Patent Publication Number: US-2022235667-A1

Title: Steam turbine seal clearance adjusting method, and steam turbine

Description:
TECHNICAL FIELD 
     The present invention relates to a steam turbine seal clearance adjusting method and a steam turbine. 
     Priority is claimed on Japanese Patent Application No. 2019-101996, filed May 31, 2019, the content of which is incorporated herein by reference. 
     BACKGROUND ART 
     A steam turbine includes a rotary shaft which rotates about an axis, a plurality of blades which are integrally provided on the rotary shaft, a casing which covers the rotary shaft and the blades from an outer peripheral side, and a vane which is provided on an inner peripheral surface of the casing. A blade shroud which faces the inner peripheral surface of the casing is provided at a radially outer end portion of the blade. In order to suppress a leakage flow of steam, a seal device which has a seal ring protruding toward an outer peripheral surface of the blade shroud is provided on the inner peripheral surface of the casing. Further, a vane shroud which faces an outer peripheral surface of the rotary shaft is provided at a radially inner end portion of the vane. In order to suppress a leakage flow as described above, a seal device which has a seal ring protruding toward the outer peripheral surface of the rotary shaft is provided on an inner peripheral surface of the vane shroud. 
     During an operation of the steam turbine, the seal ring faces the outer peripheral surface of the blade shroud or the rotary shaft with a clearance interposed therebetween. However, the rotary shaft and the blade shroud may be displaced due to some disturbance factors and come into contact with these seal rings. In this case, the tip of the seal ring is worn to absorb the displacement and maintain the clearance. On the other hand, when the wear progresses significantly, it is necessary to replace or repair the seal ring. 
     Conventionally, when the seal ring (seal device) is replaced, the method described in Patent Document 1 is adopted as an example. In this method, the casing is first divided into an upper half portion and a lower half portion and the seal device and the vane disposed on the inner peripheral surface of the casing are exposed. Here, the casing may undergo slight thermal deformation due to the aging operation of the steam turbine. Therefore, before the seal ring is replaced, the casing is temporarily assembled until an operation state and a change in clearance due to the thermal deformation of the casing is measured. Based on the change amount, a shim is disposed between the upper half portion and the lower half portion of the casing (between flange portions) to correct the change in clearance. 
     CITATION LIST 
     Patent Document 
     
         
         Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 2018-084169 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, since it takes a long time to temporarily assemble the casing, the above-described method has a problem of prolonging the construction period. Further, there may be a case in which the thermal deformation of the casing is larger than expected and the amount of deformation cannot be completely absorbed by the shim described above. In this case, it is conceivable to cut the seal ring for further correction. However, there are many restrictions on the processing work that can be performed at the plant site and it is difficult to maintain processing accuracy. Thus, there has been an increasing demand for a technique capable of replacing the seal device without temporarily assembling the casing and processing the seal ring. 
     The present invention has been made to solve the above-described problems, and an object thereof is to provide a steam turbine seal clearance adjusting method and a steam turbine capable of easily and quickly performing repair. 
     Solution to Problem 
     A steam turbine seal clearance adjusting method according to an aspect of the present invention is a steam turbine repair method for a steam turbine after being operated, in which the steam turbine includes: a rotary shaft which is configured to rotate about an axis; a blade which is provided on an outer peripheral surface of the rotary shaft; a casing which covers the rotary shaft and the blade from an outer peripheral side; a vane which is provided on an inner peripheral surface of the casing; and a seal device which includes a seal ring provided between the outer peripheral surface of the rotary shaft and the vane and a position adjusting portion configured to adjust a position of the seal ring in a radial direction with respect to the axis, and the seal clearance adjusting method includes: a measurement step of measuring a length of the seal ring in the radial direction from a predetermined reference position as a reference length; a preparation step of preparing an unused seal ring; and an adjustment step of adjusting a length of the unused seal ring from the reference position to be the reference length by the position adjusting portion. 
     According to the above-described method, the measurement step is first performed on the steam turbine after being operated for a predetermined period. In this state, the length of the seal ring in the radial direction is changed as compared with an unused state due to wear or the like. In the measurement step, the length of the seal ring worn in this manner from the reference position is measured and set as the reference length. Here, the seal ring which is worn after a certain period of operation can be considered to be in a state in which at least the length value of the clearance between the seal ring and the outer peripheral surface of the rotary shaft is optimized even when the tip of the seal ring is worn out and the performance as a fin may deteriorate. As the length of the unused seal ring is adjusted to be the reference length in the subsequent adjustment step, it is possible to replace the seal ring while optimizing the clearance. In particular, the seal ring can be replaced and the alignment can be optimized without processing the seal ring or temporarily assembling the casing, and therefore the man-hours can be reduced. 
     In the steam turbine seal clearance adjusting method, the seal ring may include a seal base portion and a plurality of fin main bodies provided on an inner peripheral surface of the seal base portion, and when falling of the fin main body in a direction of the axis has occurred after the steam turbine is operated, after the adjustment step, a first correction step of adding, to the reference length, a decrease amount of a length of the seal ring in the radial direction caused by the falling may be further performed. 
     During the operation of the steam turbine, a force (thrust force) in the direction of the axis may be applied to the rotary shaft due to some disturbance factors including a collision of foreign matter such as a scale. When the rotary shaft is displaced in the direction of the axis due to the thrust force, the seal ring and the rotary shaft may come into contact with each other and the seal ring may fall (tilt) without maintaining its initial posture. When such falling occurs, the clearance between the tip of the seal ring and the outer peripheral surface of the rotary shaft (or the tip of the fin provided at the end portion of the blade and the inner peripheral surface of the seal portion on the casing side facing the tip of the fin) increases. Thus, it may be necessary to adjust the alignment (adjust the position of the seal ring) in consideration of the change amount of the clearance due to the falling when replacing the seal ring. In the above-described method, the decrease amount of the length of the seal ring in the radial direction caused by the falling is added to the value of the reference length obtained by the measurement step. Accordingly, it is possible to reproduce a state before the falling occurs with the unused seal ring. As a result, it is possible to optimize the clearance with higher accuracy. 
     In the steam turbine seal clearance adjusting method, when a contact mark with the seal ring is generated in the rotary shaft after the steam turbine is operated, after the adjustment step, a second correction step of adding, to the reference length, a decrease amount of a length of the seal ring in the radial direction caused by contact may be further performed. 
     When the rotary shaft and the seal ring are in particularly strong contact (when hard rubbing occurs), the tip portion of the seal ring may be lost due to excessive thermal expansion caused by friction and its length may decrease more than necessary. Accordingly, the clearance between the tip of the seal ring and the outer peripheral surface of the rotary shaft increases more than necessary values. Thus, it may be necessary to adjust the alignment (adjust the position of the seal ring) in consideration of the change amount of the clearance due to the loss when replacing the seal ring. In the above-described method, the decrease amount of the length of the seal ring in the radial direction caused by the loss is added to the value of the reference length obtained by the measurement step. Accordingly, it is possible to reproduce a state before the loss occurs with the unused seal ring. As a result, it is possible to optimize the clearance setting with higher accuracy. 
     A steam turbine according to an aspect of the present invention is a steam turbine including: a rotary shaft which is configured to rotate about an axis; a blade which is provided on an outer peripheral surface of the rotary shaft; a casing which covers the rotary shaft and the blade from an outer peripheral side; a vane which is provided on an inner peripheral surface of the casing; and a seal device which includes a seal ring provided between the outer peripheral surface of the rotary shaft and the vane, a holder disposed radially outside the seal ring and configured to support the seal ring, and a position adjusting portion configured to adjust a length from a reference position of the holder to a tip of the seal ring. 
     According to the above-described configuration, it is possible to change the length from the reference position of the holder to the tip of the seal ring by the position adjusting portion. Accordingly, it is possible to reproduce a state in which the clearance is optimized without processing the unused seal ring before the replacement when replacing the seal ring. 
     In the steam turbine, the position adjusting portion may include a bolt which is configured to support the seal ring to be relatively displaceable with respect to the holder by changing a screwing amount of the bolt. 
     According to the above-described configuration, it is possible to easily change the relative position of the seal ring with respect to the holder in accordance with the rotation amount (the screwing amount) of the bolt. Accordingly, it is possible to reproduce a state in which the clearance is optimized without processing the unused seal ring before the replacement when replacing the seal ring. 
     In the steam turbine, the position adjusting portion may include: a rack gear which is provided in the seal ring and extends in the radial direction; and a pinion gear which is provided in the holder and meshes with the rack gear. 
     According to the above-described configuration, it is possible to easily change the relative position of the seal ring with respect to the holder in accordance with the relative position of the pinion gear with respect to the rack gear. Accordingly, it is possible to reproduce a state in which the clearance is optimized without processing the unused seal ring before the replacement when replacing the seal ring. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to provide a steam turbine repair method and a steam turbine capable of easily and quickly performing repair. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic view showing a configuration of a steam turbine according to a first embodiment of the present invention. 
         FIG. 2  is a side view showing a configuration of the steam turbine according to the first embodiment of the present invention. 
         FIG. 3  is an enlarged cross-sectional view of a main part of the steam turbine according to the first embodiment of the present invention. 
         FIG. 4  is a cross-sectional view showing a configuration of a seal device according to the first embodiment of the present invention. 
         FIG. 5  is a perspective view showing a configuration of a bolt which is a position adjusting portion according to the first embodiment of the present invention. 
         FIG. 6  is a flowchart showing a process of a steam turbine repair method according to the first embodiment of the present invention. 
         FIG. 7  is an explanatory diagram showing a seal ring in a state in which a falling occurs. 
         FIG. 8  is an explanatory diagram showing a seal ring in a state in which a loss occurs. 
         FIG. 9  is a cross-sectional view showing a configuration of a seal device according to a second embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     A first embodiment of the present invention will be described with reference to  FIGS. 1 to 8 . A steam turbine  100  according to this embodiment includes a rotor  3  which extends in a direction of an axis O, a casing  2  (stator) which covers the rotor  3  from an outer peripheral side, and journal bearings  4 A and a thrust bearing  4 B which support a shaft end  11  of the rotor  3  to be rotatable around the axis O. 
     The rotor  3  includes a rotary shaft  1  which extends in the axis O and a plurality of blades  30  which are provided on an outer peripheral surface of the rotary shaft  1 . The plurality of blades  30  are arranged at equal intervals in a circumferential direction of the rotary shaft  1 . A plurality of rows of the blades  30  are arranged at equal intervals in the direction of the axis O. The blade  30  includes a blade main body  31  and a blade shroud  34 . The blade main body  31  protrudes outward in a radial direction from the outer peripheral surface of the rotor  3 . The blade main body  31  has a cross section having a blade profile when viewed in the radial direction. The blade shroud  34  is provided at a tip portion (radially outer end portion) of the blade main body  31 . 
     The casing  2  is formed in a substantially tubular shape that covers the rotor  3  from the outer peripheral side. A steam supply pipe  12  for taking in steam S is provided on one side of the casing  2  in the direction of the axis O. A steam discharge pipe  13  for discharging the steam S is provided on the other side of the casing  2  in the direction of the axis O. The steam flows inside the casing  2  from one side to the other side in the direction of the axis O. In the following description, a direction in which the steam flows will be simply referred to as “a flow direction”. Further, a side where the steam supply pipe  12  is positioned when viewed from the steam discharge pipe  13  will be referred to as an upstream side in the flow direction and a side where the steam discharge pipe  13  is positioned when viewed from the steam supply pipe  12  will be referred to as a downstream side in the flow direction. 
     A plurality of rows of vanes  20  are provided on an inner peripheral surface of the casing  2 . The vane  20  includes a vane main body  21 , a vane shroud  22 , and a vane pedestal  24 . The vane main body  21  is a member having a vane shape and connected to the inner peripheral surface of the casing  2  with the vane pedestal  24  therebetween. Further, the vane shroud  22  is provided at a tip portion (radially inner end portion) of the vane main body  21 . Similar to the blade  30 , a plurality of vanes  20  are arranged on the inner peripheral surface in the circumferential direction and the direction of the axis O. The blades  30  are disposed so as to enter regions between the vanes  20  adjacent to each other. That is, the vanes  20  and the blades  30  extend in a direction (the radial direction with respect to the axis O) intersecting the flow direction of steam. 
     As shown in  FIG. 2 , the casing  2  is divided into upper and lower parts, the upper half is an upper half casing  2 U, and the lower half is a lower half casing  2 L. The upper half casing  2 U and the lower half casing  2 L are plane-symmetrical with respect to a dividing surface Sd extending in the horizontal plane (however, a pipe portion is excluded). The upper half casing  2 U includes a semi-cylindrical upper half casing main body  21 U and an upper half flange portion  22 U protruding outward from an end edge of the upper half casing main body  21 U. Similarly, the lower half casing  2 L includes a semi-cylindrical lower half casing main body  21 L and a lower half flange portion  22 L protruding outward from an end edge of the lower half casing main body  21 L. The upper half casing  2 U and the lower half casing  2 L are fastened and fixed to each other by a bolt and a nut (not shown) while a lower surface of the upper half flange portion  22 U and an upper surface of the lower half flange portion  22 L are in contact with each other in the dividing surface Sd. Although not shown in the drawings, the casing  2  is provided with a plurality of legs for supporting the casing  2  on the floor surface. Further,  FIG. 2  shows the steam turbine  100  having a configuration called an external casing as an example, but the steam turbine  100  of a double-casing structure in which another casing (internal casing) is provided inside the external casing may be used. 
     The steam S is supplied to the inside of the casing  2  having the above-described configuration via the steam supply pipe  12  on the upstream side. When the steam S passes through the inside of the steam turbine casing  2 , the steam S alternately passes through flow paths formed by the vanes  20  and the blades  30 . The vane  20  rectifies a flow of the steam S and the blade  30  applies a torque to the rotor  3  by pushing the mass of the rectified steam S against the blade  30 . A torque of the rotor  3  is taken out from the shaft end  11  and is used to drive an external equipment (a generator or the like). As the rotor  3  rotates, the steam S is discharged toward a subsequent device (a condenser or the like) through the steam discharge pipe  13  on the downstream side. 
     The journal bearing  4 A supports a load in the radial direction with respect to the axis O. One journal bearing  4 A is provided at each of both ends of the rotor  3 . The thrust bearing  4 B supports a load in the direction of the axis O. The thrust bearing  4 B is provided only at the end portion of the rotor  3  on the upstream side. 
     Next, a part around the vane  20  and the blade  30  will be described in detail with reference to  FIG. 3 . A cavity  50  recessed outward in the radial direction is formed on an inner peripheral surface of the casing main body  2 A. The blade shroud  34  is accommodated in the cavity  50 . Further, a clearance is formed between a shroud upstream surface  34 S which is a surface of the blade shroud  34  facing the upstream side and a cavity upstream surface  50 S which is a surface of the cavity  50  on the upstream side. A platform  35  which is disposed radially inside the blade main body  31  and supports the blade main body  31  is provided integrally with the rotary shaft  1 . 
     A part of the casing main body  2 A at a position corresponding to the vane  20  in the direction of the axis O is the vane pedestal  24 . A radially outer end portion of the vane main body  21  is fixed to a pedestal inner peripheral surface  24 A which is a surface of the vane pedestal  24  facing inward in the radial direction. The vane shroud  22  is provided at a radially inner end portion of the vane main body  21 . A shroud inner peripheral surface  22 A which is a surface of the vane shroud  22  facing inward in the radial direction faces a rotary shaft outer peripheral surface  1 S which is the outer peripheral surface of the rotary shaft  1  with a clearance therebetween. A seal unit  2 B (a seal device) to be described later is provided in this clearance. More specifically, the seal unit  2 B is attached to the shroud inner peripheral surface  22 A. The seal unit  2 B is provided to seal flow (leakage flow) of the steam passing between the shroud inner peripheral surface  22 A and the rotary shaft outer peripheral surface  1 S. 
     Next, a configuration of the seal unit  2 B will be described with reference to  FIG. 4 . As shown in  FIG. 4 , the seal unit  2 B includes a holder  41 , a hook plate  42 , a seal ring  43 , and a nut  45  and an adjusting bolt  46  which serve as a position adjusting portion  60 . 
     The holder  41  is a member that supports and fixes the seal ring  43  with respect to the vane shroud  22 . The holder  41  includes a holder main body  41 A and engagement protrusions  41 B. The holder main body  41 A is formed in an annular shape centering on the axis O. The pair of engagement protrusions  41 B are provided at both end edges of the holder main body  41 A in the direction of the axis O, respectively, and protrude inward in the radial direction with respect to the axis O. The hook plate  42  is accommodated in a space surrounded by the engagement protrusions  41 B and the holder main body  41 A. 
     The hook plate  42  is a member that supports and fixes the seal ring  43  to the holder  41 . The hook plate  42  is formed in an annular shape centering on the axis O. A surface (plate lower surface  42 S) of the hook plate  42  facing inward in the radial direction is in contact with a surface (protrusion upper surface  41 S) of the engagement protrusion  41 B facing outward in the radial direction. A bolt hole H is formed in the hook plate  42  and extends from a surface (plate upper surface  42 T) of the hook plate  42  facing outward in the radial direction to the plate lower surface  42 S. The nut  45  and the adjusting bolt  46  are inserted through the bolt hole H. The bolt hole H has a nut accommodating portion H 1 , an intermediate portion H 2 , and a concave portion H 3  which are disposed in this order from the outside to the inside in the radial direction. The adjusting bolt  46  fixes the seal ring  43  to the holder  41  and the hook plate  42  so that the seal ring  43  is relatively displaceable with respect to the holder  41  and the hook plate  42  (that is, the radial position of the seal ring  43  is adjustable). The configurations of the nut  45  and the adjusting bolt  46  will be described later. 
     The seal ring  43  includes a seal base portion  43 A and a plurality of fin main bodies  43 B. The seal base portion  43 A is a member that supports the fin main bodies  43 B. The seal base portion  43 A is formed in an annular shape centering on the axis O. A bolt hole  43 H through which the adjusting bolt  46  is inserted is formed in a surface (base portion upper surface  43 T) of the seal base portion  43 A facing outward in the radial direction. A screw groove is formed on an inner peripheral surface of the bolt hole  43 H. The screw groove meshes with the adjusting bolt  46 . 
     The plurality of fin main bodies  43 B are provided on a surface (base portion inner peripheral surface  43 S) of the seal base portion  43 A on the inside in the radial direction and are arranged at intervals in the direction of the axis O. Each fin main body  43 B protrudes inward in the radial direction from the base portion inner peripheral surface  43 S. The fin main body  43 B has a tapered cross-section as the length in the direction of the axis O decreases from the outside to the inside in the radial direction. In this embodiment, an example in which four fin main bodies  43 B are provided has been described, but the number of the fin main bodies  43 B is not limited to four and can be appropriately changed in accordance with the specification or design. Further, it is not necessary for all the fin main bodies  43 B to have the same shape and length, and a configuration in which the fin main bodies  43 B having a plurality of different types of shapes and lengths are alternately arranged may be adapted. 
     As shown in  FIG. 5 , the adjusting bolt  46  includes a fixed disk portion  46 A, a bolt upper portion  46 B, and a bolt lower portion  46 C. The fixed disk portion  46 A is formed in a disk shape centering on a center axis A of the adjusting bolt  46 . The fixed disk portion  46 A is accommodated in the concave portion H 3  formed in the lower surface (plate lower surface  42 S) of the hook plate  42 . The concave portion H 3  is recessed outward in the radial direction from the plate lower surface  42 S. When viewed from the radial direction, the concave portion H 3  has a circular cross-sectional shape. 
     The bolt upper portion  46 B is provided integrally with one side (surface facing outward in the radial direction when the adjusting bolt  46  is attached to the seal unit  2 B) of the fixed disk portion  46 A in the direction of the center axis A. The bolt upper portion  46 B is formed in a columnar shape centering on the center axis A and a screw groove meshing with the nut  45  is formed on an outer peripheral surface of the bolt upper portion  46 B. Further, for example, a groove  46 D which engages with a tool such as a minus driver is formed in a surface of the bolt upper portion  46 B facing outward in the radial direction. The groove  46 D has a linear shape passing through the center axis A and has a rectangular cross-section. 
     The bolt lower portion  46 C is provided integrally with the other side (surface facing inward in the radial direction when the adjusting bolt  46  is attached to the seal unit  2 B) of the fixed disk portion  46 A in the direction of the center axis A. Similarly to the bolt upper portion  46 B, the bolt lower portion  46 C is formed in a columnar shape centering on the center axis A and a male screw which engages with the screw groove of the bolt hole  43 H is formed on an outer peripheral surface of the bolt lower portion  46 C. 
     The nut  45  is fixed into the nut accommodating portion H 1  formed on the upper surface (plate upper surface  42 T) of the hook plate  42 . That is, the nut  45  is fixed to the hook plate  42  so as not to be relatively rotatable with respect to the hook plate  42 . The bolt upper portion  46 B is inserted and fixed into the nut  45  in a state in which the screw groove of the bolt upper portion  46 B meshes with the nut  45 . Further, the bolt lower portion  46 C is inserted and fixed into the bolt hole  43 H of the seal ring  43  as described above. Accordingly, the seal ring  43  is fixed to the holder  41  and the hook plate  42 . Here, when the adjusting bolt  46  is rotated around the center axis A with respect to the nut  45 , the adjusting bolt  46  moves forward and backward along the screw groove. That is, by providing the nut  45  and the adjusting bolt  46 , the position (the position in the radial direction with respect to the axis O) of the seal ring  43  can be changed. 
     Next, a seal clearance adjusting method of the steam turbine  100  according to this embodiment will be described with reference to  FIG. 6 . This adjusting method is performed to replace the seal unit  2 B when the seal unit  2 B is worn and lost after the steam turbine  100  is operated for a predetermined period. This adjusting method includes a casing opening step S 1 , a measurement step S 2 , a first determination step S 3 , a first correction step S 31 , a second determination step S 4 , a second correction step S 41 , a preparation step S 5 , an adjustment step S 6 , and a casing closing step S 7 . 
     In the casing opening step S 1 , the casing  2  is disassembled along the dividing surface Sd. Specifically, the upper half casing  2 U is separated from the lower half casing  2 L. Accordingly, the seal unit  2 B attached to the inner peripheral surface of the casing  2  is exposed. Next, the measurement step S 2  is performed. In the measurement step S 2 , the radial length of the seal ring  43  is measured, more specifically, the length from the protrusion upper surface  41 S of the holder  41  to the tip portion (radially inner end portion) of the fin main body  43 B is measured and this value is set as a reference length Lc as shown in  FIG. 4 . 
     Here, in the steam turbine  100  after being operated for a certain period of time, when the length of the fin exceeds an actual allowable clearance value, the rotary shaft  1  and the seal ring  43  (fin main body  43 B) come into contact with each other, so that the tip of the fin main body  43 B is cut. Therefore, the separation distance (clearance) between the rotary shaft outer peripheral surface  1 S of the rotary shaft  1  and the fin main body  43 B is the minimum value in a range where the smooth rotation of the rotary shaft  1  is allowed. As will be described in detail later, the radial length of the seal unit  2 B after the above-described operation is set as the reference length Lc and the reference length Lc is reproduced on a replacement unused seal unit  2 B, so that the optimal clearance is maintained. 
     The first determination step S 3  is performed after the measurement step S 2 . In the first determination step S 3 , it is determined whether or not “falling” has occurred in the fin main body  43 B. As shown as an example of  FIG. 7 , the “falling” mentioned herein means a state in which the fin main body  43 B is deformed to fall down in the direction of the axis O. In this state, as shown in  FIG. 7 , the radial position of the tip portion of the fin main body  43 B moves outward in the radial direction by a change amount D. That is, the apparent radial length of the seal unit  2 B decreases by the change amount D. 
     When it is determined that the falling has occurred by the first determination step S 3 , the first correction step S 31  is performed. In the first correction step S 31 , the decrease amount (the change amount D) of the radial length of the seal unit  2 B caused by the falling is added to the reference length Lc to be a new reference length Lc′ (that is, Lc′=Lc+D). Then, the second determination step S 4  is performed. Further, when it is determined that the falling has not occurred by the first determination step S 3 , the first correction step S 31  is not performed and the second determination step S 4  is performed. 
     In the second determination step S 4 , it is determined whether or not a contact mark with the fin main body  43 B is generated on the rotary shaft outer peripheral surface  1 S. When the fin main body  43 B comes into contact with the rotary shaft outer peripheral surface  1 S to be pressed relatively strongly (that is, when hard rubbing occurs), the fin thermally expands due to the frictional heat between the fin main body  43 B and the rotary shaft outer peripheral surface  1 S and the tip of the fin main body  43 B is lost more than when soft rubbing is performed. Due to this loss, the tip portion of the fin main body  43 B disappears as shown in  FIG. 8  as an example. Specifically, the tip portion is lost by the amount of a loss portion  43 R and the radial length of the seal unit  2 B decreases by a change amount D′. 
     When the contact mark is generated, it is possible to determine that the above-described loss occurs. In this case, the second correction step S 41  is performed. In the second correction step S 41 , the decrease amount (the change amount D′) of the radial length of the seal unit  2 B caused by the loss is added to the reference length Lc. When the first correction step S 31  is performed, D′ is further added to the value of Lc′=Lc+D to be a new reference length Lc′ 2  (=Lc′+D′). Then, the subsequent preparation step S 5  is performed. When the contact mark is not generated, the second correction step S 41  is not performed and the preparation step S 5  is performed. 
     In the preparation step S 5 , the unused seal unit  2 B (seal ring  43 ) is prepared. Next, the adjustment step S 6  is performed. In the adjustment step S 6 , the radial position of the unused seal unit  2 B is adjusted to satisfy the reference length Lc (Lc′, Lc′ 2 ) calculated by the above-described steps. Specifically, the screwing amount of the adjusting bolt  46  which is the position adjusting portion  60  is adjusted. Accordingly, when the unused seal ring  43  is attached to the casing  2 , the clearance between the fin main body  43 B and the rotary shaft outer peripheral surface  1 S is immediately optimized. In other words, the clearance formed before the replacement is reproduced on the unused seal ring  43  without undergoing work such as cutting. Then, the upper half casing  2 U and the lower half casing  2 L are combined with each other (the casing closing step S 7 ). With the above-described steps, the entire process of the repair method of the steam turbine  100  is completed. 
     As described above, in the above-described repair method, the measurement step S 2  is performed on the steam turbine  100  after being operated for a predetermined period. In this state, the radial length of the seal ring  43  is changed as compared with the unused state due to wear or the like. In the measurement step S 2 , the radial length of the seal ring  43  worn in this manner from the reference position (the protrusion upper surface  41 S) is measured and set as the reference length Lc. Here, the seal ring  43  which is worn after a certain period of operation can be considered to be in a state in which the clearance between the seal ring  43  and the rotary shaft outer peripheral surface  1 S of the rotary shaft  1  is optimized. As the length of the unused seal ring  43  is adjusted to be the reference length Lc in the subsequent adjustment step S 6 , it is possible to replace the seal ring  43  while optimizing the clearance. In particular, the seal ring  43  can be replaced and the alignment can be optimized (the clearance can be optimized) without processing the seal ring  43  or temporarily assembling the casing  2 , and therefore the man-hours can be reduced. 
     Here, a force (thrust force) in the direction of the axis O may be applied to the rotary shaft  1  due to some disturbance factors such as scale flying during the operation of the steam turbine  100 . When the rotary shaft  1  is displaced in the direction of the axis O due to the thrust force, the seal ring  43  and the rotary shaft  1  may come into contact with each other and the seal ring  43  may fall (tilt) without maintaining its initial posture. When such falling occurs, the clearance between the tip of the seal ring  43  and the rotary shaft outer peripheral surface  1 S of the rotary shaft  1  increases. Thus, it may be necessary to adjust the alignment (adjust the position of the seal ring  43 ) in consideration of the change amount of the clearance due to the falling when replacing the seal ring  43 . In the above-described method, the decrease amount (the change amount D) of the radial length of the seal ring  43  caused by the falling is added to the value of the reference length Lc obtained by the measurement step S 2 . Accordingly, it is possible to reproduce a state before the falling occurs with the unused seal ring  43 . As a result, it is possible to optimize the clearance with higher accuracy. 
     Further, when the rotary shaft  1  and the seal ring  43  are in particularly strong contact (when hard rubbing occurs), the tip portion of the seal ring  43  may be lost by the friction and its length may be decreased. Accordingly, the clearance between the tip of the seal ring  43  and the rotary shaft outer peripheral surface  1 S of the rotary shaft  1  increases. Thus, it may be necessary to adjust the alignment (adjust the position of the seal ring) in consideration of the change amount of the clearance due to the loss when replacing the seal ring  43 . In the above-described method, the decrease amount (the change amount D′) of the radial length of the seal ring  43  caused by the loss is added to the value of the reference length Lc obtained by the measurement step S 2  (or the value of the reference length Lc′ calculated by the first correction step S 31 ). Accordingly, it is possible to reproduce a state before the loss occurs with the unused seal ring  43 . As a result, it is possible to optimize the clearance with higher accuracy. 
     Additionally, according to the above-described configuration, it is possible to easily change the relative position of the seal ring  43  with respect to the holder  41  (that is, change the radial length of the seal ring  43 ) in accordance with the rotation amount (screwing amount) of the adjusting bolt  46 . Accordingly, it is possible to reproduce a state in which the clearance is optimized without processing the unused seal ring  43  before the replacement when replacing the seal ring  43 . 
     Hereinabove, the first embodiment of the present invention has been described. It is possible to make various changes and modifications to the above method and configuration without departing from the spirit of the present invention. For example, in the first embodiment, a configuration in which the seal unit  2 B is provided only in the vane  20  has been described. However, a position of the seal unit  2 B is not limited thereto and the seal unit may be provided between the blade  30  and the inner peripheral surface of the casing  2 . 
     Second Embodiment 
     Next, a second embodiment of the present invention will be described with reference to  FIG. 9 . The same components as those in the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted. In this embodiment, the configuration of a position adjusting portion  60 ′ of a seal unit  2 B′ is different from that of the first embodiment. The position adjusting portion  60 ′ includes a pinion gear  48 A which is provided in the hook plate  42  and a rack gear  48 B which meshes with the pinion gear  48 A and is fixed to the seal ring  43 . The pinion gear  48 A is supported inside the hook plate  42  to be rotatable about a rotation axis Ax extending in a direction orthogonal to the radial direction and the axis O. The rack gear  48 B extends in the radial direction and moves forward and backward in the radial direction in accordance with the rotation of the pinion gear  48 A. Accordingly, the seal ring  43  to which the rack gear  48 B is fixed moves forward and backward in the radial direction. As a result, the radial length of the seal ring  43  is changed. 
     Further, in this embodiment, an elastic member  47  for biasing the hook plate  42  inward in the radial direction is formed in the holder main body  41 A. Specifically, a leaf spring may be used as the elastic member  47 . 
     According to the above-described configuration, it is possible to easily change the relative position of the seal ring  43  with respect to the holder  41  in accordance with the relative position of the pinion gear  48 A with respect to the rack gear  48 B. Accordingly, it is possible to reproduce a state in which the clearance is optimized without processing the unused seal ring  43  before the replacement when replacing the seal ring  43 . 
     Hereinabove, the second embodiment of the present invention has been described. It is possible to make various changes and modifications to the above method and configuration without departing from the spirit of the present invention. 
     INDUSTRIAL APPLICABILITY 
     According to the present invention, it is possible to provide a steam turbine repair method and a steam turbine capable of easily and quickly performing repair. 
     REFERENCE SIGNS LIST 
     
         
         
           
               100  Steam turbine 
               1  Rotary shaft 
               1 S Rotary shaft outer peripheral surface 
               2  Casing 
               2 B,  2 B′ Seal unit 
               2 L Lower half casing 
               2 U Upper half casing 
               3  Rotor 
               4 A Journal bearing 
               4 B Thrust bearing 
               11  Shaft end 
               12  Steam supply pipe 
               13  Steam discharge pipe 
               20  Vane 
               21  Vane main body 
               22  Vane shroud 
               22 A Shroud inner peripheral surface 
               24  Vane pedestal 
               24 A Pedestal inner peripheral surface 
               30  Blade 
               31  Blade main body 
               34  Blade shroud 
               41  Holder 
               41 A Holder main body 
               41 B Engagement protrusion 
               41 S Protrusion upper surface 
               42  Hook plate 
               42 S Plate lower surface 
               42 T Plate upper surface 
               43  Seal ring 
               43 A Seal base portion 
               43 B Fin main body 
               43 S Base portion inner peripheral surface 
               43 T Base portion upper surface 
               43 H Bolt hole 
               43 R Loss portion 
               45  Nut 
               46  Adjusting bolt 
               46 A Fixed disk portion 
               46 B Bolt upper portion 
               46 C Bolt lower portion 
               46 D Groove 
               47  Elastic member 
               48 A Pinion gear 
               48 B Rack gear 
               60 ,  60 ′ Position adjusting portion 
             A Center axis 
             Ax Rotation axis 
             O Axis