Abstract:
A nozzle assembly for a turbine that may include: (1) a nozzle-blade having inner and outer sidewalls and, in part, defining a flowpath upon assembly into the turbine; (2) an outer ring; (3) a flowsplitter having a horizontal extension; (4) an interface between the outer ring and the outer sidewall having at least one of (i) a male/female interface or (ii) a radial interlock; and (5) an interface between the horizontal extension and the inner sidewall having at least one of (i) the male/female interface or (ii) the radial interlock. In some embodiments, one of the interface between the outer ring and the outer sidewall and the interface between the horizontal extension and the inner sidewall comprises a weld and one of the interface between the outer ring and the outer sidewall and the interface between the horizontal extension and the inner sidewall is weld free.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to nozzle assemblies for turbines. More specifically, but not by way of limitation, the present application relates to singlet nozzle assemblies in the first stage of a double flow steam turbine. 
       BACKGROUND OF THE INVENTION 
       [0002]    Steam turbines typically comprise static nozzle segments that direct the flow of steam onto rotating turbine blades or buckets that are connected to a rotor. In steam turbines, the nozzle, which may form an airfoil or blade, is typically called a diaphragm stage. 
         [0003]    In general, diaphragm stages are constructed using one of two methods. A first method uses a band/ring construction wherein the airfoils are first welded between inner and outer bands, which extend about 180°. Those arcuate bands with welded airfoils are then assembled and welded between the inner and outer carrier rings of the stator of the turbine. The second construction method consists of having the airfoils or blades of the nozzle welded directly to inner and outer rings. In this method, the nozzles generally have integral sidewalls that are used to make the interface with the inner and outer rings. This method is typically used for larger steam turbine units where access for creating the weld is available. 
         [0004]    There are inherent limitations using the band/ring method of construction. A principle limitation in the band/ring assembly method is the distortion that occurs to the flowpath because of the weld that is used. That is, the weld used for these assemblies is of considerable size and heat input. The weld either requires high heat input and a significant quantity of metal filler or is very deep electron beam welds. In either case, the material or heat input causes the flow path to significantly distort. For example, material shrinkage causes the airfoils to bow outward from their designed shaped into the flow path. In many cases, the airfoils of the nozzle assemblies require adjustment and stress relief after welding. 
         [0005]    The result of the steam path distortion (which may be present in some degree even after corrective post-assembly measures are taken) is reduced diaphragm stage efficiency. The surface profiles of the inner and outer bands also may change as a result of welding the nozzles into the stator assembly further causing an irregular flow path. More specifically, the nozzles and bands generally bend and distort as a result of conventional installation methods. This requires substantial finishing of the nozzle configuration to bring it into design specifications. In many cases, approximately 30% of the costs of the overall construction of the nozzle assembly is spent on deforming the nozzle assembly, including after welding and stress relief, to bring it back to its design configuration. 
         [0006]    The second nozzle construction method (i.e., having the sidewalls of the airfoils or blades of the nozzle welded directly to the inner and outer rings) also has significant issues and inefficiencies. For example, conventional assembly methods that use a single nozzle construction welded into rings lack the proper configuration to promote a determined weld depth at the interface, which generally causes problems to arise. Further, conventional systems lack assembly alignment features on both the inner and outer ring, which may aid in installation. Also, conventional systems lack retainment features that may hold the installed nozzle in place in the event of a weld failure. Finally, conventional systems require time-consuming welds at both of the nozzle-inner ring interface and the nozzle-outer ring interface. 
         [0007]    In addition, in the first stage of a double flow steam turbine, many of the issues associated with the construction of the nozzle assemblies may be exacerbated. However, certain characteristics of the first stage, which is often referred to as the tub stage, offer design opportunities that may be used to simplify nozzle assembly in that stage and make the assembly process more efficient. For example, the flow-splitter takes the place of the inner ring in the first stage and has beneficial characteristics that may be used. As discussed in more detail below, conventional nozzle design has failed to take advantage of these opportunities. 
         [0008]    Accordingly, there is a need for a first stage nozzle that is designed to be installed by either sliding the nozzle into place or with limited low input heat welds or both. In either case, such assembly will minimize or eliminate steam path distortion that results from conventional welding processes, as well as improving production and cycle costs by making assembly more efficient. Further, there is a need for a first stage nozzle assembly that facilitates alignment of nozzle assembly during installation and creates a mechanical lock to prevent downstream movement of the nozzle assembly in the event of a weld failure. Certain unique characteristics of the first stage, which are not found in the downstream stages, may be taken advantage of in first stage nozzle design to efficiently satisfy these demonstrated needs. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0009]    The present application thus describes a nozzle assembly for a turbine that may include: (1) a nozzle blade having inner and outer sidewalls and, in part, defining a flowpath upon assembly into the turbine; (2) an outer ring; (3) a flowsplitter having a horizontal extension; (4) an interface between the outer ring and the outer sidewall having at least one of (i) a male/female interface or (ii) a radial interlock; and (5) an interface between the horizontal extension and the inner sidewall having at least one of (i) the male/female interface or (ii) the radial interlock. In some embodiments, one of the interface between the outer ring and the outer sidewall and the interface between the horizontal extension and the inner sidewall includes a weld and one of the interface between the outer ring and the outer sidewall and the interface between the horizontal extension and the inner sidewall is weld free. 
         [0010]    In some embodiments, the radial interlock may include either (i) a first male step projecting axially from the inner sidewall into the horizontal extension, the first male step being flanked on its most outwardly radial side by a second male step projecting axially from the horizontal extension into the inner sidewall, or (ii) a first male step projecting axially from the outer sidewall into the outer ring, the first mail step being flanked on its most inwardly radial side by a second male step projecting axially from the outer ring into the outer sidewall. The male/female interface may include either (i) a radial female recess on the outer sidewall that corresponds with a radial male step on the outer ring, or (ii) a radial female recess in the inner sidewall that corresponds to a radial male step on the horizontal extension. 
         [0011]    In some embodiments, the interface between the outer ring and the outer sidewall may include the male/female interface positioned at a trailing edge of the outer sidewall. The interface between the horizontal extension and the inner sidewall may include the radial interlock positioned at a leading edge of the inner sidewall. The male/female interface positioned at the trailing edge of the outer sidewall may be welded. The weld may include a butt weld such that the weld is substantially limited to the area between the outer sidewall and the outer ring along the axial length of male/female interface. The axial length of male/female interface positioned at the trailing edge of the outer sidewall may be less than about ¼ of the axial extent of the registration between the outer ring and the outer sidewall. 
         [0012]    The horizontal extension further may include a downstream lip. The downstream lip may cover the downstream edge of the inner sidewall such that the downstream lip prevents axial displacement of the inner sidewall in the downstream direction. 
         [0013]    In some embodiments, the interface between the outer ring and the outer sidewall may include one of the radial interlocks positioned at both a leading edge and a trailing edge of the outer sidewall. The interface between the horizontal extension and the inner sidewall may include the male/female interface positioned at a trailing edge of the inner sidewall. The male/female interface positioned at the trailing edge of the inner sidewall may be welded using a butt weld interface such that the weld is substantially limited to the area between the inner sidewall and the horizontal extension along the axial length of male/female interface. The axial length of male/female interface positioned at the trailing edge of the inner sidewall may be less than about ¼ of the axial extent of the registration between the inner sidewall and the horizontal extension. 
         [0014]    The present application further describes a nozzle assembly for a turbine that may include: a nozzle blade having inner and outer sidewalls and, in part, defining a flowpath upon assembly into the turbine; an outer ring; a flowsplitter having a horizontal extension; an interface between the outer ring and the outer sidewall having at least one of (i) a radial interlock; (ii) a male/female interface; or (iii) a female recess flanked by radially projecting male steps at both a leading and a trailing edge of the outer sidewall; and an interface between the horizontal extension and the inner sidewall having at least one of (i) the radial interlock; (ii) the male/female interface; or (iii) the female recess flanked by radially projecting male steps at both a leading and a trailing edge of the inner sidewall. 
         [0015]    In some embodiments, the radial interlock may include either (i) a first male step projecting axially from the inner sidewall into the horizontal extension, the first male step being flanked on its most outwardly radial side by a second male step projecting axially from the horizontal extension into the inner sidewall, or (ii) a first male step projecting axially from the outer sidewall into the outer ring, the first mail step being flanked on its most inwardly radial side by a second male step projecting axially from the outer ring into the outer sidewall. The male/female interface may include either (i) a radial female recess on the outer sidewall that corresponds with a radial male step on the outer ring, or (ii) a radial female recess in the inner sidewall that corresponds to a radial male step on the horizontal extension. 
         [0016]    The interface between the outer ring and the outer sidewall may include one of the radial interlocks positioned at the leading edge and the trailing edge of the outer sidewall. The interface between the horizontal extension and the inner sidewall may include the female recess flanked by radially projecting male steps at the leading edge and the trailing edge of the inner sidewall. The interface between the male step at the trailing edge of the inner sidewall and the horizontal extension may be welded. The weld may include a butt weld such that the weld is substantially limited to the area between the inner sidewall and the horizontal extension along the axial length of male step at the trailing edge of the inner sidewall. The axial length of male step positioned at the trailing edge of the inner sidewall may be less than about ¼ of the axial extent of the registration between the inner sidewall and the horizontal extension. The inner sidewall further may be bolted to the horizontal extension by a bolt. The bolt may be positioned such that the bolt extends radially through the horizontal extensions into the inner sidewall. 
         [0017]    In some embodiments, the interface between the outer ring and the outer sidewall may include the male/female interface positioned at the trailing edge of the outer sidewall. The interface between the horizontal extension and the inner sidewall may include the female recess flanked by radially projecting male steps at the leading and the trailing edges of the inner sidewall. The interface between the male step at the trailing edge of the inner sidewall and the horizontal extension may be welded. The weld may include a butt weld such that the weld is substantially limited to the area between the inner sidewall and the horizontal extension along the axial length of the male step at the trailing edge of the inner sidewall. The axial length of male step at the trailing edge of the inner sidewall may be less than about ¼ of the axial extent of the registration between the inner sidewall and the horizontal extension. The male/female interface positioned at the trailing edge of the outer sidewall may be welded. The weld comprising a butt weld such that the weld is substantially limited to the area between the outer sidewall and the outer ring along the axial length of male/female interface. The axial length of male/female interface positioned at the trailing edge of the outer sidewall may be less than about ¼ of the axial extent of the registration between the outer sidewall and the outer ring. 
         [0018]    In some embodiments, the flow splitter may include a single piece. An vertical extension of the flow splitter may have a greater outward radial height than the outward radial height of upstream interface between the outer sidewall and the outer ring. In some embodiments, the outer ring may include a solid ring and an outer carrier ring assembly. 
         [0019]    The present application further describes a nozzle assembly for a turbine that may include: a nozzle blade having inner and outer sidewalls and, in part, defining a flowpath upon assembly into the turbine; an outer ring; a flowsplitter having a horizontal extension; means for providing a mechanical engagement that includes a weld stop and a failsafe between an interface between the outer ring and the outer sidewall; and means for providing a mechanical engagement that includes a radial interlock between an interface between the inner ring and the horizontal extension. 
         [0020]    In some embodiments, the weld stop may include a backstop that determines the depth of a weld at the interface between the outer ring and the outer sidewall. The failsafe may include a mechanical stop that prevents the downstream axial displacement of the outer sidewall. In some embodiments, the means for providing a mechanical engagement that includes a weld stop and a failsafe may include either (i) a male/female interface or (ii) a female recess flanked by radially projecting male steps at both a leading edge and a trailing edge of the outer sidewall. The male/female interface may include a radial female recess on the outer sidewall that corresponds with a radial male step on the outer ring. 
         [0021]    The means for providing a mechanical engagement that includes a radial interlock may include a first male step projecting axially from the inner sidewall into the horizontal extension. The first male step may be flanked on its most outwardly radial side by a second male step projecting axially from the horizontal extension into the inner sidewall. 
         [0022]    The present application further describes a nozzle assembly for a turbine that may include: a nozzle blade having inner and outer sidewalls and, in part, defining a flowpath upon assembly into the turbine; an outer ring; a flowsplitter having a horizontal extension; means for providing a mechanical engagement that includes a radial interlock between an interface between the outer ring and the outer sidewall; and means for providing a mechanical engagement that includes a weld stop and a failsafe between an interface between the inner ring and the horizontal extension. 
         [0023]    In some embodiments, the weld stop may include a backstop that determines the depth of a weld at the interface. The failsafe may include a mechanical stop that prevents the downstream axial displacement of the outer sidewall. In some embodiments, the means for providing a mechanical engagement that includes a weld stop and a failsafe may include either (i) a male/female interface or (ii) a female recess flanked by radially projecting male steps at both a leading edge and a trailing edge of the inner sidewall. The male/female interface may include a radial female recess on the inner sidewall that corresponds with a radial male step on the horizontal extension. 
         [0024]    In some embodiments, the means for providing a mechanical engagement that includes a radial interlock may include a first male step projecting axially from the outer sidewall into the outer ring. The first mail step may be flanked on its most inwardly radial side by a second male step projecting axially from the outer ring into the outer sidewall. 
         [0025]    The present application further describes a nozzle assembly for a turbine that may include: a nozzle blade having inner and outer sidewalls and, in part, defining a flowpath upon assembly into the turbine; an outer ring; a flowsplitter having a horizontal extension; an interface between the outer ring and the outer sidewall having at least one of (i) a radial interlock; (ii) a male/female interface; or (iii) a female recess flanked by radially projecting male steps at both a leading edge and a trailing edge of the outer sidewall; and an interface between the horizontal extension and the inner sidewall having a hook and slot connection. The hook and slot connection may include a hook that extends radially from the leading edge of inner sidewall and a corresponding circumferential slot in the horizontal extension. 
         [0026]    In some embodiments, the interface between the outer ring and the outer sidewall may include a male/female interface positioned at both the leading and the trailing edge of the outer sidewall. The male/female interface positioned at the trailing edge of the outer sidewall may be welded. The weld may include a butt weld such that the weld is substantially limited to the area between the outer sidewall and the outer ring along the axial length of male/female interface. The axial length of male/female interface positioned at the trailing edge of the outer sidewall may be less than about ¼ of the axial extent of the registration between the outer ring and the outer sidewall. The outer ring may include a solid ring and an outer carrier ring assembly. 
         [0027]    These and other features of the present application will become apparent upon review of the following detailed description of the preferred embodiments when taken in conjunction with the drawings and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]      FIG. 1  is a schematic line drawing illustrating a cross-section through the first stage of a double flow steam turbine nozzle according to the prior art. 
           [0029]      FIG. 2  is a schematic line drawing illustrating a cross-section through the first stage of a double flow steam turbine incorporating a nozzle assembly in accordance with an embodiment of the present application. 
           [0030]      FIG. 3  is a schematic line drawing illustrating a cross-section through the first stage of a double flow steam turbine incorporating a nozzle assembly in accordance with an alternative embodiment of the present application. 
           [0031]      FIG. 4  is a schematic line drawing illustrating a cross-section through the first stage of a double flow steam turbine incorporating a nozzle assembly in accordance with an alternative embodiment of the present application. 
           [0032]      FIG. 5  is a schematic line drawing illustrating a cross-section through the first stage of a double flow steam turbine incorporating a nozzle assembly in accordance with an alternative embodiment of the present application. 
           [0033]      FIG. 6  is a schematic line drawing illustrating a cross-section through the first stage of a double flow steam turbine incorporating a nozzle assembly in accordance with an alternative embodiment of the present application. 
           [0034]      FIG. 7  is a schematic line drawing illustrating a cross-section through the first stage of a double flow steam turbine incorporating a nozzle assembly in accordance with an alternative embodiment of the present application. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0035]    Referring to  FIG. 1 , there is illustrated a prior art first stage nozzle assembly generally designated  10 , which, in a double flow steam turbine system, may include the nozzle assembly  10  on each side of a flow splitter  11 . Nozzle assembly  10  may include a plurality of circumferentially spaced airfoils or blades  12 , which may be welded at opposite ends between an inner band  14  and an outer bands  16 . The outer band  16  may be welded to an outer ring  20 . The inner band  14  may be welded to a horizontal extension  21  of the flow splitter  11 . The flow splitter  11  also may have a vertical extension  22  that narrows to a peak in the approximate center of an inlet steam bowl  23 . Note that the horizontal extension  21  and the vertical extension  22  generally denote conventional parts within known flow splitters  11  and are not meant to indicate specialized parts or configurations for the flow splitter  11 . With this configuration, the vertical extension  22  of the flow splitter  11  may divide the flow of steam through the inlet steam bowl  23 , directing substantially half of the flow to each of the nozzle assemblies  10 . The flow splitter  11  may be constructed such that it includes two halves that may be brought together by a bolted connection  24 . Also illustrated is a plurality of turbine blades or buckets  26  mounted on a rotor (not shown). It will be appreciated that nozzle assembly  10  in conjunction with the buckets  22  may form a stage of a steam turbine. 
         [0036]    The airfoils  12  may be individually welded in generally correspondingly shaped holes, not shown, in the inner and outer bands  14  and  16 . The inner and outer bands  14  and  16  typically extend in two segments each of about 180 degrees. After the airfoils  12  are welded between the inner band  14  and the outer band  16 , this subassembly is then welded between the outer rings  20  and the horizontal extension  21  of the flow splitter  11  using very high heat input and deep welds. For example, the inner band  14  may be welded to the horizontal extension  21  by a weld  30  from a downstream location. The weld  30  may use a significant quantity of metal filler or requires a very deep electron beam weld to make a sufficient connection. Similarly, high heat input welds  31 ,  32 , which may include substantial quantities of metal filler or very deep electron beam welds, may be required to weld the outer band  16  to the outer ring  20  at opposite axial locations (i.e., from an upstream and downstream location), as illustrated. Thus, when the airfoils  12  are initially welded to the inner and outer bands  14 ,  16  and subsequently welded to the horizontal extension  21  and the outer ring  20 , those large welds may cause substantial distortion of the flowpath, causing the airfoils to deform from their design configuration, as a result of the high heat input and shrinking of the metal material. Also, the inner and outer bands  14 ,  16  may become irregular in shape from their designed shape, further distorting the flowpath. As a result, the nozzle assemblies, through time-consuming welding and stress relief, must be reformed back to their design configuration which, as noted previously, can result in 30% of the cost of the overall construction of the nozzle assembly. Lastly, if an electron beam weld is used, it necessarily must be completed from one direction going all the way to the opposing side, which may result in a weld of up to 4 inches thick. Beside the distortion problems associated with the heat input, such a large weld of this nature may lead to inconsistencies and connective issues at the interface. 
         [0037]    Further, in regard to conventional assembly methods, as described, there are nozzle assemblies that are welded directly to the horizontal extension  21  and the outer ring  20  using a weld, generally an electron beam weld, at the interface. However, such known nozzle assemblies lack a configuration that promotes a determined weld depth at the interface. More specifically, weld depths in conventional systems often vary because the gap between the sidewalls of the nozzle singlet and rings is not consistent. As the gap becomes larger, due to machining tolerance ranges, the weld depths and properties of the weld change. A tight weld gap may produce a shorter than desired weld. A larger weld gap may drive the weld or beam deeper and may cause voids in the weld that are undesirable. In addition, current nozzle designs that include integral inner and outer sidewalls also use weld prep at the interface, which requires an undesirable higher heat input filler weld technique to be used. The higher heat may cause undesirable flowpath distortion. Further, as described, the conventional assemblies lack alignment features, which may aid in aligning the nozzle in the proper position during installation, retainment features, which may hold an installed nozzle in place in the event of a weld failure, and require time-consuming welds at both of the nozzle-horizontal extension interface and the nozzle-outer ring interface 
         [0038]    Referring now to  FIG. 2 , there is illustrated an embodiment of a first stage nozzle assembly  40  according to the present application that utilizes a first stage singlet. As used herein, a first stage singlet is a single nozzle airfoil with sidewalls or other attachment means at each end which may be attached between the horizontal extension  21  of the flow splitter  11  and the outer ring  20  directly, for example with a low heat input weld or by slide engagement or bolting. As described herein, a first stage singlet may have mechanical features providing improved reliability and risk abatement (such as a mechanical lock at the interface between the singlet and the horizontal extension  21  and/or the outer ring  20  that holds the installed singlet in place in the event of a weld failure). As further described herein, a first stage singlet may have alignment features that aid in installation and a configuration that promotes a determined weld depth at the interface between the singlet and the horizontal extension  21  and the outer ring  20 . Note also that  FIGS. 2-6  demonstrate a conventional outer ring assembly. As used herein, outer ring is defined broadly to also include solid ring or band/outer carrier ring assemblies, such as the one described in connection with  FIG. 7 . The embodiments discussed herein are able to be used with either outer ring assembly and are not so limited to the conventional outer ring assembly of  FIGS. 2-6 . 
         [0039]    Accordingly, the exemplary embodiment of the first stage nozzle assembly  40  of  FIG. 2  may include an integrally formed first stage singlet  42 , which may include a single airfoil or blade  43  between an inner sidewall  44  and an outer sidewall  46 , respectively. The airfoil  43  and sidewalls  44 ,  46  may be machined from a near net forging or a block of material. The inner sidewall  44  may insert into a slot  47  within the horizontal extension  21  of the flow splitter  11 . The upstream side of the slot  47 /inner sidewall  44  interface may include a radial interlock  48 . As used herein, radial interlock is defined as a pair of axially overlapping male steps that prohibit radial movement of the singlet. As illustrated, this may be formed by providing a male step  50  axially projecting from the inner sidewall  44  into the horizontal extension  21  and a overlapping second male step  52  axially projecting from the horizontal extension  21  into the inner sidewall  44 . The male step  52  may flank the male step  50 , and the male step  52  may be further outward radially, such that it substantially locks the inner sidewall  44  within the slot  47  and prohibits radial movement of the first stage singlet  42 . Note that when a radial interlock is positioned on the outer sidewall  46 , as discussed below in alternative embodiments, the overlapping male step of the outer ring  20  will be further inward radially than the male step of the outer sidewall  46 . The slot  47  further may include a downstream lip  58  that covers the downstream edge of the inner sidewall  44 , thus preventing the axial displacement of the inner sidewall  44  in the downstream direction. Thus, given the configuration of the slot  47 , the inner sidewall  44  may engage the horizontal extension  21  by being slid into the slot  47 . 
         [0040]    The outer sidewall  46  may insert into a slot  53  within the outer ring  20 . At the downstream side of the slot  53 , a radial male/female interface  54  may be formed, which, as described in more detail below, may provide a weld stop (which may promote a determined, shallow depth weld for the efficient attachment of the outer sidewall  46  to the outer ring  20 ) and a failsafe (i.e., a mechanical stop or retainment features that may hold the installed nozzle in place axially in the event of a weld failure). The male/female interface  54  may include a radial female recess in the outer sidewall  46  that corresponds with a radial male step on the outer ring  20 . 
         [0041]    The configuration of first stage nozzle assembly  40  may allow for the efficient installation of first stage singlet  42 , which may proceed as follows. The first stage singlet  42  may be slid into the slot  47  and, thus, engage the horizontal extension  21  through the configuration of the radial interlock  48  and the downstream lip  58 . The outer sidewall  46  then may be introduced into the outer ring  20  and the male/female interface  54  aligned. Note that the features of the slot  47  and the slot  53 , i.e., the radial interlock  48 , the downstream lip  58 , the male/female interface  54 , etc., may provide for the proper axial and radial alignment of the first stage singlet  42  during installation. 
         [0042]    The first stage singlet  42  then may be fixed into place between the horizontal extension  21  and the outer ring  20  by using a low heat input type weld  59  at the male/female interface  54 . For example, the low heat input type weld  59  may use a butt weld interface and preferably employ a shallow electron beam weld or shallow laser weld or a shallow TIG or GTAW weld process. By using these weld processes and types of welds, the weld  59  may be limited to the area between the outer sidewall  46  and outer ring  20  along the axial length of male/female interface  54 . That is, the radial offset of the male/female interface  54  results in what is essentially a “backstop” that limits the length of the weld. Thus, the weld  59  may occur for only a short, determined axial distance, and not exceed the axial length of the male/female interface  54 . The weld  59  also may proceed without the use of filler weld material. As illustrated, less than about ¼ of the axial distance spanning the outer sidewall  46  maybe used in weld  59  to weld the first stage singlet  42  to the outer ring  20 . 
         [0043]    Accordingly, by using electron beam welding in an axial direction from the downstream side of the interface between the outer sidewall  46  and the outer ring  20 , the axial extent of the weld where the materials of the outer sidewall  46  and ring  20  coalesce is less than about ¼ of the extent of their axial interface. In conventional systems that lack the weld stop of the male/female interface  54 , if an electron beam weld is used, the weld would necessarily extend throughout the full axial extent of the registration, i.e., the length of the interface, between the sidewall  46  and the ring  20 . As previously described, this may cause distortion and issues with the weld connection to arise. 
         [0044]    As illustrated, in the first stage, the singlet  42  may be supported or held in place axially by the horizontal extension  21  of the flow splitter  11 . Because of this additional axial support, the non-weld attachment made by the radial interlock  48  and the downstream lip  58  between the inner sidewall  44  and the horizontal extension  21  may be sufficient. In the other subsequent turbine stages, nozzle and inner ring assemblies are essentially cantilevered from the outer ring and, thus, undergo substantial stressing and distortion due to the high-velocity cross-flow of steam. These conditions generally make welding the inner sidewall  44  to the inner ring necessary, a practice which also is essentially done in the first stage as the inner sidewall  44  is welded to the horizontal extension  21  of the flow splitter  11 . In the first stage, though, the horizontal extension  21  is available to provide axially support to the inner sidewall  44  (which in this embodiment is accomplished by the downstream lip  58 ), which may counter-act the stresses and distortion caused by the cross-flow of steam. Thus, the added axial support provided in the first stage may allow for a sufficient non-weld connection of the first stage singlet  42 , which has been demonstrated in  FIG. 1  with the non-weld interface between the horizontal extension  21  and the inner sidewall  44 . Thus, as demonstrated in more detail in the following exemplary embodiments, the first stage single  42  may be efficiently installed by making a single weld at only on of its sidewall interfaces (as opposed to both) or, in some embodiments, by making no welds at all. 
         [0045]    Another advantage of the above-described design and assembly method is the flexibility it allows in the design of the flow splitter  11 . Generally, in conventional systems and as shown in  FIG. 1  as the weld  31 , a weld is required at the upstream interface between the outer sidewall  46  and the outer ring  20 . Because of the axial clearance required to make this weld, the outward radial height of the vertical extension  22  of the flow splitter  11  had to be less than the outward radial height of upstream interface between the outer sidewall  46  and the outer ring  20 . With the upstream weld no longer required, the axial clearance is no longer required such that the radial height of the flow splitter  21  may be increased, which may improve the flow characteristics in the inlet steam bowl  23 . In addition, because of the axial clearance required to make the upstream weld between the upstream interface between the outer sidewall  46  and the outer ring  20 , the flow splitter  11 , in conventional systems, was constructed in two parts so that the assembly of each side of the double flow system could occur separately before the flow splitter  11  was connected the by bolted connection  24 . With the upstream weld no longer required, a two piece flow splitter  11  also is no longer needed, and a single piece flow splitter (not shown) may be used. 
         [0046]    Though not illustrated, in an alternative embodiment, the attachment systems of the inner sidewall  44  and outer sidewall  46  (as depicted in  FIG. 2 ) may be interchanged. Accordingly, the interface between the outer sidewall  46  and the outer ring  20  may have the radial interlock  48  and downstream lip  58  (as described previously for the inner sidewall  44 ). And, the interface between the inner band  44  and the horizontal extension  21  may have the radial male/female interface  52  (as described previously for the outer sidewall  46 ). In such an embodiment, except for taking into account the switching of the attachment systems, the method of assembly may proceed as described above. 
         [0047]    Referring now to  FIG. 3 , there is illustrated an alternative embodiment to the present invention, a first stage nozzle assembly  70  that utilizes a first stage singlet  72 . In this embodiment, the interface at slot  53  between the outer sidewall  46  and the outer ring  20  may include radial interlocks  76 ,  78  at both the upstream and downstream side of the outer sidewall  46 . The radial interlocks  76 ,  78  may be similar to the radial interlock  48  described in relation to the embodiment of  FIG. 2 , and thus allow for a sliding engagement between the outer sidewall  46  and the outer ring  20  and, once engaged, prevent radial movement. The interface at slot  47  between the horizontal extension  21  and the inner sidewall  44  may include radial male/female interfaces  82 ,  84 . The male/female interface  82  may not be included in some embodiments. Similar to male/female interface  54 , the male/female interface  84  may provide a weld stop (which may promote a determined, shallow depth weld for the efficient attachment of the inner sidewall  44  to the horizontal extension  21 ) and a failsafe (i.e., a mechanical stop or retainment feature that may hold the installed nozzle in place axially in the event of a weld failure). The male/female interfaces  82 ,  84  may include a radial female recess in the inner sidewall  44  that corresponds with a radial male step on the horizontal extension  21 . 
         [0048]    The configuration of first stage nozzle assembly  70  may allow for the efficient installation of first stage singlet  72 , which may proceed as follows. The outer sidewall  46  of the first stage singlet  72  may be slid into the slot  53  and, thus, engage the outer ring  20  through the configuration of the radial interlocks  76 ,  78 . The inner sidewall  44  then may be introduced into the slot  47  of the horizontal extension  21  and the male/female interfaces  82  and  84  aligned. The features of the slot  47  and slot  53 , i.e., the radial interlocks  76 ,  78  and the male/female interfaces  82 ,  84  may provide for the proper axial and radial alignment of the first stage singlet  72  during installation. The first stage singlet  72  then may be fixed into place between the horizontal extension  21  and the outer rings  20  by using a low heat input type weld  86  at the male/female interface  84 , similar to that explained above for first stage singlet  42  and male/female interface  54 . In some embodiments, the weld at the male/female interface  84  may not be used such that the first stage singlet  72  is mechanically held in place by the features of the slot  47  and slot  53 . 
         [0049]    Though not illustrated, in an alternative embodiment, the attachment systems of the inner sidewall  44  and outer sidewall  46  (as depicted in  FIG. 3 ) may be interchanged. Accordingly, the interface between the outer sidewall  46  and the outer ring  20  may have the male/female interfaces  82 ,  84  (as described previously for the inner sidewall  44 ). And, the interface between the inner band  44  and the horizontal extension  21  may have the radial interlocks  76 ,  78  (as described previously for a the outer sidewall  46 ). In such an embodiment, except for taking into account the switching of the attachment systems, the methods of assembly may proceed as described above. 
         [0050]    Referring now to  FIG. 4 , there is illustrated an alternative embodiment to the present invention, a first stage nozzle assembly  100  that utilizes a first stage singlet  102 . Similar to the embodiment of  FIG. 3 , in this embodiment, the interface at slot  53  between the outer sidewall  46  and the outer ring  20  may include radial interlocks  76 ,  78  at both the upstream and downstream side of the outer sidewall  46 . As described, such an interface may allow for a sliding engagement between the outer sidewall  46  and the outer ring  20  and, once engaged, prevent radial movement. The interface at slot  47  between the horizontal extension  21  and the inner sidewall  44  may include a female recess  106  flanked or straddled by radially inwardly projecting male steps  108  at the leading and trailing edges of the inner sidewall  44 . Similar to the male/female interface  54  and  84 , the female recess  106 /male steps  108  may provide a weld stop at the trailing edge (which may promote a determined, shallow depth weld for the efficient attachment of the inner sidewall  44  to the horizontal extension  21 ) and a failsafe (i.e., a mechanical stop or retainment feature that may hold the installed nozzle in place axially in the event of a weld failure). 
         [0051]    The configuration of first stage nozzle assembly  100  may allow for the efficient installation of first stage singlet  102 , which may proceed as follows. The first stage singlet  102  may be slid into the slot  53  and, thus, engage the outer ring  20  through the configuration of radial interlocks  76 ,  78 . The inner sidewall  46  then may be introduced into the horizontal extension  21  at slot  47  and the female recess  106 /males steps  108  aligned. The features of the slot  47  and slot  53 , i.e., the radial interlocks  76 ,  78  and the female recess  106 /males steps  108 , may provide for the proper axial and radial alignment of the first stage singlet  102  during installation. The first stage singlet  102  then may be fixed into place between the horizontal extension  21  and the outer rings  20  by using a low heat input type weld  109  at the downstream edge of the inner sidewall  44 , i.e., the male step  108 /horizontal extension  21  interface at the downstream edge, similar to that explained above for first stage singlet  42  and male/female interface  54 . 
         [0052]    In some embodiments, the weld  109  at the downstream edge of the inner sidewall  44  may not be used such that the first stage singlet  102  is held in place by the mechanical features of the slot  47  and slot  53 . Further, as demonstrated in  FIG. 5 , a bolt  112  may be introduced to augment the mechanical (non-weld) connection in this alternative embodiment. The bolt  112  may be a conventional bolt for such applications. The bolt  112  may extend in a radial direction through the horizontal extension  21  of the flow splitter  11  and into the inner sidewall  44 . In some embodiments, the bolt  112  may terminate in the outer sidewall  112 . In other embodiments, as shown, the bolt  112  may extend into the airfoil  43  of the first stage singlet  102 . 
         [0053]    Alternatively, though not illustrated, in an alternative embodiment, the attachment systems of the inner sidewall  44  and outer sidewall  46  (as depicted in  FIGS. 4 and 5 ) may be interchanged. Accordingly, the interface between the outer sidewall  46  and the outer ring  20  may have the female recess  106 /male steps  108  and/or the bolt  112  (as described previously for the inner sidewall  44 ). Note, however, that in some applications the bolt  112  may be more efficiently applied through the horizontal extension  21  of the flow splitter than the outer ring  20 . And, the interface between the inner band  44  and the horizontal extension  21  may have the radial interlocks  76 , 78  (as described previously for the outer sidewall  46 ). In such an embodiment, except for taking into account the switching of the attachment systems, the method of assembly may proceed as described above. 
         [0054]    Referring now to  FIG. 6 , there is illustrated an alternative embodiment to the present invention, a first stage nozzle assembly  120  that utilizes a first stage singlet  122 . Similar to the embodiment of  FIG. 4 , the interface at slot  47  between the horizontal extension  21  and the inner sidewall  44  may include a female recess  106  flanked or straddled by radially inwardly projecting male steps  108  at the leading and trailing edges of the inner sidewall  44 . The female recess  106 /males steps  108  may provide a weld stop (which may promote a determined, shallow depth weld for the efficient attachment of the inner sidewall  44  to the horizontal extension  21 ) and a failsafe (i.e., a mechanical stop or retainment feature that may hold the installed nozzle in place axially in the event of a weld failure). In the embodiment of  FIG. 6 , the interface at slot  53  between the outer sidewall  46  and the outer ring  20  may be similar to that described for the embodiment of  FIG. 2 . Accordingly, at the downstream side of the slot  53 , the radial male/female interface  54  may be formed, which may provide a weld stop (which may promote a determined, shallow depth weld for the efficient attachment of the outer sidewall  46  to the outer ring  20 ) and a failsafe (i.e., a mechanical stop or retainment features that may hold the installed nozzle in place axially in the event of a weld failure). The male/female interface  54  may include a radial female recess in the outer sidewall  46  that corresponds with a male step on the outer ring  20 . 
         [0055]    The configuration of first stage nozzle assembly  120  may allow for the efficient installation of first stage singlet  122 , which may proceed as follows. The first stage singlet  122  may be placed into the slot  53  and the male/female interface  54  aligned. The inner band  46  may be introduced into the horizontal extension  21  at slot  47  and the female recess  106 /males steps  108  aligned. The features of the slot  47  and slot  53 , i.e., the male/female interface  54  and the female recess  106 /males steps  108 , may provide for the proper axial and radial alignment of the first stage singlet  122  during installation. The first stage singlet  122  then may be fixed into place between the horizontal extension  21  and the outer rings  20  by using the low heat input type weld  109  at the downstream edge of the female recess  106 /males steps  108  interface and the low heat input type weld  59  at male/female interface  54  in the manner described above. 
         [0056]    Alternatively, though not illustrated, in alternative embodiment, the attachment systems of the inner sidewall  44  and outer sidewall  46  (as depicted in  FIG. 6 ) may be interchanged. Accordingly, the interface between the outer sidewall  46  and the outer ring  20  may have the female recess  106 /male steps  108  (as described previously for the inner sidewall  44 ). And, the interface between the inner band  44  and the horizontal extension  21  may have the radial male/female interface  54  (as described previously for the outer sidewall  46 ). In such an embodiment, except for taking into account the switching of the attachment systems, the assembly may proceed as described above. 
         [0057]    Referring now to  FIG. 7 , there is illustrated an alternative embodiment to the present invention, a first stage nozzle assembly  150  that utilizes a first stage singlet  152 . At the outer sidewall  46 , this embodiment demonstrates how the current concepts also may be used with band/ring construction, which may include a solid band or ring  156  fitted within an outer carrier ring  157 . Band/ring construction may include an interface between the outer sidewall  46  and the solid ring  156 , which may be similar to the interface made between the outer sidewall  46  and the outer ring  20  in the embodiments discussed above. 
         [0058]    As illustrated, the interface between the outer sidewall  46  and the solid ring  156  may include a male/female interfaces  162 ,  163  at both the leading and trailing edges of the outer sidewall  46 . In some embodiments, only one of the male/female interfaces may be used. Similar to male/female interface  54 , the male/female interfaces  162 ,  163  may provide a weld stop (which may promote a determined, shallow depth weld for the efficient attachment of the inner sidewall  44  to the horizontal extension  21 ) and a failsafe (i.e., a mechanical stop or retainment feature that may hold the installed nozzle in place axially in the event of a weld failure). The male/female interfaces  162 ,  163  may include a radial female recess in the outer sidewall  46  that corresponds with a radial male step on the solid ring  156 . 
         [0059]    The interface between the inner sidewall  44  and the horizontal extension  21  may include a hook and slot connection  166 . The hook and slot connection  166  may include a hook  168  that extends radially from the leading edge of inner sidewall  44 . A narrow circumferential slot  170  may be formed in the horizontal extension  21  of the flow splitter  11 . The slot  170  may be sized such that it may be engaged by the hook  168 . 
         [0060]    The configuration of first stage nozzle assembly  150  may allow for the efficient installation of first stage singlet  152 , which may proceed as follows. The hook  168  of the inner sidewall  44  may be inserted into the slot  170 . The outer sidewall  46  then may align with the solid ring  156  such that males step  160 /female recesses  162  are aligned. The hook and slot connection  166  and the males step  160 /female recesses  162  may provide for the proper axial and radial alignment of the first stage singlet  102  during installation. The first stage singlet  102  then may be fixed into place between the horizontal extension  21  and the solid ring  156 /outer carrier ring  157  by using a low heat input type weld  175  at the downstream edge of the interface between the solid ring  156  and the outer sidewall  46 , similar to the welding process explained above. Note that the hook and slot connection may be used opposite the other attachment systems described above and is not limited to being used opposite band/ring construction or the specific interface construction described in relation to the embodiment of  FIG. 7 . 
         [0061]    From the above description of preferred embodiments of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims. Further, it should be apparent that the foregoing relates only to the described embodiments of the present application and that numerous changes and modifications may be made herein without departing from the spirit and scope of the application as defined by the following claims and the equivalents thereof.