Method for repairing a nuclear power seawater pump shaft

Abstract

The application discloses a repairing method for a nuclear power seawater pump shaft, and comprises the following steps: S1, cleaning and detecting; S2, surfacing a key groove; S3, turning; S4, laser cladding; S5, stress relieving annealing; S6, grinding; S7, natural aging; S8, milling; S9, grinding; S10, ultrasonic rolling; and S11, testing. The repairing method can ensure that the pump shaft will not deform due to residual stress after the repairing is completed, and can ensure the performance and service life of the pump shaft. Meanwhile, the repairing method is complete, and can provide a reference for repairing the nuclear power seawater pump shaft.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of surface repair, in particular to a nuclear power seawater pump shaft repair method. BACKGROUND

[0002] The seawater pump is an important component for providing cooling water for the operation of the nuclear power plant unit, and the pump shaft is the core part of the seawater pump. During the operation of the seawater pump, the pump shaft will be subjected to the corrosion of seawater, the scouring of silt and the working stress, so the failure modes of the pump shaft mainly include corrosion, wear and deformation. Obviously, in order to prolong the service life of the pump shaft, it is necessary to make it have good corrosion resistance, wear resistance and high strength.

[0003] As the most important consumable component of the nuclear power plant, in order to reduce the cost, the repair method is gradually adopted at present. However, the conventional repair method is difficult to meet the increasing life requirement of the pump shaft, and is also difficult to meet the high-precision size requirement of the pump shaft. For example, the pump shaft with deformation is repaired by heating straightening or cold pressing straightening, but the residual stress cannot be completely removed, so the pump shaft will become curved again in the subsequent use process. For another example, the pump shaft with wear or corrosion is repaired by surfacing, chrome plating or thermal spraying, but the surfacing has a large heat input, so the deformation or even fracture may occur, and the chrome plating and thermal spraying have low bonding force, so the coating peeling is prone to occur. In addition, the thermal spraying coating also has holes, which will significantly reduce the seawater corrosion resistance of the pump shaft.

[0004] Therefore, a new repair method is urgently needed for the repair of the nuclear power seawater pump shaft. The patents CN102154642A (published on August 17, 2011), CN102078961B (announced on April 23, 2014), CN105154874A (published on December 16, 2015), CN105149860A (published on December 16, 2015) and CN108165978A (published on June 15, 2018) disclose the methods for repairing the pump shaft by laser cladding, but they all ignore a very important point, that is, how to eliminate the deformation and residual stress of the pump shaft in the repair process. In addition, these inventions do not disclose the whole process of repairing the pump shaft, but only describe the laser cladding process, which cannot support the repair method of the pump shaft. Moreover, the corrosion resistance, wear resistance and strength of the repaired pump shaft are not mentioned, which cannot ensure the service life of the repaired pump shaft. SUMMARY

[0005] The present application aims to provide a nuclear power seawater pump shaft repair method, which can ensure that the pump shaft will not deform due to residual stress after repair, and can also ensure its performance and service life. At the same time, the repair method is complete, providing a reference for nuclear power seawater pump shaft repair.

[0006] The nuclear power seawater pump shaft repair method of the present application comprises the following steps:

[0007] S1, cleaning and detection: using a cleaning agent to remove dirt on the surface of the pump shaft, and detecting the size, shape and position tolerance, surface defects, etc. of the pump shaft;

[0008] S2, build-up welding of keyway: using welding wire of the same material as the pump shaft base to build-up weld and fill the keyway position of the pump shaft;

[0009] S3, turning: according to the detection results of S1, determine the turning size of the pump shaft, and turn the outer circle of the pump shaft;

[0010] S4, laser cladding: according to the turning size, determine the number of layers and the thickness of each layer of laser cladding on the pump shaft, and use the prepared powder material to perform laser cladding on the outer surface of the pump shaft;

[0011] S5, stress relief annealing: vertically hang the laser cladded pump shaft in a pit furnace for stress relief annealing;

[0012] S6, grinding: use a high-precision cylindrical grinder to grind the outer surface of the pump shaft, and leave a 0.2-0.3mm allowance on one side according to the finished product size;

[0013] S7, natural aging: vertically place the pump shaft for one month;

[0014] S8, milling: according to the size requirements of the drawing, take the original keyway position as the reference, rotate 90℃ clockwise or counterclockwise, and re-mill the keyway;

[0015] S9, grinding: grind the outer surface of the pump shaft according to the finished product size;

[0016] S10, ultrasonic rolling: use a Hocken device to perform ultrasonic rolling treatment on the outer surface of the pump shaft;

[0017] S11, inspection: inspect the pump shaft according to the finished product requirements.

[0018] Further, the welding method used in step S2 is cold metal transfer welding technology.

[0019] Further, the turning size in step S3 is the maximum value of the maximum deformation, the maximum wear and the maximum corrosion, plus 0.2mm on one side.

[0020] Further, the powder material used in step S4 is any one of iron-based alloy, nickel-based alloy, cobalt-based alloy or a mixture thereof, and the mass fraction of alloying elements satisfies Cr+3.3*(Mo+0.5*W)+16*N>=40; the electrode potential difference between the powder material and the repaired pump shaft substrate is not more than 0.2V.

[0021] Further, after step S4 is completed, the coating has a room temperature hardness of not less than 30HRC, a bonding strength of not less than 500MPa, and no rust on the surface after a copper-accelerated acetic acid salt spray (CASS) test for 168h.

[0022] Further, in step S5, the pump shaft is heated to 500-550 DEG C at a heating rate of not more than 200 DEG C / h and is kept for 3-4h, and then is slowly cooled to room temperature in the furnace.

[0023] Further, after step S9 is completed, the pump shaft has a cylindricity of not more than 0.015mm, a coaxiality of not more than 0.015mm, a straightness of not more than 0.02mm, and an end surface perpendicularity of not more than 0.02mm.

[0024] Further, after step S10 is completed, the pump shaft has a surface roughness of not more than 0.5.

[0025] The nuclear power seawater pump shaft repairing method has the following advantages:

[0026] I. The cold metal transfer welding method is used in repairing the keyway, and the laser cladding method is used in repairing the outer cylindrical surface, so that the deformation and residual stress in the repairing process of the pump shaft can be greatly reduced.

[0027] II. The material used in the laser cladding is not limited to a certain alloy, but the alloy composition is required to satisfy Cr+3.3*(Mo+0.5*W)+16*N>=40, so that the cladding material can be selected as required on the premise of ensuring the seawater corrosion resistance, and meanwhile, considering that if the powder material and the pump shaft body are dissimilar materials, there is a large potential difference, which may cause galvanic corrosion, so the electrode potential difference between the powder material and the repaired pump shaft substrate is required to be not more than 0.2V, thereby significantly improving the corrosion resistance of the pump shaft in seawater.

[0028] III. The stress relief annealing process is set as follows: firstly, the residual stress of the pump shaft is removed as much as possible; and secondly, the heat treatment does not affect the pump shaft body and does not reduce the performance of the pump shaft body.

[0029] IV. The shape and position tolerance requirement after grinding is to ensure the high precision of the pump shaft, so that the pump shaft can meet the subsequent installation and use requirements, and also can ensure that the pump shaft does not deform due to residual stress after being put into use.

[0030] Five, ultrasonic rolling can significantly reduce the surface roughness on the one hand, but also can significantly improve the fatigue life of the pump shaft.

[0031] Six, the combination of stress relief annealing heat treatment + natural aging + ultrasonic rolling can remove the residual stress in the repair process of the pump shaft, ensure that the subsequent use process will not be deformed again due to residual stress, and ensure the dimensional accuracy of the pump shaft; Moreover, the combination of the three methods can greatly remove the stress on the one hand, and can also play their respective advantages: the heat treatment removes the residual stress with high efficiency, the natural aging removes the residual stress more thoroughly, and the ultrasonic rolling converts the residual tensile stress into residual compressive stress, thereby effectively improving the fatigue life of the pump shaft;

[0032] Seven, the performance of the laser cladding layer is room temperature hardness≥30HRC, bonding strength≥500MPa, and no rust on the surface after 168h of copper accelerated acetic acid salt spray (CASS) test, so that the pump shaft meets the working conditions and the required wear resistance, high strength and corrosion resistance;

[0033] In summary, the whole repair process of the nuclear power seawater pump shaft is disclosed, which provides support for the pump shaft repair method: the heat input of laser cladding is small, the residual stress and deformation are small, the heat effect on the pump shaft body is small, and the bonding strength is high; The combination of multiple specific steps further eliminates the deformation and residual stress of the pump shaft during the repair process; The laser cladding layer has good corrosion resistance, wear resistance and strength, which ensures the service life of the repaired pump shaft. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 The flowchart of the nuclear power seawater pump shaft repair method of the present application is shown in the figure.

[0035] Figure 2 The schematic diagram of the impeller shaft in Example 1 of the present application is shown in the figure.

[0036] Figure 3 The metallographic photograph of the laser cladding layer in Example 1 of the present application is shown in the figure.

[0037] Figure 4 The surface state of Example 1-3 after 168h of copper accelerated acetic acid salt spray (CASS) test is shown in the figure. DETAILED DESCRIPTION

[0038] In order to better understand the present application, the nuclear power seawater pump shaft repair method of the present application is further described in detail below in combination with examples.

[0039] The repairing method of the nuclear power seawater pump shaft of the application comprises the following steps: S1, cleaning and detecting: using cleaning agent to remove the dirt on the surface of the pump shaft, and detecting the size, shape tolerance and surface defects of the pump shaft; S2, surfacing the key groove: using the welding wire of the same material as the pump shaft base to fill the surfacing of the key groove position of the pump shaft; S3, turning: according to the detection result of S1, determining the turning size of the pump shaft, and turning the outer circle of the pump shaft; S4, laser cladding: according to the turning size, determining the layer number and single layer thickness of the laser cladding of the pump shaft, and using the prepared powder material to perform laser cladding on the outer circle surface of the pump shaft; S5, stress relief annealing: vertically hanging the pump shaft after laser cladding in the pit furnace to perform stress relief annealing; S6, grinding: using a high-precision cylindrical grinding machine to grind the outer circle surface of the pump shaft, and reserving a 0.2-0.3mm allowance on one side according to the finished product size; S7, natural aging: vertically placing the pump shaft for one month; S8, milling: according to the size requirement of the drawing, taking the original key groove position as the reference, rotating 90℃ clockwise or counterclockwise, and re-milling the key groove; S9, grinding: grinding the outer circle surface of the pump shaft according to the finished product size; S10, ultrasonic rolling: using the Hocken equipment to perform ultrasonic rolling treatment on the outer circle surface of the pump shaft; and S11, inspection: inspecting the pump shaft according to the finished product requirement.

[0040] Example 1

[0041] The first-stage impeller shaft of a certain nuclear power plant has a specification of φ95x3400 and is made of S32760 duplex stainless steel. The repairing method comprises the following steps:

[0042] S1, cleaning and detecting: using cleaning agent to remove the dirt on the surface of the pump shaft, and detecting the size, shape tolerance and surface defects of the pump shaft;

[0043] S2, surfacing the key groove: using S32760 duplex stainless steel welding wire, and using cold metal transfer welding method to fill the surfacing of the key groove position of the pump shaft;

[0044] S3, turning: according to the detection result of S1, determining the turning size of the pump shaft as 0.8mm on one side, i.e. turning to turning the outer circle of the pump shaft;

[0045] S4, laser cladding: according to the turning size of S3, the layer number of laser cladding is one layer, and the single layer thickness is 1.5mm, and using the prepared cobalt-based alloy powder material to perform laser cladding on the outer circle surface of the pump shaft. Through detection, the potential difference between the cobalt-based alloy powder and S32760 duplex stainless steel is 0.18V, and the mass fraction of alloying elements satisfies Cr+3.3*(Mo+0.5*W)+16*N=41.2;

[0046] S5, stress relief annealing: the cladding completed pump shaft is vertically hung in a pit furnace, and the process of stress relief annealing is carried out according to the room temperature into the furnace, the heating rate of 150 DEG C / h is heated to 500 DEG C, and the furnace is slowly cooled to room temperature for 3h;

[0047] S6, grinding: the outer circle surface of the pump shaft is ground by using a high-precision cylindrical grinding machine, and the single side allowance of 0.25-0.3mm is reserved according to the finished product size, that is, the outer circle surface is ground to

[0048] S7, natural aging: the pump shaft is vertically placed for one month;

[0049] S8, milling: according to the size requirements of the drawing, the key groove is re-milled with the original key groove position as the reference, and the key groove is rotated clockwise by 90 DEG C;

[0050] S9, grinding: the outer circle surface of the pump shaft is ground according to the finished product size and the shape and position tolerance requirements, and after grinding, the cylindricity is less than or equal to 0.015mm, the coaxiality is less than or equal to 0.015mm, the straightness is less than or equal to 0.02mm, and the end surface perpendicularity is less than or equal to 0.02mm;

[0051] S10, ultrasonic rolling: the outer circle surface of the pump shaft is treated by ultrasonic rolling by using a Haokeng device, and the surface roughness of the pump shaft is 0.4;

[0052] S11, inspection: the pump shaft is inspected according to the finished product requirements.

[0053] The schematic diagram of the pump shaft corresponding to the embodiment is shown in Figure 2 The position marked by the dashed line of the outer circle surface is the laser cladding area.

[0054] The metallographic photo of the laser cladding layer corresponding to the embodiment is shown in Figure 3 It can be seen that the microstructure of the cladding layer is mainly composed of fine dendrites.

[0055] Embodiment 2

[0056] The repair method of a secondary impeller shaft of a certain nuclear power plant includes the following steps:

[0057] S1, cleaning and detection: the pump shaft is cleaned by using a cleaning agent to remove surface stains, and the size, shape and position tolerance, and surface defects of the pump shaft are detected;

[0058] S2, build-up welding of key groove: S32760 duplex stainless steel wire is used to build-up weld and fill the key groove position of the pump shaft by using cold metal transfer welding method;

[0059] S3, turning: according to the detection result of the S1 step, the turning size of the pump shaft is determined as 1.0mm on one side, that is, the pump shaft is turned to The outer circle of the pump shaft is turned;

[0060] S4, laser cladding: according to the turning size of the S3 step, the number of laser cladding layers is one layer, the single layer thickness is 1.7 mm, and the prepared nickel-based alloy powder material is used for laser cladding on the outer circular surface of the pump shaft. The potential difference between the nickel-based alloy powder and S32760 duplex stainless steel is 0.2V, and the mass fraction of alloying elements satisfies Cr+3.3*(Mo+0.5*W)+16*N=40.4;

[0061] S5, stress relief annealing: the cladded pump shaft is vertically hung in a pit furnace, and the process of stress relief annealing is carried out according to the process of room temperature into the furnace, heating to 550℃ at a heating rate of 200℃ / h, and holding for 4h, and furnace cooling to room temperature;

[0062] S6, grinding: the outer circular surface of the pump shaft is ground by using a high-precision cylindrical grinding machine, and the single side allowance of 0.2-0.25mm is reserved according to the finished product size, that is, the outer circular surface is ground to

[0063] S7, natural aging: the pump shaft is vertically placed for one month;

[0064] S8, milling: according to the size requirements of the drawing, the key groove is re-milled with the original key groove position as the reference, and the key groove is re-milled counterclockwise by 90℃;

[0065] S9, grinding: the outer circular surface of the pump shaft is ground according to the finished product size and shape tolerance requirements, and after grinding, the cylindricity is ≤0.015mm, the coaxiality is ≤0.015mm, the straightness is ≤0.02mm, and the end surface perpendicularity is ≤0.02mm;

[0066] S10, ultrasonic rolling: the outer circular surface of the pump shaft is treated by ultrasonic rolling by using a Hauck device, and the surface roughness of the pump shaft is 0.3;

[0067] S11, inspection: the pump shaft is inspected according to the finished product requirements.

[0068] Example 3

[0069] A certain nuclear power plant intermediate shaft, specification: φ180x3000, material 304 stainless steel. The repair method includes the following steps:

[0070] S1, cleaning and detection: the cleaning agent is used to remove the stains on the surface of the pump shaft, and the size, shape and position tolerance, and surface defects of the pump shaft are detected;

[0071] S2, build-up welding of key groove: 304 stainless steel welding wire is used to build-up weld and fill the key groove position of the pump shaft by using cold metal transfer welding method;

[0072] S3, turning: according to the detection results of the S1 step, the turning size of the pump shaft is determined as 1.7mm on a single side, that is, the turning is to the outer circle of the pump shaft is turned;

[0073] S4, laser cladding: according to the turning size of the S3 step, the number of laser cladding layers is two, the thickness of a single layer is 1.2 mm, and the prepared iron-based alloy powder material is used for laser cladding on the outer circular surface of the pump shaft. It is detected that the potential difference between the iron-based alloy powder and 304 stainless steel is 0.15 V, and the mass fraction of alloying elements satisfies Cr+3.3*(Mo+0.5*W)+16*N=40;

[0074] S5, stress relief annealing: the cladded pump shaft is vertically hung in a pit furnace, and the process of stress relief annealing is carried out according to the process of room temperature into the furnace, heating to 530 DEG C at a heating rate of 180 DEG C / h, and holding for 4 h, and furnace cooling to room temperature;

[0075] S6, grinding: the outer circular surface of the pump shaft is ground by using a high-precision cylindrical grinding machine, and a single side allowance of 0.25-0.30 mm is reserved according to the finished product size, that is, the outer circular surface is ground to

[0076] S7, natural aging: the pump shaft is vertically placed for one month;

[0077] S8, milling: according to the size requirements of the drawing, the key groove is re-milled at the original key groove position as a reference, and the key groove is re-milled in a clockwise rotation of 90 DEG C;

[0078] S9, grinding: the outer circular surface of the pump shaft is ground according to the finished product size and shape and position tolerance requirements, and after grinding, the cylindricity is ≤0.015 mm, the coaxiality is ≤0.015 mm, the straightness is ≤0.02 mm, and the end surface perpendicularity is ≤0.02 mm;

[0079] S10, ultrasonic rolling: the outer circular surface of the pump shaft is treated by ultrasonic rolling by using a Hauck device, and the surface roughness of the pump shaft is 0.5;

[0080] S11, inspection: the pump shaft is inspected according to the finished product requirements.

[0081] For examples 1-3, the coating room temperature hardness, bonding strength, salt spray corrosion test and detection are carried out, and the detection results are shown in Table 1. The surface state of examples 1-3 after copper accelerated acetic acid salt spray (CASS) test for 168 h is shown in Table 1. It is obvious that the coating performance of examples 1-3 meets the requirements. Figure 4

[0082] Table 1

[0083] Example Room temperature hardness / HRC Bond strength / MPa CASS test 168 h surface condition Example 1 41.5 552 No corrosion Example 2 37.2 521 No corrosion Example 3 31.8 509 No corrosion

[0084] ​The nuclear power seawater pump shaft repaired by the repair method of the embodiments 1-3 of the present application has a service life of 1.5-2.0 times that of a new product, and the cost of spare parts replacement of the nuclear power plant is significantly reduced. Compared with the prior art, the nuclear power seawater pump shaft repair method of the present application has strong pertinence, and the deformation and residual stress generated during the repair process are small, and the wear resistance, bonding strength and corrosion resistance of the repaired shaft are improved.

Claims

1. A method for repairing a nuclear power seawater pump shaft, comprising the following steps: S1, cleaning and detection: using a cleaning agent to remove stains on the surface of the pump shaft, and detecting the size, geometric tolerance and surface defects of the pump shaft; S2, surfacing keyway: using a welding wire of the same material as the pump shaft substrate to fill the keyway position of the pump shaft by surfacing; S3, turning: determining the turning size of the pump shaft according to the detection results of S1, and turning the outer circle of the pump shaft; S4, laser cladding: determining the number of layers and the thickness of each layer of laser cladding on the pump shaft according to the turning size, and using the prepared powder material to perform laser cladding on the outer surface of the pump shaft; S5, stress relief annealing: vertically hanging the laser cladded pump shaft in a pit furnace for stress relief annealing; S6, grinding: grinding the outer surface of the pump shaft using a high-precision cylindrical grinder, and reserving a 0.2-0.3mm allowance on one side according to the finished product size; S7, natural aging: vertically placing the pump shaft for one month; S8, milling: re-milling the keyway based on the original keyway position according to the size requirements of the drawing, and rotating the keyway clockwise or counterclockwise by 90°C; S9, grinding: grinding the outer surface of the pump shaft according to the finished product size; S10, ultrasonic rolling: using a Hocken device to perform ultrasonic rolling treatment on the outer surface of the pump shaft; S11, inspection: inspecting the pump shaft according to the finished product requirements.

2. The method of repair of claim 1, wherein: The welding method used in step S2 is cold metal transfer welding technology.

3. The method of repairing according to claim 1, wherein: The turning size in step S3 is the maximum value of the maximum deformation, the maximum wear and the maximum corrosion, plus a 0.2mm allowance on one side.

4. The method of repair of claim 1, wherein: The powder material used in step S4 can be any one of iron-based alloy, nickel-based alloy, cobalt-based alloy or their mixture, and the mass fraction of alloying elements satisfies Cr+3.3*(Mo+0.5*W)+16*N≥40; the electrode potential difference between the powder material and the repaired pump shaft substrate is not more than 0.2V.

5. The method of repair of claim 4, wherein: The coating performance after step S4 is that the room temperature hardness is ≥30HRC, the bonding strength is ≥500MPa, and there is no rust on the surface after 168h of copper accelerated acetate salt mist test.

6. The method of repair of claim 1, wherein: In step S5, the pump shaft is heated to 500-550°C at a heating rate of not more than 200°C / h and then slowly cooled to room temperature in the furnace.

7. The method of repairing according to claim 1, wherein: After step S9, the pump shaft has a cylindricality of ≤0.015mm, a coaxiality of ≤0.015mm, a straightness of ≤0.02mm, and an end surface perpendicularity of ≤0.02mm.

8. The method of repairing according to claim 1, wherein: After step S10, the surface roughness of the pump shaft is ≤0.5.

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