Abstract:
A turbine diaphragm adapted to be supported in a lower turbine shell component includes a first diaphragm half portion having a pair of diametrically opposed horizontal joint surfaces and a second diaphragm half portion having a similar pair of diametrically opposed horizontal joint surfaces. The first and second diaphragm half portions are identical and interchangeable. Each diaphragm half portion is formed with mounting slots for receiving a support bar engageable with the lower turbine shell component, and with identical joint bolt holes to thereby insure interchangeability of the first and second diaphragm half portions.

Description:
This invention relates to turbomachinery and, specifically, to a system for supporting interchangeable upper and lower halves of a split, annular diaphragm radially in the steam path of a steam turbine. 
     BACKGROUND OF THE INVENTION 
     Turbomachines generally comprise stationary and rotating parts defining a flow path for fluid through the turbine. Turbomachines also include an outer fluid tight caging called an outer shell from which a number of stationary parts, including split, annular diaphragms (that mount the fixed nozzles between the stages of the turbine), generally depend radially inwardly. In some prior arrangements, the diaphragms are positioned by radial keys (at the 6 and 12 o&#39;clock positions) and are supported by support bars on opposite sides (in 9 and 3 o&#39;clock positions) of the diaphragms. 
     The outer shell or casing may also be split along a horizontal joint so that the turbine shell comprises an upper half and a lower half. In building a turbomachine, certain stationary parts are mounted in the lower half shell whereas other stationary parts are mounted in the upper half shell while the two mating components are kept apart. The two halves are then assembled along a horizontal joint after the rotor has been mounted in the lower half. 
     As already noted, the diaphragms may likewise be split along a horizontal joint and comprise upper and lower diaphragm halves. The lower diaphragm halves are each mounted in the lower half shell, and after rotor installation, the upper diaphragm halves are bolted to the lower diaphragm halves. It is necessary, however, to align the diaphragm with the rotor to insure a uniform and desired radial gap between them. 
     Traditionally, large diaphragms have been supported radially by pads bolted to the sides of the lower half diaphragm, and supported by the lower turbine shell. The current design uses a rectangular slot and bolts to fasten the diaphragm support or pad to the diaphragm. With higher turbine power density designs in fixed outer shells, however, the available space for current supporting systems has become problematic. Supporting blocks or pads, hold down bolts, sealing keys and lifting holes, etc. all vie for the limited space. 
     In addition, with current designs, alignment of the diaphragms can only be achieved by removing the rotor from the shell. In addition, the lower halves of diaphragms are the last major maintenance component to be received, and the first to be reinstalled after repair. Current designs simply do not address serviceability concerns. There is thus a need for simplified diaphragm construction that reduces alignment time, errors, and minimizes crane usage for rotor removal, and that facilitates serviceability. 
     BRIEF SUMMARY OF THE INVENTION 
     This invention provides a new system for supporting steam turbine diaphragms radially within the steam path. It also provides diaphragm alignment capability without removing the rotor from the casing. The new support system includes a support bar that incorporates a dovetail for mating engagement with a dovetail slot in the outer ring of the lower diaphragm half that carries the load and maintains radial position. This arrangement is provided on both sides of the diaphragm. 
     Specifically, the support bar in accordance with one exemplary embodiment of the invention includes a vertical body portion with an outwardly directed support flange at an upper end thereof, and an inwardly directed dovetail adjacent a lower end thereof. The supporting flange is adapted to engage a shoulder of the lower casing half via a plurality of adjustment shims, a shim pack clamping block, and a shim pack clamping bolt. The shims are employed to align the diaphragm as necessary, relative to the rotor. The dovetail is engaged with, or seated within, a mating dovetail slot formed in the diaphragm lower half, adjacent the split line (between the upper and lower diaphragm halves). 
     A set screw approximately mid-way along the support bar is used to stabilize the support bar relative to the lower diaphragm half, while an additional set screw extends through the dovetail itself, bearing on the base of the dovetail slot, thus enabling the dovetail joint to be securely locked. 
     In the exemplary embodiment, the upper and lower diaphragm halves are also made identical, so that each diaphragm half can be used as either the upper or lower half component. Thus, dovetail slots are formed in identical locations on both diaphragm halves so that the support bar described above will have a mating dovetail slot in whichever diaphragm half is used as the lower half. Similarly, the clamping bolt holes and bolt access arrangements for the support bars, as well as the joint bolts and bolt holes for securing the upper and lower diaphragm halves are also made identical. 
     The above described dovetail design eliminates the bolts and drilled holes in the outer ring of the diaphragm, and provides additional advantages with respect to design simplicity, flexibility, quicker and more accurate alignment, and decreased maintenance. Moreover, the design provides immediate servicing of the upper half of the diaphragm without waiting for the lower half to be removed. At the same time, the interchangeability feature permits assembly and alignment of the upper diaphragm halves in the lower position, again shortening outage duration. In addition, the direct alignment of turbine rotors with the stationary components (diaphragms) in the turbine shell, avoids alignment errors caused by translating data from other alignment techniques. 
     In its broader aspects, the present invention relates to a turbine diaphragm adapted to be supported in a lower turbine shell component comprising a first diaphragm half portion having a pair of diametrically opposed horizontal joint surfaces; a second diaphragm half portion having a similar pair of diametrically opposed horizontal joint surfaces; the first and second diaphragm half portions being identical, including identical mounting slots for receiving a support bar engageable with the lower turbine shell component to thereby insure interchangeability of the first and second diaphragm half portions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The FIGURE is as partial cross-section illustrating a support system for a steam turbine diaphragm in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The FIGURE illustrates a support and assembly system  10  for a steam turbine diaphragm  12 , and specifically for the lower half  14  and upper half  15  of a split diaphragm, each of which has a pair of opposed, horizontal joint surfaces  17 ,  19  (only one of each pair shown). The lower diaphragm half  14  is positioned within a lower turbine shell component  16 , partly shown. An upper turbine shell component  18  is also partly shown, with a split line  20  at the juncture of the upper and lower shells. Thus, the split line  20  also refers to the matching horizontal joint surfaces of the upper and lower shells. The upper shell  18  includes a recess or pocket  22  that facilitates the use of a horizontal edge portion  24  of the lower shell  16  along the split line  20  for supporting the diaphragm. In this regard, it will be appreciated that the upper diaphragm half  15  is supported on, and bolted to, the lower diaphragm half  14 , along a pair of opposed horizontal joint surfaces, after the lower diaphragm half  14  and rotor have been installed in the lower shell  16 . 
     A diaphragm support bar  26  in accordance with an exemplary embodiment of this invention includes a vertical body portion  28  having a 90°, outwardly directed support flange  30  at its upper end, and a 90°, inwardly projecting dovetail  32  adjacent its lower end. The dovetail  32  is adapted for mating engagement within a dovetail slot  34  formed in the outside surface  36  of the lower diaphragm half  14 . The upper support flange  30  projects into the pocket  22 , enabling the lower diaphragm half  14  to be supported on the lower shell  16 , along the split line  20 . In addition, one or more shims  38  (also referred to as a “shim pack”) are sandwiched between a lower surface  40  of the flange  30  and a shim pack clamping block  42  supported directly on the horizontal edge portion  24  of the lower shell  16 . A shim pack clamping bolt  44  (with one or more washer shims  46  to adjust hold down clearance) extends through the flange  30  and into a threaded bore in the clamping block  42 . With the lower diaphragm half  14  thus supported in the lower shell  16 , the rotor (not shown) may be installed. Subsequently, the upper diaphragm half  12  is located on the lower diaphragm half and bolted thereto as described in greater detail below. Thus, both the upper and lower diaphragm halves  14  and  15  are supported by the support bars  26  located on opposite sides of the lower diaphragm half  14 . 
     It will be appreciated that shims  38  can be added or removed to align the diaphragm relative to the rotor. Vertical adjustment can be accomplished by adding or removing a like number of shims  38  from both sides of the diaphragm, whereas side-to-side “rocking” alignment (about a radial pin, not shown, at the 6 o&#39;clock position) of the lower diaphragm half by differential addition or subtraction of shims  38  from the support bar  26  on the opposite side of the diaphragm. 
     A first set screw  48  extends through the support bar  28  above the dovetail  32  so as to engage the outer surface  36  of the lower diaphragm half  14  and thus set the support bar relative to the lower diaphragm half. 
     A second set screw  50  extends horizontally through the bar  28  and the dovetail  32  so as to engage the base  52  of the dovetail slot  34 . This enables the dovetail joint to be locked securely in the desired position. 
     In accordance with this invention, the upper diaphragm half  15  is identical to, and thus interchangeable with, the lower diaphragm half  14 . Note for example that the upper diaphragm half  15  also includes a dovetail slot  54  formed on the outside of the diaphragm, at the same location relative to the horizontal joint surfaces  20  as the dovetail slot  34  in the lower diaphragm half  14 . Dovetail slot  54  is used, however, only in the event diaphragm half  15  is used as a lower diaphragm half. 
     At the same time, each diaphragm half  14 ,  15  is formed with a partially threaded bolt holes  56 ,  58 , respectively, on opposite sides thereof (only one shown), accessed by notched areas  60 ,  62  in the upper and lower diaphragm halves. The bolt holes have threaded bore portions  64 ,  66  adjacent the respective notched areas  60 ,  62 , with smooth bore portions  68 ,  70  adjacent the split line formed by the horizontal joint surfaces  17 ,  19  on the respective diaphragm halves. A joint bolt  74  has a threaded end  76  and a smooth shank portion  78 . This arrangement facilitates the interchangeability of the diaphragm halves in that the bolts will always be threadably secured to the lower diaphragm half, clamping the upper diaphragm half  15  between the head  80  of the bolt and the lower diaphragm half  14 . These bolts are made slightly longer than conventional joint bolts, with bolt clearance designed around the horizontal joint (or split line  72 ) to facilitate only one threaded engagement at a time. In other words, the threaded end  76  of the bolt  74  does not engage threaded portion  64  of bore  56  until it passes completely through the threaded portion  66  of bore  58 . In this regard, the threaded portions  64 ,  66  of the respective bores are in the bottom (or top if considering the upper diaphragm half) 60% of the bore, as measured from the horizontal joint surfaces, or split line  72 , and the smooth shank portion  78  of the bolt is longer than the threaded end portion  76 . This arrangement allows the joint bolts  74  to be symmetrical no matter how the diaphragm halves are oriented, and will allow the same bolts to be used in either direction. Spacing the threads away from the joint surface also prevents the thread from extruding onto the horizontal joint surfaces along the split line  72  when the bolts  74  are tightened. 
     Once the sealing keys (not shown) are fitted, it becomes irrelevant to which side the keys are to be fastened. 
     The above arrangement provides interchangeability, reduces design, manufacturing, assembly, alignment and field service costs. It also permits servicing of the upper diaphragm half without removing the lower half and/or rotor. 
     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.