CN110106439A - Marine riser X65 hot rolled steel plate and preparation method thereof - Google Patents

Abstract

The invention provides an X65 hot-rolled steel plate for marine risers and a preparation method thereof. The weight percentage of the chemical composition is: C: 0.03-0.05%, Si: 0.10-0.30%, Mn: 1.10-1.35%, P: ≤0.007%, S: ≤0.0008%, Alt: 0.01-0.05%, Nb: 0.04-0.06%, Ti: 0.008-0.018%, Ni: 0.20-0.40%, Cr: 0.15-0.30%, Mo: 0.10-0.20%, N: ≤0.004%, the balance is Fe and unavoidable impurity elements; firstly, 300-500mm thick continuous casting slabs are used, rough rolling of steel slabs adopts differential temperature rolling, and finishing rolling adopts three-stage rolling to obtain fine and flattened hardened austenitic solid grains, the steel plate is cooled after rolling, the initial cooling temperature is 760-780°C, and the final cooling temperature is 200-300°C, to obtain fine ferrite and a small amount of acicular ferrite structure. The advantages are that large wall thickness, high strength, low yield ratio, low temperature toughness, fracture resistance, and acid resistance are excellent, reducing the risk of fracture and corrosion of marine risers.

Description

X65 hot-rolled steel plate for marine riser and preparation method thereof

technical field

The invention belongs to the technical field of marine risers, and in particular relates to an X65 hot-rolled steel plate for marine risers and a preparation method thereof.

Background technique

The vigorous development of offshore oil and gas development has made offshore riser technology the forefront of technological innovation in the world's petroleum industry. Offshore riser is an important part in the construction of offshore oil and gas resource development projects. At present, the United States, Japan, Germany, Brazil, Norway, Italy and other countries are at the world's advanced level in terms of marine riser technology and equipment. my country's marine riser development and laying capacity is far below the international advanced level, and the research on marine risers has just started. my country's sea area is vast, and there are about 30 billion tons of oil and gas reserves in the deep waters of the south-central South China Sea. With the rapid development of my country's national economy, the country's demand for energy is increasing day by day. Promoting the development of deep-sea oil and gas resources will play an important role in the sustainable development of my country's national economy, alleviating the pressure of oil and gas imports and improving the energy supply structure.

The marine riser connects the subsea wellhead and the offshore oil production platform, and plays the role of transporting crude oil and natural gas. The marine riser bears the strong corrosion of the transport medium and the dynamic load of ocean currents. The rupture of the marine riser will cause fire and explosion, threatening the safety of the offshore platform and the life of the staff on the platform, and the catastrophe will bring great damage to the marine ecology. Therefore, steel for marine risers has very strict requirements on product quality and grade, including: 1. High strength (yield strength 450N/mm ² ); 2. High toughness (-40°C); 3. Increased wall thickness (34-50mm ); 4. Fracture resistance (CTOD); 5. Arrest resistance (DWTT); 6. Low yield ratio (Y/T≤0.89); 7. Acid corrosion resistance (HIC, SSCC); 8. Excellent welding performance.

There is no experience in the development of X65 hot-rolled steel plates for large-wall offshore risers in China. The current X65 products for long-distance pipelines do not meet the technical requirements for marine risers and cannot meet the needs of offshore oil and gas resource exploitation engineering construction. Therefore, the bottleneck in the development of offshore oil and gas resources in the South my country Sea lies in the successful development of X65 hot-rolled steel plates for large-wall thickness marine risers.

Contents of the invention

In view of this, the present invention provides a X65 hot-rolled steel plate for marine risers and a preparation method thereof, which solves the problem of obtaining high strength, low yield ratio, low temperature toughness, fracture resistance, easy welding, and Acid corrosion problem. It is suitable for the construction of risers for offshore deepwater oil and natural gas exploration projects, which greatly reduces the risk of fracture and corrosion of marine risers.

The first aspect of the present invention provides an X65 hot-rolled steel plate for marine risers. In terms of mass percentage, the chemical composition of the steel plate includes: C: 0.03-0.05%, Si: 0.10-0.30%, Mn: 1.10-1.35%, P: ≤0.007%, S: ≤0.0008%, Alt: 0.01～0.05%, Nb: 0.04～0.06%, Ti: 0.008～0.018%, Ni: 0.20～0.40%, Cr: 0.15～0.30%, Mo: 0.10 ~0.20%, N: ≤0.004%, the balance is Fe and unavoidable impurity elements.

The chemical composition and content ratio of the X65 hot-rolled steel plate for the marine riser directly affect the product performance, wherein:

C element improves the strength performance of the material through solid solution strengthening. If the C content is less than 0.03wt%, the strength performance level is low. When the C content is greater than 0.05wt%, the acid resistance, low temperature toughness and welding level are low. Therefore, the content of C in the present invention is controlled within the range of 0.03-0.05wt%. A large number of tests have proved that only when the C content is controlled within the range of 0.03-0.05wt%, can a narrow range of strength performance control be obtained, as well as stable -40°C DWTT, CTOD performance and acid resistance HIC, SSCC performance.

The Mn element can significantly improve the strength performance. If the Mn content is too low, the tensile strength of the material is not enough. If the Mn content is too high, the acid resistance and low temperature toughness will be reduced. Therefore, the present invention has obtained through a large number of tests that Mn is controlled in the range of 1.10-1.35wt%, which not only ensures the strength level of the material, but also does not deteriorate the acid resistance and low-temperature toughness. A large number of tests have proved that only when the Mn content is controlled within the range of 1.10-1.35wt%, can stable -40°C DWTT, CTOD performance and acid resistance HIC and SSCC performance be obtained.

P and S elements are impurity elements in steel, and are easy to segregate, affecting the internal quality of continuous casting slabs. The lower the content of P and S, the better. In order to obtain good low-temperature toughness, acid resistance and welding performance, the present invention has carried out a large number of tests , It is found that the impurity elements are controlled at P: ≤0.007wt%, S: ≤0.0008wt%, in order to obtain stable -40 ℃ DWTT, CTOD performance and acid resistance HIC, SSCC performance.

Nb element has the effect of solid solution strengthening and grain refinement, so the content of Nb in the present invention is controlled within the range of 0.04-0.06wt%.

A large number of tests have been carried out on the Ti element in the present invention, and it is found that when the Ti content is greater than 0.018wt%, TiN particles with a larger particle size will affect the low-temperature toughness and acid resistance of the material. Therefore, in the present invention, the Ti content is controlled within the range of 0.008-0.018wt%, and the low-temperature toughness, welding performance and acid resistance performance are the best.

Ni element is an austenite stabilizing element, which can reduce the γ→α transformation temperature and can effectively improve the low temperature toughness of pipeline steel. Ni can improve the strength of steel through solid solution strengthening, and make up for the strength decrease caused by the increase of thickness in thick gauge steel. The most important thing is to add Ni alloy, which can further improve the strength and low temperature toughness of steel. But too much Ni will greatly increase the cost. Therefore, the present invention has carried out a lot of tests and found that when the Ni content is controlled within the range of 0.20-0.40wt%, the strength, toughness and economic efficiency are the best.

Mo element increases the hardenability, improves the uniformity of the structure in the thickness direction of the large-wall steel plate, improves the low-temperature toughness, can increase the tensile strength, reduce the yield ratio, and stabilize the strength and toughness of the material. However, the present invention has carried out a large number of tests and found that: when the Mo content is greater than 0.20%, there will be too many hard phase structures and M/A islands, etc., which will affect the acid resistance. Therefore, when the Mo content is controlled in the range of 0.10-0.20wt%, the uniformity of structure, uniformity of strength, low yield ratio, low temperature toughness and acid resistance of HIC and SSCC are optimal.

The Cr element is effective in improving the tensile strength of pipeline steel, and can significantly reduce the yield ratio of the material. However, higher Cr content will be detrimental to welding performance and acid resistance. A large number of tests have been carried out in the invention, and when the Cr content is controlled within the range of 0.15-0.30%, the strength performance, yield strength ratio, welding performance and acid resistance performance are the best.

Preferably, the microstructure of the X65 hot-rolled steel plate for marine risers is a fine and uniform ferrite structure, including acicular ferrite structure with a volume percentage of 1-8%, and the ferrite grain size is ≤ 5 μm.

Preferably, the thickness specification of the X65 hot-rolled steel plate for the marine riser is 34-50 mm.

More preferably, the mechanical properties of the above-mentioned X65 hot-rolled steel plate for marine riser are: steel plate transverse yield strength: 450-550MPa, tensile strength: 535-650MPa; steel plate longitudinal yield strength: 440-550MPa, tensile strength: 535-650MPa , elongation after fracture A50≥30%, yield strength ratio≤0.89; steel plate thickness center transverse -40 ℃ Charpy impact energy ≥400J, impact shear area ≥90%; steel plate -40 ℃ thinning drop weight DWTT sample shear Cutting area ≥ 85%; CTOD value above 0.40mm at -40°C; hardness HV10 ≤ 230; according to NACE standard, under the condition of solution A, HIC crack length rate CLR ≤ 10%, crack thickness rate CTR ≤ 3%, crack Sensitivity rate CSR≤1%, no SSCC crack.

The second aspect of the present invention provides a method for preparing the above-mentioned X65 hot-rolled steel plate for marine risers, the steps comprising:

S1. Continuous casting obtains high-clean, extra-thick continuous casting slabs that meet the chemical composition requirements. The thickness of the continuous casting slabs is 300-500mm. The central segregation is controlled at 0.5 grade C, and the non-metallic inclusions of A/B/C/D are controlled. Within level 1.5;

S2. Using differential temperature rolling and high-reduction rough rolling to fully refine the core grains;

S3. Finish rolling adopts three-stage rolling to obtain flattened and hardened austenite grains, which reduces the temperature control time, refines austenite grains, and provides more nucleation points for subsequent ferrite transformation ;

S4. The steel plate is cooled after rolling, the initial cooling temperature is 760-780°C, and the final cooling temperature is 200-300°C.

In the above preparation method, high-clean and extra-thick continuous casting slabs are used. A large number of tests show that strict control of continuous casting slab thickness, center segregation, and non-metallic inclusions according to step S1 is the prerequisite for producing X65 hot-rolled steel plates for marine risers. Stable -40°C DWTT, CTOD performance and acid resistance HIC, SSCC performance can be obtained.

The differential temperature rolling process used in rough rolling can form a low-temperature hardened layer on the surface of the billet, while the high-temperature deformation resistance of the core of the billet is small, so that the rolling deformation can fully penetrate into the core, refine the core grains, and improve the strength and strength of the core. Ultra-low temperature toughness; since the core of large-wall steel plates is often a weak position, the differential temperature rolling process and large-reduction process of the present invention can fully heal the defects in the core, refine the grains in the core, and increase the thickness of the large wall. The uniformity of the thickness and section structure of the steel plate improves the comprehensive performance of the core, and obtains stable -40°C DWTT, CTOD performance and acid resistance HIC and SSCC performance.

The finishing rolling stage adopts three-stage rolling, the advantages are: improving production efficiency, avoiding high temperature waiting time for too long; refining grains, avoiding grain growth during high temperature waiting stage; obtaining fully flattened and hardened austenite grains , to provide more nucleation points for subsequent phase transformation and grain refinement; narrow range of strength performance control can be obtained, as well as stable -40 ° C DWTT, CTOD performance and acid resistance HIC, SSCC performance.

The steel plate is cooled after rolling to obtain fine ferrite and a small amount of acicular ferrite structure, and the ferrite grain size is ≤5μm; it can obtain a narrow range of strength performance control, a lower yield ratio, and a stable- 40℃ DWTT, CTOD performance and acid resistance HIC, SSCC performance.

Preferably, in step S2, the differential temperature rolling process makes the surface temperature of the billet 100-200°C lower than the core temperature, so that the rolling deformation can fully penetrate into the core and refine the core grains. Specifically, the surface of the billet can be cooled by spraying high-pressure water to form a temperature gradient in the thickness section of the billet.

Preferably, in step S2, in the large reduction process: the maximum reduction in a single pass is 40-50 mm, and the core grains are sufficiently refined.

Preferably, in step S3, the finish rolling adopts three-stage rolling, the rolling temperature of the first stage is 900-930°C, and the temperature is waited after rolling for 3-5 passes; the starting temperature of the second stage is 840-860°C ℃, after rolling for 2-3 passes, wait for the temperature; the third-stage rolling temperature is 800-820 ℃, and the final rolling temperature is 780-800 ℃, so as to obtain fully flattened and hardened austenite grains.

Compared with the prior art, the present invention has the following advantages:

On the premise of a large wall thickness of 34-50mm, the present invention realizes high-strength, narrow-range (≤100MPa) strength performance control, low yield ratio control, and stable -40°C DWTT, CTOD performance and resistance The performance control of acidic HIC and SSCC can significantly reduce the risk of fracture and corrosion of marine risers, and has a good application prospect.

Description of drawings

Fig. 1 is the central segregation diagram of the X65 continuous casting slab for the marine riser of the present invention (Class C 0.5 grade).

Fig. 2 is the metallographic structure diagram of the X65 hot-rolled steel plate for the marine riser of the present invention, wherein a is the metallographic structure diagram of the surface layer, and b is the metallographic structure diagram of the core.

Fig. 3 is a scanning tissue diagram of an X65 hot-rolled steel plate for marine risers of the present invention, wherein a is a scanning tissue diagram of the surface layer, and b is a scanning tissue diagram of the core.

Detailed ways

In order to facilitate the understanding of the present invention, the present invention will be described more fully and in detail below in conjunction with examples, but the protection scope of the present invention is not limited to the following specific examples.

Unless otherwise defined, all technical terms used hereinafter have the same meanings as commonly understood by those skilled in the art. The terminology used herein is only for the purpose of describing specific embodiments, and is not intended to limit the protection scope of the present invention.

Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

The X65 hot-rolled steel plate for marine risers provided by the present invention and its preparation method will be described in detail below in combination with five specific examples.

Example 1

This embodiment provides a preparation method of X65 hot-rolled steel plate for marine riser, the steps include:

1) Continuous casting produces high-clean, extra-thick continuous casting slabs that meet the chemical composition requirements. The central segregation is controlled at Class C 0.5, and the non-metallic inclusions of A/B/C/D are controlled within 1.5. The thickness of the continuous casting slab And the specific chemical composition is shown in Table 1, and the central segregation of the continuous casting slab is well controlled, as shown in Figure 1;

2) The differential temperature rolling process is adopted in the rough rolling stage, and the surface of the billet is cooled by spraying high-pressure water to form a temperature gradient in the thickness section of the billet, so that the surface temperature of the billet is lower than that of the core, so that the rolling deformation can fully penetrate into the core of the billet , refine the core grains;

3) Large reduction is adopted in the rough rolling stage to fully refine the core grains;

4) Three-stage rolling is adopted in the finishing rolling stage. The first stage is rolled for 4 passes and then warmed; the second stage is rolled for 2 passes and then warmed; Celite grains.

5) The steel plate is cooled after rolling to obtain fine ferrite and a small amount of acicular ferrite structure, and the ferrite grain size is ≤5 μm.

The specific process conditions involved in the above process are shown in Table 2. The process conditions include: continuous casting slab thickness, center segregation level, non-metallic inclusion level, temperature difference between surface and core during differential rolling, coarse The maximum rolling reduction in a single pass in the rolling stage, the starting temperature of the three stages of finishing rolling, the final rolling temperature of the third stage, the starting cooling temperature and the final cooling temperature of post-rolling cooling.

In the above process, the key process parameters are listed in Table 2, and other process parameters and details involved in the preparation process are processed according to the conventional process well known to the skilled person, and will not be repeated here.

The X65 hot-rolled steel plate for marine risers prepared by the above-mentioned process has a thickness specification of 34-50mm, and the surface and core of the steel plate have good uniformity, as shown in Figures 2 and 3, and the results of mechanical property tests are shown in Table 3 shown. Steel plate hardness HV10≤230; according to NACE standard, under the condition of solution A, the acid-resistant HIC crack rate of steel plate is 0.

Example 2-5

The present invention further provides embodiments 2-5, and embodiments 2-5 respectively provide a preparation method of X65 hot-rolled steel plates for marine risers, the specific steps of which are basically the same as those in embodiment 1, adopting 400mm continuous casting slab, continuous casting The segregation in the center of the slab is well controlled, and then the continuous casting slab undergoes rough rolling, three-stage finish rolling, cooling and other processes, and the steel plate obtains a fine and uniform structure of ferrite + a small amount of acicular ferrite, and the structure of the surface and core of the steel plate is uniform sex is good. The difference from Example 1 lies in the chemical composition of the steel plate and some process parameters, as shown in Table 1 and Table 2 for details.

The marine riser obtained in Example 2-5 was tested for performance with X65 hot-rolled steel plate and the prepared pipeline. The results are shown in Table 3. The mechanical properties of the product in Example 2-5 are basically the same as in Example 1, showing high Strength, narrow strength range (≤40MPa), low yield ratio (≤0.85), stable -40°C DWTT, CTOD performance and acid resistance HIC, SSCC performance (crack rate is 0).

Table 1 steel plate chemical composition list (wt%)

The chemical composition contents in Table 1 are all in weight percent, and the balance is Fe and unavoidable impurity elements.

Table 2 preparation process parameter table

Table 3 Product Mechanical Properties Table

A large number of test results of the present invention show that the chemical composition and preparation process of the steel plate are crucial to the microstructure and mechanical properties of the product. On the premise of a large wall thickness of 34-50mm, the present invention realizes high-strength, narrow-range (≤40MPa) Strength performance control, low yield ratio control, and stable -40°C DWTT, CTOD performance and acid resistance HIC, SSCC performance control, and the steel plate has excellent processability and weldability in the manufacturing process of downstream users, The yield ratio before and after pipe making is well controlled, and there is no problem of excessive yield ratio and low temperature toughness in the welding hot zone. The final marine riser products all meet the standard requirements.

The invention is suitable for risers used in offshore oil and natural gas exploitation projects, and reduces the risk of breakage and corrosion of marine risers.

While preferred embodiments of the invention have been described, additional changes and modifications to these embodiments can be made by those skilled in the art once the basic inventive concept is appreciated. Therefore, it is intended that the appended claims be construed to cover the preferred embodiment as well as all changes and modifications which fall within the scope of the invention.

Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims (8)

1. A X65 hot-rolled steel plate for marine risers, characterized in that: in terms of mass percentage, the chemical composition of the steel plate includes: C: 0.03-0.05%, Si: 0.10-0.30%, Mn: 1.10-1.35%, P : ≤0.007%, S: ≤0.0008%, Alt: 0.01～0.05%, Nb: 0.04～0.06%, Ti: 0.008～0.018%, Ni: 0.20～0.40%, Cr: 0.15～0.30%, Mo: 0.10～ 0.20%, N: ≤0.004%, the balance is Fe and unavoidable impurity elements. 2. The X65 hot-rolled steel plate for marine risers according to claim 1, characterized in that: the microstructure of the steel plate is a fine and uniform ferrite structure, which includes 1 to 8% acicular ferrite by volume body structure, the ferrite grain size is ≤5 μm. 3. The X65 hot-rolled steel plate for marine risers according to claim 1, characterized in that: the thickness specification of the steel plate is 34-50 mm. 4. The X65 hot-rolled steel plate for marine risers as claimed in any one of claims 1-3, characterized in that: the mechanical properties of the X65 hot-rolled steel plates for marine risers are: transverse yield strength of the steel plate: 450～ 550MPa, tensile strength: 535～650MPa; longitudinal yield strength of steel plate: 440～550MPa, tensile strength: 535～650MPa, elongation after fracture A50≥30%, yield ratio≤0.89; steel plate thickness center transverse -40℃ summer Specific impact energy ≥ 400J, impact shear area ≥ 90%; steel plate -40 ℃ thinning drop hammer DWTT sample shear area ≥ 85%; steel plate - 40 ℃ CTOD value above 0.40mm; hardness HV10 ≤ 230; according to NACE standard, under the condition of A solution, HIC crack length rate CLR≤10%, crack thickness rate CTR≤3%, crack sensitivity rate CSR≤1%, no SSCC crack. 5. the preparation method of X65 hot-rolled steel plate for marine riser described in claim 1, step comprises: S1. Using continuous casting process, the thickness of the continuous casting slab is 300-500mm, the center segregation is controlled at 0.5 level of C type, and the A/B/C/D type non-metallic inclusions are all controlled within 1.5 level, and the chemical composition requirements are obtained. continuous casting slab; S2. Using differential temperature rolling and high-reduction rough rolling to fully refine the core grains; S3, three-stage finishing rolling to obtain flattened and hardened austenite grains; S4. The steel plate is cooled after rolling, the initial cooling temperature is 760-780°C, and the final cooling temperature is 200-300°C. 6 . The method for preparing X65 hot-rolled steel plates for marine risers according to claim 5 , wherein in step S2 , the differential temperature rolling process makes the surface temperature of the billet 100-200° C. lower than the core temperature. 6 . 7. The method for preparing X65 hot-rolled steel plates for marine risers as claimed in claim 5, characterized in that: in step S2, in the large reduction process: the maximum reduction in a single pass is 40-50 mm. 8. The preparation method of X65 hot-rolled steel plate for marine riser as claimed in claim 5, characterized in that: in step S3, the finish rolling adopts three-stage rolling, the rolling temperature of the first stage is 900-930°C, and the rolling Wait for temperature after 3-5 passes; the second-stage rolling temperature is 840-860°C, and wait for temperature after rolling for 2-3 passes; the third-stage rolling temperature is 800-820°C, and the final rolling temperature is 780 ~800°C.