A method for producing a thick-walled submarine sour-resistant pipeline steel X65MOS

Abstract

The application discloses a production method of thick-wall seabed acid-resistant pipeline steel X65MOS, and the thickness of the produced steel plate is 38-54 mm; the chemical component content of the steel is as follows: C=0.05%-0.07%, Si=0.15%-0.25%, Mn=1.50%-1.60%, P<=0.016%, S<=0.005%, Nb=0.040%-0.050%, Ti=0.01%-0.015%, Cr=0.22-0.28%, V=0.030-0.050%, B<=0.0005%, and the balance is Fe and inevitable impurities. Only the Cr+V+Nb component system is adopted, and low-temperature burning steel, rough rolling high-temperature large reduction and precision rolling low-temperature rolling are combined to obtain the dual-phase pipeline steel, wherein 35%-45% is bainite and 55%-65% is ferrite structure; the yield strength of the steel plate is 470-570 MPa, the tensile strength is 600-660 MPa, the yield strength ratio is 0.80-0.88, the impact toughness at-60 DEG C is 300-360 J, and the falling weight shear area at-20 DEG C is 90%-95%, so that the problems of high production cost and low falling weight low-temperature toughness shear area of the existing thick-wall seabed acid-resistant pipeline steel X65MOS steel plate are solved.

Description

Technical Field

[0001] This invention belongs to the field of pipeline steel manufacturing technology, and relates to a production method of X65MOS submarine acid-resistant pipeline steel with a thickness ≥38mm. Background Technology

[0002] Due to overexploitation of global onshore oil and gas resources, extraction volumes are declining, making offshore oil and gas development a new hotspot. As a major consumer of oil and gas energy, China began building offshore drilling platforms in 1966 and currently has over 50 offshore oil and gas development projects, with production continuously increasing. The success or failure of offshore oil and gas development projects depends on both the level of oil and gas extraction technology and the choice of transportation methods after extraction. Subsea pipelines offer the ability to transport large quantities of oil and gas continuously, and their convenience, safety, and stability have gradually made them the preferred method for transporting offshore oil and gas resources.

[0003] Currently, on the one hand, the harsh working environment of subsea pipelines places significantly higher demands on the stability of the internal quality of the pipe material compared to land-based pipeline steel, especially regarding the control of carbon equivalent and the precision of pipe end processing. Only in this way can the welding quality of subsea pipelines be guaranteed and leaks prevented. Simultaneously, the material must also possess resistance to hydrogen sulfide corrosion. On the other hand, due to the increasingly complex working environment of oil wells, the extracted crude oil and natural gas contain high levels of hydrogen sulfide, resulting in severe corrosion of pipelines during transportation. Therefore, the demand for high-strength, corrosion-resistant, and low-temperature-resistant subsea pipeline steel is increasing, making the research on thick-walled, acid-resistant subsea pipeline steel X65MOS of significant importance.

[0004] Chinese patent CN117165870A discloses a "hot-rolled steel plate for thick-walled submarine pipelines," which discloses the following chemical composition by weight percentage: C: 0.03%-0.05%, Si: 0.16%-0.24%, Mn: 1.60%-1.70%, P: ≤0.015%, S: ≤0.004%, Cr: 0.14%-0.18%, Ni: 0.11%-0.15%, Mo: 0.09%-0.13%, Nb: 0.05%-0.065%, Ti: 0.01%-0.02%, Al: 0.02%-0.05%, Pcm≤0.19%, with the remainder being Fe and impurity elements. This invention contains many expensive alloys, resulting in high manufacturing costs and prohibiting industrial-scale mass production. Furthermore, the pipeline steel of this invention lacks acid resistance and is unsuitable for use in acidic environments.

[0005] Chinese patent CN116536588A discloses "a method for producing steel for deep-sea acid-resistant pipelines". The pipeline steel disclosed also contains a lot of precious alloys, such as Ni: 0.10%~0.30% and Cu: 0.10%~0.30%, which makes the manufacturing cost high. At the same time, the drop hammer test temperature of this invention can only reach -10℃, making it difficult to apply in deep-sea environments.

[0006] Chinese patent CN112981226A discloses "a thick-walled X70 grade acid-resistant pipeline steel". This invention only discloses the smelting composition and smelting process of pipeline steel, and does not mention the crucial controlled cooling process of thick-walled pipeline steel at all. Summary of the Invention

[0007] This invention aims to provide a production method for thick-walled X65MOS anti-acid pipeline steel, producing steel plates with a wall thickness of 38~54mm, to solve the problems of high manufacturing cost and low drop-weight low-temperature toughness shear area of ​​existing thick-walled X65MOS anti-acid pipeline steel plates. The produced steel plates have a yield strength of 470~570MPa, tensile strength of 600~660MPa, yield ratio of 0.80~0.88, impact toughness of 300~360J at -60℃, and drop-weight shear area of ​​90%~95% at -20℃.

[0008] The technical solution of the present invention:

[0009] A method for producing thick-walled, acid-resistant subsea pipeline steel X65MOS, with a steel plate thickness of 38-54 mm. The chemical composition of the steel is C=0.05%-0.07%, Si=0.15%-0.25%, Mn=1.50%-1.60%, P≤0.016%, S≤0.005%, Nb=0.040%-0.050%, Ti=0.01%-0.015%, Cr=0.22-0.28%, V=0.030-0.050%, B≤0.0005%, with the balance being Fe and unavoidable impurities; key process steps include:

[0010] (1) Continuous casting: Full protection casting, superheat control 8~20℃, casting speed control 0.3~0.55m / min, dynamic light reduction, heavy reduction at the end of solidification, the two reductions at the end of solidification of the continuous casting billet are 5~7mm and 1~3mm respectively, and the secondary cooling water volume is 0.5~0.8L / kg;

[0011] (2) Heating: The steel temperature is 1100~1180℃, the time in the furnace is 450~500min, the temperature of the core of the billet is 1140~1160℃, the temperature of the upper surface of the billet is 1150~1170℃, and the temperature of the lower surface of the billet is 1130~1150℃.

[0012] (3) Rolling: The cumulative reduction of roughing is ≥64%, and the single-pass reduction is maintained at 38~43mm for 3~4 passes. The thickness of the billet after warming is 140~160mm. The cumulative reduction of finishing rolling is ≥72%, the initial rolling temperature is 800~820℃, and the final rolling temperature is 740~760℃.

[0013] (4) Cooling: Online DQ ultra-fast cooling is adopted, with an initial cooling temperature of 680~720℃, a cooling rate of 20~25℃, and a reddening temperature of 400~460℃, to obtain a ferrite + bainite dual-phase structure of steel, of which 35~45% is bainite and 55~65% is ferrite.

[0014] The inventiveness and beneficial effects of this invention are as follows: (1) The Cr+V+Nb composition system fully utilizes the fine grain, precipitation, and solid solution strengthening effects of Nb, V, and Cr. Combined with low-temperature steelmaking, it prevents the growth of the original austenite grains in the billet. The high temperature and high pressure during rough rolling further refine the austenite grain size, and the low temperature rolling and flattening deformation during finishing rolling create favorable conditions for subsequent cooling. (2) This invention uses a large cross-section billet of 450×2500mm, which effectively improves the compression ratio. The cooling process used yields a dual-phase structure with 35%~45% bainite and 55%~65% ferrite, which is very beneficial for improving the low-temperature drop hammer toughness. The produced steel plates with a wall thickness of 38~54nn have a yield strength of 470~570MPa, a tensile strength of 600~660MPa, a yield ratio of 0.80~0.88, an impact toughness of 300~360J at -60℃, and a drop hammer shear area of ​​90~95% at -20℃. This technology solves the problems of high manufacturing cost and low low-temperature toughness shear area of ​​existing thick-walled X65MOS steel plates for submarine acid-resistant pipelines. Attached Figure Description

[0015] Figure 1 The image shows the metallographic structure of the steel produced in Example 1. Detailed Implementation

[0016] The present invention will be further described below with reference to the embodiments.

[0017] Example 1: Production method of 40mm x 65MOS subsea acid-resistant pipeline steel

[0018] The steel's chemical composition is: C=0.07%, Si=0.20%, Mn=1.52%, P=0.014%, S=0.003%, Nb=0.044%, Ti=0.012%, Cr=0.27%, V=0.035%, B=0.0003%, with the balance being Fe and unavoidable impurities. Key process steps:

[0019] (1) Continuous casting: Full protection casting, superheat control at 15℃, casting speed control at 0.45m / min, dynamic light reduction is adopted, and heavy reduction is adopted at the end of solidification. The reduction force effectively penetrates to the core. The reduction of the two sections at the end of the solidification of the continuous casting billet is 5.5mm and 2.1mm respectively, and the secondary cooling water volume is 0.62L / kg.

[0020] (2) Heating: The steel temperature is 1170℃, the time is 460min, the temperature of the core of the billet is 1155℃, the temperature of the upper surface of the billet is 1160℃, and the temperature of the lower surface of the billet is 1145℃.

[0021] (3) Rolling: The cumulative reduction of roughing is 65%, and the single-pass reduction is maintained at 40mm for 4 passes. The thickness of the billet waiting to be warmed is 142mm. The cumulative reduction of finishing is 74.6%. The initial rolling temperature is 818℃ and the final rolling temperature is 756℃.

[0022] (4) Cooling: Online DQ ultra-fast cooling is adopted, with an initial cooling temperature of 715℃, a cooling rate of 22.1℃, and a reddening temperature of 445℃; the resulting steel has a dual-phase structure of ferrite + bainite, of which 38.6% is bainite and 61.4% is ferrite.

[0023] The mechanical properties of the steel plate are shown in Table 1.

[0024] Example 2: Production method of 52mm thick X65MOS subsea acid-resistant pipeline steel

[0025] The steel's chemical composition is: C=0.06%, Si=23%, Mn=1.55%, P=0.012%, S=0.002%, Nb=0.048%, Ti=0.01%-0.015%, Cr=0.27%, V=0.039%, B=0.0003%, with the balance being Fe and unavoidable impurities. Key process steps include:

[0026] (1) Continuous casting: Full protection casting, superheat control at 12℃, casting speed control at 0.41m / min, dynamic light reduction is adopted, and heavy reduction is adopted at the end of solidification. The reduction force effectively penetrates to the core. The reduction of the two sections at the end of the solidification of the continuous casting billet is 6.1mm and 2.6mm respectively, and the secondary cooling water volume is 0.72L / kg.

[0027] (2) Heating: The steel firing temperature is 1142℃, the furnace time is 480min, the core temperature of the billet is 1146℃, the upper surface temperature of the billet is 1153℃, and the lower surface temperature of the billet is 1135℃.

[0028] (3) Rolling: The cumulative reduction of roughing is 64.6%, and the single-pass reduction is maintained at 41 mm for 3 passes. The thickness of the billet waiting to be warmed is 158 mm. The cumulative reduction of finishing is 72.4%, the initial rolling temperature is 806℃, and the final rolling temperature is 748℃.

[0029] (4) Cooling: Online DQ ultra-fast cooling is adopted, with an initial cooling temperature of 692℃, a cooling rate of 21.5℃, and a reddening temperature of 436℃; the resulting steel has a dual-phase structure of ferrite + bainite, of which 39.2% is bainite and 60.8% is ferrite.

[0030] The mechanical properties of the steel plate are shown in Table 1.

[0031] Table 1. Test results of mechanical properties of X65MOS steel pipe in Example 1

[0032] .

Claims

1. A method for producing thick-walled, acid-resistant subsea pipeline steel X65MOS, wherein the steel plate thickness is 38~54mm, characterized in that: The chemical composition of the steel is C=0.05%~0.07%, Si=0.15%~0.25%, Mn=1.50%~1.60%, P≤0.016%, S≤0.005%, Nb=0.040%~0.050%, Ti=0.01%-0.015%, Cr=0.22-0.28%, V=0.030~0.050%, B≤0.0005%, with the balance being Fe and unavoidable impurities; Key process steps include: (1) Continuous casting: Full protection casting, superheat control 8~20℃, casting speed control 0.3~0.55m / min, dynamic light pressure is adopted, and heavy pressure is adopted at the end of solidification. The two-stage reduction at the end of solidification of the continuous casting billet are 5~7mm and 1~3mm respectively, and the secondary cooling water volume is 0.5~0.8L / kg; (2) Heating: The steel temperature is 1100~1180℃, the time in the furnace is 450~500min, the temperature of the core of the billet is 1140~1160℃, the temperature of the upper surface of the billet is 1150~1170℃, and the temperature of the lower surface of the billet is 1130~1150℃. (3) Rolling: The cumulative reduction of roughing is ≥64%, and the single-pass reduction is maintained at 38~43mm for 3~4 passes. The thickness of the billet after warming is 140~160mm. The cumulative reduction of finishing rolling is ≥72%. The initial rolling temperature is 800~820℃ and the final rolling temperature is 740~760℃. (4) Cooling: Online DQ ultra-fast cooling is adopted, with an initial cooling temperature of 680~720℃, a cooling rate of 20~25℃, and a reddening temperature of 400~460℃, to obtain a ferrite + bainite dual-phase structure of steel, of which 35~45% is bainite and 55~65% is ferrite.

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