A method for repairing the dimensions of a reheat valve bearing in a nuclear power turbine.

Abstract

This invention belongs to the field of protective coatings for reheat valves in nuclear power turbines, and particularly relates to a method for repairing the dimensions of turbine reheat valve bearings. This invention employs mechanical methods to remove the damaged area of ​​the reheat valve bearing, and utilizes a combination of explosive spraying and roll forming reinforcement processes to prepare a wear-resistant and lubricating coating containing Cr3C2, Cr3O2, and NiCrMo in the damaged area. The coating hardness reaches 750-950 HV, and the bonding strength is ≥120 MPa. Through roll forming reinforcement and explosive spraying techniques, low-cost and rapid repair of turbine reheat valve bearings is achieved, while simultaneously improving the corrosion resistance of the reheat valve bearing, reducing the frictional resistance of the friction pair, and extending the service life of the 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 repairing the dimensions of bearings in reheat valves of nuclear power turbines. 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 unit operation, the main steam valve opening and closing time is required to be ≤50s, and the regulating valve opening and closing time ≤5s. The working environment of the turbine reheat valve bearing is extremely harsh. Currently, the design service life of the turbine reheat valve bearing is 6 years. After repeated operation, problems such as bearing size reduction, numerous surface scratches, and localized chipping occur. Due to the long manufacturing cycle and high cost of the turbine reheat valve bearing and bearing sleeve, there is an urgent need to explore an effective repair method for turbine reheat valve bearings.

[0004] In the existing technology, such as patents CN 112410712 and CN101724804A, the main applications are in the aero-engine environment. However, the special repair requirements of nuclear radiation, high load, and friction pair matching are not considered in the repair materials, spraying process, or repair process. Summary of the Invention

[0005] To address the problems of existing technologies, the present invention aims to provide a repair method for turbine reheat valve bearings. Using the repair scheme for turbine reheat valve bearings based on the dimensions of the present invention, low-cost and rapid repair of nuclear turbine reheat valve bearings can be achieved, thereby extending the bearing's service life.

[0006] To solve this technical problem, the technical solution of the present invention is as follows:

[0007] A method for repairing the dimensions of a turbine reheat valve bearing, the method comprising the following steps:

[0008] Step 1: Removal of damaged area

[0009] Using the undamaged area of ​​the reheat valve bearing center hole as a reference, the bearing center hole is ground to ensure that the runout is less than 0.03mm. The contact damage area of ​​the reheat valve bearing and bearing sleeve is removed by mechanical processing, with a removal depth of 0.10mm to 0.50mm. During the processing, the area outside the non-contact area of ​​the reheat valve bearing and bearing sleeve is protected.

[0010] Step 2: Surface strengthening of reheat valve bearings

[0011] The surface of the reheat valve bearing and bearing sleeve contact area is strengthened by rolling strengthening process. After strengthening, the surface hardness of the parts meets 350-450HV, the surface roughness is not higher than Ra1.6μm, the surface grain size is 200nm~300nm, the grain refinement layer depth is not less than 10μm, and the surface residual compressive stress is not less than 500MPa.

[0012] Step 3: Spraying the reheat valve bearing

[0013] First, the surface reinforcement area of ​​the reheat valve is roughened by sandblasting, and the roughness after roughening meets Ra3.0-4.0μm;

[0014] Secondly, using propylene, acetylene, and oxygen as fuel, an explosive spraying process is employed to apply a wear-resistant and lubricating coating to the roughened surface of the reheat valve bearing. The coating thickness is 0.20-0.60 mm, the coating hardness meets 750-950 HV, and the bonding strength is ≥120 MPa. The powder feeding rate is 10 g / min to 15 g / min, and the spraying distance is 200 mm to 400 mm.

[0015] Subsequently, the sprayed reheat valve bearing is heated to 130℃~180℃ in an oven. After being removed, 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 0.1ppmm.

[0016] Finally, using the bearing center hole as a reference, the coated surface is ground to the specified size with a diamond grinding wheel, and the surface roughness after grinding is not higher than Ra0.4μm;

[0017] Step 4: Remove the protective layer from the bearing surface.

[0018] 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.

[0019] Preferably, the rolling strengthening process uses a cylindrical roller indenter, and the rolling parameters are: rolling depth 0.1-0.4 mm, rolling speed 10-12 r / min, and rolling times 2 times.

[0020] Preferably, the main components of the wear-resistant lubricating coating are Cr3C2, Cr3O2 and NiCrMo, with the following weight percentages: Cr3C2 content 65% to 70%, Cr3O2 content 0.1% to 10%, and NiCrMo content 20% to 25%.

[0021] Preferably, the explosive spraying process employs a six-axis robotic arm equipped with an explosive spray gun.

[0022] Preferably, the molar ratio of propylene, acetylene, and oxygen is 0.2 mol: 1.0 mol: 1.5 mol.

[0023] Preferably, the main components of the penetrating high-temperature lubricating sealant are: n-butyl acetate, 2-methylpropanol acetate, hexagonal boron nitride, and chromium oxide.

[0024] 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.

[0025] 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.

[0026] The present invention has the following beneficial effects:

[0027] 1) This invention strengthens the surface of the reheat valve bearing / bearing sleeve contact area through a rolling strengthening process, and pre-applies surface compressive stress in the shallow layer of the reheat valve bearing contact area, thereby increasing the fatigue life of the reheat valve bearing by 80%; at the same time, a nano-scale fine grain structure is generated on the surface, which significantly improves the corrosion resistance of the material in a water vapor corrosion environment.

[0028] 2) This invention prepares a Cr3C2, Cr3O2, and NiCrMo composite coating on the contact area of ​​the reheat valve bearing / bearing sleeve using an explosive spraying process. On the one hand, it achieves dimensional repair of the reheat valve bearing; on the other hand, the addition of components such as Cr3C2, Cr3O2, and Mo improves the surface hardness and high-temperature lubrication performance of the reheat valve bearing, 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 high-temperature water vapor environments.

[0029] 3) The service life of the reheat valve bearing repaired using this invention can be increased by more than 50%, and the repair cost is low and the reliability is high. Attached Figure Description

[0030] 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.

[0031] Figure 1 A schematic diagram of the turbine reheat valve bearing and bearing sleeve.

[0032] Figure 2 This is a picture of the turbine reheat valve bearing after repair.

[0033] Figure 3 The image shows the cross-sectional morphology of the coating after repairing the turbine reheat valve bearing. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0035] A method for repairing the dimensions of a turbine reheat valve bearing, the method comprising the following steps:

[0036] Step 1: Removal of damaged area

[0037] Using the undamaged area of ​​the reheat valve bearing center hole as a reference, the bearing center hole is ground to ensure that the runout is less than 0.03mm. The contact damage area of ​​the reheat valve bearing and bearing sleeve is removed by mechanical processing, with a removal depth of 0.10mm to 0.50mm. During the processing, the area outside the non-contact area of ​​the reheat valve bearing and bearing sleeve is protected.

[0038] Step 2: Surface strengthening of reheat valve bearings

[0039] The surface of the reheat valve bearing and bearing sleeve contact area is strengthened by a rolling strengthening process. After strengthening, the surface hardness of the parts meets 350-450HV, the surface roughness is not higher than Ra1.6μm, the surface grain size is 200nm-300nm, the grain refinement layer depth is not less than 10μm, and the surface residual compressive stress is not less than 500MPa. The rolling strengthening process uses a cylindrical roller indenter, and the rolling parameters are: rolling depth 0.1-0.4mm, rolling speed 10-12r / min, and rolling times 2 times.

[0040] Step 3: Spraying the reheat valve bearing

[0041] First, the surface reinforcement area of ​​the reheat valve is roughened by sandblasting, and the roughness after roughening meets Ra3.0-4.0μm;

[0042] Secondly, using propylene, acetylene, and oxygen as fuel, a wear-resistant and lubricating coating is applied to the roughened surface of the reheat valve bearing using an explosive spraying process. The coating thickness is 0.20-0.60 mm, the coating hardness meets 750-950 HV, and the bonding strength is ≥120 MPa. The main components of the wear-resistant and lubricating coating are Cr3C2, Cr3O2, and NiCrMo, with the following weight percentages: Cr3C2 content 65%-70%, Cr3O2 content 0.1%-10%, and NiCrMo content 20%-25%. The explosive spraying process uses a six-axis robot arm equipped with an explosive spray gun. The molar ratio of propylene, acetylene, and oxygen is 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] Subsequently, the sprayed reheat valve bearing is heated to 130℃~180℃ in an oven. 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 0.1ppmm. 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] Finally, using the bearing center hole as a reference, the coated surface is ground to the specified size with a diamond grinding wheel, and the surface roughness after grinding is not higher than Ra0.4μm;

[0045] Step 4: Remove the protective layer from the bearing surface.

[0046] 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.

[0047] The present invention will be further described in detail below with reference to embodiments. It should be understood that the preparation methods described in the embodiments of the present invention are merely illustrative and not intended to limit the invention. Simple modifications to the preparation methods of the present invention within the framework of the present invention's concept are all within the scope of protection claimed by the present invention. Figure 1-3 As shown:

[0048] Example 1

[0049] The reheat valve bearing base material is 0Cr17Ni16-2. Based on the undamaged area of ​​the reheat valve bearing center hole, the bearing center hole is ground to a runout of 0.02mm. The coating wear area is removed by grinding to a depth of 0.20mm.

[0050] The surface of the contact area of ​​the reheat valve bearing / bearing sleeve was strengthened using a roller burnishing process. A cylindrical roller indenter was used, and the burnishing parameters were: burnishing depth 0.2 mm, burnishing speed 10 r / min, and burnishing times 2. After strengthening, the surface hardness of the part was 398 HV, the surface roughness Ra was 1.6 μm, the surface grain size was 240 nm, the grain refinement layer depth was 10 μm, and the surface residual compressive stress was 580 MPa.

[0051] The surface reinforcement zone of the reheat valve was roughened by sandblasting. The sandblasting parameters were: 60 mesh abrasive, working pressure 0.3 MPa, and roughness Ra 3.3 μm after roughening.

[0052] Using propylene, acetylene, and oxygen as fuel, a six-axis robotic arm equipped with an explosive spray gun is used to spray a wear-resistant and lubricating coating onto the roughened surface of the reheat valve bearing using explosive spraying technology. The main components of the wear-resistant and lubricating coating are Cr3C2, Cr3O2, and NiCrMo. The weight percentages of Cr3C2, Cr3O2, and NiCrMo in the wear-resistant and lubricating coating are as follows: Cr3C2 content 69%, Cr3O2 content 6.5%, and NiCrMo content 24.5%.

[0053] 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 0.35mm, the coating hardness is 860HV, and the bonding strength is 132MPa.

[0054] The reheat valve bearing after spraying is heated to 140°C in an oven. After being removed, a penetrating high-temperature lubricating sealant is quickly brushed onto the coating surface.

[0055] Using the bearing center hole as a reference, the coated surface is ground to the specified size using a diamond grinding wheel, and the surface roughness Ra after grinding is 0.4μm.

[0056] 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.

[0057] Example 2

[0058] The reheat valve bearing base material is 0Cr17Ni16-2. Based on the undamaged area of ​​the reheat valve bearing center hole, the bearing center hole is ground to a runout of 0.02mm. The coating wear area is removed by grinding to a depth of 0.30mm.

[0059] The surface of the contact area of ​​the reheat valve bearing / bearing sleeve was strengthened using a roller burnishing process. A cylindrical roller indenter was used, and the burnishing parameters were: burnishing depth 0.3 mm, burnishing speed 10 r / min, and burnishing times 2. After strengthening, the surface hardness of the part was 416 HV, the surface roughness Ra was 1.4 μm, the surface grain size was 230 nm, the grain refinement layer depth was 10 μm, and the surface residual compressive stress was 610 MPa.

[0060] The surface reinforcement zone of the reheat valve was roughened by sandblasting. The sandblasting parameters were: 60 mesh abrasive, working pressure 0.3 MPa, and roughness Ra 3.4 μm after roughening.

[0061] Using propylene, acetylene, and oxygen as fuel, a six-axis robotic arm equipped with an explosive spray gun is used to spray a wear-resistant and lubricating coating onto the roughened surface of the reheat valve bearing using explosive spraying technology. The main components of the wear-resistant and lubricating coating are Cr3C2, Cr3O2, and NiCrMo. The weight percentages of Cr3C2, Cr3O2, and NiCrMo in the wear-resistant and lubricating coating are as follows: Cr3C2 content 69%, Cr3O2 content 6.5%, and NiCrMo content 24.5%.

[0062] The spraying parameters used were as follows: the molar ratio of propylene, acetylene and oxygen was 0.2 mol: 1.0 mol: 1.5 mol, the powder feeding rate was 12 g / min, the spraying distance was 280 mm, the coating thickness was 0.33 mm, the coating hardness was 880 HV, and the bonding strength was 127 MPa.

[0063] The reheat valve bearing after spraying is heated to 140°C in an oven. After being removed, a penetrating high-temperature lubricating sealant is quickly brushed onto the coating surface.

[0064] Using the bearing center hole as a reference, the coated surface is ground to the specified size using a diamond grinding wheel, and the surface roughness Ra after grinding is 0.4μm.

[0065] 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.

[0066] Example 3

[0067] The reheat valve bearing base material is 0Cr17Ni16-2. Based on the undamaged area of ​​the reheat valve bearing center hole, the bearing center hole is ground to a runout of 0.02mm. The coating wear area is removed by grinding to a depth of 0.20mm.

[0068] The surface of the contact area of ​​the reheat valve bearing / bearing sleeve was strengthened using a roller burnishing process. A cylindrical roller indenter was used, and the burnishing parameters were: burnishing depth 0.3 mm, burnishing speed 12 r / min, and burnishing times 2. After strengthening, the surface hardness of the part met the requirements of 426 HV, surface roughness Ra 1.3 μm, surface grain size 210 nm, grain refinement layer depth 10 μm, and surface residual compressive stress 620 MPa.

[0069] The surface reinforcement zone of the reheat valve was roughened by sandblasting. The sandblasting parameters were: 60 mesh abrasive, working pressure 0.3 MPa, and roughness Ra 3.3 μm after roughening.

[0070] Using propylene, acetylene, and oxygen as fuel, a six-axis robotic arm equipped with an explosive spray gun is used to spray a wear-resistant and lubricating coating onto the roughened surface of the reheat valve bearing using explosive spraying technology. The main components of the wear-resistant and lubricating coating are Cr3C2, Cr3O2, and NiCrMo. The weight percentages of Cr3C2, Cr3O2, and NiCrMo in the wear-resistant and lubricating coating are as follows: Cr3C2 content 69%, Cr3O2 content 6.5%, and NiCrMo content 24.5%.

[0071] 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 0.30mm, the coating hardness is 895HV, and the bonding strength is 124MPa.

[0072] The reheat valve bearing after spraying is heated to 140°C in an oven. After being removed, a penetrating high-temperature lubricating sealant is quickly brushed onto the coating surface.

[0073] Using the bearing center hole as a reference, the coated surface is ground to the specified size using a diamond grinding wheel, and the surface roughness Ra after grinding is 0.4μm.

[0074] 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 repairing the dimensions of a reheat valve bearing in a nuclear power turbine, characterized in that, Includes the following steps: Step 1: Removal of damaged area Using the undamaged area of ​​the reheat valve bearing center hole as a reference, the bearing center hole is ground to ensure that the runout is less than 0.03mm. The contact damage area of ​​the reheat valve bearing and bearing sleeve is removed by mechanical processing, with a removal depth of 0.10mm~0.50mm. During the processing, the area outside the non-contact area of ​​the reheat valve bearing and bearing sleeve is protected. Step 2: Surface strengthening of reheat valve bearings The surface of the reheat valve bearing and bearing sleeve contact area is strengthened by rolling strengthening process. After strengthening, the surface hardness of the parts meets 350-450HV, the surface roughness is not higher than Ra1.6μm, the surface grain size is 200nm~300nm, the grain refinement layer depth is not less than 10μm, and the surface residual compressive stress is not less than 500 MPa. The rolling strengthening process uses a cylindrical roller indenter, and the rolling parameters are: rolling depth 0.1~0.4mm, rolling speed 10~12r / min, and rolling times 2 times; Step 3: Spraying the reheat valve bearing First, the surface reinforcement area of ​​the reheat valve is roughened by sandblasting, and the roughness after roughening meets Ra3.0-4.0μm; Secondly, using propylene, acetylene, and oxygen as fuel, an explosive spraying process is employed to apply a wear-resistant and lubricating coating to the roughened surface of the reheat valve bearing. The coating thickness is 0.20-0.60 mm, the coating hardness meets 750-950 HV, and the bonding strength is ≥120 MPa. The powder feeding rate is 10 g / min~15 g / min, and the spraying distance is 200 mm~400 mm. Subsequently, the sprayed reheat valve bearing is heated to 130℃~180℃ in an oven. After being removed, 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. Finally, using the bearing center hole as a reference, the coated surface is ground to the specified size with a diamond grinding wheel, and the surface roughness after grinding is not higher than Ra0.4μm; The main components of the wear-resistant lubricating coating are Cr3C2, Cr3O2 and NiCrMo, with the following weight percentages: Cr3C2 content 60%~80%, Cr3O2 content 0.1%~10%, and NiCrMo content 20%~25%. The main components of the penetrating high-temperature lubricating sealant are: n-butyl acetate, 2-methylpropanol acetate, hexagonal boron nitride and chromium oxide; the content of hexagonal boron nitride is 0.1%~5%, and the particle size is 50nm~200nm; the content of chromium oxide is 1%~10%, and the particle size is 50nm~200nm. Step 4: 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 repairing the dimensions of the reheat valve bearing in a nuclear power turbine according to claim 1, characterized in that, The third step, the explosive spraying process, uses a six-axis robotic arm equipped with an explosive spray gun.

3. The method for repairing the dimensions of the reheat valve bearing in a nuclear power turbine according to claim 1, characterized in that, In step three, the molar ratio of propylene, acetylene, and oxygen is 0.2 mol: 1.0 mol: 1.5 mol.

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