Method for repairing seal fin

Abstract

A method for repairing a seal fin provided in a rotor of a steam turbine comprises: an overlay welding step for forming an additional fin at a damaged part of the seal fin by performing overlay welding at the damaged part; and a tempering treatment step for performing, on a heat-affected part which occurs in the seal fin due to the overlay welding, tempering treatment by inputting heat by arc discharge or laser.

Description

Method for Repairing Seal Fins

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[0001] The present disclosure relates to a method for repairing seal fins. This application claims priority based on Japanese Patent Application No. 2024-200272 filed with the Japan Patent Office on November 18, 2024, and incorporates its content herein by reference.

[0002] The seal fins provided on the rotor of a steam turbine are exposed to a high-temperature environment during the operation of the steam turbine, and may be damaged due to aging deterioration such as contact with members on the casing side and oxidation. Patent Document 1 discloses a method for repairing a turbine blade related to repairing damage to the seal fins at the tip of the turbine blade, in which the damaged portion of the fin is built up by welding, and after peening the boundary region between the fin and the build-up welding, a solution treatment is performed.

[0003] Japanese Unexamined Patent Application Publication No. 2009-191716

[0004] In the method for repairing seal fins described in Patent Document 1, it is necessary to remove irregularities and altered layers associated with the peening process by electrical discharge machining, and the number of steps required for repair tends to increase, which easily leads to a longer repair period.

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

[0006] To achieve the above object, a method for repairing seal fins according to at least one embodiment of the present disclosure is a method for repairing seal fins provided on the rotor of a steam turbine, comprising: a build-up welding step of forming an additional fin at the damaged portion by performing build-up welding on the damaged portion of the seal fin; and a tempering treatment step of performing a tempering treatment on the heat-affected zone generated in the seal fin by the build-up welding by applying heat to the heat-affected zone by arc discharge or laser.

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

[0008] This is a diagram illustrating the application of a repair method for seal fins 8 according to one embodiment. This is a flowchart illustrating a repair method for seal fins 8 according to one embodiment. This is a diagram illustrating an example of build-up welding. This is a diagram illustrating an example of tempering treatment. This is a diagram illustrating another example of tempering treatment. This is a diagram showing an example of correlation information (graph) indicating the relationship between parameter d related to the amount of damage to the seal fin 8 and the amount of heat input. This is a diagram illustrating the application of a repair method for seal fins 8 according to another embodiment.

[0009] Hereinafter, several embodiments of this disclosure will be described with reference to the attached drawings. However, the dimensions, materials, shapes, relative arrangements, etc., of the components described as embodiments or shown in the drawings are not intended to limit the scope of the invention, but are merely illustrative examples. For example, expressions describing relative or absolute arrangements such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial" should not only strictly represent such arrangements, but also represent states where there is a tolerance, or a relative displacement of an angle or distance sufficient to achieve the same function. For example, expressions describing things as being in an equal state such as "identical," "equal," and "homogeneous" should not only strictly represent states of equality, but also represent states where there is a tolerance, or a difference sufficient to achieve the same function. For example, expressions describing shapes such as a square shape or a cylindrical shape should not only represent geometrically precise shapes such as square shapes or cylindrical shapes, but also represent shapes including concave and concave parts, chamfered parts, etc., to the extent that the same effect can be achieved. On the other hand, expressions such as "to possess," "to be equipped with," "to have," "to include," or "to have" a single component are not exclusive expressions that exclude the existence of other components.

[0010] Figure 1 is a diagram illustrating the application of a repair method for a seal fin 8 according to one embodiment. As partially shown in Figure 1, the following describes a repair method for a seal fin 8 provided on the tip 6a of the rotor blade 6 of a steam turbine 2. In the exemplary embodiment shown in Figure 1, the seal fin 8 is provided on the tip 6a of the rotor blade 6 to suppress leakage flow through the gap between a casing (not shown) that houses the rotor 4 and the tip 6a of the rotor blade 6. The seal fin 8 may be formed from a metallic 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 the operation of the steam turbine 2, and may be damaged by contact with a casing-side component (not shown) or by deterioration over time such as oxidation. The following describes several examples of methods for repairing damaged areas 8a of the seal fin 8 using Figures 2 to 5, etc.

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

[0012] As shown in Figure 2, in S101, pre-welding treatment is performed on the damaged area 8a (see Figure 1) of the seal fin 8. For example, foreign matter, brazing material, coating, etc. adhering to the damaged area 8a are removed. Furthermore, if the amount of damage differs depending on the position in the longitudinal direction of the seal fin 8 (for example, if there is variation in the height of the seal fin 8 depending on the position in the longitudinal direction of the seal fin 8), machining may be performed on the tip of the seal fin 8 so that the height of the seal fin 8 is constant regardless of the position in the longitudinal direction of the seal fin 8. This suppresses the occurrence of welding defects and allows for good repair of the seal fin 8. Note that 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. Also, the damaged area 8a of the seal fin 8 refers to the part in which the height of the seal fin 8 has decreased from the height h0 of the seal fin 8 at the start of use of the seal fin 8.

[0013] In step S102, as shown in Figure 3, additional fins 9 are formed on the damaged area 8a of the seal fin 8 by overlay welding (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. Furthermore, the overlay welding in S102 may be extremely low heat input welding, which is MIG welding performed under extremely low heat input conditions. The heat input Q1 for 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 of a 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 for overlay welding (kJ / cm), I is the current (A) flowing through the electrode wire 14 of the welding torch 12 during overlay welding, V is the arc voltage (V) supplied to the electrode wire 14 of the welding torch 12 during overlay welding, and v is the movement speed of the welding torch 12 during overlay welding (cm / min).

[0015] When build-up welding is performed on the damaged area 8a of the seal fin 8 in S102, a heat-affected zone 8c is formed in the base material 8b of the seal fin 8 due to the heat input from the build-up welding. The heat-affected zone 8c is the part in which the metal structure of the base material 8b has changed due to the heat input from the build-up welding, and it is harder and more brittle than other parts of the base material 8b.

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

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

[0018] Regarding the tempering treatment of the heat-affected zone 8c in S103, the amount of heat input Q2 from 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. The parameter d related to the amount of damage to the seal fin 8 may be, for example, as shown in Figure 1, the amount of decrease in the height of the seal fin 8 relative to the height h0 of the seal fin 8 at the start of use, and more 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 treatment in S101 and before the build-up welding in S102). The amount of heat input Q2 here is the amount of electrical energy (kJ / cm) consumed by the arc discharge or laser in a tempering treatment of a unit length, and is determined by formula (b) when using an arc discharge, and by formula (c) when using a laser. Q2=(I×V×60) / (v×1000)...(b) Q2=W / v...(c)

[0019] In formula (b) above, Q2 is the heat input of the arc discharge in the tempering process (kJ / cm), 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 moving speed of the welding torch 22 in the tempering process (cm / min). In formula (c) above, Q2 is the heat input of the laser in the tempering process (kJ / cm), W is the output of the laser in the tempering process (W), and v is the moving speed of the laser processing head 32 in the tempering process (cm / min).

[0020] Regarding the tempering treatment of the heat-affected zone 8c in S103, if the amount of 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 amount of 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 Figure 6) (heat input determination step). Here, the correlation information R is information that shows the relationship between the parameter d related to the amount of damage to the seal fin 8 and the amount of heat input Q2 of the arc discharge or laser in the tempering treatment. In this case, in S103, the amount of heat input 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 determination step. In the example shown in Figure 6, the correlation information R shows that the larger the parameter d related to the amount of damage to the seal fin 8, the smaller the heat input Q2. By determining the heat input Q2 based on the correlation information R described above, it is possible to suppress excess heat input to the rotor blade 6 while easing the stress in the heat-affected zone 8c. Furthermore, the heat input Q2 of the arc discharge or laser during the tempering process may be smaller than the heat input Q1 of the build-up 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 S105, the surface of the rotor blade 6 and the surface of the repaired seal fin 8 are inspected for any defects such as cracks. This inspection may include, for example, fluorescent penetrant testing.

[0022] Here, we will explain the effects of the seal fin repair method described using Figure 2, etc. According to the above seal fin repair method, after forming an additional fin 9 on the damaged area 8a of the seal fin 8 by build-up welding in S102, the heat-affected zone 8c of the seal fin 8 is subjected to tempering treatment by applying heat to the heat-affected zone 8c in S103 using arc discharge or laser. This reduces the hardness of the heat-affected zone 8c, easing the internal stress in the heat-affected zone 8c and suppressing damage to the seal fin 8 after repair. Furthermore, compared to the seal fin repair method described in Patent Document 1, peening treatment and removal of unevenness and altered layers associated with peening treatment are unnecessary, thus reducing the number of steps required for repair and enabling the repair of the seal fin 8 to be carried out in a short period of time.

[0023] Furthermore, in S103, when heat is supplied to the heat-affected zone 8c by arc discharge from the tungsten electrode (when tempering treatment of the heat-affected zone 8c is performed by TIG welding), precise heat input control is possible, making it easy to adjust the hardness of the heat-affected zone 8c after build-up welding and effectively suppressing damage to the seal fin 8 after repair. In addition, in the tempering treatment of S103, there is no need to add filler material to the damaged area 8a while heat is supplied to the heat-affected zone 8c by arc discharge or laser, thus simplifying the repair method for the seal fin 8.

[0024] Furthermore, by using correlation information R, which shows the relationship between parameter d related to the amount of damage to the seal fin 8 and the amount of heat input from the arc discharge or laser during the tempering process, the amount of heat input from the arc discharge or laser during the tempering process can be determined. This allows the tempering process of the heat-affected zone 8c to be performed with an appropriate amount of heat input corresponding to the amount of damage to the seal fin 8. As a result, the hardness of the heat-affected zone 8c after build-up 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, nickel-based alloy, or austenitic stainless steel as the filler material for S102 overlay welding, hardening after heat input can be suppressed.

[0026] Furthermore, regarding the seal fins 8 formed on the tip 6a of the rotor blade 6, damage to the seal fins 8 after repair can be suppressed, thereby stably suppressing leakage flow in the gap between the tip 6a of the rotor blade 6 and the casing (stationary wall) of the steam turbine 2 (not shown).

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

[0028] This disclosure is not limited to the embodiments described above, but also includes modified forms of the embodiments described above, as well as forms that combine these forms as appropriate.

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

[0030] Furthermore, in the embodiments described above, a method of performing temper bead welding by TIG welding in S103 was exemplified in order to perform delicate heat input control to the heat-affected zone 8c. However, 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 was illustrated in which melt-run welding of the seal fin 8 and the additional fin 9 was performed without adding filler material to the damaged area 8a during the period in S103 when heat was being supplied to the heat-affected zone 8c by arc discharge or laser. However, if the amount of heat supplied to the heat-affected zone 8c can be appropriately controlled, heat may be supplied 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 is a method for repairing a seal fin (for example, a seal fin 8) provided on a rotor (for example, a rotor 4) of a steam turbine (for example, a steam turbine 2) the above, comprising: a build-up welding step of forming an additional fin (for example, an additional fin 9) on a damaged portion (for example, a damaged portion 8a) of the seal fin by build-up welding; and a tempering step of performing a tempering treatment on a heat-affected region (for example, a heat-affected region 8c) created on the seal fin by the build-up welding by applying heat to the heat-affected region by arc discharge or laser.

[0034] According to the seal fin repair method described in [1] above, after forming an additional fin at the damaged location of the seal fin by build-up welding, the heat-affected zone created in the seal fin by build-up welding is heated by arc discharge or laser to perform tempering treatment on the heat-affected zone. This reduces the hardness of the heat-affected zone, relieves internal stress in the heat-affected zone, and suppresses damage to the seal fin after repair. Furthermore, compared to the seal fin repair method described in Patent Document 1, peening treatment and removal of unevenness and altered layers associated with peening treatment are unnecessary, thus reducing the number of steps required for repair and enabling seal fin repair to be carried out in a shorter period of time.

[0035] [2] In some embodiments, in the method for repairing seal fins described in [1] above, the build-up welding in the build-up welding step is MIG welding.

[0036] According to the seal fin repair method described in [2] above, the electrode that serves as the filler material can be continuously supplied, thereby improving the efficiency of the build-up welding process. Furthermore, by performing MIG welding under extremely low heat input conditions, the hardened area of ​​the heat-affected zone after build-up welding can be reduced.

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

[0038] According to the seal fin repair method described in [3] above, precise heat input control is possible for the heat-affected zone, making it easy to adjust the hardness of the heat-affected zone after build-up welding and effectively suppressing damage to the seal fin after repair.

[0039] [4] In some embodiments, in the method for repairing a seal fin described in any of [1] to [3] above, in the tempering step, no filler material is added to the damaged area while heat is being applied 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 fins are already formed in the build-up welding step, there is no need to add filler material in the tempering step, thus simplifying the seal fin repair method.

[0041] [5] In some embodiments, the method for repairing a seal fin according to any one of [1] to [4] above further comprises a heat input determination step in which the heat input of the arc discharge or the laser in the tempering process (for example, the heat input Q2 above) is determined based on a parameter relating to the amount of damage to the seal fin (for example, parameter d above) and correlation information showing the relationship between the parameter relating to the amount of damage to the seal fin and the heat input of the arc discharge or the laser in the tempering process (for example, correlation information R above), wherein the tempering process step controls the heat input of the arc discharge or the laser in the tempering process based on the heat input determined in the heat input determination step.

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

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

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

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

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

[0047] [8] In some embodiments, in the method for repairing a seal fin according to any one of [1] to [6] above, the seal fin is formed at a position facing the stationary blade (for example, the stationary blade 5 described above) of the steam turbine on the outer peripheral surface (for example, the outer peripheral surface 4a described above) of the rotor.

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

[0049] [9] In some embodiments, in the method for repairing a seal fin according to any one of [1] to [8] above, the build-up welding in the build-up welding step is very low heat input welding.

[0050] According to the seal fin repair method described in [9] above, by making the build-up welding in the build-up welding step an extremely low heat input welding, the hardening of the heat-affected zone caused by the build-up welding can be suppressed, thereby enhancing the effect of suppressing damage to the seal fin after repair.

[0051]

[10] In some embodiments, in the method for repairing a seal fin described in any of [1] to [9] above, the heat input for the build-up welding step is 9.0 (kJ / cm) or less.

[0052] By reducing the heat input for build-up welding to the extent described in

[10] above, the hardening of the heat-affected zone caused by build-up welding can be suppressed, thereby enhancing the effect of suppressing damage to the seal fins after repair.

[0053]

[11] In some embodiments, in the method for repairing seal fins described in

[10] above, the heat input for the build-up welding step is 6.0 (kJ / cm) or less.

[0054] By reducing the heat input for build-up welding to the extent described in

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

[0055]

[12] In some embodiments, in the method for repairing seal fins described in

[11] above, the heat input for the build-up welding step is 3.0 (kJ / cm) or less.

[0056] By reducing the heat input for build-up welding to the extent described in

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

[0057] 2: Steam turbine 4: Rotor 4a: Outer surface 5: Stationary blade 6: Rotating blade 6a: Tip 8: Seal fin 8a: Damaged area 8b: Base material 8c: Heat-affected zone 9: Additional fin 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 the rotor of a steam turbine, comprising: a build-up welding step of forming an additional fin at a damaged location by build-up welding at the damaged location of the seal fin; and a tempering step of performing a tempering treatment on the heat-affected zone created in the seal fin by the build-up welding by applying heat to the heat-affected zone by arc discharge or laser.

2. The method for repairing a seal fin according to claim 1, wherein the build-up welding in the build-up welding step is MIG welding.

3. The method for repairing a seal fin according to claim 1, wherein in the tempering step, the heat-affected zone is heated by an arc discharge from a tungsten electrode to perform the tempering treatment on the heat-affected zone.

4. The method for repairing a seal fin according to claim 1, wherein in the tempering step, no filler material is added to the damaged area while the heat-affected zone is being heated by the arc discharge or the laser.

5. A method for repairing a seal fin according to claim 1, further comprising a heat input determination step in which the heat input of the arc discharge or the laser in the tempering process is determined based on a parameter relating to the amount of damage to the seal fin and correlation information showing the relationship between the parameter relating to the amount of damage to the seal fin and the heat input of the arc discharge or the laser in the tempering process, wherein in the tempering process step, the heat input of the arc discharge or the laser in the tempering process is controlled based on the heat input determined in the heat input determination step.

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

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

8. The method for repairing a seal fin according to claim 1, wherein the seal fin is formed on the outer circumferential surface of the rotor at a position facing the stator blades of the steam turbine.

9. The method for repairing a seal fin according to claim 1, wherein the build-up welding in the build-up welding step is an extremely low heat input welding.

10. The method for repairing a seal fin according to claim 1, wherein the heat input for the build-up welding step is 9.0 (kJ / cm) or less.

11. The method for repairing a seal fin according to claim 10, wherein the heat input for the build-up welding step is 6.0 (kJ / cm) or less.

12. The method for repairing a seal fin according to claim 11, wherein the heat input for the build-up welding step is 3.0 (kJ / cm) or less.

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