A surface treatment method for corrosion resistance and hydrogen embrittlement resistance of oil casing threads

Abstract

The present invention belongs to the technical field of surface treatment of metal materials, and particularly relates to a surface treatment method for corrosion resistance and hydrogen embrittlement resistance of oil casing threads. A surface treatment method for corrosion resistance and hydrogen embrittlement resistance of oil casing threads specifically includes: performing thread machining on the oil casing coupling; performing degreasing, defatting treatment, and flaw detection; performing carburizing treatment on the inner and outer surfaces; using a double-pulse power supply to deposit on the inner and outer surfaces of the coupling in a deep eutectic-based ion mixture to form a nickel-boron composite coating; cleaning, drying, and warehousing the oil casing coupling with clean water. The present invention can form a dense nickel-boron composite coating on the inner and outer surfaces of the oil casing coupling, which not only strengthens the high-temperature oxidation resistance, corrosion resistance, and wear resistance of the coupling, solves the weaknesses of oil pipe corrosion such as pitting corrosion, flow-induced corrosion, and crevice corrosion that are prone to occur in an environment containing corrosive media, the electroplating solution does not contain water, which can avoid the generation of hydrogen during electrodeposition, prevent hydrogen embrittlement of the coating, is easy to regenerate, and can be recycled.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal material surface treatment, and particularly relates to a surface treatment method for corrosion resistance and hydrogen embrittlement resistance of oil casing threads. Background Art

[0002] In recent years, China has increased the development of unconventional oil and gas resources such as tight oil and tight gas. These oil and gas wells have put forward higher requirements for the airtightness, connection strength, and corrosion resistance of threaded connections. Traditional API round threads and trapezoidal and buttress threads can no longer meet the requirements of these conditions or environments. For example, in the southwestern and Xinjiang regions of China, special threaded oil well pipes are commonly used for the exploitation of shale oil and gas.

[0003] The coupling is one of the important components for connecting oil casings, and the quality of the coupling will seriously affect the success or failure of drilling and production operations. After investigation, 64% of the oil casing failure accidents abroad occur at the threaded joints, and this proportion in China is as high as 86%. It can be seen that the threaded joint is the weakest part of the oil casing, and the thread quality will directly affect the life of the oil and gas well. As a connecting component of the oil casing, the threaded joint, together with the pipe string, is under the action of complex loads such as tension, compression, bending, internal pressure, and external pressure in the well for a long time, and its corrosion is more likely to occur. Common failure forms such as pitting corrosion, mesa erosion, flow-induced corrosion, and crevice corrosion will lead to failures such as sealing, thread failure, and tubing dropout, causing greater economic losses. Therefore, for special thread structures, it is necessary to maintain long-term sealing integrity and structural integrity under downhole atmospheric pressure, and also need to have high corrosion resistance.

[0004] The patent No. 201110007593.0 applied on January 14, 2012 involves a chromium-nickel-molybdenum composite electroplating method on the surface of special pipe joint threads for oil well pipes. An electroplating process is used to finally obtain a chromium-nickel-molybdenum composite coating on the surface of the pipe joint threads, improving the corrosion resistance of the special pipe joint threads. However, the patent uses a three-layer composite coating, and does not involve the problem of hydrogen embrittlement easily generated in aqueous electroplating of the electroplated coating and crevice corrosion generated under the action of load forces of the coupling in the well, and does not consider the pollution of the electroplating solution to industrial production and the environment. The patent No. 201911048508.8 applied on October 31, 2019 involves a tungsten plating anti-corrosion treatment process for oil pipe couplings. An electroplating process is used to finally obtain a tungsten composite coating on the surface of the oil pipe coupling, and the oil pipe coupling is dried and then heat-treated at 200 °C for nearly 8 hours of tempering to remove hydrogen and infiltrate tungsten to obtain an anti-corrosion oil pipe coupling. However, although this patent considers the hydrogen embrittlement factor of the coating, it does not consider the environmental and crevice corrosion problems. Summary of the Invention

[0005] Aiming at the problems existing in the above-mentioned existing surface treatment methods for oil casing threads, the purpose of the present invention is to provide a surface treatment method for corrosion resistance and hydrogen embrittlement resistance of oil casing threads. This method can form a dense nickel-boron composite coating on the inner and outer surfaces of the oil casing coupling, not only strengthening the high-temperature oxidation resistance, corrosion resistance and wear resistance of the coupling, solving the weaknesses of oil pipe corrosion such as pitting corrosion, flow-induced corrosion and crevice corrosion that are prone to occur in an environment containing corrosive media, but also compared with traditional electroplating solutions, the deep eutectic-based ion electroplating solution usually does not contain water, which can avoid the generation of hydrogen during electrodeposition, so the phenomenon of hydrogen embrittlement in the coating is avoided, it is easy to regenerate and can be recycled, meeting the needs of green and sustainable industrial production.

[0006] The technical solution of the present invention is as follows: A surface treatment method for corrosion resistance and hydrogen embrittlement resistance of oil casing threads, comprising the following steps:

[0007] S1: Thread processing is carried out on the oil casing coupling, and the thread depth is the designed tooth height, with a tolerance range of ±0.15 mm;

[0008] S2: After thread processing, the oil casing coupling is degreased and defatted with a cleaning agent at room temperature, and flaw detection is carried out;

[0009] S3: Carburizing treatment is carried out on the inner and outer surfaces of the oil casing coupling;

[0010] S4: The carburized oil casing coupling is placed in a deep eutectic-based ion mixture, and a double-pulse power supply is used to deposit on the inner and outer surfaces of the coupling to form a nickel-boron composite coating;

[0011] S5: The oil casing coupling is cleaned with clean water, dried and stored in the warehouse to complete the surface treatment of the oil casing thread for corrosion resistance and hydrogen embrittlement resistance.

[0012] In the thread processing of step S1, the surface roughness value Ra of the thread ≤ 3.2, and the surface roughness value Ra of the sealing surface ≤ 1.6.

[0013] In step S2, the oil casing coupling is degreased and defatted with the cleaning agent at least twice. The cleaning agent is of low alkalinity, with a PH range of 7 - 8. After degreasing and defatting, the inner and outer surfaces of the coupling are cleaned with hot water wash and water wash respectively. The hot water temperature range for hot water wash is 50°C - 60°C, and the water temperature range for water wash is 20°C - 25°C.

[0014] In step S2, the flaw detection method is dye penetrant inspection method or wet magnetic flaw detection method.

[0015] The carburizing treatment in step S3 is carried out in an industrial plasma carburizing furnace. The specific parameters of the carburizing treatment are as follows: the voltage of the power supply system of the industrial plasma carburizing furnace is 200 - 650 V, the duty cycle is 50 - 64%, and the holding time is 3 h - 7 h; when carrying out plasma carbonitriding, the flow rate of the reaction gas H2 is 300 - 450 ml / min, and the flow rate of CO2 is 10 - 25 ml / min; the air pressure during the reaction process is 100 - 200 Pa, the temperature is 300 - 500 °C, and it is cooled in the furnace after completion.

[0016] In step S4, a deep eutectic-based ionic mixture is used. The specific preparation process is as follows: according to the molar ratio, 0.3 - 0.6 parts of 2-hydroxyethyltrimethylammonium chloride and 0.6 - 1.2 parts of glycerol are mixed evenly to form a chlorine-based eutectic ionic solution ChCl-2GlyDES. In the ChCl-2Gly DES ionic solution, 2 - 3 parts of 0.5 mol / l NiCl2·6H2O and 2 - 5 parts of 0.6 mol / l WCl6·2H2O are respectively added to form a ChCl-2Gly-NiCl2·6H2O-WCl6·2H2O deep eutectic ionic electroplating solution.

[0017] In step S4, a dual-pulse power supply is used to deposit on the inner and outer surfaces of the coupling. The specific control parameters are as follows: the voltage of the dual-pulse power supply: 200 - 400 V, the number of pulses is 500 - 999, the duty cycle is 40 - 60%, and the current density is 7 A / dm 2 , and the pulse wave modulation frequency: 100 - 3000 Hz.

[0018] The thickness of the nickel-boron composite coating formed in step S4 is 15 - 45 μm.

[0019] The specific preparation process of the ChCl-2Gly DES ionic solution is as follows: 2-hydroxyethyltrimethylammonium chloride and glycerol are stirred evenly into a mixture. Under a sealed state, the mixture is heated and melted. The heating temperature is 70 °C - 80 °C. Stirring continues during the heating process until the mixture becomes a colorless and clear liquid. The obtained colorless and clear liquid is dried for at least 12 hours to form a ChCl-2Gly DES ionic solution, which is stored in a vacuum seal.

[0020] The technical effects of the present invention are as follows:

[0021] 1. After the special threaded oil casing coupling of the present invention is subjected to plasma carburizing treatment, the oxide film can be removed, the hardened layer can be effectively controlled on the thread, shoulder and coupling surface, the deformation amount can be reduced, and at the same time, growth nodes are provided for the epitaxial growth of the coating phase, improving the coating film / substrate bonding strength.

[0022] 2. The deep eutectic ionic electroplating solution of ChCl-2Gly-NiCl2·6H2O-WCl6·2H2O adopted in the present invention, compared with the traditional electroplating solution, usually does not contain water in the ionic liquid, which can avoid the generation of hydrogen during electro-deposition, so it avoids the phenomenon of hydrogen embrittlement in the coating, and there is no waste water discharge. The ionic liquid hardly generates steam, and the ionic liquid is easy to regenerate and can be recycled, which can truly achieve green production.

[0023] 3. The present invention modifies the surfaces of the threads, shoulders and couplings of the oil casing by plasma carburizing process, and adjusts the electroplating process parameters to enhance the bonding force between the material and the coating and increase the coverage rate, thereby forming a nickel-tungsten composite coating with uniform density, electrical insulation, wear resistance and corrosion resistance, improving the high-temperature oxidation resistance, corrosion resistance (crevice corrosion, pitting corrosion) and wear resistance of the special thread coupling, and prolonging its service life. Detailed implementation mode

[0024] The content of the present invention can be further understood by combining the following detailed description of the preferred implementation methods of the present invention and the included embodiments. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs. If the definition of a specific term disclosed in the prior art is inconsistent with any definition provided in the present invention, the definition provided in the present invention shall prevail.

[0025] It should be noted that the implementation conditions adopted in the embodiments can be further adjusted according to the specific experimental environment, and the implementation conditions not specified are usually the conditions in conventional experiments. The preparation methods mentioned in the present invention are all conventional methods unless otherwise specified.

[0026] A surface treatment method for corrosion resistance and hydrogen embrittlement resistance of oil casing threads includes the following steps:

[0027] S1: Process the threads of the oil casing coupling, with the thread depth being the designed tooth height and the tolerance range being ±0.15 mm;

[0028] S2: After the thread processing, degrease and defat the oil casing coupling with a cleaning agent at room temperature, and conduct flaw detection;

[0029] S3: Perform carburizing treatment on the inner and outer surfaces of the oil casing coupling;

[0030] S4: Put the carburized oil casing coupling into the deep eutectic-based ionic mixture, and use a double-pulse power supply to deposit on the inner and outer surfaces of the coupling to form a nickel-boron composite coating;

[0031] S5: Clean, dry and store the oil casing coupling with clean water to complete the surface treatment of the oil casing thread for corrosion resistance and hydrogen embrittlement resistance.

[0032] In the thread machining in step S1, the surface roughness value Ra of the thread is ≤ 3.2, and the surface roughness value Ra of the sealing surface is ≤ 1.6. The surface roughness value Ra of the thread being ≤ 3.2 and the surface roughness value Ra of the sealing surface being ≤ 1.6 can not only achieve the best sealing effect when the thread and the sealing interference fit of the coupling and the pipe body, but also enable the coating to better adhere to the surface of the oil casing coupling matrix.

[0033] In step S2, the oil casing coupling is degreased and defatted with a cleaning agent at least twice. The cleaning agent is low-alkaline, with a PH range of 7 - 8. After degreasing and defatting, the inner and outer surfaces of the coupling are cleaned with hot water wash and water wash respectively. The hot water temperature range for hot water wash is 50°C - 60°C, and the water temperature range for water wash is 20°C - 25°C. Multiple degreasing and defatting treatments with a low-alkaline cleaning agent, as well as the cleaning of the inner and outer surfaces of the coupling by hot water wash and water wash, ensure the cleanliness of the inner and outer surfaces of the oil casing coupling, facilitating subsequent carburizing treatment and electroplating treatment.

[0034] In step S2, the flaw detection method is the dye penetrant inspection method or the wet magnetic flaw detection method. The dye penetrant inspection method or the wet magnetic flaw detection method is used to inspect the part to be treated, and it is required that there are no cracks, pores, or inclusion defects in the part to be treated.

[0035] The carburizing treatment in step S3 is carried out in an industrial plasma carburizing furnace. The specific parameters of the carburizing treatment are as follows: the voltage of the power supply system of the industrial plasma carburizing furnace is 200 - 650V, the duty cycle is 50 - 64%, and the holding time is 3h - 7h; when carrying out plasma carbonitriding, the flow rate of the reaction gas H2 is 300 - 450ml / min, and the flow rate of CO2 is 10 - 25ml / min; the gas pressure during the reaction process is 100 - 200 Pa, and the temperature is 300 - 500°C. After completion, it is cooled in the furnace.

[0036] In step S4, a deep eutectic-based ionic mixture is used. The specific preparation process is as follows: in terms of molar ratio, 0.3 - 0.6 parts of 2-hydroxyethyltrimethylammonium chloride and 0.6 - 1.2 parts of glycerol are mixed evenly to form a chlorine-based eutectic ionic solution ChCl-2GlyDES. In the ChCl-2Gly DES ionic solution, 2 - 3 parts of 0.5mol / l NiCl2·6H2O and 2 - 5 parts of 0.6mol / l WCl6·2H2O are respectively added to form a ChCl-2Gly-NiCl2·6H2O-WCl6·2H2O deep eutectic ionic electroplating solution.

[0037] In step S4, a dual-pulse power supply is used to deposit on the inner and outer surfaces of the coupling. The specific control parameters are as follows: the voltage of the dual-pulse power supply: 200 - 400V, the number of pulses is 500 - 999, the duty cycle is 40 - 60%, and the current density is 7A / dm 2 , and the pulse wave modulation frequency: 100 - 3000Hz.

[0038] The thickness of the nickel-boron composite coating formed in the step S4 is 15-45 μm.

[0039] The specific preparation process of the ChCl-2Gly DES ionic solution is as follows: Stir 2-hydroxyethyltrimethylammonium chloride and glycerol evenly into a mixture. Under a sealed state, heat and melt the mixture at a heating temperature of 70°C to 80°C. Continue stirring during the heating process until the mixture becomes a colorless and clear liquid. Dry the obtained colorless and clear liquid for at least 12 hours to form the ChCl-2Gly DES ionic solution, and store it in a vacuum-sealed manner.

[0040] Example 1

[0041] Surface treatment for corrosion resistance and hydrogen embrittlement resistance of the threads of N80 steel grade 88.9 mm × 7.34 mm special threaded tubing, the specific process is as follows:

[0042] S1: First, cut two sections with a length of 1 m from the tubing blank of N80 steel grade. The size of the coupling material is 107.9 mm × 20 mm. Use an OKUMA CNC horizontal machine tool to process the internal and external threads respectively.

[0043] S2: After thread processing, at room temperature, use a low-alkaline cleaning solution for two decontamination and degreasing treatments. Secondly, perform hot water washing and water washing respectively to clean the inner and outer surfaces of the coupling, dry and set aside, and use the coloring flaw detection method to inspect the parts to be processed. It is required that there are no cracks, pores, and inclusion defects in the processed parts. Among them, the surface roughness value of the thread is Ra = 3.0, and the surface roughness of the sealing surface is Ra = 1.0.

[0044] S3: Put the prepared specimens into an industrial bell-jar type plasma carburizing furnace for carburizing treatment. During the carburizing process, control the voltage at 450 V, the duty cycle at 50%. Pass H2 and CO2 with flow rates of 400 ml / min and 20 ml / min respectively as reaction gases. During the heat preservation process, the air pressure is 150 Pa, the nitriding temperature is 500°C, and the heat preservation time is 6 h. After heat preservation is completed, cool with the furnace.

[0045] S4: Put the coupling after carburizing treatment into the deep eutectic-based ionic mixture, and use a double-pulse power supply to deposit on the inner and outer surfaces of the coupling at an electroplating solution temperature of 65-70°C. Control parameters: voltage: 200-400 V, number of pulses 500-999, duty cycle 40-60%, current density 7 A / dm 2, Pulse wave regulation frequency: 100 - 3000 Hz; Deep eutectic-based ionic mixture: Mix 2-hydroxyethyltrimethylammonium chloride and glycerol in a molar ratio of 0.5:1 and place them in a 1000 mL glass conical flask. After the two are mixed evenly, stir them with a magnetic stirrer, set the temperature at 80 °C, and heat and melt them in a sealed state. When the magnetic stirrer stirs until it shows a colorless and clear liquid, then dry the obtained ionic liquid for 12 hours, store it in a vacuum seal. Then add 0.5 mol of NiCl₂·6H₂O and 0.6 mol of WCl₆·2H₂O to form a ChCl-2Gly-NiCl₂·6H₂O-WCl₆·2H₂O deep eutectic ionic electroplating solution; finally form a 10 - 20 μm dense nickel-tungsten composite coating.

[0046] The filet knife method was used for qualitative inspection of the bonding force between the coating and the substrate. The results showed that the surface of the composite coating was bright, smooth, without pinholes and cracks, and there was no peeling or falling off after the filet knife test; Wear resistance was tested on a German SST-ST pin-on-disc friction and wear testing machine, with a friction coefficient of 0.12; The surface roughness was above Ra10; Simulate the formation solution of an oilfield, the composition is shown in Table 1. Put the coupling coating coupon sample and the prepared solution into a 15 L high-temperature and high-pressure autoclave. The sample data is shown in Table 2, the temperature is 60 °C, the rotation speed is 0.5 m / s. After 120 h, take out the coupon sample and calculate according to the following formula:

[0047]

[0048] Among them, CR represents the uniform corrosion rate, with the unit of mm / a; W is the mass loss, with the unit of mg; A is the surface area of the sample, with the unit of mm 2 ; D is the density of the material, with the unit of mg / cm 3 ; t is the experimental time, with the unit of h.

[0049] After calculation, its corrosion rate is 0.04 mm / a. According to the NACE SP0775-2018-SG standard, its corrosion resistance is good, and there is no pitting on the surface, and the coating integrity is good.

[0050] Table 1 Ionic composition of the formation aqueous solution in an oilfield (mg / l)

[0051] <![CDATA[Cl - > <![CDATA[SO4 2- > <![CDATA[CO3 2- > <![CDATA[HCO3 - > <![CDATA[Ca 2+ > <![CDATA[Na + > <![CDATA[S 2- > 1339.0 163.0 310.1 221.3 132.6 870.1 57.6

[0052] Table 2 Laboratory corrosion rate calculation data (mm / a)

[0053] Specimen number Weight before test / g Weight after test / g Length / mm Width / mm Thickness / mm <![CDATA[Surface area / mm 2 > Test time / h Corrosion rate / (mm / a) 1 11.2281 11.2227 50.26 10.08 3.06 1382.5224 120 0.0362 2 11.1958 11.1907 49.93 10.00 2.98 1355.7828 120 0.0365 3 11.2092 11.2038 50.03 10.00 3.09 1371.5854 120 0.0343

[0054] The whole pipe body was evaluated for corrosion using a full-scale corrosion physical evaluation device. A short section of N80 steel grade tubing was placed in the full-scale corrosion physical evaluation device to simulate the downhole load conditions. An axial load of 678 kN was applied to it with a bend of 15°. The prepared formation aqueous solution was passed through it for 96 h and then taken out. The short section was uncoupled, and it was observed that no corrosion occurred on the inner surface of the coupling and the outer surface of the pipe body.

[0055] Example 2

[0056] Surface treatment for corrosion resistance and hydrogen embrittlement resistance of the special thread of P110 steel grade 114.3 mm × 8.56 mm casing thread is as follows:

[0057] S1: First, two sections with a length of 1 m were cut from the casing blank of P110 steel grade. The size of the coupling material was 254.6 mm × 22 mm. The internal and external threads were processed respectively using an OKUMA CNC horizontal machine tool.

[0058] S2: After thread processing, it was decontaminated and degreased twice with a low-alkali cleaning solution at room temperature. Then, it was cleaned by hot water washing and water washing on the inner and outer surfaces of the coupling respectively, dried for standby, and the parts to be processed were inspected by the coloring flaw detection method. It was required that there were no cracks, pores, and inclusion defects in the processed parts. The surface roughness value Ra of the thread was 2.5, and the surface roughness value Ra of the sealing surface was 1.1.

[0059] S3: The prepared specimens were put into an industrial bell-jar type plasma carburizing furnace for carburizing treatment. During the carburizing process, the voltage was controlled at 550 V, the duty cycle was 60%. H2 and CO2 with flow rates of 450 ml / min and 25 ml / min were respectively introduced as reaction gases. The air pressure during the heat preservation process was 150 Pa, the nitriding temperature was 500 °C, and the heat preservation time was 8 h. After the heat preservation was completed, it was cooled in the furnace.

[0060] S4: The couplings after carburizing treatment were put into a deep eutectic-based ion mixture. A double-pulse power supply was used to deposit on the inner and outer surfaces of the couplings at an electroplating solution temperature of 65 - 70 °C. Control parameters: voltage: 200 - 400 V, number of pulses 500 - 999, duty cycle 40 - 60%, current density 7 A / dm 2, Pulse wave regulation frequency: 100 - 3000 Hz; Deep eutectic-based ionic mixture: Mix 2-hydroxyethyltrimethylammonium chloride and glycerol in a molar ratio of 0.5:1 and place them in a 1000 mL glass conical flask. After they are mixed evenly, stir them with a magnetic stirrer, set the temperature at 80 °C, and heat and melt them in a sealed state. When the magnetic stirrer stirs until it shows a colorless and clear liquid, then dry the obtained ionic liquid for 12 hours, store it in a vacuum seal. Then add 0.5 mol NiCl₂·6H₂O and 0.6 mol WCl₆·2H₂O to form a ChCl-2Gly-NiCl₂·6H₂O-WCl₆·2H₂O deep eutectic ionic electroplating solution, and finally form a 30 - 45 μm dense nickel-tungsten composite coating.

[0061] The bonding strength between the coating and the substrate was qualitatively tested by the file method. The results showed that the surface of the composite coating was bright, smooth, without pinholes and cracks, and there was no peeling or falling off after the file test; Wear resistance was tested on a German SST-ST pin-on-disc friction and wear testing machine, with a friction coefficient of 0.09; The surface roughness was above Ra10; Simulate the formation solution of an oilfield, and its composition is shown in Table 3. Put the coupling coating coupon specimen and the prepared solution into a 15 L high-temperature and high-pressure autoclave. The specimen data is shown in Table 4, with a temperature of 120 °C and a rotation speed of 0.5 m / s. After 120 h, take out the coupon specimen and calculate according to the following formula:

[0062]

[0063] Among them, CR represents the uniform corrosion rate, with the unit of mm / a; W is the mass loss, with the unit of mg; A is the surface area of the specimen, with the unit of mm 2 ; D is the density of the material, with the unit of mg / cm 3 ; t is the experimental time, with the unit of h.

[0064] After calculation, its corrosion rate is 0.06 mm / a. According to the NACE SP0775-2018-SG standard, its corrosion resistance is good, and there is no pitting corrosion on the surface, and the coating integrity is good.

[0065] Table 3 Ionic composition of the formation aqueous solution in an oilfield (mg / l)

[0066] <![CDATA[Cl - > <![CDATA[SO4 2- > <![CDATA[CO3 2- > <![CDATA[HCO3 - > <![CDATA[Ca 2+ > <![CDATA[Na + > <![CDATA[S 2- > 2339.0 163.0 310.1 221.3 132.6 870.1 57.6

[0067] Table 4 Laboratory corrosion rate calculation data (mm / a)

[0068] Specimen number Weight before test / g Weight after test / g Length / mm Width / mm Thickness / mm <![CDATA[Surface area / mm 2 > Test time / h Corrosion rate / (mm / a) 4 8.3758 8.3731 40.17 10.01 2.91 1096.251 114 0.05 5 8.3293 8.3255 39.97 10.05 2.92 1095.5138 114 0.063 6 8.1813 8.1778 40.17 10.11 2.85 1098.8334 114 0.061

[0069] The whole pipe body was evaluated for corrosion using a full-scale corrosion physical evaluation device. The P110 steel grade tubing nipple was placed in the full-scale corrosion physical evaluation device, and the downhole load condition was simulated. An axial load of 1978 kN was applied to it with a bend of 15°. After passing the configured formation aqueous solution through it for 114 h, it was taken out, and the nipple was uncoupled. It was observed that no corrosion occurred on the inner surface of the coupling and the outer surface of the pipe body.

[0070] In summary, the surface treatment method for corrosion resistance and hydrogen embrittlement resistance of the oil casing thread of the present invention is applicable to the treatment of the thread joints of steel pipes and pipe fittings with complex shapes composed of threads, sealing surfaces, shoulders, etc.

[0071] As mentioned above, the above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A surface treatment method for corrosion resistance and hydrogen embrittlement resistance of oil casing threads, characterized in that: It includes the following steps: S1: Thread the oil casing coupling, with the thread depth being the designed tooth height and the tolerance range being ±0.15 mm; S2: After threading, degrease and defat the oil casing coupling with a cleaning agent at room temperature, and perform flaw detection; S3: Perform carburizing treatment on the inner and outer surfaces of the oil casing coupling; the carburizing treatment is carried out in an industrial plasma carburizing furnace. The specific parameters of the carburizing treatment are as follows: the voltage of the power supply system of the industrial plasma carburizing furnace is 200 - 650 V, the duty cycle is 50 - 64%, and the holding time is 3 h - 7 h; when performing plasma carbonitriding, the flow rate of the reaction gas H2 is 300 - 450 ml / min, and the flow rate of CO2 is 10 - 25 ml / min; during the reaction process, the air pressure is 100 - 200 Pa, the temperature is 300 - 500 °C, and after completion, it is cooled in the furnace; S4: Place the carburized casing coupling into the deep eutectic-based ionic mixture. The specific preparation process of the deep eutectic-based ionic mixture is as follows: Mix 0.3 - 0.6 parts of 2-hydroxyethyltrimethylammonium chloride and 0.6 - 1.2 parts of glycerol evenly according to the molar ratio to form a chlorine-based eutectic ionic solution ChCl-2Gly DES. In the ChCl-2Gly DES ionic solution, add 2 - 3 parts of 0.5 mol / l NiCl2·6H2O and 2 - 5 parts of 0.6 mol / l WCl6·2H2O respectively to form a ChCl-2Gly-NiCl2·6H2O-WCl6·2H2O deep eutectic ionic electroplating solution. Use a dual-pulse power supply to deposit on the inner and outer surfaces of the coupling to form a nickel-tungsten composite coating. Use a dual-pulse power supply to deposit on the inner and outer surfaces of the coupling. The specific control parameters are: dual-pulse power supply voltage: 200 - 400 V, number of pulses 500 - 999, duty cycle 40 - 60%, current density is 7 A / dm 2 , pulse modulation frequency: 100 - 3000 Hz; S5: Clean, dry, and store the oil casing coupling with clean water to complete the surface treatment of the oil casing thread for corrosion resistance and hydrogen embrittlement resistance.

2. The surface treatment method for corrosion resistance and hydrogen embrittlement resistance of oil casing threads according to claim 1, characterized in that: In step S1, the surface roughness value Ra of the oil casing thread after threading is ≤3.2, and the surface roughness value Ra of the sealing surface is ≤1.

6.

3. The surface treatment method for corrosion resistance and hydrogen embrittlement resistance of oil casing threads according to claim 1, wherein: In step S2, the oil casing coupling is degreased and defatted with a cleaning agent at least twice. The cleaning agent is low-alkaline, with a PH range of 7 - 8. After degreasing and defatting, the inner and outer surfaces of the coupling are cleaned with hot water wash and water wash respectively. The hot water temperature range for the hot water wash is 50 °C - 60 °C, and the water temperature range for the water wash is 20 °C - 25 °C.

4. The surface treatment method for corrosion resistance and hydrogen embrittlement resistance of oil casing threads according to claim 1, characterized in that: In step S2, the flaw detection method is the dye penetrant inspection method or the wet magnetic flaw detection method.

5. The surface treatment method for corrosion resistance and hydrogen embrittlement resistance of oil casing threads according to claim 1, characterized in that: In step S4, the thickness of the formed nickel-tungsten composite coating is 15 - 45 μm.

6. The surface treatment method for corrosion resistance and hydrogen embrittlement resistance of oil casing threads according to claim 1, characterized in that: The specific preparation process of the ChCl-2Gly DES ionic solution is as follows: Stir 2-hydroxyethyltrimethylammonium chloride and glycerol evenly into a mixture. Under a sealed state, heat and melt the mixture. The heating temperature is 70 °C - 80 °C, and continue to stir during the heating process until the mixture becomes a colorless and clear liquid. Dry the obtained colorless and clear liquid for at least 12 hours to form the ChCl-2Gly DES ionic solution, and store it in a vacuum seal.