Duplex stainless steel, duplex stainless steel tube and its application in oil and gas production

Abstract

The present invention belongs to the field of stainless steel technology, and specifically relates to a duplex stainless steel, a duplex stainless steel tube billet, and their application in oil and gas production. The duplex stainless steel provided by the present invention comprises, by weight percentage: C ≤ 0.028%; Si ≤ 0.70%; Mn ≤ 1.50%; P ≤ 0.030%; S ≤ 0.010%; Cr 22.0-23.0%; Ni 5.5-6.5%; Mo 3.0-3.5%; Al ≤ 0.10%; N 0.10-0.20%; balance Fe; 36 ≤ (Cr + 3.3Mo + 16N) ≤ 39; and 2.5 ≤ Si + Al / (C + N) ≤ 4. Steel pipes made using the duplex stainless steel of the present invention can achieve a tensile strength of over 950 MPa, exhibit good corrosion resistance in oil and gas production environments, and can be used in oil and gas production projects.

Description

Technical Field

[0001] The present invention belongs to the technical field of stainless steel, and in particular relates to duplex stainless steel, a duplex stainless steel tube blank and applications thereof in oil and gas production. Background Art

[0002] In humid CO2 environments, martensitic stainless steels 9Cr-1Mo and 13Cr are commonly used. 13Cr steel has better resistance to CO2 corrosion, while 9Cr-1Mo steel has better resistance to H2S stress corrosion cracking. In order to improve the steel pipe's resistance to CO2 corrosion and SSC (sulfide stress cracking), a low-carbon SUP13Cr steel pipe with added Ni and Mo has been developed. This steel pipe can be used in wet environments with high temperatures, high CO2 concentrations, and a small amount of hydrogen sulfide.

[0003] If the temperature of the oil (gas) well containing CO2 exceeds 200℃, the martensitic stainless steel SUP13Cr cannot meet the corrosion resistance requirements, and it is necessary to use a stainless steel with good resistance to CO2 and Cl - Stress corrosion cracking properties of duplex stainless steels. Summary of the Invention

[0004] The purpose of the present invention is to address the defects of the prior art and provide a duplex stainless steel, a duplex stainless steel tube blank and their application in oil and gas production.

[0005] Specifically, the duplex stainless steel provided by the present invention includes, by weight percentage: C≤0.028%; Si≤0.70%; Mn≤1.50%; P≤0.030%; S≤0.010%; Cr 22.0-23.0%; Ni 5.5-6.5%; Mo 3.0-3.5%; Al≤0.10%; N 0.10-0.20%; balance Fe; 36≤(Cr+3.3Mo+16N)≤39; 2.5≤Si+Al / (C+N)≤4.

[0006] The duplex stainless steel comprises, by weight percentage: C 0.010-0.025%; Si 0.40-0.60%; Mn 1.20-1.50%; Cr 22.2-22.5%; Ni 5.5-5.8%; Mo 3.1-3.3%; Al 0.07-0.10%; and N 0.17-0.20%.

[0007] On the other hand, the present invention also provides a duplex stainless steel tube blank, which is prepared using the above-mentioned duplex stainless steel.

[0008] In another aspect, the present invention further provides the use of the duplex stainless steel tube in oil and gas production.

[0009] The above application is characterized in that the duplex stainless steel tube blank is used to prepare oil pipelines for oil and gas production projects.

[0010] The technical solution of the present invention has the following beneficial effects:

[0011] The steel pipe prepared by using the duplex stainless steel of the present invention can have a tensile strength of more than 950 MPa, has good corrosion resistance in the oil and gas production environment, and can be used in the production of oil and gas production projects. DETAILED DESCRIPTION

[0012] In order to fully understand the purpose, features and effects of the present invention, the present invention is described in detail through the following specific embodiments. Except for the following contents, the process of the present invention adopts conventional methods or devices in the art. Unless otherwise specified, the following terms have the meanings commonly understood by those skilled in the art.

[0013] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein are understood to include any and all subranges subsumed therein.

[0014] Specifically, according to a first aspect of the present invention, the present invention provides a duplex stainless steel comprising, by weight percentage: C ≤ 0.028%; Si ≤ 0.70%; Mn ≤ 1.50%; P ≤ 0.030%; S ≤ 0.010%; Cr 22.0-23.0%; Ni 5.5-6.5%; Mo 3.0-3.5%; Al ≤ 0.10%; N 0.10-0.20%; balance Fe; 36 ≤ (Cr + 3.3Mo + 16N) ≤ 39; 2.5 ≤ Si + Al / (C + N) ≤ 4.

[0015] C, Si, and Mn are all essential elements in stainless steel, but excessive amounts can reduce the hot workability of the steel, so their upper limits are important. The C content should be below 0.028%, preferably between 0.010 and 0.025%. The Si content should be below 0.70%, preferably between 0.40 and 0.60%. The Mn content should be below 1.50%, preferably between 1.20 and 1.50%.

[0016] Cr is an important element in stainless steel and plays a key role in its corrosion resistance. However, in order to ensure that the ratio of the AF two phases in duplex stainless steel is 40-55%, the Cr content must be controlled at 22.00-23.00%, preferably 22.2-22.5%.

[0017] Ni and Mo are key alloying elements in duplex stainless steel, enhancing the steel's corrosion resistance and providing superior high-temperature performance. However, as both Ni and Mo are precious metals, excessively high Ni and Mo content can increase manufacturing costs. Therefore, the Ni content is controlled within a range of 5.5-6.5%, preferably 5.5-5.8%, and the Mo content is controlled within a range of 3.0-3.5%, preferably 3.1-3.3%.

[0018] Al is a commonly used deoxidizer in steel. Adding a small amount of aluminum to steel can refine grain size and improve impact toughness. Combined with chromium and silicon, aluminum significantly enhances steel's resistance to high-temperature corrosion. However, Al can also affect steel's hot working properties. Therefore, the Al content should be kept below 0.10%, preferably between 0.07% and 0.10%.

[0019] Nitrogen can replace part of nickel in duplex stainless steel. As the nitrogen content increases, the tensile strength of the steel can be significantly improved, while the plasticity, especially the toughness, is significantly reduced. Therefore, the nitrogen content should be controlled at 0.10-0.20%, preferably 0.17-0.20%.

[0020] 36≤(Cr+3.3Mo+16N)≤39; 2.5≤Si+Al / (C+N)≤4

[0021] Cr, Mo, and N are all related to the material's pitting corrosion resistance. Controlling (Cr+3.3Mo+16N) between 36 and 39 can ensure the material's corrosion resistance while avoiding increased alloy costs caused by excess performance. Si and Al are deoxidizing elements in the smelting process, but when combined with C and N, they will form inclusions that reduce the purity of the steel. Therefore, Si+Al / (C+N) needs to be controlled between 2.5 and 4.

[0022] On the other hand, the present invention also provides a stainless steel tube blank prepared using the above-mentioned duplex stainless steel.

[0023] In some preferred embodiments, the duplex stainless steel tube of the present invention is prepared by the following method:

[0024] (1) Using the "EAF+AOD" process to smelt molten steel, and then obtaining mold casting ingots through mold casting;

[0025] (2) radially forging the die-cast ingot to obtain a tube blank having a diameter of 120 to 350 mm;

[0026] (3) performing a solution treatment on the tube blank, and cooling the tube blank to room temperature after the solution treatment. The method for preparing the duplex stainless steel tube blank of the present invention has the advantage of low preparation difficulty.

[0027] Among them, the technical parameters used in the process of smelting molten steel using the "EAF+AOD" process can be carried out according to the existing technology, and the present invention will not elaborate on this.

[0028] The present invention adopts the "EAF+AOD" process to smelt molten steel, which can strictly control the chemical composition of the molten steel, especially the gas content.

[0029] The matching of the tube production process and ingot shape is related to the diameter of the finished tube. Preferably, for tube diameters 120mm or less and less than 150mm, the "3-ton ingot + radial forging" process is used; for tube diameters 150mm or less and less than 350mm, the "4.5-ton ingot + radial forging" process is used.

[0030] Among them, the production processes of "3-ton ingot + radial forging" and "4.5-ton ingot + radial forging" are both carried out in accordance with existing technologies, and the present invention will not elaborate on them here.

[0031] In some preferred embodiments, the starting temperature of the radial forging is 1200-1250°C, and the final forging temperature is controlled above 980°C. This can ensure a sufficiently wide hot working range to ensure the progress of radial forging production and avoid the precipitation of brittle harmful phases in forgings.

[0032] In some preferred embodiments, the solution treatment temperature is 1020-1080°C, and the tube dwell time corresponds to the tube diameter. Specifically, when the tube diameter is 120 mm or less and less than 150 mm, the dwell time is 120 min ± 10 min; when the tube diameter is 150 mm or less and less than 350 mm, the dwell time is (120 + D / 4) min ± 10 min (D is the tube diameter). The water cooling rate is > 10°C / min.

[0033] The solution treatment carried out according to the method of the present invention can eliminate the internal stress of the forging produced by radial forging production, prevent stress cracking, and avoid the precipitation of harmful phases in the forging.

[0034] According to a third aspect of the present invention, the present invention also provides application of the above-mentioned duplex stainless steel tube in oil and gas production.

[0035] In some preferred embodiments, the duplex stainless steel tube is used to produce oil pipelines for oil and gas production projects.

[0036] Example

[0037] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. In the following examples, the experimental methods without specific conditions are based on conventional methods and conditions.

[0038] Table 1 Summary of the composition of stainless steel pipes in Examples 1-3 (wt%)

[0039]

[0040] Example 1

[0041] Molten steel is smelted using the "EAF + AOD" process, and then mold-cast to produce ingots. The composition is shown in the table above. The ingots are then processed through the "blank preparation + rough pipe preparation + finished pipe preparation" process to produce duplex stainless steel pipes for oil and gas production.

[0042] The die casting ingot uses a 3-ton round ingot, the diameter of the radial forging tube is 140mm, the radial forging start temperature is 1210℃, the final forging temperature is 985℃, the solution treatment temperature is 1040℃, the furnace dwell time is 130min, and the cooling rate is 20℃ / min.

[0043] According to the room temperature mechanical properties test of ASMT A370, the tensile strength of the pipe is 953MPa, which exceeds the ISO 13680 standard 125 steel grade (≥896MPa).

[0044] The corrosion performance was tested according to ASTM 923C method, and the corrosion rate was 5.24mdd, which was qualified (≤10mdd).

[0045] Example 2

[0046] Molten steel is smelted using the "EAF + AOD" process, and then mold-cast to produce ingots. The composition is shown in the table above. The ingots are then processed through the "blank preparation + rough pipe preparation + finished pipe preparation" process to produce duplex stainless steel pipes for oil and gas production.

[0047] The die casting ingot uses a 4.5-ton round ingot, the diameter of the radial forging tube is 280 mm, the radial forging start temperature is 1240 ° C, the final forging temperature is 990 ° C, the solution treatment temperature is 1050 ° C, the furnace time is 180 min, and the cooling rate is 15 ° C / min.

[0048] According to the room temperature mechanical properties test of ASMT A370, the tensile strength of the pipe is 962MPa, which exceeds the ISO 13680 standard 125 steel grade (≥896MPa).

[0049] The corrosion performance was tested according to ASTM 923C method, and the corrosion rate was 6.12mdd, which was qualified (≤10mdd).

[0050] Example 3

[0051] Molten steel is smelted using the "EAF + AOD" process, and then mold-cast to produce ingots. The composition is shown in the table above. The ingots are then processed through the "blank preparation + rough pipe preparation + finished pipe preparation" process to produce duplex stainless steel pipes for oil and gas production.

[0052] The die casting ingot uses a 4.5-ton round ingot, the diameter of the radial forging tube is 320 mm, the radial forging start temperature is 1250 ° C, the final forging temperature is 997 ° C, the solution treatment temperature is 1050 ° C, the furnace time is 200 min, and the cooling rate is 12 ° C / min.

[0053] According to the room temperature mechanical properties test of ASMT A370, the tensile strength of the pipe is 965MPa, which exceeds the ISO 13680 standard 125 steel grade (≥896MPa).

[0054] The corrosion performance was tested according to ASTM 923C method, and the corrosion rate was 4.95mdd, which was qualified (≤10mdd).

[0055] The present invention has been disclosed above with reference to preferred embodiments. However, those skilled in the art will appreciate that these embodiments are intended only to illustrate the present invention and are not to be construed as limiting the scope of the present invention. It should be noted that any equivalent variations and substitutions to these embodiments are to be considered encompassed within the scope of the claims of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope defined in the claims.

Claims

1. A duplex stainless steel tube, characterized in that: Prepared by the following method: (1) Using the "EAF+AOD" process to smelt molten steel, and then obtaining mold casting ingots through mold casting; The mold casting ingot comprises, by weight percentage: C≤0.028%; Si≤0.70%; Mn≤1.50%; P≤0.030%; S≤0.010%; Cr 22.2-23.0%; Ni 5.5-6.5%; Mo 3.0-3.5%; Al≤0.10%; N 0.10-0.20%; balance Fe; 36≤(Cr+3.3Mo+16N)≤39; 2.5≤Si+Al / (C+N)≤4; (2) radially forging the die-cast ingot to obtain a tube blank having a diameter of 120 to 350 mm; Among them, the starting temperature of radial forging is 1200-1250℃, and the final forging temperature is controlled above 980℃; (3) Solution treatment is performed on the tube blank, and water cooling is performed to room temperature after the solution treatment; The solution treatment temperature is 1020-1080°C; when the diameter of the tube is 120 mm or less and the diameter of the tube is less than 150 mm, the dwelling time is 120 min ± 10 min; when the diameter of the tube is 150 mm or less and the diameter of the tube is less than 350 mm, the dwelling time is (120 + the diameter of the tube / 4) min ± 10 min, and the cooling rate of the water cooling is greater than 10°C / min; The tensile strength of the duplex stainless steel tube can reach above 950 MPa, and the duplex stainless steel tube has good corrosion resistance in the oil and gas production environment.

2. The duplex stainless steel tube according to claim 1, characterized in that: Calculated by weight percentage, it includes: C 0.010-0.025%; Si 0.40-0.60%; Mn 1.20-1.50%; Cr 22.2-22.5%; Ni 5.5-5.8%; Mo 3.1-3.3%; Al 0.07-0.10%; and N 0.17-0.20%.

3. Use of the duplex stainless steel tube blank according to claim 1 in oil and gas production.

4. The use according to claim 3, characterized in that The duplex stainless steel tube blank is used for preparing oil pipelines for oil and gas production projects.

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