Preparation Method of High Temperature Corrosion Resistant Coating Inside Steel Pipe Elbow and Brush Plating Solution for the Same

Abstract

The present invention discloses a method for preparing a high-temperature corrosion-resistant coating on the inside of a steel pipe elbow and a brush plating solution therefor, which comprises at least the following steps: sandblasting: sandblasting the elbow using a nozzle; electrocleaning: pouring electrocleaning liquid into the steel pipe elbow; during electrocleaning, the anode electrode is inserted into the elbow of the steel pipe elbow, and the cathode electrode is connected to the outer wall of the elbow; after electrocleaning, water washing and hot air drying are performed; activation: pouring activation liquid into the steel pipe elbow; during activation, the anode electrode is inserted into the elbow of the steel pipe elbow, and the cathode electrode is connected to the outer wall of the elbow; after electrocleaning, water washing and hot air drying are performed; brush plating: pouring brush plating liquid into the steel pipe elbow for brush plating, and after brush plating, water washing and hot air drying are performed; heat treatment: heat treatment is performed using a high-temperature salt bath heat treatment method, and cooling is performed after leaving the furnace. The present invention provides a protective coating for high-temperature boiler pipes. The coating is locally applied and has good effect. The coating has high hardness, wear resistance and high temperature resistance, and can improve service safety and service life.

Description

Technical Field

[0001] The present invention relates to the technical field of surface treatment, in particular to a method for preparing a high-temperature corrosion-resistant coating inside a steel pipe elbow and a brush plating solution therefor. Background Art

[0002] In thermal power generating units, pipelines are mainly used to carry and transport steam to the steam turbine, thereby driving the steam turbine to convert thermal energy into electrical energy.

[0003] During their service life, the pipelines of generator sets used for waste heat recovery face multiple harsh service environments, including erosion by high-temperature flue gas outside the pipes and erosion by heat exchange circulating water inside the pipes. Their operating pressure is usually high, and the pipes must also withstand erosion by high-temperature, high-speed water flow and vibration. The designed service life is over 15 years, and the reliability requirements are very high. At present, the outside of the elbow is usually protected by a stainless steel sheath, while the inside is in a bare steel state, and the steel pipes are mostly low-carbon, non-corrosion-resistant steel such as 20g. At the same time, pipe elbows are generally delivered as finished products, and secondary surface treatment of the elbows is difficult to perform. Therefore, it is urgent to take protective measures for the bare steel inside the elbow to reduce the damage caused by internal high-temperature, high-speed water flow.

[0004] The invention patent aims to provide a method for preparing a high-temperature corrosion-resistant coating inside a steel pipe elbow and a brush plating solution therefor. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a method for preparing a high-temperature corrosion-resistant coating on the inside of a steel pipe elbow and a brush plating solution therefor.

[0006] The technical solution adopted in the present invention is as follows:

[0007] A high-temperature corrosion-resistant brush plating solution for the interior of a steel pipe elbow is provided. According to concentration measurement, the concentrations of the components in a fixed volume of the brush plating solution are 360-420 g / L of nickel sulfate, 18-28 g / L of sodium tungstate, 4-6 g / L of cobalt sulfate, 2-5 g / L of zinc sulfate, 35-45 g / L of citric acid, 30-36 g / L of boric acid, 20-27 g / L of acetic acid, 6-8 g / L of sodium sulfate, 0.02-0.045 g / L of sodium lauryl sulfate, and 4-6 g / L of sodium fluoride. The pH value of the brush plating solution is 1.5-2.2.

[0008] A method for preparing a high-temperature corrosion-resistant coating on the inside of a steel pipe elbow comprises at least the following steps:

[0009] Sandblasting: Use a nozzle to extend into the steel pipe elbow to sandblast the inner wall of the outer arc of the elbow. Hard abrasives are used in the sandblasting process. The nozzle moves toward the inner wall of the inner arc of the elbow so that all parts of the elbow are sandblasted.

[0010] Electrocleaning: Pour the electrocleaning liquid into the steel pipe elbow until the liquid level contacts the lowest point of the inner arc wall of the elbow; the inner angle of the steel pipe elbow faces upward, and the bisector of the inner angle is perpendicular to the horizontal line; during electrocleaning, the anode electrode extends into the elbow of the steel pipe elbow, and the cathode electrode is connected to the outer wall of the elbow; after electrocleaning, wash with water and dry with hot air;

[0011] Activation: Pour the activation liquid into the steel pipe elbow, with the liquid surface in contact with the lowest point of the inner arc wall of the elbow; the inner angle of the steel pipe elbow faces upward, and the bisector of the inner angle is perpendicular to the horizontal line; during activation, the anode electrode is inserted into the elbow of the steel pipe elbow, and the cathode electrode is connected to the outer wall of the elbow; after activation, wash with water and dry with hot air;

[0012] Brush plating: Pour the brush plating liquid into the steel pipe elbow for brush plating, with the inner angle of the steel pipe elbow facing upwards and the inner angle bisector perpendicular to the horizontal line; the depth of the brush plating liquid in the elbow is equal to the radius of the straight pipe. After brush plating, wash with water and dry with hot air;

[0013] Heat treatment: The inner angle of the steel pipe elbow is facing upward, and the bisector of the inner angle is perpendicular to the horizontal line; the heat treatment is carried out in a high-temperature salt bath, and the depth of the elbow immersed in the molten salt is tangent to the lowest point of the inner wall of the inner arc of the elbow, and it is cooled after being taken out of the furnace.

[0014] Furthermore, the hard abrasive grains include at least one of steel sand, aluminum oxide, quartz sand, and silicon carbide, and the particle size of the hard abrasive grains is 100-150 meshes.

[0015] Furthermore, the particle size of the hard abrasive particles is any value among 100 mesh, 110 mesh, 120 mesh, 130 mesh, 140 mesh, 150 mesh, or a range value between two values.

[0016] Furthermore, the sandblasting time is 12~15s, the outlet air pressure of the nozzle is 0.6~0.8MPa, the angle between the nozzle and the straight pipe tangent point of the steel pipe elbow is 80~85 degrees, and the distance between the nozzle and the straight pipe tangent point of the steel pipe elbow is 8~12cm.

[0017] Furthermore, the sandblasting time is any value among 12s, 13s, 14s, 15s, or a range value between two values.

[0018] Furthermore, the outlet air pressure of the nozzle is any value among 0.6 MPa, 0.7 MPa, 0.8 MPa, or a range between the two values.

[0019] Furthermore, the angle between the nozzle and the straight pipe tangent point of the steel pipe elbow is any value among 80 degrees, 81 degrees, 82 degrees, 83 degrees, 84 degrees, 85 degrees, or a range between two values.

[0020] Furthermore, the distance between the nozzle and the straight pipe tangent point of the steel pipe elbow is any value among 8 cm, 9 cm, 10 cm, 11 cm, 12 cm, or a range value between two values.

[0021] Furthermore, according to concentration measurement, the concentrations of each component in a fixed volume of electro-cleaning liquid are 25~30g / L of sodium hydroxide, 20~25g / L of sodium carbonate, 40~50g / L of sodium phosphate, and 2~3g / L of sodium chloride.

[0022] Furthermore, according to concentration measurement, the concentrations of the components in the fixed volume activation solution are 80-84 g / L sulfuric acid, 108-112 g / L ammonium sulfate, and 2.5-5 g / L nickel chloride.

[0023] Furthermore, the brush head used in the brush plating is a saddle-shaped flexible plastic brush head inlaid with an array of parallel graphite blocks.

[0024] Furthermore, a hollow insulating cover is provided outside the anode electrode. The working voltage of the electrolyte is 10-14V, and the processing time is 20-30s; the working voltage of the activation is 10-15V, and the processing time is 10-20s.

[0025] Furthermore, the working voltage of the battery is any value among 10V, 11V, 12V, 13V, 14V or a range between two values.

[0026] Furthermore, the electro-cleaning processing time is any value among 20s, 22s, 24s, 26s, 28s, 30s or a range value between two values.

[0027] Furthermore, the activation working voltage is any value among 10V, 11V, 12V, 13V, 14V, 15V, or a range between two values.

[0028] Furthermore, the activation treatment time is any value among 10s, 12s, 14s, 16s, 18s, 20s, or a range value between two values.

[0029] Furthermore, the working voltage of the brush plating is 10-13V, the movement speed of the brush head used in the brush plating is 8-12m / min, and the brush plating time is 20-40s.

[0030] Furthermore, the working voltage of the brush plating is any value among 10V, 11V, 12V, 13V or a range value between two values.

[0031] Furthermore, the brush head movement speed used in brush plating is any value among 8m / min, 9m / min, 10m / min, 11m / min, 12m / min or a range value between two values.

[0032] Furthermore, the brush plating time is any value among 20s, 25s, 30s, 35s, 40s, or a range value between two values.

[0033] Furthermore, the heat treatment temperature of the high-temperature salt bath is 380-400° C., and the holding time is 50-60 minutes.

[0034] Furthermore, the heat treatment temperature of the high temperature salt bath is any value among 380° C., 390° C., 400° C., or a range between the two values.

[0035] Furthermore, the holding time of the high-temperature salt bath is any value among 50 min, 55 min, 60 min, or a range between the two values.

[0036] The beneficial effects of the present invention include at least: the present invention provides a protective coating for high-temperature boiler pipes, the coating is locally applied, the cost is low, and the effect is good; the coating has high hardness, is wear-resistant and high-temperature resistant, and can improve service safety and life. The existing elbow corrosion-resistant coating process is mainly aimed at butt-type elbows, and the elbows are usually independent and small in size. As for the heat exchange tube elbows for generator sets, they are usually based on a hot forming process to directly bend the long tubes, and the large size makes subsequent heat treatment difficult. The present invention overcomes the above process difficulties and provides a method for preparing a high-temperature corrosion-resistant coating on the inside of a steel pipe elbow, which greatly improves the service life of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a flow chart of a method for preparing a high-temperature corrosion-resistant coating on the inside of a steel pipe elbow according to the present invention;

[0038] Figure 2 Schematic diagram of the structure of the steel pipe elbow of the present invention;

[0039] Figure 3 It is a schematic diagram of the brush head for brush plating in the brush plating of the present invention. DETAILED DESCRIPTION

[0040] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention, its application, or use. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0041] See also Figure 1-Figure 2 A method for preparing a high-temperature corrosion-resistant coating on the inside of a steel pipe elbow comprises at least the following steps:

[0042] Sandblasting: Use a nozzle to extend into the steel pipe elbow to sandblast the inner wall of the outer arc of the elbow. Hard abrasives are used in the sandblasting process. The nozzle moves toward the inner wall of the inner arc of the elbow so that all parts of the elbow are sandblasted.

[0043] The hard abrasive grains include at least one of steel sand, aluminum oxide, quartz sand, and silicon carbide, and the particle size of the hard abrasive grains is 100-150 meshes.

[0044] The sandblasting time is 12~15s, the outlet air pressure of the nozzle is 0.6~0.8MPa, the angle between the nozzle and the straight pipe tangent point of the steel pipe elbow is 80~85 degrees, and the distance between the nozzle and the straight pipe tangent point of the steel pipe elbow is 8~12cm.

[0045] Electrocleaning: Pour the electrocleaning liquid into the steel pipe elbow until the liquid level contacts the lowest point of the inner arc wall of the elbow; the inner angle of the steel pipe elbow faces upward, and the bisector of the inner angle is perpendicular to the horizontal line; during electrocleaning, the anode electrode extends into the elbow of the steel pipe elbow, and the cathode electrode is connected to the outer wall of the elbow; after electrocleaning, wash with water and dry with hot air;

[0046] According to concentration measurement, the concentrations of each component in a fixed volume of electro-cleaning solution are 25~30g / L of sodium hydroxide, 20~25g / L of sodium carbonate, 40~50g / L of sodium phosphate, and 2~3g / L of sodium chloride.

[0047] A hollow insulating cover is provided outside the anode electrode. The working voltage of the electrode is 10-14V, and the processing time is 20-30s.

[0048] Activation: Pour the activation liquid into the steel pipe elbow, with the liquid surface in contact with the lowest point of the inner arc wall of the elbow; the inner angle of the steel pipe elbow faces upward, and the bisector of the inner angle is perpendicular to the horizontal line; during activation, the anode electrode is inserted into the elbow of the steel pipe elbow, and the cathode electrode is connected to the outer wall of the elbow; after activation, wash with water and dry with hot air;

[0049] According to the concentration measurement, the concentrations of each component in the fixed volume activation solution are 80~84g / L sulfuric acid, 108~112g / L ammonium sulfate, and 2.5~5g / L nickel chloride.

[0050] A hollow insulating cover is provided outside the anode electrode. The activation working voltage is 10-15V, and the processing time is 10-20s.

[0051] Brush plating: Pour the brush plating liquid into the steel pipe elbow for brush plating, with the inner angle of the steel pipe elbow facing upwards and the inner angle bisector perpendicular to the horizontal line; the depth of the brush plating liquid in the elbow is equal to the radius of the straight pipe. After brush plating, wash with water and dry with hot air;

[0052] According to concentration measurement, the concentrations of the components in a fixed volume of brush plating solution are 360-420 g / L of nickel sulfate, 18-28 g / L of sodium tungstate, 4-6 g / L of cobalt sulfate, 2-5 g / L of zinc sulfate, 35-45 g / L of citric acid, 30-36 g / L of boric acid, 20-27 g / L of acetic acid, 6-8 g / L of sodium sulfate, 0.02-0.045 g / L of sodium lauryl sulfate, and 4-6 g / L of sodium fluoride; the pH of the brush plating solution is 1.5-2.2.

[0053] The brush head used in the brush plating is a saddle-shaped flexible plastic brush head inlaid with an array of parallel graphite blocks, such as Figure 3 shown.

[0054] The working voltage of the brush plating is 10-13V, the movement speed of the brush head used in the brush plating is 8-12m / min, and the brush plating time is 20-40s.

[0055] Heat treatment: The inner angle of the steel pipe elbow is facing upward, and the bisector of the inner angle is perpendicular to the horizontal line; the heat treatment is carried out in a high-temperature salt bath, and the depth of the elbow immersed in the molten salt is tangent to the lowest point of the inner wall of the inner arc of the elbow, and it is cooled after being taken out of the furnace.

[0056] The heat treatment temperature of the high-temperature salt bath is 380-400° C., and the holding time is 50-60 minutes.

[0057] Example 1: This example is implemented on a 20G steel pipe elbow.

[0058] Sandblasting: Use a nozzle to extend into the steel pipe elbow to sandblast the inner wall of the outer arc of the elbow. Hard abrasive steel sand is used in the sandblasting process. The particle size of the hard abrasive steel sand is 150 mesh. The nozzle moves toward the inner wall of the inner arc of the elbow so that all parts of the elbow are sandblasted. The sandblasting time is 12s, the outlet air pressure of the nozzle is 0.6MPa, the angle between the nozzle and the straight pipe tangent point of the steel pipe elbow is 80 degrees, and the distance between the nozzle and the straight pipe tangent point of the steel pipe elbow is 12cm.

[0059] Electrocleaning: Pour a fixed volume of electrocleaning solution containing 25g / L sodium hydroxide, 25g / L sodium carbonate, 45g / L sodium phosphate, and 2g / L sodium chloride into the steel pipe elbow, with the liquid level in contact with the lowest point of the inner arc wall of the elbow. The inner angle of the steel pipe elbow faces upward, with the inner angle bisector perpendicular to the horizontal line. A hollow insulating cover is provided outside the anode electrode. During electrocleaning, the anode electrode extends into the elbow of the steel pipe elbow, and the cathode electrode is connected to the outer wall of the elbow. The operating voltage of the electrocleaning is 10V, and the processing time is 20s. After electrocleaning, the solution is washed with water and dried with hot air.

[0060] Activation: Pour a fixed volume of activation solution containing 80g / L sulfuric acid, 108g / L ammonium sulfate, and 2.5g / L nickel chloride into the steel pipe elbow according to the concentration. The liquid level contacts the lowest point of the inner arc wall of the elbow. The inner angle of the steel pipe elbow faces upward, and the bisector of the inner angle is perpendicular to the horizontal line. A hollow insulating cover is provided outside the anode electrode. During activation, the anode electrode extends into the elbow of the steel pipe elbow, and the cathode electrode is connected to the outer wall of the elbow. The activation working voltage is 10V, the treatment time is 10s, and after the electrocleaning, the elbow is washed with water and dried with hot air.

[0061] Brush plating: according to the concentration and pH of 1.5, a brush plating solution with a fixed volume of each component concentration of 360g / L nickel sulfate, 18g / L sodium tungstate, 4g / L cobalt sulfate, 2g / L zinc sulfate, 35g / L citric acid, 30g / L boric acid, 20g / L acetic acid, 8g / L sodium sulfate, 0.045g / L sodium lauryl sulfate, and 6g / L sodium fluoride was poured into the steel pipe elbow for brush plating. The inner angle of the steel pipe elbow faces upward, and the bisector of the inner angle is perpendicular to the horizontal line. The height from the liquid surface of the brush plating liquid to the lowest point of the inner wall of the outer arc of the elbow is equal to the radius of the straight pipe. The brush head used in the brush plating is a saddle-shaped flexible plastic brush head inlaid with an array of parallel graphite blocks. The surface of the brush head is wrapped with absorbent cotton cloth. The working voltage of the brush plating is 10V, the movement speed of the brush head used in the brush plating is 8m / min, the brush plating time is 20s, and the brush plating is completed by water washing and hot air drying.

[0062] Heat treatment: The inner angle of the steel pipe elbow is facing upward, and the bisector of the inner angle is perpendicular to the horizontal line; the heat treatment is carried out by using a high-temperature salt bath heat treatment method, and the depth of the elbow inserted into the molten salt is tangent to the lowest point of the inner wall of the inner arc of the elbow. The heat treatment temperature is 400℃, the holding time is 60min, and it is cooled after being taken out of the furnace.

[0063] The protective coating prepared by this method has a thickness of about 830 μm and a hardness of about 540 HV, and its ratio to the hardness of the substrate before brush plating is 2.63. The coating is dense and well bonded to the substrate.

[0064] Example 2: This example is implemented on a 20G steel pipe elbow.

[0065] Sandblasting: Use a nozzle to extend into the steel pipe elbow to sandblast the inner wall of the outer arc of the elbow. Hard abrasive aluminum oxide is used in the sandblasting process. The particle size of the hard abrasive aluminum oxide is 100 mesh. The nozzle moves toward the inner wall of the inner arc of the elbow so that all parts of the elbow are sandblasted. The sandblasting time is 13s, the outlet air pressure of the nozzle is 0.7MPa, the angle between the nozzle and the straight pipe tangent point of the steel pipe elbow is 83 degrees, and the distance between the nozzle and the straight pipe tangent point of the steel pipe elbow is 11cm.

[0066] Electrocleaning: Pour a fixed volume of electrocleaning solution containing 28g / L sodium hydroxide, 22g / L sodium carbonate, 50g / L sodium phosphate, and 2.5g / L sodium chloride into the steel pipe elbow, with the liquid level contacting the lowest point of the inner arc wall of the elbow. The inner angle of the steel pipe elbow faces upward, with the bisector of the inner angle perpendicular to the horizontal line. A hollow insulating cover is provided outside the anode electrode. During electrocleaning, the anode electrode extends into the elbow of the steel pipe elbow, and the cathode electrode is connected to the outer wall of the elbow. The operating voltage of the electrocleaning is 12V, and the processing time is 25s. After electrocleaning, the solution is washed with water and dried with hot air.

[0067] Activation: Pour a fixed volume of activation solution containing 84g / L sulfuric acid, 112g / L ammonium sulfate, and 5g / L nickel chloride into the steel pipe elbow, with the liquid level in contact with the lowest point of the inner arc wall of the elbow. The inner angle of the steel pipe elbow faces upward, with the inner angle bisector perpendicular to the horizontal line. A hollow insulating cover is provided outside the anode electrode. During activation, the anode electrode extends into the elbow of the steel pipe elbow, and the cathode electrode is connected to the outer wall of the elbow. The activation voltage is 12V, the processing time is 15s, and after the electrocleaning is completed, the elbow is washed with water and dried with hot air.

[0068] Brush plating: according to the concentration and pH of 1.8, a fixed volume of each component concentration of 380g / L nickel sulfate, 28g / L sodium tungstate, 6g / L cobalt sulfate, 3g / L zinc sulfate, 45g / L citric acid, 36g / L boric acid, 27g / L acetic acid, 6g / L sodium sulfate, 0.02g / L sodium lauryl sulfate, 4g / L sodium fluoride consisting of brush plating solution is poured into the steel pipe elbow for brush plating. The inner angle of the pipe elbow faces upward, and the bisector of the inner angle is perpendicular to the horizontal line. The height from the liquid surface of the brush plating solution to the lowest point of the inner wall of the outer arc of the elbow is equal to the radius of the straight pipe. The brush head used in the brush plating is a saddle-shaped flexible plastic brush head inlaid with an array of parallel graphite blocks. The surface of the brush head is wrapped with absorbent cotton cloth. The working voltage of the brush plating is 12V, the brush head movement speed used in the brush plating is 10m / min, the brush plating time is 30s, and the brush plating is completed by water washing and hot air drying.

[0069] Heat treatment: The inner angle of the steel pipe elbow is facing upward, and the bisector of the inner angle is perpendicular to the horizontal line; the heat treatment is carried out in a high-temperature salt bath, and the depth of the elbow immersed in the molten salt is tangent to the lowest point of the inner wall of the inner arc of the elbow. The heat treatment temperature is 390℃, the holding time is 50 minutes, and it is cooled after being taken out of the furnace.

[0070] The protective coating prepared by this method has a thickness of about 910 μm and a hardness of about 549 HV, and its ratio to the hardness of the substrate before brush plating is 2.68. The coating is dense and well bonded to the substrate.

[0071] Example 3: This example is implemented on a 20G steel pipe elbow.

[0072] Sandblasting: Use a nozzle to extend into the steel pipe elbow to sandblast the inner wall of the outer arc of the elbow. Hard abrasive quartz sand is used in the sandblasting process. The particle size of the hard abrasive quartz sand is 120 mesh. The nozzle moves toward the inner wall of the inner arc of the elbow so that all parts of the elbow are sandblasted. The sandblasting time is 15s, the outlet air pressure of the nozzle is 0.8MPa, the angle between the nozzle and the straight pipe tangent point of the steel pipe elbow is 85 degrees, and the distance between the nozzle and the straight pipe tangent point of the steel pipe elbow is 8cm.

[0073] Electrocleaning: Pour a fixed volume of electrocleaning solution containing 30g / L sodium hydroxide, 20g / L sodium carbonate, 40g / L sodium phosphate, and 3g / L sodium chloride into the steel pipe elbow, with the liquid level contacting the lowest point of the inner arc wall of the elbow. The inner angle of the steel pipe elbow faces upward, with the inner angle bisector perpendicular to the horizontal line. A hollow insulating cover is provided outside the anode electrode. During electrocleaning, the anode electrode extends into the elbow of the steel pipe elbow, and the cathode electrode is connected to the outer wall of the elbow. The operating voltage of the electrocleaning is 14V, and the processing time is 30s. After electrocleaning, the solution is washed with water and dried with hot air.

[0074] Activation: Pour a fixed volume of activation solution containing 82g / L sulfuric acid, 110g / L ammonium sulfate, and 3.5g / L nickel chloride into the steel pipe elbow according to the concentration measurement. The liquid surface contacts the lowest point of the inner wall of the inner arc of the elbow. The inner angle of the steel pipe elbow faces upward, and the bisector of the inner angle is perpendicular to the horizontal line. A hollow insulating cover is provided outside the anode electrode. During activation, the anode electrode extends into the elbow of the steel pipe elbow, and the cathode electrode is connected to the outer wall of the elbow. The working voltage of the activation is 15V, and the processing time is 20s. After the electrocleaning is completed, the elbow is washed with water and dried with hot air.

[0075] Brush plating: according to the concentration and pH of 2.2, a fixed volume of each component concentration of 420g / L nickel sulfate, 24g / L sodium tungstate, 5g / L cobalt sulfate, 5g / L zinc sulfate, 40g / L citric acid, 32g / L boric acid, 25g / L acetic acid, 7g / L sodium sulfate, 0.03g / L sodium lauryl sulfate, 5g / L sodium fluoride is poured into the steel pipe elbow for brush plating. The inner angle of the pipe elbow faces upward, and the bisector of the inner angle is perpendicular to the horizontal line. The height from the liquid surface of the brush plating solution to the lowest point of the inner wall of the outer arc of the elbow is equal to the radius of the straight pipe. The brush head used in the brush plating is a saddle-shaped flexible plastic brush head inlaid with an array of parallel graphite blocks. The surface of the brush head is wrapped with absorbent cotton cloth. The working voltage of the brush plating is 13V, the brush head movement speed used in the brush plating is 12m / min, the brush plating time is 40s, and the brush plating is completed by water washing and hot air drying.

[0076] Heat treatment: The inner angle of the steel pipe elbow is facing upward, and the bisector of the inner angle is perpendicular to the horizontal line; the heat treatment is carried out in a high-temperature salt bath, and the depth of the elbow immersed in the molten salt is tangent to the lowest point of the inner wall of the inner arc of the elbow. The heat treatment temperature is 380℃, the holding time is 55 minutes, and it is cooled after being taken out of the furnace.

[0077] The protective coating prepared by this method has a thickness of about 890 μm and a hardness of about 546 HV, and its ratio to the hardness of the substrate before brush plating is 2.66. The coating is dense and well bonded to the substrate.

[0078] Example 4: This example is implemented on a 20G steel pipe elbow.

[0079] Sandblasting: Use a nozzle to extend into the steel pipe elbow to sandblast the inner wall of the outer arc of the elbow. Hard abrasive silicon carbide is used in the sandblasting process. The particle size of the hard abrasive silicon carbide is 130 mesh. The nozzle moves toward the inner wall of the inner arc of the elbow so that all parts of the elbow are sandblasted. The sandblasting time is 14s, the outlet air pressure of the nozzle is 0.6MPa, the angle between the nozzle and the straight pipe tangent point of the steel pipe elbow is 84 degrees, and the distance between the nozzle and the straight pipe tangent point of the steel pipe elbow is 10cm.

[0080] Electrocleaning: Pour a fixed volume of electrocleaning solution containing 26g / L sodium hydroxide, 21g / L sodium carbonate, 48g / L sodium phosphate, and 2g / L sodium chloride into the steel pipe elbow, with the liquid level contacting the lowest point of the inner arc wall of the elbow. The inner angle of the steel pipe elbow faces upward, with the inner angle bisector perpendicular to the horizontal line. A hollow insulating cover is provided outside the anode electrode. During electrocleaning, the anode electrode extends into the elbow of the steel pipe elbow, and the cathode electrode is connected to the outer wall of the elbow. The operating voltage of the electrocleaning is 13V, and the processing time is 28s. After electrocleaning, the solution is washed with water and dried with hot air.

[0081] Activation: Pour a fixed volume of activation solution containing 83g / L sulfuric acid, 110g / L ammonium sulfate, and 4g / L nickel chloride into the steel pipe elbow, with the liquid level in contact with the lowest point of the inner arc wall of the elbow. The inner angle of the steel pipe elbow faces upward, with the inner angle bisector perpendicular to the horizontal line. A hollow insulating cover is provided outside the anode electrode. During activation, the anode electrode extends into the elbow of the steel pipe elbow, and the cathode electrode is connected to the outer wall of the elbow. The activation voltage is 10V, the treatment time is 15s, and after the electrocleaning is completed, the elbow is washed with water and dried with hot air.

[0082] Brush plating: according to the concentration and pH of 2, a fixed volume of each component concentration of 400g / L nickel sulfate, 22g / L sodium tungstate, 4g / L cobalt sulfate, 4g / L zinc sulfate, 42g / L citric acid, 34g / L boric acid, 22g / L acetic acid, 8g / L sodium sulfate, 0.02g / L sodium lauryl sulfate, 6g / L sodium fluoride consisting of brush plating solution is poured into the steel pipe elbow for brush plating. The inner angle of the elbow faces upward, and the bisector of the inner angle is perpendicular to the horizontal line. The height from the liquid surface of the brush plating liquid to the lowest point of the inner wall of the outer arc of the elbow is equal to the radius of the straight tube. The brush head used in the brush plating is a saddle-shaped flexible plastic brush head inlaid with an array of parallel graphite blocks. The surface of the brush head is wrapped with absorbent cotton cloth. The working voltage of the brush plating is 10V, the movement speed of the brush head used in the brush plating is 8m / min, the brush plating time is 35s, and the brush plating is completed by water washing and hot air drying.

[0083] Heat treatment: The inner angle of the steel pipe elbow is facing upward, and the bisector of the inner angle is perpendicular to the horizontal line; the heat treatment is carried out by using a high-temperature salt bath heat treatment method, and the depth of the elbow inserted into the molten salt is tangent to the lowest point of the inner wall of the inner arc of the elbow. The heat treatment temperature is 400℃, the holding time is 60min, and it is cooled after being taken out of the furnace.

[0084] The protective coating prepared by this method has a thickness of about 850 μm and a hardness of about 542 HV, and its ratio to the hardness of the substrate before brush plating is 2.64. The coating is dense and well bonded to the substrate.

[0085] In summary, compared with the steel pipe elbow before the implementation of this method, the wear resistance and corrosion resistance of the steel pipe elbow after the electroplating brush coating are significantly improved. There are two reasons for this:

[0086] The plated coating is mainly composed of Ni-W fine-grained coating, and second-phase hard particles such as multiple carbides and intermetallic compounds may be precipitated inside, which significantly improves the wear resistance and erosion resistance of the material at high temperatures; at the same time, at the salt bath temperature, the coating elements and the matrix elements will also combine with each other to form new intermetallic compounds, thereby improving the density of the coating and having better implementation effect and service life.

[0087] The process of the present invention addresses the problem of internal coating plating of long pipe elbows and proposes a feasible, efficient and low-cost implementation plan. The characteristic process is proposed in combination with the external morphological characteristics, which has strong feasibility and economic benefits.

[0088] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a high-temperature corrosion-resistant coating on the inside of a steel pipe elbow, characterized in that: At least the following steps are included: Sandblasting: Use a nozzle to extend into the steel pipe elbow to sandblast the inner wall of the outer arc of the elbow. Hard abrasives are used in the sandblasting process. The nozzle moves toward the inner wall of the inner arc of the elbow so that all parts of the elbow are sandblasted. Electrocleaning: Pour the electrocleaning liquid into the steel pipe elbow until the liquid surface contacts the lowest point of the inner arc wall of the elbow; the inner angle of the steel pipe elbow faces upward, and the bisector of the inner angle is perpendicular to the horizontal line; during electrocleaning, the anode electrode extends into the elbow of the steel pipe elbow, and the cathode electrode is connected to the outer wall of the elbow; after electrocleaning, rinse with water and dry with hot air; according to concentration measurement, the concentrations of each component in a fixed volume of electrocleaning liquid are 25-30g / L of sodium hydroxide, 20-25g / L of sodium carbonate, 40-50g / L of sodium phosphate, and 2-3g / L of sodium chloride. Activation: Pour the activation solution into the steel pipe elbow until the liquid surface contacts the lowest point of the inner arc wall of the elbow; the inner angle of the steel pipe elbow faces upward, and the bisector of the inner angle is perpendicular to the horizontal line; during activation, the anode electrode extends into the elbow of the steel pipe elbow, and the cathode electrode is connected to the outer wall of the elbow; after activation, wash with water and dry with hot air; according to the concentration measurement, the concentrations of each component in a fixed volume of activation solution are 80-84g / L sulfuric acid, 108-112g / L ammonium sulfate, and 2.5-5g / L nickel chloride. Brush plating: pouring the brush plating liquid into the steel pipe elbow for brush plating, with the inner angle of the steel pipe elbow facing upward and the bisector of the inner angle perpendicular to the horizontal line; the depth of the brush plating liquid in the elbow is equal to the radius of the straight pipe, and after the brush plating is completed, washing with water and hot air drying are performed; according to concentration measurement, the concentrations of the components in the fixed volume brush plating liquid are 360-420 g / L nickel sulfate, 18-28 g / L sodium tungstate, 4-6 g / L cobalt sulfate, 2-5 g / L zinc sulfate, 35-45 g / L citric acid, 30-36 g / L boric acid, 20-27 g / L acetic acid, 6-8 g / L sodium sulfate, 0.02-0.045 g / L sodium lauryl sulfate, and 4-6 g / L sodium fluoride; the pH of the brush plating liquid is 1.5-2.2; Heat treatment: The inner angle of the steel pipe elbow is facing upward, and the bisector of the inner angle is perpendicular to the horizontal line; the heat treatment is carried out in a high-temperature salt bath, and the depth of the elbow immersed in the molten salt is tangent to the lowest point of the inner wall of the inner arc of the elbow, and it is cooled after being taken out of the furnace.

2. The method for preparing a high-temperature corrosion-resistant coating on the inside of a steel pipe elbow according to claim 1, characterized in that: The hard abrasive grains include at least one of steel sand, aluminum oxide, quartz sand, and silicon carbide, and the particle size of the hard abrasive grains is 100-150 meshes.

3. The method for preparing a high-temperature corrosion-resistant coating on the inside of a steel pipe elbow according to claim 1, characterized in that: The sandblasting time is 12~15s, the outlet air pressure of the nozzle is 0.6~0.8MPa, the angle between the nozzle and the straight pipe tangent point of the steel pipe elbow is 80~85 degrees, and the distance between the nozzle and the straight pipe tangent point of the steel pipe elbow is 8~12cm.

4. The method for preparing a high-temperature corrosion-resistant coating on the inside of a steel pipe elbow according to claim 1, characterized in that: The brush head used in the brush plating is a saddle-shaped flexible plastic brush head inlaid with array parallel graphite blocks.

5. The method for preparing a high-temperature corrosion-resistant coating on the inside of a steel pipe elbow according to claim 1, characterized in that: A hollow insulating cover is provided outside the anode electrode. The working voltage of the electrolyte is 10-14V, and the processing time is 20-30s; the working voltage of the activation is 10-15V, and the processing time is 10-20s.

6. The method for preparing a high-temperature corrosion-resistant coating on the inside of a steel pipe elbow according to claim 1, characterized in that: The working voltage of the brush plating is 10-13V, the movement speed of the brush head used in the brush plating is 8-12m / min, and the brush plating time is 20-40s.

7. The method for preparing a high-temperature corrosion-resistant coating on the inside of a steel pipe elbow according to claim 1, characterized in that: The heat treatment temperature of the high-temperature salt bath is 380-400° C., and the holding time is 50-60 minutes.

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