Fracturing fluid delivery pipe inner surface coating and preparation method thereof

Abstract

The invention discloses a fracturing fluid delivery pipe inner surface coating and a preparation method thereof, and belongs to the technical field of coatings. Comprising a bottom layer, a middle layer and a surface layer, the bottom layer comprises nickel-chromium alloy and first silane coupling agent modified titanium powder; the middle layer comprises aluminum oxide, a nickel-tungsten-molybdenum alloy and a diamond-carbon nanotube composite material; the surface layer comprises zirconium oxide, aluminum oxide and magnesium fluoride. The preparation method comprises the following steps: S1, pretreatment: carrying out sand blasting treatment on the inner surface of the pipeline; s2, spraying a bottom layer on the inner surface of the pipeline by adopting a plasma spraying method; s3, spraying a middle layer on the surface of the bottom layer by adopting a high-speed flame spraying method; s4, spraying a surface layer on the surface of the middle layer by adopting an electric arc spraying method; s5, sintering is carried out; and S6, performing hole sealing treatment on the inner surface of the sintered pipeline by adopting a second silane coupling agent. The inner surface coating of the fracturing fluid conveying pipe is of a multi-layer synergistic structure of the bottom layer, the middle layer and the surface layer, the layers are clear in function and matched with one another, and extreme working condition challenges can be handled in a targeted mode.

Description

Technical Field

[0001] The present invention relates to the technical field of coatings, in particular to an inner surface coating of a fracturing fluid delivery pipe and a preparation method thereof. Background Art

[0002] During fracturing operations in oil and gas production, fracturing fluid pipelines face extremely harsh operating environments. Fracturing fluids typically contain large amounts of chemicals, such as acids, alkalis, and salts, which can severely corrode the inner surface of the pipeline. Furthermore, the high-speed flow of fracturing fluid within the pipeline causes intense erosion and friction, leading to severe wear and tear on the pipeline, shortening its service life.

[0003] Therefore, it is of great practical significance to develop an inner surface coating for fracturing fluid delivery pipes with excellent wear resistance and corrosion resistance. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide an inner surface coating of a fracturing fluid delivery pipe and a preparation method thereof, so as to improve the wear resistance and corrosion resistance of the fracturing fluid delivery pipe.

[0005] The object of the present invention is achieved through the following technical solutions:

[0006] A fracturing fluid delivery pipe inner surface coating comprises a bottom layer, an intermediate layer and a surface layer; the bottom layer comprises a nickel-chromium alloy and titanium powder modified with a first silane coupling agent; the intermediate layer comprises aluminum oxide, a nickel-tungsten-molybdenum alloy and a diamond-carbon nanotube composite material; and the surface layer comprises zirconium oxide, aluminum oxide and magnesium fluoride.

[0007] In the above-mentioned base layer, nickel-chromium alloy provides corrosion resistance, and titanium powder forms a chemical bond (Fe-O-Ti bond) with the carbon steel substrate through a silane coupling agent, solving the problem of interface debonding of the traditional nickel-chromium base layer in CO2-containing fracturing fluid.

[0008] In the middle layer, aluminum oxide and nickel-tungsten-molybdenum alloy form a metal ceramic structure, which effectively improves the compressive strength.

[0009] Carbon nanotubes wrapped around diamonds can effectively reduce the diamond shedding rate under high-speed erosion.

[0010] Although diamond particles improve wear resistance, under high-speed solid-phase erosion, the interface between diamond and the nickel-molybdenum alloy matrix is ​​prone to microcracks due to stress concentration, causing the diamond particles to fall off. By uniformly wrapping the diamond particles with carbon nanotubes to form a three-dimensional network structure, the interface bonding strength can be effectively improved and the risk of diamond particles falling off can be reduced. At the same time, by limiting the diamond particle size to 0.5-2μm, the diamond particle size distribution can be optimized to a gradient grading of 0.5-2μm, reducing stress concentration points, effectively solving the microcrack problem, and effectively improving the wear resistance life.

[0011] In the surface layer, zirconium oxide is toughened by stress-induced phase transformation, effectively improving the fracture toughness of the surface layer. Aluminum oxide has high hardness and can provide a basic wear-resistant skeleton. However, when the pH of the fracturing fluid is ≤3 (such as acid fracturing fluid containing hydrofluoric acid), the surface zirconium oxide will slowly dissolve, resulting in an increase in the surface thickness loss rate, exposing the middle layer and accelerating the galvanic corrosion of the diamond and the metal matrix. Based on this, the introduction of magnesium fluoride in the surface layer can form a MgF2 protective film in an acidic environment, effectively blocking F - Penetration, reducing the surface thickness loss rate in HF-containing fracturing fluid.

[0012] In actual implementation, the internal pressure of the fracturing fluid delivery pipe can reach more than 90MPa. The nickel-chromium alloy of the bottom layer is close to the carbon steel substrate. The titanium powder is modified by a silane coupling agent (to enhance wettability) to enhance the bonding strength. The nickel-tungsten-molybdenum alloy in the middle layer forms a gradient transition with the bottom layer, reducing thermal stress and avoiding peeling of the coating under high pressure. In addition, the aluminum oxide in the middle layer provides a basic wear-resistant skeleton, and the diamond-carbon nanotube composite material is embedded in it, reducing the wear rate of the coating under the erosion of sand-containing fracturing fluid. The zirconium oxide on the surface forms a high-temperature stable phase with magnesium fluoride, which can protect the middle layer in acidic fracturing fluids above 150°C and reduce the corrosion rate.

[0013] In summary, the inner surface coating of the fracturing fluid delivery pipe provided by the present invention has wear resistance, corrosion resistance, and high temperature resistance.

[0014] Preferably, the bottom layer has a thickness of 50-100 μm, wherein the mass ratio of the nickel-chromium alloy to the silane coupling agent modified titanium powder is (90-97):(3-10).

[0015] When the base layer thickness is less than 50μm, the bonding strength is insufficient under high pressure (90MPa); when the thickness is greater than 100μm, thermal stress accumulation leads to cracking. By limiting the base layer thickness and the amount of each component in the base layer, it is possible to ensure that the shear strength and fatigue life of the coating interface are improved under shale gas fracturing conditions (temperature 150°C, pressure 90MPa).

[0016] Preferably, the thickness of the intermediate layer is 200-300 μm, wherein the mass ratio of aluminum oxide, nickel-tungsten-molybdenum alloy and diamond-carbon nanotube composite material is (50-65):(20-30):(15-25).

[0017] If the aluminum oxide content is below the above-mentioned dosage, the wear-resistant skeleton will be discontinuous, while if it is above the above-mentioned dosage, the coating will become brittle. If the diamond-carbon nanotube content is above the above-mentioned dosage, insufficient metal binder phase will cause particle shedding, while if it is below the above-mentioned dosage, the wear resistance improvement will be limited.

[0018] Preferably, the thickness of the surface layer is 30-50 μm, wherein the mass ratio of zirconium oxide, aluminum oxide and magnesium fluoride is (25-35):(55-65):(5-10).

[0019] If the amount of zirconium oxide is lower than the above, the thermal shock resistance is insufficient, and if it is higher than the above, the thermal expansion is mismatched with that of aluminum oxide. If the amount of magnesium fluoride is higher than the above, the density of the coating will be reduced.

[0020] Preferably, the diamond-carbon nanotube composite material is prepared by in-situ growing carbon nanotubes on the surface of diamond particles by chemical vapor deposition to form a uniformly coated composite reinforcement phase.

[0021] Preferably, the diamond particle size is 0.5-2 μm.

[0022] Preferably, a nickel-based catalyst is introduced during the chemical vapor deposition process.

[0023] The carbon nanotube coating is easily separated from the diamond under high-speed erosion. By introducing a nickel-based catalyst during the chemical vapor deposition process, it is possible to promote the formation of covalent bonds between the carbon nanotubes and the diamond, effectively improving the bonding strength between the two.

[0024] Preferably, nano-scale graphene sheets are also added to the surface layer.

[0025] Although the surface of the zirconia-alumina composite ceramic can form a dense passivation film, but with more than 3% Cl - Long-term immersion in fracturing fluid will cause pitting corrosion caused by chloride ion penetration: Cl - The radius is small and it can diffuse into the middle layer through the ceramic grain boundary gap, react with the nickel-molybdenum alloy to generate soluble chlorides, causing local peeling of the coating.

[0026] By introducing nano-scale graphene sheets into the surface ceramics, the two-dimensional barrier effect of graphene is used to block Cl - Diffusion channel, which can effectively reduce Cl - Penetration rate, improve resistance to chlorine corrosion.

[0027] In addition, to achieve the above-mentioned object, the present invention also provides a method for preparing an inner surface coating of a fracturing fluid delivery pipe, comprising the following steps S1. Pretreatment: sandblasting the inner surface of the pipe;

[0028] S2. Use plasma spraying method to spray the base layer on the inner surface of the pipeline;

[0029] S3. Using high-speed flame spraying method to spray the intermediate layer on the bottom surface;

[0030] S4. Spraying the surface layer on the surface of the intermediate layer by arc spraying;

[0031] S5. Sintering;

[0032] S6. Sealing treatment of the inner surface of the sintered pipe with a second silane coupling agent.

[0033] In the above preparation method, the sand blasting treatment of the inner surface of the pipe in step S1 can improve the roughness of the inner surface of the pipe, improve the mechanical interlocking force with the bottom layer, and avoid the overall peeling of the coating under high pressure.

[0034] In steps S3-S5, the plasma sprayed bottom layer can ensure that the modified titanium powder is fully melted to form a metallurgical bond; the high-speed flame sprayed middle layer reduces the thermal damage of the diamond; and the arc sprayed surface layer has high efficiency and is suitable for composite wire.

[0035] In the sintering process of step S5, treatment at 400-600℃ can promote atomic diffusion at the interface of each layer (such as interdiffusion depth of 2-3μm between the bottom layer titanium powder and the base material iron), reduce the pores generated by rapid cooling during thermal spraying, and at the same time avoid the structural damage of the diamond-carbon nanotube composite material caused by high temperature (>800℃).

[0036] Step S6 performs sealing treatment after sintering, which can further fill the micropores in the surface layer and form a continuous corrosion-resistant barrier, and cooperates with the sintering process to improve the long-term stability of the coating in the Cl - 、F - fracturing fluid.

[0037] Preferably, in step S6, the second silane coupling agent is γ-aminopropyl triethoxysilane. Replacing the silane coupling agent with γ-aminopropyl triethoxysilane has chlorine resistance and can effectively improve the chlorine corrosion resistance of the organic-inorganic interface.

[0038] The beneficial effects of the present application are:

[0039] 1. The inner surface coating of the fracturing fluid conveying pipe of the present application adopts a multi-layer cooperative structure of a bottom layer, a middle layer and a surface layer, each layer has a clear function and cooperates with each other, and can be targeted to respond to extreme working conditions (i.e. high pressure ≥90MPa, high temperature ≥150℃, containing Cl - 、F - 、H + and other strong corrosive substances, and high-speed solid-phase scouring working conditions ≥25m / s):

[0040] The bottom layer is based on nickel-chromium alloy to provide corrosion resistance, and the titanium powder modified by the first silane coupling agent forms a stable Fe-O-Ti chemical bond with the carbon steel base material, which not only solves the problem of interface debonding of the traditional nickel-chromium bottom layer in the CO2-containing fracturing fluid, but also makes the bonding strength of the bottom layer and the base material adapt to the internal pressure requirement of 80MPa or more, providing a reliable adhesion basis for the overall coating.

[0041] The middle layer forms a metal-ceramic structure by alumina and nickel-tungsten-molybdenum alloy, which significantly improves the compressive strength; the core wear-resistant function is realized by the diamond-carbon nanotube composite material, in which carbon nanotubes evenly wrap the diamond particles to form a three-dimensional network structure, which can effectively alleviate the interface stress concentration under high-speed solid-phase erosion and reduce the risk of diamond falling off; at the same time, the diamond particle size is limited to a gradient grading of 0.5-2μm, which further reduces stress concentration points, improves microcrack problems, and greatly extends the wear-resistant life of the coating.

[0042] In the surface layer, zirconium oxide improves fracture toughness through stress-induced phase transformation toughening, while aluminum oxide provides a basic wear-resistant skeleton. To address the problem that zirconium oxide is easily dissolved when the fracturing fluid pH is ≤ 3 (containing hydrofluoric acid), resulting in an increase in the surface thickness loss rate and accelerated galvanic corrosion of the intermediate layer, magnesium fluoride is introduced to form a MgF2 protective film in an acidic environment, which can effectively block F - Penetration; the surface layer works synergistically with the middle layer to stably protect the middle layer in acidic fracturing fluids above 150°C, significantly reducing the overall corrosion rate.

[0043] In summary, the three-layer structure complements and synergizes functions, enabling the coating to have excellent wear resistance, corrosion resistance, and high temperature resistance, allowing it to stably cope with extreme working conditions of fracturing operations.

[0044] 2. By introducing nanographene sheets into the surface layer, a two-dimensional barrier network can be formed to further block Cl - / F - Diffusion channel, effectively improving corrosion resistance (corrosion rate reduced to 0.005mm / year, no corrosion marks in 150℃, pH=2 simulated fracturing fluid for 1000 hours), wear resistance (wear loss reduced to 32μm under high-speed erosion) and sealing performance [graphene fills the surface micropores, reducing the high-pressure leakage rate to 0.8×10 -9 m 3 / (s·Pa)] to meet the internal pressure requirements of ultra-deep wells above 90MPa. DETAILED DESCRIPTION

[0045] Example 1

[0046] S1. Pretreatment: The inner surface of the fracturing fluid pipeline was sandblasted (using corundum sand with a particle size of 0.5-1 mm, sandblasted at a pressure of 0.6 MPa to a surface roughness of Ra 8-10 μm), followed by electrolytic polishing with 5 wt% sulfuric acid solution (current density 12 A / dm 2 , time 3min), rinse with deionized water and then dry at 120℃ for 30min.

[0047] S2. Spraying a bottom layer on the inner surface of the dried pipeline by plasma spraying method: mixing nickel-chromium alloy powder (mass ratio of nickel and chromium is 85:15, particle size of nickel-chromium alloy powder is 8-12 μm) and KH550 modified titanium powder (particle size of titanium powder is 8-10 μm) at a mass ratio of 95:5, using argon as carrier gas (flow rate is 35 L / min), plasma arc current is 350 A, voltage is 60 V, spraying distance is 100-120 mm, to form a bottom layer with a thickness of 65 μm.

[0048] The preparation method of the KH550 modified titanium powder is as follows:

[0049] S11. Taking titanium powder with a particle size of 8-10 μm, placing it in a 5wt% dilute hydrochloric acid solution, stirring at room temperature for 30 min (stirring rate is 200 r / min), then washing with deionized water by centrifugation until neutral, and placing it in a 80℃ vacuum drying oven for drying for 2 h to obtain surface-activated titanium powder.

[0050] Taking KH550 silane coupling agent at 2% of the mass of the titanium powder, dissolving it in an ethanol-water mixed solvent (volume ratio of ethanol to water is 3:1), stirring uniformly, then adding acetic acid to adjust the pH of the solution to 4.5-5.0, and stirring magnetically at room temperature for 30 min (rotation speed is 300 r / min) to obtain a KH550 hydrolysis solution.

[0051] S12. Adding the surface-activated titanium powder to the KH550 hydrolysis solution (solid-liquid ratio of titanium powder to hydrolysis solution is 1:8, g:mL), placing it in a constant-temperature water bath, ultrasonic dispersing at 60℃ for 15 min (power is 300 W), then mechanically stirring at 60℃ for 2 h (stirring rate is 300 r / min), centrifuging, washing and drying in a 60℃ vacuum drying oven for 4 h after the reaction to obtain KH550 modified titanium powder.

[0052] S3. Spraying an intermediate layer on the surface of the bottom layer by high-speed flame spraying method: mixing alumina powder (particle size is 6-8 μm), nickel-tungsten-molybdenum alloy powder (mass ratio of nickel, tungsten and molybdenum is 72:8:20, particle size of nickel-tungsten-molybdenum alloy powder is 12-15 μm) and diamond-carbon nanotube composite material at a mass ratio of 60:25:18, using propane-oxygen mixed gas (flow rate ratio is 1:4) as fuel, flame speed is 2000 m / s, spraying distance is 200-250 mm, to form an intermediate layer with a thickness of 250 μm.

[0053] The preparation method of the diamond-carbon nanotube composite material is as follows:

[0054] S31. Diamond particles were placed in a planetary ball mill with zirconia grinding balls of 3-5 mm diameter (ball-to-material ratio 8:1). Dry milling was performed at 200 rpm for 2 hours. The particles were then ultrasonically cleaned with a 5% hydrofluoric acid solution (50°C) for 30 minutes. The particles were then rinsed with deionized water until neutral and dried at 120°C to obtain pretreated diamond particles with a particle size of 0.5-2 μm.

[0055] S32. The pretreated diamond was dispersed in a 5% nitric acid-hydrofluoric acid mixed solution (volume ratio 3:1), ultrasonically treated for 15 minutes, and then centrifuged, washed, and vacuum-dried at 60°C to constant weight to obtain surface hydrophilic diamond.

[0056] S33. A nickel nitrate-ethanol solution with a concentration of 0.01 mol / L was prepared, followed by the addition of surface hydrophilic diamonds at a concentration of 1 / 5 of the solution weight, and polyvinylpyrrolidone (molecular weight, 55 kDa) at a concentration of 0.15% of the surface hydrophilic diamond weight as a dispersant. Ultrasonic dispersion was performed for 30 minutes to uniformly adsorb the nickel ions onto the diamond surface. The solid was then filtered and placed in a tube furnace, heated to 400°C at a rate of 5°C / min, and reduced under a hydrogen atmosphere (flow rate, 50 mL / min) for 2 hours. After cooling, the solid was washed twice with ethanol to obtain nickel-loaded diamonds.

[0057] S34. Use a horizontal quartz tube reactor with a porous corundum boat loaded with nickel diamond. Purge with argon (200 mL / min) for 30 minutes to remove air. Heat to 650°C (10°C / min) and stabilize for 30 minutes.

[0058] The reaction mixture was switched to a methane-hydrogen mixture (volume ratio 1:4, total flow rate 150 mL / min), and 0.1% ethylene was introduced as an auxiliary carbon source. The reaction temperature was maintained at 650°C, the pressure was 100 kPa, and the reaction time was 60 min. The carbon source gas was then turned off, and an argon purge was maintained (200 mL / min). The temperature was lowered to room temperature at a rate of 5°C / min. The product was collected and placed in a muffle furnace. The temperature was increased to 350°C at a rate of 10°C / min under air atmosphere. The temperature was kept for 1 hour, cooled, washed, and dried at 60°C to constant weight to obtain a diamond-carbon nanotube composite material.

[0059] S4. Arc spraying of the intermediate layer: a 2-mm diameter composite wire was prepared by mixing zirconium oxide powder (t-ZrO2 phase, particle size 4-6 μm), aluminum oxide powder (α-Al2O3 phase, particle size 4-6 μm), and magnesium fluoride powder (particle size 2-5 μm) in a mass ratio of 30:60:8. The arc voltage was 30 V, the current was 250 A, and the spraying distance was 150-180 mm, resulting in a surface layer with a thickness of 40 μm.

[0060] S5. Low-temperature sintering: Place the sprayed pipe in a sintering furnace, heat it to 550°C at a rate of 5°C / min, keep it at that temperature for 2 hours (nitrogen protective atmosphere), and cool it to room temperature with the furnace.

[0061] S6. Use a second silane coupling agent to seal the surface: apply γ-aminopropyltriethoxysilane (6.5% by mass ethanol solution) evenly to the surface and cure at 80° C. for 2 h to obtain a fracturing fluid delivery pipe.

[0062] Example 2

[0063] Compared with Example 1, the amount of each component in the bottom layer, middle layer and surface layer was adjusted. After adjustment, the components and amounts of each layer are as follows:

[0064] Bottom layer: The mass ratio of nickel-chromium alloy powder to KH550 modified titanium powder is 94:6;

[0065] Middle layer: alumina powder, nickel-tungsten-molybdenum alloy powder and diamond-carbon nanotube composite material in a mass ratio of 62:25:20;

[0066] Surface layer: The mass ratio of zirconium oxide powder, aluminum oxide powder and magnesium fluoride powder is 30:28:7.

[0067] The remaining steps and parameters are the same as in Example 1.

[0068] Example 3

[0069] Compared with Example 1, in step S3, 0.8% of the total mass of zirconium oxide powder, aluminum oxide powder and magnesium fluoride powder is added to nano-graphene sheets (thickness 3-5 nm, sheet diameter 50-80 nm), and the remaining steps and parameters are the same as Example 1.

[0070] Comparative Example 1

[0071] Compared to Example 1, steps S1 and S6 were the same as in Example 1, but the layered spraying in steps S2-S5 was changed to a one-time spraying process. That is, all the components in the three layers of Example 1 were mixed and then directly sprayed onto the inner surface of the fracturing fluid pipeline using a high-velocity flame spraying method. The spraying thickness was the same as the total thickness in Example 1.

[0072] Comparative Example 2

[0073] Compared with Example 1, KH550 modified titanium powder was not added to the bottom layer, and the remaining steps and parameters were the same as Example 1.

[0074] Comparative Example 3

[0075] Compared with Example 1, no diamond-carbon nanotube composite material is added to the middle layer, and the remaining steps and parameters are the same as Example 1.

[0076] Comparative Example 4

[0077] Compared with Example 1, magnesium fluoride powder is not added to the surface layer, and the remaining steps and parameters are the same as Example 1.

[0078] Experimental example

[0079] 1. High temperature and strong corrosion test.

[0080] 1. Preparation of simulated fracturing fluid: 4.5 parts by mass of 37wt% hydrochloric acid + 2.5 parts by mass of 40% hydrofluoric acid + 15 parts by mass of quartz sand (particle size 0.1-0.8mm) + 78 parts by mass of deionized water, pH about 2, stir evenly and then introduce nitrogen to deoxygenate.

[0081] 2. Test equipment: high temperature and high pressure reactor equipped with temperature controller and weight loss balance.

[0082] 3. Testing Procedure: 50 mm x 50 mm specimens were cut from the actual fracturing fluid delivery pipes prepared in Examples 1-3 and Comparative Examples 1-4 (sampling was performed radially; other experiments required further cutting and sampling). (The thickness of the cut specimens represents the actual thickness of the fracturing fluid delivery pipe, i.e., the combined thickness of the pipe substrate and the complete coating.) Each specimen was then weighed, suspended in an autoclave, and statically immersed at 150°C for 1000 hours. After removal, surface corrosion products were removed, and the specimens were weighed again for calculation of the corrosion rate. The results are shown in Table 1.

[0083] Table 1:

[0084]

[0085] From Table 1 we can see that:

[0086] In Example 1-2, magnesium fluoride and γ-aminopropyltriethoxysilane form a "MgF2-siloxane" composite barrier to block Cl - / F - In Example 3, the graphene sheets form a two-dimensional barrier network, Cl - / F - The degree of diffusion is further reduced, and the corrosion rate is further reduced. In Comparative Example 1, the one-time spray coating causes the porosity to increase, and the corrosive medium reaches the substrate directly through the pores, forming large-area corrosion, highlighting the necessity of layered design. In Comparative Example 2, there is no KH550 modified titanium powder, the bottom passivation film is discontinuous, and pitting spreads from the bottom to the middle layer. In Comparative Example 3, there is no diamond-carbon nanotube in the middle layer, which has little effect on the corrosiveness. In Comparative Example 4, there is no magnesium fluoride in the surface layer, HF directly reacts with zirconium oxide to form ZrF4, and the corrosion rate is significantly improved.

[0087] 2. High-speed solid phase erosion test.

[0088] The samples in Examples 1-3 and Comparative Examples 1-4 (the cutting method refers to the high-temperature strong corrosion test) were fixed on the test bench, the nozzle was 30 mm away from the sample surface, and quartz sand (particle size 0.4-0.8 mm) was sprayed at a flow rate of 25 m / s for 1000 h. The wear amount was calculated by calculating the mass before and after wear. The results are shown in Table 2.

[0089] Table 2:

[0090]

[0091]

[0092] From Table 2, it can be seen that:

[0093] In Examples 1-2, diamond-carbon nanotube forms hard point skeleton, nickel-tungsten-molybdenum alloy buffer impact, and wear is mainly micro-cutting. In Example 3, graphene sheets improve the toughness of the surface layer and reduce brittle peeling. In Comparative Example 1, the coating and substrate interface directly cracks under high-speed impact without a layered buffer. In Comparative Example 2, the titanium powder is not modified by KH550, the bottom layer has weak adhesion, and under erosion, the bottom layer is peeled off first, driving the upper layer to wear. In Comparative Example 3, there is no diamond-carbon nanotube composite material, and the intermediate layer loses its wear resistance core and is plowed by quartz sand. In Comparative Example 4, there is no magnesium fluoride, and the surface layer density decreases, resulting in a wear depth greater than that of Example 1.

[0094] III. Interlayer bonding strength test

[0095] 1. Room temperature test: A 1 mm x 1 mm grid (100 grids) was drawn on the surface of the coating prepared in Examples 1-3 and Comparative Examples 1-2 using a grid knife. After pasting 3M tape, it was quickly peeled off and the grid peeling rate was observed. The critical peeling force was determined by tensile testing (cross method).

[0096] 2. High temperature test: The sample was placed in a 150°C oven for 1 h, and immediately subjected to the above grid drawing and tensile testing to compare the room temperature performance.

[0097] The test results are shown in Table 3.

[0098] Table 3:

[0099] Group Room temperature adhesion (MPa) 150°C adhesion (MPa) High temperature retention rate Example 1 69 57 82.6％ Example 2 71 59 83.1％ Example 3 67 55 82.1％ Comparative Example 1 27 17 63.0％ Comparative Example 2 44 31 70.5％

[0100] From Table 3, it can be seen that the room temperature bonding force of Examples 1-3 is ≥67 MPa, and the high temperature retention rate is ≥82.1%, meeting the long-term service requirements. The bonding force of Comparative Examples 1-2 is significantly reduced due to structural or bonding defects, proving that the layered design and KH550 modified titanium powder are the core of interlayer stability.

[0101] IV. High pressure sealing test

[0102] 1. Sample preparation: Cut the fracturing fluid delivery pipes in Examples 1-3 and Comparative Examples 1-2 into Standard section, flanges welded at both ends and sealing gaskets installed.

[0103] 2. Test equipment: Autoclave body, equipped with pressure sensor and helium mass spectrometer leak detector.

[0104] 3. Test process: The sample was connected to a high-pressure system and nitrogen was introduced at 90 MPa. The pressure was maintained for 24 hours, and the pressure change was recorded every 2 hours. The leakage rate was finally measured, and the coating integrity was observed. The results are shown in Table 4.

[0105] Table 4:

[0106] Group <![CDATA[泄漏率

m 3 / (s·Pa)

[0107] From Table 4 we can see that:

[0108] In Examples 1-2, the multilayer gradient structure achieves uniform stress dispersion through thermal expansion coefficient matching, with no significant leakage or cracking. In Example 3, the graphene sheets fill the surface micropores to form a continuous sealing barrier, and the leakage rate is reduced compared to Example 1. In Comparative Example 1, the one-time spraying has no layered structure, and the thermal stress between the layers is concentrated, causing the coating to crack along the interface under high pressure. In Comparative Example 2, there is no KH550 modified titanium powder, the bottom layer has poor bonding with the substrate, and interface peeling occurs under high pressure, resulting in severe leakage.

[0109] In summary, Examples 1-3 of the present invention have excellent performance in various tests such as corrosion resistance, high temperature resistance, and pressure resistance, and are suitable for high pressure (≥90MPa), high temperature (≥150°C), strong corrosion (containing Cl - 、F - 、H + ) and high-speed solid phase scouring (≥25m / s) conditions.

Claims

1. A fracturing fluid delivery pipe inner surface coating, comprising a bottom layer, an intermediate layer and a surface layer; characterized in that: The bottom layer includes Nickel-chromium alloy and first silane coupling agent modified titanium powder; The intermediate layer comprises aluminum oxide, nickel-tungsten-molybdenum alloy and diamond-carbon nanotube composite material; The surface layer includes zirconium oxide, aluminum oxide and magnesium fluoride.

2. The inner surface coating of a fracturing fluid delivery pipe according to claim 1, characterized in that: The thickness of the bottom layer is 50-100 μm, wherein the mass ratio of the nickel-chromium alloy to the silane coupling agent modified titanium powder is (90-97):(3-10).

3. The inner surface coating of a fracturing fluid delivery pipe according to claim 1, characterized in that: The thickness of the intermediate layer is 200-300 μm, wherein the mass ratio of aluminum oxide, nickel-tungsten-molybdenum alloy and diamond-carbon nanotube composite material is: (50-65): (20-30): (15-25).

4. The inner surface coating of a fracturing fluid delivery pipe according to claim 1, characterized in that: The thickness of the surface layer is 30-50 μm, wherein the mass ratio of zirconium oxide, aluminum oxide and magnesium fluoride is (25-35):(55-65):(5-10).

5. The inner surface coating of a fracturing fluid delivery pipe according to claim 1, characterized in that: The diamond-carbon nanotube composite material is prepared by in-situ growing carbon nanotubes on the surface of diamond particles through a chemical vapor deposition method to form a uniformly coated composite reinforcement phase.

6. The inner surface coating of a fracturing fluid delivery pipe according to claim 5, characterized in that: The diamond particle size is 0.5-2 μm.

7. The inner surface coating of a fracturing fluid delivery pipe according to claim 6, characterized in that: Introducing nickel-based catalysts during chemical vapor deposition.

8. The inner surface coating of a fracturing fluid delivery pipe according to claim 1, characterized in that: Nano-scale graphene sheets are also added to the surface layer.

9. The method for preparing an inner surface coating of a fracturing fluid delivery pipe according to any one of claims 1 to 8, characterized in that: The steps include: S1. Pretreatment: sandblasting the inner surface of the pipe; S2. Use plasma spraying method to spray the base layer on the inner surface of the pipeline; S3. Using high-speed flame spraying method to spray the intermediate layer on the bottom surface; S4. Spraying the surface layer on the surface of the intermediate layer by arc spraying; S5. Sintering; S6. Use a second silane coupling agent to seal the inner surface of the sintered pipe.

10. The method for preparing the inner surface coating of a fracturing fluid delivery pipe according to claim 9, characterized in that: In step S6, the second silane coupling agent is γ-aminopropyltriethoxysilane.

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