A method for repairing damage to nuclear power turbine blades

Abstract

This invention belongs to the field of nuclear power turbine blade repair technology, specifically relating to a method for repairing damage to nuclear power turbine blades. The method includes: Step 1: Selecting repair materials; Step 2: Clamping the damaged blade using tooling fixtures; Step 3: Performing industrial CT flaw detection on the blade repair area; Step 4: Determining the type of damage area and removing the damaged area from the blade; Step 5: Selecting a repair method, repair path, and repair strategy, and performing damage repair; Step 6: Assessing the repair effect and the stress generation during the repair process, and determining the degree of local deformation; Step 7: Performing secondary industrial CT flaw detection on the blade repair area; Step 8: Post-processing the repaired blade. This invention enables rapid and effective repair of damaged areas on blades, thereby restoring their service performance and extending their service life.

Description

Technical Field

[0001] This invention belongs to the field of nuclear power turbine blade repair technology, specifically relating to a method for repairing damage to nuclear power turbine blades. Background Technology

[0002] Nuclear power turbines are a crucial component of the power module in nuclear power units, and blades are key parts affecting the thermal efficiency of nuclear power turbines. Nuclear power turbine blades are typically made of high-temperature alloys, which possess excellent high-temperature mechanical properties, resistance to high-temperature oxidation and corrosion, and superior fatigue, creep, and fracture resistance, thus ensuring long-term stable operation. However, due to the complex and harsh internal environment of nuclear power turbines, blades are frequently subjected to wear, impact, high-temperature gas corrosion, and thermal fatigue, making them prone to defects such as pitting corrosion, localized cracking, and damage, which seriously affect the safe and stable operation of nuclear power turbines.

[0003] Repairing nuclear power turbine blades can significantly improve their operational efficiency and stability, and substantially reduce operating costs, making it a commonly used technical approach for critical equipment maintenance. Typically, nuclear power turbine blade repair employs welding, where repair material is welded onto the damaged area, followed by machining to remove excess material. However, the high heat input during welding leads to significant deformation, coarse microstructure, and rough surface. Furthermore, the high concentration of alloying elements and precipitates in high-temperature alloys makes hot cracking prone to occur in the weld and heat-affected zone, increasing the difficulty of repair. On the other hand, traditional repair methods rarely utilize pre- and post-repair flaw detection techniques, making it difficult to ensure complete removal of blade defects during machining and to accurately determine the presence of defects after repair, thus casting doubt on the reliability of the repaired blades.

[0004] Therefore, there is an urgent need to develop a completely new set of methods for repairing nuclear power turbine blades by updating and combining flaw detection, machining, repair technology and post-processing technology. Summary of the Invention

[0005] The purpose of this invention is to provide a method for repairing damage to nuclear power turbine blades. This method can quickly and effectively repair damaged areas of the blades, thereby restoring their service performance and extending their service life.

[0006] Technical solution to achieve the purpose of this invention:

[0007] A method for repairing damage to nuclear power turbine blades, the method comprising:

[0008] Step 1: Select repair materials based on the material properties used in the manufacture of nuclear power turbine blades and the service environment requirements of nuclear power turbines;

[0009] Step 2: Use tooling fixtures to clamp the damaged blades to restrain the deformation of the nuclear power turbine blades when they are subjected to forces in multiple directions, thus preventing significant deformation of the blades during the stress process;

[0010] Step 3: Use industrial CT to perform three-dimensional flaw detection on the damaged nuclear power turbine blades to determine the location, type and geometric features of the damage, construct a three-dimensional digital model of the damaged blades, and form damage feature points of the three-dimensional digital model;

[0011] Step 4: Based on the 3D digital model of the damaged area, determine the type of damaged area, and determine the removal path, machining allowance, and geometric dimensions of the area to be repaired after machining according to the geometric characteristics of the damaged area. Remove the damaged area of ​​the blade by mechanical machining.

[0012] Step 5: Based on the geometric characteristics of the area to be repaired, select the repair method, repair path, and repair strategy to carry out damage repair; use preheating and continuous heat preservation processes to control the internal stress formed during the repair process;

[0013] Step 6: By calibrating the dimensions of the blade damage repair area and adjacent areas, determine the repair effect of the repair method, repair path and repair strategy, as well as the stress generation during the repair process. Determine the degree of local deformation of the blade before and after repair by measuring the relative position and angle data between the tooling fixture clamping point on the blade and the damage feature point of the three-dimensional digital model.

[0014] Step 7: Use industrial CT to perform three-dimensional flaw detection on the repaired area of ​​the nuclear power turbine blade again to determine the presence of defects in the repaired area; if the damaged area has been repaired, proceed to step 8; if there are still incompletely repaired areas or new defects, it is necessary to start from step 4 again.

[0015] Step 8: Post-treatment of the repaired blades.

[0016] In step one, the selected repair material is a cobalt-based alloy powder mixed with single or multiple particles of TiN, TiC, WC, and BN as a reinforcing phase, with a particle size range of 10–180 μm.

[0017] In step two, the tooling fixtures used include fixed-position clamping and adjustable-position clamping. The number of fixed clamping positions is 1 to 3, and the number of adjustable clamping positions is 3 to 8.

[0018] In step three, constructing a three-dimensional digital model of the damaged leaf includes: a complete three-dimensional digital model of the damaged leaf, a three-dimensional digital model of a single or multiple damaged areas, and the location and morphology of the damage detected on the leaf.

[0019] In steps three and seven, the industrial CT operating parameters used are: tube voltage 60-90kV, tube current 70-85μA, and scanning sampling time 80-120min.

[0020] In step four, the types of damaged areas include: cracks, defects, and pitting corrosion.

[0021] In step four, cracks are removed using a round-bottomed groove method, with a depth uniformly greater than 10% to 15% of the crack's longitudinal depth and a groove angle ≥ 90°. For blade defects, surface grinding is used for preliminary preparation, and if necessary, alcohol cleaning is used to remove dust and dirt to provide a clean surface for subsequent repair. Pitting corrosion is removed using an open cone method.

[0022] In step five, the repair method selected is laser cladding. The tooling fixture for clamping the damaged blade is placed on the equipment platform. The area to be repaired is located using the feature points of the three-dimensional digital model. The laser head is then moved by a robotic arm to perform the repair.

[0023] In step five, the repair parameters are: laser power of 1500-3000W, scanning rate of 2-20mm / s, spot diameter of 2-6mm, powder feeding rate of 0.2-2r / min, and overlap rate of 20%-60%.

[0024] In step nine, the post-processing includes: removing excess material from the surface of the repair area by means of sandblasting, machining, etc.; machining the appearance contour and high-precision polishing of the repair area to meet the precision requirements of the surface contour of the nuclear power turbine blade; and using local or overall heat treatment to relieve internal stress in the repair area so that its surface quality and performance meet the requirements of blade repair before finally being put into use.

[0025] The beneficial technical effects of this invention are as follows:

[0026] 1. In terms of the selection of repair materials, this invention uses metal powder mixed with particulate reinforcing phase and composite material powder, which can enhance the overall performance of the repaired area.

[0027] 2. The present invention adopts a tooling setup that combines fixed-position clamping and adjustable-position clamping to effectively fix deformation during the repair process and machining process;

[0028] 3. This invention uses industrial CT to identify defects and reverse-engineers a digital 3D model of the part to be repaired, providing data reference for machining to remove defects and plan repair paths. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the structure of the nuclear power turbine blade clamping fixture in an embodiment of the present invention;

[0030] Figure 2 This is a schematic diagram of the machining of the damaged area of ​​a nuclear power turbine blade in an embodiment of the present invention;

[0031] Figure 3 This is a schematic diagram of the repaired nuclear power turbine blades in an embodiment of the present invention.

[0032] In the figure: 1-Nuclear power turbine blade, 2-Tooling platform, 3-Fixed position clamping, 4-Adjustable position clamping, 5-Visible crack area of ​​nuclear power turbine, 6-Round bottom groove after crack removal, 7-Shape after laser cladding. Detailed Implementation

[0033] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0034] The present invention provides a method for repairing damage to nuclear power turbine blades, which specifically includes the following steps:

[0035] Step 1: Select Repair Materials

[0036] Based on the material properties used in the manufacture of nuclear power turbine blades and the service environment requirements of nuclear power turbines, repair materials are selected. The selected repair materials are cobalt-based alloy powders mixed with single or multiple particles of TiN, TiC, WC, and BN as reinforcing phases, with a particle size range of 10–180 μm.

[0037] Step 2: Use tooling fixtures to clamp the damaged blades.

[0038] The damaged blades are clamped using tooling fixtures to constrain the deformation of the nuclear power turbine blades when they are subjected to forces in multiple directions, thus preventing significant deformation of the blades during the stress process. The clamping methods used include fixed-position clamping and adjustable-position clamping, with 1 to 3 fixed clamping positions and 3 to 8 adjustable clamping positions.

[0039] Step 3: Perform industrial CT flaw detection on the repaired area of ​​the blade.

[0040] Industrial CT was used to perform three-dimensional flaw detection on damaged nuclear power turbine blades to determine the location, type, and geometric features (length, depth, size, etc.) of the damage. A three-dimensional digital model of the damaged blade was constructed (a complete three-dimensional digital model of the damaged blade, a three-dimensional digital model of a single or multiple damaged areas, the location of the damage and the morphology of the damage), and damage feature points of the three-dimensional digital model were formed.

[0041] Step 4: Determine the type of damage and remove the damaged area from the blade.

[0042] Based on the three-dimensional digital model of the damaged area, the type of damaged area (crack, defect, pitting corrosion) is determined. According to the geometric characteristics of the damaged area, the removal path, machining allowance, and geometric dimensions of the area to be repaired after machining are determined. The damaged area of ​​the blade is removed by mechanical machining. Cracks are removed by round-bottom grooves with a depth uniformly greater than 10% to 15% of the crack depth and a groove angle ≥ 90°. For blade defects, the surface is initially prepared by grinding. If necessary, alcohol cleaning is used to remove dust and dirt to provide a clean surface for subsequent repair. Pitting corrosion is removed by open cones.

[0043] Step 5: Select the repair method, repair path, and repair strategy to carry out damage repair.

[0044] Based on the geometric characteristics of the area to be repaired, repair methods, paths, and strategies are selected in the directions of chamfering, depth, length, and width to repair the damage and avoid defects such as cracks and holes during the repair process, forming a dense repair layer. Laser cladding can be selected as the repair method. The fixture holding the damaged blade is placed on the equipment platform, and the area to be repaired is located using feature points of a 3D digital model. A robotic arm moves the laser head to perform the repair. The repair parameters are: laser power of 1500–3000 W, scanning rate of 2–20 mm / s, spot diameter of 2–6 mm, powder feed rate of 0.2–2 r / min, and overlap rate of 20%–60%. Preheating and continuous heat preservation processes are used to control the internal stress formed during the repair process.

[0045] Step Six: Assess the repair effect and the stress generated during the repair process, and determine the degree of local deformation.

[0046] By calibrating the dimensions of the damaged repair area and the adjacent area of ​​the blade, the repair effect of the repair method, repair path and repair strategy and the stress generation during the repair process are judged. The degree of local deformation of the blade before and after repair is determined by measuring the relative position and angle data between the tooling fixture clamping point on the blade and the damage feature point of the three-dimensional digital model.

[0047] Step 7: Perform secondary flaw detection using industrial CT on the repaired area of ​​the blade.

[0048] Industrial CT was used to perform three-dimensional flaw detection on the repaired areas of the nuclear power turbine blades again. The process parameters of the industrial CT were enhanced to obtain higher resolution detection results and determine the presence of defects in the repaired areas of the blades. The operating parameters of the industrial CT used were: tube voltage 60-90kV, tube current 70-85μA, and scanning sampling time 80-120min. If the damaged area has been repaired completely, step nine can be performed. If there are still incompletely repaired areas or new defects, step four must be restarted.

[0049] Step 8: Post-treatment of the repaired blades

[0050] Excess material on the surface of the repair area is removed by sandblasting and machining. The repair area is then machined to achieve the desired appearance and high-precision polishing, meeting the surface profile accuracy requirements of nuclear power turbine blades. The repair area is then subjected to stress relief treatment using local or overall heat treatment, ensuring that its surface quality and performance meet the blade repair requirements before final delivery for use.

[0051] Example 1

[0052] The nuclear power turbine blades are made of precipitation-hardening martensitic stainless steel. The damage is a visually visible crack near the blade tip. Laser cladding technology is used to repair the nuclear power turbine blades, including the following steps:

[0053] Step 1: Based on the material characteristics used in the manufacture of nuclear power turbine blades and the service environment requirements of nuclear power turbines, select the appropriate material grade and type for repair, repair the cracked area of ​​the blade, and improve the overall high-temperature corrosion resistance, wear resistance and high-temperature strength of the blade. The selected material is NiCoCr alloy powder mixed with WC reinforcing phase particles, with a particle size range of 40 to 180 μm.

[0054] Step Two: Using designed tooling fixtures, the damaged blades are clamped to constrain deformation. To prevent significant deformation during stress, two types of clamping methods are used: fixed-position clamping (3) and adjustable-position clamping (4). Two fixed-position clamps (3) are used, one at the blade root and the other at the blade middle. Four adjustable-position clamps (4) are used, one at the upper middle part of the blade and the other at the blade tip. Both fixed-position clamps (3) and adjustable-position clamps (4) are installed on tooling platform 2. Figure 1 As shown;

[0055] Step 3: Use industrial CT to perform three-dimensional flaw detection on the damaged nuclear power turbine blades to determine the location and geometric features of the cracks, construct a three-dimensional digital model of the damaged blade (overall three-dimensional digital model of the damaged blade and three-dimensional digital model of the crack near the blade tip), and form damage feature points of the three-dimensional digital model. The operating parameters of the industrial CT are tube voltage 70-90kV, tube current 75-85μA, and scanning sampling time 80min.

[0056] Step 4: Based on the 3D digital model of the damaged area, determine the removal path, machining allowance, and geometric dimensions of the area to be repaired after machining. Remove the damaged area of ​​the blade using mechanical machining, employing a round-bottomed groove method to remove the crack. The depth should be uniformly greater than 10%–15% of the crack depth, and the groove angle should be ≥90°. Figure 2 As shown;

[0057] Step 5: Adopt the local preheating and continuous heat preservation process to control the internal stress formed during the repair process. The local preheating temperature is 150 - 350 °C, and the continuous heat preservation temperature is 200 - 300 °C. According to the geometric dimension characteristics of the area to be repaired, select the laser cladding method. Place the tooling fixture for clamping the damaged blade on the equipment platform, use the feature points of the three-dimensional digital model to locate the area to be repaired, and use the manipulator to move the laser head conformally to implement the repair. The repair parameters are as follows: the laser power is 1500 - 3000 w, the scanning speed is 2 - 20 mm / s, the spot diameter is 2 - 6 mm, the powder feeding rate is 0.2 - 2 r / min, and the overlapping rate is 20% - 60%. By selecting the repair process parameters, avoid forming defects such as cracks and holes during the repair process, and form a dense repair layer. The repair strategy is to start repairing from the middle of the bottom round bottom and implement the repair in a "return" shape until a laser cladding surplus height of 1 - 2 mm is formed, as Figure 3 shown;

[0058] Step 6: By calibrating the dimensions of the damaged repair area of the blade and the adjacent area, judge the repair effect of the repair method, repair path and repair strategy, and the generation of stress during the repair process. Determine the local deformation degree of the blade before and after repair by measuring the relative position and angular data between the clamping points of the tooling fixture on the blade and the damage feature points of the three-dimensional digital model;

[0059] Step 7: Conduct secondary industrial CT flaw detection on the repaired area of the blade. The damaged area has been repaired well, and it can enter Step 9. Use industrial CT to conduct three-dimensional scanning on the repaired area of the nuclear power steam turbine blade again, strengthen the process parameters of industrial CT, obtain a higher-resolution detection result, and judge the defect existence situation in the repaired area of the blade. The tube voltage is 78 - 85 kV, the tube current is 76 - 83 μA, and the scanning sampling time is 100 min;

[0060] Step 8: Conduct post-treatment on the repaired blade. Use the machining method to remove the surplus on the surface of the repaired area, and adopt the local heat treatment method to further remove the internal stress in the repaired area. The heat treatment temperature is 150 - 250 °C, and then conduct high-precision polishing on the surface of the repaired area to meet the precision requirements of the surface profile of the nuclear power steam turbine blade, and finally realize the delivery and reinstallation of the repaired nuclear power steam turbine blade.

[0061] The above has described the present invention in detail with reference to the accompanying drawings and embodiments. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the gist of the present invention. The content not described in detail in the present invention can all adopt the prior art.

Claims

1. A method of repairing damage to a nuclear steam turbine blade, characterized by, The method comprises: Step 1: according to the material properties used in the manufacture of nuclear steam turbine blades and the service environment requirements of nuclear steam turbine, the repair material is selected; Step 2: using a fixture to clamp the damaged blade, realizing the deformation constraint of the nuclear steam turbine blade under stress in multiple directions, and avoiding obvious deformation of the blade during the stress process; Step 3: using industrial CT to implement three-dimensional flaw detection on the damaged nuclear steam turbine blade, determining the damage location, type and geometric characteristics, constructing a three-dimensional digital model of the damaged blade, and forming a three-dimensional digital model damage feature point; Step 4: combining the three-dimensional digital model of the damage area, judging the type of the damage area, and determining the removal path, machining allowance and geometric size of the repaired area after machining of the damage area according to the geometric characteristics of the damage area, and removing the damage area of the blade by mechanical machining; Step 5: according to the geometric size characteristics of the repaired area, the repair method, repair path and repair strategy are selected, and the damage is repaired; the internal stress formed in the repair process is controlled by preheating and continuous heat preservation process; Step 6: by comparing the size of the damaged repair area and the adjacent area of the blade, the repair effect and stress generation in the repair process of the repair method, repair path and repair strategy are judged, and the local deformation degree of the blade before and after repair is determined by measuring the relative position and angle data between the clamping points of the fixture on the blade and the three-dimensional digital model damage feature point; Step 7: using industrial CT to perform three-dimensional flaw detection on the repaired area of the nuclear steam turbine blade again, and judging the existence of defects in the repaired area of the blade; if the damage area has been repaired perfectly, it can enter step 8, if the damage area still has not completely repaired area or new defects, it needs to start from step 4 again; Step 8: post-processing the repaired blade.

2. A method of repairing damage to a nuclear steam turbine blade as defined in claim 1, wherein In step 1, the repair material is a cobalt-based alloy powder mixed with TiN, TiC, WC, BN single or multiple particle mixed reinforcing phase, with a particle size range of 10-180 μm.

3. A method of repairing damage to a nuclear steam turbine blade as defined in claim 1, wherein In step 2, the fixture clamping method includes fixed position clamping and adjustable position clamping, the fixed clamping position is 1-3, and the adjustable clamping position is 3-8.

4. The method of claim 1, wherein the method further comprises: In step 3, the three-dimensional digital model of the damaged blade includes: the complete three-dimensional digital model of the damaged blade, the three-dimensional digital model of a single or multiple damage areas, the position where the blade has damage, and the damage shape.

5. The method of claim 1, wherein the method further comprises: In steps 3 and 7, the operating parameters of the industrial CT are: tube voltage 60-90 kV, tube current 70-85 μA, and scanning sampling time 80-120 min.

6. The method of claim 1, wherein the method further comprises: In step 4, the types of damage area include: cracks, defects, and pitting.

7. A method of repairing damage to a nuclear steam turbine blade as defined in claim 6, wherein In step 4, the cracks are removed in a round-bottom groove way, the depth is uniformly greater than 10%-15% of the crack depth, the groove opening angle is ≥ 90°, the blade defects are initially prepared by surface grinding, and if necessary, alcohol is used to clean and remove dust and dirt to provide a clean surface for subsequent repair, and the pitting is removed in an open cone way.

8. The method of claim 1, wherein the method further comprises: In the fifth step, the repair method is selected as a laser cladding method, the tool clamp clamping the damaged blade is placed on the equipment platform, the region to be repaired is positioned by using the characteristic points of the three-dimensional digital model, and the laser head is moved along the shape by using the manipulator to implement the repair.

9. A method of repairing damage to a nuclear steam turbine blade as defined in claim 8, wherein In the fifth step, the repair parameters are as follows: the laser power is 1500-3000w, the scanning speed is 2-20mm / s, the spot diameter is 2-6mm, the powder feeding amount is 0.2-2r / min, and the overlap rate is 20%-60%.

10. The method of claim 1, wherein the method further comprises: In the eighth step, the post-processing includes the following steps: the excess amount on the surface of the repaired region is removed by using sand blasting and mechanical processing, the appearance contour processing and high-precision polishing of the repaired region are implemented by using the mechanical processing method, the precision requirement of the surface contour of the nuclear power steam turbine blade is met, the internal stress of the repaired region is removed by using the local or overall heat treatment method, the surface quality and performance of the repaired region are improved, and the repaired region is finally delivered after meeting the blade repair requirement.

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