A method of manufacturing a seamless steel pipe for sour service L290NG pipeline resistant to delayed fracture

Abstract

The application discloses a manufacturing method of a seamless steel pipe for a ductile fracture resistant and acid service L290NG pipeline, adopts a L290NG pipeline pipe round pipe blank, and the mass fraction of the specified chemical components of the round pipe blank is as follows: C 0.09-0.12%, Si 0.20-0.30%, Mn 1.30-1.45%, P≤0.015%, S≤0.003%, V 0.03-0.05%, and the rest is Fe and inevitable impurities; and the technological process is briefly described as follows: pipe blank heating, piercing, continuous rolling, sizing, cooling, sawing, flaw detection, water pressure, artificial inspection and detection analysis. The application aims at improving the strength and impact toughness of the material and greatly reducing the alloy cost.

Description

Technical Field

[0001] This invention relates to the field of ferrous metal smelting and metal pressure processing technology, and in particular to a method for manufacturing seamless steel pipes for L290NG pipelines with resistance to ductile fracture and acidic service. Background Technology

[0002] With the continuous expansion of the West-East Gas Pipeline Project, the number of newly built and put into operation natural gas transmission stations in various regions has gradually increased in recent years. L290NS grade pipeline pipes are widely used in acidic service and hydrogen pipeline projects, possessing excellent mechanical and technological properties. With the development of gas storage and transportation technology, L290NS grade pipeline pipes have been successfully laid in various geological and geomorphologically complex environments. There is a large market demand for this series of seamless steel pipes. This invention provides an economical method for manufacturing L290NG acidic service seamless steel pipes with ductile fracture resistance, achieving economical online normalizing process production, improving product cost-effectiveness while realizing low-carbon production and enhancing product market competitiveness. Summary of the Invention

[0003] To address the aforementioned technical problems, the present invention aims to provide a method for manufacturing seamless steel pipes for L290NG pipelines in acid-resistant applications with resistance to ductile fracture. The purpose of this invention is to improve the strength and impact toughness of the material while significantly reducing alloy costs.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] This invention discloses a method for manufacturing seamless steel pipes for L290NG pipelines with resistance to ductile fracture and acidic service. The method uses a round tube blank for L290NG pipelines. The specified chemical composition of the round tube blank is as follows: C 0.09-0.12%, Si 0.20-0.30%, Mn 1.30-1.45%, P≤0.015%, S≤0.003%, V 0.03-0.05%, with the remainder being Fe and unavoidable impurities. The process flow is briefly described as follows: tube blank heating → piercing → continuous rolling → sizing → cooling → sawing → flaw detection → hydrostatic testing → manual inspection → testing and analysis; wherein:

[0006] The round billet is loaded into an annular heating furnace and heated in three stages: preheating, heating, and soaking. The preheating temperature is 790–980℃, the heating temperature is 960–1180℃, and the soaking temperature is 1200–1260℃. The soaked round billet is then pierced by a piercing mill, continuously rolled on a φ460mm PQF hot continuous rolling mill, and sized by a sizing mill. The rolling rhythm is controlled to ensure that the temperature of the seamless steel pipe coming out of the sizing mill is above 850℃. Subsequently, the steel pipe is air-cooled on a cooling bed and cut to length according to the required dimensions. After flaw detection, hydrostatic testing, manual inspection, and mechanical property testing and analysis, the finished L290NG seamless steel pipe for acidic service pipelines is produced online if the dimensional accuracy, surface quality, chemical composition, and mechanical properties are qualified.

[0007] Furthermore, carbon equivalent (CE) pcm ≤0.19.

[0008] Furthermore, the specified chemical composition of the round tube blank is as follows: C 0.11%, Si 0.25%, Mn 1.32%, P 0.011%, S 0.002%, V 0.033%, with the remainder being Fe and unavoidable impurities.

[0009] Furthermore, the specified chemical composition of the round tube blank is as follows: C 0.09%, Si 0.24%, Mn 1.34%, P 0.013%, S 0.003%, V 0.031%, with the remainder being Fe and unavoidable impurities.

[0010] Furthermore, the specified chemical composition of the round tube blank is as follows: C 0.10%, Si 0.25%, Mn 1.31%, P 0.012%, S 0.002%, V 0.032%, with the remainder being Fe and unavoidable impurities.

[0011] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0012] The chemical composition of this invention adopts a C+Mn+V alloying system, which provides a combination of solid solution strengthening and grain refinement strengthening, thereby improving the strength and impact toughness of the material while significantly reducing the cost of the alloy. Low-carbon production is achieved by producing L290NG with a wall thickness of less than 16mm through an online normalizing process. The product performance meets the requirements of API 5L standard, and the carbon equivalent CEpcm in the steel is ≤0.19.

[0013] Furthermore, the process described in this invention results in excellent performance of the steel pipe, with specific performance indicators as follows:

[0014] Yield strength: 300~350MPa; Tensile strength: 450~500MPa; Yield-to-tensile ratio: ≤0.85; Elongation: ≥36%; Transverse impact value at 0℃: AKV≥150J / cm 2 Grain size: ≥7.5 grade; impact test shear area ratio ≥85%. Attached Figure Description

[0015] The present invention will be further described below with reference to the accompanying drawings.

[0016] Figure 1 This is a microscopic tissue photograph of Example 1;

[0017] Figure 2 This is a microscopic tissue photograph of Example 2;

[0018] Figure 3 This is a microscopic tissue photograph of Example 3. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to Examples 1 to 3.

[0020] The L290NG pipeline round billet with qualified chemical composition and quality ensures that the carbon equivalent CEpcm in the steel is ≤0.19.

[0021] The production process sequence is as follows: billet heating → piercing → continuous rolling → sizing → cooling → sawing → flaw detection → hydrostatic testing → manual inspection → testing and analysis.

[0022] The specific production process is briefly described below:

[0023] 1. Produce L290NG pipeline round billets with qualified chemical composition and quality, so that the carbon equivalent CEpcm in the steel is ≤0.19.

[0024] 2. The round tube blank is loaded into the annular heating furnace and heated through three sections: preheating section, heating section, and soaking section. The temperature of the preheating section is 790~980℃, the temperature of the heating section is 960~1180℃, and the temperature of the soaking section is 1200~1260℃.

[0025] 3. The round tube billet exits the annular heating furnace and is sent to the piercing mill for piercing. The consistency of the piercing mill body and the front and rear rolling center lines is ensured, and the temperature after piercing is ≥1180℃.

[0026] 4. After piercing, the tube is fed into the φ460mm PQF hot continuous rolling mill for continuous rolling, ensuring that the temperature of the tube before entering the continuous rolling mill is ≥960℃.

[0027] 5. Depending on the wall thickness of the steel pipe, the sizing unit selects different numbers of frames for sizing to ensure that the temperature of the steel pipe after sizing is ≥850℃.

[0028] 6. After the steel pipes leave the sizing unit, they are air-cooled on the cooling bed. After being air-cooled to room temperature, they are sawed, inspected for flaws, subjected to water pressure, and manually inspected. Samples are then taken for testing and analysis of chemical composition and mechanical properties.

[0029] Seamless steel pipes for acid-resistant pipelines of L245NG with the following specifications (outer diameter × wall thickness × length): Ф406.4mm × 12.7mm × 12000mm (Example 1), Ф355.6mm × 11mm × 12000mm (Example 2), and Ф406.4mm × 12mm × 11500mm (Example 3) produced by online normalizing process were sampled and tested. The chemical composition analysis results (weight percentage content) are shown in Table 2, the mechanical property test results are shown in Table 3, the metallographic property test results are shown in Table 4, and the microstructure photographs are shown in [Table missing]. Figures 1-3 As shown.

[0030] Table 2. Chemical composition test results of the tube blank (wt%)

[0031] C Si Mn P S V <![CDATA[CE pcm ]]> Example 1 0.11 0.25 1.32 0.011 0.002 0.033 0.145 Example 2 0.09 0.24 1.34 0.013 0.003 0.031 0.146 Example 3 0.10 0.25 1.31 0.012 0.002 0.032 0.155

[0032] Table 3. Mechanical property test results of seamless steel pipes

[0033] <![CDATA[R t0.5 (MPa)]]> <![CDATA[R m (MPa)]]> <![CDATA[R t0.5 / R m ]]> A(％) <![CDATA[A KV (0℃, horizontal,]]> Shear area ratio, % Example 1 321 460 0.70 40 167,181,183 100,100,100 Example 2 332 465 0.71 42 167,183,173 100,100,100 Example 3 325 467 0.70 43 178,179,191 100,100,100

[0034] Table 4. Metallographic Performance Test Results of Seamless Steel Pipes (Grade)

[0035]

[0036] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for manufacturing a seamless steel pipe for L290NG pipelines with resistance to ductile fracture and acidic service, characterized in that: The L290NG pipeline tube blank is used, and the specified chemical composition of the blank is as follows (mass fraction): C 0.09-0.11%, Si 0.24-0.25%, Mn 1.31-1.34%, P≤0.015%, S≤0.003%, V 0.031-0.033%, with the remainder being Fe and unavoidable impurities. The process flow is briefly described as follows: blank heating → piercing → continuous rolling → sizing → cooling → sawing → flaw detection → hydrostatic testing → manual inspection → testing and analysis; wherein: The round billet is loaded into an annular heating furnace and heated in three stages: preheating, heating, and soaking. The preheating temperature is 790–980℃, the heating temperature is 960–1180℃, and the soaking temperature is 1200–1260℃. The soaked round billet is then pierced by a piercing mill, continuously rolled on a φ460mm PQF hot continuous rolling mill, and sized by a sizing mill. The rolling rhythm is controlled to ensure that the temperature of the seamless steel pipe exiting the sizing mill is above 850℃. Subsequently, the steel pipe is air-cooled on a cooling bed and cut to length according to the required dimensions. After flaw detection, hydrostatic testing, manual inspection, and mechanical property testing and analysis, the finished L290NG seamless steel pipe for acidic service pipelines is produced online if the dimensional accuracy, surface quality, chemical composition, and mechanical properties are qualified.

2. The method for manufacturing seamless steel pipe for L290NG pipelines with resistance to ductile fracture and acidic service according to claim 1, characterized in that: Carbon Equivalent (CE) pcm ≤0.

19.

3. The method for manufacturing seamless steel pipe for acid-resistant L290NG pipelines with ductile fracture resistance according to claim 1, characterized in that: The specified chemical composition of the round tube blank is as follows: C 0.11%, Si 0.25%, Mn 1.32%, P 0.011%, S 0.002%, V 0.033%, with the remainder being Fe and unavoidable impurities.

4. The method for manufacturing seamless steel pipe for L290NG pipelines with resistance to ductile fracture and acidic service according to claim 1, characterized in that: The specified chemical composition of the round tube blank is as follows: C 0.09%, Si 0.24%, Mn 1.34%, P 0.013%, S 0.003%, V 0.031%, with the remainder being Fe and unavoidable impurities.

5. The method for manufacturing seamless steel pipe for L290NG pipelines with resistance to ductile fracture and acidic service according to claim 1, characterized in that: The specified chemical composition of the round tube blank is as follows: C 0.10%, Si 0.25%, Mn 1.31%, P 0.012%, S 0.002%, V 0.032%, with the remainder being Fe and unavoidable impurities.

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