X80QS thick-wall seamless pipeline steel pipe and preparation method thereof

Abstract

The invention 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 comprises the following chemical components in percentage by mass: 0.08 to 0.12 percent of C, 0.20 to 0.50 percent of Si, 1.00 to 1.40 percent of Mn, less than or equal to 0.010 percent of P, less than or equal to 0.003 percent of S, 0.20 to 0.50 percent of Cr, 0.20 to 0.50 percent of Mo, 0.20 to 0.50 percent of Ni, 0.05 to 0.20 percent of V, 0.01 to 0.05 percent of Nb, less than or equal to 0.05 percent of Cu, less than or equal to 0.040 percent of Al, less than or equal to 0.040 percent of Ti and the balance of iron and inevitable impurity elements. The crack sensitivity index CEPcm of the steel pipe is less than or equal to 0.25%; and the wall thickness of the steel pipe is more than 40mm. The preparation method provided by the invention solves the problem that the core structure of the thick-wall tube is not uniform.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of seamless pipeline steel pipe manufacturing, in particular to an X80QS thick-wall seamless pipeline steel pipe and a preparation method thereof. BACKGROUND

[0002] At present, fossil energy such as oil and natural gas occupies a dominant position in the world energy demand. With the development of the world economy and the dramatic changes in the international situation, the demand for fossil energy is also growing rapidly. After a hundred years of exploitation, the land and marine nature oil and natural gas resources have faced exhaustion, so the development of the acid oil and natural gas field has gradually begun to increase. The characteristics of the acid oil and gas field are that a certain amount of H2S, HCl and other acid gases are contained in the oil or natural gas. Such acid gases can cause serious corrosion to the conveying pipeline, thereby causing the pipeline to leak, break and other serious consequences. For such acid gas-containing oil and gas conveying seamless pipeline pipes, the highest steel grade currently applied is X70QS, and there is no report on the application of X80QS steel grade.

[0003] The acid-resistant pipeline pipe mainly bears two corrosion modes of HIC (hydrogen-induced cracking) and SSCC (hydrogen sulfide stress corrosion). With the increase of the strength of the steel pipe, the corrosion sensitivity of the material to the acid increases continuously, and the risk of crack or even fracture increases exponentially. The steel pipe manufactured by the traditional process is difficult to meet the corrosive requirements.

[0004] In addition, the pipeline pipe needs to be welded, so the material is required to have a low carbon equivalent (CE Pcm ≤0.25), which leads to poor hardenability of the material. For thick-wall pipes (wall thickness ≥ 25.4 mm), poor hardenability will result in that the center part of the organization cannot be completely converted into martensite structure during the heat treatment process, thereby causing problems such as uneven performance, poor corrosion resistance and the like.

[0005] Therefore, the present application is proposed. SUMMARY

[0006] The present application aims to provide X80QS thick wall seamless pipeline steel pipe and its manufacturing method; since steel purity has great influence on HIC and SSCC performance, the present application controls S below 0.003%, and adopts Ca treatment mode to spheroidize sulfide inclusions, thereby reducing stress concentration in corrosion process; the content of Mn is controlled below 1.4%, and Mn segregation is controlled from process, thereby obtaining good original structure, i.e. controlling structure segregation in steel through continuous casting+high temperature diffusion (billet heat treatment)+specific rolling process; meanwhile, through quenching strengthening water cooling heat treatment process in the tempering step, (such as 40-60mm wall thickness steel pipe, the surface of the steel pipe should be cooled to room temperature within 5 minutes of entering water, 61-80mm wall thickness steel pipe, the surface of the steel pipe should be cooled to room temperature within 8 minutes of entering water), the problem of uneven core structure of thick wall pipe is solved, thereby obtaining X80QS pipeline steel pipe with good conventional performance and excellent HIC and SSCC resistance.

[0007] In order to achieve the above-mentioned purpose, the present application adopts the following technical scheme: The first aspect of the present application provides a kind of X80QS thick wall seamless pipeline steel pipe, the chemical composition and mass percentage of the thick wall 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%, Nb0.01-0.05%, Cu≤0.05%, Al≤0.040%, Ti≤0.040%, the rest is iron and inevitable impurity element; The crack sensitivity index CEPcm of the steel pipe is ≤0.25%; The wall thickness of the steel pipe is 40mm or more.

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

[0009] Further, the yield strength of the steel pipe is 555-705Mpa, the tensile strength is 625-825Mpa, the yield strength ratio is ≤0.90, the elongation is ≥21%, and the impact energy at-40℃ is ≥100J.

[0010] The second aspect of the present application provides a preparation method of the X80QS thick wall seamless pipeline steel pipe of the first aspect, and the method comprises the following steps in sequence: KR desulfurization, converter smelting, LF refining, RH vacuum treatment, continuous casting, billet heat treatment, rolling and tempering step.

[0011] Further, in the LF refining step, Ca-Si wire of 3-7mm / ton of molten steel is added; and the A sulfide type, B alumina type, C silicate type, and D globular oxide type inclusions in the molten steel are controlled to be not higher than 0.5 level.

[0012] Further, the diameter of the continuous casting round billet prepared in the continuous casting step is 155-500mm.

[0013] Further, in the billet heat treatment step, the continuous casting round billet is heated and held, the holding temperature is less than or equal to 1280℃, preferably 1260-1280℃, and the holding time is greater than or equal to 4 hours, preferably 6-8h.

[0014] Further, the rolling is performed by using an ASSEL pipe rolling mill; the rolling starting temperature is greater than 1280℃, and the finishing temperature is greater than 900℃.

[0015] Further, the quenching heat treatment and the tempering heat treatment are included in the quenching and tempering step.

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

[0017] The X80QS thick-wall seamless pipe line steel pipe and the manufacturing method thereof have the following beneficial effects: (1) S is controlled to be below 0.003%, and Ca treatment is used to make sulfide inclusions spheroidized, so that the purity of the steel material is improved, and stress concentration in the corrosion process is reduced; (2) Mn content is controlled to be below 1.4%, and Mn segregation is controlled from the process, so that good original structure is obtained, that is, the structure segregation in the steel is controlled by continuous casting+high temperature diffusion (billet heat treatment)+specific rolling process; and the problem of uneven structure in the thick-wall pipe core is solved by strengthening the water cooling heat treatment process. DETAILED DESCRIPTION

[0018] In order to make the objects, technical solutions and advantages of the present application clearer, the following will describe the technical solutions in the embodiments of the present application clearly and completely in combination with the embodiments of the present application. It should be appreciated by those skilled in the art that the embodiments are only used for understanding the present application and should not be regarded as specific limitation on the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative effort should fall into the scope of protection of the present application. The process parameters not specified in the following embodiments are usually according to the conventional conditions.

[0019] The endpoints of the ranges and any values described herein are not limited to the precise values stated. The ranges and values should be construed to be approximations that allow for significant variation. Various embodiments can have different values for the same parameters and such values are used to illustrate the embodiments. It is therefore understood that within the scope of the present application, modifications can be made to the embodiments without departing from the spirit of the present application.

[0020] According to a first aspect of the present application, the present application provides an X80QS thick wall seamless pipe line steel pipe, the chemical composition and mass percentage of the thick wall seamless pipe line 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%, and the rest is iron and inevitable impurity elements; The crack sensitivity index CE of the steel pipe Pcm ≤0.25; The wall thickness of the steel pipe is more than 40mm.

[0021] The calculation formula of CE in the present application Pcm is as follows: CE Pcm =C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B, wherein C, Si, Mn, V, Ni, Cr, Cu, Mo respectively represent the mass percentage of each chemical composition.

[0022] The present application is mainly aimed at thick wall pipe with wall thickness more than 40mm, and the hardenability of the material is increased by increasing alloy such as Ni to ensure the performance uniformity of the whole section.

[0023] The application controls S to be below 0.003%, and adopts Ca treatment mode, so that sulfide inclusions are spheroidized, the purity of the steel material is improved, and stress concentration in the corrosion process is reduced; the content of Mn is controlled to be below 1.4%, and Mn segregation is controlled from the process, so that good original structure is obtained.

[0024] As a preferred embodiment of the X80QS thick-walled seamless pipeline steel pipe, 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%, and the rest is iron and inevitable impurity elements.

[0025] In the chemical composition of the preferred steel pipe, the content of V is mainly controlled to increase the hardenability and strength of the material and refine the grain; the content of Nb is mainly controlled to refine the grain, and Nb can be reduced accordingly after the content of V is increased.

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

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

[0028] In the present application, the X80QS thick wall seamless pipeline steel pipe is sampled and detected according to the standard of NACE TM 0284, the sample is soaked in a water solution containing 5wt% NaCl and 0.5wt% CH3COOH, and H2S gas with a pressure of 15 PSI is introduced, and after 72 hours, the CLR of the steel pipe is ≤15%, and / or the CTR is ≤5%, and / or the CSR is ≤2%.

[0029] In the present application, the X80QS thick wall seamless pipeline steel pipe is sampled and detected according to the standard of NACE MR 0177, the sample is soaked in a water solution containing 5wt% NaCl and 0.5wt% CH3COOH, and H2S gas with a pressure of 15 PSI is introduced, and at the same time, a pressure of 400 MPa is applied to the sample, and after 720 hours, the sample should not be broken. According to the second aspect of the present application, the present application provides a preparation method of the X80QS thick wall seamless pipeline steel pipe of the first aspect, which comprises the following steps in sequence: KR desulfurization, converter smelting, LF refining, RH vacuum treatment, continuous casting, casting blank heat treatment, rolling and quenching and tempering.

[0030] In the present application, quenching and tempering includes quenching-tempering. Through forced cooling in the quenching process, the present application solves the problem of uneven organization in the thick wall pipe core. The organization segregation in the steel is controlled through continuous casting + high temperature diffusion (homogenization treatment in the casting blank heating process) + specific rolling process.

[0031] In the present application, the method steps not described in detail are conventional steps in the art, such as KR desulfurization, which refers to a process of deeply removing sulfur elements in molten iron by strongly mechanically stirring the desulfurizer and the molten iron to fully mix and react. Converter smelting is to smelt the molten iron and scrap steel, and the core task is to decarburize, heat up and dephosphorize.

[0032] As an optional embodiment of the preparation method of the X80QS thick wall seamless pipeline steel pipe of the present application, in the LF refining step, Ca-Si wire with a diameter of 3-7 mm per ton of molten steel is added; and the A sulfide type, B alumina type, C silicate type and D globular oxide type inclusions in the molten steel are controlled to be not higher than 0.5 level.

[0033] In the LF refining step of the present application, the added Ca-Si is mainly used to improve the size of A type inclusions, thereby reducing the influence of corrosion sensitivity.

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

[0035] As an optional embodiment of the preparation method of the X80QS thick-walled seamless pipeline steel pipe, the diameter of the continuous casting round billet prepared in the continuous casting step is 155-500 mm (such as 160 mm, 180 mm, 200 mm, 250 mm, 280 mm, 300 mm, 350 mm, 400 mm, 450 mm, 480 mm).

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

[0037] As an optional embodiment of the preparation method of the X80QS thick-walled seamless pipeline steel pipe, the rolling is performed by an ASSEL pipe rolling machine; the opening rolling temperature of the rolling is greater than 1280℃, and the finish rolling temperature is greater than 900℃.

[0038] The ASSEL pipe rolling machine adopted in the present application is suitable for rolling thick-walled pipes.

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

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

[0041] The cooling mode of the present application can help solve the problem of uneven core organization of thick-walled pipes, and also improve the 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. An X80QS heavy wall seamless line pipe characterized in that, The thick-walled 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 sensitive index CE of the steel pipe Pcm ≤0.25%; The wall thickness of the steel pipe is greater than 40 mm.

2. The X80 QS heavy wall seamless line pipe steel pipe according to claim 1, characterized in that, The outer diameter of the steel pipe is 219-533 mm, and the wall thickness is 40-80 mm.

3. The X80 QS heavy wall seamless line pipe steel pipe according to claim 1, characterized in that, The yield strength of the steel pipe is 555-705 MPa, the tensile strength is 625-825 MPa, the yield strength ratio is less than or equal to 0.90, the elongation is greater than or equal to 21%, and the impact energy at -40 ℃ is greater than or equal to 100 J.

4. A method of manufacturing an X80 QS heavy wall seamless line pipe steel pipe according to any one of claims 1 to 3, characterized in that, The method sequentially comprises the following steps: KR desulfurization, converter smelting, LF refining, RH vacuum treatment, continuous casting, cast blank heat treatment, rolling, and quenching and tempering.

5. The method of producing an X80 QS heavy wall seamless line pipe steel pipe according to claim 4, characterized in that, In the LF refining step, Ca-Si wire with a diameter of 3-7 mm per ton of molten steel is added, and the A sulfide, B alumina, C silicate, and D globular oxide inclusions in the molten steel are controlled to be not higher than 0.5 level.

6. The method of producing an X80 QS heavy wall seamless line pipe steel pipe according to claim 4, characterized in that, The continuous casting round billet has a diameter of 155-500 mm.

7. The method of producing an X80 QS heavy wall seamless line pipe steel pipe according to claim 4, characterized in that, In the cast blank heat treatment step, the continuous casting round billet is heated and held at a temperature less than or equal to 1280 ℃, preferably 1260-1280 ℃, for a time greater than or equal to 4 hours, preferably 6-8 h.

8. The method of producing an X80 QS heavy wall seamless line pipe steel pipe according to claim 4, characterized in that, The rolling is performed by using an ASSEL pipe rolling machine, and the rolling temperature is greater than 1280 ℃, and the finish rolling temperature is greater than 900 ℃.

9. The method of producing an X80 QS heavy wall seamless line pipe steel pipe according to claim 4, characterized in that, The quenching and tempering step comprises quenching heat treatment and tempering heat treatment.

10. The method of producing an X80 QS heavy wall seamless line pipe steel pipe according to claim 9, characterized in that, The quenching heat treatment has a quenching holding temperature of 920-960 ℃, and the holding time is greater than 1 min / mm, preferably 1.5-2.5 min / mm, calculated according to the wall thickness of the steel pipe. And / or, the quenching cooling of the quenching heat treatment is water cooling to room temperature of the surface of the steel pipe; preferably, the cooling rate is greater than or equal to 117 ℃ / min; more preferably, for the steel pipe with a wall thickness of 40-60 mm, the water cooling rate is greater than or equal to 187 ℃ / min; for the steel pipe with a wall thickness greater than 60 mm and not greater than 80 mm, the water cooling rate is greater than or equal to 117 ℃ / min. And / or, the tempering heat treatment has a temperature of 580-650 ℃, preferably 580-620 ℃, and a holding time greater than 2.5 min / mm, more preferably 3-5 min / mm, calculated according to the wall thickness of the steel pipe.

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