipes, the steel pipe surface should be cooled to room temperature within 5 minutes of immersion in water; for 61-80mm wall thickness steel pipes, the steel pipe surface should be cooled to room temperature within 8 minutes of immersion in water) solves the problem of uneven microstructure in the core of thick-walled pipes, thus obtaining X80QS pipeline steel pipe with good conventional properties and excellent resistance to HIC and SSCC.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides an X80QS thick-walled seamless pipeline steel pipe, wherein the chemical composition and mass percentage of the thick-walled seamless pipeline steel pipe are as follows: C 0.08-0.12%, Si 0.20-0.50%, Mn 1.00-1.40%, P≤0.010%, S≤0.003%, Cr 0.20-0.50%, Mo 0.20-0.50%, Ni 0.20-0.50%, V 0.05-0.20%, Nb 0.01-0.05%, Cu≤0.05%, Al≤0.040%, Ti≤0.040%, with the remainder being iron and unavoidable impurity elements; The crack sensitivity index (CEPcm) of the steel pipe is ≤0.25%; The wall thickness of the steel pipe is 40mm or more.

[0008] Furthermore, the outer diameter of the steel pipe is 219-533mm, and the wall thickness is 40-80mm.

[0009] Furthermore, the steel pipe has a yield strength of 555-705 MPa, a tensile strength of 625-825 MPa, a yield-to-tensile ratio of ≤0.90, an elongation of ≥21%, and an impact energy of ≥100 J at -40℃.

[0010] A second aspect of the present invention provides a method for preparing the X80QS thick-walled seamless pipeline steel pipe described in the first aspect, the method comprising the following steps in sequence: KR desulfurization, converter smelting, LF refining, RH vacuum treatment, continuous casting, billet heat treatment, rolling, and quenching and tempering.

[0011] Furthermore, in the LF refining step, the Ca-Si line added is 3-7 mm / ton of molten steel; and the inclusions in the molten steel, namely A sulfides, B alumina, C silicates, and D spherical oxides, are controlled to be no higher than grade 0.5.

[0012] Furthermore, the diameter of the continuously cast round billet obtained by the continuous casting step is 155-500mm.

[0013] Furthermore, in the heat treatment step of the billet, the continuously cast round billet is heated and held at a temperature of less than or equal to 1280°C, preferably 1260~1280°C, and the holding time is greater than or equal to 4 hours, preferably 6~8 hours.

[0014] Furthermore, the rolling process is carried out using an ASSEL tube rolling mill; the initial rolling temperature is greater than 1280℃, and the final rolling temperature is greater than 900℃.

[0015] Furthermore, the quenching and tempering step includes quenching heat treatment and tempering heat treatment.

[0016] Furthermore, the quenching holding temperature of the quenching heat treatment is 920-960℃, and the holding time is calculated according to the wall thickness of the steel pipe, which is greater than 1 minute / mm, preferably 1.5-2.5 minutes / mm; And / or, the quenching cooling of the quenching heat treatment is water cooling until the surface of the steel pipe is at room temperature; preferably, the cooling rate is greater than or equal to 117°C / min; more preferably, for steel pipes with a wall thickness of 40-60mm, the water cooling rate is greater than or equal to 187°C / min; for steel pipes with a wall thickness greater than 60mm and not greater than 80mm, the water cooling rate is greater than or equal to 117°C / min. And / or, the temperature of the tempering heat treatment is 580-650℃, preferably 580-620℃; the holding time is calculated according to the wall thickness of the steel pipe and is greater than 2.5 minutes / mm, more preferably 3-5 minutes / mm.

[0017] The beneficial effects of the X80QS thick-walled seamless pipeline steel pipe and its manufacturing method provided by this invention are as follows: (1) By controlling S to below 0.003% and using Ca treatment to spheroidize sulfide inclusions, the purity of steel can be improved and stress concentration during corrosion can be reduced. (2) Control the Mn content to below 1.4% and control the Mn segregation from the process to obtain a good original structure. That is, control the segregation of the steel structure by continuous casting + high temperature diffusion (cast billet heat treatment) + specific rolling process; at the same time, solve the problem of uneven structure in the core of thick-walled tubes by strengthening the water cooling heat treatment process. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0019] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0020] According to a first aspect of the present invention, the present invention provides an X80QS thick-walled seamless pipeline steel pipe, wherein the chemical composition and mass percentage of the thick-walled seamless pipeline steel pipe are as follows: C 0.08-0.12%, Si 0.20-0.50%, Mn 1.00-1.40%, P≤0.010%, S≤0.003%, Cr 0.20-0.50%, Mo 0.20-0.50%, Ni 0.20-0.50%, V 0.05-0.20%, Nb 0.01-0.05%, Cu≤0.05%, Al≤0.040%, Ti≤0.040%, with the remainder being iron and unavoidable impurity elements; The crack sensitivity index CE of the steel pipe Pcm ≤0.25; The wall thickness of the steel pipe is 40mm or more.

[0021] In this invention, CE Pcm The calculation formula is: CE Pcm =C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B, where C, Si, Mn, V, Ni, Cr, Cu, and Mo represent the mass percentage of each chemical component.

[0022] This invention is mainly aimed at thick-walled pipes with a wall thickness of 40mm or more. By adding alloys such as Ni, the hardenability of the material is increased, so as to ensure the uniformity of the performance of the entire cross section.

[0023] This invention controls the sulfur content to below 0.003% and uses Ca treatment to spheroidize sulfide inclusions, which can improve the purity of the steel and reduce stress concentration during corrosion. It also controls the manganese content to below 1.4% and controls manganese segregation through process control, thereby obtaining a good original microstructure.

[0024] As a preferred embodiment of the X80QS thick-walled seamless pipeline steel pipe of the present invention, the chemical composition and mass percentage of the thick-walled seamless pipeline steel pipe are as follows: C 0.1-0.12%, Si 0.3-0.50%, Mn 1.2-1.3%, P≤0.010%, S≤0.001%, Cr 0.30-0.40%, Mo 0.30-0.40%, Ni 0.30-0.40%, V 0.15-0.16%, Nb 0.01-0.02%, Cu≤0.01%, Al≤0.030%, Ti≤0.010%, with the remainder being iron and unavoidable impurity elements.

[0025] In the chemical composition of the preferred steel pipe of the present invention, the control of V content is mainly to increase the hardenability and strength of the material and refine the grains; the control of Nb content mainly plays the role of refining the grains, and Nb can be reduced accordingly after the V content is increased.

[0026] As an optional embodiment of the X80QS thick-walled seamless pipeline steel pipe of the present invention, the outer diameter of the steel pipe is 219-533mm (e.g., 250mm, 300mm, 350mm, 400mm, 450mm, 500mm), and the wall thickness is 40-80mm (e.g., 50mm, 60mm, 70mm).

[0027] As an optional embodiment of the X80QS thick-walled seamless pipeline steel pipe of the present invention, the steel pipe has a yield strength of 555-705 MPa (e.g., 580 MPa, 600 MPa, 620 MPa, 640 MPa, 660 MPa, 680 MPa, 700 MPa), a tensile strength of 625-825 MPa (e.g., 650 MPa, 680 MPa, 700 MPa, 720 MPa, 740 MPa, 760 MPa, 780 MPa, 800 MPa, 820 MPa), a yield strength ratio ≤0.90, an elongation ≥21%, and an impact energy ≥100J at -40℃.

[0028] In this invention, the X80QS thick-walled seamless pipeline steel pipe is sampled and tested according to the NACE™ 0284 standard. The sample is immersed in an aqueous solution containing 5wt% NaCl and 0.5wt% CH3COOH, and H2S gas at a pressure of 15PSI is introduced. After maintaining this for 72 hours, the steel pipe has a CLR ≤ 15%, and / or CTR ≤ 5%, and / or CSR ≤ 2%.

[0029] In this invention, the X80QS thick-walled seamless pipeline steel pipe is sampled and tested according to the NACE MR 0177 standard. The sample is a type C sample. The sample is immersed in an aqueous solution containing 5 wt% NaCl and 0.5 wt% CH3COOH, and H2S gas at a pressure of 15 PSI is introduced. At the same time, a pressure of 400 MPa is applied to the sample and maintained for 720 hours. The sample should not break. According to a second aspect of the present invention, the present invention provides a method for preparing the X80QS thick-walled seamless pipeline steel pipe described in the first aspect, the method comprising the following steps in sequence: KR desulfurization, converter smelting, LF refining, RH vacuum treatment, continuous casting, billet heat treatment, rolling and tempering.

[0030] In this invention, tempering includes quenching and tempering. This invention solves the problem of uneven microstructure in the core of thick-walled tubes through forced cooling during the quenching process. Microstructural segregation in the steel is controlled through continuous casting + high-temperature diffusion (homogenization treatment during billet heating) + a specific rolling process.

[0031] In this invention, the method steps not described in detail are conventional steps in the art. For example, KR desulfurization refers to a process in which the desulfurizing agent is thoroughly mixed and reacted with molten iron through strong mechanical stirring, thereby deeply removing sulfur from the molten iron. Converter smelting involves mixing molten iron and scrap steel for smelting, and its core tasks are decarburization, heating, and dephosphorization.

[0032] As an optional embodiment of the preparation method of X80QS thick-walled seamless pipeline steel pipe of the present invention, in the LF refining step, the amount of Ca-Si wire added is 3-7 mm / ton of molten steel; and the inclusions of A sulfides, B alumina, C silicates and D spherical oxides in the molten steel are controlled to be no higher than grade 0.5.

[0033] In the LF refining step of this invention, the added Ca-Si is mainly used to improve the size of Class A inclusions, thereby reducing their impact on corrosion sensitivity.

[0034] In this invention, the sulfur content is controlled below 0.003%, and Ca treatment is used to spheroidize sulfide inclusions, which can improve the purity of the steel and reduce stress concentration during the corrosion process.

[0035] As an optional embodiment of the preparation method of X80QS thick-walled seamless pipeline steel pipe of the present invention, the diameter of the continuously cast round billet obtained by the continuous casting step is 155-500mm (e.g., 160mm, 180mm, 200mm, 250mm, 280mm, 300mm, 350mm, 400mm, 450mm, 480mm).

[0036] As an optional embodiment of the preparation method of the X80QS thick-walled seamless pipeline steel pipe of the present invention, in the billet heat treatment step, the continuously cast round billet is heated and held at a temperature of less than or equal to 1280℃, preferably 1260~1280℃ (e.g., 1262℃, 1264℃, 1268℃, 1270℃, 1272℃, 1274℃, 1276℃, 1278℃), and the holding time is greater than or equal to 4 hours, preferably 6~8 hours (e.g., 6.2 hours, 6.4 hours, 6.6 hours, 6.8 hours, 7.0 hours, 7.2 hours, 7.4 hours, 7.6 hours, 7.8 hours).

[0037] As an optional embodiment of the preparation method of the X80QS thick-walled seamless pipeline steel pipe of the present invention, the rolling is carried out using an ASSEL tube rolling mill; the initial rolling temperature is greater than 1280℃ and the final rolling temperature is greater than 900℃.

[0038] The ASSEL tube rolling mill used in this invention is suitable for rolling thick-walled tubes.

[0039] As an optional embodiment of the preparation method of the X80QS thick-walled seamless pipeline steel pipe of the present invention, the quenching and tempering step includes quenching heat treatment and tempering heat treatment.

[0040] As an optional embodiment of the preparation method of the X80QS thick-walled seamless pipeline steel pipe of the present invention, the quenching heat treatment quenching holding temperature is 920-960℃ (e.g., 925℃, 930℃, 935℃, 940℃, 945℃, 950℃, 955℃), and the holding time is calculated according to the wall thickness of the steel pipe and is greater than 1 minute / mm, preferably 1.5-2.5 minutes / mm; The quenching and cooling process of the heat treatment is water cooling until the surface temperature of the steel reaches room temperature (e.g., 25°C); the water cooling is an overall immersion water cooling method for the steel pipe; preferably, the water cooling rate is greater than or equal to 117°C / min; more preferably, for steel pipes with a wall thickness of 40-60mm, the water cooling rate is greater than or equal to 187°C / min; for steel pipes with a wall thickness greater than 60mm and not greater than 80mm, the water cooling rate is greater than or equal to 117°C / min.

[0041] The cooling method of the present invention can help solve the problem of uneven structure in the core of thick-walled tubes, and can also improve cooling efficiency.

[0042] As an optional embodiment of the preparation method of the X80QS thick-walled seamless pipeline steel pipe of the present invention, the tempering heat treatment temperature is 580-650℃ (e.g., 585℃, 600℃, 610℃, 620℃, 630℃, 640℃, 645℃, 648℃), preferably 580-620℃ (e.g., 585℃, 590℃, 600℃, 610℃, 615℃); the holding time is calculated according to the wall thickness of the steel pipe and is greater than 2.5 minutes / mm, more preferably 3-5 minutes / mm (e.g., 3.2 minutes / mm, 3.4 minutes / mm, 3.6 minutes / mm, 3.8 minutes / mm, 4.0 minutes / mm, 4.2 minutes / mm, 4.4 minutes / mm, 4.6 minutes / mm, 4.8 minutes / mm).

[0043] The present invention will now be described in further detail with reference to specific embodiments and comparative examples.

[0044] Examples and Comparative Examples Prepare materials according to the chemical composition of thick-walled seamless pipeline steel pipe in Table 1. The production method of thick-walled seamless pipeline steel pipe is carried out in sequence as follows: KR desulfurization, converter smelting, LF refining, RH vacuum treatment, continuous casting, billet heat treatment, rolling and tempering.

[0045] Table 1 is a list of the chemical composition (wt.%) of the steel pipes prepared in the various embodiments and comparative examples of the present invention; Table 2 is a list of the main process parameters for each embodiment and comparative example of the present invention; Table 3 is a statistical table of the main performance tests of the steel pipes prepared in the various embodiments and comparative examples of the present invention; Table 4 shows the corrosion resistance test results of the steel pipes prepared in the various embodiments and comparative examples of the present invention.

[0046] Table 1 Table 2 The quenching cooling rates of the quenching heat treatment in Examples 1-5 and Comparative Examples 1-7 are all within the range defined in this application. For steel pipes with a wall thickness of 40-60mm, the cooling rate of water cooling to room temperature of 25°C is 187-197°C / min; for steel pipes with a wall thickness greater than 60mm and not greater than 80mm, the cooling rate of water cooling to room temperature of 25°C is 117-127°C / min.

[0047] Comparative Example 8 The only difference between this comparative example and Example 2 is that the cooling rate of the quenching heat treatment to room temperature of 25°C is about 160-170°C / min, which is less than 187°C / min.

[0048] Table 3 Sampling location: Center of wall thickness.

[0049] The tensile testing method is ASTM E8; The impact test method is ASTM E45, and the grain size test method is ASTM E112.

[0050] Table 4 Sampling location: Center of wall thickness.

[0051] The HIC detection method is NACE™ 0284; The SSCC detection method is: NACE MR 0177.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing X80QS thick-walled seamless pipeline steel pipe, characterized in that, The method includes, in sequence, the following steps: KR desulfurization, converter smelting, LF refining, RH vacuum treatment, continuous casting, billet heat treatment, rolling, and quenching and tempering. The chemical composition and mass percentage of the thick-walled seamless pipeline steel pipe are as follows: C 0.08-0.12%, Si 0.20-0.50%, Mn 1.00-1.40%, P≤0.010%, S≤0.003%, Cr 0.20-0.50%, Mo 0.20-0.50%, Ni 0.20-0.50%, V 0.05-0.20%, Nb 0.01-0.05%, Cu≤0.05%, Al≤0.040%, Ti≤0.040%, with the remainder being iron and unavoidable impurity elements; The crack sensitivity index (CEPcm) of the steel pipe is ≤0.25%; The wall thickness of the steel pipe is 40mm or more; The quenching and tempering steps include quenching heat treatment and tempering heat treatment; The tempering heat treatment temperature is 580-650℃.

2. The method for preparing X80QS thick-walled seamless pipeline steel pipe according to claim 1, characterized in that, The outer diameter of the steel pipe is 219-533mm, and the wall thickness is 40-80mm.

3. The method for preparing X80QS thick-walled seamless pipeline steel pipe according to claim 1, characterized in that, The steel pipe has a yield strength of 555-705 MPa, a tensile strength of 625-825 MPa, a yield-to-tensile ratio of ≤0.90, an elongation of ≥21%, and an impact energy of ≥100 J at -40℃.

4. The method for preparing X80QS thick-walled seamless pipeline steel pipe according to claim 1, characterized in that, In the LF refining step, the amount of Ca-Si wire added is 3-7 mm / ton of molten steel; and the inclusions of A-sulfides, B-alumina, C-silicates, and D-spherical oxides in the molten steel are controlled to be no higher than grade 0.

5.

5. The method for preparing X80QS thick-walled seamless pipeline steel pipe according to claim 1, characterized in that, The diameter of the continuously cast round billet obtained by the continuous casting step is 155-500mm.

6. The method for preparing X80QS thick-walled seamless pipeline steel pipe according to claim 1, characterized in that, In the billet heat treatment step, the continuously cast round billet is heated and held at a temperature of less than or equal to 1280°C for a duration of more than or equal to 4 hours.

7. The method for preparing X80QS thick-walled seamless pipeline steel pipe according to claim 1, characterized in that, In the heat treatment step of the billet, the continuously cast round billet is heated and held at a temperature of 1260~1280℃.

8. The method for preparing X80QS thick-walled seamless pipeline steel pipe according to claim 1, characterized in that, In the billet heat treatment step, the continuously cast round billet is heated and held at a temperature for 6-8 hours.

9. The method for preparing X80QS thick-walled seamless pipeline steel pipe according to claim 1, characterized in that, The rolling process is performed using an ASSEL tube rolling mill; the initial rolling temperature is greater than 1280℃, and the final rolling temperature is greater than 900℃.

10. The method for preparing X80QS thick-walled seamless pipeline steel pipe according to claim 1, characterized in that, The quenching heat treatment has a quenching holding temperature of 920-960℃ and a holding time calculated based on the wall thickness of the steel pipe, which is greater than 1 minute / mm. And / or, the quenching cooling of the quenching heat treatment is water cooling until the surface of the steel pipe is at room temperature; the cooling rate is greater than or equal to 117°C / min; And / or, the temperature of the tempering heat treatment is 580-620℃; the holding time is calculated according to the wall thickness of the steel pipe and is greater than 2.5 minutes / mm.

11. The method for preparing X80QS thick-walled seamless pipeline steel pipe according to claim 1, characterized in that, The holding time for the quenching treatment is calculated to be 1.5-2.5 minutes / mm based on the wall thickness of the steel pipe.

12. The method for preparing X80QS thick-walled seamless pipeline steel pipe according to claim 1, characterized in that, The quenching cooling process is water cooling until the surface of the steel pipe is at room temperature. For steel pipes with a wall thickness of 40-60mm, the water cooling rate is greater than or equal to 187℃ / min; for steel pipes with a wall thickness greater than 60mm and not greater than 80mm, the water cooling rate is greater than or equal to 117℃ / min.

13. The method for preparing X80QS thick-walled seamless pipeline steel pipe according to claim 1, characterized in that, The holding time for the tempering treatment is calculated based on the wall thickness of the steel pipe, and is 3-5 minutes per millimeter.

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