How to repair seal fins

Abstract

A method for repairing seal fins, capable of repairing seal fins provided on a rotor of a steam turbine in a short period of time. [Solution] A method for repairing a seal fin provided on a rotor of a steam turbine, comprising: an overlay welding step in which an additional fin is formed at the damaged portion of the seal fin by overlay welding; and a tempering step in which heat is applied by arc discharge or laser to the heat-affected portion created in the seal fin by the overlay welding, thereby tempering the heat-affected portion.

Description

[Technical Field]

[0001] The present disclosure relates to a method for repairing a sealing fin. [Background technology]

[0002] Seal fins provided on the rotor of a steam turbine are exposed to a high-temperature environment during operation of the steam turbine, and may be damaged by contact with components on the casing side or by aging deterioration such as oxidation. Patent Document 1 discloses a method for repairing damage to a seal fin at the tip of a turbine rotor blade, in which the damaged portion of the fin is overlaid with welding, the boundary region between the fin and the overlaid weld is peened, and then a solution treatment is performed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-191716 Summary of the Invention [Problem to be solved by the invention]

[0004] The seal fin repair method described in Patent Document 1 requires the removal of irregularities and altered layers caused by peening treatment by electrical discharge machining, which tends to increase the number of steps required for repair and therefore tends to lengthen the repair period.

[0005] In view of the above circumstances, at least one embodiment of the present disclosure aims to provide a seal fin repair method that can repair seal fins provided on a rotor of a steam turbine in a short period of time. [Means for solving the problem]

[0006] In order to achieve the above object, a method for repairing a seal fin according to at least one embodiment of the present disclosure includes: A method for repairing a seal fin provided on a rotor of a steam turbine, comprising: an overlay welding step of forming an additional fin at the damaged portion of the seal fin by overlay welding the damaged portion of the seal fin; a tempering step of tempering the heat-affected portion generated in the seal fin by the overlay welding by applying heat by arc discharge or laser to the heat-affected portion; Equipped with. [Effects of the Invention]

[0007] According to at least one embodiment of the present disclosure, there is provided a method for repairing seal fins that can repair seal fins provided on a rotor of a steam turbine in a short period of time. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram for explaining an application target of a method for repairing a seal fin 8 according to an embodiment. [Figure 2] 4 is a flowchart showing a method for repairing a seal fin 8 according to one embodiment. [Figure 3] FIG. 1 is a diagram for explaining an example of build-up welding. [Figure 4] FIG. 2 is a diagram illustrating an example of tempering treatment. [Figure 5] FIG. 10 is a diagram for explaining another example of tempering treatment. [Figure 6] 10 is a diagram showing an example of correlation information (graph) showing the relationship between a parameter d relating to the amount of damage to the seal fin 8 and the amount of heat input. FIG. [Figure 7] 10A and 10B are diagrams for explaining an application target of a method for repairing a seal fin 8 according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, several embodiments of the present disclosure will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the invention. For example, expressions expressing relative or absolute arrangement such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial" not only express such an arrangement exactly, but also express a state in which there is a relative displacement with a tolerance or an angle or distance to the extent that the same function is obtained. For example, expressions such as "identical," "equal," and "homogeneous" that indicate that something is in an equal state not only indicate a state of strict equality, but also indicate a state in which there is a tolerance or a difference to the extent that the same function is obtained. For example, expressions representing shapes such as a square shape or a cylindrical shape not only represent shapes such as a square shape or a cylindrical shape in the strict geometric sense, but also represent shapes including uneven portions, chamfered portions, etc., to the extent that the same effect can be obtained. On the other hand, the expressions "comprise," "include," "have," "includes," or "have" of one element are not exclusive expressions that exclude the presence of other elements.

[0010] FIG. 1 is a diagram for explaining an application target of a method for repairing a seal fin 8 according to one embodiment. As partially shown in FIG. 1 , a method for repairing a seal fin 8 provided on the tip 6 a of a moving blade 6 of a rotor 4 of a steam turbine 2 will be described below. In the exemplary embodiment shown in FIG. 1 , the seal fin 8 is provided on the tip 6 a of the moving blade 6 so as to suppress leakage flow passing through a gap between a casing (not shown) that houses the rotor 4 and the tip 6 a of the moving blade 6. The seal fin 8 may be formed from a metal material such as high-chromium steel, low-chromium steel, low-alloy steel, or nickel-based alloy. The seal fin 8 provided on the rotor 4 of the steam turbine 2 is exposed to a high-temperature environment during operation of the steam turbine 2, and may be damaged by contact with a member on the casing side (not shown) or by aging degradation such as oxidation. Below, several examples of methods for repairing damaged portions 8 a of the seal fin 8 will be described using FIGS. 2 to 5 , etc.

[0011] Fig. 2 is a flowchart showing a method for repairing a seal fin 8 according to one embodiment. Fig. 3 is a diagram for explaining an example of build-up welding. Fig. 4 is a diagram for explaining an example of tempering treatment. Fig. 5 is a diagram for explaining another example of tempering treatment.

[0012] As shown in FIG. 2, in S101, pre-welding maintenance is performed on the damaged portion 8a of the seal fin 8 (see FIG. 1). For example, foreign matter, brazing material, coating, etc. adhering to the damaged portion 8a is removed. Furthermore, if the amount of damage varies depending on the longitudinal position of the seal fin 8 (for example, if the height of the seal fin 8 varies depending on the longitudinal position of the seal fin 8), the tip of the seal fin 8 may be machined so that the height of the seal fin 8 is constant regardless of the longitudinal position of the seal fin 8. This prevents welding defects and allows the seal fin 8 to be repaired properly. The longitudinal direction of the seal fin 8 may be the axial direction of the rotor 4, and the height direction of the seal fin 8 may be the radial direction of the rotor 4. The damaged portion 8a of the seal fin 8 refers to a portion of the seal fin 8 where the height of the seal fin 8 has decreased relative to the height h0 of the seal fin 8 at the start of use.

[0013] In S102, as shown in FIG. 3 , an additional fin 9 is formed at the damaged portion 8a of the seal fin 8 by overlay welding the damaged portion 8a (overlay welding step). The overlay welding performed in S102 may be MIG welding (Metal Insert Gas Welding), and the weld metal used for the overlay welding may be a cobalt-based alloy, a nickel-based alloy, or an austenitic stainless steel. The overlay welding in S102 may also be ultra-low heat input welding, in which MIG welding is performed under ultra-low heat input conditions. The heat input Q1 of the overlay welding in S102 may be, for example, 9.0 (kJ / cm) or less, preferably 6.0 (kJ / cm) or less, and more preferably 3.0 (kJ / cm) or less. The heat input Q1 here is the amount of electrical energy consumed in overlay welding per unit length, and is determined by the following formula (a): Q1=(I×V×60) / (v×1000) ···(a)

[0014] In the above formula (a), Q1 is the heat input (kJ / cm) of the overlay welding, I is the current (A) flowing through the electrode wire 14 of the welding torch 12 during the overlay welding, V is the arc voltage (V) supplied to the electrode wire 14 of the welding torch 12 during the overlay welding, and v is the moving speed (cm / min) of the welding torch 12 during the overlay welding.

[0015] When overlay welding is performed on the damaged portion 8a of the seal fin 8 in S102, a heat-affected zone 8c is generated in the base material 8b of the seal fin 8 due to the heat input of the overlay welding. The heat-affected zone 8c is a portion where the metal structure of the base material 8b has changed due to the heat input of the overlay welding, and is likely to be harder and more brittle than other portions of the base material 8b.

[0016] Therefore, in S103, the heat-affected zone 8c generated in the seal fin 8 is subjected to a tempering treatment by applying heat to the heat-affected zone 8c by arc discharge or laser (tempering treatment step). For example, as shown in FIG. 4, a welding torch 22 equipped with a tungsten electrode 20 may be used to apply heat to the heat-affected zone 8c by applying heat to the heat-affected zone 8c by arc discharge from the tungsten electrode 20. In this case, the welding torch 22 is used for TIG (Tungsten Inert Gas) welding. Alternatively, a welding torch for Inert Gas Welding (IG Welding) may be used, or temper bead welding may be performed by TIG welding, which allows for delicate heat input control. Instead of the method using the welding torch 22, as shown in FIG. 5, a laser processing head 32 (e.g., a laser processing head for laser welding) equipped with a lens 30 may be used, and heat may be input to the heat-affected zone 8c by a laser that has passed through the lens 30, thereby tempering the heat-affected zone 8c. Note that the build-up welding on the damaged area 8a in S102 corresponds to quenching, and the tempering treatment in S103 is performed after the additional fin 9 formed on the damaged area 8a has cooled.

[0017] In S103, the heat-affected zone 8c may be tempered without adding filler metal to the damaged zone 8a. In this case, during the period in which heat is being input to the heat-affected zone 8c by arc discharge or laser in S103, no filler metal is added to the damaged zone 8a, and melt-run welding between the seal fin 8 and the additional fin 9 is performed.

[0018] Regarding the tempering treatment of the heat-affected zone 8c in S103, the heat input Q2 of the arc discharge or laser in the tempering treatment may be determined based on a parameter d related to the amount of damage to the seal fin 8. Note that the parameter d related to the amount of damage to the seal fin 8 may be the amount of decrease in the height of the seal fin 8 based on the height h0 of the seal fin 8 at the start of use, as shown in FIG. 1, for example. Specifically, it may be the difference (= h0 - h1) between the height h0 of the seal fin 8 at the start of use and the height h1 of the seal fin 8 immediately before repair of the seal fin 8 (for example, after the pre-welding maintenance in S101 and before the overlay welding in S102). Note that the heat input Q2 here is the amount of electrical energy (kJ / cm) consumed by the arc discharge or laser in the tempering treatment per unit length, and is determined by formula (b) when arc discharge is used, or by formula (c) when a laser is used. Q2=(I×V×60) / (v×1000) ···(b) Q2=W / v (c)

[0019] In the above formula (b), Q2 is the heat input (kJ / cm) of the arc discharge in the tempering process, I is the current (A) flowing through the tungsten electrode 20 of the welding torch 22 in the tempering process, V is the arc voltage (V) supplied to the tungsten electrode 20 of the welding torch 22 in the tempering process, and v is the movement speed (cm / min) of the welding torch 22 in the tempering process. Also, in the above formula (c), Q2 is the heat input (kJ / cm) of the laser in the tempering process, W is the laser output (W) in the tempering process, and v is the movement speed (cm / min) of the laser processing head 32 in the tempering process.

[0020] Regarding the tempering treatment of the heat-affected zone 8c in S103, when the heat input Q2 of the arc discharge or laser in the tempering treatment is determined based on a parameter d related to the amount of damage to the seal fin 8, the heat input Q2 of the arc discharge or laser in the tempering treatment in S103 may be determined based on the parameter d related to the amount of damage to the seal fin 8 and predetermined correlation information R (see FIG. 6) (heat input amount determination step). Here, the correlation information R is information indicating the relationship between the parameter d related to the amount of damage to the seal fin 8 and the heat input Q2 of the arc discharge or laser in the tempering treatment. In this case, in S103, the heat input Q2 of the arc discharge or laser in the tempering treatment is controlled to Q2 based on the heat input Q2 determined in the heat input amount determination step. Note that in the example shown in FIG. 6, the correlation information R indicates that the heat input Q2 decreases as the parameter d related to the amount of damage to the seal fin 8 increases. By determining the heat input Q2 based on the correlation information R, it is possible to reduce stress in the heat-affected zone 8c while suppressing excess heat input to the bucket 6. Furthermore, the heat input Q2 of the arc discharge or laser in the tempering treatment may be smaller than the heat input Q1 of the overlay welding, from the viewpoint of suppressing the occurrence of defects such as cracks in the heat-affected zone 8c.

[0021] Next, in S104, post-welding maintenance is performed. Specifically, the tabs and jigs used in welding are removed. In addition, in S105, the surfaces of the rotor blades 6 and the surfaces of the repaired seal fins 8 are inspected for defects such as cracks. This inspection may be performed using, for example, fluorescent penetrant testing.

[0022] Here, the effects of the repair method for the seal fin 8 explained with reference to FIG. 2 etc. will be described. According to the above-described method for repairing a seal fin 8, after forming an additional fin 9 at a damaged portion 8a of the seal fin 8 by overlay welding in S102, heat is applied to a heat-affected zone 8c generated in the seal fin 8 by arc discharge or laser in S103, thereby tempering the heat-affected zone 8c, thereby reducing the hardness of the heat-affected zone 8c and alleviating internal stress in the heat-affected zone 8c, thereby suppressing damage to the seal fin 8 after repair. Furthermore, compared to the method for repairing a seal fin described in Patent Document 1, this method does not require peening or removal of irregularities or affected layers that accompany the peening, thereby reducing the number of steps required for repair and enabling the seal fin 8 to be repaired in a short period of time.

[0023] Furthermore, in S103, when heat is input to the heat-affected zone 8c by arc discharge from a tungsten electrode (when tempering the heat-affected zone 8c by TIG welding), the heat input to the heat-affected zone 8c can be carefully controlled, making it easy to adjust the hardness of the heat-affected zone 8c after overlay welding and effectively suppressing damage to the seal fin 8 after repair. Furthermore, in the tempering process of S103, it is not necessary to add filler material to the damaged location 8a while heat is being input to the heat-affected zone 8c by arc discharge or laser, which simplifies the repair method for the seal fin 8.

[0024] Furthermore, by determining the heat input of the arc discharge or laser in the tempering process using correlation information R that indicates the relationship between the parameter d related to the amount of damage to the seal fin 8 and the heat input of the arc discharge or laser in the tempering process, the heat-affected zone 8c can be tempered with an appropriate heat input according to the amount of damage to the seal fin 8, so that the hardness of the heat-affected zone 8c after overlay welding can be appropriately adjusted and damage to the seal fin 8 after repair can be effectively suppressed.

[0025] Furthermore, by using a cobalt-based alloy, a nickel-based alloy, or an austenitic stainless steel as a filler material for overlay welding of S102, hardening after heat input can be suppressed.

[0026] In addition, since damage to the seal fins 8 formed on the tips 6a of the rotor blades 6 can be suppressed after repair, leakage flow in the gap between the tips 6a of the rotor blades 6 and the casing (stationary wall) (not shown) of the steam turbine 2 can be stably suppressed.

[0027] Furthermore, by performing the buildup welding in S102 using extremely low heat input welding, hardening of the heat-affected zone 8c caused by the buildup welding can be suppressed, thereby enhancing the effect of suppressing damage to the seal fin 8 after repair.

[0028] The present disclosure is not limited to the above-described embodiments, but also includes modifications to the above-described embodiments and appropriate combinations of these modifications.

[0029] For example, while Figure 1 illustrates a seal fin 8 formed at the tip of a rotor blade 6 of a steam turbine 2, the repair method for the seal fin 8 described using Figure 2 can also be applied to a seal fin 8 formed on the outer surface 4a of a rotor 4 of the steam turbine 2 at a position facing a stator blade 5 of the steam turbine 2, as shown in Figure 7, for example.

[0030] Furthermore, in the above-described embodiment, in S103, a method of performing temper bead welding by TIG welding to perform delicate heat input control to the heat-affected zone 8c was exemplified, but the welding method performed in S103 is not particularly limited as long as delicate heat input control to the heat-affected zone 8c can be performed.

[0031] Furthermore, in the above-described embodiment, a method has been exemplified in which melt-run welding is performed between the seal fin 8 and the additional fin 9 without adding filler material to the damaged area 8a during the period in which heat is input to the heat-affected zone 8c by arc discharge or laser in S103. However, if the amount of heat input to the heat-affected zone 8c can be appropriately controlled, heat may be input to the heat-affected zone 8c by arc discharge or laser while adding filler material to the damaged area 8a in S103.

[0032] The contents described in each of the above embodiments can be understood, for example, as follows.

[0033] [1] A method for repairing a seal fin according to at least one embodiment of the present disclosure includes: A method for repairing a seal fin (e.g., the above-mentioned seal fin 8) provided on a rotor (e.g., the above-mentioned rotor 4) of a steam turbine (e.g., the above-mentioned steam turbine 2), comprising: an overlay welding step of forming an additional fin (for example, the above-mentioned additional fin 9) at a damaged portion of the seal fin (for example, the above-mentioned damaged portion 8a) by overlay welding at the damaged portion; a tempering step of tempering a heat-affected zone (for example, the heat-affected zone 8c) generated in the seal fin by the overlay welding by applying heat by arc discharge or laser to the heat-affected zone; Equipped with.

[0034] According to the seal fin repair method described in [1] above, after an additional fin is formed at a damaged portion of the seal fin by overlay welding, the heat-affected zone created in the seal fin by overlay welding is tempered by applying heat by arc discharge or laser to the heat-affected zone, thereby reducing the hardness of the heat-affected zone and alleviating internal stress in the heat-affected zone, thereby suppressing damage to the seal fin after repair. Furthermore, compared to the seal fin repair method described in Patent Document 1, this method does not require peening or the removal of unevenness and affected layers that accompany peening, so it is possible to reduce the number of steps required for repair and to repair the seal fin in a short period of time.

[0035] [2] In some embodiments, in the seal fin repair method described in [1] above, The overlay welding in the overlay welding step is MIG welding.

[0036] According to the seal fin repair method described in [2] above, the filler electrode can be continuously supplied, improving the work efficiency of the overlay welding. In addition, by performing MIG welding under extremely low heat input conditions, the hardened area of ​​the heat-affected zone after overlay welding can be reduced.

[0037] [3] In some embodiments, in the seal fin repair method described in [1] or [2] above, In the tempering step, the heat-affected zone is tempered by applying heat to the heat-affected zone by arc discharge from a tungsten electrode.

[0038] According to the seal fin repair method described in [3] above, the heat input to the heat-affected zone can be carefully controlled, making it easy to adjust the hardness of the heat-affected zone after overlay welding, and effectively suppressing damage to the seal fin after repair.

[0039] [4] In some embodiments, in the seal fin repair method according to any one of [1] to [3] above, In the tempering step, no filler material is added to the damaged area while heat is being input to the heat-affected zone by arc discharge or laser.

[0040] According to the seal fin repair method described in [4] above, since the additional fin is already formed in the buildup welding step, there is no need to add filler material in the tempering treatment step, and the seal fin repair method is simplified.

[0041] [5] In some embodiments, in the seal fin repair method described in any one of [1] to [4] above, a heat input amount determination step of determining a heat input amount of the arc discharge or the laser in the tempering treatment (for example, the above-mentioned heat input amount Q2) based on a parameter related to the amount of damage to the seal fin (for example, the above-mentioned parameter d) and correlation information (for example, the above-mentioned correlation information R) indicating a relationship between the parameter related to the amount of damage to the seal fin and the heat input amount of the arc discharge or the laser in the tempering treatment, In the tempering step, the heat input amount of the arc discharge or the laser in the tempering step is controlled based on the heat input amount determined in the heat input amount determining step.

[0042] According to the sealing fin repair method described in [5] above, the heat-affected zone can be tempered with an appropriate heat input according to the amount of damage to the sealing fin, so that the hardness of the heat-affected zone after overlay welding can be appropriately adjusted and damage to the sealing fin after repair can be effectively suppressed.

[0043] [6] In some embodiments, in the seal fin repair method described in any one of [1] to [5] above, The filler metal used for the overlay welding in the overlay welding step is a cobalt-based alloy, a nickel-based alloy, or an austenitic stainless steel.

[0044] According to the seal fin repair method described in [6] above, by using a cobalt-based alloy, a nickel-based alloy or an austenitic stainless steel as a filler material for overlay welding, hardening after heat input can be suppressed.

[0045] [7] In some embodiments, in the seal fin repair method described in any one of [1] to [6] above, The seal fin is formed on the tip (for example, the tip 6a) of the rotor blade (for example, the rotor blade 6) of the rotor.

[0046] According to the seal fin repair method described in [7] above, damage to the seal fins formed at the tips of the rotor blades can be effectively suppressed after repair, so that leakage flow in the gap between the tips of the rotor blades and the casing (stationary wall) of the steam turbine can be stably suppressed.

[0047] [8] In some embodiments, in the seal fin repair method described in any one of [1] to [6] above, The seal fins are formed on the outer peripheral surface of the rotor (for example, the outer peripheral surface 4a) at positions facing the stator blades of the steam turbine (for example, the stator blades 5).

[0048] According to the seal fin repair method described in [8] above, damage to the seal fins formed on the outer peripheral surface of the rotor at a position facing the stator blades of the steam turbine can be effectively suppressed after repair, and leakage flow in the gap between the outer peripheral surface of the rotor and the stator blades can be stably suppressed.

[0049] [9] In some embodiments, in the seal fin repair method according to any one of [1] to [8] above, The overlay welding in the overlay welding step is extremely low heat input welding.

[0050] According to the seal fin repair method described in [9] above, by performing the overlay welding in the overlay welding step with extremely low heat input welding, it is possible to suppress hardening of the heat-affected zone caused by the overlay welding, thereby enhancing the effect of suppressing damage to the seal fin after repair.

[0051]

[10] In some embodiments, in the seal fin repair method according to any one of [1] to [9] above, The heat input of the overlay welding in the overlay welding step is 9.0 (kJ / cm) or less.

[0052] By reducing the heat input of the overlay welding to the level described in

[10] above, it is possible to suppress hardening of the heat-affected zone caused by the overlay welding, thereby enhancing the effect of suppressing damage to the seal fin after repair.

[0053]

[11] In some embodiments, in the seal fin repair method described in

[10] above, The heat input of the overlay welding in the overlay welding step is 6.0 (kJ / cm) or less.

[0054] By reducing the heat input of the overlay welding to the level described in

[11] above, hardening of the heat-affected zone caused by the overlay welding can be further suppressed, thereby enhancing the effect of suppressing damage to the seal fin after repair.

[0055]

[12] In some embodiments, in the seal fin repair method described in

[11] above, The heat input of the overlay welding in the overlay welding step is 3.0 (kJ / cm) or less.

[0056] By reducing the heat input of the overlay welding to the level described in

[12] above, the hardening of the heat-affected zone caused by the overlay welding can be further suppressed, thereby improving the effect of suppressing damage to the seal fin after repair. [Explanation of symbols]

[0057] 2: Steam turbine 4: Rotor 4a: Outer surface 5: Stator blade 6: Moving blade 6a: Tip 8: Seal fin 8a: Damaged area 8b: Base material 8c: Heat affected zone 9: Additional fins 12,22: Welding torch 14: Electrode wire 20: Tungsten electrode 30: Lens 32: Laser processing head

Claims

1. A method for repairing a seal fin provided on a rotor of a steam turbine, comprising: an overlay welding step of forming an additional fin at the damaged portion of the seal fin by overlay welding the damaged portion of the seal fin; a tempering step of tempering the heat-affected portion generated in the seal fin by the overlay welding by applying heat by arc discharge or laser to the heat-affected portion; Equipped with a heat input amount determination step of determining a heat input amount of the arc discharge or the laser in the tempering treatment based on a parameter related to the amount of damage to the seal fin and correlation information indicating a relationship between the parameter related to the amount of damage to the seal fin and a heat input amount of the arc discharge or the laser in the tempering treatment, A method for repairing a seal fin, wherein in the tempering step, the heat input amount of the arc discharge or the laser in the tempering treatment is controlled based on the heat input amount determined in the heat input amount determining step.

2. The seal fin repair method according to claim 1 , wherein the overlay welding in the overlay welding step is MIG welding.

3. The seal fin repair method according to claim 1 , wherein the tempering step includes tempering the heat-affected zone by applying heat to the heat-affected zone by arc discharge from a tungsten electrode.

4. The seal fin repair method according to claim 1 , wherein in the tempering treatment step, no filler material is added to the damaged portion while heat is being input to the heat-affected zone by the arc discharge or the laser.

5. The seal fin repair method according to claim 1 , wherein a filler material used for the overlay welding in the overlay welding step is a cobalt-based alloy, a nickel-based alloy, or an austenitic stainless steel.

6. The seal fin repair method according to claim 1 , wherein the seal fin is formed at a tip of a blade of the rotor.

7. 2. The seal fin repair method according to claim 1, wherein the seal fin is formed on the outer circumferential surface of the rotor at a position facing a stationary blade of the steam turbine.

8. The seal fin repair method according to claim 1 , wherein the overlay welding in the overlay welding step is extremely low heat input welding.

9. 2. The seal fin repair method according to claim 1, wherein a heat input of the overlay welding in the overlay welding step is 9.0 (kJ / cm) or less.

10. The seal fin repair method according to claim 9, wherein a heat input of the overlay welding in the overlay welding step is 6.0 (kJ / cm) or less.

11. The seal fin repair method according to claim 10, wherein a heat input of the overlay welding in the overlay welding step is 3.0 (kJ / cm) or less.

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