Steam turbine singlet nozzle design for breech loaded assembly

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.

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 singlet105having an airfoil106with integral inner sidewall102and outer sidewall104as shown inFIG. 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 airfoil106and sidewalls102,104may be machined, for example, from a near net forging or a block of material. The inner ring102may include a step136, which is received in complementary recess138of inner sidewall102. The outer sidewall135may include a step136, which is received in complimentary recess138of outer ring135. Alternative arrangements of steps and recesses may be formed between the sidewalls and the rings. The interfaces101between the sidewall115and inner ring102and the interfaces104between the sidewall135and outer ring104are stopped by each side of steps136, limiting length of weld and enabling axially short, low heat input welds e.g., e-beam welds. These complementary steps136and recesses138mechanically interlock the singlet105between the inner ring115and the outer ring135, 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 edge118and the trailing edge119interfaces103for the outer sidewall135with the outer ring104and at the interface101of the inner sidewall115and the inner ring102. Access must be available to the leading edge118and the trailing edge119of both interfaces101,103for 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 assembly205for a turbine, as illustrated inFIG. 2. The Singlet nozzle assembly205includes a Singlet airfoil206with integral inner sidewall215and outer sidewall235, and an inner ring202and an outer ring204. 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 sidewalls215,235or the rings202,204having a protruding hook220and the other having a corresponding hook recess222. InFIG. 2, the hooks220are shown on the sidewalls215,235. The interface can also include an axial stop250and a radial mechanical stop255. 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 stop250on the radial interface between outer sidewall235and the associated outer ring204, and a single weld at the trailing edge219interface207between each sidewall and the associated ring are provided. The axial positioning and failsafe stop is formed by a radially projecting ledge251of the outer ring204. The axial positioning feature at the sidewalls establishes a length of a trailing edge weld along the interface203. The same inward projecting ledge251of the outer ring204acts as the failsafe feature preventing axial downstream movement of the nozzle airfoil206towards 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 stop255in proximity to the trailing edge219of the interface203. The radial stop surface of the ring sets the radial positioning of the sidewall relative to the outer ring204. 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 assemblies205with airfoils206including integral inner sidewall202and outer sidewalls204and an upstream facing hook245on 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 nozzle225into 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.

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. 3is a schematic illustration of an exemplary opposed-flow steam turbine10that may include nozzle assembly configurations of the present invention. Turbine10includes first and second low-pressure (LP) sections12and14. Each turbine section12and14includes a plurality of stages of nozzle assemblies (not shown inFIG. 1). A rotor shaft16extends through sections12and14along radial centerline15. Each LP section12and14includes a nozzle18and20. A single outer shell or casing22is divided along a horizontal plane and axially into upper and lower half sections24and26, respectively, and spans both LP sections12and14. A central section28of shell22includes a low-pressure steam inlet30. Within outer shell or casing22, LP sections12and14are arranged in a single bearing span supported by journal bearings32and34. A flow splitter40extends between first and second turbine sections12and14. AlthoughFIG. 1illustrates 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 inlet30receives low-pressure/intermediate temperature steam50from a source, for example, an HP turbine or IP turbine through a crossover pipe (not shown). The steam50is channeled through inlet30wherein flow splitter40splits the steam flow into two opposite flow paths52and54. More specifically, the steam50is routed through LP sections12and14wherein work is extracted from the steam to rotate rotor shaft16. The latter stages52,54in 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 sections12and14and is routed, for example, to a condenser or other heat sink (not shown).

FIG. 4is an enlarged schematic front view of an exemplary nozzle assembly100that may be used with steam turbine10(shown inFIG. 1). In one embodiment, nozzle assembly100may be a last stage nozzle assembly of steam turbine10. The nozzle assembly100includes an annular inner ring102, an annular outer ring104, and a plurality of Singlet nozzle airfoils106, with integral inner and outer sidewalls (not shown), extending there-between. Outer ring104is radially outward of, and substantially concentrically aligned with, inner ring102. Nozzle airfoils106are spaced circumferentially between rings102and104and each extends substantially radially between inner and outer rings102and104, respectively. A radially outer surface110of inner ring102and a radially inner surface112of outer ring104define radially inner and radially outer boundaries of a steam flowpath defined through nozzle assembly100.

FIG. 5illustrates 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 sidewall335of Singlet nozzle325is shown engaged with outer ring304during assembly. Forward hook330of outer sidewall335is inserted in complimentary recess331of the outer ring304. Interface303between outer sidewall335and outer ring304mate under the weight of the Singlet nozzle325.

Inner ring302is shown positioned to mate with inner sidewall315. Inner sidewall315includes forward projection340including forward hook345. A length of forward projection340is length341. Inner sidewall also includes center recess342and end projection343with surface344. Inner ring302includes central recess360with partially enclosed hook engagement recess361. Recess360is set between inner ring projection362with hook retainer364and inner ring projection363. The entrance365to recess360is sized to accept length341of forward projection340. When inner ring302is moved to engagement with inner sidewall315, forward projection340is inserted through entrance365to recess360, projection363on inner ring302enters recess342of inner sidewall, and surface344on inner sidewall contacts surface366on inner ring. Hook recess361of inner ring is sized to accept forward hook345of 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 nozzles325associated with the half ring.

A breech loading arrangement is also available, as illustrated inFIG. 6, where a forward hook is provided on the inner ring and a hook recess is provided on the inner sidewall. Here, outer sidewall435of Singlet nozzle425is shown engaged with outer ring404during assembly. Forward hook430of outer ring404is inserted in complimentary recess431of the outer sidewall435. Interface403between outer sidewall435and outer ring404mate under the weight of the Singlet nozzle425.

Inner ring402is shown positioned to mate with inner sidewall415. Inner ring402includes forward projection440including forward hook445. A length of forward projection440is length441. Inner ring402also includes center recess442and end projection443with surface444. Inner sidewall415includes central recess460with partially enclosed hook engagement recess461. Recess460is set between inner sidewall projection462with hook retainer464and inner sidewall projection463. The entrance465to recess460is sized to accept length441of forward projection440. When inner ring402is moved to engagement with inner sidewall415, forward projection440is inserted through entrance465to recess460, projection463on inner sidewall415enters recess442of inner ring, and surface444on inner ring contacts surface466on inner sidewall. Hook recess461of inner sidewall is sized to accept forward hook445of 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 nozzles425onto the inner ring402. 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 nozzle325with integral inner sidewall and outer sidewall.FIG. 7illustrates an expanded view of the outer sidewall325to outer ring304interface. The upstream face of the outer sidewall includes forward hook330. These features also include radial mechanical positioning and shrinkage stop355and the axial positioning and failsafe stop357. 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 weld310along the interface303thereby determining the axial weld length. Trailing edge weld310for this embodiment may be an electron beam weld (EBW). The same inward projecting ledge380of 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 surface332of outer ring304and surface333of outer sidewall335at hook330. Near line-to-line contact is provided at radial stop355interface of surface358of outer ring304and surface359of outer sidewall335. 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 interface565(FIG. 13) between outer surface of the hook540of inner sidewall502and opposing surface564(FIG. 12) of the inner ring515. A slight gap of about 0.002 is provided for opposing surfaces at the radial stop570(FIG. 13) between inner sidewall515and inner ring502.

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 Ktfactors, 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. 8illustrates 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. 9-13illustrate a method for loading the singlet nozzles into inner and outer rings for a nozzle assembly according to the present invention.FIG. 14illustrates a flowchart for loading of Singlet nozzles into inner and outer rings according to the present invention.

FIG. 9illustrates an axial view of an outer ring504, a Singlet nozzle525including airfoil506with integral outer sidewall535and inner sidewall515and inner ring502arranged in preparation for assembly. Upstream surface508of the outer ring and leading edge518of the airfoil506are on top. Outer ring504is fixed510in place to maintain orientation during assembly. The outer ring recess538is oriented in a horizontal plane for accepting forward hook530of the outer sidewall535. The hook recess531of the outer ring is positioned to face downward. The Singlet nozzle525is then tilted511slightly to facilitate a slight swing entrance of forward hook530into complimentary recess531of outer ring504.

FIG. 10illustrates the outer sidewall535of Singlet nozzle525swung512into the outer ring504with forward hook530of outer sidewall engaging complimentary outer ring recess531and seating outer sidewall recess on outer sidewall projection556which forms the axial stop557. Here the axial stop557supports the Singlet nozzle during loading and subsequent welding of downstream interface503. Outer sidewall535for the Singlet nozzles are sequentially loaded at the end entrance of the outer ring504and moved in the circumferential direction until the nozzles are in proper place with the outer ring fully loaded.

FIG. 11illustrates the inner ring502positioned for loading to engage inner sidewall515of Singlet nozzle525. The inner ring502is positioned to establish vertical alignment of the forward hook projection540of inner sidewalls515of the Singlet nozzle525held in outer ring504. The inner ring502is then translated horizontally to insert the inner sidewall front hook projection540into inner ring recess560.FIG. 12illustrates the forward hook projection540of inner sidewall502inserted within recess560of inner ring502. Projection563of inner ring502is inserted within recess542of inner sidewall. Radial weld surface544of inner sidewall515and interface surface566of outer ring502are aligned.FIG. 13illustrates the inner ring502lowered514(FIG. 12) to engage forward hook projection540into hook recess561of inner ring502. This assures a very tight assembly that leads to negligible movement of the parts before or after welding downstream interfaces103.

FIG. 14illustrates 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. Step610fixedly positions outer ring so recess opening of outer ring is faced by complimentary outer sidewall of Singlet Nozzle. Step620tilts forward hook of outer sidewall of singlet nozzle toward recess opening of outer ring. Step630swings outer sidewall of Singlet nozzle into recess of outer ring. Step640circumferentially slides outer sidewall of Singlet nozzle into circumferential position within recess of outer ring. Step650repeats loading of outer sidewall with other Singlet Nozzles. Step660positions inner ring with central recess vertically aligned with forward hook projections of sidewalls for loaded singlet nozzles. Step670translates inner ring toward inner sidewalls so forward hook projections of inner sidewall for loaded Singlet nozzles enter opposing central recesses of inner sidewalls. Step680lowers inner ring so forward hook projections of inner sidewall for loaded Singlet Nozzles enter complimentary hook recesses of inner ring. Step690welds 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. 15illustrates a half ring of a Singlet nozzle assembly for a steam turbine. Singlet nozzle assembly590includes inner ring502, outer ring504loaded with Singlet nozzles125including integral inner sidewall515and outer sidewall535.

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.