High-strength seamless line pipe resistant to oil and gas field microbial corrosion and having yield strength of 360~600mpa and its production method

Abstract

The present application belongs to the field of production of pipeline pipes for oil and gas industry transportation, and relates to a seamless pipeline pipe with yield strength of 360-600 MPa and oil and gas field microbial corrosion resistance and a preparation method thereof, the components are calculated according to percentage by weight: C 0.01-0.08%, Si 0.20-0.60%, Mn 0.20-0.80%, Nb 0.010-0.050%, V 0.01-0.05%, Mo 0.020-0.30%, Ni 0.03-0.30%, Cr 2.80-3.30%, Cu≤0.2%, Ti 0.008-0.030%, O≤0.0040%, CEpcm≤0.25%, and the rest is Fe and inevitable inclusions. The pipeline pipe product of the present application can achieve high dimensional accuracy, high performance stability, high toughness and high ductility, and has excellent microbial corrosion resistance and low temperature toughness.

Description

Technical Field

[0001] This invention belongs to the field of pipeline production for oil and gas transportation, and particularly relates to a high-strength seamless pipeline with a yield strength of 360~600MPa that is resistant to microbial corrosion in oil and gas fields and its preparation method. Background Technology

[0002] Microbial corrosion is one of the main failure modes in oil and gas pipelines, with localized corrosion being a primary characteristic, especially pitting corrosion leading to perforation. A typical microbial group involved is sulfate-reducing bacteria (SRB), which produce hydrogen sulfide (H2S) through their metabolic activities, leading to hydrogen-induced cracking (HIC) and stress corrosion cracking (SSC). Currently, the conventional corrosion prevention method used in oil and gas fields involves adding bactericides to carbon steel. This requires continuous and regular application of bactericides, and the development of bacterial resistance necessitates periodic replacement of the bactericide. This method involves large-scale investment and also poses potential environmental impacts.

[0003] Currently, existing technologies for improving the resistance to microbial corrosion from the perspective of the material itself mainly focus on adding high Cu content. For example, Chinese patent CN110184536A improves resistance to microbial corrosion by increasing Cu content. The mechanism involves using the biotoxicity of Cu ions to inhibit the formation and growth of SRB biofilms. Some solutions also use aging treatment to precipitate Cu-rich phases to further enhance corrosion resistance. However, for seamless pipeline pipes, increasing Cu content significantly deteriorates their hot working properties, leading to rolling defects such as cracks, scale, and outward folds, increasing the difficulty and cost of the rolling process. Achieving stable production of high Cu alloys under piercing-continuous rolling processes presents significant technical obstacles.

[0004] To avoid the processing problems caused by adding high levels of Cu, existing technologies also include adding high levels of corrosion-resistant alloying elements such as Cr, Mo, and Ni to improve the corrosion resistance of pipeline pipes. While this approach can improve corrosion performance to some extent, its alloy cost is high, making it difficult to meet the demand for economical pipe materials in the oil and gas transportation sector.

[0005] In addition, microbial corrosion in actual service environments is often accompanied by CO2 and Cl. -The synergistic effect of multiple corrosive media, including H2S, makes corrosion behavior more complex. Existing technologies for pipelines resistant to microbial corrosion mostly focus on performance verification under single SRB (Self-Strain Boring) environments, lacking sufficient research on corrosion behavior under multi-factor coupled conditions, making it difficult to comprehensively guide practical engineering applications. Yield strength ranges from 360 to 600 MPa, including steel grades X52 / L360, X56 / L390, X60 / L415, X65 / L450, and X70 / L485. Among these, X52 / L360 and X60 / L415 are commonly used grades for onshore transportation, especially in high-pressure environments. Higher strength increases susceptibility to bacterial corrosion, leading to more prone hydrogen embrittlement and stress corrosion.

[0006] Therefore, how to achieve a balance between the material's resistance to microbial corrosion and its manufacturing cost without over-reliance on expensive alloying elements has become a pressing technical challenge in this field. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a seamless pipeline pipe with a yield strength of 360~600MPa that is resistant to microbial corrosion in oil and gas fields, and its preparation method. This invention aims to meet the demand for microbial corrosion resistant pipe materials for oil and gas field transportation pipelines, while also considering mechanical properties, economic costs, and adaptability to thermal processing. It also solves problems such as localized corrosion and leakage caused by microbial corrosion in pipeline pipes under certain operating environments.

[0008] The technical problem solved by this invention is achieved through the following technical solution: This invention discloses a seamless pipeline with a yield strength of 360~600MPa and resistance to microbial corrosion in oil and gas fields. The chemical composition and weight percentage of the seamless pipeline are as follows: C 0.01~0.08%, Si 0.20~0.60%, Mn 0.20~0.80%, Nb 0.010~0.050%, V 0.01~0.05%, Mo 0.020~0.30%, Ni 0.03~0.30%, Cr 2.80~3.30%, Cu≤0.2%, Ti 0.008~0.030%, O≤0.0040%, Al≤0.040%; B≤0.0005%, P≤0.020%, S≤0.005%, CEpcm≤0.25%, with the remainder being Fe and unavoidable inclusions.

[0009] Preferably, the seamless pipeline has a yield strength of 360~600MPa, a tensile strength of 460~760MPa, a yield-to-tensile ratio of ≤0.90, a ductile-brittle transition temperature of ≤-60℃, a strength fluctuation of ≤120MPa, an elongation of ≥30%, a transverse full-size impact energy of greater than 200J at -10℃, and a hardness of ≤250HV10.

[0010] Preferably, the seamless pipeline tube has a dual-phase microstructure consisting of tempered bainite and tempered sorbite.

[0011] Another aspect of the present invention discloses a method for preparing the above-mentioned seamless pipeline tube, comprising: (1) Smelting Using the aforementioned chemical composition and weight percentage content, the material is smelted in an EAF electric furnace, refined in an LF ladle, and vacuum treated with AOD. The billet is then continuously cast, forged, or rolled, and the billet is pit-cooled to below 200°C. (2) Rolling The billet prepared in step (1) is subjected to cold centering, ring furnace heating, tube billet descaling, hot centering, piercing-continuous rolling, tube removal, high-pressure water descaling, hot sizing, cold straightening, and flaw detection processes in sequence to obtain rolled tube; the ring furnace heating temperature is 1200-1280℃, and the sizing temperature is >800℃; (3) Heat treatment The heat treatment process is quenching and tempering, in which the rolled tube is sequentially subjected to high-temperature walking beam heating, high-temperature quenching, high-pressure water descaling, high-temperature tempering, high-pressure water descaling, and high-temperature hot straightening, and then the entire tube is air-cooled on a cooling bed to obtain a seamless pipeline tube.

[0012] Preferably, the forging ratio of the forging or the rolling ratio of the rolling in step (2) is ≥3.

[0013] Preferably, an MPM continuous rolling mill, a PQF continuous rolling mill (including 168PQF, 258PQF, 460PQF, 508PQF, etc.) or a 720REM spin-expanding mill is used, wherein the 720REM uses the mother tube produced by the PQF rolling mill as raw material for skew rolling and spin-expanding.

[0014] Preferably, the high-temperature walking beam heating adopts a high-temperature walking beam furnace, a double cross-limiting proportional control method, a slightly positive pressure reducing atmosphere, and a furnace pressure ≤10Pa.

[0015] Preferably, the quenching temperature is 900-950℃, the holding time is ≥15min, the water temperature is ≤30℃, the tempering temperature is 600-700℃, the holding time is ≥20min, and the high-pressure water descaling pressure is 10~22MPa.

[0016] The specific optimized chemical composition is explained below: C: Limit its content, considering welding performance and corrosion resistance, so its content is controlled within the range of 0.01~0.08%.

[0017] Si: Considering toughness and corrosion resistance, its content is controlled within the range of 0.20% to 0.60%.

[0018] Mn: a strength element. Considering low-temperature toughness and corrosion resistance, its content is controlled within the range of 0.20% to 0.80%.

[0019] Nb: A microalloying element that refines grains and improves corrosion resistance. Its content should be controlled within the range of 0.010–0.050%.

[0020] V: A microalloying element that enhances the strength of steel through precipitation strengthening. The V content should be controlled within the range of 0.01% to 0.05%.

[0021] Ti: A microalloying element that refines grains and improves strength and surface quality. Its content is controlled between 0.008% and 0.030%. Micro-Ti treatment improves the thermoplasticity of steel pipes and ensures their surface quality by adding a small amount.

[0022] Cr: A strong basic element, Cr is the core corrosion-resistant element and a fundamental alloying element that improves corrosion resistance. It can combine with microbial biofilms to form a protective film on the surface of steel pipes, preventing further corrosion and pitting. Excessive Cr content will worsen the weldability of steel; therefore, the Cr content is controlled within the range of 2.8% to 3.30%. Mo: An alloying element that improves strength and corrosion resistance. It should be added appropriately according to the wall thickness of the steel pipe, and its content should be controlled within the range of 0.02% to 0.30%.

[0023] Ni: An alloying element that improves strength, corrosion resistance, and low-temperature toughness. Its content should be controlled within the range of 0.05% to 0.30%.

[0024] Cu: A residual element that affects carbon equivalent and welding performance; its content should be controlled within the range of ≤0.20%.

[0025] O: Gaseous element. Considering corrosion performance, surface quality, etc., the content should be controlled as low as possible, O≤0.0040%.

[0026] The other elements include Al, B, P, and S, and the weight percentages of the components in the other elements satisfy the following: Al ≤ 0.040%; B ≤ 0.0005%, P ≤ 0.020%, and S ≤ 0.005%.

[0027] This invention focuses on the combination of the steel pipe surface with a microbial corrosion biofilm to form a protective film that inhibits biofilm growth. The main strengthening mechanisms are structural strengthening, precipitation strengthening, and grain refinement. Low-carbon Cr elements combined with V+Nb microalloying and controlled texture ensure good resistance to microbial corrosion within a certain microbial content range. This invention differs from existing high-Cu microbial corrosion resistant pipeline steel technologies. Existing technologies utilize the biotoxicity of Cu ions to inhibit the formation and growth of SRB biofilms, while this invention controls Cu as a residual element rather than a functional element (≤0.20%). Cr (2.80~3.30%) combines with the microbial biofilm to form a protective film on the steel pipe surface, preventing further corrosion and pitting. While Cr provides basic corrosion resistance, the addition of microalloying elements such as V (0.01~0.05%), Nb (0.010~0.050%) and Ti (0.008~0.030%) creates a synergistic strengthening effect through grain refinement (Nb / Ti), precipitation strengthening (V / Nb), and improved thermoplasticity (Ti microtreatment), ensuring a yield strength of 360~600MPa under low carbon equivalent (CEpcm≤0.25%) conditions.

[0028] In terms of rolling technology, considering the hot working characteristics of the above-mentioned composition system, high-precision continuous rolling mills (MPM or PQF continuous rolling mills or 720REM spin expanders) are used to ensure the uniformity of outer diameter, wall thickness, and inner and outer surface quality by optimizing the pass profile and matching rolling tools, thus achieving consistency in the dimensional accuracy and surface quality of the steel pipe. Combined with a process window of ring furnace heating temperature >1225℃ and sizing temperature >800℃, and through full-process control of piercing-continuous rolling-tube removal-sizing, high-precision pipes with wall thickness uniformity ≤20%t and outer diameter out-of-roundness ≤3mm are obtained, providing a dimensional prerequisite for the uniformity of microstructure in subsequent heat treatment.

[0029] In terms of heat treatment process, quenching and tempering are employed to optimize the heat treatment process for long materials, ensuring precise temperature control, sufficient hardenability, and stable microstructure transformation. This achieves the dimensional accuracy and performance stability of the heat-treated material, meeting the application performance requirements of oil and gas pipelines in microbial environments. Specifically, a tempering treatment route of quenching (≥900℃ holding ≥15min, water temperature ≤30℃) + high-temperature tempering (≥600℃ holding ≥20min, air cooling) is adopted. During the quenching stage, alloying elements such as Cr and Mo are fully dissolved, resulting in a fine lath martensite structure. During the high-temperature tempering stage, the martensite decomposes into a dual-phase structure of tempered bainite + tempered sorbite. Among them, tempered sorbite provides a good balance of strength and toughness and low-temperature toughness (ductile-brittle transition temperature ≤-60℃), while retaining a certain proportion of fine tempered bainite helps maintain a high strength level (yield-to-tensile ratio ≤0.90). By using the dual-cross limiting ratio control of the walking beam furnace and the micro-positive pressure reducing atmosphere (furnace pressure ≤10Pa), the furnace temperature uniformity (holding section ±10℃) and hardenability are ensured, achieving performance stability with strength fluctuation ≤120MPa after heat treatment.

[0030] In summary, this invention uses Cr as the core corrosion-resistant element, V+Nb+Ti microalloying to synergistically compensate for strength, and high-precision rolling + quenching and tempering as process assurance, forming a complete technical chain from composition design to process control to performance output. It solves the problems of poor hot workability of existing high Cu solutions, high cost of high Cr / Mo / Ni solutions, and insufficient multi-factor corrosion verification.

[0031] The advantages and positive effects of this invention are: (1) This invention uses low Cr (2.80~3.30%) to replace high Cu as the core corrosion-resistant element, and Cu is only used as a residual element and controlled at ≤0.20%, which effectively avoids rolling defects such as hot working cracks, scabs, and outward folds caused by the addition of high Cu. At the same time, the addition of Mo (0.020~0.30%) and Ni (0.03~0.30%) is low, and no special elements such as Cu, Ga, and Ce are added, which significantly reduces the cost of the alloy.

[0032] (2) The present invention adopts a quenching and tempering treatment route of quenching + high temperature tempering to obtain a dual-phase structure of tempered bainite + tempered sorbite, achieving a good balance of strength and toughness. By controlling the double cross-limit ratio of the walking beam furnace and the micro-positive pressure reducing atmosphere, the furnace temperature uniformity and hardenability are ensured, achieving performance stability with strength fluctuation ≤120MPa.

[0033] (3) The high-strength seamless pipeline pipe of the present invention, which is resistant to microbial corrosion in oil and gas fields and has a pressure range of 360~600MPa, can meet the transportation pressure range of up to 10MPa, and the SRB (sulfate-reducing bacteria) concentration is >10. 4The test was conducted for 720 hours in an environment with SRB concentration > 10 μL and total pressure > 6 MPa. The average corrosion rate was < 0.015 mm / a, and the maximum pitting depth was < 10 μm. 4 It produces a product with a per-L capacity, increasing the CO2 partial pressure environment to a maximum of 0.8MPa, an average corrosion rate of <0.076mm / a, a maximum pitting depth of <25μm, and achieving high dimensional accuracy (outer diameter tolerance ±1.6mm, out-of-roundness ≤3mm), high performance stability (strength fluctuation range ≤120MPa), high toughness (ductile-brittle transition temperature ≤-60℃), high ductility (elongation ≥30%), and high resistance to SSC corrosion (80% AYS four-point bending for 720 hours without fracture). It exhibits excellent resistance to microbial corrosion. Yield strength 360~600MPa, tensile strength 460~760MPa, elongation ≥30%, yield strength ratio ≤0.90, hardness ≤250HV10, strength fluctuation ≤120MPa, transverse impact energy at -10℃ >200J, and ductile-brittle transition temperature ≤-60℃. Attached Figure Description

[0034] Figure 1 This is a magnified 500x micrograph of the tissue from Example 1; Figure 2 The image shows the surface pitting morphology and depth of the seamless pipeline in Example 1 after it was corroded by a pure bacterial environment, magnified 100 times.

[0035] Figure 3 The ductile-brittle transition temperature curve is shown for the seamless pipeline tube in Example 1. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0037] A seamless pipeline pipe with a yield strength of 360~600MPa and resistant to corrosion by microorganisms in oil and gas fields has the following chemical composition and weight percentage content: C: 0.01~0.08%, Si: 0.20~0.60%, Mn: 0.20~0.80%, Nb: 0.010~0.050%, V: 0.01~0.05%, Mo: 0.020~0.30%, Ni: 0.03~0.30%, Cr: 2.80~3.30%, Cu≤0.2%, Ti: 0.008~0.030%, Al≤0.040%; B≤0.0005%, P≤0.020%, S≤0.005%, O≤0.0040%, CEpcm≤0.25%, with the remainder being Fe and unavoidable inclusions.

[0038] The preparation method includes smelting, rolling, heat treatment, and steel pipe processing; details are as follows: 1. Smelting process The smelting process adopts a short-process electric arc furnace smelting six-strand square-round billet continuous casting process, including: (1) High-quality scrap steel, pig iron and molten iron are used as raw materials according to chemical composition and weight percentage content, and hot charging process is used for molten iron. (2) The UHP-EAF ultra-high power electric arc furnace has a unique power supply system, furnace wall water-cooled carbon and oxygen spray gun, foam slag submerged arc smelting operation process, and eccentric furnace bottom steel tapping. (3) A single-cover double-station ladle refining furnace is used to heat the molten steel, adjust the composition and temperature of the molten steel, create white slag, and use argon blowing and stirring to deoxidize and desulfurize, promote the floating of non-metallic inclusions in the molten steel, and uniformly adjust the composition and temperature of the molten steel. (4) AOD vacuum degassing process; (5) Continuous casting, forging or rolling of round billets (forging ratio or rolling ratio ≥3), and the billet is pit-cooled to below 200 ℃.

[0039] 2. Rolling process The round billet obtained in step 1 is subjected to the following processes in sequence: cold centering, ring furnace heating, billet descaling, hot centering, piercing-continuous rolling (two-roll 250MPM or three-roll 168PQF, 258PQF, 460PQF, 508PQF continuous rolling mill), tube removal, high-pressure water descaling, hot sizing, cold straightening, and flaw detection, ensuring that the obtained tube wall thickness non-uniformity is ≤20% and ovality is ≤1%; specifically including: (1) Ring furnace heating: control the heating temperature to 1200-1280℃; (2) Centering: divided into cold centering and hot centering; a six-set centering roller automatic centering hydraulic hot centering machine to ensure the quality of tube blank centering, thereby improving the accuracy of tube wall thickness; (3) Two-roll skew rolling conical piercing mill or mushroom piercing mill, guide plate or guide plate, through the tube blank piercing preparation, secondary biting and piercing, tube wall reduction, flattening inner and outer surfaces, uniform wall thickness and rounding process, so that the tube blank becomes a tube with the required size. (4) Continuous rolling in two-roll MPM or three-roll PQF continuous rolling mills; (5) Tube removal machine: removes the rough tube from the mandrel and increases the final rolling temperature.

[0040] (6) Sizing achieves the final size. Micro-tension sizing units with 14 single stands or 10 single stands are used. The maximum reduction rate of a single stand is 1.9%, and the maximum total reduction rate is 15.1%, which improves the surface quality of the steel pipe.

[0041] (7) The cold straightening machine adopts the cold deformation process and adopts a vertical 2-2-2 six-roll cold straightening machine with skew rolls. The 720REM skew rolling and expansion process uses the mother tube provided by the 460PQF or 508PQF hot rolling process, which is heated in a walking beam furnace, skew rolling and expansion, and four sets of cold rolling rolls are used to cold sizing the steel pipe to form a uniform wall thickness.

[0042] 3. Heat treatment process The heat treatment process includes high-temperature walking beam heating, high-pressure water descaling, high-temperature quenching, high-temperature tempering, high-pressure water descaling, high-temperature hot straightening, and air cooling of the entire tube on a cooling bed.

[0043] The high-temperature walking beam heating system utilizes a high-temperature walking beam furnace with sub-high-speed burners. The highest furnace temperature reaches 1100℃. The maximum temperature deviation in the high-temperature walking beam heating section is ±20℃, and in the holding section, it is ±10℃. To ensure uniform furnace temperature, the furnace pressure should be maintained at a slightly positive pressure during normal production, typically 3-5 Pa, with a controlled pressure ≤10 Pa, to prevent outside air from entering the furnace. High-pressure water descaling devices are installed at the outlet of the quenching furnace and high-temperature tempering furnace. The descaling water pressure is adjusted to 10-22 MPa to remove iron oxide scale from the outer surface, improving surface quality. The high-pressure water descaling devices are adjusted appropriately, selecting suitable descaling stages based on different specifications.

[0044] In this embodiment, the high-temperature walking beam heating uses a walking beam tempering furnace. The combustion system uses a sub-high-speed burner, and the burner combustion is controlled by pulse. The tempering holding time should be ≥20 min. The quenching temperature is 900-950℃, the holding time is greater than 15 min, the water temperature is ≤30℃, and the tempering temperature is 600-700℃.

[0045] As an example, in the embodiments and comparative examples, several high-strength seamless pipelines of L450QS-CM steel grade with a specification of 219.1mm×12.7mm were prepared, and their chemical compositions are shown in Table 1 and Table 2 below.

[0046] The smelting process yields a 250mm round billet, which is then rolled into a 219.1mm x 12.7mm specification using 258PQF rolling. The dimensional accuracy of the pipe is shown in Table 3.

[0047] After quenching at 940℃ and tempering at 680℃, the mechanical stability properties of the examples and comparative examples are shown in Table 4. Performance tests were conducted according to ASTM A370 standard.

[0048] The impact energy curve for Example 1 is shown below. Figure 3 Impact tests were conducted at different temperatures according to ASTM A370, and the ductile-brittle transition temperature was ≤-40℃. (SRB concentration 10) 5The test was conducted for 720 hours in an environment with a corrosion rate of 1 / L and a total pressure of 6.5 MPa. The average corrosion rate and maximum pitting depth are shown in Table 5. The average corrosion rate and maximum pitting depth were also tested in an environment with an increased CO2 partial pressure of 0.5 MPa.

[0049] Figure 1 This is a magnified image of the microstructure of Example 1 of this product after 500X magnification. After heat treatment, a metallographic sample was taken for microstructure analysis. The image was taken at a magnification of 500X. As can be seen from the image, the microstructure is uniform and the grains are fine, indicating that the microstructure is relatively uniform.

[0050] Figure 2 The surface condition of this product after pure bacterial corrosion in Example 1 is mainly observed by the pitting corrosion. The pitting pits are relatively shallow, and there is no large-area pitting corrosion, indicating good resistance to microbial corrosion.

[0051] Comparative Example 2 The only difference from Example 1 is that the Cu content is 0.50%. Under the formulation and process of this invention, the performance is not optimized with a high Cu content, and the surface quality of the steel pipe is defective, requiring local grinding.

[0052] Comparative Example 3 The only difference from Example 1 is that the Cr content is 1.5%. Under the formulation and process of this invention, if the Cr content is too low, the performance will decrease.

[0053] Comparative Example 4 The only difference from Example 1 is that the Cr content is 3.5%. Under the formulation and process of this invention, the Cr content is too high, the performance has not been further optimized, and the increase in Cr content increases the manufacturing cost.

[0054] Comparative Examples 3 and 4 highlight the non-obviousness of the Cr content range in this invention.

[0055] Table 1 Chemical composition of pipeline pipes

[0056] Note: The comparative example is a material used in a typical acidic environment. Cu is a residue from electric furnace smelting and was not intentionally added. It should be noted that the pipeline's chemical composition contains other impurity elements, as shown in Table 2: Table 2

[0057] Table 3. Dimensional tolerances for pipeline pipes

[0058] Table 4 Mechanical properties of seamless pipeline pipes

[0059] Note: The specimen type is a plate-shaped specimen with a width of 38.1 mm and a gauge length of 50 mm; Rt0.5: specified total elongation strength, MPa; Rm: tensile strength, MPa; A: elongation after fracture; Y / T: yield strength ratio.

[0060] Table 5. Average corrosion rate and maximum pitting depth under different environments.

[0061] Note: Simulated environment (40℃; CO2 partial pressure: 0.5MPa; total pressure: 10MPa (N2 supplement); solution: distilled water) The prepared SRB bacterial culture medium had a pH of 7.5 and an SRB count of 3 × 10⁻⁶. 4 The average corrosion rate was increased and the number of pitting pits decreased in the control group in the carbon dioxide-containing environment.

[0062] The above embodiments have provided a detailed description of the present invention, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent variations and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A seamless pipeline pipe with a yield strength of 360~600MPa and resistant to microbial corrosion in oil and gas fields, characterized in that, The chemical composition and weight percentage of the seamless pipeline are as follows: C 0.01~0.08%, Si 0.20~0.60%, Mn 0.20~0.80%, Nb 0.010~0.050%, V 0.01~0.05%, Mo 0.020~0.30%, Ni 0.03~0.30%, Cr 2.80~3.30%, Cu≤0.2%, Ti 0.008~0.030%, O≤0.0040%, Al≤0.040%; B≤0.0005%, P≤0.020%, S≤0.005%, CEpcm≤0.25%, with the remainder being Fe and unavoidable inclusions.

2. The seamless pipeline pipe according to claim 1, characterized in that, The seamless pipeline tube has a yield strength of 360~600MPa, a tensile strength of 460~760MPa, a yield-to-tensile ratio of ≤0.90, a ductile-brittle transition temperature of ≤-60℃, a strength fluctuation of ≤120MPa, an elongation of ≥30%, a transverse full-size impact energy of greater than 200J at -10℃, and a hardness of ≤250HV10.

3. The seamless pipeline pipe according to claim 1, characterized in that, The seamless pipeline has a dual-phase microstructure consisting of tempered bainite and tempered sorbite.

4. The seamless pipeline pipe according to claim 1, characterized in that, The seamless pipeline pipe has an SRB concentration > 10. 4 Tested for 720 hours in an environment with SRB concentration of 10 μL and total pressure > 6 MPa, the average corrosion rate was < 0.015 mm / a, and the maximum pitting depth was < 10 μm; 4 In an environment with a CO2 partial pressure of 0.5 MPa and a corrosion rate of 0.076 mm / a, the average corrosion rate is <0.076 mm / a and the maximum pitting depth is <25 μm.

5. A method for preparing a seamless pipeline pipe as described in any one of claims 1-4, characterized in that, Includes the following steps: (1) Smelting: Using the chemical composition and weight percentage content, the billet is smelted in an EAF electric furnace, refined in an LF ladle, treated in an AOD vacuum, continuously cast, forged or rolled, and the billet is pit cooled to 200°C or below. (2) Rolling: The billet obtained in step (1) is subjected to cold centering, ring furnace heating, tube billet descaling, hot centering, piercing-continuous rolling, tube removal, high-pressure water descaling, hot sizing, cold straightening, and flaw detection in sequence to obtain a rolled tube; (3) Heat treatment: The rolled tube obtained in step (2) is subjected to heat treatment, and is successively heated by high temperature walking beam, quenched at high temperature, descaled by high pressure water, tempered at high temperature, descaled by high pressure water, straightened at high temperature, and air-cooled on a cooling bed to obtain a seamless pipeline tube.

6. The preparation method according to claim 5, characterized in that, The ring furnace heating temperature is 1200~1280℃, and the sizing temperature is >800℃; the piercing-continuous rolling adopts an MPM continuous rolling mill, a PQF continuous rolling mill, or a 720REM spin-expanding mill, wherein the 720REM uses the mother tube produced by the PQF rolling mill as raw material for skew rolling and spin-expanding.

7. The preparation method according to claim 5, characterized in that, The quenching temperature is 900~950℃, the holding time is ≥15min, and the water temperature is ≤30℃; the tempering temperature is 600~700℃, the holding time is ≥20min; and the high-pressure water descaling pressure is 10~22MPa.

8. The preparation method according to claim 5, characterized in that: The high-temperature walking beam heating in step (3) adopts a high-temperature walking beam furnace, a double cross-limiting proportional control method, a slightly positive pressure reducing atmosphere, and a furnace pressure ≤10Pa.

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