Seamless steel pipe and method for producing the same

Abstract

This invention proposes a seamless steel pipe and its preparation method. The cylindrical steel billet used to prepare the seamless steel pipe comprises, by mass percentage: C 0.05%-0.1%, Si 0.15%-0.2%, Zr 0.08%-0.4%, Mn 0.2%-0.5%, P≤0.02%, S≤0.012%, Cr 2%-2.5%, Mo 0.3%-0.4%, Al 0.4%-0.6%, and Ti The content of Si:Zr is 0.4%-0.9%, with the balance being matrix Fe, wherein the mass ratio of Si:Zr is 1:(0.5-2). The preparation method of seamless steel pipe includes: firstly, heating a cylindrical steel billet to 1100-1250℃, placing it in a piercing mill, and performing piercing treatment to obtain a steel pipe billet; then, hot rolling the pierced steel pipe billet to obtain a seamless pipe billet with the target outer diameter and wall thickness; finally, pickling and phosphating the seamless pipe billet, and then continuously cold rolling the seamless pipe billet to obtain a seamless steel pipe with the target outer diameter and wall thickness. The seamless steel pipe of the present invention has good corrosion resistance to high temperature and high pressure steam and can be used as a pipe in a steam reformer.

Description

Technical Field

[0001] This invention relates to the field of seamless steel pipe manufacturing technology, and in particular to a seamless steel pipe and its manufacturing method. Background Technology

[0002] 08Cr2AlMo is a low-alloy high-temperature alloy steel with excellent high-temperature strength and creep resistance, making it suitable for high-temperature and high-pressure environments, such as related reaction equipment in the petrochemical industry.

[0003] Although 08Cr2AlMo steel pipes have good corrosion resistance to high temperature and high pressure environments, they can still be corroded under certain special conditions. For example, in steam reformers, distillation towers, and catalytic units, 08Cr2AlMo steel pipes often need to deal with high temperature and high pressure steam and other corrosive gases. In these situations, 08Cr2AlMo steel pipes are prone to water vapor corrosion. This is because, under extreme high temperature and high pressure conditions, water vapor and the oxidizing atmosphere in the water vapor will cause an oxide layer to form on the surface of the 08Cr2AlMo steel pipe. Under the influence of humidity and airflow velocity, the oxide layer is more likely to peel off, thereby increasing the rate of oxidation corrosion.

[0004] Improving the stability of 08Cr2AlMo steel pipes under high temperature and high pressure steam environment has become one of the urgent technical problems to be solved. Summary of the Invention

[0005] In view of this, the present invention proposes a seamless steel pipe and its preparation method, aiming to improve the corrosion resistance of the steel pipe in a high temperature and high pressure steam environment.

[0006] The technical solution of the present invention is implemented as follows: The present invention provides a method for preparing a seamless steel pipe, wherein the chemical composition of the seamless steel pipe comprises, by mass percentage: C 0.05%-0.1%, Si 0.15%-0.2%, Zr 0.08%-0.4%, Mn 0.2%-0.5%, P≤0.02%, S≤0.012%, Cr 2%-2.5%, Mo 0.3%-0.4%, Al 0.4%-0.6%, Ti 0.4%-0.9%, with the balance being the matrix Fe, wherein the mass ratio of Si:Zr is 1:(0.5-2).

[0007] The method for preparing this seamless steel pipe includes:

[0008] (1) Heat the cylindrical steel billet to 1100-1250℃, put it into the piercing machine, and pierce it to obtain a steel pipe billet;

[0009] (2) The steel billet after piercing is hot rolled to obtain a seamless billet with the target outer diameter and wall thickness.

[0010] (3) Pickling and phosphating are performed on the seamless tube blank, and then the seamless tube blank is continuously cold rolled to obtain a seamless steel pipe with the target outer diameter and wall thickness.

[0011] When 08Cr2AlMo seamless steel pipes are used in high-temperature steam environments, the combined effects of high temperature and steam corrosion cause various metal oxides to form on the pipe surface. In certain specific applications, the steam may contain acidic substances such as hydrogen sulfide, which react with the steel pipe to form sulfides or other metal salts. Simultaneously, alkaline substances may also corrode the pipe in the high-temperature, high-pressure steam environment, leading to the corrosion of the aluminum in the 08Cr2AlMo seamless steel pipe. The oxides and salts produced after corrosion are then washed away by the high-temperature steam flow and peeled off again, exposing the metal layer once more, only to be corroded again. In the above embodiments, by adding a certain amount of zirconium, the dense oxide formed by zirconium and silicon is used to prevent water vapor from further eroding the metal inside the seamless steel pipe. At the same time, the dense oxide formed by the alloy of zirconium and silicon has good self-healing properties. When metal oxides or salts at other sites are peeled off due to water vapor erosion, the dense oxide formed by zirconium and silicon uses this self-healing property to perform surface healing and shielding on the exposed metal after peeling, thereby improving the corrosion resistance of the seamless steel pipe in a high-temperature water vapor environment. After screening the proportions, it was found that the corrosion resistance of the seamless steel pipe is best when the mass ratio of Si:Zr is 1:(0.5-2).

[0012] In some embodiments, the mass ratio of Ti to Al in the chemical composition of the seamless steel pipe is (1-1.5):1.

[0013] In the above embodiments, one beneficial effect of adding Ti is that it can form an alloy oxide with Al. Because aluminum oxide is easily hydrolyzed under high temperature and pressure, this reduces the stability of the dense protective layer on the surface of the seamless steel pipe, making it susceptible to gradual corrosion under high temperature and pressure steam conditions. By adding Ti to form a more stable Ti-Al-O oxide, the hydrolysis of aluminum oxide is effectively prevented. Simultaneously, Ti oxides also possess good self-healing properties.

[0014] In some embodiments, in step (3), the phosphating solution used for phosphating treatment contains 5-10 g / L of copper phosphate, 30-50 g / L of zinc dihydrogen phosphate, the pH of the phosphating solution is 3-4, the temperature of the phosphating solution is 55-70°C, and the phosphating time is 4-10 min.

[0015] In the above embodiments, phosphating treatment is used to bring better corrosion resistance and wear resistance to the surface of seamless steel pipe. At the same time, some copper phosphating agent is added to the phosphating solution. By introducing some copper element, it has been verified through experiments that when a small amount of copper is added to the surface, the corrosion resistance of seamless steel pipe in water vapor environment is improved to a certain extent.

[0016] In some embodiments, the method further includes step (4) of solution treatment of the seamless steel pipe, wherein the solution treatment step includes heating the seamless steel pipe to 1180-1210°C, holding it at that temperature for 10-15 minutes, and then water cooling it.

[0017] In the above embodiments, after solution treatment, the grain size inside the seamless steel pipe is refined. Under the scouring environment of high-temperature water vapor, the point stress corrosion on the surface of the seamless steel pipe is greatly improved. In particular, under the scouring of high-temperature and high-pressure water vapor, the protective layer peeled off under stress will amplify the subsequent stress effect. However, after solution treatment, the refinement of the internal grains greatly reduces the stress concentration points formed after peeling. At the same time, combined with the self-healing ability of the alloy oxides formed by Zr and Ti with Si and Al respectively introduced above, the stress corrosion concentration points can be more easily repaired, greatly improving the corrosion resistance to water vapor.

[0018] In some embodiments, step (5) is also included to perform stress-relief annealing on the solution-treated seamless steel pipe, and the finished seamless steel pipe is obtained after passing the test.

[0019] In some embodiments, in step (5), the stress-relief annealing temperature is 450-550℃, the holding time is 10-30min, and after the holding time is completed, the temperature is air-cooled to room temperature.

[0020] In some embodiments, step (5) includes a straightening treatment at 300-400°C after stress-relief annealing and before air cooling to room temperature.

[0021] In some embodiments, the temperature of hot rolling in step (2) is 980-1100°C.

[0022] Secondly, the present invention also provides a seamless steel pipe, which is prepared by the above-described preparation method.

[0023] Thirdly, the seamless steel pipe provided by this invention can be used as a pipe for a steam reformer.

[0024] The seamless steel pipe and its preparation method of the present invention have the following advantages over the prior art:

[0025] This invention provides a seamless steel pipe prepared from 08Cr2AlMo steel billet. Zirconium and titanium are added to the billet. By using a specific ratio of zirconium and silicon, and a specific ratio of aluminum and titanium, a corresponding dense and self-healing oxide is formed on the surface of the seamless steel pipe, thereby improving the corrosion resistance of the seamless steel pipe in a high-temperature water vapor environment and further expanding the application field of 08Cr2AlMo seamless steel pipe. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiments of this invention pertain. If any definition stated in this section is contrary to or otherwise inconsistent with a definition stated in a patent, patent application, published patent application, or other publication incorporated herein by reference, the definitions listed here shall prevail over those incorporated herein by reference.

[0028] Example 1

[0029] This embodiment describes a pipe in a steam reformer, and its chemical composition and weight percentage are as follows:

[0030] C 0.0547%, Si 0.1521%, Zr 0.1514%, Mn 0.2133%, P 0.0132%, S 0.0089%, Cr 2.12%, Mo 0.3225%, Al 0.4351%, Ti 0.4268%, balance Fe matrix.

[0031] The seamless steel pipe in this embodiment is manufactured according to the following procedures:

[0032] The cylindrical steel billet with the above composition is heated to 1100℃-1250℃, placed in a piercing mill, and pierced to obtain a steel pipe billet with an outer diameter of 80mm and a wall thickness of 6mm.

[0033] The steel billet is then subjected to continuous hot rolling at a temperature of 980℃-1100℃, resulting in a seamless billet with an outer diameter of 60mm and a wall thickness of 4mm.

[0034] The seamless tube blank is pickled with hydrochloric acid, washed with water, and phosphated. The phosphate solution used for phosphate treatment contains 5 g / L copper phosphate and 30 g / L zinc dihydrogen phosphate. The pH of the phosphate solution is 3, the temperature of the phosphate solution is 55℃, and the phosphate treatment time is 5 min. After phosphate treatment, it is washed with water, filtered and dried, and then continuously cold rolled to obtain a seamless steel tube with an outer diameter of 45 mm and a wall thickness of 2 mm.

[0035] Comparative Example 1

[0036] Based on Example 1, the preparation process remains unchanged, and the chemical composition and weight percentage of the cylindrical steel billet are as follows:

[0037] C 0.0526%, Si 0.1533%, Mn 0.2142%, P 0.0128%, S 0.0085%, Cr 2.11%, Mo 0.3148%, Al 0.4289%, Ti 0.4277%, balance Fe matrix.

[0038] Comparative Example 2

[0039] Based on Example 1, the preparation process remains unchanged, and the chemical composition and weight percentage of the cylindrical steel billet are as follows:

[0040] C 0.0532%, Si 0.1531%, Zr 0.1518%, Mn 0.2134%, P 0.0130%, S 0.0086%, Cr 2.12%, Mo 0.3217%, Al 0.4274%, balance Fe matrix.

[0041] Comparative Example 3

[0042] Based on Example 1, the preparation process remains unchanged, and the chemical composition and weight percentage of the cylindrical steel billet are as follows:

[0043] C 0.0527%, Si 0.1534%, Mn 0.2135%, P 0.0126%, S 0.0085%, Cr 2.12%, Mo 0.3186%, Al 0.4271%, balance Fe matrix.

[0044] Example 2

[0045] Based on Example 1, with other conditions remaining unchanged, the seamless steel pipe obtained after cold rolling is heated to 1180-1210℃, held for 10 minutes, and then water-cooled to obtain a seamless steel pipe.

[0046] Example 3

[0047] Based on Example 1, with other conditions remaining unchanged, the seamless steel pipe obtained after cold rolling is heated to 1180-1210℃, held for 15 minutes, and then water-cooled to obtain a seamless steel pipe.

[0048] Comparative Example 4

[0049] Based on Example 1, with other conditions remaining unchanged, the seamless steel pipe obtained after cold rolling is heated to 1180-1210℃, held for 5 minutes, and then water-cooled to obtain a seamless steel pipe.

[0050] Comparative Example 5

[0051] Based on Example 1, with other conditions remaining unchanged, the seamless steel pipe obtained after cold rolling is heated to 1180-1210℃, held for 20 minutes, and then water-cooled to obtain a seamless steel pipe.

[0052] Comparative Example 6

[0053] Based on Example 1, with other conditions remaining unchanged, the method further includes heating the seamless steel pipe obtained after cold rolling to 1000-1180°C, holding it at that temperature for 10 minutes, and then water cooling it to obtain the seamless steel pipe.

[0054] Comparative Example 7

[0055] Based on Example 1, with other conditions remaining unchanged, the method further includes heating the seamless steel pipe obtained after cold rolling to 1210-1300℃, holding it at that temperature for 10 minutes, and then water cooling it to obtain the seamless steel pipe.

[0056] Example 4

[0057] Based on Example 2, with other conditions remaining unchanged, the water-cooled seamless steel pipe is heated to 450-550°C, kept at that temperature for 10 minutes, and then air-cooled to room temperature.

[0058] Example 5

[0059] Based on Example 4, with other conditions remaining unchanged, after heat preservation for 10 minutes, a straightening process is also performed at 300-400℃.

[0060] Examples 6-8 and Comparative Examples 8-11

[0061] Examples 6-8 and Comparative Examples 8-11 are based on Example 1, with the same preparation process. The chemical composition and weight percentage of the cylindrical steel billets are shown in the table below:

[0062] Example 6 0.0546 0.153 0.079 0.214 0.0127 0.0088 2.12 0.322 0.435 0.427 Example 7 0.0546 0.153 0.295 0.214 0.0127 0.0087 2.12 0.321 0.435 0.427 Example 8 0.0546 0.152 0.151 0.214 0.0126 0.0087 2.12 0.321 0.434 0.652 Comparative Example 8 0.0546 0.152 0.041 0.214 0.0126 0.0087 2.12 0.321 0.434 0.426 Comparative Example 9 0.0546 0.152 0.352 0.214 0.0127 0.0087 2.12 0.321 0.434 0.426 Comparative Example 10 0.0546 0.153 0.152 0.214 0.0125 0.0086 2.12 0.322 0.434 0.312 Comparative Example 11 0.0546 0.153 0.152 0.214 0.0126 0.0086 2.12 0.322 0.135 0.761

[0063] Comparative Example 12

[0064] Based on Example 1, the raw materials and percentages of the cylindrical steel billet remain unchanged, but the phosphating solution used in the phosphating treatment is changed. The phosphating solution contains 30 g / L of zinc dihydrogen phosphate, does not contain copper phosphate, has a pH of 3, a temperature of 5°C, and a phosphating time of 5 min.

[0065] Comparative Example 13

[0066] Based on Comparative Example 12, with other conditions remaining unchanged, the seamless steel pipe obtained after cold rolling was heated to 1180-1210℃, held for 10 minutes, and then water-cooled to obtain a seamless steel pipe.

[0067] Comparative Example 14

[0068] Based on Comparative Example 13, with other conditions remaining unchanged, the seamless steel pipe that had been water-cooled was heated to 450-550℃, kept at that temperature for 10-30 minutes, and then air-cooled to room temperature.

[0069] The mechanical properties of the seamless steel pipes prepared in Examples 1-8 and Comparative Examples 1-14 were tested respectively, and the results are shown in the table below:

[0070]

[0071] The mechanical properties of the comparative example group are shown in the table below:

[0072]

[0073]

[0074] Water vapor corrosion resistance test:

[0075] The seamless steel pipes prepared in Examples 1-8 and Comparative Examples 1-14 were used as reaction pipes, and high-temperature and high-pressure steam was introduced into them. The steam temperature was 800°C, the pressure was 10 MPa, and the steam flow rate was 1 m / s. 3 The test was conducted at a rate of 1000 m / min for 360 h. After the test, the wall thickness change was measured and the corrosion rate (mm / a) was calculated. The data are shown in the table below.

[0076]

[0077] The comparative data is shown in the table below:

[0078]

[0079]

[0080] The experimental data above clearly show that the seamless steel pipe prepared by the method of the present invention has good mechanical properties, and the seamless steel pipe prepared by the method of the present invention exhibits good corrosion resistance when applied to high temperature and high pressure steam.

[0081] Examples 9-11

[0082] Based on Example 1, while keeping the preparation process unchanged, the mass percentage of each component was changed, as shown in the table below:

[0083] Example 9 0.0624 0.167 0.172 0.318 0.0124 0.0085 2.31 0.357 0.482 0.403 Example 10 0.081 0.182 0.398 0.422 0.0123 0.0086 2.42 0.373 0.567 0.684 Example 11 0.0976 0.194 0.227 0.489 0.0126 0.0086 2.49 0.396 0.598 0.903

[0084] The seamless steel pipes prepared in Examples 9-11 above were subjected to mechanical property tests and water vapor corrosion resistance tests, and the following results were obtained:

[0085]

[0086] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of producing a seamless steel pipe for a steam reformer pipe, characterized by, The chemical composition of seamless steel pipes, by mass percentage, includes: C 0.05%-0.1%, Si 0.15%-0.2%, Zr 0.08%-0.4%, Mn 0.2%-0.5%, P≤0.02%, S≤0.012%, Cr 2%-2.5%, Mo 0.3%-0.4%, Al 0.4%-0.6%, Ti 0.4%-0.9%, with the balance being Fe matrix. The mass ratio of Si to Zr is 1:(0.5-2), and the mass ratio of Ti to Al is (1-1.5):

1. The preparation method of seamless steel pipes includes the following steps: (1) Heat the cylindrical steel billet to 1100-1250℃, put it into the piercing mill, and pierce it to obtain the steel pipe billet; (2) The steel billet after piercing is hot rolled at 980-1100℃ to obtain a seamless billet with the target outer diameter and wall thickness; (3) The seamless tube blank is pickled and phosphated. The phosphate solution used for phosphate treatment contains 5-10 g / L of copper phosphate and 30-50 g / L of zinc dihydrogen phosphate. The pH of the phosphate solution is 3-4, the temperature of the phosphate solution is 55-70℃, and the phosphate time is 4-10 min. Then the seamless tube blank is continuously cold rolled to obtain a seamless steel pipe with the target outer diameter and wall thickness. (4) The seamless steel pipe after continuous cold rolling is subjected to solution treatment. The solution treatment steps include: heating the seamless steel pipe to 1180-1210℃, holding it for 10-15 minutes and then water cooling it. (5) The seamless steel pipe after solution treatment is subjected to stress relief annealing. The stress relief annealing temperature is 450-550℃ and the holding time is 10-30min. After the holding time is completed, it is air-cooled to room temperature. After passing the test, the finished seamless steel pipe is obtained.

2. The method of producing a seamless steel pipe for a steam reformer tube according to claim 1, characterized by, In step (5), after stress-relief annealing and heat preservation, before air cooling to room temperature, a straightening treatment at 300-400℃ is also included.

3. A seamless steel pipe for a steam reformer tube, characterized by, It is prepared by any of the preparation methods described in claims 1-2.

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