Method for repairing stay vanes of hydraulic machinery

Abstract

To provide a stay vane repair method of a hydraulic machine which enables improvement of reliability of a stay vane after welding repair.SOLUTION: In a stay vane repair method of a hydraulic machine according to an embodiment, buildup welding is performed in a recessed part to form an internal buildup part having an expanding part expanding relative to a surface of a stay vane. Subsequently, the expanding part of the internal buildup part is removed and hammer peening is performed to a surface of the internal buildup part. Then, buildup welding is performed to a surface of the internal buildup part with a material having higher corrosion resistance than the internal buildup part to form an anticorrosive buildup part. Hammer peening is performed on a surface of the anticorrosive buildup part.SELECTED DRAWING: Figure 15

Description

[Technical field]

[0001] An embodiment of the present invention relates to a method for repairing a stay vane of a hydraulic machine. [Background technology]

[0002] In general, in hydraulic machines such as Francis turbines, stay vanes are provided to rectify the water flow that flows from the casing through the guide vanes into the runner. The stay vanes are arranged between the casing and the guide vanes, and a plurality of stay vanes are arranged in the circumferential direction of the runner. Each stay vane is fixed to the casing. More specifically, an upper plate and a lower plate are fixed to the casing by welding. Each stay vane is interposed between the upper plate and the lower plate, and is fixed to the upper plate and the lower plate by welding, respectively. The stay vanes are generally manufactured from carbon steel, and their surfaces are painted.

[0003] Cavitation can occur around the stay vanes during turbine operation. When cavitation occurs, the paint peels off, which can cause erosion of the stay vanes and damage them.

[0004] The casing, the upper plate, and the lower plate are embedded in concrete. This makes it difficult to replace the stay vane even if it is eroded. For this reason, the eroded part of the stay vane may be repaired by grinding it with a grinder or the like. However, in this case, the surface shape and plate thickness of the stay vane cannot be restored.

[0005] To address this issue, it is possible to carry out welding repair. In this case, the surface shape and plate thickness of the stay vane can be restored by overlay welding at the eroded area. However, as described above, the stay vane is fixed to the casing embedded in concrete. For this reason, it is difficult to carry out heat treatment to reduce the residual stress generated after welding, and the reliability of the stay vane after repair becomes an issue. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Utility Model Application Publication No. 57-184270 Summary of the Invention [Problem to be solved by the invention]

[0007] The embodiment has been made taking these points into consideration, and aims to provide a method for repairing a stay vane of a hydraulic machine that can improve the reliability of the stay vane after welding repair. [Means for solving the problem]

[0008] A method for repairing a stay vane of a hydraulic machine according to an embodiment is a method for repairing a damaged portion formed in a stay vane of a hydraulic machine. The method for repairing a stay vane of a hydraulic machine includes a damaged portion removal step, an internal buildup step, a bulge removal step, an internal peening step, a corrosion-resistant buildup step, and a corrosion-resistant buildup peening step. In the damaged portion removal step, the damaged portion is removed in a concave shape to form a recess. In the internal buildup step, buildup welding is performed in the recess, and an internal buildup portion having a bulge that bulges out from the surface of the stay vane is formed. In the bulge removal step, the bulge portion of the internal buildup is removed. In the internal peening step, after the bulge removal step, a hammer-type peening treatment is performed on the surface of the internal buildup portion. In the corrosion-resistant buildup step, after the internal peening step, buildup welding is performed on the surface of the internal buildup portion with a material that is more corrosion-resistant than the internal buildup portion, to form a corrosion-resistant buildup portion. In the corrosion-resistant buildup peening process, a hammer peening treatment is performed on the surface of the corrosion-resistant buildup. Effect of the Invention

[0009] According to the embodiment, the reliability of the stay vane after welding repair can be improved. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a vertical sectional view showing the overall configuration of a hydraulic machine according to this embodiment. [Diagram 2] FIG. 2 is a cross-sectional view of the stay vane of FIG. 1 as viewed in the direction of water flow. [Diagram 3] FIG. 3 is a schematic cross-sectional view illustrating a damaged portion removing step in the stay vane repair method for a hydraulic machine according to the present embodiment. [Figure 4] FIG. 4 is a schematic cross-sectional view for illustrating the first layer forming step in the method for repairing a stay vane of a hydraulic machine according to the present embodiment. [Diagram 5] FIG. 5 is a schematic cross-sectional view for illustrating the first layer peening step in the method for repairing a stay vane of a hydraulic machine according to the present embodiment. [Figure 6] FIG. 6 is a schematic cross-sectional view illustrating the second layer forming step in the method for repairing a stay vane of a hydraulic machine according to the present embodiment. [Figure 7] FIG. 7 is a schematic cross-sectional view for illustrating the second layer peening step in the method for repairing a stay vane of a hydraulic machine according to the present embodiment. [Figure 8] FIG. 8 is a schematic cross-sectional view for illustrating the bulge portion forming step in the stay vane repair method for a hydraulic machine according to the present embodiment. [Figure 9] FIG. 9 is a schematic cross-sectional view illustrating a bulge removing step in the stay vane repair method for a hydraulic machine according to the present embodiment. [Figure 10] FIG. 10 is a schematic cross-sectional view for illustrating an internal peening step in the method for repairing a stay vane of a hydraulic machine according to the present embodiment. [Figure 11] FIG. 11 is a schematic cross-sectional view for illustrating the corrosion-resistant building up step in the method for repairing a stay vane of a hydraulic machine according to the present embodiment. [Figure 12] FIG. 12 is a schematic cross-sectional view showing a toe of a corrosion-resistant buildup portion in the method for repairing a stay vane of a hydraulic machine according to the present embodiment. [Figure 13] FIG. 13 is a schematic cross-sectional view showing the toe shown in FIG. 12 after TIG dressing. [Figure 14] FIG. 14 is a schematic cross-sectional view showing the toe portion shown in FIG. 13 after it has been shaped by a grinder. [Figure 15] FIG. 15 is a schematic cross-sectional view for illustrating the corrosion-resistant buildup portion peening step in the stay vane repair method for a hydraulic machine according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, a method for repairing a stay vane of a hydraulic machine according to an embodiment of the present invention will be described with reference to the drawings. The method for repairing a stay vane of a hydraulic machine is a method for repairing a damaged portion formed in a stay vane of the hydraulic machine.

[0012] First, a hydraulic machine and a stay vane according to the present embodiment will be described with reference to Figures 1 to 3. In the present embodiment, a Francis turbine will be taken as an example of the hydraulic machine.

[0013] As shown in FIG. 1, the Francis turbine 1 includes a spiral casing 2 into which water flows from an upper reservoir through a penstock (none of which are shown in the figures) during turbine operation, a number of stay vanes 3, a number of guide vanes 4, and a runner 5. The stay vanes 3 are members for rectifying the flow of water flowing from the casing 2 into the runner 5. The stay vanes 3 are arranged at predetermined intervals in the circumferential direction, and a flow path through which water flows is formed between the stay vanes 3 adjacent in the circumferential direction. The guide vanes 4 are arranged at predetermined intervals in the circumferential direction, and a flow path through which water flows is formed between the guide vanes 4 adjacent in the circumferential direction. Each guide vane 4 is configured to be rotatable, and the flow rate of water flowing into the runner 5 can be adjusted. In this manner, the amount of power generated by a generator (not shown), which will be described later, can be adjusted.

[0014] The runner 5 is configured to be rotatable about the rotation axis X relative to the casing 2. When the turbine is in operation, the runner 5 is rotationally driven by the water flowing in from the casing 2. In other words, the runner 5 is a member for converting the pressure energy of the water flowing into the runner 5 into rotational energy.

[0015] A generator (not shown) is connected to the runner 5 via a main shaft 6. This generator is configured to generate electricity by transmitting the rotational energy of the runner 5 during turbine operation.

[0016] A draft pipe 7 is provided downstream of the runner 5 during turbine operation. This draft pipe 7 is connected to a lower reservoir or a discharge channel (not shown), so that the water that drives the runner 5 to rotate recovers pressure and is discharged into the lower reservoir or the discharge channel (not shown).

[0017] The Francis turbine 1 may be capable of pumping (pumping) as a pump turbine. In this case, the generator also functions as an electric motor, and is configured to rotate the runner 5 when power is supplied. This allows water to be sucked up from the lower reservoir through the suction pipe 7 and discharged into the upper reservoir, enabling pumping. At this time, the opening of the guide vanes 4 is changed so that an appropriate amount of water is pumped according to the pump head.

[0018] As shown in Figures 1 and 2, an upper plate 8 and a lower plate 9 are fixed to the casing 2 by welding. The upper plate 8 and the lower plate 9 are formed in a ring shape. Each stay vane 3 is interposed between the upper plate 8 and the lower plate 9 and fixed to the upper plate 8 and the lower plate 9 by welding, respectively. The upper plate 8 and the lower plate 9 are buried in concrete C together with the casing 2 as shown in Figure 1.

[0019] When the turbine is in operation, the upper plate 8 and the lower plate 9 are subjected to the pressure of the inflowing water flow. As a result, the upper plate 8 is subjected to upward pressure and the lower plate 9 is subjected to downward pressure, which causes a tensile load to act on the stay vanes. It is possible to reduce the stress caused by this tensile load by making the stay vanes 3 thicker. In this case, the flow path of the water flow becomes narrower, and losses such as pressure loss occurring in the water flow may increase. For this reason, the thickness of the stay vanes 3 is limited to the minimum thickness allowable in terms of strength, and the stay vanes 3 may experience stress close to the allowable stress.

[0020] On the other hand, during turbine operation of the Francis turbine 1, cavitation may occur around the stay vanes 3. Furthermore, if the Francis turbine 1 is configured as a pump turbine, cavitation may occur around the stay vanes 3 even during pump operation. For example, when the pump starts up, jet water collides with the stay vanes 3. That is, when the pump starts up, the opening of the guide vanes 4 is small, so that water ejects as jet water from small gaps between the guide vanes 4 adjacent in the circumferential direction. As the jet water passes around the stay vanes 3, cavitation may occur in the vicinity of the stay vanes 3.

[0021] When cavitation occurs, erosion occurs in the stay vane 3, forming a damaged portion 20 (see FIG. 3). The damaged portion 20 tends to occur at a location where the highest stress occurs among the stresses generated in the stay vane 3 during operation of the turbine.

[0022] The method for repairing a stay vane of a hydraulic machine according to this embodiment is a method for repairing damaged portion 20 caused by erosion or the like as described above. Hereinafter, the method for repairing a stay vane of a hydraulic machine according to this embodiment (hereinafter simply referred to as the repair method) will be described with reference to Figs. 3 to 15.

[0023] The repair method according to this embodiment may include a damaged portion removing step, an internal buildup step, a bulge removing step, an internal peening step, a corrosion-resistant buildup step, and a corrosion-resistant buildup peening step.

[0024] [Damaged part removal process] The damaged portion removing step is a step of removing the damaged portion 20 in a concave shape to form a recess 21, as shown in FIG.

[0025] More specifically, as shown in Fig. 3, the damaged portion 20 formed in the stay vane 3 is removed. At this time, the recess 21 may be formed so as to have a planar area wider than the damaged portion 20 and to be deeper than the damaged portion 20. In this way, the recess 21 is formed so that no surface of the damaged portion 20 remains. The recess 21 may be formed, for example, by grinding the periphery of the damaged portion 20 using a grinder.

[0026] [Internal overlay process] After the damaged portion removing step, an internal build-up step is performed. The internal build-up step is a step of performing build-up welding in the recess 21 to form an internal build-up portion 30 having a bulging portion 31 that bulges out from the surface 3a of the stay vane 3. The internal build-up portion 30 may be made of the same material as the base material of the stay vane 3.

[0027] The internal cladding step may include a first layer forming step, a first layer peening step, a second layer forming step, a second layer peening step, and a bulge forming step.

[0028] (1st layer formation process) First, a first layer forming step is performed as shown in Fig. 4. The first layer forming step is a step of performing build-up welding in recess 21 to form first weld bead 33 constituting first weld bead layer 32.

[0029] More specifically, as shown in Fig. 4, a plurality of first weld beads 33 are formed to extend in a predetermined direction. A plurality of first weld beads 33 are arranged in a direction (left-right direction in Fig. 4) perpendicular to the longitudinal direction of first weld beads 33 (direction perpendicular to the paper surface in Fig. 4) to form first weld bead layer 32. Adjacent first weld beads 33 may partially overlap each other. The number of first weld beads 33 formed in recess 21 is not limited to multiple.

[0030] The material of each first weld bead 33 may be made of the same material as the base material of the stay vane 3. In this case, the welding rod (not shown) used in the first layer formation step is made of the same material as the base material of the stay vane 3.

[0031] (First layer peening process) After the first layer forming process, a first layer peening process is performed as shown in Fig. 5. The first layer peening process is a process in which a hammer peening process is performed on surface 32a of first weld bead layer 32. The hammer peening process is a process in which compressive stress is imparted to the surface by hitting the surface with a hammer. Examples of the hammer peening process include an air hammer peening process in which a hammer is driven by compressed air, and an electric hammer peening process in which a hammer is driven electrically.

[0032] By performing a hammer peening process on the surface 32a of the first weld bead layer 32, a compressive stress is applied to the surface 32a. This can reduce the tensile stress remaining in the surface 32a due to the heat input during welding, or can change the tensile stress to a minute compressive stress. As a result, deformation of the first weld bead layer 32 can be suppressed. The peening tool 100 moves along the surface 32a while locally applying a compressive stress by hitting the surface 32a with a hammer. This can perform the hammer peening process over the entire surface 32a of the first weld bead layer 32. The range of the peening process in the first layer peening process corresponds to the range of the recess 21, and is indicated by the range R1 shown in FIG. 5.

[0033] (Second layer formation process) After the first layer peening process, a second layer forming process is performed as shown in Fig. 6. The second layer forming process is a process of forming second weld bead 35 constituting second weld bead layer 34 laminated on first weld bead layer 32.

[0034] More specifically, as shown in Fig. 6, a plurality of second weld beads 35 are formed to extend in a predetermined direction. A plurality of second weld beads 35 are arranged in a direction (left-right direction in Fig. 6) perpendicular to the longitudinal direction of second weld beads 35 (direction perpendicular to the paper surface in Fig. 6) to form second weld bead layer 34. Adjacent second weld beads 35 may partially overlap each other. The number of second weld beads 35 formed in recess 21 is not limited to multiple.

[0035] Second weld bead 35 may be formed so as to extend in a direction perpendicular to the longitudinal direction of first weld bead 33, and the longitudinal direction and arrangement direction of second weld bead 35 are arbitrary. Also, while Fig. 6 shows an example in which second weld bead 35 is formed in alignment with the position of first weld bead 33, this is not limiting, and second weld bead 35 may be formed in a position offset from first weld bead 33 so that second weld bead 35 is formed above the boundary between adjacent first weld beads 33.

[0036] The material of each second weld bead 35 may be the same as the material of first weld bead 33 .

[0037] (Second layer peening process) After the second layer forming step, as shown in FIG. 7, a second layer peening step is performed. The second layer peening step is a step of performing a hammer peening process on the surface 34a of the second weld bead layer 34. The second layer peening step may be performed in the same manner as the first layer peening step. This applies a compressive stress to the surface 34a, and it is possible to reduce the tensile stress remaining in the surface 34a due to the heat input during welding, or to change the tensile stress to a minute compressive stress. Therefore, it is possible to suppress deformation of the second weld bead layer 34. The range of the peening process in the second layer peening step corresponds to the range of the recess 21, and is indicated by the range R1 shown in FIG. 7.

[0038] (bulge forming process) After the second layer peening step, as shown in Fig. 8, a plurality of weld bead layers are formed in the same manner as the first layer forming step and the second layer forming step. By forming one or a plurality of weld bead layers, a bulging portion 31 that bulges out from the surface 3a of the base material of the stay vane 3 is formed. The recess 21 is filled with the weld bead. When a plurality of weld bead layers are formed, a hammer-type peening process may be performed on the weld bead layers other than the uppermost weld bead layer in the same manner as the first layer peening step described above.

[0039] In this manner, the inner build-up portion 30 according to this embodiment is formed.

[0040] [Bulge removal process] After the internal buildup process, a bulge removing process is performed as shown in Fig. 9. The bulge removing process is a process for removing the above-mentioned bulge 31 from the internal buildup portion 30. More specifically, the bulge 31 bulging from the surface 3a of the stay vane 3 is removed so that the surface 30a of the internal buildup portion 30 is continuous with the surface 3a of the stay vane 3. The bulge 31 may be removed by, for example, grinding it with a grinder.

[0041] [Internal peening process] After the bulge removing step, an internal peening step is performed as shown in Fig. 10. The internal peening step is a step of performing a hammer peening treatment on the surface 30a of the internal buildup portion 30.

[0042] More specifically, as shown in FIG. 10, a hammer peening process may be performed on the surface 30a of the internal buildup portion 30, similarly to the first layer peening process and the like. This applies compressive stress to the surface 30a, and the tensile stress remaining on the surface 30a due to the removal of the bulging portion 31 can be reduced or the tensile stress can be changed to compressive stress. As a result, deformation of the internal buildup portion 30 can be suppressed. The peening tool 100 is moved along the surface 30a while locally applying compressive stress by hitting the surface 30a with a hammer. This allows the hammer peening process to be performed over the entire surface 30a of the internal buildup portion 30.

[0043] The peening treatment is performed on the entire surface 30a of the internal buildup portion 30, and may also be performed on the surface 3a of the base material of the stay vane 3 around the internal buildup portion 30. The range of the peening treatment in the internal peening process is indicated by range R2 in Fig. 10. Range R2 is wider than the above-mentioned range R1, and corresponds to a range including the periphery of the recess 21.

[0044] [Corrosion-resistant cladding process] After the internal peening step, a corrosion-resistant build-up step is performed as shown in Fig. 11. The corrosion-resistant build-up step is a step of performing build-up welding on the surface 30a of the internal build-up portion 30 to form a corrosion-resistant build-up portion 40. The build-up welding in the corrosion-resistant build-up step is performed with a material having higher corrosion resistance than the internal build-up portion 30. The corrosion-resistant build-up portion 40 may be made of a material having higher corrosion resistance against water than the internal build-up portion 30. For example, the corrosion-resistant build-up portion 40 may be made of stainless steel.

[0045] Corrosion-resistant buildup portion 40 may be composed of one or more corrosion-resistant weld bead layers 41. In this embodiment, corrosion-resistant weld bead layer 41 comprises two corrosion-resistant weld bead layers 41. Corrosion-resistant weld bead layer 41 may be formed of one or more corrosion-resistant weld beads 42. In this embodiment, corrosion-resistant weld bead layer 41 is formed of a plurality of corrosion-resistant weld beads 42.

[0046] More specifically, as shown in Fig. 11, a plurality of corrosion-resistant weld beads 42 are formed to extend in a predetermined direction. The plurality of corrosion-resistant weld beads 42 are arranged in a direction (left-right direction in Fig. 11) perpendicular to the longitudinal direction of the corrosion-resistant weld beads 42 (direction perpendicular to the paper surface in Fig. 11) to form one corrosion-resistant weld bead layer 41. Adjacent corrosion-resistant weld beads 42 may partially overlap each other. The number of surface beads is not limited to being multiple.

[0047] The corrosion-resistant weld bead layer 41 thus configured has a two-layer configuration to form the corrosion-resistant buildup portion 40 according to this embodiment. When a plurality of corrosion-resistant weld bead layers 41 are formed, the corrosion-resistant weld bead layers 41 other than the uppermost corrosion-resistant weld bead layer 41 may be subjected to a hammer peening process in the same manner as the first layer peening process described above.

[0048] The corrosion-resistant build-up portion 40 is formed on the surface 30 a of the internal build-up portion 30 , and may also be formed on the surface 3 a of the base metal of the stay vane 3 around the internal build-up portion 30 .

[0049] The corrosion-resistant buildup portion 40 is formed so as to bulge from the surface 3a of the base material of the stay vane 3. The height of the corrosion-resistant buildup portion 40 from the surface 3a may be a height that can tolerate loss occurring in the flow of water around the stay vane 3 during operation of the water turbine or pump.

[0050] The material of each of the corrosion-resistant weld beads 42 may have corrosion resistance. For example, each of the corrosion-resistant weld beads 42 may be made of stainless steel. In this case, a welding rod (not shown) used in the corrosion-resistant build-up portion forming step is made of stainless steel.

[0051] [Toe processing process] After the corrosion-resistant build-up process, a toe treatment process is carried out. The toe treatment process is a process for performing a residual stress reduction process on the toe 43 of the corrosion-resistant build-up portion 40. The toe treatment process may include a dressing process and a grinding process. The toe 43 means a portion of the corrosion-resistant weld bead layer 41 that contacts the boundary between the corrosion-resistant weld bead 42 and the base metal of the stay vane 3, as shown in FIG. 12.

[0052] (Dressing process) First, as shown in Figure 13, a dressing step is performed. The dressing step is a step of Tig-dressing the toe 43. The Tig-dressing step is a step of remelting the toe 43 with a Tig torch 110 and modifying the toe 43 to have a rounded shape. When remelting the toe 43, it is not necessary to supply material with a welding rod or the like. In this way, it is possible to reduce or remove the tensile stress remaining in the toe 43 due to the heat input of welding, and to prevent deformation of the toe 43.

[0053] (Grinding process) After the dressing process, the grinding process is performed as shown in Figure 14. The grinding process is a process in which the toe 43 is ground into a smooth shape by a grinder. This makes it possible to smooth the shape of the toe 43. This makes it possible to alleviate stress concentration at the toe 43 and prevent deformation of the toe 43.

[0054] [Corrosion-resistant cladding peening process] After the toe treatment process, a corrosion-resistant buildup peening process is performed as shown in Fig. 15. The corrosion-resistant buildup peening process is a process in which a hammer peening process is performed on the surface 40a of the corrosion-resistant buildup 40.

[0055] More specifically, as shown in FIG. 15, a hammer peening process may be performed on the surface 40a of the corrosion-resistant buildup portion 40, similarly to the first layer peening process and the like. This imparts compressive stress to the surface 40a, and it is possible to reduce the tensile stress remaining on the surface 40a due to the heat input during welding, or to change the tensile stress to compressive stress. As a result, it is possible to suppress deformation of the corrosion-resistant buildup portion 40. The peening tool 100 is moved along the surface 40a while locally imparting compressive stress by hitting the surface 40a with a hammer. This allows the hammer peening process to be performed over the entire surface 40a of the corrosion-resistant buildup portion 40.

[0056] The peening treatment is performed on the entire surface 40a of the corrosion-resistant buildup portion 40, and may also be performed on the surface 3a of the base metal of the stay vane 3 around the corrosion-resistant buildup portion 40. The range of the peening treatment in the corrosion-resistant buildup portion peening process is shown as range R3 in Fig. 15. Range R3 is wider than the above-mentioned range R2, and corresponds to a range including the periphery of the corrosion-resistant buildup portion 40.

[0057] In this manner, the damaged portion 20 of the stay vane 3 is repaired.

[0058] [Measurement process] After the corrosion-resistant buildup peening process, a measurement process may be performed. The measurement process may be a process of measuring the residual stress of the corrosion-resistant buildup 40. The residual stress may be measured using a strain gauge or may be measured using X-rays. If the measured residual stress is equal to or less than a desired reference value, the measurement process may be terminated.

[0059] If the measured residual stress is equal to or less than the desired reference value, the repair method according to this embodiment may be terminated. If the measured residual stress exceeds the reference value, the corrosion-resistant build-up portion peening process may be performed again.

[0060] The measurement step may be performed after at least one of the internal peening step and the corrosion-resistant buildup peening step. In the measurement step after the internal peening step, the residual stress of the internal buildup 30 is measured. If the measured residual stress exceeds a reference value, the internal peening step may be performed again. Furthermore, the measurement step may be performed after at least one of the first layer peening step, the second layer peening step, the internal peening step, and the corrosion-resistant buildup peening step. In the measurement step after the first layer peening step, the residual stress of the first weld bead layer 32 is measured, and if the measured residual stress exceeds a reference value, the first layer peening step may be performed again. In the measurement step after the second layer peening step, the residual stress of the second weld bead layer 34 is measured, and if the measured residual stress exceeds a reference value, the second layer peening step may be performed again.

[0061] Thus, according to this embodiment, the internal buildup portion 30 is formed in the recess 21 formed in the damaged portion 20 of the stay vane 3, and the bulge portion 31 of the internal buildup portion 30 is removed. Next, a hammer peening treatment is performed on the surface 30a of the internal buildup portion 30. This makes it possible to reduce the tensile stress remaining in the internal buildup portion 30. Thereafter, a corrosion-resistant buildup portion 40 is formed on the surface 30a of the internal buildup portion 30, and a hammer peening treatment is performed on the surface 40a of the corrosion-resistant buildup portion 40. This makes it possible to reduce the tensile stress remaining in the corrosion-resistant buildup portion 40. Therefore, the damaged portion 20 can be repaired while reducing the residual stress. As a result, the reliability of the stay vane 3 after the welding repair can be improved.

[0062] Moreover, according to this embodiment, the corrosion-resistant buildup portion 40 is made of a material that is more corrosion resistant than the inner buildup portion 30. This makes it possible to prevent the inner buildup portion 30 from corroding, and improve the reliability of the stay vane 3 after the weld repair.

[0063] Furthermore, according to this embodiment, in the internal peening process, the peening treatment is performed on the surface 30a of the internal buildup portion 30, and also on the surface 3a of the base material of the stay vane 3 around the internal buildup portion 30. This makes it possible to reduce the tensile stress remaining on the surface 3a of the stay vane 3 due to the heat input during welding. This makes it possible to improve the reliability of the stay vane 3 after the weld repair.

[0064] Furthermore, according to this embodiment, in the corrosion-resistant build-up peening process, the peening treatment is performed on the surface 40a of the corrosion-resistant build-up 40, and also on the surface 3a of the base metal of the stay vane 3 around the corrosion-resistant build-up 40. This makes it possible to reduce the tensile stress remaining on the surface 3a of the stay vane 3 due to the heat input during welding. This makes it possible to improve the reliability of the stay vane 3 after the weld repair.

[0065] Furthermore, according to this embodiment, the corrosion-resistant buildup portion 40 is formed on the surface 30a of the internal buildup portion 30, and is also formed on the surface 3a of the base metal of the stay vane 3 around the internal buildup portion 30. This makes it possible to prevent the internal buildup portion 30 from being exposed from the corrosion-resistant buildup portion 40. This makes it possible to further prevent corrosion of the internal buildup portion 30, and improve the reliability of the stay vane 3 after welding repair.

[0066] Furthermore, according to this embodiment, after the corrosion-resistant build-up process and before the corrosion-resistant build-up peening process, a residual stress reduction process is performed on the toe 43 of the corrosion-resistant build-up portion 40. This makes it possible to reduce the tensile stress remaining in the toe 43. This makes it possible to improve the reliability of the stay vane 3 after the weld repair.

[0067] According to the present embodiment, the internal build-up process includes a first layer forming process, a first layer peening process, and a second layer forming process. In the first layer forming process, a first weld bead 33 constituting a first weld bead layer 32 is formed, and in the first layer peening process, a hammer-type peening process is performed on a surface 32a of the first weld bead layer 32. In the second layer forming process, a second weld bead 35 constituting a second weld bead layer 34 laminated on the first weld bead layer 32 is formed. This allows a peening process to be performed on the surface 32a of the first weld bead layer 32 before the second weld bead layer 34 is formed, and the tensile stress remaining in the first weld bead layer 32 can be reduced. Therefore, even if the internal build-up portion 30 is formed of a plurality of weld bead layers, the residual stress inside the internal build-up portion 30 can be reduced, and the reliability of the stay vane 3 after the weld repair can be improved.

[0068] Moreover, according to this embodiment, the inner buildup portion 30 is made of the same material as the base material of the stay vane 3. This allows the mechanical strength of the inner buildup portion 30 to be the same as the strength of the base material, and ensures the mechanical strength of the stay vane 3 after welding repair.

[0069] Furthermore, according to this embodiment, at least one of the residual stress of the internal buildup portion 30 after the internal peening process and the residual stress of the corrosion resistant buildup portion 40 after the corrosion resistant buildup portion peening process is measured. As a result, when the measurement process is performed after the internal peening process, it is possible to confirm that the residual stress of the internal buildup portion 30 has been reduced. When the measurement process is performed after the corrosion resistant buildup portion peening process, it is possible to confirm that the residual stress of the corrosion resistant buildup portion 40 has been reduced. This makes it possible to improve the reliability of the stay vane 3 after welding repair.

[0070] According to the embodiment described above, the reliability of the stay vane after welding repair can be improved.

[0071] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims. In addition, it is of course possible to combine these embodiments in part as appropriate within the gist of the present invention. [Explanation of symbols]

[0072] 1: Francis turbine, 3: stay vane, 3a: surface, 20: damaged portion, 21: recess, 30: internal build-up portion, 30a: surface, 31: bulge, 32: first weld bead layer, 32a: surface, 33: first weld bead, 34: second weld bead layer, 35: second weld bead, 40: corrosion resistant build-up portion, 40a: surface, 43: toe

Claims

1. A method for repairing a damaged portion formed in a stay vane of a hydraulic machine, comprising the steps of: a damaged portion removing step of removing the damaged portion to form a recess; an internal build-up process in which build-up welding is performed in the recess to form an internal build-up portion having a bulge that bulges out from the surface of the stay vane; a bulge removing step of removing the bulge from the internal build-up portion; an internal peening step of performing a hammer peening treatment on a surface of the internal buildup portion after the bulge removing step; a corrosion-resistant build-up process in which, after the internal peening process, a material having a corrosion resistance higher than that of the internal build-up portion is overlaid on a surface of the internal build-up portion by overlay welding to form a corrosion-resistant build-up portion; and a corrosion-resistant buildup peening step of performing a hammer peening treatment on the surface of the corrosion-resistant buildup.

2. 2. The method for repairing a stay vane of a hydraulic machine according to claim 1, wherein in the internal peening step, a peening treatment is performed on a surface of the internal buildup portion and on a surface of the base metal of the stay vane around the internal buildup portion.

3. 3. The method for repairing a stay vane of a hydraulic machine according to claim 1 or 2, wherein in the corrosion-resistant buildup peening step, a peening treatment is performed on the surface of the corrosion-resistant buildup and on the surface of the base metal of the stay vane around the corrosion-resistant buildup.

4. The method for repairing a stay vane of a hydraulic machine according to any one of claims 1 to 3, wherein in the corrosion-resistant buildup process, the corrosion-resistant buildup portion is formed on the surface of the internal buildup portion and is formed on the surface of the base material of the stay vane around the internal buildup portion.

5. 5. The method for repairing a stay vane of a hydraulic machine according to claim 1, further comprising a toe treatment step of performing a residual stress reduction treatment on a toe of the corrosion-resistant buildup portion after the corrosion-resistant buildup step and before the corrosion-resistant buildup portion peening step.

6. The internal cladding process includes: a first layer forming step of forming a first weld bead constituting a first weld bead layer; a first layer peening process for performing a hammer peening treatment on a surface of the first weld bead layer; and a second layer forming step of forming, after the first layer peening step, a second weld bead constituting a second weld bead layer laminated on the first weld bead layer.

7. The method for repairing a stay vane of a hydraulic machine according to any one of claims 1 to 6, wherein the internal buildup portion is made of the same material as a base material of the stay vane.

8. The method for repairing a stay vane of a hydraulic machine according to any one of claims 1 to 7, further comprising a measurement step of measuring at least one of a residual stress of the internal buildup portion after the internal peening step and a residual stress of the corrosion-resistant buildup portion after the corrosion-resistant buildup portion peening step.

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