Steel casting powder for oil casing and preparation method of steel casting powder

Abstract

The invention discloses steel casting powder for a petroleum casing and a preparation method of the steel casting powder, and relates to the technical field of metallurgy, and the steel casting powder comprises the following chemical components in percentage by mass: 30.1-36.5% of CaO, 26.0-30.0% of SiO2, 12.4-15.6% of Al2O3, less than or equal to 2.0% of F, less than or equal to 3.0% of Na2O and 12.0-15.0% of C. The crystallizer casting powder special for the steel for the H2S stress corrosion resistant oil casing is designed by regulating and controlling the formula of the casting powder, the crack defect rate of a casting blank can be effectively reduced, and the rolling yield is increased.

Description

Technical Field

[0001] The present invention relates to the technical field of metallurgy, in particular to a steel protective slag for petroleum casing and a preparation method thereof. Background Art

[0002] With the growing demand for energy, oil and natural gas production has increased year by year, and the corrosion and protection of buried oil and gas pipelines has gradually become a focus of widespread concern. The corrosion of oil and gas pipelines is mainly caused by two gas media, CO2 and H2S. If these corrosion protection measures are not adopted properly, it will not only shorten the life of the equipment and cause serious waste of steel resources, but also seriously threaten the safe operation of the pipeline. Once the pipeline is damaged, perforated, or leaks, it will cause serious harm to the public and the environment. Among them, H2S corrosion, due to the existence of two types of corrosion and hydrogen-induced damage, not only will it cause thinning of the pipe wall or local pitting and perforation, but the hydrogen atoms generated during the corrosion process will be absorbed by the steel and enriched in the metallurgical defect areas of the pipe, which will also cause embrittlement and cracking of the steel. Therefore, compared with CO2 pitting corrosion, H2S corrosion is a more complex and fatal type of corrosion.

[0003] Focusing on the H2S corrosion behavior of high-grade acid-resistant oil casing steel, research from the perspective of enhancing the material's resistance to hydrogen sulfide stress corrosion cracking (SSC) has pointed out that some strong carbide-forming elements (V, Ti, Nb, etc.) form dispersed carbides that can pin the movement of dislocations, becoming irreversible strong traps for hydrogen, and preventing hydrogen accumulation from causing stress damage. The above-mentioned (V, Ti, Nb, etc.) microalloying elements are prone to microcracks in the ingot during the smelting and casting process. The mold slag composition needs to be designed from the perspective of solving crack problems, so the requirements for the mold slag are very stringent.

[0004] Currently, there are few mold protection slags specifically for H2S stress corrosion resistant oil casing steel. When most steel mills produce corrosion resistant steel, they use protection slags of steel grades with similar compositions. However, since the process parameters may not be completely consistent, there are potential quality risks during continuous casting. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a steel protective slag for petroleum casing and a preparation method thereof.

[0006] In order to solve the above technical problems, the technical solutions of the present invention are as follows: A protective slag for oil casing steel has the following chemical composition and mass percentages: CaO: 30.1-36.5%, SiO2: 26.0-30.0%, Al2O3: 12.4-15.6%, F: ≤2.0%, Na2O: ≤3.0%, and C: 12.0-15.0%.

[0007] As a preferred solution of the steel protective slag for petroleum casing of the present invention, the moisture content of the protective slag is less than 0.2wt%.

[0008] As a preferred solution of the steel protective slag for petroleum casing of the present invention, the particle size of the protective slag is 200 mesh.

[0009] As a preferred solution of the steel protective slag for petroleum casing of the present invention, the basicity of the protective slag is 1.18-1.25.

[0010] As a preferred solution of the steel protective slag for petroleum casing of the present invention, the viscosity of the protective slag is 0.8-1.0 Pa.s.

[0011] As a preferred solution of the steel protective slag for petroleum casing of the present invention, the melting point of the protective slag is 1210-1250°C.

[0012] The present invention also provides a method for preparing steel protective slag for petroleum casing based on any one of the above, comprising: Mix the raw materials of the protective slag in a preset ratio, add them into the crucible furnace, heat and melt, and then cool them naturally to room temperature; The cooled solidified slag is dried until the moisture content is less than 0.2wt%; The solidified slag is ground to a particle size of 200 mesh to obtain the finished protective slag.

[0013] The beneficial effects of the present invention are: (1) The present invention designs a special mold protection slag for H2S stress corrosion resistant oil casing steel by regulating the protection slag formula, which can effectively reduce the crack defect rate of the ingot and improve the rolling yield.

[0014] (2) In the protective slag for oil casing provided by the present invention, CaO and SiO2 are the main components of the protective slag, Al2O3 and MgO play a role in increasing the melting point and viscosity of the protective slag, F and Na2O play a role in reducing the melting point and viscosity of the protective slag, and C plays a role in controlling the slag sintering properties and adjusting the melting rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0016] Figure 1A schematic diagram of the surface quality appearance of a casting billet produced using the protective slag for oil casing steel provided in an embodiment of the present application; Figure 2 This is a schematic diagram of the surface quality appearance of the ingot produced using the protective slag for oil casing steel provided in the comparative example. DETAILED DESCRIPTION

[0017] In order to make the contents of the present invention more clearly understood, the present invention is further described below in detail based on specific implementation methods in conjunction with the accompanying drawings.

[0018] The present invention provides a steel mold slag for oil casing, which is composed of a base slag material, a flux, and a melting rate regulator. The chemical composition and mass percentages of the mold slag are as follows: CaO: 30.1-36.5%, SiO2: 26.0-30.0%, Al2O3: 12.4-15.6%, F: ≤2.0%, Na2O: ≤3.0%, and C: 12.0-15.0%.

[0019] Among them, CaO and SiO2 are the main components of the protective slag, Al2O3 and MgO play a role in increasing the melting point and viscosity of the protective slag, F and Na2O play a role in reducing the melting point and viscosity of the protective slag, and C plays a role in controlling the sintering properties of the protective slag and adjusting the melting rate.

[0020] Specifically, the control and effects of the chemical components in the mold slag provided by the present invention are as follows: CaO: It is one of the main components of protective slag. CaO will decompose into Ca2+ and O2- at high temperature. O2- will react with the silicon-oxygen tetrahedral structure to break the silicon-oxygen bond and reduce the viscosity of the protective slag. However, too low viscosity will cause uneven filling of the slag film, which may easily lead to longitudinal cracks and steel leakage accidents. Therefore, the present invention controls the CaO content to 30.1-36.5%.

[0021] SiO2: It is a compound of silicon and oxygen anions. When the SiO2 content increases, the basicity of the protective slag decreases, the proportion of the glass increases, and the lubrication effect increases. However, if the proportion of the glass is too large, it will easily lead to rapid heat transfer and cracks on the surface of the shell. Therefore, the present invention controls the SiO2 content to 12.4-15.6%.

[0022] Al2O3: It is an amphoteric oxide. When the basicity is high, Al2O3 is added in the form of an acidic oxide. Al3+ combines with silicon oxide complex ion groups to form a more complex network structure, which increases the melting point and viscosity of the protective slag. When the basicity is low, Al2O3 is added in the form of a basic oxide. Al2O3 is a network exosome, which can dissociate the complex anion groups and reduce the melting point and viscosity of the protective slag. Therefore, the Al2O3 content should not be too low or too high. The present invention controls the Al2O3 content to be: 12.4-15.6%.

[0023] F: F exists in the slag in the form of F-, which has a small electrostatic potential and a large amount. It can easily replace O2- in the slag, causing the complex structure of silicon oxide complex ions formed by polymerization in the slag to split into relatively simple silicon oxide complex ions. Therefore, F plays a role of flux in the protective slag. The present invention controls the F content to ≤2.0%.

[0024] Na2O: Similar to F, it is a flux for the protective slag. Na+ forms a bond with one corner of the silicon-oxygen tetrahedron, preventing the silicon-oxygen tetrahedron from forming a network chain or causing the network chain to break. O2-, as a non-bridging oxygen, can destroy the complex network structure and disperse it into simple anion groups. The combined effect of the two ions greatly reduces the melting point and viscosity of the protective slag. The present invention controls the Na2O content to ≤3.0%.

[0025] C: plays a role of skeleton in the mold slag. When the carbon content is too low, the heat transfer rate is fast, which can easily lead to cracks on the surface of the casting. When the carbon content is too high, the melting speed of the mold slag is slow, which is not conducive to the melting of the mold slag. Therefore, the present invention controls the C content to be: 12.0-15.0%.

[0026] The moisture content of the protective slag provided by the present invention is controlled below 0.2wt%, and the particle size is 200 meshes.

[0027] The basicity of the mold slag provided by the present invention is 1.18 to 1.25. When the basicity varies within the range of 1.18 to 1.25, as the basicity increases, the O2- in the CaO dissociates the silicon-oxygen complex anion group, greatly improving the flowability of the mold slag. However, when the basicity is higher than 1.25, the crystallization performance is too strong, which in turn increases the melting point of the mold slag.

[0028] The protective slag provided by the present invention has a viscosity of 0.8-1.0 Pa.s and a melting point of 1210-1250°C.

[0029] The technical solution of the present invention is further described below with reference to the embodiments.

[0030] The protective slag provided in the embodiment of the present invention is mainly used for the production of a steel for oil casing that resists H2S stress corrosion. The components and proportions of the continuous casting protective slag in the embodiments of the present invention and the comparative examples are shown in Table 1, the typical chemical composition data of the corresponding steel grades of the embodiments of the present invention and the comparative examples are shown in Table 2, the performance of the protective slag in the embodiments of the present invention are shown in Table 3, the use conditions of the protective slag in the embodiments of the present invention and the comparative examples are shown in Table 4, and the use effects of the protective slag in the embodiments of the present invention and the comparative examples are shown in Table 5. The surface quality appearance diagram of the ingots in the embodiments of the present invention and the comparative examples is shown in Table 1. Figure 1 and Figure 2 .

[0031]

[0032] Table 1 Chemical composition percentages of mold slag in various examples and comparative examples (wt%)

[0033] Table 2 Typical chemical composition data of corresponding steel grades / %

[0034] Table 3 Performance data of mold slag in various embodiments and comparative examples

[0035] Table 4 Conditions for using protective slag in various examples and comparative examples

[0036] Table 5 Effects of using protective slag in various examples and comparative examples Therefore, the present invention designs a special mold protection slag for H2S stress corrosion resistant oil casing steel by regulating the protection slag formula, which can effectively reduce the crack defect rate of the casting billet and improve the rolling yield.

[0037] In addition to the above embodiments, the present invention may also have other implementation methods; any technical solutions formed by equivalent replacement or equivalent transformation fall within the protection scope required by the present invention.

Claims

1. A steel protection slag for oil casing, characterized by: Its chemical composition and mass percentage are as follows: CaO: 30.1-36.5%, SiO2: 26.0-30.0%, Al2O3: 12.4-15.6%, F: ≤2.0%, Na2O: ≤3.0%, C: 12.0-15.0%.

2. The protective slag for oil casing according to claim 1, characterized in that: The moisture content of the protective slag is less than 0.2 wt %.

3. The protective slag for oil casing according to claim 1, characterized in that: The particle size of the protective slag is 200 mesh.

4. The protective slag for oil casing according to claim 1, characterized in that: The basicity of the protective slag is 1.18~1.

25.

5. The protective slag for oil casing according to claim 1, characterized in that: The viscosity of the protective slag is 0.8~1.0 Pa.s.

6. The protective slag for oil casing according to claim 1, characterized in that: The melting point of the protective slag is 1210-1250°C.

7. A method for preparing steel mold slag for petroleum casing according to any one of claims 1 to 6, characterized in that: include: Mix the raw materials of the protective slag in a preset ratio, add them into the crucible furnace, heat and melt, and then cool them naturally to room temperature; The cooled solidified slag is dried until the moisture content is less than 0.2wt%; The solidified slag is ground to a particle size of 200 mesh to obtain the finished protective slag.

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