Abstract:
Disclosed herein is a seal assembly for a rotary machine having a plurality of arcuate segments and at least one seal. The plurality of arcuate segments are arrayed in an annulus and have butt joints, each of the arcuate segments has a radially outermost surface and a downstream face. The at least one seal is arranged to minimize leakage through the butt joints. The at least one seal has a first portion configured to minimize leakage at the radially outermost surface and a second portion configured to minimize leakage at the downstream face.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This application relates generally to rotary machines, and more specifically to seal assemblies between components of a rotary machine. In rotary machines, such as steam turbines for example, it is customary to employ a seal assembly having a plurality of arcuate segments to form a seal between two stationary components and between a stationary component and a rotating component. Generally, the arcuate segments are disposed in an annular groove of one of the components. Each arcuate segment further has a sealing face in opposition to the other component. The sealing function is achieved by creating relatively tight clearances between the sealing face of the arcuate segments and the opposing component. 
         [0002]    During the operation of the rotary machine, and more particularly during startup, shutdown or transient operations, components experience different thermal expansion rates, which in turn governs the spacing between the arcuate segments as the components expand and contract. The ability to minimize leakage between the arcuate segments allows for the formation of an effective seal between the components. Minimizing leakage between the arcuate segments also significantly improves rotary machine performance and efficiency. 
         [0003]    Accordingly, there is a need to provide a seal assembly having enhanced sealing capabilities throughout all phases of the rotary machine operation. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    Disclosed herein is a seal assembly for a rotary machine having a plurality of arcuate segments and at least one seal. The plurality of arcuate segments are arrayed in an annulus and have butt joints, each of the arcuate segments has a radially outermost surface and a downstream face. The at least one seal is arranged to minimize leakage through the butt joints. The at least one seal has a first portion configured to minimize leakage at the radially outermost surface and a second portion configured to minimize leakage at the downstream face. 
         [0005]    Further disclosed herein is a rotary machine having a first component, a seal assembly, a second component, and at least one seal. The first component has an annular groove. The seal assembly has a plurality of arcuate segments and is disposed within the annular groove. The second component is disposed adjacent to the arcuate seal segments. The at least one seal is disposed between the segments such that a first portion of the at least one seal has a surface complementary to a radially outermost surface of the segments. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Referring to the drawings wherein like elements are numbered alike in the several Figures: 
           [0007]      FIG. 1  is a cross section view of a portion of a rotary machine; 
           [0008]      FIG. 2  is a perspective view of an exemplary seal assembly; 
           [0009]      FIG. 3  is a partial plan view of the seal assembly of  FIG. 2 ; 
           [0010]      FIG. 4  is a perspective view of an exemplary seal; 
           [0011]      FIG. 5  is an enlarged front plan view of the seal assembly of  FIG. 2 ; 
           [0012]      FIG. 6  is a section view of the seal assembly of  FIG. 2  at a maximum butt gap width; and 
           [0013]      FIG. 7  is a section view of the seal assembly of  FIG. 2  at a minimum butt gap width. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    Referring to  FIG. 1 , there is illustrated a cross section view of a portion of a rotary machine, for example, a steam turbine, generally designated  10 , having a first stationary component  12  and a second stationary component  14 . To minimize leakage between the first stationary component  12  and the second stationary component  14 , a seal assembly  16  is provided at a component-to-component (e.g., the first stationary component  12  and the second stationary component  14 ) interface separating high and low pressure regions  18  and  20  respectively. The seal assembly  16  is formed of an annular array of arcuate segments  22  (further illustrated in  FIG. 2 ). Each seal segment  22  also has a sealing face  24  with projecting radial teeth  26  acting as partial barriers to a fluid medium, such as steam for example, flowing from the high to low pressure regions  18  and  20 . It will be appreciated that although  FIG. 2  shows eight arcuate segments  22 , the number of arcuate segments  22  within the seal assembly  16  may be varied, to a greater or fewer number, according to operational considerations. 
         [0015]    The radial outer portions of the segments  22  include segment locating flanges  28  which extend from the segment  22  in axially opposite directions away from one another. An axially reduced neck  30  extends between the segment sealing face  24  and the segment locating flanges  28 . The segments  22  are disposed in an annular groove  32 , having a “T” shaped cross section, within the first stationary component  12 . The annular groove  32  is defined along the radially innermost portions of the stationary component  12  by a pair of stationary component locating flanges  34  which extend axially toward one another defining a slot  36  therebetween. The segments  22  are positioned such that the axially reduced neck  30  of the segments  22  is fitted within the stationary component slot  36 . 
         [0016]    The seal assembly  16  configuration pursuant to this disclosure is useful with a wide variety of parts and components disposed within a rotary machine  10 . While the following discussion will be with reference to seal assemblies disposed between two stationary components, such as between two turbine shells for example, it should be understood that the disclosed seal assembly  16  may also be disposed between a stationary component and a rotating component, such as between a turbine diaphragm and a shaft for example. 
         [0017]    A plurality of seals having an “L” shape (best illustrated in  FIGS. 3 and 4 ), hereinafter referred to as “L” seals  38 , are disposed at a plurality of butt gaps  40  (best shown in  FIGS. 2-3  and  5 - 7 ) between the arcuate segment  22  ends. Each end of the segments  22  has a radial slot  42  configured to accept a half of the “L” seal. The “L” seals  38  have an axial portion  44 , substantially parallel to a central axis of the seal assembly  16 , and a radial portion  46 , substantially perpendicular to the central axis of the seal assembly  16 . When installed, the “L” seals  38  are disposed such that the axial portion  44  is adjacent to a radially outermost surface  48  of the segments  22  and the radial portion  46  is disposed within the slot formed between two adjacent ends of the segments  22 . Although the figures show the axial portion  44  shorter than the radial portion  46 , it is to be understood that these lengths can vary depending on segment  22  geometry and application specific considerations. Additionally, although the figures and following discussion describe the “L” seals  38  as having an “L” shape with one portion substantially parallel to the central axis of the seal assembly and another portion substantially perpendicular to the central axis of the seal assembly, it is should be appreciated that other shapes, with portions complimentary to the profile of the surrounding segment, are envisioned. Further it is to be understood that although the “L” seals  38  are illustrated and described as being freely disposed within the radial slot  42  between the segments  22 , it is to be understood that each of the “L” seals  38  may alternatively be attached to an adjacent segment at one end of the “L” seal and free to move within the radial slot of the other adjacent segment at the other end of the “L” seal. 
         [0018]    The “L” seals  38  may further comprise features to enhance the sealing capability at the butt gap regions. For example, in one embodiment, the segment tooth adjacent to the “L” seal may be configured to have one side parallel to the radial portion  46  of the “L” seal  38 . As can be seen in  FIG. 1 , the segment teeth  26  not adjacent to the “L” seal  38  have sides that are not parallel to the segment seal. Having a segment tooth with one side parallel to the “L” seal promotes sealing along the entire radial length of the interface between the radial portion  46  of the “L” seal  38  and the segment  22 . In particular, having a segment tooth with one side parallel to the “L” seal  38  helps reduce leakage around the seal at the “L” seal-to-tooth interface (best illustrated in  FIG. 1 ) by minimizing the gap between the “L” seal  38  and the segment teeth  26 . Further, it will be appreciated that although  FIG. 1  shows the segments  22  having three teeth  26 , any number of teeth  26  are envisioned. 
         [0019]    For example, in another embodiment, the axial portion  44  of the “L” seal may be configured to have a complementary surface  50  to that of the radially outermost surface  48  of the segments  22 . The desired shape of the complementary surface  50  may be achieved by manufacturing methods such as machining, forming or casting operations for example. The complementary surface  50  creates mating surfaces between the “L” seal  38  and the segments  22  which provides for additional sealing capability in the region of the butt gaps  40  (best illustrated in  FIG. 5 ) by minimizing the gap between the outermost surface  48  of the segments  22  and the complementary surface  50  of the “L” seal  38 . Additionally, the “L” seal  38  may be fabricated from the same material as that of the adjacent segments  22 . Having a common material between the segments  22  and the “L” seals  38  allows for maximizing the sealing capability in the region of the butt gaps by minimizing differential thermal expansion between the mating parts. Having common materials, or materials with similar thermal expansion rates, allows for the “L” seals  38  to thermally expand at the same rate the segments  22  expand thus promoting proper alignment of the “L” seals  38 . The material common to the segments  22  and the “L” seals  38  may be metal alloys such as carbon steel, low carbon steel, 1¼ Cr-½ Mo alloy steel, and 2¼ Cr-1 Mo alloy steel for example. 
         [0020]    And for example, in yet another embodiment, the innermost radial surface  52  of the radial portion  46  may have a contoured edge matching the innermost radius  54  of the segments  22 . This configuration of the innermost radial surface  52  provides for proper alignment of the “L” seal  38  and limits leakage at the seal assembly to the second stationary component interface (best illustrated in  FIG. 5 ). In particular, the innermost radial surface  52  minimizes leakage at the seal assembly  16  to the second stationary component  14  interface in the butt gap region, as there is a gap between the teeth  26  of the adjacent segments  22 . 
         [0021]    Additionally, the sizing of the individual “L” seals  38  may be modular, while allowing for dimensions such as the complementary surface  50  diameter and overall width to be customized with specific unit configuration, to allow for proper orientation and effective sealing of the “L” seals  38 . 
         [0022]    During operation of the rotary machine  10 , a fluid medium, such as steam, from the higher pressure region builds a pressure upon the axial and radial portions of the “L” seal, as depicted by arrows  56  in  FIG. 1 . This pressure build up forces the “L” seal to contact the segments  22 , wherein the axial portion  44  comes into contact with the radially outermost surface  48  of the segments  22  and the radial portion  46  comes into contact with a first downstream face  58  (within the radial slot  42 ) of the segments  22 , and creates a seal at the butt gap region. At operational extremes, such as during startup/shutdown or transient operations for example, the butt gaps  40  between the segments  22  may vary, due to different thermal expansion rates between the components, between a maximum butt gap width, as illustrated in  FIG. 6 , to a minimum butt gap width, wherein the segments  22  are in close proximity to or in contact with each other, as illustrated in  FIG. 7 . The “L” seals  38  and the radial slots  42  have dimensions capable of maintaining proper alignment of the “L” seals  38  throughout the full operating range of the rotary machine  10 . 
         [0023]    Significant advantages in rotary machine  10  performance may be attained by the disclosed seal assembly  16  configuration. The “L” seal configuration provides improved leakage performance thus resulting in increased overall efficiency of the rotary machine  10 . 
         [0024]    While the invention has been described with reference to a preferred embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims.