A method for preparing a bearing sleeve for a nuclear power steam turbine reheat valve

Abstract

This invention belongs to the field of protective coatings for reheat valves in nuclear power turbines, and particularly relates to a method for preparing a turbine reheat valve bearing sleeve. The invention employs a ring forging process to prepare the base material, and utilizes a combination of explosive spraying and shot peening to prepare a wear-resistant and lubricating coating containing Cr3C2, Cr3O2, and NiCrMo in the coating area. The coating hardness reaches 450-650 HV, and the bonding strength is ≥120 MPa. Through shot peening and explosive spraying techniques, a turbine reheat valve bearing sleeve with high wear resistance, high corrosion resistance, and lubrication function is prepared, effectively improving the water vapor corrosion resistance of the bearing sleeve, reducing the rotational torque of the bearing friction pair, and extending the service life of the bearing friction pair components.

Description

Technical Field

[0001] This invention belongs to the field of protective coatings for reheat valves of nuclear power turbines, and particularly relates to a method for preparing a bearing sleeve for a reheat valve of a nuclear power turbine. Background Technology

[0002] The steam turbine of a pressurized water reactor (PWR) nuclear power plant uses saturated wet steam as its inlet, with a steam flow rate almost twice that of a thermal power unit of the same power rating. Therefore, the high-pressure cylinder, steam-water separator reheater, and piping of the nuclear power turbine contain a large amount of steam and water. During an accident shutdown or load shedding, the pressure downstream of the main steam valve decreases, and residual water may flash into steam. This steam can cause turbine overspeed, endangering the safe operation of the turbine. The function of the nuclear power plant reheat valve assembly is firstly to prevent a large amount of steam from the steam-water separator reheater and piping from continuing to enter the low-pressure cylinder, thus preventing the risk of overspeed operation. Secondly, it regulates the steam flow rate of the turbine and controls the steam intake of the low-pressure cylinder. The reheat valve plays a crucial role in the operation of a nuclear power unit. If the reheat valve malfunctions and cannot close during operation, turbine overspeed may occur during an accident shutdown or load shedding.

[0003] The friction pair consisting of the turbine reheat valve bearing and bearing sleeve is the main moving component of the turbine reheat valve. Operating in a complex environment of steam and water at 16 bar and 300℃, the theoretical contact stress between the bearing and bearing sleeve exceeds 500 MPa. During turbine operation, the main steam valve opening and closing time must be ≤50s, and the regulating valve opening and closing time ≤5s. The working environment of the turbine reheat valve bearing is extremely harsh. The surface of the turbine reheat valve bearing is typically hardened with a wear-resistant coating, achieving a hardness of 750-950 HV, while the bearing sleeve has a lower hardness of 300-350 HV. During use, factors such as insufficient machining precision of the bearing sleeve, low bearing sleeve hardness, and corrosion from the water vapor environment frequently lead to abnormal wear and peeling of the friction pair surface between the turbine reheat valve bearing and bearing sleeve. This results in increased frictional resistance of the turbine reheat valve bearing, causing jamming or even shutdown. There is an urgent need to develop a nuclear power turbine reheat valve bearing sleeve with a longer service life, high wear resistance, high corrosion resistance, and lubrication function. Summary of the Invention

[0004] To address the problems in existing technologies, the present invention aims to provide a method for manufacturing a reheat valve bearing sleeve for a nuclear power turbine. The manufacturing method of the nuclear power turbine reheat valve bearing sleeve of the present invention can effectively improve the water vapor corrosion resistance of the bearing sleeve, reduce the rotational torque of the bearing friction pair, and extend the service life of the bearing friction pair components. The technical solution of the present invention to solve this technical problem is as follows:

[0005] A method for preparing a reheat valve bearing sleeve for a nuclear power turbine, the method comprising the following steps:

[0006] Step 1: Base forging

[0007] The base material is made of nuclear-grade stainless steel ring forgings with a machining allowance of not less than 5 mm, a Co content of ≤0.25%, and a tensile strength of 800~950MPa;

[0008] Step 2: Rough machining of the substrate

[0009] Using the bearing center hole as a reference, machine the outer circular surface and inner hole surface of the substrate to ensure that the coaxiality of the outer circular surface and the inner hole surface meets 0.02mm. The machining allowance in the non-coated area is not less than 0.5mm, and the coating area has a reserved thickness of 0.20-0.50mm.

[0010] Step 3: Shot peening of internal holes

[0011] The inner surface of the bearing sleeve is shot-peened using a sandblasting process. Spherical zirconia ceramic pellets are used, with a hardness of HRC 55-65 and a surface residual compressive stress of 400-600 MPa.

[0012] Step 4: Internal hole spraying

[0013] A wear-resistant and lubricating coating is applied to the inner surface of the bearing sleeve using an explosive spraying process. The coating thickness is 0.30-0.60 mm, the coating hardness is 450-650 HV, and the bonding strength is ≥120 MPa. The reheat valve bearing sleeve is then heated to 130℃~180℃ in an oven after spraying. After removal, a penetrating high-temperature lubricating sealant is quickly brushed onto the coating surface. The long-term working temperature of the sealant is not lower than 300℃, and the fluorine impurity content of the sealant is not higher than 0.1 ppm.

[0014] Step 5: Internal hole grinding

[0015] Using the bearing center hole as a reference, align the coaxiality of the outer circular surface to meet 0.02mm, and use a diamond grinding wheel to grind the inner hole coating surface to the specified size. The surface roughness after grinding should not exceed Ra0.4μm.

[0016] Step Six: Remove the protective layer from the bearing surface.

[0017] The bearing was ultrasonically cleaned using an alkaline cleaning agent and industrial acetone in sequence. Finally, the bearing was soaked in deionized water with a fluoride content of no more than 0.1 ppm for no less than 4 hours.

[0018] Preferably, the shot peening process parameters are: shot size 100-200μm, shot peening intensity 0.15-0.30A, and surface coverage 200%.

[0019] Preferably, the main components of the wear-resistant lubricating coating are Cr3C2, Cr2O3 and NiCrMo, with the following weight percentages: Cr3C2 content 60% to 65%, Cr2O3 content 0.1% to 10%, and NiCrMo content 25% to 30%.

[0020] Preferably, the explosive spraying process employs a six-axis robotic arm equipped with an explosive spray gun.

[0021] Preferably, the explosive spraying process uses propylene, acetylene, and oxygen as fuel, with a molar ratio of propylene, acetylene, and oxygen of 0.2 mol: 1.0 mol: 1.5 mol, a powder feeding rate of 10 g / min to 15 g / min, and a spraying distance of 200 mm to 400 mm.

[0022] Preferably, the main components of the penetrating high-temperature lubricating sealant are: n-butyl acetate, 2-methylpropanol acetate, hexagonal boron nitride, and chromium oxide.

[0023] Preferably, the penetrating high-temperature lubricating sealant contains 0.1% to 5% hexagonal boron nitride and has a particle size of 50 nm to 200 nm.

[0024] Preferably, the chromium oxide content in the penetrating high-temperature lubricating sealant is 1% to 10%, and the particle size is 50 nm to 200 nm.

[0025] The present invention has the following beneficial effects:

[0026] 1) This invention prepares the base material of the turbine reheat valve bearing sleeve through ring forging process, and pre-applies compressive stress on the inner hole surface through shot peening treatment, which improves the fatigue life of the reheat valve bearing by 80%; at the same time, the surface produces a nano-scale fine grain structure, which significantly improves the corrosion resistance of the material in the water vapor corrosion environment.

[0027] 2) This invention prepares a composite coating of Cr3C2, Cr3O2 and NiCrMo on the inner surface of the bearing sleeve using an explosive spraying process. The addition of components such as Cr3C2, Cr3O2 and Mo improves the hardness and high-temperature lubrication performance of the inner surface of the reheat valve bearing sleeve, and reduces the contact friction coefficient of the reheat valve bearing / bearing sleeve. The coating is sealed by a penetrating high-temperature lubricating sealant, which further improves the coating's lubrication characteristics and corrosion resistance in a high-temperature water vapor environment.

[0028] 3) The service life of the reheat valve bearing sleeve prepared using the present invention can be increased by more than 50%, and the preparation cost is low and the reliability is high. Attached Figure Description

[0029] To more clearly illustrate the technical solutions implemented in this invention, the accompanying drawings used in the embodiments of this invention will be briefly explained below. Obviously, the drawings described below are merely some embodiments of this invention. Those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0030] Figure 1 A schematic diagram of the turbine reheat valve bearing sleeve and bearing.

[0031] Figure 2 This is a picture of the turbine reheat valve bearing sleeve after it has been coated.

[0032] Figure 3 The image shows the cross-sectional morphology of the coating after spraying the bearing sleeve of the turbine reheat valve. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0034] A method for preparing a reheat valve bearing sleeve for a nuclear power turbine, the method comprising the following steps:

[0035] Step 1: Base forging

[0036] The base material is made of nuclear-grade stainless steel ring forgings with a machining allowance of not less than 5 mm, a Co content of ≤0.25%, and a tensile strength of 800~950MPa;

[0037] Step 2: Rough machining of the substrate

[0038] Using the bearing center hole as a reference, machine the outer circular surface and inner hole surface of the substrate to ensure that the coaxiality of the outer circular surface and the inner hole surface meets 0.02mm. The machining allowance in the non-coated area is not less than 0.5mm, and the coating area has a reserved thickness of 0.20-0.50mm.

[0039] Step 3: Shot peening of internal holes

[0040] The inner surface of the bearing sleeve is shot-peened using a sandblasting process. Spherical zirconia ceramic pellets are used, with a hardness of HRC 55-65 and a surface residual compressive stress of 400-600 MPa. The shot-peening parameters are: pellet size 100-200 μm, shot peening intensity 0.15-0.30A, and surface coverage 200%.

[0041] Step 4: Internal hole spraying

[0042] A wear-resistant and lubricating coating is applied to the inner surface of the bearing sleeve using an explosive spraying process. The coating thickness is 0.30-0.60 mm, the coating hardness meets the requirement of 450-650 HV, and the bonding strength is ≥120 MPa. The main components of the wear-resistant and lubricating coating are Cr3C2, Cr2O3, and NiCrMo, with the following weight percentages: Cr3C2 content 60%-65%, Cr2O3 content 0.1%-10%, and NiCrMo content 25%-30%. The explosive spraying process uses a six-axis robot arm equipped with an explosive spray gun. The explosive spraying process uses propylene, acetylene, and oxygen as fuel gas, with a molar ratio of propylene, acetylene, and oxygen of 0.2 mol: 1.0 mol: 1.5 mol. The powder feeding rate is 10 g / min-15 g / min, and the spraying distance is 200 mm-400 mm.

[0043] The sprayed reheat valve bearing is heated in an oven to 130℃~180℃. After removal, a penetrating high-temperature lubricating sealant is quickly brushed onto the coating surface. The long-term operating temperature of the sealant is not lower than 300℃, and the fluorine impurity content of the sealant is not higher than 0.1ppm. The main components of the penetrating high-temperature lubricating sealant are: n-butyl acetate, 2-methylpropanol acetate, hexagonal boron nitride, and chromium oxide. In the penetrating high-temperature lubricating sealant, the hexagonal boron nitride content is 0.1%~5%, and the particle size is 50nm~200nm. In the penetrating high-temperature lubricating sealant, the chromium oxide content is 1%~10%, and the particle size is 50nm~200nm.

[0044] Step 5: Internal hole grinding

[0045] Using the bearing center hole as a reference, align the coaxiality of the outer circular surface to meet 0.02mm, and use a diamond grinding wheel to grind the inner hole coating surface to the specified size. The surface roughness after grinding should not exceed Ra0.4μm.

[0046] Step Six: Remove the protective layer from the bearing surface.

[0047] The bearing was ultrasonically cleaned using an alkaline cleaning agent and industrial acetone in sequence. Finally, the bearing was soaked in deionized water with a fluoride content of no more than 0.1 ppm for no less than 4 hours.

[0048] The present invention will be further described in detail below with reference to the embodiments. It should be understood that the preparation methods described in the embodiments of the present invention are merely for illustrating the present invention and are not intended to limit the present invention. Simple improvements to the preparation methods of the present invention under the premise of the concept of the present invention are all within the scope of protection of the present invention.

[0049] Example 1

[0050] The turbine reheat valve bearing sleeve base is made of nuclear-grade stainless steel ring forging with a machining allowance of 5mm, a Co content of 0.2%, and a tensile strength of 870MPa;

[0051] Using the bearing center hole as a reference, machine the outer circular surface and inner hole surface of the substrate to ensure that the coaxiality of the outer circular surface and the inner hole surface meets 0.02mm. The machining allowance in the non-sprayed area is 0.5mm, and the coating area has a reserved thickness of 0.30mm.

[0052] The inner surface of the bearing sleeve is shot-peened using a sandblasting process. Spherical zirconia ceramic pellets are used, with a pellet hardness of HRC62, a pellet size of 150μm, a shot peening intensity of 0.20A, a surface coverage of 200%, and a surface residual compressive stress of 580MPa.

[0053] Using propylene, acetylene, and oxygen as fuel, a six-axis robot arm is used to carry an explosive spray gun to spray a wear-resistant and lubricating coating onto the inner surface of the bearing sleeve using an explosive spraying process. The main components of the wear-resistant and lubricating coating are Cr3C2, Cr2O3, and NiCrMo, with the following weight percentages: Cr3C2 content 69%, Cr2O3 content 1.5%, and NiCrMo content 29.5%.

[0054] The spraying parameters used are as follows: the molar ratio of propylene, acetylene and oxygen is 0.2mol:1.0mol:1.5mol, the powder feeding rate is 12g / min, the spraying distance is 300mm, the coating thickness is 0.45mm, the coating hardness is 580HV, and the bonding strength is 135MPa.

[0055] The sprayed reheat valve bearing was placed in an oven and heated to 140°C. After removal, a penetrating high-temperature lubricating sealant was quickly brushed onto the coating surface. The main components of the sealant were: n-butyl acetate, 2-methylpropanol acetate, hexagonal boron nitride, and chromium oxide. The hexagonal boron nitride content was 2% with a particle size of 150 nm; the chromium oxide content was 5% with a particle size of 100 nm; and the fluorine impurity content of the sealant was 0.05 ppm.

[0056] Using the bearing center hole as a reference, the coaxiality of the outer circular surface is aligned to meet 0.02mm. The inner hole coating surface is ground to the specified size using a diamond grinding wheel, and the surface roughness Ra after grinding is 0.4μm.

[0057] The bearing was ultrasonically cleaned using an alkaline cleaning agent and industrial acetone in sequence, and finally soaked in deionized water with a fluorine content of 0.01 ppm for 4 hours.

[0058] Example 2

[0059] The turbine reheat valve bearing sleeve base is made of nuclear-grade stainless steel ring forging with a machining allowance of 5mm, a Co content of 0.2%, and a tensile strength of 890MPa;

[0060] Using the bearing center hole as a reference, machine the outer circular surface and inner hole surface of the substrate to ensure that the coaxiality of the outer circular surface and the inner hole surface meets 0.02mm. The machining allowance for the non-coated area is 0.5mm, and the thickness of the coating area is reserved at 0.35mm.

[0061] The inner surface of the bearing sleeve is shot-peened using a sandblasting process. Spherical zirconia ceramic pellets are used, with a pellet hardness of HRC62, a pellet size of 150μm, a shot peening intensity of 0.25A, a surface coverage of 200%, and a surface residual compressive stress of 600MPa.

[0062] Using propylene, acetylene, and oxygen as fuel, a six-axis robot arm is used to carry an explosive spray gun to spray a wear-resistant and lubricating coating onto the inner surface of the bearing sleeve using an explosive spraying process. The main components of the wear-resistant and lubricating coating are Cr3C2, Cr2O3, and NiCrMo, with the following weight percentages: Cr3C2 content 69%, Cr2O3 content 1.5%, and NiCrMo content 29.5%.

[0063] The spraying parameters used are as follows: the molar ratio of propylene, acetylene and oxygen is 0.2mol:1.0mol:1.5mol, the powder feeding rate is 12g / min, the spraying distance is 280mm, the coating thickness is 0.40mm, the coating hardness is 615HV, and the bonding strength is 128MPa.

[0064] The sprayed reheat valve bearing was placed in an oven and heated to 140°C. After removal, a penetrating high-temperature lubricating sealant was quickly brushed onto the coating surface. The main components of the sealant were: n-butyl acetate, 2-methylpropanol acetate, hexagonal boron nitride, and chromium oxide. The hexagonal boron nitride content was 2% with a particle size of 150 nm; the chromium oxide content was 5% with a particle size of 100 nm; and the fluorine impurity content of the sealant was 0.05 ppm.

[0065] Using the bearing center hole as a reference, the coaxiality of the outer circular surface is aligned to meet 0.02mm. The inner hole coating surface is ground to the specified size using a diamond grinding wheel, and the surface roughness Ra after grinding is 0.4μm.

[0066] The bearing was ultrasonically cleaned using an alkaline cleaning agent and industrial acetone in sequence, and finally soaked in deionized water with a fluorine content of 0.01 ppm for 4 hours.

[0067] Example 3

[0068] The turbine reheat valve bearing sleeve base is made of nuclear-grade stainless steel ring forging with a machining allowance of 5mm, a Co content of 0.2%, and a tensile strength of 880MPa;

[0069] Using the bearing center hole as a reference, machine the outer circular surface and inner hole surface of the substrate to ensure that the coaxiality of the outer circular surface and the inner hole surface meets 0.02mm. The machining allowance in the non-sprayed area is 0.5mm, and the coating area has a reserved thickness of 0.40mm.

[0070] The inner surface of the bearing sleeve is shot-peened using a sandblasting process. Spherical zirconia ceramic pellets are used, with a pellet hardness of HRC62, a pellet size of 150μm, a shot peening intensity of 0.30A, a surface coverage of 200%, and a surface residual compressive stress of 620MPa.

[0071] Using propylene, acetylene, and oxygen as fuel, a six-axis robot arm is used to carry an explosive spray gun to spray a wear-resistant and lubricating coating onto the inner surface of the bearing sleeve using an explosive spraying process. The main components of the wear-resistant and lubricating coating are Cr3C2, Cr2O3, and NiCrMo, with the following weight percentages: Cr3C2 content 69%, Cr2O3 content 1.5%, and NiCrMo content 29.5%.

[0072] The spraying parameters used are as follows: the molar ratio of propylene, acetylene and oxygen is 0.2mol:1.0mol:1.5mol, the powder feeding rate is 12g / min, the spraying distance is 260mm, the coating thickness is 0.38mm, the coating hardness is 636HV, and the bonding strength is 122MPa.

[0073] The sprayed reheat valve bearing was placed in an oven and heated to 140°C. After removal, a penetrating high-temperature lubricating sealant was quickly brushed onto the coating surface. The main components of the sealant were: n-butyl acetate, 2-methylpropanol acetate, hexagonal boron nitride, and chromium oxide. The hexagonal boron nitride content was 2% with a particle size of 150 nm; the chromium oxide content was 5% with a particle size of 100 nm; and the fluorine impurity content of the sealant was 0.05 ppm.

[0074] Using the bearing center hole as a reference, the coaxiality of the outer circular surface is aligned to meet 0.02mm. The inner hole coating surface is ground to the specified size using a diamond grinding wheel, and the surface roughness Ra after grinding is 0.4μm.

[0075] The bearing was ultrasonically cleaned using an alkaline cleaning agent and industrial acetone in sequence, and finally soaked in deionized water with a fluorine content of 0.01 ppm for 4 hours.

Claims

1. A method for preparing a reheat valve bearing sleeve for a nuclear power turbine, characterized in that, Includes the following steps: Step 1: Matrix Forging The base material is made of nuclear-grade stainless steel ring forgings with a machining allowance of not less than 5 mm, a Co content of ≤0.25%, and a tensile strength of 800~950MPa; Step 2: Rough machining of the substrate Using the bearing center hole as a reference, machine the outer circular surface and inner hole surface of the substrate to ensure that the coaxiality of the outer circular surface and the inner hole surface meets 0.02mm. The machining allowance in the non-coated area is not less than 0.5mm, and the coating area has a reserved thickness of 0.20-0.50mm. Step 3: Shot peening of internal holes The inner surface of the bearing sleeve is shot-peened using a sandblasting process. Spherical zirconia ceramic pellets are used, with a hardness of HRC 55-65 and a surface residual compressive stress of 400-600 MPa. Step 4: Internal hole spraying A wear-resistant and lubricating coating is applied to the inner surface of the bearing sleeve using an explosive spraying process. The coating thickness is 0.30-0.60 mm, the coating hardness meets 450-650 HV, and the bonding strength is ≥120 MPa. The main components of the wear-resistant and lubricating coating are Cr3C2, Cr2O3, and NiCrMo, with the following weight percentages: Cr3C2 content 60%-65%, Cr2O3 content 0.1%-10%, and NiCrMo content 25%-30%. After spraying, the reheat valve bearing is placed in an oven and heated to 130℃~180℃. After taking it out, a penetrating high-temperature lubricating sealant is quickly brushed onto the coating surface. The long-term working temperature of the sealant is not lower than 300℃, and the fluorine impurity content of the sealant is not higher than 0.1ppm. Step 5: Internal hole grinding Using the bearing center hole as a reference, align the coaxiality of the outer circular surface to meet 0.02mm, and use a diamond grinding wheel to grind the inner hole coating surface to the specified size. The surface roughness after grinding should not exceed Ra0.4μm. Step Six: Remove the protective layer from the bearing surface. The bearing was ultrasonically cleaned using an alkaline cleaning agent and industrial acetone in sequence. Finally, the bearing was soaked in deionized water with a fluoride content of no more than 0.1 ppm for no less than 4 hours.

2. The method for preparing the reheat valve bearing sleeve of a nuclear power turbine according to claim 1, characterized in that, The parameters for the shot peening strengthening treatment in step three are: shot size 100-200μm, shot peening intensity 0.15-0.30A, and surface coverage 200%.

3. The method for preparing the reheat valve bearing sleeve of a nuclear power turbine according to claim 1, characterized in that, The fourth step, the explosive spraying process, uses a six-axis robotic arm equipped with an explosive spray gun.

4. The method for preparing the reheat valve bearing sleeve of a nuclear power turbine according to claim 1, characterized in that, Step four, the explosive spraying process, is as follows: using propylene, acetylene, and oxygen as fuel, with a molar ratio of 0.2 mol: 1.0 mol: 1.5 mol, a powder feeding rate of 10 g / min to 15 g / min, and a spraying distance of 200 mm to 400 mm.

5. The method for preparing the reheat valve bearing sleeve of a nuclear power turbine according to claim 1, characterized in that, The main components of the penetrating high-temperature lubricating sealant in step four are: n-butyl acetate, 2-methylpropanol acetate, hexagonal boron nitride, and chromium oxide.

6. The method for preparing the reheat valve bearing sleeve of a nuclear power turbine according to claim 1, characterized in that, In the penetrating high-temperature lubricating sealant of step four, the content of hexagonal boron nitride is 0.1% to 5%, and the particle size is 50nm to 200nm.

7. The method for preparing the reheat valve bearing sleeve of a nuclear power turbine according to claim 1, characterized in that, In the penetrating high-temperature lubricating sealant of step four, the chromium oxide content is 1% to 10%, and the particle size is 50nm to 200nm.

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