Abstract:
A steam turbine nozzle airfoil with integral inner and outer sidewalls is engaged with an inner ring and an outer ring in a nozzle assembly. Previous designs required large clearances between radial surfaces to permit simultaneous circumferential loading of the inner and outer sidewall into the inner and outer rings. The inventive arrangement provides for breech loading of the inner sidewall into the inner ring which allows near line-to-line radial contact on the hooks between the rings and the integral sidewalls of the Singlet nozzle airfoil. Tighter radial clearance overcome problems with loose assembly such as movement during welding, gaps leading to stress risers and performance issues associated with nozzle throat control.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates generally to steam turbines and more specifically to the arrangement of nozzle assemblies for a breech loaded assembly. 
     Steam turbines typically include static nozzle segments that direct the flow of steam into rotating buckets that are connected to a rotor. In steam turbines, the nozzle, including the airfoil or blade construction, is typically called a nozzle assembly or diaphragm stage. 
     Conventional diaphragm stages are constructed principally using one of two methods. A first method uses a band/ring construction wherein the airfoils are first welded between inner and outer bands extending circumferentially about 180 degrees. Those arcuate bands with welded airfoils are then assembled, i.e., welded between the inner and outer rings of the stator of the turbine. The second method often consists of airfoils welded directly to inner and outer rings using a fillet weld at the interface. The latter method is typically used for larger airfoils where access for creating the weld is available. 
     There are inherent limitations using the band/ring method of assembly. A principle limitation in the band/ring assembly method is the inherent weld distortion of the flowpath, i.e., between adjacent blades and the steam path sidewalls. The weld used for these assemblies is of considerable size and heat input. Alternatively, the welds are very deep gas metal arc welds (GMAW or MIG), or electron beam welds without filler metal. This material or heat input causes the flow path to distort e.g., material shrinkage causes the airfoils to bow out of their designed shaped in the flow path. In many cases, the airfoils require adjustment after welding and stress relief. The result of this steam path distortion is reduced stator efficiency. The surface profiles of the inner and outer bands can also change as a result of welding the nozzles into the stator assembly further causing an irregular flow path. The nozzles and bands thus generally bend and distort. This requires substantial finishing of the nozzle configuration to bring it into design criteria. Also, methods of assembly using single nozzle construction welded into rings do not have determined weld depth, lack assembly alignment features on both the inner and outer ring, and also lack retention features in the event of a weld failure. 
     Steam turbine nozzles may be provided as singlets. Burdgick et al. (U.S. Pat. No. 7,427,187) introduced a steam turbine nozzle singlet  105  having an airfoil  106  with integral inner sidewall  102  and outer sidewall  104  as shown in  FIG. 1 . SINGLET® nozzle assembly is a registered trademark of the General Electric Co. and will herein after be referred to as Singlet airfoil or Singlet nozzle assembly. The airfoil  106  and sidewalls  102 ,  104  may be machined, for example, from a near net forging or a block of material. The inner ring  102  may include a step  136 , which is received in complementary recess  138  of inner sidewall  102 . The outer sidewall  135  may include a step  136 , which is received in complimentary recess  138  of outer ring  135 . Alternative arrangements of steps and recesses may be formed between the sidewalls and the rings. The interfaces  101  between the sidewall  115  and inner ring  102  and the interfaces  104  between the sidewall  135  and outer ring  104  are stopped by each side of steps  136 , limiting length of weld and enabling axially short, low heat input welds e.g., e-beam welds. These complementary steps  136  and recesses  138  mechanically interlock the singlet  105  between the inner ring  115  and the outer ring  135 , preventing displacement of the singlet in the event of weld failure. The low heat input welds minimize or eliminate distortion of the nozzle flow path. 
     The arrangement of Burdgick et al. (U.S. Pat. No. 7,427,187) however, includes some disadvantages. A weld, albeit low heat input, must be performed on each of the leading edge  118  and the trailing edge  119  interfaces  103  for the outer sidewall  135  with the outer ring  104  and at the interface  101  of the inner sidewall  115  and the inner ring  102 . Access must be available to the leading edge  118  and the trailing edge  119  of both interfaces  101 ,  103  for the welds. Based on the axial dimension of the inner ring and the outer ring, the corresponding axial dimension of the inner sidewall and outer sidewalls may need to be comparably sized to have access at the leading and trailing edges for welds at both locations. Large axial dimensions of the rings would dictate large axial sidewalls that would require a large block of material for the singlet be supplied and that significant machining be applied for a given nozzle size, resulting in added cost and time. 
     Burdgick et al. (US 2010/0252934) disclosed a Singlet nozzle assembly  205  for a turbine, as illustrated in  FIG. 2 . The Singlet nozzle assembly  205  includes a Singlet airfoil  206  with integral inner sidewall  215  and outer sidewall  235 , and an inner ring  202  and an outer ring  204 . Each of these sidewalls and rings are coupled together at an interface through a combination of a mechanical interconnection on one end and a welded connection on the other end. The mechanical interconnection includes either the sidewalls  215 ,  235  or the rings  202 ,  204  having a protruding hook  220  and the other having a corresponding hook recess  222 . In  FIG. 2 , the hooks  220  are shown on the sidewalls  215 ,  235 . The interface can also include an axial stop  250  and a radial mechanical stop  255 . The configuration may further include one or more surfaces at an interface between a ring and a sidewall angled away from the interface to form a narrow groove (not shown). The configuration further may include a ring with a consumable root portion (not shown). 
     More specifically, the axial positioning and failsafe stop  250  on the radial interface between outer sidewall  235  and the associated outer ring  204 , and a single weld at the trailing edge  219  interface  207  between each sidewall and the associated ring are provided. The axial positioning and failsafe stop is formed by a radially projecting ledge  251  of the outer ring  204 . The axial positioning feature at the sidewalls establishes a length of a trailing edge weld along the interface  203 . The same inward projecting ledge  251  of the outer ring  204  acts as the failsafe feature preventing axial downstream movement of the nozzle airfoil  206  towards the associated downstream rotor blade (not shown) in the event of failure of the trailing edge weld. The radial interfaces may further include a radial positioning and shrinkage stop  255  in proximity to the trailing edge  219  of the interface  203 . The radial stop surface of the ring sets the radial positioning of the sidewall relative to the outer ring  204 . Further, because the radial stop positions the sidewall relative to the ring, weld shrinkage in the radial weld space at the trailing edge cannot change the radial positioning of the sidewall relative to the ring, because the positioning is fixed by the shrinkage stop. 
     With the arrangement as described above, employing Singlet nozzle assemblies  205  with airfoils  206  including integral inner sidewall  202  and outer sidewalls  204  and an upstream facing hook  245  on the inner sidewall and outer sidewall, and axial and radial stops for the outer sidewall to outer ring interface, simultaneous circumferential loading of the Singlets nozzle  225  into the outer and inner rings has been required. The inner ring and the outer ring are positioned concentrically with the inner ring fixedly positioned symmetrically with respect to the outer ring. Singlet airfoils are sequentially loaded circumferentially into the assembly with the inner sidewall sliding within the recess of the inner ring and the outer sidewall sliding within the recess of the outer ring. Because the radial surfaces of the inner sidewall must slide circumferentially with respect to the radial surfaces of the inner ring and at the same time the radial surfaces of the of the outer sidewall must slide circumferentially with respect to the radial surfaces of the outer ring, this arrangement could not be designed with tight radial gaps between the rings and the singlet sidewalls. Currently large radial gaps must be provided at these interfaces to assemble the nozzles in a circumferential direction into the hooks of both the inner ring and the outer ring simultaneously. These gaps may be required to be greater than 0.01 inch. 
     Gaps of such size raise concerns about the integrity of the fit. A first concern is with having a loose assembly. The gaps may allow for movement of the singlet nozzle during welding and may not allow all of the nozzle hook interfaces to be in contact in a cold condition. The gaps will lead to stress risers in the design. Also, the gaps may allow the nozzle assembly to move downstream until contact is made with the hooks. Additionally, the nozzle torque may allow the nozzles to twist and move in the circumferential direction until the hooks are loaded. This causes stress issues and also nozzle aerodynamic performance issues as the nozzle throat can change. 
     Accordingly, it would be desirable to provide an arrangement for a nozzle assembly for singlet nozzles with integral inner and outer sidewalls where the singlet nozzles can be easily loaded between the rings and at the same time maintain tight radial clearances at the sidewall to ring interfaces. Additionally, it would be desirable to improve turbine performance through improved airfoil tolerances and throat control. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Briefly in accordance with one aspect of the present invention, a nozzle assembly for a turbine is provided. The nozzle assembly includes at least one airfoil having an integral inner sidewall and an integral outer sidewall. An inner ring is mechanically coupled to the inner sidewall at an interface including an upstream side interface and a downstream side interface where the upstream side interface includes either a hook interface or a weld interface and where the downstream side interface includes the other of a hook interface or a weld interface. An outer ring is mechanically coupled to the outer sidewall at an interface including an upstream side interface and a downstream side interface where the upstream side interface includes either a hook interface or a weld interface and where the downstream side interface includes either the other of a hook interface or a weld interface. 
     The hook interface between the outer ring and outer sidewall may be formed with either a projection or a complimentary recess on the upstream face of the outer sidewall wherein the downstream face of the outer ring includes the other of the projection and the complimentary recess. The hook interface between the inner ring and inner sidewall may be formed with either a projection or a complimentary recess on the upstream face of the inner sidewall wherein the downstream face of the inner ring includes the other of a projection and the complimentary recess. A mechanical radial stop is provided at the interface of the outer sidewall and the outer ring, where the mechanical radial stop configured to maintain the airfoil in a correct radial position. Near line-to-line contact is provided on at least one radial surface of the interface between the outer sidewall and the outer ring and on at least one radial surface of the interface between the inner sidewall and the inner ring. 
     According to another aspect of the present invention, a method is provided for loading a nozzle assembly with airfoils that include an integrated inner sidewall and outer sidewall, where each of the interfaces between inner sidewall and the inner ring and between the outer sidewall and the outer ring include a forward hook and recess on the upstream side of the nozzle assembly. The method includes positioning the outer ring to accept the outer sidewall for each of a plurality of airfoils. The method then includes circumferentially loading the outer ring with the outer sidewall of each of the plurality of airfoils. The method then provides for positioning the inner ring to engage with the inner sidewall of each of the plurality of airfoils. The method further includes engaging a recess of the inner sidewall of each of the plurality of airfoils with a projection of the outer ring. 
     A further aspect of the present invention provides a steam turbine comprising a nozzle assembly including a radial outer ring configured to extend substantially circumferentially within the steam turbine, a radial inner ring configured to extend substantially circumferentially within the steam turbine, and one or more nozzle airfoils with integral outer sidewall and integral inner sidewall extending substantially radially between the inner ring and the outer ring. The inner ring is mechanically coupled to the inner sidewall at an interface including an upstream side interface and a downstream side interface where the upstream side interface includes either a hook interface and a weld interface and where the downstream side interface includes the other of a hook interface and a weld interface. The outer ring is mechanically coupled to the outer sidewall at an interface including an upstream side interface and a downstream side interface where the upstream side interface includes either a hook interface and a weld interface and where the downstream side interface includes the other of a hook interface and a weld interface. 
     The hook interface between the outer ring and outer sidewall is formed with either a projection and a complimentary recess on the outer sidewall where the outer ring includes the other of the projection and the complimentary recess. The hook interface between the inner ring and inner sidewall being formed with either a projection and a complimentary recess on the inner sidewall wherein the inner ring includes the other of the projection and the complimentary recess. A mechanical radial stop at the interface of at least one of the inner sidewall with the inner ring and the outer sidewall and the outer ring. The mechanical radial stop is configured to maintain the airfoil in a correct radial position. Near line-to-line contact is provided on at least one radial surface of the interface between the outer sidewall and the outer ring and on at least one radial surface of the interface between the inner sidewall and the inner ring. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  illustrates a prior art Singlet nozzle arrangement for a steam turbine; 
         FIG. 2  illustrates a prior art Singlet nozzle arrangement for a steam turbine with circumferential loading of the airfoil sidewall into the inner and outer rings where the inner and outer sidewalls include a forward hook; 
         FIG. 3  schematically illustrates an exemplary opposed flow steam turbine; 
         FIG. 4  schematically illustrates an exemplary nozzle assembly that may be used with the steam turbine illustrated in  FIG. 3 ; 
         FIG. 5  illustrates an embodiment for the inventive arrangement for nozzle assemblies allowing for breech loading of the inner ring to the inner sidewalls; 
         FIG. 6  illustrates another embodiment for the inventive arrangement for nozzle assemblies allowing for breech loading of the inner ring to the inner sidewalls; 
         FIG. 7  illustrates an expanded view of an outer sidewall for the inventive arrangement for nozzle assemblies; 
         FIG. 8  illustrates an embodiment for the inventive arrangement of nozzle assemblies that include a narrow groove at a downstream interface of the sidewall and ring for a MIG weld; 
         FIG. 9  illustrates an axial view of an outer ring, a Singlet nozzle, inner sidewall and inner ring arranged in preparation for assembly; 
         FIG. 10  illustrates the outer sidewall of Singlet nozzle swung into the outer ring forward hook of outer sidewall engaging complimentary outer ring recess; 
         FIG. 11  illustrates the inner ring positioned for loading to engage inner sidewall of Singlet nozzle; 
         FIG. 12  illustrates the forward hook projection of inner sidewall inserted within recess of inner ring; 
         FIG. 13  illustrates the inner ring lowered to engage forward hook projection into hook recess of inner ring; 
         FIG. 14  illustrates a flow chart for a method of breech loading embodiments of the inventive arrangement for nozzle assemblies; and 
         FIG. 15  illustrates a half of an inventive embodiment for Singlet nozzle assembly for steam turbine. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following embodiments of the present invention have many advantages, including providing an arrangement and method for fabrication of nozzle assemblies with Singlet nozzles that require only low heat input welding with welds being made on only the downstream trailing edge interface of the sidewalls and rings, thereby reducing weld distortion effects. With the limited welded configurations and avoidance of need for post-weld adjustment and simplified construction, the costs for the nozzles will also be lowered. The arrangement allows for breech loading of the singlets between the outer and inner rings to form the nozzle assembly. By avoiding the need for simultaneous circumferential loading of the singlets, significantly tighter dimensional constraints may be placed on radial interface surfaces between the sidewalls and rings. Tighter dimensional constraints, reduced misalignment and avoidance of weld distortion effects lead to improved adherence to design tolerances of nozzle shape and flow clearances, enhancing nozzle performance. 
     Incorporation of a successful hooked and welded design that eliminates the necessity to machine significant material off the individual Singlet nozzles, further helps to keep the design economical. Yet further, assembly can be done without the need for specialized fixtures, reducing assembly time and costs. 
       FIG. 3  is a schematic illustration of an exemplary opposed-flow steam turbine  10  that may include nozzle assembly configurations of the present invention. Turbine  10  includes first and second low-pressure (LP) sections  12  and  14 . Each turbine section  12  and  14  includes a plurality of stages of nozzle assemblies (not shown in  FIG. 1 ). A rotor shaft  16  extends through sections  12  and  14  along radial centerline  15 . Each LP section  12  and  14  includes a nozzle  18  and  20 . A single outer shell or casing  22  is divided along a horizontal plane and axially into upper and lower half sections  24  and  26 , respectively, and spans both LP sections  12  and  14 . A central section  28  of shell  22  includes a low-pressure steam inlet  30 . Within outer shell or casing  22 , LP sections  12  and  14  are arranged in a single bearing span supported by journal bearings  32  and  34 . A flow splitter  40  extends between first and second turbine sections  12  and  14 . Although  FIG. 1  illustrates a double flow low pressure turbine, as will be appreciated by one of ordinary skill in the art, the present invention is not limited to being used with low-pressure turbines and can be used with any double flow turbine including, but not limited to intermediate pressure (IP) turbines or high pressure (HP) turbines. In addition, the present invention is not limited to being used with double flow turbines, but rather may be used with single flow steam turbines as well, for example. 
     During operation, low-pressure steam inlet  30  receives low-pressure/intermediate temperature steam  50  from a source, for example, an HP turbine or IP turbine through a crossover pipe (not shown). The steam  50  is channeled through inlet  30  wherein flow splitter  40  splits the steam flow into two opposite flow paths  52  and  54 . More specifically, the steam  50  is routed through LP sections  12  and  14  wherein work is extracted from the steam to rotate rotor shaft  16 . The latter stages  52 ,  54  in the steam flow path may be called margin stages and include the inventive nozzle assemblies (not shown). Such a steam turbine may include the inventive nozzle assemblies (not shown). The steam exits LP sections  12  and  14  and is routed, for example, to a condenser or other heat sink (not shown). 
       FIG. 4  is an enlarged schematic front view of an exemplary nozzle assembly  100  that may be used with steam turbine  10  (shown in  FIG. 1 ). In one embodiment, nozzle assembly  100  may be a last stage nozzle assembly of steam turbine  10 . The nozzle assembly  100  includes an annular inner ring  102 , an annular outer ring  104 , and a plurality of Singlet nozzle airfoils  106 , with integral inner and outer sidewalls (not shown), extending there-between. Outer ring  104  is radially outward of, and substantially concentrically aligned with, inner ring  102 . Nozzle airfoils  106  are spaced circumferentially between rings  102  and  104  and each extends substantially radially between inner and outer rings  102  and  104 , respectively. A radially outer surface  110  of inner ring  102  and a radially inner surface  112  of outer ring  104  define radially inner and radially outer boundaries of a steam flowpath defined through nozzle assembly  100 . 
       FIG. 5  illustrates a mechanical arrangement of an embodiment of an inventive nozzle assembly according to the present invention. Prior art Singlet type designs, described previously that rely on simultaneous circumferential loading into the inner and outer rings of the nozzle assembly, cannot be assembled with small radial gaps between the rings and sidewalls of the Singlet assemblies. The present inventive breech loaded (axial assembly) design allows for near line-to-line contact on the hooks between the rings and singlet interface. Here, outer sidewall  335  of Singlet nozzle  325  is shown engaged with outer ring  304  during assembly. Forward hook  330  of outer sidewall  335  is inserted in complimentary recess  331  of the outer ring  304 . Interface  303  between outer sidewall  335  and outer ring  304  mate under the weight of the Singlet nozzle  325 . 
     Inner ring  302  is shown positioned to mate with inner sidewall  315 . Inner sidewall  315  includes forward projection  340  including forward hook  345 . A length of forward projection  340  is length  341 . Inner sidewall also includes center recess  342  and end projection  343  with surface  344 . Inner ring  302  includes central recess  360  with partially enclosed hook engagement recess  361 . Recess  360  is set between inner ring projection  362  with hook retainer  364  and inner ring projection  363 . The entrance  365  to recess  360  is sized to accept length  341  of forward projection  340 . When inner ring  302  is moved to engagement with inner sidewall  315 , forward projection  340  is inserted through entrance  365  to recess  360 , projection  363  on inner ring  302  enters recess  342  of inner sidewall, and surface  344  on inner sidewall contacts surface  366  on inner ring. Hook recess  361  of inner ring is sized to accept forward hook  345  of inner sidewall when the engaged inner ring is then moved to insert the forward hook. The above-described mechanical arrangement permits the simultaneous breech loading of the inner ring onto all the Singlet nozzles  325  associated with the half ring. 
     A breech loading arrangement is also available, as illustrated in  FIG. 6 , where a forward hook is provided on the inner ring and a hook recess is provided on the inner sidewall. Here, outer sidewall  435  of Singlet nozzle  425  is shown engaged with outer ring  404  during assembly. Forward hook  430  of outer ring  404  is inserted in complimentary recess  431  of the outer sidewall  435 . Interface  403  between outer sidewall  435  and outer ring  404  mate under the weight of the Singlet nozzle  425 . 
     Inner ring  402  is shown positioned to mate with inner sidewall  415 . Inner ring  402  includes forward projection  440  including forward hook  445 . A length of forward projection  440  is length  441 . Inner ring  402  also includes center recess  442  and end projection  443  with surface  444 . Inner sidewall  415  includes central recess  460  with partially enclosed hook engagement recess  461 . Recess  460  is set between inner sidewall projection  462  with hook retainer  464  and inner sidewall projection  463 . The entrance  465  to recess  460  is sized to accept length  441  of forward projection  440 . When inner ring  402  is moved to engagement with inner sidewall  415 , forward projection  440  is inserted through entrance  465  to recess  460 , projection  463  on inner sidewall  415  enters recess  442  of inner ring, and surface  444  on inner ring contacts surface  466  on inner sidewall. Hook recess  461  of inner sidewall is sized to accept forward hook  445  of inner ring when the engaged inner ring is then lowered to insert the forward hook. The above-described mechanical arrangement permits the simultaneous breech loading of all the Singlet nozzles  425  onto the inner ring  402 . A method for Singlet nozzles into the outer ring and inner ring will later be described in greater detail. 
     The present inventive embodiment maintains advantageous elements of previous interfaces for Singlet nozzle  325  with integral inner sidewall and outer sidewall.  FIG. 7  illustrates an expanded view of the outer sidewall  325  to outer ring  304  interface. The upstream face of the outer sidewall includes forward hook  330 . These features also include radial mechanical positioning and shrinkage stop  355  and the axial positioning and failsafe stop  357 . The radial stop and axial stop can be implemented regardless of the chosen weld configuration, as this hook and weld arrangement may incorporate various low heat input welding techniques. The radial positioning feature accurately locates the part in the correct radial position during welding while also providing accurate axial placement without the need for an axial assembly fixture. The axial positioning feature at the sidewalls establishes a length of a trailing edge weld  310  along the interface  303  thereby determining the axial weld length. Trailing edge weld  310  for this embodiment may be an electron beam weld (EBW). The same inward projecting ledge  380  of the associated ring acts as the failsafe feature preventing axial downstream movement of the nozzle blade towards the associated downstream rotor blade in the event of failure of the trailing edge weld. The radial stop of the ring sets the radial positioning of the sidewall relative to the ring. Further, because the radial stop positions the sidewall relative to the ring, weld shrinkage in the radial weld space at the trailing edge cannot change the radial positioning of the sidewall relative to the ring, because the positioning is fixed by the shrinkage stop. Prior art configurations could cause distortion or movement in the radial direction during welding based on shrinkage and the solidification rate of the weld. Prior art configurations could also cause the nozzle to tilt front to back while welding. 
     Near line-to-line contact is provided at inner radial interface of surface  332  of outer ring  304  and surface  333  of outer sidewall  335  at hook  330 . Near line-to-line contact is provided at radial stop  355  interface of surface  358  of outer ring  304  and surface  359  of outer sidewall  335 . Near line-to-line contact between opposing surfaces of the hook and between opposing surfaces of radial stop may be taken to mean nominal dimension of the opposing surfaces are the same. Near line-to-line contact is also provided at interface  565  ( FIG. 13 ) between outer surface of the hook  540  of inner sidewall  502  and opposing surface  564  ( FIG. 12 ) of the inner ring  515 . A slight gap of about 0.002 is provided for opposing surfaces at the radial stop  570  ( FIG. 13 ) between inner sidewall  515  and inner ring  502 . 
     The inventive arrangement for the singlet uses a mechanical hook interface and a welded interface on each side of the steam path. That is both the hook and the weld are on the outer sidewall to outer ring interface and on the inner sidewall to inner ring interface. This arrangement further aids in improving the manufacturability of the Singlet nozzle assembly, while minimizing the amount of distortion introduced into the part during welding. Additionally, the hood and weld arrangement aids in improving the assembly and cost of the product by reducing the fixturing required to assemble the design prior to welding. The hook on the steam entrance side (upstream face) of the sidewall keeps the nozzle positioned radially as it is assembled and helps in containing the nozzle when pressure is applied while the nozzles are stacked in the assembly prior to welding. During manufacture of the nozzle assembly when the (downstream) opposing side is welded, the weld will tend to shrink. Radial shrinkage on the downstream side will tend to radially lift the upstream side of the sidewall with the hook. However, the hook further assists in the manufacture of the nozzle assembly by holding the nozzle in place while the downstream side is welded. Further, the hook allows for more determinant stress concentration K t  factors, as compared to a sharp discontinuity that is caused when welding at the same interface. The moment on the nozzle is typically downstream which causes a tensile force on the weld. The present arrangement allows the force to be transferred via. a hook (forward hook), which known stress concentrations factors. This will ease in the engineering cycle and improve the fatigue life of the part. The downstream weld is typically in compression that allows for less concern with the weld Kt. 
     The hook and weld arrangement is intended to be used with welding processes that are considered to be of lower heat input, e.g. electron beam welding (EBW), laser beam welding (LBW), tungsten inert gas (TIG) (GTAW) or gas metal inert (MIG) (GMAW) welding. The TIG weld process may include 1) a narrow groove TIG weld process using either hot or cold wire automated feed using either a one-sided or two-sided J prep, 2) a consumable at the root weld and/or fixture stop, 3) weld discontinuity in the vertical direction as opposed to the horizontal direction that would have then been in-line with the force acting on the weld. 
       FIG. 8  illustrates an embodiment for the inventive arrangement of nozzle assemblies that include a one-sided narrow groove weld prep at a downstream interface of the sidewall and ring for a MIG weld. 
     The advantage of the axial mechanical stop is that it creates a built-in weld stopper for an EBW weld and moves the unwelded interface (crack starter) 90 degrees to the direction main part strains for the root weld of the TIG or MIG designs. The designs have been illustrated with female fit shown on the rings, but that fit can be moved to the Singlet (male fit) depending on manufacturing preference. The MIG configurations provide a weld preparation that minimized the weld and heat input while still maintaining structural integrity. 
       FIGS. 9-13  illustrate a method for loading the singlet nozzles into inner and outer rings for a nozzle assembly according to the present invention.  FIG. 14  illustrates a flowchart for loading of Singlet nozzles into inner and outer rings according to the present invention. 
       FIG. 9  illustrates an axial view of an outer ring  504 , a Singlet nozzle  525  including airfoil  506  with integral outer sidewall  535  and inner sidewall  515  and inner ring  502  arranged in preparation for assembly. Upstream surface  508  of the outer ring and leading edge  518  of the airfoil  506  are on top. Outer ring  504  is fixed  510  in place to maintain orientation during assembly. The outer ring recess  538  is oriented in a horizontal plane for accepting forward hook  530  of the outer sidewall  535 . The hook recess  531  of the outer ring is positioned to face downward. The Singlet nozzle  525  is then tilted  511  slightly to facilitate a slight swing entrance of forward hook  530  into complimentary recess  531  of outer ring  504 . 
       FIG. 10  illustrates the outer sidewall  535  of Singlet nozzle  525  swung  512  into the outer ring  504  with forward hook  530  of outer sidewall engaging complimentary outer ring recess  531  and seating outer sidewall recess on outer sidewall projection  556  which forms the axial stop  557 . Here the axial stop  557  supports the Singlet nozzle during loading and subsequent welding of downstream interface  503 . Outer sidewall  535  for the Singlet nozzles are sequentially loaded at the end entrance of the outer ring  504  and moved in the circumferential direction until the nozzles are in proper place with the outer ring fully loaded. 
       FIG. 11  illustrates the inner ring  502  positioned for loading to engage inner sidewall  515  of Singlet nozzle  525 . The inner ring  502  is positioned to establish vertical alignment of the forward hook projection  540  of inner sidewalls  515  of the Singlet nozzle  525  held in outer ring  504 . The inner ring  502  is then translated horizontally to insert the inner sidewall front hook projection  540  into inner ring recess  560 .  FIG. 12  illustrates the forward hook projection  540  of inner sidewall  502  inserted within recess  560  of inner ring  502 . Projection  563  of inner ring  502  is inserted within recess  542  of inner sidewall. Radial weld surface  544  of inner sidewall  515  and interface surface  566  of outer ring  502  are aligned.  FIG. 13  illustrates the inner ring  502  lowered  514  ( FIG. 12 ) to engage forward hook projection  540  into hook recess  561  of inner ring  502 . This assures a very tight assembly that leads to negligible movement of the parts before or after welding downstream interfaces  103 . 
       FIG. 14  illustrates a flow chart for breech loading Singlet nozzles with integral inner and outer rings with near line-to-line contact on radial surfaces into outer and inner rings. Step  610  fixedly positions outer ring so recess opening of outer ring is faced by complimentary outer sidewall of Singlet Nozzle. Step  620  tilts forward hook of outer sidewall of singlet nozzle toward recess opening of outer ring. Step  630  swings outer sidewall of Singlet nozzle into recess of outer ring. Step  640  circumferentially slides outer sidewall of Singlet nozzle into circumferential position within recess of outer ring. Step  650  repeats loading of outer sidewall with other Singlet Nozzles. Step  660  positions inner ring with central recess vertically aligned with forward hook projections of sidewalls for loaded singlet nozzles. Step  670  translates inner ring toward inner sidewalls so forward hook projections of inner sidewall for loaded Singlet nozzles enter opposing central recesses of inner sidewalls. Step  680  lowers inner ring so forward hook projections of inner sidewall for loaded Singlet Nozzles enter complimentary hook recesses of inner ring. Step  690  welds downstream interface surfaces of outer sidewall to outer ring and downstream interfaces surfaces of inner sidewall and inner ring using low heat input weld techniques. 
       FIG. 15  illustrates a half ring of a Singlet nozzle assembly for a steam turbine. Singlet nozzle assembly  590  includes inner ring  502 , outer ring  504  loaded with Singlet nozzles  125  including integral inner sidewall  515  and outer sidewall  535 . 
     While various embodiments are described herein, it will be appreciated from the specification that various combinations of elements, variations or improvements therein may be made, and are within the scope of the invention.