Abstract:
In certain embodiments of the present disclosure a turbine casing assembly is described. The turbine casing assembly includes an inner casing and an outer casing surrounding the inner casing. The outer casing includes a first outer casing section and a second outer casing section that join together along a flange. Two bolts extend through the flange and join together the first outer casing section and the second outer casing section. A pin having a first segment having a first diameter and a second segment having a second diameter extends through the inner casing and the outer casing and supports the inner casing relative to the outer casing. The pin has a first diameter that is greater than the second diameter and is located between the two bolts along the axis of the flange.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention generally involves a turbine casing assembly mounting pin and method for utilizing the same. In particular embodiments, a mounting pin joins an inner casing with an outer casing in a manner that reduces distortion and eccentricity between the inner and outer casings while transferring torque and gravity loads. 
       BACKGROUND OF THE INVENTION 
       [0002]    Conventional turbine casings generally include one or more outer turbine casings that surround one or more inner turbine casings. The outer turbine casing is often split into two hemispherical casings bolted together by flanges on a horizontal plane to facilitate maintenance and repair. The inner turbine casing is often supported through to the outer turbine casing by one or more axially spaced circumferential arrays of pins 
         [0003]    Generally, active clearance controls are employed to radially displace inner and outer turbine casings from one another during transient turbine operations. This has the effect of controlling tip clearance between buckets and shrouds, which can be beneficial since decreasing tip clearance improves turbine performance by reducing tip leakage as long as bucket tips are prevented from transiently contacting and thereby rubbing shrouds. 
         [0004]    With both active and passive systems in many configurations relative movement occurs between the inner and outer turbine casings due to differential thermal growth of their respective components. The aforementioned pins which are used to join the outer turbine casing with the inner turbine casing tangentially can reduce eccentricity caused by the relative movement. However, such pins can affect outer casing bolt spacing if the primary vertical support pins are placed near a preferred center-line supported configuration and thus intersect the outer casing bolted flange. Wider bolt spacing at the pinned locations can lead to horizontal joint overboard leakage and thus performance degradation. 
         [0005]    Thus, a need exists for pins that allow for mounting of an inner turbine casing with an outer turbine casing without impacting outer turbine casing bolt spacing. Methods relating to such pins would also be beneficial. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0006]    Aspects and advantages of the invention are set forth below in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
         [0007]    In certain embodiments of the present disclosure a turbine casing assembly is described. The turbine casing assembly includes an inner casing and an outer casing surrounding the inner casing. The outer casing includes a first outer casing section and a second outer casing section that join together along a flange. Two bolts extend through the flange and join together the first outer casing section and the second outer casing section. A pin having a first segment having a first diameter and a second segment having a second diameter extends through the inner casing and the outer casing and supports the inner casing relative to the outer casing. The pin has a first diameter that is greater than the second diameter and is located between the two bolts along the axis of the flange. 
         [0008]    In other embodiments of the present disclosure, a turbine is described. The turbine includes an inner casing and an outer casing. The inner casing carries nozzles and shrouds, the shrouds surrounding tips of buckets carried by a turbine rotor within the inner casing. The outer casing has a first outer casing section and a second outer casing section that join together along a flange. Two bolts extend through the flange and joining together the first outer casing section and the second outer casing section. A pin having a first segment having a first diameter and a second segment having a second diameter extends through the inner casing and the outer casing and supports the inner casing relative to the outer casing. The first diameter is greater than the second diameter. The pin is located between the two bolts. 
         [0009]    In still other embodiments of the present disclosure, a method for assembling a turbine casing is described. The method includes joining together an inner casing and an outer casing with a pin, the pin including a first segment having a first diameter and a second segment having a second diameter. The first diameter is greater than the second diameter, the pin extending through the inner casing and the outer casing. The method includes joining together a first outer casing section and a second outer casing section with two bolts, the pin being located between the two bolts. The method also includes surrounding the inner casing with the outer casing. 
         [0010]    Those of ordinary skill in the art will better appreciate the features and aspects of such embodiments, and others, upon review of the specification. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    A full and enabling disclosure of the present invention, including the best mode thereof to one skilled in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which: 
           [0012]      FIG. 1  is a cross-sectional perspective view of a turbine in accordance with certain embodiments of the present disclosure; 
           [0013]      FIG. 2  is a cross-sectional schematic view of the turbine casing shown in  FIG. 1  in accordance with certain aspects of the present disclosure; 
           [0014]      FIG. 3A  illustrates an expanded view of a pin assembly in accordance with certain aspects of the present disclosure; 
           [0015]      FIG. 4  illustrates a perspective view of a pin assembly positioned between bolts in accordance with certain aspects of the present disclosure; and 
           [0016]      FIG. 5 . illustrates a perspective view of a pin assembly positioned between bolts in accordance with certain aspects of the present disclosure 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    Reference will now be made in detail to present embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the invention. 
         [0018]    Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope or spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
         [0019]    Referring to  FIG. 1 , there is illustrated a turbine casing assembly  10  cross-section, having an outer structural casing  12  and an inner casing  14  supported by the outer casing  12 . The inner casing  14  carries an array of nozzles  16  and  18  forming parts of first and second stages, respectively, of the turbine. The inner casing  14  also surrounds a rotor, generally designated  20 , rotatable about an axis  22 . The rotor  20  includes circumferential arrays of buckets mounted on wheels arranged alternately with spacers, the wheels and spacers forming the body of the rotor. For example, the first and second-stage wheels  24  and  26  with an intervening spacer  28  are illustrated, the wheels  24  and  26  mounting buckets  28  and  30 , respectively. It will be appreciated that the buckets and the nozzles of the various stages in part define the annular hot gas path through the turbine. The wheels and spacers of the rotor are secured to one another by bolts  32  circumferentially spaced one from the other about the rotor. 
         [0020]      FIG. 2  illustrates a schematic end view of an assembly  10  according to one embodiment of the present disclosure. The turbine assembly  10  generally includes one or more inner casings  14  and one or more outer casings  12 . The one or more inner casings  14  and outer casings  12  are typically fabricated from alloys, superalloys, coated ceramics, or other material capable of withstanding temperatures associated with turbines. For example, a casing for a turbine in a gas turbine system would be fabricated from materials capable of withstanding temperatures associated with nozzle and shroud hook temperatures which are driven by among other factors combustion gases flowing through the gas turbine system. 
         [0021]    Referring again to  FIG. 1 , the inner casing  14  comprises a forward section  36  and an aft section  38  interconnected by an axially extending annular rib  40 . The forward and aft sections  36  and  38  are annular and have radially inwardly directed dovetails  42  and  44 , respectively, for carrying shrouds  46  and  48 . The shrouds provide a minimum clearance with the tips of the buckets. It will be appreciated that the inner casing  14  is secured to the outer casing along radial planes normal to the axis of the rotor and at axial locations, preferably in alignment with the first and second-stage buckets and shrouds. 
         [0022]    The outer casing  14  generally surrounds the one or more inner casings  12  and together form the turbine  10 . In this manner, the inner casings  12  generally conform to the outer perimeter of the rotating component, and the outer casing  14  provides an enclosure around the rotating component. 
         [0023]    Referring again to  FIG. 2 , there is schematically illustrated a cross-sectional view of turbine  10  comprised of upper and lower outer casing casings  125  and  126  respectively, upper and lower inner casing casings  145  and  146  respectively and a rotor  20 . Bolts  50  secure the upper and lower outer casing casings  125  and  126  to one another along a flange  52  that can extend across a section of the horizontal midline on either side of the turbine  10 . With reference to bolts  50 , as used herein, the term “bolts” refers to any structures such as a bolts, studs, pins, or the like that are positioned in flange bolt opening. 
         [0024]    To support the inner casing relative to the outer casing, one or more pin assemblies  54  pass through the outer casing  12  for connection with the inner casing  14 . For instance, the pin assemblies can pass through flange  52  of outer casing  12 . One or more pin assemblies  54  can be spaced along each flange  52  that extends across a section of the horizontal midline on either side of the turbine  10 . 
         [0025]    Referring to  FIGS. 3A-3C , a pin assembly  54  is illustrated. The pin assembly  54  includes an inner pin portion  56  and an outer pin portion  58 . The inner bore of the outer pin is eccentric to the outer diameter of the outer pin. This allows for the outer pin to be rotated and thus change the centerline location of the inner pin. Eccentric pins are often used in turbine systems to allow for precise external alignment capability of the inner casing relative to the rotor. Inner pin portion  56  includes an expanded ledge  60  on the radial innermost end  62  of the inner pin portion  56 . Ledge  60  can have a generally square shape that interfaces with a complimentary female receiver defined by inner shell (shown in  FIG. 2 ). Bolt section  64  extends from ledge  60  and can be generally cylindrical in shape. Bolt section  64  can include one or more contact pads  70  which allow for deterministic loading with outer pin portion  58 . Bolt section  64  includes a section  66  having smaller diameter to accommodate pin assembly  54  being located between two bolts as will be further described herein. The outermost end  67  of inner pin portion  56  can define threads to receive an inner nut  68 . 
         [0026]    Outer pin portion  58  includes an enlarged head  71  having a bolt circle  72  with one or more circumferentially defined bolt openings  74 . Bolt circle further defines an opening  80  that outermost end  67  of inner pin portion  56  can extend through. The bolt openings can be configured to receive one or more bolts  76  that react out pin rotation through friction which can set alignment of inner and outer turbine casings. Alignment portion  78  extends from bolt circle  72  and defines an opening (not shown) in communication with bolt circle opening  80  which can receive inner pin portion and also allow for outer pin rotations after assembly within the alignment requirements of the unit. Alignment portion includes contact pads  84  that allow deterministic loading with the inner and outer turbine casings and which are generally aligned with contact pads  70  of inner pin portion. Alignment portion includes one or more alignment scallops  82  which permit pin assembly  54  to be located between two bolts as will be further described herein. Alignment scallops  82  are defined, in part, by ridge portions  85  that each have a width that is approximately the same as or less than the diameter of section  66  of bolt section  64  to allow for outer pin rotations and subsequent inner pin eccentricity after assembly during unit alignment. In this manner, alignment portion  78  does not obstruct the bolts that secure the upper and lower outer casing casings. 
         [0027]    When assembled, inner pin portion  56  can interface with an inner casing section and be joined to outer pin portion  58  which contacts outer casing through the outer casing flange. Inner nut  68  can secure inner pin portion  56  to outer pin portion  58  and can be covered by a bore cap  86  which is secured to bolt circle  72 . 
         [0028]    As illustrated in  FIGS. 4 and 5 , pin assembly  54  can be utilized for mounting and/or alignment of an inner turbine casing (not shown) through a horizontal joint flange  52  of outer turbine casing  14  without impacting outer casing bolt  50  spacing and/or leakage. For instance, as can be seen from  FIG. 5 , which represents a view in which the inner turbine casing and outer turbine casing are not shown, the section  66  and ridge portions  85  permit pin assembly to be located between bolts  50  which are utilized to secure the upper and lower outer casing casings. 
         [0029]    One of ordinary skill in the art will readily appreciate that the structure previously described with respect to  FIGS. 1-5  provides a method for assembling a turbine  10 . The method generally includes joining the inner casing and the outer casing together with a pin assembly as described herein. A first outer casing section and a second outer casing section are joined together with two bolts. The inner casing is surrounded with the outer casing. 
         [0030]    Empirical testing and computer-generated models indicate that various embodiments of the present disclosure can one or more benefits over existing turbine casing assembly mechanisms and methods. The pin assemblies described herein can provide a convenient and reliable structure for ensuring the inner casings  12  are concentrically attached to the outer casing  14  during assembly without impacting casing bolt spacing and/or leakage. 
         [0031]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other and examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.