Steel sleeve for drilling mud pump and inner coating and preparation method thereof

Abstract

This invention discloses a steel sleeve for drilling mud pumps, its inner coating, and its preparation method. The inner coating uses nickel-based tungsten carbide self-fluxing alloy powder as the matrix, and adds niobium powder, boron powder, and rare earth modifier La2O3 for composite modification. It is prepared by oxyacetylene flame spraying combined with horizontal rotary remelting, which can generate NbC and NbB2 combined hard phases in situ. Niobium can refine the coating microstructure and inhibit tungsten carbide particle agglomeration, while boron can fill grain boundary pores and improve coating density. The synergistic effect of these two significantly improves the coating's hardness, bonding strength, resistance to mud erosion and wear, and resistance to hydrogen sulfide and chloride ion corrosion. The process of this invention is stable and controllable, resulting in a coating with high bonding strength and good density, which can effectively extend the service life of the drilling mud pump steel sleeve.

Description

Technical Field

[0001] This invention relates to the field of wear-resistant and corrosion-resistant technology for drilling equipment, specifically to a drilling mud pump steel sleeve, its inner coating, and its preparation method. Background Technology

[0002] Drilling mud pump steel sleeves operate under complex conditions such as sand-containing mud erosion, hydrogen sulfide corrosion, and chloride ion corrosion, making them highly susceptible to abrasive wear, adhesive spalling, and corrosion perforation, severely impacting equipment lifespan. Currently, the industry commonly uses nickel-based tungsten carbide self-fluxing alloy coatings to improve the wear resistance of steel sleeves. However, conventional coatings still suffer from poor microstructure uniformity, uneven distribution of hard phases, and high porosity, making them prone to cracking and localized spalling under the combined effects of strong erosion and corrosion.

[0003] To improve coating performance, some technologies modify coatings by adding a single alloying element. While this can increase hardness to some extent, it is difficult to simultaneously address defects such as low coating density, insufficient bonding strength, and poor resistance to adhesive wear. This is especially true in the preparation of coatings for thick, large-diameter steel sleeve inner bores, where uneven heating and incomplete remelting are prone to occur. Furthermore, existing spraying-remelting processes often suffer from insufficient parameter matching and difficulty in effectively eliminating internal coating defects, resulting in coatings whose overall performance cannot meet the requirements of deep and ultra-deep well drilling conditions.

[0004] Based on this, we developed a mud pump steel sleeve inner coating with uniform and dense structure, excellent wear and corrosion resistance, and stable and controllable process, as well as its preparation method. By controlling the in-situ generation of a two-phase hard phase through composite micro-alloying, and optimizing the spraying and horizontal rotary remelting processes, this has important engineering significance for improving the service stability and service life of drilling mud pumps. Summary of the Invention

[0005] To address the problems of insufficient wear and corrosion resistance and numerous process defects in the inner coating of existing drilling mud pump steel casings, this invention provides a drilling mud pump steel casing, its inner coating, and a preparation method. By generating a hard phase in situ through niobium-boron composite modification, and combined with an optimized spraying and remelting process, the coating achieves both high density and excellent bonding strength, meeting the requirements of complex drilling conditions.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A steel sleeve for a drilling mud pump and its inner coating, wherein the inner surface of the steel sleeve is provided with an inner coating; the inner coating has a thickness of 0.8-1.2 mm and is prepared from the following raw materials in parts by weight: The raw materials consist of 98.2-99.1 parts of nickel-based tungsten carbide self-fluxing alloy powder, 0.6-0.9 parts of niobium powder, 0.2-0.8 parts of boron powder, and 0.1-0.3 parts of rare earth modifier. The raw materials are sprayed, remelted, and reacted in situ to generate a dispersed NbC and NbB2 composite hard phase, the volume fraction of which is 12-18%.

[0007] Optionally, in the nickel-based tungsten carbide self-fluxing alloy powder, the mass fraction of tungsten carbide is 30-40%, and the remainder is a nickel-based self-fluxing alloy.

[0008] Optionally, the inner coating has a hardness of 750-850 HV, a porosity of 0.5%-1.5%, and a bonding strength with the steel sleeve substrate of 35-45 MPa.

[0009] Optionally, the steel sleeve substrate is 42CrMo alloy steel or 20CrMnTi alloy steel.

[0010] Optionally, the preparation method of the steel sleeve and its inner coating for the drilling mud pump is as follows: S1. Weigh out nickel-based tungsten carbide self-fluxing alloy powder, niobium powder, boron powder and rare earth modifier, put them into a powder mixer and mix them at a speed of 150-250 rpm for 2-4 hours to obtain a uniformly mixed powder. S2. Grind, degrease, and remove rust from the inner hole surface of the steel sleeve substrate until the surface roughness Ra is 3.2-6.3μm, then clean with anhydrous ethanol and dry. S3. Feed the mixed powder into the oxy-acetylene flame spray gun and spray it vertically into the inner hole of the steel sleeve substrate. The spraying power is 18-22kW, the oxygen pressure is 0.4-0.6MPa, the acetylene pressure is 0.08-0.12MPa, the spraying distance is 150-200mm, the steel sleeve rotation speed is 120-180rpm, and the axial movement speed of the spray gun is 5-8mm / s, forming an initial coating with a thickness of 1.0-1.4mm. S4. Fix the sprayed steel sleeve to a horizontal rotating fixture and rotate it at a speed of 80-120 rpm. Use an oxy-acetylene flame for remelting treatment. The remelting power is 20-25 kW, the oxygen pressure is 0.5-0.7 MPa, the acetylene pressure is 0.1-0.15 MPa, the axial movement speed of the flame gun is 3-5 mm / s, and the remelting temperature is 1180-1220℃. After holding at this temperature for 3-5 minutes, cool it to room temperature with the furnace to obtain an inner coating with a thickness of 0.8-1.2 mm.

[0011] Optionally, in step S1, the niobium powder has a purity of ≥99.5% and a particle size of 5-20 μm; the boron powder is amorphous boron powder with a purity of ≥99.0% and a particle size of 10-30 μm; and the rare earth modifier La2O3 has a purity of ≥99.0% and a particle size of 5-15 μm.

[0012] Optionally, in step S4, the distance between the flame gun and the inner surface of the steel sleeve during remelting is 100-150 mm, and the flame type is a neutral flame.

[0013] The beneficial effects of this invention are as follows: In-situ generation of uniformly dispersed NbC and NbB2 composite hard phases through niobium-boron composite microalloying results in a coating hardness of 750-850 HV, exhibiting significant wear and erosion resistance; Optimized spraying-horizontal rotary remelting process combined with boron densification reduces coating porosity to as low as 0.5%-1.5%, significantly improving corrosion resistance; The coating forms a stable metallurgical bond with the steel sleeve substrate, achieving a bonding strength of 35-45 MPa, effectively preventing coating peeling; The entire process is stable and controllable, suitable for large-size steel sleeve fabrication, and can significantly extend its service life under complex working conditions. Attached Figure Description

[0014] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0015] Figure 1 This is a schematic diagram of the actual structure of the steel sleeve for the drilling mud pump described in this invention. The outer wall is a protective coating layer, and the inner working surface is a niobium-boron synergistic reinforced nickel-based tungsten carbide composite inner coating prepared in this invention. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0017] Example 1: A steel sleeve for a drilling mud pump and its inner coating in Example 1. The inner coating is prepared from the following raw materials in parts by weight: 98.7 parts of nickel-based tungsten carbide self-fluxing alloy powder (35% tungsten carbide), 0.7 parts of niobium powder (99.5% purity, 10.2 μm particle size), 0.4 parts of boron powder (99.0% purity, 19.8 μm particle size), and 0.2 parts of rare earth modifier (La2O3, 99.0% purity, 10.3 μm particle size); steel casing matrix: 42CrMo alloy steel; This embodiment describes a method for preparing a steel sleeve and its inner coating for a drilling mud pump. The specific preparation steps are as follows: S1. Weigh each raw material according to the above ratio, put them into a planetary mixer, and mix them at a speed of 200 r / min for 3 hours to obtain a uniformly dispersed mixed powder. S2. The surface of the inner hole of the steel sleeve is roughened by mechanical grinding, then wiped with acetone to remove oil, then rinsed with 5% hydrochloric acid solution for 30 seconds to remove rust, and then polished step by step with sandpaper and monitored in real time with a roughness tester to control the surface roughness of the inner hole Ra=4.8μm. Finally, it is cleaned with anhydrous ethanol and placed in an 80℃ oven to dry for 30 minutes. S3. Using an oxy-acetylene flame spraying device, the mixed powder is sprayed onto the inner surface of the steel sleeve: spraying power 20kW, oxygen pressure 0.5MPa, acetylene pressure 0.1MPa, spraying distance 180mm, steel sleeve rotation speed 150r / min, spray gun axial movement speed 6mm / s, forming an initial coating with a thickness of 1.2mm after spraying. S4. Fix the sprayed steel sleeve on a horizontal rotating fixture, start the rotating mechanism to make the steel sleeve rotate at a constant speed of 100 r / min, and use an oxyacetylene neutral flame for remelting: remelting power 22kW, oxygen pressure 0.6MPa, acetylene pressure 0.12MPa, distance between the flame gun and the inner surface of the steel sleeve 120mm, axial movement speed of the flame gun 4mm / s, remelting temperature controlled at 1200℃, hold for 4min and then turn off the flame, and let it cool naturally to room temperature with the furnace to finally obtain an inner coating with a thickness of 1.0mm.

[0018] Example 2: A steel sleeve for a drilling mud pump and its inner coating in Example 2. The inner coating is prepared from the following raw materials in parts by weight: 98.5 parts of nickel-based tungsten carbide self-fluxing alloy powder (35% tungsten carbide), 0.9 parts of niobium powder (99.5% purity, 10.2 μm particle size), 0.4 parts of boron powder (99.0% purity, 19.8 μm particle size), and 0.2 parts of rare earth modifier (La2O3, 99.0% purity, 10.3 μm particle size); steel casing matrix: 42CrMo alloy steel; In this embodiment, the preparation method of the steel sleeve and its inner coating for a drilling mud pump is the same as that in Example 1, except that the niobium powder is increased to 0.9 parts.

[0019] Example 3: A steel sleeve for a drilling mud pump and its inner coating in Example 3. The inner coating is prepared from the following raw materials in parts by weight: 98.3 parts of nickel-based tungsten carbide self-fluxing alloy powder (35% tungsten carbide), 0.7 parts of niobium powder (99.5% purity, 10.2 μm particle size), 0.8 parts of boron powder (99.0% purity, 19.8 μm particle size), and 0.2 parts of rare earth modifier (La2O3, 99.0% purity, 10.3 μm particle size); steel casing matrix: 42CrMo alloy steel; In this embodiment, the preparation method of the steel sleeve and its inner coating for a drilling mud pump is the same as that in Example 1, except that the boron powder is increased to 0.8 parts.

[0020] Comparative Example 1: The inner coating of Comparative Example 1 was prepared from the following parts by weight of raw materials: 99.4 parts of nickel-based tungsten carbide self-fluxing alloy powder (35% tungsten carbide), 0.4 parts of boron powder (99.0% purity, 19.8 μm particle size), 0.2 parts of rare earth modifier (La2O3, 99.0% purity, 10.3 μm particle size); steel casing matrix: 42CrMo alloy steel; The preparation method of the inner coating in this comparative example is the same as that in Example 1, except that niobium powder is not added.

[0021] Comparative Example 2: The inner coating of Comparative Example 2 was prepared from the following parts by weight of raw materials: 99.1 parts of nickel-based tungsten carbide self-fluxing alloy powder (35% tungsten carbide), 0.7 parts of niobium powder (99.5% purity, 10.2 μm particle size), 0.2 parts of rare earth modifier (La2O3, 99.0% purity, 10.3 μm particle size); steel casing matrix: 42CrMo alloy steel; The preparation method of the inner coating in this comparative example is the same as that in Example 1, except that boron powder is not added.

[0022] Performance testing 1. Vickers hardness test The prepared steel sleeve sample was cut into a cross section along the axial direction. After grinding and polishing, a smooth and scratch-free observation surface was obtained. Using a Vickers hardness tester, a test load of 500g was selected and maintained for 15s. Five non-overlapping test points were evenly selected on the coating surface (avoiding edges, pores, and obvious defect areas). Pressure was applied to each point to form a diamond-shaped indentation. The diagonal length of each indentation was read using the hardness tester's built-in measurement system. The hardness value of each test point was calculated according to the Vickers hardness calculation formula. Finally, the arithmetic mean of the hardness of the five test points was taken as the Vickers hardness result of the coating.

[0023] Table 1. Vickers hardness test data for different samples

[0024] The Vickers hardness of the coatings in all embodiments of the present invention is significantly higher than that of the comparative example, indicating that niobium powder and boron powder can synergistically generate high-hardness ceramic hard phases such as NbC and NbB2 during the sintering process, thereby significantly improving the overall hardness of the coating and providing support for excellent wear resistance.

[0025] 2. Coating porosity test The coated samples were inlaid, progressively water-ground, and polished until the surface was free of obvious scratches. The coated area was observed using a metallographic microscope at a magnification of 200x. Five fields of view were randomly selected for each sample for photography. The pore area in each field of view was statistically analyzed using professional image analysis software, and the pore area ratio of a single field of view was calculated. The average value of the five fields of view was taken as the porosity of the coating of the sample.

[0026] Table 2. Test data on the porosity of coatings for different samples

[0027] The porosity of the coatings in the examples was significantly lower than that in the comparative examples, indicating that the niobium and boron components, together with the rare earth oxide La2O3, effectively improved the melting and solidification behavior of the coating, reduced internal pores and defects, and made the coating more dense; the lack of niobium powder or boron powder would lead to a significant decrease in the density of the coating.

[0028] 3. Coating-substrate bonding strength test The coating-substrate bond strength was tested using the pull-out method. The prepared steel sleeve samples were cut into specimens of uniform size according to standards. The coating surface of the specimen was firmly bonded to the pull-out fixture using a special adhesive. After the adhesive was fully cured, the assembled specimen was installed on a universal testing machine, and a tensile force was applied at a loading rate of 5 mm / min in a direction perpendicular to the coating surface until the coating separated from the substrate or broke. The peak tensile force was recorded. Based on the effective stress area of ​​the coating of the specimen, the bond strength between the coating and the substrate was calculated using the formula "bond strength = peak tensile force / effective stress area". Each sample was tested in parallel for 3 sets, and the arithmetic mean was taken as the final test result.

[0029] Table 3. Test data on the bonding strength between coatings and substrates of different samples.

[0030] The bonding strength between the coating and the substrate in the examples was better than that in the comparative examples, indicating that the addition of niobium and boron and rare earth modification can optimize the interfacial bonding state, promote the formation of a stable metallurgical bond between the coating and the substrate, and significantly improve the interfacial adhesion; while the interfacial bonding strength of the comparative examples was significantly reduced due to the lack of key components.

[0031] 4. Tests on resistance to mud erosion and wear / dry sliding wear This invention uses a mud erosion abrasion tester and a pin-disc abrasion tester to test the mud erosion abrasion resistance and dry sliding abrasion resistance of the coating. During the mud erosion wear test, a standard-sized coated sample was fixed in a fixture. A simulated mud was prepared by adding 5% quartz sand (particle size 50-100μm) to a 5% NaCl solution. The sample was eroded for 60 minutes at a pressure of 0.8MPa and a flow rate of 3m / s. After erosion, the sample was cleaned, dried, and the mass loss was measured. The volumetric wear was then calculated. During the dry sliding wear test, a coated pin sample was paired with a 45# steel grinding ring. A load of 50N, a rotation speed of 300r / min, and a sliding time of 60min were set. After sliding, the sample was cleaned, dried, and the mass loss was measured to calculate the volumetric wear. Both tests were performed in parallel for three times per group, and the average value was taken as the final performance data.

[0032] Table 4. Test data on mud erosion wear resistance / dry sliding wear resistance of different samples.

[0033] The volumetric wear of the embodiment under both mud erosion and dry sliding wear conditions was much lower than that of the comparative example, indicating that the hard phase dispersed inside the coating can effectively resist abrasive cutting and erosion damage, and the synergistic strengthening effect of niobium and boron gives the coating excellent wear resistance.

[0034] 5. Corrosion resistance test The corrosion resistance test was conducted using an immersion corrosion method to simulate the drilling environment. Coated samples were machined to standard dimensions of 20mm × 20mm × 5mm, cleaned of surface oil with anhydrous ethanol, and allowed to air dry. The initial mass of the samples was weighed using an electronic balance with an accuracy of 0.001g. A simulated drilling corrosion medium (5% NaCl + 0.5% H2S mixed solution, pH adjusted to 6.5) was prepared, and the samples were completely immersed in the medium, sealed, and placed in a constant temperature environment of 25℃ for 72 hours. During this period, the state of the medium and changes on the sample surface were observed periodically. After immersion, the samples were removed, and the surface corrosion products were rinsed with deionized water. After dehydration with anhydrous ethanol and drying in an oven at 80℃ for 30 minutes, the mass was weighed again, and the mass corrosion rate of the samples was calculated. Simultaneously, the surface morphology of the coating after corrosion was observed using a metallographic microscope. Each sample was tested in triplicate, and the arithmetic mean was taken as the final corrosion resistance test result.

[0035] Table 5 Corrosion resistance test data for different samples

[0036] The embodiment showed a significantly lower mass corrosion rate in a simulated drilling corrosion environment, thanks to the effective barrier of the coating's high-density structure against corrosive media. At the same time, the presence of niobium and boron elements optimized the electrochemical stability of the coating, enabling it to exhibit good corrosion resistance in salt-containing and hydrogen sulfide-containing media.

[0037] 6. Coating thickness test The coating thickness was tested using a combination of metallographic profile method and magnetic thickness gauge verification. A cross-section of the steel sleeve sample was cut along the axial direction. After mounting, progressive water grinding (using 400#, 800#, 1200#, and 2000# sandpaper), and polishing, the interface between the coating and the substrate was observed under a metallographic microscope at 200x magnification. The coating thickness (vertical distance from the substrate-coating interface to the outer surface of the coating) was measured at five randomly selected locations. Simultaneously, a magnetic thickness gauge was used to uniformly select 10 test points on the outer surface of the sample for non-destructive thickness measurement. The test data from both methods were cross-validated, and the arithmetic mean of all valid measurements was taken as the final coating thickness result for the sample.

[0038] Table 6. Test data of coating thickness for different samples

[0039] The coating thickness of all samples was consistently controlled at around 1.0 mm, with minimal deviation between groups. This indicates that the preparation process used in this invention has good stability and uniform, controllable thickness, which can eliminate the interference of thickness differences on the comparison results of hardness, wear resistance, corrosion resistance, and other properties.

[0040] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A steel sleeve for a drilling mud pump and its inner coating, characterized in that, The inner surface of the steel sleeve is provided with an inner coating; the inner coating has a thickness of 0.8-1.2 mm and is prepared from the following raw materials in parts by weight: The raw materials consist of 98.2-99.1 parts of nickel-based tungsten carbide self-fluxing alloy powder, 0.6-0.9 parts of niobium powder, 0.2-0.8 parts of boron powder, and 0.1-0.3 parts of rare earth modifier. The raw materials are sprayed, remelted, and reacted in situ to generate a dispersed NbC and NbB2 composite hard phase, the volume fraction of which is 12-18%.

2. The steel sleeve and its inner coating for a drilling mud pump according to claim 1, characterized in that, The nickel-based tungsten carbide self-fluxing alloy powder contains 30-40% tungsten carbide by mass, with the remainder being a nickel-based self-fluxing alloy.

3. The steel sleeve and its inner coating for a drilling mud pump according to claim 1, characterized in that, The inner coating has a hardness of 750-850 HV, a porosity of 0.5%-1.5%, and a bonding strength with the steel casing substrate of 35-45 MPa.

4. The steel sleeve and its inner coating for a drilling mud pump according to claim 1, characterized in that, The steel sleeve substrate is 42CrMo alloy steel or 20CrMnTi alloy steel.

5. A method for preparing a steel sleeve and its inner coating for a drilling mud pump, used to prepare the steel sleeve and its inner coating for a drilling mud pump as described in any one of claims 1-4, characterized in that, The specific preparation method is as follows: S1. Weigh out nickel-based tungsten carbide self-fluxing alloy powder, niobium powder, boron powder and rare earth modifier, put them into a powder mixer and mix them at a speed of 150-250 rpm for 2-4 hours to obtain a uniformly mixed powder. S2. Grind, degrease, and remove rust from the inner hole surface of the steel sleeve substrate until the surface roughness Ra is 3.2-6.3μm, then clean with anhydrous ethanol and dry. S3. Feed the mixed powder into the oxy-acetylene flame spray gun and spray it vertically into the inner hole of the steel sleeve substrate. The spraying power is 18-22kW, the oxygen pressure is 0.4-0.6MPa, the acetylene pressure is 0.08-0.12MPa, the spraying distance is 150-200mm, the steel sleeve rotation speed is 120-180rpm, and the axial movement speed of the spray gun is 5-8mm / s, forming an initial coating with a thickness of 1.0-1.4mm. S4. Fix the sprayed steel sleeve to a horizontal rotating fixture and rotate it at a speed of 80-120 rpm. Use an oxy-acetylene flame for remelting treatment. The remelting power is 20-25 kW, the oxygen pressure is 0.5-0.7 MPa, the acetylene pressure is 0.1-0.15 MPa, the axial movement speed of the flame gun is 3-5 mm / s, and the remelting temperature is 1180-1220℃. After holding at this temperature for 3-5 minutes, cool it to room temperature with the furnace to obtain an inner coating with a thickness of 0.8-1.2 mm.

6. The method for preparing a steel sleeve and its inner coating for a drilling mud pump according to claim 5, characterized in that, In step S1, the niobium powder has a purity of ≥99.5% and a particle size of 5-20 μm; the boron powder is amorphous boron powder with a purity of ≥99.0% and a particle size of 10-30 μm; and the rare earth modifier La2O3 has a purity of ≥99.0% and a particle size of 5-15 μm.

7. The method for preparing a steel sleeve and its inner coating for a drilling mud pump according to claim 5, characterized in that, In step S4, during remelting, the distance between the flame gun and the inner surface of the steel sleeve is 100-150mm, and the flame type is neutral flame.

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