Patent Publication Number: US-8118550-B2

Title: Turbine singlet nozzle assembly with radial stop and narrow groove

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This patent application relates to commonly-assigned U.S. patent application Ser. No. 12/402,081 entitled “TURBINE SINGLET NOZZLE ASSEMBLY WITH MECHANICAL AND WELD FABRICATION”, filed concurrently with this application. 
     FIELD OF THE INVENTION 
     The invention relates generally to turbine technology. More particularly, the invention relates to a turbine singlet nozzle assembly design with a radial stop and a narrow groove for weld preparation. 
     BACKGROUND OF THE INVENTION 
     Turbines, including gas or steam turbines, include nozzle assemblies that direct a flow of steam or gas into rotating blades that are coupled to a rotating shaft so as to cause the rotating shaft to turn. One configuration for the nozzle assemblies includes a singlet design, including a blade, or airfoil, between inner and outer sidewalls, with the sidewalls coupled to an inner and outer ring, respectively, and with a mechanical axial stop at the interface between the sidewalls and the rings. 
     Current methods of fabricating these singlet nozzle assemblies require welding the various parts of the nozzle assembly together across the interface of sidewalls and rings. However, certain welding technologies can introduce large amounts of heat, along with significant amounts of weld filler material, that can distort the parts of the singlet nozzle being welded. Therefore, lower heat weld types such as shallow electron beam welds, shallow laser welds are typically used, while higher heat weld types such as gas tungsten arc welds (GTAW) (also known as tungsten inert gas (TIG) welding) and gas metal arc welds (GMAW) (also known as metal inert gas (MIG) welding) are not preferred as they may distort the parts being welded due to the significant weld filler material and/or high heat input. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Embodiments of this invention include a nozzle assembly for a turbine, the nozzle assembly including an airfoil, inner and outer sidewalls, and inner and outer rings. The inner ring and inner sidewall (and similarly the outer ring and the outer sidewall) are interconnected, via mechanical elements and welding, at an interface. The interconnection includes axial and radial mechanical stops to allow for an accurate assembly, to ensure correct radial and axial positions of the parts during welding, to minimize weld shrinkage and to control an axial weld length. 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. The configuration further may include a ring with a consumable root portion to facilitate the weld, and to provide a fixturing stop to further ensure that the parts remain in the correct position. The configuration further is configured such that the stress concentration on a root of the weld is in a substantially vertical direction. 
     A first aspect of the disclosure provides a nozzle assembly for a turbine, the nozzle assembly comprising: at least one airfoil having an outer sidewall; an outer ring mechanically coupled to the outer sidewall at an interface; a mechanical axial stop at the interface of the outer sidewall and the outer ring, the mechanical axial stop configured to maintain the at least one airfoil in a correct axial position; and a mechanical radial stop at the interface of the outer sidewall and the outer ring, the mechanical radial stop configured to maintain the at least one airfoil in a correct radial position, wherein at least one of (a) a portion of the outer ring at the interface and (b) a portion of the outer sidewall at the interface, is angled away from the interface to form a narrow groove between the outer ring and the outer sidewall. 
     A second aspect of the disclosure provides a nozzle assembly for a turbine, the nozzle assembly comprising: at least one airfoil having an inner sidewall; an inner ring mechanically coupled to the inner sidewall at an interface; a mechanical axial stop at the interface of the inner sidewall and the inner ring, the mechanical axial stop configured to maintain the at least one airfoil in a correct axial position; and a mechanical radial stop at the interface of the inner sidewall and the inner ring, the mechanical radial stop configured to maintain the at least one airfoil in a correct radial position, wherein at least one of (a) a portion of the inner ring at the interface and (b) a portion of the inner sidewall at the interface, is angled away from the interface to form a narrow groove between the inner ring and the inner sidewall. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic of a nozzle assembly for a turbine according to embodiments of this invention. 
         FIG. 2  shows a three-dimensional schematic of a nozzle assembly for a turbine according to embodiments of this invention. 
         FIGS. 3-5  show exploded cross-sectional views of the interface between a sidewall and a ring of a nozzle assembly according to embodiments of this invention. 
         FIGS. 6-7  show exploded cross-sectional views of the interface between a sidewall and a ring of a nozzle assembly according to embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings,  FIG. 1  shows a line drawing schematic of nozzle assembly  100  for a gas or steam turbine (not shown), while  FIG. 2  shows a three-dimensional schematic of nozzle assembly  100 . Nozzle assembly  100  includes at least one airfoil  102  having an inner sidewall  104  and an outer sidewall  106 . Nozzle assembly  100  further includes an inner ring  108  and an outer ring  110 . Inner and outer, as used herein, refer to a radial position relative to a rotor (not shown) to which an inner end of airfoil  102  is coupled via inner ring  108 . Inner ring  108  and inner sidewall  104  are coupled together, mechanically and by welding, at an interface, and similarly, outer ring  110  and outer sidewall  106  are coupled together, mechanically and by welding, at an interface  80 , which is understood to refer to the entire area where rings and sidewalls are adjacent and coupled. Inner ring  108  and inner sidewall  104  (and similarly outer ring  110  and outer sidewall  106 ) are welded together at several points along interface  80 . The multiple welded areas of interfaces  80  that are welded together are shown generally as areas  90  in  FIG. 1 . 
     Interfaces  80  between rings  108 ,  110  and sidewalls  104 ,  106  each include a mechanical radial stop  109  which maintains blade  102  in the correct radial position during welding and prevents weld shrinkage. Interfaces  80  each further include a mechanical axial stop  107  which maintains blade  102  in the correct axial position and controls the weld length depth. These mechanical stops  107 ,  109  comprise an interconnection of a series of male steps which engage in corresponding female steps of the complementary part as described in more detail herein. As such, interfaces  80  include both welded areas  90  and mechanical interconnections  107 ,  109 . 
     An exploded view of interface  80  between outer ring  110  and outer sidewall  106  is shown in  FIGS. 3 and 4 .  FIG. 3  shows a line drawing of interface  80  of outer ring  110  and outer sidewall  106 , exaggerated for purposes of explanation, with outer ring  110  and outer sidewall  106  not yet connected. As shown in  FIG. 4 , once outer ring  110  and outer sidewall  106  are mated together, interface  80  between sidewall  106  and ring  110  includes mechanical axial and radial stops  107 ,  109 , i.e., an interconnection of a series of male steps which engage in corresponding female steps of the complementary part. 
     For example, as shown in  FIG. 3 , mechanical axial stop  107  can be formed by outer ring  110  including a first female step  112  and outer sidewall  106  including a corresponding first male step  114 . Mechanical radial stop  109  can be formed by outer ring  110  having a second female step  116 , adjacent to first female step  112 , and outer sidewall  106  including a corresponding second male step  118 , adjacent to first male step  114 .  FIG. 4  shows an exploded view of interface  80  of outer ring  110  and outer sidewall  106  after coupling, including mechanical radial stop  109  and mechanical radial stop  107 . 
     Alternatively, as shown in  FIG. 5 , mechanical axial stop  107  and mechanical radial stop  109  can be formed by reversing the interconnection of male steps which engage in the female steps of the complementary part. In other words, while it is shown in the other figures that outer sidewall  106  includes central male steps and outer ring  110  is shown with central female steps, the reverse, as shown in  FIG. 5 , is also disclosed. Outer sidewall  106  may instead include central female steps, while outer ring  110  can include central male steps. It is also noted that while the female and male steps are shown in the two-dimensional figures as substantially horizontal, these parts may also be angled to assist proper placement of the parts of the nozzle assembly. 
     Another embodiment of interface  80  between outer sidewall  106  and outer ring  110  of nozzle assembly  100  according to an embodiment of the invention is disclosed in  FIG. 6 . As shown in  FIG. 6 , outer sidewall  106  is coupled to outer ring  110  through interface  80  that, as discussed above, includes an interconnection of male steps which engage in the corresponding female steps of the complementary part to provide mechanical axial stop  109  and mechanical radial stop  107 . In addition, one or more surfaces at interface  80  can be angled away from the interface to form a narrow groove  120 . In the embodiment shown in  FIG. 6 , a portion of outer ring  110 , shown as portion  111 , is angled away from interface  80  to form narrow groove  120 . Narrow groove  120  can be formed by angling portion  111  of outer ring  110  at an angle in the range of approximately 0° to approximately 11°. While outer ring  110  is shown as having portion  111  angled away from interface  80 , outer sidewall  106  could instead have a portion angled away from interface  80 . 
     As also shown in the embodiment shown in  FIG. 6 , outer ring  110  can further include a protruding consumable root portion  122  that extends toward interface  80  between outer sidewall  106  and outer ring  110 . Consumable root portion  122  can include a material having any shape and size suitable for facilitating a weld at interface  80  between outer ring  110  and outer sidewall  106 . For example, consumable root portion  122  can include a chamfer, or a square bottom groove. Consumable root portion  122  can act as a consumable root for a weld, such as a TIG weld or can act as a fixturing stop for a weld, such as an electron beam weld (EBW), to ensure that the parts remain in the correct position. 
     While outer ring  110  and outer sidewall  106  can be welded together using conventional low heat welding techniques, the nozzle assembly of this disclosure also allows for high heat welds, such as GTAW (either using an energized or non-energized filler wire), GMAW or EBW. If a GTAW (also known as TIG) weld is used, a manual TIG weld or fully-automated TIG weld can be used. 
     Using the configuration of embodiments of this invention, the stress concentration on the root of a weld between outer sidewall  106  and outer ring  110  is in a substantially vertical direction. In addition, the ratio of weld depth to width of the weld is preferably in the range of approximately 3:1 to 10:1. 
     In another embodiment of this invention, shown in  FIG. 7 , an edge of outer sidewall  106 , shown as portion  105 , that abuts outer ring  110  is also angled away from interface  80 . In contrast to  FIG. 6 , where only one surface at the ring/sidewall interface was angled away from interface  80 , the embodiment shown in  FIG. 7  includes both surfaces  105 ,  111  angled away from interface  80  to form narrow groove  120 . Again, portion  105  can be angled away from interface  80  at an angle in the range of approximately 0° to approximately 11°. 
     It is also noted that while this disclosure discusses embodiments of this invention with respect to outer sidewall  106  and outer ring  110 , similar embodiments are disclosed for inner sidewall  104  and inner ring  108 . With respect to inner sidewall  104  and inner ring  108 , the configuration of male steps which engage in the corresponding female steps of the complementary part can either be identical to those used for outer sidewall  106  and outer ring  110 , or can be a mirror image of that configuration. 
     The terms “first,” “second,” and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another, and the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context, (e.g., includes the degree of error associated with measurement of the particular quantity). The suffix “(s)” as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including one or more of that term (e.g., the metal(s) includes one or more metals). Ranges disclosed herein are inclusive and independently combinable (e.g., ranges of “up to about 25 wt %, or, more specifically, about 5 wt % to about 20 wt %”, is inclusive of the endpoints and all intermediate values of the ranges of “about 5 wt % to about 25 wt %,” etc). 
     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 by those skilled in the art, and are within the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.