Abstract:
A stator shroud segment is provided that includes an outer shroud having a leading edge groove and a trailing edge groove, both grooves of the outer shroud opening in a first, axial direction; and a plurality of inner shrouds each having a leading edge hook and a trailing edge hook. The hooks of the inner shrouds project in a second, axial direction, diametrically opposite the first axial direction and the leading and trailing hooks of each of the inner shrouds are respectively engaged with the leading and trailing edge grooves of the outer shroud so as to axially and radially lock the inner shrouds to the outer shroud. The assembly simplifies access to and removal of the inner shroud(s) without added complexity.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    In an industrial gas turbine, shroud segments are fixed to turbine shell hooks in an annular array about the turbine rotor axis to form an annular shroud radially outwardly and adjacent the tips of buckets forming part of the turbine rotor. The inner wall of the shroud defines part of the gas path. Conventionally, the shroud segments are comprised of inner and outer shrouds provided with complimentary hooks and grooves adjacent their leading and trailing edges for joining the inner and outer shrouds to one another. The outer shroud is, in turn, secured to the turbine shell or casing hooks. In an exemplary configuration, each shroud segment has one outer shroud and two or three inner shrouds.  
           [0002]    Two common approaches have been taken for the configuration of inner shrouds in the past; an opposite hook design and a C-clip design. The opposite hook design is the more traditional approach and incorporates oppositely projecting hooks on the leading and trailing edges that are retained by the outer shroud. The main service disadvantage with such an arrangement is that the inner shroud cannot be removed in the axial direction; it can only be slid out of the casing circumferentially. This access limitation requires any mating shroud assemblies to be removed before the shroud of interest can be accessed.  
           [0003]    Thus, for the traditional opposite hook design, to remove a particular inner shroud, all preceding shrouds had to be removed by disengaging their anti-rotation pins and then sliding them out circumferentially, one-by-one, until the shroud of interest is accessible. For a 6C-engine part count of 66, this would require removing as many as 5 additional outer shrouds, along with 15 inner shrouds, before the inner shroud of interest is accessible.  
           [0004]    The second conventional approach mentioned above, the C-clip design, provides a service enhancement to the opposite hook approach that allows axial access to the inner shroud. A conventional C-clip design is schematically illustrated in FIG. 1. As can be seen, like the traditional opposite hook approach, this arrangement also comprises leading and trailing edge hooks  10 , 12  projecting in opposite directions. However, the trailing edge hook  12  is retained with a separate C-clip  14 , as opposed to being retained by the outer shroud  16 . By removing the C-clip  14 , the inner shroud  18  can be removed in the axial direction as shown by arrow A, thereby enhancing service access by allowing only the shroud  18  of interest to be removed. It should be noted, however, that at least one adjacent inner shroud, approximately one to three shrouds on each side (not shown), must still be shifted circumferentially to clear the cloth seals.  
           [0005]    There are two main disadvantages of the above-described C-clip arrangement. The first is the added complexity of the additional C-clip components and features. These components and features include the C-clip itself, an anti-rotation pin, and the machined features required to accommodate axial and radial locating surfaces, a bearing surface for the C-clip, and the retention pin holes. A second disadvantage of the C-clip arrangement is that to allow service access to the C-clip pin, the stage two nozzles in the area of interest must be shifted circumferentially, which requires removal of the nozzle anti-rotation pins.  
         BRIEF DESCRIPTION OF THE INVENTION  
         [0006]    Thus, further service enhancements, such as improved service access and reduced complexity, would be desirable.  
           [0007]    The present invention proposes to modify the stage one inner shroud to reverse the leading edge hooks as compared to the traditional opposite hook design and C-clip design to allow for axial removal of the shroud of interest without removal of additional shrouds. Providing a reverse hook arrangement in accordance with an embodiment of the invention simplifies access without the added complexity of the C-clip design.  
           [0008]    Thus the invention may be embodied in a stator shroud segment comprising: an outer shroud having a, leading, upstream edge and a trailing, downstream edge, and radially inner and radially outer faces, said outer shroud comprising a leading edge hook and a trailing edge hook, both said hooks of said outer shroud projecting in a first, axial direction; a plurality of inner shrouds each having a leading, upstream edge and a trailing, downstream edge, and radially inner and radially outer faces, said inner shroud comprising a leading edge hook and a trailing edge hook, both said hooks of said inner shroud projecting in a second, axial direction, diametrically opposite said first axial direction; said leading and trailing hooks of each said inner shroud being respectively engaged with said leading and trailing hooks of said outer shroud, said engagement axially and radially locking said inner shroud to said outer shroud.  
           [0009]    The invention may also be embodied in a stator shroud of a multi-stage gas turbine comprising: a shroud segment having a surface for, in part, defining the hot gas path through one stage and over laying tips of buckets of said one stage forming part of a turbine rotor, said shroud segment having a leading, upstream edge and a trailing, downstream edge; said shroud segment comprising an outer shroud and at least one inner shroud connected thereto; said outer shroud having a groove defined adjacent and along each of said leading and trailing edges thereof, said grooves opening axially in a same direction; and said inner shroud having a leading edge axially projecting tab portion and a trailing edge axially projecting tab portion for respectively engaging said grooves of said outer shroud, said engagement axially and radially locking said inner shroud to said outer shroud.  
           [0010]    The invention may further be embodied in a method of disengaging and removing a first inner shroud having a leading edge hook and a trailing edge hook from an outer shroud having a leading edge groove and a trailing edge groove mutually engaged with said leading and trailing edge hooks of said first inner shroud, said leading and trailing edge hooks of said first inner shroud projecting in a same axial direction, said method comprising: one of removing and axially displacing a mating part on an upstream side of said first inner shroud; removing a first inner shroud anti-rotation pin engaging said first inner shroud and said outer shroud; removing anti-rotation pins from circumferentially adjacent inner shrouds and sliding said circumferentially adjacent inner shrouds until clear of cloth seals therebetween; sliding said first inner shroud axially to disengage the leading and trailing edge hooks from said leading and trailing edge hooks of said outer shroud; and displacing said first shroud radially to disengage and remove said first inner shroud. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    These and other objects and advantages of this invention, will be more completely understood and appreciated by careful study of the following more detailed description of the presently preferred exemplary embodiments of the invention taken in conjunction with the accompanying drawings, in which:  
         [0012]    [0012]FIG. 1 is a schematic shroud segment circumferential end view, showing a conventional C-clip inner shroud retention design;  
         [0013]    [0013]FIG. 2 is a schematic circumferential end view of a shroud segment embodying the invention;  
         [0014]    [0014]FIG. 3 is a perspective view of the shroud segment of FIG. 2 with two of the inner shroud segments omitted to reveal the radially inner configuration of the outer shroud;  
         [0015]    [0015]FIG. 4 is a perspective view from above of the assembly shown in FIG. 3; and  
         [0016]    [0016]FIG. 5 is a perspective view of an inner shroud according to an embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]    As mentioned above, FIG. 1 schematically illustrates a conventional C-clip design. As shown, the inner shroud  18  includes an inner shroud leading or upstream edge inner shroud hook  10  and an inner shroud trailing or downstream edge hook  12  for engagement with corresponding leading and trailing edge hooks  20 ,  22  of the outer shroud  16 . The inner shroud trailing edge hook  12  is secured to the trailing edge hook  22  of the outer shroud  16  with a separate C-clip  14 , rather than being maintained by the outer shroud structure. To remove the inner shroud, the C-clip  14  must be removed, the inner shroud  18  is moved radially (Arrow R) or, more specifically, rotated about the leading edge hook  10  until the trailing edge of the inner shroud clears the outer shroud  16 , and then the inner shroud  18  is shifted axially (Arrow A) until fully clear of the outer shroud  16 . As noted above, in addition to the added complexity of the additional C-clip components and features, the C-clip arrangement requires that the stage two nozzles in the area of interest be shifted circumferentially, which requires removal of the nozzle anti-rotation pins, to allow service access to the C-clip pin (not shown).  
         [0018]    Referring to FIGS.  2 - 5 , there is illustrated a shroud segment, generally designated  100 , comprised of an outer shroud  116  and a plurality of inner shrouds  118 . Typically two or three inner shrouds are provided. The illustrated shroud segment  100  is adapted to include three inner shrouds  118 , only one of which is shown for clarity. As described in greater detail below, the inner shrouds have hooks  110  and  112  adjacent their leading and trailing edges, respectively, for circumferentially slidable engagement in grooves  126  and  128  defined by hooks  120 , 122  of the outer shroud  116  in final assembly. In the illustrated embodiment, an impingement cooling plate  124  is mounted between the shrouds for impingement cooling of the inner wall surfaces of the shroud segment  100 , in a conventional manner.  
         [0019]    In the illustrated embodiment, the outer shroud  116  has a radially outer dovetail  130  for engagement in a dovetail groove  132  defined by leading and trailing hooks  134 , 136  forming part of the fixed turbine shell or casing for securing the shroud segment to the casing. It is to be understood that as an alternative to the configuration illustrated, the outer shroud may be provided with a radially outer dovetail groove for receiving a correspondingly shaped dovetail formed as a part of the turbine casing. It will be appreciated that an annular array of shroud segments  100  are formed about the rotor of the gas turbine and about the tips of the buckets on the rotor, thereby defining an outer wall or boundary for the hot gas flowing through the hot gas path of the turbine. In FIG. 2, the inner shroud seal slots  170 , the stage one nozzle structure  172 , stage one bucket  174  and stage two nozzle structure  176  are shown for completeness and reference.  
         [0020]    As mentioned above, as an embodiment of the invention, a reverse hook shroud configuration is provided to engage and hold the inner shrouds  118  to the outer shroud  116 , to enhance service and assembly. With reference to FIG. 2, which is a detailed circumferential end view of a shroud segment  100  showing mating parts, it can be seen that the outer shroud  116  is engaged by leading and trailing casing hooks  134 , 136 , as described above, and an outer shroud anti-rotation pin  138  is provided to extend into a corresponding slot  140  (FIG. 4) to circumferentially lock the outer shroud  116  with respect to the casing  142 . In the illustrated embodiment, outer shroud seal slots  144  are shown as are air metering holes  146  and impingement plate  124 . At the leading edge of the outer shroud, inner shroud anti-rotation pin bores  148  are further provided to align with corresponding holes  150  and to receive inner shroud anti-rotation pins  152 .  
         [0021]    In contrast to the conventional configuration described above and illustrated in FIG. 1, the leading edge hook  120  of the outer shroud  116  is reversed so as to include a tab portion  154  projecting axially upstream, away from the trailing edge. The trailing edge hook  122  of the outer shroud  116  also includes a tab portion  156  that projects axially upstream, toward the leading edge, in the same direction as the tab portion  154  of the leading edge hook  120 . Thus, the grooves  126  and  128  of the outer shroud  116  both open axially in the upstream direction.  
         [0022]    The hooks  110  and  112  of the inner shroud  118  are engaged with the leading and trailing edge hooks  120 ,  122 , and in particular with the grooves  126 ,  128  of the outer shroud  116 . More particularly, in the illustrated embodiment, the leading edge hook  110  of the inner shroud comprises a tab portion  158  that projects axially downstream, towards the trailing edge, so as to axially and radially engage the hook  120  of the outer shroud  116 , to axially and radially lock the outer and inner shrouds. It should be noted that the stage one retaining ring, i.e., stage one nozzle hardware, contributes to locking the inner shroud as well. That is, the retaining ring prevents the shroud from shifting far enough forward to clear the leading edge hook of the outer shroud. Furthermore, in the illustrated embodiment, as mentioned above, a receptacle or hole  150  is defined in the leading edge hook of the inner shroud for receiving the inner shroud anti-rotation pin  152  inserted through the corresponding bore  148  defined in the outer shroud leading edge portion.  
         [0023]    The trailing edge hook of the inner shroud similarly includes a tab portion  160  extending axially downsteam, towards the trailing edge, in the same direction as the leading edge tab portion  158  to axially and radially lock with the trailing edge hook  122  of the outer shroud.  
         [0024]    To remove an inner shroud of interest, first the retaining ring  178  (mating part) is removed or slid forward or in an upstream direction approximately 1 inch. Then the inner shroud leading edge W seal  180  is removed and the inner shroud anti-rotation pin  152  is backed out. Then, the anti-rotation pins of the at least one adjacent inner shroud on each side are removed and those inner shrouds are slid circumferentially until clear of cloth seals. The target inner shroud is then removed by sliding axially to disengage the leading and trailing edge hooks  110 , 112  and then radially. A new inner shroud is then installed by inserting radially and then sliding axially, repositioning the adjacent inner shrouds to engage cloth seals and reinstalling the inner shroud anti-rotation pins.  
         [0025]    Compared to the C-clip design, the reverse hook configuration eliminates the need to remove the C-clip and stage two nozzle anti-rotation pins. That is, in the C-clip design, one must slide enough stage two nozzles circumferentially until the C-clip retention pin is accessible. This requires removing all proceeding stage two nozzle anti-rotation pins. These steps are all eliminated with the reverse hook design of the illustrated embodiment.  
         [0026]    The illustrated shroud assembly achieves axial installation and removal by reversing the leading edge hook  110  as compared to the traditional and C-clip designs. From the standpoint of service and assembly, the ability to remove the inner shroud axially can eliminate or reduce service steps including removal of mating outer shrouds, C-clips and stage two nozzle anti-rotation pins. This arrangement also simplifies producibility by reducing the number of machined features required as compared to the C-clip design while achieving the same service enhancement objectives.  
         [0027]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.