Seal rings, seal ring assemblies, and steam turbines

Abstract

The goal is to reduce the manufacturing cost of the seal ring while improving its corrosion resistance. [Solution] The seal ring is positioned radially outward relative to the final stage blade row of the steam turbine rotor. The seal ring has a circumferentially extending ring and a fin projecting radially inward from the ring and extending circumferentially. The ring has a circumferentially extending ring body and an erosion-resistant layer bonded to the ring body. The ring body has an inner circumferential surface, a front end, and a rear end. The fin projects radially inward from a region in the axial direction between the front end and the rear end of the body on the inner circumferential surface. The erosion-resistant layer is bonded to the inner circumferential surface but not to the tip portion, including the tip of the fin. The erosion-resistant layer is formed of a Co-containing alloy.

Description

Technical Field

[0001] The present disclosure relates to a seal ring, a seal ring assembly, and a steam turbine.

Background Art

[0002] A steam turbine includes a steam turbine rotor that rotates about an axis, a seal ring, and a casing that covers the steam turbine rotor and the seal ring. The seal ring is disposed radially outside the final stage moving blade row of the steam turbine rotor.

[0003] The following Patent Document 1 describes this seal ring. This seal ring has a cover portion (ring) extending in the circumferential direction with respect to the axis, and fins protruding radially inward from the cover portion and extending in the circumferential direction.

[0004] Inside the casing, around the final stage stationary blade row or around the final stage moving blade row located on the downstream side of the axis of the final stage stationary blade row, a part of the steam condenses to form steam drain. A part of the steam drain adheres to the final stage stationary blade row and the final stage moving blade row. A part of the steam drain adhering to the final stage stationary blade row and the final stage moving blade row scatters radially outward and collides with the seal ring. Also, a part of the steam drain that does not adhere to the final stage stationary blade row and the final stage moving blade row scatters radially outward and collides with the seal ring. Therefore, erosion by the steam drain easily progresses on the surface facing the radially inner side of the seal ring.

[0005] Therefore, in the seal ring described in the following Patent Document 1, the cover portion (ring) and the fins are formed of 12 chromium steel to enhance the erosion resistance performance of this seal ring.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

[0007] As mentioned earlier, seal rings require high corrosion resistance.

[0008] Therefore, the purpose of this disclosure is to provide a seal ring, a seal ring assembly, and a steam turbine that can improve corrosion resistance while keeping manufacturing costs down. [Means for solving the problem]

[0009] One embodiment of a seal ring for achieving the above objective is a seal ring positioned radially outward with respect to the axis of the final stage blade row of a steam turbine rotor that is rotatable about the axis. The seal ring comprises a ring extending circumferentially with respect to the axis, and a fin extending circumferentially and projecting radially inward from the ring, opposite to the radially outward direction. The ring comprises a ring body extending circumferentially and an erosion-resistant layer bonded to the ring body. The ring body has an inner circumferential surface that faces radially inward and extends in the circumferential direction and the axial direction in which the axis extends, a front end of the body facing the upstream side of the axis and a rear end of the body facing the downstream side of the axis. The fin projects radially inward from a region on the inner circumferential surface of the body between the front end and the rear end of the body in the axial direction. The erosion-resistant layer is made of a metal with higher erosion resistance than the metal forming the ring body and the fin. The erosion-resistant layer is bonded to the inner circumferential surface of the body, but not to the tip portion including the tip of the fin.

[0010] As steam flows through the steam channel downstream along the axis, its pressure and temperature gradually decrease. As a result, this steam becomes wet steam around the final stage stator and rotor blade rows. In other words, some of this steam condenses into steam condensate. Some of the steam condensate adheres to the final stage stator and rotor blade rows. Some of the steam condensate adhering to the final stage stator and rotor blade rows scatters radially outward and collides with the seal ring. Some of the steam condensate that does not adhere to the final stage stator and rotor blade rows also scatters radially outward and collides with the seal ring. Therefore, erosion by steam condensate is more likely to occur on the radially inward-facing surface of the seal ring.

[0011] In this embodiment, an etching-resistant layer is bonded to the inner circumferential surface of the ring body, that is, to the surface of the ring body facing radially inward. Therefore, the etching resistance of the seal ring in this embodiment can be improved.

[0012] Incidentally, the final stage rotor blade row has multiple final stage rotor blades arranged in the circumferential direction. The final stage rotor blade has a blade body that extends radially with an airfoil-shaped cross-section perpendicular to the radial direction, and a shroud that is joined to the radially outer edge of the blade body and extends in the circumferential and axial directions. Due to this shroud, the steam condensate that adheres to the final stage stator blade row and the final stage rotor blade row and is scattered radially outward hardly directly collides with the fins provided in the region between the front and rear ends of the ring body. Even if the steam condensate scattered radially outward were to directly collide with the fins, the collision angle of the steam condensate with the radially extending fin surface is small. For this reason, erosion by the steam condensate is less likely to occur on the fins.

[0013] In this embodiment, taking the above circumstances into consideration, an etching-resistant layer is bonded to the inner surface of the main body, but not to the tip of the fin.

[0014] Therefore, in this embodiment, the manufacturing cost of the seal ring can be reduced while improving its corrosion resistance.

[0015] A seal ring assembly as one embodiment for achieving the aforementioned objective is: The present invention comprises a seal ring as described above, and a support member extending in the circumferential direction and positioned radially outward of the seal ring. The ring body has an outer circumferential surface that faces radially outward and extends in the circumferential and axial directions. The seal ring has a mounting portion that protrudes radially outward from the outer circumferential surface of the ring body. The ring body, the fin, and the mounting portion are integrally formed from the same metal. The support member has an inner circumferential surface that faces radially inward and extends in the circumferential direction, and a groove that is recessed radially outward from the inner circumferential surface of the member and extends in the circumferential direction. The mounting portion fits into the groove, and the outer circumferential surface of the ring body faces the inner circumferential surface of the member radially with respect to the axis.

[0016] In this embodiment, the seal ring can be attached to the support member by fitting the mounting portion of the seal ring into the groove of the support member. Furthermore, by moving the seal ring relative to the support member in the circumferential direction, the mounting portion of the seal ring that was fitted into the groove of the support member can be removed from this groove. Therefore, in this embodiment, the seal ring attached to the support member can be replaced with a new seal ring.

[0017] A steam turbine as one embodiment for achieving the aforementioned objective is: The steam turbine rotor comprises a seal ring assembly as described above, the steam turbine rotor, and a casing covering the seal ring assembly and the steam turbine rotor. The support member of the seal ring assembly is fixed to the casing. The final stage rotor blade row of the steam turbine rotor has a plurality of final stage rotor blades arranged in the circumferential direction. Each of the plurality of final stage rotor blades has a blade body extending in the radial direction and a shroud joined to the radially outer edge of the blade body and extending in the circumferential and axial directions. The shroud has a front end facing the upstream side of the axis and a rear end facing the downstream side of the axis. The distance from the front end of the shroud to the tip of the fin in the axial direction is 40% or more and 60% or less of the distance from the front end of the shroud to the rear end of the shroud in the axial direction.

[0018] In this embodiment, the distance from the front end of the shroud to the tip of the fin in the axial direction is 40% to 60% of the distance from the front end of the shroud to the rear end of the shroud. In other words, in the axial direction, the fin is located in the central part of the shroud. Therefore, in this embodiment, most of the steam condensate that adheres to the final stage stator blade row and the final stage rotor blade row and is scattered radially outward does not directly collide with the fin due to the shroud of the final stage rotor blade. Thus, in this embodiment, erosion of the fin by steam condensate can be suppressed. [Effects of the Invention]

[0019] According to this disclosure, it is possible to reduce the manufacturing cost of the seal ring while improving its corrosion resistance. [Brief explanation of the drawing]

[0020] [Figure 1] This is a schematic overall cross-sectional view of a steam turbine in one embodiment relating to this disclosure. [Figure 2] This is a cross-sectional view of the seal ring assembly of a steam turbine in one embodiment of the present disclosure. [Figure 3] This is an enlarged cross-sectional view of part III in Figure 2. [Figure 4] It is a sectional view taken along line IV-IV in FIG. 3.

Embodiments for Carrying Out the Invention

[0021] Hereinafter, a seal ring, a seal ring assembly, and a steam turbine in embodiments of this invention will be described with reference to the drawings.

[0022] "Embodiments of Steam Turbine" Embodiments of the steam turbine will be described in detail with reference to FIG. 1.

[0023] As shown in FIG. 1, the steam turbine in this embodiment is a two-flow type steam turbine. This steam turbine includes a first steam turbine section ST1 and a second steam turbine section ST2. Both the first steam turbine section ST1 and the second steam turbine section ST2 include a steam turbine rotor (hereinafter simply referred to as the rotor) 10 that rotates about an axis Ar, a casing 20 that covers the rotor 10, a plurality of blade rings 18 arranged in the casing 20, one or more stationary blade rows 19 held by each blade ring 18, a bearing 15, a steam inlet pipe 16, and a seal ring assembly 30. The rotor 10 of the first steam turbine section ST1 and the rotor 10 of the second steam turbine section ST2 are located on the same axis Ar and are integrally rotatably connected. For the convenience of the following description, the direction in which the axis Ar extends is defined as the axial direction Da. Also, of the two sides in the axial direction Da, one side is the first side Da1 and the other side is the second side Da2. Further, the radial direction perpendicular to the axis Ar is simply referred to as the radial direction Dr, the side approaching the axis Ar in this radial direction Dr is the radially inner side Dri, and the opposite side of this radially inner side Dri is the radially outer side Dro. Furthermore, the circumferential direction with respect to the axis Ar is simply referred to as the circumferential direction Dc.

[0024] The first steam turbine section ST1 and the second steam turbine section ST2 share a steam inlet pipe 16. In the first steam turbine section ST1, all components except the steam inlet pipe 16 are arranged on the first side Da1 in the axial direction Da with respect to the steam inlet pipe 16. In the first steam turbine section ST1, the second side Da2 forms the upstream side Dau, and the first side Da1 forms the downstream side Da. Similarly, in the second steam turbine section ST2, all components except the steam inlet pipe 16 are arranged on the second side Da2 with respect to the steam inlet pipe 16. In the second steam turbine section ST2, the first side Da1 forms the upstream side Dau, and the second side Da2 forms the downstream side Da. The first steam turbine section ST1 and the second steam turbine section ST2 are identical in shape and structure. However, the second steam turbine section ST2 has a shape that is a left-right inversion of the first steam turbine section ST1, with the position of the steam inlet pipe 16 in the axial direction Da as the reference point. Therefore, the axial upstream side Dau in the second steam turbine section ST2 is on the opposite side in the axial direction Da from the axial upstream side Dau in the first steam turbine section ST1.

[0025] Each rotor 10 in the first steam turbine section ST1 and the second steam turbine section ST2 has a rotor shaft 11 extending in the axial direction Da with respect to the axis Ar, and a plurality of rotor blade rows 12 fixed to the outer circumference of the rotor shaft 11 and arranged in the axial direction Da. A bearing 15 is provided on the downstream side Da of the rotor shaft 11 to rotatably support the rotor shaft 11. Each of the plurality of rotor blade rows 12 has a plurality of rotor blades arranged in the circumferential direction Dc. Each of the plurality of stator blade rows 19 is arranged in the axial direction Da. One of the plurality of stator blade rows 19 is positioned at the upstream side Dau of each rotor blade row 12. Each of the plurality of stator blade rows 19 has a plurality of stator blades arranged in the circumferential direction Dc.

[0026] Each of the multiple blade rings 18 is cylindrical with respect to the axis Ar. The vane rings 18 are aligned in the axial direction Da. Each of the multiple blade rings 18 holds one or more of the multiple stator blade rows 19. The annular space between the inner circumference of the multiple blade rings 18 and the outer circumference of the rotor shaft 11 forms a steam flow path 17 that communicates with the steam inlet pipe 16.

[0027] Each casing 20 in the first steam turbine section ST1 and the second steam turbine section ST2 includes an inner casing 21, an exhaust casing 22, and a diffuser 23. The inner casing 21 is cylindrical with its axis Ar as the center. Multiple blade rings 18 are attached to the inner circumference of this inner casing 21.

[0028] The seal ring assembly 30 is positioned on the outer circumference of the final stage rotor blade row 12r. This seal ring assembly 30 is attached to the inner casing. The final stage rotor blade row 12r is the rotor blade row 12 furthest downstream of the axis Da among the multiple rotor blade rows 12. The seal ring assembly 30 will be described in detail later as an embodiment.

[0029] The diffuser 23 forms an annular shape around the axis Ar, and gradually widens radially outward towards Dad downstream of the axis, forming a diffuser space 23s. Steam S that has passed through the final stage rotor blade row 12r flows into the diffuser space 23s. This diffuser 23 has an inner diffuser (or bearing cone) 24 and an outer diffuser (or flow guide) 25. The inner diffuser 24 has an outer circumferential surface that faces radially outward towards Dad downstream of the axis, and gradually widens radially outward towards Dad downstream of the axis. This outer circumferential surface defines the inner edge of the diffuser space 23s. The outer diffuser 25 has an outer diffuser inner circumferential surface 25i that faces radially inward towards Dad downstream of the axis, and gradually widens radially outward towards Dad downstream of the axis. This outer diffuser inner circumferential surface 25i defines the outer edge of the diffuser space 23s.

[0030] The exhaust casing 22 has an exhaust port 27. This exhaust port 27 opens radially outward from the inside and vertically downward. A condenser C that returns steam S back to water is connected to this exhaust port 27. The exhaust casing 22 forms an exhaust space 22s through which the steam S that has passed through the diffuser space 23s flows. This exhaust space 22s extends circumferentially Dc with respect to the axis Ar around the outer circumference of the diffuser 23, guiding the steam S that flows in from the diffuser space 23s to the exhaust port 27.

[0031] The exhaust casing 22 of the first steam turbine section ST1 and the exhaust casing 22 of the second steam turbine section ST2 are connected to each other and integrated into one unit.

[0032] The steam S that flows into the steam inlet pipe 16 flows into the steam passage 17 of the first steam turbine section ST1 and the steam passage 17 of the second steam turbine section ST2. As the steam S that flows into the steam passage 17 flows toward the downstream side Da along the axis, it collides with multiple rotor blades of each of the multiple rotor blade rows 12, causing the rotor 10 to rotate. The steam that has passed through the final stage rotor blade row 12r passes through the diffuser space 23s and the exhaust space 22s, and is exhausted from the exhaust port 27 of the exhaust casing 22 and flows into the condenser C.

[0033] "Embodiment of a seal ring and seal ring assembly" Embodiments of the seal ring and seal ring assembly will be described in detail with reference to Figures 2 to 4.

[0034] As described above, the seal ring assembly 30 in this embodiment comprises, as shown in Figures 2 and 3, a plurality of seal rings 33 arranged radially outward Dro of the final stage rotor blade row 12r, an outer diffuser 25, and a plurality of support members 31 that support the seal rings 33 and the outer diffuser 25. The outer diffuser 25 is also part of the casing 20, as mentioned above with reference to Figure 1.

[0035] Multiple support members 31 are arranged radially outward Dro of multiple seal rings 33. The multiple support members 31 are arranged in the circumferential direction Dc, forming an annular shape with respect to the axis Ar. Each support member 31 is connected to the inner casing 21. Each support member 31 has an inner circumferential surface 31i that faces radially inward Dri and extends in the circumferential direction Dc, a front end surface 31f that faces upstream Dau on the axis, a rear end surface 31b that faces downstream Dad on the axis, and a groove 32 that is recessed radially outward Dro from the inner circumferential surface 31i and extends in the circumferential direction Dc.

[0036] The groove 32 has a first groove portion 32a that is recessed radially outward from the inner circumferential surface 31i of the member Dro and extends in the circumferential direction Dc, and a second groove portion 32b that is formed radially outward from the first groove portion 32a Dro and extends in the circumferential direction Dc. The first groove portion 32a is open at the position of the inner circumferential surface 31i of the member. The second groove portion 32b is recessed radially outward from the first groove portion 32a Dro and communicates with the first groove portion 32a. The width of the second groove portion 32b in the axial direction Da is wider than the width of the first groove portion 32a in the axial direction Da.

[0037] The inner circumferential surface 25i of the outer diffuser has an outer diffuser upstream inner circumferential surface 25iu that extends from the end of the outer diffuser upstream side Dau to the end of the outer diffuser downstream side Da and widens in the circumferential direction Dc, and an outer diffuser downstream inner circumferential surface 25id that gradually extends radially outward Dro from the end of the outer diffuser upstream inner circumferential surface 25iu to the end of the outer diffuser downstream side Da and widens in the circumferential direction Dc. The inner diameter of the outer diffuser upstream inner circumferential surface 25iu is the same at any position in the axial direction Da.

[0038] The upstream end Dau of the outer diffuser 25 is joined to the rear end surface 31b of the member so that the upstream inner surface 25iu of the outer diffuser is smoothly continuous with the inner surface 31i of the member.

[0039] Multiple seal rings 33 are arranged in the circumferential direction Dc to form an annular ring around the axis Ar. Each seal ring 33 has a ring 34 extending in the circumferential direction Dc, a mounting portion 38 protruding radially outward Dro from the ring 34 and extending in the circumferential direction Dc, and a fin 37 protruding radially inward Dri from the ring 34 and extending in the circumferential direction Dc.

[0040] The ring 34 has a ring body 35 extending in the circumferential direction Dc, and an erosion-resistant layer 36 bonded to the radially inner Dri of the ring body 35. The ring body 35 has an inner circumferential surface 35i facing radially inner Dri and extending in the circumferential direction Dc and axial direction Da, an outer circumferential surface 35o facing radially outer Dro and extending in the circumferential direction Dc and axial direction Da, a front end 35f facing the axial upstream side Dau, and a rear end 35b facing the axial downstream side Dad.

[0041] The fin 37 protrudes radially inward Dri from the region between the front end 35f and the rear end 35b of the main body in the axial direction Da on the inner circumferential surface 35i of the main body. The inner circumferential surface 35i of the ring 34 has an upstream layer-forming surface 35iu, a downstream layer-forming surface 35id, and an inclined surface 35is. The upstream layer-forming surface 35iu extends from the edge of the front end 35f of the main body to the edge of the fin 37 on the axial upstream side Dau. The downstream layer-forming surface 35id extends from the edge of the fin 37 on the axial downstream side Da towards the axial downstream side Da. The inclined surface 35is extends from the edge of the downstream layer-forming surface 35id on the axial downstream side Da to the edge of the rear end 35b of the main body. This inclined surface 35is is inclined with respect to the downstream layer-forming surface 35id so as it moves toward the axial downstream side Da, it gradually widens radially outward Dro.

[0042] The mounting portion 38 fits into the groove 32 of the support member 31. As a result, the outer circumferential surface 35o of the ring body 35 faces the inner circumferential surface 31i of the member in the radial direction Dr. The mounting portion 38 has a first mounting portion 38a that protrudes radially outward Dro from the region between the front end 35f and the rear end 35b of the ring body in the axial direction Da on the outer circumferential surface 35o, and a second mounting portion 38b that protrudes radially outward Dro from the first mounting portion 38a. The width of the first mounting portion 38a in the axial direction Da is narrower than the width of the first groove portion 32a in the axial direction Da. For this reason, after the first mounting portion 38a is inserted into the first groove portion 32a, it can be inserted into and removed radially inward Dri from the first groove portion 32a. The width of the second mounting portion 38b in the axial direction Da is wider than the width of the first groove portion 32a in the axial direction Da, and narrower than the width of the second groove portion 32b in the axial direction Da. Therefore, after the second mounting portion 38b is inserted into the second groove portion 32b, it cannot be inserted into or removed from the second groove portion 32b in the radially inward direction Dri. The second mounting portion 38b has a storage recess 38r formed on the surface facing the radially outward direction Dro that is recessed in the radially inward direction Dri. An elastic body 39 compressed in the radial direction Dr is housed in this storage recess 38r. The end of the elastic body 39 in the radially inward direction Dri is in contact with the bottom surface of the storage recess 38r, and the end of the elastic body 39 in the radially outward direction Dro is in contact with the bottom surface of the second groove portion 32b. Therefore, within the second groove portion 32b, the second mounting portion 38b is pushed in the radially inward direction Dri by the elastic body 39. In Figure 3, the elastic body 39 is shown as a coil spring, but the elastic body 39 is not limited to a coil spring; for example, it may be a leaf spring or the like.

[0043] When the mounting portion 38 is fitted into the groove 32 of the support member 31 and the seal ring 33 is supported by the support member 31, the position of the front end 35f of the main body in the axial direction Da coincides with the position of the front end surface 31f of the member in the axial direction Da, and the position of the rear end 35b of the main body in the axial direction Da is located downstream Da of the axial direction Da. Therefore, a portion of the downstream Da of the ring body 35 overlaps radially Dr with a portion of the upstream Dau of the outer diffuser 25. Note that the statement above that "the position of the front end 35f of the main body in the axial direction Da coincides with the position of the front end surface 31f of the member in the axial direction Da" includes not only the case where the position of the front end 35f of the main body and the position of the front end surface 31f of the member perfectly coincide, but also the case where their positions are shifted by a few millimeters.

[0044] The ring body 35, fins 37, and mounting portion 38 are integrally formed from the same metal. The ring body 35, fins 37, and mounting portion 38 are formed from, for example, martensitic stainless steel casting material.

[0045] The erosion-resistant layer 36 is bonded to the inner circumferential surface 35i of the main body, but not to the tip portion 37tp of the fin 37, including the tip 37t. The tip portion 37tp of the fin 37 is the portion Dri radially inward from the surface of the erosion-resistant layer 36 within the fin 37. This erosion-resistant layer 36 has an upstream erosion-resistant layer 36u that extends from the edge of the upstream side Dau of the fin 37 to the front end 35f of the main body, and a downstream erosion-resistant layer 36d that extends from the edge of the downstream side Dad of the fin 37 to Dad. That is, the upstream erosion-resistant layer 36u is bonded to the upstream layer-forming surface 35iu in the inner circumferential surface 35i of the main body. The downstream erosion-resistant layer 36d is bonded to the downstream layer-forming surface 35id in the inner circumferential surface 35i of the main body. However, this downstream erosion-resistant layer 36d is not bonded to the inclined surface 35is in the inner circumferential surface 35i of the main body. That is, although the downstream erosion-resistant layer 36d extends from the edge of the downstream Da of the fin 37 to the downstream Da of the axial line, it is not formed in the region of Da downstream of the axial line beyond the rear end surface 31b of the member. In other words, the downstream erosion-resistant layer 36d does not extend to the position of the rear end 35b of the main body.

[0046] The ring 34, which has a ring body 35 and an erosion-resistant layer 36, has an inner circumferential surface 34i that faces radially inward Dri and extends in the circumferential direction Dc and axial direction Da. The rear end of this ring 34 is the aforementioned rear end 35b of the main body. The inner circumferential surface 34i has an upstream inner circumferential surface 34iu formed on the surface of the erosion-resistant layer 36, and a downstream inner circumferential surface 34id that extends from the axially downstream Dad end of the upstream inner circumferential surface 34iu to the rear end 35b of the main body, and gradually widens radially outward Dro as it approaches the axially downstream Dad. A part of the downstream inner circumferential surface 34id is formed by an inclined surface 35is in the main body inner circumferential surface 35i. The downstream inner circumferential surface 25id of the outer diffuser is in contact with a virtual extension surface L that extends this downstream inner circumferential surface 34id toward the axially downstream Dad.

[0047] The erosion-resistant layer 36 is made of a metal with higher erosion resistance than the metals forming the ring body 35, fins 37, and mounting portion 38. Specifically, the erosion-resistant layer 36 in this embodiment is made of a cobalt (Co)-based alloy. The erosion-resistant layer 36 has, for example, a (Co+Ni) content of 55.00 wt% or more and a Ni content of 3.00 wt% or less. That is, the erosion-resistant layer 36 has, for example, a Co content of 52.00 wt% or more.

[0048] The erosion-resistant layer 36 may contain, for example, Cr and W. In this case, the Cr content is 27.00 wt% or more and 33.00 wt% or less, and the W content is 3.00 wt% or more and 19.00 wt% or less. This erosion-resistant layer 36 may further be formed from an alloy containing C. In this case, the C content is 0.10 wt% or more and 3.25 wt% or less. This erosion-resistant layer 36 may contain, for example, 9.50 wt% or less of other elements.

[0049] The seal ring 33 described above can be manufactured by forming an erosion-resistant layer 36 on a metal member having a ring body 35, fins 37, and mounting portion 38. In this case, the erosion-resistant layer 36 is formed on the metal member using a type of additive manufacturing (AM) method, such as laser powder welding or plasma powder welding.

[0050] Incidentally, in this embodiment, a final stage rotor blade row 12r is arranged on the radially inner Dri of the seal ring 33. As shown in Figures 3 and 4, this final stage rotor blade row 12r has a plurality of final stage rotor blades 13 arranged in the circumferential direction Dc. Each of the plurality of final stage rotor blades 13 has a blade body 13b that extends radially in the Dr direction with a cross section perpendicular to the radial direction Dr forming an airfoil shape, and a shroud 13s that is joined to the radially outer edge Dro of the blade body 13b and extends in the circumferential direction Dc and the axial direction Da. The shroud 13s has a front end 13sf of the shroud facing the axial upstream side Dau, and a rear end 13sb of the shroud facing the axial downstream side Dad.

[0051] Here, as shown in Figure 4, the distance ds from the front end 13sf of the shroud to the rear end 13sb of the shroud in the axial direction Da is set to 100%. In this case, the distance df from the front end 13sf of the shroud to the tip point 37t of the fin 37 in the axial direction Da in this embodiment is 40% or more and 60% or less of the distance ds. Also, as shown in Figure 3, the distance dm from the front end surface 31f of the member to the rear end surface 31b of the member in the axial direction Da is longer than the distance ds from the front end 13sf of the shroud to the rear end 13sb of the shroud in the axial direction Da. Furthermore, the distance dr from the front end 35f of the main body to the rear end 35b of the main body in the axial direction Da is longer than the distance dm from the front end surface 31f of the member to the rear end surface 31b of the member in the axial direction Da.

[0052] As the steam S flows through the steam channel 17 toward the downstream side Dad along the axis, its pressure and temperature gradually decrease. As a result, the steam S becomes wet steam around the final stage stator blade row 19r and the final stage rotor blade row 12r. In other words, a portion of this steam S condenses to become steam drain SD. The final stage stator blade row 19r is the stator blade row 19 located furthest downstream of the axis Dad among the multiple stator blade rows 19. A portion of the steam drain SD adheres to the final stage stator blade row 19r and the final stage rotor blade row 12r. A portion of the steam drain SD that adheres to the final stage stator blade row 19r and the final stage rotor blade row 12r scatters radially outward towards Dro and collides with the seal ring 33. In addition, a portion of the steam drain SD that does not adhere to the final stage stator blade row 19r and the final stage rotor blade row 12r also scatters radially outward towards Dro and collides with the seal ring 33. Therefore, the surface of the seal ring 33 facing the radially inward Dri is prone to erosion by steam drain SD.

[0053] In this embodiment, an erosion-resistant layer 36 is bonded to the inner circumferential surface 35i of the ring body 35, that is, to the surface facing the radially inner Dri of the ring body 35. Therefore, the erosion resistance of the seal ring 33 in this embodiment can be improved. In particular, since the erosion-resistant layer 36 in this embodiment is formed of an alloy containing Cr and W, the erosion resistance of this seal ring 33 can be improved compared to when the ring 34 is formed of 12-chromium steel.

[0054] In this embodiment, the distance df from the front end 13sf of the shroud to the tip 37t of the fin 37 in the axial direction Da is 40% or more and 60% or less of the distance ds. In other words, in the axial direction Da, the fin 37 is located in the central part of the shroud 13s. For this reason, in this embodiment, most of the steam drain SD that adheres to the final stage stator blade row 19r and the final stage rotor blade row 12r and is scattered radially outward towards Dro is blocked by the shroud 13s which extends in the circumferential direction Dc and the axial direction Da of the final stage rotor blade 13, and does not directly collide with the fin 37. Even if the steam drain SD scattered radially outward towards Dro were to directly collide with the fin 37, the collision angle of the steam drain SD with the surface of the fin 37 extending radially in Dr is small. Therefore, as in this embodiment, even if the erosion-resistant layer 36 is not bonded to the tip portion 37tp of the fin 37, erosion of the fin 37 by steam drain SD can be suppressed. From the above, in this embodiment, the erosion resistance performance of the seal ring 33 can be improved while keeping the manufacturing cost of the seal ring 33 down.

[0055] Furthermore, in this embodiment, the erosion-resistant layer 36 is not bonded to the inclined surface 35is on the inner circumferential surface 35i of the main body. Also, the erosion-resistant layer 36 is not bonded to the region Dad downstream of the rear end surface 31b of the member on the inner circumferential surface 35i of the main body. In other words, in this embodiment, the erosion-resistant layer 36 is formed in the parts where erosion is likely to progress, and not in the parts where erosion is unlikely to progress. Therefore, in this embodiment, the manufacturing cost of the seal ring 33 can be reduced from this viewpoint as well.

[0056] In this embodiment, the rear end 35b of the ring body 35 is located downstream of the rear end surface 31b of the support member 31 in the axis direction Da. Therefore, a portion of the ring body 35 is located radially inward Dri of the rear end surface 31b of the support member 31, which is the joint position between the outer diffuser 25 and the support member 31. Thus, in this embodiment, erosion by steam drain SD at the joint portion between the outer diffuser 25 and the support member 31 can be suppressed.

[0057] In this embodiment, the seal ring 33 can be attached to the support member 31 by fitting the mounting portion 38 of the seal ring 33 into the groove 32 of the support member 31. Furthermore, by moving the seal ring 33 relative to the support member 31 in the circumferential direction Dc, the mounting portion 38 of the seal ring 33 that was fitted into the groove 32 of the support member 31 can be removed from the groove 32. Therefore, in this embodiment, the seal ring 33 attached to the support member 31 can be replaced with a new seal ring 33.

[0058] "Other variations" In the above embodiment, the blade ring 18 that holds the final stage stator blade row 19r does not support the seal ring 33. However, the blade ring 18 that holds the final stage stator blade row 19r may support the seal ring 33, and this blade ring 18 may be a support member.

[0059] The steam turbine in the above embodiment has a plurality of blade rings 18. However, the number of blade rings 18 may be one.

[0060] The steam turbine in the above embodiment is a two-flow type steam turbine. However, the steam turbine does not have to be a two-flow type. Also, the steam turbine in the above embodiment is a downward-exhausting type steam turbine. However, the steam turbine does not have to be a downward-exhausting type; for example, it may be a side-exhausting type.

[0061] This disclosure is not limited to the embodiments described above. Various additions, modifications, substitutions, partial deletions, etc., are possible without departing from the conceptual idea and spirit of the present invention derived from the claims and their equivalents.

[0062] "Addendum" The seal ring 33 in the above embodiments and modified examples can be understood, for example, as follows.

[0063] (1) The seal ring 33 in the first embodiment is a seal ring 33 positioned radially outward Dro with respect to the axis Ar of a steam turbine rotor 10 that is rotatable about the axis Ar. The seal ring 33 has a ring 34 extending in the circumferential direction Dc with respect to the axis Ar, and a fin 37 projecting radially inward Dri on the opposite side of the radially outward Dro from the ring 34 and extending in the circumferential direction Dc. The ring 34 has a ring body 35 extending in the circumferential direction Dc and an erosion-resistant layer 36 joined to the ring body 35. The ring body 35 has an inner circumferential surface 35i that faces the radially inward Dri and extends in the circumferential direction Dc and the axial direction Da to which the axis Ar extends, a front end 35f of the ring body that faces the upstream side Dau of the axial direction Da, and a rear end 35b of the ring body that faces the downstream side Da. The fin 37 protrudes radially inward Dri from the region between the front end 35f and the rear end 35b of the ring body in the axial direction Da within the inner circumferential surface 35i. The ring body 35 and the fin 37 are integrally formed from the same metal. The erosion-resistant layer 36 is made of a metal with higher erosion resistance than the metal forming the ring body 35 and the fin 37. The corrosion-resistant layer 36 is bonded to the inner circumferential surface 35i of the main body, but not to the tip portion 37tp, including the tip 37t of the fin 37.

[0064] As the steam S flows through the steam channel 17 toward the downstream side Dad along the axis, its pressure and temperature gradually decrease. As a result, the steam S becomes wet steam around the final stage stator blade row 19r and the final stage rotor blade row 12r. In other words, a portion of this steam S condenses to become steam drain SD. A portion of the steam drain SD adheres to the final stage stator blade row 19r and the final stage rotor blade row 12r. A portion of the steam drain SD that adheres to the final stage stator blade row 19r and the final stage rotor blade row 12r scatters radially outward towards Dro and collides with the seal ring 33. In addition, a portion of the steam drain SD that does not adhere to the final stage stator blade row 19r and the final stage rotor blade row 12r also scatters radially outward towards Dro and collides with the seal ring 33. As a result, erosion by steam drain SD is likely to progress on the surface of the seal ring 33 facing radially inward Dri.

[0065] In this embodiment, the erosion-resistant layer 36 is bonded to the inner circumferential surface 35i of the ring body 35, that is, to the surface facing the radially inner Dri of the ring body 35. Therefore, the erosion resistance performance of the seal ring 33 in this embodiment can be improved.

[0066] Incidentally, the final stage rotor blade row 12r has a plurality of final stage rotor blades 13 arranged in the circumferential direction Dc. The final stage rotor blade 13 has a blade body 13b that extends in the radial direction Dr with a cross section perpendicular to the radial direction Dr forming an airfoil shape, and a shroud 13s that is joined to the radially outer edge Dro of the blade body 13b and extends in the circumferential direction Dc and the axial direction Da. Due to this shroud 13s, the steam drain SD that adheres to the final stage stationary blade row 19r and the final stage rotor blade row 12r and is scattered toward the radially outer Dro hardly directly collides with the fin 37 provided in the region between the front end 35f and the rear end 35b of the ring body 35. Even if the steam drain SD scattered toward the radially outer Dro were to directly collide with the fin 37, the collision angle of the steam drain SD with the surface of the fin 37 extending in the radial direction Dr is small. Therefore, erosion by steam drain SD is less likely to occur in fin 37.

[0067] In this embodiment, taking the above circumstances into consideration, an erosion-resistant layer 36 is bonded to the inner circumferential surface 35i of the main body, but the erosion-resistant layer 36 is not bonded to the tip portion 37tp of the fin 37.

[0068] Therefore, in this embodiment, the manufacturing cost of the seal ring 33 can be reduced while improving the corrosion resistance of the seal ring 33.

[0069] (2) The seal ring 33 in the second embodiment is In the seal ring 33 of the first embodiment, the erosion-resistant layer 36 is formed of a Co-based alloy.

[0070] (3) The seal ring 33 in the third embodiment is In the seal ring 33 of the first embodiment described above, the etching-resistant layer 36 is formed of an alloy containing (Co+Ni), Cr, W, and C. (Co+Ni) is 55.00 wt% or more, and Ni is 3.00 wt% or less. Cr is 27.00 wt% or more and 33.00 wt% or less. W is 3.00 wt% or more and 19.00 wt% or less. C is 0.10 wt% or more and 3.25 wt% or less. Others are 9.50 wt% or less.

[0071] The corrosion-resistant layer 36 in this embodiment can further enhance the corrosion resistance of the seal ring 33.

[0072] (4) The seal ring 33 in the fourth embodiment is In the seal ring 33 according to any one of the first to third embodiments, the erosion-resistant layer 36 comprises an upstream erosion-resistant layer 36u extending from the edge of the fin 37 upstream side Dau to the front end 35f of the main body, and a downstream erosion-resistant layer 36d extending from the edge of the fin 37 downstream side Dad to the downstream side Dad.

[0073] (5) The seal ring 33 in the fifth embodiment is In the seal ring 33 according to the fourth embodiment, the inner circumferential surface 35i of the ring body 35 has an upstream layer-forming surface 35iu extending from the edge of the front end 35f of the body to the edge of the fin 37 on the upstream side Dau along the axis, a downstream layer-forming surface 35id extending from the edge of the fin 37 on the downstream side Da along the axis toward the downstream side Da, and an inclined surface 35is extending from the edge of the downstream layer-forming surface 35id on the downstream side Da along the axis to the edge of the rear end 35b of the body. The inclined surface 35is is inclined with respect to the downstream layer-forming surface 35id such that it gradually widens radially outward Dro as it approaches the downstream side Da along the axis. The upstream erosion-resistant layer 36u is bonded to the upstream layer-forming surface 35iu, and the downstream erosion-resistant layer 36d is bonded to the downstream layer-forming surface 35id, but not to the inclined surface 35is.

[0074] The seal ring assembly 30 in the above embodiments and modified examples can be understood, for example, as follows. (6) The seal ring assembly 30 in the sixth embodiment is The device comprises a seal ring 33 in any one of the first to fifth embodiments described above, and a support member 31 extending in the circumferential direction Dc and positioned on the radially outer side Dro of the seal ring 33. The ring body 35 has an outer circumferential surface 35o facing the radially outer side Dro and extending in the circumferential direction Dc and the axial direction Da. The seal ring 33 has a mounting portion 38 protruding from the outer circumferential surface 35o to the radially outer side Dro. The ring body 35, the fin 37 and the mounting portion 38 are integrally formed from the same metal. The support member 31 has a front end surface 31f facing the axial upstream side Dau, a rear end surface 31b facing the axial downstream side Dad, an inner circumferential surface 31i facing the radially inward side Dri and extending in the circumferential direction Dc, and a groove 32 recessed from the inner circumferential surface 31i to the radially outer side Dro and extending in the circumferential direction Dc. The inner circumferential surface 31i of the member connects the radially inner edge Dri of the front end surface 31f of the member and the radially inner edge Dri of the rear end surface 31b of the member. The mounting portion 38 fits into the groove 32, and the outer circumferential surface 35o of the ring body 35 faces the inner circumferential surface 31i of the member in the radial direction Dr with respect to the axis Ar.

[0075] In this embodiment, the seal ring 33 can be attached to the support member 31 by fitting the mounting portion 38 of the seal ring 33 into the groove 32 of the support member 31. Furthermore, by moving the seal ring 33 relative to the support member 31 in the circumferential direction Dc, the mounting portion 38 of the seal ring 33 that was fitted into the groove 32 of the support member 31 can be removed from the groove 32. Therefore, in this embodiment, the seal ring 33 attached to the support member 31 can be replaced with a new seal ring 33.

[0076] (7) The seal ring assembly 30 in the seventh embodiment is The seal ring assembly 30 in the sixth embodiment has an outer diffuser 25 that is annular around the axis Ar and gradually extends radially outward towards Dro as it moves toward the downstream side Da along the axis. The inner circumferential surface 31i of the member connects the edge of the radially inward Dri of the front end surface 31f of the member and the edge of the radially inward Dri of the rear end surface 31b of the member. The outer diffuser 25 has an outer diffuser inner circumferential surface 25i that faces the radially inward Dri and gradually extends radially outward towards Dro as it moves toward the downstream side Da along the axis. The outer diffuser 25 is joined to the rear end surface 31b of the member. The position of the rear end 35b of the main body in the axial direction Da is located downstream of the axis Da in Da than the position of the rear end surface 31b of the member in the axial direction Da. The corrosion-resistant layer 36 is not bonded to the region Dad downstream of the axis from the rear end surface 31b of the member within the inner circumferential surface 35i of the main body.

[0077] In this embodiment, the rear end 35b of the ring body 35 is located downstream of the rear end surface 31b of the support member 31 in the axis direction Da. Therefore, a portion of the ring body 35 exists radially inward Dri of the rear end surface 31b of the support member 31, which is the joint position between the outer diffuser 25 and the support member 31. Thus, in this embodiment, erosion by steam drain SD at the joint portion between the outer diffuser 25 and the support member 31 can be suppressed.

[0078] In this embodiment, the erosion-resistant layer 36 is not bonded to the region Da downstream of the rear end surface 31b of the member within the inner circumferential surface 35i of the main body. In other words, in this embodiment, the erosion-resistant layer 36 is formed in the parts where erosion is likely to progress, and not in the parts where erosion is unlikely to progress. Therefore, in this embodiment, the manufacturing cost of the seal ring 33 can be reduced.

[0079] (8) The seal ring assembly 30 in the eighth embodiment is In the seal ring assembly 30 according to the seventh embodiment, the outer diffuser 25 is joined to the rear end surface 31b of the member such that the inner circumferential surface 25i of the outer diffuser is smoothly continuous with the inner circumferential surface 31i of the member.

[0080] (9) The seal ring assembly 30 in the ninth embodiment is In the seal ring assembly 30 according to the seventh embodiment, the position of the front end 35f of the main body in the axial direction Da coincides with the position of the front end surface 31f of the member in the axial direction Da.

[0081] (10) The seal ring assembly 30 in the tenth embodiment is In the seal ring assembly 30 according to the seventh embodiment, the inner circumferential surface 25i of the outer diffuser has an outer diffuser upstream inner circumferential surface 25iu extending from the end of the outer diffuser 25 on the axial upstream side Dau to the axial downstream side Dad, and an outer diffuser downstream inner circumferential surface 25id that gradually widens radially outward Dro from the end of the outer diffuser upstream inner circumferential surface 25iu toward the axial downstream side Dad. The outer diffuser 25 is joined to the rear end surface 31b of the member such that the outer diffuser upstream inner circumferential surface 25iu is smoothly continuous from the inner circumferential surface 31i of the member. The ring 34 has a ring inner circumferential surface 34i that faces radially inward Dri and widens in the circumferential direction Dc and the axial direction Da. The inner circumferential surface 34i of the ring has an upstream inner circumferential surface 34iu formed on the surface of the erosion-resistant layer 36, and a downstream inner circumferential surface 34id extending from the downstream Dad end of the upstream inner circumferential surface 34iu to the rear end 35b of the main body, and gradually widening radially outward Dro as it approaches the downstream Dad. The downstream inner circumferential surface 25id of the outer diffuser is in contact with a virtual extension surface L that extends the downstream inner circumferential surface 34id toward the downstream Dad.

[0082] In this embodiment, the steam separation phenomenon can be suppressed at the outer peripheral edge of the steam flow path 17, at Dad downstream of the axis of the final stage rotor blade row 12r, and the steam can be smoothly guided into the diffuser space 23s.

[0083] The steam turbines in the above embodiments and modifications can be understood, for example, as follows. (11) The steam turbine in the eleventh embodiment is The steam turbine rotor 10 comprises a seal ring assembly 30 according to any one of the sixth to tenth embodiments, the steam turbine rotor 10, and a casing 20 covering the seal ring assembly 30 and the steam turbine rotor 10. The support member 31 of the seal ring assembly 30 is fixed to the casing 20. The final stage rotor blade row 12r of the steam turbine rotor 10 has a plurality of final stage rotor blades 13 arranged in the circumferential direction Dc. Each of the plurality of final stage rotor blades 13 has a blade body 13b extending in the radial direction Dr, and a shroud 13s joined to the radially outer edge Dro of the blade body 13b and extending in the circumferential direction Dc and the axial direction Da. The shroud 13s has a front end 13sf facing the upstream side Dau of the axis and a rear end 13sb facing the downstream side Dad of the axis. The distance df from the front end 13sf of the shroud to the tip 37t of the fin 37 in the axial direction Da is 40% or more and 60% or less of the distance ds from the front end 13sf of the shroud to the rear end 13sb of the shroud in the axial direction Da.

[0084] In this embodiment, the distance df from the front end 13sf of the shroud to the tip 37t of the fin 37 in the axial direction Da is 40% or more and 60% or less of the distance ds. In other words, in the axial direction Da, the fin 37 is located in the central part of the shroud 13s. Therefore, in this embodiment, most of the steam drain SD that adheres to the final stage stationary blade row 19r and the final stage rotor blade row 12r and is scattered radially outward towards Dro does not directly collide with the fin 37 due to the shroud 13s of the final stage rotor blade 13. Thus, in this embodiment, erosion of the fin 37 by steam drain SD can be suppressed.

[0085] (12) The steam turbine in the twelfth embodiment is In the steam turbine according to the eleventh embodiment, the distance dm from the front end surface 31f of the member to the rear end surface 31b of the member in the axial direction Da is longer than the distance ds from the front end 13sf of the shroud to the rear end 13sb of the shroud in the axial direction Da. The distance dr from the front end 35f of the main body to the rear end 35b of the main body in the axial direction Da is longer than the distance dm from the front end surface 31f of the member to the rear end surface 31b of the member in the axial direction Da. [Explanation of symbols]

[0086] 10: Steam turbine rotor (or simply rotor) 11: Rotor shaft 12: Moving blade row 12r: Final stage rotor blade row 13:Final stage rotor blade 13b: Wing body 13s: Shroud 13sf: Shroud front end 13sb: Shroud rear end 15: Bearings 16: Steam inlet pipe 17: Steam flow path 18: Wing ring 19: Static Wing Arrow 19r: Final stage stator blade row 20: Casing 21: Inner casing 22: Exhaust casing 22s: Exhaust space 23: Diffuser 23s: Diffuser space 24: Internal diffuser (or bearing cone) 25: External diffuser (or flow guide) 25i; Outer diffuser inner surface 25iu: Outer diffuser upstream inner surface 25id: Outer diffuser downstream inner surface 27: Exhaust vent 30: Seal ring assembly 31: Support member 31i: Inner surface of the member 31f: Front end surface of member 31b: Part rear end surface 32: Groove 32a: First groove 32b: Second groove 33: Seal ring 34: Ring 34i: Inner circumference of the ring 34iu: Inner surface on the upstream side of the ring 34id: Inner surface on the downstream side of the ring 35: Ring body 35i: Inner surface of main body 35iu: Upstream layer formation surface 35id: Downstream layer formation surface 35is: Inclined surface 35o: Main body outer surface 35f: Front end of main body 35b: Rear end of main body 36: Erosion-resistant layer 36u: Upstream erosion-resistant layer 36d: Downstream Erosion-Resistant Layer 37: Finn 37t: Tip 37tp:Tip 38: Mounting part 38a: First mounting section 38b; Second mounting section 38r: Storage recess 39: Elastic body C: Condenser S: Steam SD: Steam drain L: Virtual extension plane ST1: First Steam Turbine Section ST2: Second Steam Turbine Section Ar: Axis line Ap: tube axis Da: Axial direction Da1: First side Da2: Second side Dau: Axis upstream side Dad: Downstream side of the axis Dc: Circumferential direction Dr: Radial direction Dri: Radial inner side Dro: Radial outer side

Claims

1. In a seal ring positioned radially outward from the axis of a steam turbine rotor's final stage blade row, which is rotatable about an axis, A ring extending in the circumferential direction with respect to the aforementioned axis, A fin protrudes radially inward from the ring, on the opposite side from the radially outward direction, and extends in the circumferential direction, It has, The ring comprises a ring body extending in the circumferential direction and an etching-resistant layer bonded to the ring body. The ring body has an inner circumferential surface that faces radially inward and extends in the circumferential direction and the axial direction in which the axis extends, a front end of the body facing the upstream side of the axis and a rear end of the body facing the downstream side of the axis, The fins protrude radially inward from the region between the front end and rear end of the main body in the axial direction within the inner circumferential surface of the main body, The ring body and the fin are integrally formed from the same metal. The aforementioned corrosion-resistant layer is formed of a metal with higher corrosion resistance than the metal forming the ring body and the fin. The corrosion-resistant layer is bonded to the inner circumferential surface of the main body, but not to the tip portion including the tip of the fin. Seal ring.

2. In the seal ring according to claim 1, The aforementioned corrosion-resistant layer is formed of a Co-based alloy. Seal ring.

3. In the seal ring according to claim 1, The aforementioned etching-resistant layer is It is formed from an alloy containing (Co + Ni), Cr, W, and C. (Co + Ni) is 55.00 wt% or more, Ni is 3.00 wt% or less, Cr is between 27.00 wt% and 33.00 wt%, W is 3.00 wt% or more and 19.00 wt% or less. C is 0.10 wt% or more and 3.25 wt% or less. Other components make up 9.50 wt% or less. Seal ring.

4. In the seal ring according to claim 1, The anti-erosion layer comprises an upstream anti-erosion layer extending upstream from the upstream edge of the fin along the axis to the front end of the main body, and a downstream anti-erosion layer extending downstream from the downstream edge of the fin along the axis. Seal ring.

5. In the seal ring according to claim 4, The inner circumferential surface of the ring body has an upstream layer-forming surface extending from the edge of the front end of the body to the upstream edge of the fin along the axis, a downstream layer-forming surface extending from the downstream edge of the fin along the axis toward the downstream side of the axis, and an inclined surface extending from the downstream edge of the downstream layer-forming surface along the axis to the edge of the rear end of the body. The inclined surface is inclined with respect to the downstream layer-forming surface such that it gradually widens radially outward as it moves downstream along the axis. The upstream erosion-resistant layer is bonded to the upstream layer-forming surface, and the downstream erosion-resistant layer is bonded to the downstream layer-forming surface and not bonded to the inclined surface. Seal ring.

6. The seal ring according to claim 1, A support member extending in the circumferential direction and positioned radially outward of the seal ring, It has, The ring body has an outer circumferential surface that faces radially outward and extends in the circumferential and axial directions. The seal ring has a mounting portion that protrudes radially outward from the outer circumferential surface of the main body, The ring body, the fin, and the mounting portion are integrally formed from the same metal. The support member has a front end surface facing the upstream side of the axis, a rear end surface facing the downstream side of the axis, an inner circumferential surface that faces radially inward and extends circumferentially, and a groove that is recessed radially outward from the inner circumferential surface and extends circumferentially. The inner circumferential surface of the member connects the radially inner edge of the front end face of the member and the radially inner edge of the rear end face of the member. The mounting portion fits into the groove, and the outer circumferential surface of the ring body faces the inner circumferential surface of the member in the radial direction with respect to the axis. Seal ring assembly.

7. In the seal ring assembly described in claim 6, It has an outer diffuser that forms an annular shape around the aforementioned axis and gradually extends radially outward as it moves downstream of the axis, The outer diffuser has an inner circumferential surface that faces radially inward and gradually widens radially outward as it moves downstream along the axis, The outer diffuser is joined to the rear end surface of the member, The position of the rear end of the main body in the axial direction is located downstream of the axis than the position of the rear end surface of the member in the axial direction. The aforementioned etching-resistant layer is not bonded to the region downstream of the axis of the main body's inner circumferential surface, beyond the rear end surface of the member. Seal ring assembly.

8. In the seal ring assembly described in claim 7, The outer diffuser is joined to the rear end surface of the member such that the inner surface of the outer diffuser is smoothly continuous with the inner surface of the member. Seal ring assembly.

9. In the seal ring assembly described in claim 7, The position of the front end of the main body in the axial direction coincides with the position of the front end surface of the member in the axial direction. Seal ring assembly.

10. In the seal ring assembly described in claim 7, The outer diffuser inner surface comprises an outer diffuser upstream inner surface extending from the outer diffuser's upstream end toward the downstream end of the axis, and an outer diffuser downstream inner surface that gradually widens radially outward from the downstream end of the outer diffuser's upstream inner surface toward the downstream end of the axis. The outer diffuser is joined to the rear end surface of the member such that the inner circumferential surface of the member and the inner circumferential surface of the outer diffuser on the upstream side are smoothly continuous. The ring has an inner circumferential surface that faces radially inward and extends in the circumferential and axial directions. The inner circumferential surface of the ring has an upstream inner circumferential surface formed on the surface of the etching-resistant layer, and a downstream inner circumferential surface that extends from the downstream end of the upstream inner circumferential surface to the rear end of the main body and gradually widens radially outward as it moves toward the downstream side of the axis. The downstream inner surface of the outer diffuser is in contact with a virtual extension surface obtained by extending the downstream inner surface of the ring toward the downstream side of the axis. Seal ring assembly.

11. A seal ring assembly according to any one of claims 6 to 10, The steam turbine rotor and, The seal ring assembly and the casing covering the steam turbine rotor, Equipped with, The support member of the seal ring assembly is fixed to the casing. The final stage rotor blade row of the steam turbine rotor has a plurality of final stage blades arranged in the circumferential direction, Each of the aforementioned multiple final stage rotor blades has a wing body extending in the radial direction and a shroud joined to the radially outer edge of the wing body and extending in the circumferential and axial directions. The shroud has a front end facing upstream of the axis and a rear end facing downstream of the axis. The distance from the front end of the shroud to the tip of the fin in the axial direction is 40% or more and 60% or less of the distance from the front end of the shroud to the rear end of the shroud in the axial direction. Steam turbine.

12. In the steam turbine according to claim 11, The distance from the front end surface of the member to the rear end surface of the member in the axial direction is longer than the distance from the front end of the shroud to the rear end of the shroud in the axial direction. The distance from the front end to the rear end of the main body in the axial direction is longer than the distance from the front end surface to the rear end surface of the member in the axial direction. Steam turbine.

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